embodiments of the present disclosure as described herein can be combined in many ways to treat one or more diseases of a patient such as a disease of the eye . the embodiments as described herein are well suited to treat patients with a therapeutic agent for an extended time , such as may be provided with a device that can be at least partially implanted into the eye . although specific reference is made to ophthalmic treatment of the eye , the methods and apparatus to place a therapeutic fluid in implantable device can be used with many implantable devices and treatments of one or more of many diseases , such as systemic medication to treat systemic disease , orthopedic treatment to treat orthopedic disorders , or dental treatment , for example . the exchange apparatus and methods as described herein are well suited for use with many drug delivery devices , such as refillable diffusion based devices , and can be exceptionally well suited for diffusion devices having a porous drug release structure configured for extended release in which the porous structure inhibits flow of fluid during exchange . the exchange apparatus and methods as described herein are well suited for diagnoses and treatment of the eye , for example with diagnosis and treatment of the eye based on the implantable device fluid received with the exchange apparatus with the fluid is injected . the implantable device can be combined with one or more known methods of analysis of biomarkers , for example commercially available beads and arrays to detect and measure biomarkers . the methods and apparatus as described herein are well suited for combination with analysis of samples as described in u . s . pat . app . ser . no . 61 / 538 , 736 , entitled “ diagnostic methods and apparatus ”, filed : sep . 23 , 2011 ( attorney docket no . 93161 - 821804 ( 000140us ), the full disclosure of which is incorporated herein by reference . examples of injector apparatus , therapeutic devices , valves and mechanisms to provide the bolus injection are described in u . s . patent application ser . no . 12 / 696 , 678 , filed on jan . 29 , 2010 , entitled “ posterior segment drug delivery ”, publication no . 2010 / 0255061 ; and u . s . pct pat . app . no . pct / us2011 / 046812 , filed aug . 5 , 2011 , entitled “ injector apparatus and method for drug delivery ”, the entire disclosures of which are incorporated herein by reference . pct patent application no . pct / us2012 / 049654 , filed aug . 3 , 2012 entitled “ small molecule delivery with implantable therapeutic device ” is also incorporated herein by reference in its entirety . as used herein like numerals and / or letters denote like elements in the drawings and text as will be apparent to a person of ordinary skill in the art . fig1 shows an eye 10 suitable for incorporation of the therapeutic device . the eye has a cornea 12 and a lens 22 configured to form an image on the retina 26 . the cornea extends to a limbus 14 of the eye , and the limbus connects to a sclera 24 of the eye . a conjunctiva 16 of the eye is disposed over the sclera 24 . a tenon &# 39 ; s capsule 17 extends between the conjunctiva 16 and the sclera 24 . the lens can accommodate to focus on an object seen by the patient . the eye has an iris 18 that may expand and contract in response to light . the eye also comprises a choroid 28 disposed between the sclera 24 and the retina 26 . the retina comprises the macula 32 . the eye comprises a pars plana , which comprises an example of a region of the eye suitable for placement and retention , for example anchoring , of the therapeutic device as described herein . the pars plana region may comprise sclera 24 and conjunctiva 16 disposed between the retina 26 and cornea 12 . the therapeutic device can be positioned so as to extend from the pars plana region into the vitreous humor 30 to release the therapeutic agent . the therapeutic agent can be released into the vitreous humor 30 , such that the therapeutic agent arrives at the retina 26 and choroid 28 for therapeutic effect on the macula 32 . the vitreous humor of the eye 30 comprises a liquid disposed between the lens 22 and the retina 26 . the vitreous humor 30 may comprise convection currents to deliver the therapeutic agent to the macula 32 . fig2 shows a therapeutic device 100 implanted under the conjunctiva 16 and extending through the sclera 24 . fig3 a shows an exemplary embodiment of the therapeutic device 100 . the device 100 is configured to release a therapeutic agent 110 into vitreous humor 30 of the eye 10 so as to treat the retina of the eye . the therapeutic device 100 may comprise a retention structure 120 such as a smooth protrusion configured for placement along the sclera 24 and under the conjunctiva 16 , such that the conjunctiva 16 can cover and protect the therapeutic device 100 . when the therapeutic agent 110 is inserted into the device 100 , the conjunctiva 16 may be lifted away , incised , or punctured with a needle to access the therapeutic device 100 . the eye 10 may comprise an insertion of the tendon of the superior rectus muscle to couple the sclera of the eye to the superior rectus muscle . the device 100 may be positioned in many locations of the pars plana region , for example away from tendon and one or more of posterior to the tendon , anterior to the tendon , under the tendon , or with nasal or temporal placement of the therapeutic device . while the implant can be positioned in the eye in many ways , work in relation to embodiments suggests that placement in the pars plana region 25 can release therapeutic agent into the vitreous 30 to treat the retina 26 , for example therapeutic agent comprising an active ingredient composed of large molecules . therapeutic agents 110 suitable for use with device 100 include many therapeutic agents , for example as listed in table 1a , herein below . the therapeutic agent 110 of device 100 may comprise one or more of an active ingredient of the therapeutic agent , such as a formulation of the therapeutic agent , a commercially available formulation of the therapeutic agent , a physician prepared formulation of therapeutic agent , a pharmacist prepared formulation of the therapeutic agent , or a commercially available formulation of therapeutic agent having an excipient . the therapeutic agent may be referred to with generic name or a trade name , for example as shown in table 1a . the therapeutic device 100 can be implanted in the eye to treat the eye for as long as is helpful and beneficial to the patient . for example the device can be implanted for at least about 5 years , such as permanently for the life of the patient . alternatively or in combination , the device can be removed when no longer helpful or beneficial for treatment of the patient . the therapeutic agent 110 can be placed in the therapeutic device 100 in many ways . in many embodiments , a therapeutic fluid 260 ( fig2 ) comprising therapeutic agent 110 is exchanged with an implantable device fluid 262 contained within therapeutic device 100 , as shown in fig2 . an exchange apparatus 200 can be configured to place the therapeutic fluid 260 and to receive the implantable device fluid displaced from the implantable device when the therapeutic fluid is placed . with reference to fig2 , an exemplary embodiment of the exchange apparatus 200 comprises an elongate structure 201 that can be placed substantially within the implantable device . the elongate structure 201 comprises an opening to place the therapeutic fluid in the reservoir chamber of the implantable device and one or more openings to receive the implantable device fluid from the reservoir chamber . the exchange apparatus 200 may comprise the therapeutic fluid 260 and the receiver container 250 to receive fluid 262 of the implantable device . the therapeutic device 100 may comprise a reservoir chamber to store an amount of the therapeutic agent 110 . the reservoir chamber may comprise a fluid 262 of the implantable device 100 . the fluid 262 of the implantable device can be displaced when the therapeutic fluid 260 is injected , for example , and a receiver container 250 can be provided to receive the implantable fluid 262 from the implantable device . the reservoir chamber of the implantable device may comprise a substantially rigid walls and a substantially fixed volume , for example . the exchange apparatus 200 can be configured in many ways , and may be coupled to a syringe 300 with one or more of many connectors , such as a luer connector , a luer - lok ™ connector , for example . alternatively or in combination , the exchange apparatus may comprise syringe 300 , for example . the exchange apparatus 200 may comprise an elongate structure 201 to for insertion into the reservoir chamber of the implantable device , and a stop 240 to limit a depth of insertion of the elongate structure 201 into the reservoir chamber of the implantable device . the exchange apparatus 200 may comprise a receiver container 250 to receive the implantable device fluid from the reservoir chamber of the implantable device , and the elongate structure may comprise a plurality of openings coupled to the receiver container so as to receive the fluid of the implantable device through the plurality of openings when the fluid is injected . alternatively , the therapeutic fluid may be drawn into the reservoir chamber of the implantable device with aspiration of the implantable device fluid into chamber 310 of the syringe , such that the therapeutic fluid placed in chamber 250 can be drawn into the reservoir chamber of the implantable device , for example . fig3 a shows a therapeutic device 100 comprising a container 130 having a penetrable barrier 184 disposed on a first end , a porous structure 150 disposed on a second end to release therapeutic agent for an extended period , and a retention structure 120 comprising an extension protruding outward from the container to couple to the sclera and the conjunctiva . the container 130 may comprise an axis 100 a . the inner surfaces of the container 130 may define a reservoir chamber having a volume sized to provide therapeutic amounts of the therapeutic agent for the extended time . the extending protrusion of the retention structure may comprise a diameter 120 d . the retention structure may comprise an indentation 120 i sized to receive the sclera . the container may comprise a tubular barrier 160 that defines at least a portion of the reservoir , and the container may comprise a width , for example a diameter 134 . the diameter 134 can be sized within a range , for example within a range from about 0 . 5 to about 4 mm , for example within a range from about 1 to 3 mm and can be about 2 mm , for example . the container may comprise a length 136 sized so as to extend from the conjunctive to the vitreous along axis 100 a to release the therapeutic agent into the vitreous . the length 136 can be sized within a range , for example within a range from about 2 to about 1 4 mm , for example within a range from about 4 to 10 mm and can be about 7 mm , for example . the volume of the reservoir may be substantially determined by an inner cross sectional area of the tubular structure and distance from the porous structure to the penetrable barrier . the retention structure may comprise an annular extension having a retention structure diameter greater than a diameter of the container . the retention structure may comprise an indentation configured to receive the sclera when the extension extends between the sclera and the conjunctive . the penetrable barrier may comprise a septum disposed on a proximal end of the container , in which the septum comprises a barrier that can be penetrated with a sharp object such as a needle for injection of the therapeutic agent . the porous structure may comprise a cross sectional area 150 a sized to release the therapeutic agent for the extended period . the porous structure 150 may comprise a control release mechanism . the porous structure 150 can be configured in many ways to provide controlled sustained release , for example with a release rate index , or a size and number of openings , for example . the porous structure 150 may comprise a first side 150 s 1 coupled to the reservoir and a second side 150 s 2 to couple to the vitreous . the first side may comprise a first area 150 a 1 and the second side may comprise a second area 150 a 2 . the porous structure may comprise a thickness 105 t . the porous structure many comprise a diameter 150 d . the porous structure 150 may comprise one or more of a release control element , a release control mechanism , permeable membrane , a semipermeable membrane , a material having at least one hole disposed therein , channels formed in a rigid material , straight channels , nano - channels , nano - channels etched in a rigid material , laser drilled holes , laser etched nano - channels , a capillary channel , a plurality of capillary channels , one or more tortuous channels , sintered material , sintered rigid material , sintered glass , sintered ceramic , sintered metal , tortuous micro - channels , sintered nano - particles , an open cell foam or a hydrogel such as an open cell hydrogel . additional examples of porous structures are described in u . s . patent application ser . no . 12 / 696 , 678 , filed on jan . 29 , 2010 , entitled “ posterior segment drug delivery ”, publication no . 2010 / 0255061 ; and u . s . pct pat . app . no . pct / us2011 / 046812 , filed aug . 5 , 2011 , entitled “ injector apparatus and method for drug delivery ”, the entire disclosures of which have been previously incorporated herein by reference . the volume of the reservoir chamber may comprise from about 5 μl to about 2000 μl of therapeutic agent , or for example from about 10 μl to about 200 μl of therapeutic agent . the reservoir may comprise an axial length 136 c extending between the penetrable barrier 184 and the porous structure 150 . the therapeutic agent stored in the reservoir of the container comprises at least one of a solid comprising the therapeutic agent , a solution comprising the therapeutic agent , a suspension comprising the therapeutic agent , particles comprising the therapeutic agent adsorbed thereon , or particles reversibly bound to the therapeutic agent . for example , reservoir may comprise a suspension of a cortico - steroid such as triamcinolone acetonide to treat inflammation of the retina . the reservoir may comprise a buffer and a suspension of a therapeutic agent comprising solubility within a range from about 1 μg / ml to about 100 μg / ml , such as from about 1 μg / ml to about 40 μg / ml . for example , the therapeutic agent may comprise a suspension of triamcinolone acetonide having a solubility of approximately 19 μg / ml in the buffer at 37 ° c . when implanted . the release rate index may comprise many values , and the release rate index with the suspension may be somewhat higher than for a solution in many embodiments , for example . the release rate index may be no more than about 5 , and can be no more than about 2 . 0 , for example no more than about 1 . 5 , and in many embodiments may be no more than about 1 . 2 , so as to release the therapeutic agent with therapeutic amounts for the extended time . the release rate index can be at about 0 . 01 , for example . the therapeutic device , including for example , the retention structure and the porous structure , may be sized to pass through a lumen of a catheter . the porous structure may comprise a needle stop that limits penetration of the needle . the porous structure may comprise a plurality of channels configured for the extended release of the therapeutic agent . the porous structure may comprise a rigid sintered material having characteristics suitable for the sustained release of the material . fig3 b shows a porous structure comprising a plurality of substantially straight channels 150 sc extending substantially straight through a disk . the channels 150 sc can extend from a first side 150 s 1 to a second side 150 s 2 a distance comprising thickness 150 t of the porous structure . each of the channels comprises a cross - sectional dimension across , for example a diameter , and a corresponding area across the cross section . the combined cross - sectional area of the plurality of channels , the thickness 150 t , the diffusion coefficient of the therapeutic agent , the concentration of therapeutic agent within the reservoir chamber and the volume of the reservoir chamber determine substantially the release rate profile of the therapeutic agent . the size and number of the plurality of channels 150 sc and thickness of the porous structure can be configured so as to provide the release rate profile . the porous structure 150 may comprise the control release mechanism having one or more straight channels 150 sc through which material ( e . g ., fluid that contains therapeutic agent ) can pass . there can be at least 3 , for example at least 6 and even more typically at least 10 channels . there may be fewer than 1000 channels , for example no more than 200 and in many embodiments no greater than 50 of the channels 150 sc . material , particularly ophthalmic pharmaceutical composition and aqueous humor fluid , is typically allowed to freely flow and / or diffuse into and out of the reservoir chamber 140 ( fig3 a ) with the size of the openings of channels 150 sc assisting in controlling the rate of flow and / or diffusion into and out of the reservoir chamber 140 . the openings of the plurality of channels 150 sc , particularly for a passive system , have a cross - sectional area that controls the rate at which material , particularly therapeutic agent , flows out of the reservoir and into the eye . that cross - sectional area can be at least 8 μm 2 , more typically at least 15 μm 2 and even more typically at least 50 μm 2 . that same cross - sectional area can also be no greater than 4000 μm 2 , for example no greater than 2000 μm 2 and in many embodiments no greater than 500 μm 2 . the cross - sectional area of the opening may comprise any sectional area of the opening wherein the outer perimeter of the opening is fully defined by the material of the control release mechanism and wherein , for fluid to pass through the opening into or out of the reservoir chamber 140 , it also passes through the cross - sectional area . in the illustrated embodiments , as shown in fig3 b , the porous structure 150 comprising the control release mechanism can be a plate 150 pl . the plurality of channels 150 sc extends through the plate 150 pl . the plate 150 pl may have opposing substantially parallel surfaces through with the channels extend to the opening on each surface . in the embodiments shown , the channels 150 sc are cylindrical shape although they may be shaped otherwise as well . the channels 150 sc may have a diameter of at least about 0 . 2 microns , for example at least about 2 microns and in many embodiments at least about 8 microns . the diameter of the openings may be no greater than about 100 microns , for example no greater than 40 microns and in many embodiments no greater than about 25 microns . while it is understood that a generally uniform distribution of the openings over the surface of the plate 150 pl is desirable , other non - uniform distribution of opening the openings are also possible . a suitable thickness for the plate will typically be at least about 0 . 05 mm , more typically at least about 0 . 08 mm and will typically no greater than 0 . 5 mm and more typically no greater than 0 . 3 mm . the porous structure 150 comprising the control release mechanism may comprise a plate 150 pl . the plate 150 pl may be formed of a variety of materials such as metals or polymeric materials . in many embodiments , the plate 150 pl is formed of an etchable material such as silicon , which allows the channels 150 sc to be etched into the material . the number and size of each of the openings provides a combined cross - sectional surface area for the plate 150 pl . the combined cross - sectional surface area of the channels 150 sc may be no more than about 100 , 000 μm 2 , so as to provide sustained release of the therapeutic agent for an extended time . while the combined cross - sectional surface area can be within a range from about 1000 μm 2 to about 100 , 000 μm 2 , in many embodiments the combined cross - sectional area is within a range from about 2 , 000 μm 2 to about 30 , 000 μm 2 , for example about 2 , 000 to about 10 , 000 μm 2 . the combined cross - sectional area can be determined based on one or more of the thickness of the plate 150 pl , the diffusion coefficient of the therapeutic agent , the volume of the reservoir chamber , the concentration of the therapeutic agent placed in the reservoir chamber , or the targeted release rate profile of the therapeutic agent above a minimum inhibitory concentration for a predetermined amount of time , or combinations thereof , for example . fig4 shows an exemplary apparatus 200 to exchange fluid of a device implanted in an eye . the apparatus 200 may comprise or be coupled to a syringe 300 to inject a therapeutic fluid comprising a therapeutic agent in to the device implanted in the eye . the apparatus 200 comprise an elongate structure 201 comprising a distal portion 210 , and intermediate portion 220 and a proximal portion 230 . the elongate structure 201 extends along an axis 202 from a stop 240 to position the distal portion 210 , the intermediate portion 220 , and the proximal portion 230 corresponding locations of the reservoir chamber . the distal portion 210 comprises a distal tip 212 to penetrate tissue and the penetrable barrier of the implantable device and an opening 214 to inject therapeutic fluid into the implantable device . the intermediate portion 220 comprises a tapered section 224 to gradually increase a size of the channel formed in the penetrable barrier when the needle is advanced through the penetrable barrier , so as to maintain integrity of the penetrable barrier and inhibit damage to the penetrable barrier . in many embodiments , the tapered portion 224 may extend along axis 202 without holes so as to decrease pressure to the penetrable barrier that may otherwise occur near the edge of a hole . the proximal portion 230 may comprise a plurality of openings 236 to receive the fluid from the reservoir chamber of the implantable device . the proximal portion 230 may comprise an extension 238 extending from the stop 240 . the extension 238 may extend from the stop 240 without holes to inhibit leakage when the fluid is exchanged and the stop 240 engages the conjunctiva . fig5 shows the apparatus 200 coupled to an implantable device 100 . the stop 240 is positioned to engage the conjunctiva 16 , and the elongate structure 201 extends through the conjunctiva 16 and penetrable barrier 184 into the reservoir chamber 140 of the implantable device 100 when the apparatus 200 is coupled thereto . the elongate structure 201 can be sized so as to place distal tip 212 at a location within the reservoir chamber of the implantable device when the surface of the stop contacts the conjunctiva , for example . the distal tip 212 can be located on elongate structure 201 so as to place the distal tip 212 at a location from the penetrable barrier within implantable device 100 that is no more than a desired length , such as about ¾ of the length 136 of the implantable device , and in some embodiments no more than about half of the distance 136 c of the reservoir chamber . the plurality of openings 236 is located near the penetrable barrier 184 so as to receive fluid contacting the reservoir chamber . the extension 238 extends substantially through the penetrable barrier 184 , for example at least about half way through the penetrable barrier so as to position the plurality of openings away from an external surface of the penetrable barrier and to inhibit leakage . fig6 shows an enlarged view of the elongate structure 201 of the apparatus 200 . the elongate structure 201 extends along axis 202 between the distal tip 212 and stop 240 . the distal portion 210 may comprise an extension 211 having a substantially constant cross - sectional size extending between the tip 212 to penetrate tissue and the intermediate portion 220 . in many embodiments , the extension 211 comprises a portion of a needle 270 extending between the stop 240 and the tip 212 to penetrate tissue , which tip may comprise the tip of the needle to penetrate conjunctival tissue . the tip to penetrate tissue 212 and the opening 214 can be located a distance 204 from the stop and the plurality of opens to provide efficient exchange of the fluid within the reservoir chamber of the implanted device . in many embodiments , the opening 214 is placed within the reservoir chamber at a distance from the stop 240 greater than the plurality of openings 236 to inhibit mixing of the injected therapeutic fluid with the fluid within the reservoir chamber of the implanted device . the opening 214 can be separated from the plurality of openings with a distance 208 , such that the opening 214 can be located below the plurality of openings when the therapeutic fluid is injected . the therapeutic fluid may comprise a density greater than the fluid of the implanted device and opening 214 can be placed below the plurality of openings 236 when the therapeutic fluid is injected to inhibit mixing . the axis 100 a ( see fig3 a ) of the implantable device and the corresponding axis of the reservoir chamber can be oriented away from horizontal , such that porous structure 150 may be located below the penetrable barrier 184 when the therapeutic fluid is injected . the axis 202 can oriented away from horizontal such that opening 214 can be placed below the plurality of openings 236 . the therapeutic fluid comprising the greater density can flow toward the distal end of the therapeutic device and the displaced fluid of the implantable device having the lesser density can be received by the plurality of openings 236 located above the opening 214 . examples of therapeutic agents and corresponding formulations and fluids that may have a density greater than the density of the fluid within the chamber of the implanted device are listed in table 1a . for example , one or more of the therapeutic agent or a stabilizer can increase the density of the therapeutic fluid . in many embodiments the therapeutic fluid having the greater density comprises a stabilizer , such as trehalose , and the therapeutic agent such as a protein comprising an antibody fragment . alternatively or in combination , the therapeutic formulation may comprise an amount of therapeutic agent sufficient to provide a density greater than the fluid of the implanted device . the difference in density can be within a range from about 1 % to about 10 % and can depend on the density of the fluid within the reservoir chamber of the therapeutic device and density of the therapeutic fluid placed in the reservoir chamber with the exchange apparatus . the density of the therapeutic fluid may correspond to a density of the therapeutic agent and a density of the stabilizer ( when present ). in many embodiments , the density of the fluid of the reservoir chamber may correspond to a density of phosphate buffered saline , or plasma , or an amount of therapeutic fluid remaining in the reservoir from a prior exchange , or combinations thereof , for example . when injected into a device implanted within the patient , the distance 204 may correspond to no more than approximately the distance of the reservoir chamber of device 140 . the distance 204 may correspond substantially to the length of the reservoir chamber so as to place the distal tip near the porous structure , and the elongate structure of the exchange apparatus can be aligned with an elongate axis of the implantable device . in many embodiments , the distance 204 may correspond to no more than about half the distance of the reservoir chamber , such that the elongate structure 201 can be readily aligned with the implantable device . work in relation to embodiments suggests than a distance providing a tolerance for angular alignment error of the axis 100 a with the axis 202 can facilitate exchange and improve efficiency of the exchange . the distance 204 from stop 240 to tip 212 comprising no more than about half of the axial distance of the implantable device can facilitate alignment during injection . the intermediate portion 220 may comprise an extension 222 extending between tapered portion 224 and the distal portion 210 . the extension 222 may comprise a cross - sectional size that is smaller than the tapered portion 224 . the extension 222 may comprise a smooth outer surface to penetrate tissue . the tapered portion 224 may comprise a smother outer surface to penetrate tissue and the penetrable barrier . the outer surface of the tapered portion can extend at an angle of inclination relative to the axis , and the tapered portion 224 may comprise a conic section having an angle with the axis such that the outer surface extends at the angle of inclination relative the axis . the angle of inclination of the tapered portion 224 can be no more than about 25 degrees , for example . the angle of inclination can be about 1 degree , about 2 degrees , about 5 degrees , about 10 degrees , about 15 degrees , about 20 degrees , or about 25 degrees , for example . the extension portion 216 may comprise a first cross - sectional dimension , and the portion having the plurality of openings may comprise a second cross sectional dimension greater than the first dimension , such that tapered portion having the angle of inclination extends there between to connect the extension portion 216 with the portion having the plurality of openings 236 . the proximal portion 230 may comprise the plurality of openings 236 spaced apart along the axis 202 and distributed circumferentially around the proximal portion to receive fluid from a plurality of circumferential and axial locations when the stop 240 engages the conjunctiva to place the plurality of openings within the reservoir chamber . at least one 237 of the plurality of openings can be separated from the stop 240 with a distance 206 corresponding substantially to the thickness of the penetrable barrier 184 , such that the at least one 237 of the plurality of openings 236 can be placed near the inner surface of the penetrable barrier to receive fluid contacting the inner surface of the penetrable barrier . in many embodiments , the thickness of the penetrable barrier is within a range from about 0 . 25 to about 2 mm , for example within a range from about 0 . 5 to about 1 . 5 mm , such that the thickness of the penetrable barrier is substantially greater than a thickness of the conjunctiva which can be approximately 100 μm . the distance 206 corresponding substantially to the thickness of the penetrable barrier may correspond substantially to the thickness of the penetrable barrier and the epithelium of the patient . a sheath 280 can be configured to extend over at least a portion of needle 270 . the sheath 280 may extend along the intermediate portion 220 and the proximal portion 230 , and the needle 270 can extend through the sheath . the sheath 280 may comprise the plurality of openings 236 and provide one or more channels extending along needle 270 to pass the fluid of the implantable device through the septum . the sheath 280 may comprise portions corresponding to the intermediate and proximal portions of the elongate structure 201 . the extension 222 may comprise a distal portion sheath 280 having an inner surface sized to engage an outer surface of the needle , and the diameter of the portion to engage the needle may comprise an inner cross sectional diameter less than the needle to engage the needle with at least one or of pressure or friction . the tapered portion 224 may comprise an intermediate portion of sheath 280 , in which the sheath 280 comprises tapered surface to penetrate the tissue and penetrable barrier 184 . the proximal portion 230 may comprise a proximal portion of the sheath 280 comprising the plurality of openings 236 and the extension 238 . a channel 239 can extend along an outer surface of the needle to the plurality of openings 236 . the channel 239 can extend proximally along extension portion 238 toward a container 250 ( see fig8 a ) to receive the fluid of the implantable device . the channel 239 may couple the plurality of openings to the container to receive the fluid of the implantable device . fig7 shows a cross - sectional view of an elongate structure of the apparatus exchange fluid comprising the sheath 280 over the needle 270 . the needle may comprise channel 219 , for example a lumen , extending distally to the opening 214 ( see fig6 ) and proximally to a connector to couple the channel 219 to a syringe , for example . a wall 252 of container 250 comprises sufficient strength to resist deformation when the stop 240 engages the tissue , and the stop 240 may comprise a deformable stop to couple to the tissue ( see fig8 a ). an outlet channel 254 extends from container 250 to at least one vent opening 258 to atmospheric pressure ( see fig8 a ). fig7 a shows an exchange apparatus comprising a locking connector to couple to a syringe . the connector 290 may comprise a locking connector having an extension 292 sized to fit in a channel of connector 320 of syringe 300 , for example ( see fig8 b ). the exchange apparatus 200 may comprise components of a standard locking needle assembly , for example a standard locking needle such as a luer - lok ™ fitting . the wall 252 that defines container 250 and sheath 280 can fit over the needle 270 which may comprise a standard needle assembly . the wall 252 can extend a substantial distance from stop 240 to opening 258 , for example , so as to define container 250 and channel 254 extending between the locking needle assembly and the wall . fig7 b shows the elongate structure 201 and receiver container 250 of the exchange apparatus 200 of fig7 a . the wall 252 can extend around a distal portion of receiver container 250 . the needle 270 and sheath 280 may extend through the wall 250 . the stop 240 can be located on a distal portion of wall 252 and may comprise a soft material , for example a soft elastomeric material such as silicone elastomer . the stop 240 may fit within a recess formed on the surface of wall 252 , and the needle 270 and the sheath 280 may extend through the soft elastomer stop 240 , for example . the sheath 280 may comprise the tapered portion 224 proximal to the plurality of openings 236 . the needle 270 can extend from tip 212 through chamber 250 to the connector 290 ( see fig7 a ), for example . the sheath 280 can extend from a first end 281 distal of the tapered portion 224 to a second end 283 . the second end 283 may comprise an opening 285 into chamber 250 . the outflow path of the displaced fluid from the implantable device may extend through the plurality of openings 236 to channel 239 , along channel 239 to opening 285 , and through opening 285 and into receiver container 250 . fig7 c shows sheaths suitable for combination with the exchange apparatus of fig7 a and 7b . the sheath 280 can be configured in many ways ( see 280 a through 280 k ), and may comprise a wall thickness from about 0 . 0001 inches to about 0 . 01 inches , for example about 0 . 001 inches ( 1 / 1000 inch , 25 μm ). the sheath 280 may comprise an inside diameter sized larger than the outside diameter of needle 270 so as to provide an annular channel extending axially between the needle and the sheath from the plurality of openings 236 to the opening 285 . the diameter of each of the holes can be within a range from about 0 . 0001 inches to about 0 . 1 inches , for example within a range from about 0 . 001 inches to about 0 . 01 inches . the plurality of openings 236 may comprise one or more of many shapes and can be arranged in many ways . each row may comprise from about 2 to about 20 holes , for example , and may comprise circular , oval , elliptical or other shapes , for example . the sheath 280 may comprise a sheath 280 a having four rows of circular holes . each of the holes may have a diameter of no more than about one half of the thickness of the outside diameter of the sheath 280 , for example , and may be located circumferentially at 90 degrees to each other , for example . each of the four rows may extend axially along the sheath 280 . the rows can be spaced angularly at 90 degrees to each other , for example . the sheath 280 may comprise sheath 280 b having about two rows , each row comprising about four holes , each hole having a diameter of no more than about one eighth of the diameter of the outside diameter of the sheath 280 . the two rows may be spaced apart circumferentially at 180 degrees , and the holes may comprise holes cross - drilled through both sides of the sheath , such that each hole has a corresponding hole on the other row on an opposite side of the sheath . the sheath 280 may comprise sheath 280 c comprising about four cross drilled holes , each hole having a diameter of no more than about three quarters of the diameter of the outside diameter of the sheath 280 , for example . the holes may comprise pairs of holes , in which the holes of each pair have corresponding axial locations . the holes can be arranged in two rows spaced circumferentially at 180 degrees . the sheath 280 may comprise sheath 280 d comprising at least about three rows of at least about 3 holes , each hole having a diameter of no more than about one quarter of the diameter of the outside diameter of the sheath 280 . the rows can be spaced apart circumferentially at about 120 degrees , for example . the sheath 280 may comprise sheath 280 e comprising at least about 40 holes , each hole having a diameter of no more than about one tenth of the diameter of the outside diameter of the sheath 280 . the sheath 280 may comprise sheath 280 f comprising slots . each of the slots may comprise a narrow dimension across and a long dimension across . the long dimension can extend axially along the sheath 280 and may extend a distance greater than the narrow dimension across . the long dimension can extend a distance greater than the outside diameter of the sheath 280 where the slots are located , for example . the narrow dimension across each slot may comprise no more than about half of the outside diameter of the sheath , for example . the sheath 280 may comprise sheath 280 g comprising staggered rows of holes . the plurality of openings 236 may comprise a first row and a second row of cross drilled holes 236 a , in which the holes of the first row are paired with the holes of the second row at a common axial location for each pair . a third row of holes and a fourth row of holes may comprise cross drilled holes 236 b located at 180 degrees to each other and 90 degrees to the first row and the second row . the axial locations of the third and fourth rows of holes can be staggered from the first and second rows of holes , such that the axial locations of the holes 236 a of the first row and second row correspond to axial locations away from the holes 236 b of the first row and the second row , for example . the sheath 280 may comprise sheath 280 h comprising oval holes having a long dimension and a short dimension , with the long dimension extending transverse to the axis of the sheath 280 and the short dimension extending along the axis of the sheath 280 . the oval holes can be spaced apart and located in rows extending along the axis of the sheath as described herein , for example . the sheath 280 may comprise sheath 280 i comprising elongate oval holes having the long axis of the oval extending along the axis of the sheath and the narrow dimension of the oval extending transverse to the long axis of the sheath , for example . the sheath 280 may comprise sheath 280 j comprising at least about three rows of at least about 3 oval holes , each oval hole having a maximum dimension across of no more than about one quarter of the diameter of the outside diameter of the sheath 280 . the rows can be spaced apart circumferentially at about 120 degrees as described herein , for example . the sheath 280 may comprise sheath 280 k comprising at least about 40 holes , each hole having a diameter of no more than about one tenth of the diameter of the outside diameter of the sheath 280 . the holes can be located on opposite sides of the sheath 280 , and may comprise cross drilled holes , for example . fig7 d shows one of the sheath openings 236 having a beveled channel surface 284 to inhibit degradation of the penetrable barrier . the thickness 286 of the sheath wall may be within a range from about 0 . 0001 to about 0 . 01 inches , for example . the corner of 282 of the beveled channel surface of the opening may comprise an angle to inhibit degradation of the penetrable barrier , such as tearing with repeated injections . fig7 e shows one of the sheath openings 236 having a rounded channel surface of the opening and edge to inhibit degradation such as tearing of the penetrable barrier with repeated injections , in accordance with embodiments of the present disclosure ; fig7 f shows a schematic illustration of the parallel outflow paths from the reservoir chamber 140 . the first outflow path 140 p 1 extends from the reservoir chamber 140 to the receiver container 250 , and the second outflow path 140 p 2 extends from the reservoir chamber 140 across the porous structure 150 to the vitreous humor 30 of the eye . as the intraocular pressure of the eye may be substantially less than the pressure of the implantable device during exchange , the intraocular pressure of the eye approximates atmospheric pressure . the second outflow path 140 p 2 extends comprises a pressure drop dp across the porous structure 150 . the first outflow path 140 p 1 comprises the pressure drop dp across the plurality of openings 236 , along the one or more channels 239 extending from the plurality of openings to the opening 285 , and through the one or more openings 285 into the receiver container 250 . in many embodiments , the channel 254 and the opening 258 each comprise air , such that the resistance to flow 254 r of the channel 254 and the resistance to flow 258 r of the opening such that the pressure drop across channel 254 and the opening 258 can be substantially less than the pressure drop dp , for example negligible . in many embodiments , a valve 256 v can be provided , so as to vary the resistance to flow of the outflow path to provide a bolus . the valve 256 v may comprise a porous structure 256 , for example , or a stop , plunger or other mechanism so as to increase pressure and provide the bolus when the exchange apparatus 200 has received a predetermined amount of displaced liquid from the reservoir container 140 . the porous structure 256 may comprise a gas such as air initially , and be configured to contact the liquid from the reservoir chamber when the predetermined amount of fluid has been received and provide a substantial increase in the resistance to flow 156 r , such that the bolus is passed through porous structure 150 . examples of valves and mechanisms to provide the bolus injection are described in u . s . pct pat . app . no . pct / us2011 / 046812 , filed aug . 5 , 2011 , entitled “ injector apparatus and method for drug delivery ”, the entire disclosure of which has been previously incorporated herein by reference . the pressure drops can be configured in many ways so as to inhibit a bolus release into the eye when the therapeutic fluid is exchanged with the implantable device fluid , or so as to release a bolus of therapeutic fluid through the porous structure of the implantable device , for example . the therapeutic fluid 260 comprising therapeutic agent 110 is injected through needle 270 into the reservoir chamber 140 of the implantable device , so as to pressurize the implantable device chamber with a force sufficient to pass a substantial portion of the implantable device fluid 262 into the receiver container 250 . a pressure drop dp extends from the reservoir chamber of the implantable device through the plurality of openings 236 , along channel 239 extending to opening 285 , and through opening 285 , such that the implantable device fluid 262 is received in receiver container 250 . the outflow path from the reservoir chamber of the implantable device to the receiver container 250 comprises a resistance to flow corresponding to a resistance to flow 236 r of the plurality of openings 236 , the resistance to flow 239 r of the channel 239 , and the resistance to flow 285 r of opening 285 , for example . the resistance 150 r to flow of the porous structure corresponds to an amount of therapeutic fluid 260 passed from the reservoir chamber of the implantable device to the chamber of the eye containing vitreous humor , for example . the amount of fluid into the receiver container such as the chamber 250 relative to the amount of fluid through the porous structure is related to the resistances based on parallel flow . the amounts of flow to the receiver container 250 and through the porous structure 150 correspond substantially to the following equations : ( amount through porous structure )/( amount through receiver )=( resistance 236 r + resistance 239 r )/( resistance 150 r ) ( amount through porous structure )=( amount through receiver )*( resistance 236 r + resistance 239 r )/( resistance 150 r ) ( amount to receiver container )=( amount through porous structure )*( resistance 150 r )/( resistance 236 r + resistance 239 r ) the resistance 150 r corresponding to extended release of the therapeutic agent can be substantially greater than the resistance of the outflow path to the receiver container 250 comprising resistance 236 r and resistance 239 r , such that the amount of bolus of therapeutic fluid 260 and implantable device fluid 262 through the porous structure 150 can be less than about 1 μl combined , for example . alternatively , the resistance to flow of the outflow path can be sufficient such that a substantial amount of therapeutic agent 110 is released through porous structure 150 with a bolus during exchange . the resistance to flow along the outflow path may comprise one or more of the resistance to flow 236 r of the plurality of openings 236 , the resistance to flow 239 r of the channel 239 extending from the plurality of openings to the opening 285 , or the resistance to flow 285 r of the opening 285 , for example , or combinations thereof . the size and number of the plurality of openings 236 and the thickness 286 of the sheath can determine substantially the resistance 236 r of the plurality of openings . the length of the channel 239 extending from the plurality of openings 236 to the opening 285 , and the transverse dimensions of the channel can determine substantially the resistance to flow 239 r . for example the channel 239 may comprise a plurality of channels extending from the plurality of openings opening 236 to the reservoir container 250 . the resistance to flow 150 r can vary with the rri of the porous structure 150 . in many embodiments , the resistance to flow 150 r of porous structure 150 is inversely related to the rri of the porous structure . for example , experimental testing with syringes and test therapeutic devices has shown that a bolus can be achieved through a porous structure 150 having an rri of about 0 . 06 when the resistance to flow of outflow path is sufficiently large and device 100 is constructed such that chamber 140 can be pressurized to at least about one atmosphere , for example . however , porous structures having lower rris can provide a substantial resistance to flow so as to inhibit release of a substantial bolus . for example a porous structure 150 having an rri of about 0 . 02 has a resistance to flow 150 r such that an attempt to pass a substantial bolus amount through the porous structure 150 with a clinically acceptable injection time of 30 seconds or less may result in substantial pressure , for example greater than about four atmospheres . the resistance to flow 150 r of the porous structure 150 comprising the plurality of straight channels 150 sc varies with one or more of the combined cross - sectional surface area of the channels 150 sc , the number of openings , the size of each of the openings , or the thickness 150 t , and combinations thereof . the combined cross - sectional surface area of the channels 150 sc may be no more than about 100 , 000 μm 2 , so as to provide a resistance to flow 150 r of the porous structure 150 sufficient decrease flow through the porous structure and provide exchange as described herein . the combined cross - sectional surface area can be within a range from about 1000 μm 2 to about 100 , 000 μm 2 , for example , so as to provide a resistance to flow 150 r greater than the resistance to flow of the outflow path 140 p 1 . for example , the combined cross - sectional area within a range from about 1 , 000 μm 2 to about 30 , 000 μm 2 may provide a substantial resistance to flow 150 r , which may be substantially greater than the resistance to flow of the outflow path . in many embodiments , the combined surface area is within a range from about 1 , 000 μm 2 to about 10 , 000 μm 2 , and the resistance to flow 150 r is substantially greater than the resistance to flow of the outflow path so as to inhibit bolus release through the porous structure ( see also fig3 a and 3b ). the resistance to flow of the outflow path comprising resistance 236 r and 239 r may comprise about 5 per cent of the resistance 150 r to flow of the porous structure 150 , such that about 5 μl of fluid flows through the porous structure and about 95 μl flows through the plurality of openings 236 and channel 239 . the size and number of the plurality of openings and dimensions of channel 239 can be determined by a person of ordinary skill in the art based on the teachings described herein so as to provide a target amount of bolus for a target amount of injected therapeutic fluid . as the therapeutic fluid 260 can be denser than the implantable device fluid 262 , a substantial portion of the fluid through the porous structure 150 may comprise the therapeutic fluid 260 , for example . fig8 a shows a cross - sectional view of the apparatus to exchange fluid as in fig5 and 6 coupled to a syringe . the channel 239 extends from the plurality of openings 236 to a container 250 to receive the fluid of the implantable device . the distal portion 210 comprising tip 212 and opening 214 comprise a distal portion of needle 270 . the channel 219 extends along an axis 202 from the opening 214 to a connector 290 . the connector 290 is configured to couple to a connector 320 of an injector . the injector may comprise a syringe 300 ( not to scale ). the injector may comprise a container 310 comprising a therapeutic fluid for injection , and the container 310 can be fluidically coupled to the opening 214 on distal tip 212 when the connector 320 engages the connector 290 . the sheath may comprise an annular configuration shaped for placement over the substantially annular needle , such that the sheath and needle comprise a substantially concentric configuration extending along axis 202 . the connector 290 of the exchange apparatus and the connector 320 of the injector can be configured in many ways . for example , the connector 290 and the connector 320 may comprise a standard connector such as a luer connector or a pressure fit connector . alternatively , the connector 290 may comprise a non - standard connector to limit access to the exchange apparatus 200 . for example the connector 290 may comprise a star connector or other connector , and connector 290 may comprise a lock and key mechanism . the lock and key mechanism may comprise a lock on the exchange apparatus configured to receive a key of the injector , such that the lock of connector 290 can receive the key of connector 320 to couple the injector to the exchange apparatus and permit injection from chamber 310 through opening 214 . alternatively , the syringe 300 may be affixed to exchange apparatus 200 , and syringe 300 provided with a single dose of therapeutic agent . the container 250 of the exchange apparatus may have a volume to limit and amount of fluid received from the implantable device and to limit use of the apparatus to a single use . for example , the volume of the container may comprise no more than about 100 μl , for example no more than about 50 μl , so as to limit and amount of fluid exchanged with the implantable device and inhibit reuse of the exchange apparatus from patient to patient . the implantable device can be provided to a health care provider with an amount of gas , such as air within the receiver container 250 , and the receiver container may comprise a structure along a vent path to limit the amount of fluid that can be received by the container 250 . the exchange apparatus 200 may comprise a porous structure 256 to inhibit passage of the fluid of the implantable device and limit the amount of fluid exchanged . the porous structure 256 may comprise a material to pass a gas , such as air and inhibit flow of a liquid , such as the fluid of the implantable device . the material may comprise one or more of a fabric , a porous fabric , a semipermeable membrane , an air permeable material , a moisture vapor transfer waterproof fabric , a hydrophilic porous material , or a porous sintered material , for example . the channels extending through the porous structure 256 may comprise a gas , such as air and a lower resistance to flow of the gas and a substantially greater resistance to flow of a liquid , such as the therapeutic fluid , such that the exchange is substantially inhibited when receiver container 250 is substantially filled with fluid of implanted device and the fluid exchanged with the implanted device contacts the porous structure 256 . the porous structure 256 may comprise one or more of a fabric , a porous fabric , a semipermeable membrane , an air permeable material , a moisture vapor transfer waterproof fabric , a hydrophilic porous material , or a porous material or a porous sintered material , for example . the exchange apparatus may comprise a structure 259 composed of a material penetrable with a needle to draw a sample from the receiver container . the structure 259 may comprise one or more materials suitable for penetration with a needle such as one or more of rubber or silicone elastomer , for example . the structure 259 may comprise the porous structure 256 , for example , and the material penetrable with the needle may comprise one or more of a fabric , a porous fabric , a semipermeable membrane , an air permeable material , a moisture vapor transfer waterproof fabric , a hydrophilic porous material , or a porous material or a porous sintered material , for example . fig8 b shows an embodiment of an implantable therapeutic device 100 comprising a lock and key mechanism 850 to place a therapeutic agent in the implantable device . the lock and key mechanism 350 comprises a lock 360 and a key 370 . the lock 360 can be located on the implantable device to inhibit access to the reservoir chamber of the implantable device . the exchange apparatus 200 comprises the key 370 to access the reservoir chamber to place the therapeutic agent 110 as described herein . the lock can be configured in many ways and may comprise one or more of a deflected channel , a curved channel , a helical channel , a serpentine channel , engagement structures , a magnet , a door , a movable door , a tumbler , a cylinder , pins or a shear line , for example . the key can be configured in many ways so as to correspond to the lock and may comprise one or more of a deflectable elongate structure , a curved elongate structure , a helical elongate structure , a serpentine elongate structure , engagement structures sized to engage engagement structures of the lock , for example . in many embodiments , the lock 360 inhibits access with a straight rigid needle , so as to inhibit placement of the therapeutic agent which may be ineffective or inappropriate when placed in the therapeutic device . for example , the exchange apparatus 200 can be delivered to the physician with a predetermined therapeutic agent formulation and key , and the implantable device has the lock configured to receive the key to place the therapeutic agent , such that access to the implantable device can be limited substantially . in many embodiments , the lock 360 comprises the deflected channel 364 , which may comprise one or more of a bent channel , a curved channel , a helical channel , or a serpentine channel , for example . the lock 360 may comprise a stiff substantially non - penetrable biocompatible material , for example one or more of rigid plastic , polymethylmethacrylate ( hereinafter “ pmma ”), polycarbonate , metal , or titanium , for example . the key 370 may comprise one or more of many components and structures of elongate structure 201 as described herein . the key 370 may comprise one or more of a deflectable key or a deflected key configured to extend along the deflected channel 364 to deliver the therapeutic fluid 260 and receive the implantable device fluid 262 . the lock comprises an engagement structure 362 to engage an engagement structure 372 of the key . the engagement structure 362 may comprise an inner surface of the channel 364 , and the outer surface of the deflectable key engages the inner surface of the channel so as to deflect the elongate structure 201 to advance along channel 364 . fig8 b 1 shows an embodiment of a deflectable elongate structure 201 in an unloaded configuration prior to insertion in the lock 360 of fig8 b . the elongate structure comprises an axis 202 , and the elongate structure may extend substantially along the axis 202 so as to provide column strength to the elongate structure 201 to penetrate the penetrable barrier 184 of access port 180 . the elongate structure 201 may comprise a resistance to deflection sufficiently low so as to advance along channel 364 and a column strength sufficient to penetrate tissue and the penetrable barrier . the deflectable elongate structure 201 can be deflected substantially away from axis 202 when advanced into the lock 360 . the lock 360 may comprise a rigidity sufficient to inhibit penetration with a straight needle , and the channel 364 can be extend internally with lock 360 . the key 370 comprising the elongate structure 201 can extend through tissue such as the conjunctiva and epithelium to reach the lock 360 , and the key can be configured to penetrate the tissue . the penetration of the tissue and penetrable barrier 184 inhibits contamination of the reservoir chamber as the barrier function of the conjunctiva 16 and tenon &# 39 ; s capsule 17 can be substantially maintained . the deflectable elongate structure 201 can be made of one or more of many components and may comprise sheath 280 and needle 270 . the needle and sheath can be configured to deflect together when advanced along channel 364 . the deflectable needle may comprise a metal , for example nitinol , and the sheath may comprise a polymer such as polyimide , for example . fig8 b 2 shows an embodiment of a deflected elongate structure 201 in an unloaded configuration prior to insertion in the lock of fig8 b . the key 370 comprising deflected elongate structure may comprise one or more of many materials providing a stiffness sufficient to retain the deflected shape in the unloaded configuration . in the unloaded configuration , the deflected elongate structure 201 of key 370 extends away from axis 202 . the deflected elongate structure 201 may comprise a preformed deflection profile corresponding to the path of channel 364 extending through the lock 360 from a first side of the lock toward the conjunctiva to a second side of the lock toward the reservoir chamber 140 . fig8 c 1 shows an embodiment of an implantable therapeutic device 100 comprising a lock 360 and an exchange apparatus 200 comprising a rotatable key 370 to the lock 360 . the exchange apparatus 200 can be advanced toward the implantable device 100 and rotated as shown with arrows 374 . the engagement structures 372 of the key couple to the engagement structures 362 of the lock , such that the lock 360 opens to allow access of the elongate structure 201 . the engagement structures may comprise one or more of many structures , for example magnets , teeth , or notches , and the engagement structures can be spaced apart at appropriate distances such that the engagement structures of the lock are keyed to the engagement structures of the key to allow access . for example the engagement structures 372 of the key may comprise magnets , and the engagement structure of the lock may comprise a magnetic material such that the key can be opened with the lock and the magnetic field extending through the conjunctiva 16 and the tenon &# 39 ; s capsule 17 , for example . alternatively , the conjunctiva and / or tenon &# 39 ; s capsule can be displaced and the engagement structures 372 of the key can contact the engagement structures 362 of the lock to allow access to the reservoir chamber . fig8 c 2 shows an embodiment of the implantable therapeutic device 100 of fig8 c 1 in a unlocked configuration in which the elongate structure 201 extends through the open lock and penetrable barrier 184 to access the reservoir chamber 140 of the implantable device 100 . the exchange apparatus can place the therapeutic fluid 260 in the implantable device 100 and receive the implantable device fluid 262 in the receiver container 250 as described herein . fig8 d 1 shows an embodiment of an implantable therapeutic device comprising 100 a slide lock 360 and exchange apparatus 200 comprising a slidable key to engage the slide lock . the exchange apparatus 200 can be advanced toward the implantable device 100 and slid as shown with arrows 374 . the engagement structures 372 of the key couple to the engagement structures 362 of the lock , such that the lock 360 opens to allow access of the elongate structure 201 . the engagement structures of the slide lock 360 and slide key 370 may comprise structures similar to the rotatable key and lock described with reference to fig8 c 1 . fig8 d 2 shows an embodiment of an implantable therapeutic device 100 in an unlocked configuration in which the elongate structure 201 extends through the open lock 360 and penetrable barrier 184 to access the reservoir chamber 140 of the implantable device . the exchange apparatus can place the therapeutic fluid 260 in the implantable device 100 and receive the implantable device fluid 262 in the receiver container 250 as described herein . fig8 e shows an embodiment of an implantable therapeutic device 100 comprising a lock 360 and the elongate structure 201 of the exchange apparatus 200 comprising the key 370 . the elongate structure 201 can be configured in many ways so as to comprise the key 370 . the engagement structures 372 of the key 370 can be located near a distal end 212 of the elongate structure 201 , for example . the engagement structures 272 can be affixed to the needle 270 and may comprise annular structures extending around the needle . alternatively or in combination , the sheath 280 of the elongate structure may comprise the engagement structures . for example , the one or more openings 289 of the sheath 280 can be sized and located so as to comprise the engagement structures 372 of the key 370 . the lock can be configured in many ways to receive the key , and the engagement structures 362 of the lock may comprise pins aligned to a shear plane 368 when the key is inserted , for example . fig9 shows a container 400 to receive and store the exchange apparatus 200 . the container 400 may comprise a barrier material 410 to inhibit evaporation from within the container to the outside environment , a cap 430 and a base supporting a soft penetrable material 420 . the cap 430 may comprise a protrusion such as an annular protrusion 432 to seal around an outer portion of the wall of the container . the cap 430 may comprise a retention structure to hold the injector apparatus , for example a second protrusion , such as an annular protrusion 434 to receive and hold the exchange apparatus 200 . the cap 430 may comprise a soft barrier material , such as an elastomer , for example . fig1 shows an exchange apparatus 200 having the implantable device fluid 262 comprising a fluid sample 264 within the receiver container 250 . the receiver container 250 can be coupled to the elongate structure 201 . the channel 254 can extend from the container to 250 to opening 258 . the receiver container 250 may comprise a combination of one or more of the therapeutic fluid 260 , the implantable device fluid 262 comprising sample fluid 264 . depending on the exchange apparatus and orientation , the implantable device fluid 262 comprising sample fluid 264 may comprise a substantial majority of the fluid of the receiver container 250 . fig1 shows the exchange apparatus 200 having the fluid sample 264 placed partially within the storage container 400 . the cap 430 is shown over but not yet covering the vent channel 254 extending from the receiver container 250 to the opening 258 . fig1 shows a cap 430 of the storage container placed over the outlet channel opening 258 of channel 254 coupled to the receiver container 250 of the exchange apparatus , so as to inhibit one or more of leakage or evaporation from container 250 . fig1 shows an elongate structure 201 of the exchange apparatus placed within a soft penetrable material 420 near the bottom of the storage container and the cap placed over the container so as to seal the exchange apparatus container . the soft penetrable material 420 may comprise a soft material capable of sealing , for example a soft elastomeric material such as silicone elastomer . fig1 shows an apparatus 500 to remove the sample fluid from the receiver container 250 of the exchange apparatus 200 . the apparatus 500 comprises a sample container 400 , a plug 520 , a syringe 540 to pressurize the receiver container 250 , and a coupling 530 to couple the syringe to the receiver container of the exchange apparatus 200 . the coupling 530 may comprise a receptacle 536 to receive the proximal end portion of the exchange apparatus 200 . the receptacle 536 may comprise a structure 532 to couple the syringe to the coupling , for example a luer connector , a luer - lok ™ connector , or other known connector , for example . the retention structure 532 to retain the exchange apparatus 200 and a contact structure 534 to contact the outer wall of the exchange apparatus and fluidly couple the syringe to the opening 528 when the exchange apparatus 200 is retained with the coupling 530 . the contact structure 534 may inhibit flow of injection fluid from syringe 540 , such as air , between the retention structure 532 and wall 252 of the exchange apparatus , for example with a seal between the retention structure 532 and the wall 252 of the exchange apparatus 200 . fig1 shows a cap 520 placed on the connector 290 to couple the syringe to the exchange apparatus , so as to inhibit fluidic flow from syringe 540 through the needle of the elongate structure 201 . fig1 shows the exchange apparatus placed within receptacle 536 of the coupling 530 so as to couple the receiver container 250 with the syringe 540 . the syringe 540 can pressurize the channel 254 so as to displace the implantable device fluid comprising the sample fluid 264 from the receiver container 250 into a sample container 400 for analysis . the annular protrusion 534 can engage the outer wall 252 of the exchange apparatus 200 form a seal and pressurize chamber 250 when the plunger of syringe 540 is depressed . the pressurization of chamber 250 urges the implantable device fluid 262 fig1 shows an exchange apparatus 200 coupled to a removable receiver container 250 . the removable container 250 may comprise a penetrable barrier , for example a septum . the exchange apparatus 200 can be coupled to a syringe 300 . the exchange apparatus can be coupled to a device 100 implanted in an eye with the elongate structure 201 configured to extend through the conjunctiva 16 and the penetrable barrier 184 . the exchange apparatus may comprise a first channel coupled to the plurality of openings to receive the fluid from the implantable device , and a second channel coupled to a vent . the first channel 239 may extend to a first needle 710 to puncture container 250 and the second channel may extend to a second needle 720 to puncture the container 250 . the first needle may have a first opening 712 , and the second needle may have a second opening 722 . the first opening can be located below the second opening , such that the second opening allows air to pass when liquid passes through the first opening . fig1 shows the exchange apparatus 200 coupled to the implanted device 100 so as to exchange fluid and receive sample fluid 264 from the implanted device . the container 250 can be coupled to the exchange apparatus during exchange . fig1 shows the exchange apparatus 200 removed from the implanted device 100 and the receiver container 250 detached from the exchange apparatus 200 . the sample fluid 264 from the implantable device can be contained within the container 250 . fig2 a shows components of a container 400 to remove a sample fluid 264 from exchange apparatus 200 . the container 400 may comprise a sealable container having a wall composed of a barrier material 410 to inhibit evaporation , a cap 430 and an annular protrusion 432 . a support 450 can be placed within container to receive and hold the exchange apparatus 200 within the container . the support 450 may comprise a piece of soft elastomeric tubing such as silicone tubing , for example . fig2 b shows an exchange apparatus 200 placed in the container 400 having components as in fig2 a . the exchange apparatus is placed such that the wall 252 of container 250 rests on the support 450 . the elongate structure 201 extends below the support 450 . the container 400 comprises an axis 400 a , which axis may be aligned with the axis of exchange apparatus 200 . the opening 258 coupled to container 250 with channel 254 is exposed to air . fig2 c and 20d show removal of implantable device fluid 262 comprising sample fluid 264 from exchange apparatus . the sample fluid 264 may be drawn into the container 400 with aspiration . a syringe 300 can be coupled to the exchange apparatus 200 with a connector 320 such as a locking connector , for example . the syringe 300 may comprise a piston 302 connected to a plunger 304 which allows the piston to be advanced and pulled back . the syringe 300 comprises a chamber 310 having a volume defined with the location of piston 302 . the piston of the syringe can be drawn outward to draw air from chamber 440 , which chamber draws sample fluid 264 into chamber 440 . fig2 shows a method 1800 of removal from an exchange apparatus with a removal container as in fig2 a to 20d . a step 1810 removes the exchange apparatus 200 from the syringe after injection of the therapeutic fluid . the implantable device fluid comprising the sample fluid is contained in the receiver container 250 . a step 1810 removes therapeutic fluid 260 from the needle of the elongate structure 201 with injection of a gas comprising air from a syringe 300 . a step 1830 places the exchange apparatus 200 on the support 450 of container 400 with the exchange apparatus coupled to syringe 300 . the support 450 coupled to exchange apparatus 200 may define a chamber 440 . the support 450 can be shaped to inhibit air flow between and outer surface of the exchange apparatus and an inner surface of the support 450 , for example with a seal formed between the outer surface of the exchange apparatus 200 and the inner surface of the support 450 . the support may comprise a soft material , such as a soft elastomeric material , for example . a step 1840 draws air from chamber 440 with syringe 300 through the injection needle of the elongate structure extending into chamber 440 . the implantable device fluid 262 comprising sample fluid 264 is displaced from the receiver container with air drawn into the receiver container 250 through opening 258 of channel 254 . the implantable device fluid 262 comprising sample fluid 264 falls to the lower end of chamber 440 and is contained on an inner surface of container 400 . a step 1850 removes the exchange apparatus 200 and syringe 300 from the sample container 400 . the cap 430 is placed on the container 400 , so as to inhibit evaporation of the implantable device fluid 260 comprising sample fluid 264 . fig2 shows an exchange apparatus 200 having a receiver container 250 comprising a penetrable barrier structure 259 on a side port to remove a sample from the receiver container with a needle and syringe . the syringe can draw implantable device fluid 262 comprising sample fluid 264 from the receiver container 250 through a needle 330 passing through the penetrable barrier structure 259 on the side port . fig2 a shows an exchange apparatus 200 having a receiver container 250 coupled to a sample container 400 and a syringe 300 to displace fluid from the receiver container 250 . the sample container 400 is placed over the plurality of openings 236 and a needle 330 of a syringe 300 extends into a chamber 440 the sample container . the syringe 300 can draw fluid from chamber 440 so as to displace fluid from the receiver container 250 . the channel 254 extends from container 250 to opening 258 . fluid drawn through needle 330 into syringe 300 urges the implantable device fluid 262 comprising sample fluid 264 through the one or more openings comprising the plurality of openings 236 , and air can move inward through opening 258 and along channel 254 to displace the implantable device fluid 262 comprising sample fluid 264 . the needle 270 extends through the sample container 400 such that the distal end of the needle extends beyond sample container 400 . the plurality of openings 236 may comprise a plurality of openings of sheath 280 . fig2 b shows the sample container 400 of fig2 a placed over the plurality of openings 236 of the exchange apparatus . the sample container 400 may comprise a first penetrable barrier comprising penetrable barrier material 420 and a second penetrable barrier comprising penetrable barrier material 420 . a first septum 422 can be located opposite a second septum 422 , for example . the elongate structure 201 can extend through the first penetrable barrier and the second penetrable barrier so as to position the one or more openings between the first penetrable barrier and the second penetrable barrier . the sample container 400 may comprise a wall composed of a barrier material 410 , and the wall may comprise an amount of rigidity sufficient to resist deflection when the sample is drawing with needle 330 . the wall may comprise an annular shape , for example a tubular geometry . the needle 270 may extend through the second penetrable barrier so as to inhibit fluidic coupling of the syringe 300 and needle 330 with the opening on the distal end of needle 270 . the sample container 400 can be shaped in many ways , for example with a spherical ball or other shape having a walls composed of penetrable barrier material 410 such that the needle tip can extend through both side of the container 400 . fig2 a and 24b show an exchange apparatus having a receiver container 250 coupled to a syringe 300 with a sample container 400 placed over openings 236 of the exchange apparatus 200 so as to remove a sample fluid 264 from the receiver container 250 . the sample container 400 comprises a chamber 440 enclosed with a wall comprising a barrier material 410 and a penetrable barrier material 420 , in which the penetrable barrier material may comprise a septum , for example . the wall of the container 400 may comprise one or more of many shapes such as annular , spherical , cubic , ellipsoidal or oval , for example . the elongate structure 201 comprising needle 270 and sheath 280 can be advanced into the container 400 so as to place at least one opening of the plurality of openings 236 within the chamber 440 and the distal needle tip comprising the opening to place therapeutic fluid within the chamber 440 . the needle can be coupled to syringe 300 , and fluid drawn from chamber 440 with syringe 300 through an opening in the distal tip of needle 270 . the fluid drawn through the needle 270 is replaced with the fluid passed through the plurality of openings 236 . the receiver container 250 comprising the implantable device fluid 262 comprising sample fluid 264 is fluidically coupled to the plurality of openings as described herein such that the implantable device fluid 262 comprising the therapeutic fluid 264 is passed through the plurality of openings . the channel 254 extends from the receiver container 250 to the opening 258 such that air may be drawn into the receiver container 250 to replace the volume of the displaced implantable device fluid 262 comprising sample fluid 264 . in many embodiments , the implantable device fluid 262 comprising the sample fluid 264 comprises a liquid comprising water as described herein . fig2 a shows an exchange apparatus 200 comprising a removable receiver container 250 comprising a removable sheath 280 placed over a needle 270 . the receiver container 250 may comprise the sample container 400 . the wall 252 of container 250 and needle 270 can be configured for removal and separation from the needle 270 so as to provide the sample container 400 . the sheath 280 may be supported on a distal end of the wall 252 of container 250 , such that the sheath 280 can be supported with the wall 252 of container 400 when removed . a plug 960 comprising penetrable barrier material 420 can be placed over the sheath 280 needle 270 prior to removal of the needle to inhibit leakage of the implantable device fluid 262 comprising sample fluid 264 . fig2 b shows the removable container 400 of fig2 a with a plug 960 comprising penetrable barrier material 420 placed over the sheath 280 and the needle 270 removed , such that the sheath 280 is supported with the container 400 . the implantable device fluid 262 comprising sample fluid 264 remain in the receiver container 250 comprising sample container 400 subsequent to removal of the needle 200 . fig2 c shows the removable container of fig2 a and 25b with plug 960 placed over the sheath 280 and a cap 430 over the removable receiver container . the cap 430 can inhibit one or more of evaporation or leakage of the implantable device fluid 262 comprising sample fluid 264 . fig2 a to 26e show a centrifuge used to remove the fluid sample from the receiver container of the exchange apparatus . fig2 a shows the exchange apparatus 200 comprising the receiver container 250 having the implantable device fluid 262 comprising the sample fluid 264 contained therein , in which the exchange apparatus is configured for placement within the sample container 400 . the sample container 400 may comprise a centrifuge tube having a support 450 as described herein . the exchange apparatus 200 may comprise a channel 254 extending from receiver container 450 to opening 258 , so as to couple the opening 258 to the plurality of openings 236 . as the implantable device fluid 262 comprising sample fluid 264 contained within receiver container 250 comprises a density greater than air , the fluid within the receiver container can be displaced through the plurality of openings 236 of the exchange apparatus 200 . air can pass through opening 258 and channel 254 into the receiver container 250 to replace the volume of implantable device fluid 262 comprising sample fluid 264 displaced from receiver container 250 and through the plurality of openings 236 . fig2 b shows the exchange apparatus 200 placed in the sample container 400 . fig2 c shows the exchange apparatus 200 in the sample container 400 configured for placement in a centrifuge 500 . fig2 d shows the exchange apparatus 200 in the sample container 400 placed in a centrifuge 500 . fig2 e shows the exchange apparatus 200 within the sample container 400 subjected to force within the centrifuge 500 , such that the force of the centrifuge 500 is sufficient to displace the implantable device fluid 262 comprising sample fluid 264 from the receiver container 400 through the plurality of openings 236 as described herein . the implantable device fluid 262 comprising sample fluid 264 is deposited on the lower end portion of an inner surface the sample container 400 . fig2 f shows an embodiment comprising exchange apparatus 200 placed in a sample container 400 comprising a centrifuge tube . the container 400 may comprise a barrier material 410 to inhibit evaporation from within the container to the outside environment , a cap 430 and a base supporting a soft penetrable material as described herein . the cap 430 may comprise a protrusion such as an annular protrusion 432 to seal around an outer portion of the wall of the container , for example . when the cap 430 is placed on the top of the tube , the chamber 440 can be sealed so as to inhibit evaporation , for example . the barrier 410 may comprise sufficient strength so as to inhibit penetration with the needle of the elongate structure 201 when placed in a centrifuge , for example . fig2 g shows an embodiment comprising an exchange apparatus 200 placed in a sample container 400 comprising a centrifuge tube , in which the centrifuge tube comprises a support 450 comprising an annular shoulder 450 s of the tube to engage and hold the exchange apparatus . the support 450 can engage the exchange apparatus 200 to support the exchange apparatus in a centrifuge , for example , with a gap extending between the lower surface of the tube and the distal tip of the needle of the exchange apparatus so as to inhibit penetration of the sample container with the needle . the container 400 may comprise additional structures as described herein . fig2 h shows an embodiment of an exchange apparatus 200 placed in a sample container 400 comprising a centrifuge tube , in which the centrifuge tube comprises a support 450 comprising restricted portion to hold the exchange apparatus . the support 450 may comprise a rib to engage the exchange apparatus 400 , for example . the rib 450 r can be formed with a recess in the outer surface of the container 400 . the support comprising the rib can engage and support the exchange apparatus such that a gap extends between the distal end of elongate structure 201 and the lower surface of the tube fig2 a shows an embodiment of a collapsible fluid separator 510 for use with a therapeutic device . the collapsible fluid separator 510 may comprise a plunger and can be penetrable with a needle and configured to form a seal around the outer perimeter . the fluid separator 510 may comprise a distal shape profile corresponding to the distal portion of the reservoir chamber so as to displace fluid from the distal portion near the porous structure 150 as described herein . the fluid separator 510 may be penetrated with a needle and may comprise a septum , for example . the penetrable fluid separator can be penetrated with a needle for fluid removal and refill . in many embodiments , the fluid separator 510 is configured to expand and contract so as to contact the inner wall of the reservoir chamber 140 and form a seal with wall of the reservoir chamber . the fluid separator 510 can be configured to expand and contract to maintain contact with a wall having a varying cross - sectional dimension such as a varying diameter . in many embodiments , the fluid separator 510 is configured to contract so as to decrease the volume of the fluid separator such that the volume of the reservoir chamber available to receiver therapeutic fluid 260 can be substantially maintained . fig2 b shows an embodiment of plunging structure 520 comprising an exchange needle 522 and an engagement structure comprising shoulder 524 suitable for use with the collapsible fluid separator as in fig2 a and a therapeutic device . the needle 522 comprises an internal channel to receiver fluid to remove the implantable device fluid and place the therapeutic fluid in the reservoir chamber . the plunging structure may comprise an engagement structure , for example shoulder 524 , so as to engage the collapsible separator and advance the fluid separator 510 distally toward the porous structure with a thrusting movement . fig2 c shows an embodiment of the collapsible fluid separator as in fig2 b placed within a reservoir chamber 140 of a therapeutic device 100 . the collapsible separator 510 is shown near the proximal end of the implantable therapeutic device 100 , which comprises the access port 180 and retention structure 120 . the access port 180 may comprise a penetrable barrier 184 capable of penetration with the needle of the plunging structure , or a removable structure such as a cap , plug or the like which can be removed to introduce the plunging structure . fig2 d shows an embodiment of the plunger 520 comprising the exchange needle and shoulder as in fig2 b advanced into the access port 180 of the therapeutic device having the collapsible fluid separator 510 placed within the reservoir chamber 140 of the therapeutic device as in fig2 c . fig2 e shows an embodiment of the plunging structure 520 and collapsible fluid separator 510 advanced within the reservoir chamber 140 of the therapeutic device as in fig2 d so as to displace the implantable device fluid 562 from the reservoir chamber through the needle . the collapsible fluid separator 510 has expanded from a first cross - sectional dimension across , for example a first diameter , to a second cross - sectional dimension across , for example a second cross - sectional diameter larger than the first . the expandable and collapsible fluid separator 510 can expand or collapse so as to contact the side wall of the reservoir chamber 140 and inhibit flow between a lower side and an upper side of the expandable and collapsible fluid separator 510 . the inhibited flow around the outer perimeter of the fluid separator can provide pressurization of the implantable device fluid near the tip of exchange needle 522 so as to drive implantable device fluid into the exchange needle . alternatively or in combination , suction can be applied to the exchange needle so as to draw implantable fluid from the exchange needle 522 and advance the separator 510 toward the porous structure 150 . in many embodiments , the porous structure 150 comprises a resistance to flow sufficient to inhibit flow of one or more of the implantable device fluid or the therapeutic fluid through the porous structure during the exchange as described herein . fig2 f shows an embodiment of the collapsible fluid separator 510 advanced within the reservoir chamber to a location near the distal end of the reservoir chamber so as to displace most of the implantable device fluid from the reservoir chamber through the needle 522 . the needle 522 may contact porous structure 150 , which may comprise a rigid porous structure as described herein . fig2 g shows an embodiment of the collapsible fluid separator 510 moved from the distal end of the reservoir chamber comprising porous structure 150 . the collapsible fluid separator 510 can be moved in one or more of many ways to place the therapeutic fluid in the distal portion of the reservoir container . the therapeutic fluid can be injected through the needle 522 , or another needle for example , so as to place the therapeutic fluid 260 in the distal portion of the container . alternatively or in combination , the expandable and collapsible fluid separator can be pulled toward the proximal end of the reservoir chamber so as to draw therapeutic device fluid through the needle and into the reservoir chamber from an external container of the exchange apparatus as described herein . fig2 h shows an embodiment of the collapsible fluid separator 510 moved from the distal end of the reservoir chamber to the proximal end of the reservoir chamber so as to fill substantially the reservoir chamber with therapeutic fluid 260 . the collapsible fluid separator 510 comprises a substantially decreased size and volume so as to fit substantially within the neck of the reservoir chamber such that a substantial amount of the volume of the reservoir is filled with therapeutic fluid 260 . fig2 i shows an embodiment of a substantially non - collapsible fluid separator 510 placed within the reservoir chamber 140 of therapeutic device 100 having a substantially fixed cross sectional size . the container 130 comprising reservoir chamber 140 may comprise a substantially cylindrical tubular barrier 160 . the fluid separator may comprise a piston slidable within the tubular barrier 160 , for example . fig2 a shows an embodiment of an exchange apparatus 550 comprising a balloon 560 supported on a elongate tubular member 580 capable of introduction into an implantable therapeutic device 100 as to exchange the implantable device fluid 262 with a therapeutic fluid 260 . the exchange apparatus 550 may comprise an elongate tubular structure 570 shaped to penetrate tissue , for example a needle . the elongate tubular structure 570 shaped to penetrate tissue can be advanced into access port 180 through penetrable barrier 184 , followed by balloon 560 and the distal end of elongate tubular member 580 , such that balloon 560 is placed in the reservoir chamber . the balloon 560 may comprise a highly compliant balloon . as the balloon 560 is inflated , implantable device fluid is displaced out of the reservoir chamber . the balloon 560 may comprise pebax ™ or another highly elastic material such as silicone , for example , or a non - elastic material capable of being one or more of folded , rolled or compressed , for example . the balloon 560 may comprise a tubular structure and supported on the outside diameter of the needle or a sheath over the needle prior to inflation . the balloon may be designed to inflate proximally to distally , e . g . top down , to contact the inner wall of the reservoir chamber and displace fluid toward the vent needle opening . the balloon may be inflated with therapeutic fluid 260 . the balloon may be retractable within a sheath , for example . a sheath may be provided to deliver the balloon through the penetrable barrier , for example with the sheath penetrating the penetrable barrier to protect and place the balloon in the reservoir chamber without substantial contact of the balloon to the penetrable barrier when the balloon is placed . the exchange apparatus 550 comprises components and structure to inflate balloon 560 and remove implantable device fluid 262 from the reservoir chamber 140 . the elongate tubular structure 570 shaped to penetrate tissue may comprise a channel 572 to fluidically couple the reservoir chamber 140 with an external container , for example . the elongate tubular member 580 may comprise a first lumen 582 and a second lumen 584 , for example . the elongate tubular member 580 can be connected to one or more containers , syringes , or pumps , for example . the elongate tubular member 580 may comprise a first connector 588 fluidically coupled to first lumen 582 , and a second connector 586 fluidically coupled to the second lumen 584 , for example . the first lumen 582 of the elongate tubular member 580 can fluidically couple to channel 572 and external connector 588 , for example , such that the implantable device fluid 262 can be received in a receiver container as described herein . the second lumen 584 can fluidically couple the connector 586 to balloon 560 , so as to allow inflation of the balloon , for example with a syringe . the connector 586 and the connector 588 may each comprise standard known connectors as described herein , for example . the exchange apparatus 550 may comprise one or more catheter components known to a person of ordinary skill in the art in the field of catheter design and suitable for combination in accordance with the teachings described herein , for example . fig2 b shows an embodiment of the balloon 260 as in fig2 a inflated within the therapeutic device to displace the implantable device fluid 262 . the balloon 560 may be inflated with the therapeutic fluid 260 as described herein , for example . the therapeutic fluid 260 , or another fluid , can be injected into the balloon with a syringe coupled to connector 586 such that the injected fluid travels along lumen 584 to inflate the balloon 560 . the implantable device fluid 262 can be displaced with the balloon so as to urge the implantable device fluid 262 into channel 572 of the elongate structure 260 shaped to penetrate tissue . the porous structure 150 may comprise a substantial resistance to flow to inhibit flow of implantable device fluid 262 through the porous structure . fig2 c shows an embodiment of the balloon 560 deflated within the therapeutic device 100 to provide space for the therapeutic fluid 260 . in many embodiments , the receiver container as described herein , for example a bag , can be disconnected from connector 588 , and a syringe comprising therapeutic fluid 560 coupled to connector 580 . the syringe or other fluid source used to fill balloon 560 can be decoupled from lumen 582 , and the therapeutic fluid 560 can be injected into elongate structure 570 to place therapeutic fluid 260 in reservoir chamber 140 such that the fluid within balloon 560 is displaced and the size of balloon 560 decreased . when the size of balloon 560 has decreased sufficiently , the balloon 560 and elongate structure 570 can be removed from the implantable device 100 by passing through the penetrable barrier 184 . the balloon 560 and elongate structure 570 can be removed in many ways , for example by one or more of pulling on elongate tubular member 580 or injecting therapeutic fluid 560 into reservoir chamber 140 , so as to displace balloon 560 and elongate structure 570 from the reservoir chamber 140 . in many embodiments , reservoir chamber 140 can be pressurized with injection of therapeutic fluid 260 so as to displace the balloon 560 and elongate structure 570 through the penetrable barrier 184 with pressure . fig2 d shows an embodiment of the balloon 560 punctured within the therapeutic device 100 so as to release the therapeutic fluid 260 from the balloon to the reservoir chamber 140 of the therapeutic device 100 . the therapeutic 100 may comprise internal structures 590 to puncture the balloon and release the therapeutic agent . the internal structure 290 may comprise a sharp tip , for example a needle tip to penetrate the balloon 560 and release the therapeutic agent . the internal structure 590 can be supported on the wall of the reservoir chamber , for example . fig2 a shows an embodiment of a deflectable fluid separator 600 placed within an implantable therapeutic device 100 . the deflectable fluid separator 600 inhibits mixing of the implantable device fluid 262 with the therapeutic fluid 260 . the deflectable fluid separator 600 can separate portions of the reservoir chamber so as to define a first portion 141 on a first side of the chamber and a second portion 143 on a second side of the reservoir chamber . the first portion 141 of the reservoir chamber 140 may be coupled to a first porous structure 151 to provide sustained release from the first portion and the second portion 143 of the reservoir chamber 140 may be coupled to a second porous structure 153 to provide sustained release from the second portion . the porous structures can be substantially similar to porous structure 150 as described herein . the deflectable fluid separator 600 may comprise a barrier material to inhibit flow of the therapeutic agent , and may comprise one or more of a bladder , diaphragm , a membrane , or a sheet of distensible material , for example . the deflectable fluid separator may comprise an expandable bladder capable of deflection to either side of the reservoir chamber , for example . the deflectable fluid separator may be used with exchange apparatus 200 as described herein . the elongate structure 201 of the exchange apparatus may comprise a bi - needle design as described herein , for example with a first needle to advance fluid into a first side of the bladder and a second needle to receiver fluid from a second side of the bladder , in no particular order , or simultaneously , for example . fig2 b shows an embodiment of the deflectable fluid separator as in fig2 a displaced to the second side of the reservoir chamber to remove fluid from the second portion 143 of the reservoir chamber . the removal of fluid from portion 143 can be achieved in many ways . for example , the deflectable fluid separator can be displaced with injection into first portion 141 so as to displace implantable device fluid 262 from second portion 143 . a first needle 611 and a second needle 613 can be advanced so as to extend through penetrable barrier 184 into first portion 141 and into second portion 143 , respectively . the first needle can inject fluid into first portion 141 to displace fluid from second portion 143 . alternatively or in combination , the second needle 613 can be aspirated to draw fluid from second portion 143 with suction , and a fluid may be drawn into first portion 141 through first needle 611 . fig2 c shows an embodiment of the deflectable fluid separator 600 as in fig2 b displaced to the first side of the reservoir chamber with a therapeutic fluid 260 placed in the second portion 143 of the reservoir chamber 140 . the therapeutic agent 110 contained within second portion 143 can be released through porous structure 153 in a manner similar to porous structure 150 as described herein . when a sufficient amount of therapeutic agent has been released from second chamber 143 for an extended time through porous structure 153 , the fluid can be removed from second portion 143 as described herein and a second amount of therapeutic fluid 260 placed in first portion 141 for sustained release for another extended time through porous structure 151 . the removal and placement of fluid with the deflectable separator can be repeated as many times as is helpful to treat the patient . fig3 a shows an embodiment of an exchange apparatus 200 comprising a valve 700 to direct flow toward a second receiver container 704 when a sample 264 of the implantable device fluid 262 has been placed in a first receiver container 702 . the valve 700 can inhibit mixing of the implantable device fluid 262 with the therapeutic fluid 260 , such that sample fluid 264 may comprise no substantially amount of therapeutic fluid 260 . the sample fluid 264 can be removed used for one or more assays as described herein . the valve 700 may comprise one or more of a porous structure , a float valve , an annular float valve , a ball float valve , a flap valve , a flap valve with a float , a duckbill valve , or a stopcock . the valve 700 may comprise a manual valve , or may comprise one or more structures to automatically close or open when a sufficient amount of fluid has been placed in the first receiver container . the receiver container 250 may comprise the first receiver container 702 and the second receiver container 704 . the exchange apparatus 200 may comprise one or more of the elongate structure 201 , needle 270 , sheath 280 , receiver container 250 , at least one opening 258 , connector 290 , syringe 300 , piston 302 , plunger 304 , chamber 310 , or connector 320 as described herein , for example . the valve 700 may be configured in many ways to provide sample 264 of implantable device fluid 262 . with elongate structure 301 introduced into therapeutic device 100 , an initial amount of implantable device fluid 262 can be placed in first receiver container 702 with valve 700 comprising a first configuration . the first configuration of valve 700 can fluidically couple one or more openings 236 of elongate structure 201 with the first receiver container 702 and inhibit fluidic coupling of the one or more openings of elongate structure 201 with second receiver container 702 . when a sufficient amount of implantable device fluid 262 has been placed in the first receiver container 702 , the configuration valve 700 can change from the first configuration to the second configuration . the second configuration of valve 700 can fluidically couple the one or more openings 236 with the second receiver container 704 and inhibit flow to the first receiver container 702 , such that a majority of the therapeutic fluid 260 mixed with implantable device fluid 262 is placed in second receiver container 704 . the valve 700 may comprise a manual valve 710 operable by a user , and may comprise one or more of many valves known to a person of ordinary skill in the art , for example a stopcock or other manual or automatic valve , for example . the sample 264 within first container 702 can be removed for analysis with one or more of many methods or structures as described herein . fig3 b shows an embodiment of an exchange apparatus 200 having a valve 700 comprising a porous structure 720 to direct flow toward a second receiver container 704 when sample 264 of the implantable device fluid 262 has been placed in first receiver container 702 . the valve 720 may comprise a substantially dry porous structure in an initial open configuration and a gas such as air can be situated within first receiver container 702 . implantable device fluid 262 accumulates in the first receiver container 702 and rises inside the first container 702 from a distal end near the elongate structure to a proximal end of the first container . when a sufficient amount of implantable device fluid 262 is placed on first container 702 , the valve 720 contacts the implantable device fluid 262 comprising liquid and the resistance to flow of the valve 720 increases substantially . the wetted valve 720 comprises a substantially closed configuration such that the implantable device fluid 262 passes through a flow resistance structure 722 . the flow resistance structure 722 comprises a resistance to flow when wet that is greater than the resistance to flow of valve 720 in the dry configuration and substantially less than the resistance to flow of valve 720 in the wet configuration , such that the dry valve 720 corresponds to a substantially open configuration and the wet valve 720 corresponds to a substantially closed configuration . the valve 720 and the flow resistance structure 722 may each comprise a porous structure similar to the porous structure for sustained release of the therapeutic agent as described herein , for example . the valve 720 and flow resistance structure 722 can be configured in many ways to provide sample 264 of implantable device fluid 262 with no substantial portion of therapeutic fluid 260 . the relative resistance to flow of the porous structure 720 when we can be substantially greater than the resistance to flow of the resistance structure 722 when wet , for example at least about twice , and in many embodiments at least about five times the resistance to flow of the flow resistance structure . the flow resistance structure 722 may comprise a valve that opens under pressure such as a duckbill valve or flap with a spring , for example . a baffle 728 , a channel , or other internal structure can be provided to inhibit mixing of the therapeutic fluid 260 and implantable device fluid 262 with the sample fluid 264 when valve 720 is wet and comprises the closed configuration . fig3 c shows an embodiment of an exchange apparatus 200 in which valve 700 comprises a float valve 730 . the float valve 730 comprises a float ball 732 to direct flow toward a second receiver container 704 when a sample 264 of the implantable device fluid 262 has been placed in a first receiver container 702 . the valve 732 can slide along first container 702 . a valve 736 such as a flap valve or duckbill valve , for example , can be provided to provide a resistance to flow and drive fluid into the first receiver container 702 . when the implantable device fluid 262 advances into container 702 , float ball 732 rises in the first container 702 until the float ball contacts a seat 734 and inhibits flow into the first container . when float ball 732 contacts seat 734 additional flow into first container 702 is inhibited and valve 736 opens to allow implantable device fluid 262 into the second receiver container 704 . the received implantable device fluid 262 mixed with therapeutic fluid 260 may displace a gas such as air through opening 258 . a flow resistance structure 738 such as a second duck bill valve or baffle can be provided near the opening to the first container to inhibit mixing of sample 264 of the first receiver container 702 , for example . fig3 d shows an embodiment of an exchange apparatus 200 having a valve 700 comprising a float valve 740 . the float valve 740 comprises a sliding annular structure 744 to direct flow toward a second receiver container 704 when a sample 264 of the implantable device fluid 262 has been placed in first receiver container 702 . the sliding annular structure 744 may comprise an annular float ring 742 coupled to a tube having an opening 745 to pass fluid when the valve 740 is open . the sheath 280 can extend over needle 270 upward from the first receiver container 702 to the second receiver container 704 . the sheath 280 may comprise one or more openings 236 to pass the implantable device fluid 262 into the first receiver container 702 through opening 745 . as the first receiver container 702 receives implantable device fluid 262 , valve 740 rises and slides axially along sheath 280 such that a portion 747 of annular structure 744 slides over one or more openings 236 to inhibit flow to the first receiver container 702 . in the closed configuration , valve 740 directs flow of the implantable device fluid 262 and therapeutic fluid 260 into second receiver container 704 through holes 748 in sheath 280 . the exchange apparatus may comprise connector 290 to couple to a syringe as described herein . fig3 e shows an embodiment of an exchange apparatus 200 in which valve 700 comprises a float valve 750 to direct flow toward a second receiver container when a sample of the implantable device fluid has been placed in a first receiver container . float valve 750 comprises a flap 752 . the flap 750 allows sample fluid 262 to enter the first receiver container 702 through openings 757 of sheath 280 , and when a sufficient amount of sample fluid has been received with sample container 702 , float valve 750 closes to inhibit flow through openings 757 . the implantable device fluid 262 is passed through opening 758 into second receiver container 704 when the float valve 750 is closed . fig3 a 1 shows an embodiment of an exchange apparatus 200 having a receiver container 250 comprising a fluid separator 800 comprising an internal channel 822 sized to support the implantable device fluid 262 with a pocket of air . the fluid separator 800 may comprise a tubular structure 820 , for example a column , having an internal dimension such as a diameter sized to support the implantable device fluid with an immiscible separator fluid . the immiscible separator fluid may comprise one or more of an oil , a hydrophobic liquid , a gas , or air , for example . the exchange apparatus may comprise one or more of many structures as described herein such as connectors to couple to a syringe and an elongate structure comprising a sheath and needle . the internal channel 822 of fluid separator 800 can be fluidly coupled to openings 236 to receive implantable device fluid 262 as described herein . the fluid received from the implantable device can be received in receiver container so as to separate the implantable device fluid 262 from the therapeutic fluid 260 . the internal channel 822 may initially comprise a gas such as air which can be displaced through opening 258 of receiver container 250 . while the exchange apparatus can be used in many ways with an immiscible separator fluid such as a gas comprising air , in many embodiments the therapeutic fluid 260 is first drawn into a syringe 300 , and then the immiscible separator fluid such as air drawn into syringe 300 . the syringe 300 can be coupled to the exchange apparatus 200 with the therapeutic fluid supported with the immiscible separator fluid such as air within the container , for example . in many embodiments , the barrel of the syringe comprises an inner diameter sized such that the therapeutic fluid 260 can remain free standing within the barrel of the syringe and may be supported with air , such that the air can be injected into the implantable device before the air is injected . the implantable device may comprise a maximum cross - sectional dimension , for example a maximum diameter , such the implantable device fluid can be supported and displaced with the immiscible separator fluid 810 placed in the lower portion of the reservoir chamber 140 near porous structure 150 . injection of the immiscible separator fluid 810 displaces implantable device fluid 262 through one or more openings 236 of sheath 280 and upward into channel 822 . when a substantial portion of the implantable device fluid has been displaced from the reservoir chamber , for example with air , the therapeutic fluid 260 can enter the reservoir chamber such that the implantable device fluid 262 remains substantially separated from the therapeutic fluid 260 introduced into the reservoir chamber 140 . the separator fluid 810 may comprise a miscible separator fluid , for example saline or other liquid capable of mixing with the therapeutic fluid 260 and the implantable device fluid 262 , and the separator fluid 810 may comprise a sufficient volume so as to inhibit mixing of the therapeutic fluid 260 with the implantable device fluid 262 . in many embodiments , the separator fluid 810 comprises a fluid not miscible with the therapeutic fluid 260 and implantable device fluid 262 , each of which may comprise substantial amounts of water . the immiscible separator fluid 810 can inhibit mixing of the implantable device fluid 262 and the therapeutic fluid 260 with the separator fluid 810 , such that the separator fluid 810 may comprise a barrier and inhibit mixing of the components of the implantable device fluid 262 with components of the therapeutic fluid 260 . fig3 a 2 shows an embodiment of the exchange apparatus 200 of fig3 a 1 having the implantable device fluid 262 supported with a pocket of immiscible separator fluid 810 such as air 812 , so as to separate the implantable device fluid 262 from the therapeutic fluid 260 . an interface 818 extends between the immiscible separator fluid 810 and the implantable device fluid 262 . an interface 814 extends between the immiscible separator fluid 810 and the therapeutic fluid 260 . in many embodiments , immiscible separator fluid 810 comprises a gas , and implantable device fluid 262 and therapeutic fluid 260 each comprise liquid such that interface 814 comprises a meniscus and interface 818 comprise a meniscus . fig3 b 1 shows an embodiment of an exchange apparatus 200 having a fluid separator 800 comprising an internal channel having a first portion 852 sized to support the implantable device fluid with a pocket of an immiscible separator fluid air and a second portion 854 sized to pass an immiscible separator fluid such as air through the implantable device fluid . the first portion may comprise a volume approximating the volume of the reservoir chamber , for example . the exchange apparatus may comprise one or more of the structures of the exchange apparatus 200 as described herein , for example receiver container 200 and container wall 252 may have dimensions so as to define the first portion 852 and the second portion 854 . fig3 b 2 shows an embodiment of the exchange apparatus of fig3 b 1 having the first portion 852 supporting the implantable device fluid 262 with the immiscible separator fluid 810 such as air 812 . the tip 212 of needle 270 may extend to the distal end of the reservoir chamber 140 such that the bubble forms at the distal end of the reservoir to increase exchange efficiency , for example . the reservoir chamber 140 and the first portion 852 may comprise immiscible separator fluid 810 such as air 812 . fig3 b 3 shows an embodiment of the exchange apparatus of fig3 b 1 and 31 b 2 having the first portion 852 supporting the implantable device fluid 262 with the pocket of immiscible separator fluid 810 and therapeutic fluid 260 , and the second portion containing the implantable device fluid . as additional gas such as air moves upward from the first portion 852 to the second portion 854 , the immiscible separator fluid comprising a gas such as air forms bubbles in second portion 854 having the increased inner dimensions and the bubble can travel upward to escape through opening 258 . the first portion 852 and the second portion 854 may each comprise an annular channel having an inner dimension determined by the outside diameter of needle 270 , for example . the increased outer dimension of the annular channel of the second portion 854 allows bubbles to form in the implantable device fluid 262 contained in the second portion such that the bubbles can rise and escape through valve 258 . fig3 c shows an embodiment of exchange apparatus 200 coupled to a syringe 300 comprising a separator structure 860 to inject a separation fluid 810 and a therapeutic fluid into therapeutic device 100 to collect a sample 264 of implantable device fluid 262 . the separator structure 860 may comprise one or more of a piston 862 , a plunger , a disk or a plug having one or more holes 862 . the holes 864 may comprise a sufficient resistance to flow such that the piston 864 moves downward toward the elongate structure 201 when the piston 302 is advanced . the piston 864 can displace the immiscible separator fluid 810 comprising air , such that the immiscible separator fluid 810 is displaced into reservoir chamber 140 and forms an interfacial boundary 816 . the interfacial boundary 816 moves toward sheath 280 as the implantable device fluid is displaced with the immiscible separator fluid 810 . when the piston 810 has advanced a sufficient distance , movement of piston 864 along the cylinder barrel is inhibited , and the therapeutic fluid 260 is displaced through the one or more holes 862 with piston 302 . the displaced therapeutic fluid 260 is placed in reservoir chamber 140 , for example with injection through needle 270 . the immiscible separator fluid 810 is displaced with therapeutic fluid 260 such that the immiscible separator fluid 810 enters receiver container 250 . in many embodiments the receiver container 250 comprises a volume that is at least the volume of the injected material comprising therapeutic fluid 260 and immiscible separator fluid 810 , such that the volume of the receiver container 250 is sufficient to retain the implantable device fluid 262 and the immiscible separator fluid 810 . the volume of immiscible separator fluid 810 injected with the therapeutic fluid can be less than , approximately the same as , or greater than the volume of the therapeutic agent injected . in many embodiments , the immiscible separator fluid 810 comprises a volume sufficient to separate the therapeutic fluid from the implantable device fluid and which is substantially less than the volume of the reservoir chamber . for example , the amount of immiscible separator fluid 810 may comprise a volume that is sufficient to form a bubble within the reservoir chamber 140 and that is substantially less than the volume of the volume of reservoir chamber 140 . the receiver container 250 can be configured in many ways to receive the implantable device fluid 262 and the immiscible separator fluid 810 . for example , the receiver container 250 may comprise the inside dimension sufficient to support the implantable device fluid with the immiscible separator fluid along a majority of the length of the receiver container 250 . alternatively , the first portion 852 of the receiver container may comprise the inside dimension sufficient to support the implantable device fluid 262 and the second portion 854 of the receiver container may comprise the inside dimension sufficiently large so as to pass the immiscible separator fluid 810 through the implantable device fluid . a person or ordinary skill in the art can determine the internal dimensions of the first portion and the second portion based on the teachings of the present disclosure . fig3 shows an embodiment of an exchange apparatus coupled to syringe 300 to draw therapeutic fluid into the implantable device from the container 250 . the implantable device fluid 262 can be drawn from the reservoir chamber in one or more of many ways , for example with syringe so to provide aspirating suction of the implantable device fluid from the implantable device into the syringe . as the needle 272 extends through penetrable barrier 184 so as to provide a seal and the porous structure 150 comprises a resistance to flow of components of the eye , the movement of the implantable device fluid 262 into the chamber of syringe 300 results in therapeutic fluid 260 moving from chamber 250 through the one or more openings 289 in sheath 280 . air at approximately atmospheric pressure can move into container 250 to urge and displace the therapeutic fluid 260 into the reservoir chamber when the implantable device fluid 262 is drawn with the syringe . fig3 shows an embodiment of a curved needle 270 of an exchange apparatus to direct therapeutic fluid 260 toward a wall 260 of a container 230 of the reservoir chamber 240 . the curved needle can be placed near the porous structure 150 and may result in a reproducible flow pattern of the therapeutic fluid 260 placed in the container . the reproducible flow pattern provided by the curved needle 270 can provide a consistent flow pattern over porous structure 150 and may provide a more uniform amount of bolus through porous structure 150 . fig3 shows an embodiment of a covering 870 on a porous structure of a therapeutic device to inhibit bolus release when the therapeutic fluid is introduced . the covering 870 can inhibit bolus release when the needle is oriented toward the porous structure 150 and the covering 870 , for example . fig3 shows an embodiment of a first exchange apparatus 200 a coupled to a double barrel syringe 300 to exchange a first exchange fluid 900 with the implantable device fluid 262 , and a second exchange apparatus 200 b to exchange the first exchange fluid placed in the therapeutic device with therapeutic fluid 260 . the first exchange fluid 900 may comprise the separator fluid 810 as described herein . the first exchange fluid 900 may comprise water , for example phosphate buffered saline ( hereinafter “ pbs ”). alternatively , the first exchange fluid may comprise an immiscible separator fluid as described herein . the first exchange apparatus 200 a and the second exchange apparatus 200 b may each comprise many of the structures of exchange apparatus 200 as described herein . for example , the first exchange apparatus 200 a and the second exchange apparatus 200 b may each comprise the elongate structure 201 and receiver container 250 as described herein . the double barrel syringe 300 may comprise the therapeutic fluid and the first exchange fluid 900 . the double barrel syringe 300 may comprise a first chamber 910 containing the first exchange fluid 900 and a second chamber 920 containing the therapeutic fluid 260 . the first chamber 910 may be coupled to a first piston 912 and plunger 914 having a first length . the second chamber 920 may be coupled to a second piston 922 and plunger 924 having a second length . the first length can be longer than the second length to that the contents of the first chamber are injected before the second chamber . the first exchange apparatus 200 a can be connected to the syringe 300 and the elongate structure 201 inserted into the implantable device as described herein , and the first plunger advanced so as to displaced the implantable device fluid 262 from the reservoir chamber 140 with the first exchange fluid 900 . the first exchange apparatus 200 a can be removed from therapeutic device implanted in the eye . the first exchange apparatus 200 a can be disconnected from the syringe 300 , and the second exchange apparatus 200 b connected to the syringe 300 and advanced into the therapeutic device 100 . the second plunger 924 can be advanced to displace the first exchange fluid 900 from the reservoir chamber 140 of the implantable device with the therapeutic fluid 260 as described herein . in many embodiments , one or more of the components of the first exchange apparatus 200 a and the second exchange apparatus 200 b can be combined for use with the double barrel syringe so that the first exchange fluid and the therapeutic fluid can each be exchanged sequentially when the exchange apparatus 200 is placed in the implantable device and without removing the exchange apparatus from the implanted device . for example , the exchange apparatus 200 may comprise the first receiver 702 container to receive the implantable device fluid and the second receiver container 704 as described herein to receive the first exchange fluid , and the first receiver container and the second receiver container can be coupled to one or more valves as described herein such that the implantable device fluid 262 is directed to the first receiver container when the valve comprises a first configuration and the first exchange fluid is directed to the second receiver container when the valve comprises a second configuration as described herein . fig3 shows an experimental test apparatus . the test apparatus comprised an injector coupled to a bi - needle exchange apparatus 200 to inject a therapeutic fluid comprising a therapeutic agent into a test implantable device 100 . the therapeutic fluid comprised a 100 mg / ml formulation of ranibizumab prepared in accordance with u . s . pat . pub . no . 2010 / 0015157 , entitled “ antibody formulations ”, the full disclosure of which is incorporated by reference . the injected formulation comprised a density at least about 1 % greater than the fluid of the implantable device , which comprised saline . the therapeutic fluid was injected through the penetrable barrier comprising a septum of silicone elastomer . the injector needle was approximately 33 gauge and coupled to a syringe and positioned below the receiver needle . the receiver needle received liquid from the implantable device and extended upward to a receiver container . axis of the injector needle 202 and the axis of the implantable device 100 a were oriented to obtain samples . the reservoir chamber of the implantable device comprised about 25 μl , and about 50 μl were injected . the orientation of the axes varied from 0 degrees ( horizontal ) 45 degrees away from horizontal . at the − 45 degree orientation the penetrable barrier was located above the reservoir chamber and the opening to the receiver needle located above the opening to the injector needle . fig3 shows experimental results obtained with the test apparatus of fig3 . the refill efficiency corresponded to the amount of therapeutic fluid placed in the reservoir chamber of the implantable device when the 50 ul had been injected . for 0 degrees , the efficiency was about 80 %. the efficiency increased with the angle to about 95 % at − 45 degrees . table 2 shows device angles and fill efficiencies corresponding to the values in the graph of fig3 . a concentric needle device was also tested and provided similar results . pressure studies have been conducted with the injector apparatus having the plurality of openings . the sheath comprised polyimide placed over a 33 gauge needle . a first pressure gauge was coupled to a syringe on the input side of the needle , and a second pressure gauge was coupled to the implantable device reservoir chamber where the porous structure is shown above . the input pressure to the syringe of 12 n produced a pressure of 85 pounds per square inch ( hereinafter “ psi ”) into the needle and implantable device chamber had a pressure of about 45 psi . this amount of input pressure corresponds to a clinically acceptable exchange time of about 5 seconds , for example . additional experiments can be conducted by a person of ordinary skill in the art based on the teachings described herein , for example experiments with an exchange apparatus comprising a polyimide sheath comprising a plurality of openings over a needle as described herein . additional experiments can be conducted with one or more of many release control mechanisms to determine the resistance to flow of the release control mechanism suitable for use in accordance with embodiments described herein . for example , studies can be conducted with porous structures of varying dimensions , release rates , and manufacturing processes , in order to measure the flow through the frits with pressure so as to determine the resistance to flow . while the exemplary embodiments have been described in some detail , by way of example and for clarity of understanding , those of skill in the art will recognize that a variety of modifications , adaptations , and changes may be employed .
the present invention features methods and pharmaceutical compositions for the treatment of hepatitis c in a human in need thereof comprising administering a compound of formula , , , , , or described herein or a pharmaceutically acceptable salt thereof in combination with one or more additional hepatitis c therapeutic agents .