reference is now made in detail to the exemplary embodiments of the invention , examples of which are illustrated in the accompanying drawings . wherever possible , the same reference numbers are used throughout the drawings to refer to the same or like parts . fig2 is one view of an ophthalmic medical device including a disposable tip segment and a limited reuse assembly according to an embodiment of the present invention . in fig2 , the medical device includes a tip segment 205 and a limited reuse assembly 250 . the tip segment 205 includes a needle 210 , a housing 215 , and an optional light 275 . the limited reuse assembly 250 includes a housing 255 , a switch 270 , a lock mechanism 265 , and a threaded portion 260 . tip segment 205 is capable of being connected to and removed from limited reuse assembly 250 . in this embodiment , tip segment 205 has a threaded portion on an interior surface of housing 215 that screws onto the threaded portion 260 of limited reuse assembly 250 . in addition , lock mechanism 265 secures tip segment 215 to limited reuse assembly 250 . lock mechanism 265 may be in the form of a button , a sliding switch , or a cantilevered mechanism . other mechanisms for connecting tip segment 205 to limited reuse assembly 250 , such as those involving structural features that mate with each other , are commonly known in the art and are within the scope of the present invention . needle 210 is adapted to deliver a substance , such as a drug , into an eye . needle 210 may be of any commonly known configuration . preferably , needle 210 is designed such that its thermal characteristics are conducive to the particular drug delivery application . for example , when a heated drug is to be delivered , needle 210 may be relatively short ( several millimeters ) in length to facilitate proper delivery of the drug . switch 270 is adapted to provide an input to the system . for example , switch 270 may be used to activate the system or to turn on a heater . other switches , buttons , or user - directed control inputs are commonly known and may be employed with limited reuse assembly 250 and / or tip segment 205 . optional light 275 is illuminated when tip segment 205 is ready to be used . optional light 275 may protrude from housing 215 , or it may be contained within housing 215 , in which case , optional light 275 may be seen through a clear portion of housing 215 . in other embodiments , optional light 275 may be replaced by an indicator , such as a liquid crystal display , segmented display , or other device that indicates a status or condition of disposable tip segment 205 . for example , optional light 275 may also pulse on and off to indicate other states , such as , but not limited to a system error , fully charged battery , insufficiently charged battery or faulty connection between the tip segment 205 and limited use assembly 250 . while shown on tip segment 205 , optional light 275 or other indicator may be located on limited reuse assembly 250 . fig3 is another embodiment of a limited reuse assembly according to the principles of the present invention . limited reuse assembly 250 includes a button 308 , a display 320 , and a housing 330 . disposable tip segment 205 attaches to end 340 of limited reuse assembly 250 . button 308 is actuated to provide an input to the system . as with switch 270 , button 308 may activate a heater or other temperature control device or initiate actuation of a plunger . display 320 is a liquid crystal display , segmented display , or other device that indicates a status or condition of disposable tip segment 205 or limited reuse assembly 250 . fig4 is a cross section view of a disposable tip segment and a limited reuse assembly according to an embodiment of the present invention . fig4 shows how tip segment 205 interfaces with limited reuse assembly 250 . in the embodiment of fig4 , tip segment 205 includes plunger interface 420 , plunger 415 , dispensing chamber housing 425 , tip segment housing 215 , temperature control device 450 , thermal sensor 460 , needle 210 , dispensing chamber 405 , interface 530 , and tip interface connector 453 . limited reuse assembly 250 includes mechanical linkage interface 545 , actuator shaft 510 , actuator 515 , power source 505 , controller 305 , limited reuse assembly housing 255 , temperature release mechanism 400 , interface 535 , and limited reuse assembly interface connector 553 . in tip segment 205 , plunger interface 420 is located on one end of plunger 415 . the other end of plunger 415 forms one end of dispensing chamber 405 . plunger 415 is adapted to slide within dispensing chamber 405 . the outer surface of plunger 415 is fluidly sealed to the inner surface of dispensing chamber housing 425 . dispensing chamber housing 425 surrounds the dispensing chamber 405 . typically , dispensing chamber housing 425 has a cylindrical shape . as such , dispensing chamber 405 also has a cylindrical shape . needle 210 is fluidly coupled to dispensing chamber 405 . in such a case , a substance contained in dispensing chamber 405 can pass through needle 210 and into an eye . temperature control device 450 at least partially surrounds dispensing chamber housing 425 . in this case , temperature control device 450 is adapted to heat and / or cool dispensing chamber housing 425 and any substance contained in dispensing chamber 405 . interface 530 connects temperature control device 450 with tip interface connector 453 . optional thermal sensor 460 provides temperature information to assist in controlling the operation of temperature control device 450 . thermal sensor 460 may be located near dispensing chamber housing 425 and measure a temperature near dispensing chamber housing 425 or may be located in thermal contact with dispensing chamber housing 425 , in which case it measures a temperature of dispensing chamber housing 425 . thermal sensor 460 may be any of a number of different devices that can provide temperature information . for example , thermal sensor 460 may be a thermocouple or a resistive device whose resistance varies with temperature . thermal sensor 460 is also electrically coupled to interface 530 or other similar interface . the components of tip segment 205 , including dispensing chamber housing 425 , temperature control device 450 , and plunger 415 are at least partially enclosed by tip segment housing 215 . in one embodiment consistent with the principles of the present invention , plunger 415 is sealed to the interior surface of dispensing chamber housing 425 . this seal prevents contamination of any substance contained in dispensing chamber 405 . for medical purposes , such a seal is desirable . this seal can be located at any point on plunger 415 or dispensing chamber housing 425 . in limited reuse assembly 250 , power source 505 provides power to actuator 515 . an interface ( not shown ) between power source 505 and actuator 515 serves as a conduit for providing power to actuator 515 . actuator 515 is connected to actuator shaft 5 10 . when actuator 515 is a stepper motor , actuator shaft 510 is integral with actuator 515 . mechanical linkage interface 545 is connected to actuator shaft 510 . in this configuration , as actuator 515 moves actuator shaft 510 upward toward needle 210 , mechanical linkage interface 545 also moves upward toward needle 210 . in other embodiments of the present invention , mechanical linkage interface 545 and actuator shaft 510 are a single component . in other words , a shaft connected to actuator 515 includes both actuator shaft 510 and mechanical linkage interface 545 as a single assembly . in limited reuse assembly 250 , power source 505 is typically a rechargeable battery , such as a lithium ion battery , although other types of batteries may be employed . in addition , any other type of power cell is appropriate for power source 505 . power source 505 provides current to dispensing chamber housing 425 to heat / cool it and change its shape . optionally , power source 505 can be removed from housing 255 through a door or other similar feature ( not shown ). controller 305 is connected via interface 535 to limited reuse assembly interface connecter 553 . limited reuse assembly interface connecter 553 is located on a top surface of limited reuse assembly housing 255 adjacent to mechanical linkage interface 545 . in this manner , both limited reuse assembly interface connector 553 and mechanical linkage interface 545 are adapted to be connected with tip interface connector 453 and plunger interface 420 , respectively . controller 305 and actuator 515 are connected by an interface ( not shown ). this interface ( not shown ) allows controller 305 to control the operation of actuator 515 . in addition , an interface between power source 505 and controller 305 allows controller 305 to control operation of power source 505 . in such a case , controller 305 may control the charging and the discharging of power source 505 when power source 505 is a rechargeable battery . controller 305 is typically an integrated circuit with power , input , and output pins capable of performing logic functions . in various embodiments , controller 305 is a targeted device controller . in such a case , controller 305 performs specific control functions targeted to a specific device or component , such as a temperature control device or a power supply . for example , a temperature control device controller has the basic functionality to control a temperature control device . in other embodiments , controller 305 is a microprocessor . in such a case , controller 305 is programmable so that it can function to control more than one component of the device . in other cases , controller 305 is not a programmable microprocessor , but instead is a special purpose controller configured to control different components that perform different functions . while depicted as one component in fig4 , controller 305 may be made of many different components or integrated circuits . limited reuse assembly 250 also includes temperature release mechanism 400 . temperature release mechanism 400 allows actuator 515 to be activated to deliver the substance only when the substance is in the proper temperature range . temperature release mechanism 400 and its operation are more fully described below . tip segment 205 is adapted to mate with or attach to limited reuse assembly 250 . in the embodiment of fig4 , plunger interface 420 located on a bottom surface of plunger 415 is adapted to mate with mechanical linkage interface 545 located near a top surface of limited reuse assembly housing 255 . in addition , tip interface connector 453 is adapted to connect with limited reuse assembly interface connector 553 . when tip segment 205 is connected to limited reuse assembly 250 in this manner , actuator 515 and actuator shaft 510 are adapted to drive plunger 415 upward toward needle 210 . in addition , an interface is formed between controller 305 and temperature control device 450 . a signal can pass from controller 305 to temperature control device 450 through interface 535 , limited reuse assembly interface connector 553 , tip interface connector 453 , and interface 530 . in operation , when tip segment 205 is connected to limited reuse assembly 250 , controller 305 controls the operation of actuator 515 . actuator 515 is activated by temperature release mechanism . when actuator 515 is actuated , actuator shaft 510 is moved upward toward needle 210 . in turn , mechanical linkage interface 545 , which is mated with plunger interface 420 , moves plunger 415 upward toward needle 210 . a substance located in dispensing chamber 405 is then expelled through needle 210 . in addition , controller 305 controls the operation of temperature control device 450 . temperature control device 450 is adapted to heat and / or cool dispensing chamber housing 425 and its contents . since dispensing chamber housing 425 is at least partially thermally conductive , heating or cooling dispensing chamber housing 425 heats or cools a substance located in dispensing chamber 405 . temperature information can be transferred from thermal sensor 460 through interface 530 , tip interface connector 453 , limited reuse assembly interface connector 553 , and interface 535 back to controller 305 . this temperature information can be used to control the operation of temperature control device 450 . when temperature control device 450 is a heater , controller 305 controls the amount of current that is sent to temperature control device 450 . the more current sent to temperature control device 450 , the hotter it gets . in such a manner , controller 305 can use a feed back loop utilizing information from thermal sensor 460 to control the operation of temperature control device 450 . any suitable type of control algorithm , such as a proportional integral derivative ( pid ) algorithm , can be used to control the operation of temperature control device 450 . a substance to be delivered into an eye , typically a drug suspended in a phase transition compound , is located in dispensing chamber 405 . in this manner , the drug and phase transition compound are contacted by the inner surface of dispensing chamber housing 425 . the phase transition compound is in a solid or semi - solid state at lower temperatures and in a more liquid state at higher temperatures . such a compound can be heated by the application of current to temperature control device 450 to a more liquid state and injected into the eye where it forms a bolus that erodes over time . in one embodiment of the present invention , the substance located in dispensing chamber 405 is a drug that is preloaded into the dispensing chamber . in such a case , tip segment 205 is appropriate as a single use consumable product . such a disposable product can be assembled at a factory with a dosage of a drug installed . while shown as a two - piece device , the injection system of fig4 may be a single piece device . in such a case , the tip segment is integrated into the limited reuse assembly to form a single medical device . fig5 is an exploded cross section view of a tip segment for an ophthalmic medical device according to an embodiment of the present invention . in fig5 , tip segment 205 includes dispensing chamber housing 425 , tip segment housing 215 , thermal sensor 460 , needle 210 , dispensing chamber 405 , plunger 415 , plunger shaft 380 , plunger interface 420 , temperature control device 450 , interface 530 , tip interface connector 453 , and temperature release mechanism 400 . in the embodiment of fig5 , temperature control device 450 is activated to bring a substance in dispensing chamber 405 to within a proper temperature range . thermal sensor 460 provides temperature information to controller 305 ( not shown ) to control temperature control device 450 . after the substance has reached the proper temperature , temperature release mechanism 400 is actuated to drive plunger toward needle 210 to dispense a substance contained in dispensing chamber 405 . temperature release mechanism 400 can only be activated when the substance is in the proper temperature range . in this manner , the substance in dispensing chamber 405 is delivered only when it is in the proper temperature range . in addition , the embodiment of fig5 includes a plunger shaft 380 that is connected to plunger 415 . in this embodiment , plunger 415 may be over - molded onto plunger shaft 380 . plunger shaft 380 is generally cylindrical in shape with a middle diameter that is less than a diameter on its distal and proximal ends . plunger interface 420 is a surface on the proximal end of plunger shaft 380 . plunger shaft 380 is typically made of a rigid material such as stainless steel . plunger 415 is made of a rubber or polymer material . in another embodiment of the present invention , the distal end of plunger shaft 380 has a lip over which plunger 415 can be applied . plunger 415 can be press - fitted onto plunger shaft 380 and is retained in place by a lip on the distal end of plunger shaft 380 . this allows for easier assembly . instead of over molding plunger 415 onto a shaft , plunger 415 can be manufactured as a separate part and pushed onto the distal end of plunger shaft 380 . plunger interface 420 can be of any suitable shape . as seen in fig5 , temperature release mechanism may be incorporated into tip segment 205 , in which case it is not present in limited reuse assembly 250 . in this manner , temperature release mechanism may be located in tip segment 205 or in limited reuse assembly 250 . when a single integrated unit ( integrating tip segment 205 and limited reuse assembly 250 into a single device ), temperature release mechanism may be located in the integrated unit . temperature release mechanism 400 may be located such that it operates to allow dispensing of the substance only when the substance is in the proper temperature range . since different materials can be used to make temperature release mechanism 400 ( as described below ), the location of temperature release mechanism is dependent on its structure and the materials used to make it . for example , when temperature release mechanism 400 includes a nitinol member ( as described below ), temperature release mechanism 400 should be positioned such that it can be activated only when the substance is in the proper temperature range . in this case , temperature release mechanism 400 may be placed near temperature control device 450 and dispensing chamber housing 425 , so that heat produced by temperature control device 450 and conducted by dispensing chamber housing 425 alters the shape of the nitinol member in such a way as to permit dispensing of the substance when it is in the proper temperature range . fig6 a and 6b are exploded cross section views of a temperature release mechanism according to the principles of the present invention . temperature release mechanism 400 includes button 605 , spring 610 , shaft 615 , locking mechanism 620 , and triggering device 625 . in fig6 b , shape memory alloy member 630 and disk 635 are also depicted . button 605 is located on top of shaft 615 . shaft 615 is located in a notch in locking mechanism 620 . spring 610 biases shaft 615 upward and away from locking mechanism 620 . spring 610 also provides some resistance to button 605 when it is pushed . triggering device 625 is located below locking mechanism 620 . as shown in fig6 b , shape memory alloy member 630 and disk 635 are located in locking mechanism 620 . shape memory alloy member 630 is connected to disk 635 . in one embodiment consistent with the principles of the present invention , shape memory alloy member 630 and disk 635 are made out of the same shape memory alloy material . triggering device 625 is a switch , contact , or other similar device that can initiate the actuation of substance delivery . for example , triggering device 625 may be a switch that activates actuator 515 to drive actuator shaft 510 and mechanical linkage mechanism 545 toward needle 210 to deliver the substance from dispensing chamber 405 . in fig6 b , shape memory alloy member 630 is made of a shape memory alloy (“ sma ”). shape memory alloys , such as various nitinol ( a nickel - titanium alloy ) alloys , hold a deformed shape at room temperature . when heated to a higher temperature , the sma reverts to its non - deformed shape . in other words , a shape memory alloy ( also known as a smart alloy or memory metal ) is a metal that “ remembers ” its geometry . after an sma has been deformed from its original atomic configuration , it regains its original geometry by itself during heating . these properties are due to a temperature - dependent martensitic phase transformation from a low - symmetry to a highly symmetric crystallographic structure . those crystal structures are known as martensite and austenite . the three main types of sma are copper - zinc - aluminum , copper - aluminum - nickel , and nickel - titanium ( ni — ti ) alloys . the temperatures at which the sma changes its crystallographic structure are characteristic of the alloy , and can be tuned by varying the elemental ratios . for a shape memory alloy member 630 made out of nitinol , the nitinol is in a deformed shape at room temperature . in this deformed shape , the nitinol has a martenistic crystal structure . in this deformed shape , when shape memory alloy member 630 is a wire - type structure , it has first length . as the temperature of shape memory alloy member 630 rises , its shape changes . when the temperature of shape memory alloy member 630 reaches 60 or 70 degrees celsius , the nitinol will revert to its non - deformed shape . in this process , the nitinol changes from a martenistic crystal structure to an austenic crystal structure . in this non - deformed shape , when shape memory alloy member 630 is a wire - type structure , it has a second length . as the temperature of shape memory alloy member 630 increases , the transition from the first length to the second length can be gradual . in fig6 b , shape memory alloy member 630 is at the desired temperature range . in this temperature range , shaft 615 is able to traverse locking mechanism 620 through an opening in disk 635 . in this embodiment , shape memory alloy member 630 is a wire - type structure . however , shape memory alloy member 630 may be any convenient structure , such as a coil . in other embodiments , shape memory alloy member 630 is toroidal in shape , in which case the opening in the toroid can be varied by varying its temperature . in operation , when shape memory alloy member 630 in locking mechanism 620 is at room temperature , shaft 615 is not able to contact triggering device 625 ( as shown in fig6 a ). as shape memory alloy member 630 is heated , its shape changes . as its shape changes , disk 635 slides in locking mechanism 620 . when shape memory alloy member 630 reaches the proper temperature range , disk 635 is located such that shaft 615 is able to pass through it and contact triggering device 625 . fig7 a - 7h are exploded cross section views of a portion of a temperature release mechanism according to the principles of the present invention . fig7 a - 7d are top cross section views , and fig7 e - 7h are side cross section views . fig7 a and 7e are top and side cross section views of locking mechanism 620 . an opening 705 is shown . locking mechanism 620 is hollow and , in this case , tubular . shaft 615 is located above opening 705 , such that it can pass through opening 705 to activate triggering device 625 ( as shown in fig6 b ). in fig7 b and 7f , shape memory alloy member 630 is at room temperature or in a low temperature range . shape memory alloy member 630 is shown as a coil . in this position , disk 635 blocks opening 705 , thus preventing shaft 615 from contacting triggering device 625 . the opening in disk 635 is not aligned with opening 705 . in fig7 c and 7g , shape memory alloy member 630 is in a proper temperature range . in this position , the opening in disk 635 is aligned with opening 705 , thus allowing shaft 615 to pass through locking mechanism 620 and contact triggering device 625 . in this manner , when the substance in the dispensing chamber is in the proper temperature range ( and the opening in disk 635 is aligned with opening 705 ), actuator 515 can be activated to deliver the substance into an eye . in fig7 d and 7h , shape memory alloy member 630 is in a high temperature range . in this position , disk 635 blocks opening 705 , thus preventing shaft 615 from contacting triggering device 625 . the opening in disk 635 is not aligned with opening 705 . when temperature release mechanism 400 is located near dispensing chamber housing 425 ( or temperature control device 450 ), shape memory alloy member 630 can be altered by the heat produced by temperature control device 450 ( when it is a heater ). as temperature control device 450 heats up , a substance located in dispensing chamber 405 also heats up . this in turn causes shape memory alloy member 630 to change shape and move disk 635 . when the substance is in the proper temperature range , shape memory alloy member 630 has changed shape so that the opening in disk 635 is aligned with opening 705 in locking mechanism 620 . when these two openings are aligned , shaft 615 can pass through locking mechanism 620 and disk 635 to contact triggering device 625 . in this case , when button 605 is pushed , the substance ( which is in the correct temperature range ) is delivered into an eye . if the substance is too hot , then the button cannot be depressed as the opening in disk 635 is not aligned with the opening 705 in locking mechanism 620 . in this manner , the actuation of drug delivery device only occurs when the drug is in the proper temperature range . from the above , it may be appreciated that the present invention provides an improved system for delivering precise volumes of a substance into an eye . the present invention provides a temperature release mechanism that ensures that a substance is delivered into an eye only when it is in a proper temperature range . in one embodiment , a disposable tip segment that interfaces with a limited reuse assembly is employed . in another embodiment , a single unit is employed . the present invention is illustrated herein by example , and various modifications may be made by a person of ordinary skill in the art . while the present invention is described in the context of a single - use drug delivery device , the present invention encompasses any single - use medical device . other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein . it is intended that the specification and examples be considered as exemplary only , with a true scope and spirit of the invention being indicated by the following claims .
an ophthalmic injection device has a dispensing chamber housing , a plunger , an actuator for driving the plunger , a temperature control device , and a temperature release mechanism . the dispensing chamber housing has an inner surface and an outer surface . the inner surface partially defines a dispensing chamber for holding a quantity of a substance . the plunger is engaged with the inner surface of the dispensing chamber housing , is capable of sliding in the dispensing chamber housing , and is fluidly sealed to the inner surface of the dispensing chamber housing . the temperature control device at least partially surrounds the dispensing chamber housing and is capable of altering the temperature of the substance in the dispensing chamber . the temperature release mechanism is in a locked position when the substance is outside the proper temperature range and an unlocked position when the substance is in the proper temperature range .