the invention will now be described more fully with reference to the accompanying examples , in which certain preferred embodiments of the invention are shown . this invention may , however , be embodied in many different forms and should not be construed as limited to the embodiments set forth herein ; rather , these embodiments are provided so that this disclosure will be thorough and complete , and will fully convey the scope of the invention to those skilled in the art . surgically removing only the morbid part of an internal organ , such as a kidney , or only a selected portion of hyperplastic tissue , as in benign prostate hyperplasia , can be beneficial for the patient in that at least part of the functionality of the organ can often be spared . however , many of the organs that might benefit the patient if only part of the organ is removed are soft , and / or prone to bleed extensively , and / or have differing compartments , whose contents should not be allowed to mix ( e . g ., the kidney or liver ). for example , essentially normal kidney function can be preserved with less than one - half of the normal functionality of one of the two kidneys , and the liver can regenerate if sufficient detoxification potential is retained or provided artificially . the challenge to the surgeon is to efficiently and completely close such organs , after removal of a tumor or other abnormality , so that blood does not leak into the abdominal cavity , and so that the separation functions of the organs can rapidly regenerate . we have found , as published in patents and patent applications , that the use of a reverse - gelling polymer — i . e ., a polymer that gels as the temperature rises above a certain temperature ( tg )— can temporarily embolize the arteries ( us 2005 / 0008610 , incorporated herein by reference ) and other internal organs ( schwartz et al ., u . s . 60 / 874 , 062 , incorporated herein by reference ; raymond et al ., biomaterials 2004 vol . 25 , p . 3983 ). preliminary preclinical and clinical results appear promising . however , there are some uncertainties in the procedure and areas that can be improved . one uncertainty that one would like to reduce is the length of time needed to reperfuse the organ , after surgery and any necessary sealing or suturing is complete . this is because when the circulation is blocked , the affected region becomes anoxic . for brief periods , the anoxia is largely reversible , but damage does accrue , and the ability to reverse the damage upon reperfusion declines with the time of anoxia , at a rate that is organ dependent . hence , rapid reversal of the temporary embolization is highly desirable . application of cold solutions , such as cool or cold isotonic saline , will reverse the gelled state of the rgp , but it is not always feasible to do this quickly via the circulation itself , since the circulation is locally blocked by the reverse gelled polymer gel . hence , reperfusion is dependent on a combination of external cooling , and gradual dilution of the gel by the diffusion of molecules from the gel into the upstream or downstream circulation , or into tissue interstitial spaces and the like . another problem to be addressed is the avoidance of hemostasis of an entire organ , when what is required is hemostasis in the vicinity of a particular site . if circulation can be maintained in those parts of the organ not requiring surgery , and if the volume of tissue subjected to hemostasis can be minimized , then outcome can be improved , and in particular the likelihood of the organ remaining at least partially functional at the end of the procedure is markedly improved . another problem to be addressed is to prevent the flow of blood , in an organ being treated by heat or radiant energy , from distorting the zone of treatment by carrying heat from tissue intended to be treated , to other tissue outside the treatment zone . in response to these and other needs , a new approach to the problems of creating an embolized zone at the site of an operative procedure , and of removing an embolizing gel at the end of the procedure , and of maintaining perfusion in zones of the organ away from the operative site , has been invented . the new approach arises from the production of a reverse gelling polymer that gels over a relatively narrow range that is a few degrees above body temperature . gelation , and local embolization producing hemostasis , is then produced by replacing some or all of the blood in the organ with a reversible heat - gellable polymer solution . where possible , the gellable polymer is only instilled into regions of the organ that are to be treated . in particular , in the materials and procedures of the invention , the gelation temperature is greater than local body temperature . body temperature is about 37 ° c . internally , and so gelling temperatures of the heat - gellable polymer solution , for internal use , should be in the range of 38 ° c . or preferably at least 39 ° c ., up to about 48 ° c ., more preferably below about 45 ° c ., still more preferably in the range below about 42 ° c . if the polymer is to be used in or near the skin for a procedure , or otherwise in a body region where the overall temperature is below 37 ° c ., the preferred reverse gelling temperature of the gel may be lower , depending on the temperature to be induced in the particular tissue by the heating procedure . if the tissue is to be treated at a temperature above 37 ° c ., then perfusion with a polymer gelling above 37 ° c . is appropriate without regard to local tissue temperature . it is known that in certain concentration ranges , the gelling temperature of a reverse gelling polymer changes as the polymer concentration is varied . ( most commonly , the gelling temperature increases as the concentration is reduced , until the polymer fails to gel ). hence , it is possible to select gelling temperatures of rgp solutions by selection of a poloxamer or other rgp composition , and by adjustment of its concentration if required . poloxamers are preferred rgps in the invention . poloxamers are a well - known class of polyalkyleneoxide copolymers , typically composed of a core block of polypropylene oxide ) tipped at each terminus with a block of poly ( ethylene oxide ). most commonly , the polymer is unbranched . poloxamers having a higher proportion of propylene oxide tend to exhibit the reverse gelling phenomenon . as specific examples , the use of basf poloxamer 288 at a concentration of about 18 % in water , or of basf poloxamer 237 at a concentration of about 20 % in water , will produce a material which will gel as the temperature is raised into the range of about 39 - 42 ° c . (“ reverse ” gelation ). the poloxamer solution is preferably fractionated to narrow the gelling range . fractionation is described for example by reeve et al ., in u . s . pat . no . 5 , 800 , 711 , u . s . pat . no . 6 , 761 , 824 and u . s . pat . no . 6 , 977 , 045 ( incorporated herein by reference ). the fractionation procedure also tends to reduce the width of the temperature range over which viscosity rises rapidly with temperature , which simplifies the mechanical requirements , such as applied pressure , for administration of the polymer . other poloxamers , such as basf poloxamers 407 , 188 , 338 , 1107 and 1307 , and “ pluronic ” brand poloxamers , for example f127 and 108 , may also be suitable , after purification and selection of concentration , for use in 37 ° c . environments , or in colder environments near body surfaces . in use , the polymer is provided in a sterile solution of suitable salinity or tonicity for the task or procedure to be conducted . poloxamines , in which amine groups replace oxygens in the backbone or ends , can also be used . a preferred poloxamer is poloxamer 188 ( basf ). the poloxamer is purified as described by reeve et al ., cited above . effective concentrations of purified poloxamer 188 of about 35 % have gelling temperatures just above body temperature . using these concentrations as guidelines , gelling temperatures of the poloxamer solution can be adjusted within a reasonable range by varying the concentration of the poloxamer in the solution . ( all percentages of polymer is solvent cited herein are weight / weight ( w / w ) unless specified otherwise .) other suitable poloxamers include purified basf rtp 238 at 20 % in saline ; rtp 237 at 20 % in saline ; rtp 288 at 14 - 15 % in saline ; and rtp 288 at 15 % in tris buffered saline . the methods of the invention can be used in any organ or situation in the body where temporary but completely reversible hemostasis is desired . the salient feature of the invention , as opposed to other inventions involving temporary hemostasis with reverse gelling polymers , is that the polymers in the present invention are selected to gel at temperatures somewhat above the local tissue temperature . consequently , no gelation occurs unless an additional source of heating is provided . such heating may be provided by any source , and the heating need not have therapeutic effect . however , the methods of the invention are particularly advantageous when used in conjunction with a therapeutic effect of the localized heating . the treatment in which the reverse gelling polymer is provided may be for any purpose , including without limitation treatment for the removal or cure of a cancer , a benign tumor or growth , or a hemorrhage . any tissue may be involved , including without limitation liver , uterus , prostate , brain , spleen , pancreas , gall bladder , lung , breast , and kidney . the local embolization of tissue and organs with reverse gelling polymers has been described elsewhere , for example in other patent applications by applicants ( e . g ., us 2005 / 0008610 ), for local embolization occurring without an ancillary heat source . a system not requiring local heating will generally be simpler when it is effective , and so will be preferred . however , in some situations , the use of embolization with reverse - gelling polymers upon heating above body temperature is preferred , and has several advantages . first , a general advantage of the procedure is that it tends to minimize the amount of polymer temporarily deposited in the organ . second , it tends to minimize the volume of tissue in which hemostasis is established , minimizing anoxia in tissues of the organ of interest and in surrounding tissues . third , the re - liquefaction of the polymer at temperatures above body temperature leads to rapid cessation of hemostasis at the conclusion of the procedure . fourth , the need for additional heating allows a more precise localization of the tissue region in which hemostasis is achieved . any method of heating can be used . the heating of the organ can be provided by one or more of electromagnetic radiation , sonic energy , heated fluid , a heating pad , a heating element , and heat produced by a surgical tool or instrument . suitable methods include , without limitation , the use of microwaves , radio - frequency waves , infrared and visible light , and other non - ionizing electromagnetic radiation . electromagnetic radiation can be delivered to the exterior of a body or organ , or to interior sites via catheters , local generators , or the like . direct heating can be used by contact of a heating unit with the exterior of a body or tissue , or via catheters or other internal probes . heating of the target site can also be via electrical heating of a resistance , or by circulation of a heated fluid inside a device in contact with the tissue site . heating can be accomplished by heating a natural fluid , particularly blood or a temporary substitute for blood that is placed into the circulation , that will circulate to the site . heating can be accomplished by suspending the organ , or a region of the body , in a heated fluid , such as water , saline or the like . heating can be achieved via ultrasound and other vibratory mechanisms . the temperature rise at the site must be sufficient to cause the selected gelling solution to gel at the site . for example , if the poloxamer solution rises rapidly in viscosity above 39 ° c . and forms a firm gel at 42 ° c ., then the target temperature at the site is at least 42 ° c . if the poloxamer solution rises rapidly in viscosity above 35 ° c . and gels firmly at 38 ° c ., then a temperature of at least 38 ° c . will be sufficient . in a situation where the viscosity rises rapidly , but without gelation , in the physiological temperature range , it may be necessary to use a relatively large - bore device for injecting the polymer solution , or to cool the polymer solution below body temperature before administering it . fig1 illustrates the advantage of local gelation of polymers in the circulation that passes through a treatment site . a treatment zone 10 is created by a source of warmth 15 , which can be a probe situated below the plane of the drawing , perhaps in another artery or vein . the theoretical outer limit of the treatment zone 10 , in this example , is an essentially circular boundary 18 , at which the degree of heating drops below a therapeutic level . a blood vessel 20 flows through the treatment zone and branches into two smaller vessels 24 and 28 . natural circulation , indicated by small arrows , passes through vessel 20 and out of vessels 24 and 28 . however , the blood flow picks up heat from the treatment zone . this causes cooling in the vicinity of the blood entrance into the heating zone , shown as hatched area 32 , and causes heating at regions beyond the target zone 10 along the exiting blood vessels , shown as hatched areas 36 and 38 . it is likely that tissue in the area 32 will not be properly treated , and that tissue in areas 36 and 38 will be treated even though outside the target zone . this is undesirable . however , if heating is begun , and then followed by instillation of a reverse - gelling poloxamer solution at a location upstream of the target region , leading to vessel 20 , then a gel will form in the region being treated . the gel may begin to form in the distal vessels 26 and 28 , and once formed , will stop circulation through the treatment site . then the heat distribution in the zone 10 will more closely approximate the distribution planned for the treatment , having a treatment boundary at the circular border 18 . once heating element 15 is turned off , the tissue will rapidly drop to body temperature by heat transfer through the treated tissue to tissue outside the treatment zone 10 . the gelled polymer solution in the vessels 20 , 24 , and 28 will re - liquefy , and circulation will resume . the reperfusion of the organ may be accelerated , if desired , by circulation of isotonic fluid at a temperature of less than 37 ° c ., or even less than 30 ° c . circulation may be exterior to the organ , and / or through regions of the organ where circulation has not been blocked by gelation of polymer . if the site needs to be closed after treatment , closure may be attained with any conventional method , including without limitation one or more of sutures , staples , sealant , adhesive , and hemostatic agent , before the reduction of temperature to allow reperfusion of the organ by blood . in addition to thermotherapy , the reversible local embolization technique of the invention is applicable to surgical procedures removing tissue , particularly for removing part of a vascularized or compartmented organ , such as partial removal of liver or kidney . such highly metabolically active organs require minimization of the anoxia produced by embolization , both spatially and in terms of duration . in such tissues , a portion of the tissue is embolized by local warming , which may include local perfusion , in the normal direction or its reverse , with a warming solution , as well as local heating by other means . then , when the region adjacent to the region to be excised has been sufficiently warmed , it is perfused with an embolizing solution containing a reverse gelling polymer . the warmth causes local embolization . the tissue to be removed is quickly excised , and a sealing barrier layer is created by conventional means , for example and without limitation by one or more of local cautery , provision of tissue adhesives and barrier materials , and suturing . with proper timing , the rest of the organ can be de - embolized within a few minutes as the applied warming dissipates . the dissected and sealed organ can also be cooled immediately to accelerate reperfusion . the reverse gelling polymer solution can further comprise other medical materials . these may include , among others , a contrast - enhancing agent , which may be selected from the group consisting of radiopaque materials , paramagnetic materials , heavy atoms , transition metals , lanthanides , actinides , dyes , and radionuclide - containing materials . the solution may further comprises a biologically active agent , which , for example , may comprise one or more of anti - inflammatories , antibiotics , antimicrobials , antivirals , analgesics , antiproliferatives , and chemotherapeutics , or other biologically active agents . all of the patents and publications cited herein are hereby incorporated by reference in jurisdictions permitting the same . those skilled in the art will recognize , or be able to ascertain using no more than routine experimentation , many equivalents to the specific embodiments of the invention described herein . such equivalents are intended to be encompassed by the following claims .
precision in thermotherapy is obtained by providing a reverse gelling polymer composition which gels when its temperature is raised above body temperature . the composition is injected into the blood supply of the tissue being treated , at the beginning of thermotherapy . the temperature increase caused by the heating gels the composition , which temporarily blocks the flow of blood in the region being treated . this improves the predictability and stability of treatment . on cessation of heating , the composition liquefies , removing the temporary embolization . the use of local heating can also expedite removal of tumors and the like from soft organs , even when the heating itself has no therapeutic effect .