Title of Invention

A PROCESS FOR THE PREPARATION OF POLYURETHANE GRAFT COPOLYMERS

Abstract

A process for the preparation of a polymethane graft copolymer for the encapsulation and immunoisolation of living cells, comprising the steps of reacting an isocyanate with a solution of a polyol in the presence of a catalyst followed by adding a chain extender thereto to form a mixture and curing the mixture to obtain the polyurethane, subjecting the polyuretnane to a step of swelling in a solution of a vinyl monomer,initiator and crosslinker to obtain the swollen polymer followed by irra- diation to form the polyurethane graft copolymer.

Full Text

FIELD OF THE INVENTION This invention relates to polymethane graft polymer for the encapsulation and Immune Isolation of living cells, and a process for the preparation thereof. BACKGROUND OF THE INVENTION Type t diabetes, an autoimmune disorder of endocrine pancreas Is a major health concern worldwide and has long term systemic complications. Transplantation of isolated insulin secreting islet cells can be considered as an alternate treatment for diabetes. Immunorejection of the Islet cells Is a major concern of such transplant procedures. Critical shortage of donor islet cells is another concern of such technology. It is hence desirable to Immunoisoiate or encapsulate Islet cells in semipermeable membranes and form biohybrld pancreatic devices. The membrances of the device are expected to permit the crossover of molecular weight substances such as nutrient electrolytes, oxygen and biosecretor products but not of transplant effectors. Potymeric membranes such as alginate-poly (L-iysine), polycarbonate, poly-vinyl chloride-acrylic copolymers, poly (2-hydroxy ethyl methacrylate) agarose, polyvinyl alcohol have been proposed as immunoisolation matrices. Such membranes have been used in various device connguratlons Including microcapsules, AV shunts, hollow fibres and planar diffusion chambers. However, fibrotic reactions, blocompatlbility, mechanical fragility and reduced permeation have been reported to be the limiting factors for the widespread use of these candidate materials. It Is the basic requirement that the membrane materials should exhibit satisfactory biocompatibility, I.e. the ability of the material to allow the cells to retain their viability in contact with the materials. The function of the membrane material is also not expected to alter when in contact with the cells. It should also be possible to retrieve the material after use without degradation for a successful application of this technology as the degraded membranes may pose problems In the long term by inducing antigenic reactions. OBJECTS OF THE INVENTION It Is therefore an object of this Invention to propose a graft polymer which does not Induce fibrotic reactions. It is a further object of this Invention to propose a graft polymer which is biocompatible. Another object of this invention is to propose a graft polymer which is effective for the treatment at diabetes without Immunosuppression. Yet another object of this invention is to propose a graft polymer for Immune Isolating and encapsulating ceils within the membrane and which permit the cells to be viable. Other objects and advantages of this invention will be apparent from the ensuing description. BRIEF DESCRIPTION Thus according to this invention is provided a polyurethane graft polymer for the encapsulation and immunoisolation of living cells. in accordance with this invention, the polymeric material has a composition which is mostly 80-90 wt% of a biocompatible polyurethane and 10-20 wt% of a biocompatible vinyl polymer. The polymeric composition is a graft copolymer where the first polymer rs a polyurethane and the second or consecutive polymers are hydrophobic and hydrophilic vinyl polymers. The vinyl polymers are selected from polyvinyl pyrroNdone, polyhydroxyethyl methacryiate, polyethyihexyl acryiate. The polyurethane is a linear segmented polyurethane which has hard and soft segments and may be aromatic or aliphatic in nature. The soft segment is, for eg. a poiyoi. The hard segment is formed by reacting a diol or diamine with an isocyanate. According to this invention is further provided a process for the preparation of polyurethane graft copolymers. In accordance with this invention is further provided a process for the preparation of (he graft copolymer which comprises in a first step of forming (he pofyurethane by reacting an isocyanate with a polyol In stoichiometric amounts to form a prepolymer of a polyurethane and further extension of the prepoiymer by reacted with a stoichiometric amount of diof chain extender and curing. The polyurethane is first formed into a flat sheet or tube or other configuration and further grafted with a vinyl polymer by radiation grafting technique. The step of grafting is carried out by allowing the polyurethane to swell in a mixture of vinylmonomer, initiator and cross-linker for fixed time periods followed by polymerisation. The grafted polyurethane Is extensively cleaned with distilled water, and organic solvents to remove unreacted components and render the materials biocompatible. Preparation of polyurethane 1-2 molar toluene dissocyanate (TDI) solution is taken on a polymer reactor fitted with water condenser, stirred, and nitrogen purge 0.10 to 0.50 molar polyol which may be either polytetramethylene glycol or polypropylene glycol dissolved in solvent dimethyl for mamide Is added slowly to the TDI solution with continuous stirring and nitrogen gas purge. A catalyst dibutyl tin dilaurate of 0.01 wt% Is added and temperature raised to 60-70°C for one to two hours. Chain extension is carried out by bringing down the temperature to 40°C and addition of 0.70 to 0.80 moles of 1. 4-butandlol. Temperature was once again raised to 60-70°C for 48 hours curing In polyethylene molds. After curing, the polyurethanes were subjected to extraction by water before further characterisation. Concentration of TDi, polyol and chain extender may be varied from 0-101 in each case to prepare different hard segments in the polyurethane. Preparation of graft copolymer A polyurethane polymer with 10 to 40% hard segments was used for grafting purposes. Polyurethane was allowed to swell in vinyl monomers such as hydroxyethyllmethacryiate N-vinyl pyrrolldone and ethyl hexyl acrylate, ethyline glycol dimeth acrylate or any other vinyl crosslinker. A crosslinker of 1-3 wt% of vinyl monomer concentration was added to the vinyl monomer 0.009 u Cu+ was also added. Swollen polymer samples were lightly pressed between fitter paper to remove adhered monomer and immediately subjected to gamma irradiation from Co50 source, under a blanket of nitrogen. Dose rates of 0.2S-ju rad was used for grafting and grafting yields of 5 to 25% were obtained. Grafted polyurethanes were extracted with distilled water and methanol for removing any unreacted monomers. The membranes thus obtained are selectively permeable to cell nutrients, metabolites and waste molecules that are having molecular weights of less than 60,000 and Impermeable to the higher molecular weight components of the physiologic system including immunoglobulins. Further, the membranes are biocompatible to living cells that include islet ceils but are not restricted to islet cells only. The Invention Is also not restricted to the permeation of molecules of lesser molecular weight than 60.000 that are relevant for the treatment of diabetes, but to the treatment of any other disease, that requires such selective permeation characteristics for immunolsolation of living ceils. The Invention will now be explained In greater details with the help of the following non-limiting examples. Example 1.05 molar TDI was taken in polymer reactor. 0.25 M of polytetramethyiene glycol was added with 0.01 wt% of dibutyltindtlaurate. 25 mi of dimethyl formamide was used as solvent and reaction carried out under nitrogen purge. After heating for 1 hour at 60°C temperature was reduced to 40°Cand 0.70 moles of 1,4-butanedtoi added as chain extender and reacted for 30 minutes. The mixture was then poured into a polyethylene mold and allowed to cure at 48 hours at 60°C before extraction In distilled water. The above polyurethane 32% has a hard segmentation of Polyurethane - graft - ethyl -hexyl acrylate A 32% hard segmented polyurethane was cut In the form of a strip of 10 x 1 x 0.1 cm, weighed and was swollen in Ethyl hexyl acrylate monomer for 20 minutes. The swollen polyurethane film was removed, plotted between filter paper and subjected to gamma irradiation under a blanket of nitrogen in a Co50 panoromic batch modulator. A dose of 0.5 used was given. The material was allowed to polymerise and then extracted with water and methanol and dried and weighed to get the weight of graded copolymer. WE CLAIMS 1. A process for the preparation of a polyurethane graft copolymer comprising the steps of reacting an isocyanate with a solution of a polyol in the presence of a catalyst followed by adding a chain extender thereto to form a mixture and curing the mixture to obtain the polyurethane, subjecting the polyuretnane to a step of swelling in a solution of a vinyl monomer, initiator and crosslinker to obtain the swollen polymer followed by irradiation to form the polyurethane graft copolymer. 2. The process as claimed in claim 19 wherein said isocyanate is toluene diisocyanate (TDI) 3. The process as claimed in claim 1, wherein said polyol is such as polytetramethylene glycol 9 polypropylene glycol. 4. The process as claimed in claim 1 wherein a solution of the isocyanate and polyol is prepared in a polar solvent such as for example dimethyl formamide. 5. The process as claimed in claim 19 wherein said catalyst is a organotin catalyst such as for example dibutyl tin dilaurate. 6. The process as claimed in claim 19 wherein said chain extender is for eg 19 4-butanediol• 7. The process as claimed in claim 1, wherein a 1 to 2 molar isocyanate solution is treated with a 0.10 to 0.50 molar solution of polyol- 8. The process as claimed in claim 1, wherein the isocyanate and polyol are reacted at a temperature in the range of 60 to o 70 C for 1 to 2 hours. 9. The process as claimed in claim 19 wherein said 0.7 to 0.8 moles of chain extender is added. 10. The process as claimed in claim 15 wherein said step of curing is carried out at a temperature in the range of 60 to 70oC. 11. The process as claimed in claim 1 wherein the vinyl monomer is selected from hydroxyethylmethacrylate, N-vinylpyrro- lidone and ethyl hexyl aerylate. 12. The process as claimed in claim 1 wherein said initiator is for example a copper salt. 13. The process as claimed in claim 1, wherein said cross-linker is a vinyl monomer such as for eg ethylene glycol dimetha-crylate or any other vinyl crosslinker. 14. The process as claimed in claim 1, wherein said cross-linker is added in 1 to 3 wt, of the vinyl monomer. 15. The process as claimed in claim 1 wherein said swollen polymers are dried and subjected to gamma irradiation at a dose rate of 0-25 to 1µ rad. Dated this 16th day of FEBRUARY, 2004

Documents:

853-mas-2002-abstract.pdf

853-mas-2002-claims filed.pdf

853-mas-2002-claims granted.pdf

853-mas-2002-correspondnece-others.pdf

853-mas-2002-correspondnece-po.pdf

853-mas-2002-description(complete)filed.pdf

853-mas-2002-description(complete)granted.pdf

853-mas-2002-description(provisional).pdf

853-mas-2002-form 1.pdf

853-mas-2002-form 26.pdf

853-mas-2002-form 3.pdf

853-mas-2002-form 4.pdf

853-mas-2002-form 5.pdf