Biostable polyurethane products

Abstract

A biostable porous polyether or polycarbonate polyurethane implant is manufactured from diphenyl methane diisocyanate, difunctional polytetramethylene ether glycol or a polycarbonate polyol, a trimerisation catalyst, a chain extender, water, a cross-linking agent, a blowing and/or gelling catalyst and a surfactant. The porous biomaterial has isocyanurate linkages and avoid content in excess of 85%. The implant may be used as an occluder or a tissue bridge.

1 . A biostable porous polyurethane foam implant material, the material containing isocyanurate linkages derived from diphenyl methane diisocyanate (MDI), and having a cross-linked structure, and a void content of at least 85%.  
     
     
         2 . An implant as claimed in  claim 1  wherein the material has a void content in excess of 90%.  
     
     
         3 . An implant as claimed in  claim 1  wherein the material has a void content in excess of 95%.  
     
     
         4 . An implant as claimed in  claim 1  wherein the material has a void content in excess of 97%.  
     
     
         5 . An implant as claimed in any preceding claim wherein the material is manufactured from 
 diphenyl methane diisocyanate (MDI) with a 2,4 μMDI isomer content of less than 3%;    a linear, long chain diol which is free of tertiary carbon linkages;    water;    a cross-linking agent;    a trimerisation catalyst;    a blowing and/or gelling catalyst; and    a surfactant.    
     
     
         6 . An implant as claimed in  claim 5  wherein the diol is polytetramethylene ether glycol (PTMEG).  
     
     
         7 . An implant as claimed in  claim 5  wherein the diol is a polycarbonate diol.  
     
     
         8 . An implant as claimed in  claim 7  wherein the polycarbonate diol is a reaction product of one or more diols with a carbonate monomer.  
     
     
         9 . An implant as claimed in any of  claims 5  to  8  wherein the diol molecular weight is between 400 and 5000.  
     
     
         10 . An implant as claimed in  claim 9  wherein the diol molecular weight is between 500 and 2500.  
     
     
         11 . An implant as claimed in any of  claims 5  to  10  wherein the trimerisation catalyst is a carboxylate.  
     
     
         12 . An implant as claimed in  claim 11  wherein the trimerisation catalyst is a potassium acetate.  
     
     
         13 . An implant as claimed in  claim 12  wherein potassium acetate is present in the reaction formulation in an amount of from 0.02% to 0.12% by mass of the formulation.  
     
     
         14 . An implant as claimed in any of  claims 5  to  13  wherein the cross-linking agent is present in the reaction formulation in an amount of from 1% to 5% by mass.  
     
     
         15 . An implant as claimed in  claim 14  wherein the cross-linking agent is trialkanol amine.  
     
     
         16 . An implant as claimed in  claim 15  wherein the cross-linking agent is triethanolamine.  
     
     
         17 . An implant as claimed in any preceding claim wherein the isocyanate index of the reaction formulation is from 1.03 to 1.20.  
     
     
         18 . An implant as claimed in  claim 17  wherein the index is approximately 1.13.  
     
     
         19 . An implant as claimed in any of  claims 5  to  18  wherein the reaction formulation includes a chain extender.  
     
     
         20 . An implant as claimed in  claim 19  wherein the chain extender is a linear aliphatic diol.  
     
     
         21 . An implant as claimed in  claim 20  wherein the linear aliphatic diol is 1, 4 butane diol.  
     
     
         22 . An implant as claimed in any of  claims 19  to  21  wherein the chain extender is present in the formulation in an amount of less than 7% by mass.  
     
     
         23 . An implant as claimed in  claim 22  wherein the chain extender is present in the formulation in an amount of less than 4% by mass.  
     
     
         24 . An implant as claimed in any of  claims 5  to  23  wherein water is present in the reaction formulation in an amount of from 0.6% to 1.8% by mass.  
     
     
         25 . An implant as claimed in any preceding claim wherein the implant has a hard segment content of from 35 to 65%.  
     
     
         26 . An implant as claimed in  claim 25  wherein the implant has a hard segment content of from 35 to 55%.  
     
     
         27 . An implant as claimed in  claim 25  or  26  wherein the implant has a hard segment content of from 40 to 50%.  
     
     
         28 . An implant as claimed in any preceding claim in the form of an occluder.  
     
     
         29 . An implant as claimed in any of  claims 1  to  27  in the form of a tissue bridge.  
     
     
         30 . A process for preparing a biostable polyurethane implant as claimed in any of  claims 1  to  29  comprising the steps of: 
 preparing an isocyanate terminated prepolymer in an excess of MDI with a 4, 4 MDI isomer content of greater than 97%;  
 preparing a diol reaction mixture comprising a diol, a cross-linking agent, a trimerising catalyst, water, a blowing and/or gelling catalyst, and a surfactant;  
 mixing the prepolymer and the diol;  
 dispensing the mixed reaction ingredients into a preheated mould which permits free rise of the foam;  
 post curing the foam;  
 demoulding the foam; and  
 machining the foam to form an implant.  
 
     
     
         31 . A process as claimed in  claim 30  wherein the foam is post cured in a carbon dioxide rich environment.  
     
     
         32 . A process as claimed in  claim 30  or  31  including the step of preheating the mould prior to dispensing of the mixed reaction ingredients.  
     
     
         33 . A process as claimed in any of  claims 30  to  32  including the step, after demoulding, of crushing the foam to increase the open cell content of the foam.  
     
     
         34 . A process as claimed in any of  claims 30  to  33  wherein the prepolymer is prepared from a prepolymer reaction mixture at a temperature of from 70 to 80° C.  
     
     
         35 . A process as claimed in any of  claims 30  to  34  wherein the prepolymer reaction mixture is reacted for a period of from 1 to 2 hours.  
     
     
         36 . A process as claimed in any of  claims 30  to  35  wherein the prepolymer reaction mixture is stirred continuously under a dry inert atmosphere.  
     
     
         37 . A process as claimed in any of  claims 30  to  36  wherein during moulding the mould temperature is maintained at a temperature of greater than 50° C.  
     
     
         38 . A process as claimed in  claim 37  wherein the mould temperature is from 80 to 90° C.  
     
     
         39 . A process as claimed in any of  claims 30  to  38  wherein the post curing is carried out at a temperature of at least 50° C. for a period of at least 30 minutes.  
     
     
         40 . A process as claimed in  claim 39  wherein the post-curing is carried out at a temperature of approximately 80° C.  
     
     
         41 . A process as claimed in any of  claims 30  to  40  wherein the shot size is less than 10 g.  
     
     
         42 . A process as claimed in claim  41  wherein the shot size is less than 5 g.  
     
     
         43 . A process as claimed in claim  41  or  42  wherein the shot size is less than 3 g.