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.

Description

[0001] This invention relates to biostable biocompatible polyurethane implants suitable for short and long term implantation in vivo.[0002] Known medical grade polyether polyurethane elastomers are susceptible to phagocyte mediated Environmental Stress Cracking (ESC). Because of this known surface phenomenon such polyether polyurethanes are not suitable candidates to provide a foam implant. Conventional polyurethane foam structures have ether linkages which are subject to oxidation induced by an inflammatory response in vivo. This is the first stage in ESC which for foam materials ultimately represents a complete loss of material and device integrity.[0003] There is therefore a need for a polyurethane based foam implant material which will overcome these problems.[0004] In particular it is an object of the current invention to provide a new class of low density biostable polymers suitable for implantation.STATEMENTS OF INVENTION[0005] According to the invention there is provided a b...

AI Technical Summary

Benefits of technology

[0007] We have surprisingly been able to produce low density polyether and polycarbonate polyurethane porous foam that is highly biostable. The biostability of the materials of the invention is especially surprising in view of the known problems with conventional polyether polyurethanes and the high surface area to volume ratio of the materials. The excellent biostability of the soft phase of the material is attributable, in part, to the method of manufacture. The material is prepared in a manner whereby the molecules in the material are virtually stress free. The stress free configuration of the molecules of the system provides the highest activation energy barrier to degradation. The materials are processed using a reaction blow moulding free rise method. The stability of the hard phase is ensured by the incorporation of highly stable isocyanurate linkages. A high level of cross-linking in the hard phase enhances its stability.

[0120] The materials of this invention can be manufactured to indentation hardness which match the compliance of tissues in given applications. The materials of example 1 and 2 have characteristics which approximately match those of tissue. An important advantage of these highly porous foams in tissue applications is that the indentation force does not increase rapidly with the level of indentation. Harder grades of material are easily prepared using already established principles.

Problems solved by technology

Known medical grade polyether polyurethane elastomers are susceptible to phagocyte mediated Environmental Stress Cracking (ESC).

Because of this known surface phenomenon such polyether polyurethanes are not suitable candidates to provide a foam implant.

This is the first stage in ESC which for foam materials ultimately represents a complete loss of material and device integrity.

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