Crosslinked Polyurethane Medical Prosthesis

Illustrative and non-limiting Examples of processes according to the present invention which are used to form a product according to the present invention are given below. It should, however, be appreciated that the Examples given below describe the invention purely by way of illustration, and that modifications of detail can be made within the scope of the invention.

1. A polytetramethylene ether polyurethane urea resin (Biomer, supplied by Ethicon) was dissolved in dimethyl acetamide and was electrostatically spun according to the process described in GB-A-2,120,946 or GB-A-2,121,286 onto cylindrical formers to produce a number of tubular electrostatically spun fibrous products having a fiber on the average about one micrometer in diameter.

One such product was immersed in a bath of dimethyl acetamide and had completely dissolved within two hours of immersion.

A second such product was placed, on its former, in a sealable glass container which was then evacuated to remove gas from the container and the product. A quantity of chloromethylisocyanate was introduced into the evacuated container without it directly contacting the product. The product was retained in that container for 24 hours at a temperature of approximately 20.degree. C., whereupon the container is returned to atmospheric pressure, excess liquid chloromethylisocyanate is removed and the product is washed in water to remove any unreacted cross-linking agent adsorbed on the fibers.

The microscopic and macroscopic appearance of the thus treated product was compared with that of a similar, untreated product, which were observed to be substantially the same. It was also observed that the flexibility and porosity of the treated product was substantially the same as those of the untreated product. However, the elongation, flexural and burst strength and the resistance to creep of the treated product were superior to those of the untreated product.

The treated product was then immersed in a bath of dimethyl acetamide. After 24 hours immersion very little, if any of the product had dissolved, indicating that the fibers had been highly cross-linked. This also shows that the cross-linked material could not have been used in an electrostatic spinning process.

Thus, the process of the present invention produces an electrostatically spun product having improved strength and creep resistance properties but in which its porosity, flexibility and handleability have not been substantially adversely affected.

2. Solutions of Biomer in N,N dimethylacetamide may be easily cross-linked by direct addition of chloromethyl isocyanate.

Typically 10 grams of a 15% w/w solution of Biomer in N,N dimethyl acetamide is gelled within seconds by direct addition of 0.5 ml neat chloromethyl isocyanate to ultimately yield a hard elastomeric network which is no longer soluble in any non-degrading liquid.

3. Films of poly(ether urethanes) Tecoflex (Thermedic) prepared by extrusion and Pellethane (Bayer) cast from N,N dimethyl acetamide solution (2% w/w) were cross-linked by immersion in a solution of chloromethyl isocyanate in hexane (10% v/v) for 24 hours. After washing and drying all films having received this treatment were found to swell but not dissolve in N,N dimethyl acetamide unlike all untreated samples. The mechanical properties of the cross-linked films were found to be markedly superior to those which were untreated.