Absorbable implant materials having controlled porosity

#The present invention relates to bioabsorbable materials having controlled porosity. The materials are especially suitable for use as implants or dressings in wound healing applications.

#A number of attempts have been made to fashion solid, bioabsorbable implant and/or dressing materials for application to wounds to protect the wounds and assist wound healing and tissue regeneration.

#A solid wound implant material should preferably include the properties of gradual, controllable degradation and absorption in situ as the wound heals, low antigenicity, mechanical strength, conformability, and optimised porosity. The controlled porosity is important because the healing of wounds depends on the production by the wound of substantial quantities of matrix materials and granulation tissue involving the migration of fibroblast cells and connective tissue into the implant.

#Specific embodiments of the present invention will now be described further, by way of example, with reference to the accompanying figures, in which:

#FIG. 1 shows a scanning electron micrograph of a collagen sponge implant material obtained by a prior art method;

#FIG. 2 shows a scanning electron micrograph, on the same scale as FIG. 1, of a collagen sponge implant obtained by a process according to the present invention;

#Fibrous collagen was obtained from bovine hides in pure form as an insoluble slurry in water, as described in U.S. Pat. No. 4,320,201 and U. Pat. No. 3,823,212, the entire contents of which are hereby expressly incorporated by reference. The fibrous slurry is made basic with sodium hydroxide to pH 9.0, and water is added to adjust the solids concentration to 5% by weight.

#The aqueous dispersion of collagen fibers is then diluted to 0.5% solids. A cross-linker, HMDI (hexamethylene diisocyanate), is added in an amount corresponding to 5%by weight of the collagen in the dispersion with mixing, and the mixture is then snap frozen in a blast freezer. The frozen dispersion is then dried by freeze drying under standard conditions.

#A cross-section through a collagen sponge made in this way is shown in FIG. 1. It can be seen that the sponge comprises interconnected pores. The median pore size is approximately 0.1 mm.