In vitro and in vivo evaluation of gelatin–chondroitin sulphate hydrogels for controlled release of antibacterial proteins

Chemically cross-linked gelatin–chondroitin sulphate (ChS) hydrogels, impregnated in Dacron, were evaluated as drug delivery systems for antibacterial proteins. The gelatin–chondroitin sulphate gels, plain or impregnated in Dacron, were cross-linked with a water-soluble carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The release of lysozyme and recombinant thrombocidin (rTC-1), an antibacterial protein derived from human blood platelets, from the gelatin–ChS gels in Dacron in phosphate-buffered saline at 37°C was determined, and compared to the release from gelatin gels in Dacron and plain gelatin–ChS gels. The incorporation of chondroitin sulphate into gelatin gels, caused a marked increase in lysozyme loading capacity, and a slower release rate. The relative release profiles for rTC-1 and lysozyme were equal for cross-linked gelatin as well as for cross-linked gelatin–ChS gels. Furthermore, rTC-1 showed no loss of antibacterial activity after 1 week of release. The lysozyme concentration profiles in the samples and in the surrounding medium as a function of time were calculated using mathematical solutions for Ficks second law of diffusion for a semi-infinite composite medium, which is a schematic representation of a slab in a surrounding medium. The biocompatibility and degradation of the Dacron matrices impregnated with gelatin–ChS gels was studied after implantation in subcutaneous pockets in rats. Chemically cross-linked gelatin–ChS gels showed a mild tissue reaction, and almost complete degradation within 18 weeks of implantation.