In vivo biocompatibility of carbodiimide-crosslinked collagen matrices: Effects of crosslink density, heparin immobilization, and bFGF loading

Collagen matrices, crosslinked using N-(3-dimethylaminopropyl)-N'-ethylcarb odiimide (E) and N-hydroxvsuccinimide (N), were previously developed as a s ubstrate for endothelial cell seeding of small-diameter vascular grafts. In the present study, the biocompatibility of various EN-crosslinked collagen matrices was evaluated following subcutaneous implantation in rats for per iods up to 20 weeks. The effects of the crosslink density, referred to as t he number of free primary amino groups per 1,000 amino acid residues (EN10, EN14, EN18, or EN22), the amount of heparin immobilized to EN14, and the e ffect of preloading heparinized EN14 with basic fibroblast growth factor (b FGF) on the induced tissue reaction were studied. EN-crosslinked collagen w as biocompatible at both early and late time intervals, and matrices with h igh crosslink densities (i.e., EN14, EN10) especially demonstrated a signif icantly decreased antigenic response when compared to non-crosslinked colla gen. Furthermore, increased crosslinking resulted in a decreased degradatio n rate. Immobilization of heparin onto EN14 resulted in a similar to EN14 ( thus without heparin) or somewhat reduced tissue reaction, but fibrin forma tion and vascularization were increased with increasing quantities of immob ilized heparin. Matrices preloaded with bFGF also demonstrated good biocomp atibility, especially in combination with higher amounts of immobilized hep arin. The latter matrices [EN14 with high heparin and bFGF, thus EN14-H (0. 4)F and EN14-H(1.0)F] demonstrated significantly increased vascularization for periods up to 3 weeks. Neither heparin immobilization nor bFGF preloadi ng induced an increased antigenic response. It is concluded that the result s of this study justify further evaluation of bFGF preloaded, heparin immob ilized EN14 collagen, as a matrix for endothelial cell seeding in experimen tal animals. (C) 2001 John Wiley & Sons, Inc.