Successive epoxy and carbodiimide cross-linking of dermal sheep collagen

Abstract

Cross-linking of dermal sheep collagen (N-DSC, T s=46°C, number of amine groups =31 (n/1000) ) with 1,4-butanediol diglycidyl ether (BDDGE) at pH 9.0 resulted in a material (BD90) with a high T s (69° C) , a decreased number of amine groups of 15 ( n/1000) and a high resistance towards collagenase and pronase degradation. Reaction of DSC with BDDGE at pH 4.5 yielded a material (BD45) with a T s of 64°C, hardly any reduction in amine groups and a lower stability towards enzymatic degradation as compared to BD90. The tensile strength of BD45 (9.2 MPa) was substantially improved as compared to N-DSC (2.4 MPa), whereas the elongation at break was reduced from 210 to 140%. BD90 had a tensile strength of 2.6 MPa and an elongation at break of only 93%. To improve the resistance to enzymes and to retain the favorable tensile properties, BD45 was post-treated with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) in the presence of N-hydroxysuccinimide (NHS) to give BD45EN. Additional cross-linking via the formation of amide bonds took place as indicated by the T s of 81°C and the residual number of amine groups of 19 ( n/1000). BD45EN was stable during exposure to both collagenase and pronase solutions. The tensile properties (tensile strength 7.2 MPa, elongation at break 100%) were comparable to those of BD45 and glutaraldehyde treated controls (G-DSC). Acylation of the residual amine groups of BD45 with acetic acid N-hydroxysuccinimide ester (HAc-NHS) yielded BD45HAc with a large reduction in amine groups to 10 ( n/1000) and a small reduction in T s to 62°C. The stability towards enzymatic degradation was reduced, but the tensile properties were comparable to BD45.