Successive epoxy and carbodiimide cross-linking of dermal sheep collagen

Cross-linking of dermal sheep collagen (N-DSC, T-s = 46 degrees C, number o f 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 degrees C), a de creased 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 degrees C, hardly any reduction in amine groups and a lower stability towards enzymatic degradation as comp ared to BD90. The tensile strength of BD45 (9.2 MPa) was substantially impr oved as compared to N-DSC (2.4 MPa), whereas the elongation at break was re duced from 210 to 140%. BD90 had a tensile strength of 2.6 MPa and an elong ation at break of only 93%. To improve the resistance to enzymes and to ret ain the favorable tensile properties, BD45 was post-treated with 1-ethyl-3- (3-dimethyl aminopropyl) carbodiimide (EDC) in the presence of N-hydroxysuc cinimide (NHS) to give BD45EN. Additional cross-linking via the formation o f amide bonds took place as indicated by the T-s of 81 degrees C and the re sidual number of amine groups of 19 (n/1000). BD45EN was stable during expo sure to both collagenase and pronase solutions. The tensile properties (ten sile strength 7.2 MPa, elongation at break 100%) were comparable to those o f BD45 and glutaraldehyde treated controls (G-DSC). Acylation of the residu al amine groups of BD45 with acetic acid N-hydroxysuccinimide ester (HAc-NH S) yielded BD45HAc with a large reduction in amine groups to 10 (n/1000) an d a small reduction in T-s to 62 degrees C. The stability towards enzymatic degradation was reduced, but the tensile properties were comparable to BD4 5. (C) 1999 Elsevier Science Ltd. All rights reserved.