EFFECT OF APPLIED UNIAXIAL-STRESS ON RATE AND MECHANICAL EFFECTS OF CROSS-LINKING IN TISSUE-DERIVED BIOMATERIALS

Conformational changes in collagen fibrils, and indeed the triple heli x, can be produced by application of mechanical stress or strain. We h ave demonstrated that the rate of cross-linking in glutaraldehyde and epoxide homobifunctional reagents can be modulated by uniaxial stress (strain). Two poly(glycidyl ether) epoxides were used: Denacol(R) EX-8 10 (a small bifunctional reagent), and Denacol EX-512 (a large polyfun ctional reagent). To prevent any possible effect from being masked by saturation of cross-linking sites, bovine pericardium was cross-linked to such an extent that the increase in collagen denaturation temperat ure, T-d, was one-half of the maximal rise achievable with each reagen t. Uniaxial tensile stress of 0, 15, 124 or 233 kPa was applied during cross-linking. Cross-linking rate (as observed by increase in T-d) in creased with increasing stress to a maximum at 124 kPa in glutaraldehy de at pH 7 but decreased in EX-810 at pH 7. In each case, the effect w as small but statistically significant. No effect was observed with th e larger EX-512. Cross-linking under increasing stress also showed sys tematic effects on mechanical properties: decreasing extensibility and plastic strain while increasing tensile strength. In each case, the e ffects of the epoxides were slightly different from those of glutarald ehyde. In preparation for the above experiments, studies of the effect of pH, temperature, and exposure time were carried out for each epoxi de and (to a lesser extent) for glutaraldehyde. Again, systematic chan ges in mechanical properties were observed with increasing T-d. Confor mational changes in collagen produced by mechanical stress (strain) mo dulate the rate of cross-linking and the resulting mechanical properti es; however, the effects are sensitive to the reagent employed. (C) 19 96 Elsevier Science Limited