Altered mechanical properties in aortic elastic tissue using glutaraldehyde/solvent solutions of various dielectric constant.

Abstract

The extent to which elastic tissue can be crosslinked in aldehydes and the mechanism of such action is unresolved in the literature. We have used glutaraldehyde/solvent solutions of decreasing dielectric constant (phosphate buffer, methanol, 95% ethanol, n-propanol, n-butanol) to alter the mechanical properties of aortic elastic tissue obtained from autoclaved and CNBr-purified bovine aortae. Treated and untreated hoop samples were examined for stress-strain and stress relaxation behavior and for residual stress using opening angle experiments as per Fung. The extent of exogenous crosslinking was analyzed through amino acid analysis. Mechanical properties of autoclaved elastic tissue varied with dielectric constant in glutaraldehyde/solvent treatments; however, solvent treatment alone produced no effect. Extensibility decreased with decreasing dielectric constant while tensile modulus changed over a range from -2.4% (-0.86 kPa) for glutaraldehyde/buffer to +35.3% (+14.3 kPa) for glutaraldehyde/n-propanol (untreated-treated). Residual stress experiments similarly showed a systematic decrease in opening angle with decreasing dielectric constant. Differences ranged from 10.5 degrees for glutaraldehyde/buffer to 22.2 degrees for glutaraldehyde/n-butanol. Interestingly, purification of aortae with CNBr reduced the effects of glutaraldehyde/n-butanol treatment. We hypothesize that CNBr differentially degraded the elastin-associated microfibrillar proteins in aortic elastic tissue, thus producing the observed differences in mechanical behavior. The observed phenomena in this study may be attributed to the composite structure of elastic tissue: elastin and microfibrillar protein. During treatment, conformational changes in elastin facilitated by polar/nonpolar interactions occurred which then were "locked" in by glutaraldehyde crosslinking of the microfibrillar proteins. By this mechanism the increases in both stiffness and time-dependent behavior observed after treatment may be explained.