Evaluation of alternative glutaraldehyde stabilization strategies for collagenous biomaterials

A range of alternative crosslinking conditions based on glutaraldehyde were examined for their effectiveness for stabilizing collagen-based materials using test samples of a collagen-polymer composite tube. Stabilization of collagen was performed with various concentrations of glutaraldehyde at acid pH, in the absence or presence of 0.7 m NaCl to control collagen swelling. For each condition, some samples were further treated at neutral pH. These test samples were compared with samples treated with glutaraldehyde at neutral pH and with samples of Omniflow vascular prosthesis. The effectiveness of the stabilization was examined by amino acid analysis, to assess the extent of modification, isometric tension analysis, to evaluate the extent of crosslinking, compliance and accelerated fatigue testing, to evaluate mechanical properties, and by a rat subcutaneous model to evaluate tissue response and propensity to calcification. The data indicated that effective crosslinking could be achieved at low pH and that this can be increased slightly by the presence of NaCl. At low pH, the extent of calcification was low compared to samples treated at pH 7. Subsequent treatment at pH 7 of samples given an initial low pH glutaraldehyde (GA) treatment generally did not alter shrinkage temperatures although the extent of lysine modification and calcification did increase. In general, a more inflammatory response was observed in samples tanned at low pH, although this was not as severe as responses to untreated tissue implants. The Omniflow vascular prosthesis showed excellent chemical and mechanical properties and did not show any calcification.