Failure characteristics of multiple-component fibrin-based adhesives

A series of analyses were performed on fibrin-based adhesives to describe t heir failure characteristics. Two test methods were used: uniaxial, monoton ic tensile testing of the bulk material, and blister testing using fresh po rcine-source skin graft as the adherend. Two fibrin concentrations, high (H FC), and low (LFC), were used to investigate the effects of the gel matrix density upon mechanical properties. In tensile tests, fibrin gels strain ha rdened, as functions of percent strain and of strain rate. An increase in m odulus of elasticity (E) was seen with increasing strain and strain rate at both tested fibrin concentrations. Mode I failure mechanisms were predomin ant. Both adhesives appeared to fracture from the outer edge to the interio r of the specimen at slower strain rate tests. This trend reversed as strai n rate increased, becoming a classic "cup and cone" ductile fracture. Syner esis occurred at both concentrations at lower strain rates, but was more pr onounced for the LFC. Ultimate tensile strength and E were greater for the HFC than for the LFC at all strain rates, decreasing with increasing strain rate. In the blister test, the failure locus changed from cohesive to adhe sive as the strain rate was increased for the HFC. Failure of fibrin gels l ikely occurs by percolation of the pressurized saline, displacing the entra pped liquid phase of the gel in regions of relatively low moduli and streng th, leading to fracture of the matrix. For LFC, the overall fracture locus remained predominantly cohesive regardless of strain rate. Burst strength a nd failure energy were higher for HFC than for LFC. It would appear that fi brin acts more as a viscous liquid than a rubberlike/elastic material at lo wer concentrations because adhesive failures had a higher burst strength an d fracture energy (Gc) than did cohesive failures. (C) 2001 John Wiley & So ns, Inc.