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.