Fracture behaviour of collagen: effect of environment

Collagen forms one-third of the human-body proteome and finds a wide range of applications in a biomedical field thanks to its mechanical stability, biocompatibility and biodegradability. Collagen can be produced in a form of films suitable for scaffolds, tissue regeneration, flexible electronics etc. significant differences in the mechanical properties were observed for collagen films tested in-aqua environment. Considering this and potential biomedical applications of collagen films, their mechanical testing should be performed in aqua to mimic the in-vivo conditions. Hence, this study reported the fracture behaviour of collagen in-aqua compared with that at ambient (in-air) loading conditions. Single-edged notched tension (SENT) specimens of collagen films demonstrated completely different stress-strain curves in-aqua conditions. A reduction in their tensile strength (by 90%) and fracture energy (by 40%) accompanied with an increase in the failure strain (by 1600%) was observed for such conditions. Crack propagation was rapid for in-air specimens, with a brittle failure, while for in-aqua specimens the crack opening was rather slow and accompanied with by crack blunting, leading to large plastic deformation (ductile failure). These behaviours encouraged the quantification of the fracture toughness of collagen films using different fracture toughness parameters: KIC (linear elastic fracture mechanics) for in-air specimens and JC-integral (elastic-plastic fracture mechanics) for in-aqua specimens.