Collagen peptide simulated bending after applied axial deformation.

Structural proteins in the extracellular matrix are subjected to a range of mechanical loading conditions, including varied directions of force application. Molecular modeling suggests that these mechanical forces directly affect collagen's conformation and the subsequent mechanical response at the molecular level is complex. For example, tensile forces in the axial direction result in collagen triple helix elongation and unwinding, while perpendicular forces can cause local triple helix disruption. However, the effects of more complicated mechanical loading, such as the effect of axial pretension on collagen bending and triple helix microunfolding are unknown. In this study we used steered molecular dynamics to first model a collagen peptide under axial tension and then apply a perpendicular bending force. Axial tension causes molecular elongation and increased the subsequent perpendicular bending stiffness, but surprisingly did not increase the predicted collagen triple helix microunfolding threshold. We believe these results elucidate a key potential mechanism by which microscale mechanical loads translate from cellular and micro scales down to the nano and atomistic. Further, these data predict that cryptic force-induced collagen triple helix unwinding is axial-deformation independent, supporting the possibility that cell traction forces could be a key molecular mechanism to alter the cellular matrix microenvironment to facilitate collagen enzymatic degradation and subsequent cellular migration, such as in tumor extravasation.