TISSUE ENGINEERING SCIENCE - CONSEQUENCES OF CELL TRACTION FORCE

Blood and tissue cells mechanically interact with soft tissues and tis sue-equivalent reconstituted collagen gels in a variety of situations relevant to biomedicine and biotechnology. A key phenomenon in these i nteractions is the exertion of traction force by cells on local collag en fibers which typically constitute the solid network of these tissue s and gels and impart gross mechanical integrity. Two important conseq uences of cells exerting traction on such collagen networks are first, when the cells co-ordinate their traction, resulting in cell migratio n, and second, when their traction is sufficient to deform the network . Such cell-collagen network interactions are coupled in a number of w ays. Network deformation, for example, can result in net alignment of collagen fibers, eliciting contact guidance, wherein cells move with b idirectional bias along an axis of fiber alignment, potentially leadin g to a nonuniform cell distribution. This may govern cell accumulation in wounds and be exploited to control cell infiltration of bioartific ial tissues and organs. Another consequence of cell traction is the re sultant stress and strain in the network which modulate cell protein a nd DNA synthesis and differentiation. We summarize, here, relevant mat hematical theories which we have used to describe the inherent couplin g of cell dynamics and tissue mechanics in cell-populated collagen gel s via traction. The development of appropriate models based on these t heories, in an effort to understand how events in wound healing govern the rate and extent of wound contraction, and to measure cell tractio n forces in vitro, are described. Relevant observations and speculatio n from cell biology and medicine that motivate or serve to critique th e assumptions made in the theories and models are also summarized.