What do tissues and cells know of mechanics?

Many tissues and cells adapt to their mechanical environment, i.e. the stresses and strains to which the tissues are exposed during daily activities. Simple mechanical explanations of such adaptation naturally provide appeal, yet fail to predict accurately tissue appearance and behaviour. Continuum mechanics, the field from which our concepts of stress and strain arise, assumes a solid continuous structure, an assumption that does not apply at cell level. Merely correlating a given stress or strain magnitude with tissue behaviour does not per se account for the time over which responses occur. Tissues undoubtedly 'temporally process' mechanical signals, responding to some portion of the mechanical environment, and ignoring others. Further, the deformation that cells experience will depend upon their nonrigid connections to the matrix, so that the strains in the tissue may not be those experienced by the cell (and those causing the adaptation). Relatively simple mechanical models incorporating temporal features may adequately predict tissue adaptation, but the noncontinuum nature of tissues suggests that such models cannot adequately explain either tissue adaptation or the responses leading to adaptation.