Georgia Institute of Technology Office of Contract Administration Sponsored Project Initiation

Quantification of microstructure in conjunction with mechanical testing and modeling may provide new insight into problems of soft tissue mechanics with potential clinical significance. Some general observations concerning this as well as brief discussions of specific examples are presented. Introduction There is an extensive literature on the mechanics of soft tissues. Important results are reviewed by Fling (1973). For simplicity, the following discussion will be limited to observations of "passive" (muscle inactive or missing) behavior in the more controlable, albeit less physiologically desirable, in vitro situation. • It is generally accepted that elastin and collagen are primarily responsible for observations of p assive mechanical behavior. It is also generally accepted that, because of their high water content, soft tissues are incompressible i.e. the volume of a tissue sample is unchanged by deformation (Carew et al 1968). Other simplifications, though usually made, are less well-founded. In particular, assuming homogeniety is contrary to the observed variations of microstructure in soft tissues. Also, preferred orientations of collagen and elastin fibers in the tissues arc generally ignored, though doing so can significantly affect the mechanical data. Additional complications arise. For example, mechanical behavior is very strongly load-history dependent. This posses the difficulty of defining a reference state from which forces and elongations may be measured. Also, the control of several variables, such as, in the case of artery, length, pressure, diameter and stretching force, poses a difficult problem for the experimentalist. Nevertheless, the study of soft tissue mechanics is an important one. The purpose of this paper is to briefly describe some problem areas and how mierostructuial quantification may prove useful.