Because of the advantage of better control of experimental conditions, in vitro model systems have been developed to examine the effects of mechanical loading on cells. Previous studies have shown that cyclic stretching causes cells to change orientation, proliferation and gene expression (Buck et al., 1980; Wang et al., 1995; Leung et al., 1976). However, one drawback of these model systems is that they are unable to control cell alignment and shape, and in addition, some provide heterogeneous strains to cells during stretching (See review by Schaffer, 1994). Consequently, cellular responses in these systems may not be similar to those in vivo. For example, tendon and ligament fibroblasts align with collagen fibers in vivo and are hence subjected to stretching along the tissue long axis. In contrast, in many existing systems, cells either randomly orient or orient away from the stretching direction.

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