Biochemical, biomechanical, and physical changes in the skin in an experimental animal model of therapeutic tissue expansion.

Biochemical, biomechanical, and physical changes occurring in the skin during tissue expansion have been studied using an animal model in which a Silastic expander was inserted into the peritoneal cavity. Forty-eight Sprague-Dawley rats were divided into four groups to be studied at 4, 8, 16 and 32 days after expansion. In the experimental animals (6 per group) the expander was inflated by a single injection of 120 ml of saline. Sixteen hours prior to sacrifice each animal received a single injection of tritiated proline. Sixteen days after expansion both the specific activity and the total content of hydroxyproline in the skin were significantly elevated in experimental animals. Intrinsic skin tension increased dramatically at the time of inflation but fell almost to control values at the end of 32 days. Skin thickness, initially decreased, returned to normal by the end of the experiment. There were no significant differences in breaking strengths between skin from experimental and control animals. Skin surface area, initially increased by stretching at the time of inflation, increased further between Days 0 and 8, possibly as a result of stress relaxation combined with enhanced remodelling of connective tissue macromolecules, and again from Days 24 to 32. We conclude that, during tissue expansion, there is a net accumulation of collagen in the skin and that this allows the local cellular environment to return to normal with respect to pressure and/or tension.