Effects of Modulus of Elasticity of Collagen Sponges on Their Cell-Mediated Contraction In Vitro

Highly porous collagen-glycosaminoglycan (CG) sponges, ultimately to be used as cell-seeded implants to facilitate the regeneration of selected soft tissues, were synthesized and cross-linked to various degrees using both chemical (ethanol, glutaraldehyde) and physical (dehydrothermal, ultraviolet irradiation) methods. Tendon fibroblasts were seeded into the scaffolds and the contraction of the sponges evaluated at 3, 7, 14, and 21 days post-seeding. The cell-mediated contraction of the sponges was calculated as the difference between contraction of the seeded sponges and unseeded control scaffolds exposed to the same in vitro conditions, normalized by the DNA content of the sponges. The cell-mediated contraction for each cross-link group was then plotted against the modulus of elasticity for that group, as determined by mechanical testing. Immunohistochemistry using a monoclonal antibody to a-smooth muscle actin was performed to determine if the contractile actin isoform was associated with the cell contraction of the sponges. Linear regression analysis showed a trend of decreasing cell-mediated contraction with increasing modulus of elasticity, and that dehydrothermal (DHT) treatment of CG sponges alone is not sufficient to resist contraction by seeded tendon fibroblasts in vitro. Cross-linking of collagen sponges so that their elastic moduli is at least three times that of sponges cross-linked by DHT alone may be necessary to sufficiently improve their contraction resistance. Alpha-smooth muscle actin was seen in the cytoplasm of most cells in all sponges at all time periods. This ubiquitous presence of myofibroblasts suggests that these specialized contractile cells are responsible for the contraction of the CG sponges. Thesis Supervisor: Myron Spector Title: Senior Lecturer, Department of Mechanical Engineering