Measurements of the mechanical properties of contracted collagen gels populated with rat fibroblasts or cardiomyocytes

Abstract

In this paper the mechanical properties of contracted collagen gels populated with rat fibroblasts or cardiomyocytes were investigated by means of uniaxial tensile testing. Rat type I collagen–Dulbecco's modified Eagle's medium (DMEM) gels (each 2 ml in volume, 0.5 mg/ml collagen concentration) populated with different numbers of rat fibroblasts or cardiomyocytes were made in 31 × 17-mm wells cut in silicone rubber located in a 100-mm diameter plastic dish. Identically treated gels were incubated for 4 days floating in DMEM and then were subjected to uniaxial tensile testing. Rapid contraction occurred within the first 3 days for both the fibroblast and cardiomyocyte gels, but the cardiomyocyte gels consistently contracted to smaller sizes than the fibroblast gels for each number of cells used. The tension–strain curve of the contracted collagen gels demonstrated exponential behavior in the low stress region, followed by a linear section, and finally a maximum tension point, giving the ultimate strength of the gel tested. The cardiomyocyte gels had higher tension–strain curves than the fibroblast gels for each number of cells used. The tension relaxation and cyclic creep phenomena were observed in both kinds of gels, and these phenomena coincide with prior observations in collagen gels contracted by human fibroblasts. This experiment shows that type I collagen gels can be significantly contracted by rat fibroblasts or cardiomyocytes so as to achieve a certain mechanical strength. The contracted collagen structures made in these experiments have potential for developing tissue-engineered structures for cardiac muscle studies.