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Cell-seeded collagen hydrogels have been used in the engineering of many tissue types, from skin and vasculature to spinal cord. One of the primary limitations of collagen-based hydrogels for use in tissue-engineered grafts is that cells seeded within the gel cause it to contract as much as 70%. By forming a composite gel by adding short collagen fibers, Gentleman et al. (Tissue Eng. 10, 421, 2004) determined that the contraction due to fibroblasts was decreased and permeability was increased. Before these composite hydrogels can be used to design soft tissue replacements, however, the effect of fiber number and serum concentration should be addressed. Consequently, short collagen fibers were included in adult rat bone marrow stem cell-seeded hydrogels for composite support. The mass of fibers was varied from 1.6 to 31.3 mg per gel, and the effect of serum concentration in the growth medium was examined. It was determined that increasing fiber mass and decreasing serum concentration significantly decreased contraction, which plateaued after day 10. Cell number increased throughout the experiment, demonstrating the compatibility of bone marrow stem cells with the collagen composite gels. By using short collagen fibers to create a collagen composite gel, preservation of the original dimensions can be achieved without compromising cellular viability.