The mechanical strength of collagen gels containing glycosaminoglycans and populated with fibroblasts

Collagen gels provide a biocompatible matrix for replacing soft tissues, but it is essential to determine whether the mechanical properties of the matrix can be retained after cell ingrowth into the collagen scaffold. We have determined the mechanical strength of four collagen gel compositions (plain collagen; collagen-chrondroitin-6-sulphate glycosaminoglycan (GAG); collagen crosslinked with carbodiimide and putrescine, and collagen-GAG with the crosslinkers) in the presence of either 3T3 mouse fibroblasts or human skin fibroblasts, to determine whether cellular activity influences the mechanical properties of the matrix, and whether the cross-linking processes alter the effects of the cells. The presence of GAG and the crosslinkers increased the strength and stiffness of the unseeded gels, but there was no evidence for synergy between these treatments. In all cases, the gels became significantly weaker after 6 days in the presence of either human or mouse fibroblasts, as judged by the decrease in the values of the maximum load and stress before failure, and the stiffness decreased as shown by the lower values of the incremental modulus. With most parameters, the effect of the cells was independent of gel composition, and the presence of cross-linkers or GAG did not impart resistance to the cell-induced decrease in strength.