Collagen bioassay by the contraction of fibroblast-populated collagen lattices

The ability of fibroblasts to induce contraction of a collagen gel was studied with respect to the quantity and the quality of type I acid-soluble collagen. The speed of contraction and the appearance of the fibre bundles obtained after contraction depend not only on the ratio of the amount of collagen to fibroblasts but also on the process of the collagen purification. When collagen lattices made with a pepsinized collagen were compared to lattices made with a non-pepsinized collagen of the same amount, the fibres from pepsinized collagen seemed fewer (only 13% of the observed surface against 51% in the case of non-pepsinized collagen) and the lattices appeared by electron microscopy to be almost empty as if the lattices were comprised of less collagen. The importance of the non-helical domain of the collagen molecule for the identification and organization of collagen by fibroblasts is discussed. Collagen retained by fibroblasts was maximum (80–99%) when collagen was prepared in the presence of protease inhibitors and decreased when proteolysis was not avoided, for example when collagen was prepared in the presence of pepsin. A test using an estimation of the percentage of collagen retained by fibroblasts in a contracted collagen lattice is proposed to check the biological quality of collagen samples.