Fibroblasts within concentrated collagen hydrogels favour chronic skin wound healing.

Apligraf(®), a skin substitute currently used in skin chronic wound treatment, acts as a source of macromolecules and cytokines to promote wound healing. Normal collagen hydrogel (NCH), obtained from collagen at low concentration (0.66 mg/ml), is the base of the dermal layer. Apligraf has several drawbacks, such as poor persistence of fibroblasts within the normal collagen hydrogel. In the present study we have evaluated concentrated collagen hydrogels at 5 mg/ml (CCH5s) as dermal substitutes for the treatment of skin chronic wounds. The effect of raised collagen concentration on hydrogel stability, cell growth, apoptosis and fibroblast phenotype was evaluated over 21 days in culture. In contrast to NCHs, CCH5s were more stable because no contraction was observed during the first week. CCH5 favoured cell proliferation and protected fibroblasts against apoptosis. At day 21, cell number assessed in CCH5 was around one million, i.e about 10 times higher than in NCH. Matrix metalloproteinases detection appeared lower in CCH5 than in NCH. In CCH5, fibroblasts exhibited a sustained collagen I gene expression for 14 days, while it was inhibited from day 4 in NCH. Moreover, gene expression of KGF was constant in CCH5 and that of VEGFA increased from day 7. Taken together, our results demonstrate that concentrated collagen hydrogels at 5 mg/ml can be considered as new candidates for cell therapy in chronic skin wounds. They are stable, enhance cell viability and allow gene expression of matrix macromolecules and cytokines involved in re-epithelialization or neovascularization.