Concentrated collagen hydrogels as dermal substitutes

Collagen hydrogels first appeared promising for skin repair. Unfortunately, their extensive contraction and their poor mechanical properties constituted major disadvantages toward their utilization as permanent graft. The present study has investigated a way to correct these drawbacks by increasing the collagen concentration in controlled conditions. Concentrated collagen hydrogels (CCH) at 1.5, 3 and 5 mg/ml were obtained. The effect of raised collagen concentration on contraction, cell growth and remodeling activities was evaluated for 21 days in culture. Subsequently, in vivo integration of CCH and normal collagen hydrogels (NCH) was assessed. Compared to NCH, CCH contraction was delayed and smaller. At day 21, surface area of CCH at 3 mg/ml was 18 times more important than that of NCH. Whatever the initial fibroblast density, CCH favored cell growth that reached about 10 times the initial cell number at day 21; cell proliferation was inhibited in NCH. Gelatinase A activities appeared lower in CCH than within NCH. In vivo studies in rats revealed a complete hydrolysis of NCH 15 days after implantation. In contrast, CCH at 3 mg/ml was still present after 30 days. Moreover, CCH showed cell colonization, neovascularization and no severe inflammatory response. Our results demonstrate that concentrated collagen hydrogels can be considered as new candidates for dermal substitution because they are is easy to handle, do not contract drastically, favor cell growth, and can be quickly integrated in vivo.