Collagen composite biomaterials resist contraction while allowing development of adipocytic soft tissue in vitro

Soft tissue defects resulting from tumor resection or trauma require surgery to restore the body's contours. Because autologous tissues or synthetic implant reconstructions can be less than ideal, engineered tissues produced in vitro are being developed as alternatives. Collagen gels have been proposed for this application because they are biocompatible and can be shaped to fill a specific defect. In the present study, constructs of collagen gels with embedded short collagen fibers (which are more permeable than plain collagen gels and which maintain size and shape in culture) were seeded with preadipocytes and cultured in vitro. The addition of increasing volume fractions of embedded fibers limited cell-mediated contraction of the constructs. Including epithelial cell-seeded collagen gel layers resulted in more contraction, but still less than that observed in constructs without fibers. Constructs with embedded collagen fibers contained significantly more cells at all time points examined when compared to constructs without embedded fibers. Mature adipocytes were observed throughout constructs after 21 days in culture; spectroscopic analyses indicated lipid inclusion in constructs seeded with preadipocytes, which differed from analyses of natural porcine adipose tissue. These results support the promise of collagen composites as a biomaterial for use in producing soft tissues in vitro.