Fusion of concentrically layered tubular tissue constructs increases burst strength

Tubular tissue constructs prepared from neonatal human dermal fibroblasts entrapped in fibrin gel were incubated on a mandrel for three weeks to allow for initial fibrin remodeling into tissue before being concentrically layered and incubated for an additional three weeks on the mandrel. Upon harvest, double layer constructs were not statistically different from single layer control constructs in terms of length, collagen density, cell density, tensile modulus, or ultimate tensile strength. However, the thickness and burst pressure were both approximately twice the single layer control values. Metabolically active cells were detected at the interface, and scanning electron microscopy revealed fiber structures bridging the two layers, co-localizing with the cells, which exhibited minimal migration across the layers. In contrast, double layer constructs where tissue fusion was prohibited by mechanical distraction of the layers showed no increase in burst pressure despite having increased thickness and the same collagen and cell densities of the single layer control constructs; moreover, the burst failure occurred sequentially in the layers in contrast to simultaneous failure for the fused double layer constructs. This study provides insight into the nature of the interface and the role of cell behavior when tissue fusion occurs between two layers of bioartificial tissue in vitro. It also suggests a method for improving the burst strength of fibrin-based tubular tissue constructs by increasing the construct thickness via concentrically layering and fusing two constructs.