Fibrin-filled scaffolds for bone-tissue engineering: An in vivo study

Recently, fibrin sealants that typically contain supra physiological concentrations of fibrinogen and thrombin have been investigated as matrices to facilitate the delivery of cells within biodegradable scaffolds for tissue engineering applications. It is well known from in vitro experiments that the thrombin concentration present during fibrin polymerization influences the structural properties of fibrin, and these can affect cell invasion. This study was conducted to determine whether the structural properties of fibrin can affect bony wound healing in vivo. Drill hole defects were created in the distal femurs of 20 rats. Four experimental groups were used: nontreated defects, scaffolds alone, and scaffolds filled with fibrin polymerized with either a low thrombin concentration [fibrin(low T)] or a high thrombin concentration [fibrin(high T)]. The area of bone formed at 2, 5, and 11 days after implantation was determined histomorphometrically. After 5 days, scaffolds filled with fibrin(high T) were infiltrated with less bone than empty scaffolds (p < 0.05), but no statistical difference was found between the empty scaffolds and the scaffolds filled with fibrin(low T). After 11 days, both fibrin-filled scaffolds significantly delayed bony wound healing (p < 0.004). Reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis of the two fibrin formulations showed no difference in gamma-gamma crosslink formation. This work demonstrates that fibrin sealants in their present state are not ideal for enhancing bone-tissue invasion into scaffolds, and that the structural properties of fibrin matrices may be an important design parameter for maximizing host tissue invasion during wound healing.