Characterization of the early stages of long bone regeneration in fractures and critical size defects in Xenopus Laevis
Traumatic injuries or cancer irradiation can cause critical sized defects in long bones. Regeneration capabilities of most mammals in their long bones are robust in small defects such as fractures but diminish in large defects due to lack of proper cellular cues. A small animal in vivo model has been developed to study the effect of two biocompatible scaffolds, an artificial polymer scaffold (HDDA) and a protein (zein) scaffold, on regeneration of long bone defects in adult African Clawed Frogs (Xenopus laevis) hind limbs. The HDDA scaffolds loaded with growth factors BMP4 and VEGF and zein scaffolds loaded with growth factors BMP4 and FGF10 were implanted in the critical defect site in the tarsus of the Xenopus Laevis. Defects in control frogs were left empty. Fractures were also induced in some frogs to study the mechanisms of endochondral ossification. The limbs were harvested at a series of early time points ranging from 3 days to 6 weeks after implantation. Standard histology was used to evaluate tissue types and the anatomical relationships. In frogs treated with growth factor-soaked HDDA scaffolds, the defect site was completely filled with cartilage by 3 weeks showing a biological response which appeared to be similar to the fracture healing mechanism. In frogs treated with growth factor soaked zein scaffolds, the defect site was partially bridged by cartilage and was filled with a large wound healing immune response. Blood vessels had invaded the cartilage and a response also similar to fracture healing was observed. Histology in the early time points has shown a vast amount of vascular in-growth at 1 week and the beginning of cartilage formation as early as 2 weeks in the scaffold-implanted defects. In contrast, defects in control frogs showed formation of fibrous scar tissue and negligible cartilage formation. These studies demonstrate the feasibility of using scaffolds loaded with carefully selected growth factors to repair long bone defects over gaps of critical size by fracture healing and developmental regeneration mechanisms.
Bone, Regeneration, scaffold, growth factors, critical size defect
University of Illinois - Urbana-Champaign
Networked Digital Library of Theses and Dissertations
University of Illinois at Urbana-Champaign