Large Long Bone Defect Repair by Regeneration
Our work focused on strategies for healing critical size defects in long bones resulting from traumatic injuries or diseases. We have developed a small animal in vivo load bearing model to study the effect of a biocompatible artificial polymer scaffold on regeneration of long bone defects in adult African Clawed Frogs (Xenopus laevis) hind limbs. We first designed and fabricated scaffolds made of 1,6 hexanediol diacrylate (HDDA) using an innovative three dimensional microfabrication technology called Projection Micro-Stereolithography. Critical size defects were made in one bone of the dual skeletal element hind limb tarsus bone in adult Xenopus laevis frog. HDDA scaffolds were soaked with two growth factors: BMP4 and VEGF. Defects in control frogs were left empty, or were implanted with scaffolds lacking growth factors. The limbs were harvested at a series of time points ranging from 3 weeks to 6 months after implantation. We employed Micro-CT to assess the shape and density of the regenerated tarsus, and standard histology to evaluate tissue types and the anatomical relationships. In frogs treated with growth factors soaked scaffolds, five out of eight defects were completely filled with cartilage by 6 weeks. Blood vessels had invaded the cartilage, and bone was beginning to form in ossifying centers. By 3 months these processes were well advanced. In contrast, defects in control frogs showed formation of fibrous scar tissue and the negligible cartilage formation was observed in defects. Our studies demonstrate the feasibility of using scaffolds loaded with carefully selected growth factors to repair long bone defects over gaps of critical size by developmental regeneration.