A novel phosphonate for the repair of critical size bone defects

Bone has the ability to spontaneously regenerate itself. However, the treatment of critical size bone defects can be problematic. In this study, the healing potential of critical size neonatal mouse parietal defects was evaluated using a scaffold composed of poly (ε-caprolactone) (PCL) and polyvinyl phosphonic co-acrylic acid (PVPA) (referred to as PCL/PVPA). Full thickness 1.5 mm circular defects were created in parietal bones obtained from one litter of 4-day-old CD1 mice. The bones were divided into two groups and embedded with PCL or PCL/PVPA scaffolds. The healing response was evaluated using microcomputed tomography, dissecting microscopy, phase contrast microscopy, scanning electron microscopy, and energy dispersive spectroscopy. There was a significant increase (P<0.05) in bone fill percentage in the presence of the PCL/PVPA scaffold (63.57%) compared with PCL scaffolds (29.64%). The formation of tissue and deposition of extracellular matrix was confirmed by scanning electron microscopy. There was evidence of collagen fibre deposition as well as hydroxyapatite and overall woven bone formation. PCL/PVPA scaffolds were better integrated into the defect site. The potential formation of hydroxyapatite was evaluated using energy dispersive spectroscopy. Results showed a significant increase in calcium and phosphorus levels in the presence of PCL/PVPA scaffold. Histological analysis using Masson's trichrome staining confirmed the presence of collagen above and below the PCL/PVPA scaffold within the defect site. In conclusion, this study showed that the PCL/PVPA scaffold is a novel system that has the potential for use as a bone graft substitute and in assisting in the healing of critical size defects.