Appropriate pore size for bone formation potential of porous collagen type I-based recombinant peptide.

Introduction: In this study, we developed porous medium cross-linked recombinant collagen peptide (mRCP) with two different ranges of interconnected pore sizes, Small-mRCP (S-mRCP) with a range of 100-300 μm and Large-mRCP (L-mRCP) with a range of 200-500 μm, to compare the effect of pore size on bone regeneration in a calvarial bone defect. Methods: Calvarial bone defects were created in Sprague-Dawley rats through a surgical procedure. The rats were divided into 2 groups: S-mRCP implanted group and L-mRCP implanted group. The newly formed bone volume and bone mineral density (BMD) was evaluated by micro-computed tomography (micro-CT) immediately after implantation and at 1, 2, 3, and 4 weeks after implantation. In addition, histological analyses were carried out with hematoxylin and eosin (H&E) staining at 4 weeks after implantation to measure the newly formed bone area between each group in the entire defect, as well as the central side, the two peripheral sides (right and left), the periosteal (top) side and the dura matter (bottom) side of the defect. Results: Micro-CT analysis showed no significant differences in the amount of bone volume between the S-mRCP and L-mRCP implanted groups at 1, 2, 3 and 4 weeks after implantation. BMD was equivalent to that of the adjacent native calvaria bone at 4 weeks after implantation. H&E images showed that the newly formed bone area in the entire defect was significantly larger in the S-mRCP implanted group than in the L-mRCP implanted group. Furthermore, the amount of newly formed bone area in all sides of the defect was significantly more in the S-mRCP implanted group than in the L-mRCP implanted group. Conclusion: These results indicate that the smaller pore size range of 100-300 μm is appropriate for mRCP in bone regeneration.