Abstract: BACKGROUND: Allogeneic bone repair materials have good effect on bone defect repair, but they have drawbacks such as immune rejection, high cost, and low rigidity.
OBJECTIVE: To evaluate the bone repair ability, tissue response and degradation performance of three kinds of 3D-printed allogeneic bone and artificial polymer composite porous scaffold materials.
METHODS: Three kinds of bone repair materials were prepared: (1) Sample A: A bone repair material was prepared by mixing polylactic acid-glycolic acid copolymer with allogeneic bone powder at a mass ratio of 1:4, using low-temperature deposition 3D printing. (2) Sample B: A bone repair material was prepared by mixing polycaprolactone with allogeneic bone powder at a mass ratio of 1:4, using low-temperature deposition 3D printing. (3) Sample C: A bone repair material was prepared by mixing polycaprolactone with allogeneic bone powder at a mass ratio of 3:7, using high-temperature melt 3D printing. A 5 mm diameter circular bone defect was created on each side of the sagittal suture in 35 SD rats. Ten defects received no intervention (blank control group), 15 defects were implanted with allogeneic bone material (positive control group), 15 defects were implanted with sample A (sample A group), 15 defects were implanted with sample B (sample B group), and 15 defects were implanted with sample C (sample C group). Samples were collected at 2, 4, 8, 12, and 26 weeks post-surgery. Hematoxylin-eosin staining was used to observe material degradation, tissue response at the implantation site, and new bone formation. Masson staining was used to observe collagen fiber formation. Immunohistochemical staining was used to observe the expression of RUNT-related transcription factor 2 and type I collagen.
RESULTS AND CONCLUSION: (1) Hematoxylin-eosin staining: During the experimental period, all implanted materials showed varying degrees of degradation. Samples A and B degraded faster, followed by the positive control, while sample C degraded more slowly. With time, the inflammatory response in all implanted material groups showed a decreasing trend, but fibrous tissue hyperplasia and neovascularization remained relatively significant. At 26 weeks post-surgery, the inflammatory response in sample A group was significantly reduced, followed by sample B group and the positive control group, while the reduction trend in sample C group was not obvious. A small amount of new bone formation was observed in sample B group at 8 weeks post-surgery, and new bone formation was observed in sample A group and the positive control group at 12 weeks post-surgery. A large amount of new bone formation was observed in these three groups at 26 weeks post-surgery. No significant new bone formation was observed in sample C group throughout the study. (2) Masson staining: At 2 weeks post-surgery, a small amount of irregularly arranged collagen deposition was observed in all implanted material groups. At 26 weeks post-surgery, a large amount of regularly arranged collagen deposition was observed in all implanted material groups. (3) Immunohistochemical staining: With time, RUNT-related transcription factor 2 and type I collagen expression increased in all implanted material groups. The expression of RUNT-related transcription factor 2 and type I collagen in the positive control group, sample A group, and sample B group at 12 and 26 weeks post-surgery was higher than that in sample C group. (4) The results showed that samples 3D printed with polylactic acid-glycolic acid copolymer or polycaprolactone and allogeneic bone powder at low temperature degraded faster, showed less inflammatory response, and exhibited more significant osteogenic factor expression and new bone formation compared with samples printed with high-content polycaprolactone and allogeneic bone powder at high temperature.

Key words: 3D printing, allogeneic bone, artificial polymer materials, skull defect, bone repair, in vivo study, rat