[Feasibility of polyetheretherketone loaded with bone morphogenetic protein 2 for orbital fracture repair]

Objective: To investigate the osteogenic activity of polyetheretherketone (PEEK) modified with bone morphogenetic protein 2 (BMP2) composite hyaluronic acid hydrogel (HAH) and its feasibility for orbital fracture repair. Methods: An experimental study was conducted from July 2022 to July 2023. PEEK scaffolds were modified with BMP2-loaded HAH to form PEEK-BMP2-HAH specimens. Rat bone marrow mesenchymal cells were transplanted into PEEK or PEEK-BMP2-HAH specimens and cultured for osteogenesis induction. Cell adhesion was observed using scanning electron microscopy (SEM). Cell proliferation was assessed using the Cell Counting Kit-8 (CCK-8). Osteogenic activity was evaluated by alkaline phosphatase (ALP) staining. Mineralized nodule formation was detected by Alizarin red staining. The relative messenger ribonucleic acid (mRNA) expression levels of Runt-related transcription factor 2 (Runx 2), osteoblast-specific transcription factor (Osterix), and osteopontin (OPN) were measured by real-time quantitative polymerase chain reaction (qPCR). A rat orbital defect model was established, and PEEK specimens (PEEK implantation group) and PEEK-BMP2-HAH specimens (PEEK-BMP2-HAH implantation group) were implanted. Bone formation was observed by hematoxylin-eosin (HE) staining, and osteocalcin (OCN) expression was detected by immunohistochemical staining. Results: Bone marrow mesenchymal cells adhered to and grew on the surface of both PEEK and PEEK-BMP2-HAH specimens. After 7 days of osteogenic induction, ALP staining revealed brown-black aggregated areas on PEEK discs, while PEEK-BMP2-HAH discs exhibited distinct black particles. The ALP activity in the PEEK-BMP2-HAH group [(2.36±0.18) μmol·min⁻¹·ng⁻¹ protein] was higher than that in the PEEK group [(1.00±0.18) μmol·min⁻¹·ng⁻¹ protein], with a statistically significant difference (t=12.15, P<0.001). After 14 days of osteogenic induction, Alizarin red staining demonstrated red aggregated areas on PEEK discs, whereas the PEEK-BMP2-HAH group displayed prominent reddish-brown mineralized nodules. The semi-quantitative absorbance value of Alizarin red staining in the PEEK-BMP2-HAH group (0.55±0.05) was more pronounced than that in the PEEK group (0.22±0.03), with a statistically significant difference (t=13.33, P<0.001). After 7 and 14 days of osteogenic induction, the relative mRNA expression of Runx 2 in the PEEK-BMP2-HAH group (3.25±0.22, 2.36±0.14) was significantly higher than that in the PEEK group (1.01±0.05, 1.03±0.07), with statistically significant differences (t=22.33, P<0.001; t=17.50, P<0.001). The relative mRNA expression of OPN in the PEEK-BMP2-HAH group (1.71±0.11, 2.11±0.15) was also significantly higher than that in the PEEK group (1.03±0.08, 1.04±0.10), with statistically significant differences (t=10.47, P<0.001; t=11.10, P<0.001). After 7 days of osteogenic induction, there was no significant difference in the mRNA expression of Osterix between the PEEK group (1.01±0.08) and the PEEK-BMP2-HAH group (1.12±0.09) (t=1.87, P=0.099). However, after 14 days of osteogenic induction, the relative mRNA expression of Osterix in the PEEK-BMP2-HAH group (1.77±0.17) was significantly higher than that in the PEEK group (1.02±0.06), with a statistically significant difference (t=8.95, P<0.001). HE staining of the bone defect model showed that the formation of new bone tissue was increased in the PEEK-BMP2-HAH group compared to the PEEK group. Immunohistochemical staining revealed that 12 weeks after implantation, the expression of OCN in the PEEK-BMP2-HAH group (1.98±0.25) was significantly higher than that in the PEEK group (0.98±0.11), with a statistically significant difference (t=8.07, P<0.001). Conclusion: The BMP2-HAH-modified PEEK repair material exhibits stronger cell adhesion ability, proliferation activity, and osteogenic activity compared with unmodified PEEK repair material, and can promote bone tissue regeneration in a rat orbital defect model.