An innovative hierarchical porous oxide surface with enhanced surface area for promoting early-stage bone regeneration potential

In this study, an innovative hierarchical porous oxide surface (HPOS) with an increased surface area was developed on biomedical 316L stainless steel (SS) implants to promote early bone and implant integration. The surface features and in vivo performance of the HPOS implant were examined using field-emission scanning electron microscopy, nanoindenter, roughness measurement instrument, contact angle goniometer, micro-computed tomography, and histological analysis. Results showed that the HPOS consisted of a hybrid micro-nano-pores structure and had a relatively low elastic modulus (150.6 ± 7.8 GPa, *p < 0.05), high roughness (8.6 ± 1.2 μm, **p < 0.01), and a low contact angle (15.6 ± 1.8°, ***p < 0.001). Additionally, rapid new bone formation was observed on the HPOS of the 316L SS implant modified at 5 V for 5 min, producing pore sizes from approximately 300 nm to 13.5 μm, with bone contact interfaces exceeding 64% at 12 weeks. The HPOS maintained mechanical interlocking ability at the microscale, which positively influenced osseointegration. Moreover, the difference in new bone formation thickness between the unmodified control group (0.45 ± 0.11 mm) and the modified 316L SS implant with HPOS (0.66 ± 0.13 mm) was statistically significant at 12 weeks post-implantation (*p < 0.05). These findings suggest that forming an innovative HPOS on a 316L SS implant could offer a potential solution to enhance early-stage osseointegration in clinical applications.