Optimising bionic pore designs in a spiral blade implant to enhance bone ingrowth and stability: A combined CFD and...

This study aimed to evaluate the effects of different Bionic Pore geometries (circular, triangular, and rectangular) and diameters (0.8 mm, 1 mm, 2 mm, and 3 mm) on fluid shear stress (FSS) distribution and bone ingrowth in a bionic spiral blade implant.

Twelve Bionic Pore structures were modeled using CAD software, and computational fluid dynamics (CFD) analysis was performed to simulate the FSS distribution in a bone environment. Based on these simulation results, the circular hole design was selected and manufactured via electron beam melting (EBM). It was then incorporated into a bionic spiral blade (length: 50 mm, outer diameter: 6 mm, and a central canal of 2 mm for surgical pin placement). Four female sheep (weighing 35-40 kg) were implanted with these spiral blades, divided into 3-month and 6-month follow-up groups. After surgery, X-ray imaging, micro-CT, and histological evaluation were used to assess implant stability, bone bridging, and tissue response within the bionic pores.

CFD simulations showed that circular pores generated a more optimal and uniform FSS distribution; the 0.8 mm circular pore produced an average FSS of 0.0086 ± 0.00013 Pa, representing a 79.1% and 68.0% reduction compared to identically sized triangular (0.0412 ± 0.0176 Pa) and rectangular pores (0.0269 ± 0.0056 Pa), respectively. In vivo experiments demonstrated that small-diameter holes significantly accelerated osteogenesis. At 3 months, the 0.8 mm group achieved a bone tissue area ratio (BTA/BHA) of 15.44 ± 1.94%, which was 98.7% higher than that of the 3 mm group (7.77 ± 3.03%). By 6 months, the 0.8 mm group reached a BTA/BHA of 39.79 ± 7.80%, demonstrating a 131.2% greater bone occupancy compared to the 3 mm group (17.21 ± 3.97%, p < 0.01), alongside significantly higher bone volume fractions (BV/TV, p < 0.0001). Larger holes (2 mm and 3 mm) initially exhibited fibrous tissue formation, but as the pores gradually narrowed over time, local FSS increased, supporting later-stage bone formation. Radiographic and histological analyses confirmed that the bionic spiral blades remained stable in vivo.

This study indicates that optimizing the geometry and size of bionic pores can improve FSS conditions and promote bone ingrowth. Small-diameter circular holes, in particular, favor early and robust osseointegration. Moreover, this work underscores the potential of combining advanced manufacturing techniques with mechanobiological principles to design customized bionic implants for enhanced orthopedic outcomes. Importantly, the close agreement between CFD predictions and in vivo outcomes validates computational fluid dynamics as a practical prescreening tool for optimizing pore designs in load-bearing implants.

This "bench-to-bedside" research has established a robust framework for clinical translation. Leveraging the aforementioned optimized parameters, a novel bionic internal fixation device has been developed, which has successfully secured a U.S. utility patent and obtained a medical device registration certificate. This bionic device facilitates trabecular bone ingrowth and remodeling in parallel with cortical bone healing. Consequently, the findings of this study provide a validated, evidence-based foundation for the future design and development of bionic orthopedic implants.