Tree-inspired magnesium hybrid column for preventing hip collapse in steroid-associated osteonecrosis in bipedal emus

Biodegradable magnesium (Mg)-based materials show promise in managing musculoskeletal diseases, attributed to their desired proper mechanical strength, and facilitating self-regenerative processes via spatiotemporal degradation during treatments for non-weight-bearing skeletal sites. However, to achieve a long-term steady state of the local biomechanical environment, it is essential to coupling implant degeneration and neo-tissue ingrowth without sacrificing local mechanical integrity. Steroid-associated osteonecrosis (SAON) presents a formidable clinical challenge, necessitating robust mechanical support to prevent collapse of weight-bearing hip joints while reversing pathological progression. Herein, a novel tree-inspired Mg hybrid column (Mg + BC) incorporating cannulated Mg screw and injectable Mg-containing bone cement (BC) is reported. Mg + BC tuned the gradual release of mineral ions (Mg, Ca, P), OH^– and H₂ via electrochemical suppression and crystal re-deposition during degradation. Finite element analysis demonstrated that Mg + BC significantly reduced the proportion of relatively high load-bearing regions (CD: 26.0 %, Mg: 26.6 %, BC: 18.2 %, Mg + BC: 17.5 %) and effectively shifted the predominant loading from subchondral trabeculae to the femoral shaft cortex. The efficacy of the tree-inspired Mg hybrid column was validated in a clinically relevant bipedal emu model of SAON. Compared to standalone Mg screws, Mg + BC exhibited sustained degradation and enhanced bone-implant contact, indicating improved alignment between material degradation and tissue regeneration. After 6 months in vivo, the implant residue volume was significantly higher in the Mg + BC group (73.53 ± 10.90 %) compared to the Mg screw group (39.10 ± 11.31 %). The optimized degradation pattern of Mg + BC facilitated bone regeneration through modulation of macrophage recruitment and M1-to-M2 polarization shift. Notably, Mg + BC treatment significantly reduced hip joint collapse incidence (1/10) compared to CD group (7/10). The Mg + BC group maintained greater articular cartilage thickness in the intact region (1.74 ± 0.25 mm) compared to CD group (0.71 ± 0.15 mm). Gait analysis revealed substantial improvement in stride length for the Mg + BC group (87.14 ± 2.29 cm) compared to CD group (60.03 ± 1.31 cm), indicating maintenance of the hip anatomical structure and functional performance. Taken together, the tree-inspired Mg hybrid column is expected to be a unique hybrid system for bone tissue regeneration and prevention of joint collapse in weight-bearing regions affected by SAON, offering promising translational potential for clinical application.