Abstract
Spinal arthrodesis is a standard surgical intervention for stabilizing degenerate or traumatized vertebral segments; however, conventional rigid instrumentation utilizing titanium or cobalt-chromium alloys frequently leads to stress shielding, adjacent segment disease, and long-term hardware-associated complications. Bioresorbable magnesium (Mg) alloys present an appealing alternative due to an elastic modulus closely matched to native cortical bone and intrinsic osteopromotive biological activity. Nevertheless, premature mechanical failure and localized gas accumulation secondary to uncontrolled corrosion have limited their clinical translation in spinal instrumentation. In this study, we developed a novel bioresorbable Mg-2.0Zn-0.5Zr-0.2Ca (wt.%) pedicle screw functionalized with a dense, dual-layer silane-derived dicalcium phosphate dihydrate coating to achieve balanced corrosion kinetics. The coated implants exhibited a tenfold reduction in degradation rate relative to untreated controls in simulated body fluid, effectively dampening initial hydrogen evolution while maintaining structural integrity. In vitro evaluations using human bone marrow mesenchymal stem cells confirmed elevated alkaline phosphatase activity, extracellular matrix mineralization, and the upregulation of osteogenic gene expression (Runx2 and Osteocalcin) stimulated by physiological concentrations of released magnesium ions. Biomechanical pullout testing in synthetic polyurethane bone models demonstrated baseline axial retention comparable to medical-grade titanium screws. An in vivo ovine lumbar fusion model revealed continuous osseointegration, substantial de novo peri-implant bone formation, and continuous mechanical stability over 24 weeks without pathological gas pockets or systemic toxicity. These findings establish the feasibility of customized bioresorbable magnesium pedicle screws to provide transient mechanical fixation while actively driving biologic arthrodesis.
