Effect of LIPUS on the degradation behavior of magnesium alloy scaffolds for bone repair: Insights from in vitro and in vivo studies

• LIPUS accelerates magnesium scaffold degradation via cavitation effects. • LIPUS detaches Ca-P salts and promotes BSA adsorption on scaffolds in vitro . • LIPUS promotes Ca-P salt deposition and stabilizes degradation in vivo . • Degradation differs in vitro and in vivo due to differences in their environments. • LIPUS combined with magnesium ion promotes bone repair. Magnesium (Mg) alloys have excellent biocompatibility and biodegradability, making them promising for clinical applications. However, their rapid degradation compared to bone healing limits their effectiveness. In this study, low-intensity pulsed ultrasound (LIPUS), widely used clinically to promote bone healing, was combined with Mg alloy scaffolds to evaluate scaffold degradation under dynamic conditions, in vitro using Hanks’ balanced salt solution + BSA solution and in vivo in the femoral condyles of male SD rats. Results showed that LIPUS accelerated the initial degradation of the scaffold in both in vivo and in vitro experiments. In vitro , LIPUS increased BSA adsorption on scaffold surfaces, with adsorption increasing alongside LIPUS intensity. Limited BSA replenishment led to a thin organic-inorganic film that provided weak resistance to corrosive ions, accelerating degradation. Cavitation induced by LIPUS caused microbubble collapse, detaching Ca-P salts from scaffold surfaces. In vivo , LIPUS enhanced cell membrane permeability and activity, promoting the secretion of substances that formed a thicker organic-inorganic composite layer. Continuous material replenishment in the in vivo environment ensured the protective effect of this layer against corrosive ions, while embedded Ca-P salts were less likely to detach. In addition, LIPUS promotes bone modification. These findings highlight the potential of combining LIPUS with Mg alloys to regulate scaffold degradation, offering innovative strategies for clinical bone repair.