Natural potential difference induced functional optimization mechanism for Zn-based multimetal bone implants.

Zn-based biodegradable metals (BMs) are regarded as revolutionary biomaterials for bone implants. However, their clinical application is limited by insufficient mechanical properties, delayed degradation, and overdose-induced Zn toxicity. Herein, innovative multi-material additive manufacturing (MMAM) is deployed to construct a Zn/titanium (Ti) hetero-structured composite. The biodegradation and biofunction of Zn exhibited intriguing characteristics in composites. A potential difference of about 300 mV naturally existed between Zn and Ti. This natural potential difference triggered galvanic coupling corrosion, resulting in 2.7 times accelerated degradation of Zn. The excess release of Zn induced by accelerated degradation enhanced the antibacterial function. A voltage signal generated by the natural potential difference also promoted osteogenic differentiation through activating the PI3K-Akt signaling pathway, and inhibited the toxicity of overdose Zn , significantly improving bone regeneration. Furthermore, MMAM technology allows for the specific region deployment of components. In the future, Ti and Zn could be respectively deployed in the primary and non-load-bearing regions of bone implants by structural designs, thereby achieving a functionally graded application to overcome the insufficient mechanical properties of Zn-based BMs. This work clarifies the functional optimization mechanism for multimetal bone implants, which possibly breaks the application dilemma of Zn-based BMs.