Zinc alloy microwires with uniform degradation, cytocompatibility, and microbiota modulation for intestinal applications.

Abstract

Zinc and its alloys emerge as promising candidates for next-generation biodegradable implants due to their acceptable biodegradability and biocompatibility, while issues such as localized corrosion and potential cytotoxicity remain to be addressed. Both issues get complicated in intestinal microenvironment with diverse microbiota, especially the effects of Zn degradation on intestinal probiotics viability. Here, Zn-0.1Li and Zn-0.2Mg alloy microwires were manufactured and investigated for their mechanical integrity, degradation behavior, and biological performance toward colorectal surgical applications as staples or self-expanding stents. Alloying with Li and Mg enhanced tensile and yield strengths via second-phase strengthening, together with markedly a more uniform and stable degradation in simulated intestinal fluid (SIF) than in Hanks' solution. The resulting steady Zn²⁺ release in SIF reduced excessive local ion accumulation. Biological assessments confirmed >80% viability of Human Umbilical Vein Endothelial cells (HUVECs) and Caco-2 cells. In particular, we found a growth-promoting effect of Zn²⁺ on Lactobacillus rhamnosus GG (LGG) (probiotics) and antibacterial activity against Escherichia coli(E. coli) and Staphylococcus aureus (S. aureus) (pathogen). Furthermore, Zn²⁺ selectively precipitated cytotoxic secondary bile acids than Mg²⁺. The integrated time-frequency analysis of electrochemical noise signals and spatio-temporal evolution of interfacial pH and O₂ levels attributed the uniform degradation of Zn alloys microwires to the strong local pH buffering effect of SIF. These findings highlight that Zn-Li and Zn-Mg microwires couple uniform degradation with cytocompatibility, antibacterial activity, and metabolites regulation, is bio-adaptive for intestinal implant applications. STATEMENT OF SIGNIFICANCE: This work demonstrates that Zn-0.1Li and Zn-0.2Mg alloy microwires showed an ultimate tensile strength of 264 MPa and 199 MPa. Multi-scale in operando electrochemical analyses, electrochemical impedance spectroscopy (EIS) and electrochemical noise (ECN) integrated with mapping of interfacial pH and oxygen reveals that the Zn alloy wires underwent uniform corrosion in simulated intestinal fluid (SIF) but localized corrosion in Hanks' solution. Both Zn-0.1Li and Zn-0.2Mg alloy microwires showed favorable biocompatibility with intestinal epithelial and endothelial cells, along with strong antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), and further promoted the probiotic Lactobacillus rhamnosus GG (LGG). Moreover, released Zn²⁺ ions engaged in selective coordination with secondary bile acids, thereby attenuating metabolite-induced epithelial stress. These findings highlight Zn-based alloys as promising candidates for next-generation biodegradable intestinal implants.