Photo-controlled biodegradable Zn alloy bone implant

Area of Science:

• Biomaterials Engineering
• Orthopedic Regenerative Medicine
• Nanotechnology

Background:

• Zinc (Zn)-based biodegradable implants offer potential for orthopedic applications but face challenges with uncontrolled corrosion and variable Zn²⁺ release.
• Early-stage excessive Zn²⁺ release can be toxic, while later stages may lack sufficient osteogenic stimulation, hindering clinical translation.

Purpose of the Study:

• To engineer a stage-adaptive hybrid coating for Zn-based biodegradable implants to regulate corrosion and Zn²⁺ release.
• To achieve on-demand control of Zn²⁺ release for enhanced biocompatibility and osteogenic stimulation.

Main Methods:

• A hybrid coating comprising indocyanine green-loaded zeolitic imidazolate framework-8 (ICG@ZIF-8) and polycaprolactone (PCL) was developed on a Zn-Li-Mg alloy.
• The coating's corrosion behavior and Zn²⁺ release kinetics were evaluated with and without near-infrared (NIR) irradiation.
• In vitro osteogenic differentiation and in vivo bone regeneration in critical-sized femoral defects were assessed.

Main Results:

• The PCL component initially slowed corrosion (∼3.84 μm yr^-1) and Zn²⁺ release, ensuring biocompatibility.
• NIR irradiation triggered ICG@ZIF-8 photothermal conversion, causing PCL deformation and increasing corrosion (∼8.53 μm yr^-1) for sustained Zn²⁺ release.
• Enhanced osteogenic differentiation and mineralization were observed in vitro, linked to Wnt/β-catenin/TCF pathway activation.
• In vivo studies showed a 26% increase in new bone formation in femoral defects.

Conclusions:

• The NIR-responsive hybrid coating provides spatiotemporal control over corrosion and Zn²⁺ release from biodegradable Zn implants.
• This smart material strategy effectively enhances osteogenic stimulation and promotes bone defect regeneration.
• The developed platform offers a promising approach for advanced orthopedic bone repair applications.