Rational design of pH-responsive hydrogel micropatterns on magnesium alloy with enhanced biological activity

Biodegradable magnesium alloy (MgA) is a promising candidate material for orthopedic implants due to its excellent biocompatibility and mechanical properties. However, its poor corrosion resistance, susceptibility to infection, and differences in mechanical properties with human tissues always hinder its application in biomedical fields. Therefore, the construction of MgA surface with good corrosion resistance, excellent antimicrobial properties, and suitable mechanical properties is highly desired for its clinical applications. Herein, we have designed micro/nano composited structures containing pH-responsive hydrogel micropatterns and inorganic nanomaterials onto the surface of MgA (MgA-MgO-HANRs-Micropatterns) to improve its biological activities. Firstly, a MgO film was prepared on the surface of MgA using micro-arc oxidation method. Then, hydroxyapatite nanorods (HANRs) were grown on the MgO film using microwave-assisted hydrothermal method. Further, using UV light and photomasking technique, 2-hydroxyethyl methacrylate (HEMA) and 2,2-dimethylacryloyloxy-1-ethoxypropane (DMAEP) were polymerized on the surface of HANRs with loading of antibacterial agent carvacrol to construct pH-responsive hydrogel-carvacrol micropatterns at different sizes. The hydrophilicity, antimicrobial, antifouling and biocompatibility of MgA-MgO-HANRs-Micropatterns are significantly enhanced in comparison with MgA. In bacterial infections and inflammatory environments at pH = 5.0, the micropatterned hydrogel coating releases carvacrol due to ketone bond cleavage, which enhances the antimicrobial capacity of the MgA samples. Compared with MgA, the corrosion current density of MgA-MgO-HANRs-5 μm is reduced by four orders of magnitude and could be maintained even immersing in the simulated body fluids for 30 days. In addition, the bactericidal rates of MgA-MgO-HANRs-5 μm against S. aureus and E. coli are 96 % and 89 %, respectively, and the sample shows long-term and stable antimicrobial performance with the ability to kill nearly 75 % of S. aureus and 82 % of E. coli after 14 days of immersion.