Anti-corrosion and stable osteointegration of a biodegradable magnesium implant by chitosan-combined calcium phosphate coating

Magnesium (Mg) implants used for bone fixation are biodegradable and have superior mechanical properties. However, there is a problem with H₂ formation and an increase in pH due to rapid corrosion. Bioceramic coatings on magnesium can improve not only the corrosion resistance but also the bioactivity. However, their brittleness can easily damage coating layers. Surface exposure to damage causes rapid biodegradability, which may affect localized corrosion of the implant and damage the surrounding tissue. Polymer-combined coatings can complement the weaknesses of ceramic coating layers and are effective in promoting cell adhesion and osseointegration. Therefore, in this study, to prevent corrosion from damage and to induce stable bone regeneration, the magnesium surface was modified with precipitating chitosan (Cs)-combined apatite by hydrothermal treatment for 1 h at 90 °C with chitosan and calcium phosphate. After the hydrothermal treatment, fine flower-like CaP particles precipitated along with a thin Mg(OH)₂ layer on the Mg surface. As the mixing ratio of Cs increased, the particle size decreased and the particle layer became uniform and dense. This polymeric bioceramic layer effectively inhibited the localized corrosion of the Mg implant, with an increase in the layer resistance (R_l) and charge-transfer resistance (R_ct). The Cs-combination increased the adhesion of osteoblasts, and mixing Cs up to 20% in the CaP-based mixture was gradually effective in increasing cell proliferation. Consequently, a suitable combination of Cs on the CaP coating layer could lead to successful bone regeneration by improving the corrosion resistance and proliferation of osteoblasts on Mg.