Hydrothermal deposition of high strength calcium phosphate coatings on magnesium alloy for biomedical applications

Abstract

Magnesium and Mg-alloys are suitable replacement to metallic implants (Titanium, stainless steel, Co-Cr alloys) in terms of stress shielding effect and repeated surgery requirement. However, the only hindrance in their successful use as biodegradable orthopedic implants is their high corrosion rates in physiological environment. Thus, in present study, we developed the single step hydrothermal process to deposit bioactive coatings that may lower the corrosion rate. Highly crystalline, cytocompatible, bioresorbable and high strength monetite (CaHPO4) coating successfully produced on Ca-containing Mg-alloy via hydrothermal process. Deposition parameters have significant influence on coatings morphology and degree of crystallinity. XRD pattern indicates sharp, intense and well-defined peaks of monetite along with minor peaks of brucite and spinel phases. SEM study reveals that compact and defects free coatings were deposited at 100 °C. FTIR analysis showed all characteristic peaks that confirms the presence of monetite. Corrosion behavior of coated and uncoated specimen were analyzed using potentiodynamic polarization scan in simulated body fluid (SBF) at 37 °C. Calcium phosphate (CaP) coating significantly improve the degradation rate of Mg-alloy. Corrosion rate was 80% lower in CaP coated Mg-alloy specimens than bare Mg-alloy. Adhesion strength of coatings was determined using lap shear test demonstrating a cohesive failure at 21.89 MPa stress. Furthermore, cytotoxicity of coated and uncoated alloy was assessed by using Alamar Blue (AB) assay on NIH3T3 mouse fibroblast cell line for 9 days indicate no significant difference in proliferation of cells for CaP coated Mg-alloy and positive control. These results suggest that hydrothermal method reported here can potentially be used to deposit compact, highly crystalline, bioresorbable, cytocompatible and protective coatings with high adhesion strength on intricate geometries for degradable implant applications.