Feasibility Study of Strontium-Containing Calcium Phosphate Coatings on Micro-Arc Oxidized AZ31

Abstract

Highlights: What are the main findings? Strontium (Sr)-doped calcium phosphate (CaP) coatings deposited on micro-arc oxidation pretreated AZ31 exhibit increased corrosion resistance. Sr content within the CaP coatings positively influences the attachment and proliferation of MC3T3-E1 cells. What is the implication of the findings? Sr-doped CaP coatings have the potential to control the in-vitro corrosion of bone tissue scaffolds. Incorporation of Sr within the CaP coatings increases the overall cytocompatibility of the MAO pretreated AZ31. Calcium phosphate coatings are known for their osteoconductive prowess. In this work, calcium phosphate coatings were studied on a model biodegradable magnesium alloy of AZ31, primarily to provide improved corrosion protection and, more importantly, to confer in vitro cytocompatibility to the AZ31 alloy. Correspondingly, an aqueous-based approach was developed to deposit Sr2+-substituted calcium phosphates on micro-arc oxidized AZ31. Micro-arc oxidation was used mainly as a pretreatment technique due to improved homogeneity and adhesion strength in comparison to the coatings formed by the traditionally used alkaline and acidic pretreatment. Calcium phosphate coatings with up to 11.5 mol. % Sr were formed on micro-arc oxidized AZ31 substrates. Despite observation of greater than the intended 10 mol. % Sr to the calcium phosphate coatings as measured within the measurement error, biphasic mixtures of dicalcium phosphate dihydrate and poorly crystalline hydroxyapatite were formed. Micro-arc oxidation treatment, nevertheless, provided a slight improvement in corrosion protection compared to uncoated AZ31. However, much-improved corrosion protection was provided by the calcium phosphate coatings prepared either with or without Sr2+. The calcium phosphate coatings prepared with Sr2+ were also observed to support improved MC3T3-E1 murine pre-osteoblast cell proliferation compared to the calcium phosphate coated substrates prepared without Sr2+.