Fabrication of calcium phosphate/chitosan coatings on AZ91D magnesium alloy with a novel method

Four calcium phosphate/chitosan composite films were fabricated on the surface of micro-arc oxidized (MAO)-AZ91D alloy through electrophoretic deposition (EDP) followed by a conversion process of the coatings in a phosphate buffer solution (PBS). In the EPD process, nano hydroxyapatite (n-HA, Ca10(PO4) 6(OH)2) and Ca(OH)2 in the layers were obtained from a n-HA/ethanol suspension and a n-HA/chitosan–acetic acid aqueous solution, respectively. After immersion into PBS, brushite (DCPD, CaHPO4·2H2O) and new HA were introduced into the deposited layers. The percentage of Ca(OH)2 in the deposited layers played an important role in developing the new phase in the conversion layers. When the percentages of Ca(OH)2 in the deposited layers were 32 wt. % and 54 wt. %, the main phase of the conversion layers was DCPD with a little HA. However, when the percentages of Ca(OH)2 were 64 wt. % and 100 wt. %, the main phase of the conversion layers became HA with a little DCPD. The calcium phosphate/chitosan coatings with more homogeneous bioactive layers and better adhesion strength on MAO-AZ91D alloy substrate were obtained from the electrolyte whose volume percentages of the n-HA/chitosan–acetic acid aqueous solution being 60% and 80%.So, EPD combined with a conversion process into PBS could be a promising method for the preparation of new calcium phosphate/chitosan coatings.