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

摘要

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, Ca_(10)(PO_4) _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, CaHPO_4·2H_2O) 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 32wt. % and 54wt. %, the main phase of the conversion layers was DCPD with a little HA. However, when the percentages of Ca(OH)_2 were 64wt. % and 100wt. %, 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.