Protein conformation and electric attraction adsorption mechanisms on anodized magnesium alloy by molecular dynamics simulations

Abstract

Protein adsorption preferentially occurs and significantly affects the physicochemical reactions once the biodegradable magnesium alloys as bone replacements have been implanted. To date, interactions mechanisms between Mg implants and proteins remain unclear at a molecular level. Thereby, a combination of molecular dynamic (MD) simulations and experimental exploration is used to investigate the adsorption behavior and conformational change of bovine serum albumin (BSA), a representative protein of blood plasma, upon the surface of micro-arc oxidation (MAO) coated Mg alloy AZ31. The influences of absorbed proteins on the cytocompatibility of MAO coating are evaluated by virtue of cytotoxicity assay. Results indicate that the negatively charged O atoms (BSA) exhibit strong interaction with Mg 2+ ions of Mg(OH) 2 , revealing that BSA molecules are ionically adsorbed on the AZ31 surface. Interestingly, MD simulation reveals that MAO coating demonstrates superior ability to capture BSA molecules during the process of adsorption owing to strong electric attraction between the negatively charged O atoms in BSA molecules with Mg atoms of MgO in MAO coating. Moreover, the α -helix part of absorbed BSA molecules on AZ31 substrate and MAO coating markedly decreases with an increase in β -sheet, β -turn and unordered contents, which is attributed to the reduction in the number of hydrogen bonds in BSA molecules. Furthermore, the adsorbed BSA molecules improve the cytocompatibility of MAO coating since the positively charged -NH 3 + group and β -sheet content of absorbed BSA molecules mediate the cell adhesion by interacting with the negatively charged cell membrane.