Adsorption of maleic acid monomer on the surface of hydroxyapatite and TiO2: a pathway toward biomaterial composites

Poly(styrene-alt-maleic acid) adsorption on hydroxyapatite and TiO2 (rutile) was studied using experimental techniques and complemented by \textit{ab initio} simulations of adsorption of a maleic acid segment as a subunit of the copolymer. Ab initio calculations suggest that the maleic acid segment forms a strong covalent bonding to the TiO2 and hydroxyapatite surfaces. If compared to vacuum, the presence of a solvent significantly reduces the adsorption strength as the polarity of the solvent increases. The results of first-principle calculations are confirmed by the experimental measurements. We found that adsorbed poly(styrene-alt-maleic acid) allowed efficient dispersion of rutile and formation of films by the electrophoretic deposition. Moreover, rutile can be co-dispersed and co-deposited with hydroxyapatite to form composite films. The coatings showed an enhanced corrosion protection of metallic implants in simulated body fluid solutions, which opens new avenues for the synthesis, dispersion, and colloidal processing of advanced composite materials for biomedical applications.