Poly(methyl methacrylate)-silica-calcium phosphate coatings for the protection of Ti6Al4V alloy

Poly(methyl methacrylate) (PMMA)-silica coatings modified with calcium phosphates (CaPs) in the form of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) have been developed to improve the corrosion resistance and bioactivity of Ti6Al4V titanium alloys, applied in medical and dental implants. PMMA-silica hybrids containing 1000 ppm HA or β-TCP were prepared by combining the sol-gel reactions of tetraethylorthosilicate (TEOS) with the radical polymerization of methyl methacrylate (MMA) and 3-methacryloxypropyl trimethoxysilane (MPTS), used as molecular coupling agent. Bi-layer coatings about 15 μm thick, deposited by immersion on Ti6Al4V, are homogeneous, defect-free, and exhibit strong adhesion to the substrate (>14 MPa). The addition of HA and β-TCP led to a slight increase in thermal stability, without affecting the structural integrity of the highly crosslinked PMMA-silica matrix. The greater hydrophilicity and surface roughness of coatings containing HA and β-TCP are associated with the size and chemical composition of CaPs, necessary for effective osteointegration. The modified coatings showed high anti-corrosion efficiency with low-frequency impedance modulus values of up to 73 GΩ cm 2 , remaining stable after 150 days of exposure to simulated body fluid (SBF) solution. Graphical Abstract To protect the Ti6Al4V alloy used for orthopedic and orthodontic implants, poly(methyl methacrylate) (PMMA)-silica-calcium phosphates coatings were obtained by the addition of bioactive additives such as β-tricalcium phosphate (β-TCP) and hydroxyapatite (HA). Bi-layer coatings of about 15 µm thickness formed by a calcium phosphate-modified surface layer and an unmodified barrier base layer, were deposited by immersion on the Ti6Al4V substrates. The high corrosion resistance and long durability of the coatings in simulated body fluid (SBF) solution are related to a highly reticulated nanostructure of uniformly distributed silica nanodomains covalently conjugated with the polymer matrix.