Effect of the terminal group of phosphonate self-assembled films formed on Ti surfaces on the biomimetic layer formation and cell adhesion

Abstract

ObjectivesTo evaluate the effect of different Self-Assembled Films (SAFs) on the development of calcium-phosphate (Ca/P) biomimetic layers on commercially pure titanium (cpTi) and the final cell adhesion on these coatings. Materials and methodsA total of five different surfaces were evaluated. Alkyl phosphonate Self-Assembled Films (SAFs) with three different ending groups (methyl [–CH3], carboxyl [–COOH], and phosphonate [–PO(OH)2]) were used to cover ultra-polished cpTi surfaces. These functionalized surfaces were compared with a hydroxylated ultra-polished cpTi surface. A biomimetic Ca/P layer was deposited on each surface by precipitation. A control cpTi sample with no precipitates was introduced in the study. Topography (AFM), morphology (ESEM), chemistry (XPS, EDX), crystallography (XRD), wettability (dynamic contact angle), layer thickness (WLCM), percolation (fluid retention) and cell response analysis were used for surface characterization. ResultsXRD showed the formation of hydroxyapatite (HA) in the four biomimetic coatings. The Ca/P ratios obtained by XPS in the four biomimetic coatings showed similar values (≈1.40) corresponding to amorphous hydroxyapatite. The water wettability of the biomimetic coatings was similar but the surface morphology was different. The thickest biomimetic coating with lower percolation threshold and greater cell adhesion was obtained on the carboxyl-terminated SAF. The biomimetic coatings improved the cell adhesion but it was further improved by the presence of underlying SAFs that bond the coating to cpTi surface. ConclusionsThe use of SAFs chemically stabilizes the biomimetic precipitates and guarantees higher cell adhesion than in absence of SAFs. The apatite nucleation and growth depended on the underlying SAF. Biomimetic coatings on hydroxylated surface increases cell adhesion but on SAFs functionalized surfaces achieve higher cell response. The SAFs with carboxyl ending group promoted the formation of thick and interconnected biomimetic coatings, with low fluid retention and a very significant cell response.