The atomic ordering and its correlation to protein adsorption on biocompatible metal oxide coatings

Abstract

Event Abstract Back to Event The atomic ordering and its correlation to protein adsorption on biocompatible metal oxide coatings Phaedra Silva-Bermudez1, 2, Margarita Rivera3 and Sandra E. Rodil2 1 Instituto Nacional de Rehabilitación, Tissue Engineering, Cell Therapy and Regenerative Medicine Unit, Mexico 2 Universidad Nacional Autónoma de México, Instituto de Investigaciones en Materiales, Mexico 3 Universidad nacional Autónoma de México, Instittuto de Física, Mexico Introduction: Biomaterials that can, simultaneously, direct an adequate biological response and meet biomechanical requirements are essential for dental implants. Coatings are interesting options to tailor the surface properties of mechanically-adequate bulk materials and, consequently, their biological response. Correlations between biological response and surface properties such as roughness (Ra), chemistry or wettability have been widely studied; however, the atomic ordering (AO) and surface free energy (SFE) effects are less understood[1],[2]. The use of amorphous (a-) and crystalline (c-) coatings can confer novel nanotopographies or SFE to materials and constitute controlled models to study the biological effects of specific surface properties; e.g. it is possible to modify the Ra or the wettability while keeping the surface chemistry. One of the first events occurring upon material-biological media interaction is protein adsorption, which influences the development of cell-surface interactions. Thus, in this study, c- and a- ZrO2 and TiO2 coatings, biocompatible oxides of interest for dental implants, were used to study the correlations among atomic ordering, surface properties and protein adsorption. Bovine Serum Albumin (BSA) was used as model protein. Materials and Methods: a- and c- ZrO2 and TiO2 thin films were deposited on Si substrates by Reactive Magnetron Sputtering in Ar/O2 atmosphere, from Zr or Ti targets. Substrates were heated to 250°C or 300°C during deposition to obtain c-ZrO2 and c-TiO2, respectively. Coatings surface properties (AO, wettability, SFE, Ra and chemical composition) were characterized by X-ray Diffraction, Contact Angle, Atomic Force Microscopy, Profilometry, Ellipsometry (ELP) and X-ray Photoelectron Spectroscopy (XPS). Coatings samples were immersed in BSA solutions and a set of ELP angles was acquired in-situ every 2 s at 3 eV for 2400 s. At equilibrium, ELP spectra (1.5-4.2 eV) were acquired and fitted to a four phase optical model to obtain the adsorbed BSA surface mass concentration. Then, samples were rinsed, dried in N2 and analyzed by XPS to quantify the adsorbed protein through analysis of C 1s and N 1s energy regions. Statistical significance was examined by ANOVA with Bonferroni’s modification. Results and Discussion: Coating roughness and water contact angle (WCA) increased with atomic ordering; more notoriously for a-TiO2 and c-TiO2. Different morphologies were observed for c- and a- coatings. Coatings had similar SFE; mainly dispersive with a small polar contribution (γAB). The highest and the smallest γAB were observed for a-TiO2 and a-ZrO2, respectively. γAB was mainly basic (γ_) for all coatings but c-TiO2 with γAB of acidic nature (γ+). A higher BSA adsorption was observed on c- oxides than on their corresponding a- oxides. BSA adsorption was higher on ZrO2 than on TiO2, independently of the atomic ordering. Conclusions: The higher BSA adsorption on c- coatings, compared to the a- ones, seems to be chemistry-related: on TiO2, it may be, mainly, due to an increment of electrostatic interactions between BSA and c-TiO2; γ+ for c-TiO2 > γ+ for a-TiO2. On ZrO2, it may be due to the higher available surface area (Ra) on c-ZrO2 than on a-ZrO2. Coadsorption of H2O and BSA molecules on TiO2 may explain the smaller BSA adsorption on TiO2 than on ZrO2, independently of the atomic ordering. This presents the possibility to tailor specific molecules/ions adsorption through modifying the coatings atomic ordering. Acknowledgements to the financial funding from CONACYT under the research Grant CONACyT-CB-152995 and from DGAPA under the research Grants DGAPA-PAPIIT-IG100113, DGAPA-PAPIIT-IN118814 and DGAPA-PAPIIT-IN118914