Investigating protein adsorption on surfaces for biomedical applications: a comparative study on bioactive materials

Introduction Adsorption of proteins on biomaterials and biomedical devices is a major field of interest. Proteins are thought to cover medical device surfaces almost immediately after they are in contact with body fluids and form the interphase for cellular interactions. Understanding how surface properties affect the adsorbed proteins will provide guidelines for novel and better biomaterial design. This work aims to study how proteins interact with titanium based materials designed for bone-bonding and to define a set of techniques that can be applied to characterize protein-surface interaction on different materials. Materials and methods Ti and Ti6Al4V alloys with three different chemical treatments for osteointegration were soaked in a solution of bovine albumin (20 mg/ml) at physiological pH 7.4. Surfaces were characterized by confocal microscopy, zeta potential titration, XPS, Kelvin probe force microscopy (KPFM), ATR-FTIR, and contact angle measurements with different liquids. The adsorbed proteins were quantified by BCA assay and analyzed by using conventional (XPS, fluorescence microscopy, FTIR) and novel (zeta potential titration and KPFM) techniques to determine their conformation and the layer structure. Result and discussion The investigated surfaces differ for chemistry (density and chemical reactivity of the surface OH groups) and thickness of the surface oxide layer, surface zeta potential, wettability, and roughness. BSA is adsorbed and forms continuous layer on all surfaces. Comparing the results of different techniques, BSA shows different interaction mechanisms with the different surfaces: its conformation and chemistry upon adsorption may vary on different substrates. Conclusion Protein adsorption is deeply affected by surface properties, such as surface charge, surface energy, and surface functional groups. They dictated amount and conformation of the adsorbed proteins and the interactions with the substrates, which may vary even on materials with similar chemical composition. Our results suggest a protocol of characterization useful to obtain information on the adsorption process and protein structure on bulk materials that are intended and designed for biomedical applications.