Cell-protein-material Interactions on Bioceramics and Model Surfaces

Abstract: The objective of this thesis was to investigate and characterize the interaction between blood proteins and different surfaces with emphasis on protein adsorption to bioceramics and model surfaces. Special effort was made to monitor the spontaneous and selective adsorption of proteins from human plasma and to examine the orientation, conformation and functional behavior of single proteins after adsorption. Five different ceramic biomaterials: alumina (Al2O3), zirconia (ZrO2), hydroxyapatite (Ca10(PO4)6(OH)2) and two glass-ceramics, AP40 (SiO2-CaO-Na2O-P2O5-MgO-K2O-CaF2) and RKKP (AP40 with Ta2O3-La2O3), were exposed to human plasma and their protein binding capacities and affinities for specific proteins were studied by chromatography, protein assays, two-dimensional gel electrophoresis and Western blotting. The studies showed that all materials adsorbed approximately the same high amount of plasma proteins and that they therefore should be fully covered by proteins in an in vivo setting. The adsorbed proteins were different for most materials which could explain their previously observed different levels of tissue integration in vivo. Four of the proteins that behaved differently, ceruloplasmin, prothrombin, ?2-HS-glycoprotein and ?1-antichymotrypsin, were selected for characterization with atomic force microscopy and ellipsometry. The studies, which were performed on ultraflat silicon wafers (silica), showed that the proteins oriented themselves with their long axis parallel to the surface or as in case of ceruloplasmin with one of its larger sides towards the surface. All of them had globular shapes but other conformational details were not resolved. Furthermore, prothrombin (none of the others) formed multilayers at high proteins concentrations. The functional behaviour of the adsorbed proteins, referring to their cell binding and cell spreading capacity on silica and a positive cell adhesion reference surface (Thermanox®), was affected by the underlying substrate. Ceruloplasmin, ?2-HS-glycoprotein and ?1-antichymotrypsin stimulated cell attachment to silica, but suppressed attachment to Thermanox®. Prothrombin stimulated cell attachment to both surfaces. The attachment was in most cases mediated both by cell membrane-receptors (integrins) and by non-specific interactions between the cell and the material. This thesis showed that the compositional mixture, orientation, conformation and functional behavior of the adsorbed proteins are determined by the properties of the underlying surface and if these parameters are controlled very different cellular responses can be induced.