The Adsorption of Proteins on Metal Surfaces

High-performance scaffolds on titanium surfaces: osteoblast differentiation and mineralization promoted by a globular fibrinogen layer through cell-autonomous BMP signaling

Titanium has been widely used as a dental implant material. However, it takes several months for the implant body to bind with the jawbone. To develop new bioactive modification on titanium surfaces to achieve full osseointegration expeditiously, we used fibrinogen and fibronectin as bioactive scaffolds on the titanium plate, which are common extracellular matrix (ECM) proteins. We analyzed the features of the surface of ECM-modified titanium plates by atomic force microscopy and Fourier transform infrared spectrophotometry. We also evaluated the effect of ECM modification on promoting the differentiation and mineralization of osteoblasts on these surfaces. Fibrinogen had excellent adsorption on titanium surfaces even at low concentrations, due to the binding ability of fibrinogen via its RGD motif. The surface was composed of a fibrinogen monolayer, in which the ratio of β-sheets was decreased. Osteoblast proliferation on ECM-modified titanium surface was significantly promoted compared with titanium alone. Calcification on the modified surface was also accelerated. These ECM-promoting effects correlated with increased expression of bone morphogenetic proteins (BMPs) by the osteoblasts themselves and were inhibited by Noggin, a BMP inhibitor. These results suggest that the fibrinogen monolayer-modified titanium surface is recognized as bioactive scaffolds and promotes bone formation, resulting in the acceleration of osseointegration.

Protein adsorption to a bioactive glass with special reference to precorrosion

The protein adsorption properties of the bioactive glass S53P4 were studied using albumin, IgG, and fibrinogen solutions (1 mg/mL) as well as diluted plasma, serum, and 1:1:1 mixtures of albumin, IgG, and fibrinogen. The bioactive glass granules (315-500 microns) were used in the experiments without pretreatments or as precorroded with an Si-rich or a Ca,P-rich layer. The protein adsorption properties of S53P4 were compared to a commercial bioactive glass (Bioglass), an inert glass, an experimental glass ceramic, titanium (Ti), and hydroxyapatite (HA). The untreated S53P4 bound in Trisbuffered saline mainly albumin from diluted plasma and serum and the 1:1:1 (1 mg of each) mixture of albumin, IgG, and fibrinogen. No binding of fibrinogen was observed. The omission of NaCl from the buffer used in the experiments increased the number of proteins bound by the S53P4. Most of the albumin bound by the glass could be detached with 0.5-1M NaCl speaking for electrostatic protein bonding. The protein adsorption properties of Bioglass resembled those of S53P4. The Ca,P-rich layer glass, the inert glass, the glass ceramic, HA, and Ti all bound several plasma and serum proteins, including fibrinogen. The Si-rich layer glass showed protein binding properties resembling the untreated glass more than the Ca,P-rich layer glass. The protein adsorption test used in the present study revealed differences in the protein adsorption properties of the studied materials, which may reflect differences in their surface potentials. It also functioned in registration of corrosion-induced changes in the surface properties of the S53P4. As judged by the protein adsorption properties, the untreated S53P4 could have a higher biocompatibility than the two precorroded glasses. Precorrosion, especially the formation of the Ca,P-rich layer, increased the number of proteins bound by the S53P4. Thus, a precorroded glass as compared to the untreated glass could be a better carrier of specific proteins that may be used to improve the biocompatibility of the bioactive glass.

Adsorption of salivary proteins onto prosthetic titanium components

In vivo adsorption of salivary proteins onto prosthetic titanium components was analyzed after exposure of titanium abutments to the oral environment for a period of 2 to 6 weeks. Gel electrophoresis and Western immunoblotting were used to separate and identify the proteins, which were mainly alpha-amylase and serum albumin. Selective adsorption of proteins enables attachment of specific oral bacteria and thus may alter the composition of the dental plaque formed on titanium surfaces.

Wettability and interfacial interactions in bioceramic-body-liquid systems

Wetting experiments, by the sessile drop technique, were carried out at 37 degrees C in air to determine the surface and interfacial interactions that take place in various solid bioceramics based on Al2O3, ZrO2(YPZ), SiO2, and TiO2 in contact with water, Ringer solution, artificial synovial fluid, calf serum, human plasma, and whole blood (+ EDTA). The surface energy of the liquids was measured by the ring method. The calculated values of the energy of interaction (work of adhesion) reveal that intermolecular forces act across the solid-liquid interfaces. The contribution of the dispersion and polar interactions to the surface energy of the polar liquids and the pure or mixed oxides was determined assuming that in the system of Mn-steel-liquids only dispersion forces act at the interface. It was found that the contribution of the polar interactions to the energy of interaction at the solid-liquid interface increases with the glassy phase content of the oxide that causes reduction of the measured contact angle.

Titanium-protein interaction: changes with oxide layer thickness

Since titanium is being used for various biomedical applications requiring enhanced blood compatibility, which may be partly due to its extremely stable oxide layer, an attempt is made here to understand the effect of oxide layer thickness on protein adsorption. Different thickness of oxide layers have been coated on titanium foil using anodizing method and thickness of oxide layers deposited have been measured by an ellipsometer. Studies of competitive adsorption of proteins, using I125 labelled protein from a mixture of 25 mg% albumin, 15 mg% gamma-globulin and 7.5 mg% fibrinogen indicate an increased adsorption of proteins onto the oxide layer coated surfaces compared to the bare surface.

Albumin adsorption on to aluminium oxide and polyurethane surfaces

The changes in protein adsorption onto aluminium surfaces coated with different thicknesses of oxide layers were examined. The oxide layers on aluminium substrates were derived by the anodizing technique. Protein adsorption studies were conducted using 125I-labelled albumin and the amount of albumin adsorbed was estimated with the help of a gamma counter. An increase in albumin adsorption was observed on oxide layer coated aluminium surfaces. The effect of anti-Hageman factor on albumin and fibrinogen adsorption on to bare aluminium, oxide layer coated aluminium and bare polyether urethane urea surfaces was also investigated. It was observed that the presence of anti-Hageman factor increased the adsorption of albumin and fibrinogen on to all these substrates.

Protein absorption and desorption phenomena on clean metal surfaces

The noncompetitive adsorption of the proteins albumin and fibrinogen onto 17 different metal surfaces has been studied in vitro using 125I-labeled proteins. Although many of the metals showed very similar adsorption characteristics to polymers, several of them adsorbed considerably greater amounts. Copper, gold, and silver were the most significant in this respect, all three being face-centered cubic, group 1B metals known to bind to many types of protein in vitro and in vivo. The desorption of the proteins was studied in an in vivo model in which preproteinized metals were implanted in rats. There was considerable variations in the amounts of the proteins removed from the various metal surfaces. Generally those metals onto which protein is most readily adsorbed tend to lose the protein quickly, whereas others, such as iron, with only moderate adsorbed amounts, may retain a large part of the adsorbed layer for a long time.