| Over the last decades, a large fraction of the scientific community has been dedicated to developing synthetic materials that can be used as implants or replacements for bones, organs, joints, tissues, skin, etc. These artificial materials must not only accomplish a specific function, but also be inert in the biological environment to which they are exposed. Surfaces covered with polyethylene glycol (PEG, HO-(CH2-CH2-O)n -H) have been shown to be biocompatible because PEG's properties yield nonimmunogenicity, nonantigenicity and protein rejection. To produce a biocompatible surface coating, we have developed a method for grafting PEG onto activated silica films. We first deposit an amorphous silica film by plasma enhanced chemical vapor deposition (PECVD) from SiH4 and O2 gases, which provides the flexibility to coat diverse materials having different chemistries and shapes. The silica films are activated by exposure to water plasma, which increases the number of silanol groups (Si-OH) on their surface. The surface silanol groups are then chemically reacted with the hydroxyl end of PEG to form an ester bond, Si-O-C, and to cover the surface with PEG. The surface reactions were monitored using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The PEG-covered surfaces were physically characterized by atomic force microscopy (AFM), Auger electron spectroscopy, ellipsometry, contact angle and surface forces apparatus (SFA) measurements. These characterization techniques provide additional evidence for the existence of chemically bonded PEG on the surfaces. Efficacy of protein rejection on PEG-covered surfaces was studied through ATR-FTIR spectroscopy and measurements of the fluorescence intensity of labeled proteins adsorbed in such surfaces. The proteins tested included human fibrinogen (HFb) and human serum albumin (HSA). These proteins were brought in contact with silica, water plasma-treated silica, and PEG-covered silica at different solution concentrations for various incubation times at 37°C and pH = 7.4 (imitating physiological conditions). Significantly less protein adsorption is observed on surfaces covered with PEG compared to uncovered surfaces.; The mechanical properties and surface interactions, such as friction and cohesion forces, are also important parameters in determining whether or not a novel material can be used as a biomaterial. The adhesion and tribological properties were measured in dry air and in bulk water with the SFA. The presence or absence of water alters the frictional behavior from smooth-sliding to stick-slip motion. We discuss the friction, wear and lubrication properties of symmetric surfaces of PEG-covered silica surfaces where the friction force increases with sliding velocity, indicating possible shear thickening behavior under confined conditions. In contrast, as-deposited silica surfaces have the highest friction and least resistance to wear. |
