CONICET | Buscador de Institutos y Recursos Humanos

Fabrication of PDMS-like nano-films were realized on standard silicon wafers which were cleaned, dried at 80°C for 4 hours, and immersed, under gentle stirring, in solutions containing n-dimethylsiloxane (dissolved in dichloromethane) for 3 hours. This approach is simpler and faster than others previously reported; and resulted in uniform layers of PDMS and is thus compatible with ellipsometric measurements. The PDMS-like nanofilms produced in the present study using deposition of 1,7-dicholoro-octamethyltetrasiloxane were characterized by nuclear magnetic resonance (500 MHz 1H-NMR), reflectance Fourier-transformed infrared spectroscopy (FTIR), reflectance UV-vis spectrophotometry, scanning electron microscopy (SEM), atomic force microscopy (AFM), and spectroscopic ellipsometry. Dynamic adsorption of various proteins specifically, fibrinogen, collagen type-I, and bovine serum albumin, was investigated as a function of protein concentrations and pH values and measured using an ellipsometer. Adhesion of human dermal micovascular cells onto the PDMS-like nanofilms in the presence of each pre-adsorbed protein was also investigated. The results of the present study provided unique insights into the amount and arrangement of proteins adsorbed onto nanofilms of a material with similar (if not identical) properties to commercial PDMS. In agreement with literature reports, the highest amount of protein was adsorbed when the pH of the buffer solution was close to, or near, the isoelectric point of the respective protein. Measurements of the initial adsorption rate were achieved using a small amount of protein and were completed in a relatively short (~20 min) time; maximizing the adsorption rate is an effective way to minimize structural rearrangements (such as spreading) of the adsorbing protein molecules. On the other hand, measurements of protein saturation required significantly longer (~175 min) time periods. For this reason, protein post-adsorption influences interpretation of the results. Furthermore, the importance of hydrophobic interactions in the adsorption of the proteins tested is evidenced by the strong adsorption observed even under unfavorable electrostatic conditions. Although the number of adhering cells was similar on all substrate surfaces tested, differences in cell morphology were observed. Cells adhering onto PDMS-like surfaces modified with either absorbed collagen type-I or fibrinogen at 0.01 mg/mL or 0.0001 mg/mL concentrations exhibited more spread-out morphology than cells adhering onto either unmodified silicon, PDMS-like without adsorbed protein, or PDMS-like with pre-adsorbed bovine serum albumin at all concentrations tested.