Surface modification of porous alumina membranes by collagen layers: Performance and characterization

In this study, surface properties of alumina microfiltration membranes were modified by spin coating the surface with thin layers of collagen while controlling other critical surface properties such as pore size and surface charge. Collagen was spin deposited in layers of 1, 3, 6 or 9 onto an alumina membrane surface and IR spectra confirmed the presence of collagen protein on the substrate layer. The surface topography and pore morphology were studied using atomic force microscopy and scanning electron microscopy and revealed that the alumina surfaces were covered with collagen even for the single layer modification. The contact angle values for alumina membrane surfaces were measured to be 38 ± 6°, whereas the contact angle increased to 78 ± 6° when six layers of collagen were spun onto the membranes. The zeta potential of alumina membranes at a pH of 5.5 was 27 mV, whereas it decreased to 8 mV when 9 layers were spun onto the surface. The average pure water permeability was 7 × 10−6 m/(s kPa) for the sulfuric acid-etched alumina membrane, and decreased after collagen was deposited. The pure water flux at 207 kPa for sulfonated alumina was 14 × 10−4 m/s, but the flux dropped by nearly 50% for 3 layer membranes to 7 × 10−4 m/s, and by roughly 95% (to 0.7 × 10−4 m/s)) for 6 and 9 spun-on layers. The molecular weight cut off of the 3-layer modified membranes was 270 kDa and decreased to 80 kDa (6 layers) and 50 kDa (9 layers) as collagen layers increased. Permeability, flux and MWCO values for the collagen-coated membranes are comparable to ultrafiltration and loose nanofiltration membranes, and are expected to be suitable for biomolecular separations.