Study of protein adsorption effects on crossflow filtration using BSA and milk protein.

Three membrane materials were tested under similar conditions to determine the effects of membrane material on the performance and cleanability of the filters. The membrane materials investigated were stabilized cellulose (Hydrosart, Sartorius Corporation), cellulose triacetate, and polyethersulfone; all having a 10 kilodalton molecular weight cutoff. Stabilized cellulose is a cellulose-based membrane material, modified for low non-specific protein adsorption combined with high pH-resistance. When analyzing the data, three phenomena were considered: adsorption of protein to the membrane, gel layer formation, and osmotic pressure due to concentration polarization. Throughout these studies, the effects of a gel layer and the osmotic pressure were approximately equivalent in all cassettes. However, the stabilized cellulose was resistant to protein adsorption while the other two membranes exhibited significant decreases in permeate flux due to adsorption. Using a 0.2% BSA (MW = 67,000 kD) solution with a crossflow rate of 5 L/min and transmembrane pressure of 35 psi, the permeate flux through the stabilized cellulose membrane was 3% lower than the baseline saline flux, whereas the cellulose triacetate and polyethersulfone membranes lost 33% and 60% of baseline flux, respectively. The decrease in flux occurring in the latter two membranes is due to adsorption. Another study evaluated adsorption by alternating between crossflow and static operation. After three cycles, the stabilized cellulose maintained the original crossflow flux level. The polyethersulfone lost cumulatively 17% of its crossflow flux after three cycles and the cellulose triacetate lost 13%. The stabilized cellulose and polyethersulfone membranes were also evaluated using a milk solution. The results indicate that the stabilized cellulose is not susceptible to adsorption of any of the milk components while the polyethersulfone permeate flux was limited by adsorption. The saline flux of the stabilized cellulose immediately after testing with the milk solution was 3% lower than the baseline flux, while the polyethersulfone membrane saline flux was 81% lower. The results consistently indicated that, unlike the cellulose triacetate and polyethersulfone membranes, the stabilized cellulose membrane was not subject to adsorption.