Analysis of Initial Protein Surface Coverage on Fouled Ultrafiltration Membranes

Area of Science:

• Membrane science
• Biomaterials science
• Physical chemistry

Background:

• Protein adsorption on membranes is a critical factor in ultrafiltration performance.
• Understanding initial protein-membrane interactions is key to mitigating fouling.
• Bovine serum albumin (BSA) is a model protein for studying these phenomena.

Purpose of the Study:

• To analyze the internal surface coverage of protein in membranes during the initial phase of ultrafiltration.
• To investigate the influence of solution properties (pH and ionic strength) on protein adsorption.
• To compare experimental data with models of surface coverage.

Main Methods:

• Ultrafiltration of Bovine Serum Albumin (BSA) solutions using 100,000-MWCO polysulfone membranes.
• Varying solution conditions: pH 5 and 7, NaCl concentrations of 0.05 M and 0.15 M.
• Quantification of membrane mass uptake using electron paramagnetic resonance (EPR) spectroscopy over 4 hours.

Main Results:

• Significant protein loading was observed within a very short exposure time during ultrafiltration.
• Initial protein uptake was largely independent of solution properties.
• Solution properties affected the resistance per mass of adsorbed species, particularly near BSA's isoelectric point (pH 5).

Conclusions:

• Protein adsorption during the initial phase of ultrafiltration is rapid and substantial.
• At pH 7, adsorbed BSA primarily occupied the membrane's ultrathin skin layer.
• At pH 5 and low ionic strength, BSA adsorbed and lodged throughout the membrane substructure, indicating different fouling mechanisms.