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Membrane fouling commonly occurs in all filter types during virus filtration in protein-based biopharmaceutical manufacturing. Mechanisms of decline in virus filter performance due to membrane fouling were investigated using a cellulose-based virus filter as a model membrane. Filter performance was critically dependent on solution conditions; specifically, ionic strength. To understand the interaction between immunoglobulin G (IgG) and cellulose, sensors coated with cellulose were fabricated for surface plasmon resonance and quartz crystal microbalance with energy dissipation measurements. The primary cause of flux decline appeared to be irreversible IgG adsorption on the surface of the virus filter membrane. In particular, post-adsorption conformational changes in the IgG molecules promoted further irreversible IgG adsorption, a finding that could not be adequately explained by DLVO theory. Analyses of adsorption and desorption and conformational changes in IgG molecules on cellulose surfaces mimicking cellulose-based virus removal membranes provide an effective approach for identifying ways of optimizing solution conditions to maximize virus filter performance. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:379-386, 2018.

We developed a method to identify proteins adsorbed on solid surfaces from a solution containing a complex mixture of proteins by using Matrix-Assisted Laser Desorption/Ionization-Time of Flight mass (MALDI-ToF mass) spectroscopy. In the method, we performed all procedures of peptide mass fingerprint method including denaturation, reduction, alkylation, digestion, and spotting of matrix on substrates. The method enabled us to avoid artifacts of pipetting that could induce changes in the composition. We also developed an algorithm to identify the adsorbed proteins. In this work, we demonstrate the identification of proteins adsorbed on self-assembled monolayers (SAMs). Our results show that the composition of proteins on the SAMs critically depends on the terminal groups of the molecules constituting the SAMs, indicating that the competitive adsorption of protein molecules is largely affected by protein-surface interaction. The method introduced here can provide vital information to clarify the mechanism underlying the responses of cells and tissues to biomaterials.