Structure retention of proteins interacting electrostatically with TEMPO-oxidized cellulose nanofiber surface

In this study, we evaluated the adsorption of proteins to 2,2,6,6-tetramethylpiperidine-1-oxyl oxidized cellulose nanofibers (TOCNs) and their structures on the TOCN surface. TOCNs derived from bleached pulp are as thin as 4 nm and have a very high specific surface area and a high density of surface carboxyl groups. The adsorption of two model proteins (lysozyme (Lyz) and bovine serum albumin (BSA)), which is driven by electrostatic attraction between the positively charged proteins and the negatively charged TOCN surface bearing ionized carboxyl groups, is demonstrated to occur only at pH values below their isoelectric points. Notably, pristine BSA and Lyz retain their native structures after adsorption onto TOCN, which is ascribed to the very low width of TOCN, and consequently the low area of contact between the protein and cellulose fiber. Thus, this work paves the way to the fabrication of TOCN-based biomaterials with the retention of the structure of the adsorbed proteins.