Multi-size optimization of macroporous cellulose beads as protein anion exchangers: Effects of macropore size, protein size, and ligand length

•Multi-size optimization of macroporous cellulose microspheres.•Larger macropores are beneficial to the mass transfer of proteins.•Smaller macropores can also improve uptake kinetic by surface diffusion.•Increasing the ligand length significantly improves the adsorption performance. Multi-size optimization of ion exchangers based on protein characteristics and understanding of underlying mechanism is crucial to achieve maximum separation performance in terms of adsorption capacity and uptake kinetic. Herein, we characterize the effects of three different sizes, macropore size, protein size, and ligand length, on the protein adsorption capacity and uptake kinetic of macroporous cellulose beads, and provide insights into the underlying mechanism. In detail, (1) for smaller bovine serum albumin, macropore size has a negligible effect on the adsorption capacity, while for larger γ-globulin, larger macropores improve the adsorption capacity due to the high accessibility of binding sites; (2) there is a critical pore size (CPZ), at which the adsorption uptake kinetic is minimum. When pore sizes are higher than the CPZ, uptake kinetics are enhanced by pore diffusion. When pore sizes are lower than CPZ, uptake kinetics are enhanced by surface diffusion; (3) increasing ligand length improves the adsorption capacity by three-dimensionally extended polymer chains in pores and enhances uptake kinetic by improved surface diffusion. This study offers an integrated perspective to qualitatively assess the effects of multiple sizes, providing guidance for designing advanced ion exchangers for protein chromatography.