Use of pH Gradients in Responsive Polymer Hydrogels for the Separation and Localization of Proteins from Binary Mixtures

Abstract

Using a molecular-level equilibrium theory where proteins are described using their crystallographic structure, we have studied protein adsorption from binary and ternary mixtures of myoglobin, lysozyme, and cytochrome c to poly(methacrylic acid) hydrogel films. The pH gradients these films induce can lead to selective protein adsorption, where the solution pH provides a sensible dial to externally control protein separation. Changing the chemical composition of the polymer network, adding either another acidic or a neutral comonomer, allows for protein localization to controlled spatial regions of the film with nanometer resolution. As pH-sensitive polymer hydrogels are promising candidates for smart, responsive biomaterials, understanding the complexity of competitive protein adsorption is essential. In this work, we highlight the decisive role of amino acid protonation in selective protein adsorption. We present conditions such that the hydrogel film will selectively incorporate the more weakly charged protein, provided that it requires less work to protonate its amino acids.