Tuning coacervate properties via protein partner selection: A structural and dynamic comparison of gelatin- and...

The rational design of advanced biomaterials hinges on our ability to precisely control their microscopic architecture and dynamic properties. Complex coacervation between proteins and polyelectrolytes offers a powerful avenue for self-assembly, yet the selection of the protein partner remains a critical, and often poorly understood, determinant of the final material's performance. Herein, we dissect the impact of protein choice by conducting a head-to-head structural and dynamic comparison. We contrast the behavior of a single strong polyanion, PSSMA, when complexed with either the flexible, disordered protein Gelatin or the compact, globular protein Ovalbumin (OVA). By coupling turbidimetry with ultra-small angle light scattering (USALS), we map the phase diagrams and reveal fundamentally different aggregate architectures. Crucially, using image dynamic light scattering (IDLS), we probe the dynamics within the dense coacervate phase itself. Our findings demonstrate that Gelatin forms tenuous, dynamically arrested networks, whereas OVA assembles into more compact, fluid-like structures. This work unravels how protein architecture dictates the self-assembly trajectory, providing a framework for selecting either kinetically arrested amorphous solids or fluid-like precursors for ordered materials.