Nature-Inspired Materials Design

The diversity and complexity of both structure and function in biological macromolecules is driven by precisely balanced interactions. Charge-driven interactions are particularly key in biological systems, but a detailed understanding of their role in the assembly of materials is still lacking. Polyelectrolyte complexation provides an ideal platform to study the self-assembly of a wide range of soft materials ranging from dehydrated thin film and bulk solids to dense, polymer-rich liquid complex coacervates, and more complex hierarchical structures such as micelles and hydrogels. Factors that affect the self-assembly of these materials include the ratio of polycation to polyanion, temperature, pH, salt concentration, stereochemistry, polymer architecture, and the density and/or patterning of charges present. Among these factors, the ability to pattern charges and other chemical functionalities represents a powerful strategy for the design and manipulation of material properties. Until recently, the effect of specific chemical sequences has been rarely studied, due to the difficulty of synthesizing polyelectrolytes with equal chain length and charge density, but different distributions of charge or other functionalities. However, polypeptides and polypeptide derivatives represent a model platform for the synthesis and study of polyelectrolytes with precisely controlled polymer architecture and sequence patterning at the molecular level. Furthermore, polypeptides have direct relevance as biological materials and can be used in a variety of biological, medical, and industrial applications. We utilize experimental, theoretical, and simulations-based approaches to examine the effect of charge density, charge patterning, amino acid chirality and polymer architecture on the stability and overall material properties of polyelectrolyte complexes formed from positively- and negatively-charged polypeptides with matched and mismatched sequences of charged residues. The goal of this systematic investigation is to elucidate design rules that facilitate the tailored creation of materials based on polyelectrolyte complexation with defined properties for a wide range of applications.