Polyelectrolyte complexes present new opportunities for self-assembled soft matter. Factors determining whether the phase of the complex is solid or liquid remain unclear. Ionic polypeptides enable examination of the effects of stereochemistry on complex formation. Here we demonstrate that chirality determines the state of polyelectrolyte complexes, formed from mixing dilute solutions of oppositely charged polypeptides, via a combination of electrostatic and hydrogen-bonding interactions. Fluid complexes occur when at least one of the polypeptides in the mixture is racemic, which disrupts backbone hydrogen-bonding networks. Pairs of purely chiral polypeptides, of any sense, form compact, fibrillar solids with a β-sheet structure. Analogous behaviour occurs in micelles formed from polypeptide block copolymers with polyethylene oxide, where assembly into aggregates with either solid or fluid cores, and eventually into ordered phases at high concentrations, is possible. Chirality is an exploitable tool for manipulating material properties in polyelectrolyte complexation.

Complex coacervation is an electrostatically-driven phase separation phenomenon that is utilized in a wide range of everyday applications and is of great interest for the creation of self-assembled materials. Here, we utilized turbidity to characterize the effect of salt type on coacervate formation using two vinyl polyelectrolytes, poly(acrylic acid sodium salt) (pAA) and poly(allylamine hydrochloride) (pAH), as simple models for industrial and biological coacervates. We confirmed the dominant role of salt valence on the extent of coacervate formation, while demonstrating the presence of significant secondary effects, which can be described by Hofmeister-like behavior. These results revealed the importance of ion-specific interactions, which are crucial for the informed design of coacervate-based materials for use in complex ionic environments, and can enable more detailed theoretical investigations on the role of subtle electrostatic and thermodynamic effects in complex coacervation.

Polyelectrolyte complex micelles have great potential as gene delivery vehicles because of their ability to encapsulate charged nucleic acids forming a core by neutralizing their charge, while simultaneously protecting the nucleic acids from non-specific interactions and enzymatic degradation. Furthermore, to enhance specificity and transfection efficiency, polyelectrolyte complex micelles can be modified to include targeting capabilities. Here, we describe the design of targeted polyelectrolyte complex micelles containing inhibitors against dys-regulated microRNAs (miRNAs) that promote atherosclerosis, a leading cause of human mortality and morbidity. Inhibition of dys-regulated miRNAs in diseased cells associated with atherosclerosis has resulted in therapeutic efficacy in animal models and has been proposed to treat human diseases. However, the non-specific targeting of microRNA inhibitors via systemic delivery has remained an issue that may cause unwanted side effects. For this reason, we incorporated two different peptide sequences to our miRNA inhibitor containing polyelectrolyte complex micelles. One of the peptides (Arginine-Glutamic Acid-Lysine-Alanine or REKA) was used in another micellar system that demonstrated lesion-specific targeting in a mouse model of atherosclerosis. The other peptide (Valine-Histidine-Proline-Lysine-Glutamine-Histidine-Arginine or VHPKQHR) was identified via phage display and targets vascular endothelial cells through the vascular cell adhesion molecule-1 (VCAM-1). In this study we have tested the in vitro efficacy and efficiency of lesion- and cell-specific delivery of microRNA inhibitors to the cells associated with atherosclerotic lesions via peptide-targeted polyelectrolyte complex micelles. Our results show that REKA-containing micelles (fibrin-targeting) and VHPKQHR-containing micelles (VCAM-1 targeting) can be used to carry and deliver microRNA inhibitors into macrophages and human endothelial cells, respectively. Additionally, the functionality of miRNA inhibitors in cells was demonstrated by analyzing miRNA expression as well as the expression or the biological function of its downstream target protein. Our study provides the first demonstration of targeting dys-regulated miRNAs in atherosclerosis using targeted polyelectrolyte complex micelles and holds promising potential for translational applications.