Shear-Induced Counterion Release of a Polyelectrolyte

Shear-induced rotation enhances protein adsorption

Theories predicted that shear promotes desorption, but due to the presence of factors such as aggregation effects, it is difficult to observe how shear influences the adsorption and desorption of individual protein molecules. In this study, we employed high-throughput single-molecule tracking and molecular dynamics simulations to investigate how shear flow affects the adsorption kinetics of plasma proteins (including human serum albumin, immunoglobulin G, and fibrinogen) at solid-liquid interfaces. Over the studied shear rate range of 0 - 103 s-1, shear stress did not trigger the protein desorption. Notably, we observed a significant increase, up to two orders of magnitude, in the adsorption rate constants ka, in the dilute limit at solid-liquid interfaces. However, this shear-induced increase in ka diminished with increasing the protein concentrations. At least in the scenarios studied, these trends were consistent across all three types of proteins and two types of surfaces investigated. Through a systematic analysis combining control experiments, coarse-grained, and all-atom molecular dynamics simulations, we identified that the shear-induced increase in ka could be attributed to enhanced protein rotational diffusion, thereby increasing the likelihood of favorable surface proximity for adsorption.

A torrent intercepts the ionic flow in a polyelectrolyte solution

An anomalous flow response of electric properties was observed in 0.01 wt% aqueous solutions of polyacrylic acid sodium salt (NaPAA) by electric measurements under shear flow using a newly developed apparatus. This response is considered to be caused by the migration of PAA- ions being intercepted by the turbulent flow generated by the high shear rate, resulting in the inability to form macroscopic polarizations.

Dilute polyelectrolyte solutions: recent progress and open questions

Polyelectrolytes are a class of polymers possessing ionic groups on their repeating units. Since counterions can dissociate from the polymer backbone, polyelectrolyte chains are strongly influenced by electrostatic interactions. As a result, the physical properties of polyelectrolyte solutions are significantly different from those of electrically neutral polymers. The aim of this article is to highlight key results and some outstanding questions in the polyelectrolyte research from recent literature. We focus on the influence of electrostatics on conformational and hydrodynamic properties of polyelectrolyte chains. A compilation of experimental results from the literature reveals significant disparities with theoretical predictions. We also discuss a new class of polyelectrolytes called poly(ionic liquid)s that exhibit unique physical properties in comparison to ordinary polyelectrolytes. We conclude this review by listing some key research challenges in order to fully understand the conformation and dynamics of polyelectrolytes in solutions.

Biopolymer Filament Entanglement Softens Then Hardens with Shear

It is unsatisfactory that regarding the problem of entangled macromolecules driven out of equilibrium, experimentally based understanding is usually inferred from the ensemble average of polydisperse samples. Here, confronting with single-molecule imaging this common but poorly understood situation, over a wide range of shear rate we use single-molecule fluorescence imaging to track alignment and stretching of entangled aqueous filamentous actin filaments in a homebuilt rheo-microscope. With increasing shear rate, tube "softening" is followed by "hardening." Physically, this means that dynamical localization first weakens from molecular alignment, then strengthens from filament stretching, even for semiflexible biopolymers shorter than their persistence length.