Thermoresponsivity of poly(N-isopropylacrylamide) microgels in water-trehalose solution and its relation to protein behavior

TL;DR

This study investigates how trehalose affects the swelling and molecular dynamics of PNIPAM microgels, revealing mechanisms similar to protein interactions, which enhances understanding of bioprotectant effects at the colloidal level.

Contribution

It provides the first detailed comparison of trehalose's interaction mechanisms with PNIPAM microgels and proteins, elucidating how trehalose influences polymer hydration and dynamics.

Findings

Trehalose preserves hydration of PNIPAM microgels across the transition.

Trehalose significantly inhibits local motions of the polymer and hydration shell.

Mechanisms are similar to trehalose-protein interactions, involving slowdown of dynamics and preferential exclusion.

Abstract

Hypotheses: Additives are commonly used to tune macromolecular conformational transitions. Among additives, trehalose is an excellent bioprotectant and among responsive polymers, PNIPAM is the most studied material. Nevertheless, their interaction mechanism so far has only been hinted without direct investigation, and, crucially, never elucidated in comparison to proteins. Detailed insights would help understand to what extent PNIPAM microgels can effectively be used as synthetic biomimetic materials, to reproduce and study, at the colloidal scale, isolated protein behavior and its sensitivity to interactions with specific cosolvents or cosolutes. Experiments: The effect of trehalose on the swelling behavior of PNIPAM microgels was monitored by dynamic light scattering; Raman spectroscopy and molecular dynamics simulations were used to explore changes of solvation and dynamics across the swelling-deswelling transition at the molecular scale. Findings: Strongly hydrated trehalose molecules develop water-mediated interactions with PNIPAM microgels, thereby preserving polymer hydration below and above the transition while drastically inhibiting local motions of the polymer and of its hydration shell. Our study, for the first time, demonstrates that slowdown of dynamics and preferential exclusion are the principal mechanisms governing trehalose effect on PNIPAM microgels, at odds with preferential adsorption of alcohols, but in full analogy with the behavior observed in trehalose-protein systems.