pH-Responsive Saloplastics Based on Weak Polyelectrolytes: From Molecular Processes to Material Scale Properties

Abstract

Compact polyelectrolyte complexes (COPECs), also named saloplastics, represent a new class of material with high fracture strain and self-healing properties. Here, COPECs based on poly-(methacrylic acid) (PMAA) and poly(allylamine hydrochloride) (PAH) were prepared by centrifugation at pH 7. The influence of postassembly pH changes was monitored chemically by ATR-FTIR, ICP, DSC, and TGA, morphologically by SEM, and mechanically by strain to break measurements. Postassembly pH stimuli misbalanced the charge ratio in COPECs, impacting their concentration in counterions, cross-link density, and polymer chain mobility. At the material level, changes were observed in the porosity, composition, water content, and mechanical properties of COPECs. The cross-link density was a prominent factor governing the saloplastic's composition and water content. However, the porosity and mechanical properties were driven by several factors including salt-induced plasticization and conformational changes of polyelectrolytes. This work illustrates how multiple-scale consequences arise from a single change in the environment of COPECs, providing insights for future design of stimuli-responsive materials.

Safety of oral administration of high doses of ivermectin by means of biocompatible polyelectrolytes formulation

“…Since both macromolecules are weak polyelectrolytes, the charge balance between COO À and NH 3 þ groups, which are pH-dependent, triggers structure characteristics as well the interaction with the biological media [14,16]. Similar features have been reported in compact polyelectrolyte complexes of poly(methacrylic acid)/poly(allylamine hydrochloride) [28,29] for which the destabilization of the charge balance leaded changes in their properties at multiple scales, including microstructure and mechanical features. For our micro hydrogel particles formulation, when pH rises and the environment becomes moderately alkaline as in the intestinal tract (pH ¼ 7.8), a transition from mass to surface fractal was observed, leading to structures with rough surfaces where the interface between particles and the surrounding medium is diffuse [14].…”

Explicit Ion Effects on the Charge and Conformation of Weak Polyelectrolytes

“…This can be immensely useful, as monomer groups may protonate or deprotonate depending upon the local environmental conditions, enabling tunable “smart” materials [12,13,14]. Important recent examples include the pH-responsive swelling and collapse of poly(acrylic acid) [PAA] in functionalized nanoporous membranes [15], pH-responsive Saloplastics/Compact polyelectrolyte complexes (COPECs) [16] synthesized using Poly(methacrylic acid) (PMAA) poly(allylamine hydrochloride) (PAH), which find applications in tissue engineering by mimicking mechanical properties of a cartilage [17], self-assembled polyelectrolyte capsules and multilayer thin films for drug delivery purposes [18,19,20].…”

Weak Polyelectrolytes as Nanoarchitectonic Design Tools for Functional Materials: A Review of Recent Achievements

“…This gel elaboration approach has been successfully applied to several other weak polyelectrolytes, including PAA, ALG, PAH, and CHI, yielding self-healing gels with applications as biomaterials and catalyst supports ( Table 6 ). The compaction process by ultracentrifugation initially represented a bottleneck for the larger-scale production of COPECs, triggering the development of alternative synthesis approaches based on simple centrifugation [ 158 ], injection [ 159 ], and sedimentation [ 160 ]. The properties of the resulting saloplastics vary greatly with the charge density and balance of their polyelectrolyte components both during and after synthesis, typically adjusted by pH and ionic force parameters.…”