Cation-induced morphological transitions and aggregation of thermoresponsive PNIPAM nanogels

Yuchen Zhu; Jiaxin Hou; Dominic M. Gray; Tom O. McDonald; Ahu Gümrah Dumanli

Heliyon (Jun 2024)

Cation-induced morphological transitions and aggregation of thermoresponsive PNIPAM nanogels

Yuchen Zhu,
Jiaxin Hou,
Dominic M. Gray,
Tom O. McDonald,
Ahu Gümrah Dumanli

Affiliations

Yuchen Zhu: Department of Materials, The University of Manchester, Oxford Rd, Manchester, M13 9PL, UK; Henry Royce Institute, The University of Manchester, Oxford Rd, Manchester, M13 9PL, UK
Jiaxin Hou: Department of Materials, The University of Manchester, Oxford Rd, Manchester, M13 9PL, UK; Henry Royce Institute, The University of Manchester, Oxford Rd, Manchester, M13 9PL, UK
Dominic M. Gray: Department of Chemistry, University of Liverpool, Crown Street, Liverpool, L69 7ZD, UK
Tom O. McDonald: Department of Materials, The University of Manchester, Oxford Rd, Manchester, M13 9PL, UK; Henry Royce Institute, The University of Manchester, Oxford Rd, Manchester, M13 9PL, UK; Department of Chemistry, University of Liverpool, Crown Street, Liverpool, L69 7ZD, UK
Ahu Gümrah Dumanli: Department of Materials, The University of Manchester, Oxford Rd, Manchester, M13 9PL, UK; Henry Royce Institute, The University of Manchester, Oxford Rd, Manchester, M13 9PL, UK; Corresponding author. Department of Materials, The University of Manchester, Oxford Rd, Manchester, M13 9PL, UK.

Journal volume & issue: Vol. 10, no. 12
p. e32184

Abstract

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Poly(N-isopropylacrylamide) (PNIPAM) nanogels are promising responsive colloidal particles that can be used in pharmaceutical applications as drug carriers. This work investigates the temperature-dependent morphological changes and agglomeration of PNIPAM nanogels in the presence of mono- and multi-valent cationic electrolytes. We described the deswelling, flocculation, thermal reversibility behaviour and aggregated morphology of PNIPAM nanogels over a range of electrolyte concentrations and temperatures revealing the critical transition points from stable suspension to spontaneous agglomeration. We demonstrated that the flocculating ability and the rate of aggregate formation follow the order of deswelling behaviour. Transmission electron microscopy and atomic force microscopy analysis revealed the presence of a shell-like layer with varying density in the multivalent electrolyte solutions when compared to those in aqueous medium. We identified a concentration threshold of the thermally induced reversible aggregation/dispersion for the PNIPAM nanogels in the presence of Na+ and K+ ions at 10 mM, for Mg2+ and Ca2+ ions at 1 mM and for Al3+ ions at 0.1 mM concentrations. Such concentration thresholds indicated the effective destabilization of the electrolyte system with multivalency following the Schulze–Hardy rule. Our findings were supported by applying a Debye screening model that accounts for the shielding effect of multivalent cationic electrolytes on these nanogel systems. Our experiments and the models confirmed the compression of the electric double layer as the valency and ionic strength increased, except for Al3+ at higher concentrations which seemed to disrupt the electrical double layer and cause reversal of zeta potential. Our work highlights the significant impact the presence of multivalent cations can impose on the stability and morphology of nanogels, and this understanding will help in designing responsive nanogel systems based on PNIPAM nanogels.

Published in Heliyon

ISSN: 2405-8440 (Online)
Publisher: Elsevier
Country of publisher: United Kingdom
LCC subjects: Science: Science (General); Social Sciences: Social sciences (General)
Website: https://www.cell.com/heliyon/home

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