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Deswelling studies of pH and temperature-sensitive ultra-low cross-linked microgels with cross-linked cores

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Abstract

Microgels prepared without exogenous crosslinker have recently been explored for diverse applications in biotechnology. However, our fundamental understanding of structure-property relationships for this class of materials is still lacking, especially in the context of more complex structures such as core-shell particles. In this article, core-shell microgels were prepared by seed-mediated, surfactant-free emulsion polymerization using a N,N′-methylenebis (acrylamide) (BIS) cross-linked poly(N-isopropylacrylamide) (pNIPAm) microgel core upon which a crosslinker-free poly(N-isopropylacrylamide)-co-acrylic acid (ULC10AAc) shell was synthesized. Dynamic light scattering (DLS) and phase analysis light scattering (PALS) measurements show that the hydrodynamic radius and electrophoretic mobility of the core-shell microgels increase significantly with increasing pH due to the pH responsive ULC10AAc shell, while the temperature sensitivity of the microgels is also strongly pH dependent. The turbidity and the temperature-dependent scattering intensity plots of microgels at different pH also provide insight into the charged state of the microgels under the studied conditions. For example, we observe multiple temperature-induced transitions when the pH is either 4.5 or 6.5, illustrating that the core and shell domains, while remaining mechanically connected, are only partially coupled thermodynamically. These studies provide insight into the perturbation of ULC microgel behavior that might be brought about due to the presence of a higher density core region. Complex architectures such as these are relevant in biotechnology applications where the soft, deformable ULC shell is advantageous to control the polymer-biology interface, but a denser core region might be required to obtain a higher loading of encapsulated therapeutics, tracking dyes, or oligonucleotides. Thus, it is important to understand the synthetic conditions that allow a ULC shell to remain “ULC-like” despite the presence of a denser core.

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Funding

The study is financially supported by the National Institute of Health (R01HL130918).

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Authors and Affiliations

  1. Schmid College of Science and Technology, Chapman University, Orange, CA, 92866, USA

    Molla R. Islam & L. Andrew Lyon

  2. Dale E. and Sarah Ann Fowler School of Engineering, Chapman University, Orange, CA, 92866, USA

    L. Andrew Lyon

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  1. Molla R. Islam
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Correspondence to L. Andrew Lyon.

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Dr. Lyon is a co-founder and holds an equity stake in SelSym, Inc., an early-stage biotechnology company aimed at the commercialization of artificial platelet technologies based on ULC microgels.

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Islam, M.R., Lyon, L.A. Deswelling studies of pH and temperature-sensitive ultra-low cross-linked microgels with cross-linked cores. Colloid Polym Sci 298, 395–405 (2020). https://doi.org/10.1007/s00396-020-04620-9

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  • DOI: https://doi.org/10.1007/s00396-020-04620-9

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