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pH-responsive microgels containing hydrophilic crosslinking co-monomers: shell-exploding microgels through design

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Abstract

pH-responsive microgels are crosslinked polymer colloids that swell when the pH approaches the pK a of the particles. They have potential application for injectable gels for tissue repair and drug delivery systems. This study focuses on the pH-triggered gelation behaviour of a series of poly (EA/MAA/X) microgels. EA and MAA are ethylacrylate and methacrylic acid. Here, we investigate the effect of crosslinking monomer type (X) on microgel properties. The crosslinking monomers used were poly (ethyleneglycol) dimethacrylate (PEGD), ethyleneglycol dimethacrylate (EGD) and butanediol diacrylate (BDD). The microgel containing PEGD (m-PEGD) is a new system. The microgel containing BDD (m-BDD) was used as a control system. The concentrated microgel dispersions formed physical gels when the pH was increased to 5.3–6.7, and the polymer volume fractions (ϕ p ) were above about 0.05. Evidence from photon correlation spectroscopy (PCS) and dynamic rheology was presented for abrupt pH-triggered increases, and then decreases of the hydrodynamic diameters for m-PEGD and the microgel prepared using EGD (m-EGD). This appears to be tuneable through crosslinker structure. An unexpected gelation behaviour, which may involve a new gel state for microgels, was found for m-PEGD dispersions. Uniquely, those dispersions formed gels at pH values less than the microgel's pK a . This behaviour was linked to an outer-shell electrostatic repulsive interaction. The data point to a phenomenon, whereby the m-PEGD shells appear to explode at pH values above 7.0. The control microgel prepared, using BDD (m-BDD), did not show any evidence of shell fragmentation at any pH. That microgel has potential as a model pH-responsive microgel system in that the properties measured by PCS and rheology agreed well. To probe that system in more detail, the rheological data for m-BDD was analysed using scaling theory. The variation of the storage modulus (G') with ϕ p gave a scaling exponent of 2.0.

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Acknowledgements

We are grateful to the enterprise, medicine and material schools of the University of Manchester for funding this project. We are also grateful to Prof. Peter Lovell for access to the PCS instrument. We are also grateful for the helpful suggestions for experiments made by one of the reviewers of this manuscript.

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Authors and Affiliations

  1. Biomaterials Research Group, School of Materials, The University of Manchester, Grosvenor Street, Manchester, M13 9PL, UK

    Sarah Lally & Brian R. Saunders

  2. Tissue Injury and Repair Group, School of Medicine, Stopford Building, The University of Manchester, Oxford Road, Manchester, M13 9PT, UK

    Tony J. Freemont

  3. Laboratory of Polymers and Biomaterials, School of Pharmacy, The University of Manchester, Oxford Road, Manchester, M13 9PT, UK

    Francesco Cellesi

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  1. Sarah Lally
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  2. Tony J. Freemont
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  3. Francesco Cellesi
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  4. Brian R. Saunders
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Correspondence to Brian R. Saunders.

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Lally, S., Freemont, T.J., Cellesi, F. et al. pH-responsive microgels containing hydrophilic crosslinking co-monomers: shell-exploding microgels through design. Colloid Polym Sci 289, 647–658 (2011). https://doi.org/10.1007/s00396-010-2366-8

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  • DOI: https://doi.org/10.1007/s00396-010-2366-8

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