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    Dynamically Cross-Linked Self-Assembled Thermoresponsive Microgels with Homogeneous Internal Structures

    Year: 2018

    Journal: Langmuir, Volume 34, JAN 30, page 1601–1612

    Authors: Mueller, Eva; Alsop, Richard J.; Scotti, Andrea; Bleuel, Markus; Rheinstadter, Maikel C.; Richtering, Walter; Hoare, Todd

    Organizations: Natural Sciences and Engineering Research Council of Canada (NSERC) [RGPIN 356693]; Ontario Early Researcher Awards (Ontario Ministry of Research and Innovation) [ERA ER09-06-185]; National Science Foundation [DMR-1508249]; McMaster University; Alexander von Humboldt Foundation; Deutsche Forschungsgemeinschaft [SFB 985]; Ronald William Merkel Travel Scholarship

    The internal morphology of temperature-responsive degradable poly(N-isopropylacrylamide) (PNIPAM) microgels formed via an aqueous self-assembly process based on hydrazide and aldehyde-functionalized PNIPAM oligomers is investigated. A combination of surface force measurements, small angle neutron scattering (SANS), and ultrasmall angle neutron scattering (USANS) was used to demonstrate that the self-assembled microgels have a homogeneously cross-linked internal structure. This result is surprising given the sequential addition process used to fabricate the microgels, which was expected to result in a densely cross-linked shell-diffuse core structure. The homogeneous internal structure identified is also significantly different than conventional microgels prepared via precipitation polymerization, which typically exhibit a diffuse shell-dense core structure. The homogeneous structure is hypothesized to result from the dynamic nature of the hydrazone cross-linking chemistry used to couple with the assembly conditions chosen that promote polymer interdiffusion. The lack of an internal cross-linking gradient within these degradable and monodisperse microgels is expected to facilitate more consistent drug release over time, improved optical properties, and other potential application benefits.
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