Collective motions observed in living organism, such as flock of birds, schools of fish, self-organization of bacterial colonies, formation of tissues from cells, etc. serve important biological functions. Over the last decades, synthetic materials that mimic those collective motions powered by external stimuli, so called “active matter”, have attracted increasing attention for biomedical applications including directed molecular delivery. However, many of the reported active matters so far consist of hard condensed materials within which guest molecules are hard to be encapsulated. Thus, it is of great importance to prepare the active matter from stimuli-responsive soft materials as potential delivery vehicles. Herein, we report the preparation of active colloids consisting of nanogels (NGs) which vary their physical properties in response to external stimuli, e.g. pH, temperature, and UV light irradiation. The NGs were synthesized via RAFT polymerization-induced thermal self-assembly (PITSA) of N-isopropylacrylamide (NIPAM) with a small amount of N,N’-methylenebis(acrylamide) (MBAM) as a cross-linker mediated by hydrophilic macromolecular chain transfer agent (macro-CTA) of poly(methacrylic acid) (PMAA) and 4,4’-azobis(4-cyanopentanoic aicd) (ACPA) as a radical initiator in water at 70 °C, a temperature higher than the lower critical solution temperature (LCST) of the PNIPAM, followed by post-polymerization functionalization of the NGs with a photo-responsive spiropyran (SP) derivative. The hydrodynamic radii (Rh) of the NGs vary with phase transition of the PNIPAM moiety by heating/cooling around their cloud point temperatures (Tcp). The Tcp and thermo-responsive property of the NGs vary by adjusting pH below/above pKa of MAA (pKaMAA = 4.36). Photoisomerization of the SP moiety on the surface of the NGs from nonionic SP form to highly polarized zwitterionic merocyanine (MC) form induced self-propelled collective motion of the colloids toward UV light source.

Preparation of multi-stimuli-responsive active colloids via RAFT polymerization-induced thermal self-assembly

256th National Meeting (2018)

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