Porous thermo-responsive pNIPAM microgels

• Porous pNIPAM microgels formed by CaCO3 templating.
• Microgels are T- and pH-sensitive.
• Collapse of the porous microgels in size by order of magnitude.

Thermo-responsive poly(N-isopropylacrylamide) (pNIPAM) gels are very attractive for biological applications due to a phase transition at temperature (32 °C) closed to that of biologically relevant. This stimulates the usage of this polymer for cell culture, biosensing, drug delivery, etc. Herein we develop a new simple approach to synthesize porous pNIPAM microgels by hard templating using porous CaCO3 cores. For this purpose, the mesoporous CaCO3 cores have been infiltrated with pNIPAM-4-acryloylbenzophenone (pNIPAM-ABP) followed by chemical crosslinking of the polymer molecules by UV-light and further core removal in HCl. The formed microgels possess reversible temperature response with LCST similar to that of the pure pNIPAM-ABP. Phase transition results in dramatic collapse of the porous microgels with the decrease of their size by up to ten times due to the pore closure. The porous structure is reorganized after the reversible heating–cooling cycle resulting in closure of larger pores and thus more homogeneous polymer distribution. The microgels are both temperature and pH sensitive that makes them attractive for drug delivery applications.

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