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The paper describes the choice of a thermoresponsive material for the implementation of untethered medical microrobots and other microdevices. These entities can be propelled at a specific location in the body using a Magnetic Resonance Imaging (MRI) system while being actuated for various functions such as the release of drugs by a volume change induced by hyperthermia of nanoparticles embedded in the hydrogel. This paper presents some preliminary results showing that poly(N-isopropylacrylamide) (PNIPA) might be an interesting choice, because of the important volume decrease when temperature is increased of some degrees. Using PNIPA based microparticles could be an interesting choice because, according to our results, volume changes are more important when the volume is smaller, and shrinking rate is higher when there are nanoparticles embedded in the hydrogel.

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This paper describes the synthesis of thermoresponsive hydrogel bead for the implementation of untethered medical microrobots and other microdevices. These entities will have magnetic nanoparticles embedded, and will be targeted inside the body with an adapted Magnetic Resonance Imaging (MRI) system, and then triggered by the application of an alternating magnetic field for various functions, including but not limited to drug delivery and release. A method is presented here to synthesize PNIPA particles, within alginate mold, which can be dissolved when hydrogel is completely polymerized and particles with diameter around 1mm are synthesized, with possibility of reducing the size with an electrostatic fields. Interesting volume losses has been recorded, depending of the crosslinker concentration. Hydrogel with nanoparticles embedded has also been synthesized, without affecting the polymerization, and with no significant effect on the volume change. Finally, transition temperature has been increase over the body temperature by copolymerization with acrylic acid.