Qualification of polymer objects to undergo autonomous motion, i.e., driven and directed (i) rotation, (ii) vibration/oscillation or (iii) translation (locomotion), requires the particles to do work. This in turn requires a local energy input. Furthermore, because of the low Reynolds numbers, the actuation must not generate a reciprocating change in the particles conformation or shape. Hence, the most efficient locomotor systems of microorganisms such as flagella or rotational motors rely on complex internal motility, and attempts to mimic flagella synthetically are still in their infancy. Here we report on a rather facile and versatile LCST-hydrogel system where the motion is affected by volume change and bending of the micro object and where it can be precisely controlled by the (i) design of the geometrical shape, (ii) the widely variable material properties and (iii) by the energy intake via infra-red irradiation that can be modulated in time and intensity to affect volume changes and bending. The volume change phase transition is not caused by heating of the whole system, but by strictly localized temperature changes generated inside the particles. For this purpose the gels were equipped with 1-4 gold nanorods per mm<sup>3</sup> that absorb light at 780 nm and convert it practically instantaneously to heat. The fact that the critical phase segregation can be switched within milliseconds and that the dynamics and the change in shape can be designed by the geometrical shape and n the hydrogel structure provides a means to transform radiation energy to shape and time controlled bending, constriction and whipping. We will report on the motility of microfabricated gel particles with asymmetric and symmetrical mechanical properties that undergo directed rotational and translational motion, and exhibit a characteristic time dependence in the amplitude of the bending as well as characteristic resonance effects.

Functional and light-actuated microgels - from responsive hydrogels toward microscopic locomotor systems<br />

249th National Meeting (2015)

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