Low Reynolds Number Swimming of Stimuli Responsive Hydrogels

The controlled motion of microparticles in a liquid environment is of interest for many biomedical applications. In nature the self propulsion of bacteria is achieved either by shape changes (amoeba) or by a motile system (flagellum, cilia), which usually undergo periodic changes in time. Inspired by nature we have fabricated objects with an irregular shape and features in the 10’s micrometers that can move when placed in an environment with periodically changing conditions (temperature, pH). For the fabrication of such objects we have used stimuli-sensitive hydrogels. The hydrogels are cross-linked swollen polymer networks that can reversibly absorb and release water in response to external stimulus such as temperature or pH. The swelling/shrinking of the hydrogels is accompanied by a significant volume change (up to 60 %). In our study of low Reynolds number swimming, the temperature responsive poly(N-isopropylacrylamide) – PNIPAM and pH responsive Inulin based hydrogels were used. The PNIPAM and Inulin hydrogels exhibit volume change at 32 °C and pH 5, respectively.