The thermoresponsive microjet

27 March 2014 - Making It move XIV

microjet.PNGIn our ongoing making-it-move coverage (previous episode here) now the thermoresponsive microjet as reported by Magdanz here. We have seen hydrogen peroxide / metal / vesicle based micro-swimmers before but the dimension added is on-demand weaponisation. Key is the vesicle construction material. It consists of a polymer bilayer of poly(N-isopropylacrylamide-4-acryloylbenzophenone) (PNIPAM-BA) dip-coated with polycaprolactone. This film was cross-linked by irradiation across a photo-mask, uncross-linked material was rinsed off and finally a platinum layer was added by sputter coating. The resulting trilayer reversibly folds into 30 micron diameter tubes and unfolds again below and above 28°C in water by a process of swelling and unswelling. In a hydrogen peroxide solution at low temperatures the tubes behave as microjets propelled by oxygen bubbles. Increasing the temperature above 28°C makes the tubes unfold and the movement stops.