A few unassuming drops of liquid locked in a very precise game of “follow the leader” could one day be found in mobile phone cameras, medical imaging equipment, implantable drug-delivery devices – possibly even implantable eye lenses. Researchers at Rensselaer Polytechnic Institute have developed liquid pistons with oscillating droplets of ferrofluid that precisely displace a surrounding liquid. Saturated with metal nanoparticles, the ferrofluid droplets can be used to pump small volumes of liquid when pulsated and can function as liquid lenses that constantly move, bringing objects into and out of focus. Researchers at Rensselaer Polytechnic Institute have developed liquid pistons composed of droplets of nanoparticle-infused ferrofluids, which function as liquid lenses that vibrate at high speeds and move in and out of focus as they change shape. The pistons could enable a new generation of mobile phone cameras, medical imaging equipment, implantable drug-delivery devices and, possibly, implantable eye lenses. Courtesy of Amir Hirsa, RPI. The liquid pistons are highly tunable, scalable and – because they lack any solid moving parts – suffer no wear and tear. As such, the researchers believe that they could be exploited to create a host of devices, ranging from microdisplacement pumps and liquid switches to adaptive lenses and advanced drug-delivery systems. The scientists’ work appears in Lab on a Chip, Vol. 11, pp. 393-397 (2011). Situated in a chamber filled with water, the piston is composed of two ferrofluid droplets placed on a substrate approximately the size of a piece of chewing gum. Its substrate features two holes, each hosting one droplet. Using an electromagnet, pulses are created that provoke one of the ferrofluid droplets to vibrate back and forth, prompting a combination of magnetic, capillary and inertial forces that cause the second droplet to vibrate in an inverted pattern. The two vibrating droplets then create a piston, which resonates back and forth with speed and springlike force. The strength and speed can be controlled by exposing the ferrofluid to different magnetic fields. Acting as a liquid resonator, the droplets can move the surrounding liquid back and forth to act as a pump. As the droplets move, the shift in volume can displace from the chamber an equal volume of the surrounding liquid. This discovery could be integrated into an implantable device that could accurately release tiny, timed doses of drugs into a patient’s body, the scientists report. Passing light through the droplets, when vibrating, transforms the device into a miniature camera lens. As the droplets vibrate, their shape changes, acting as a camera focus. The images are then captured electronically, and software is used to edit out any unfocused frames, leaving only clear, focused video. Providing a lighter alternative to camera lenses, the liquid devices also could be used for homeland security applications and, possibly, replacement eye lenses that can be fine-tuned using high-powered magnets.