A team of engineers at MIT, Cambridge, MA, have fabricated a new elastic material covered with microscopic, hair-like structures that tilt in response to a magnetic field. Depending on the field’s orientation, they say, the microhairs uniformly tilt to form a path through which fluid can flow. They say the material could be embedded in lab-on-a-chip devices to magnetically direct the flow of cells and other biological material through a diagnostic chip’s microchannels.
Each microhair or pillar, about 70 microns high and 25 microns wide. The engineers first created molds, which they electroplated with nickel, then stripped the molds away, and bonded the nickel pillars to a soft, transparent layer of silicone. They exposed the material to an external magnetic field, placing it between two large magnets, and saw they could control the angle and direction of the pillars, which tilted toward the angle of the magnetic field.
In experiments, the team piped a water solution through a syringe and onto the microhair array. Under a magnetic field, the liquid only flowed in the direction in which the pillars tilted, while being fixed in all other directions, even seen when the researchers stood the array against a wall. Through a combination of surface tension and tilting pillars, water climbed up the array, following the direction of the pillars against gravity.