MIT engineers have developed microscopic, hairlike structures that tilt in response to a magnetic field and can be used to move materials in any direction, including up, against gravity.
Depending on the field's orientation, the microhairs can tilt to form a path through which fluid can flow; the material can even direct water upward, against gravity, researchers said.
Each microhair, made of nickel, is about 70 microns high and 25 microns wide - about one-fourth the diameter of a human hair. The researchers fabricated an array of the microhairs onto an elastic, transparent layer of silicone.
In experiments, the magnetically activated material directed not just the flow of fluid, but also light - much as window blinds tilt to filter the sun.
Researchers said the work could lead to waterproofing and anti-glare applications, such as "smart windows" for buildings and cars.
"You could coat this on your car windshield to manipulate rain or sunlight," said Yangying Zhu, a graduate student in Massachusetts Institute of Technology's Department of Mechanical Engineering.
"So you could filter how much solar radiation you want coming in, and also shed raindrops," Zhu said.
The material could also 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.
The inspiration for the microhair array comes partly from nature, Zhu said.
For example, human nasal passages are lined with cilia - small hairs that sway back and forth to remove dust and other foreign particles. Zhu sought to engineer a dynamic, responsive material that mimics the motion of cilia.
Zhu and colleagues manufactured an array of microscopic pillars that uniformly tilt in response to a magnetic field. To do so, they first created molds, which they electroplated with nickel.
They then stripped the molds away, and bonded the nickel pillars to a soft, transparent layer of silicone.
The researchers exposed the material to an external magnetic field, placing it between two large magnets, and found they were able to control the angle and direction of the pillars, which tilted toward the angle of the magnetic field.
"We can apply the field in any direction, and the pillars will follow the field, in real time," Zhu said.
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 highly "pinned," or fixed, in all other directions - an effect that was 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.
The study is published in the journal Advanced Materials.
