AMHERST, Mass. – Drawing inspiration from highly magnified images of tapered bristles on the leg of an ant, researchers at the University of Massachusetts Amherst are building a new type of sensor that can be used in wearable technology for health monitoring, prosthetics and other advanced tools to measure the body’s mechanical signals. The new sensors are also 10-times more efficient than conventional mechanical sensors. The research is featured in the journal Nature Communications.
Jun Yao, an assistant professor of electrical and computer engineering at UMass Amherst, says he and his team developed the bioinspired, ultrasensitive pressure and strain sensors using microparticles of zinc oxide that feature tapered spines resembling the bristles or tactile hairs that are common on insects. He says they refer to these particles as “sea urchin-shaped microparticles” and found that a thin film made of them proved to be very sensitive because they could collect mechanical stimuli from all directions.
Yao and his team, Bing Yin, Xiaomeng Liu, Hongyan Gao, and Tianda Fu, describe their new technology, saying, “We mimic these [insect] features by using synthetic zinc-oxide (ZnO) microparticles, each having spherically-distributed, high-aspect-ratio, and high-density nanostructured spines resembling biological bristles. Sensors based on thin films assembled from these micro-particles…show supreme overall performance.”
The discovery process for the sensors began when Bing Yin, a postdoctoral research associate in Yao’s laboratory, found that by mixing sodium hydroxide and zinc acetate dihydrate solutions at a temperature of
40 °C he could produce many synthetic ZnO microparticles, each featuring a forest of high-density nanostructured spines.
“The microparticle resembled a miniaturized sea urchin – about 10,000 times smaller than life-size,” recalls Yao. “I thought the structures were interesting but did not have a concrete idea as to how they could be utilized.”
At around the same time, “We invited high-school students from a local public school to our lab in an effort to promote science, technology, engineering, and mathematics among pre-college students,” Yao says. As part of this program, Yao’s team captured some ants and showed them under the scanning electron microscope or SEM. “In fact, not only did the students show great interest, but I myself was unexpectedly intrigued by the microscopic features of the ant,” says Yao. “Although I knew in a general sense that insects can have tactile hairs as mechano-sensory organelles, it was the first time I had visualized the fine structures in these hairs under the SEM.”
Yao says he instantly saw that tapering geometry of the ant hair was similar to nanostructured spines covering the ZnO microparticles. Some quick research showed that the tapering spines (or bristles) in insects not only serve as lever arms to promote mechanical-signal transduction, but also, a clever strategy to protect it from mechanical breakage.
“We hypothesized that a thin-film sensor made from ZnO microparticles, covered with spines having both geometric and distributional similarities to the bristles in insects, could yield high sensitivity as well as durability,” Yao says.
Yao explains that the subsequent fabrication of the thin-film sensors was relatively straightforward, but the result surprised his lab. The biomimicry led to vastly superior overall performance in the sensors, with a 10-fold improvement in key comparisons with many conventional mechanical sensors.