Purdue University researchers embedded a liquid-alloy pattern in an elastic polymer to form a network of sensors, which can be used to create smart, stretchable materials.

Purdue University researchers embedded a liquid-alloy pattern in an elastic polymer to form a network of sensors, which can be used to create smart, stretchable materials.

Credit: Rebecca Kramer/Purdue University

The development of sensory skins and wearable technology is causing researchers to re-evaluate the nature of these charged, data-collecting electronic systems. In a 2007 interview, Akira Wakita, a wearable computing and robotics expert and a professor in the environment and information studies department at Keio University in Japan, described a future for soft—rather than hard—interfaces. "Nowadays, most products are rigid,” he said. "However, the use of soft, elastic shells may be another solution—and closer to the nature of the human body itself. So, I like to think about the skin of the product, which may be another means of conveying the electricity in wearable computing.”

Researchers at Purdue University may have found an alternative to conventionally rigid electronics by developing a way to fabricate “soft machines” made of elastic materials and liquid metals. Led by mechanical engineering professor Rebecca Kramer, the research team embedded devices made of liquid gallium-indium alloy in a silicon-based elastomer called polydimethylsiloxane, or PDMS. The liquid alloy was used to create patterns of lines, forming a senor network.

The gallium posed a challenge because of its tendency toward rapid oxidation, which results in the formation of a thick skin. Kramer used the skin for its structural stability. "This means you can print liquid on a surface and it will maintain stable structures without moving around," she said in a press release. "Once you print it, you can flip it over or turn it on its side because the liquid is encased by this oxide skin." As a result, the team could embed electronics in the elastomer without damaging or otherwise altering the printed structures.

For their first soft machine, Kramer and her team created a gauge to measure material deformation, or strain. Unlike conventional, inflexible strain gauges, which can only measure a 1-percent change prior to failure, Kramer's soft iteration can stretch with the material to measure the full extent of its strain. The researchers’ improved approach may also be used to create other devices such as capacitors, conductors, pressure sensors, and tactile keypads—opening up possibilities for consumer electronics, medicine, and robotics.

Integrated-media pioneers, such as Wakita, will also see significant design potential in Kramer’s development, which could be used to make other kinds of soft interfaces, environments, and smart textiles. "In the cyber world, we can make anything we want,” Wakita said in the 2007 interview. "So I’d like to break the wall between the cyber world and the real world—with real textiles that convey texture maps and bump maps, and textiles that move independently. Textiles may then embody a kind of hybrid reality. In this spirit, we can do more to awaken the latent possibilities within materials.”

Blaine Brownell, AIA, is a regularly featured columnist whose stories appear on this website each week. His views and conclusions are not necessarily those of ARCHITECT magazine nor of the American Institute of Architects.