Improving the flexible sensor | WSU Insider

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Engineer looking at a computer and 3D printer. — Researchers at WSU Tri-Cities have developed a new way to 3D print flexible sensors.

By Maegan Murray, WSU Tri-Cities

RICHLAND, Wash. – Scientists at Washington State University Tri-Cities and a colleague in Germany have developed a way to 3D print flexible sensors using nanomaterials and a special type of plastic. Their research is helping advance what is possible with flexible sensors.

Flexible sensors have applications in soft robotics, prosthetics, physical therapy and structural health monitoring, all of which require materials and other components with a degree of movement, compression or flex. The sensors can measure how much and how often an object stretches, compresses and moves.

Manufacturers have traditionally found it challenging to create sensors that integrate seamlessly with materials in a larger system. The WSU Tri-Cities team addresses this issue by 3D printing sensors from several materials in tandem. Their research would allow manufacturers to better create complex and conductive pattern designs and specifically tailor the general manipulation needed with each type of sensor. Their method uses extrusion to make feedstock material and mass–produce the sensors on a commercial scale.

WSU Tri-Cities researchers Josef Christ, Nahal Aliheidari and Amir Ameli, along with Petra Pötschke of the Leibniz Institute of Polymer Research, recently published their findings in Polymers.

Varied potential and recyclable

Ameli, a WSU Tri-Cities assistant professor of mechanical engineering, said they started with nanomaterials called carbon nanotubes and a flexible polymer called thermoplastic polyurethane, which can be combined in different amounts and in different ways depending on the type of use.

“We can design sensors with different sensitivities and different ranges of flexibility,” he said. “We can go as high as 100 percent deformation, which has wide use for applications including soft robotics. It is conformable, it is soft, it is flexible, and at the same time, it has a good sensitivity to sense the change in dimensions.”

A flexible sensor — A 3D-printed flexible sensor

Using 3D printing, Ameli said he and his colleagues have designed bi-directional sensors that detect deformation in two different directions.

“By monitoring the change in the electrical resistance, we can probe how much deformation is applied to the sensors, which is called piezoresistivity,” he said. “We can print these with conductive traces of nanomaterial with different patterns and in different directions. That gives us the ability to design sensors with tuned sensitivity and in any direction we are interested in.”

Ameli said the material is also recyclable.

“We can melt it and then re-melt it, and through the melting process, we can recycle the material,” he said.

Applications in robotics, physical therapy

So far, the researchers have done initial tests with the sensors in a glove prototype, with a robot that is being developed at WSU to pick apples, as well as with a few other applications. They also have plans for printing nanomaterials that can be used in supercapacitors, or those that can hold and store large amounts of energy, in addition to a number of other areas.

With the glove prototype, they used the sensors in the fingers of the glove, measuring how much the sensor contracted and expanded with the movement of the fingers. The sensors could also be used to sense the strain in the movement, which could simulate the strain that a person’s hand endures with a particular movement. It could also monitor the amount of times a person moves particular parts of their hands for studies in physical therapy and ways to improve movement.

In the robot being developed for picking apples, the sensor would be applied on the device that would grip the apples to trace the amount of pressure needed in order to not bruise apples.

“For example, if we want a robotic hand to touch and grab sensitive objects, like in apple-picking, the apple is sensitive and we don’t want to use a hard gripper to grip it because it will bruise the apple,” Ameli said. “We can sense where the touch is made and send the feedback to the computer controlling the device.”