‘Epidermal VR’ Has Applications in Prosthetics

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Anderson, left, shakes hands while testing the technology.

Photographs courtesy of Northwestern University.

Northwestern University researchers have developed a thin, wireless system that adds a sense of touch to any virtual reality (VR) experience. They have tested the technology to provide prosthetic devices with sensory feedback.


Referred to as an "epidermal VR" system, the device communicates touch through a fast, programmable array of miniature vibrating actuators embedded into a thin, soft, flexible material. The 15cm by 15cm sheet-like prototypes laminate onto the curved surfaces of the skin without bulky batteries and cumbersome wires.


"We leveraged our knowledge in stretchable electronics and wireless power transfer to put together a superior collection of components, including miniaturized actuators, in an advanced architecture designed as a skin-interfaced wearable device—with almost no encumbrances on the user," said John A. Rogers, PhD, a professor of materials science and biomedical engineering and co-leader of the research. "We feel that it's a good starting point that will scale naturally to full-body systems and hundreds or thousands of discrete, programmable actuators.


"With this wireless power delivery scheme, we completely avoid the need for batteries, with their weight, size, bulk and limited operating lifetimes," Rogers said. "The result is a thin, lightweight system that can be worn and used without constraint, indefinitely."


U.S. Army veteran Garrett Anderson, whose arm was severed during his service in the Iraq War, recently tried Northwestern's system, integrated with his prosthetic arm. When wearing the patch on his upper arm, Anderson could feel sensations from his prosthetic fingertips transmitted to his arm. The vibration's intensity changed depending on the firmness of his grip.


"Users develop an ability to sense touch at the fingertips of their prosthetics through the sensory inputs on the upper arm," Rogers explained. "Over time, your brain can convert the sensation on your arm to a surrogate sense of feeling in your fingertips. It adds a sensory channel to reproduce the sense of touch."


The device incorporates a distributed array of 32 individually programmable, millimeter-scale actuators, each of which generates a discrete sense of touch at a corresponding location on the skin. Each actuator resonates most strongly at 200 cycles per second, where the skin exhibits maximum sensitivity.


"We can adjust the frequency and amplitude of each actuator quickly and on-the-fly through our graphical user interface," Rogers said. "We tailored the designs to maximize the sensory perception of the vibratory force delivered to the skin."


The patch wirelessly connects to a touchscreen interface on a smartphone or tablet. When a user touches the screen, that pattern of touch transmits to the patch. If the user draws an X pattern on the touchscreen, for example, the devices produce a sensory pattern, simultaneously and in real-time, in the shape of an X through the vibratory interface to the skin.


Aside from use in prosthetic devices, the researchers say the technology can be used in telemedicine, allowing for virtual touch—with negligible time delay and with pressures and patterns that can be controlled through the touchscreen interface.


An open view of the patch, showing its 32 actuators embedded in soft silicone.

The actuators are embedded into a soft and slightly tacky silicone polymer that adheres to the skin without tape or straps. Wireless and battery-free, the device communicates through near-field communication protocols, the same technology used in smart phones for electronic payments.


Rogers views the current device as a starting point. "This is our first attempt at a system of this type," he said. "It could be very powerful for social interactions, clinical medicine, and applications that we cannot conceive of today, beyond the obvious opportunities in gaming and entertainment."


He and engineer Yonggang Huang, PhD, are already working to make the current device slimmer and lighter. They also plan to exploit different types of actuators, including those that can produce heating and stretching sensations. With thermal inputs, for example, a person might be able to sense how hot a cup of coffee is through prosthetic fingertips.


"Virtual reality is a very important emerging area of technology," Rogers said. "Currently, we're just using our eyes and our ears as the basis for those experiences. The community has been comparatively slow to exploit the body's largest organ: the skin. Our sense of touch provides the most profound, deepest, emotional connection between people."


The research, Skin-integrated wireless haptic interfaces for virtual and augmented reality, is published in the journal Nature.


Editor's note: This story was adapted from materials provided by Northwestern University.