Haptiknit: A New Frontier in Wearable Technology

Researchers at Stanford Engineering have developed Haptiknit, a comfortable flexible knit sleeve that can deliver accurate pressure-based haptic feedback.

Wearable haptic devices, which provide touch-based feedback, offer more immersive experiences in virtual reality, aid in rehabilitation, and create new possibilities for silent communication. Most current devices rely on vibration, as pressure-based haptics typically require users to wear bulky exoskeletons or structures.

Now, researchers at Stanford Engineering have developed a comfortable, flexible knit sleeve called Haptiknit, which provides realistic pressure-based haptic feedback. Their design, published on Dec. 18 in Science Robotics, suggests that pressure may be more effective than vibration for certain applications and marks the beginning of a new category of haptic devices.

Their design demonstrates that pressure may be more effective than vibration in some applications, and it marks the first step toward a new category of haptic devices. It is much more lightweight, wearable, and comfortable.

Allison Okamura, Study Senior Author and Richard W. Weiland Professor, Stanford University

A Knit Solution

Okamura and her team designed a battery-powered pneumatic system using pressure actuators, which are small inflatable pouches that quickly fill with air. However, they needed a way to hold these pouches against the skin without relying on a cumbersome exoskeleton.

If you put air into a balloon next to your skin but don’t anchor it there, it’s going to expand in all directions. You are going to waste most of the inflation potential.

Cosima du Pasquier, Study First Author and Postdoctoral Researcher, Stanford University

Du Pasquier, who enjoys making clothes as a hobby, realized knit fabric could be the solution. The researchers designed a soft textile that would be stiff in certain areas to hold the pressure actuators against the skin while remaining flexible in others to allow for movement and comfort.

They collaborated with the MIT Self-Assembly Lab to produce the Haptiknit prototype using a knitting machine, featuring space for eight actuators arranged in two rows. The sleeve was primarily made of nylon and cotton, with thermoplastic fiber incorporated into the actuator backing areas. After knitting, the researchers applied heat to melt the thermoplastic fibers, which hardened to stiffen those regions.

“A challenge in the field of soft robotics is how do you stick together something hard and something soft – they tend to delaminate. But putting these fibers into knitting makes a totally seamless transition from parts that are hard to parts that are soft because it is one continuous fabric,” Okamura added.

The researchers tested the Haptiknit prototype with 32 users and found that participants could more accurately identify the location of individual touches from the pressure actuators than from a similarly arrayed vibrational device. They also experimented with inflating the actuators consecutively at different speeds to simulate the sensation of a continuous stroke, as opposed to discrete touches (or the discomfort of feeling a spider crawl on one’s arm). Participants generally found that faster, overlapping indentations created the feeling of a continuous stroke, unlike vibration.

In a third test, participants were asked to recognize six emotions—attention, gratitude, happiness, calming, love, and sadness—conveyed through the pressure signals. Using touch patterns established in prior research, participants identified the emotions correctly at a higher-than-chance rate, though the gestures for “calming” and “love” were easily confused.

More Comfortable Haptics

Overall, participants found the Haptiknit sensations to be as pleasant as or more pleasant than vibrations. They also reported that the prototype sleeve was comfortable and easy to use, which bodes well for long-term applications.

“What was particularly interesting was that there was a correlation between whether someone had tried a haptic device before and how highly they rated the comfort of our sleeve. Essentially, if they had tried out other haptic devices, they scored our sleeves much higher,” du Pasquier added.

With lighter, more comfortable haptic devices, the researchers foresee new ways to convey information through touch. Du Pasquier suggested that hapticnit could be used in navigation, military communication, and even dog training.

Okamura, du Pasquier, and their colleagues are continuing to refine their knitting patterns and are working on developing larger-scale devices, potentially even a full suit, for virtual reality interactions. They also hope to incorporate their work into assistive devices to aid movement or rehabilitation.

Okamura concluded, “We can use this to start testing how people actually interpret and respond to this type of haptic information. Whether the purpose is entertainment, communication, training, or physical assistance, this really brings these wearable devices toward things that people might actually want to use in their everyday lives.”

Demo video of the “Knit Haptic Pneumatic Sleeve” | Video Credit: Skylar Tibbits, MIT Self-Assembly Lab; Image credit: Susan Williams, MIT Self-Assembly Lab

Journal Reference:

du Pasquier, C., et. al. (2024) Haptiknit: Distributed stiffness knitting for wearable haptics. Science Robotics. doi.org/10.1126/scirobotics.ado3887