Poster Z1 - Integrating Soft Tactile Sensors with Variable Resonance Frequency Flexible Tactors Generates an Event-Cue Feedback Devices

Introduction: Wearable devices for the somatosensory system are designed to provide event-cue feedback and therapeutic stimulation to the peripheral nervous system, eliciting neurological responses that are communicated back to the central nervous system. Unlike virtual reality tools, these devices precisely target peripheral mechanoreceptors with specific stimuli. Given the varying density and types of mechanoreceptors across different body locations, adaptable flexible electronics are crucial for effective targeting. In this context, we have developed a sensing-actuation platform using advanced manufacturing techniques. This platform seamlessly integrates soft carbon nanotube (CNT)-elastomer tactile sensors with custom flexible silicone-based actuators, enabling the creation of wearable electronics that deliver responsive feedback. By optimizing the cantilevers of the actuators, these sensors can operate across a broad spectrum of driving frequencies.

We present three functional event-cue feedback devices—a prosthetic, a sole, and a glove—demonstrating their ability to utilize CNT sensors to detect pressure variations from weight, gait, and grip. These devices transmit signals to flexible tactors, eliciting vibrotactile cues on healthy skin areas. The innovative deployment of these devices holds promise for stimulating peripheral nerves, augmenting prosthetic functionality, and enhancing grip control and tactile sensation in individuals with limited nervous system function.

Materials and

Methods: Sensor Fabrication: The sensors were fabricated using 3D printing techniques. A composite of carbon nanotubes (CNTs) and elastomer was used to create flexible sensors capable of converting compressive pressure into electrical signals. The high conductivity and flexibility of the CNT composite allowed for precise quantification of incident pressure through resistance changes. Inspired by layered architectures, the sensor design included 'on-off' functionality.

Actuator Design and Fabrication: Custom tactile actuators were created with 3D-printed flexible walls and customizable cantilevers. These actuators were designed to provide a broad spectrum of sizing options and vibratory behaviors. The diameters of the finished tactors ranged from ~10 mm to 4 mm, ensuring exceptional flexibility. Four distinct cantilever designs were developed, with resonant peaks spanning from ~100 to ~425 Hz, capable of delivering penetrative vibration at an average depth of ~29.3 µm.

Integration and Assembly: The sensors and actuators were integrated onto flexible substrates using 3D printing. These components were connected to wearable alternating current (AC) signal generators and Bluetooth chips through flexible electrodes.

Device Construction
Prosthetic Device: Equipped with 3D-printed CNT sensors for pressure detection. Signals were transmitted to a flexible tactor positioned on healthy skin areas to deliver a vibrotactile cue.
Sole Device: Incorporated CNT sensors to detect pressure variations from gait. Signals were transmitted to a flexible tactor on the dorsum of the foot.
Glove Device: Featured five pressure sensors that, upon compression, sent signals to a second glove to induce vibration.

Results, Conclusions, and Discussions: Using CNT elastomer pressure sensors and custom flexible tactors, we have developed responsive sensor-actuator systems that interpret mechanical stimuli and provide corresponding vibration feedback. The 3D-printed CNT sensor changes resistance in proportion to the pressure applied, enabling precise pressure quantification and 'on-off' functionality. The flexible, customizable vibrohaptic tactors deliver frequency-dependent vibrations to human skin. By systematically testing tactors with varying cantilever angles and physical geometries, we explore the relationship between design parameters and tactor performance. Experimental measurements and simulations help identify optimal configurations that maximize resonance and vibration effectiveness, delivering strong vibrations with an average penetration depth of ~29.3 µm.

These sensing and actuating devices are 3D-printed onto flexible substrates and integrated with wearable AC generators and Bluetooth chips. We fabricated three functional feedback devices: a prosthetic, a sole, and a glove. Each device uses 3D-printed CNT sensors to detect pressure, transmitting this information to a flexible tactor that delivers a vibrotactile cue on a healthy skin area. The prosthetic device detects unsafe postures via pressure changes on the socket and actuates the healthy innervated quadriceps. The flexible sole uses plantar sensors to monitor gait pressure, inducing vibration on the dorsum of the foot. The glove, equipped with five pressure sensors, sends signals to a second glove to induce vibration upon compression. This comprehensive investigation advances wearable technology and has potential applications in prosthetics, mobility aids, and assistive technology.

By bridging the gap between human physiology and technological innovation, this platform can drive future developments in wearable devices, fostering more seamless and integrated human-machine interfaces. Future studies could focus on refining sensor technologies for enhanced sensitivity and durability, integrating additional sensing modalities, and developing advanced signal processing algorithms to improve real-time data analysis and user interaction, particularly for patients with degenerative nervous system diseases like Parkinson’s disease, peripheral neuropathy, and prosthetic users.

Acknowledgements (Optional): This research was partially supported by the Commonwealth Health Research Board (CHRB) under Award No. 236-08-21. D. J. acknowledges the support from VCU’s CHS Seed award. S. H. P. acknowledges the support from the Renewable Surplus Sector Coupling Technology Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20226210100050).