@article{vargas_whitehouse_huang_zhu_hu_2019, title={Evoked Haptic Sensation in the Hand With Concurrent Non-Invasive Nerve Stimulation}, volume={66}, ISSN={["1558-2531"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85077396250&partnerID=MN8TOARS}, DOI={10.1109/TBME.2019.2895575}, abstractNote={Objective: Haptic perception is critical for prosthetic users to control their prosthetic hand intuitively. In this study, we seek to evaluate the haptic perception evoked from concurrent stimulation trains through multiple channels using transcutaneous nerve stimulation. Methods: A 2 × 8 electrode grid was used to deliver current to the median and ulnar nerves in the upper arm. Different electrodes were first selected to activate the sensory axons, which can elicit sensations at different locations of the hand. Charge-balanced bipolar stimulation was then delivered to two sets of electrodes concurrently with a phase delay (dual stimulation) to determine whether the evoked sensation can be constructed from sensations of single stimulation delivered separately at different locations (single stimulation) along the electrode grid. The temporal delay between the two stimulation trains was altered to evaluate potential interference. The short-term stability of the haptic sensation within a testing session was also evaluated. Results: The evoked sensation during dual stimulation was largely a direct summation of the sensation from single stimulations. The delay between the two stimulation locations had minimal effect on the evoked sensations, which was also stable over repeated testing within a session. Conclusion: Our results indicated that the haptic sensations at different regions of the hand can be constructed by combining the response from multiple stimulation trains directly. The interference between stimulations were minimal. Significance: The outcomes will allow us to construct specific haptic sensation patterns when the prosthesis interacts with different objects, which may help improve user embodiment of the prosthesis.}, number={10}, journal={IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING}, author={Vargas, Luis and Whitehouse, Graham and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2019}, month={Oct}, pages={2761–2767} }
 @article{yao_vargas_hu_zhu_2018, title={A Novel Finger Kinematic Tracking Method Based on Skin-Like Wearable Strain Sensors}, volume={18}, ISSN={["1558-1748"]}, DOI={10.1109/jsen.2018.2802421}, abstractNote={Deficits in hand function are common in a majority of stroke survivors. Although hand performance can be routinely assessed during rehabilitation training, a lack of hand usage information during daily activities could prevent clinicians or therapists from making informative therapeutic decisions. In this paper, we demonstrated and validated the application of silver nanowire-based capacitive strain sensors for finger kinematic tracking. The fabricated strain sensors show high sensitivity (gauge factor close to one), low hysteresis, good linearity, large stretchability (150%), and skin-like mechanical property (Young’s modulus of 96 kPa). All these features allow the sensors to be conformally attached onto the skin to track finger joint movement with minimal interference to daily activities. Recordings of the skin deformation from the strain sensors and joint angles from reflective markers are highly correlated (>93%) for different joint oscillation speeds in a stroke survivor and a control subject, indicating the high accuracy of the strain sensors in joint motion tracking. With the wearable silver nanowire-based strain sensors, accurate hand utility information on the impaired hand of stroke survivors can be acquired in a continuous and unobtrusive manner.}, number={7}, journal={IEEE SENSORS JOURNAL}, author={Yao, Shanshan and Vargas, Luis and Hu, Xiaogang and Zhu, Yong}, year={2018}, month={Apr}, pages={3010–3015} }