(G-266) Proof-of-Concept for a Human-powered Sensory Neuroprosthesis Based On Soft Robotics

Peripheral neuropathy (PN) is damage to the peripheral nervous system and loss of feeling or numbness in the hands and feet [1]. This can cause pain, difficulty walking, and increase the fall rate of patients [2], ultimately lowering one's quality of life. While 70-80% of patients with PN caused by Type 1 and 2 diabetes, the remaining 20-30% percent can be caused by other conditions, such as traumas, various cancer treatments, and autoimmune disorders. Although there are limited studies that pertain to aiding the patient's walking performance, Walkasins, a medical device created for those with PN has been shown to be promising. The Walkasins device is a wearable, lower limb, sensory prosthesis that utilizes pressure sensors on the bottom of the foot to translate plantar pressure information from gait into mechanical tactile stimuli on the calf, where sensory function is not impaired. This has yielded positive results in improving a patient's Functional Gait Assessment score [3]. In this study, we report on a new device that accomplishes a similar task through the use of soft robotics powered solely by the action of walking.

The device is based on the action of underfoot sensory air bladders and stimulus air bladders located on the leg, which are connected in series. As the gait cycle begins with heel strike, the underfoot sensory bladders are loaded and compressed, sending air upstream to the stimulus bladders on the calf, which inflate to be felt by the user. During lift-off, the air flows down from the calf to the foot, restarting the cycle in time with the patient's next step. The air bladders were fabricated by heating layers of Thermoplastic Polyurethane (TPU; Perfectex ET20-C30) together using a heat press with a glassine center to form an air pocket. [4] The air bladders were connected in a closed system via polyurethane tubing. There can be multiple sets of bladders to localize gait information from different parts of the foot, such as the heel and medial and lateral forefoot. For proof-of-concept bench testing, we compressed the heel sensory bladder with 184N using an Instron (5967). Simultaneously, we recorded the stimulus force against a manakin leg using a pressure sensor (loadpad MT, Novel). The stimulus bladders were held to the calf using an adjustable band. The band is designed to be more expandable in the inward direction to maximize force transfer and stimulate the calf. The raw data was analyzed for the average force against the leg and the rise time of the stimulus response.

Data collected from testing, showed the device’s ability to yield positive results using the intended mechanism of mechanical air transfer. Figure 1 exhibits the device producing significant forces against the calf with a short response time when compared to the area of the foot that the sensing data originates from. In this case, the heel sensory bladder was used. The average force against the calf was 12.17 N, determined as the baseline corrected peak force. Studies show that the skin’s mechanoreceptors are responsive to as low as even .3 N of force [8]. Thus putting the force exerted on the calf well into the range of touch. Additionally, the average rise time was 10.13 seconds, determined as the time for the signal to go from 10% to 90% of the peak force. Overall, the results indicate that the calf is stimulated within a short amount of time as pressure from the foot is applied to the sensory bladder.

In theory, this device will improve PN patients’ gait over time. Studies have shown that vibrotactile sensory substitution devices can improve gait and balance function in those with sensory deficits. [5]. This is due to the skin's ability, as a mechanoreceptor, to convey tactile messages to the brain via afferent nerves [6]. The skin is sensitive to touch, roughly 250 hz. Feedback is critical to the performance of motor skills [7].

The results conclude  that the device is successful in the sense of rapidly stimulating the calf while force is applied to the foot. We plan to conduct additional testing using the Instron on all sensory bladders subject to a variety of loading conditions. Additionally, we plan to explore different methods of securing the sensory bladders underfoot, such as embedding them in a shoe or sock to ensure that the device is easy to use. Following device characterization, we plan to conduct a safety study on healthy subjects while walking. The long term goal is to evaluate the device on patients with PN.

1. 
   

   Mayo Foundation for Medical Education and Research. (2022, August 11). Peripheral neuropathy. Mayo Clinic. Retrieved April 23, 2023, from https://www.mayoclinic.org/diseases-conditions/peripheral-neuropathy/symptoms-causes/syc-20352061 

   
   


2. 
   

   James K. Richardson, Edward A. Hurvitz, Peripheral Neuropathy: A True Risk Factor for Falls, The Journals of Gerontology: Series A, Volume 50A, Issue 4, July 1995, Pages M211–M215, https://doi.org/10.1093/gerona/50A.4.M211

   
   


3. 
   

   Bisson, T., Cohen, H. S., Iloputaife, I., Jacobs, L., Kung, D., Lipsitz, L. A., Manor, B., McCracken, P., Rumsey, Y., Wrisley, D. M., & Koehler-McNicholas, S. R. (2022). Extended effects of a wearable sensory prosthesis on gait, balance function and falls after 26 weeks of use in persons with peripheral neuropathy and high fall risk—the walk2wellness trial. Frontiers in Aging Neuroscience, 14. https://doi.org/10.3389/fnagi.2022.931048 

   
   


4. 
   

   Marcee, A., & Treadway, E. (2022). Self-powered microgravity resistance exercise with soft pneumatic exoskeletons. 2022 IEEE Aerospace Conference (AERO). 

   
   


5. 
   

    D. M. Eagleman and M. V. Perrotta, “The future of sensory substitution, addition, and expansion via haptic devices,” Frontiers, https://www.frontiersin.org/articles/10.3389/fnhum.2022.1055546/full (accessed Jul. 21, 2023).

   
   


6. 
   

   Haptic wearables as sensory replacement, sensory augmentation and trainer – a review | Journal of NeuroEngineering and Rehabilitation | Full Text (biomedcentral.com)TIKL: Development of a Wearable Vibrotactile Feedback Suit for Improved Human Motor Learning | IEEE Journals & Magazine | IEEE Xplore

   
   


7. 
   

   TIKL: Development of a Wearable Vibrotactile Feedback Suit for Improved Human Motor Learning | IEEE Journals & Magazine | IEEE Xplore

   
   


8. 
   

    C. Zippenfennig, B. Wynands, and T. L. Milani, “Vibration perception thresholds of skin mechanoreceptors are influenced by different contact forces,” Journal of clinical medicine, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8307596/ (accessed Jul. 24, 2023).