Implantable optical tactile sensor for neuroprosthetic feedback

About This Grant

Stroke and spinal cord injuries can result in paralysis, which affects both movement and sense of touch. Treatments that are designed to restore movement, but do not help restore a sense of touch, have limited benefits to patients. A treatment to restore the sense of touch will rely on a sensor that can measure the force skin exerts on an object when the object is touched. Currently available wearable sensors are bulky, and they interfere with the way skin interacts with touched objects. To address this technology gap, this project will develop a minimally invasive, wireless device that can be placed under the skin and can determine forces caused by touching an object. The device will do this by using light to measure changes in blood volume. The implantable sensor will send signals that bypass damaged nerves and communicate with the brain. Such a device could significantly improve the quality of life for people who have suffered stroke or spinal cord injury. In addition, the project will help train a future workforce by involving a team comprising high school, undergraduate, and graduate students to participate in sensor design and fabrication. The sense of touch is critical to dexterous use of the hands and thus an essential component to efforts to restore hand function after paralysis. The latest advance in functional restoration of a patient’s own paralyzed hand is reanimation through brain-controlled functional electrical stimulation (BC-FES). However, to date, this approach has not included somatosensory feedback. BC-FES places additional demands on tactile sensor design not incurred with brain-controlled robotic limbs. In this project, minimally invasive implantable tactile sensors suitable for long-term use in a patient’s own home will be developed. The proposed implantable sensors utilize an optical sensing mechanism, photoplethysmography (PPG), to indirectly infer tactile forces acting on the skin from blood volume changes in the compressed skin capillaries. The strategy has previously been validated, but only with bulky wearable devices. This project will develop and test a fully wireless, battery free, and hermetically sealed PPG sensor for subcutaneous deployment as an artificial mechanoreceptor. Fundamental engineering knowledge will be gained in the refinement of the three main functional components of the system: (1) an ultralow-power custom integrated circuit for PPG, (2) support for wireless radiofrequency (RF) power and data links, and (3) an optically and RF transparent, hermetic, fused silica package for long-term viability under the skin. Wireless functionality and hermeticity of prototype sensor systems will be rigorously tested in preclinical models in vivo. Beyond the intended neuroprosthetic use case, implantable PPG sensors could have tremendous impact in other applications, given that the PPG signal contains information on respiratory, vascular, cardiac, and autonomic nervous system functions. Technology development here could directly translate to a minimally invasive device for continuous physiological monitoring relevant to many chronic conditions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.