ABSTRACT

Neurologically impaired people such as stroke patients often need assistance in moving their joints. However, current wearable rehabilitation and assistive devices are either 1) powerful and active but bulky and made of rigid elements such as exoskeletons and artificial limbs, or 2) flexible but passive with limited functionality such as joint braces. In spite of recent advances in soft robotics, there is still no soft actuator (motion-generating device) that is portable, i.e. can be operated by on-board power sources, scalable to be adapted to different joint sizes and still have the short response time and high output force-to-size ratio needed to assist joint motions. To address this need, the goal of this project is to design, fabricate and evaluate a novel Electromagnetic Soft Actuator (ESA) that can be easily powered by on-board batteries and can produce linear force and contraction in a manner that mimics the behavior of the contractile filaments (Actin and Myosin) inside a sarcomere (the basic human muscle actuation unit). The ESA is highly scalable and can be miniaturized to create an artificial sarcomere when assembled in parallel and in series. A series of artificial sarcomeres will create an ExoFiber. As the primary activation unit, each artificial sarcomere will be electrically excited separately. The ExoFibers straps will then be embedded into joint braces to make them active. Being activated based on the principle of electromagnetism, the ExoFibers can be quickly energized to generate force and motion. The performance of an ExoFibers-actived brace for the human elbow joint will be evaluated in a small-scale pilot study in humans with and without elbow disabilities. Findings will advance the next generation of flexible, powerful and portable active braces through scalable soft actuators for joint motion assistance and rehabilitation applications and will lay the foundations for interdisciplinary research on the design and analysis of soft actuator networks with dynamic system and materials design and rehabilitation therapy. Education and outreach impact will be achieved through the development of a new graduate level class in Soft Rehabilitation Robotics and working with the UTSA Center for Excellence in Engineering Education (CE3) and iTEC to involve students from underrepresented groups from San Antonio in the project.

This exploratory project investigates the possibility of fabricating an Electromagnetic Soft Actuator (ESA) that can be powered by on-board batteries, can produce linear force and contraction in a manner that mimics the behavior of the contractile actin and myosin filaments inside a sarcomere and can be miniaturized to create an artificial sarcomere when assembled in a bioinspired parallel and series pattern. The artificial sarcomeres can be networked into ExoFibers that can be embedded in a human elbow brace that can be used for rehabilitation or as an assistive device. The Research Plan is organized under two aims. AIM 1 is focused on design and fabrication. The ESA design consists of two antagonistic solenoids with a spring linkage in between and an internal ferromagnetic core built with soft materials. By injecting electric current into micro-coils, two antagonistic electromagnetic fields will be induced, resulting in repulsive or attractive forces that stretch or compress the springy linkage. The artificial sarcomere and ExoFibers designs will be assembled using ESAs that have been bioprinted to facilitate ease of production. The number of ESAs assembled in parallel will determine the output source and the number of ESAs in series defines the overall contraction. AIM 2 is focused on development and evaluation of dynamic properties of an active brace, i.e., brace embedded with an ExoFiber. Experimental platforms will be set up to test performance at three levels: single ExoFiber, active brace, and human elbow. The output performance can be defined in terms of: 1) contraction length, output force, linear stiffness and bandwidth for ExoFiber, 2) flexion range, torque, angular stiffness and bandwidth for active brace, and 3) flexion range and comfort and ease of use with a human elbow. The active brace level will be evaluated while the brace is placed on a bioprinted arm model. The human elbow level will be evaluated by conducting a small-scale pilot study in two cohorts of adults: healthy individuals and subjects with elbow weakness, decreased range of motion, or stiffness due to stroke. Participants will be asked to perform three types of exercises: 1) to hold their arm at 5 different flexion-extension stationary angles while suddenly perturb by a 2Nm torque, 2) to flex and extend their arm while holding a 2Kg weight at two different speeds (slow and normal) and 3) to flex their arm while working against a constant torque of 2Nm.

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.

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