Soft Robotics

Multi-material fluidic actuators

Soft fluidic actuators consisting of elastomeric matrices with embedded flexible materials (e.g. cloth, paper, fiber, particles) are of particular interest to the robotics community because they are lightweight, affordable and easily customized to a given application. These actuators can be rapidly fabricated in a multi-step molding process and can achieve combinations of contraction, extension, bending and twisting with simple control inputs such as pressurized fluid. In our approach is to use new design concepts, fabrication approaches and soft materials to improve the performance of these actuators compared to existing designs. In particular, we use motivating applications (e.g. heart assist devices, soft robotic gloves) to define motion and force profile requirements. We can then embed mechanical intelligence into these soft actuators to achieve these performance requirements with simple control inputs.

Modeling of soft actuators

Characterizing and predicting the behavior of soft multi-material actuators is challenging due to the nonlinear nature of both the hyper-elastic material and the large bending motions they produce. We are working to comprehensively describe the principle of operation of these actuators through analytical, numerical and experimental approaches and characterize their outputs (motion and force) as a function of input pressure as well as geometrical and material parameters. Both models and experiments offer insight into the actuator behavior and the design parameters that affect it. We envision this work will lead to improved predictive models that will enable us to rapidly converge on new and innovative applications of these soft actuators.

Sensing and control

In order to control soft actuators, we need means of monitoring their kinematics, interaction forces with objects in the environment and internal pressure. We accomplish this through the use of fully soft sensors, developed with collaborators, and miniature or flexible sensors that can be incorporated into the actuator design during the manufacturing process. For power and control, we use off the shelf components such as electronic valves, pumps, regulators, sensors, and control boards etc. to rapidly modulate the pressure inside the chambers of the actuators using feedback control of pressure, motion and force. In addition, we can use the analytical models we develop to estimate state variables that may be difficult to measure directly.

Translational applications

There are approximately four million chronic stroke survivors with hemiparesis in the US today and another six million in developed countries globally. In addition, there are millions of other individuals suffering from similar conditions. For the majority of these cases, loss of hand motor ability is observed, and whether partial or total, this can greatly inhibit activities of daily living (ADL) and can considerably reduce one’s quality of life. To address these challenges, we are developing a modular, safe, portable, consumable, at-home hand rehabilitation and assistive device that aims to improve patient outcomes by significantly increasing the quantity (i.e. time) and quality of therapy at a reduced cost while also improving independence of users with chronic hand disabilities by enabling them to perform activities of daily living.

In the United States, the lifetime risk of developing heart failure is roughly 20%. The current clinical standard treatment is implantation of a ventricular assist device that contacts the patient’s blood and is associated with thromboembolic events, hemolysis, immune reactions and infections. We are applying the field of soft robotics to develop a benchtop cardiac simulator and a Direct Cardiac Compression (DCC) device employing soft actuators in an elastomeric matrix. DCC is a non-blood contacting method of cardiac assistance for treating heart failure involving implantation of a device that surrounds the heart and contracts in phase with the native heartbeat to provide direct mechanical assistance during the ejection phase (systole) and the relaxation phase (diastole) of the cardiac cycle.

Associated Papers

C. J. Payne, et al., “An Implantable Extracardiac Soft Robotic Device for the Failing Heart: Mechanical Coupling and Synchronization,” Soft Robotics, 2017. Publisher's VersionAbstract
Soft robotic devices have significant potential for medical device applications that warrant safe synergistic interaction with humans. This article describes the optimization of an implantable soft robotic system for heart failure whereby soft actuators wrapped around the ventricles are programmed to contract and relax in synchrony with the beating heart. Elastic elements integrated in to the soft actuators provide recoiling function so as to aid refilling during the diastolic phase of the cardiac cycle. Improved synchronization with the biological system is achieved by incorporating the native ventricular pressure in to the control system to trigger assistance and synchronize the device with the heart. A three-state electro-pneumatic valve configuration allows the actuators to contract at different rates to vary contraction patterns. An in vivo study was performed to test three hypotheses relating to mechanical coupling and temporal synchronization of the actuators and heart. First, that adhesion of the actuators to the ventricles improves cardiac output. Second, that there is a contraction–relaxation ratio of the actuators which generates optimal cardiac output. Third, that the rate of actuator contraction is a factor in cardiac output.
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