All Publications

2018
M. A. Horvath, et al., “Towards Alternative Approaches for Coupling of a Soft Robotic Sleeve to the Heart,” Annals of Biomedical Engineering, 2018. Publisher's VersionAbstract
Efficient coupling of soft robotic cardiac assist devices to the external surface of the heart is crucial to augment cardiac function and represents a hurdle to translation of this technology. In this work, we compare various fixation strategies for local and global coupling of a direct cardiac compression sleeve to the heart. For basal fixation, we find that a sutured Velcro band adheres the strongest to the epicardium. Next, we demonstrate that a mesh-based sleeve coupled to the myocardium improves function in an acute porcine heart failure model. Then, we analyze the biological integration of global interface material candidates (medical mesh and silicone) in a healthy and infarcted murine model and show that a mesh interface yields superior mechanical coupling via pull-off force, histology, and microcomputed tomography. These results can inform the design of a therapeutic approach where a mesh-based soft robotic DCC is implanted, allowed to biologically integrate with the epicardium, and actuated for active assistance at a later timepoint. This strategy may result in more efficient coupling of extracardiac sleeves to heart tissue, and lead to increased augmentation of heart function in end-stage heart failure patients.
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C. J. Walsh, “Human-in-the-loop development of soft wearable robots,” Nature Review Materials, 2018. Publisher's VersionAbstract

The field of soft wearable robotics offers the opportunity to wear robots like clothes to assist the movement of specific body parts or to endow the body with functionalities. Collaborative efforts of materials, apparel and robotics science have already led to the development of wearable technologies for physical therapy. Optimizing the human–robot system by human-in-the-loop approaches will pave the way for personalized soft wearable robots for a variety of applications.

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D. P. Holland, C. J. Walsh, and G. J. Bennett, “A qualitative investigation of design knowledge reuse in project-based mechanical design courses,” European Journal of Engineering Education, pp. 1-16, 2018. Publisher's Version PDF
D. Holland, S. Berndt, M. Herman, and C. Walsh, “Growing the Soft Robotics Community Through Knowledge-Sharing Initiatives,” Soft Robotics, vol. 5, no. 2, pp. 119-121, 2018. Publisher's Version PDF
S. Mohammed, et al., “Wearable Robotics for Motion Assistance and Rehabilitation [TC Spotlight],” IEEE Robotics Automation Magazine, vol. 25, no. 1, pp. 19-28, 2018. PDF
J. Gafford, H. Aihara, C. Thompson, R. Wood, and C. Walsh, “Distal Proprioceptive Sensor for Motion Feedback in Endoscope-Based Modular Robotic Systems,” IEEE Robotics and Automation Letters, vol. 3, no. 1, pp. 171-178, 2018. PDF
O. Araromi, S. Castellanos, C. Walsh, and R. Wood, “Compliant low profile textile-integrated multi-axis force sensors,” in IEEE International Conference on Robotics and Automation (ICRA), Brisbane, Australia, May 21-25, 2018.
S. Lee, et al., “Autonomous Multi-Joint Soft Exosuit for Assistance with Walking Overground,” in IEEE International Conference on Robotics and Automation (ICRA), Brisbane, Australia, May 21-25, 2018.
J. Kim, et al., “Autonomous and portable soft exosuit for hip extension assistance with online walking and running detection algorithm,” in IEEE International Conference on Robotics and Automation (ICRA), Brisbane, Australia, May 21-25, 2018.
E. Suarez, J. Huaroto, A. Reymundo, D. Holland, C. Walsh, and E. Vela, “A Soft Pneumatic Fabric-Polymer Actuator for Wearable Biomedical Devices: Proof of Concept for Lymphedema Treatment,” in IEEE International Conference on Robotics and Automation (ICRA), Brisbane, Australia, May 21-25, 2018.
C. Payne, et al., “Textile-Based Soft Robotic Force Control for Wearable Mechanotherapy Devices,” in IEEE International Conference on Robotics and Automation (ICRA), Brisbane, Australia, May 21-25, 2018.
J. Bae, et al., “A lightweight and efficient portable soft exosuit for paretic ankle assistance in walking after stroke ,” in IEEE International Conference on Robotics and Automation (ICRA), Brisbane, Australia, May 21-25, 2018.
J. Bae, et al., “Biomechanical mechanisms underlying exosuit-induced improvements in walking economy after stroke,” Journal of Experimental Biology, 2018. Publisher's VersionAbstract
{Stroke-induced hemiparetic gait is characteristically asymmetric and metabolically expensive. Weakness and impaired control of the paretic ankle contribute to reduced forward propulsion and ground clearance—walking subtasks critical for safe and efficient locomotion. Targeted gait interventions that improve paretic ankle function after stroke are therefore warranted. We have developed textile-based, soft wearable robots that transmit mechanical power generated by off-board or body-worn actuators to the paretic ankle using Bowden cables (soft exosuits) and have demonstrated the exosuits can overcome deficits in paretic limb forward propulsion and ground clearance, ultimately reducing the metabolic cost of hemiparetic walking. This study elucidates the biomechanical mechanisms underlying exosuit-induced reductions in metabolic power. We evaluated the relationships between exosuit-induced changes in the body center of mass (COM) power generated by each limb, individual joint powers, and metabolic power. Compared to walking with an exosuit unpowered, exosuit assistance produced more symmetrical COM power generation during the critical period of the step-to-step transition (22.4±6.4% more symmetric). Changes in individual limb COM power were related to changes in paretic (R2= 0.83
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Y. Ding, M. Kim, S. Kuindersma, and C. J. Walsh, “Human-in-the-loop optimization of hip assistance with a soft exosuit during walking,” Science Robotics, vol. 3, no. 15, pp. eaar5438, 2018. Publisher's VersionAbstract
Wearable robotic devices have been shown to substantially reduce the energy expenditure of human walking. However, response variance between participants for fixed control strategies can be high, leading to the hypothesis that individualized controllers could further improve walking economy. Recent studies on human-in-the-loop (HIL) control optimization have elucidated several practical challenges, such as long experimental protocols and low signal-to-noise ratios. Here, we used Bayesian optimization—an algorithm well suited to optimizing noisy performance signals with very limited data—to identify the peak and offset timing of hip extension assistance that minimizes the energy expenditure of walking with a textile-based wearable device. Optimal peak and offset timing were found over an average of 21.4 ± 1.0 min and reduced metabolic cost by 17.4 ± 3.2% compared with walking without the device (mean ± SEM), which represents an improvement of more than 60% on metabolic reduction compared with state-of-the-art devices that only assist hip extension. In addition, our results provide evidence for participant-specific metabolic distributions with respect to peak and offset timing and metabolic landscapes, lending support to the hypothesis that individualized control strategies can offer substantial benefits over fixed control strategies. These results also suggest that this method could have practical impact on improving the performance of wearable robotic devices.
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2017
C. J. Payne, et al., “Soft robotic ventricular assist device with septal bracing for therapy of heart failure,” Science Robotics, vol. 2, no. 12, 2017. Publisher's VersionAbstract
Previous soft robotic ventricular assist devices have generally targeted biventricular heart failure and have not engaged the interventricular septum that plays a critical role in blood ejection from the ventricle. We propose implantable soft robotic devices to augment cardiac function in isolated left or right heart failure by applying rhythmic loading to either ventricle. Our devices anchor to the interventricular septum and apply forces to the free wall of the ventricle to cause approximation of the septum and free wall in systole and assist with recoil in diastole. Physiological sensing of the native hemodynamics enables organ-in-the-loop control of these robotic implants for fully autonomous augmentation of heart function. The devices are implanted on the beating heart under echocardiography guidance. We demonstrate the concept on both the right and the left ventricles through in vivo studies in a porcine model. Different heart failure models were used to demonstrate device function across a spectrum of hemodynamic conditions associated with right and left heart failure. These acute in vivo studies demonstrate recovery of blood flow and pressure from the baseline heart failure conditions. Significant reductions in diastolic ventricle pressure were also observed, demonstrating improved filling of the ventricles during diastole, which enables sustainable cardiac output.
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O. Atalay, A. Atalay, J. Gafford, and C. J. Walsh, “Highly Sensitive Capacitive-Based Soft Pressure Sensor Based on Conductive Fabric and Micro-porous Dielectric Layer,” Advanced Materials Technologies, 2017. Publisher's VersionAbstract
In this paper, the design and manufacturing of a highly sensitive capacitive-based soft pressure sensor for wearable electronics applications are presented. Toward this aim, two types of soft conductive fabrics (knitted and woven), as well as two types of sacrificial particles (sugar granules and salt crystals) to create micropores within the dielectric layer of the capacitive sensor are evaluated, and the combined effects on the sensor's overall performance are assessed. It is found that a combination of the conductive knit electrode and higher dielectric porosity (generated using the larger sugar granules) yields higher sensitivity (121 × 10−4 kPa−1) due to greater compressibility and the formation of air gaps between silicone elastomer and conductive knit electrode among the other design considerations in this study. As a practical demonstration, the capacitive sensor is embedded into a textile glove for grasp motion monitoring during activities of daily living.
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F. A. Panizzolo, et al., “Lower limb biomechanical analysis during an unanticipated step on a bump reveals specific adaptations of walking on uneven terrains,” Journal of Experimental Biology, vol. 220, no. 22, pp. 4169–4176, 2017. Publisher's VersionAbstract
Although it is clear that walking over different irregular terrain is associated with altered biomechanics, there is little understanding of how we quickly adapt to unexpected variations in terrain. This study aims to investigate which adaptive strategies humans adopt when performing an unanticipated step on an irregular surface, specifically a small bump. Nine healthy male participants walked at their preferred walking speed along a straight walkway during five conditions: four involving unanticipated bumps of two different heights, and one level walking condition. Muscle activation of eight lower limb muscles and three-dimensional gait analysis were evaluated during these testing conditions. Two distinct adaptive strategies were found, which involved no significant change in total lower limb mechanical work or walking speed. An ankle-based strategy was adopted when stepping on a bump with the forefoot, whereas a hip-based strategy was preferred when stepping with the rearfoot. These strategies were driven by a higher activation of the plantarflexor muscles (6–51%), which generated a higher ankle joint moment during the forefoot conditions and by a higher activation of the quadriceps muscles (36–93%), which produced a higher knee joint moment and hip joint power during the rearfoot conditions. These findings provide insights into how humans quickly react to unexpected events and could be used to inform the design of adaptive controllers for wearable robots intended for use in unstructured environments that can provide optimal assistance to the different lower limb joints.
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C. J. Payne, et al., “An Implantable Extracardiac Soft Robotic Device for the Failing Heart: Mechanical Coupling and Synchronization,” Soft Robotics, vol. 4, no. 3, pp. 241-250, 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 into 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 into 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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M. Kim, et al., “Human-in-the-loop Bayesian optimization of wearable device parameters,” PLOS ONE, vol. 12, no. 9, pp. 1-15, 2017. Publisher's VersionAbstract
The increasing capabilities of exoskeletons and powered prosthetics for walking assistance have paved the way for more sophisticated and individualized control strategies. In response to this opportunity, recent work on human-in-the-loop optimization has considered the problem of automatically tuning control parameters based on realtime physiological measurements. However, the common use of metabolic cost as a performance metric creates significant experimental challenges due to its long measurement times and low signal-to-noise ratio. We evaluate the use of Bayesian optimization—a family of sample-efficient, noise-tolerant, and global optimization methods—for quickly identifying near-optimal control parameters. To manage experimental complexity and provide comparisons against related work, we consider the task of minimizing metabolic cost by optimizing walking step frequencies in unaided human subjects. Compared to an existing approach based on gradient descent, Bayesian optimization identified a near-optimal step frequency with a faster time to convergence (12 minutes, p < 0.01), smaller inter-subject variability in convergence time (± 2 minutes, p < 0.01), and lower overall energy expenditure (p < 0.01).
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J. B. Gafford, H. Aihara, C. Thompson, R. J. Wood, and C. J. Walsh, “Distal Proprioceptive Sensor for Motion Feedback in Endoscope-Based Modular Robotic Systems,” IEEE Robotics and Automation Letters, vol. PP, 2017. Publisher's VersionAbstract
Modular robotic systems that integrate with commercially-available endoscopic equipment have the potential to improve the standard-of-care in therapeutic endoscopy by granting clinicians with capabilities not present in commercial tools, such as precision dexterity and motion sensing. With the desire to integrate both sensing and actuation distally for closed-loop position control in fully-deployable, endoscope-based robotic modules, commercial sensor and actuator options that acquiesce to the strict form-factor requirements are sparse or nonexistent. Herein we describe a proprioceptive angle sensor for potential closed-loop position control applications in distal robotic modules. Fabricated monolithically using printed-circuit MEMS, the sensor employs a kinematic linkage and the principle of light intensity modulation to sense the angle of articulation with a high degree of fidelity. On-board temperature and environmental irradiance measurements, coupled with linear regression techniques, provide robust angle measurements that are insensitive to environmental disturbances. The sensor is capable of measuring +/-45 degrees of articulation with an RMS error of 0.98 degrees. An integrated demonstration shows that the sensor can give real-time proprioceptive feedback when coupled with an actuator module, opening up the possibility of fully-distal closed-loop control.
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