Soft Robotics

2018
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
2017
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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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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D. Van Story, et al., “Approaches to Real-Time Ventricular Wall Strain Measurement for the Control of Soft Robotic Ventricular Assist Devices,” The 9th Hamlyn Symposium on Medical Robotics. 2017. PDF
C. J. Payne, et al., “Wearable Soft Robotic Device Supports the Failing Heart In Vivo,” The 9th Hamlyn Symposium on Medical Robotics. 2017. PDF
C. O'Neill, N. Phipps, L. Cappello, S. Paganoni, and C. J. Walsh, “Soft Robotic Shoulder Support: Design, Characterization, and Preliminary Testing,” in 15th IEEE International Conference on Rehabilitation Robotics (ICORR), London, July 17-20, 2017. PDF
M. A. Horvath, et al., “An Intracardiac Soft Robotic Device for Augmentation of Blood Ejection from the Failing Right Ventricle,” Annals of Biomedical Engineering, pp. 1-12, 2017. Publisher's VersionAbstract

We introduce an implantable intracardiac soft robotic right ventricular ejection device (RVED) for dynamic approximation of the right ventricular (RV) free wall and the interventricular septum (IVS) in synchrony with the cardiac cycle to augment blood ejection in right heart failure (RHF). The RVED is designed for safe and effective intracardiac operation and consists of an anchoring system deployed across the IVS, an RV free wall anchor, and a pneumatic artificial muscle linear actuator that spans the RV chamber between the two anchors. Using a ventricular simulator and a custom controller, we characterized ventricular volume ejection, linear approximation against different loads and the effect of varying device actuation periods on volume ejection. The RVED was then tested in vivo in adult pigs (n = 5). First, we successfully deployed the device into the beating heart under 3D echocardiography guidance (n = 4). Next, we performed a feasibility study to evaluate the device's ability to augment RV ejection in an experimental model of RHF (n = 1). RVED actuation augmented RV ejection during RHF; while further chronic animal studies will provide details about the efficacy of this support device. These results demonstrate successful design and implementation of the RVED and its deployment into the beating heart. This soft robotic ejection device has potential to serve as a rapidly deployable system for mechanical circulatory assistance in RHF.

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F. Connolly, C. J. Walsh, and K. Bertoldi, “Automatic design of fiber-reinforced soft actuators for trajectory matching,” Proceedings of the National Academy of Sciences (PNAS), vol. 114, no. 1, pp. 51-56, 2017. Publisher's VersionAbstract

Soft actuators are the components responsible for producing motion in soft robots. Although soft actuators have allowed for a variety of innovative applications, there is a need for design tools that can help to efficiently and systematically design actuators for particular functions. Mathematical modeling of soft actuators is an area that is still in its infancy but has the potential to provide quantitative insights into the response of the actuators. These insights can be used to guide actuator design, thus accelerating the design process. Here, we study fluid-powered fiber-reinforced actuators, because these have previously been shown to be capable of producing a wide range of motions. We present a design strategy that takes a kinematic trajectory as its input and uses analytical modeling based on nonlinear elasticity and optimization to identify the optimal design parameters for an actuator that will follow this trajectory upon pressurization. We experimentally verify our modeling approach, and finally we demonstrate how the strategy works, by designing actuators that replicate the motion of the index finger and thumb.

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Z. Wang, P. Polygerinos, J. T. B. Overvelde, K. C. Galloway, K. Bertoldi, and C. J. Walsh, “Interaction Forces of Soft Fiber Reinforced Bending Actuators,” IEEE/ASME Transactions on Mechatronics, vol. 22, no. 2, pp. 717-727, 2017. Publisher's VersionAbstract

Soft bending actuators are inherently compliant, compact, and lightweight. They are preferable candidates over rigid actuators for robotic applications ranging from physical human interaction to delicate object manipulation. However, characterizing and predicting their behaviors are challenging due to the material nonlinearities and the complex motions they can produce. This paper investigates a soft bending actuator design that uses a single air chamber and fiber reinforcements. Additionally, the actuator design incorporates a sensing layer to enable real-time bending angle measurement for analysis and control. In order to study the bending and force exertion characteristics when interacting with the environment, a quasistatic analytical model is developed based on the bending moments generated from the applied internal pressure and stretches of the soft materials. Comparatively, a finite-element method model is created for the same actuator design. Both the analytical model and the finite-element model are used in the fiber reinforcement analysis and the validation experiments with fabricated actuators. The experimental results demonstrate that the analytical model captures the relationships of supplied air pressure, actuator bending angle, and interaction force at the actuator tip. Moreover, it is shown that an off-the-shelf bend angle sensor integrated to the actuator in this study could provide real-time force estimation, thus eliminating the need for a force sensor.

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Soft robotic sleeve supports heart function
E. T. Roche, et al., “Soft robotic sleeve supports heart function,” Science Translational Medicine, vol. 9, no. 373, 2017. Publisher's VersionAbstract

There is much interest in form-fitting, low-modulus, implantable devices or soft robots that can mimic or assist in complex biological functions such as the contraction of heart muscle. We present a soft robotic sleeve that is implanted around the heart and actively compresses and twists to act as a cardiac ventricular assist device. The sleeve does not contact blood, obviating the need for anticoagulation therapy or blood thinners, and reduces complications with current ventricular assist devices, such as clotting and infection. Our approach used a biologically inspired design to orient individual contracting elements or actuators in a layered helical and circumferential fashion, mimicking the orientation of the outer two muscle layers of the mammalian heart. The resulting implantable soft robot mimicked the form and function of the native heart, with a stiffness value of the same order of magnitude as that of the heart tissue. We demonstrated feasibility of this soft sleeve device for supporting heart function in a porcine model of acute heart failure. The soft robotic sleeve can be customized to patient-specific needs and may have the potential to act as a bridge to transplant for patients with heart failure.

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D. P. Holland, et al., “The Soft Robotics Toolkit: Strategies for Overcoming Obstacles to the Wide Dissemination of Soft-Robotic Hardware,” IEEE Robotics and Automation Magazine, Special Issue on Open Source and Widely Disseminated Robot Hardware, vol. 24, no. 1, pp. 57-64, 2017. Publisher's VersionAbstract

The Soft Robotics Toolkit (SRT) is an open-access website containing detailed information about the design, fabrication, and characterization of soft-robotic components and systems (Figure 1). Soft robotics is a growing field of research concerned with the development of electromechanical technology composed of compliant materials or structures. The SRT website hosts design files, multimedia fabrication instructions, and software tutorials submitted by an international community of soft-robotics researchers and designers. In this article, we describe the development of the SRT and some challenges in developing widely disseminated robotic-hardware resources. Our attempts to overcome these challenges in the development of the toolkit are discussed by focusing on strategies that have been used to engage participants ranging from K-12 grade students to robotics research groups. A series of design competitions encouraged people to use and contribute to the toolkit. New fabrication methods requiring only low-cost and accessible materials were developed to lower the entry barriers to soft robotics and instructional materials and outreach activities were used to engage new audiences. We hope that our experiences in developing and scaling the toolkit may serve as guidance for other open robotic-hardware projects.

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2016
F. Connolly, C. J. Walsh, and K. Bertoldi, “Using Analytical Modeling to Design Customized Fiber-Reinforced Soft Actuators,” Society of Engineering Science 53rd Annual Technical Meeting. 2016. PDF
D. P. Holland, G. J. Bennett, G. M. Whitesides, R. J. Wood, and C. J. Walsh, “The 2015 Soft Robotics Competition,” IEEE Robotics & Automation Magazine, vol. 23, no. 3, pp. 25-27, 2016. Publisher's Version PDF
2015
F. Connolly, C. J. Walsh, and K. Bertoldi, “Modelling Geometrically Constrained Fluidic Soft Actuators,” 9th European Solid Mechanics Conference. 2015. PDF
P. Polygerinos, K. C. Galloway, S. Sanan, M. Herman, and C. J. Walsh, “EMG controlled soft robotic glove for assistance during activities of daily living,” in 14th IEEE International Conference on Rehabilitation Robotics (ICORR), Singapore, 2015, pp. 55-60. [Best Paper Award]. Publisher's VersionAbstract

This paper presents further developments, characterization and initial evaluation of a recently developed assistive soft robotic glove for individuals with hand pathologies. The glove technology utilizes a combination of elastomeric and inextensible materials to create soft actuators that conform to the user's hand and can generate sufficient hand closing force to assist with activities of daily living. User intent (i.e. desire to close or open hand) is detected by monitoring gross muscle activation signals with surface electromyography electrodes mounted on the user's forearm. In particular, we present an open-loop sEMG logic that distinguishes muscle contractions and feeds the information to a low-level fluidic pressure controller that regulates pressure in pre-selected groups of the glove's actuators. Experiments are conducted to determine the level of assistance provided by the glove by monitoring muscle effort and mapping the pressure distribution during a simple grasping task when the glove is worn. Lastly, quantitative and qualitative results are presented using the sEMG-controlled glove on a healthy participant and on a patient with muscular dystrophy.

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W. Whyte, et al., “A Replenishable Cell Delivery System for the Heart,” 4th TERMIS World Congress. 2015. Poster
E. T. Roche, et al., “Design And Fabrication Of A Soft Robotic Direct Cardiac Compression Device,” in Proceedings of the ASME 2015 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE 2015), Boston, MA, 2015. Publisher's Version PDF
M. A. Horvath, E. T. Roche, D. M. Vogt, D. J. Mooney, F. A. Pigula, and C. J. Walsh, “Soft Pressure Sensing Sleeve For Direct Cardiac Compression Device,” in Proceedings of the ASME 2015 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE 2015), Boston, MA, USA, August 2-5, 2015. Publisher's VersionAbstract
A direct cardiac compression (DCC) device is a non-blood contacting sleeve placed around the failing heart to actively assist blood pumping function. For design optimization of a DCC device, it is necessary to monitor the surface pressure exerted on the heart surface at multiple points during active assist, and to correlate this with device performance and cardiac output. In this paper, we present the design, fabrication and characterization of a soft, elastic, conformable pressure sensing sleeve that is placed at the heart/device interface to monitor device performance without affecting device function. This sleeve enables identification of optimal pre-tensioning, positioning and user-controlled parameters of the DCC device. Individual sensors (8×8×3 mm) were fabricated using a surface mount device (SMD) barometer on a custom double-sided flexible printed circuit board and casting the assembly in urethane rubber. A typical sensor has a dynamic range of 2.5 kPa to 50 kPa with a sensitivity of 11.3 counts per kPa. An array of up to 24 sensors was integrated into a flexible, stretchable circuit embedded in a thin (500 micron) silicone sheet using a multi-step layering fabrication process. Continuous magnet wires were wrapped around an alignment fixture, soldered to individual sensors in place and the entire circuit was transfer printed on to a silicone sheet. This assembly allows stretch corresponding to the fractional shortening of the heart muscles (up to 50%). The sleeve successfully measured static and dynamic pressures with a mechanical tensile tester and did not affect DCC device performance. Preliminary results demonstrated that the sleeve is robust enough to withstand >10000 cycles, compression forces from the DCC device and can achieve sensing range and repeatability suitable for procedural pressure monitoring for a DCC device. In addition to allowing performance measurements for iterating DCC device designs, the sensing sleeve can enable increased understanding of the response of the cardiovascular system to compressive assistance.
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F. Connolly, P. Polygerinos, C. J. Walsh, and K. Bertoldi, “Mechanical Programming of Soft Actuators by Varying Fiber Angle,” Soft Robotics, vol. 2, no. 1, pp. 26-32, 2015. Publisher's VersionAbstract

In this work we investigate the influence of fiber angle on the deformation of fiber-reinforced soft fluidic actuators and examine the manner in which these actuators extend axially, expand radially and twist about their axis as a function of input pressure. We study the quantitative relationship between fiber angle and actuator deformation by performing finite element simulations for actuators with a range of different fiber angles, and we verify the simulation results by experimentally characterizing the actuators. By combining actuator segments in series, we can achieve combinations of motions tailored to specific tasks. We demonstrate this by using the results of simulations of separate actuators to design a segmented wormlike soft robot capable of propelling itself through a tube and performing an orientation-specific peg insertion task at the end of the tube. Understanding the relationship between fiber angle and pressurization response of these soft fluidic actuators enables rapid exploration of the design space, opening the door to the iteration of exciting soft robot concepts such as flexible and compliant endoscopes, pipe inspection devices, and assembly line robots.

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E. Rogers, P. Polygerinos, C. J. Walsh, and E. Goldfield, “Smart and Connected Actuated Mobile and Sensing Suit to Encourage Motion in Developmentally Delayed Infants,” ASME Design of Medical Devices Conference. 2015. PDF

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