Wearable sensing technology is an emerging area and can be utilized for human motion monitoring, physiology monitoring, and human–machine interaction. In this paper, a new manufacturing approach is presented to create highly stretchable and soft capacitance-based strain sensors. This involves a rapid surface modification technique based on direct-write laser rastering to create microstructured surfaces on prestrained elastomeric sheets. Then, to impart conductivity, sputtering technology is utilized to deposit aluminum and silver metal layers on the bottom and top surfaces of the elastomer sheet, creating a soft capacitor. During benchtop characterization of the sensors, this study demonstrates that the fabricated electrodes maintain their electrical conductivity up to the 250% strain, and the sensor shows a linear and repeatable output up to 85% strain. Finally, their potential is demonstrated for monitoring human motion and respiration through their integration into a wearable arm sleeve and a thoracic belt, respectively.
Background Wearable assistive devices have demonstrated the potential to improve mobility outcomes for individuals with disabilities, and to augment healthy human performance; however, these benefits depend on how effectively power is transmitted from the device to the human user. Quantifying and understanding this power transmission is challenging due to complex human-device interface dynamics that occur as biological tissues and physical interface materials deform and displace under load, absorbing and returning power.
Methods Here we introduce a new methodology for quickly estimating interface power dynamics during movement tasks using common motion capture and force measurements, and then apply this method to quantify how a soft robotic ankle exosuit interacts with and transfers power to the human body during walking. We partition exosuit end-effector power (i.e., power output from the device) into power that augments ankle plantarflexion (termed augmentation power) vs. power that goes into deformation and motion of interface materials and underlying soft tissues (termed interface power).
Results We provide empirical evidence of how human-exosuit interfaces absorb and return energy, reshaping exosuit-to-human power flow and resulting in three key consequences: (i) During exosuit loading (as applied forces increased), about 55% of exosuit end-effector power was absorbed into the interfaces. (ii) However, during subsequent exosuit unloading (as applied forces decreased) most of the absorbed interface power was returned viscoelastically. Consequently, the majority (about 75%) of exosuit end-effector work over each stride contributed to augmenting ankle plantarflexion. (iii) Ankle augmentation power (and work) was delayed relative to exosuit end-effector power, due to these interface energy absorption and return dynamics.
Conclusions Our findings elucidate the complexities of human-exosuit interface dynamics during transmission of power from assistive devices to the human body, and provide insight into improving the design and control of wearable robots. We conclude that in order to optimize the performance of wearable assistive devices it is important, throughout design and evaluation phases, to account for human-device interface dynamics that affect power transmission and thus human augmentation benefits.
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.
When defining requirements for any wearable robot for walking assistance, it is important to maximize the user’s metabolic benefit resulting from the exosuit assistance while limiting the metabolic penalty of carrying the system’s mass. Thus, the aim of this study was to isolate and characterize the relationship between assistance magnitude and the metabolic cost of walking while also examining changes to the wearer’s underlying gait mechanics. The study was performed with a tethered multiarticular soft exosuit during normal walking, where assistance was directly applied at the ankle joint and indirectly at the hip due to a textile architecture. The exosuit controller was designed such that the delivered torque profile at the ankle joint approximated that of the biological torque during normal walking. Seven participants walked on a treadmill at 1.5 meters per second under one unpowered and four powered conditions, where the peak moment applied at the ankle joint was varied from about 10 to 38% of biological ankle moment (equivalent to an applied force of 18.7 to 75.0% of body weight). Results showed that, with increasing exosuit assistance, net metabolic rate continually decreased within the tested range. When maximum assistance was applied, the metabolic rate of walking was reduced by 22.83 ± 3.17% relative to the powered-off condition (mean ± SEM).
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.
Abstract: Flexible endoscopes are still the gold standard in most natural orifice translumenal endoscopic surgery (NOTES) procedures; however their flexibility (necessary for navigating through the GI tract) limits their capabilities in terms of distal manipulation and stability. We propose a deployable endoscopic add-on aimed at locally counteracting forces applied at the tip of an endoscope. We analyze different designs: a fully soft version and two hybrid soft-folded versions. The hybrid designs exploit either an inextensible structure pressurized by a soft actuator or the stiffness provided by the unfolded “magic cube” origami structure. We focus on the fabrication and experimental characterization of the proposed structures and present some preliminary designs and integration strategies to mount them on top of current flexible endoscopes.
‘Snap-On’ robotic modules that can integrate distally with existing commercially-available endoscopic equipment have the potential to provide new capabilities such as enhanced dexterity, bilateral manipulation and feedback sensing with minimal disruption of the current clinical workflow. However, the desire for fully-distal integration of sensors and actuators and the resulting form factor requirements preclude the use of many off-the-shelf actuators capable of generating the relevant strokes and forces required to interact with tools and tissue. In this work, we investigate the use of millimeter-scale, optimally-packed helical shape memory alloy (SMA) actuators in an antagonistic configuration to provide distal actuation without the need for a continuous mechanical coupling to proximal, off-board actuation packages to realize a truly plug-and-play solution. Using phenomenological modeling, we design and fabricate antagonistic helical SMA pairs and implement them in an at-scale roboendoscopic module to generate strokes and forces necessary for deflecting tools passed through the endoscope working port, thereby providing a controllable robotic ‘wrist’ inside the body to otherwise passive flexible tools. Bandwidth is drastically improved through the integration of targeted fluid cooling. The integrated system can generate maximum lateral forces of 10N and demonstrates an additional 96 degrees of distal angulation, expanding the reachable workspace of tools passed through a standard endoscope.