Single-to-four core optical fiber coupling using a two-photon polymerization produced waveguide.

Optical coupling between single core to multi-core optical fibers usually takes place by means of optical fiber fan-ins / fan-outs, delicate free space optics, or laser inscribed freeform waveguides. In the present work, the two-photon polymerization technique is used for the first time to create a waveguide manifold on top of a four-core optical fiber tip as a means to couple light into and from a single core optical fiber, in a fast and low-cost fashion. It is demonstrated that the performance is influenced by the numerical aperture mismatch between the fabricated and the coupled waveguides. Insertion losses below 5 dB are observed when the numerical aperture mismatch is minimized, with further reduction potential, making this approach applicable to sensing or tweezer applications.

A Soft-Bodied Aerial Robot for Collision Resilience and Contact-Reactive Perching.

Current aerial robots demonstrate limited interaction capabilities in unstructured environments when compared with their biological counterparts. Some examples include their inability to tolerate collisions and to successfully land or perch on objects of unknown shapes, sizes, and texture. Efforts to include compliance have introduced designs that incorporate external mechanical impact protection at the cost of reduced agility and flight time due to the added weight. In this work, we propose and develop a lightweight, inflatable, soft-bodied aerial robot (SoBAR) that can pneumatically vary its body stiffness to achieve intrinsic collision resilience. Unlike the conventional rigid aerial robots, SoBAR successfully demonstrates its ability to repeatedly endure and recover from collisions in various directions, not only limited to in-plane ones. Furthermore, we exploit its capabilities to demonstrate perching where the three-dimensional collision resilience helps in improving the perching success rates. We also augment SoBAR with a novel hybrid fabric-based bistable (HFB) grasper that can utilize impact energies to perform contact-reactive grasping through rapid shape conforming abilities. We exhaustively study and offer insights into the collision resilience, impact absorption, and manipulation capabilities of SoBAR with the HFB grasper. Finally, we compare the performance of conventional aerial robots with the SoBAR through collision characterizations, grasping identifications, and experimental validations of collision resilience and perching in various scenarios and on differently shaped objects.

Design, Development, and Control of a Fabric-Based Soft Ankle Module to Mimic Human Ankle Stiffness.

This paper investigates the design of a robotic fabric-based, soft ankle module capable of generating 50% of the human ankle stiffness, in plantarflexion and dorsiflexion for walking. Kinematics, dynamics, and anatomy of the human ankle joint are studied to set the functional requirements of the module. The design of the compliant and lightweight soft ankle module uses fabric-based inflatable actuator arrays for actuation. Models for the human ankle stiffness, as well as a data-driven model of soft ankle module is presented. A high-level stiffness controller utilizing the human ankle and soft ankle model with a low-level pressure controller is implemented. We demonstrate the ability to closely follow the ankle stiffness trajectory using soft ankle module.

Soft Poly-Limbs: Toward a New Paradigm of Mobile Manipulation for Daily Living Tasks.

We present the design and development of the fluid-driven, wearable, Soft Poly-Limb (SPL), from the Greek word polys, meaning many. The SPL utilizes the numerous traits of soft robotics to enable a novel approach in providing safe and compliant mobile manipulation assistance to healthy and impaired users. This wearable system equips the user with a controllable additional limb that is capable of complex three-dimensional motion in space. Similar to an elephant trunk, the SPL is able to manipulate objects using a variety of end effectors, such as suction adhesion or a soft grasper, as well as its entire soft body to conform around an object, able to lift 2.35 times its own weight. To develop these highly articulated soft robotic limbs, we provide a novel set of systematic design rules, obtained through varying geometrical parameters of the SPL through experimentally verified finite element method models. We investigate performance of the limb by testing the lifetime of the new SPL actuators, evaluating its payload capacity, operational workspace, and capability of interacting close to a user through a spatial mobility test. Furthermore, we are able to demonstrate limb controllability through multiple user-intent detection modalities. Finally, we explore the limb's ability to assist in multitasking and pick and place scenarios with varying mounting locations of the SPL around the user's body. Our results highlight the SPL's ability to safely interact with the user while demonstrating promising performance in assisting with a wide variety of tasks, in both work and general living settings.

A Soft-Inflatable Exosuit for Knee Rehabilitation: Assisting Swing Phase During Walking.

In this paper, we present a soft-inflatable exosuit to assist knee extension during gait training for stroke rehabilitation. The soft exosuit is designed to provide 25% of the knee moment required during the swing phase of the gait cycle and is integrated with inertial measurement units (IMUs) and smart shoe insole sensors to improve gait phase detection and controller design. The stiffness of the knee joint during level walking is computed using inverse dynamics. The soft-inflatable actuators, with an I cross-section, are mechanically characterized at varying angles to enable generation of the required stiffness outputs. A linear relation between the inflatable actuator stiffness and internal pressure as a function of the knee angle is obtained, and a two-layer stiffness controller is implemented to assist the knee joint by providing appropriate stiffness during the swing phase. Finally, to evaluate the ability of the exosuit to assist in swing motion, surface-electromyography (sEMG) sensors are placed on the three muscle groups of the quadriceps and two groups of the hamstrings, on three healthy participants. A reduction in muscle activity of the rectus femoris, vastus lateralis, and vastus medialis is observed, which demonstrates feasibility of operation and potential future usage of the soft inflatable exosuit by impaired users.

A light-reflecting balloon catheter for atraumatic tissue defect repair.

A congenital or iatrogenic tissue defect often requires closure by open surgery or metallic components that can erode tissue. Biodegradable, hydrophobic light-activated adhesives represent an attractive alternative to sutures, but lack a specifically designed minimally invasive delivery tool, which limits their clinical translation. We developed a multifunctional, catheter-based technology with no implantable rigid components that functions by unfolding an adhesive-loaded elastic patch and deploying a double-balloon design to stabilize and apply pressure to the patch against the tissue defect site. The device uses a fiber-optic system and reflective metallic coating to uniformly disperse ultraviolet light for adhesive activation. Using this device, we demonstrate closure on the distal side of a defect in porcine abdominal wall, stomach, and heart tissue ex vivo. The catheter was further evaluated as a potential tool for tissue closure in vivo in rat heart and abdomen and as a perventricular tool for closure of a challenging cardiac septal defect in a large animal (porcine) model. Patches attached to the heart and abdominal wall with the device showed similar inflammatory response as sutures, with 100% small animal survival, indicating safety. In the large animal model, a ventricular septal defect in a beating heart was reduced to <1.6 mm. This new therapeutic platform has utility in a range of clinical scenarios that warrant minimally invasive and atraumatic repair of hard-to-reach defects.

MRI-compatible intensity-modulated force sensor for cardiac catheterization procedures.

This paper presents a novel, magnetic resonance imaging (MRI)-compatible, force sensor suitable for cardiac catheterization procedures. The miniature, fiber-optic sensor is integrated with the tip of a catheter to allow the detection of interaction forces with the cardiac walls. The optical fiber light intensity is modulated when a force acting at the catheter tip deforms an elastic element, which, in turn, varies the distance between a reflector and the optical fiber. The tip sensor has an external diameter of 9 Fr (3 mm) and can be used during cardiac catheterization procedures. The sensor is able to measure forces in the range of 0-0.85 N, with relatively small hysteresis. A nonlinear method for calibration is used and real-time MRI in vivo experiments are carried out, to prove the feasibility of this low-cost sensor, enabling the detection of catheter-tip contact forces under dynamic conditions.

A fibre-optic catheter-tip force sensor with MRI compatibility: a feasibility study.

This paper presents the development of a low-cost, Magnetic Resonance Imaging (MRI) compatible fibre-optic sensor for integration with catheters allowing the detection of contact forces between blood vessel walls and the catheter tip. Three plastic optical-fibres are aligned inside a plastic catheter in a circular pattern. A reflector is attached to a separate small part of the catheter tip, which is connected with a small deformable material to the aligned optical-fibres. In this manner a force at the catheter tip leads to a deformation of the elastic material and thus a modulation of the light yields, this is sent and received through the optical-fibres. An electronic circuit amplifies the retrieved light signal and the output voltage is used to classify the forces on the tip. The materials used are of the shelf and have a low magnetic susceptibility making this sensor fully MRI-compatible and inexpensive. Preliminary, experimental results demonstrated good force linearity in static loading and unloading conditions. The sensor was also tested in an artificial blood artery showing good dynamic response.