Untethered microtools that can be precisely navigated into deep in vivo locations are important for clinical procedures pertinent to minimally invasive surgery and targeted drug delivery. In this mini-review, untethered soft grippers are discussed, with an emphasis on a class of autonomous stimuli-responsive gripping soft tools that can be used to excise tissues and release drugs in a controlled manner. The grippers are composed of polymers and hydrogels and are thus compliant to soft tissues. They can be navigated using magnetic fields and controlled by robotic path-planning strategies to carry out tasks like pick-and-place of microspheres and biological materials either with user assistance, or in a fully autonomous manner. It is envisioned that the use of these untethered soft grippers will translate from laboratory experiments to clinical scenarios and the challenges that need to be overcome to make this transition are discussed.

Independent control of microrobots is a cardinal challenge for manipulation at micro/nano scale. In this paper, we design and assemble an electromagnetic setup to overcome some of the major obstacles in the independent control of microrobots. The demanding magnetic requirements are met by the presented experimental testbed that is able to produce magnetic fields and gradients of, respectively, 160 mT and 3.6 T/m at the center of the workspace. Through the design process of this testbed, we analyze the importance of design parameters and derive a quantitative analysis of the requirements for the dissipation of the generated heat. Further, we present and develop the model and software infrastructure, capable of running at 25 Hz, necessary for independent control of multiple microrobots. We also introduce two novel techniques for current-minimizing mapping of the desired forces into currents at the electromagnet. Finally, the capabilities of the setup are demonstrated through independent control of two, both identical and nonidentical, soft-magnetic microspheres in three-dimensional space-with average root mean square errors of 102 µm and peak velocities of up to 331 µm/s.

Automated steering of endovascular catheters has a potential of improving the outcome of minimally invasive surgical procedures. Nevertheless, actuation, tracking, and closed-loop position control of catheters remain a challenge. In this study, we present a modular framework for a three-dimensional (3-D) position control of magnetically actuated endovascular catheter. The catheter is fitted with a permanent magnet and deflected using externally generated magnetic field provided by BigMag-An array of mobile electromagnets. Pseudorigid-body modeling is used to formulate an inverse-model closed-loop position controller of the catheter. The shape feedback is reconstructed from a 3-D point cloud of catheter silhouette, obtained using stereo vision. Magnetic actuation is enabled using an inverse field map technique, mapping the reference magnetic field to BigMag configuration variables. The framework is tested in a series of experiments. The inverse map is validated, showing a mean magnetic field error of 2.20%. The accuracy of the shape reconstruction algorithm is 0.59 mm. Finally, the magnetically actuated catheter is steered across a series of trajectories with maximum reported catheter deflection of 68.43 • and maximum tip speed of 5 mm/s. Across all trajectories, the best control performance metrics are the mean error of 0.57 mm and the RMS error of 0.77 mm.

Abstract-The flying hand is a robotic hand consisting of a swarm of UAVs able to grasp an object where each UAV contributes to the grasping task with a single contact point at the tooltip. The swarm of robots is teleoperated by a human hand whose fingertip motions are tracked, e.g., using an RGB-D camera. We solve the kinematic dissimilarity of this unique master-slave system using a multi-layered approach that includes: a hand interpreter that translates the fingertip motion in a desired motion for the object to be manipulated; a mapping algorithm that transforms the desired object motions into a suitable set of virtual points deviating from the planned contact points; a compliant force control for the case of quadrotor UAVs that allows to use them as indirect 3D force effectors. Visual feedback is also used as sensory substitution technique to provide a hint on the internal forces exerted on the object. We validate the approach with several human-inthe-loop simulations including the full physical model of the object, contact points and UAVs.

The use of small, maneuverable, untethered and reconfigurable robots could provide numerous advantages in various micromanipulation tasks. Examples include microassembly, pick-and-place of fragile micro-objects for lab-on-a-chip applications, assisted hatching for in-vitro fertilization and minimally invasive surgery. This study assesses the potential of soft untethered magnetic grippers as alternatives or complements to conventional tethered or rigid micromanipulators. We demonstrate closed-loop control of untethered grippers and automated pick-and-place of biological material on porcine tissue in an unstructured environment. We also demonstrate the ability of the soft grippers to recognize and sort non-biological micro-scale objects. The fully autonomous nature of the experiments is made possible by the integration of planning and decision-making algorithms, as well as by closed-loop temperature and electromagnetic motion control. The grippers are capable of completing pick-and-place tasks of biological material at an average velocity of 1.8 ±0.71 mm/s and a drop-off error of 0.62 ±0.22 mm. Color-sensitive sorting of three micro-scale objects is completed at a velocity of 1.21 ±0.68 mm/s and a drop-off error of 0.85 ±0.41 mm. Our findings suggest that improved autonomous untethered grippers could augment the capabilities of current soft-robotic instruments especially in advancedtasks involving manipulation.