Untethered robots miniaturized to the length scale of millimeter and below attract growing attention for the prospect of transforming many aspects of health care and bioengineering. As the robot size goes down to the order of a single cell, previously inaccessible body sites would become available for high-resolution in situ and in vivo manipulations. This unprecedented direct access would enable an extensive range of minimally invasive medical operations. Here, we provide a comprehensive review of the current advances in biomedical untethered mobile milli/microrobots. We put a special emphasis on the potential impacts of biomedical microrobots in the near future. Finally, we discuss the existing challenges and emerging concepts associated with designing such a miniaturized robot for operation inside a biological environment for biomedical applications.

Biomedical Applications of Untethered Mobile Milli/Microrobots

Flexible magnetic small-scale robots use patterned magnetization to achieve fast transformation into complex three-dimensional (3D) shapes and thereby achieve locomotion capabilities and functions. These capabilities address current challenges for microrobots in drug delivery, object manipulation, and minimally invasive procedures. However, possible microrobot designs are limited by the existing methods for patterning magnetic particles in flexible materials. Here, we report a method for patterning hard magnetic microparticles in an elastomer matrix. This method, based on ultraviolet (UV) lithography, uses controlled reorientation of magnetic particles and selective exposure to UV light to encode magnetic particles in planar materials with arbitrary 3D orientation with a geometrical feature size as small as 100 micrometers. Multiple planar microrobots with various sizes, different geometries, and arbitrary magnetization profiles can be fabricated from a single precursor in one process. Moreover, a 3D magnetization profile allows higher-order and multi-axis bending, large-angle bending, and combined bending and torsion in one sheet of polymer, creating previously unachievable shape changes and microrobotic locomotion mechanisms such as multi-arm power grasping and multi-legged paddle crawling. A physics-based model is also presented as a design tool to predict the shape changes under magnetic actuation.

Millimeter-scale flexible robots with programmable three-dimensional magnetization and motions

The field of microrobotics has seen tremendous advances in recent years. The principles governing the design of such submillimeter scale robots rely on an understanding of microscale physics, fabrication, and novel control strategies. This monograph provides a tutorial on the relevant physical phenomena governing the operation and design of microrobots, as well as a survey of existing approaches to microrobot design and control. It also provides a detailed practical overview of actuation and control methods that are commonly used to remotely power these designs, as well as a discussion of possible future research directions. Potential high-impact applications of untethered microrobots such as minimally invasive diagnosis and treatment inside the human body, biological studies or bioengineering, microfluidics, desktop micromanufacturing, and mobile sensor networks for environmental and health monitoring are reported.

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Micro-Scale Mobile Robotics

Robots the size of several microns have numerous application in medicine, biology, and manufacturing. However, simultaneous control of multiple robots at this scale is difficult since the robot itself is too small to carry power, sensors, communication, and control on-board. In this paper, we have summarized different approaches, ranging from specialized robot design and fabrication to specialized ways of actuating robots, with the aim of independent control of a team/swarm of microrobots. We have also discussed the challenges for each approach. In the light of the challenges, we have proposed some directions where the future researchers can focus in order to solve the problem of independent control of a team of microrobots.

Controlling multiple microrobots: recent progress and future challenges

In this paper, we introduce an indirect pushing based technique for automated micromanipulation of biological cells. In indirect pushing, an optically trapped glass bead pushes a freely diffusing intermediate bead that in turn pushes a freely diffusing target cell towards a desired goal. Some cells can undergo significant changes in their behaviors as a result of direct exposure to a laser beam. Indirect pushing eliminates this problem by minimizing the exposure of the cell to the laser beam. We report an automated feedback planning algorithm that combines three motion maneuvers, namely, push, align, and backup for micromanipulation of cells. We have developed a dynamics based simulation model of indirect pushing dynamics and also identified parameters of measurement noise using physical experiments. We present an optimization-based approach for automated tuning of planner parameters to enhance its robustness. Finally, we have tested the developed planner using our optical tweezers physical setup and carried out a detailed analysis of the experimental results. The developed approach can be utilized in biological experiments for studying collective cell migration by accurately arranging the cells in arrays without exposing them to a laser beam.

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Indirect pushing based automated micromanipulation of biological cells using optical tweezers

Magnetic principles have proved successful for untethered submillimeter microrobotics, although challenges still exist in areas of propulsion and control. This paper presents the design, analysis, and performance results for a bimorph thin film magnetic microrobot utilizing the magnetostrictive principle as a secondary oscillating operation mode. The microrobot is no larger than 580 µm in its planar dimension and its total thickness is less than 5 µm. As a robot with magnetic material, it can be operated in a pushing/pulling mode in orthogonal directions for movement in a plane, while it's powered with an external magnetic field as low as 1 mT. For the secondary oscillating operation mode utilizing the magnetostrictive principle, in-plane strain is induced, resulting in bending and blocking forces on the robot. These forces are theoretically calculated to prove enough drive force can be generated in this mode. The design is further abstracted and translated into a piezoelectric cantilever FEM model to confirm the theorectical results. Microrobot fabrication and test-bed development based on this analysis is shown, which enabled us to participate in the final competition in the 2010 NIST Mobile Microrobot Challenge, with good performance in the dash and freestyle events. Finally, we discuss the testing results in various dry and fluid environments along with recommendations for future investigation and improvements. Keywords: microrobot, magnetostrictive, bimorph

http://multiscalerobotics.org/wp-content/uploads/2014/09/AMagneticThinFilmMicrorobotwithTwoOperatingModes-p1119.pdf

A magnetic thin film microrobot with two operating modes

In this paper, we present a novel approach to micromanipulation and assembly tasks using caging micro-manipulation motion primitives for 2D and 3D autonomous micromanipulation and assembly tasks. A flexible, multi-scale test-bed, developed for use in conjunction with these primitives, is described first. The approach and motion primitives are then discussed. An autonomous micromanipulation and assembly task is described and manipulation plans using the methodology are generated and experimentally executed. The autonomous task shows promising results with a success rate of 93% for 27 individual micro-assembly experiments.

Towards flexible, automated microassembly with caging micromanipulation

In this paper, we demonstrate a systematic way to determine configurations for up to four coordinated micro-manipulators to form caging grasps for transporting micro-scale planar, polygonal parts. We exploit the geometry of the part, noting the presence and location of convex corners and non-convex corners, and form opposing force equivalents with the micromanipulator probe tips around the micro-scale parts that define a caging polygon. We perform an error bound analysis for caging grasps derived in this manner and provide theoretical values of this bound for four micro-parts of interest. We demonstrate experimental results of the caging micromanipulation transport primitive using these feature-defined grasps and compare them with the expected error bounds. Finally, we combine this caging transport primitive along with rotational and one-sided-pushing motion primitives, to carry out a representative microassembly task.

http://multiscalerobotics.org/wp-content/uploads/2014/09/Caging-Grasps-for-Micromanipulation-and-Microassembly-IROS2011.pdf

Caging grasps for micromanipulation & microassembly

In this paper we demonstrate coordinated control of multiple micromanipulators for use in 2D and 3D micromanipulation tasks. We develop a feature-defined (FD) micro-caging transport primitive for 2D micromanipulation and use a similar methodology to extend it to the 3D case. Simultaneous movements of the coordinated micromanipulators allow for both 2D planar micro-caging grasps and micro-force closure grasps suitable for 3D micro-transporting tasks. Experimental results illustrate the success and accuracies of both the 2D and 3D methodologies. The new transport primitives are used in conjunction with our previous micromanipulation primitives and coordinated XY stage movements to semi-autonomously execute a number of representative 2D and 3D micromanipulation tasks.

Caging for 2D and 3D micromanipulation

In this paper we demonstrate coordinated control of multiple micromanipulators for use in automated 3D micromanipulation and assembly tasks. We build on our previous work on caging micromanipulation by using a similar methodology and extend it to the 3D case. Simultaneous movements of the coordinated micromanipulators normal to the caging polygon allows for the transition of 2D planar micro-caging grasps to micro-force closure grasps suitable for 3D micro-transporting tasks. Experimental results illustrate the success and accuracies of both the micro-grasps’ transitions and 3D pick-and-place tasks. Finally, the new 3D transportation primitive is used in conjunction with our previous 2D micromanipulation primitives and an encoded XY stage to semi-autonomously execute some representative 3D microassembly tasks.© 2012 ASME

http://multiscalerobotics.org/wp-content/uploads/2014/09/DETC2012-71436.pdf

Zhenbo Fu

Papers

A magnetic thin film microrobot with two operating modes

Towards flexible, automated microassembly with caging micromanipulation

Caging grasps for micromanipulation & microassembly

Caging for 2D and 3D micromanipulation

Cooperative Micromanipulators for 3D Micromanipulation and Assembly