Eric D. Diller

Biomedical Applications of Untethered Mobile Milli/Microrobots

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.

Untethered micro-robotic coding of three-dimensional material composition

Complex functional materials with three-dimensional micro- or nano-scale dynamic compositional features are prevalent in nature. However, the generation of three-dimensional functional materials composed of both soft and rigid microstructures, each programmed by shape and composition, is still an unsolved challenge. Herein, we describe a method to code complex materials in three-dimensions with tunable structural, morphological, and chemical features using an untethered magnetic micro-robot remotely controlled by magnetic fields. This strategy allows the micro-robot to be introduced to arbitrary microfluidic environments for remote two- and three-dimensional manipulation. We demonstrate the coding of soft hydrogels, rigid copper bars, polystyrene beads, and silicon chiplets into three-dimensional heterogeneous structures. We also use coded microstructures for bottom-up tissue engineering by generating cell-encapsulating constructs.

Independent control of multiple magnetic microrobots in three dimensions

A major challenge for untethered microscale mobile robotics is the control of many agents in the same workspace for distributed operation. In this work, we present a new method to independently control multiple sub-mm microrobots in three dimensions (3D) using magnetic gradient pulling as the 3D motion generation method. Motion differentiation is accomplished through the use of geometrically or magnetically distinct microrobots which assume different magnetization directions in a rotating or oscillating magnetic field. This allows for different magnetic forces to be exerted on each, enabling independent motion control and path following of multiple microrobots along arbitrary 3D trajectories. Path following in 3D with less than 310 μ m mean error is shown for a set of two microrobots of size 350 μ m and 1500 μ m, and independent motions are shown with three microrobots. It is also shown that control of more microrobots could be possible using improved magnetic coil hardware. Microrobot diversity is analyzed with regards to the effect on independent control. The proposed addressability method could be used for the 3D control of a team of microrobots inside microfluidic channels or in the human body for localized therapy or diagnostics.

Control of Multiple Heterogeneous Magnetic Microrobots in Two Dimensions on Nonspecialized Surfaces

In this paper, we propose methods to control multiple untethered magnetic microrobots (called Mag-μBots), with all dimensions under 1 mm, without the need for a specialized surface. We investigate sets of Mag-μBots that are geometrically designed to respond uniquely to the same applied magnetic fields. By controlling the magnetic field waveforms, individual and subgroups of Mag-μBots are able to locomote in a parallel but dissimilar fashion. The control of geometrically dissimilar Mag-μBots and a group of identically fabricated Mag-μBots are investigated, and control strategies are developed for 1-D and 2-D motion. This is accomplished by learning the velocity response of each microrobot to various control signals and using the uniqueness of each microrobot response to achieve independent control. The effect of high-level control parameters are investigated in simulation and in experiments, and the simultaneous independent global positioning of two and three microrobots is demonstrated in 2-D space. As this control method is accomplished without the use of a specialized surface, it has potential applications in areas such as microfluidic systems and biomanipulation.

Two-Dimensional Autonomous Microparticle Manipulation Strategies for Magnetic Microrobots in Fluidic Environments

This study develops autonomous manipulation strategies for a mobile untethered microrobot that operates on a 2-D surface in a fluidic environment. The microrobot, which is a permanent magnet, is under m in all dimensions and is actuated by oscillating external magnetic fields. Two types of manipulations are considered: 1) front pushing, where the microrobot pushes a micro-object by direct contact; and 2) side pushing, which can result in noncontact pushing, where the fluid flow fields that are generated by a translating microrobot are used to displace a micro-object. Physical models are provided to estimate the displacement of the micro-object due to the fluid motion. Model-based controllers to perform contact and noncontact manipulation are proposed, which iteratively correct emerging manipulation behaviors to improve performance. It is found that using a model-based solution as a feed-forward input, which is combined with a learning controller, can significantly improve micro-object pushing performance. Finally, we begin to address the problem to assemble two micro-objects together using the microrobot, which is only successful by using a side-pushing method.

Micro-Scale Mobile Robotics

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.

Assembly and disassembly of magnetic mobile micro-robots towards deterministic 2-D reconfigurable micro-systems

A primary challenge in the field of reconfigurable robotics is scaling down the size of individual robotic modules. We present a novel set of permanent magnet modules that are under 1 mm in all dimensions, called Mag-µMods, for use in a reconfigurable micro-system. The modules are actuated by oscillating external magnetic fields of several mT in strength, and are capable of locomoting on a 2-D surface. Multiple modules are controlled by using an electrostatic anchoring surface, which can selectively prevent specific modules from being driven by the external field while allowing others to move freely. We address the challenges of both assembling and disassembling two modules. Assembly is performed by bringing two modules sufficiently close that their magnetic attraction causes them to combine. Disassembly is performed by electrostatically anchoring one module to the surface, and applying magnetic torques from external sources to separate the unanchored module.

Control methodologies for a heterogeneous group of untethered magnetic micro-robots

In this work, we develop methods for controlling multiple untethered magnetic micro-robots (Mag-µBots) without the need for a specialized substrate. We investigate Mag-µBots that are geometrically and magnetically designed to respond uniquely to the same input magnetic fields. Designs include: (1) geometrically similar Mag-µBots with different values of magnetization; (2) geometrically dissimilar Mag-µBots with similar magnetization; and (3) geometrically dissimilar Mag-µBots with dissimilar magnetization. The responses of both magnetically hard and soft Mag-µBots are investigated. By controlling the input magnetic fields, individual and sub-groups of Mag-µBots are able to locomote in a parallel fashion. Specifically, the magnitude and frequency of the imposed driving magnetic fields are used as selection methods among the Mag-µBots. Various methods for accomplishing motion discrimination are discussed, modeled, and tested. It is found that while fully decoupled control is not possible with this method, parallel actuation of sub-groups of Mag-µBots is possible and controllable.

Continuously distributed magnetization profile for millimeter-scale elastomeric undulatory swimming

We have developed a millimeter-scale magnetically driven swimming robot for untethered motion at mid to low Reynolds numbers. The robot is propelled by continuous undulatory deformation, which is enabled by the distributed magnetization profile of a flexible sheet. We demonstrate control of a prototype device and measure deformation and speed as a function of magnetic field strength and frequency. Experimental results are compared with simple magnetoelastic and fluid propulsion models. The presented mechanism provides an efficient remote actuation method at the millimeter scale that may be suitable for further scaling down in size for micro-robotics applications in biotechnology and healthcare.

Micro-manipulation using rotational fluid flows induced by remote magnetic micro-manipulators

We present a non-contact manipulation method for micron scale objects using locally induced rotational fluid flows created by groups of untethered magnetic micro-manipulators. The magnetic micro-manipulators are rotated in a viscous fluid by an externally generated magnetic field to create rotational flows, which act to move micro-objects in the flow region. One single spherical micro-manipulator is used to manipulate one object at a time, while an array of micro-manipulators spin in synchrony on a surface patterned with magnetic micro-docks to create reconfigurable fluidic channels for simultaneous transportation of multiple objects. The induced rotational flow field and the resulting hydrodynamic forces on the micro-objects are studied using both finite element solutions and analytical models from previous studies. These results are compared with experiment to determine manipulation characteristics for the complex flows. Due to its untethered and non-contact operation, this micro-manipulation method cou...