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Three-dimensional heterogeneous assembly of coded microgels using an untethered mobile micro gripper

Three-dimensional (3D) heterogeneous assembly of coded microgels in enclosed aquatic environments is demonstrated using a remotely actuated and controlled magnetic microgripper by a customized electromagnetic coil system. The microgripper uses different ‘stick-slip’ and ‘rolling’ locomotion in 2D and also levitation in 3D by magnetic gradient-based pulling force. This enables the microrobot to precisely manipulate each microgel by controlling its position and orientation in all x-y-z directions. Our microrobotic assembly method broke the barrier of limitation on the number of assembled microgel layers, because it enabled precise 3D levitation of the microgripper. We used the gripper to assemble microgels that had been coded with different colours and shapes onto prefabricated polymeric microposts. This eliminates the need for extra secondary cross-linking to fix the final construct. We demonstrated assembly of microgels on a single micropost up to ten layers. By increasing the number and changing the distribution of the posts, complex heterogeneous microsystems were possible to construct in 3D.

Pick and place based 3D mobile micromanipulation in enclosed

liquid environments

Su Eun Chung, Xiaoguang Dong and Metin Sitti, "Three-dimensional heterogeneous assembly of coded microgels using an untethered mobile microgripper" Lab Chip, 2015, Accepted Manuscript DOI: 10.1039/C5LC00009B

Gecko Inspired Directional and Controllable Adhesion

Arrays of gecko-inspired angled polymer microfibers with angled mushroom tips adhere with similar strength to gecko subdigital toe-pads in their gripping direction (∼100 kPa) on smooth surfaces (see image), but are easily released in the opposite direction. Control of adhesion in the normal direction is also possible by controlling drag distance during loading.

Gecko‐Inspired Directional and Controllable Adhesion

MP Murphy, B Aksak, M Sitti

Small 5 (2), 170-175

Gecko Inspired Directional and Controllable Adhesion

Enhanced Adhesion by Gecko-Inspired Hierarchical Fibrillar Adhesives

The complex structures that allow geckos to repeatably adhere to surfaces consist of multilevel branching fibers with specialized tips. We present a novel technique for fabricating similar multilevel structures from polymer materials and demonstrate the fabrication of arrays of two- and three-level structures, wherein each level terminates in flat mushroom-type tips. Adhesion experiments are conducted on two-level fiber arrays on a 12-mm-diameter glass hemisphere, which exhibit both increased adhesion and interface toughness over one-level fiber samples and unstructured control samples. These adhesion enhancements are the result of increased surface conformation as well as increased extension during detachment.

Enhanced adhesion by gecko-inspired hierarchical fibrillar adhesives

MP Murphy, S Kim, M Sitti

ACS applied materials & interfaces 1 (4), 849-855

Mushroom shaped microfibers

Gecko inspired hierarchical fiber

A Novel Water Running Robot Inspired by Basilisk Lizards

Water Running Robot Slow Motion

Water Running Robot Test

This paper introduces a novel robot which can run on the surface of water in a manner similar to basilisk lizards.  Previous studies on the lizards themselves have characterized their method of propulsion and their means of staying afloat. By slapping and stroking their feet into the water, the lizard effects a momentum transfer which provides both forward thrust and lift. The design of a biomimetic robot utilizing similar principles is discussed, modeled, and prototyped. Functionally, the robot uses a pair of identical four bar mechanisms, with a 180deg phase shift to achieve bipedal locomotion on the water’s surface. Computational and experimental results are presented and reviewed with the focus being a maximization of the lift to power ratio. After optimization, two legged models can experimentally provide 12-15 g/W of lift while four legged models can provide 50 g/W of lift. This work opens the door for bipedal and quadrupedal robots to become ambulatory over both land and water, and represents a first step toward studies in amphibious stride patterns; step motions equally conducive to propulsion on water and land.

Water Running Robot Test B

Floyd, Steven, Terence Keegan, John Palmisano, and Metin Sitti. “A Novel Water Running Robot Inspired by Basilisk Lizards.” In IROS, 5430–36, 2006.

Liftoff of a Motor-driven, Flapping Wing Micro Aerial Vehicle Capable of Resonance

This study presents the design of a novel minimalist liftoff-capable flapping-wing microaerial vehicle. Two wings are each directly driven by a geared pager motor by utilizing an elastic element for energy recovery, resulting in a maximum lift-to-weight ratio of 1.4 at 10 Hz for the 2.7 g system. Separate directly driven wings allow the system to both resonate and control individual wing flapping angle, reducing necessary power consumption, as well as allowing the production of roll and pitch body torques. With a series of varied prototypes, system performance is examined with change in wing offset from center of rotation and elastic element stiffness. Prototype liftoff is demonstrated with open loop driving a tethered prototype without guide wires. A dynamic model of the system is adapted and compared with the prototype experimental results for later use in prototype optimization.

L. Hines, D. Campolo, M. Sitti, "Liftoff of a Motor-driven, Flapping Wing Micro Aerial Vehicle Capable of Resonance," IEEE Trans. on Robotics, vol. 30, no. 1, 2014, pp. 220 - 232.

Motor-driven, Flapping Wing Micro Areal Vehicle

Design and rolling locomotion of a magnetically actuated soft capsule endoscope

Magnetic Capsule Endoscope

This paper proposes amagnetically actuated soft capsuled endoscope (MASCE) as a tetherless miniature mobile robot platform for diagnostic and therapeutic medical applications inside the stomach. Two embedded internal permanent magnets and a large external magnet are used to actuate the robot remotely. The proposed MASCE has three novel features. First, its outside body is made of soft elastomer-based compliant structures. Such compliant structures can deform passively during the robot–tissue contact interactions, which makes the device safer and less invasive. Next, it can be actively deformed in the axial direction by using external magnetic actuation, which provides an extra degree of freedom that enables various advanced functions such as axial position control, drug releasing, drug injection, or biopsy. Finally, it navigates in three dimensions by rolling on the stomach surface as a new surface locomotion method inside the stomach. Here, the external attractive magnetic force is used to anchor the robot on a desired location, and the external magnetic torque is used to roll it to another location, which provides a stable, continuous, and controllable motion. The paper presents design and fabrication methods for the compliant structures of the robot with its axial deformation and position control capability. Rolling-based surface locomotion of the robot using external magnetic torques is modeled, and its feasibility is tested and verified on a synthetic stomach surface by using a magnetically actuated capsule endoscope prototype.

S. Yim and M. Sitti, “Design and rolling locomotion of a magnetically actuated soft capsule endoscope,” IEEE Trans. Robotics, vol. 28, no. 1, pp. 183–194, 2012.

This paper proposes a self-assembling soft modular matter, called SoftCubes, where soft-bodied modules are disassembled into a flexible string by an external tension and self-assemble into the preprogrammed three-dimensional (3D) shape. The developed soft modular matter has three main design features. Firstly, entire modules of the 3D shape are serially connected. Such a structure allows all the modules to be disassembled by external tension. Secondly, the outer body of the modules and the connecting parts are made of soft stretchable elastomer. Due to the soft body of the modules, after disassembling, the serially connected modules become a highly flexible and soft string, and have an extreme shape adaptation capability. Also, if the external tension is removed, the preprogrammed 3D shape is recovered by the elastic restoring force of soft-bodied modules. Finally, embedded small permanent magnets induce magnetic self-assembling forces and maintain a mechanical robustness of the 3D shape of module assembly. Due to the magnetic self-assembly, the soft modules are precisely aligned with neighboring modules in a lattice structure. The paper also presents an algorithm to generate the serial connection path of modules for creating a given 3D shape. Various physical interactions between self-assembling module prototypes are visualized in two-dimensional motion tracking experiments. Finally, the shape reconfiguration ability of soft modular matter is demonstrated. SoftCubes is a new class of programmable modular matter where shape memory ability is embedded in the structure, and shows a physical implementation of various 3D shapes with a high resolution and a high scalability.

SoftCubes: Stretchable and self-assembling three-dimensional soft modular matter


S. Yim and M. Sitti, “SoftCubes: Stretchable and self-assembling three-dimensional soft modular matter,” The International Journal of Robotics Research, The International Journal of Robotics Research, vol. 33 no. 8, 2014, pp. 1083-1097.

Continuously Distributed Magnetization Profile for Millimeter-Scale Elastomeric Undulatory Swimming

Soft Microrobots

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 microrobotics applications in biotechnology and healthcare

E. Diller*, J. Zhuang*, G. Lum, M. Edwards, and M. Sitti, "Continuously Distributed Magnetization Profile for Millimeter-Scale Elastomeric Undulatory Swimming," Applied Physics Letters, vol. 104, no. 174101. *equally contributing authors.

Six-Degrees-of-Freedom Remote Actuation of Magnetic Microrobots

Teleoperated star-shaped Mag-μBot

Existing remotely-actuated microrobots powered by magnetic coils far from the workspace exhibit a maximum of only five-degrees-of-freedom (DOF) actuation, as a driving torque about the magnetization axis is not achievable. This lack of orientation control limit the effectiveness of existing microrobots for precision tasks of object manipulation and orientation for advanced medical, biological and micro-manufacturing applications. This paper presents a novel magnetic actuation method that allows these robots to achieve full six-DOF actuation by allowing for a non-uniform magnetization profile within the microrobot body. This non-uniform magnetization results in additional rigid-body torques to be induced from magnetic forces via a moment arm. A general analytical model presents the working principle for continuous and discrete magnetization profiles. Using this model, microrobot design guidelines are introduced which guarantee six-DOF actuation capability. Several discrete magnetization designs which possess reduced coupling between magnetic forces and induced rigid-body torques are also presented. A simple permanent-magnet decoupled prototype is fabricated and used to quantitatively demonstrate the accuracy of the analytical model in a constrained-DOF environment and qualitatively for free motion in a viscous liquid three-dimensional environment. Results show that desired forces and torques can be created with high precision and limited parasitic actuation, allowing for full six-DOF actuation using limited feedback control.

Eric Diller, Joshua Giltinan, Guo Zhan Lum, Zhou Ye, and Metin Sitti, “Six-Degrees-of-Freedom Remote Actuation of Magnetic Microrobots,” Robotics and Science Systems 2014.

Mag-μBot in translation

Modular microrobotic assembly through magnetic actuation and thermal bonding

We present and compare new heat-activated bonding methods for use in modular microrobotic systems. Such modular systems prove to provide on-demand creation of arbitrary micro-scale physical shapes in remote inaccessible spaces. The externally induced heating quickly forms strong bonds on the thermoplastic or solder binding sites integrated into each module face, addressing problems of assembly strength and electrical conductivity.

Modular Microrobotic Assemblies

E. Diller, N. Zhang, and M. Sitti, “Modular microrobotic assembly through magnetic actuation and thermal bonding,” J. Micro-Bio Robot., vol. 8, no. 3–4, pp. 121–131, Nov. 2013.

500 μm Mag-μMods assembling

Magnetically actuated programmable self-assembly

We reported a two-dimensional module reconfiguration based on interactions between microscale magnetic modules. By selective switching the magnetization directions of individual modules, we achieve programmable magnetic pattern formation with three or four modules. This programmable microscale magnetic modules can have potential applications in automatic microfabrication, non-invasive diagnoses, micro-surgery, and drug delivery at unreachable sites.

Experimental video showing the reconfiguration of the assembly of four 500-μm magnetic micro-modules

S Miyashita, E Diller, M Sitti, "Two-dimensional magnetic micro-module reconfigurations based on inter-modular interactions" The International Journal of Robotics Research 32 (5), 591-613


Three-dimensional programmable assembly by untethered magnetic robotic micro-grippers

Mobile sub-millimeter microrobots have demonstrated untethered motion and transport of cargo in remote, confined or enclosed environments. However, limited by simple design and actuation, they lack remotely-actuated on-board mechanisms required to perform complex tasks such as object assembly. A flexible patterned magnetic material which allows internal actuation, resulting in a mobile micro-gripper which is driven and actuated by magnetic fields, is introduced here. By remotely controlling the magnetization direction of each micro-gripper arm, a gripping motion which can be combined with locomotion for precise transport, orientation, and programmable three-dimensional assembly of micro-parts in remote environments is demonstrated. This allows the creation of out-of-plane 3D structures and mechanisms made from several building blocks. Using multiple magnetic materials in each micro-gripper, the addressable actuation of gripper teams for parallel, distributed operation is also demonstrated. These mobile micro-grippers can potentially be applied to 3D assembly of heterogeneous meta-materials, construction of medical devices inside the human body, the study of biological systems in micro-fluidic channels, 3D micro-device prototyping or desktop micro-factories.

Assembly of 3D four-bar linkage

E. Diller and M. Sitti, “Three-dimensional programmable assembly by untethered magnetic robotic micro-grippers,” Adv. Funct. Mater., vol. 24, no. 28, pp. 4397–4404, Jul. 2014.

Untethered microrobotic coding of three-dimensional material composition

A method is used to code complex materials in three-dimensions with tunable structural, morphological and chemical features using an untethered magnetic microrobot remotely controlled by magnetic fields. This strategy allows the microrobot 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.

S. Tasoglu, E. Diller, S. Guven, et al., “Untethered microrobotic coding of three-dimensional material composition,” Nat. Commun., vol. 5, p. 3124, Jan. 2014.

Microrobotic coding of a heterogeneous structure

Dynamic trapping and two-dimensional transport of swimming microorganisms using a rotating magnetic microrobot

Manipulation of microorganisms with intrinsic motility is a challenging yet important task for many biological and biomedical applications. Currently, such a task has only been accomplished using optical tweezers, while at the risk of averse heating and photodamage of the biological samples. Here, we proposed a new microrobotic approach for fluidic trapping and two-dimensional transportation of motile microorganisms near a solid surface in fluids. We demonstrated selective trapping and transportation of individual freely swimming multi-flagellated bacteria over a distance of 30 μm (7.5 body length of the carrier) on a surface, using the rotational flows locally induced by a rotating magnetic microparticle. Only a weak uniform magnetic field (<3 mT) was applied to actuate the microparticle. The microparticle can translate on a glass substrate by rotating at a speed of up to 100 μm s−1, while providing a fluidic force of a few to tens of pico-Newtons.

Transport of Swimming Microorganisms

Z. Ye and M. Sitti, “Dynamic trapping and two-dimensional transport of swimming microorganisms using a rotating magnetic microrobot”, Lab on Chip 14, 2177-2182.

Chemotactic Steering of Bacteria Propelled Microbeads

Flagellated bacteria have been embraced by the microrobotics community as a highly efficient microscale actuation method, capable of converting chemical energy into mechanical actuation for microsystems that require a small payload and high rate of actuation. Along with being highly motile, Serratia marcescens (S. marcescens), our bacterium species of interest, is a highly agile biomotor capable of being steered via chemotaxis. In this paper, we attached S. marcescens bacteria to polystyrene microbeads towards creating biohybrid that can propel themselves towards an attractive chemical source. Using a three-channel microfluidic device, linear chemical gradients are generated to compare the behavior of bacteria-propelled beads in the presence and absence of a chemoattractant, L-aspartate. We tested and compared the behavior of three different bacteria-attached bead sizes (5, 10 and 20 μm diameter) using a visual particle-tracking algorithm, and noted their behavioral differences. The results indicate that in the presence of a chemoattractant, the S. marcescens-attached polystyrene beads exhibit a clear indication of directionality and steering control through the coordination of the bacteria present on each bead. This directionality is observed in all bead size cases, suggesting potential for targeted payload delivery using such a biohybrid microrobotic approach.

Bacteria Propelled Microbeads (2012)

D. Kim, A. Liu, E. Diller, and M. Sitti, "Chemotactic Steering of Bacteria Propelled Microbeads," Biomed Microdevices 14, 1009-17, Dec 2012.

Bacterial Flagella-Based Propulsion and On/Off Motion Control of Microscale Objects

Miniaturization of the power source and on-board actuation is the main bottleneck for the development of microscale mobile robots. As a possible solution, this letter proposes the use of flagellar motors inside the intact cell of Serratia marcescensbacteria for controlled propulsion of swimming robotic bodies. The feasibility of the proposed idea is demonstrated by propelling 10μm polystyrene beads at an average speed of 15±6μm∕s  by several bacteria randomly attached on their surface. On/off motion control of the bead is achieved by introducing copper ions to stop the bacteria flagellar motors and ethylenediaminetetraacetic acid to resume their motion.

Polystyrene (PS) microbead propelled by attached bacteria  (2007)

B. Behkam and M. Sitti, "Bacterial Flagella-Based Propulsion and On/Off Motion Control of Microscale Objects," Applied Physics Letters, vol. 90, pp. 23902-23904, 14 Jan. 2007. Also appeared on the Virtual Journal of Nanoscale Science & Technology, vol. 15, no. 2, January 15, 2007.

Swimming robot traveling through viscous fluid

Swimming millirobot  (2005)

World Science Festival, Sitti talks

Working at a small scale has big challenges. Nanoroboticist Metin Sitti designs and builds microscopic robots that can venture into the human body. What does it take to build tiny robots? Will this advancing nanotechnology revolutionize medicine?

How Do You Make a Nanobot?

The Nanorobot Surgeon You Can Swallow

Waalbot II: Adhesion Recovery and Improved Performance of a Climbing Robot using Fibrillar Adhesives

This paper presents the design and optimization of a wall-climbing robot along with the incorporation of autonomous adhesion recovery and a motion planning implementation. The result is Waalbot II, an untethered 85 g robot able to climb on smooth vertical surfaces with up to a 100 g payload (117% body mass) or, when unburdened, on planar surfaces of any orientation at speeds up to 5 cm/s. Bio-inspired climbing mechanisms, such as Waalbot II’s gecko-like fibrillar adhesives, passive peeling, and force sensing, improve the overall climbing capabilities compared with initial versions, resulting in the ability to climb on non-smooth surfaces as well as on inverted smooth surfaces. Robot length scale optimization reveals and quantifies trends in the theoretical factor of safety and payload carrying capabilities. Autonomous adhesion recovery behavior provides additional climbing robustness without additional mechanical complexity to mitigate degradation and contamination. An implementation of a motion planner, designed to take into account Waalbot II’s kinematic constraints, results in the ability to navigate to a goal in complex three-dimensional environments while properly planning plane-to-plane transitions and avoiding obstacles. Experiments verified the improved climbing capabilities of Waalbot II as well as its novel semi-autonomous adhesion recovery behavior and motion planning.

Waalbot-II, IJRR, 2011

MP Murphy, C Kute, Y Mengüç, M Sitti, "Waalbot II: adhesion recovery and improved performance of a climbing robot using fibrillar adhesives" The International Journal of Robotics Research 30 (1), 118-133



Gecko Manipulator

Gecko-inspired angled elastomer micropillars with flat or round tip endings are presented as compliant pick-and-place micromanipulators. The pillars are 35 μm in diameter, 90 μm tall, and angled at an inclination of 20°. By gently pressing the tip of a pillar to a part, the pillar adheres to it through intermolecular forces. Next, by retracting quickly, the part is picked from a given donor substrate. During transferring, the adhesion between the pillar and the part is high enough to withstand disturbances due to external forces or the weight of the part. During release of the part onto a receiver substrate, the contact area of the pillar to the part is drastically reduced by controlled vertical or shear displacement, which results in reduced adhesive forces. The maximum repeatable ratio of pick-to-release adhesive forces is measured as 39 to 1. It is found that a flat tip shape and shear displacement control provide a higher pick-to-release adhesion ratio than a round tip and vertical displacement control, respectively. A model of forces to serve as a framework for the operation of this micromanipulator is presented. Finally, demonstrations of pick-and-place manipulation of micrometer-scale silicon microplatelets and a centimeter-scale glass cover slip serve as proofs of the concept. The compliant polymer micropillars are safe for use with fragile parts, and, due to exploiting intermolecular forces, could be effective on most materials and in air, vacuum, and liquid environments.

Gecko adhesive for pick and place of a fragile object

Y Mengüç, SY Yang, S Kim, JA Rogers, M Sitti, "Gecko‐Inspired Controllable Adhesive Structures Applied to Micromanipulation", Advanced Functional Materials 22 (6), 1245-1245



Gecko adhesive integrated to a humanoid robot finger

Gecko adhesive strip attached to one of the fingers of the Humanoid Robot enables the robot hand to turn book pages by attachment and detachment. Such adhesive fingers will change the robotic manipulation methods drastically!

Gecko adhesive for a Humanoid Robot to turn book pages


In this paper we propose a tank-like climbing robot, called Tankbot, using flat (non-patterned) and soft elastomer adhesive treads. This wheeled climbing robot design enables continuous, vibration-free, and strong attachment to wide range of smooth and rough surfaces, relatively fast and smooth motion, and improved capability to traverse obstacles and to carry high payloads. Tankbot is lightweight (60–150 g) and can climb on any slope from 0° to 360° on smooth surfaces. Moreover, climbing vertically up, down, and laterally on relatively rough surfaces, such as a wooden door, a painted wall, and a brick wall, is also possible. A passive or active tail is added to Tankbot to transfer the peeling force to the front wheel and to assist for transitioning to different surface slopes. It is shown that the normal component of the peeling force with respect to the surface is crucial and has to be maximized to maximize the climbing stability. Moreover, it is demonstrated that the tread tension should be in a specific range to maximize the normal peeling force. With the aid of the derived models, different Tankbot prototypes with different body and tread dimensions are manufactured and tested for different tasks. It is shown that a 115 g Tankbot can carry up to 300 g on a regular painted wall. Tankbot can go over obstacles of up to 16 mm in diameter, perform both internal and external vertical wall to ceiling transitions, steer in two dimensions with a minimum turning diameter of 80 cm, and loiter on painted walls for up to 5 min.

Overview of TankBot Capabilities

O Unver, M Sitti, "Tankbot: A palm-size, tank-like climbing robot using soft elastomer adhesive treads" The International Journal of Robotics Research, 0278364910380759


Waal-E : Wheeled Climbing Robot Using Bio-Inspired Fibrillar Adhesive

Wheel climbing robot using gecko-liked adhesive

Water walking (strider) robot

Recent biological studies on water strider insects revealed how they maintain stability and maneuver on the surface of water. While macroscale bodies use buoyancy, these very small insects use surface tension force to balance their weight on water. This paper proposes a biologically inspired miniature robot that utilizes the unique scaling advantage of these insects. The paper focuses on understanding the physics of the interaction between the insect and the surface of water and on designing a robot that mimics their key features. Hydrophobic Teflon coated wire legs optimized to take the most advantage of the surface tension force are used to support the weight of the 1-g robot. It is shown that twelve of these legs can support up to 9.3 g of payload. A T-shape actuation mechanism with three piezoelectric unimorph actuators is designed and studied to enable controlled locomotion. Static and dynamic properties of the robot are analyzed and compared with the experimental results. The tethered robot can successfully make both linear and rotational motions. Maximum forward speed is measured to be 3 cm/s, and the rotational speed is 0.5 rad/s. This robot proposes a new way of locomotion on water surface for future robots and devices.

Water walking (strider) robot

YS Song, M Sitti,"Surface-tension-driven biologically inspired water strider robots: Theory and experiments", Robotics, IEEE Transactions on 23 (3), 578-589