Publications
The research of Dong Lab will focus on three aspects:
The design, manufacture and control of miniature soft robots, and their applications in minimally invasive medicine, biomechanics and microfluidics.
The design, manufacture and control of miniature swarm robots, and their applications in biomedicine and biomechanics.
The modeling, design, manufacture and control of intelligent soft materials and devices based on mechanics model and machine learning.
For previous publications, please visit Google Scholar. For selective publications, please see follows.
Minimally Invasive Medical Devices
Keywords: Bioinspired structures, bioelectronics, sensors, actuators
Wirelessly Actuated Microfluidic Pump and Valve for Controlled Liquid Delivery in Dental Implants
Xu, Y#., Lin, H.#, Xiao, B., Tanoto, H., Berinstein, J., Khoshnaw, A., Young, S., Zhou, Y.* and Dong, X.*, 2024. Wirelessly Actuated Microfluidic Pump and Valve for Controlled Liquid Delivery in Dental Implants. Advanced Healthcare Materials, p.2402373. Link
Enabling minimally invasive and precise control of liquid release in dental implants is crucial for therapeutic functions such as delivering antibiotics to prevent biofilm formation, infusing stem cells to promote osseointegration, and administering other biomedicines. However, achieving controllable liquid cargo release in dental implants remains challenging due to the lack of wireless and miniaturized fluidic control mechanisms. Here wireless miniature pumps and valves that allow remote activation of liquid cargo delivery in dental implants, actuated and controlled by external magnetic fields (<65 mT), are reported. A magnet-screw mechanism in a fluidic channel to function as a piston pump, alongside a flexible magnetic valve designed to open and close the fluidic channel, is proposed. The mechanisms are showcased by storing and releasing of liquid up to 52 µL in a dental implant. The liquid cargos are delivered directly to the implant–bone interface, a region traditionally difficult to access. On-demand liquid delivery is further showed by a metal implant inside both dental phantoms and porcine jawbones. The mechanisms are promising for controllable liquid release after implant placement with minimal invasion, paving the way for implantable devices that enable long-term and targeted delivery of therapeutic agents in various bioengineering applications.
Wireless Peristaltic Pump for Transporting Viscous Fluids and Solid Cargos in Confined Spaces
Sharma, S., Jung, L.C., Lee, N., Wang, Y., Kirk‐Jadric, A., Naik, R. and Dong, X., 2024. Wireless Peristaltic Pump for Transporting Viscous Fluids and Solid Cargos in Confined Spaces. Advanced Functional Materials, p.2405865. Link
The transport of fluids and solids is a vital process inside the human body, facilitated by the wave-like motion in the lumen called peristalsis. However, peristalsis may be compromised due to tumor growth, resulting in difficulties in lumen motility. The dysmotility of the human lumen can result in blockages and pose numerous challenges, including aspiration in the lungs and reproductive issues in the female oviduct. Restoring peristalsis in medical devices, such as medical stents, can prevent device blockage and promote effective transport. Here, a wirelessly actuated soft robotic undulating pump designed to efficiently transport both viscous fluidic and solid cargos is proposed. The kinematics of the single sheet and the coordination between pairs are systematically designed to generate undulation and peristalsis, enabling the pumping of both liquids and solids. The integration of the undulating pump is demonstrated onto an esophageal stent. The same undulating motion-based pumping mechanism can be adapted for usage in other organs, such as the female oviduct, thereby offering potential applications for treating lumen dysmotility in various diseases. The proposed wirelessly actuated robotic pumping mechanism holds promise in facilitating diverse implantable medical devices aimed at treating diseases characterized by impaired peristalsis and dysmotility.
Wirelessly Actuated Ciliary Airway Stent for Excessive Mucus Transportation
Wang, Y., Sharma, S., Maldonado, F. and Dong, X., Wirelessly Actuated Ciliary Airway Stent for Excessive Mucus Transportation. Advanced Materials Technologies, p.2301003. Link, Cover
Small-scale cilia-like devices that can manipulate fluids in narrow spaces have great potential in microfluidics, biomechanics, biomedical engineering, and other applications. However, prior studies mostly focus on artificial cilia for pumping fluids in lab-on-a-chip microfluidic applications. The design and control of artificial cilia for transporting viscous mucus in confined and tubular structures remain challenging and medical devices such as airway stents with ciliary function are still missing. Herein, a method is reported that enables integrating artificial cilia arrays on 3D curved surfaces and an airway ciliary stent is presented for excessive mucus transportation. The method allows encoding bioinspired non-reciprocal motion and metachronal waves for efficient fluid pumping in tubular structures. The method also introduces a lubricant hydrogel coating layer on artificial cilia inspired by the periciliary layer in airway cilia, which further enhances viscous fluid transportation. It is demonstrated that a novel ciliary airway stent can transport viscous porcine mucus in a lung phantom even faster than the respiratory cilia in a healthy human lung. The methods of designing, integrating, and controlling artificial cilia on 3D curved surfaces thus enable the unprecedented function of removing excessive mucus beyond traditional airway stents for treating various lung diseases in a minimally invasive manner.
Artificial cilia with integrated sensors for sensing fluidic cues
Han, J.#, Dong, X.#,*, Yin, Z., Zhang, S., Li, M., Zheng, Z., Ugurlu, M.C., Jiang, W., Liu, H. and Sitti, M.*, 2023. Actuation-enhanced multifunctional sensing and information recognition by magnetic artificial cilia arrays. Proceedings of the National Academy of Sciences, 120(42), p.e2308301120. (# Co-first, * Corresponding), Link
Abstract: Artificial cilia integrating both actuation and sensing functions allow simultaneously sensing environmental properties and manipulating fluids in situ, which are promising for environment monitoring and fluidic applications. However, existing artificial cilia have limited ability to sense environmental cues in fluid flows that have versatile information encoded. This limits their potential to work in complex and dynamic fluid-filled environments. Here, we propose a generic actuation-enhanced sensing mechanism to sense complex environmental cues through the active interaction between artificial cilia and the surrounding fluidic environments. The proposed mechanism is based on fluid–cilia interaction by integrating soft robotic artificial cilia with flexible sensors. With a machine learning-based approach, complex environmental cues such as liquid viscosity, environment boundaries, and distributed fluid flows of a wide range of velocities can be sensed, which is beyond the capability of existing artificial cilia. As a proof of concept, we implement this mechanism on magnetically actuated cilia with integrated laser-induced graphene-based sensors and demonstrate sensing fluid apparent viscosity, environment boundaries, and fluid flow speed with a reconfigurable sensitivity and range. The same principle could be potentially applied to other soft robotic systems integrating other actuation and sensing modalities for diverse environmental and fluidic applications.
Artificial cilia for biofluid pumping and studying biomechanics
Dong, X.#, Lum, G.Z.#, Hu, W.#, Zhang, R., Ren, Z., Onck, P.R. and Sitti, M.*, 2020. Bioinspired cilia arrays with programmable nonreciprocal motion and metachronal coordination. Science advances, 6(45), p.eabc9323. Link
Coordinated nonreciprocal dynamics in biological cilia is essential to many living systems, where the emergentmetachronal waves of cilia have been hypothesized to enhance net fluid flows at low Reynolds numbers (Re). Experimental investigation of this hypothesis is critical but remains challenging. Here, we report soft miniature devices with both ciliary nonreciprocal motion and metachronal coordination and use them to investigate the quantitative relationship between metachronal coordination and the induced fluid flow. We found that only antiplectic metachronal waves with specific wave vectors could enhance fluid flows compared with the synchronized case. These findings further enable various bioinspired cilia arrays with unique functionalities of pumping and mixing viscous synthetic and biological complex fluids at low Re. Our design method and developed soft miniature devices provide unprecedented opportunities for studying ciliary biomechanics and creating cilia-inspired wireless microfluidic pumping, object manipulation and lab- and organ-on-a-chip devices, mobile microrobots, and bioengineering systems.
Wireless Medical Miniature Robots
Keywords: Droplet robots, drug delivery, robotic capsule endoscopes, magnetic actuation and localization
Wireless miniature soft robots for sensing mucus properties
Xiao, B., Xu, Y., Edwards, S., Blakumar, L. and Dong, X., 2023. Sensing Mucus Physiological Property In Situ by Wireless Millimeter‐Scale Soft Robots. Advanced Functional Materials, p.2307751. Link
The physiological property of mucus is an important biomarker for monitoring the human health conditions and helping understand disease development, as mucus property such as viscosity is highly correlated with inflammation and other diseases. However, it remains challenging to sense mucus viscosity using pure medical imaging. Collecting and analyzing mucus sample in vitro using flexible endoscopes and capsule endoscope robots is also challenging due to their difficulty of accessing very confined, tortuous, and small spaces, and the sample may not reflect the real mucus property. Here a novel method is proposed to enable sensing mucus viscosity in situ by wireless miniature sensors actuated by magnetic fields and tracked by medical imaging. These miniature viscosity sensors can be delivered with minimal invasion using a novel sensor delivery mechanism by controlling a magnetically actuated millimeter-scale soft climbing robot. As the soft robot can access confined and narrow spaces, and reliably deploy the sensor on soft tissue surfaces, multiple sensors can be delivered on soft biological tissues to sense biofluid viscosity spatiotemporally. The proposed minimally invasive robotic delivery and viscosity sensing method thus paves the way toward sensing biofluid properties deep inside the body for future disease monitoring and early diagnosis functions.
Wireless miniature soft robots for sensing tissue properties
Wang, C.#, Wu, Y.#, Dong, X.#,*, Armacki, M. and Sitti, M.*, 2023. In situ sensing physiological properties of biological tissues using wireless miniature soft robots. Science advances, 9(23), p.eadg3988. Link. (#, Co-first, * Co-responding)
Implanted electronic sensors, compared with conventional medical imaging, allow monitoring of advanced physiological properties of soft biological tissues continuously, such as adhesion, pH, viscoelasticity, and biomarkers for disease diagnosis. However, they are typically invasive, requiring being deployed by surgery, and frequently cause inflammation. Here we propose a minimally invasive method of using wireless miniature soft robots to in situ sense the physiological properties of tissues. By controlling robot-tissue interaction using external magnetic fields, visualized by medical imaging, we can recover tissue properties precisely from the robot shape and magnetic fields. We demonstrate that the robot can traverse tissues with multimodal locomotion and sense the adhesion, pH, and viscoelasticity on porcine and mice gastrointestinal tissues ex vivo, tracked by x-ray or ultrasound imaging. With the unprecedented capability of sensing tissue physiological properties with minimal invasion and high resolution deep inside our body, this technology can potentially enable critical applications in both basic research and clinical practice.
Wireless soft climbing robots with omnidirectional steerability for drug delivery
Y Xu#, B Xiao#, L Balakumar, KL Obstein, X Dong*, IEEE Robotics and Automation Letters, 08, 2023. Link.
Wirelessly actuated miniature soft robots actuated by magnetic fields that can overcome gravity by climbing soft and wet tissues are promising for accessing challenging enclosed and confined spaces with minimal invasion for targeted medical operation. However, existing designs lack the directional steerability to traverse complex terrains and perform agile medical operations. Here we propose a rod-shaped millimeter-size climbing robot that can be omnidirectionally steered with a steering angle up to 360 degrees during climbing beyond existing soft miniature robots. The design innovation includes the rod-shaped robot body, its special magnetization profile, and the spherical robot footpads, allowing directional bending of the body under external magnetic fields and out-of-plane motion of the body for delivery of medical patches. With further integrated bio-adhesives and microstructures on the footpads, we experimentally demonstrated inverted climbing of the robot on porcine gastrointestinal (GI) tract tissues and deployment of a medical patch for targeted drug delivery.
Wireless soft climbing robots for drug delivery
Y. Wu#, X. Dong#, J. Kim#, C. Wang, M. Sitti*, “Wireless soft millirobots for climbing three-dimensional surfaces in confined spaces”, Science Advances, 8, eabn3431 (2022). Link.
Wireless soft-bodied robots at the millimeter-scale allow traversing very confined unstructured terrains with minimal invasion and safely interacting with the surrounding environment. However, existing untethered soft millirobots still lack the ability of climbing, reversible controlled surface adhesion, and long-term retention on unstructured three-dimensional (3D) surfaces, limiting their use in biomedical and environmental applications. Here we report a fundamental peeling-and-loading mechanism to allow untethered soft-bodied robots to climb 3D surfaces, by utilizing both the soft-body deformation and whole-body motion of the robot under external magnetic fields. This generic mechanism is implemented with different adhesive robot footpad designs, allowing vertical and inverted surface climbing on diverse 3D surfaces with complex geometries and different surface properties. With the unique robot footpad designs by integrating microstructured adhesives and tough bioadhesives, the soft climbing robot could achieve controllable adhesion and friction to climb 3D soft and wet surfaces including porcine tissues, which paves the way for future environmental inspection and minimally invasive medicine applications.
Magnetically actuated endoscopes for GI tract medical operation
Son, D., Dong, X. and Sitti, M.*, 2018. A simultaneous calibration method for magnetic robot localization and actuation systems. IEEE Transactions on Robotics, 35(2), pp.343-352. link
This paper proposes a method of simultaneously calibrating magnetic localization and actuation systems for magnetically actuated robots. In this method, uncalibrated magnetic localization and actuation systems are calibrated simultaneously with minimal human intervention, which enables self-calibration, flexible reconfiguration, and long-term correctness of the system parameters. This method employs a bundle adjustment framework using a quadratic measurement model for sensors and the magnetic dipole model for actuators. The proposed method has been verified in comparison with finite element simulations and existing calibration methods for magnetic actuators and sensor arrays. In the experiments, the determinant of coefficient (R2 value) was 99.84% for the sensor system and 99.45% for the actuator system after the calibration, comparable with individual state-of-art calibration methods of calibrating magnetic actuators and sensor arrays. This method has potential to improve the reconfigurability and long-term accuracy of magnetic robot localization and actuation systems, such as magnetically actuated capsule endoscopes.
Bioinspired Soft Robots
Keywords: soft robots, bioinspiration, biomechanics, swimming robots, fluidic manipulation
Design methodology of magnetic soft robots
Lum, G.Z.#, Ye, Z.#, Dong, X.#, Marvi, H., Erin, O., Hu, W. and Sitti, M.*, 2016. Shape-programmable magnetic soft matter. Proceedings of the National Academy of Sciences, 113(41), pp.E6007-E6015. Link
At small scales, shape-programmable magnetic materials have significant potential to achieve mechanical functionalities that are unattainable by traditional miniature machines. Unfortunately, these materials have only been programmed for a small number of specific applications, as previous work can only rely on human intuition to approximate the required magnetization profile and actuating magnetic fields for such materials. Here, we propose a universal programming methodology that can automatically generate the desired magnetization profile and actuating fields for soft materials to achieve new time-varying shapes. The proposed method can enable other researchers to fully capitalize the potential of shape-programming technologies, allowing them to create a wide range of novel soft active surfaces and devices that are critical in robotics, material science, and medicine.
Bio-inspired swimming robots
Ren, Z.#, Hu, W.#, Dong, X. and Sitti, M., 2019. Multi-functional soft-bodied jellyfish-like swimming. Nature communications, 10(1), pp.1-12. Link
The functionalities of the untethered miniature swimming robots significantly decrease as the robot size becomes smaller, due to limitations of feasible miniaturized on-board components. Here we propose an untethered jellyfish-inspired soft millirobot that could realize multiple functionalities in moderate Reynolds number by producing diverse controlled fluidic flows around its body using its magnetic composite elastomer lappets, which are actuated by an external oscillating magnetic field. We particularly investigate the interaction between the robot’s soft body and incurred fluidic flows due to the robot’s body motion, and utilize such physical interaction to achieve different predation-inspired object manipulation tasks. The proposed lappet kinematics can inspire other existing jellyfish-like robots to achieve similar functionalities at the same length and time scale. Moreover, the robotic platform could be used to study the impacts of the morphology and kinematics changing in ephyra jellyfish.
Droplet soft robots with extreme deformation
Fan, X.#, Dong, X.#, Karacakol, A.C., Xie, H. and Sitti, M.*, 2020. Reconfigurable multifunctional ferrofluid droplet robots. Proceedings of the National Academy of Sciences, 117(45), pp.27916-27926. Link
Magnetically actuated miniature soft robots are capable of programmable deformations for multimodal locomotion and manipulation functions, potentially enabling direct access to currently unreachable or difficult-to-access regions inside the human body for minimally invasive medical operations. However, magnetic miniature soft robots are so far mostly based on elastomers, where their limited deformability prevents them from navigating inside clustered and very constrained environments, such as squeezing through narrow crevices much smaller than the robot size. Moreover, their functionalities are currently restricted by their predesigned shapes, which is challenging to be reconfigured in situ in enclosed spaces.
Here, we report a method to actuate and control ferrofluid droplets as shape-programmable magnetic miniature soft robots, which can navigate in two dimensions through narrow channels much smaller than their sizes thanks to their liquid properties. By controlling the external magnetic fields spatiotemporally, these droplet robots can also be reconfigured to exhibit multiple functionalities, including on-demand splitting and merging for delivering liquid cargos and morphing into different shapes for efficient and versatile manipulation of delicate objects. In addition, a single-droplet robot can be controlled to split into multiple subdroplets and complete cooperative tasks, such as working as a programmable fluidic-mixing device for addressable and sequential mixing of different liquids. Due to their extreme deformability, in situ reconfigurability and cooperative behavior, the proposed ferrofluid droplet robots could open up a wide range of unprecedented functionalities for lab/organ-on-a-chip, fluidics, bioengineering, and medical device applications.
Swarm Microrobots
Keywords: control, collective motion, cooperative behaviors
Reconfigurable and cooperative swarms
Dong, X. and Sitti, M.*, 2020. Controlling two-dimensional collective formation and cooperative behavior of magnetic microrobot swarms. The International Journal of Robotics Research, 39(5), pp.617-638. Link
Magnetically actuated mobile microrobots can access distant, enclosed, and small spaces, such as inside microfluidic channels and the human body, making them appealing for minimally invasive tasks. Despite their simplicity when scaling down, creating collective microrobots that can work closely and cooperatively, as well as reconfigure their formations for different tasks, would significantly enhance their capabilities such as manipulation of objects. However, a challenge of realizing such cooperative magnetic microrobots is to program and reconfigure their formations and collective motions with under-actuated control signals. This article presents a method of controlling 2D static and time-varying formations among collective self-repelling ferromagnetic microrobots (100 μm to 350 μm in diameter, up to 260 in number) by spatially and temporally programming an external magnetic potential energy distribution at the air–water interface or on solid surfaces. A general design method is introduced to program external magnetic potential energy using ferromagnets. A predictive model of the collective system is also presented to predict the formation and guide the design procedure. With the proposed method, versatile complex static formations are experimentally demonstrated and the programmability and scaling effects of formations are analyzed. We also demonstrate the collective mobility of these magnetic microrobots by controlling them to exhibit bio-inspired collective behaviors such as aggregation, directional motion with arbitrary swarm headings, and rotational swarming motion. Finally, the functions of the produced microrobotic swarm are demonstrated by controlling them to navigate through cluttered environments and complete reconfigurable cooperative manipulation tasks.
Microrobots for Manipulation
Keywords: soft microgrippers, control and motion planning, 3D assseembly, tissue engineering
3D dexterous manipulation
Chung, S.E.#, Dong, X.# and Sitti, M.*, 2015. Three-dimensional heterogeneous assembly of coded microgels using an untethered mobile microgripper. Lab on a Chip, 15(7), pp.1667-1676. Link
Abstract: 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.
Motion planning for automatic grasping
Dong, X. and Sitti, M.*, 2017, May. Planning spin-walking locomotion for automatic grasping of microobjects by an untethered magnetic microgripper. In 2017 IEEE International Conference on Robotics and Automation (ICRA) (pp. 6612-6618). IEEE. Link
Most demonstrated mobile microrobot tasks so far have been achieved via pick-and-placing and dynamic trapping with teleoperation or simple path following algorithms. In our previous work, an untethered magnetic microgripper has been developed which has advanced functions, such as gripping objects. Both teleoperated manipulation in 2D and 3D have been demonstrated. However, it is challenging to control the magnetic microgripper to carry out manipulation tasks, because the grasping of objects so far in the literature relies heavily on teleoperation, which takes several minutes with even a skilled human expert. Here, we propose a new spin-walking locomotion and an automated 2D grasping motion planner for the microgripper, which enables time-efficient automatic grasping of microobjects that has not been achieved yet for untethered microrobots. In its locomotion, the microgripper repeatedly rotates about two principal axes to regulate its pose and move precisely on a surface. The motion planner could plan different motion primitives for grasping and compensate the uncertainties in the motion by learning the uncertainties and planning accordingly. We experimentally demonstrated that, using the proposed method, the microgripper could align to the target pose with error less than 0.1 body length and grip the objects within 40 seconds. Our method could significantly improve the time efficiency of micro-scale manipulation and have potential applications in microassembly and biomedical engineering.