Microorganisms move in challenging environments by periodic changes in body shape. In contrast, current artificial microrobots cannot actively deform, exhibiting at best passive bending under external fields. Here, by taking advantage of the wireless, scalable and spatiotemporally selective capabilities that light allows, we show that soft microrobots consisting of photoactive liquid-crystal elastomers can be driven by structured monochromatic light to perform sophisticated biomimetic motions. We realize continuum yet selectively addressable artificial microswimmers that generate travelling-wave motions to self-propel without external forces or torques, as well as microrobots capable of versatile locomotion behaviours on demand. Both theoretical predictions and experimental results confirm that multiple gaits, mimicking either symplectic or antiplectic metachrony of ciliate protozoa, can be achieved with single microswimmers. The principle of using structured light can be extended to other applications that require microscale actuation with sophisticated spatiotemporal coordination for advanced microrobotic technologies.

/pdf/structured-light-enables-biomimetic-swimming-and-versatile-3stuc2oacn.pdf

Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft 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.

Biomedical Applications of Untethered Mobile Milli/Microrobots

Fabrication of Micro/Nanoscale Motors.

Manipulation and navigation of micro and nanoswimmers in different fluid environments can be achieved by chemicals, external fields, or even motile cells Many researchers have selected magnetic fields as the active external actuation source based on the advantageous features of this actuation strategy such as remote and spatiotemporal control, fuel-free, high degree of reconfigurability, programmability, recyclability, and versatility This review introduces fundamental concepts and advantages of magnetic micro/nanorobots (termed here as "MagRobots") as well as basic knowledge of magnetic fields and magnetic materials, setups for magnetic manipulation, magnetic field configurations, and symmetry-breaking strategies for effective movement These concepts are discussed to describe the interactions between micro/nanorobots and magnetic fields Actuation mechanisms of flagella-inspired MagRobots (ie, corkscrew-like motion and traveling-wave locomotion/ciliary stroke motion) and surface walkers (ie, surface-assisted motion), applications of magnetic fields in other propulsion approaches, and magnetic stimulation of micro/nanorobots beyond motion are provided followed by fabrication techniques for (quasi-)spherical, helical, flexible, wire-like, and biohybrid MagRobots Applications of MagRobots in targeted drug/gene delivery, cell manipulation, minimally invasive surgery, biopsy, biofilm disruption/eradication, imaging-guided delivery/therapy/surgery, pollution removal for environmental remediation, and (bio)sensing are also reviewed Finally, current challenges and future perspectives for the development of magnetically powered miniaturized motors are discussed

Magnetically Driven Micro and Nanorobots

Wireless capsule endoscopy (WCE) can be considered an example of disruptive technology since it represents an appealing alternative to traditional diagnostic techniques. This technology enables inspection of the digestive system without discomfort or need for sedation, thus preventing the risks of conventional endoscopy, and has the potential of encouraging patients to undergo gastrointestinal (GI) tract examinations. However, currently available clinical products are passive devices whose locomotion is driven by natural peristalsis, with the drawback of failing to capture the images of important GI tract regions, since the doctor is unable to control the capsule's motion and orientation. To address these limitations, many research groups are working to develop active locomotion devices that allow capsule endoscopy to be performed in a totally controlled manner. This would enable the doctor to steer the capsule towards interesting pathological areas and to accomplish medical tasks. This review presents a research update on WCE and describes the state of the art of the basic modules of current swallowable devices, together with a perspective on WCE potential for screening, diagnostic, and therapeutic endoscopic procedures.

Capsule Endoscopy: From Current Achievements to Open Challenges

Various types of actuation methods for microrobots have been proposed. Among the actuation methods, electromagnetic based actuation (EMA) has been considered a promising actuation mechanism. In this paper, a new EMA system for three-dimensional (3D) locomotion and drilling of the microrobot is proposed. The proposed system consists of four fixed coil pairs and one rotating coil pair. In detail, the coil system has three pairs of stationary Helmholtz coil, a pair of stationary Maxwell coil and a pair of rotating Maxwell coil. The Helmholtz coil pairs can magnetize and align the microrobot to the desired direction and the two pairs of Maxwell coil can generate the propulsion force of the microrobot. In addition, the Helmholtz coil pairs can rotate the microrobot about a desired axis. The rotation of the microrobot is a drilling action through an occlusion in a vessel. Through various experiments, the 3D locomotion and drilling of the microrobot by using the proposed EMA system are demonstrated. Compared with other EMA systems, the proposed system can provide the advantages of consecutive locomotion and drilling of the microrobot.

/pdf/novel-electromagnetic-actuation-system-for-three-dimensional-4y4k8aicxc.pdf

Novel electromagnetic actuation system for three-dimensional locomotion and drilling of intravascular microrobot

This paper proposes a new two-dimensional (2D) actuation method for a microrobot that uses a stationary two-pair coil system. The coil system actuates the microrobot by controlling the magnitude and direction of the external magnetic flux. The actuation of the microrobot consists of an alignment to the desired direction and a linear movement of the microrobot by non-contact electromagnetic actuation. Firstly, the actuation mechanism of the stationary coil system is theoretically derived and analyzed. Secondly, the tendency of the magnetic flux in the coil system are analyzed and compared by preliminary theoretical analysis. Through various locomotive experiments of the microrobot, the performance of the electromagnetic actuation by the proposed stationary two-pair coil system is evaluated. Using the proposed 2D actuation method, the microrobot is aligned to the desired direction by Helmholtz coils and is driven to the aligned direction by Maxwell coils. By the successive current control of the coil system, the microrobot can move along a desired path, such as a rectangular-shaped or a diamond-shaped path.

Two-dimensional actuation of a microrobot with a stationary two-pair coil system

A new electromagnetic actuation (EMA) method is proposed for 3-dimensional locomotion of a microrobot. Generally, the EMA system uses Helmholtz coils and Maxwell coils. The Helmholtz coil pair generates a uniform magnetic flux density and the Maxwell coil pair generates a uniform gradient magnetic flux. The microrobot can be aligned to the desired direction by the Helmholtz coils and then, be propelled in the aligned direction by the Maxwell coils. However, many previous EMA systems have been restricted to 2-dimensional planar actuation. The EMA system proposed in this paper consists of a pair of stationary Helmholtz–Maxwell coils and a pair of rotational Helmholtz–Maxwell coils. This new EMA system can manipulate a microrobot in 3-dimensional space. For accurate actuation of a microrobot, the gravitational force, which influences the motion of microrobot, has to be analyzed and compensated. Through various experiments, the performance of the proposed EMA system was evaluated. Finally, a microrobot was test-driven in a blood vessel phantom, and the result of the test drive verified the feasibility of 3-dimensional motion of a microrobot by the new EMA system.

Novel electromagnetic actuation (EMA) method for 3-dimensional locomotion of intravascular microrobot

In this paper, we study the locomotion of a microrobot for intravascular therapy. As an intravascular microrobot has to be small, a conventional actuator, such as a micro-motor, and a battery cannot be integrated. To solve this integration problem, we analyze a microrobot with an electromagnetic actuation (EMA) system. Previously, an EMA system using two stationary coil pairs was proposed for the 2-dimensional (D) planar locomotion of a microrobot. The EMA system used two stationary pairs of Helmholtz coils and two stationary pairs of Maxwell coils in the x- and y-direction, respectively. This paper proposes a novel stationary EMA system using two pairs of Helmholtz coils and one pair of Maxwell coils. The 2D locomotion of the microrobot using the proposed EMA system is analyzed and verified by various experiments. The microrobot actuated by the proposed EMA system was able to move in the desired direction on the desired path. The comparison between the proposed EMA system and the previous EMA system showed that the proposed system had an 18% smaller volume and used 91% less coil current for the same actuation force than the previous EMA system. The proposed EMA system produced 2D locomotion of the microrobot, while having a small volume and a lower power consumption than the previous EMA system.

http://iopscience.iop.org/article/10.1088/0964-1726/18/11/115017/pdf

Two-dimensional locomotion of a microrobot with a novel stationary electromagnetic actuation system

https://www.tpbin.com/Uploads/Subjects/8dd640a2-8a6d-4db7-930c-84f907a6782a.pdf

Swimming microrobot actuated by two pairs of Helmholtz coils system

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