Inspired by highly efficient natural motors, synthetic micro/nanomotors are self-propelled machines capable of converting the supplied fuel into mechanical motion A significant advance has been made in the construction of diverse motors over the last decade These synthetic motor systems, with rapid transporting and efficient cargo towing abilities, are expected to open up new horizons for various applications Utilizing emergent motor platforms for in vivo applications is one important aspect receiving growing interest as conventional therapeutic methodology still remains limited for cancer, heart, or vasculature diseases In this review we will highlight the recent efforts towards realistic in vivo application of various motor systems With ever booming research enthusiasm in this field and increasing multidisciplinary cooperation, micro/nanomotors with integrated multifunctionality and selectivity are on their way to revolutionize clinical practice

Micro/nanomotors towards in vivo application: cell, tissue and biofluid.

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

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3D Printed Enzymatically Biodegradable Soft Helical Microswimmers

Micro-/nanorobots (m-bots) have attracted significant interest due to their suitability for applications in biomedical engineering and environmental remediation. Particularly, their applications in in vivo diagnosis and intervention have been the focus of extensive research in recent years with various clinical imaging techniques being applied for localization and tracking. The successful integration of well-designed m-bots with surface functionalization, remote actuation systems, and imaging techniques becomes the crucial step toward biomedical applications, especially for the in vivo uses. This review thus addresses four different aspects of biomedical m-bots: design/fabrication, functionalization, actuation, and localization. The biomedical applications of the m-bots in diagnosis, sensing, microsurgery, targeted drug/cell delivery, thrombus ablation, and wound healing are reviewed from these viewpoints. The developed biomedical m-bot systems are comprehensively compared and evaluated based on their characteristics. The current challenges and the directions of future research in this field are summarized.

Trends in Micro-/Nanorobotics: Materials Development, Actuation, Localization, and System Integration for Biomedical Applications.

Magnetocatalytic hybrid Janus micromotors encapsulating phenylboronic acid (PABA) modified graphene quantum dots (GQDs) are described herein as ultrafast sensors for the detection of deadly bacteria endotoxins. A bottom-up approach was adopted to synthesize an oil-in-water emulsion containing the GQDs along with a high loading of platinum and iron oxide nanoparticles on one side of the Janus micromotor body. The two different "active regions" enable highly efficient propulsion in the presence of hydrogen peroxide or magnetic actuation without the addition of a chemical fuel. Fluorescence quenching was observed upon the interaction of GQDs with the target endotoxin (LPS), whereby the PABA tags acted as highly specific recognition receptors of the LPS core polysaccharide region. Such adaptive hybrid operation and highly specific detection hold considerable promise for diverse clinical, agrofood, and biological applications and integration in future lab-on-chip technology.

Magnetocatalytic Graphene Quantum Dots Janus Micromotors for Bacterial Endotoxin Detection.

Current wound sealing systems such as nanoparticle-based gluing of tissues allow almost immediate wound sealing. The assistance of a laser beam allows the wound sealing with higher controllability due to the collagen fiber melting which is defined by loss of tertiary protein structure and restoration upon cooling. Usually one employs dyes to paint onto the wound, if water absorption bands are absent. In case of strong bleeding or internal wounds such applications are not feasible due to low welding depth in case of water absorption bands, dyes washing off, or the dyes becoming diluted within the wound. One possible solution of these drawbacks is to use autonomously movable particles composing of biocompatible gold and magnetite nanoparticles and biocompatible polyelectrolyte complexes. In this paper a proof of principle study is presented on the utilization of thermophoretic Janus particles and capsules employed as dyes for infrared laser-assisted tissue welding. This approach proves to be efficient in sealing the wound on the mouse in vivo. The temperature measurement of single particle level proves successful photothermal heating, while the mechanical characterizations of welded liver, skin, and meat confirm mechanical restoration of the welded biological samples.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201600206

Guidable Thermophoretic Janus Micromotors Containing Gold Nanocolorifiers for Infrared Laser Assisted Tissue Welding

Self-Propelled Rolled-Up Polyelectrolyte Multilayer Microrockets

This communication sheds light on the production method and motion patterns of autonomous moving bubble propelled two dimensional micro-plate motors. The plate motors are produced by the well-known layer-by-layer self-assembly process in combination with micro-contact printing. The motion analysis covers instances of oscillating bubble development on one or more nucleation sites, which influence the motion speed and direction.

Self-propelled two dimensional polymer multilayer plate micromotors

Cell transport is important to renew body functions and organs with stem cells, or to attack cancer cells with immune cells. The main hindrances of this method are the lack of understanding of cell motion as well as proper transport systems. In this publication, bubble-propelled polyelectrolyte microplates are used for controlled transport and guidance of HeLa cells. Cells survive attachment on the microplates and up to 22 min in 5% hydrogen peroxide solution. They can be guided by a magnetic field whereby increased friction of cells attached to microplates decreases the speed by 90% compared to pristine microplates. The motion direction of the cell-motor system is easier to predict due to the cell being opposite to the bubbles.

Narisu Hu

Papers

Guidable Thermophoretic Janus Micromotors Containing Gold Nanocolorifiers for Infrared Laser Assisted Tissue Welding

Self-Propelled Rolled-Up Polyelectrolyte Multilayer Microrockets

Self-propelled two dimensional polymer multilayer plate micromotors

Forecastable and Guidable Bubble-Propelled Microplate Motors for Cell Transport.

Magnetically Actuated Rolling of Star‐Shaped Hydrogel Microswimmer