Biomedical Micro‐/Nanomotors: From Overcoming Biological Barriers to In Vivo Imaging

Abstract

Self‐propelled micro‐ and nanomotors (MNMs) have shown great potential for applications in the biomedical field, such as active targeted delivery, detoxification, minimally invasive diagnostics, and nanosurgery, owing to their tiny size, autonomous motion, and navigation capacities. To enter the clinic, biomedical MNMs request the biodegradability of their manufacturing materials, the biocompatibility of chemical fuels or externally physical fields, the capability of overcoming various biological barriers (e.g., biofouling, blood flow, blood–brain barrier, cell membrane), and the in vivo visual positioning for autonomous navigation. Herein, the recent advances of synthetic MNMs in overcoming biological barriers and in vivo motion‐tracking imaging techniques are highlighted. The challenges and future research priorities are also addressed. With continued attention and innovation, it is believed that, in the future, biomedical MNMs will pave the way to improve the targeted drug delivery efficiency.

Medical Micro/Nanorobots in Precision Medicine

“…[370][371][372] A key aspect for medical micro/nanorobotic translation in the clinic will rely on individual or population monitoring, with consideration of tissue background signal. [373] In this direction, micro/nanorobots could benefit the current medical imaging modalities, as they could be easily localized and guided inside the body, and even send signals to induce triggered release. Current conventional medical imaging techniques study organ and tissue physiology, and more recently, track the distribution of molecular imaging agents and nanoparticles inside a patient's body.…”

A Journey of Nanomotors for Targeted Cancer Therapy: Principles, Challenges, and a Critical Review of the State‐of‐the‐Art

“…To close this section, and to direct readers to sources of information beyond this current review, we list the following excellent review articles on nanomotors for biomedical applications, on the topics of 1) overall overviews, [36,[72][73][74][75] 2) drug delivery/cargo transportation, [32,34,38,40,[76][77][78][79][80][81] 3) diagnosis, [82] 4) sensing, [77][78][79]83] 5) in vivo applications, [34,[84][85][86] 6) surface coating, [87] 7) cancer therapy, [33,37,88,89] 8) biocompatibility, [66] 9) biological barriers/complex environment/entering a cell [39,[90][91][92] and 10) imaging, [90,93,94] as well as on particular types of nanomotors for biomedical application, such as those made of hydrogel [95] or those powered by magnetic fields. [96] This list of review articles-a total of 35 and counting-is by no means comprehensive, and only covers the period of 2013-2020 (see the book by Prof. Joseph Wang [7] for pre-2013 reviews).…”

“…Finally, a nanomotor that actively navigates through a maze of blood vessels in search of its target requires some sort of imaging technique to either confirm it is on the correct path, or to provide visual guidance for the human operator to steer the motor. Several techniques have been applied to image and track nanomotors in real time, [90] such as fluorescent imaging, [23,137,138] ultrasound imaging, [139,140] magnetic resonance imaging, [141] photoacoustic computed imaging, [21] and radionuclide imaging. [142] Because a single nanomotor is much smaller than the resolution of any of current medical imaging technologies, recent focus in this front is on imaging 1) a swarm of nanomotors, [29,143] 2) motors that are much larger than nano-or micrometer scales, or 3) motors that amplify the imaging signals with bubbles or photoacoustic agents (see ref.…”

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

“…In recent years, in addition to studying individual m‐bots, the motion control of swarms has also been widely studied as they offer several advantages for practical biomedical applications. [ 41–43 ] First, swarm motion and control of m‐bots are promising for the delivery of large doses of drugs, cargo materials, or cells, as well as energy such as the heat based on photothermal conversion and magnetic thermal conversion. Second, the swarming pattern may, as an entity, provide much better imaging contrast than that provided by individual agents at the micro‐ or nanoscale due to the accumulative effect, thereby facilitating the localization.…”