External Field‐Driven Untethered Microrobots for Targeted Cargo Delivery

Abstract

Untethered microrobots (UMRs) propelled by multiple external power sources have emerged as promising tools for biomedical applications, such as targeted cargo delivery (TCD), microsurgery, thrombolysis, medical imaging, etc. In particular, owing to their minimal invasiveness and capability of accessing hard‐to‐reach regions of the human body in a controllable manner, the application of UMRs for TCD is of great interest in recent years. Here, the state‐of‐the‐art UMRs in this regard are presented, focused on targeted drug and cell delivery systems. Meanwhile, this review systematically details recent research studies on the use of UMRs in TCD, containing their constituent materials (functional, scaffold, and smart materials), fabrication methods, and three types of external propulsion energy sources concerning their mechanisms and corresponding typical designs. Subsequently, various strategies for controlled drug release are summarized, as well as the latest targeted cell delivery systems and relevant cell manipulation in vitro or in ex vivo. Finally, the current challenges to clinical translation faced by the UMRs and future perspectives on this field are highlighted.

Acoustic Trapping and Manipulation of Hollow Microparticles under Fluid Flow Using a Single-Lens Focused Ultrasound Transducer

“…Furthermore, like other solid microparticles, hollow microparticles have the advantage of high-throughput fabrication and versatile chemical modification capabilities, such as surface coating, 36,60 drug loading, 61,62 and cargo attachment. 63 These drug-loaded microparticles can be trapped with submillimeter accuracy in proximity to diseased tissue and then release the drugs through a series of ultrasound pulses. Additionally, the buoyancy of these hollow microparticles can be adjusted to match the medium in which they are immersed, which eliminates the issue of sedimentation and makes their manipulation with acoustics more manageable.…”

“…As ultrasound agents, these hollow microparticles not only provide high contrast for deep tissue imaging but also can form stable aggregates at specific locations and be manipulated within the circulatory system while under fluid flow. Furthermore, like other solid microparticles, hollow microparticles have the advantage of high-throughput fabrication and versatile chemical modification capabilities, such as surface coating, , drug loading, , and cargo attachment . These drug-loaded microparticles can be trapped with submillimeter accuracy in proximity to diseased tissue and then release the drugs through a series of ultrasound pulses.…”

Dynamically reversible cooperation and interaction of multiple rotating micromotors

“…There is great interest in developing and designing various micromotors for potential applications and fundamental studies of behaviours. The immense potential of these micromotors in biomedical applications [15][16][17] (e.g., drug delivery, [18][19][20] cell delivery, 21,22 medical imaging 23 ) and selforganizing systems 24,25 has been demonstrated. In particular, hydrogel-based micromotors have been shown to have promising applications in these biomedical areas.…”

Flow lithography for structured microparticles: fundamentals, methods and applications

“…Structured microparticles with customizable shapes, sizes, and chemistries (chemical and material compositions) 1 have demonstrated value across multiple fields including diagnostics, 23 drug/cargo delivery microrobots, [4][5][6][7] tissue engineering, [8][9][10] multiplexed assays, 11,12 self-assembly, [13][14][15] photonics, 16 optics, 17,18 and pharmaceuticals. 19 Particularly for numerous biomedical applications, these structured microparticles provide solid surfaces for barcoded or shapecoded molecular assays, 20,21 act as scaffolds to promote cell growth and infiltration for tissue regeneration, 22,23 enable uniform compartmentalization for high-throughput single-cell analysis, 24 serve as carriers for adhesive cell lines in imagingbased cytometry studies, 25 etc.…”