The phenomenon was linked to the ability of some tumors to mutate, inhibit antiproteases, injure local tissues, and therefore promote tumor heterogeneity, invasion, and metastasis. Propelled navigation to promote cancer cell targetingĬancer cells have been found to generate oxidative stress by producing an elevated level of hydrogen peroxide (H 2O 2). Collectively, as reviewed below, the development of micro/nanomotors has provided a new approach to addressing some pressing challenges in cancer diagnostics and therapies.Ģ. Progress made in these areas has offered tremendous inspiration and opportunities aimed for enhancing the efficiency and precision of drug targeting to cancer cells, improving the capability of delivering anti-cancer drug into cytoplasm for bioactivity, and enabling more rapid and sensitive cancer cell detection. These areas include: (1) propelled navigation to promote cancer cell targeting, (2) powered cell membrane penetration to enhance intracellular delivery, and (3) isolation of circulating cancer cells (CTCs) for detection. In this perspective, we identify three areas, where micro/nanomotors have demonstrated unique properties and contributions. This review article is focused on the current development of micro/nanomotors for potential use in cancer cell targeting and isolation.
(Reprinted with permission from the references.) Schematic illustration (left column), representative scanning electron microscopic image (middle column), and motion image (right column) of various types of micro/nanomotors including (A) tubular, (B) Janus, (C) stomatocyte, (D) helical, and (E) flexible motors. Furthermore, flexible micro/nanomotors exploit the deformation of flexible filaments that allow the propagation of a traveling wave to generate propulsion. In addition, helical micro/nanomotors, as inspired by helical bacterial flagella, propel upon rotation posed by external magnetic fields. For example, micro/nanomotors such as tubular microrockets, Janus spheres, and stomatocytes feature an asymmetric geometry that provides one additional degree of freedom to escape the constraints from the scallop theorem. To transfer the forces to translational movement with a high efficiency, micro/nanomotors are tailored-made into distinct geometries to adapt specific actuation principles ( Figure 1). Alternatively, ‘fuel free’ motors exploit external sources such as magnetic and acoustic field gradients to generate driving forces. To meet the power demands, motors are made to harness local chemical fuels to generate driving forces through catalytic reactions. For this purpose, efficient energy harvest and conversion are key elements in motor designs. Micro/nanomotor designs need to overcome the low Reynolds number and Brownian motion, which work together against the motor's locomotion. In reality, micro/nanoscale propulsion in fluids is challenging owing to the absence of the inertial forces common for macroscopic objects. Collectively, these intriguing advantages have triggered a number of creative micro/nanomotor designs with remarkable functionalities for cancer-specific applications. Furthermore, micro/nanomotors can be equipped with cargo manipulation mechanisms to pickup, transport, and release “heavy” cargos such as cancer cells on demand, making them suitable for in situ cancer cell isolation and sorting. In addition, by engaging movements powered through in situ energy conversion, micro/nanomotors can gain considerable propelling force that enable the motors to penetrate into deep tumor tissues beyond regular diffusion limits.
tumors) in an active targeting manner, bypassing the reliance on random diffusion and systemic circulation for navigation.
When combined with remote steering, the propelled motion allows micro/nanomotors to enter physiological sites (e.g. With this distinct feature, micro/nanomotors have been pursued for numerous biomedical applications including targeted delivery, precision surgery, sensing and detoxification. Among these platforms, micro/nanomotors represent an emerging and powerful system that is capable for effectively converting diverse energy sources into driving forces and autonomous movement. Nanomedicine platforms that allow for precise and remote manipulation of nanoscale objects in biological environment have enabled exciting opportunities for innovative diagnostics and therapies of numerous diseases including cancer.
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