Medical micro/nanorobots have received tremendous attention over the past decades owing to their potential to be navigated into hard-to-reach tissues for a number of biomedical applications ranging ...from targeted drug/gene delivery, bio-isolation, detoxification, to nanosurgery. Despite the great promise, the majority of the past demonstrations are primarily under benchtop or in vitro conditions. Many developed micro/nanoscale propulsion mechanisms are based on the assumption of a homogeneous, Newtonian environment, while realistic biological environments are substantially more complex. Moving toward practical medical use, the field of micro/nanorobotics must overcome several major challenges including propulsion through complex media (such as blood, mucus, and vitreous) as well as deep tissue imaging and control in vivo. In this review article, we summarize the recent research efforts on investigating how various complexities in biological environments impact the propulsion of micro/nanoswimmers. We also highlight the emerging technological approaches to enhance the locomotion of micro/nanorobots in complex environments. The recent demonstrations of in vivo imaging, control and therapeutic medical applications of such micro/nanorobots are introduced. We envision that continuing materials and technological innovations through interdisciplinary collaborative efforts can bring us steps closer to the fantasy of "swallowing a surgeon".
Synthetic micro‐/nanomotors (MNMs) are capable of performing self‐propelled motion in fluids through harvesting different types of energies into mechanical movement, with potential applications in ...biomedicine and other fields. To address the challenges in these applications, a promising strategy that combines controlled assembly (bottom‐up approaches) with top‐down approaches for engineering autonomous, multifunctionalized MNMs is under investigation, beginning in 2012. These MNMs, derived from layer‐by‐layer assembly or molecular self‐assembly, display the advantages of: i) mass production, ii) response to the external stimuli, and iii) access to multifunctionality, biocompatibility, and biodegradability. The advance on how to integrate diverse functional components into different architectures based on controlled assemblies, to realize controlled fabrication, motion control (including the movement speed, direction, and state), and biomedical applications of MNMs, directed by the concept of nanoarchitectonics, are highlighted here. The remaining challenges and future research directions are also discussed.
Nanoarchitectonics is highlighted as an emerging, promising strategy for the fabrication, motion control, and applications of artificial micro‐/nanomotors based on diverse assembled architectures. The strategy affords assembled micro‐/nanomotors with multifunctionality, stimuli‐response properties, and the feasibility of mass production, which favors the applications of micro‐/nanomotors in biomedical fields.
We report an ultrasound-driven gold-nanoshell-functionalized polymer multilayer tubular nanoswimmer that can photomechanically perforate the membrane of a cancer cell by assistance of near-infrared ...(NIR) light. The nanoswimmers were constructed by a template-assisted layer-by-layer technique and subsequent functionalization of Au nanoshells inside the big opening. The nanoswimmers exhibit efficient and controllable movement toward target cells through the manipulation of the acoustic field. Next, the nanoswimmers with end-on attachment onto the HeLa cells achieve the poration of the cell membrane within 0.1 s under the irradiation of NIR light. The experimental and theoretical results suggest that the instantaneous photothermal effect provides enough photomechanical force to open the cell membrane. Such NIR-light-assisted nanoswimmers-enabled cell membrane poration possesses various advantages including active targeting, short time, and precision in single cells that conventional chemical and physical cell poration techniques could not achieve and, thus, provides considerable promise in a variety of biomedical applications such as gene delivery and artificial insemination.
The combination of bottom‐up controllable self‐assembly technique with bioinspired design has opened new horizons in the development of self‐propelled synthetic micro/nanomotors. Over the past five ...years, a significant advances toward the construction of bioinspired self‐propelled micro/nanomotors has been witnessed based on the controlled self‐assembly technique. Such a strategy permits the realization of autonomously synthetic motors with engineering features, such as sizes, shapes, composition, propulsion mechanism, and function. The construction, propulsion mechanism, and movement control of synthetic micro/nanomotors in connection with controlled self‐assembly in recent research activities are summarized. These assembled nanomotors are expected to have a tremendous impact on current artificial nanomachines in future and hold potential promise for biomedical applications including drug targeted delivery, photothermal cancer therapy, biodetoxification, treatment of atherosclerosis, artificial insemination, crushing kidney stones, cleaning wounds, and removing blood clots and parasites.
Bioinspired self‐propelled nanomotors based on controlled molecular self‐assembly permit the achievement of autonomously synthetic micro/nanomotors with engineering features, such as sizes, shapes, composition, propulsion mechanism, and function. Recent progress toward the construction, propulsion strategy, and movement regulation of controllable self‐assembled micro/nanomotors is summarized. Such assembled motors hold considerable promise in performing various tasks and diverse applications.
We describe fuel-free, near-infrared (NIR)-driven Janus mesoporous silica nanoparticle motors (JMSNMs) with diameters of 50, 80, and 120 nm. The Janus structure of the JMSNMs is generated by vacuum ...sputtering of a 10 nm Au layer on one side of the MSNMs. Upon exposure to an NIR laser, a localized photothermal effect on the Au half-shells results in the formation of thermal gradients across the JMSNMs; thus, the generated self-thermophoresis can actively drive the nanomotors to move at an ultrafast speed, for instance, up to 950 body lengths/s for 50 nm JMSNMs under an NIR laser power of 70.3 W/cm2. The reversible “on/off” motion of the JMSNMs and their directed movement along the light gradient can be conveniently modulated by a remote NIR laser. Moreover, dynamic light scattering measurements are performed to investigate the coexisting translational and rotational motion of the JMSNMs in the presence of both self-thermophoretic forces and strong Brownian forces. These NIR-powered nanomotors demonstrate a novel strategy for overcoming the necessity of chemical fuels and exhibit a significant improvement in the maneuverability of nanomotors while providing potential cargo transportation in a biofriendly manner.
We report a fuel-free, near-infrared （NIR）-driven Janus microcapsule motor. The Janus microcapsule motors were fabricated by template-assisted polyelectrolyte layer-by-layer assembly, followed by ...spraying of a gold layer on one side. The NIR-powered Janus motors achieved high propulsion with a maximum speed of 42μm.s-1 in water. The propulsion mechanism of the Janus motor was attributed to the self-thermophoresis effect： The asymmetric distribution of the gold layer generated a local thermal gradient, which in turn generated thermophoretic force to propel the Janus motor. Such NIR-propelled Janus capsule motors can move efficiently in cell culture medium and have no obvious effects on the cell at the power of the NIR laser, indicating considerable promise for future biomedical applications.
We demonstrate the first example of a self-propelled Janus polyelectrolyte multilayer hollow capsule that can serve as both autonomous motor and smart cargo. This new autonomous Janus capsule motor ...composed of partially coated dendritic platinum nanoparticles (Pt NPs) was fabricated by using a template-assisted layer-by-layer (LbL) self-assembly combined with a microcontact printing method. The resulting Janus capsule motors still retain outstanding delivery capacities and can respond to external stimuli for controllable encapsulation and triggered release of model drugs. The Pt NPs on the one side of the Janus capsule motors catalytically decompose hydrogen peroxide fuel, generating oxygen bubbles which then recoil the movement of the capsule motors in solution or at an interface. They could autonomously move at a maximum speed of above 1 mm/s (over 125 body lengths/s), while exerting large forces exceeding 75 pN. Also, these asymmetric hollow capsules can be controlled by an external magnetic field to achieve directed movement. This LbL-assembled Janus capsule motor system has potential in making smart self-propelling delivery systems.
Inspired by the dynamics of bacterial swarming, we report a swarm of polymer‐brush‐grafted, glucose‐oxidase‐powered Janus gold nanoswimmers with a positive, macroscale chemotactic behavior. These ...nanoswimmers are prepared through the grafting of polymer brushes onto one side of gold nanoparticles, followed by functionalization with glucose oxidase on the other side. The resulting polymer‐brush‐functionalized Janus gold nanoswimmers exhibit efficient propulsion with a velocity of up to approximately 120 body lengths s−1 in the presence of glucose. The comparative analysis of their kinematic behavior reveals that the grafted polymer brushes significantly improve the translational diffusion of Janus gold nanoswimmers. Particularly, these bacteria‐mimicking Janus gold nanoswimmers display a collectively chemotactic motion along the concentration gradient of a glucose resource, which could be observed at the macroscale.
Go with the flow: Polymer‐brush‐functionalized, glucose‐oxidase‐powered, Janus gold nanoswimmers, prepared by modifying one side of a gold nanoparticle with polymer brushes and the opposite side with glucose oxidase, move towards a glucose resource in a manner resembling that of bacteria.
We report the reconfigurable assembly of rod‐shaped eutectic gallium–indium alloy (EGaIn) liquid metal colloidal motors by mimicking the growth behavior of a dandelion. EGaIn nanorods with a diameter ...of 210 nm and a length of 850 nm were synthesized via an ultrasound‐assisted physical dispersion method. The nanorods possess a core–shell structure with a 30 nm GaOOH shell and zero‐valent liquid core. The EGaIn motors move autonomously at a speed of 41.2 μm s−1 under an acoustic field. By modulating the frequency of the applied acoustic field, the EGaIn colloidal motors self‐organize into various striped and circular patterns, followed by a flower‐like cluster. The dandelion‐like EGaIn colloidal motor clusters move collectively and redisperse when the applied acoustic frequency is changed. Numerical simulations reveal that the flower‐like clusters are created by the acoustic propulsion in combination with steric repulsion and hydrodynamics.
Rod‐shaped liquid metal colloidal motors were fabricated from a eutectic gallium—indium (EGaIn) alloy. On application of an acoustic field, the EGaIn colloidal motors move autonomously and they are able to self‐organize into a flower‐like cluster.
The ecosystem of the Source Region of Yangtze River (SRYR) is highly susceptible to climate change. In this study, the spatial-temporal variation of NPP from 2000 to 2014 was analyzed, using outputs ...of Carnegie-Ames-Stanford Approach model. Then the correlation characteristics of NPP and climatic factors were evaluated. The results indicate that: (1) The average NPP in the SRYR is 100.0 gC/m
from 2000 to 2014, and it shows an increasing trend from northwest to southeast. The responses of NPP to altitude varied among the regions with the altitude below 3500 m, between 3500 to 4500 m and above 4500 m, which could be attributed to the altitude associated variations of climatic factors and vegetation types; (2) The total NPP of SRYR increased by 0.18 TgC per year in the context of the warmer and wetter climate during 2000-2014. The NPP was significantly and positively correlated with annual temperature and precipitation at interannual time scales. Temperature in February, March, May and September make greater contribution to NPP than that in other months. And precipitation in July played a more crucial role in influencing NPP than that in other months; (3) Climatic factors caused the NPP to increase in most of the SRYR. Impacts of human activities were concentrated mainly in downstream region and is the primary reason for declines in NPP.
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