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Nanomachines in living systems - on route to microcyborgs

(Nanowerk Spotlight) From interaction with bacteria, propulsion based on cells, in vivo medical applications to even intracellular applications, the rapidly expanding development of micro- and nanomachines with sizes comparable to or even smaller than mammalian cells, has led this field to advance from understanding of basic motion mechanisms to applications in living biosystems.
The field of nanomachines has developed rapidly over the last few years, with several groups exploring new methods of navigation and demonstrating their potential benefits as therapeutic tools. In the future, these nanomachines could be used in a clinical environment, where they are injected close to a specific diseased site and they are navigated to a deep location of a tissue in a completely untethered and safe manner. The nanomachines can then perform tasks like sensing or therapy at the particular site, without affecting the functionality of adjoining cells and tissues.
We have written numerous Nanowerk Spotlights on the fabrication and applications of nanomachines. Some are concerning the movement of nanomachines, including basic issues like switching their movement on and off all the way to the design of nanotransportation systems. Researchers even designed a graphene nanomotor that mimics an internal combustion engine.
Nature has excelled in designing molecular motors, which has led researchers to mimic bacterial flagella-based propulsion for nanomotors and use live bacteria as mechanical actuators in fluid systems.
Increasingly, miniaturized artificial machines are designed for in vivo medical applications, for instance by coupling drug nanocarriers with self-propelled nanoshuttles in order to deliver therapeutic nanoparticles right to the spot where they are needed (e.g. a tumor site). Ultimately, we will see synthetic DNA nanomachines that go to work inside living cells to work as sensors or therapeutic agents.
Interaction of micro/nanomachines with bacteria
Interaction of micro/nanomachines with bacteria. A) Ultrasound-driven receptor-functionalized nanomotors for selective capture and transport of E. coli with magnetic guidance. Reproduced with permission (© American Chemical Society). B) SEM image of an E. coli bacterium with surface morphology changes upon contacting the Ag-coated nanocoils. Scale bar is 200 nm. Reproduced with permission (© Wiley-VCH).
A recent review in Advanced Functional Materials ("Micro/Nanomachines and Living Biosystems: From Simple Interactions to Microcyborgs") highlights the recent efforts for and toward application of micro/nanomachines in living biosystems, including microorganisms, biological cells, and human body.
The authors, professors Hong Wang (China University of Mining and Technology) and Martin Pumera (Nanyang Technological University), review the applications of micro/nanomachines in living biosystems from two aspects: their interaction with other microscopic organisms or biological units, and the efforts toward their application in the human body. They discuss four key application areas of micro- and nanomachines in living biosystems. Regarding the first aspect: interaction with bacteria and propulsion based on cells. Regarding the second aspect: in vivo applications and intracellular applications.
Wang and Pumera discuss examples that demonstrate the feasibility and enormous potential of employing micro/nanomachines in biosystems.
Utilizing different functionalization strategies, micro/nanomachines are capable of detecting, selectively capturing and broad spectrum killing of bacteria. Biological cells could be employed as actuators of micro/nanomachines to form coordinated biohybrid systems whereas the tiny machines could in turn carry sperm cells with motion deficiencies to implement natural function.
Intracellular applications of micro/nanomachines
Intracellular applications of micro/nanomachines. A) Gene silencing based on US-propelled nanomotors. Reproduced with permission (© American Chemical Society). B) Intracellular delivery of Caspase-3 by US-propelled nanomotors to induce cell apoptosis (© American Chemical Society).
To translate micro/nanomachines into clinical applications, substantial efforts have been devoted to pushing them to in vivo studies and a series of novel strategies to address biomedical problems in diagnosis and treatment of diseases have proven to be effective. Nanomachines could also be engineered down to perform tasks at cellular level, thus enabling intracellular sensing, drug delivery, and genetic intervention.
The two scientists caution, though, that despite the tremendous progress obtained in recent years, micro- and nanoscale machines are far from mature in both theory and applications. To push forward in-depth applications of micro/nanomachines in biosystems, they list improvements that still are needed in many aspects:
Most of the current bactericidal operations were conducted in vitro conditions and extension to in vivo studies would pave way for treatment of infection by multidrugresistant bacteria in deep regions inside the body.
Collective behavior of micro/nanomachine in swarms is of great interest, as parallel or distributed operations are usually required in practice. However, the researches on this aspect are still limited.
Biohybrid micro/nanomachines fusing biological cells with the synthetic functional component inherit the natural intelligence of cells and are good candidates to fill this gap.
Clinical translation of micro/nanomachines demands a wider variety of structures beyond the simple tube, sphere geometric structures, and materials with good biocompatibility, immunogenically safety, and low waste profiles, the combination of which relies on the reasonable design and fabrication of micro/nanomachines.
Despite the high-performance control systems of magnetically propelled micro/nanomachines, the control of the micro/nanomachines with other propulsion systems needs to be enhanced to achieve precise guidance and distribution.
For intracellular applications, the movement of micro/nanomachines inside cells should be better regulated to allow targeted delivery to specific cytoplasmic organelles and the operations should be carried forward from in vitro to in vivo conditions."
"Just as today’s automatic machines were well beyond the initial expectations of many people at the start of industrial evolution, continuing research on multiple disciplines will doubtless fuel the development of micro/nanomachines and may far surpass what we can forecast today," the authors conclude.
By Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology: The Future is Tiny. Copyright © Nanowerk

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