Robotic swimmers, self-propelling nanomotors, Max Planck Research Group Peer Fischer, Stuttgart, Germany

Scientific Work was conducted in the Lab for Micro Nano and Molecular Systems, Prof. Peer Fischer
Max Planck Institute for Intelligent Systems, Stuttgart, Germany

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Tissue and biological fluids are complex viscoelastic media with a nanoporous macromolecular structure. Here, we demonstrate that helical nanopropellers can be controllably steered through such a biological gel. The screw-propellers have a filament diameter of about 70 nm and are smaller than previously reported nanopropellers as well as any swimming microorganism. We show that the nanoscrews will move through high-viscosity solutions with comparable velocities to that of larger micropropellers, even though they are so small that Brownian forces suppress their actuation in pure water. When actuated in viscoelastic hyaluronan gels, the nanopropellers appear to have a significant advantage, as they are of the same size range as the gel’s mesh size. Whereas larger helices will show very low or negligible propulsion in hyaluronan solutions, the nanoscrews actually display significantly enhanced propulsion velocities that exceed the highest measured speeds in Newtonian fluids. The nanopropellers are not only promising for applications in the extracellular environment but small enough to be taken up by cells. (ACS Nano (2014), DOI: 10.1021/nn502360t.)

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Biological microorganisms swim with flagella and cilia that execute non reciprocal motions for low Reynolds number (Re) propulsion in viscous fluids. This symmetry requirement is a consequence of Purcell’s scallop theorem, which complicates the actuation scheme needed by micro-swimmers. However, most biomedically important fluids are non-Newtonian where the scallop theorem no longer holds. It should therefore be possible to realize a micro-swimmer that moves with reciprocal periodic body-shape changes in non-Newtonian fluids. Here, we report a symmetric “micro-scallop”, a single-hinge micro-swimmer that can propel in shear thickening and shear thinning (non-Newtonian) fluids by reciprocal motion at low Re. Excellent agreement between our measurements and both numerical and analytical theoretical predictions indicates that the net propulsion is caused by modulation of the fluid viscosity upon varying the shear rate. This reciprocal swimming mechanism opens new possibilities in designing biomedical micro-devices that can propel by a simple actuation scheme in non-Newtonian biological fluids. (Nat. Commun. 5: 5119 (2014). doi: 10.1038/ncomms6119.)

Tian Qiu, Tung-Chun Lee, Andrew G. Mark, Konstantin I. Morozov, Raphael
Munster, Otto Mierka, Stefan Turek, Alexander M. Leshansky, and Peer
Fischer. Swimming by Reciprocal Motion at Low Reynolds Number. Nat. Commun.
5: 5119 doi: 10.1038/ncomms6119 (2014).

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Video for Design challenge:
Video entry won the “Microrobotics Design Challenge” at the Hamlyn Symposium in London. (June, 2016).
Helical Micro and Nanopropellers for Applications in Biological Fluidic Enviroments
Debora Walker, Tian Qiu, Andrew G. Mark, Alejandro Posada, Peer Fischer

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A tiny robot with moves inspired by caterpillars and jellyfish is small enough to crawl, walk and swim inside the human body.

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This four millimetre long robot was designed by the Max Planck Institute for Intelligent Systems to move through the human body. It can walk, roll, swim, jump and even carry cargo and may be used in minimally invasive surgery or to deliver drugs to specific parts inside the body.

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An international team of scientists, some from the “Micro, Nano and Molecular Systems” Lab at the Max-Planck-Instritute for Intelligent Systems in Stuttgart, developed specially coated nano-robots that can be magnetically moved through dense tissue like the vitreous of the eye. This has never been achieved before! So far, the transport of these so called nano-vehicles has only been demonstrated in model systems or biological fluids, but not in real tissue. The work was published in the journal Science Advances and constitutes one step further towards nano-robots becoming minimally-invasive tools for precisely delivering medicine to where it is needed.

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