Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Microrobots learn from ciliates

26.02.2016

Ciliates can do amazing things: Being so tiny, the water in which they live is like thick honey to these microorganisms. In spite of this, however, they are able to self-propel through water by the synchronized movement of thousands of extremely thin filaments on their outer skin, called cilia.

Researchers from the Max Planck Institute for Intelligent Systems in Stuttgart are now moving robots that are barely perceptible to the human eye in a similar manner through liquids. For these microswimmers, the scientists are neither employing complex driving elements nor external forces such as magnetic fields.


Light-driven microswimmers: the material of the swimming body, which measures just under one millimeter in length, is chosen so that it changes shape when exposed to green light. This causes wave-shaped protrusions to form along the swimmer and drive it in the opposite direction when light patterns move over its surface.

Credit: Alejandro Posada/ Max Planck Institute for Intelligent Systems, Stuttgart

The team of scientists headed by Peer Fischer have built a ciliate-inspired model using a material that combines the properties of liquid crystals and elastic rubbers, rendering the body capable of self-propelling upon exposure to green light. Mini submarines navigating the human body and detecting and curing diseases may still be the stuff of science fiction, but applications for the new development in Stuttgart could see the light-powered materials take the form of tiny medical assistants at the end of an endoscope.

Their tiny size makes life extremely difficult for swimming microorganisms. As their movement has virtually no momentum, the friction between the water and their outer skin slows them down considerably -- much like trying to swim through thick honey.

The viscosity of the medium also prevents the formation of turbulences, something that could transfer the force to the water and thereby drive the swimmer. For this reason, the filaments beat in a coordinated wave-like movement that runs along the entire body of the single-celled organism, similar to the legs of a centipede. These waves move the liquid along with them so that the ciliate -- measuring roughly 100 micrometres, i.e. a tenth of a millimetre, as thick as a human hair -- moves through the liquid.

"Our aim was to imitate this type of movement with a microrobot," says Stefano Palagi, first author of the study at the Max Planck Institute for Intelligent Systems in Stuttgart, which also included collaborating scientists from the Universities of Cambridge, Stuttgart and Florence.

Fischer, who is also a Professor for Physical Chemistry at the University of Stuttgart, states that it would be virtually impossible to build a mechanical machine at the length scale of the ciliate that also replicates its movement, as it would need to have hundreds of individual actuators, not to mention their control and energy supply.

Liquid-crystal elastomers behave like Mikado Sticks

Researchers therefore usually circumvent these challenges by exerting external forces directly on the microswimmer: such as a magnetic field that is used to turn a tiny magnetic screw, for example. "This only produces a limited freedom of movement," says Fischer. What the Stuttgart-based researchers wanted to construct, however, was a type of universal swimmer that would be capable of moving freely through a liquid on an independent basis, without external forces being applied and without a pre-defined pace.

They managed to achieve this with an astonishingly simple method, using so-called liquid-crystal elastomers as the swimming bodies. These change shape when they are exposed to light or heat. Like a liquid crystal, they consist of rod-like molecules that initially have a parallel alignment, similar to a bundle of Mikado Sticks before being thrown by the player. The molecules are connected to one another, which lends the liquid crystal a certain degree of solidity, like a rubber. When heated, the sticks lose their alignment and this causes the material to change its shape, much like the way Mikado Sticks occupy more space on the ground when they are thrown.

The heat was generated by the scientists in Stuttgart in their experiments by exposing the material to green light. The light also causes the shape of the actual molecules themselves to change. These molecules have a chemical bond that acts like a joint. The radiation causes the rod-like molecule at the joint to bend in the shape of a U. This serves to aggravate the molecular disorder, which causes the material to expand even more. The material responds very quickly to the light being switched on and off. When the light it switched off, the material returns immediately to its original shape.

Protrusions follow the light along the swimming body

The researchers produced two types of microrobots: one in the form of an elongated cylinder, roughly one millimetre long and about two hundred micrometres thick, and the other in the form of a tiny disk about 50 micrometres thick and with a diameter of two hundred or four hundred micrometres.

In a first experiment, Fischer's team projected a striped pattern of light onto the cylindrical robot with the aid of a microscope. They observed protrusions forming in the illuminated areas. They then allowed the light pattern to sweep across the cylinder, which prompted the protrusions to also move down along the body like waves. "The movement is generated by the robots from the inside," emphasizes Fischer. The light simply transfers energy to the swimmer, without exerting any force whatsoever. A worm moves along in a similar manner: it creates waves in its body, whereby ring-shaped protrusions and longitudinally aligned elongations run from one end of the worm's body to the other. The specialist term for this is peristalsis.

The peristaltic movement triggered by the light pattern transports liquid along the body of the microswimmer, causing it to move in the opposite direction. In this way, the microrobot reached a speed of about 2.1 micrometres per second and covered a distance of 110 micrometres.

An unknown range of movements for microswimmers

Peer Fischer and his colleagues also demonstrated that they can control the robots with a great degree of flexibility. This is because, in principle, any light pattern can be projected on the swimmers. The researchers generate a pattern using a micromirror device, an array of almost 800,000 tiny mirrors that can be moved individually. In this way, they projected light patterns onto a disk robot and varied the direction so that the microswimmer followed a rectangular trajectory.

They then caused the disk to rotate by projecting a light pattern resembling a fan on to its surface. They even succeeded in controlling two disk robots independently of one another: one turned clockwise, the other counter-clockwise. "This means that a wide range of movements are possible within the very same microrobot, which was previously unheard of in this field," emphasizes Stefano Palagi.

"Another important question was whether our swimmers could be made even smaller," adds co-author Andrew Mark. A theoretical calculation showed that this should be possible: smaller microswimmers could also self-propel using wave-shaped movements. This is the motivation behind the work of the Stuttgart-based researchers: "Our ultimate goal is to imitate as closely as possible the work of nature itself," says Fischer.

###

Original paper:

Stefano Palagi, Andrew G. Mark, Shang Yik Reigh, Kai Melde, Tian Qiu, Hao Zeng, Camilla Parmeggiani, Daniele Martella, Alberto Sanchez-Castillo, Nadia Kapernaum, Frank Giesselmann, Diederik S. Wiersma, Eric Lauga and Peer Fischer Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots Nature Materials, Feb. 15, 2016; doi:10.1038/nmat4569

Media Contact

Stefano Palagi, Ph.D.
palagi@is.mpg.de
49-711-689-3516

 @maxplanckpress

http://www.mpg.de 

Stefano Palagi, Ph.D. | EurekAlert!

More articles from Materials Sciences:

nachricht Simple processing technique could cut cost of organic PV and wearable electronics
06.12.2016 | Georgia Institute of Technology

nachricht InLight study: insights into chemical processes using light
05.12.2016 | Fraunhofer-Institut für Lasertechnik ILT

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Simple processing technique could cut cost of organic PV and wearable electronics

06.12.2016 | Materials Sciences

3-D printed kidney phantoms aid nuclear medicine dosing calibration

06.12.2016 | Medical Engineering

Robot on demand: Mobile machining of aircraft components with high precision

06.12.2016 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>