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Researchers Create Dynamic Self-Assembly Process for Building Mobile Micromachines

Shape-encoded assembly of magnetic microactuators in the form of a microvehicle.

A micromachine has the potential to maniupulate and probe the microscopic world, and can be made up of multiple chemistries, materials, or parts in order to address different functions, such as actuation, delivery, sensing, and transport. Its performance and functional modes can be commanded by the interaction and organization of its variable constituents, and it can be 3D printed, but it’s difficult to build programmable structural assemblies into mobile micromachines.

A group of researchers from the Max Planck Institute for Intelligent Systems and ETZ Zurich published a study in Nature Materials, titled “Shape-encoded dynamic assembly of mobile micromachines,” in which they introduced a new directed, dynamic self-assembly process of building mobile compound micromachines, with specific configurations.

The process use pre-programmed physical interactions between structural and motor units, and is driven by dielectrophoretic interactions (DEP) that are encoded in the 3D shape of individual parts. These DEP forces modulate the part’s 3D geometry in order to “encode precisely controlled distribution of electric field gradients around a body.”

Spatial encoding of DEP attraction sites by modulating the 3D geometry.

First, the researchers – Yunus Alapan, Berk Yigit, Onur Beker, Ahmet F. Demirörs, and Metin Sitti – programmed field gradients around a construct, so they could use DEP interactions to “drive the assembly of micromachine parts” at specific locations.

“The working principle of the device under electric fields relied on the shape-dependent regulation of electric fields around polarizable bodies of the assembled micromachine,” a Phys.org piece states.

The team needed a way to program local gradients, and looked into how they could modulate non-electric fields around different geometries. Then, they were able to control the mobile micromachine’s self-assembly, which was influenced by electric fields, using a microvehicle as an example. It had a large, spherical, non-magnetic dielectric, body, with several smaller magnetic actuators surrounding it. When an electric field was applied in the Z axis, the large body was able to generate enough local electric field gradients so as to attract smaller microactuators; these acted as wheels, and the researchers could steer the microvehicle by simply changing the direction of the magnetic field.

Assembly and translation of a compound microvehicle with magnetic actuators.

When they increased the number of microactuators, the microvehicle’s velocity also grew, but when the voltage was increased, the velocity went down. The researchers think this is due to increased mechanical coupling, during DEP interactions, between the microparticles and the substrate.

At lower voltages, small DEP forces “led to a loose lubrication-based coupling phenomenon” that made it possible for microactuators to move freely around the pole. This means it’s possible to regulate the strength of the DEP forces between the microactuators and passive body to adjust their mechanical coupling, in order to control the microvehicle’s rotational degrees of freedom.

Reversible assembly of magnetic microactuators with a non-magnetic body using DEP forces.

The researchers used shape-encoded physical interactions to make programmable self-assembling mobile micromachines by developing frames that had specific 3D geometries to help generate electric field gradients. The framework, made with two-photon lithography, attracts microactuators to specific locations on the frame. In one example, they made a microcar with four-wheel pockets that generated DEP forces and helped guide the magnetic microactuators into said pockets. Within just second of applying an electric field, the microcar completed an on-demand self-assembly: the magnetic wheels inside the pockets went into a free rotation due to the vertically rotating magnetic field.

The prototype was expanded in order to build reconfigurable micromachines, which are run by self-propelled micromotors. Self-propelled Janus silica (SiO2) microparticles with a gold cap were used to assemble these micromachines, and their DEP response and frequency-dependent self-propulsion made it possible to create mobile micromachines that featured self-repair and reconfigurable spatial organization. Then, the researchers defined the physical interactions between these mobile micromachines by expanding the shape-encoded DEP interactions in a two-level hierarchical assembly:

  • Level 1: self-propelled actuators assembled with two microstructure units form mobile micromachines with linear translation
  • Level 2: generation of low electric fields cause second and first units to assemble together laterally

R-L: Shape-encoded reconfigurable assembly of micromachines with self-propelled microactuators for frequency-tunable locomotion; Hierarchical assembly of multiple micromachines via shape-encoded DEP interactions.

The research team was able to extend their current design into the manipulation of 3D microactuators, and micromachine assembly, and say that it even has the potential to be used with lab-on-a-chip devices for digital manipulation, sorting, continuous transport, and microfluidic flow generation.

“The site-selective assembly strategy was versatile and could be demonstrated on different, reconfigurable, hierarchical and 3D mobile micromachines. The scientists anticipate the design principles presented in the work to advance and inspire the development of more sophisticated micromachines integrated in multiscale hierarchical systems.”

This design strategy makes it possible to achieve programmable self-assembly through the use of micromachines’ shape-directed dynamic assembly, which will give scientists more control over functions and dynamics. Because the team was able to incorporate heterogenous components for actuation, cargo loading, and sensing in a single step, their work may make it possible for others to engineer multifunctional, multimaterial microrobots.

The researchers will now focus on optimizing and expanding on “the irreversible assembly of micro-components” for better performance in applications that don’t use electric fields, such as in vivo biomedical applications.

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[Source/Images: Phys.org]

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Update On Made In Space’s 3D Printed Asteroid Spacecraft Research

California 3D printing and space technology firm Made In Space is responsible for such out of this world innovations as the first commercial 3D printer on the International Space Station, the multi-armed 3D printing space robot Archinaut, and the manufacture of the first extended 3D printed objects in a space-like environment. The company works closely with NASA, and two years ago received funding from the agency for its ambitious plan to turn asteroids into autonomous spaceships, which could help NASA finalize its long-term goal of constructing human colonies in space.

Right now, NASA can only bring back small pieces of space rock. But Project RAMA (Reconstituting Asteroids into Mechanical Automata) hopes to establish the concept feasibility of using analog computers and mechanisms – along with 3D printing – to convert asteroids into huge mechanical spacecraft, which could carry large amounts of raw asteroid material. This could be the impetus for the off-Earth mining that will be necessary if humanity wants to survive and thrive among the stars.

Artist’s illustration of an asteroid that has been turned into a giant mechanical spacecraft, which could fly itself to a mining outpost. [Image: Made In Space]

Asteroids are pretty cool – many of them contain valuable resources, such as water and platinum-group metals, and roughly 100 tons of asteroid and comet material hit the Earth’s atmosphere each day. As part of the plan to turn these massive rock formations into functioning spacecraft, Made In Space plans to send an advanced, robotic seed craft out to space, in order to to meet with several near-Earth asteroids.

This craft would then harvest space rock material and turn it into feedstock, which can be 3D printed to build energy storage, navigation, propulsion, and other important systems on-site. Once the converted asteroid is ready, it can be programmed to autonomously fly to a mining station; according to Made In Space representatives, this approach is far more efficient than having to launch new capture probes out to space rocks.

While we don’t currently have the ability or the technology to 3D print something like a digital guidance computer with materials found on an asteroid, Made In Space realized that one doesn’t have to rely on digital electronics if a huge amount of raw material, with no constraints on mass or volume, is available instead.

“At the end of the day, the thing that we want the asteroid to be is technology that has existed for a long time,” said Made In Space Co-Founder and CTO Jason Dunn. “The question is, ‘Can we convert an asteroid into that technology at some point in the future?’ We think the answer is yes.”

Two years ago, NASA’s Innovative Advanced Concepts (NIAC) program, which encourages development of space-exploration technologies, awarded Made In Space a $100,000 Phase 1 grant for nine months of initial feasibility studies. During this phase, the company focused on how the seed craft would have to work, defining its requirements, and building a technological roadmap. If the company chooses, it can also apply for a two-year, $500,000 Phase 2 award for continuing concept development. In the meantime, Made In Space is counting on NASA to push forward in-situ resource utilization (ISRU) – the art of living off the land, which is necessary for astronauts who could someday live on planetary outposts.

Required capabilities of the RAMA craft, arranged in approximate order of mass requirements, showing the source of the materials used to provide each capability as assumed for the rest of this study.

These asteroid ships will probably not look much like traditional spaceships, with their electronic circuitry and rocket engines, but instead would use analog computers and a catapult type of propulsion system that will launch asteroid material in a controlled way. By using mass drivers to shoot chunks of itself in one direction, an asteroid could potentially accelerate itself in the opposite direction. While this method is only about 10% as efficient as a chemical rocket engine, the propellant is free.

3D printing could be used to make some of the asteroid spacecraft parts, like flywheel gyros for guidance and stabilization, tanks for storing volatile materials, and solar concentrators to generate mechanical power through the release of pressure to open the tanks.

While Project RAMA is still moving forward, Dunn acknowledges that its completion is still way in the future…and that eventually, it could even have applications on Earth.

Dunn explained, “The anticipation is that the RAMA architecture is a long time line, and when it becomes capable is about the same time that people really need the resources.

“You could build infrastructure in remote locations somewhat autonomously, and convert resources into useful devices and mechanical machines. This actually could solve some pretty big problems on Earth, from housing to construction of things that make people’s lives better.”

Diagram of an asteroid that has been converted into a mechanical spacecraft by a robotic “Seed Craft.” [Image: Zoe Brinkley]

The other goal of Project RAMA is to be able to make asteroids into self-assembled spacecraft.

“One of the big questions is, how do you take today’s most intricate machines and make them replicate themselves? That seems really hard: how do you replicate electronics and processing units and so on,” Dunn said. “And that’s when we had this concept that there are types of machines that could potentially be easy to self-replicate, and those would be very basic, analog type devices. The problem is if you have a small mechanical machine, it’s not very useful. But what if the machine itself was the size of an asteroid? What could you do with a mechanical machine that large?”

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