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MIT Micro Robots

Tiny motor can “walk” to carry out tasks

Years ago, MIT Professor Neil Gershenfeld had an audacious thought. Struck by the fact that all the world’s living things are built out of combinations of just 20 amino acids, he wondered: Might it be possible to create a kit of just 20 fundamental parts that could be used to assemble all of the different technological products in the world?

Gershenfeld and his students have been making steady progress in that direction ever since. Their latest achievement, presented this week at an International robotics conference, consists of a set of five tiny fundamental parts that can be assembled into a wide variety of functional devices, including a tiny “walking” motor that can move back and forth across a surface or turn the gears of a machine.

Previously, Gershenfeld and his students showed that structures assembled from many small, identical subunits can have numerous mechanical properties. Next, they demonstrated that a combination of rigid and flexible part types can be used to create morphing airplane wings, a longstanding goal in aerospace engineering. Their latest work adds components for movement and logic, and will be presented at the International Conference on Manipulation, Automation and Robotics at Small Scales (MARSS) in Helsinki, Finland, in a paper by Gershenfeld and MIT graduate student Will Langford.

Their work offers an alternative to today’s approaches to contructing robots, which largely fall into one of two types: custom machines that work well but are relatively expensive and inflexible, and reconfigurable ones that sacrifice performance for versatility. In the new approach, Langford came up with a set of five millimeter-scale components, all of which can be attached to each other by a standard connector. These parts include the previous rigid and flexible types, along with electromagnetic parts, a coil, and a magnet. In the future, the team plans to make these out of still smaller basic part types.

Using this simple kit of tiny parts, Langford assembled them into a novel kind of motor that moves an appendage in discrete mechanical steps, which can be used to turn a gear wheel, and a mobile form of the motor that turns those steps into locomotion, allowing it to “walk” across a surface in a way that is reminiscent of the molecular motors that move muscles. These parts could also be assembled into hands for gripping, or legs for walking, as needed for a particular task, and then later reassembled as those needs change. Gershenfeld refers to them as “digital materials,” discrete parts that can be reversibly joined, forming a kind of functional micro-LEGO.

The new system is a significant step toward creating a standardized kit of parts that could be used to assemble robots with specific capabilities adapted to a particular task or set of tasks. Such purpose-built robots could then be disassembled and reassembled as needed in a variety of forms, without the need to design and manufacture new robots from scratch for each application.

Langford’s initial motor has an ant-like ability to lift seven times its own weight. But if greater forces are required, many of these parts can be added to provide more oomph. Or if the robot needs to move in more complex ways, these parts could be distributed throughout the structure. The size of the building blocks can be chosen to match their application; the team has made nanometer-sized parts to make nanorobots, and meter-sized parts to make megarobots. Previously, specialized techniques were needed at each of these length scale extremes.

“One emerging application is to make tiny robots that can work in confined spaces,” Gershenfeld says. Some of the devices assembled in this project, for example, are smaller than a penny yet can carry out useful tasks.

To build in the “brains,” Langford has added part types that contain millimeter-sized integrated circuits, along with a few other part types to take care of connecting electrical signals in three dimensions.

The simplicity and regularity of these structures makes it relatively easy for their assembly to be automated. To do that, Langford has developed a novel machine that’s like a cross between a 3-D printer and the pick-and-place machines that manufacture electronic circuits, but unlike either of those, this one can produce complete robotic systems directly from digital designs. Gershenfeld says this machine is a first step toward to the project’s ultimate goal of “making an assembler that can assemble itself out of the parts that it’s assembling.”

“Standardization is an extremely important issue in microrobotics, to reduce the production costs and, as a result, to improve acceptance of this technology to the level of regular industrial robots,” says Sergej Fatikow, head of the Division of Microrobotics and Control Engineering, at the University of Oldenburg, Germany, who was not associated with this research. The new work “addresses assembling of sophisticated microrobotic systems from a small set of standard building blocks, which may revolutionize the field of microrobotics and open up numerous applications at small scales,” he says.

Materials Provided By Massachusetts Institute of Technology

Paper sensor

A paper sensor detects food spoilage

Worldwide, nearly a third of all food is wasted. Much of it is still safe to eat, but consumers throw it away because it’s close to or beyond its printed expiration date. That waste could be mitigated if food were packaged with a sensor that monitored its spoilage in real time. But such a device would need to be low cost, easy to produce, and unambiguous to read. Toward that end, Firat Güder of Imperial College London in the UK and his colleagues have designed a paper sensor that detects the gases emitted during food decomposition.

At typical levels of humidity, a paper surface becomes coated with a thin layer of water, which absorbs water-soluble gases from the environment (right panel of the figure). The gas molecules contribute positive and negative ions that change the water’s electrical conductivity by an amount proportional to the gases’ concentration. To access that electrical information, Güder and his team drew electrodes on paper (left panel) with commercial carbon ink and a ballpoint pen. The device’s conductivity was sensitive to the concentration of ammonia and trimethylamine (TMA), two water-soluble gases associated with food spoilage.

Güder and his colleagues used the sensor to monitor the spoilage of a chicken breast and codfish at room temperature and codfish in the fridge. As the meats decomposed, they produced ammonia, TMA, and dimethylamine, and the sensor’s response increased by up to a factor of 10.

The team integrated the paper sensor into a commercial near-field-communication tag so it could talk to a smartphone. Below a threshold amount of ammonia, the sensor responded to the smartphone; above the threshold, the tag was unresponsive. In a practical application of the sensor, a manufacturer would set the threshold to an appropriate concentration for the product, and the consumer would check the freshness with their phone.

The sensor does have a couple of drawbacks. Its response depends strongly on humidity and doesn’t distinguish among species of water-soluble gases. But the humidity is stable in some environments, such as packaged food, or can be monitored separately, and chemical additives are able to tune water’s sensitivity for specific gases. (G. Barandun et al., ACS Sens., 2019, doi:10.1021/acssensors.9b00555; thumbnail photo credit: Lance Cheung/USDA.

Materials provided by American Institute of Physics

micro submarines

‘Submarines’ small enough to deliver medicine inside human body

Cancers in the human body may one day be treated by tiny, self-propelled ‘micro-submarines’ delivering medicine to affected organs after UNSW Sydney chemical and biomedical engineers proved it was possible.

In a paper published in Materials Today, the engineers explain how they developed micrometre-sized submarines that exploit biological environments to tune their buoyancy, enabling them to carry drugs to specific locations in the body.

Corresponding author Dr Kang Liang, with both the School of Biomedical Engineering and School of Chemical Engineering at UNSW, says the knowledge can be used to design next generation ‘micro-motors’ or nano-drug delivery vehicles, by applying novel driving forces to reach specific targets in the body.

“We already know that micro-motors use different external driving forces – such as light, heat or magnetic field – to actively navigate to a specific location,” Dr Liang says.

“In this research, we designed micro-motors that no longer rely on external manipulation to navigate to a specific location. Instead, they take advantage of variations in biological environments to automatically navigate themselves.”

What makes these micro-sized particles unique is that they respond to changes in biological pH environments to self-adjust their buoyancy. In the same way that submarines use oxygen or water to flood ballast points to make them more or less buoyant, gas bubbles released or retained by the micro-motors due to the pH conditions in human cells contribute to these nanoparticles moving up or down.

This is significant not just for medical applications, but for micro-motors generally.

“Most micro-motors travel in a 2-dimensional fashion,” Dr Liang says.

“But in this work, we designed a vertical direction mechanism. We combined these two concepts to come up with a design of autonomous micro-motors that move in a 3D fashion. This will enable their ultimate use as smart drug delivery vehicles in the future.”

Dr Liang illustrates a possible scenario where drugs are taken orally to treat a cancer in the stomach or intestines. To give an idea of scale, he says each capsule of medicine could contain millions of micro-submarines, and within each micro-submarine would be millions of drug molecules.

“Imagine you swallow a capsule to target a cancer in the gastrointestinal tract,” he says.

“Once in the gastrointestinal fluid, the micro-submarines carrying the medicine could be released. Within the fluid, they could travel to the upper or bottom region depending on the orientation of the patient.

“The drug-loaded particles can then be internalised by the cells at the site of the cancer. Once inside the cells, they will be degraded causing the release of the drugs to fight the cancer in a very targeted and efficient way.”

For the micro-submarines to find their target, a patient would need to be oriented in such a way that the cancer or ailment being treated is either up or down – in other words, a patient would be either upright or lying down.

Dr Liang says the so-called micro-submarines are essentially composite metal-organic frameworks (MOF)-based micro-motor systems containing a bioactive enzyme (catalase, CAT) as the engine for gas bubble generation. He stresses that he and his colleagues’ research is at the proof-of-concept stage, with years of testing needing to be completed before this could become a reality.

Dr Liang says the research team – comprised of engineers from UNSW, University of Queensland, Stanford University and University of Cambridge – will be also looking outside of medical applications for these new multi-directional nano-motors.

“We are planning to apply this new finding to other types of nanoparticles to prove the versatility of this technique,” he says.

Materials provided by University of New South Wales

new battery technology

Accidentally created new battery technology can last 400 times longer

Researchers in the US have created a battery capable of being recharged hundreds of thousands of times without showing signs of wear, spelling a potential end to electronics rendered useless by dead cells.

The batteries of today are mainly lithium, and over time that lithium corrodes inside the battery.
Instead of lithium, researchers at UC Irvine have used gold nanowires to store electricity, and have found that their system is able to far outlast traditional lithium battery construction. The Irvine team’s system cycled through 200,000 recharges without significant corrosion or decline.

The original aim of the experiment was simply to make a solid-state battery that used an electrolyte gel rather than a liquid to hold its charge – lithium batteries contain liquid, which makes them extremely combustible and also sensitive to temperature.

But when they started experimenting with gold nanowires suspended in this electrolyte gel, they found that the system was incredibly resilient. In fact, it was way, way more resilient than any other battery system.

Watch: How batteries work

The use of nanowires, which are thousands of times thinner than human hair, highly conductive and have a large surface area, in batteries is not new.

Lithium-ion batteries, used in most smartphones, are also made up of nanowires, but they are fragile and prone to breaking after repeated charges.

As such, batteries are currently designed to withstand a certain number of “cycles” – the equivalent of a battery fully draining.

By coating the nanowires in both a shell and the gel, the US researchers managed to prevent the nanowires from growing brittle.

During testing, it withstood 200,000 charges over three months. In that time the researchers failed to notice any decline in charge capacity or damage within the battery. Regular batteries currently on the market normally die after 7,000 charges at most, the study claimed.

The study was published in the American Chemical Society’s Energy Letters on April 20.