Scientists have been trying to create a miniature robot based on magnetic microparticles for a long time. But the previously demonstrated developments in this area (we will discuss them below) did not have the desired characteristics: they were either too hard and not adaptive enough, or they had very low mechanical strength.
At the end of January 2023, the research journal Matter published an article about a new liquid robot created from a magnetically active phase-transition substance. According to scientists, the invention was not inspired by the famous T-1000 from Terminator 2: Doomsday, but by sea cucumber, an invertebrate echinoderm that can go from a semi-liquid state to a solid state in a few seconds.
The basis for the miniature robot was gallium, a metal that melts at a temperature of 29.7646°C. Adding magnetic microparticles of neodymium to it, gland and boron made it possible to quickly transfer matter from solid to liquid using a tuned magnetic field. By placing alloy between two variable magnets, scientists not only melted the metal without external heat sources, but were also able to correct the direction of motion of the liquid robot. The presented miniature prototype has:
Potentially, the robot can be used to place electronic components on boards. The presentation showed the use of the robot as a smart solder: it was used to install and attach a small diode to a chip. Scientists have also demonstrated the possibility of using their development in medicine, for example, to remove foreign objects from the stomach or to deliver drugs locally.
So far, this only demonstrates the ability of metal alloys to be dynamically controlled reconfigurable. But engineers hope that such technologies will be widely used in the field of biomedicine in the future.
This is not the first time scientists have shown experiments with gallium. In 2018, an international team of researchers from China and Australia created a robot consisting of a plastic wheel, a lithium power supply, and a droplet of liquid gallium.
The structure rotated as liquid metal moved through a tube located inside the wheel. The movements of molten gallium, in turn, were controlled by changing the voltage supplied by the built-in lithium battery.
Lee Xiangpeng, a professor of robotics who developed this robot, said in his speech that tiny gallium-based nanorobots will soon be able to deliver cancer drugs to the human body in a targeted manner, as well as track down new malignant cells and localize them. He later added that such miniature vehicles would also be used in the military-intelligence field.
A magnetically active phase-transition substance created on the basis of gallium is not the first material presented by scientists that can transition from solid to liquid. Engineers have been developing miniature plastic “robots” that can deliver drugs in a targeted manner for a long time.
In 2022, a team of scientists from Suzhou State University introduced a microscopic robot that can break down into droplets and then reassemble. The study was published in the scientific journal Science Advances. According to the article, the robot consists of ferrofluid — magnetic iron oxide nanoparticles combined with hydrocarbon oil. To demonstrate the development capabilities, scientists assembled a labyrinth with obstacles and narrow sections, through which a soft robot was successfully guided. Using an external magnetic field, the inventors controlled droplets of liquid: they stretched them, squeezed them, made them rotate, jump and perform other actions.
In general, scientists have been creating microrobots from ferrofluids for medical purposes for a long time. Back in 2011, engineers from the US Department of Energy's National Research Center created magnetic robots smaller than 1 mm in size that can move and assemble into different shapes in an organized manner under the influence of an external magnetic field.
Unfortunately, ferrofluids, like elastomers (silicones) used to create soft robots, have a number of limitations. The former are considered to be a very unstable material, which significantly narrows the scope of application. The latter have too low plasticity, and therefore are poorly exposed to programmable deformations.
Not only elastomers, ferrofluids and gallium are suitable for creating soft-bodied robots. In 2022, another Hong Kong scientist presented a slime robot consisting of a mixture of PVA (polyvinyl alcohol) and sodium tetraborate (borax). The magnetic particles in the polymer made it possible to control the movement of the substance using a magnetic field, and the ability of the resulting material to self-repair was to combine individual particles into a single whole.
At the presentation, the researchers showed that the created material can adapt to changing mechanical conditions (compression, bending, stretching), which makes it possible to manufacture dynamic motion sensors based on it. The robot is also able to remove swallowed objects from the stomach without using surgical instruments. So far, the mucus presented is poisonous to humans, but if you place it in a shell of silicon dioxide, you can prevent toxins from entering the body when using it.
The field of liquid robotics is just beginning to develop, but it is already showing great promise. The potential use of new developments in medicine will make it possible to diagnose complex diseases at an early stage, treat serious diseases locally without killing healthy body cells, and save more lives. Liquid technologies can also help people with disabilities and contribute to a technological breakthrough in the field of biomechanics.
