Tiny robots
Computer graphic of a microvehicle with iron wheels (gold) and a polymer chassis (red). The vehicle measures just 0.25 millimetres long. Credit: Alcântara et al. Nature Communications 2020

Scientists at ETH Zurich have built up a technique with which they can manufacture machines as small as micrometers in which several materials are interwoven in a complex way. Such microrobots are set to revolutionize medicine one day.

Robots are so tiny that they can move through our blood vessels and deliver medications to specific points in the body. Scientists have been pursuing this goal for quite a long time. Presently, scientists at ETH Zurich have succeeded for the first time in building such “micromachines” out of plastic and metal, in which these two materials are interlocked as intently as links in a chain. This is conceivable gratitude to a new manufacturing method they have devised.

Carlos Alcântara, formerly a doctoral student in Salvador Pané’s group at the Institute of Robotics and Intelligent Systems explains, “Polymers and metals have different properties, and both materials offer specific advantages in building micromachines. Our goal was to benefit from all these properties simultaneously by combining the two.” 

As a rule, micromachines are powered from outside the body utilizing magnetic fields, which means they should have magnetic metal parts installed. Polymers, in contrast, have the advantage that they can be utilized to construct soft, flexible components as well as parts that dissolve inside the body. If medication is embedded in this kind of soluble polymer, it’s possible to specifically supply active substances to specific points in the body.

Microscopic image of the two-component micro vehicle shown above. Credit: Alcântara et al. Nature Communications 2020

High-tech manufacturing method

The new manufacturing method depends on the expertise of ETH professor Salvador Pané. For years he has been working with a high-accuracy 3D printing technology that can be utilized to produce complex objects on a micrometer scale: 3D lithography. The ETH researchers utilized this technology to produce a type of casting mold for their micromachines. The latter have thin channels that fill in as a negative and are filled with the appropriate material.

The specialists utilize electrochemical deposition to fill some channels with metal, while others fill them with polymers. At long last, the mold is dissolved with solvents.

Fabian Landers a doctoral student in Pané’s group says, “We were able to develop this method because electrical engineers, mechanical engineers, chemists, and materials scientists work closely together in our interdisciplinary group.” 

A vehicle with tiny magnetic wheels

Microscopic images of further examples of two-component micromachines. (Image: Alcântara et al. Nature Communications 2020)

As confirmation of the attainability of joined micromachines, the ETH engineers created different tiny vehicles with plastic chassis and magnetic metal wheels that can be driven by a rotating magnetic field. These include those that can be proceeded onward a glass surface and others that – relying upon the polymer utilized – can swim in liquid or on a liquid surface.

The researchers will presently build up their two-part micromachines further and experiment with other materials. They will also attempt to make more complex shapes and machines, including those that fold and unfold. In addition to the active substance-releasing ferries, future application possibilities include micromachines with which aneurysms (blood vessel bulges) can be treated or other operations performed. Another research goal is expandable stents (tubular vascular supports), which can be brought to the desired location in the body with magnetic fields.

More information: C. C. J. Alcântara et al. Mechanically interlocked 3D multi-material micromachines, Nature Communications (2020). DOI: 10.1038/s41467-020-19725-6