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Many scientists agree that the future is microbotic – and possibly also nanobotic.

They argue that fleets of tiny robots can offer a great deal of benefit to many industries, including healthcare and national defense. However, these robotic swarms will need a lot of power to achieve their ends.

An alternative energy sources

It’s thought that electricity from conventional sources may not cut it for the purpose of powering these tiny robots.

A team of researchers has developed a possible workaround for this problem: a new form of tiny robot that uses reactions to humidity to get around. Their brand of artificial movement can apply to two or three dimensions, and be used to complete simple tasks. The ‘hygrobots’, as they are known, could be a viable alternative to more traditional, mechanical robots with more moving parts.

The ‘hygrobot’ is in fact a kind of actuator, although its movement can look more compellingly biological and complex than you may expect from such a simple machine.

Much like the plant parts they are inspired by, they can achieve motions such as crawling forward, reaching upward or even twisting into loose coils as a result of absorbing miniscule amounts of water that are in their vicinity. They are the work of a group of researchers at Seoul National University’s Department of Mechanical and Aerospace Engineering; College of Medicine; Institute of Advanced Machines and Design and Department of Plastic and Reconstructive Surgery. Led by Professor Ho-Young Kim, they intend their hygrobots to be applied to areas of human medicine such as next-generation dermal and transdermal therapies.

The hygrobots are composed of two layers, much like the motile seed layers they are inspired by. One is made of nanofibres that can swell rapidly in response to the directionality, or amount, of humidity in its immediate vicinity. This causes a narrow strip of the complete hygrobot material to achieve vertical movement, meaning that it jerks upwards abruptly. At this point, the second layer kicks in to regulate the movement, which can result in the strip moving forwards rather than upwards. It has a friction coefficient that opposes that of the nanofibre layer; therefore, it modifies the oscillation of the nanofibres’ movement, ultimately keeping an entire hygrobot strip moving forwards.

The team of researchers can also create strips with different conformations or proportions of each layer’s material, thus varying the nature of hygrobot movement. Alternatively, hygrobots in shapes besides the simple strip, or attached to paper ‘skeletons’ of different shapes could be capable of differential motions. The team demonstrated these possibilities by exhibiting hygrobots with paper ‘legs’ that could not only crawl along while bending in the middle, but move forwards as a result of coiling at a ‘tail’ end while pushing a T-shaped ‘head’. In addition, a robot with alternating paper and hygrobot sections could move on its narrow edge while coiling loosely, while another on its edge could move by swishing a hygrobot ‘tail’.

Possible applications for hygrobots

In their present form, the hygrobots do not move very fast, although they do so patently and visibly in real time. They are also macroscopic, being about 2.5 centimetres long and a few millimetres in width. However, they may have useful applications even at this scale.

The team also showcased an experiment in which a simple hygrobot impregnated with antibiotics was placed in a Petri dish of culture medium. The dish was then inoculated with bacteria, which take over the entire surface of the medium with colonies in the normal course of things. However, the hygrobot could drag itself across the medium, eradicating all the bacteria in its path as it moved from one end of the dish from the other.

Therefore, the hygrobots could conceivably be used to deliver drugs such as antibiotics to surfaces such as infected skin. They may be able to achieve wide coverage in this way, as they can move about following the moisture naturally released by this organ into the external environment. The hygrobots – which are currently manufactured using conventional processes such as electrospinning – are also non-toxic. The researchers, who published a paper on their work in the journal Science Robotics did not report any data on the suitability of their current materials for human administration, so further studies will be required to find out if it is non-reactive or allogenic.

The paper did however, give more details on how the bilayered structure of the hygrobot was developed and composed, which gave a favorable profile of humidity response times and overall bending direction of the two layers and how they related to each other. The researchers claimed that this led to vast improvements in how the hygrobots moved. In other words, their hygrobots showed a reproducible and predictable curving motion in response to humidity, whereas other similar materials previously designed to do the same tended to twist and bend uncontrollably. This may make the hygrobot the most sophisticated humidity-controlled robot currently in existence.

The hyrgobot is a form of actuating strip that bends upwards in the direction of a humidity source, but is forced to curve back downwards, thus moving forwards, by a second strip made of non-hygroresponsive material. This complete ‘machine’ has been proposed by its creators, a team of researchers from a South Korean university, as a kind of ‘artificial leech’ that could move across infected or injured skin to deliver drugs to such surfaces in the future.

Alternatively, this new material could also be incorporated to provide a possible new generation of microbots with electricity-free motion. This biologically-inspired mechanism represents an emerging trend in molecular robotics that could significantly enhance the future of technology.

Top image: Hydrobot prototype. South Korean university


Shin B, Ha J, Lee M, Park K, Park GH, Choi TH, et al. Hygrobot: A self-locomotive ratcheted actuator powered by environmental humidity. Science Robotics. 2018;3(14).

Potenza A. Forget batteries: this tiny, wriggly robot runs on moisture. The Verge. 2018. Available at:

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Deirdre O’Donnell

Deirdre O’Donnell received her MSc. from the National University of Ireland, Galway in 2007. She has been a professional writer for several years. Deirdre is also an experienced journalist and editor with particular expertise in writing on many areas of medical science. She is also interested in the latest technology, gadgets and innovations.Read More

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