The rise of the robot jellyfish

A swimming device just a few millimetres long uses a magnetic drive to propel movement modelled on baby jellyfish

July 15, 2019

Marine animals have long been the inspiration for miniaturized submarines. Scientists at the Max Planck Institute for Intelligent Systems have now presented a swimming body just a few millimetres in size and made of rubber, which looks and moves like a jellyfish. Just like its natural counterpart, this tiny robot jellyfish is shaped like a star. It can be propelled with the help of a magnetic drive and can also capture small particles. Tiny swimming devices such as these could be put to use for environmental protection or medicinal purposes, but they could also help with investigations of how their natural counterpart copes with changing environmental conditions.

A swimming robot performs the dance of the seven veils: Using a green dye, Max Planck researchers can visually demonstrate the flows a jellyfish-shaped robot creates when a magnetic field is used to open and close it like an umbrella. The mechanism enables the robot jellyfish to swim through the water like its natural counterpart.

Beach holidaymakers are not the only people with whom jellyfish are unpopular. Fishermen and marine ecologists also dread them, as in many places they are rampant, devouring everything across entire marine regions and robbing fish of their food. Their distribution depends strongly on the survival of their juveniles, the ephyra larvae. The chances of survival of the ephyra larvae are in turn influenced by their swimming and predatory behaviour. To investigate this under changing environmental conditions, biologists could in future use a robot model of baby jellyfish. The researchers at the Max Planck Institute for Intelligent Systems in Stuttgart have now constructed a swimming body about five millimetres in size, using these molluscs as their model.

“We are learning from a range of biological systems and are using them as our inspiration to develop tiny bio-inspired robots,” says Metin Sitti, Director at the Max Planck Institute for Intelligent Systems in Stuttgart. “We use them to study and better understand biological systems. But more importantly: one day, such robots may be able to help overcome critical scientific and technological challenges in healthcare and the environment.”

The robotic jellyfish can be opened and closed like an umbrella

The robot is constructed from a piece of star-shaped silicone rubber which is peppered with magnetic particles. The ‘rays’ of this rubber star are extended by non-magnetic plastic extensions. By applying a magnetic field of alternating direction and strength to an aquarium containing the robot jellyfish, the researchers open and close the rubber star like an umbrella, propelling the miniature swimmer along. Just like its natural counterparts, the robotic jellyfish can use its closing body to trap particles floating in the water. However, in addition to natural jellyfish-like movement, it can also open and close in a slightly modified fashion, enabling it to carry out a part of the movement more quickly, take a longer time overall to open and close, or perform an extra glide phase.

Using nature’s blueprint: When constructing their new swimming robot, Stuttgart Max Planck researchers took inspiration from the young form of the Scyphozoa jellyfish (Scyphomedusae ephyra, left). The robot jellyfish consists of a star-shaped magnetic piece of rubber (centre, brown). Each lappet of the magnetic rubber piece is extended by two non-magnetic plastic pieces (grey), which are connected by joints to each other and to the central rubber piece. The researcher use a pipette to place a bubble (greenish) into the centre of the robot jellyfish, to reduce the density of the miniature swimmer. A photo (right) shows what the robot actually looks like.

The additional features are also helpful in experiments on the behaviour of baby jellyfish in the sea. Robotic simulation has a great advantage: “It's much easier to record and measure the swimming behaviour of our robot than that of real jellyfish,” says Ziyu Ren, who helped develop the miniature swimmer. “The motion data are cleaner and we can ask questions, such as what happens to the fluid around it if the jellyfish swims in a different way.” Experiments with the robot jellyfish could simulate what happens when the environmental conditions for jellyfish change - for example, due to warming or acidification of the oceans, or due to pollutants. Such changes could affect the swimming and predatory behaviour of the jellyfish, which in turn would affect the corresponding ecosystems.

A model to study the mixing of the oceans

“We can use the little robot to study important environmental issues,” says Metin Sitti. “The jellyfish plays an important role in the ecosystem of the ocean.” These marine animals also stir up the water and create currents. Changes in their swimming behaviour could therefore also affect their ability to mix the seawater. “Understanding the relationship between the robot’s movement and the resulting fluid flow can help us evaluate the potential effects of climate change on water mixing,” says Metin Sitti.

In addition to answering environmental questions, the robot jellyfish could also find other practical applications. The miniature swimmer can not only capture and transport objects, it can also mix different fluids or chemicals in a solvent, or even dig into the bottom of a body of water.

The miniature swimming robot may also have applications in the field of medicine. One possible application scenario is to use ultrasound imaging to steer the robot so that it swims into the bladder and connects to a target, such as cancerous tissue. Once there, it could release a controlled dose of cancer medication over a prolonged period. This would avoid or at least reduce the discomfort of conventional treatment, while at the same time increasing the treatment's efficiency.

LB/PH

Go to Editor View