Biodegradable artificial muscles: going green in soft robotics

Artificial muscles are an advanced technology that may one day allow robots to function like living organisms. Such muscles open up new possibilities for how robots can shape the world around us; from wearable aids that can redefine our physical abilities in old age, to rescue robots that can navigate rubble in search of the lost. But just because artificial muscles can have a strong social impact during use, doesn’t mean they have to leave a strong environmental impact after use.

The topic of sustainability in soft robotics has been brought into focus by an international team of researchers from the Max Planck Institute for Intelligent Systems (MPI-IS) in Stuttgart (Germany), Johannes Kepler University (JKU) in Linz (Austria), and University of Colorado (CU Boulder). , Boulder (USA). Scientists collaborate to design high-performance artificial muscles that are completely biodegradable – based on gelatin, oil and bioplastics. They demonstrated the potential of this biodegradable technology by using it to power a robot gripper, which could be very useful in single-use uses such as for garbage collection (watch Youtube video). At the end of its life, this artificial muscle can be disposed of in the municipal compost bin; under monitored conditions, they decompose completely within six months.

We see an urgent need for sustainable materials in the accelerated field of soft robotics. Biodegradable parts can offer sustainable solutions especially for single-use applications, such as for medical operations, search and rescue missions, and manipulation of hazardous substances. Instead of piling up in landfills at the end of product life, future robots can become compost for future plant growth,” said Ellen Rumley, visiting scientist from CU Boulder who works in the Department of Robotic Materials at MPI-IS. Rumley is the paper’s first co-author “Biodegradable electrohydraulic actuators for sustainable soft robots”published in Science Advances.

Specifically, the research team built an electrically actuated artificial muscle called HAZEL. In essence, HASELs are oil-filled plastic bags partially covered by a pair of electrical conductors called electrodes. Applying a high voltage to the pair of electrodes causes opposing charges to build up on them, producing a force between them that pushes the oil into the electrode-free region of the pocket. This oil migration causes the sac to contract, much like a real muscle. The main requirement for HASEL to deform is that the material that forms the plastic bag and oil is an electrical insulator, capable of sustaining the high electrical pressure generated by charged electrodes.

One of the challenges for the project was developing electrodes that were conductive, malleable and fully biodegradable. Researchers at Johannes Kepler University came up with a recipe based on a mixture of biopolymer gelatin and salt that can be directly thrown into a HASEL actuator. “It was important to us to manufacture suitable electrodes for these high-performance applications, but with readily available components and accessible fabrication strategies. Because the formulation we present can be easily integrated in many types of electrically driven systems, it serves as a building block for future biodegradable applications,” said David Preninger, first co-author on this project and a scientist in the Division of Soft Matter Physics at JKU.

The next step is to find suitable biodegradable plastics. Engineers for this type of material are primarily concerned with properties such as rate of degradation or mechanical strength, not with electrical insulation; requirements for HASEL operating at several thousand Volts. Nonetheless, some bioplastics show good material compatibility with gelatin electrodes and adequate electrical insulation. HASEL made from a certain combination of materials can even withstand 100,000 actuation cycles at several thousand Volts without signs of electrical failure or reduced performance. This biodegradable artificial muscle competes electromechanically with its non-biodegradable counterpart; exciting results for promoting sustainability in artificial muscle technology.

“By demonstrating the outstanding performance of this new material system, we are incentivizing the robotics community to consider biodegradable materials as a viable material option for building robots,” continues Ellen Rumley. “The fact that we achieved such great results with bio-plastics also hopefully motivates other materials scientists to create new materials with optimized electrical performance in mind.”

With the rise of green technology, the team’s research project is an important step towards a paradigm shift in soft robotics. Using biodegradable materials to build artificial muscles is just one step towards a future for sustainable robotic technology.

The goal of the Max Planck Institute for Intelligent Systems is to investigate and understand the organizing principles of intelligent systems and the perception-action-learning loop that underlies them.

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