Muscles in the body expand and contract effortlessly when wriggling toes or lifting groceries. Some polymers can act as artificial muscles when activated by dangerously high voltages.
Researchers have identified a series of thin, elastic films that respond to significantly lower electrical charges. The materials are a step toward creating artificial muscles that could one day be used safely in medical devices. The study was published in ACS Applied Materials & Interfaces.
Artificial muscles could be essential in developing movable soft robotic implants and functional artificial organs. Electroactive elastomers, such as bottlebrush polymers, are promising materials for this task as they start soft but stiffen when stretched. When electrically charged, they can alter their shape.
However, available bottlebrush polymer films only move at voltages more than 4000 V, which exceeds the 50 V maximum recommended by the US Occupational Safety and Health Administration.
Lowering the thickness of these films to less than 100 µm could reduce the required voltages, although this has yet to be done successfully with bottlebrush polymers. Dorina Opris and her colleagues hoped to develop an easy solution to make thinner films.
The bottlebrush polymers were created by reacting norbornene-grafted polydimethylsiloxane macromonomers and cross-linking the products with UV light. With an operating voltage of 1000 V, a 60- µm-thick material was the most electroactive, stretching more than earlier recorded elastomers.
A circular actuator from that material expanded and contracted more than 10,000 times before degrading. In another set of studies, the researchers added polar side chains to polymers and created materials that could respond to voltages as low as 800 V. They did not extend as much as the team’s most electroactive film. According to the findings, the material might be used to build durable implants and other medical devices that operate at lower voltages with some alterations.
The study received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation program, the Swiss National Science Foundation, the Swiss Federal Laboratories for Materials Science and Technology, and the China Scholarship Council.
Adeli, Y., et al. (2023). On-Demand Cross-Linkable Bottlebrush Polymers for Voltage-Driven Artificial Muscles. ACS Applied Materials & Interfaces. doi.org/10.1021/acsami.2c23026.