Soft Artificial Muscles Show Promise in Quieting Hand Tremors

For the estimated 80 million people worldwide living with tremors, simple daily activities like holding a coffee cup can be frustratingly difficult. Now, researchers have developed slim, lightweight artificial muscles that could one day be discreetly worn to suppress these involuntary movements.

Scientists at the Max Planck Institute for Intelligent Systems, the University of Tübingen, and the University of Stuttgart have demonstrated that a pair of artificial muscles, strapped along a person’s forearm, can effectively counteract the back-and-forth movement caused by tremors.

The technology, detailed in a study published March 6 in the journal Device, uses soft materials that contract and relax in response to electrical signals, working against the tremor’s rhythm to stabilize hand movement.

“We see a great potential for our muscles to become the building blocks of a garment one can wear very discreetly so that others don’t even realize the person suffers from a tremor,” said Alona Shagan Shomron, a postdoc in the Robotic Materials Department at Max Planck Institute for Intelligent Systems and first author of the research paper.

The team’s approach addresses a significant gap in current tremor treatments. While medications and surgical interventions like deep brain stimulation can help many patients, these options may come with side effects or become less effective over time. Some patients can’t use these treatments at all.

Testing Without Patients

To avoid putting experimental technology directly on patients, the researchers developed what they call a “mechanical patient” – a robotic arm that can reproduce tremors recorded from actual patients. This allows them to test how well their artificial muscles work without subjecting real people to early-stage technology.

The robotic arm can be programmed to mimic various tremor patterns, from mild to severe, and at different frequencies. This covers the range typical of conditions like Parkinson’s disease and essential tremor.

In tests, the artificial muscles – technically known as Peano-HASEL actuators – reduced tremor amplitude by 76 to 94 percent across various intensities and frequencies.

“We showed that our artificial muscles, which are based on the HASEL technology, are fast and strong enough for a large range of tremors in the wrist,” Shagan Shomron said.

The team also created computer simulations to verify that the forces generated by these artificial muscles would be sufficient to suppress tremors in actual human arms, not just their mechanical model.

A Different Kind of Muscle

The artificial muscles used in the study are unlike traditional rigid robotic components. Measuring just about one millimeter thick and weighing only 15 grams, they’re made of thin polyester sheets with carbon-based electrodes, filled with silicone oil.

When voltage is applied, the liquid inside is displaced, causing the material to contract like a natural muscle. This design allows them to respond quickly enough to counteract the rapid, rhythmic movements of a tremor.

The softness and flexibility of these actuators make them potentially more comfortable and less obtrusive than rigid devices, addressing a key barrier to patient acceptance of wearable assistive technology.

From Lab to Life

Current tremor treatments span from medication to invasive surgery, but limitations persist with these approaches. Some patients develop tolerance to treatments over time, while others experience significant side effects. The team believes their technology could offer a non-pharmacological, non-surgical alternative.

“With the combination of mechanical patient and biomechanical model we can measure if any tested artificial muscles are good enough to suppress all tremors, even very strong ones. So if we ever created a wearable device, we could adjust it to respond individually to each tremor,” said Daniel Häufle, a professor at the Hertie Institute for Clinical Brain Research at the University of Tübingen who worked on the computer simulation and collected tremor data from patients.

The research remains in early stages, and several challenges must be addressed before these artificial muscles could become part of a wearable device for patients. The current design works at a single wrist position, and safety systems for the electrical components would need further development.

There’s also the question of how such a device would distinguish between voluntary movements and involuntary tremors – something the current research doesn’t address but which would be essential for a practical application.

Beyond Tremors

The testing platform developed for this study could accelerate research in other movement disorders as well. Syn Schmitt, Professor for Computational Biophysics and Biorobotics at the University of Stuttgart, highlighted the value of their approach for early-stage research.

“The mechanical patient allows us to test the potential of new technologies very early in the development, without the need for expensive and time-consuming clinical testing on real patients,” Schmitt said. “A lot of good ideas are often not further pursued, as clinical testing is expensive and time-consuming and hard to fund at very early stages of technology development. Our mechanical patient is the solution which allows us to test the potential very early in the development.”

For people living with tremors, the prospect of a lightweight, inconspicuous device that could steady their hands without medication or surgery represents a promising avenue of research, though commercial applications likely remain years away.

“Robotics has great potential for healthcare applications. This successful project highlights the key role that soft robotic systems, based on flexible and deformable materials, will play,” concluded Christoph Keplinger, the Director of the Robotic Materials Department at the Max Planck Institute for Intelligent Systems.