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Triboelectric nanogenerator for shoulder rehabilitation


Patients living with shoulder related musculoskeletal impairments – originating from chronic conditions or acute events such as injury or stroke – rely on both passive supports and prescribed physical exercises to aid in their rehabilitation.

Video games are an increasingly popular tool used by occupational therapists working with these patients. The combination of visual simulation and physical movement can make the experience more fun. And now, a group of engineers from KAIST (Korea Advanced Institute of Science and Technology) have developed a self-powered, wearable gravity support device that they say can aid in gaming-based exercises for shoulder rehabilitation. They write about their device in a forthcoming issue of Nano Energy [DOI: 10.1016/j.nanoen.2022.107179],

They started by 3D printing a structure from thermoplastic polyurethane, complete with foldable joints.  Its design was based on the so-called ‘waterbomb base model’ – a traditional origami fold that turns a 2D plate into a 3D structure. Once folded, the joint’s stiffness was countered and assisted using tension and torsion springs respectively, to provide appropriate support to the wearer’s shoulder.

A pair of triboelectric nanogenerators (TENGs) made from nanopatterned PTFE and aluminium tape were constructed and inserted into to the folded structure, so that the wearer’s motion would activate their repeated contact-separation interaction. The authors also built a simple signal digitization and game control system using custom fabricated PCB and Arduino Pro Mini. This acted as the interface between the TENG outputs and the software that ran a table-tennis computer game.

With all of the elements in place, the team began a pilot clinical study with four participants – one without any upper-arm impairment, one with mild impairment, and two with severe impairment. Each participant wore the support device on their impaired shoulder, with the main structure nestled within the armpit, while they carried out a range of tasks.

The participant’s range of motion (ROM) and angular velocity were measured using an optical marker tracking system, while the output voltage of the TENGs was measured. They found a relationship between the two, leading the authors to suggest that “the output signal from Origami TENG could be used to assess patient upper-arm impairment severity with respect to ROM and motion speed.” They also investigated muscle fatigue with and without the origami TENG, to understand its use as a support device. Non-supported deltoid muscles showed much greater fatigue than when the device was worn, but results were inconclusive for the upper trapezius and pectoralis major muscle groups.

Next, participants were asked to play a table tennis game, which involved moving their supported arm horizontally from side-to-side. The game control sensitivity was such that only a slight movement of the arm was needed. However, this low-frequency arm motion did not generate a sufficiently high TENG output to charge the capacitor. Energy harvesting was achieved when the participants moved their arm more aggressively.

Participants also had to complete a survey, which asked questions about how comfortable the device was to wear, whether the exercises and device provided an engaging rehab experience, and if they’d want to use it again. All responded positively, describing the ability see immediate progress as “motivating” and “engaging”, and said that they “would be willing to use the device at home to help with their recovery.”


This story was written for Materials Today, and it was published on their site on 11th April 2022:

Original research paper: Divij Bhatia, Kyoung-Soub Lee, Muhammad Umer Khan Niazi, Hyung-Soon Park “Triboelectric nanogenerator integrated origami gravity support device for shoulder rehabilitation using exercise gaming,” Nano Energy In press. Available online 23 March 2022, 107179. DOI: 10.1016/j.nanoen.2022.107179