Reviewed by Lexie CornerOct 23 2024
A recent study published in the Proceedings of the ACM on Interactive, Mobile, Wearable, and Ubiquitous Technologies introduces two new types of on-skin electronics that can be built and customized directly on the body. These innovative technologies hold potential for applications in biometric sensing, medical monitoring, interactive prosthetic makeup, and other fields.
An ECSkin on-body display, composed of modular electrochromic films, is flexible and soft and easily conforms to complex body parts such as the wrist. Image Credit: Hybrid Body Lab/Provided
An on-skin electronic interface called SkinLink, developed by the Hybrid Body Lab under the leadership of Cindy Hsin-Liu Kao, an assistant professor of human-centered design at the College of Human Ecology, offers design flexibility tailored to specific uses. Additionally, the electrochromic display interface, ECSkin, can be created directly on the body and features a modular design with tiles that can be arranged as needed.
SkinLink has potential applications in vital sign and posture monitoring, proximity sensing, and body art.
Both of these projects are modular prototyping toolkits, to enable much more intricate on-skin circuitry prototyping. And users are able to build the circuitry directly on the skin surface.
Cindy Hsin-Liu Kao, Assistant Professor, Cornell University
Pin-Sung Ku, a doctoral student and lab member, is the lead author of the paper titled "SkinLink: On-body Construction and Prototyping of Reconfigurable Epidermal Interfaces," which was presented in early October at UbiComp/ISWC '24, the Association for Computing Machinery's international joint conference on pervasive and ubiquitous computing.
This study received the Distinguished Paper Award from the Proceedings of the ACM on Interactive, Mobile, Wearable, and Ubiquitous Technologies, first published in June 2023. Another project from the lab, ECSkin: Tessellating Electrochromic Films for Reconfigurable On-skin Displays, was also presented at the conference and will be published in the same journal on May 15th, 2024, with Ku as the lead author and Cindy Hsin-Liu Kao as the senior author on both papers.
SkinLink builds upon the lab’s previous work, SkinKit, which was introduced at UbiComp in 2021. SkinKit featured slim, flexible printed circuit boards in temporary tattoo form. However, the earlier version had predefined behaviors and larger surface areas, limiting its customizability.
There were several issues we didn’t address in SkinKit, such as how to allow users to program the modules the way they want to. For SkinKit, everything was pre-programmed; users had to attach things in a certain order. With SkinLink, there is more customizability of the functions they like.
Pin-Sung Ku, Doctoral Student, Cornell University
For example, with SkinKit, the circuitry had to be fully constructed before being applied to the body. In contrast, SkinLink allows users to add more customization by placing one module on the body first and then adding others as needed.
The SkinLink toolkit includes functional circuit modules made from flexible printed circuit boards, along with custom-designed flexible wiring, known as trace modules or traces, which connect the sensor and actuator modules to the microcontroller board.
This marks a significant improvement over SkinKit. The smaller circuit boards in SkinLink connect via flexible wiring, providing greater freedom of movement while maintaining consistent connectivity.
Ku added, “The circuit boards are somewhat rigid but we created the traces to be elastic, stretchable and flexible, so as not to hinder body movement.”
The on-body fabrication process for SkinLink begins with selecting and programming the circuit board and trace modules. During this stage, the microcontroller board can be programmed multiple times to fine-tune the circuit’s functions. The modules can be temporarily placed on the body for customization before being permanently installed.
In a 14-person study, the researchers conducted A/B testing to compare the usability of SkinLink and SkinKit. They found that SkinLink offers a more flexible wiring process, allowing for unrestricted circuit arrangement and improved wearability. SkinLink has a smaller footprint, is more stretchable, easier to fabricate, and wears more seamlessly than SkinKit.
Kao described SkinKit as providing a "low floor"—a term coined by computer scientist Ben Shneiderman—meaning that even people with little to no experience could quickly begin designing and prototyping wearable technology. She explained that SkinLink takes it a step further.
Kao added, “Another goal is what we call ‘high ceilings and wide walls. High ceilings means increasing the complexity of the prototypes; wide walls refers to the vast array of things that could be designed. That’s what I think SkinLink really does.”
Kao described SkinLink and ECSkin as "enabling technologies" with diverse applications. In studies using SkinLink, participants included artists, wearable tech researchers, and psychology researchers for physiological sensing. Kao also envisions applications extending beyond human use.
She concluded, “Being able to use this as a functional technology for physiological sensing or artistic practice is one application. Our work has focused on skin interfaces for humans, but I think there could also be potential for designing ‘skin’ interfaces for other living beings, such as animals, and sensing for agricultural purposes, even on plants. We are interested in bringing SkinLink to broader disciplines to support on-skin prototyping.”
National Science Foundation supported the study.
Journal Reference:
Ku, P.-S. et. al. (2024) SkinLink: On-body Construction and Prototyping of Reconfigurable Epidermal Interfaces. ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies. doi.org/10.1145/3596241