These aint your grandpa’s medical electrodes.
In the olden days, electrodes were metallic and inflexible – great for durability, but lousy for remaining connected to any human being who’s actually moving (which humans tend to do unless they’re dead). If you’re undergoing physiotherapy or rehabilitation, you might actually need to move your body under your therapist’s observation to get better. So, electrodes that fall off or go flying are anything but ideal.
For at least a decade, the better option was hydrogel electrodes, squishy pieces of sponge-like med-tech that could absorb water and stretch with movement. But because (again like a sponge) hydrogel also dries, sooner or later the electrodes stop stretching and fall off.
Enter the latest generation of electrodes. Not made of rigid metal, or jelly, they’re an electrically conductive “inktelligent” technology you can paint onto the body to receive electroencephalographic (EEG) readings from the brain, electrocardiographic (ECG) signals from the heart, and electromyographic (EMG) signals from muscular contractions.
Larry Cheng, corresponding author of his team’s Proceedings of the National Academy of Sciences paper and Professor of Engineering Science and Mechanics at Pennsylvania State University, writes that their inktelligence tech “supports personalized designs for improved user acceptance, and is potentially compatible with MRI imaging.”
While customizability may seem trivial from a purely mechanical standpoint, medicine is a science for psychologically and socially diverse human beings. One of the many reasons that Google Glass failed was that few people wanted to parade in public looking like cyber-dorks. As the U-Penn paper explains, “lack of personalization further discourages long-term use, particularly among children, adolescents, and individuals sensitive to stigma.”
“The ink itself almost behaves like face paint,” says Cheng of the substance, composed of polymers and acids in a watery solution. Although gluey when applied, it can dry in under 10 minutes, and even faster with a hair dryer. Once dry, it can stretch to 150% of its original size without breaking while still accurately recording electrical signals.
While the inks starts “almost transparent,” says Cheng, “you can use food dye to pigment the ink into whatever colors you need to paint whatever design you have in mind – like a cartoon or Superman. This allows us to completely personalize the wearable [sensor] to a person’s preference.”
That customizability means the ink can be as invisible as the wearer desires, unlike pale pink “flesh tone” bandages that were anything but for around two-thirds of humanity.
Wanqing Zhang
In addition to being paintable onto dry skin, these electronic tattoos are so thin they’re almost unnoticeable (and thus non-irritating) to the wearer, adhere a long time, can be adapted into any image with a range of colors, and enable, as the paper says, “seamless integration with porous silver textile connectors, yielding an interlocked junction with a built-in modulus gradient for stable signal transmission.”
As EMG sensors, the inktelligence uses machine learning to recognize gestures, and allows robotic hand control. Because the technology doesn’t produce image artifacts, it may also one day permit electrophysiology and multimodal MRIs.
Another way that the U-Penn system offers a massive improvement over previous rigid and hydrogel electrodes – which poorly adhere to hairy skin, or skin wet from perspiration – is in their actual dermal application.
“Most commercial electrodes are prefabricated in a lab or factory and then layered on the skin, meaning there is an air-gap between the skin and the electrode [which degrades] sensing performance,” says Wanqing Zhang, lead author and an engineering science and mechanics doctoral candidate. But because his team’s conductive ink conforms to skin, it has no air-gap at all, and thus provides far more accurate EEG, ECG, and EMG.
While other electrodes accumulate irritating moisture and dirt over days of use, because the inktelligence is porous, Cheng says it “can allow moisture or hair to better pass through the material, making the electrodes more conductive, adhesive and comfortable,” even across 12 hours or during exercise. In the future, “a single bottle of ink could provide enough material to paint multiple electrodes over the course of several days or a week.”
Another remarkable EMG achievement was tracking electrical signals from a co-author’s forearm. After sending the telemetry into robotic hand, the co-author could control it without touching it.
If the team’s plans succeed, future inktelligence will be able to detect cortisol, glucose, and other biomarkers, with robust uses for pediatricians. They may even develop “smart plants” for tracking chemical exposures and their effects on plant health. As a skin-deep sensor, inktelligence may be the ultimate in wearable technology.
Source: Pennsylvania State University
