Imperceptible sensors made from ‘electronic spider silk’ can be printed directly onto human skin

Researchers have developed a method to create adaptive and environmentally friendly sensors that can be printed directly and imperceptibly onto a wide range of biological surfaces, whether that’s a finger or a petal.

The method, developed by researchers at the University of Cambridge, is inspired by spider silk, which can adapt and adhere to a variety of surfaces. This ‘spider silk’ also contains bioelectronics, so that various detection capabilities can be added to the ‘web’.

The fibers, at least 50 times smaller than a human hair, are so light that the researchers printed them directly onto the fluffy seed head of a dandelion without collapsing its structure. When printed on human skin, the fiber sensors conform to the skin and expose sweat pores so the wearer does not detect their presence. Tests of the fibers printed on a human finger suggest they could be used as continuous health monitors.

This low-waste, low-emission method for augmenting living structures could be used in a range of areas, from healthcare and virtual reality to electronic textiles and environmental monitoring. The results are reported in the journal Natural electronics.

Although human skin is remarkably sensitive, augmenting it with electronic sensors could fundamentally change the way we interact with the world around us. For example, sensors printed directly on the skin can be used for continuous health monitoring, for understanding skin sensations, or can enhance the sensation of reality in gaming or virtual reality applications.

Although wearable technologies with built-in sensors, such as smartwatches, are widely available, these devices can be uncomfortable, intrusive, and hinder the skin’s intrinsic sensations.

“If you want to accurately observe something on a biological surface such as a skin or a leaf, the interface between the device and the surface is crucial,” says Professor Yan Yan Shery Huang from Cambridge’s Department of Engineering, who led the research. “We also want bioelectronics that are completely unnoticeable to the user, so that they do not interfere in any way with the way the user interacts with the world, and we want them to be sustainable and produce little waste.”

There are several methods for making wearable sensors, but they all have disadvantages. For example, flexible electronics are normally printed on plastic film that does not allow gas or moisture to pass through, so it would be like wrapping your skin in plastic film. Other researchers have recently developed flexible electronics that are gas-permeable, such as artificial skins, but these still interfere with normal sensation and rely on energy- and waste-intensive production techniques.

3D printing is another potential route for bioelectronics because it is less wasteful than other manufacturing methods but leads to thicker devices that can disrupt normal behavior. Spinning electronic fibers results in devices that are imperceptible to the user, but without a high degree of sensitivity or sophistication, and are difficult to transfer to the object in question.

Now the Cambridge-led team has developed a new way to create high-performance bioelectronics that can adapt to a wide range of biological surfaces, from a fingertip to the fluffy seed head of a dandelion, by applying them directly to that surface. to print. Their technique is partly inspired by spiders, which use minimal materials to create refined and strong web structures that are adapted to their environment.

The researchers spun their bioelectronic ‘spider silk’ from PEDOT:PSS (a biocompatible conductive polymer), hyaluronic acid and polyethylene oxide. The high-performance fibers were produced from a water-based solution at room temperature, allowing the researchers to control the “spinnability” of the fibers. The researchers then designed an orbital spinning approach to turn the fibers into living surfaces, even down to microstructures such as fingerprints.

Tests of the bioelectronic fibers, on surfaces such as human fingers and dandelion seed heads, showed they delivered high-quality sensor performance while remaining unnoticeable to the host.

“Our spinning approach allows the bioelectronic fibers to track the anatomy of different shapes, both at the micro and macro scales, without the need for any image recognition,” said Andy Wang, the paper’s first author. “It opens up a completely different angle when it comes to how sustainable electronics and sensors can be made. It’s a much simpler way to produce sensors for large surfaces.”

Most high-resolution sensors are made in an industrial cleanroom and require toxic chemicals in a multi-step and energy-intensive manufacturing process. The sensors developed by Cambridge can be made anywhere and use a small part of the energy that regular sensors require.

The bioelectronic fibers, which are repairable, can simply be washed away when they reach the end of their useful life, generating less than one milligram of waste. By comparison, a typical single load of laundry produces between 600 and 1,500 milligrams of fiber waste.

“Using our simple manufacturing technique, we can place and repair sensors virtually anywhere where and when they are needed, without the need for a large printing machine or a centralized production facility,” said Huang. “These sensors can be made on demand, exactly where they are needed, producing minimal waste and emissions.”

The researchers say their devices could be used in applications ranging from health monitoring and virtual reality to precision agriculture and environmental monitoring. In the future, other functional materials could be incorporated into this fiber printing method to build integrated fiber sensors for extending the living systems with display, computation and energy conversion functions. The research is being commercialized with the support of Cambridge Enterprise, the university’s commercialization arm.