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Porous silicone boosts comfort and resolution of wearable biosensors

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US-based researchers have created a porous silicone material which could be integrated into more comfortable wearables biosensors to allow for sweat evaporation.

Wearable biosensors are becoming increasingly popular for both medical and everyday health and fitness monitoring. However, as these sensors can become very uncomfortable and sometimes inaccurate when worn for extended periods of time, it is important to find the right materials to bind them together and adhere them to surfaces.

Now, biomedical engineers from Binghamton University, State University of New York, have suggested a possible solution to make biosensors worn on the skin more comfortable.

The engineers worked with polydimethylsiloxane (PDMS), a silicone popular for use in biosensors due to its biocompatibility and mechanical properties, such as its softness. However, as it is usually used in a solid film, non-porous form, it can cause discomfort due to lack of breathability and sweat evaporation.

“In athletic monitoring, if you have a device on your skin, sweat can build up under that device,” said Matthew Brown, a PhD student at Binghamton’s department of biomedical engineering. “That can cause inflammation and also inaccuracies in continuous monitoring applications.

“For instance, one experiment with electrocardiogram analysis showed that the porous PDMS allowed for the evaporation of sweat during exercise, capable of maintaining a high-resolution signal. The non-porous PDMS did not provide the ability for the sweat to readily evaporate, leading to a lower signal resolution after exercise.”

Brown and his colleagues created a porous PDMS material through electrospinning, a technique which uses an electric force to draw charged nanofibres of polymer solutions.

During testing, the engineers found that the new material acted like the collagen and elastic fibres of the human epidermis, and was also capable of acting as a dry adhesive for the electronics to strongly laminate on the skin for adhesive-free monitoring. Biocompatibility and viability testing also showed better results after a week of use, compared to the standard non-porous PDMS film.

“You can use this in a wide variety of applications where you need fluids to passively transfer through the material – such as sweat – to readily evaporate through the device,” said Brown.

The materials’ permeable structure is capable of biofluid, small-molecule, and gas diffusion, making it appropriate for integration with all sorts of soft biological tissue including skin, neural, and cardiac tissue. This reduces inflammation at the site of application. Brown hopes that the material could be incorporated into electronics for long-term healing of chronic wounds, as well as breathable electronics for respiratory monitoring, and real-time in-vitro chemical and biological monitoring.

Professor Ahyeon Koh, who oversaw the study, described this as a “cornerstone of [her] research”.

“My lab is very interested in developing a biointegrated sensing system beyond wearable electronics. At the moment, technologies have advanced to develop durable and flexible devices over the past 10 years. But we always want to go even further, to create sensors that can be used in more non-visible systems that aren’t just on the skin,” said Koh.

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