Materials What is a biosensor?
A biosensor comprises two distinct parts: ■The biological component, which acts as the sensor. ■The electronic component, which detects and transmits the signal.
The biological element interacts with an analyte (the substance whose chemical constituents are being identified and measured) and the biological response is then converted into an electrical signal by the electronic element. In a health context, biosensors can be applied to or worn on the skin, allowing continuous monitoring of data. They are typically laminated to the skin via a patch or film-like device and can capture a range of data – such as body temperature, blood pressure, oxygen saturation or blood flow.
than just attaching to it. Their study, ‘Electronic- ECM: A permeable microporous elastomer for an advanced bio-integrated continuous sensing platform’, was published in research journal Advanced Materials Technologies in May 2020.
“With this technology, we can control the fibre diameter and structure of the porous membrane, and that gives us more ability to adhere [a device] to the skin without any adhesive to support it.”
Ahyeon Koh
Below: Electrospun PDMS mimics the properties of collagen and elastin in the skin.
Right: It is also porous enough for biofluids like sweat to pass through it.
“Most types of biosensors predominantly use PDMS because of its soft mechanics, and its silicon dioxide silane group enables us to covalently bond it with the electronics,” explains Matthew Brown, the study’s lead author and a PhD candidate at Binghamton’s Koh Laboratory, situated in the Watson School of Engineering and Applied Science. “However, a limitation of these biosensors is that sweat can’t diffuse through their impenetrable substrates. In long-term monitoring applications, sweat can build up underneath a biosensor on the skin, causing inflammation and irritation, and leading to inaccuracies. “What we tried to do was create a permeable nanofibrous elastomer for these kinds of
applications, where sweat can readily diffuse through the overall device.”
Led by assistant professor Ahyeon Koh (from whom the lab takes its name), the study entailed using a process called electrospinning that applies a very high-voltage electric force to a polymeric solution, elongating the polymer and spinning it like spider silk into a nanofibrous structure similar to that of the extracellular matrix of human tissue. In this study, the goal was to recreate the properties of collagen, which strengthens tissues and makes them flexible, and elastin, which allows stretched tissue to ‘bounce back’ to its original shape and form. In other words, the electrospinning process gives the PDMS – already similar in its mechanics to human skin – yet more skin-like properties. This synthetic ‘electronic extracellular matrix’ (e-ECM) also has the permeability that allows biofluids like sweat to evaporate through it. “With this technology, we can control the fibre diameter and structure of the porous membrane, and that gives us more ability to adhere [a device] to the skin without any adhesive to support it,” says Koh.
Film versus mesh
Brown, Koh and colleagues first assessed the biocompatibility of skin keratinocyte cells on different PDMS substrates – a nonporous PDMS film (the type typically used in bioelectronics) and the new, permeable, fibrous PDMS mesh material – in vitro, comparing cells’ viability after three and seven days. The fibrous PDMS mesh yielded higher cell viability by day seven, and “allowed for increased cellular respiration and transport of nutrients, as indicated by significantly [fewer] necrotic cell clusters”. Conversely, the PDMS film “established an environment for the cells to undergo necrosis”. The team also carried out electrocardiogram (ECG) testing in a human subject, comparing the signal responses and performance of a synthetic e-ECM device with commercial ECG surface electrodes, with the aim of demonstrating that the
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Medical Device Developments /
www.nsmedicaldevices.com
Matthew Brown, Binghamton University
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