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International Journal of Bioprinting PEDOT/PSS-based sensors

layers for two independent sensors on a single substrate, gel-based electrodes in terms of quality. Additionally,
interconnected in a serial combination, it enables a single textile electrodes coated with PEDOT:PSS via the layer-
humidity sensing device with good properties, such as by-layer technique not only exhibit low impedance and
high sensitivity that exhibits exceptionally high sensitivity excellent skin contact properties, but can also reliably
and responds to a wide range of relative humidity. detect high-quality heart rate signals in both wet and dry
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Integrating multiple sensors may address the limitations conditions and maintain stability through 20–30 wash
of separate sensors and at the same time combine their cycles and 120–130 bending cycles. The highly porous
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advantages. For instance, integrating strain and pH sensors PEDOT:PSS hydrogels, formed through self-assembly on
with a humidity detector based on PEDOT:PSS into a paper fibers, enable efficient electron transmission and
single demonstrator enables simultaneous monitoring of substance diffusion. They can function as low-impedance
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multiple biomedical parameters. 114 ECG electrodes and highly sensitive glucose sensors,
providing simultaneous real-time monitoring of ECG
Furthermore, the synergistic use of various materials is
also a common approach for developing multi-functional and biochemical signals (glucose levels) in sweat during
physical activity. 3D-printed PEDOT-based eutectogels,
sensors. Printing commercial silver nanoparticle ink and known for their flexibility, stretchability, strong adhesion,
PEDOT:PSS onto glossy inkjet photo paper allows the and excellent capacity as conformal electrodes, can
formation of an interdigitated electrode array and curved continuously record epidermal physiological signals such
micro-ribbon, which enable concurrent measurement of as electrocardiograms and electromyograms over extended
relative humidity, temperature, as well as compression and periods. However, when prepared as concentric ring
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tensile bending. 115 electrodes, silver electrodes provide a more stable response
4.7. Electrocardiogram sensor (fewer saturations and alterations) to intentionally induced
As a critical tool used in healthcare sector, subject movement, as compared with PEDOT:PSS
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electrocardiography (ECG) provides a clear picture about concentric rings. When PEDOT conductive polymer
cardiac activity. Commercially available Ag/AgCl electrodes inks are added to thermoplastic styrene-ethylene-butylene-
are commonly used to capture ECG signals. However, styrene elastomers for micro-extrusion 3D printing, the
they may cause skin irritation and lead to unreliable data resulting PEDOT composites demonstrate conductivity
during prolonged use. In contrast, PEDOT:PSS hydrogels and stretchability lower than those of silver micro-flakes
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offer a promising alternative due to their low electrode and carbon black nanoparticles. Although they exhibit
interface impedance and excellent biocompatibility. unique properties due to their ionic conductivity, the
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ECG signals acquired with PEDOT:PSS electrodes closely application of PEDOT conductive polymers in ECG signal
resemble those obtained with commercial electrodes. detection requires further exploration.
Remarkably, these electrodes maintain their electrical
properties and functionality even after several washing 5. Recent advances of 3D-printed
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cycles when subjected to physical stretching. In certain PEDOT/PSS conductive hydrogel for
electrolyte conditions, the skin contact impedance and biomedical sensors
physiological signal extraction characteristics closely In summary, the recent advances of 3D-printed PEDOT/
resemble those achieved with disposable gelled Ag/AgCl PSS conductive hydrogel for biomedical sensors are rooted
electrodes (rho >0.99). Therefore, PEDOT:PSS electrodes in the development of strategies for fabricating PEDOT/
can potentially replace commercial electrodes in wearable PSS conductive hydrogels using 3D printing technology,
devices for health monitoring under both static and allowing for the amalgamation of the conductivity of
dynamic conditions. In addition, the dual ionic and PEDOT with the water solubility and processability of
electronic conductivity properties of PEDOT:PSS endow PSS. This unique combination makes PEDOT:PSS an
the electrodes the ability to record ECG signals on dry skin exceptional candidate for biomedicine sensors. The main
conditions. Signal amplification occurs when moisture achievements in this field are summarized in the following:
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evaporates from the skin or common emollients are
applied, making the recorded ECG signals comparable to 5.1. Fabrication methods: from traditional methods
those obtained with copper-wired Ag/AgCl electrodes. This to 3D printing
phenomenon may be attributed to PEDOT:PSS’s ability to The evolution of PEDOT:PSS-based sensor fabrication
reduce contact impedance of dry electrodes. Therefore, methods has traversed various stages. Initially, simple
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dry electrodes which are reusable, comfortable to use, and coating and spraying methods were employed to apply
suitable for long-term measurements permit the collection PEDOT:PSS onto substrates in the process of creating
of electrocardiograms comparable to those collected with basic sensors. After gaining significant understanding

Volume 10 Issue 2 (2024) 17 doi: 10.36922/ijb.1725