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International Journal of Bioprinting PEDOT/PSS-based sensors

4. 2D/3D-printed PEDOT/PSS conductive In response to the challenge posed by the challenge of
hydrogel for biomedical sensors poor processability of conductive polymer PEDOT:PSS in
solution, low electrical resistance PEDOT particles were
In this section, we discuss the recent advances of 2D/3D- first synthesized and applied via brush painting, enabling
printed PEDOT/PSS conductive hydrogel for biomedical the fabrication of pH and strain sensors on hydrophobic
sensors, including strain sensors, pressure sensors, surfaces such as 3D printable thermoplastics. 69
stretchable sensors, electrochemical sensors, temperature
sensors, humidity sensors, and electrocardiogram sensors. Furthermore, a robust fluidic strain sensor was
developed, using biocompatible PEDOT:PSS/multi-wall
4.1. Strain sensor CNTs liquid. This sensor had shown high linear response,
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The initial studies on PEDOT:PSS-based strain sensors minimal hysteresis, and stable response across a full
primarily focused on optimizing ink formulations and humidity range and at temperatures between 20°C and
conducting tests under various tensile conditions and 40°C. Additionally, it demonstrated good biocompatibility,
strain histories. These efforts aimed to highlight the as confirmed through cell viability assessment using
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correlation between electrical response, applied strain, human epidermal keratinocytes and human umbilical cord
time, and mechanical history. As the research progressed, vascular endothelial cells.
attention shifted toward investigating the feasibility of
printing conductive patterns on flexible polyimide film 4.2. Pressure sensor
substrates using graphene/PEDOT:PSS multi-component The PEDOT:PSS hydrogel possesses exceptional electrical
ink materials. The effect of different graphene doping conductivity, inherent flexibility, and mechanical
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amounts on composite ink performance and printing robustness. This unique combination of attributes
processes was thoroughly analyzed. empowers the hydrogel to adeptly convert mechanical
pressure into electrical signals, allowing for precise and
Subsequent research endeavors aimed to enhance sensitive pressure detection. By incorporating PEDOT:PSS
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specific characteristics of strain sensors. For instance, hydrogel-based pressure sensors into robotic systems or
novel hybrid inks were developed by incorporating foam interactive surfaces, it becomes possible to enhance the
graphene foam/PEDOT:PSS hybrid ink using 2-propanol safety and precision of human–robot interactions. These
and ethylene glycol as solvents. This innovation resulted sensors can detect changes in pressure distribution and
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in conductive patterns with a gauge factor of 4.3, rendering intensity, enabling robots to respond intelligently to human
them suitable for low strain sensor applications. However, touch and providing a more natural and intuitive user
deposition of PEDOT:PSS thin films onto treated flexible experience. PEDOT:PSS hydrogel-based pressure sensors
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substrate surfaces using inkjet printed technique achieves have gained substantial attention in the realm of wearable
high gauge factors and showcases the materials potential in fields. They can be seamlessly integrated into clothing,
high-strain sensing applications (Figure 2). gloves, or even attached directly to the skin, providing
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To minimize interference from skin deformation real-time pressure monitoring in various contexts.
caused by skin-contact strain sensors, an ultra-thin strain A commonly employed strategy involves combining
sensor was developed using PEDOT:PSS inkjet-printed on PEDOT:PSS with polydimethylsiloxane, either by coating
polystyrene-polybutadiene-polystyrene nanosheets. This or drop-casting it onto 3D-printed polydimethylsiloxane
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sensor demonstrated the capability to accurately detect sheets as the active layer, or formulating it as a composite
minor skin strains (approximately 2%), offering a new electrode in conjunction with polydimethylsiloxane.
approach for precisely monitoring the movement of both These pressure sensors exhibit remarkable sensitivity and
human and artificial soft robotic skin. linearity, rendering them suitable for detecting diverse
health signals such as wrist pulses, swallowing, and speech
In the pursuit of enhancing the gauge factor of 22,73,74
piezoresistive strain sensors, a novel approach was articulation (Figure 3).
employed, introducing a high resistive path perpendicular Another intriguing approach involves crafting pressure
to the sensing direction, driven by phase separation of sensing patches by sandwiching conductive cotton fabric
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PEDOT:PSS polymer material. Inspired by sesame between two parallel electrodes. In essence, this method
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candy, a PEDOT:PSS-based conductive nanocomposite entails mixing carbon-based paste with the organic conductor
with viscoelasticity was crafted through electrostatic/ PEDOT-PSS to create a conductive nanocomposite solution.
coordination interactions and hydrogen bonds. A nanofibrous and stretchable cotton fabric was then selected
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This composite material was used to create epidermal and immersed in the nanocomposite solution to serve as the
electrodes and strain sensors for monitoring human pressure sensing layer. The resulting sensors, when tested,
electrocardiogram/electromyogram and movement signals. demonstrated the ability to record resistance variation as

Volume 10 Issue 2 (2024) 8 doi: 10.36922/ijb.1725