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International Journal of Bioprinting PEDOT/PSS-based sensors

electrostatic interaction between PEDOT and PSS allows 3. 3D-printed PEDOT/PSS
for the homogeneous dispersion of the complex in water, conductive hydrogel
creating a stable and conductive aqueous solution. Its
water solubility and compatibility with solution-based 3D printing technology, commonly referred to as additive
processing techniques make it an attractive choice for manufacturing, offers distinct advantages for replicating
various applications, enabling the realization of cost- natural tissue micro-structures and has gained prominence
effective and scalable manufacturing processes. A in recent years for the fabrication of conductive hydrogels.
solvent-free strategy using laser-based heating enhances The method relies on layer-by-layer deposition of materials
the conductivity of PEDOT:PSS thin films up to three using methods such as heating and melting, laser sintering,
orders of magnitude. Furthermore, laser-induced phase or photopolymerization. These processes enable the design
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separation enhances aqueous stability of PEDOT:PSS and fabrication of complex structures that are challenging to
which allows the transformation of PEDOT:PSS into achieve through conventional manufacturing methods. Based
water-stable hydrogels and maintains electrochemical on the different forming methods, 3D printing technology
properties even after 6 months in a physiological can be categorized into three main types (Table 1).
environment. 3.1. Extrusion-based 3D printing technology
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Throughout the year, we have witnessed the rapid Extrusion-based 3D printing technology represents a
development of PEDOT:PSS from being a mere material method for fabricating 3D objects, wherein materials are
to sophisticated sensors. Various manufacturing deposited layer by layer through an extrusion process. One
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processes, including coating, printing, and lithography, of the most representative techniques in this category is
have made it possible to produce PEDOT:PSS nanowires fused deposition modeling (FDM), along with direct ink
with exceptional sensing capabilities. However, neat writing (DIW) and inkjet printing.
PEDOT:PSS lacks the flexibility and stretchability FDM stands out a popular and accessible 3D printing
required for wearable electronic applications. Enhancing technique that employs a thermoplastic filament as the
the mechanical flexibility of conductive polymers like printing material. The filament is fed through a heated
PEDOT:PSS for wearable electronics has been achieved nozzle, where it undergoes melting and is then precisely
through methods such as polymerization directly on deposited onto the build platform, layer by layer. It is worth
textiles, coating/dyeing, and printing. These techniques noting that the reports on PEDOT:PSS materials being
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involve combining PEDOT:PSS with commercially exclusively used with FDM technology for 3D printing are
available polymers known for their high flexibility and scarce. The majority of significant reports typically involve
stretchability, such as polyurethane. PEDOT-based PEDOT:PSS material forming an active or functional
conductive composite materials, whether in gel, fiber, or layer on the substrate via FDM technology, often through
film form, have found extensive applications in strain, methods like spray deposition or drop-casting.
pressure, and temperature sensors within the realm
of wearable bioelectronics. This integration not only DIW is another extrusion-based 3D printing method
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leverages the superior sensing properties of PEDOT:PSS that finds particularly suitable for printing soft and
but also ensures the necessary mechanical durability and bioactive materials such as hydrogels and living cells. In
adaptability required for wearable electronic applications. DIW, a viscous ink or bioink is directly extruded from
At present, PEDOT/PSS conductive hydrogels are a nozzle, enabling the precise deposition of material in
regarded as promising materials, exhibiting advantages a controlled manner. The resulting PEDOT:PSS-based
for application in sensors compared with other materials. supercapacitors exhibit exceptional energy storage
However, there is a conspicuous dearth of comprehensive performance, outstanding cyclic stability, and remarkable
reports systematically summarizing the applications bending stability. 24,28,38 By incorporating various additives
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of 3D printing technology in the production of such as deep eutectic solvents, glucose, and ascorbic acid,
PEDOT:PSS conductive hydrogels for biosensors. Thus, or by combining with other materials like MXene and
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in this context, we delve into the discussion of various 3D carbon methyl cellulose, the conductivity of PEDOT:PSS
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printing techniques employed in fabricating PEDOT:PSS can be significantly enhanced. The introduction of
hydrogel electronic devices. We also provide an overview thermally crosslinkable N-(hydroxymethyl)acrylamide
of the progress made in the application of 3D-printed segments and the combination with graphene oxide
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PEDOT:PSS hydrogels in biomedical sensors, including (GO) nanosheets and anionic polyurethane, or
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strain sensors, pressure sensors, stretchable sensors, post-printing freeze-thawing treatment, facilitated
electrochemical sensors, temperature sensors, humidity the development of flexible, tough, and stretchable
sensors, and electrocardiogram sensors. PEDOT:PSS-based hydrogels. The organic electrochemical
Volume 10 Issue 2 (2024) 4 doi: 10.36922/ijb.1725