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International Journal of Bioprinting PEDOT/PSS-based sensors

influencing PEDOT:PSS inkjet printing progress has been indispensable for modern industrial revolution. While
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investigated. The results highlight that resolution, substrate SLS and SLM are highly effective technologies for working
treatment, and print head height are the most pivotal with powder materials, they are not particularly well-
factors affecting printing quality. The properties of the suited for use with hydrogels.
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PEDOT:PSS-based temperature-sensitive layer have also
been evaluated and analyzed, encompassing aspects like 3.3. Photopolymerization-based
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sensitivity, time drift, and mechanical flexibility. 49 3D printing technology
Photopolymerization-based 3D printing falls under the
Electrohydrodynamic (EHD) printing technology, umbrella of additive manufacturing techniques that utilize
also known as electrohydrodynamic inkjet printing light-induced polymerization to create 3D objects layer by
technology, is an innovative approach of inkjet printing. layer. These techniques rely on the solidification of liquid
It distinguishes itself from conventional inkjet techniques, photopolymer resins when exposed to specific wavelengths
which rely on pressure or jetting force to control ink flow. of light. They offer precise control over geometry and are
Instead, EHD printing operates by applying an electric particularly suitable for producing intricate and finely
field to precisely regulate the movement and distribution detailed structures characterized by smooth surface
of ink during the printing process. This groundbreaking finishes. The commonly photopolymerization-based 3D
technology seamlessly combines principles from both printing methods for constructing PEDOT:PSS-based
electrochemistry and printing, resulting in significantly conductive hydrogels are stereolithography (SLA) and
enhanced precision and superior print quality. Typically, digital light processing (DLP).
EHD jet printing operates in four jetting modes: Renowned for its ability to produce high-resolution
dripping, micro-dripping, cone-jet, and multi-jet. models and prototypes with intricate details, SLA
When working with PEDOT:PSS, the cone-jet mode employs an ultraviolet laser to selectively cure a liquid
is typically the preferred choice. To further improve photopolymer resin layer by layer. Within the realm
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PEDOT:PSS properties, silicon-based hardeners are used of conductive hydrogels, SLA technology has achieved
to enhance conductivity and solvent resistance, while the success in fabricating such materials using a blend of
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incorporation of CNTs provides exceptional dimensional PEDOT:PSS and polyethylene glycol diacrylate (PEGDA)
stability. The addition of the surfactant Triton X-100 as the photopolymerizable matrix. The optimization of the
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not only increases the conductivity of PEDOT:PSS films photocurable resin’s composition has been accomplished
but also optimizes surface tension, enabling multiple through three aspects: photoinitiator, surfactant, and
jetting modes. In comparison to traditional EHD jet filler concentrations. This optimization process has
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printing methods, when operating under similar printing yielded printed objects possessing noteworthy electrical
conditions, the EHD jet printing method employing conductivity and mechanical properties. Furthermore,
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high-voltage electrostatic focusing lenses achieves the utilization of the PEGDA:PEDOT resin mixture is
higher resolution. PEDOT:PSS prepared using the low- able to facilitate the rapid prototyping of 3D organic
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temperature cone-jet mode exhibits tunable conductive electrochemical transistors, highlighting the promising
and thermal properties, making it potentially valuable for potential of this methodology for generating functional
applications in flexible and wearable micro-devices. 56 electronic devices with excellent sensing capabilities. 34
3.2. Powder-based 3D printing technology Similar to SLA, DLP uses a digital light processor
The powder-based approach involves the utilization (DLP chip) to project an entire layer’s image onto the
of powdered materials to achieve the layer-by-layer liquid photopolymer resin, allowing for the simultaneous
fabrication of 3D objects through selective sintering curing of the entire layer and thereby achieving faster
or melting processes. This technique encompasses two printing speeds. Within DLP process, PEDOT:PSS plays
primary methodologies: selective laser sintering (SLS) a dual role: It expedites the photoinitiation process and
and selective laser melting (SLM), both employing a imparts the resulting hydrogels with high conductivity
heat source such as a laser or electron beam. SLS has and exceptional electrical stability. 35,61 The 3D-printed
shown remarkable potential in the production of medical PEDOT:PSS-based electrodes developed via DLP maintain
devices, and SLS-based 3D-printed dosage forms hold the a notably high specific discharge capacity, accompanied by
promise of revolutionizing the production of personalized an extremely low-capacity fade, showcasing remarkable
drugs. On the other hand, SLM technology excels at flexibility. Incorporating PEDOT:PSS-coated silver
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rapidly processing metal powder to obtain the necessary selenide nanowires as a filler enhances the thermoelectric
parts with outstanding metal structure performance figure of merit and mechanical properties of the cured
and excellent metal thermal performance, making it composite material. 37

Volume 10 Issue 2 (2024) 7 doi: 10.36922/ijb.1725