3D Printing of Multifunctional Conductive Polymer Composite Hydrogels

Abstract

Functional conductive hydrogels are widely used in various application scenarios, such as artificial skin, cell scaffolds, and implantable bioelectronics. However, their novel designs and technological innovations are severely hampered by traditional manufacturing approaches. Direct ink writing (DIW) is considered a viable industrial‐production 3D‐printing technology for the custom production of hydrogels according to the intended applications. Unfortunately, creating functional conductive hydrogels by DIW has long been plagued by complicated ink formulation and printing processes. In this study, a highly 3D printable poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)‐based ink made from fully commercially accessible raw materials is demonstrated. It is shown that complex structures can be directly printed with this ink and then precisely converted into high‐performance hydrogels via a post‐printing freeze–thawing treatment. The 3D‐printed hydrogel exhibits high electrical conductivity of ≈2000 S m−1, outstanding elasticity, high stability and durability in water, electromagnetic interference shielding, and sensing capabilities. Moreover, the hydrogel is biocompatible, showing great potential for implantable and tissue engineering applications. With significant advantages, the fabrication strategy is expected to open up a new route to create multifunctional hydrogels with custom features, and can bring new opportunities to broaden the applications of hydrogel materials.

Omnidirectional Printing of PEDOT:PSS for High-Conductivity Spanning Structures

“…For PEDOT:PSS contents below 9 wt %, inks were self-supporting but lacked adequate shear stiffness for overhangs (τ y < 1200 Pa). Content of 9–15 wt % with higher τ y (compared with previous reports , ) met omnidirectional printing requirements without collapse (Figure f, inset). Further increasing the concentration led to nozzle clogging due to PEDOT:PSS aggregates.…”

“…The electrical conductivity of the dehydrated fiber substantially increased, reaching 65378 S/ m after 60 min, 170 times improvement over untreated fiber and surpassing reported values. 5,7,34 The conductivity of the swollen fiber, at 7190 S/m, notably surpassed the previously reported value. 32,34 PEDOT:PSS loading affected the diameter and conductivity (Figure 3b).…”

“…5,7,34 The conductivity of the swollen fiber, at 7190 S/m, notably surpassed the previously reported value. 32,34 PEDOT:PSS loading affected the diameter and conductivity (Figure 3b). Diameter gradually increased with higher loading due to extrusion swell, 43 and conductivity followed suit.…”

“…Research findings have highlighted that PEDOT:PSS ink formulations generated through the reconstitution of lyophilized PEDOT:PSS powders 34 or the concentration of aqueous solutions of PEDOT:PSS 38 exhibit an upper limit of solid content (<7 wt %). These formulations, characterized by restricted rheological attributes with values of η a (<300 Pa s), G′ (<3000 Pa), and τ y (<200 Pa), are suitable solely for the creation of rudimentary structures, such as continuous fibers or layerwise printed pseudo-3D configurations, with challenges inherent in producing intricate vertical geometries.…”

“…However, the pristine dispersion of PEDOT:PSS, with low solids (1.0–1.3 wt %), displays a liquid-like property that impedes direct deposition. To circumvent this, strategies involving meniscus-guided printing, compounding with additives, − redispersion of lyophilized concentrate, , coagulation bath, and interface assembly have been proposed to enhance printability. Despite these innovative efforts, challenges still exist, encompassing issues such as low printing speed, intricate ink formulation, the inevitably repeated annealing–swelling postprocession, the inability to print omnidirectionally and in 3D interconnected modes, as well as low electrical conductivity and resolution .…”