3D Fabrication of PEDOT:PSS Containing Microstructures via Two-Photon Polymerization

Electro-conductive polymers have garnered great interest due to their numerous applications such as electroluminescent and thermoelectric devices, photovoltaic solar panels, sensors, and electrical interfaces with biological samples. One of the most prominent conductive polymers studied to date is poly(3 ,4-ethylenedioxithiophene): poly(styrenesulfonate) (PEDOT:PSS), due to its high electrical conductivity, biocompatibility, stability in aqueous media and commercial availability in a wide range of formulations.¹ The formation of conductive films using PEDOT:PSS and the different strategies to enhance their conductivity have been widely studied, with the fabrication of more complex structures achieved through inkjet printing,² extrusion-based printing,³ and stereolithography.⁴ In the context of 3D printing and microfabrication, the fabrication of conductive microstructures through two-photon polymerization (TPP) using PEDOT:PSS is only very recent. One example has shown the fabrication of microstructure, using polyethylene glycol diacrylate and 3,4-ethylenedioxithiophene (EDOT), by TPP followed by oxidative polymerization of the EDOT contained in the polymer structures, to achieve a conductivity of 0.04 S/cm.⁵ Another approach consisted of the fabrication of microstructures, with a photoresist composed of multi-wall carbon nanotubes (MWCNT) functionalized with polyethylene glycol. Infiltration of a PEDOT:PSS solution resulted in an increase in conductivity of the structures to 42.5 S/cm.⁶ While these are promising approaches, in both cases, the PEDOT:PSS network is only introduced in the second step (via oxidative polymerization of EDOT,⁵ or absorption of PEDOT⁶), limiting the design, resolution and application of such structures.<br/>Herein, we describe for the first time, a one-step fabrication of PEDOT:PSS containing microstructures via TPP. For this purpose, several photoresists composed of commercially available Clevios PH1000 (aqueous PEDOT:PSS dispersion) were developed and optimized using a range of organic solvents, cross-linkers, and photoinitiators. The fabrication of PEDOT:PSS-based microstructures via TPP and the systematic study of the influence of the fabrication parameters on the electrical and mechanical properties of the resulting structures are detailed along with the full characterization of the microstructures through spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and conductive-AFM.<br/><br/>1. Shi, H.; Liu, C.; Jiang, Q.; Xu, J. <i>Adv. Electron. Mater.</i> <b>2015</b>, <i>1</i>, 1500017.<br/>2. Lu, B.; Yuk, H.; Lin, S.; Jian, N.; Qu, K.; Xu, J.; Zhao, X. <i>Nat. Commun.</i> <b>2019</b>, <i>10</i>, 1043.<br/>3. Dominguez-Alfaro, A.; Gabirondo, E.; Alegret, N.; De León-Almazán, C. M.; Hernandez, R.; Vallejo-Illarramendi, A.; Prato, M.; Mecerreyes, D. <i>Macromol. Rapid Commun.</i> <b>2021</b>, <i>42</i>, 2100100.<br/>4. Heo, D. N.; Lee, S.-J.; Timsina, R.; Qiu, X.; Castro, N. J.; Zhang, L. G. <i>Mater. Sci. Eng. C</i> <b>2019</b>, <i>99</i>, 582-590.<br/>5. Kurselis, K.; Kiyan, R.; Bagratashvili, V. N.; Popov, V. K.; Chichkov, B. N. <i>Opt. Express</i> <b>2013</b>, <i>21</i>, 31029-31035.<br/>6. Tao, Y.; Wei, C.; Liu, J.; Deng, C.; Cai, S.; Xiong, W. <i>Nanoscale</i> <b>2019</b>, <i>11</i>, 9176-9184.<br/><br/>This research received funding from the European Research Council (ERC) Starting Grant (No. 802929 - ChemLife), and the European Horizon 2020 Research and Innovation Programme (No. 899349 - 5D NanoPrinting).