Microelectrode arrays (MEAs) are widely used platforms in bioelectronics to study electrogenic cells. In recent years, the processing of conductive polymers for the fabrication of three-dimensional electrode arrays has gained increasing interest for the development of novel sensor designs. Here, additive manufacturing techniques are promising tools for the production of MEAs with three-dimensional electrodes. In this work, a facile additive manufacturing process for the fabrication of MEAs that feature needle-like electrode tips, so-called μ-needles, is presented. To this end, an aerosol-jet compatible PEDOT:PSS and multiwalled carbon nanotube composite ink with a conductivity of 323 ± 75 S m −1 is developed and used in a combined inkjet and aerosol-jet printing process to produce the μ-needle electrode features. The μ-needles are fabricated with a diameter of 10 ± 2 μm and a height of 33 ± 4 μm. They penetrate an inkjet-printed dielectric layer to a height of 12 ± 3 μm. After successful printing, the electrochemical properties of the devices are assessed via cyclic voltammetry and impedance spectroscopy. The μ-needles show a capacitance of 242 ± 70 nF at a scan rate of 5 mV s −1 and an impedance of 128 ± 22 kΩ at 1 kHz frequency. The stability of the μ-needle MEAs in aqueous electrolyte is demonstrated and the devices are used to record extracellular signals from cardiomyocyte-like HL-1 cells. This proof-of-principle experiment shows the μ-needle MEAs' cell-culture compatibility and functional integrity to investigate electrophysiological signals from living cells.

Recent investigations into cardiac or nervous tissues call for systems that are able to electrically record in 3D as opposed to 2D. Typically, challenging microfabrication steps are required to produce 3D microelectrode arrays capable of recording at the desired position within the tissue of interest. As an alternative, additive manufacturing is becoming a versatile platform for rapidly prototyping novel sensors with flexible geometric design. In this work, 3D MEAs for cell-culture applications were fabricated using a piezoelectric inkjet printer. The aspect ratio and height of the printed 3D electrodes were user-defined by adjusting the number of deposited droplets of silver nanoparticle ink along with a continuous printing method and an appropriate drop-to-drop delay. The Ag 3D MEAs were later electroplated with Au and Pt in order to reduce leakage of potentially cytotoxic silver ions into the cellular medium. The functionality of the array was confirmed using impedance spectroscopy, cyclic voltammetry, and recordings of extracellular potentials from cardiomyocyte-like HL-1 cells.

Current investigations on neuronal or cardiac tissues call for systems that can electrically monitor cellular activity in three dimensions as opposed to classical planar approaches. Typically the fabrication of such 3D microelectrode arrays (3D MEAs) relies on advanced cleanroom fabrication techniques. However, additive manufacturing is becoming an ever versatile alternative for rapid prototyping of novel sensor designs due to its low cost and material expense. Here, the possibility of fabricating high‐resolution 3D MEAs is demonstrated by using electrohydrodynamic inkjet printing. The height and aspect ratio of the 3D electrodes can be readily tuned by adjusting the printing conditions and number of deposited ink droplets per electrode. The fabrication of pillar electrode arrays with electrode diameters of sintered structures below 3 µm is shown. The functionality of the array is confirmed using impedance spectroscopy and extracellular recordings of action potentials from HL‐1 cells.

Both stereolithographic printing of microfluidics and inkjet printing of electronics are promising tools for the fabrication of lab‐on‐a‐chip devices. However, the combination of these two technologies has been a challenge so far, as the 3D‐printed components usually have to be bonded manually to the substrates functionalized with printed electronics. Here, a surface modification method is demonstrated for enabling the direct stereolithographic printing of microfluidic structures onto a variety of different substrates that are usually employed for printed electronics. The approach makes use of an acrylate‐terminated silane that covalently binds substrate and polymer network of the 3D print. The bonding strength is quantified and the compatibility of the concept with printed electrodes in a microfluidic channel is evaluated.

We present a photocurable, biocompatible, and flexible silicone-hydrogel hybrid material for stereolithographic (SLA) printing of biomedical devices. The silicone-hydrogel polymer is similar to mixtures used for contact lenses. It is flexible and stretchable with a Young’s modulus of 78 MPa and a maximum elongation at break of 51%, shows a low degree of swelling (<4% v/v) in water, and can be bonded easily to flat glass substrates via a surface-modification method. The in vitro cytotoxicity of the material is assessed with a WST-8 cell viability assay using five different cell lines: HT1080, L929, and Hs27 fibroblasts, cardiomyocyte-like HL-1 cells, and neuronal-phenotype PC-12 cells. On this account, the silicone-hydrogel polymer is compared to several other common SLA printing materials used for cell-culture applications and polydimethylsiloxane (PDMS). A simple extraction step in water is sufficient for reaching biocompatibility of the material with respect to the tested cell types. The oxygen permeability of the silicone-hydrogel material is investigated and compared to that of PDMS, Medicalprint cleara commercial resin for medical products, and a short-chain hydrogel-based resin. As a proof of concept, we demonstrate a 3D-printed microfluidic device with integrated valves and mixers. Furthermore, we show a printed culture chamber for analyzing signal propagation in HL-1 cardiomyocyte cell networks. Ca2+ imaging is used to observe the signal propagation through the cardiac cell layers grown in the microchannels. The cells are shown to maintain normal electrophysiological activity within the printed chambers. Overall, the biocompatible silicone-hydrogel material will be an advancement for SLA printing in cell-culture and microfluidic lab-on-a-chip applications.