Cleanroom-Free Direct Laser Micropatterning of Polymers for Organic Electrochemical Transistors in Logic Circuits and Glucose Biosensors.

Organic electrochemical transistors (OECTs) are promising devices for bioelectronics, such as biosensors. However, current cleanroom-based microfabrication of OECTs hinders fast prototyping and widespread adoption of this technology for low-volume, low-cost applications. To address this limitation, a versatile and scalable approach for ultrafast laser microfabrication of OECTs is herein reported, where a femtosecond laser to pattern insulating polymers (such as parylene C or polyimide) is first used, exposing the underlying metal electrodes serving as transistor terminals (source, drain, or gate). After the first patterning step, conducting polymers, such as poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), or semiconducting polymers, are spin-coated on the device surface. Another femtosecond laser patterning step subsequently defines the active polymer area contributing to the OECT performance by disconnecting the channel and gate from the surrounding spin-coated film. The effective OECT width can be defined with high resolution (down to 2 µm) in less than a second of exposure. Micropatterning the OECT channel area significantly improved the transistor switching performance in the case of PEDOT:PSS-based transistors, speeding up the devices by two orders of magnitude. The utility of this OECT manufacturing approach is demonstrated by fabricating complementary logic (inverters) and glucose biosensors, thereby showing its potential to accelerate OECT research.

Probabilistic cell seeding and non-autofluorescent 3D-printed structures as scalable approach for multi-level co-culture modeling.

To model complex biological tissue in vitro, a specific layout for the position and numbers of each cell type is necessary. Establishing such a layout requires manual cell placement in three dimensions (3D) with micrometric precision, which is complicated and time-consuming. Moreover, 3D printed materials used in compartmentalized microfluidic models are opaque or autofluorescent, hindering parallel optical readout and forcing serial characterization methods, such as patch-clamp probing. To address these limitations, we introduce a multi-level co-culture model realized using a parallel cell seeding strategy of human neurons and astrocytes on 3D structures printed with a commercially available non-autofluorescent resin at micrometer resolution. Using a two-step strategy based on probabilistic cell seeding, we demonstrate a human neuronal monoculture that forms networks on the 3D printed structure and can establish cell-projection contacts with an astrocytic-neuronal co-culture seeded on the glass substrate. The transparent and non-autofluorescent printed platform allows fluorescence-based immunocytochemistry and calcium imaging. This approach provides facile multi-level compartmentalization of different cell types and routes for pre-designed cell projection contacts, instrumental in studying complex tissue, such as the human brain.

Ultrafast and Resist-Free Nanopatterning of 2D Materials by Femtosecond Laser Irradiation.

The performance of two-dimensional (2D) materials is promising for electronic, photonic, and sensing devices since they possess large surface-to-volume ratios, high mechanical strength, and broadband light sensitivity. While significant advances have been made in synthesizing and transferring 2D materials onto different substrates, there is still the need for scalable patterning of 2D materials with nanoscale precision. Conventional lithography methods require protective layers such as resist or metals that can contaminate or degrade the 2D materials and deteriorate the final device performance. Current resist-free patterning methods are limited in throughput and typically require custom-made equipment. To address these limitations, we demonstrate the noncontact and resist-free patterning of platinum diselenide (PtSe2), molybdenum disulfide (MoS2), and graphene layers with nanoscale precision at high processing speed while preserving the integrity of the surrounding material. We use a commercial, off-the-shelf two-photon 3D printer to directly write patterns in the 2D materials with features down to 100 nm at a maximum writing speed of 50 mm/s. We successfully remove a continuous film of 2D material from a 200 µm × 200 µm substrate area in less than 3 s. Since two-photon 3D printers are becoming increasingly available in research laboratories and industrial facilities, we expect this method to enable fast prototyping of devices based on 2D materials across various research areas.

Corrigendum to "Probabilistic cell seeding and non-autofluorescent 3D-printed structures as scalable approach for multi-level co-culture modeling" [Mater. Today Bio 21, August 2023, 100706].

[This corrects the article DOI: 10.1016/j.mtbio.2023.100706.].

3D Microvascularized Tissue Models by Laser-Based Cavitation Molding of Collagen.

3D tissue models recapitulating human physiology are important for fundamental biomedical research, and they hold promise to become a new tool in drug development. An integrated and defined microvasculature in 3D tissue models is necessary for optimal cell functions. However, conventional bioprinting only allows the fabrication of hydrogel scaffolds containing vessel-like structures with large diameters (>100 µm) and simple geometries. Recent developments in laser photoablation enable the generation of this type of structure with higher resolution and complexity, but the photo-thermal process can compromise cell viability and hydrogel integrity. To address these limitations, the present work reports in situ 3D patterning of collagen hydrogels by femtosecond laser irradiation to create channels and cavities with diameters ranging from 20 to 60 µm. In this process, laser irradiation of the hydrogel generates cavitation gas bubbles that rearrange the collagen fibers, thereby creating stable microchannels. Such 3D channels can be formed in cell- and organoid-laden hydrogel without affecting the viability outside the lumen and can enable the formation of artificial microvasculature by the culture of endothelial cells and cell media perfusion. Thus, this method enables organs-on-a-chip and 3D tissue models featuring complex microvasculature.

Bactericidal surfaces prepared by femtosecond laser patterning and layer-by-layer polyelectrolyte coating.

Antimicrobial surfaces are important in medical, clinical, and industrial applications, where bacterial infection and biofouling may constitute a serious threat to human health. Conventional approaches against bacteria involve coating the surface with antibiotics, cytotoxic polymers, or metal particles. However, these types of functionalization have a limited lifetime and pose concerns in terms of leaching and degradation of the coating. Thus, there is a great interest in developing long-lasting and non-leaching bactericidal surfaces. To obtain a bactericidal surface, we combine micro and nanoscale patterning of borosilicate glass surfaces by ultrashort pulsed laser irradiation and a non-leaching layer-by-layer polyelectrolyte modification of the surface. The combination of surface structure and surface charge results in an enhanced bactericidal effect against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria. The laser patterning and the layer-by-layer modification are environmentally friendly processes that are applicable to a wide variety of materials, which makes this method uniquely suited for fundamental studies of bacteria-surface interactions and paves the way for its applications in a variety of fields, such as in hygiene products and medical devices.

Scalable Manufacturing of Single Nanowire Devices Using Crack-Defined Shadow Mask Lithography.

Single nanowires (NWs) have a broad range of applications in nanoelectronics, nanomechanics, and nanophotonics, but, to date, no technique can produce single sub-20 nm wide NWs with electrical connections in a scalable fashion. In this work, we combine conventional optical and crack lithographies to generate single NW devices with controllable and predictable dimensions and placement and with individual electrical contacts to the NWs. We demonstrate NWs made of gold, platinum, palladium, tungsten, tin, and metal oxides. We have used conventional i-line stepper lithography with a nominal resolution of 365 nm to define crack lithography structures in a shadow mask for large-scale manufacturing of sub-20 nm wide NWs, which is a 20-fold improvement over the resolution that is possible with the utilized stepper lithography. Overall, the proposed method represents an effective approach to generate single NW devices with useful applications in electrochemistry, photonics, and gas- and biosensing.

Electrically Driven Microengineered Bioinspired Soft Robots.

To create life-like movements, living muscle actuator technologies have borrowed inspiration from biomimetic concepts in developing bioinspired robots. Here, the development of a bioinspired soft robotics system, with integrated self-actuating cardiac muscles on a hierarchically structured scaffold with flexible gold microelectrodes is reported. Inspired by the movement of living organisms, a batoid-fish-shaped substrate is designed and reported, which is composed of two micropatterned hydrogel layers. The first layer is a poly(ethylene glycol) hydrogel substrate, which provides a mechanically stable structure for the robot, followed by a layer of gelatin methacryloyl embedded with carbon nanotubes, which serves as a cell culture substrate, to create the actuation component for the soft body robot. In addition, flexible Au microelectrodes are embedded into the biomimetic scaffold, which not only enhance the mechanical integrity of the device, but also increase its electrical conductivity. After culturing and maturation of cardiomyocytes on the biomimetic scaffold, they show excellent myofiber organization and provide self-actuating motions aligned with the direction of the contractile force of the cells. The Au microelectrodes placed below the cell layer further provide localized electrical stimulation and control of the beating behavior of the bioinspired soft robot.

Bioprinted 3D vascularized tissue model for drug toxicity analysis.

To develop biomimetic three-dimensional (3D) tissue constructs for drug screening and biological studies, engineered blood vessels should be integrated into the constructs to mimic the drug administration process in vivo. The development of perfusable vascularized 3D tissue constructs for studying the drug administration process through an engineered endothelial layer remains an area of intensive research. Here, we report the development of a simple 3D vascularized liver tissue model to study drug toxicity through the incorporation of an engineered endothelial layer. Using a sacrificial bioprinting technique, a hollow microchannel was successfully fabricated in the 3D liver tissue construct created with HepG2/C3A cells encapsulated in a gelatin methacryloyl hydrogel. After seeding human umbilical vein endothelial cells (HUVECs) into the microchannel, we obtained a vascularized tissue construct containing a uniformly coated HUVEC layer within the hollow microchannel. The inclusion of the HUVEC layer into the scaffold resulted in delayed permeability of biomolecules into the 3D liver construct. In addition, the vascularized construct containing the HUVEC layer showed an increased viability of the HepG2/C3A cells within the 3D scaffold compared to that of the 3D liver constructs without the HUVEC layer, demonstrating a protective role of the introduced endothelial cell layer. The 3D vascularized liver model presented in this study is anticipated to provide a better and more accurate in vitro liver model system for future drug toxicity testing.