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.

Organic mixed ionic-electronic conductors are promising materials for interfacing and monitoring biological systems, with the aim of overcoming current challenges based on the mismatch between biological materials and convectional inorganic conductors. The conjugated polymer/polyelectrolyte complex poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT/PSS) is, up to date, the most widely used polymer for in vitro or in vivo measurements in the field of organic bioelectronics. However, PEDOT/PSS organic electrochemical transistors (OECTs) are limited by depletion mode operation and lack chemical groups that enable synthetic modifications for biointerfacing. Recently introduced thiophene-based polymers with oligoether side chains can operate in accumulation mode, and their chemical structure can be tuned during synthesis, for example, by the introduction of hydroxylated side chains. Here, we introduce a new thiophene-based conjugated polymer, p(g42T-T)-8% OH, where 8% of the glycol side chains are functionalized with a hydroxyl group. We report for the first time the compatibility of conjugated polymers containing ethylene glycol side chains in direct contact with cells. The additional hydroxyl group allows covalent modification of the surface of polymer films, enabling fine-tuning of the surface interaction properties of p(g42T-T)-8% OH with biological materials, either hindering or promoting cell adhesion. We further use p(g42T-T)-8% OH to fabricate the OECTs and demonstrate for the first time the monitoring of epithelial barrier formation of Caco-2 cells in vitro using accumulation mode OECTs. The conjugated polymer p(g42T-T)-8% OH allows organic-electronic-based materials to be easily modified and optimized to interface and monitor biological systems.

Biological processes in the human body are regulated through complex and precise arrangements of cell structures and their interactions. In vivo models serve as the most accurate choice for biological studies to understand these processes. However, they are costly, time-consuming, and raise ethical issues. Microphysiological systems have been developed to create advanced in vitro models that mimic in vivo-like microenvironments. They are often combined with integrated sensing technologies to perform real-time measurements to gain additional information. However, conventional sensing electrodes, made of inorganic materials such as gold or platinum, differ fundamentally from biological materials. Organic bioelectronic devices made from conjugated polymers are promising alternatives for biological sensing applications and aim to improve the interconnection between abiotic electronics and biotic materials. The widespread use of these devices is partly hindered by the limited availability of materials and low-cost fabrication methods. In this thesis, we provide new tools and materials that facilitate the use of organic bioelectronic devices for in vitro sensing applications. We developed a method to pattern the conducting polymer poly(3,4‑ethylenedioxythiophene) polystyrene sulfonate and to fabricate organic microelectronic devices using wax printing, filtering, and tape transfer. The method is low-cost, time-effective, and compatible with in vitro cell culture models. To achieve higher resolution, we further developed a patterning method using femtosecond laser ablation to fabricate organic electronic devices such as complementary inverters or biosensors. The method is maskless and independent of the type of conjugated polymer. Besides fabrication processes, we introduced a newly synthesized material, the semiconducting conjugated polymer p(g42T‑T)‑8%OH. This polymer contains hydroxylated side chains that enable surface modifications, allowing control of cell adhesion. Using the new femtosecond laser-based patterning method, we could fabricate p(g42T‑T)‑8%OH‑based organic electrochemical transistors to monitor cell barrier formations in vitro. Microphysological systems are further dependent on precise compartmentalization to study cellular interaction. We used femtosecond laser 3D printing to develop a co-culture neurite guidance platform to control placement and interactions between different types of brain cells. In summary, the thesis provides new tools to facilitate the fabrication of organic electronic devices and microphysiological systems. This increases their accessibility and widespread use to interface, monitor, and model biological systems. 

Biologiska processer i människokroppen regleras genom komplexa och exakta arrangemang av cellstrukturer och deras interaktioner. In vivo modeller är det mest exakta valet för biologiska studier för att förstå dessa processer. Men de är dyra, tidskrävande och behäftade med etiska dilemman. Mikrofysiologiska system har utvecklats för att skapa avancerade in vitro-modeller för att efterlikna mikromiljöer som finns in vivo. Dessa system kombineras ofta med integrerade sensortekniker för att utföra mätningar i realtid för att få ytterligare information. Konventionella elektroder, gjorda av oorganiska material som guld eller platina, skiljer sig dock fundamentalt från biologiska material. Organiska bioelektroniska komponenter tillverkade av konjugerade polymerer är intressanta alternativ för biologiska sensortillämpningar eftersom de har potential att förbättra sammankopplingen mellan abiotisk elektronik och biotiska material. Deras användning hindras delvis av den begränsade tillgången på material och billiga tillverkningsmetoder. I den här avhandlingen tillhandahåller vi nya verktyg och material som underlättar användningen av organiska bioelektroniska komponenter för in vitro avkänningstillämpningar. Vi utvecklade en metod för att mönstra den ledande polymeren poly(3,4-etylendioxitiofen) polystyrensulfonat och tillverka organiska mikroelektroniska komponenter med hjälp av vaxtryck, filtrering och tejpöverföring. Metoden har låg kostnad, är tidseffektiv och kompatibel med in vitro cellodlingsmodeller. För att uppnå högre upplösning vidareutvecklade vi en mönstringsmetod med femtosekundlaserablation för att tillverka organiska elektroniska enheter såsom komplementära växelriktare eller biosensorer. Metoden involverar inga masker och är inte beroende av typen av konjugerad polymer. Förutom tillverkningsprocesser introducerade vi ett nytt material, den konjugerade polymeren p(g42T‑T)‑8%OH. Denna polymer innehåller hydroxylerade sidokedjor som möjliggör ytmodifieringar, vilket tillåter kontroll av celladhesion. Med den nya femtonsekundslaser baserade mönstringsmetoden kunde vi tillverka p(g42T‑T)‑8%OH-baserade organiska elektrokemiska transistorer för att följa cellbarriärformationer in vitro. Slutligen använde vi femtonsekundslaserutskrift för att tillverka en plattform som kan guida neuriter i co-kultur  för att undersöka cellinteraktionerna mellan olika typer av hjärnceller. Sammanfattningsvis beskriver avhandlingen nya verktyg för att underlätta tillverkningen av organiska elektroniska enheter och mikrofysiologiska system. Detta ökar deras tillgänglighet och möjliggör utbredd användning för gränssnitt, övervakning och modellering av biologiska system.

Astrocytes play an important role in the central nervous system, contributing to the development of and maintenance of synapses, recycling of neurotransmitters, and the integrity and function of the blood-brain barrier. Astrocytes are also linked to the pathophysiology of various neurodegenerative diseases. Astrocyte function and organization are tightly regulated by interactions mediated by the extracellular matrix (ECM). Engineered hydrogels can mimic key aspects of the ECM and can allow for systematic studies of ECM-related factors that govern astrocyte behaviour. In this study, we explore the interactions between neuroblastoma (SH-SY5Y) and glioblastoma (U87) cell lines and human fetal primary astrocytes (FPA) with a modular hyaluronan-based hydrogel system. Morphological analysis reveals that FPA have a higher degree of interactions with the hyaluronan-based gels compared to the cell lines. This interaction is enhanced by conjugation of cell-adhesion peptides (cRGD and IKVAV) to the hyaluronan backbone. These effects are retained and pronounced in 3D bioprinted structures. Bioprinted FPA using cRGD functionalized hyaluronan show extensive and defined protrusions and multiple connections between neighboring cells. Possibilities to tailor and optimize astrocyte-compatible ECM-mimicking hydrogels that can be processed by means of additive biofabrication can facilitate the development of advanced tissue and disease models of the central nervous system.

To model complex biological tissue in vitro, a specific layout for the position and numbers of each cell type isnecessary. Establishing such a layout requires manual cell placement in three dimensions (3D) with micrometricprecision, which is complicated and time-consuming. Moreover, 3D printed materials used in compartmentalizedmicrofluidic models are opaque or autofluorescent, hindering parallel optical readout and forcing serial charac-terization 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 structuresprinted with a commercially available non-autofluorescent resin at micrometer resolution. Using a two-stepstrategy based on probabilistic cell seeding, we demonstrate a human neuronal monoculture that forms net-works on the 3D printed structure and can establish cell-projection contacts with an astrocytic-neuronal co-cultureseeded on the glass substrate. The transparent and non-autofluorescent printed platform allows fluorescence-based immunocytochemistry and calcium imaging. This approach provides facile multi-level compartmentaliza-tion of different cell types and routes for pre-designed cell projection contacts, instrumental in studying complextissue, such as the human brain.

Organic ionic/electronic conductors (OMIECs) offer a promising alternative to metals and inorganic semiconductors for direct interfacing between human-made electronics and biological tissues. A device that takes advantage of the mixed ionic/electronic conductivity of OMIEC materials is the organic electrochemical transistor (OECT). High-density OECTs are typically fabricated using costly cleanroom-based lithography and complex lift-off processes. To simplify the fabrication of OECTs, we propose laser direct writing of conjugated polymers using a commercial two-photon polymerization 3D printer. Ultrafast laser direct writing allows single-digit micrometer resolution and high-speed processing, thereby enabling a cost-effective and simple fabrication process.

Structures that are periodic on a microscale in three dimensions are abundant in nature, for example, in the cellular arrays that make up living tissue. Such structures can also be engineered, appearing in smart materials(1-4), photonic crystals(5), chemical reactors(6), and medical(7) and biomimetic(8) technologies. Here we report that fluid-fluid interfacial energy drives three-dimensional (3D) structure emergence in a micropillar scaffold. This finding offers a rapid and scalable way of transforming a simple pillar scaffold into an intricate 3D structure that is periodic on a microscale, comprising a solid microscaffold, a dispersed fluid and a continuous fluid. Structures generated with this technique exhibit a set of unique features, including a stationary internal liquid-liquid interface. Using this approach, we create structures with an internal liquid surface in a regime of interest for liquid-liquid catalysis. We also synthesize soft composites in solid, liquid and gas combinations that have previously not been shown, including actuator materials with temperature-tunable microscale pores. We further demonstrate the potential of this method for constructing 3D materials that mimic tissue with an unprecedented level of control, and for microencapsulating human cells at densities that address an unresolved challenge in cell therapy.