Volker Nock

Meniscus-guided printing (MGP) has emerged as a versatile additive manufacturing strategy for the high-resolution fabrication of three-dimensional (3D) microarchitectures. However, the widespread implementation of soft, high-aspect-ratio conducting polymer (CP) microelectrodes for advanced bioelectronics remains limited by the lack of predictive frameworks linking printing parameters to print fidelity, mechanical stability, and electrochemical performance. We previously reported the direct MGP of high-aspect-ratio poly(3,4‑ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) pillar microelectrode arrays with tunable structural and electrochemical properties. Herein, we build on these studies by systematically correlating fundamental printing parameters, including ink composition, rheological properties, printing dynamics, and post-print thermal annealing conditions, with the mechanical and electrochemical performance of the 3D PEDOT:PSS pillar microelectrodes. The 3D-printed pillar microelectrodes were fabricated with high aspect ratios (up to 17), excellent geometric uniformity, mechanical integrity, and reliable electrochemical properties. Electrochemical performance showed a strong dependence on microelectrode architecture, pillar height, and thermal processing conditions. Notably, the 50 µm-tall PEDOT:PSS pillar microelectrodes demonstrated an eightfold increase in electrochemically active surface area (ECSA) and a 46% reduction in interfacial impedance at 100 Hz compared with planar PEDOT:PSS microelectrodes. Further optimization of pillar height and thermal annealing at 180 °C for 10 min enabled the 200 µm-tall PEDOT:PSS pillar microelectrodes to achieve a 3.7-fold higher ECSA, three times larger double-layer capacitance, and 82% lower charge-transfer resistance than the 50 µm-tall PEDOT:PSS pillar microelectrodes. Overall, this work provides a customizable material-process-property optimization paradigm for the robust MGP of soft 3D PEDOT:PSS microelectrode arrays for next-generation bioelectronic interfaces, tissue engineering, and electrochemical biosensing technologies.

Polydimethylsiloxane (PDMS) is an excellent material for the construction of biomimetic leaf replicas which reproduce leaf surfaces with high fidelity. This allows for the study of leaf surface-colonizing bacteria and the impact of the leaf topology on bacterial distributions and behavior. However, their application is limited to short-term experiments, as long term survival of microorganisms on their surface is not possible due to a lack of nutrient replenishment. On living leaves, nutrients diffuse across the cuticle via leaching, a process not yet replicated in biomimetic systems. Here, we explore whether water and fructose can be supplied to microbial colonizers on PDMS membranes by mimicking leaching. We created hybrid membranes by incorporating polymers (Carbopol, Pemulen, cellulose microfibers, cellulose nanocrystals, and polyvinylpyrrolidone) to enhance nutrient transport. We determined that bulk diffusion of water correlated negatively with membrane thickness and positively with polymer concentration. Further, fructose diffusion across hybrid membranes reached similar rates compared to isolated Populus × canescens leaf cuticles. Under high relative humidity, these membranes supported long-term bacterial survival. Our findings represent important steps towards the development of topomimetic leaf surfaces that sustain microbial life, enabling further investigation into the microbe-microbe interactions that take place on leaves.

Rust fungi cause significant economic and biodiversity losses worldwide, yet effective control strategies for them remain limited. A major challenge in identifying control targets is the inability to culture them through the different stages of their life cycle in the laboratory, thereby restricting their study. Current research suggests that a complex interplay of physical and chemical plant properties influences rust fungal infection, and successful culture protocols likely need to incorporate multiple aspects of the plant host environment into an artificial system. These include plant surface moisture, charge, hardness, hydrophobicity, topography, texture and chemical make-up. This review outlines key plant characteristics that influence infection by rust fungi, examines attempts to replicate these characteristics in vitro , and assesses the level of success. We conclude by proposing a potential culture approach that integrates inoculation methods, media composition, physical properties of media, chemical additives, and environmental conditions.

Early detection of plant pathogens is essential to maintain global food production and ecosystem resilience, especially as climate change creates new ecological niches that favour the emergence and spread of novel pathogens. Laboratory‐based diagnostic methods, including ELISA and PCR, while accurate, are unsuitable for on‐site (directly at the point of sample collection) testing. Recent advances in microfluidics, including polydimethylsiloxane (PDMS)‐based chips and paper‐based platforms, offer solutions for this by enabling rapid and sensitive diagnostics with results obtained directly in the field. This mini review gives a short overview of channel‐flow, paper, droplet and digital microfluidics‐based platforms integrated with nucleic acid amplification, immunosensors or morphological methods for fungal, oomycete, bacterial and viral detection. We touch on recent material enhancements and sample preparation strategies that have improved the performance of these devices. Finally, we explore the challenges and opportunities of deploying miniature diagnostic devices across diverse agricultural and environmental settings, emphasising the need for specificity and reliability in detecting plant pathogens, supporting timely disease management.

Optical force-induced assembly is a promising yet scarcely explored approach for developing functional tools and objects at the microscale, with a wide range of potential applications. Our previous work was the first to investigate the manipulation of these assemblies in the XY plane. Here, we expand on these techniques by systematically exploring optical trap manipulation with the addition of Z-axis control. Manipulation of the Z-axis is referred to as axial displacement and is a viable approach for actively manipulating the assembly morphology. Experiments are conducted for the first time to explore and detail the response of the assembly during active 3D trap manipulation, informing the development of an autonomous control algorithm over the 2D area of the assembly during motion. This control presents techniques to increase assembly stability or alter the area of the assembly for tasks such as passing through constrictions. This work aims to develop the control techniques required to create a unique micromanufacturing approach inspired by the Kilobot thousand-robot swarm.

New flow control elements in capillaric circuits are key to achieving ever more complex lab-on-a-chip functionality while maintaining their autonomous and easy-to-use nature. Capillary field effect transistors valves allow for flow in channels to be restricted and cut off utilising a high pressure triggering channel and occluding air bubble. The reversible capillary field effect transistor presented here provides a new element that can restore fluid flow in closed microchannels via autonomous circuit feedback. This allows new flow switching functionality without the need for direct user input. The valve design utilises new circuitry that draws on competing capillary pressures to withdraw liquid from a reservoir connected to the valve, creating a suction pressure that removes the occluding bubble from the channel to allow flow past the valve. The resulting reopening restores flow to the closed channel and allows for enhanced autonomous control over fluid flows. This new functionality is flexible and has the potential to be applied in a wide variety of situations, as shown here by use in several extended proof of concept arrangements. Firstly, we demonstrate how to reopen one valve while closing another using the same trigger to achieve simultaneous flow switching. We then show how a single trigger can be used for the parallel reopening of multiple valves for simultaneous release of liquids. Finally, we show the reversible capillary field effect transistor used to achieve autonomous transient mixing ratios between multiple liquids utilising a series of triggering events to determine which liquid channels are open or closed as flow progresses. The functionality this valve adds to the capillaric toolbox opens up new possibilities for applications in the creation of fully automatic diagnostic capillaric devices.

Using a bi-directional dual-flow RootChip with integrated force sensing micropillars, root growth and signalling responses to stress gradients and pathogens were studied in Arabidopsis thaliana , Nicotiana benthamiana and Solanum lycopersicum .

The versatility of spin coating technology makes it a preferred method for producing the thin film layers used to manufacture products from solar panels and smartphones to sunglasses and CDs. However, the process requires a flat, rigid substrate to produce uniform films, which limits its use to planar devices. A novel multi-axis manipulator has been developed to extend the application of spin coating, enabling controlled thin film deposition onto curved surfaces. Various rotational schemes were studied to link the flow of a liquid film over a curved surface to forces induced by complex rotational dynamics. When the angular velocity exceeds a threshold, centrifugal force dominates the flow, pushing the fluid away from the instantaneous axis of rotation. This produces axisymmetric coating profiles when using consistent single or dual-axis rotation. Areas of near uniformity present around the spin axis poles for single-axis rotation and around the substrate’s equator for dual-axis schemes. Sensitivities between the spherical substrate dynamics and the evolving fluid flow were investigated, exploring the parameters that promoted the production of uniform curved film layers for microfabrication processes. This enabled the evolution of the spin coating technique to effectively form curved polymer coatings with improved thickness control. The presented research outlines the capabilities of a multi-axis spin coating machine when used to coat spherical substrates. Therefore, enabling the use of fluid mechanics models to identify the optimal motion kinematics required to create uniform curved films.

Although the accumulation of random genetic mutations have been traditionally viewed as the main cause of cancer progression, altered mechanobiological profiles of the cells and microenvironment also play a major role as a mutation-independent element. To probe the latter, we have previously reported a microfluidic cell-culture platform with an integrated flexible actuator and its application for sequential cyclic compression of cancer cells. The platform is composed of a control microchannel in a top layer for introducing external pressure, and a polydimethylsiloxane (PDMS) membrane from which a monolithically-integrated actuator protrudes downwards into a cell-culture microchannel. When actively actuated, the integrated actuator, referred to as micro-piston, transfers the pressure from the control channel as a mechanical force to the cells underneath. When not actuated, the micro-piston remains suspended above cells, separated from the latter via a liquid-filled gap of ∼108 µm. Despite the lack of direct physical contact between the micro-piston and cells in the latter arrangement, we observed distinct alignment of SKOV-3 ovarian cancer cells to the piston shape. To characterize this observation, micro-piston localization, shape, and size were adjusted and the directionality of a mono-layer of SKOV-3 cells relative to the suspended structure was probed. Cell alignment analysis was performed in a novel, label-free approach by measuring elongation angles of whole cell bodies with respect to micro-piston peripheries. Alignment of SKOV-3 cells to the structure outline was significant for circular, triangular and square micro-piston when compared to control areas without micro-piston on the same chip. The effect was present irrespective of whether cells were loaded with micro-pistons in static position (∼108 µm gap) or actively retracted using vacuum (>108 µm gap). Similar alignment was not observed for MCF7 cancer cells and MCF10A non-cancerous epithelial cells. The reported observation of directional movement and growth of SKOV-3 cells towards the region under micro-pistons point towards a to-date unexplored mechanotactic behaviour of these cells, warranting future investigations regarding the mechanisms involved and the role these may play in cancer.