Multiphoton Lithography of Organic Semiconductor Devices for 3D Printing of Flexible Electronic Circuits, Biosensors, and Bioelectronics

Multi-material Electrohydrodynamic Printing of Bioelectronics with Sub-Microscale 3D Gold Pillars for In Vitro Extra- and Intra-Cellular Electrophysiological Recordings

Micro/nanoscale 3D bioelectrodes gain increasing interest for electrophysiological recording of electroactive cells. Although 3D printing has shown promise to flexibly fabricate 3D bioelectronics compared with conventional microfabrication, relatively-low resolution limits the printed bioelectrode for high-quality signal monitoring. Here, a novel multi-material electrohydrodynamic printing (EHDP) strategy is proposed to fabricate bioelectronics with sub-microscale 3D gold pillars for in vitro electrophysiological recordings. EHDP is employed to fabricate conductive circuits for signal transmission, which are passivated by polyimide via extrusion-based printing. Laser-assisted EHDP is developed to produce 3D gold pillars featuring a diameter of 0.64 ± 0.04 µm. The 3D gold pillars demonstrate stable conductivity under the cell-culture environment. Living cells can conformally grow onto these sub-microscale 3D pillars with a height below 5 µm, which facilitates the highly-sensitive recording of extracellular signals with amplitudes <15 µV. The 3D pillars can apply electroporation currents to reversibly open the cellular membrane for intracellular recording, facilitating the measurement of subtle cellular electrophysiological activities. As a proof-of-concept demonstration, fully-printed chips with multiple culturing chambers and sensing bioelectronics are fabricated for zone-specific electrophysiological recording in drug testing. The proposed multi-material EHDP strategy enables rapid prototyping of organ-on-a-chip systems with 3D bioelectronics for high-quality electrophysiological recordings.

3D printing of highly conductive and strongly adhesive PEDOT:PSS hydrogel-based bioelectronic interface for accurate electromyography monitoring

PEDOT

PSS hydrogel-based bioelectronic interfaces have gained significant attention in various fields including biomedical devices, wearable devices, and epidermal electronics. However, the development of high-performance bioelectronic interfaces that integrate excellent conductivity, strong adhesion, and advanced processing compatibility remains a challenge. Herein, we develop a high-performance bioelectronic interface by 3D printing of a novel poly(vinyl alcohol-formaldehyde) (PVAF)-PEDOT:PSS composite ink. Such a PEDOT:PSS-PVAF ink exhibits favorable rheological properties for direct-ink-writing 3D printing, enabling the fabrication of high-resolution patterns and three-dimensional structures with high aspect ratios. Hydrogel bioelectronic interface printed by such PEDOT:PSS-PVAF ink simultaneously achieves high conductivity (over 100 S m-1), strong adhesion (31.44 ± 7.07 kPa), as well as stable electrochemical performance (charge injection capacity of 13.72 mC cm-2 and charge storage capacity of 18.80 mC cm-2). We further integrate PEDOT:PSS-PVAF hydrogel bioelectronic interface to fabricate adhesive skin electrodes for electromyography (EMG) signal recording. The resultant EMG skin electrodes demonstrate superior performance and stability compared to commercial products, maintaining high signal-to-noise ratio of > 10 dB under varying weights and repetitive motions. These advantageous performance of PEDOT:PSS-PVAF based hydrogel bioelectronic interfaces may be helpful for diverse bioelectronic applications like healthcare monitoring and epidermal bioelectronics.

Fabrication of 3D Functional Nanocomposites Through Post-Doping of Two-Photon Microprinted Nanoporous Architectures

Two-photon lithography (TPL) enables the fabrication of complex 3D structures with sub-micrometer precision. Incorporation of new functionalities into TPL-printed structures is key to advance their applications. A prevalent approach to achieve this is by directly adding functional nanomaterials into the photoresist (called "pre-doping"), which has several inherent challenges including material compatibility, light scattering, and nanoparticle agglomeration. Here, a conceptually different "post-doping" strategy is proposed, where the functionality of the TPL-printed architectures is achieved by impregnating functional materials into their nanoporous 3D mimics. Using the principle of polymerization-induced phase separation, TPL printing of complex microarchitectures with well-defined nanoporous structures having pores of ≈420 nm is realized, which allows spontaneous impregnation of functional liquids via capillary effect. Importantly, unlike the "pre-doping" approach that requires printing optimization for each photoresist, this strategy is highly versatile in terms of functionalities possible. As a proof-of-concept, the impregnation of several functional liquids into TPL-printed porous microstructures is demonstrated: a fluorinated-lubricant, an ionic liquid, and three types of fluorescent liquids, conferring the microstructures with slippery, conductive, and localized fluorescence properties, respectively. Such versatility to fabricate complex microstructures with tailorable and localized functionalities is expected to open new possibilities in wide fields including bionics, electronics, and cell biology.

Photoresist Development for 3D Printing of Conductive Microstructures via Two-Photon Polymerization

The advancement of electronic devices necessitates the development of three-dimensional (3D) high-precision conductive microstructures, which have extensive applications in bio-electronic interfaces, soft robots, and electronic skins. Two-photon polymerization (TPP) based 3D printing is a critical technique that offers unparalleled fabrication resolution in 3D space for intricate conductive structures. While substantial progress has been made in this field, this review summarizes recent advances in the 3D printing of conductive microstructures via TPP, mainly focusing on the essential criteria of photoresist resins suitable for TPP. Further preparation strategies of these photoresists and methods for constructing 3D conductive microstructures via TPP are discussed. The application prospects of 3D conductive microstructures in various fields are discussed, highlighting the imperative to advance their additive manufacturing technology. Finally, strategic recommendations are offered to enhance the construction of 3D conductive microstructures using TPP, addressing prevailing challenges and fostering significant advancements in manufacturing technology.

Signal amplification strategies in photoelectrochemical sensing of carcinoembryonic antigen

Early detection of cancer markers is critical for cancer diagnosis and cancer therapy since these markers may indicate cancer risk, incidence, and disease prognosis. Carcinoembryonic antigen (CEA) is a type of non-specific and broad-spectrum cancer biomarker commonly utilized for early cancer diagnosis. Moreover, it serves as an essential tool to assess the efficacy of cancer treatment and monitor tumor recurrence as well as metastasis, thus garnering significant attention for precise and sensitive CEA detection. In recent years, photoelectrochemical (PEC) techniques have emerged as prominent methods in CEA detection due to the advantages of PEC, such as simple equipment requirements, cost-effectiveness, high sensitivity, low interference from background signals, and easy of instrument miniaturization. Different signal amplification methods have been reported in PEC sensors for CEA analysis. Based on these, this article reviews PEC sensors based on various signal amplification strategies for detection of CEA during the last five years. The advantages and drawbacks of these sensors were discussed, as well as future challenges.

Materials for 3D printing in healthcare sector: A review

Additive Manufacturing (AM) encompasses various techniques creating intricate components from digital models. The aim of incorporating 3D printing (3DP) in the healthcare sector is to transform patient care by providing personalized solutions, improving medical procedures, fostering research and development, and ultimately optimizing the efficiency and effectiveness of healthcare delivery. This review delves into the historical beginnings of AM's 9 integration into medical contexts exploring various categories of AM methodologies and their roles within the medical sector. This survey also dives into the issue of material requirements and challenges specific to AM's medical applications. Emphasis is placed on how AM processes directly enhance human well-being. The primary focus of this paper is to highlight the evolution and incentives for cross-disciplinary AM applications, particularly in the realm of healthcare by considering their principle, materials and applications. It is designed for a diverse audience, including manufacturing professionals and researchers, seeking insights into this transformative technology's medical dimensions.

Advancing the dynamic mechanical analysis of organic semiconductor materials

Dynamic mechanical analysis (DMA) is a powerful technique for characterizing the mechanical properties of a wide range of materials. However, the importance of DMA in studying organic/polymer semiconductors has not been fully appreciated. In this Highlight, we explore recent advancements in the use of DMA in understanding the viscoelastic and mechanical properties and thermal transitions of organic semiconductor materials. In particular, the insights gained from DMA can serve as new guides for the device optimisation of organic solar cells towards stable operation. Furthermore, we present key findings, challenges, and future directions to advance the application of DMA in organic electronics.

Genetic Algorithm-Based Data-Driven Process Selection System for Additive Manufacturing in Industry 4.0

Additive manufacturing (AM) has impacted the manufacturing of complex three-dimensional objects in multiple materials for a wide array of applications. However, additive manufacturing, as an upcoming field, lacks automated and specific design rules for different AM processes. Moreover, the selection of specific AM processes for different geometries requires expert knowledge, which is difficult to replicate. An automated and data-driven system is needed that can capture the AM expert knowledge base and apply it to 3D-printed parts to avoid manufacturability issues. This research aims to develop a data-driven system for AM process selection within the design for additive manufacturing (DFAM) framework for Industry 4.0. A Genetic and Evolutionary Feature Weighting technique was optimized using 3D CAD data as an input to identify the optimal AM technique based on several requirements and constraints. A two-stage model was developed wherein the stage 1 model displayed average accuracies of 70% and the stage 2 model showed higher average accuracies of up to 97.33% based on quantitative feature labeling and augmentation of the datasets. The steady-state genetic algorithm (SSGA) was determined to be the most effective algorithm after benchmarking against estimation of distribution algorithm (EDA) and particle swarm optimization (PSO) algorithms, respectively. The output of this system leads to the identification of optimal AM processes for manufacturing 3D objects. This paper presents an automated design for an additive manufacturing system that is accurate and can be extended to other 3D-printing processes.

E-Suture: Mixed-Conducting Suture for Medical Devices

Modern implantable bioelectronics demand soft, biocompatible components that make robust, low-impedance connections with the body and circuit elements. Concurrently, such technologies must demonstrate high efficiency, with the ability to interface between the body's ionic and external electronic charge carriers. Here, a mixed-conducting suture, the e-suture, is presented. Composed of silk, the conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), and insulating jacketing polymers,the resulting e-suture has mixed-conducting properties at the interface with biological tissue as well as effective insulation along its length. The e-suture can be mechanically integrated into electronics, enabling the acquisition of biopotentials such as electrocardiograms, electromyograms, and local field potentials (LFP). Chronic, in vivo acquisition of LFP with e-sutures remains stable for months with robust brain activity patterns. Furthermore, e-sutures can establish electrophoretic-based local drug delivery, potentially offering enhanced anatomical targeting and decreased side effects associated with systemic administration, while maintaining an electrically conducting interface for biopotential monitoring. E-sutures expand on the conventional role of sutures and wires by providing a soft, biocompatible, and mechanically sound structure that additionally has multifunctional capacity for sensing, stimulation, and drug delivery.

Conducting polymer hydrogels for biomedical application: Current status and outstanding challenges

Conducting polymer hydrogels (CPHs) are composite polymeric materials with unique properties that combine the electrical capabilities of conducting polymers (CPs) with the excellent mechanical properties and biocompatibility of traditional hydrogels. This review aims to highlight how the unique properties CPHs have from combining their two constituent materials are utilized within the biomedical field. First, the synthesis approaches and applications of non-CPH conductive hydrogels are discussed briefly, contrasting CPH-based systems. The synthesis routes of hydrogels, CPs, and CPHs are then discussed. This review also provides a comprehensive overview of the recent advancements and applications of CPHs in the biomedical field, encompassing their applications as biosensors, drug delivery scaffolds (DDSs), and tissue engineering platforms. Regarding their applications within tissue engineering, a comprehensive discussion of the usage of CPHs for skeletal muscle prosthetics and regeneration, cardiac regeneration, epithelial regeneration and wound healing, bone and cartilage regeneration, and neural prosthetics and regeneration is provided. Finally, critical challenges and future perspectives are also addressed, emphasizing the need for continued research; however, this fascinating class of materials holds promise within the vastly evolving field of biomedicine.

Fibres-threads of intelligence-enable a new generation of wearable systems

Fabrics represent a unique platform for seamlessly integrating electronics into everyday experiences. The advancements in functionalizing fabrics at both the single fibre level and within constructed fabrics have fundamentally altered their utility. The revolution in materials, structures, and functionality at the fibre level enables intimate and imperceptible integration, rapidly transforming fibres and fabrics into next-generation wearable devices and systems. In this review, we explore recent scientific and technological breakthroughs in smart fibre-enabled fabrics. We examine common challenges and bottlenecks in fibre materials, physics, chemistry, fabrication strategies, and applications that shape the future of wearable electronics. We propose a closed-loop smart fibre-enabled fabric ecosystem encompassing proactive sensing, interactive communication, data storage and processing, real-time feedback, and energy storage and harvesting, intended to tackle significant challenges in wearable technology. Finally, we envision computing fabrics as sophisticated wearable platforms with system-level attributes for data management, machine learning, artificial intelligence, and closed-loop intelligent networks.

Light-Based 3D Multi-Material Printing of Micro-Structured Bio-Shaped, Conducting and Dry Adhesive Electrodes for Bioelectronics

In this work, a new method of multi-material printing in one-go using a commercially available 3D printer is presented. The approach is simple and versatile, allowing the manufacturing of multi-material layered or multi-material printing in the same layer. To the best of the knowledge, it is the first time that 3D printed Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) micro-patterns combining different materials are reported, overcoming mechanical stability issues. Moreover, the conducting ink is engineered to obtain stable in-time materials while retaining sub-100 µm resolution. Micro-structured bio-shaped protuberances are designed and 3D printed as electrodes for electrophysiology. Moreover, these microstructures are combined with polymerizable deep eutectic solvents (polyDES) as functional additives, gaining adhesion and ionic conductivity. As a result of the novel electrodes, low skin impedance values showed suitable performance for electromyography recording on the forearm. Finally, this concluded that the use of polyDES conferred stability over time, allowing the usability of the electrode 90 days after fabrication without losing its performance. All in all, this demonstrated a very easy-to-make procedure that allows printing PEDOT:PSS on soft, hard, and/or flexible functional substrates, opening up a new paradigm in the manufacturing of conducting multi-functional materials for the field of bioelectronics and wearables.

Microneedle Patches-Integrated Transdermal Bioelectronics for Minimally Invasive Disease Theranostics

Wearable epidermal electronics with non- or minimally-invasive characteristics can collect, transduce, communicate, and interact with accessible physicochemical health indicators on the skin. However, due to the stratum corneum layer, rich information about body health is buried under the skin stratum corneum layer, for example, in the skin interstitial fluid. Microneedle patches are typically designed with arrays of special microsized needles of length within 1000 µm. Such characteristics potentially enable the access and sample of biomolecules under the skin or give therapeutical treatment painlessly and transdermally. Integrating microneedle patches with various electronics allows highly efficient transdermal bioelectronics, showing their great promise for biomedical and healthcare applications. This comprehensive review summarizes and highlights the recent progress on integrated transdermal bioelectronics based on microneedle patches. The design criteria and state-of-the-art fabrication techniques for such devices are initially discussed. Next, devices with different functions, including but not limited to health monitoring, drug delivery, and therapeutical treatment, are highlighted in detail. Finally, key issues associated with current technologies and future opportunities are elaborated to sort out the state of recent research, point out potential bottlenecks, and provide future research directions.

Direct Laser Writing of Silica Nanoparticle Nanocomposites: Probing Mechanical Reinforcement and Understanding Structural Color from Design Parameters

Nanocomposite materials have been thoroughly exploited in additive manufacturing, as a means to alter physical, chemical, and optical properties of resulting structures. Herein, nanocomposite materials suitable for direct laser writing (DLW) by two-photon polymerization are presented. These materials, comprising silica nanoparticles, bring significant added value to the technology through physical reinforcement and controllable photonic properties. Incorporation into acrylate photoresists, via a one-step fabrication process, enables the formation of complex structures with large overhangs. The inclusion of 150 nm silica nanoparticles in DLW photoresists at high concentrations, allows for the fabrication of composite microstructures that show reflected color, a product of the relative contributions from the quasi-ordering and random scattering. Using common DLW design parameters, such as slicing distance and structure dimension, a wide gamut of structural color, in solution, using a set concentration of nanoparticles is demonstrated. Numerical modeling is employed to predict the reflected wavelength of the pixel arrays, across the visible spectrum, and this information is used to encode reflected colors into different pixel arrays.

Flexible wearable sensors for crop monitoring: a review

Crops were the main source of human food, which have met the increasingly diversified demand of consumers. Sensors were used to monitor crop phenotypes and environmental information in real time, which will provide a theoretical reference for optimizing crop growth environment, resisting biotic and abiotic stresses, and improve crop yield. Compared with non-contact monitoring methods such as optical imaging and remote sensing, wearable sensing technology had higher time and spatial resolution. However, the existing crop sensors were mainly rigid mechanical structures, which were easy to cause damage to crop organs, and there were still challenges in terms of accuracy and biosafety. Emerging flexible sensors had attracted wide attention in the field of crop phenotype monitoring due to their excellent mechanical properties and biocompatibility. The article introduced the key technologies involved in the preparation of flexible wearable sensors from the aspects of flexible preparation materials and advanced preparation processes. The monitoring function of flexible sensors in crop growth was highlighted, including the monitoring of crop nutrient, physiological, ecological and growth environment information. The monitoring principle, performance together with pros and cons of each sensor were analyzed. Furthermore, the future opportunities and challenges of flexible wearable devices in crop monitoring were discussed in detail from the aspects of new sensing theory, sensing materials, sensing structures, wireless power supply technology and agricultural sensor network, which will provide reference for smart agricultural management system based on crop flexible sensors, and realize efficient management of agricultural production and resources.

Multiscale Transfer Printing via Shape Memory Polymer with High Adhesion and Modulus Switchability

Flexible electronics have gained significant attention as an innovative solution to meet the growing need for information collection from the human body and the environment. However, a critical challenge lies in the need for a transfer printing technique that can fabricate rigid and brittle devices on flexible organic substrates. Here, we develop a multiscale transfer printing technique using an ultraviolet-curable shape memory polymer (SMP) that serves as both the stamp and the receiver substrate. The SMP demonstrates exceptional mechanical performance with toughness at room temperature and remarkable flexibility near its glass transition temperature. The SMP material exhibits an impressive shape recovery ratio and remarkable adhesion switchability. We demonstrate robust transfer printing of diverse objects with different materials and morphologies and in situ transfer of multiscale metallic structures. In addition, the in situ fabricated transparent hyperthermia patches with embedded metal grids are demonstrated, offering potential application in the field of sensors, wearable devices, and electronic skin.

Carbon Nanotube-Based Printed All-Organic Microelectrode Arrays for Neural Stimulation and Recording

In this paper, we report a low-cost printing process of carbon nanotube (CNT)-based, all-organic microelectrode arrays (MEAs) suitable for in vitro neural stimulation and recording. Conventional MEAs have been mainly composed of expensive metals and manufactured through high-cost and complex lithographic processes, which have limited their accessibility for neuroscience experiments and their application in various studies. Here, we demonstrate a printing-based fabrication method for microelectrodes using organic CNT/paraffin ink, coupled with the deposition of an insulating layer featuring single-cell-sized sensing apertures. The simple microfabrication processes utilizing the economic and readily available ink offer potential for cost reduction and improved accessibility of MEAs. Biocompatibility of the fabricated microelectrode was suggested through a live/dead assay of cultured neural cells, and its large electric double layer capacitance was revealed by cyclic voltammetry that was crucial for preventing cytotoxic electrolysis during electric neural stimulation. Furthermore, the electrode exhibited sufficiently low electric impedance of 2.49 Ω·cm2 for high signal-to-noise ratio neural recording, and successfully captured model electric waves in physiological saline solution. These results suggest the easily producible and low-cost printed all-organic microelectrodes are available for neural stimulation and recording, and we believe that they can expand the application of MEA in various neuroscience research.

Direct laser writing-enabled 3D printing strategies for microfluidic applications

Over the past decade, additive manufacturing-or "three-dimensional (3D) printing"-has attracted increasing attention in the Lab on a Chip community as a pathway to achieve sophisticated system architectures that are difficult or infeasible to fabricate via conventional means. One particularly promising 3D manufacturing technology is "direct laser writing (DLW)", which leverages two-photon (or multi-photon) polymerization (2PP) phenomena to enable high geometric versatility, print speeds, and precision at length scales down to the 100 nm range. Although researchers have demonstrated the potential of using DLW for microfluidic applications ranging from organ on a chip and drug delivery to micro/nanoparticle processing and soft microrobotics, such scenarios present unique challenges for DLW. Specifically, microfluidic systems typically require macro-to-micro fluidic interfaces (e.g., inlet and outlet ports) to facilitate fluidic loading, control, and retrieval operations; however, DLW-based 3D printing relies on a micron-to-submicron-sized 2PP volume element (i.e., "voxel") that is poorly suited for manufacturing these larger-scale fluidic interfaces. In this Tutorial Review, we highlight and discuss the four most prominent strategies that researchers have developed to circumvent this trade-off and realize macro-to-micro interfaces for DLW-enabled microfluidic components and systems. In addition, we consider the possibility that-with the advent of next-generation commercial DLW printers equipped with new dynamic voxel tuning, print field, and laser power capabilities-the overall utility of DLW strategies for Lab on a Chip fields may soon expand dramatically.

4D printing for biomedical applications

While three-dimensional (3D) printing excels at fabricating static constructs, it fails to emulate the dynamic behavior of native tissues or the temporal programmability desired for medical devices. Four-dimensional (4D) printing is an advanced additive manufacturing technology capable of fabricating constructs that can undergo pre-programmed changes in shape, property, or functionality when exposed to specific stimuli. In this Perspective, we summarize the advances in materials chemistry, 3D printing strategies, and post-printing methodologies that collectively facilitate the realization of temporal dynamics within 4D-printed soft materials (hydrogels, shape-memory polymers, liquid crystalline elastomers), ceramics, and metals. We also discuss and present insights about the diverse biomedical applications of 4D printing, including tissue engineering and regenerative medicine, drug delivery, in vitro models, and medical devices. Finally, we discuss the current challenges and emphasize the importance of an application-driven design approach to enable the clinical translation and widespread adoption of 4D printing.

Spiers Memorial Lecture: Challenges and prospects in organic photonics and electronics

While a substantial amount of research activity has been conducted in fields related to organic photonics and electronics, including the development of devices such as organic field-effect transistors, organic photovoltaics, and organic light-emitting diodes for applications encompassing organic thermoelectrics, organic batteries, excitonic organic materials for photochemical and optoelectronic applications, and organic thermoelectrics, this perspective review will primarily concentrate on the emerging and rapidly expanding domain of organic bioelectronics and neuromorphics. Here we present the most recent research findings on organic transistors capable of sensing biological biomarkers down at the single-molecule level (i.e., oncoproteins, genomes, etc.) for the early diagnosis of pathological states and to mimic biological synapses, paving the way to neuromorphic applications that surpass the limitations of the traditional von Neumann computing architecture. Both organic bioelectronics and neuromorphics exhibit several challenges but will revolutionize human life, considering the development of artificial synapses to counteract neurodegenerative disorders and the development of ultrasensitive biosensors for the early diagnosis of cancer to prevent its development. Moreover, organic bioelectronics for sensing applications have also triggered the development of several wearable, flexible and stretchable biodevices for continuous biomarker monitoring.

Resorbable conductive materials for optimally interfacing medical devices with the living

Implantable and wearable bioelectronic systems are arising growing interest in the medical field. Linking the microelectronic (electronic conductivity) and biological (ionic conductivity) worlds, the biocompatible conductive materials at the electrode/tissue interface are key components in these systems. We herein focus more particularly on resorbable bioelectronic systems, which can safely degrade in the biological environment once they have completed their purpose, namely, stimulating or sensing biological activity in the tissues. Resorbable conductive materials are also explored in the fields of tissue engineering and 3D cell culture. After a short description of polymer-based substrates and scaffolds, and resorbable electrical conductors, we review how they can be combined to design resorbable conductive materials. Although these materials are still emerging, various medical and biomedical applications are already taking shape that can profoundly modify post-operative and wound healing follow-up. Future challenges and perspectives in the field are proposed.

All-organic transparent plant e-skin for noninvasive phenotyping

Real-time in situ monitoring of plant physiology is essential for establishing a phenotyping platform for precision agriculture. A key enabler for this monitoring is a device that can be noninvasively attached to plants and transduce their physiological status into digital data. Here, we report an all-organic transparent plant e-skin by micropatterning poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on polydimethylsiloxane (PDMS) substrate. This plant e-skin is optically and mechanically invisible to plants with no observable adverse effects to plant health. We demonstrate the capabilities of our plant e-skins as strain and temperature sensors, with the application to Brassica rapa leaves for collecting corresponding parameters under normal and abiotic stress conditions. Strains imposed on the leaf surface during growth as well as diurnal fluctuation of surface temperature were captured. We further present a digital-twin interface to visualize real-time plant surface environment, providing an intuitive and vivid platform for plant phenotyping.

Electrically Controlled Vasodilator Delivery from PEDOT/Silica Nanoparticle Modulates Vessel Diameter in Mouse Brain

Vascular damage and reduced tissue perfusion are expected to majorly contribute to the loss of neurons or neural signals around implanted electrodes. However, there are limited methods of controlling the vascular dynamics in tissues surrounding these implants. This work utilizes conducting polymer poly(ethylenedioxythiophene) and sulfonated silica nanoparticle composite (PEDOT/SNP) to load and release a vasodilator, sodium nitroprusside, to controllably dilate the vasculature around carbon fiber electrodes (CFEs) implanted in the mouse cortex. The vasodilator release is triggered via electrical stimulation and the amount of release increases with increasing electrical pulses. The vascular dynamics are monitored in real-time using two-photon microscopy, with changes in vessel diameters quantified before, during, and after the release of the vasodilator into the tissues. This work observes significant increases in vessel diameters when the vasodilator is electrically triggered to release, and differential effects of the drug release on vessels of different sizes. In conclusion, the use of nanoparticle reservoirs in conducting polymer-based drug delivery platforms enables the controlled delivery of vasodilator into the implant environment, effectively altering the local vascular dynamics on demand. With further optimization, this technology could be a powerful tool to improve the neural electrode-tissue interface and study neurovascular coupling.

Fast Visible-Light 3D Printing of Conductive PEDOT:PSS Hydrogels

Functional inks for light-based 3D printing are actively being searched for being able to exploit all the potentialities of additive manufacturing. Herein, a fast visible-light photopolymerization process is showed of conductive PEDOT:PSS hydrogels. For this purpose, a new Type II photoinitiator system (PIS) based on riboflavin (Rf), triethanolamine (TEA), and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is investigated for the visible light photopolymerization of acrylic monomers. PEDOT:PSS has a dual role by accelerating the photoinitiation process and providing conductivity to the obtained hydrogels. Using this PIS, full monomer conversion is achieved in less than 2 min using visible light. First, the PIS mechanism is studied, proposing that electron transfer between the triplet excited state of the dye (3 Rf*) and the amine (TEA) is catalyzed by PEDOT:PSS. Second, a series of poly(2-hydroxyethyl acrylate)/PEDOT:PSS hydrogels with different compositions are obtained by photopolymerization. The presence of PEDOT:PSS negatively influences the swelling properties of hydrogels, but significantly increases its mechanical modulus and electrical properties. The new PIS is also tested for 3D printing in a commercially available Digital Light Processing (DLP) 3D printer (405 nm wavelength), obtaining high resolution and 500 µm hole size conductive scaffolds.

Oxygen-Induced Lattice Strain for High-Performance Organic Transistors with Enhanced Stability

Integrating the merits of low cost, flexibility, and large-area processing, organic semiconductors (OSCs) are promising candidates for the next-generation electronic materials. The mobility and stability are the key figures of merit for its practical application. However, it is greatly challenging to improve the mobility and stability simultaneously owing to the weak interactions and poor electronic coupling between OSCs molecules. Here, an oxygen-induced lattice strain (OILS) strategy is developed to achieve OSCs with both high mobility and high stability. Utilizing the strategy, the maximum mobility of dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) organic field-effect transistor (OFET) rises to 15.3 cm2  V-1  s-1 and the contact resistance lowers to 25.5 Ω cm. Remarkably, the thermal stability of DNTT is much improved, and a record saturated power density of ≈3.4 × 104  W cm-2 is obtained. Both the experiments and theoretical calculations demonstrate that the lattice compressive strain induced by oxygen is responsible for their high performance and stability. Furthermore, the universality of the strategy is manifested in both n-type and p-type small OSCs. This work provides a novel strategy to improve both the mobility and the stability of OSCs, paving the way for the practical applications of organic devices.

Organic Electronics in Biosensing: A Promising Frontier for Medical and Environmental Applications

The promising field of organic electronics has ushered in a new era of biosensing technology, thus offering a promising frontier for applications in both medical diagnostics and environmental monitoring. This review paper provides a comprehensive overview of organic electronics' remarkable progress and potential in biosensing applications. It explores the multifaceted aspects of organic materials and devices, thereby highlighting their unique advantages, such as flexibility, biocompatibility, and low-cost fabrication. The paper delves into the diverse range of biosensors enabled by organic electronics, including electrochemical, optical, piezoelectric, and thermal sensors, thus showcasing their versatility in detecting biomolecules, pathogens, and environmental pollutants. Furthermore, integrating organic biosensors into wearable devices and the Internet of Things (IoT) ecosystem is discussed, wherein they offer real-time, remote, and personalized monitoring solutions. The review also addresses the current challenges and future prospects of organic biosensing, thus emphasizing the potential for breakthroughs in personalized medicine, environmental sustainability, and the advancement of human health and well-being.

3D Printing of High Viscosity UV-Curable Resin for Highly Stretchable and Resilient Elastomer

Elastomers prepared via vat photopolymerizationus ually exhibit unsatisfied mechanical properties owing to their insufficient growth of molecular weight upon UV exposure. Increasing the weight ratio of oligomer in the resin system is an effective approach to enhance the mechanical properties, yet the viscosity of the UV-curable resin increases dramatically; this hinders its printing. In this study, a linear scan-based vat photopolymerization (LSVP) system which can print high-viscosity resins is implemented to 3D print the oligomer-dominated UV-curable resin via a dual-curing mechanism. A polyurethane methacrylate blocking oligomer is first synthesized and then mixed with a commercialized bifunctional oligomer, photoinitiator, and primary amine as a chain extender to prepare high-viscosity UV-curable resin for the LSVP system. The deblocked isocyanate is further crosslinked with a chain extender via thermal treatment to construct a highly entangled polymer chain network. The optimal thermal treatment parameters are investigated, and the resilience of the 3D-printed elastomer is evaluated through continuous tensile loading and unloading tests. Subsequently, complex structured elastomers are printed, exhibiting favorable mechanical durability without defects. The results obtained from this work will provide a reference for preparing elastomeric devices with excellent physical properties and expand the application scope of vat photopolymerization to new fields.

Investigation and multiscale modeling of PVA/SA coated poly lactic acid scaffold containing curcumin loaded layered double hydroxide nanohybrids

Applying hydrophilic coatings on polymeric nanofibers combined with layered double hydroxide (LDH) not only enhances the efficiency of drug delivery systems but also increases cell adhesion. This work aimed to prepare poly(vinyl alcohol)/sodium alginate (PVA/SA) (2/1)-coated poly(lactic acid) (PLA) nanofibers containing curcumin-loaded layered double hydroxide (LDH) and to investigate their drug release and mechanical properties and their biocompatibility. The optimum PLA nanofibrous sample was considered to be that based on 3 wt% of curcumin-loaded LDH (PLA-3%LDH) with a drug encapsulation efficiency of ∼18% in which a minimum average nanofiber diameter of ∼476 nm along with a high tensile strength of 3.00 MPa were obtained. In the next step, a PVA/SA (2/1) layer was coated on the PLA-3%LDH; as a result, the hydrophilicity of the sample was improved and the elongation at break was decreased remarkably. In this regard the cell viability reached 80% for the coated PLA. Moreover, the formation of a layer of (PVA/SA) on the PLA nanofibers lowered the burst release and resulted in a more sustained drug release, which is a vital feature in dermal applications. A multiscale modeling method was applied for simulation of the mechanical properties of the composite scaffold and the results showed that this method can predict the data with 83% accuracy. The results of this study indicate that the formation of a layer of PVA/SA (2/1) has a significant effect on hydrophilicity and consequently improves cell adhesion and proliferation.

Technology Roadmap for Flexible Sensors

Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

Advances in Microfluidics for Single Red Blood Cell Analysis

The utilizations of microfluidic chips for single RBC (red blood cell) studies have attracted great interests in recent years to filter, trap, analyze, and release single erythrocytes for various applications. Researchers in this field have highlighted the vast potential in developing micro devices for industrial and academia usages, including lab-on-a-chip and organ-on-a-chip systems. This article critically reviews the current state-of-the-art and recent advances of microfluidics for single RBC analyses, including integrated sensors and microfluidic platforms for microscopic/tomographic/spectroscopic single RBC analyses, trapping arrays (including bifurcating channels), dielectrophoretic and agglutination/aggregation studies, as well as clinical implications covering cancer, sepsis, prenatal, and Sickle Cell diseases. Microfluidics based RBC microarrays, sorting/counting and trapping techniques (including acoustic, dielectrophoretic, hydrodynamic, magnetic, and optical techniques) are also reviewed. Lastly, organs on chips, multi-organ chips, and drug discovery involving single RBC are described. The limitations and drawbacks of each technology are addressed and future prospects are discussed.

3D printing of bone and cartilage with polymer materials

Damage and degeneration to bone and articular cartilage are the leading causes of musculoskeletal disability. Commonly used clinical and surgical methods include autologous/allogeneic bone and cartilage transplantation, vascularized bone transplantation, autologous chondrocyte implantation, mosaicplasty, and joint replacement. 3D bio printing technology to construct implants by layer-by-layer printing of biological materials, living cells, and other biologically active substances in vitro, which is expected to replace the repair mentioned above methods. Researchers use cells and biomedical materials as discrete materials. 3D bio printing has largely solved the problem of insufficient organ donors with the ability to prepare different organs and tissue structures. This paper mainly discusses the application of polymer materials, bio printing cell selection, and its application in bone and cartilage repair.

Responsive hydrogel microfibers for biomedical engineering

Responsive hydrogel microfibers can realize multiple controllable changes in shapes or properties under the stimulation of the surrounding environment, and are called as intelligent biomaterials. Recently, these responsive hydrogel microfibers have been proved to possess significant biomedical values, and remarkable progress has been achieved in biomedical engineering applications, including drug delivery, biosensors and clinical therapy, etc. In this review, the latest research progress and application prospects of responsive hydrogel microfibers in biomedical engineering are summarized. We first introduce the common preparation strategies of responsive hydrogel microfibers. Subsequently, the response characteristics and the biomedical applications of these materials are discussed. Finally, the present opportunities and challenges as well as the prospects for future development are critically analyzed.

Recent Advancements in Nanobiosensors: Current Trends, Challenges, Applications, and Future Scope

In recent years, there has been immense advancement in the development of nanobiosensors as these are a fundamental need of the hour that act as a potential candidate integrated with point-of-care-testing for several applications, such as healthcare, the environment, energy harvesting, electronics, and the food industry. Nanomaterials have an important part in efficiently sensing bioreceptors such as cells, enzymes, and antibodies to develop biosensors with high selectivity, peculiarity, and sensibility. It is virtually impossible in science and technology to perform any application without nanomaterials. Nanomaterials are distinguished from fine particles used for numerous applications as a result of being unique in properties such as electrical, thermal, chemical, optical, mechanical, and physical. The combination of nanostructured materials and biosensors is generally known as nanobiosensor technology. These miniaturized nanobiosensors are revolutionizing the healthcare domain for sensing, monitoring, and diagnosing pathogens, viruses, and bacteria. However, the conventional approach is time-consuming, expensive, laborious, and requires sophisticated instruments with skilled operators. Further, automating and integrating is quite a challenging process. Thus, there is a considerable demand for the development of nanobiosensors that can be used along with the POCT module for testing real samples. Additionally, with the advent of nano/biotechnology and the impact on designing portable ultrasensitive devices, it can be stated that it is probably one of the most capable ways of overcoming the aforementioned problems concerning the cumulative requirement for the development of a rapid, economical, and highly sensible device for analyzing applications within biomedical diagnostics, energy harvesting, the environment, food and water, agriculture, and the pharmaceutical industry.