3D printing for customized carbon electrodes

3D printed electrochemical sensor and microfluidic system for the detection of L-tryptophan using degradable material

Herein, we constructed an integrated system for L-tryptophan (L-Trp) detection by assembling an electrochemical sensor and a microfluidic platform. Amongst, the sensor was printed using conductive polymer filaments and then chemically activated to expose porous nanostructure on the surface. A calibration curve was established between 31.26-1000.00 μmol/L and the limit of detection (LOD) was 10.41 μmol/L. The sensor exhibited satisfactory reproducibility, selectivity and stability. The recovery ranged between 99.06-102.09 % with relative standard deviations less than 5.21 %. The results show that L-Trp undergoes a two-proton, two-electron transfer in the anodic reaction. Once integrated into a printed microfluidic module from photosensitive resin, the sensor showed a wider detection range (15.00-70.00, 100-4000 μmol/L) with a lower LOD (5.00 μmol/L), which may be due to faster mass transfer in microfluidics. The consistency and validity were affirmed with ultra-visible spectrophotometer and HPLC. The integrated system allows point-of-testing owing to its small size, portability and low cost.

3D-printed electrodes for electrochemical detection of environmental analytes

Environmental monitoring faces increasing demands for rapid, sensitive, and cost-effective analytical methods to detect various pollutants. Three-dimensional (3D) printing technology has emerged as a transformative approach for fabricating electrochemical sensors, offering unprecedented flexibility in electrode design and potential for customization. This comprehensive review examines recent advances in 3D-printed electrochemical sensors for environmental analysis, focusing on manufacturing technologies, materials development, and surface modification strategies. We analyze various printing approaches, including fused deposition modeling, stereolithography, and selective laser melting, discussing their relative advantages and limitations for electrode fabrication. The review explores conductive materials development, from carbon-based composites to novel metal-containing filaments, and examines crucial surface modification techniques that enhance sensor performance. Key applications in environmental monitoring are evaluated, including the detection of heavy metals, pathogens, antibiotics, and organophosphates, with particular attention to analytical performance metrics and real-world applicability. Technical challenges are critically assessed, including limitations in printing resolution, material conductivity, and long-term stability. The review concludes by identifying promising research directions, such as the integration of advanced materials and the development of automated manufacturing processes, highlighting opportunities for improving sensor performance and commercial viability in environmental monitoring applications.

Two new doping-free manufacturing processes for bread-derived carbon electrodes with control over micro- and macro-topological surface features

Pyrolyzed carbon electrodes (PCEs) can provide sustainable alternatives in electric devices, but it is difficult to control their surface geometries during their semi-destructive fabrication procedure. Impressive contributions have been made to the field of PCE fabrication in terms of the nanoscale, functionalization, and separation applications; however, further progress towards an emphasis on a sustainable life cycle is the next step forward. Here, we propose two new methodologies for creating sustainable PCEs: stamping, where a user-designed, 3D printed electrode precursor (EP) imparts a shape on an organic material, and reconstitution, where the same EP acts as a mould as a mixture of agitated organic material and water dries to leave behind a rigid shape. Both methods allow for the reuse of the EP and the upcycling of biologically derived waste products as a pyrolytic input, and they do not require chemical modification. A comparison of the two methodologies is discussed as surface features of PCEs scale by a factor of 0.78 during the reconstitution process and by a factor of 0.68 during the stamping process. These PCEs maintain defined structures on the micro-scale and demonstrate previously unachievable resolution to the naked eye prior to these two novel pathways.

Screen-Printing vs Additive Manufacturing Approaches: Recent Aspects and Trends Involving the Fabrication of Electrochemical Sensors

A few decades ago, the technological boom revolutionized access to information, ushering in a new era of research possibilities. Electrochemical devices have recently emerged as a key scientific advancement utilizing electrochemistry principles to detect various chemical species. These versatile electrodes find applications in diverse fields, such as healthcare diagnostics and environmental monitoring. Modern designs have given rise to innovative manufacturing protocols, including screen and additive printing methods, for creating sophisticated 2D and 3D electrochemical devices. This perspective provides a comprehensive overview of the screen-printing and additive-printing protocols for constructing electrochemical devices. It is also informed that screen-printed sensors offer cost-effectiveness and ease of fabrication, although they may pose challenges due to the use of toxic volatile inks and limited design flexibility. On the other hand, additive manufacturing, especially the fused filament fabrication (or fused deposition modeling) strategies, allows for intricate three-dimensional sensor designs and rapid prototyping of customized equipment. However, the post-treatment processes and material selection can affect production costs. Despite their unique advantages and limitations, both printing techniques show promise for various applications, driving innovation in the field toward more advanced sensor designs. Finally, these advancements pave the way for improved sensor performance and expand possibilities for academic, environmental, and industrial applications. The future is full of exciting opportunities for state-of-the-art sensor technologies that will further improve our ability to detect and determine various substances in a wide range of environments as researchers continue to explore the many possibilities of electrochemical devices.

Mechanically stabilized UiO-66-NH2-MB screen printed carbon electrode for high-performance electrochemical ratiometric quantification of miR-21-5p

The ratiometric sensing strategy, which uses dual-signal output, drastically compensates for the background noise and interference from the detection environment, compared to the sensing methods that rely on a single-signal output. However, the stability of the reference signal has become the primary challenge in constructing a ratiometric detection sensor. Therefore, in order to achieve stable ratiometric signal sensing, methylene blue (MB) was encapsulated in the UiO-66-NH2 framework and printed as a reference signal onto a screen-printed carbon electrode (SPCE), facilitating the precise detection of miR-21-5p. Subsequently, based on the ultra-sensitive detection mechanism of catalytic hairpin assembly (CHA), the combination of miR-21-5p with H1 sequence on the Au-deposited SPCE triggered the loop-open of H1. After that, ferrocene-labeled H2 (H2-Fc) and H3-Fc sequences were sequentially added to form a stable "T-shaped" structure, and miR-21-5p was released into the next cycle. Thus, the detection of miR-21-5p was quantified by the current ratio of Fc to MB, obtaining an ultra-low detection limit of 2.7 fM. This ratiometric sensing strategy based on SPCE offers a promising pathway for highly sensitive sensing platforms.

The cutting-edge progress in bioprinting for biomedicine: principles, applications, and future perspectives

Bioprinting is a highly promising application area of additive manufacturing technology that has been widely used in various fields, including tissue engineering, drug screening, organ regeneration, and biosensing. Its primary goal is to produce biomedical products such as artificial implant scaffolds, tissues and organs, and medical assistive devices through software-layered discrete and numerical control molding. Despite its immense potential, bioprinting technology still faces several challenges. It requires concerted efforts from researchers, engineers, regulatory bodies, and industry stakeholders are principal to overcome these challenges and unlock the full potential of bioprinting. This review systematically discusses bioprinting principles, applications, and future perspectives while also providing a topical overview of research progress in bioprinting over the past two decades. The most recent advancements in bioprinting are comprehensively reviewed here. First, printing techniques and methods are summarized along with advancements related to bioinks and supporting structures. Second, interesting and representative cases regarding the applications of bioprinting in tissue engineering, drug screening, organ regeneration, and biosensing are introduced in detail. Finally, the remaining challenges and suggestions for future directions of bioprinting technology are proposed and discussed. Bioprinting is one of the most promising application areas of additive manufacturing technology that has been widely used in various fields. It aims to produce biomedical products such as artificial implant scaffolds, tissues and organs, and medical assistive devices. This review systematically discusses bioprinting principles, applications, and future perspectives, which provides a topical description of the research progress of bioprinting.

3D-Printed Carbon Nanoneedle Electrodes for Dopamine Detection in Drosophila

In vivo electrochemistry in small brain regions or synapses requires nanoelectrodes with long straight tips for submicron scale measurements. Nanoelectrodes can be fabricated using a Nanoscribe two-photon printer, but annealed tips curl if they are long and thin. We propose a new pulling-force strategy to fabricate a straight carbon nanoneedle structure. A micron-width bridge is printed between two blocks. The annealed structure shrinks during pyrolysis, and the blocks create a pulling force to form a long, thin, and straight carbon bridge. Parameterization study and COMSOL modeling indicate changes in the block size, bridge size and length affect the pulling force and bridge shrinkage. Electrodes were printed on niobium wires, insulated with aluminum oxide, and the bridge cut with focused ion beam (FIB) to expose the nanoneedle tip. Annealed needle diameters ranged from 400 nm to 5.25 μm and length varied from 50.5 μm to 146 μm. The electrochemical properties are similar to glassy carbon, with good performance for dopamine detection with fast-scan cyclic voltammetry. Nanoelectrodes enable biological applications, such as dopamine detection in a specific Drosophila brain region. Long and thin nanoneedles are generally useful for other applications such as cellular sensing, drug delivery, or gas sensing.

Adaptive Fabrication of Electrochemical Chips with a Paste-Dispensing 3D Printer

Electrochemical (EC) detection is a powerful tool supporting simple, low-cost, and rapid analysis. Although screen printing is commonly used to mass fabricate disposable EC chips, its mask is relatively expensive. In this research, we demonstrated a method for fabricating three-electrode EC chips using 3D printing of relatively high-viscosity paste. The electrodes consisted of two layers, with carbon paste printed over silver/silver chloride paste, and the printed EC chips were baked at 70 °C for 1 h. Engineering challenges such as bulging of the tubing, clogging of the nozzle, dripping, and local accumulation of paste were solved by material selection for the tube and nozzle, and process optimization in 3D printing. The EC chips demonstrated good reversibility in redox reactions through cyclic voltammetry tests, and reliably detected heavy metal ions Pb(II) and Cd(II) in solutions using differential pulse anodic stripping voltammetry measurements. The results indicate that by optimizing the 3D printing of paste, EC chips can be obtained by maskless and flexible 3D printing techniques in lieu of screen printing.

Additive manufacturing-derived free-standing 3D pyrolytic carbon electrodes for sustainable microbial electrochemical production of H2O2

Producing H2O2 via microbial electrosynthesis is a cost-effective and environmentally favorable alternative to the costly and environmentally hazardous anthraquinone method. However, most studies have relied on carbon electrodes with two-dimensional (2D) surfaces (e.g., graphite), which have limited surface area and active sites, resulting in suboptimal H2O2 production. In this study, we demonstrate the enhanced efficiency of microbial H2O2 synthesis using three-dimensional (3D) electrodes produced through additive manufacturing technology due to their larger surface area than conventional carbon electrodes with 2D surfaces. This work innovatively combines 3D printed pyrolytic carbon (3D PyrC) electrodes with highly defined outer geometry and internal mesh structures derived from additive manufacturing with high-temperature resin precursors followed by pyrolysis with microbial electrochemical platform technology to achieve efficient H2O2 synthesis. The 3D PyrC electrode produced a maximum of 129.2 mg L-1 of H2O2 in 12 h, which was 2.3-6.9 times greater than conventional electrodes (e.g., graphite and carbon felt). Furthermore, the scalability, reusability and mechanical properties of the 3D PyrC electrode were exemplary, showcasing its practical viability for large-scale applications. Beyond H2O2 synthesis, the study explored the application of the 3D PyrC electrode in the bio-electro-Fenton process, demonstrating its efficacy as a tertiary treatment technology for the removal of micropollutants. This dual functionality underscores the versatility of the 3D PyrC electrode in addressing both the synthesis of valuable chemicals and environmental remediation. This study shows a novel electrode design for efficient, sustainable synthesis of H2O2 and subsequent environmental remediation.

Solvent-activated 3D-printed electrodes and their electroanalytical potential

This work is a comprehensive study describing the optimization of the solvent-activated carbon-based 3D printed electrodes. Three different conductive filaments were used for the preparation of 3D-printed electrodes. Electrodes treatment with organic solvents, electrochemical characterization, and finally electroanalytical application was performed in a dedicated polyamide-based cell also created using 3D printing. We have investigated the effect of the used solvent (acetone, dichloromethane, dichloroethane, acetonitrile, and tetrahydrofuran), time of activation (from immersion up to 3600 s), and the type of commercially available filament (three different options were studied, each being a formulation of a polylactic acid and conductive carbon material). We have obtained and analysed a significant amount of collected data which cover the solvent-activated carbon-based electrodes surface wettability, microscopic insights into the surface topography analysed with scanning electron microscopy and atomic force microscopy, and finally voltammetric evaluation of the obtained carbon electrodes electrochemical response. All data are tabulated, discussed, and compared to finally provide the superior activation procedure. The electroanalytical performance of the chosen electrode is discussed based on the voltammetric detection of ferrocenemethanol.

Use of 3D Printing Techniques to Fabricate Implantable Microelectrodes for Electrochemical Detection of Biomarkers in the Early Diagnosis of Cardiovascular and Neurodegenerative Diseases

This Review provides a comprehensive overview of 3D printing techniques to fabricate implantable microelectrodes for the electrochemical detection of biomarkers in the early diagnosis of cardiovascular and neurodegenerative diseases. Early diagnosis of these diseases is crucial to improving patient outcomes and reducing healthcare systems' burden. Biomarkers serve as measurable indicators of these diseases, and implantable microelectrodes offer a promising tool for their electrochemical detection. Here, we discuss various 3D printing techniques, including stereolithography (SLA), digital light processing (DLP), fused deposition modeling (FDM), selective laser sintering (SLS), and two-photon polymerization (2PP), highlighting their advantages and limitations in microelectrode fabrication. We also explore the materials used in constructing implantable microelectrodes, emphasizing their biocompatibility and biodegradation properties. The principles of electrochemical detection and the types of sensors utilized are examined, with a focus on their applications in detecting biomarkers for cardiovascular and neurodegenerative diseases. Finally, we address the current challenges and future perspectives in the field of 3D-printed implantable microelectrodes, emphasizing their potential for improving early diagnosis and personalized treatment strategies.

4D Printing Shape-Morphing Hybrid Biomaterials for Advanced Bioengineering Applications

Four-dimensional (4D) printing is an innovative additive manufacturing technology used to fabricate structures that can evolve over time when exposed to a predefined environmental stimulus. 4D printed objects are no longer static objects but programmable active structures that accomplish their functions thanks to a change over time in their physical/chemical properties that usually displays macroscopically as a shapeshifting in response to an external stimulus. 4D printing is characterized by several entangled features (e.g., involved material(s), structure geometry, and applied stimulus entities) that need to be carefully coupled to obtain a favorable fabrication and a functioning structure. Overall, the integration of micro-/nanofabrication methods of biomaterials with nanomaterials represents a promising approach for the development of advanced materials. The ability to construct complex and multifunctional triggerable structures capable of being activated allows for the control of biomedical device activity, reducing the need for invasive interventions. Such advancements provide new tools to biomedical engineers and clinicians to design dynamically actuated implantable devices. In this context, the aim of this review is to demonstrate the potential of 4D printing as an enabling manufacturing technology to code the environmentally triggered physical evolution of structures and devices of biomedical interest.

3D Printed Customizable Microsampling Devices for Neuroscience Applications

Multifunctional devices that incorporate chemical or physical measurements combined with ways to manipulate brain tissue via drug delivery, electrical stimulation, or light for optogenetics are desired by neuroscientists. The next generation in vivo brain devices will likely utilize the extensive flexibility and rapid processing of 3D printing. This Perspective demonstrates how close we are to this reality for advanced neuroscience measurements. 3D printing provides the opportunity to improve microsampling-based devices in ways that have not been previously available. Not only can 3D printing be used for actual device creation, but it can also allow printing of peripheral objects necessary to assemble functional devices. The most probable 3D printing set up for microsampling devices with appropriate nm to μm feature size will likely require 2-photon polymerization-based printers. This Perspective describes the advantages and challenges for 3D printing of microsampling devices as an initial step to meet the next generation device needs of neuroscientists.

Electrochemical Determination of the Drug Colchicine in Pharmaceutical and Βiological Samples Using a 3D-Printed Device

In this work, a simple, fast, and sensitive voltammetric method for the trace determination of the alkaloid drug colchicine (Colc) using a 3D-printed device is described. The electrochemical method was based on the adsorptive accumulation of the drug at a carbon-black polylactic acid (CB/PLA) working electrode, followed by voltammetric determination of the accumulated species. The plastic sensor was printed in a single step by a low-cost dual extruder 3D-printer and featured three CB/PLA electrodes (serving as working, reference, and counter electrodes) and a holder, printed from a non-conductive PLA filament. The electrochemical parameters that affected the response of the device towards Colc determination, such as accumulation time and potential, solution pH, and other variables, were optimized. Under the selected conditions, the oxidation current of Colc was proportional to the concentration of Colc, and its quantification was conducted in the concentration range of 0.6-2.2 μmol L^-1 with a limit of detection of 0.11 μmol L^-1 in phosphate buffer (pH 7.0). Both within-device and between-device reproducibility were lower than 9%, revealing satisfactory operational and fabrication reproducibility. Furthermore, the 3D-printed device was employed for the voltammetric determination of Colc in pharmaceutical tablets and in human urine with satisfactory results, justifying its suitability for low-cost routine analysis of Colc.

Polymer/Graphene Nanocomposites via 3D and 4D Printing—Design and Technical Potential

Graphene is an important nanocarbon nanofiller for polymeric matrices. The polymer–graphene nanocomposites, obtained through facile fabrication methods, possess significant electrical–thermal–mechanical and physical properties for technical purposes. To overcome challenges of polymer–graphene nanocomposite processing and high performance, advanced fabrication strategies have been applied to design the next-generation materials–devices. This revolutionary review basically offers a fundamental sketch of graphene, polymer–graphene nanocomposite and three-dimensional (3D) and four-dimensional (4D) printing techniques. The main focus of the article is to portray the impact of 3D and 4D printing techniques in the field of polymer–graphene nanocomposites. Polymeric matrices, such as polyamide, polycaprolactone, polyethylene, poly(lactic acid), etc. with graphene, have been processed using 3D or 4D printing technologies. The 3D and 4D printing employ various cutting-edge processes and offer engineering opportunities to meet the manufacturing demands of the nanomaterials. The 3D printing methods used for graphene nanocomposites include direct ink writing, selective laser sintering, stereolithography, fused deposition modeling and other approaches. Thermally stable poly(lactic acid)–graphene oxide nanocomposites have been processed using a direct ink printing technique. The 3D-printed poly(methyl methacrylate)–graphene have been printed using stereolithography and additive manufacturing techniques. The printed poly(methyl methacrylate)–graphene nanocomposites revealed enhanced morphological, mechanical and biological properties. The polyethylene–graphene nanocomposites processed by fused diffusion modeling have superior thermal conductivity, strength, modulus and radiation- shielding features. The poly(lactic acid)–graphene nanocomposites have been processed using a number of 3D printing approaches, including fused deposition modeling, stereolithography, etc., resulting in unique honeycomb morphology, high surface temperature, surface resistivity, glass transition temperature and linear thermal coefficient. The 4D printing has been applied on acrylonitrile-butadiene-styrene, poly(lactic acid) and thermosetting matrices with graphene nanofiller. Stereolithography-based 4D-printed polymer–graphene nanomaterials have revealed complex shape-changing nanostructures having high resolution. These materials have high temperature stability and high performance for technical applications. Consequently, the 3D- or 4D-printed polymer–graphene nanocomposites revealed technical applications in high temperature relevance, photovoltaics, sensing, energy storage and other technical fields. In short, this paper has reviewed the background of 3D and 4D printing, graphene-based nanocomposite fabrication using 3D–4D printing, development in printing technologies and applications of 3D–4D printing.