Functional Inks Research Articles

3D-printed Bio-inspired porous electrode by bidirectional enhancement strategy with high mass loading and enhanced energy density for supercapacitors

The effective strategy for increasing areal capacity involves the use of 3D printed thick-electrode with high mass loading. However, thick-electrode still encounters challenges such as incomplete electrolyte penetration and slow ion transport. Here, we successfully prepared lignocellulosic nanofibrils (LCNFs) from abundant bamboo biomass and developed functional ink composed of LCNFs/ carbon nanotubes (CNTs) / polyaniline (PANI) / polyvinyl alcohol (PVA) for printing. An innovative 3D printing bidirectional enhancement strategy was proposed to increase the mass loading of active materials in the vertical direction and construct ion transport channels in the transverse direction. The biomimetic porous N-doped electrode obtained after annealing treatment exhibits a more continuous conductive network, larger surface area, higher utilization of active materials, and smoother ion transport pathways compared to thick-electrode. Therefore, the Triangles biomimetic electrode exhibits an enhanced areal/specific capacitance compared to thick-electrode, reaching 5.30F·cm−2 (184.03F·g−1) and 4.40F·cm−2 (122.22F·g−1) at 2 mA·cm−2, respectively. The symmetric device demonstrates an areal capacitance of 1.34F·cm−2 at 1 mA·cm−2 and achieves an energy density of 0.186 mWh·cm−2 at a power density of 0.49 mW·cm−2. The work provides valuable insights into the design of electrode structures for high-performance supercapacitors.

One‐Step Room Temperature Synthesis of Printable Carbon Quantum Dots Ink for Visual Encryption and High‐Performance Photodetector

AbstractCarbon quantum dots (CQDs) have emerged as promising materials for optoelectronic applications and have garnered much interest as potential competitors to conventional inorganic or hybrid semiconductor quantum dots because of carbon's intrinsic merits of high stability, low cost, and environment‐friendliness. The ability of easy formulation of functional ink of CQDs is necessary for the development of industrial‐scale, reliable, inexpensive printing/coating processes, for its full exploitation in the ever‐growing class of applications in sensors, optoelectronics, and energy storage and conversion. Here a facile one‐step room‐temperature synthesis of printable, fluorescent CQD ink is demonstrated. The as‐synthesized fluorescent CQD ink is used for invisible fingerprint stamps, printing of micro‐patterns, and soft lithographic patterning with a resolution down to 1.5 µm. This functional CQD ink is also used to fabricate a high‐performance CQD‐ZnO heterojunction ultraviolet (UV) photodetector with a photo‐responsivity of 3.85 A W−1, detectivity of 6.78 × 1010 Jones, and an external quantum efficiency (EQE) of 15.3%. The enhanced device performance can be attributed to CQD's high photocurrent generation efficiency and rational combination of the asymmetric electrode materials. This work enables a high‐temperature stable CQD fluorescent ink synthesis method to fulfill the processing requirements of printing and soft lithographic patterning for visual encryption and optoelectronics.

Comparative analysis of iPSC-derived NK cells from two differentiation strategies reveals distinct signatures and cytotoxic activities.

The ability to generate natural killer (NK) cells from induced pluripotent stem cells (iPSCs) has given rise to new possibilities for the large-scale production of homogeneous immunotherapeutic cellular products and opened new avenues towards the creation of "off-the-shelf" cancer immunotherapies. However, the differentiation of NK cells from iPSCs remains poorly understood, particularly regarding the ontogenic landscape of iPSC-derived NK (iNK) cells produced in vitro and the influence that the differentiation strategy employed may have on the iNK profile. To investigate this question, we conducted a comparative analysis of two sets of iNK cells generated from the same iPSC line using two different protocols: (i) a short-term, clinically compatible feeder-free protocol corresponding to primitive hematopoiesis, and (ii) a lymphoid-based protocol representing the definitive hematopoietic step. Our work demonstrated that both protocols are capable of producing functional iNK cells. However, the two sets of resulting iNKs exhibited distinct phenotypes and transcriptomic profiles. The lymphoid-based differentiation approach generated iNKs with a more mature and activated profile, which demonstrated higher cytotoxicity against cancer cell lines compared to iNK cells produced under short-term feeder-free conditions suggesting that the differentiation strategy must be considered when designing iNK cell-based adoptive immunotherapies.

Citrus peel powder alters the rheological properties and 3D printing performance of potato starch gel

Owing to the growing interest in sustainable resource utilization, the current study explores the potential replacement of pectin with citrus peel powder (CP) in starch-based 3D food printing ink formulations. The effect of different concentrations of pectin (1 %, 2 %, 3 %) and CP (1 %, 2 %, 3 %) on the printing fidelity, microstructure, rheological and textural properties of potato starch gel were investigated. The results showed that the 3D printing performance of CP-added inks was higher than that of pectin-added inks at all tested concentrations. The storage modulus of CP-added ink was higher than that of pectin-added ink proving higher printing fidelity of CP-added inks. Additionally, hardness, gumminess, springiness and chewiness of food ink increased with an increase in the concentration of CP while decreased with an increase in concentration of pectin. Interestingly, pectin and CP-added inks displayed similar in vitro digestibility, suggesting an insignificant effect of replacing pectin with CP on in vitro glucose release. Moreover, the antioxidant activity of CP-added ink was higher than pectin-added ink demonstrating the potential applications of CP-added ink in functional ink development. Therefore, this study claims for effective replacement of pectin with CP in starch-based 3D food printing ink formulations as a promising sustainable additive.

Studies on cytocompatibility of human dermal fibroblasts on carbon nanofiber nanoparticle-containing bioprinted constructs

Functional nanocomposite-based printable inks impart strength, mechanical stability, and bioactivity to the printed matrix due to the presence of nanomaterials or nanostructures. Carbonaceous nanomaterials are known to improve the electrical conductivity, osteoconductivity, mechanical, and thermal properties of printed materials. In the current work, we have incorporated carbon nanofiber nanoparticles (CNF NPs) into methacrylated gelatin (GelMA) to investigate whether the resulting nanocomposite printable ink constructs (GelMA-CNF NPs) promote cell proliferation. Two kinds of printable constructs, cell-laden bioink and biomaterial ink, were prepared by incorporating various concentrations of CNF NPs (50, 100, and 150 µg/mL). The CNF NPs improved the mechanical strength and dielectric properties of the printed constructs. The in vitro cell line studies using normal human dermal fibroblasts (nHDF) demonstrated that CNF NPs are involved in cell-material interaction without affecting cellular morphology. Though the presence of NPs did not affect cellular viability on the initial days of treatment, it caused cytotoxicity to the cells on days 4 and 7 of the treatment. A significant level of cytotoxicity was observed in the highly CNF-concentrated bioink scaffolds (100 and 150 µg/mL). The unfavorable outcomes of the current work necessitate further study of employing functionalized CNF NPs to achieve enhanced cell proliferation in GelMA-CNF NPs-based bioprinted constructs and advance the application of skin tissue regeneration.Graphical abstract

Nonsymmetrical thermal conductivity along the director field in ferroelectric nematic liquid crystals.

The synthesis of ferroelectric nematic liquid crystals (FNLCs) concludes the long wait for their existence and potential usage in multiple liquid crystal based applications. In FNLCs, electric polarization in the nematic phase significantly decreases the switching time of in-on display pixels. In this article, we report the occurrence of translation symmetry breaking for heat propagation along the director field n[over ̂] in the ferroelectric nematic phase. Due to the C_{∞V} symmetry of such a phase and close similarity to the bent-core polar liquid crystal phase, a rank-3 tensor describes its scalar order parameter and algebraic deductions. The finite element simulations show the occurrence of the nonsymmetrical thermal conductivity along n[over ̂]. The preferential heat transport in FNLCs can allow them to work as an all-thermal monophase non-nanostructured single-material thermal rectifier. We expect that this study will contribute towards the FNLCs application as functional layers and inks.

Eco‐Friendly, Recyclable Supramolecular Inks Incorporating Multi‐Walled Carbon Nanotubes

AbstractIn contemporary society, with its emphasis on environmental stewardship, the development of “green” (eco‐friendly) inks is of paramount importance. These inks are utilized across a broad spectrum of applications, ranging from the printing of packaging material to the 3D printing of functional components. This study explores the synthesis of eco‐friendly, biodegradable supramolecular polymer materials predicated on ureido‐pyrimidinone (UPy). The subsequent formulation of these materials into functional inks is achieved by the incorporation of multi‐walled carbon nanotubes (MWCNTs). These resultant inks exhibit outstanding photothermal conversion properties, robust electrical conductivity, intrinsic self‐repair capabilities, and superior writability. Moreover, this research demonstrates the recyclability of MWCNTs within the ink matrix, exhibiting a recovery efficiency of ≈90%. Such a high recovery rate offers a novel perspective on the sustainable reuse of conductive fillers in polymer‐based inks.

On-Demand Picoliter-Level-Droplet Inkjet Printing for Micro Fabrication and Functional Applications.

With the advent of Internet of Things (IoTs) and wearable devices, manufacturing requirements have shifted toward miniaturization, flexibility, environmentalization, and customization. Inkjet printing, as a non-contact picoliter-level droplet printing technology, can achieve material deposition at the microscopic level, helping to achieve high resolution and high precision patterned design. Meanwhile, inkjet printing has the advantages of simple process, high printing efficiency, mask-free digital printing, and direct pattern deposition, and is gradually emerging as a promising technology to meet such new requirements. However, there is a long way to go in constructing functional materials and emerging devices due to the uncommercialized ink materials, complicated film-forming process, and geometrically/functionally mismatched interface, limiting film quality and device applications. Herein, recent developments in working mechanisms, functional ink systems, droplet ejection and flight process, droplet drying process, as well as emerging multifunctional and intelligence applications including optics, electronics, sensors, and energy storage and conversion devices is reviewed. Finally, it is also highlight some of the critical challenges and research opportunities. The review is anticipated to provide a systematic comprehension and valuable insights for inkjet printing, thereby facilitating the advancement of their emerging applications.

Graphene-enhanced manganese dioxide functional ink infused with polyaniline for high-performance screen-printed micro supercapacitor

In the world of miniature advancements in technology, a current champion has emerged: the micro supercapacitors. In order to fabricate these micro-supercapacitors, we have developed a promising and user-friendly approach for printing a conductive functional ink containing a ternary composite of manganese dioxide (MnO2) nanoparticles, Graphene, and polyaniline (PANI) as a dopant. Screen-printing technique was employed to fabricate micro-supercapacitors using the nanocomposite conductive ink. The performance of the energy storage device was examined using flexible symmetric and asymmetric, with an aqueous 1 M KOH electrolyte. According to this strategy, the characterisation and electrochemical study results revealed that doping PANI into both symmetric and asymmetric devices significantly increased the material’s capacitive performance of areal capacitance 167 mFcm−2 for MnO2/Graphene/PANI-5 composite (MGP-5) and 292.5 mFcm−2 for asymmetric supercapacitor (ASSC) at 5 mVs−1. Furthermore, the asymmetric supercapacitor displayed outstanding cyclic stability, retaining 93.6% of its capacitance after 10000 cycles. This underscores the possibility of incorporating polyaniline (PANI) into MnO2 and graphene matrices as efficient blueprints for the development of superior electrode materials. The improvement represents a significant step forward, opening avenues for the future development of novel devices and their integration into top-of-the-line flexible energy storage systems.

Coordinating the pore size of paper substrates and aspect ratio of silver nanowires to improve printed electronics

The internet of things is advancing toward a world of ubiquitous electronic devices, composed in large part of low-cost printed electronics (PE) such as sensors. PE typically use plastic substrates, such as polyethylene terephthalate (PET), but these materials are not biodegradable. The proliferation of PE devices and their degradation to form micro- and nanoplastics pose significant environmental hazards. Paper is a promising substrate to replace PET for greener PE due to its recyclability, affordability, and compatibility with many printing processes. However, the porous cellulosic structure of paper can be an obstacle when trying to print active inks due to wicking of the ink into the paper pores, which disperses the functional ink and negatively impacts electronic performance. Filling the pores of paper with a polymer to planarize the surface is a commonly used remedy, although this approach can compromise recyclability. Here, we present an approach to manage the dispersion of silver nanowires, a widely used and printable 1D nanomaterial ink, in paper substrates. We deposit solutions of short (20–30 μms) and long (100–200 μms) silver nanowires onto various graded filter papers that differ in pore size and examine the trends in wicking distance, wicking speed, and electrical properties. We show that with careful selection of AgNW length and the pore size of the paper, it is possible to control the lateral spreading of the ink and minimize the concentration of the AgNWs needed to achieve a specific electrical performance.

A library of 2D electronic material inks synthesized by liquid-metal-assisted intercalation of crystal powders

Solution-processable 2D semiconductor inks based on electrochemical molecular intercalation and exfoliation of bulk layered crystals using organic cations has offered an alternative pathway to low-cost fabrication of large-area flexible and wearable electronic devices. However, the growth of large-piece bulk crystals as starting material relies on costly and prolonged high-temperature process, representing a critical roadblock towards practical and large-scale applications. Here we report a general liquid-metal-assisted approach that enables the electrochemical molecular intercalation of low-cost and readily available crystal powders. The resulted solution-processable MoS2 nanosheets are of comparable quality to those exfoliated from bulk crystals. Furthermore, this method can create a rich library of functional 2D electronic inks ( >50 types), including 2D wide-bandgap semiconductors of low electrical conductivity. Lastly, we demonstrated the all-solution-processable integration of 2D semiconductors with 2D conductors and 2D dielectrics for the fabrication of large-area thin-film transistors and memristors at a greatly reduced cost.

A review of functional E-jet inks for manufacturing flexible sensors

A review of functional E-jet inks for manufacturing flexible sensors

Tailoring interlayer spacing of Ti3C2Tx MXene with organic acid doped polyaniline and polypyrrole for more stable supercapacitors

Polyaniline (PANI) and polypyrrole (PPy) are promising for use as spacers materials to prevent re-stacking of MXene layers and to increase their electrochemical properties. However, these conducting polymers (CPs) may undergo hydrolysis during long charge-discharge cycles. The use of organic acids to dope CPs may lead to better polymer cyclic stability. However, PANI and PPy used as spacers in MXene are mainly doped with inorganic acids. Herein, we applied dodecylbenzenesulfonic acid (DBSA) doped PANI and PPy as effective spacers and additional pseudocapacitance agents for Ti3C2Tx MXene. Taking advantage of the favored dispersibility of the functional inks in water, we easily prepared the electrodes by drop casting. X-ray diffractograms confirmed that the CPs are effectively allocated among MXenes sheets. Spectroscopic analyses showed that the functional groups of Ti3C2Tx may work as effective dopants for PANI and PPy. The enhanced interlayer spacing of MXenes and increased high conductivity of CPs boosted capacitance from 175 F g−1 (Ti3C2Tx) to 255 F g−1 and 270 F g−1 at 1 A g−1 after addition of 10 wt% of PANI and PPy, respectively, at a three-electrode setup. The Dunn’s and Trasatti’s methods showed greater pseudocapacitive contribution after addition of PPy and greater double layer capacitance contribution after addition of PANI. Similarly, symmetric solid-state SCs exhibited enhancement of 72 % in specific capacitance for Ti3C2Tx/PANI and 208 % for Ti3C2Tx/PPy, when compared to pristine Ti3C2Tx. SCs based on Ti3C2Tx/CPs also yielded outstanding capacitance retentions (>98 %) after 5000 cycles against only 88 % of the Ti3C2Tx pristine device. These results indicate that the organic doped-CPs modulated interlayer spacing of MXene sheets, preventing their re-stacking during the charge and discharge cycles. Finally, the aqueous Ti3C2Tx/CPs based inks is an eco-friendly and low-cost alternative to fabricate SCs with enhanced capacitance and stability.

Assessment and improvement of adhesion of printed silver-based inks on alumina produced by fused filament fabrication

More efficient electronic systems need more temperature-stable substrate materials and more flexible production possibilities. Ceramics such as alumina can be used for 2D and 3D base bodies, since they provide better thermal properties than their polymeric counterparts and can be additively manufactured utilizing e.g. Fused Filament Fabrication. Proper functionalization can be achieved by applying methods of printed electronics. Here, adhesion of the functional ink to a substrate is a crucial issue and especially challenging on ceramic substrates. This contribution reached a noteworthy increase in this matter, using a modified silver-based ink with piezojet-printing, while preserving very low electrical resistance after convection sintering. Adhesion is determined by pull-off testing, based on ISO 4624. By the approach shown in this work, printed ceramics could become a more viable choice for use in functional electronic systems.

Scalable Fabrication of Flexible Supercapacitor Electrodes Using Sustainable Water‐Based Onion‐like Carbon Inks

AbstractThe increasing usage of electrical energy storage solutions demands for cost effective, scalable and sustainable manufacturing technologies. Deposition of functional inks, carrying electrochemically active materials is a suitable technique as it delivers material with selected properties only to required locations. However, the production of stable dispersions featuring high concentrations of active material ‐ necessary for effective deposition ‐ is challenging. Here we present an approach to print supercapacitor electrodes with onion‐like carbon as active material, using a simple, cost‐effective process as well as a water‐based ink. The ink is highly stable and can be deposited by spray and inkjet techniques. The fabricated electrodes offer a capacitance of up to 14 mF cm−2 (27 F g−1) and retained 97 % of their initial capacitance after 5000 cycles, demonstrating excellent performance and stability of the coating.

Transient charge-driven 3D conformal printing via pulsed-plasma impingement

Seamless integration of microstructures and circuits on three-dimensional (3D) complex surfaces is of significance and is catalyzing the emergence of many innovative 3D curvy electronic devices. However, patterning fine features on arbitrary 3D targets remains challenging. Here, we propose a facile charge-driven electrohydrodynamic 3D microprinting technique that allows micron- and even submicron-scale patterning of functional inks on a couple of 3D-shaped dielectrics via an atmospheric-pressure cold plasma jet. Relying on the transient charging of exposed sites arising from the weakly ionized gas jet, the specified charge is programmably deposited onto the surface as a virtual electrode with spatial and time spans of ~mm in diameter and ~μs in duration to generate a localized electric field accordantly. Therefore, inks with a wide range of viscosities can be directly drawn out from micro-orifices and deposited on both two-dimensional (2D) planar and 3D curved surfaces with a curvature radius down to ~1 mm and even on the inner wall of narrow cavities via localized electrostatic attraction, exhibiting a printing resolution of ~450 nm. In addition, several conformal electronic devices were successfully printed on 3D dielectric objects. Self-aligned 3D microprinting, with stacking layers up to 1400, is also achieved due to the electrified surfaces. This microplasma-induced printing technique exhibits great advantages such as ultrahigh resolution, excellent compatibility of inks and substrates, antigravity droplet dispersion, and omnidirectional printing on 3D freeform surfaces. It could provide a promising solution for intimately fabricating electronic devices on arbitrary 3D surfaces.

Large-scale manufacturing of functional single-atom ink for convenient glucose sensing

Large-scale manufacturing of functional single-atom ink for convenient glucose sensing

Inkjet Printing Optimization: Toward Realization of High‐Resolution Printed Electronics

AbstractThe printed electronics (PEs) market has witnessed substantial growth, reaching a valuation of USD 10.47 billion in the previous year. Driven by its extensive use in a multitude of applications, this growth trend is expected to continue with a projected compound annual growth rate of 22.3% from 2022 to 2032. Compared to screen printing, the adoption of inkjet printing (IJP) technology to manufacture PEs has been limited to laboratory‐scale research only. The fact that IJP's inability to maintain consistent high‐resolution quality over large printing areas has made transitioning IJP for commercial production arduous. Most of the previous literatures have focused on holistic discussion on material design for IJP, but this review provides insight into key aspects in material processing up to printing optimization to realize high‐resolution PEs. This review also highlights the challenges in controlling the functional ink properties and their interaction with the substrate as well as printing parameters to deliver the desired quality of the droplets and final prints. Imminent application of IJP in PEs and future perspectives are also included in this review.

Synthesis and characterization of fluorescent and thermochromic bifunctional composites: Polydiacetylene/zinc oxide quantum dots

Composites of polydiacetylenes (PDA) and zinc oxide (ZnO) find diverse applications in thermochromic inks, colorimetric sensors, and anticounterfeiting, albeit often with complex preparation methods, single functionality, and high color-changing temperature ranges. This study presents environmentally friendly aqueous composites exhibiting dual thermochromic and fluorescent properties, achieved by integrating ZnO quantum dots (QDs) with particle sizes below 10 nm with PDA. By varying the concentration ratio of ZnO QDs to PDA, the effects on fluorescence and thermochromic properties were systematically explored. The interaction between ZnO QDs and PDA interfaces causes alterations to the energy states in the conjugated π-orbital array within PDA molecules. In contrast to pure PDA solutions, the composite materials not only exhibit thermochromism but also fluorescence. Demonstratively, the composite was applied as functional ink or paste for writing, film production, and inkjet printing, maintaining robust thermochromic sensitivity and fluorescence properties in the resulting specimens. This methodology imparts excellent multifunctionality to composite materials, enhancing and broadening their application potential.

Recognising small colour changes with unsupervised learning, comparison of methods

Colour differentiation is crucial in machine learning and computer vision. It is often used when identifying items and objects based on distinct colours. While common colours like blue, red, green, and yellow are easily distinguishable, some applications require recognising subtle colour variations. Such demands arise in sectors like agriculture, printing, healthcare, and packaging. This research employs prevalent unsupervised learning techniques to detect printed colours on paper, focusing on CMYK ink (saturation) levels necessary for recognition against a white background. The aim is to assess whether unsupervised clustering can identify colours within QR-Codes. One use-case for this research is usage of functional inks, ones that change colour based on environmental factors. Within QR-Codes they serve as low-cost IoT sensors. Results of this research indicate that K-means, C-means, Gaussian Mixture Model (GMM), Hierarchical clustering, and Spectral clustering perform well in recognising colour differences when CMYK saturation is 20% or higher in at least one channel. K-means stands out when saturation drops below 10%, although its accuracy diminishes significantly, especially for yellow or magenta channels. A saturation of at least 10% in one CMYK channel is needed for reliable colour detection using unsupervised learning. To handle ink densities below 5%, further research or alternative unsupervised methods may be necessary.