Composite Ink Research Articles

Development and optimization of starch-based biomaterial inks and the effect of infill patterns on the mechanical, physicochemical, and biological properties of 3D printed scaffolds for tissue engineering

Plant-based hydrogels have wide application as scaffolds in tissue engineering and regenerative medicine due to their low cost and excellent biocompatibility. Scaffolds act as vehicles for cell-based therapeutics and regenerating diseased tissue. While there is a plethora of methods to generate hydrogels with tunable properties to mimic the tissue of interest, 3D bioprinting is a novel emerging technology with the capability to generate versatile patient-specific scaffolds typically embedded with tissue specific cells. Starch-based hydrogels are garnering attention in extrusion-based 3D printing, however owing to their poor mechanical strength and degradation render this material inefficient in its native form. Additionally, the effect of various printing process parameters on mechanical strength and bioactivity is poorly understood. In the present study, we investigate the use of starch and gelatin as composite biomaterial ink and its effect on mechanical, physical and biological properties. We also investigated printability of composite hydrogels with the aim to understand the correlation between two infill patterns and its effect on mechanical, physicochemical, and biological properties. Our results showed that the composite hydrogels had competent mechanical properties and suitable bioactivity when seeded with H9C2 cardiomyocytes. Rheometric analyses provided a broader insight into the required viscosity for printing and has a direct correlation with the composition of the hydrogel. Thus, the composite materials are found to have tissue-specific mechanical properties and may serve as a better, cheaper and personalized alternative to existing scaffolds for the fabrication of engineered cardiac tissue.

Design and Fabrication of Flexible Woodpile Structured Nanocomposite for Microwave Absorption Using Material Extrusion Additive Technique

The explosive growth of electronics and the widespread use of transient power sources have given rise to an undesirable and uncontrolled consequence of electromagnetic interference (EMI). It is crucial to address and mitigate the issues caused by EMI by developing effective shielding techniques. The material extrusion additive technique provides a solution through its versatile 3D printing of polymeric ink, offering advantages such as design flexibility, structural complexity, and environmental sustainability. The primary objective of this study is to investigate the rheological properties, electromagnetic properties, and thermal stability of nanocomposites consisting of Polydimethylsiloxane (PDMS) and Multi-Walled Carbon Nanotubes (CNTs). The aim is to utilize these findings for the design and 3D printing of a microwave absorber with high efficiency. Composite inks containing 50 vol% (C50) and 60 vol% (C60) of CNTs exhibit favorable shear-thinning behavior and shape retention. On the other hand, lower CNT percentages result in inconsistent viscosity, rendering the inks non-printable. Thermogravimetry analysis reveals that an increase in CNT vol% leads to a decrease in the thermal stability of 3D-printed PDMS-CNT nanocomposites. Higher CNT proportion enhances electric polarization, and attenuation capacity, as evidenced by measurements of complex permittivity and dielectric loss tangent. X-Ray Diffraction analysis was employed to examine the effect of CNT inclusion in the composites. A woodpile-structured metamaterial microwave absorber based on gradient index (GWMMA) was designed by manipulating geometric parameters and CNT vol%. Fifteen unit cell configurations were generated and subsequently chosen based on their exceptional attenuation capabilities, low impedance, and narrower filament width for simulations. The GWMMA demonstrates exceptional absorption performance, surpassing reflection loss values of −10dB. Incorporating a third filament stacking into the woodpile structure augments its efficacy, yet further additions of stackings result in diminishing returns. Experimental validation of a selected 3D-printed GWMMA structure of C60 with a width of 0.75 mm confirms its absorption capabilities, closely aligning with the simulated results. The GWMMA exhibits promising performance for microwave absorption, with absorption values exceeding 90%. Simulations indicate the adjustability of the GWMMA's bandwidth and absorption capabilities through alterations in array periodicity and cell size. Its spatial scale aligns with sub-wavelength structures, establishing it as a representative Metamaterial Absorber (MMA).

Realizing Intrinsically Stretchable Transparent Electrodes via Silver Nanowires/PEDOT:PSS/Polyvinyl Alcohol Composites on the Polyurethane Substrate

AbstractStretchable transparent electrodes (STEs) have garnered considerable attention as a fundamental architectural component in the realm of conformable and wearable electronics. This study presents a novel approach utilizing composite inks based on silver nanowires to fabricate STEs, with the incorporation of a conductive polymer as the leveling agent and polyvinyl alcohol as the bonding agent. The resulting STE demonstrates several desirable properties, including low sheet resistance (15.6 Ω sq−1) and surface roughness facilitated by poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate. Moreover, the STE demonstrates strong adhesive strength to various plastic substrates, high transparency (>80%), and remarkable stretchability of up to 100%. Notably, the STE exhibits exceptional thermal stability under thermal stress at 200 °C for extended durations of up to 300 min. As a result, flexible organic solar cells employing this composite STE achieve outstanding performance in terms of high efficiency, robust mechanical durability, and remarkable thermal stability.

Dual-Functional Electrochromic Smart Window Using WO3·H2O-rGO Nanocomposite Ink Spray-Coated on a Low-Cost Hybrid Electrode.

Electrochromic windows have gained growing interest for their ability to change their optical state in the visible and NIR ranges with minimal input power, making them energy-efficient. However, material processing costs, fabrication complexity, and poor electrochromic properties can be barriers to the widespread adoption of this technology. To address these issues, electrochromic material and fabrication processes are designed to realize their potential as a cost-effective and energy-efficient technology. In this work, an electrochromic composite material-based ink is synthesized consisting of WO3·H2O nanoplates supported on rGO (reduced graphene oxide) nanosheets (WH-rGO), wherein an optimized amount of rGO (0.05 to 0.5 wt %) is introduced for providing a higher conduction pathway for efficient charge transport without sacrificing the electrochromic performance of WO3·H2O nanoplates. The stable ink dispersion prepared in the study is deposited by spray coating on transparent conducting electrodes over large areas (25 cm2). The WH-rGO nanocomposite (0.4 wt %) results in 43% optical modulation at 700 nm, with bleaching and coloration times of 6 and 8 s, respectively. Interestingly, the device also possesses an electrochemical energy storage capability with an areal capacitance of 16.3 mF/cm2. The electrochromic composite material is successfully translated on tin doped indium oxide (ITO)-coated Al metal mesh hybrid electrodes (T = 80%, Rs = 40 Ω/□) to replace ITO. Finally, an electrochromic device of 5 × 5 cm2 is fabricated by spray-coating the ink on cost-effective ITO/Al-mesh hybrid electrodes. The device displays blue to colorless modulation with an excellent bleaching time of 0.43 s and a coloration time of 2.16 s, making it one among the fast-operating devices fabricated by complete solution processing. This work showcases the economical production of a dual-function electrochromic device, which can be a feasible option as an alternative to existing ITO-based devices in both automotive and infrastructure applications.

Predicting dimensional accuracy in 3D printed polydimethylsiloxane‐carbon nanotubes composites via machine learning

AbstractDirect ink writing (DIW) is a rapidly expanding additive manufacturing (AM) technique valued for its cost‐efficiency and material adaptability. While DIW offers substantial process flexibility, achieving precise manufacturing demands a thorough understanding of its printability parameters. Key process variables such as printing speed, nozzle‐bed gap, pulses for extrusion, and extrusion multiplier wield significant influence over the shape and dimensions of printed components. In this study, a machine learning model based on k‐nearest neighbors is employed to predict dimensional accuracy. The model is trained using measured width and thickness data from printed rings, with flow and printing‐speed tests defining parameter boundaries for printing. The final model demonstrates an accuracy of 81% and 74% for two PDMS‐CNT composite ink compositions. The principal components analysis underscores the pivotal roles of the extrusion factor and printing speed in achieving superior geometric fidelity. Additionally, retraction‐residual tests were conducted, revealing that the initial 10 seconds of extrusion hold critical importance as they can lead to distortions when traversing printed regions or perimeters, necessitating consideration in part design. To evaluate layer adhesion strength, a crucial aspect of AM, T‐peel tests were performed. Furthermore, rheological tests provided insights into extrudability, printable reinforcing percentages, shape retention, and yield stress.Highlights Rheological tests yield insights into minimum reinforcing% and shape retention. Developed k‐NN model predicts accuracy using measured printed rings' data. PC analysis shows key roles of extrusion factor and print speed. Retraction‐residual tests reveal initial 10 seconds are critical. Model validation results show 83.45% and 77.95% accuracy, close to prediction.

Direct ink writing printed flexible double-layer staggered woodpile structure for multi-band compatible absorption of gigahertz and terahertz waves

Soft multi-band compatible electromagnetic wave absorbers have wide applications in 6G communication, radar stealth, detection instruments, and radio astronomy. In this context, a kind of double-layer staggered woodpile absorber is designed and manufactured by the direct ink writing (DIW) technology with a composite ink system composed of reduced graphene oxide (RGO)/spherical carbonyl iron (SCI) and polydimethylsiloxane (PDMS). The as-prepared absorber shows compatible absorption in both microwave and terahertz frequency bands. The effective absorption bandwidth (EAB) and minimum reflection loss (RLmin) reach 8.24 GHz and −52.2 dB at a thickness of 3.2 mm, respectively. In the terahertz band (0.5–3.5 THz), it shows effective absorption (absorption rate greater than 99 %) and achieves RL < -20 dB throughout the entire tested band. In addition, the double-layer staggered woodpile absorber has good flexibility and can be conveniently used for curved substrates. This work enables the potential for rapid manufacturing of flexible and compatible absorbing devices through DIW 3D printing for applications in 5/6G communication, military stealth and flexible wearable intelligent devices.

Photo‐Mediated Cascade Growth of Ag Nanocrystals in Flow Reactors for High‐Performance Flexible Transparent Electrodes

AbstractPhoto‐mediated synthesis wielding localized surface plasmon resonance (LSPR) of nanoscale metal is widely applied to sculpt silver (Ag) nanocrystals with controllable dimensions and morphologies. However, this photo‐mediated strategy remains underutilized owing to low efficiency and inferior quality in conventional batch reactors. Here, the effective synthesis of Ag nanocrystals is demonstrated via flow reactors and elucidates the photo‐mediated anisotropic growth mechanism. The investigation reveals that the intersection between excitation wavelengths and LSPR of Ag nanocrystals is a prerequisite for their growth. The final morphology is highly correlated with excitation wavelengths, which modulate the redox potential (reaction barrier) of Ag nanocrystals featuring distinct defective structures. Thus, by utilizing tandem‐connected flow reactors, size‐controllable Ag nanoplates can be yielded in a highly efficient cascade growth manner. In addition, composite conductive ink (submicron/nano‐Ag particles) is employed to create high‐performance flexible transparent electrodes. A sixfold conductivity enhancement especially under low sintering temperature (&lt;80 °C), along with superior transmittance (over 90%), and distinguished cyclic durability (negligible resistance change over 1000 cycles) are achieved simultaneously. The study not only establishes comprehensive insights into the acquisition of well‐defined Ag nanocrystals in flow reactors but also ushers in enormous feasibility toward high‐performance and cost‐effective flexible electronics.

Preparation of persistently luminescent polyacrylic acid-based nanocomposite ink for secure encoding

Security encoding that use photochromism has been an appealing method for fabricating efficient authentication substrates. In order to overcome counterfeiting, a unique photochromic ink was created to be utilized as a stamped film, that persistently emits light under both ultraviolet rays and darkness. Nanoparticles of lanthanide-doped aluminate (NLDA) dispersed in a polymer binder was utilized to produce a smart composite ink. In order to develop a transparent film, NLDA must be evenly distributed throughout the polyacrylic acid ink solution. Cellulosic paper sheets were stamped with the fluorescent and color-tunable nanocomposite ink. As proved by CIE (Commission Internationale de ĺEclairage) Lab parameters, a transparent appearance was achieved by stamping a homogeneous ink layer onto paper surface. Using photoluminescence spectroscopy, the stamped surfaces exhibited an absorbance peak at 365 nm and a fluorescent band at 519 nm. The stamped pattern is invisible under daylight; however, a change in color was detected from colorless to green under UV rays. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to explore the structure of NLDA. Infrared spectroscopy (FTIR), energy-dispersive X-ray (EDS), scanning electron microscopy (SEM), and X-ray fluorescence (XRF) were all employed to determine the morphological features of the stamped papers. The imprinted paper sheets exhibited photochromism that could be switched back and forth between visible (colorless) and ultraviolet (green) lights without fatigue. Persistent greenish-yellow emission was detectable in the dark after exposure to smartphone light for a few seconds. Stamped sheets were analyzed for their mechanical properties, and the rheology of the photoluminescent ink was studied.

Development of 3D-printing composite inks based on photoreactive cartilage extracellular matrix and gelatin nanoparticles

Decellularized extracellular matrix (dECM)-based materials possess innate biochemical cues to drive cell recruitment and differentiation and are of interest for cartilage tissue engineering. While 3D-printing (3DP) provides a means for achieving the precise architecture needed for cartilage tissue engineering, dECM hydrogels have proven difficult to translate to 3DP due to low viscosity and weak mechanical properties. In this study, a cartilage dECM (cdECM, 3 w/v%) was combined with varied amounts of gelatin nanoparticles (GNPs; 10, 12.5, 15 w/v%) to form novel hydrogel-colloidal composite materials for 3DP. The addition of GNPs increased the viscosity and rheological properties of the cdECM hydrogel in a dose-dependent manner, directly improving the printability of cdECM 3DP inks. Additionally, functionalization of both materials yielded a UV-crosslinkable material for post-printing crosslinking, and increased GNP content increased post-UV storage moduli with 15 w/v% GNPs yielding a storage modulus 26x greater than that of cdECM alone. 3DP construct swelling and degradation were decreased as a function of increased UV-crosslinking dosage (0, 1.5, and 3 J/cm2). After 14 d of swelling in PBS, construct non-porous area was increased by ∼40 % and pore area was increased by ∼30 % for uncrosslinked (0 J/cm2) constructs versus highly crosslinked (3 J/cm2) constructs. Roughly 40 % higher mass retention was observed across GNP content groups for 3 J/cm2 versus 0 J/cm2 UV exposure after 14 d of enzymatic degradation, showing the potential for tuning physicochemical properties via UV exposure. Likewise, the retention of key biochemical components of cdECM over the course of degradation was evaluated. Sulfated glycosaminoglycans, a key reservoir for tissue-specific growth factors, were found to be retained within scaffolds over 14 d of degradation and to be released relative to construct degradation and UV-crosslinking. The results suggest that a photoreactive dECM and colloidal composite material provides a platform for increasing the printability of dECM inks and the delivery of complex biochemical cues for regenerative medicine applications.

A Review of Carbon-Based Conductive Inks and Their Printing Technologies for Integrated Circuits

In recent years, researchers prepared composite conductive inks with high conductivity, high thermal conductivity, strong stability, and excellent comprehensive mechanical properties by combining carbon-based materials such as graphene and carbon nanotubes with metal-based materials. Through new electronic printing technologies, conductive inks can be used not only to promote the development of integrated circuits but also in various new electronic products. The conductive mechanism and the main types of conductive inks are introduced in this review. The advantages of electronic printing technology for preparing integrated circuits are analyzed. The research progress of fabricating integrated circuits with different electronic printing processes, such as screen printing, gravure printing, flexographic printing, and inkjet printing, are summarized. The development trend of carbon-based composite conductive ink for integrated circuits is prospected.

Rheology and 3D printing characteristics of heat-inducible pea protein-carrageenan-glycyrrhizic acid emulsions as edible inks

Protein-based emulsion gels, especially those induced by heat, have been widely used in food 3D printing. However, the rheology and texture of protein-based gels are important factors restricting 3D printing. In this study, glycyrrhizic acid (GA) was used to improve the rheology properties of pea protein (PP)-Kappa carrageenan (κCA) composite emulsion inks, and the suitability of these inks for extrusion 3D food printing was investigated. The results showed that all emulsion inks have shear thinning behavior and could be smoothly extruded during 3D printing. Herschel-Bulkley model fitting results proved that with the increase of PP concentration (from 5% to 10%), the yield stress (σ0) increased from 15.4 to 28.19 Pa, and the consistency coefficient (k) increased from 1.09 to 2.66 Pa.sn. The objects printed with 10% PP-GA0.3 inks showed excellent self-supporting capability, a smooth surface texture, and high printing accuracy. Emulsion inks had good temperature stability and could form emulsion gels following heat induction. The results of small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS) tests confirmed that the addition of GA improved the strength of the gels. This research provides valuable insights for the advancement of food 3D printing inks.

Mg-Doped PLA Composite as a Potential Material for Tissue Engineering-Synthesis, Characterization, and Additive Manufacturing.

Magnesium (Mg)/Polylactic acid (PLA) composites are promising materials for bone regeneration and tissue engineering applications. PLA is a biodegradable and biocompatible polymer that can be easily processed into various shapes and structures, such as scaffolds, films, and fibers, but has low biodegradability. Mg is a biocompatible metal that has been proven to have good biodegradability and osteoconductivity, which makes it suitable for bone tissue engineering. In this study, we prepared and characterized a Mg/PLA composite as a potential material for direct ink writing (DIW) in 3D printing. The results showed that the addition of Mg has a significant impact on PLA's thermal and structural properties and has also significantly increased the degradation of PLA. XRD was used to determine the degree of crystallinity in the PLA/Mg composite, which provides insight into its thermal stability and degradation behavior. The crystallization temperature of PLA increased from 168 to 172 °C for a 15 wt% Mg incorporation, and the melting temperature reduced from 333 °C to 285 °C. The surface morphology and composition of these films were analyzed with SEM. The films with 5 wt% of Mg particles displayed the best-ordered honeycomb structure in their film form. Such structures are considered to affect the mechanical, biological and heat/mass transfer properties of the Mg/PLA composites and products. Finally, the composite ink was used as a feed for direct ink writing in 3D printing, and the preliminary 3D printing experiments were successful in resulting in dimensionally and structurally integral scaffold samples. The shape fidelity was not very good, and some research is needed to improve the rheological properties of the ink for DIW 3D printing.

Facile and direct 3D printing of smart glove for gesture monitoring

The distinctive characteristics of electrically conductive fabrics, including their flexibility, breathability, and comfort, have led to their recognition as a viable substitute for silicon wafers in wearable electronics. However, the difficulty of constructing sensors with three-dimensional (3D) structure on woven fabrics significantly limits their sensitivity and sensing range. Layer-by-layer 3D printing of entire smart textile sensing components has enabled the development of high-performance sensors with enhanced sensitivity and sensing range. This research endeavors to produce a smart glove with superior performance by incorporating strain and pressure sensors by 3D printing a composite conductive ink, consisting of multi-walled carbon nanotubes (MWCNTs), graphene nanosheets (GNSs), fumed silica (FSiO2) and Ecoflex, and encapsulated ink directly onto a commercially available fabric glove. The 3D structure of the sensing layer and the sensing material were intentionally designed to achieve desired performance. The smart glove demonstrates a high gauge factor (GF ∼ 35) and a strain range of 0–50% for strain detection. Additionally, it exhibits a high sensitivity of ∼0.07 kPa−1 and a sensing range of 1000 kPa for pressure examination, which facilitates precise detection of finger bending angles and fingertip contact pressures. The smart glove also shows excellent linearity, repeatable resistance response, favorable cycling characteristics in both strain and pressure detecting, and were unaffected by temperature and humidity. The combination of the smart glove with a Long Short-Term Memory (LSTM) deep learning model achieves a high accuracy (100%) for dynamic gesture recognition and manipulator control, demonstrating their potential for smart wearable electronics and human-computer interaction.

Multiprocess 3D printing of sodium-ion batteries via vat photopolymerization and direct ink writing

In this work, the ability to print shape-conformable batteries with multi-process additive manufacturing is reported. Vat photopolymerization (VPP) 3D printing process is employed to manufacture gel polymer electrolytes (GPEs) for sodium-ion batteries (SIBs), while direct ink writing process is used to prepare positive electrodes. The sodium-ion chemistry has proven to be an adequate substitute to lithium-ion due to the availability of resources and their potential lower production cost and enhanced safety. Three-dimensional printing technologies have the potential to revolutionize the production of shape-conformable batteries with intricate geometries that have been demonstrated to increase the specific surface area of the electrode and ion diffusion, thus leading to improved power performances. This study shows the preparation of composite UV-photocurable resins with different polymer matrix-to-liquid electrolyte ratios, designed to act as GPEs once printed via VPP. The impact of the liquid electrolyte ratio within the GPEs is thoroughly examined through a variety of electrochemical techniques. The exposure time printing parameter is optimized to ensure adequate print accuracy of the GPE. Using the optimized resin composition as material feedstock, shape-conformable 3D printed GPE exhibiting an ionic conductivity of 3.3 × 10−3 S·cm−1 at room temperature and a stability window up to 4.8 V vs. Na0/Na+ is obtained. In parallel, a composite ink loaded with Na0.44MnO2 and conductive additives is developed to 3D print via direct ink writing positive electrodes. After demonstrating the functionality of the independent 3D printed components in SIBs, the last part of this work is focused on combining the 3D printed Na0.44MnO2 electrode and the 3D printed GPE into the same battery cell to pave the way towards the manufacturing of a complete 3D printed battery thanks to different additive manufacturing processes.

Low-temperature sintering of silver-ammonia complex organic composite ink shows high conductivity for humidity sensors

The development of flexible electronic devices is faced with the challenge of difficult fabrication of complex functional structures on flexible substrates. In this paper, a high viscosity ink of silver-ammonia complex was developed based on the reductive ink principle. Using the electrohydrodynamic direct writing, composite fiber patterned printing was achieved on a flexible substrate. By low-temperature sintering of precursor fibers for reduction, a dense silver structure was formed on the surface, resulting in the formation of Ag/PEO conductive fibers. This approach avoided the high temperature damage to the flexible substrate and the adhesion of materials, while demonstrating good conductivity. The Ag/PEO conductive fibers exhibited different sensitivities to H2O molecules in low, medium, and high humidity environments, which were used to design a flexible Ag structure humidity sensor (ASHS) as a functional material. The ASHS showed a linear response relationship and a fast response speed in an environmental humidity range of 11 % to 75 %RH, enabling real-time monitoring of human respiration. This study demonstrates a promising application prospect of the silver-ammine complex ink in the field of flexible electronic devices.

High performance fully-printed strain-sensing e-textile for human posture recognition

Developing strain-sensing electronic textiles (e-textiles) that combine the functionality of stretchable strain sensors with the wearing comfort of textiles is an important development direction for wearable electronics. However, achieving low-cost and high-volume fabrication of strain-sensing e-textiles with both a wide strain working range and high sensitivity remains a huge challenge. Herein, we report high-performance printed strain-sensing e-textiles by designing the composite conductive ink from the perspective of optimizing polymer binders. The composite conductive inks based on different polymer binders present different rheological properties, volume shrinkage, and mechanical properties, which further affect the sensing performance of printed strain-sensing e-textiles. Compared with other four composite conductive inks, the carbon blacks/high elastic transparent glue-based printed strain-sensing e-textile with microcrack structure exhibits higher sensitivity (120.6 at a strain range of 0–100%) over a wide strain working range (150%), while also exhibiting low detection limits (0.1%) and outstanding dynamic stability (10000 cycles). On this basis, the demonstration of smart clothing integrated with 9 printed strain-sensing elements in human body posture recognition and monitoring proves its application prospects in human–machine interaction and virtual reality. This work opens a new research idea for constructing high-performance strain-sensing e-textiles.

Flexible and Printable Composite Ink for Thermal Management of Soft Electronics

AbstractSince heat generation in electronic devices causes thermal failure, heat dissipation is of critical importance. Furthermore, deformable devices are subjected to mechanical stress, therefore, mechanically stable thermal management material should be considered. Herein, a strategy for printable, thermally conductive, and mechanically stable composite ink for thermal management is introduced. Based on the galvanic replacement between eutectic gallium indium (EGaIn) nanoparticles and silver (Ag) flakes, decoration of the EGaIn nanoparticles on Ag flakes is resulted from the difference in standard reduction potential between Ag, Ga, and In. The resultant alloy formation(Ag–Ga or Ag–In) serves as the thermal transport junction between Ag flakes, leading to high thermal and electrical conductivity (≈140 W mK−1 and ≈106 S m−1, respectively). In addition, owing to the polymer binder, the printed ink is mechanically stable on a substrate exhibiting stable thermal conductivity and sheet resistance under the cyclic bending test. Notably, the heat dissipation of the light‐emitting diode (LED) showed better performance when applied with the developed composite ink compared to commercial Ag paste and thermal paste. The junction temperature of the LED is reduced effectively, resulting in a longer lifetime of the LED. The thermal management solution can be utilized in next‐generation soft electronics.

Polyaniline-Based Ink for Inkjet Printing for Supercapacitors, Sensors, and Electrochromic Devices

In recent years, there has been a huge surge in interest in improving the efficiency of smart electronic and optoelectronic devices via the development of novel materials and printing technologies. Inkjet printing, known to deposit ‘ink on demand’, helps to reduce the consumption of materials. Printing inks on various substrates like paper, glass, and fabric is possible, generating flexible devices that include supercapacitors, sensors, and electrochromic devices. Newer inks being tested and used include formulations of carbon nanoparticles, photochromic dyes, conducting polymers, etc. Among the conducting polymers, PANI has been well researched. It can be synthesized and doped easily and allows for the easy formation of composite conductive inks. Doping and the addition of additives like metal salts, oxidants, and halide ions tune its electrical properties. PANI has a large specific capacitance and has been researched for its applications in supercapacitors. It has been used as a sensor for pH and humidity as well as a biosensor for sweat, blood, etc. The response is generated by a change in its electrical conductivity. This review paper presents an overview of the investigations on the formulation of the inks based on conductive polymers, mainly centered around PANI, and inkjet printing of its formulations for a variety of devices, including supercapacitors, sensors, electrochromic devices, and patterning on flexible substrates. It covers their performance characteristics and also presents a future perspective on inkjet printing technology for advanced electronic, optoelectronic, and other conductive-polymer-based devices. We believe this review provides a new direction for next-generation conductive-polymer-based devices for various applications.

4D Printing of Reprogrammable Liquid Crystal Elastomers with Synergistic Photochromism and Photoactuation.

4D printing of liquid crystal elastomers (LCEs) via direct ink writing has opened up great opportunities to create stimuli-responsive actuations for applications such as soft robotics. However, most 4D-printed LCEs are limited to thermal actuation and fixed shape morphing, posing a challenge for achieving multiple programmable functionalities and reprogrammability. Here, a 4D-printable photochromic titanium-based nanocrystal (TiNC)/LCE composite ink is developed, which enables the reprogrammable photochromism and photoactuation of a single 4D-printed architecture. The printed TiNC/LCE composite exhibits reversible color-switching between white and black in response to ultraviolet (UV) irradiation and oxygen exposure. Upon near-infrared (NIR) irradiation, the UV-irradiated region can undergo photothermal actuation, allowing for robust grasping and weightlifting. By precisely controlling the structural design and the light irradiation, the single 4D-printed TiNC/LCE object can be globally or locally programmed, erased, and reprogrammed to achieve desirable photocontrollable color patterns and 3D structure constructions, such as barcode patterns and origami- and kirigami-inspired structures. This work provides a novel concept for designing and engineering adaptive structures with unique and tunable multifunctionalities, which have potential applications in biomimetic soft robotics, smart construction engineering, camouflage, multilevel information storage, etc.

Facile Fabrication of Carbon Nanocolloid‐Silver Composite Ink for the Application of All Inkjet‐Printed Wearable Electronics

AbstractCurrently, owing to the increasing demand for continuous monitoring of health status, it is highly expected to develop functional sensors with satisfied performance. However, traditional sensors generally suffer from the disadvantages of inherent rigidity, limited range, and complicated fabricating methods, failing to provide the required detection. Well‐developed printing technologies have opened a new era for fabricating electronics. The advantages of flexibility, easy scalability, and high resolution endow inkjet printing with the ability to manufacture devices with desired properties. In this work, a green carbon nanocolloid‐silver composite ink is facilely prepared and successfully applied in inkjet printing of strain sensors. Good performance such as high sensitivity (a gauge factor of 267.5), fast response (114 ms), long service life, and outstanding stability (&gt;3000) is demonstrated for the as‐fabricated sensors. Moreover, the printed sensors are revealed to be capable of monitoring multiscale human motions for practical application as a wearable device.