Composite Ink Research Articles

Applicability of normalized resistance rate model for predicting fatigue life and resistance evolution in composite conductive inks

The electrical resistance of metal-polymer conductive inks increases as they undergo cyclic loading, posing a major challenge to their reliability as interconnect materials for flexible electronic devices. To characterize an ink’s fatigue performance, extensive electro-mechanical testing is usually performed. Phenomenological models that can accurately predict the resistance increase with cyclic loading can save time and be useful in flexible conductor design against fatigue failure. One such model was recently developed for only one composite ink type. The model is based on experiments monitoring resistance under monotonic stretch data and multiple experiments measuring the rate of increase of the resistance under different strain amplitudes and mean strains. The current work examines whether such resistance rate model could be generalized to apply for more types of composite inks. Two composite inks with different binder material, metal flake sizes and shapes, and substrate material were experimentally tested under monotonic and cyclic loading. It was found that the two new inks are also more sensitive to strain amplitude than mean strain. The resistance rate model accurately predicts early/catastrophic failure (<1000 cycles) in all inks and conservatively estimates high fatigue life for low strain amplitudes. A protocol detailing the procedures for applying the resistance model to new inks is outlined.

Vapor-induced phase-separation-enabled versatile direct ink writing

Versatile printing of polymers, metals, and composites always calls for simple, economic approaches. Here we present an approach to three-dimensional (3D) printing of polymeric, metallic, and composite materials at room conditions, based on the polymeric vapor-induced phase separation (VIPS) process. During VIPS 3D printing (VIPS-3DP), a dissolved polymer-based ink is deposited in an environment where nebulized non-solvent is present, inducing the low-volatility solvent to be extracted from the filament in a controllable manner due to its higher chemical affinity with the non-solvent used. The polymeric phase is hardened in situ as a result of the induced phase separation process. The low volatility of the solvent enables its reclamation after the printing process, significantly reducing its environmental footprint. We first demonstrate the use of VIPS-3DP for polymer printing, showcasing its potential in printing intricate structures. We further extend VIPS-3DP to the deposition of polymer-based metallic inks or composite powder-laden polymeric inks, which become metallic parts or composites after a thermal cycle is applied. Furthermore, spatially tunable porous structures and functionally graded parts are printed by using the printing path to set the inter-filament porosity as well as an inorganic space-holder as an intra-filament porogen.

Designing of a Multifunctional 3D-Printed Biomimetic Theragenerative Aerogel Scaffold via Mussel-Inspired Chemistry: Bioactive Glass Nanofiber-Incorporated Self-Assembled Silk Fibroin with Antibacterial, Antiosteosarcoma, and Osteoinductive Properties.

Biomaterial-mediated bone tissue engineering (BTE) offers an alternative, interesting approach for the restoration of damaged bone tissues in postsurgery osteosarcoma treatment. This study focused on synthesizing innovative composite inks, integrating self-assembled silk fibroin (SF), tannic acids (TA), and electrospun bioactive glass nanofibers 70SiO2-25CaO-5P2O5 (BGNF). By synergistically combining the unique characteristics of these three components through self-assembly and microextrusion-based three-dimensional (3D) printing, our goal was to produce durable and versatile aerogel-based 3D composite scaffolds. These scaffolds were designed to exhibit hierarchical porosity along with antibacterial, antiosteosarcoma, and bone regeneration properties. Taking inspiration from mussel foot protein attachment chemistry involving the coordination of dihydroxyphenylalanine (DOPA) amino acids with ferric ions (Fe3+), we synthesized a tris-complex catecholate-iron self-assembled composite gel. This gel formation occurred through the coordination of oxidized SF (SFO) with TA and polydopamine-modified BGNF (BGNF-PDA). The dynamic nature of the coordination ligand-metal bonds within the self-assembled SFO matrix provided excellent shear-thinning properties, allowing the SFO-TA-BGNF complex gel to be extruded through a nozzle, facilitating 3D printing into scaffolds with outstanding shape fidelity. Moreover, the developed composite aerogels exhibited multifaceted features, including NIR-triggered photothermal antibacterial and in vitro photothermal antiosteosarcoma properties. In vitro studies showcased their excellent biocompatibility and osteogenic features as seeded cells successfully differentiated into osteoblasts, promoting bone regeneration in 21 days. Through comprehensive characterizations and biological validations, our antibacterial scaffold demonstrated promise as an exceptional platform for concurrent bone regeneration and bone cancer therapy, setting the stage for their potential clinical application.

Structural Effects of 3D Inkjet-Printed Ni(O)-YSZ Pillared Electrodes on Performances of Solid Oxide Electrochemical Reactors.

Increasing densities of reaction sites for gaseous reactants in solid oxide electrochemical reactors (SOERs), is a key strategy for achieving enhanced performance in either fuel cell or electrolysis modes. Fabrication of 3D structured components in SOERs can enhance those densities of reaction sites, which is achieved by 3D inkjet printing with high reproducibility, having developed inks with appropriate properties. First, the effects of pillar geometries on SOER performances are predicted through numerical simulations, enabling subsequent 3D printing to focus on the more effective geometries. Herein, the study reports the results of experimental validation of those predictions by evaluating the electrochemical performances of cells with various heights of 3D inkjet-printed Ni(O)- yttria stabilized zirconia (YSZ) pillars and YSZ pillars. Those measurements prove that increasing pillar heights generally increases SOER peak power densities in fuel cell mode and increased current densities at the thermoneutral potential (1.285V) in steam electrolysis mode, as predicted by simulations. With increasing pillar heights, more limitations in performance enhancement are found with YSZ electrolyte pillars than with Ni-YSZ pillars, again as predicted by simulations. The subsequent microstructural analysis of Ni-YSZ pillars proves the suitability of the Ni(O)-YSZ composite particle ink formulation and the reliability of 3D printing.

Three-dimensional printed silk fibroin and fenugreek based bio-composites scaffolds

When treating orthopaedic damage or illness and accidental fracture, bone grafting remains the gold standard of treatment. In cases where this approach doesn't seem achievable, bone tissue engineering can offer scaffolding as a substitute. Defective and fractured bone tissue is extracted and substituted with porous scaffold structures to aid in the process of tissue regeneration. Three-dimensional bioprinting has demonstrated enormous promise in recent years for producing scaffold structures with the necessary capabilities. In order to create composite biomaterial inks for three-dimensional bioprinting, four different materials were combined such as silk fibroin, bone particles (B), synthetic biopolymer poly (ε-caprolactone), and Fenugreek (F). These biomaterials were mixed together in certain proportion to develop a silk fibroin + bovine bone + polycaprolactone + fenugreek powder composites biomaterial which was later three-dimensional bioprinted to fabricated composite bio-scaffold. The biomechanical, structural, and biological elements of the manufactured composite scaffolds were characterized in order to determine their suitability as a possible biomaterial for the production of bone tissue. The in vitro bioactivity of the composite scaffolds was assessed in the simulated body fluids, and the swelling and degradation characteristics of the two developed scaffolds were analyzed separately over time. The results showed that the mechanical durability of the composite scaffolds was enhanced by the bovine bone particles, up to a specific concentration in the silk fibroin matrix. Furthermore, the incorporation of bone particles improved the bioactive composite scaffolds’ capacity to generate hydroxyapatite in vitro. The combined findings show that the three-dimensional printed bio-composites scaffolds have the required mechanical strength and may be applied to regeneration of bone tissue and restoration, since they resemble the characteristics of native bone.

Dip-coated graphene nanoplatelets and multiwall carbon nanotubes composite ink electrode for metal-free paper-based flexible heating device

A paper-based flexible heating device (PFHD - paper-based flexible heating device) composed of a cellulose paper substrate and a carbonaceous functional electrode is reported. The functional composite electrodes containing graphene nanoplatelets (GNP - graphene nanoplatelets) and multi-walled carbon nanotubes (MWCNT) in various compositional ratios were prepared by dip-coating the oxygen plasma-treated paper substrate into the composite ink, and subsequently dried at 110 ℃ for 30 min to prepare PFHDs. The electrochemical characteristics and heat generation properties of PFHDs indicated that the GNP component in the functional electrode enhanced the electrical conductivity of the electrode, and the physical stability was enhanced mainly by the MWCNT component. Accordingly, PFHD0.33 which contains 33 % GNP and 67 % MWCNT in the functional electrode shows excellent heating performance with high stability and areal rated power of 0.68 W cm−2 (specific rated power = 45 W g−1). The measured sensitivity of PFHD0.33 is 31.50 ℃ V−1 at the applied DC voltage of 0.1–2.0 V.

Formulation of Nickel Oxide–Graphene Composite Ink and the Fabrication of Thin-Film Electrodes Using Direct Ink Writing

Formulation of Nickel Oxide–Graphene Composite Ink and the Fabrication of Thin-Film Electrodes Using Direct Ink Writing

Chitin nanofibrils assisted 3D printing all-chitin hydrogels for wound dressing

The direct ink writing technique used in 3D printing technology is generally applied to designing biomedical hydrogels. Herein, we proposed a strategy for preparing all-chitin-based inks for wound dressing via direct ink writing technique. The β-chitin nanofibers (MACNF) with a high aspect ratio were applied as a nanofiller to modulate the rheological properties of the alkaline dissolved chitin solution. The printing fidelity significantly depends on the MACNF introduction amount to the composite ink. 5–10 wt% MACNF ratio showed superior printing performance. The printed scaffold showed a uniform micron-sized pore structure and a woven network of nanofibers. Due to the good biocompatibility of chitin and the stereoscopic spatial skeleton, this scaffold showed excellent performance as a wound dressing, which can promote cell proliferation, collagen deposition and the angiogenesis of wounds, demonstrating its potential in biomedical applications. This approach successfully balanced the chitinous printability and biofunctions.

Flow mechanisms and their influence on the properties of EGaIn-graphene-poly(ethylene) oxide composites during material extrusion-based additive manufacturing

Polymer composites featuring room temperature liquid alloy particles complimenting other conductive fillers enable unique thermal and electrical properties. Direct-ink-writing approach is an intriguing processing path for these material systems, offering high resolution microstructural and property control. This paper investigates the composition-process-property relationships for material extrusion-based additive manufacturing of EGaIn-Graphene-Poly(ethylene) Oxide composites. Particularly, the influence of composite composition, printing nozzle size and flow rate on electrical conductivity is studied through a mechanistic approach. In that, capillary rheometry and flow modeling was performed to describe the contribution of shear flow and wall slip to the ink flow and how they drive the conductivity of printed structures for various composite ink compositions and process parameters. Influence of composition on material property and process driven conductivity were separately analyzed. Results indicate that EGaIn particles hinder material property-driven baseline average conductivity at high graphene loading. Shear flow and wall slip both increase conductivity. Graphene and total active material concentration increase wall slip and decrease shear flow, leading to a net negative effect of total active material concentration on conductivity. These findings will contribute to composite and process design towards additive manufacturing of composites with as-designed properties.

Body-temperature softening electronic ink for additive manufacturing of transformative bioelectronics via direct writing.

Mechanically transformative electronic systems (TESs) built using gallium have emerged as an innovative class of electronics due to their ability to switch between rigid and flexible states, thus expanding the versatility of electronics. However, the challenges posed by gallium's high surface tension and low viscosity have substantially hindered manufacturability, limiting high-resolution patterning of TESs. To address this challenge, we introduce a stiffness-tunable gallium-copper composite ink capable of direct ink write printing of intricate TES circuits, offering high-resolution (~50 micrometers) patterning, high conductivity, and bidirectional soft-rigid convertibility. These features enable transformative bioelectronics with design complexity akin to traditional printed circuit boards. These TESs maintain rigidity at room temperature for easy handling but soften and conform to curvilinear tissue surfaces at body temperature, adapting to dynamic tissue deformations. The proposed ink with direct ink write printing makes TES manufacturing simple and versatile, opening possibilities in wearables, implantables, consumer electronics, and robotics.

3D-Printing of Hierarchical Porous Copper-Based Metal-Organic-Framework Structures for Efficient Fixed-Bed Catalysts.

Metallic structures with hierarchical open pores that span several orders of magnitude are ideal candidates for various catalyst applications. However, porous metal materials prepared using alloy/dealloy methods still struggle to achieve continuous pore distribution across a broad size range. Herein, we report a printable copper (Cu)/iron (Fe) composite ink that produces a hierarchical porous Cu material with pores spanning over 4 orders of magnitude. The manufacturing process involves four steps: 3D-printing, annealing, dealloying, and reannealing. Because of the unique annealing process, the resulting hierarchical pore surface becomes coated with a layer of Cu-Fe alloy. This feature imparts remarkable catalytic ability and versatile functionality within fixed bed reactors for 4-nitrophenol (4-NP) reduction and Friedländer cyclization. Specifically, for 4-NP reduction, the porous Cu catalyst demonstrates an excellent reaction rate constant (kapp = 86.5 × 10-3 s-1) and a wide adaptability of the substrate (up to 1.26 mM), whilst for Friedländer cyclization, a conversion over 95% within a retention time of only 20 min can be achieved by metal-organic-framework-decorated porous Cu catalyst. The utilization of dual metallic particles as printable inks offers valuable insights for fabricating hierarchical porous metallic structures for applications, such as advanced fixed-bed catalysts.

Phenolic carbon fiber composite inks for the additive manufacturing of carbon/carbon (C/C)

Additive manufacturing (AM) is a crucial development area for high temperature, inorganic and ceramic materials which, using conventional methods, are difficult to process into complex shapes. In particular, carbon/carbon (C/C) composites produced using AM techniques are underexplored compared to other ceramics and ceramic matrix composites. This work investigated and optimized the development of phenolic resin/carbon fiber inks for the material extrusion technique of direct ink writing (DIW) to form C/C composites. Utilizing recent advances in the material extrusion of ceramics, namely the DIW preceramic polymers and preceramic polymer-based suspensions or slurries, we were able to create C/C composites. AM processes can be used to obtain complex geometries and material extrusion processes also facilitate the alignment of high aspect ratio fillers, like carbon fiber, which affects material properties like strength or stiffness. Formulation of material extrusion inks from phenolic resole resin, pitch-based milled carbon fiber as a reinforcement, and a low-density carbon black filler is reported herein. The effects of carbon fiber content and filler, which was used to obtain a printable rheology and appreciable yield stress are discussed in the context of printability.

Multimaterial coextrusion (bio)printing of composite polymer biomaterial ink and hydrogel bioink for tissue fabrication

Bone tissue engineering strategies face considerable challenges owing to the complexity of the bone. This study introduces an unconventional method based on multimaterial 3D coextrusion-(bio)printing to address some of these challenges. The strategy enables simultaneous (bio)printing of a poly(lactic-co-glycolic acid)-based polymer ink laden with hydroxyapatite and a gelatin methacryloyl (GelMA)-based hydrogel bioink containing mesenchymal stem cells (MSCs). The resulting composite scaffolds exhibited a trabecular bone-like porosity and favorable compressive properties, surpassing those of GelMA alone. The (bio)printed MSCs demonstrated favorable viability, proliferation, morphology, and differentiation. This converged approach in multimaterial (bio)printing has the potential to transform the field of bone tissue engineering, offering a more efficient and effective way to regenerate skeletal tissues.

Architected Poly(ionic liquid) Composites with Spatially Programmable Mechanical Properties and Mixed Conductivity.

Structural electrolytes present advantages over liquid varieties, which are critical to myriad applications. In particular, structural electrolytes based on polymerized ionic liquids or poly(ionic liquids) (pILs) provide wide electrochemical windows, high thermal stability, nonvolatility, and modular chemistry. However, current methods of fabricating structural electrolytes from pILs and their composites present limitations. Recent advances have been made in 3D printing pIL electrolytes, but current printing techniques limit the complexity of forms that can be achieved, as well as the ability to control mechanical properties or conductivity. We introduce a method for fabricating architected pIL composites as structural electrolytes via embedded 3D (EMB3D) printing. We present a modular design for formulating ionic liquid (IL) monomer composite inks that can be printed into sparse, lightweight, free-standing lattices with different functionalities. In addition to characterizing the rheological and mechanical behaviors of IL monomer inks and pIL lattices, we demonstrate the self-sensing capabilities of our printed structural electrolytes during cyclic compression. Finally, we use our inks and printing method to spatially program self-sensing capabilities in pIL lattices through heterogeneous architectures as well as ink compositions that provide mixed ionic-electronic conductivity. Our free-form approach to fabricating structural electrolytes in complex, 3D forms with programmable, anisotropic properties has broad potential use in next-generation sensors, soft robotics, bioelectronics, energy storage devices, and more.

Artificial Cells and HepG2 Cells in 3D-Bioprinted Arrangements.

Artificial cells are engineered units with cell-like functions for different purposes including acting as supportive elements for mammalian cells. Artificial cells with minimal liver-like function are made of alginate and equipped with metalloporphyrins that mimic the enzyme activity of a member of the cytochrome P450 family namely CYP1A2. The artificial cells are employed to enhance the dealkylation activity within 3D bioprinted structures composed of HepG2 cells and these artificial cells. This enhancement is monitored through the conversion of resorufin ethyl ether to resorufin. HepG2 cell aggregates are 3D bioprinted using an alginate/gelatin methacryloyl ink, resulting in the successful proliferation of the HepG2 cells. The composite ink made of an alginate/gelatin liquid phase with an increasing amount of artificial cells is characterized. The CYP1A2-like activity of artificial cells is preserved over at least 35 days, where 6nM resorufin is produced in 8 h. Composite inks made of artificial cells and HepG2 cell aggregates in a liquid phase are used for 3D bioprinting. The HepG2 cells proliferate over 35 days, and the structure has boosted CYP1A2 activity. The integration of artificial cells and their living counterparts into larger 3D semi-synthetic tissues is a step towards exploring bottom-up synthetic biology in tissue engineering.

Conductivity enhancement of Ag nanowire ink by decorating in situ formed Ag particles under low-temperature sintering

Silver nanowires (AgNWs) have attractive applications in the fabrication of flexible electronics because of their adequate electrical conductivity, mechanical properties, and oxidation resistance. However, the film produced by AgNW ink needs to be sintered at temperatures above 200 °C to obtain high electrical conductivity, which is incompatible with commonly used flexible substrates such as paper or polymer materials. In this study, the AgNW network was decorated by in situ reduced Ag particles (AgPs) to improve the structural integrity and conductivity of the film. After sintering at 80 °C, the pores and voids within the AgNW network were filled with Ag particles smaller than 200 nm, and the porosity of the film was markedly reduced. The lowest resistivity value was 3.9 × 10–5 Ω cm after sintering at 100 °C, only 10.8% and 8.5% of the resistivity values of the films produced from AgNW and ion inks, respectively. During sintering, Ag nucleated on the surface of AgNWs, and its growth and agglomeration resulted in interconnections between the AgNWs and Ag particles. Thereafter, the bridging and filling effect of the Ag particles facilitated the formation of a compact and firm network, improving the film conductivity. The line film printed from the composite ink with 10 layers exhibited a low resistivity of 7.3 × 10–7 Ω·m. Even after 5000 bending cycles, the resistivity of the line only increased by 4.47 × 10–6 Ω·cm from the initial value. The composite ink reported in this study is a promising candidate for the low-cost printing of ultralow-power-consumption wearable electronic devices.

Energy storage and catalytic behaviour of cmWave assisted BZT and flexible electrospun BZT fibers for energy harvesting applications

High-performance lead-free Barium Zirconium Titanate (BZT) based ceramics have emerged as a potential candidate for applications in energy storage, catalysis for electro chemical energy conversion and energy harvesting devices as presented in this work. In the present study hybrid microwave sintered BZT are studied for dielectric, ferroelectric and phase transition properties. BZT ceramic exhibits tetragonal structure as confirmed by the Retvield refinement studies. XPS studies confirms the elemental composition of BZT and presence of Zr. Polarization versus electric field hysteresis loops confirms the ferroelectric behaviour of BZT ceramic. Encouragingly, the BZT showed a moderate energy storage efficiency of 30.7 % and relatively good electro chemical energy conversion (HER). Excellent catalytic activity observed for BZT electrode in acid medium with low Tafel slope 77 mV dec-1. Furthermore, electrospun nanofibers made of PVDF-HFP and BZT are used to make flexible piezoelectric nano generators (PENGs). FTIR studies show that the 16 wt% BZT composite ink exhibits a higher electroactive beta phase. The optimized open-circuit voltage and short circuit current of the flexible PENG exhibits 7Vpp and 750 nA under an applied force of 3N. Thus, flexible and self-powered BZT PENGs are alternative source of energy due to its reliability, affordability and environmental-friendly nature.

Nanocellulose‐Based Ink for Vertically 3D Printing Micro‐Architectures with High‐Resolution

AbstractNanocellulose has become an important renewable component for composite inks, owing to its desirable physical properties, reinforcing capabilities, and tunable self‐assembly behavior. However, it is difficult to improve the rheological performance of the nanocellulose‐based composite to meet the requirement for 3D printing high resolution microarchitectures. Herein, a strategy is proposed that incorporation of amphiphilic molecular surfactant into nanocellulose gel can increase the molecular interaction via hydrophobic bonds and enhance the ink viscoelasticity. Following the design, a composite ink is formulated by adding xylan and Nonaethylene glycol monododecyl ether (C12E9) within nanocellulose gel. A new printing program is designed to achieve vertical writing of the composite ink and obtain free‐standing micropillars and microhemispheres with high resolution in dozens of micrometers. The microhemisphere on an atomic force microscope (AFM) cantilever can be used as colloidal probe. This work proves that nanocellulose composite ink is a candidate for 3D printing functional devices with special microstructures.

High-conductivity graphene/carbon black inks via interpenetrating networks for wearable fabric-based heaters and strain sensors

A highly dispersed and conductive Gr/CB dispersion has been developed through a sand-milling. A Gr/CB composite ink with an interpenetrating conductive network structure has been prepared for wearable fabric-based heaters and strain sensors.

Multi-MXene assisted large-scale manufacturing of electrochemical biosensors based on enzyme-nanoflower enhanced electrodes for the detection of H2O2 secreted from live cancer cells.

In situ monitoring of H2O2 in cellular microenvironments plays a critical role in the early diagnosis and pretreatment of cancer, but is limited by the lack of efficient and low-cost strategies for the large-scale preparation of real-time biosensors. Herein, a universal strategy for MXene-based composite inks combined with a scalable screen-printing process is validated in large-scale manufacturing of electrochemical biosensors for in situ detection of H2O2 secreted from live cells. Compositing biocompatible carboxymethyl cellulose (CMCS) with excellent conductive MXene, a water-based ink electrode (MXene/CMCS) with tunable viscosity is efficiently printed with desirable printing accuracy. Subsequently, the MXene/CMCS@HRP electrochemical biosensor exhibits stable electrochemical performance through HRP nanoflower modification, showing rapid electron transport and high electrocatalytic capacity, and demonstrating a low limit of detection (0.29 μM) with a wide linear detection range (0.5 μM-3 mM), superior sensitivity (56.45 μA mM-1 cm-2), long-term stability and high anti-interference ability. Moreover, this electrochemical biosensor is effectively employed for in situ detection of H2O2 secreted from HeLa cells, revealing good biocompatibility and outstanding biosensing capability. This proposed strategy not only extends the possibility of low-cost biomedical devices, but also provides a promising approach for early diagnosis and treatment of cancer.