Composite Ink Research Articles

3D printable SiO2 nanoparticle ink for patient specific bone regeneration.

Sodium alginate and gelatin are biocompatible & biodegradable natural polymer hydrogels, which are widely investigated for application in tissue engineering using 3D printing and 3D bioprinting fabrication techniques. The major challenge of using hydrogels for tissue fabrication is their lack of regeneration ability, uncontrolled swelling, degradation and inability to hold 3D structure on their own. Free hydroxyl groups on the surface of SiO2 nanoparticles have the ability to chemically interact with alginate–gelatin polymer network, which can be explored to achieve the above parameters. Hence validating the incorporation of SiO2 nanoparticles in a 3D printable hydrogel polymer network, according to the patient's critical defects has immense scope in bone tissue engineering. In this study, SiO2 nanoparticles are loaded into alginate–gelatin composite hydrogels and chemically crosslinked with CaCl2 solution. The effect of SiO2 nanoparticles on the viscosity, swelling, degradation, compressive modulus (MPa), biocompatibility and osteogenic ability were evaluated on lyophilized scaffolds and found to be desirable for bone tissue engineering. A complex irregular patient-specific virtual defect was created and the 3D printing process to fabricate such structures was evaluated. The 3D printing of SiO2 nanoparticle hydrogel composite ink to fabricate a bone graft using a patient-specific virtual defect was successfully validated. Hence this type of hydrogel composite ink has huge potential and scope for its application in tissue engineering and nanomedicine.

Effect of gel electrolytes on the performance of a minimized flexible micro-supercapacitor based on graphene/PEDOT composite using pen lithography

The objective of this study was to fabricate a minimized all solid-state micro-supercapacitor (MSC) with a patterned graphene flake (GF)/polyethylenedioxythiophene (PEDOT) composite electrode using pen lithography. This MSC demonstrated properties of a suitable gel electrolyte. It involved direct writing of GF/PEDOT composite inks with a layer-by-layer assembly and polymerization method by pen lithography on a very small area (0.38cm2) without needing complex processing or a cleanroom environment. Furthermore, performances of three different gel electrolytes (PVA/H2SO4, LiClO4, and H3PO4) in the MSC were investigated to obtain an MSC with high power density. Results revealed that GF/PEDOT-MSC with PVA/H2SO4 gel electrolyte demonstrated excellent electrochemical features such as maximum operating potential window (1.2V), specific capacitance of 37.08 mF cm−2, and energy density of 6.4 mWh cm−2 with extended cycling stability up to capacitance retention rate of 89% after 2500 cycles. This study suggests potential applications of these electrode materials for an easy and scalable fabrication of a wide variety of devices.

GO-graphene ink-derived hierarchical 3D-graphene architecture supported Fe3O4 nanodots as high-performance electrodes for lithium/sodium storage and supercapacitors

Transition metal oxides/carbon materials are of great interest for promising highly efficient energy storage applications owing to their low cost and eco-friendlines. Nevertheless, creating an electrode material with enhanced conductivity and electrochemical activity remains a great challenge. Here a design and fabrication of Fe3O4 nanodots (∼5.2 nm) loading onto the hierarchical three dimensional graphene (Fe3O4/3D-graphene) via an interesting strategy is reported. The key factor in developing the unique 3D-graphene architecture assemblies with a graphene oxide-graphene composite ink and modifying sol-gel chemistry method is a promising strategy. The 3D-graphene with 3D omnibearing conductive and interconnecting pores can facilitate the penetration of electrolyte, accommodate the volume change and inhibit the aggregation of Fe3O4 nanodots upon cycling. Benefiting from the advantages of the positive synergistic effects of Fe3O4 nanodots and multilevel structures of graphene, the Fe3O4/3D-graphene electrode exhibits excellent electrochemical performances for Li/Na-ion batteries and electrochemical capacitors. As a result of the enhanced electrochemical performance, Fe3O4/3D-graphene hybrids could be regarded as a promising electrode for Li/Na-ion battery and supercapacitor.

Two-Layered and Stretchable e-Textile Patches for Wearable Healthcare Electronics.

Wearable healthcare systems require skin-adhering electrodes that allow maximal comfort for patients as well as an electronics system to enable signal processing and transmittance. Textile-based electronics, known as "e-textiles," is a platform technology that allows comfort for patients. Here, two-layered e-textile patches are designed by controlled permeation of Ag-particle/fluoropolymer composite ink into a porous textile. The permeated ink forms a cladding onto the nanofibers in the textile substrate, which is beneficial for mechanical and electrical properties of the e-textile. The printed e-textile features conductivity of ≈3200 S cm-1 , whereas 1000 cycles of 30% uniaxial stretching causes the resistance to increase only by a factor of ≈5, which is acceptable in many applications. Controlling over the penetration depth enables a two-layer design of the e-textile, where the sensing electrodes and the conducting traces are printed in the opposite sides of the substrate. The formation of vertical interconnected access is remarkably simple as an injection from a syringe. With the custom-developed electronic circuits, a surface electromyography system with wireless data transmission is demonstrated. Furthermore, the dry e-textile patch collects electroencephalography with comparable signal quality to commercial gel electrodes. It is anticipated that the two-layered e-textiles will be effective in healthcare and sports applications.

Influence of Biopolymer Carrageenan and Glycerine on the Properties of Extrusion Printed Inks of Carbon Nanotubes.

This article focuses on the preparation of extrusion printing composite inks of multiwall carbon nanotube (MWNT) dispersed separately in iota-carrageenan (IC) and glycerine (G) solution. Both composites (IC-MWNT and G-MWNT) showed shear-thinning behavior when their flow characteristics were tested. Conductive solid tracks/patterns of both printed composite inks were deposited on glass slide, PET (polyethylene terephthalate) sheet, and IC gel films substrates. The conductive patterns were characterized with microscopy, scanning electron microscopy (SEM), and profilometer. Moreover, their contact angle and electrical conductivity were measured. Profilometry showed that increased number of extruded layers gave increased cross-sectional area. SEM study showed that printing ink is embedded into the surface of IC film, discontinuous on glass slide and smoother on PET sheet. Conductivity of IC-MWNT track was 9 ± 1 S/m and that of G-MWNT was 2942 ± 84 S/m on glass substrate of one layer thick. This is because fewer carbon nanotubes (CNT) are present in G-MWNT track as confirmed by SEM study. The nature of substrate also affects the conductivity of printed patterns. The impressive result of conductivity of printed patterns of composite inks can make them useful for bioelectronic application.

All-printed solid-state substrate-versatile and high-performance micro-supercapacitors for in situ fabricated transferable and wearable energy storage via multi-material 3D printing

Micro-supercapacitors are a kind of state-of-the-art energy storage devices and have great potential to be developed in portable and wearable electronics. Here, we report a novel strategy for scalable fabrication of all-printed solid-state micro-supercapacitors with multilayer structure via multi-material 3D printing technique. To obtain electrode materials, we synthesize polypyrrole/polyaniline coaxis nanotubes by utilizing the self-degraded template polymerization method and in situ electrochemical polymerization. The as-prepared aqueous composite electrode ink shows significant shear thinning behavior and excellent processability: a complex electrode patterning with 484 retractions was proved. In addition, the inks are well-adapted to various substrates (paper, texitle, plastic film etc), allowing the device to be printed onto different substrates, even directly on the desired surface. As a conceptual exhibition, we design two schemes of in situ fabricated energy storage devices to meet the ever-changing energy needs and expand the application range of micro-supercapacitors. The transferable tape-type micro-supercapacitors can be stuck to any surfaces where energy is needed immediately. The in situ fabricated wearable micro-supercapacitor on lab-gown shows promising performance and excellent flexibility.

4D Printing of Complex Structures with a Fast Response Time to Magnetic Stimulus.

A poly(dimethylsiloxane)/Fe (PDMS/Fe) composite ink was developed for reversible four-dimensional (4D) printing to create magnetically responsive three-dimensional (3D) structures with a fast response time for their structure evolvements under external magnetic field. These 3D structures could obtain or lose high magnetization immediately by the on or off of an external magnetic field due to the low magnetic coercive force and the high magnetic permittivity of soft magnetic Fe particles in this composite ink, whereas PDMS in this composite ink served as the flexible matrix component to ensure their shape recovery. As exampled by a 3D butterfly with the fast flapping of its wings under an external magnetic field, complex 3D structures created by 4D printing with this PDMS/Fe ink could have the reversible magnetically stimulated structure evolvement property and develop designed magnetically induced motions with a fast response time for various magnetomechanical applications. Furthermore, structure evolvements of these 3D structures could also induce structure-related property changes, as demonstrated by a 3D terahertz photonic crystal (3D-TPC) device with remotely tunable terahertz properties, which could create novel functionalities for various functional devices created by 4D printing from this kind of ink through external magnetic field stimulation.

High Efficiency Electrothermal Graphene/Tourmaline Composite Fabric Joule Heater with Durable Abrasion Resistance via a Spray Coating Route

Durable abrasion resistance is the critical capability for the functional textile via coating treatment routes. Here, an abrasion resistant fabric-based Joule heater with sandwich structure was fabricated via spraying in sequence of water-soluble polyurethane (WPU), then composite ink of graphene, WPU and tourmaline, and at last WPU. The composite fabrics with the incorporation of tourmaline exhibited favorable electrothermal performance, which could achieve a steady-state temperature of 75.4 °C in 30 s under 10 V voltage, and possessed a high power density (2 × 103 W/m2). The flexible heater exhibited remarkable abrasion shielding performance, only resulting in 21.1% electrical conductivity reduction after a 2500-cycles abrasion test, far less than the 87.0% of fabrics without a sandwich structure. The application on thermal therapy of the hand exhibited 1.8 °C rise of blood vessel around the heater under 8 V voltage. Therefore, the as-obtained Joule heater can be widely applied in functional protective ...

Responsive cellulose-hydrogel composite ink for 4D printing

Sustainable and cost-effective solutions are crucial for the widespread adoption of 4D printing technology. This paper focuses on the development of a cellulose-hydrogel composite ink for additive manufacture, presenting the development and physical characterisation (stability, swelling potential and rheology) of the cellulose-hydrogel composite to establish its suitability for 4D printing of responsive structures. The use of a carboxymethyl cellulose (CMC) hydrocolloid with incorporated cellulose pulp fibres resulted in an ink with a high total cellulose content (fibre volume fraction ≈50% for the dehydrated composite) and good dispersion of fibres within the hydrogel matrix. The composite ink formulation developed in this study permitted smooth extrusion using an open source 3D printer to achieve controlled material placement in 3D space while retaining the functionality of the cellulose. The addition of montmorillonite clay not only resulted in enhanced storage stability of the composite ink formulations but also had a beneficial effect on the extrusion characteristics. The ability to precisely apply the ink via 3D printing was demonstrated through fabrication of a complex structure capable of morphing according to pre-determined design rules in response to hydration/dehydration.

Three-Dimensionally Printed Interconnects for Smart Contact Lenses.

One of the ultimate wearable heath-monitoring gears, smart contact lens, requires miniaturized devices compounded and interconnected with each other on the lens for a successful system functioning. Because of the different device thickness, the interconnect patterns need to be three-dimensional (3D) conforming the steps given by the diversified on-lens devices. Also, the patterns should be low-temperature processed and flexible considering the mechanical and thermal property of the lens material. We demonstrate the 3D interconnects electrosprayed on a contact lens platform with Ag-Ag nanowire (NWs) composite ink conforming the steps. Quantitative and informative analysis on the interconnects is presented. Thick polyimide film (12.5 μm) in C-shape is employed as a primary substrate to form the 3D patterns that is to be transferred onto the contact lens. The AgNWs act as frames to support the Ag ion inks printed across the steps. The resultant interconnects realized with the Ag/AgNW composite ink with 0.3 wt % AgNW have the sheet resistance ( Rs) of 0.396 Ω/□ spanning the height difference of 300 μm. AgNWs also provide durability to the patterns against crack formation and propagation under significant device deformation. Unlike pure Ag pattern which shows the Rs changes of 86.1% in the bending condition, the optimally formulated composite pattern shows the suppressed Rs change of only 15.2% with a bending radius of 3 mm.

3D-Printing of Microfibrous Porous Scaffolds Based on Hybrid Approaches for Bone Tissue Engineering.

In recent times, tremendous progress has been evidenced by the advancements in various methods of generating three-dimensional (3D) porous scaffolds. However, the applicability of most of the traditional approaches intended for generating these biomimetic scaffolds is limited due to poor resolution and strict requirements in choosing materials. In this work, we fabricated 3D porous scaffolds based on the composite inks of gelatin (Gel), nano-hydroxyapatite (n-HA), and poly(lactide-co-glycolide) (PLGA) using an innovative hybrid strategy based on 3D printing and freeze-drying technologies for bone tissue engineering. Initially, the PLGA scaffolds were printed using the 3D printing method, and they were then coated with the Gel/n-HA complex, yielding the Gel/n-HA/PLGA scaffolds. These Gel/n-HA/PLGA scaffolds with exceptional biodegradation, mechanical properties, and biocompatibility have enabled osteoblasts (MC3T3-E1) for their convenient adhesion as a layer and have efficiently promoted their growth, as well as differentiation. We further demonstrated the bone growth by measuring the particular biomarkers that act as key players in the ossification process (i.e., alkaline phosphatase (ALP), osteocalcin (OC), and collagen type-I (COL-I)) and the total proteins of the MC3T3-E1 cells. We anticipate that the convenient generation of highly porous 3D scaffolds based on Gel/n-HA/PLGA fabricated through an innovative combinatorial approach of 3D printing technology and freeze-drying methods may undoubtedly find widespread applications in regenerative medicine.

High-Performance and Lightweight Thermal Management Devices by 3D Printing and Assembly of Continuous Carbon Nanotube Sheets.

Free-standing carbon nanotube films or buckypaper can provide a significant platform to develop practical applications of nanocarbon materials. For this research, buckypaper with high thermal conductivity (20 W/m K) and large surface area (350 m2/g) was mass produced in-house to investigate for use in lightweight thermal management devices. Floating catalyst chemical vapor deposition carbon nanotube sheets were also studied in this work. We introduced two manufacturing techniques to use the sheets for heat dissipation: (1) printing conductive composite ink on the sheets to make lightweight thermal devices, such as heat sinks and (2) assembling the sheets directly into 3D structures that were mounted on the back of heat-generating devices. These manufacturing techniques resulted in extremely lightweight, high-performance heat dissipation devices compared with other heat sink materials.

Nickel-reduced graphene oxide composite foams for electrochemical oxidation processes: towards biomolecule sensing

Abstract

A Modularized and Switchable Component for Flexible Passive Device: Terahertz Photonic Crystals with Fine‐Tuning

AbstractIn this work, tunable terahertz photonic crystals (PCs) used as modularized and switchable components in flexible passive device are designed and prepared. Flexible woodpile structures created by the direct‐writing technology with a composite ink system composed of barium strontium titanate nanoparticles and polydimethylsiloxane are immersed in 5CB liquid crystals (LCs), where the orientation of LC molecule is modulated by the external magnetic field. Each of these can work in terahertz wavelength with specific position and depth of the dips in the transmittance spectra due to different geometries as well as having the ability of fine‐tuning. Experiments show that the photonic gaps of these PCs can cover from 0.2 to 0.3 THz, as well as about 7.5% fine tunability of photonic gap appearing with the orientation change of the magnetic field. More interestingly, the dips of photonic gaps keep the same position but become deeper with the increase of layer, an ability to realize another dimensional switchover. This work demonstrates that efficient terahertz PCs with different geometry parameters could be dynamically tuned by the orientation of magnetic field and it can open a universal approach to shrinking the size of device and rapid manufacturing in a large throughput.

Filtration-induced production of conductive/robust Cu films on cellulose paper by low-temperature sintering in air.

Cellulose paper is an attractive substrate for paper electronics because of its advantages of flexibility, biodegradability, easy incorporation into composites, low cost and eco-friendliness. However, the micrometre-sized pores of cellulose paper make robust/conductive films difficult to deposit onto its surface from metal-nanoparticle-based inks. We developed a Cu-based composite ink to deposit conductive Cu films onto cellulose paper via low-temperature sintering in air. The Cu-based inks consisted of a metallo-organic decomposition ink and formic-acid-treated Cu flakes. The composite ink was heated in air at 100°C for only 15 s to give a conductive Cu film (7 × 10−5 Ω cm) on the cellulose paper. Filtration of the Cu-based composite ink accumulated Cu flakes on the paper, which enabled formation of a sintered Cu film with few defects. A strategy was developed to enhance the bending stability of the sintered Cu films on paper substrates using polyvinylpyrrolidone-modified Cu flakes and amine-modified paper. The resistance of the Cu films increased only 1.3-fold and 1.1-fold after 1000 bending cycles at bending radii of 5 mm and 15 mm, respectively. The results of this study provide an approach to increasing the bending stability of Cu films on cellulose paper.

3D printing of poly(ε-caprolactone)/poly(D,L-lactide-co-glycolide)/hydroxyapatite composite constructs for bone tissue engineering

Abstract

Control of the Surface Morphology of Ceramic/Polymer Composite Inks for Inkjet Printing

The use of organic/inorganic composite inks in the Drop on Demand inkjet printing technology is a promising as well as demanding approach for the fabrication of composite thick films. Therefore, a versatile ceramic/polymer composite ink system for inkjet printing is developed in this study, containing Ba0.6Sr0.4TiO3 (BST) and poly(methyl methacrylate) (PMMA). When developing such inks suitable for a one‐step fabrication, the major challenge is to fulfill the requirements of the inkjet printing technology and to obtain homogeneous surface morphologies after drying. Thus, possible influencing factors like the solvent composition, the solids content, and the ratio of ceramic to polymer are investigated to obtain a detailed knowledge for the general ink development. The fluid mechanical properties, viscosity, density, and surface tension are characterized. The main focus of this study lies on the drying behavior of the different inks, with the interactions of the ceramic particles, and the dissolved polymer molecules being highlighted. Furthermore, the drying behavior depending on the ink composition is shown. This study provides new insights into the possibility of using composite inks for the inkjet printing process and the fabrication of printed composite thick films in a single process step.

In situ characterization of low-viscosity direct ink writing: Stability, wetting, and rotational flows

HypothesisDirect ink writing (DIW) of composites can be coupled with magnetic, electric, or acoustic fields to control spatial variations of microstructure that enhance performance. The use of such external fields often requires inks with lower viscosities than conventional DIW, which presents new challenges with regards to maintaining the stability of printed lines and targeted microstructures. In-situ monitoring of the print bead, combined with slot-die models, can be used to predict printing modality and guide printing protocols for low viscosity inks. ExperimentsUsing videos of the nozzle-substrate gap, we systematically study how ink composition, stand-off distance, and nozzle and substrate surface coatings influence the printing process. We establish in-situ digital image analysis techniques to evaluate filament stability, nozzle wetting, and rotational flows in low viscosity composite inks. FindingsVariations in the fluid-substrate contact line position and angle can be used to evaluate stability on-the-fly, and lubrication theory can be used to predict filament-to-droplet transitions. To limit nozzle wetting and disruption of microstructures established in the nozzle, it is necessary to use low flow to stage speed ratios, in regimes close to those associated with instabilities. However, low viscosities, small stand-off distances, and functionalized nozzles can improve the print line’s resilience against instabilities.

Zein Increases the Cytoaffinity and Biodegradability of Scaffolds 3D-Printed with Zein and Poly(ε-caprolactone) Composite Ink.

Electrohydrodynamic printing (EHDP) has attracted extensive interests as a powerful technology to fabricate micro- to nano-scale fibrous scaffolds in a custom-tailored manner for biomedical applications. A few synthetic biopolymer inks are applicable to this EHDP technology, but the fabricated scaffolds suffered from low mechanical strength, biocompatibility, and biodegradability. In this study, a series of poly(ε-caprolactone) (PCL)/zein composite inks were developed and their printability was examined on a solution-based EHDP system for scaffold fabrication. Multilayer grid scaffolds were manufactured by PCL, PCL/zein-10, and PCL/zein-20 inks, respectively and characterized. The mechanical strength of scaffolds printed by PCL/zein composite inks was remarkably enhanced in terms of Young's modulus and yield stress. The enzyme-accelerated in vitro degradation study demonstrated that zein-containing scaffolds exhibited dose-responsive improvement on the degradation rate as evidenced by surface morphological change of fibers. Moreover, the biocompatibility of PCL/zein scaffolds, tested on mice embryonic fibroblast (NIH/3T3) and human nonsmall lung cancer cell (H1299), manifested better cell affinity. Our findings suggest that scaffolds fabricated by the solution-based EHDP with PCL/zein composite inks can significantly improve Young's modulus, yield stress, biocompatibility, and biodegradability and have potential applications in drug delivery systems, 3D cell culture modeling, or tissue engineering.

Experimental realization of Mie-resonance terahertz absorber by self-assembly method.

Mie-resonance terahertz absorbers by self-assembly method are designed and demonstrated in experiments and simulations. A monolayer of zirconium dioxide (ZrO2) microspheres fixed on a copper film with designed grids that were manufactured by direct writing with a composite ink system composed of polydimethylsiloxane (PDMS). More importantly, different spacing and array configurations were created economically and efficiently, showing visual performance. Magnetic resonance leads to near-unity absorption at about 0.4 THz in the samples. This work demonstrates efficient terahertz absorbers and highlights a novel direct writing fabrication method that can be extended to produce other optical devices for applications.