Simple Printing Research Articles

Inkjet Printing of Highly Sensitive, Transparent, Flexible Linear Piezoresistive Strain Sensors

Flexible strain sensors are fabricated by using a simple and low-cost inkjet printing technology of graphene-PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) conductive ink. The inkjet-printed thin-film resistors on a polyethylene terephthalate (PET) substrate exhibit an excellent optical transmittance of about 90% over a visible wavelength range from 400 to 800 nm. While an external mechanical strain is applied to thin-film resistors as strain sensors, a gauge factor (GF) of the piezoresistive (PR) strain sensors can be evaluated. To improve the GF value of the PR strain sensors, a high resistive (HR) path caused by the phase segregation of the PEDOT:PSS polymer material is, for the first time, proposed to be perpendicular to the PR strain sensing direction. The increase in the GF with the increase in the HR number of the PR strain sensors without a marked hysteresis is found. The result can be explained by the tunneling effect with varied initial tunneling distances and tunneling barriers due to the increase in the number of HR. Finally, a high GF value of approximately 165 of three HR paths is obtained with a linear output signal at the strain range from 0% to 0.33%, further achieving for the inkjet printing of highly sensitive, transparent, and flexible linear PR strain sensors.

PERFORMING RELIABLE ABSORBANCE AND FLUORESCENCE MEASUREMENTS WITH LOW BUDGET – A TUTORIAL FOR BEGINNERS

Molecular absorbance and fluorescence measurements are usually performed by benchtop or portable USB spectrophotometers or fluorometers. However, even the simplest configuration of these instruments requires considerable financial input, which is not affordable to many universities and research groups especially when public politics withdraw funds from science. Light-emitting diodes (LEDs) based devices can be an interesting alternative for low-cost, portable yet reliable measurements of absorbance of fluorescence. Especially if associated with the fabrication of 3D structures by additive manufacturing techniques. Although there are many reviews in the literature dedicated to discussing the theoretical aspects and analytical performance of LED-based devices, we consider that these reviews are not easily applicable for beginners in electronics. It results in the intimidation to employ such powerful tools which could have a huge impact mainly to small and/or initial groups. In this tutorial, we present a guide that will help students and researchers to construct “lab-built” devices based on simple optoelectronic components and 3D printing to perform molecular absorbance and fluorescence measurements for analytical methods. Finally, with this tutorial guide, we anticipate a large spread of the usage of LED devices for reliable analytical measurements that can be extensively used in many scenarios.

All-Polymer Wearable Thermoelectrochemical Cells Harvesting Body Heat

Wearable thermoelectrochemical cells (thermocells) have attracted increasing interest due to their ability to turn human body heat into electricity. Here, we have fabricated a flexible, cost-effective, and 3D porous all-polymer electrode on an electrical conductive polymer substrate via a simple 3D printing method. Due to the high degree of electrolyte penetration into the 3D porous electrode materials for redox reactions, the all-polymer based porous 3D electrodes deliver an increased power output of more than twice that of the film electrodes under the same mass loading using either n-type or p-type gel electrolytes. To realize the practical application of our thermocell, we fabricated 18 pairs of n-p devices through series connection of n-type and p-type single devices. The strap shaped thermocell arrangement was able to charge up a commercial supercapacitor to 0.27 V using the body heat of the person upon which it was being worn and in turn power a typical commercial lab timer.

Stretchable, Healable, and Degradable Soft Ionic Microdevices Based on Multifunctional Soaking-Toughened Dual-Dynamic-Network Organohydrogel Electrolytes.

Electronic materials and devices that can mimic biological systems featured with elasticity, toughness, self-healing, degradability, and environmental friendliness drive the technological developments in fields spanning from bioelectronics, biomedical diagnosis and therapy, electronic skin, and soft robotics to Internet-of-Things with "green" electronics. Among them, ionic devices based on gel electrolytes have emerged as attractive candidates for biomimetic systems. Herein, we presented a straightforward approach to demonstrate soft ionic microdevices based on a versatile organohydrogel platform acting as both a free-standing, stretchable, adhesive, healable, and entirely degradable support and a highly conductive, dehydration- and freezing-tolerant electrolyte. This is achieved by forming a gelatin/ferric-ion-cross-linked polyacrylic acid (GEL/PAA) dual dynamic supramolecular network followed by soaking into a NaCl glycerol/water solution to further toughen the gelatin network via solvent displacement, thus obtaining a high toughness of 1.34 MJ·cm-3 and a high ionic conductivity (>7 mS·cm-1). Highly stretchable and multifunctional ionic microdevices are then fabricated based on the organohydrogel electrolytes by simple transfer printing of carbon-based microelectrodes onto the prestretched gel surface. Proof-of-concept microdevices including resistive strain sensors and microsupercapacitors are demonstrated, which displayed outstanding stretchability to 300% strain, resistance to dehydration for >6 months, autonomous self-healing, and rapid room-temperature degradation within hours. The present material design and fabrication approach for the organohydrogel-based ionic microdevices will provide promising scope for life-like and sustainable electronic systems.

Preparation of Chitosan-Based Enzyme Inks for Paper-Based Screen-Printed Biofuel Cells

We have developed paper-based screen-printed biofuel cells using MgO-templated carbon (MgOC) as an electrode material1) in which a mediator and an enzyme were immobilized by dropping the solutions on the MgOC surface. However, the immobilization scheme should be shortened for practical applications. In this study, we newly prepare an enzyme-modified carbon ink using chitosan, which has high bio-affinity as a binder. By preparing chitosan-based enzyme ink, it becomes possible to immobilize the enzyme on the electrode by a simple printing process. A paper-based glucose/O2 biofuel cell was fabricated by screen printing with the enzyme-modified carbon inks. In this abstract, we describe the results of the glucose anode.Firstly, a glucose oxidase (GOx) and 1,2-naphthoquinone (1,2-NQ) were physically adsorbed in the pores of the MgOC. Then a chitosan-based enzyme ink was prepared by mixing the GOD and 1,2-NQ immobilized MgOCwith chitosan, and then cross-linked with genipin. A commercially available carbon ink and the as-prepared chitosan-based enzyme ink were successively printed on a water-repellent Japanese paper and dried overnight in a refrigerator to prepare a bioanode. In this study, we used two kinds of carbon. One is an untreated MgOC (normal MgOC). Another is a “washed MgOC”, which were washed with 0.25M NaOH and pure water before the chitosan-based enzyme ink was prepared.Anodes prepared with chitosan-based enzyme inks using normal MgOC and washed MgOC were evaluated by chronoamperometry (measurement potential: 0.2 V) in phosphate buffer containing 100 mM glucose (Fig.1 (a)).The catalytic oxidation reaction was not observed in the anode using normal MgOC, whereas the catalytic oxidation current of about 0.5 mA/cm2 was obtained after 500 seconds in the anode using the washed MgOC. From the SEM (accelerating voltage: 15.0 kV) of the anode using washed MgOC, a structure with many macroporesof about 5 to 10 µm was observed clearly. (Fig. 1(b)). On the other hand, no such macropores were observed in the anode using normal MgOC.The surface of normal MgOC has many functional groups such as -COOH, and it shows acidity when mixed with water. The cross-linking reaction does not occur sufficiently in between genipin and chitosan under acidic condition. On the other hand, in the neutral condiiton, the cross-linking reaction that accompanies the self-polymerization of genipin proceeds enough to form long and flexible chains 2). Therefore, the neutralization of the MgOC surface by the washing treatment forms an electrode with macropores between carbons, resulting in increase of glucose supply to the GOD immobilized in the mesopore of MgOC. References 1) Isao Shitanda et al., J. Electrochem. Soc, 166(12) (2019) B1063-B1068.2) Elí Emanuel Esparza Floreset et al., Process Biochemistry, 84, (2019) 73-80. Acknowledgements This work was partially supported by JST-ASTEP Grant Number JPMJTS1513, JSPS Grant Number 17H02162 and Private University Research Branding Project (2017-2019) from Ministry of Education, Culture, Sports, Science and Technology, and Tokyo University of Science Grant for President's Research Promotion． Figure 1

A highly integrated sensing paper for wearable electrochemical sweat analysis

Wearable electrochemical sensors have attracted tremendous attention in recent years. Significant progress has been achieved, particularly in device integration. Most wearable devices are integrated on thin-film polymer, however, less attention is paid to the sweat flow at human-device interfaces, which is of great significance for continuous real-time analysis and long-term skin comfort. Here, we reported a low-cost, freestanding and disposable highly integrated sensing paper (HIS paper) for real-time analysis of sweat. By using a simple printing process, the HIS paper combining hydrophobic protecting wax, conducting electrodes, and the incorporated MXene/methylene blue (Ti3C2Tx/MB) active materials was assembled. In particular, the printed paper was folded into a multi-layer structure, in which a reasonable designed three-dimensional (3D) sweat diffusion path is established by connecting the hydrophilic regions of each layer, providing efficient pathways for the collection and diffusion of sweat along the vertical direction of the folded HIS paper. More importantly, the independent 3D position of three-electrode facilitates the decoration and fixation of enzymes, as well as the accessibility of electrolytes. In addition, a dual-channel electrochemical sensor that can simultaneously detect glucose and lactate with sensitivity of 2.4 nA μM−1 and 0.49 μA mM−1 respectively was produced based on the HIS paper. This HIS paper provides a miniaturized, low-cost and flexible solution for a range of biochemical platforms, including wearable bioelectronics.

Fabrication of strontium-substituted hydroxyapatite scaffolds using 3D printing for enhanced bone regeneration

The use of porous three-dimensional (3D) bioceramic scaffolds to facilitate the regeneration of bone defects has attracted great attention because their structures closely mimic the natural extracellular matrix. 3D printing is a versatile method for the fabrication of 3D scaffolds. In this study, 3D strontium-substituted hydroxyapatite (Sr-HA) bioceramic scaffolds were prepared by simple precipitation and 3D printing method. The resulting scaffolds exhibited interconnected microporous structures of strands and a single-phase crystal due to HA, meaning that no changes in the phase composition and microstructure of the scaffolds with the Sr content were observed. However, their dissolution rate and biological performance were substantially influenced by changes in the Sr content of the scaffolds. The optimal Sr content in the Sr-HA scaffolds for enhanced proliferation and differentiation of cells were identified by comparing four compositions of the Sr-HA scaffolds. The results of in vitro bioactivity tests demonstrated that the Sr5-HA scaffold with 0.05 of Sr/(Ca + Sr) molar ratio promoted more rapid cell proliferation, osteogenic differentiation, and cellular mineralization compared with the other scaffolds. Therefore, Sr-HA scaffolds have the potential for application in bone regeneration as new bone graft substitutes.

Low-cost Fabrication of Cu doped ZnO (Zn0.95Cu0.05O) Film for Enhanced Gas Sensing Applications

Cu doped ZnO film (Zn0.95Cu0.05O) was fabricated by simple and cost-effective screen printing method. The structural and optical properties of prepared film was studied through X-ray diffraction (XRD) and UV-Vis spectroscopy techniques respectively. XRD analysis revealed the polycrystalline nature of prepared film with hexagonal structure. The optical band gap determined from UV-Vis analysis was found to be 3.40 eV. The gas sensing performance of prepared film was studied at room temperature toward different concentrations of NO2 ranging in between 1ppm – 5ppm. The response and recovery time was noted as 13s and 92s respectively. All these outcomes shows that the Cu doped ZnO film shows enhanced gas sensing performance and can be utilized for industrial scale production of gas sensors.

A Novel Graphene Conductive Ink Based Circular Patch Antenna for 2.4 GHz Application

Graphene conductive ink based microstrip line fed circular patch is presented in this paper. The main objective of this work is to replace copper with graphene which is an emerging promising material, in the field of patch antennas with conventional rigid substrates using a simple printing technique and to measure its performance. The prototyped screen printed graphene antenna is perfectly radiating and the return loss, VSWR and gain of the graphene antenna is found to be better than conventional copper antenna. Also, the bandwidth of the graphene antenna is 1.6 times greater than that of the conventional copper antenna on rigid substrate.

Screen printing coating of (ZnO)0.8(CdO)0.2 material for optoelectronic applications

Here we report X-ray response and optical properties of composite (ZnO)0.8(CdO)0.2 thick film deposited by simple, easy and low cost screen printing technique on glass substrates followed by sintering at 500 °C. X-ray diffraction pattern confirms the polycrystalline structure of the film having hexagonal and cubic structures with preferred orientations of grains along (101) plane for ZnO and (111) plane for CdO. While Raman spectra exhibited strong peaks of E2 (high) phonon and overtone of surface phonon modes at 431 cm−1 and 1145 cm−1 respectively. The absorption coefficient and band gap which are essential for the optoelectronic applications were determined by using UV–visible absorbance data. Photoluminescence spectroscopy of the (ZnO)0.8(CdO)0.2 films showed a strong emission peak at 407 nm near the band edge along with a weak green–yellow emission peak spanning the wavelength range from 450 to 500 nm. The Arrhenius plot of DC conductivity shows semiconductor nature with existing activation energy of about 0.33 eV. The film thickness was measured by profilometry, obtaining a thickness of around 3 µm.

Inkjet printing of graphene oxide and dopamine on nanofiltration membranes for improved anti-fouling properties and chlorine resistance

Anti-fouling properties and chlorine resistance nature are highly desirable features for membranes used in nanofiltration (NF). Conventional polymeric NF membranes often suffer from fouling issues and poor stability under chlorine based chemicals. Therefore, in this work, a thin film composite (TFC) NF membrane was modified by coating a binding agent polydopamine (PDA) and graphene oxide (GO) using a simple and scalable inkjet printing process where the GO deposition was controlled by the number of printing cycles. The NF test results revealed the PDA-GO printed NF membranes exhibited higher salt rejection while achieving slightly lower permeate flux compared to control membrane. Moreover, the PDA-GO printed membrane exhibited enhanced anti-fouling properties where only 20% of permeate flux reduction was observed while the control membrane displayed significant reduction in flux up to 48%. Furthermore, chlorine resistance of the PDA-GO printed membrane showed reduction in salt rejection was effectively suppressed compared to the control membrane for the chlorination time of 1 and 3 h. Our work demonstrates an effective strategy to mitigate fouling and chlorine stability issues in NF membranes as well as validate inkjet printing as a versatile technique for the formation of advanced nanomaterial based membranes with high controllability of membrane properties.

36‐3: Novel and Simple Patterning process of Quantum Dots via Transfer Printing for Active Matrix QD‐LED

The next generation of a self‐emitting display requires precise and stable patterning techniques to shape Red, Green, and Blue pixels using quantum dots. In this study, we propose the novel and simple transfer printing process for the active matrix QD‐LEDs.

Exploration of Direct-Ink-Write 3D Printing in Space: Droplet Dynamics and Patterns Formation in Microgravity

As a simple, fast and effective 3D printing method, direct-ink-writing (DIW) has potential applications in repairing the circuit board in orbit, printing the wearable devices for the astronaut, and producing the solar cells for the energy supply in space. To expand the DIW technology to space, we designed the colloidal material box (CMB) as the prototype printer of DIW and verified its applicability in the Chinese SJ-10 satellite. The colloidal suspensions was adopted as a diluted ink model to investigate two key processes of DIW under microgravity environment: manipulation of the droplet and formation of the patterns. We have showed the dynamics of the droplet, which would determine the size of the features, could be controlled through tuning the wettability of the needles and the solid surface. Compared to the ground, the “coffee ring” effect was weakened for the drying patterns because of strong interfacial effect under weightless conditions. We have found that fast evaporation could assist for fabricating more uniform and ordered structures.

Engineered dual-scale poly (ε-caprolactone) scaffolds using 3D printing and rotational electrospinning for bone tissue regeneration

Large bone defects due to trauma or disease present a significant clinical challenge with limited efficacy of current therapies. A key aim is to develop biomimetic scaffolds that reflect the native tissue structure with 3D printing being an important enabling technology. However, the incorporation of multiple length scales and anisotropic features, mimicking the native architecture, is difficult with current processes. In this study, we propose a simple and versatile hybrid printing process using a screw-assisted additive manufacturing technique combined with rotational electrospinning to fabricate dual-scale anisotropic scaffolds. 3D microscale porous polycaprolactone (PCL) structures with highly aligned nanoscale fibres were successfully produced layer-by-layer. The scaffolds were morphological, mechanical and biological characterised. Human adipose-derived stem cells (hADSCs) were seeded on the hybrid scaffold to evaluate the effects of structural and anisotropic topographic cues on cell attachment, proliferation and osteogenesis differentiation. Results show that the 3D printed microscale structures have uniform and well-defined geometries and the alignment of nanoscale electrospun fibres increases by increasing the electrospinning rotational velocity. Mechanical results show that there is no significant difference between 3D printed scaffolds with or without electrospun meshes. In vitro results show higher cell seeding efficiency and proliferation in dual-scale scaffolds with high density electrospun meshes. A more stretched and elongated cell morphology was observed in aligned nanofibre scaffolds showing higher anisotropic cytoskeletal organization than 3D printed PCL scaffolds without electrospun meshes. The dual-scale scaffolds present improved overall osteogenic markers expressions (COL-1, ALP and OCN). However, no statistical difference between normalised osteogenic marker expressions were observed between dual-scale scaffolds and 3D printed scaffolds. This might be attributed to the poor bioactivity of the substrate material, PCL, suggesting topographical cues might not be sufficient to stimulate cell fate towards to an osteogenic linage. The results suggest that the proposed fabrication strategy is a promising approach for the design of novel bone scaffolds to modulate cell fates by integrating the topographic cue reported in this paper with biochemical cues associated to the use of more bioactive materials.

Microfluidic Printing of Slippery Textiles for Medical Drainage around Wounds.

Surface materials with specific wettability play significant roles in existing fields from environmental protection to biomedicine. Here, a 3D droplet transport microfiber textile with slippery liquid‐infused porous surface is presented for medical drainage around wounds. The textile is fabricated by using a simple capillary microfluidic printing method to continuously spin polyurethane microfibers with liquid paraffin‐infused porous surface and print them into a 3D‐structure. Benefiting from the specific surface porous structure and oil encapsulation of the microfibers, aqueous droplets could be nondestructively and rapidly transported not only in simple single, double or multiple microfiber systems, but also in the microfibers composed stereoscopic textile through the microfluidic 3D printing. Based on this feature, it is demonstrated that the 3D slippery microfiber textile coupled with a vacuum sealing drainage therapy could significantly enhance the wound exudation drainage efficiency, reduce tissue injury, and prolong the effective service life in versatile wounds management. Thus, it is believed that the slippery microfiber textiles have potential for clinical applications.

Multifunctional smart electronic skin fabricated from two-dimensional like polymer film

Smart skin-like electronics are urgently crucial for artificial muscles, while the development of self-powered two-dimensional-like multifunctional material systems remains significant challenges. Here, we demonstrate a new class of printed smart electronic skin (SES) with multi-sensing properties and energy conversion capability using simple and cost-effective printing techniques. The resulting all-organic self-powering SES functioning as a human-monitoring device where it can detect a variety of external stimuli and works as an ultra-flexible biomechanical energy harvester. Remarkably, our SES exhibits excellent antibacterial properties in addition to self-adaptive performance under various conditions, such as being bent, cut, sewed, hammered, punctured, and washed. The proposed SES devices here have the promise for broad applications in future functional-wearables for human-machine interface, soft robotics, and skin prosthetics.

Enhanced electroluminescence in fully printable powder electroluminescent device with flexible invisible silver‐grid transparent electrode

Powder electroluminescent devices (PELDs) have a high potential for commercial application because of flat light emission devices and simple printing process fabrication with low-cost production, without semiconductor processes using vacuum and plasma. In conventional PELDs, indium tin oxide (ITO) has been used as a transparent electrode. However, ITO is unfavourable in flexible electronic devices due to its intrinsic brittleness. The authors evaluated the current and luminance characteristics of PELDs prepared on gravure offset-printed invisible silver-grid (Ag-grid) electrodes that were laminated with and without poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate) (PEDOT:PSS) transparent electrodes. The PELD on the Ag-grid laminated with PEDOT:PSS electrode shows the maximum luminance of ∼250 cd/m2 at 200 μm spacing, which is five-fold greater than the luminance of PELD without PEDOT:PSS electrode lamination.

Low-Cost iPhone-Assisted Processing to Obtain Radiotherapy Bolus Using Optical Surface Reconstruction and 3D-Printing

Patient specific boluses can increase the skin dose distribution better for treating tumors located just beneath the skin with high-energy radiation than a flat bolus. We introduce a low-cost, 3D-printed, patient-specific bolus made of commonly available materials and easily produced using the “structure from motion” and a simple desktop 3D printing technique. Nine pictures were acquired with an iPhone camera around a head phantom. The 3D surface of the phantom was generated using these pictures and the “structure from motion” algorithm, with a scale factor calculated by a sphere fitting algorithm. A bolus for the requested position and shape based on the above generated surface was 3D-printed using ABS material. Two intensity modulated radiation therapy plans were designed to simulate clinical treatment for a tumor located under the skin surface with a flat bolus and a printed bolus, respectively. The planned parameters of dose volume histogram, conformity index (CI) and homogeneity index (HI) were compared. The printed bolus plan gave a dose coverage to the tumor with a CI of 0.817 compared to the CI of 0.697 for the plan with flat bolus. The HIs of the plan with printed bolus and flat bolus were 0.910 and 0.887, respectively.

3D printed cellulose-based high-efficiency oil-water separation mesh

In this study, a high-performance oil-water separation mesh based on cellulose was fabricated by Direct Ink Writing (DIW) 3D printing technology. The 3D printing process can be undergo in a natural environment by using a cellulose acetate/ethyl acetate solution as a DIW printing ink. This oil-water separation mesh prepared has various advantages, such as uniform size, controllable aperture, simple and easy printing process, and rapid prototyping. The super high separation efficiency of 96 % and the high flux of 400 000 L·m−2·h−1 can be realized when the average pore size of the 3D printed super-hydrophilic cellulose mesh is 280 μm or less. Moreover, oil-water separation mesh prepared based on highly hydrophilic cellulose are chemically resistant to extreme acidity and alkalinity. It is also capable of separating oils of various viscosities. In addition, the cellulose mesh can cope with the mechanical force caused by high-frequency vibration, and maintain excellent oil-water separation efficiency in the external force field. Therefore, this highly efficient oil-water separation mesh can be used in oil-water separation processes in a variety of applications.

Tunable ionic pressure sensor based on 3D printed ordered hierarchical mesh structure

Flexible pressure sensors play an indispensable role in numerous future technologies for human beings, especially those with high sensitivity, broad sensing range and tunable fabrication methods. Herein, we demonstrate a tunable ionic pressure sensor based on the dielectric layer with ordered hierarchical mesh structure (OHMS). The OHMS layer was fabricated by a simple and adaptable 3D printing technique, therefore the performance of the sensor can be tuned. Owing to the OHMS and electrical double layers (EDL), the sensor exhibits a high sensitivity of 72.86 kPa−1 in the ultralow pressure range (<0.4 kPa), a fast response time within 43 ms, a high stability for over 7300 cycles, and a broad pressure sensing range from 1 Pa to 400 kPa. The sensor is demonstrated with practical applications, including Morse code, solvent evaporation detection, breathing, swallowing, wrist pulse, and plantar pressure measurement. This work may provide a new approach to tailor and improve the performance of ionic pressure sensors, which have great potential for innovative applications in wearable health-monitoring devices and human-machine interface systems.