Printable Solution Research Articles

Utilisation of waste wool through fabrication of 3D water-resistant polyvinyl alcohol composite: Impact of micro-sized wool powders

Polyvinyl alcohol (PVA) is a biodegradable polymer that has applications in several industries, such as textiles and paper manufacturing. Due to the water solubility, it is also a useful solvent in 3D dispensing to extrude printable solutions at a low temperature. However, its hydrophilicity is a drawback when considering the property of the end-use material if water contact is required. Using the water solubility of PVA as a benefit during 3D dispensing but avoiding the hydrophilicity in the printed material is tricky and unresolved. This study proposes a technique to achieve this phenomenon by taking advantage of the natural hydrophobicity of wool waste by using it as a filler in PVA. There is no previous knowledge on how wool could impact the water resistance characteristic of PVA. Three types of micro-sized wool powder (22.2–46.3 μm) were used and their impact on the wool/PVA (25/75) 3D composite properties was investigated. The wool powders reinforced in PVA were able to resist water drops from penetrating the surface for the full length of the experiment (10 min). Water solubility test also showed a greater resistance of the 3D composite samples due to the incorporation of wool powders. Though tensile strength and crystallinity of PVA were decreased by including the wool particles, powders prepared with finer wool showed minimum influence on this reduction. The rheology and thermal properties also suggested better compatibility in the wool/PVA system when finer wool was used. Overall results indicate that wool waste could be effectively utilised to naturally induce water-resistant performance in PVA composite. This finding could be beneficial not only in 3D dispensing, but also in many other areas, such as packaging, where the use of PVA is still limited due to its sensitivity to water.

Environmentally Friendlier Printable Conductive and Piezoresistive Sensing Materials Compatible with Conformable Electronics.

Flexible and conformable conductive composites have been developed using different polymers, including water-based polyvinylpyrrolidone (PVP), chemical-resistant polyvinylidene fluoride (PVDF), and elastomeric styrene-ethylene-butylene-styrene (SEBS) reinforced with nitrogen-doped reduced graphene oxide with suitable viscosity in composites for printable solutions with functional properties. Manufactured by screen-printing using low-toxicity solvents, leading to more environmentally friendly conductive materials, the materials present an enormous step toward functional devices. The materials were enhanced in terms of filler/binder ratio, achieving screen-printed films with a sheet resistance lower than Rsq < 100 Ω/sq. The materials are biocompatible and support bending deformations up to 10 mm with piezoresistive performance for the different polymers up to 100 bending cycles. The piezoresistive performance of the SEBS binder is greater than double that the other composites, with a gauge factor near 4. Thermoforming was applied to all materials, with the PVP-based ones showing the lowest electrical resistance after the bending process. These conductive materials open a path for developing sustainable and functional devices for printable and conformable electronics.

The mechanical reliability of vat photopolymerization 3D printing of isosorbide-derived polyester porous tissue engineering scaffolds.

Photo-crosslinkable polymers are being studied as a potential 3D printable solution to the well-established need for biocompatible, highly elastic, and resorbable materials. Among the emerging materials that meet this need is a sugar-based polymer, an isosorbide-derived polyester, which represents a candidate for use in tissue engineered medical devices. Isosorbide polyesters are known to exhibit time-certain resorption profiles, offering not just biocompatibility and biodegradability, but can also be 3D printed by photocrosslinking. The 3D printing of medical devices requires accuracy, minimally, in the 10’s of microns range. Preliminary data showing isosorbide-derived polyester 3D printing of scaffolds with an internal porosity is reported here. The pore geometry we used is Schoen’s gyroid. Using an EnvisionTEC 3D printer (Dearborn, MI) we designed cylinders with 81% porosity using the gyroid pore geometry with a pore size of 800 µm and a strut size of 1000 µm.

Leveling and Drying Dynamics of Printed Liquid Films of Organic Semiconductor Solutions in OLED/OPV Applications

AbstractPrinting process development for fabrication of organic electronic devices is described, with focus on semiconductor layers for organic light‐emitting diodes and photovoltaic cells. This development is considerably more complex than for a graphical printing process. Key aspects are an adequate dosing and transfer of highly volatile inks, the reliable coalescence of the droplets deposited on the substrate to a closed liquid film, and the successful relaxation and leveling of the liquid–air interface in the solvent evaporation phase in the presence of Marangoni stresses and pattern formation instabilities. The conditions for successful implementation of a gravure or inkjet process, using steadily developing, new generations of polymer as well as small molecule semiconductors are, to a large extent, but not exclusively, originating from the molecular features of organic semiconductors and their printable solutions. In addition, recent developments in surface technology, and in the physics of thin‐film dynamics and spontaneous pattern formation contribute to a proper understanding of liquid layer dynamics in printed electronics. The role of ink formulation, Marangoni stresses related to concentration and temperature gradients, the effect of the disjoining pressure, and solvent evaporation are discussed.

Photocrosslinking-based 3D printing of unsaturated polyesters from isosorbide: A new material for resorbable medical devices

Clinically used tissue-engineered devices are few and far between. The search for biocompatible materials has been a great focus for the field for the past 30 years. The ones that exist are hard to work with when manufacturing patient-specific shapes with complex external and internal pore geometries because of their material and mechanical properties. Photo-cross-linkable polymers have arisen as a potential 3D printable solution for this problem. Here we present a new sugar-based polymer, isosorbide-derived polyester as a potential candidate to help fill this gap.Isosorbide-derived polyesters containing different amount of double bonds were synthesized to allow the material to be crosslinked or functionalized. Three resin formulations with different amounts of double bonds available (5, 12 and 17%) were used. After initial thermal and photo-crosslinking studies, Isosorbide-derived unsaturated polyesters were then mixed with a photoinitiator, co-crosslinker, and solvent to form a 3D printable resin formulation. Thin films of that resin were then cured using a Digital Light Projection (DLP) printer and analyzed. An attempt was made to modulate the cured thickness by adding HMB as a photoattenuator. We assessed 3D printing success and tensile green strength for the 3 resin formulations.We were able to 3D print unsaturated polyesters from isosorbide with a DLP printer when enough double bonds were present to facilitate crosslinking and curing of the material. Finally, thin films were then seeded with fibroblasts following the ISO 10993-5 protocol. These coupons were found safe (i.e., non-cytotoxic and biocompatible), potentially marking the beginning of a new approach to preparing resorbable implants for tissue engineering uses.

Feasibility study on additive manufacturing of recyclable objects for space applications

Future exploration missions beyond low-Earth orbit would significantly benefit from a closed loop recyclable Additive Manufactured capability, allowing the production of general purpose tools and items in a time and cost effective manner. To realize this ambition, we present a feasibility study of a Solvent-Cast Direct-Write method using Polyvinyl Alcohol as biodegradable material. Process parameters such as solution viscosity, evaporation rate, print pressure and scan speed are optimized in order to achieve a consistent and reliable print outcome. We demonstrate the process by fabricating test complex geometries of sample specimens. Moreover, we report on the mechanical properties of printed geometries as well as the recyclability aspects. Physical and chemical properties of the printable solutions were investigated and the viability of the method for space is discussed.

Solution processed flexible resistive switching memory based on Al-In-O self-mixing layer

In this work, a solution processed Al-In-O/InOx bilayer resistive switching random access memory (RRAM) is demonstrated at temperature as low as 180 °C. The memory cell exhibits remarkable forming free resistive switching characteristics with stable data retention and low set/reset voltages. More importantly, this solution processed bilayer shows stable memory properties under different bending angles on a flexible substrate. The resistive switching mechanism was systematically investigated. Compared to single layer devices, an Al-In-O mixing layer is induced by the solution process in the bilayer RRAM. The first principle calculation confirms that in the Al-In-O mixing layer, the formation energy of oxygen vacancies is significantly reduced compared with the AlOx layer. As a result, the formation of the oxygen vacancy based conductive filament is realized without the electroforming process. The RRAM fabricated by the printable solution process at low temperature shows great application potential in next generation wearable electronics.

3D printing of SiC ceramic: Direct ink writing with a solution of preceramic polymers

3D structured SiC ceramics with varying feature sizes (100–400 μm) were achieved by direct ink writing of polycarbosilane (PCS)/n-hexane solution. The rheological properties of the PCS solution and printing parameters were tailored for optimum writing behaviour. The integrity and clear surface of the filaments indicated the printing ability of forming the self-supporting features along with the rapid evaporation of solvent. As-printed 3D structured PCS was processed by oxidative crosslinking and pyrolysis and converted to SiC ceramic. Although strong shrinkage occurred during the pyrolysis, SiC ceramic maintained the original 3D structure. Both proper viscoelasticity of printable solutions and the homogeneous shrinkage in the pyrolysis determine the integrity and feature characteristic of 3D structured SiC using direct ink writing preceramic polymer.

Flash-evaporation printing methodology for perovskite thin films

Printing solutions have attracted wide attention from various research fields, but thin films made by printing technologies still cannot match the quality of the films made by conventional thin-film deposition methods. In this study, a flash-evaporation printing (FEP) technology, which employed a freestanding carbon nanotube (CNT) flash evaporator, was developed to address this issue and to achieve a compact physical vapor deposition geometry. The target material precoated on the CNT flash evaporator was printed onto a substrate by gas-phase transportation. The FEP methodology presented a printable solution for hybrid perovskite thin films. The as-fabricated photovoltaic devices showed power conversion efficiencies of ∼10.3%, and the thin films were also utilized as potential photodetectors. In addition, this technology can also be used to print patterns and a wide variety of materials on large panels. The environmentally friendly and cost-effective FEP technology will be of significant benefit to printed electronics, organic electronics and future flexible electronics.

Scalable nanomanufacturing of surfactant-free carbon nanotube inks for spray coatings with high conductivity

Spray-coated carbon nanotube films offer a simple and printable solution for fabricating low cost, lightweight, and flexible thin-film electronics. However, current nanotube spray inks require either a disruptive surfactant or destructive surface functionalization to stabilize dispersions at the cost of the electrical properties of the deposited film. We demonstrate that high-purity few-walled carbon nanotubes may be stabilized in isopropanol after surface functionalization and that optimizing the ink stability dramatically enhances the conductivity of subsequent spray-coated thin films. We consequently report a surfactant-free carbon nanotube ink for spray-coated thin films with conductivities reaching 2,100 S/cm. Zeta-potential measurements, used to quantify the nanotube ink dispersion quality, directly demonstrate a positive correlation with the spraycoated film conductivity, which is the key metric for high-performance printed electronics.

Printable sensors for explosive detonation

Here, we report the development of an organic thin film transistor (OTFT) based on printable solution processed polymers and employing a quantum tunnelling composite material as a sensor to convert the pressure wave output from detonation transmission tubing (shock tube) into an inherently amplified electronic signal for explosives initiation. The organic electronic detector allows detection of the signal in a low voltage operating range, an essential feature for sites employing live ordinances that is not provided by conventional electronic devices. We show that a 30-fold change in detector response is possible using the presented detector assembly. Degradation of the OTFT response with both time and repeated voltage scans was characterised, and device lifetime is shown to be consistent with the requirements for on-site printing and usage. The integration of a low cost organic electronic detector with inexpensive shock tube transmission fuse presents attractive avenues for the development of cheap and simple assemblies for precisely timed initiation of explosive chains.

Application of Inkjet Printing Technology to Produce Test Materials of 1,3,5-Trinitro-1,3,5 Triazcyclohexane for Trace Explosive Analysis

The feasibility of the use of piezoelectric drop-on-demand inkjet printing to prepare test materials for trace explosive analysis is demonstrated. RDX (1,3,5-trinitro-1,3,5 triazcyclohexane) was formulated into inkjet printable solutions and jetted onto substrates suitable for calibration of the ion mobility spectrometry (IMS) instruments currently deployed worldwide for contraband screening. Gravimetric analysis, gas chromatography/mass spectrometry (GC/MS), and ultraviolet-visible (UV-vis) absorption spectroscopy were used to verify inkjet printer solution concentrations and the quantity of explosive dispensed onto test materials. Reproducibility of the inkjet printing process for mass deposition of the explosive RDX (1,3,5-trinitro-1,3,5 triazcyclohexane) was determined to be better than 2% for a single day of printing and better than 3% day-to-day.