Inkjet Printing Of Polymers Research Articles

Inkjet-printed stretchable and low voltage synaptic transistor array

Wearable and skin electronics benefit from mechanically soft and stretchable materials to conform to curved and dynamic surfaces, thereby enabling seamless integration with the human body. However, such materials are challenging to process using traditional microelectronics techniques. Here, stretchable transistor arrays are patterned exclusively from solution by inkjet printing of polymers and carbon nanotubes. The additive, non-contact and maskless nature of inkjet printing provides a simple, inexpensive and scalable route for stacking and patterning these chemically-sensitive materials over large areas. The transistors, which are stable at ambient conditions, display mobilities as high as 30 cm2 V−1 s−1 and currents per channel width of 0.2 mA cm−1 at operation voltages as low as 1 V, owing to the ionic character of their printed gate dielectric. Furthermore, these transistors with double-layer capacitive dielectric can mimic the synaptic behavior of neurons, making them interesting for conformal brain-machine interfaces and other wearable bioelectronics.

Supercritical impregnation of polymer matrices spatially confined in microcontainers for oral drug delivery: Effect of temperature, pressure and time

The present study is aimed to enhance the oral bioavailability of ketoprofen by inserting it into the matrix of poly(vinylpyrrolidone) (PVP) K10 spatially confined into microcontainers, by means of supercritical CO2-aided impregnation. Microcontainers are cylindrical reservoirs, with typical sizes in the micrometer range, with a cavity open on one side, where the drug formulation is loaded. Differently to traditional tablets, microcontainers have a higher surface area per unit volume, and release the drug only in one direction. This design is meant to enhance the absorption of problematic drugs, like those with poor solubility in water. In a previous study we introduced a novel technique for drug loading of microcontainers, based on inkjet printing and supercritical impregnation (SCI). We showed that SCI produces accurate and reproducible drug loading for large arrays of microcontainers. In the attempt of enhancing the throughput of the loading methods, we propose the replacement of polymer inkjet printing with an easier manual compression of the PVP powder into the microcontainers. As the second step, the polymer powder filled-microcontainers were submitted to SCI. The separate role of different impregnation parameters (temperature, pressure, time, drug concentration in the supercritical phase) was elucidated with respect to the loading capacity. The microcontainer filling was observed by means of optical macroimaging, X-ray microtomography and scanning electron microscopy. The physical state of the drug was investigated by means of Raman spectroscopy and compared with selected representative PVP-ketoprofen physical mixtures. Finally, the drug loading was estimated by means of in vitro dissolution tests.The characterization study shows that the present loading method is a valuable alternative to the one previously described. The drug loading can be controlled with high accuracy and reproducibility and the impregnated drug is in amorphous state. These results demonstrate that SCI can be used as a high throughput loading technique for microfabricated devices for oral drug delivery.

Controlling the solid-state microstructure of organic semiconducting materials by molecular compound formation

Controlling the thin-film nano- and microstructure of active components in organic-based electronic devices such as organic field-effect transistors, organic light-emitting diodes and organic photovoltaic devices is still a challenging but crucial task [Sirringhaus H, Brown PJ, Friend RH, Nielsen MM, Bechgaard K, Langeveld-Voss BMW, Spiering AJH, Janssen RAJ, Meijer EW, Herwig P, de Leeuw DM. Two-dimensional charge transport in self-organized, high-mobility conjugated polymers. Nature. 1999;401:685–688; Yu G, Gao J, Hummelen JC, Wudl F, Heeger AJ. Polymer photovoltaic cells: enhanced efficiencies via a network of internal donor-acceptor heterojunctions. Science. 1995;270:1789–1791; Ray B, Alam MA. Optimum morphology and performance gains of organic solar cells. 2011 37th IEEE Photovoltaic Specialists Conference. IEEE;2011;2:003477–003481]. Over the past decade, numerous strategies have been explored for this purpose, including chemical modification of relevant materials and substrates, optimisation of existing processing procedures (through selection of solvents and processing conditions, annealing procedures, etc.), as well as the development of entirely new deposition techniques [Subramanian S, Park SK, Parkin SR, Podzorov V, Jackson TN, Anthony JE. Chromophore fluorination enhances crystallization and stability of soluble anthradithiophene semiconductors. J. Am. Chem. Soc. 2008;130:2706–2707; Reese C, Roberts M, Ling M, Bao Z. Organic thin film transistors. Mater. Today. 2004;7:20–27; Halik M, Klauk H, Zschieschang U, Maisch S, Effenberger F, Dehm C, Schu M, Brunnbauer M, Stellacci F. Low-voltage organic transistors with an amorphous molecular gate dielectric. Nature. 2004;431:963–966; Kim CS, Lee S, Gomez ED, Anthony JE, Loo YL. Solvent-dependent electrical characteristics and stability of organic thin-film transistors with drop cast bis(triisopropylsilylethynyl) pentacene. Appl. Phys. Lett. 2008;93:103302–103304; Dickey KC, Anthony JE, Loo YL. Improving organic thin-film transistor performance through solvent-vapor annealing of solution-processable triethylsilylethynyl anthradithiophene. Adv. Mater. 2006;18:1721–1726; Street RA. Thin-film transistors. Adv. Mater. 2009;21:2007–2022; de Gans BJ, Duineveld PC, Schubert US. Inkjet printing of polymers: state of the art and future developments. Adv. Mater. 2004;16:203–213; Krebs FC. Fabrication and processing of polymer solar cells: a review of printing and coating techniques. Sol. Energy Mater. Sol. Cells. 2009;93:394–412]. Additives have thereby been shown to provide extra means to significantly influence the molecular assembly and order in the solid state of the active species [Peet J, Kim JY, Coates NE, Ma WL, Moses D, Heeger AJ, Bazan GC. Efficiency enhancement in low-bandgap polymer solar cells by processing with alkane dithiols. Nat. Mater. 2007;6:497–500; Wei Q, Lin Y, Anderson ER, Briseno AL, Gido SP, Watkins JJ. Additive-driven assembly of block copolymer-nanoparticle hybrid materials for solution processable floating gate memory. ACS Nano. 2012;6:1188–1194]. Here, we will discuss the use of a class of additives that can form molecular compounds with the active materials, adding to the extensive tool box for microstructural control because crystalline solid-state structures can be realised where chromophores are spatially separated from each other by the additive molecules without compromising the overall long-range order of the system.

A Glucose Sensor Fabricated by Piezoelectric Inkjet Printing of Conducting Polymers and Bienzymes

Piezoelectric inkjet printing of polymers and proteins holds great promise for fabrication of miniaturized bioelectronic devices, such as biochips and biosensors. In this study, a bienzymatic glucose biosensor prototype based on poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (PEDOT-PSS), glucose oxidase (GOD), and horseradish peroxidase (HRP) was fabricated by a piezoelectric inkjet printer. An aqueous bioelectrical ink containing PEDOT-PSS, GOD, and HRP was prepared and printed on an indium-tin-oxide (ITO)-coated poly(ethylene terephthalate) (PET) film. The PEDOT-PSS/GOD/HRP sensor was covered with a cellulose acetate membrane. The use of bienzymatic sensing combined with conducting polymers via piezoelectric inkjet printing showed a synergistic effect resulting in significant amplification of the response signal. The glucose sensor reached steady-state current density within 3 s, indicating a fast response time, and exhibited a linear dose-dependent electrochemical response with high sensitivity. The overall result demonstrates that a glucose sensor with high sensitivity could be readily fabricated by a piezoelectric inkjet printing system.

Construction of Micro-Patterned Polymer Structures by Piezoelectric Inkjet Printing

It is not simple to accurately deposit minute quantities of polymeric materials by inkjet printing systems. High viscosity, nozzle clogging, agglomeration, precipitation, and uncontrollable drying patterns are serious problems which are frequently encountered in polymer inkjet printing. In this study, we investigated how inkjet printability of polymers correlates with the polymer ink formulations and inkjet process variables. After a systematic study with different variables, various patterns such as dots, cross stripes, and honeycombs were fabricated on flexible polyimide (PI) films and the pattern morphology and spatial distribution of the resulting polymer deposits after solvent drying were characterized.

Polymer inkjet printing: Construction of three-dimensional structures at micro-scale by repeated lamination

Solution-based, direct-write patterning by an automated, computer-controlled, inkjet technique is of particular interest in a wide variety of industrial fields. We report the construction of three-dimensional (3D), micropatterned structures by polymer inkjet printing. A piezoelectric, drop-on-demand (DOD) inkjet printing system and a common polymer, PVA (poly(vinyl alcohol)), were explored for 3D construction. After a systematic preliminary study with different solvent systems, a mixture of water and DMSO was chosen as an appropriate solvent for PVA inks. The use of water as a single solvent resulted in frequent PVA clogging when the nozzles were undisturbed. Among the tested polymer ink compositions, the PVA inks in a water/DMSO mixture (4/1 v/v) with concentrations of 3 to 5 g/dL proved to be appropriate for piezoelectric DOD inkjet printing because they were well within the proper viscosity and surface tension range. When a dot was printed, the so-called ‘coffee-ring effect’ was significant, but its appearance was not prominent in line printing. The optimal polymer inkjet printing process was repeated slice after slice up to 200 times, which produced a well-defined, 3D micro-patterned surface. The overall results implied that piezoelectric DOD polymer inkjet printing could be a powerful, solid-freeform, fabrication technology to create a controlled 3D architecture.

Inkjet Printing of Polymers: State of the Art and Future Developments

AbstractInkjet printing is considered to be a key technology in the field of defined polymer deposition. This article provides an introduction to inkjet printing technology and a short overview of the available instrumentation. Examples of polymer inkjet printing are given, including the manufacturing of multicolor polymer light‐emitting diode displays, polymer electronics, three‐dimensional printing, and oral dosage forms for controlled drug release. Special emphasis is placed upon the utilized polymers and conditions, such as polymer structure, molar mass, solvents, and concentration. Studies on viscoelastic fluid jets and the formation of viscoelastic droplets under gravity indicate that strain hardening is the key parameter that determines the inkjet printability of polymer solutions.