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We demonstrated that the vertically aligned gold nanorods (AuNRs) were quickly and easily formed by using inkjet printing when aqueous dispersion of AuNRs containing a small amount of ethylene glycol (EG) was employed as an ink. It was observed that the content of EG in water suppressed rapid drying and convection in the droplets, which is favorable for the formation of the nanostructures.

In this study, magnesium oxide (MgO)-templated mesoporous carbon (MgOC) and chitosan cross-linked with genipin (chitosan–genipin) were considered bio-composite inks for screen-printed bioanodes. The fabrication processes were optimized using rheological and structural data, and a bioanode ink containing glucose oxidase (GOx) and 1,2-naphthoquinone (1,2-NQ) was successfully developed. The optimal bioanode-ink contained MgOC pre-treated by washing to achieve a hydrophilic and neutral surface, which helped maintain enzyme activity and resulted in a highly porous electrode structure, which is essential for the accessibility of glucose to GOx. A bioanode fabricated using this ink showed a linear response current dependency up to 8 mM glucose with a sensitivity of 25.83 μA cm−2 mM−1. Combined with a conventional biocathode, an electromotive force of 0.54 V and a maximal power density of 96 μW cm−2 were achieved. These results show that this bio-composite ink can be used to replace the multi-step process of printing with conventional ink followed by drop-casting enzyme and mediator with a one-step printing process.

Disposable temperature sensors have great advantages in public health security and infectious disease control. However, complicated fabrication processes and poor performances persistently restrict their practical applications. In this paper, a flexible temperature sensor is firstly developed by directly writing or mask spraying commonly-used paper with a highly thermo-sensitive graphene nanoribbon (GNR) ink. The inexpensive, green materials and process endow the GNR sensors with the properties of being low cost, degradable and pollution free. The band gap and the local traps of GNRs, caused by the nanoscale effect and oxygen doping, make the sensor highly thermo-sensitive. The sensor also shows fast response, precise resolution and good bendable properties. As demonstrated, the sensor achieves monitoring of respiratory rate, measurement of body temperature, identification of human touch and constituting a 5 × 5 array for temperature mapping. These results demonstrate that the GNRs sensor is highly promising as an economical disposable device for personal healthcare and disease monitoring.

We developed a method to perform direct ink writing (DIW) three-dimensional (3D) printing of milk products at room temperature by changing the rheological properties of the printing ink. 3D printing of food products has been demonstrated by different methods such as selective laser sintering (SLS) and hot-melt extrusion. Methods requiring high temperatures are, however, not suitable to creating 3D models consisting of temperature-sensitive nutrients. Milk is an example of such foods rich in nutrients such as calcium and protein that would be temperature sensitive. Cold-extrusion is an alternative method of 3D printing, but it requires the addition of rheology modifiers and the optimization of the multiple components. To address this limitation, we demonstrated DIW 3D printing of milk by cold-extrusion with a simple formulation of the milk ink. Our method relies on only one milk product (powdered milk). We formulated 70 w/w% milk ink and successfully fabricated complex 3D structures. Extending our method, we demonstrated multi-material printing and created food with various edible materials. Given the versatility of the demonstrated method, we envision that cold extrusion of food inks will be applied in creating nutritious and visually appealing food, with potential applications in formulating foods with various needs for nutrition and materials properties, where food inks could be extruded at room temperature without compromising the nutrients that would be degraded at elevated temperatures.

We fabricated a complementary electrochromic device (ECD) by using water-dispersible nanoparticles (NP) of Prussian blue (PB) and WO3 by using a wet process, which involved just coating. Although the ECD had a thick WO3 film, it showed much higher contrast compared to other techniques. In addition, the ECD also showed fast optical switching speed and high durability over 100 cycles because of wettability control of NP inks.

Smart windows, which control the amount of light entering buildings, houses, and automobiles, are promising in terms of energy conservation and their low environmental impact. Particularly, a next-generation smart window for automobiles will require high optical modulation, along with flexibility to adapt to various intelligent designs. We have previously fabricated electrochromic devices (ECDs) by wet coating glass substrates with nanoparticles (NPs), such as water-dispersive ink containing tungsten oxide (WO3), and Prussian blue (PB), and have evaluated and confirmed the various electrochromic (EC) properties, such as optical modulation, cyclic durability, and colouration efficiency, of the ECDs. However, glass substrates are heavy and difficult to adapt by deformation to meet the demand of next-generation automobiles. In this study, we aim to prepare complementary ECDs by wet coating WO3 and PB thin films on indium tin oxide (ITO)-coated flexible polyethylene terephthalate (PET) substrates. Chromaticity and haze of ECDs were investigated in detail as evaluation indexes to verify specifications for practical use in automotive applications. Repeated switching, bending, and twisting did not degrade the ECD properties, thereby demonstrating its durability and mechanical robustness. These excellent electrochromic properties of the flexible ECDs suggest that they are promising materials for application in next-generation smart windows for automobiles.

A novel and flexible oxygen sensing patch was successfully developed for wearable, industrial, food packaging, pharmaceutical and biomedical applications using a cost-efficient and rapid prototypable additive inkjet print manufacturing process. An oxygen sensitive ink was formulated by dissolving ruthenium dye and ethyl cellulose polymer in ethanol in a 1 : 1 : 98 (w/w/w) ratio. The patch was fabricated by depositing the oxygen sensitive ink on a flexible parchment paper substrate using an inkjet printing process. A maximum absorbance from 430 nm to 480 nm and a fluorescence of 600 nm was observed for the oxygen sensitive ink. The capability of the oxygen sensitive patch was investigated by measuring the fluorescence quenching lifetime of the printed dye for varying oxygen concentration levels. A fluorescence lifetime decay (τ) from ≈4 μs to ≈1.9 μs was calculated for the printed oxygen sensor patch, for oxygen concentrations varying from ≈5 mg L−1 to ≈25 mg L−1. A sensitivity of 0.11 μs mg L−1 and a correlation coefficient of 0.9315 was measured for the printed patches. The results demonstrated the feasibility of employing an inkjet printing process for the rapid prototyping of flexible and moisture resistant oxygen sensitive patches which facilitates a non-invasive method for monitoring oxygen and its concentration levels.

Wearable electrochemical sensors have attracted tremendous attention in recent years. Here, a three-dimensional paper-based microfluidic electrochemical integrated device (3D-PMED) was demonstrated for real-time monitoring of sweat metabolites. The 3D-PMED was fabricated by wax screen-printing patterns on cellulose paper and then folding the pre-patterned paper four times to form five stacked layers: the sweat collector, vertical channel, transverse channel, electrode layer and sweat evaporator. A sweat monitoring device was realized by integrating a screen-printed glucose sensor on polyethylene terephthalate (PET) substrate with the fabricated 3D-PMED. The sweat flow process in 3D-PMED was modelled with red ink to demonstrate the capability of collecting, analyzing and evaporating sweat, due to the capillary action of filter paper and hydrophobicity of wax. The glucose sensor was designed with a high sensitivity (35.7 μA mM−1 cm−2) and low detection limit (5 μM), considering the low concentration of glucose in sweat. An on-body experiment was carried out to validate the practicability of the three-dimensional sweat monitoring device. Such a 3D-PMED can be readily expanded for the simultaneous monitoring of alternative sweat electrolytes and metabolites.

In this work, 1,3,6,8-pyrenesulfonic acid sodium salt (PTSA) was successfully synthesized via a one-step sulfonating reaction. This method is more convenient, effective and eco-friendly than the traditional one. The as-prepared PTSA exhibits pure blue fluorescence under UV light. Due to its excellent fluorescent properties and water solubility, PTSA was used to prepare water-soluble invisible inks based on hydroxyethyl cellulose (HEC) aqueous solution. Notably, the resulting inks possessed acceptable stability after being stored for 30 days. Besides, the red/green/blue fluorescent inks were obtained by adding extra pigments, all of which exhibited excellent rheology and thixotropy properties. Subsequently, various patterns, including a QR code, the logo of Wuhan University, Chinese characters and so on, were printed on non-background paper through ink-jet and screen printing, and the as-prepared materials exhibited good water solubility and outstanding fluorescence performances, indicating that the fluorescent PTSA material is a promising candidate for anti-counterfeiting applications.

In the history of civilization, Xuan paper with its superior texture, durability and suitable characteristics for writing and painting, has played an important role in the dissemination of culture and art. Xuan paper has won the reputation of "the king of paper that lasts for 1000 years" and was inscribed on the Representative List of the Intangible Cultural Heritage of Humanity by the Educational, Scientific and Cultural Organization of the United Nations in 2009. However, the surface of the commercial unprocessed Xuan paper has a large number of large-sized pores with a poor resistance to water, allowing ink droplets to easily spread during the writing and painting process. In this study, we report a new kind of nanocomposite Xuan (HNXP) paper comprising ultralong hydroxyapatite (HAP) nanowires and plant cellulose fibers with unique ink wetting performance, high whiteness and excellent durability. The as-prepared HNXP paper sheets with various weight ratios of ultralong HAP nanowires ranging from 10% to 100% are all superhydrophilic with a water contact angle of zero. In contrast, the ink contact angle of the HNXP paper can be well controlled by adjusting the weight ratio of ultralong HAP nanowires, and the ink contact angle of the HNXP paper increases with increasing weight ratio of ultralong HAP nanowires. The experimental results show the unique ink wetting behavior of the as-prepared HNXP paper, which is absent in the traditional Xuan paper. This new kind of nanocomposite Xuan paper comprising ultralong hydroxyapatite nanowires and plant cellulose fibers is promising for applications in calligraphy and painting arts.

We demonstrate black conductive ink (BCI) that is writable and paintable on traditional handmade Korean paper (Hanji) for application as a high performing electrode. By optimal mixing of Ag nanowire (Ag NW) suspension and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) solution in standard charcoal-based blank ink, we synthesized BCI suitable for writing and painting on Hanji with a normal paintbrush. Due to the shear stress induced by the paintbrush bristles, the Ag NW and PEDOT:PSS mixture was uniformly coated on the porous cellulose structure of Hanji and showed a low sheet resistance of 11.7 Ohm per square even after repeated brush strokes. Moreover, the brush-painted electrodes on Hanji showed a constant resistance during tests of inner/outer bending and folding due to the outstanding flexibility of the Ag NW and PEDOT:PSS mixture that filled the porous cellulose structure of Hanji. Therefore, the pictures drawn in the BCI on Hanji exhibited a level of flexibility and conductivity sufficiently high to enable the BCI to function as an effective electrode even when the paper substrate is wrinkled or crumpled. The successful operation of the paintable interconnector and heater on Hanji indicates the high potential of the brush-painted electrodes that can be used in various social and cultural fields, including fine art, fashion, interior design, architecture, and heating industry.

In this study, the effect of the thickness of a copper oxide-shell on flash light sintering of Cu nanoparticles (NPs) was investigated. The electrical properties of Cu nano-ink films with various oxide-shell thicknesses were examined by measuring the sheet resistance. Furthermore, the amount of PVP in the Cu NP-ink was varied to reduce the copper oxide-shell efficiently and enhance the flash light sintering of the Cu NPs. Also, to investigate the reduction and sintering phenomena of Cu NPs with respect to the copper oxide shell thickness, the sheet resistances of the Cu films were measured in real-time using an in situ resistance measuring system during the flash light sintering process. The results of this study established the maximum allowable thickness of the copper oxide shell that allows flash light sintering and also provided the optimal amount of PVP in Cu nano-ink for a particular copper oxide shell thickness.

The reactive pigment composite particles were fabricated by a two-step method. Phthalocyanine Blue (PB) was encapsulated with silica through a Sol–Gel method in the first step, and the encapsulation conditions were optimized. 3-(Trimethoxysilyl)propyl methacrylate was then grafted onto the silica encapsulated organic pigment (EPB) in the second step, and the FT-IR analysis indicated that the relevant functional groups had been introduced onto the EPB. The particle size, hydrophilicity and the color characteristics of the Reactive Phthalocyanine Blue (RPB) changed little in comparison with PB. The photo-polymerization performance of the RPB-based ink showed a certain increase, and the fastness toward crocking of the printed fabrics was coordinately improved.

In this study, we report a large-scale and facile synthetic method for silver nanoparticles via a microwave method, which is quite time-saving and efficient. The obtained silver nanoparticles maintained a uniform size, and the average size was less than 20 nm although the concentration of the silver source was very high. The obtained silver nanoparticles could be homogeneously dispersed in deionized water, which was beneficial for the fabrication of the conductive ink. For large-scale industrialization, the synthetic process window was widened to a great extent via a series of experiments. We injected the ink into a blank mark pen to fabricate a conductive pen, via which the tracks drawn on the photo paper could immediately become conductive at room temperature with an electrical conductivity of 2.4 μΩ cm (about 1.5 times that of the bulk Ag). The mechanical properties of the tracks were examined for a twistable application. After bending at a radius of 4 mm and 2 mm for 5000 circles, only a slight increase in their resistance of 1.20 and 1.78 relative to their initial resistance, respectively, was observed. The as-prepared conductive ink and fabricated pen have potential applications in flexible electronics.

Development of oxidation resistant conductive inks with low curing temperatures is a challenging problem in printed electronics. The present work introduces a newly formulated room temperature curable conducting ink using multiwalled carbon nanotubes (MWCNTs) for printable electronic application. The organic vehicle composition of the ink is meticulously controlled based on their rheological characteristics. The ink was screen printed on different flexible substrates like paper, Mylar®, photopaper, cellulose acetate sheets and silicone rubber. A morphological study of the printed pattern was also performed using SEM and AFM. The electrical characterization of the ink printed on flexible substrates was studied and a sheet resistance of 0.5–13 Ω sq−1 for three strokes was reported.

Developing printed optoelectronic devices based on metal oxide inks requires synthesizing stable suspensions of the desired materials. In this work, pure and manganese doped zinc oxide inks were synthesized by a top-down wet milling route and the role of solvent in ink stabilization and printing was analyzed. Fluid properties of the as-prepared inks were measured and used for studying jettability criteria for inkjet printing. Among the various solvents evaluated, ethylene glycol produced stable oxide inks and satisfied the jetting conditions. The inks were evaluated using a commercial drop-on-demand piezoelectric inkjet printer. The morphology of the patterns printed on glass substrates, for various ink volumes, was investigated and was found to be continuous and showed good optical transmittance. We also investigated the particle segregation in these inks using a custom built direct writing system. This top-down approach, by separating the material development and ink synthesis, can be extended to a variety of metal oxide based inks.

The transfer of bio-functionality from natural living organisms to stable engineered environments opens a wide horizon of applications. Our work focusses on the creation of materials and devices that transform bio traits and collect, process and act on the information in response to changes in their local environment, thus promoting additive manufacturing from 3D space to a four-dimensional, functional space. In this work we have expanded the set of tools enabling the incorporation of biological function as an intrinsic property in the devices we print with a new class of light curable bio nano ink. This novel approach allows the 3D printing of acrylic polymer compositions containing biological materials, especially, membrane proteins using a photo (407 nm) curing stereolithography (SLA)/digital light processing (DLP) 3D printer. Retaining the bio functionality of these proteins gives a fourth dimensional (4D) aspect to this construct. Herein, we report the 4D printing of a bio-inspired nano hybrid electrode for water-splitting applications using a polymeric resin with proton-pumping bacteriorhodopsin (bR), silver nanoparticles (Ag NP) and carbon nanotubes (CNT). These printed photo electrochemical cells exhibit high durability, low onset over potential, and upon light irradiation (535 nm) produces hydrogen by a synergistic effect of Ag NP and bR.

In this study, a printable GO ink was prepared by dispersing 120 mg GO in 30 ml mixed solvents (deionized water : ethanol : ethylene glycol = 1 : 1 : 1). The prepared ink was inkjet-printed onto the flexible substrate PET. Printed patterns were reduced with intense pulsed light (IPL) without damaging the substrate PET. By adjusting the distance between the intense light and the patterns and number of pulses in a given time, patterns with low resistance and good flexibility were achieved. Upon printing 20 passes, the resistance decreased from 56.77 MΩ for the patterns before IPL treatment to 760.4 Ω for the patterns after IPL treatment. It was lowered by nearly four orders of magnitude. It was proved that IPL reduction on the GO ink could be used as an effective method for the synthesis of flexible electronics such as sensors.

There is an increasing interest on robust electrically conductive textiles with light weight and flexibility to meet the applications in wearable electronics. Current challenge is to fabricate such structures with feasible application strategies that can be readily scalable and provide higher mechanical stability of the conductive media on the textile matrix to withstand constant stretch and shear forces. We report a strategy to address these challenges, by using a “screen printing process” employing conductive carbon black ink. We produced conductive fabrics with liner resistance of less than 71 Ω cm−1. These textile materials showed stable conductivity up to 25% strain. Microscopic studies revealed that at strains lower than 25%, percolation pathways in the conductive media increases resulting lowering of the liner resistance. However, further stretching of over 25% resulted increase of resistance due to separation of conductive pathways. Ohmic heating application of the resulted fabrics showed fast response rate and no significant hysteresis. The conductive print was stable over long period of heating over number of cycles. These feasible conductive fabric fabrication pathways can provide new avenues in designing and manufacturing of wearable heat management and electronic applications.

Direct writing deposition of energetic materials has been an area of interest for fuzing applications, novel initiation/booster trains, and for studying small scale detonations. Herein, we present a simple and efficient strategy to fabricate a high explosive ink formulation with good stability as well as excellent performance. Sub-micro CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) was prepared by the ball milling method and then mixed with an energetic binder consisting of GAP (glycidyl azide polymer binder) and N100 (polyisocyanate). The emulation curing process of GAP and N100 was illustrated by FT-IR spectra. Sub-micro CL-20 based ink shows wettability and good uniformity without cracks, porosity and voids. Moreover, the printed sample has lower sensitivity for impact heat stability than pure CL-20. A directly deposited sample in small grooves can provide steady detonation at a size of under 0.4 × 0.4 mm.

Quaternary Cu2ZnSnS4 (CZTS) thin films were prepared by a low-cost, simple and environmentally-friendly ink method. By depositing molecular solution on the nanoparticle thin film, the quality of as-prepared CZTS thin films was greatly improved (e.g. reduction of fine grain layer formation and improved crystallinity). The effect of the number of spin-coated layers from molecular solution on solar cell performance was investigated. The results indicated that the CZTS thin film had the best performance when 5 layers were spin-coated from molecular solution on the nanoparticle thin film. The crystallinity of the as-prepared CZTS thin film and the interface at Mo/CZTS was found to be obviously enhanced by addition of a molecular solution layer. Finally, a CZTS thin film solar cell with an efficiency of 4.92% has been fabricated.

Cu–Ag-based highly conductive patterns were drawn directly on a flexible substrate using a roller pen filled with Cu–Ag NPs ink. The particle packing density is important for the pattern's conductivity. First, the addition of smaller Cu NPs (∼6.5 nm) between the larger Ag particles (∼16.5 nm) improves the particle packing density by filling the pores, which can help improve conductivity at lower temperatures. Furthermore, combination of temperature and stress by hot sintering & hot-pressure sintering makes the residual pore space decrease and improves the conductivity of the patterns. Finally, compared to bulk Cu wire (1.72 μΩ cm), the resistivity of the Cu–Ag patterns sintered at 160 °C is reduced to 6.2 ± 0.4 μΩ cm, which is acceptable for conductive patterns. Samples with a decorative logo drawn by the Cu–Ag NPs exhibited excellent conductive performance and mechanical integrity.

We describe in detail a process for generating three-dimensional patterns of microbes on an optimum substrate in such a way that the patterns are amenable for engineering applications. Further, we demonstrate approaches that make it possible to use the three-dimensional microbial patterns for applications outside the realm of the life sciences. Specifically, the microbes are normally grown on a gel media. In order to separate the grown patterns from the gel, we have introduced a permeable membrane. These membranes provide support for the growth of microbial colonies and allow them to be used in other applications. Among the membranes, a polyvinylidene fluoride membrane could be made suitable after its surface treatment to promote microbe adherence. We demonstrate two approaches for generating the required patterns. In both cases, a two dimensional pattern of an ink is dispensed on the membrane kept on the media. The subsequent growth of microbes is used to acquire the three dimensional pattern. The two proposed approaches are a microbial approach and an antimicrobial approach. In the former, baker's yeast, which was found to be the most suitable among the microbes tested, is dispensed in an ink form on selected locations on a PVDF membrane. The same pattern evolves upon growth. In the antimicrobial approach, the PVDF membrane is fully coated with yeast ink and iso-amyl alcohol as growth inhibitor is dispensed in a pattern. After growth of the yeast, the pattern evolved is the negative of the dispensed pattern. The fabricated patterns are proposed to be used in applications such as stamps for printing micro-electronics, microlenses, microfluidics and for direct use in braille printing. A polydimethyl siloxane stamp fabricated using a grown yeast pattern for micro-contact printing is also demonstrated.

In this study, 7-(4-vinylbenzyloxyl)-4-methylcoumarin (VM) and maleic anhydride (MA) were polymerized through free radical copolymerization to form a photosensitive alternating copolymer P(VM-alt-MA) (PVMA). PVMA was used as a soft template to achieve the oxidative polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT). We obtained a stable PEDOT:PVMA photosensitive aqueous dispersion with an average diameter in the range of 140 to 210 nm. We then used this aqueous dispersion as the ink for fabricating humidity sensors through inkjet-printing on a paper substrate. The printed photosensitive conductive film PEDOT:PVMA could be cross-linked after photo-dimerisation of coumarin groups, leading to a small decrease of electrical conductivity, but also appreciable improvements in water resistance and sensor robustness. The humidity sensing ability of these PEDOT:PVMA/paper sensors was investigated by exposing them to a wide range of relative humidity, namely 11–97% at room temperature. These paper sensors could selectively and reversibly detect water vapor with a significant linear relationship. The response strength and the response/recovery time of the sensors show a substantial improvement compared with those of previous reports. The photo-dimerisation of PEDOT:PVMA improves the stability of humidity response and the response/recovery time of the sensors.

The recent trend toward the Internet of Things (IoT) has increased the importance of technologies for the mass production of high-sensitivity flexible antennas for efficient wireless communication. Here, we describe the rapid low-temperature fabrication of high-sensitivity flexible antennas based on hot-water sintering of silver (Ag) precursor-based ink. Ag precursor-based ink was printed on various flexible substrates such as plastic films and cellulose nanofiber paper, followed by pre-drying the ink solvent and then treatment at 80 °C and 95% relative humidity for 2 min. The resulting printed Ag lines achieved a volume resistivity of approximately 6 μΩ cm, providing excellent sensitivity as dipole antennas for wireless communication. This technique enables the mass production of printed high-sensitivity antennas, which will likely be required for a future IoT society.

The use of conductive inks and direct writing techniques for the fabrication of electronic circuits on complex substrates is attracting ever increasing interest. However, the existing knowledge is only focused on the electrical performances of the produced smart objects with no direct correlation with the conductive paths morphology and printing conditions. In order to evaluate the printing quality of a direct writing process using an eccentric screw dispenser, a printing device for the deposition of silver paste on 3D objects was developed. Lines of different widths were printed on flat PC + ABS substrates by means of the developed printing device and a conventional screen printing process. The developed process permitted printing lines as thin as possible with screen printing but with a better regularity of their edges. However unlike screen printed lines, the thickness of the lines was dependent on their width. Finally, the possibility to print on 3D objects was demonstrated.

Surface-enhanced Raman spectroscopy (SERS) has been identified as a suitable technique for the analysis of colorants in works of art. Herein, the application of SERS to the identification of dye compositions in historical felt-tip pens is reported, which is of paramount importance for the development of appropriate conservation protocols for historical drawings. In this study, three pens (pink, green, and blue colors) belonging to the film director Federico Fellini were analyzed. SERS measurements were performed directly on the pen lines drawn on a commercial paper by the deposition of Ag colloidal pastes, which allowed fast in situ dye identification without the need for extraction or hydrolysis treatments. Eosin Y was identified as the only dye present in the pink pen ink, whereas erioglaucine was found to be the main dye component in green and blue pen inks. SERS also resulted in highly efficient identification of the individual dyes erioglaucine, crystal violet, and rhodamine present as a mixture in the blue pen ink. The high SERS sensitivity was ascribed to the plasmonic effects and efficient quenching of the fluorescence interference of dyes. A comparison with contemporary pen inks highlighted minor differences in the chemical composition. These results prove that SERS can be used as a fast and sensitive analytical tool for ink analysis that provides invaluable support for the general assessment of the date, provenance, and originality of the historical drawings as well as for the development of preventive conservation protocols.

Desktop inkjet printers are ubiquitous and relatively inexpensive among the variety of available printers. These inkjet printers use an array of micro fluidic pumps, nozzles based on piezoelectric actuation, to dispense individual picoliter volume ink droplets at high speed. In this paper, we show that individual pumps in desktop printers can be accessed to dispense droplets on demand. Access was obtained using the printer’s command language programming. A detailed description of the access procedure is discussed. Droplets were printed on a paper as it rolled underneath the printhead, and with a minor hardware modification, they were also printed on a glass substrate. With this access, individual droplets were deposited, the smallest having an average diameter of 62 μm with a standard deviation of 6.9 μm, with a volume of ∼4 pL. From the intended position, the droplets had a standard deviation of 5.4 μm and 8.4 μm in the vertical and horizontal directions, respectively. The ink droplets were dispensed at a rate of 7.1 kHz. A circularity factor of 0.86 was obtained indicating that the dispensed droplets are of good quality. By replacing the ink in the cartridges with liquids of choice (e.g. cells, proteins, nanoparticles etc.), we believe it provides an opportunity for low-cost, high-speed, high-precision, picoliter volume printing for a variety of applications.

The creation of a suitable inorganic photocatalyst for use in a scalable coating process is a key step in the development of practical photocatalysis. Herein, we present the deterministic synthesis of mixed-phase Fe2O3/ZnO hollow spheres with submicron pores and demonstrate that ink based on these hollow spheres can be used to manufacture stable photocatalytic papers. The hollow spheres are formed through the self-organization of well crystallized Fe2O3 and ZnO nanoparticles, and they are different from traditional hollow spheres in their innovative submicron pores (width ∼ 500 nm). This morphological feature makes the interior and exterior of the hollow spheres readily accessible and enables them to enrich either small or large pollutants rapidly, as visually determined by the adsorption of the fluorescent molecules and nanoparticles. Moreover, the intimate contact of the wide bandgap ZnO to the narrow bandgap Fe2O3 within the hollow spheres leads to the extension of the light-collection range (spanning the full ultraviolet-visible wavelength) and the emergence of the mixed-phase effects (e.g., enhanced charge separation and transfer). As a conceptual demonstration of the target application of the Fe2O3/ZnO hollow spheres as an ink, we manufacture the photocatalytic paper by the spraying method. The hollow spheres show a perfect geometric match to the cellulose networks within the paper due to the similar dimensions. The tests of the performances of the photocatalytic paper demonstrate that it can efficiently degrade 2,4,6-trichlorophenol (TCP) under the irradiation of the solar light, with a first order rate constant of 0.014 min−1. After ten recycles of the TCP photodegradation, the photocatalytic paper retains constant activity, proving its high stability and durability. As a whole, the photocatalytic paper can be more readily recycled than conventional powder photocatalysts, and should be promising for various environmental applications, including water and air purification.

Self-folding represents an attractive way to convert two-dimensional (2D) material sheets into three-dimensional (3D) objects in a hands-free manner. This paper demonstrates a simple approach to self-fold thin pre-strained polystyrene (PS) sheets using microwaves. While the PS sheets are transparent to microwaves, patterns of screen-printed ink containing graphene absorb microwaves and cause the underlying printed sections of the sheet to warm up. When the local temperature in the inked region exceeds the glass transition temperature of PS (∼103 °C), the strain in the inked regions of the film relaxes gradually across the sheet thickness, which causes the PS sheet to fold. The resulting dihedral angle is proportional to the width of the hinge printed by graphene ink. The geometry and azimuthal orientation of the sample inside the microwave reactor affect the quality of the folding due to the non-uniformity of the microwave energy inside the reactor. While self-folding has previously utilized heat, light, photo-chemistry, and solvent swelling, this paper reports the use of microwaves, which can deliver large amounts of energy remotely.

In this letter, customized protein-based micro/nano-wires with diameters of ≥150 nm have been facilely fabricated from bovine serum albumin (BSA) aqueous ink by maskless and noncontact femtosecond laser direct writing (FsLDW) technology. With the reproducible optimized morphology, the protein-based micro/nano-wires here can be applied as optical micro/nano-waveguides with transmission loss of ∼0.059 dB μm−1 for 633 nm light. Based on the nature of as-formed protein micro/nano-hydrogels (stimuli-responsive shrinking or swelling), their “smart” environmental stimuli (e.g., pH) responsive features are proved experimentally (∼50% output light decrease corresponding to pH value tunning range of ∼0.4).

Thermally cross-linkable poly(methylsilsesquioxane) (PMSQ) has been investigated as a printable dielectric ink to make the gate insulator for solution processed metal oxide (IGZO) thin-film transistors by aerosol jet printing. It was found that by increasing the curing temperature from 150 to 200 °C, the dielectric constant and loss tangent of the printed PMSQ layer reduces dramatically. The mobility, leakage current and gate current of the PMSQ enabled thin-film transistor reduces accordingly, while the on/off ratio increases with the increase of curing temperature. An interfacial layer was introduced to further improve the on/off ratio to 3 × 105 and reduce the leakage current to 2.6 × 10−10 A, which is the best result for the solution processed IGZO thin-film transistors using the PMSQ as the gate insulator at a curing temperature of only 150 °C. The study has demonstrated the feasibility of fabricating IGZO thin-film transistors by an all solution-based process.

A printed aluminum cathode with low sintering temperature has been achieved using an aluminum precursor ink, AlH3·O(C3H7)2, which in the presence of a TiCl4 catalyst can be printed to give the required pattern and then sintered at 80 °C for 30 s to form an Al film. The Al cathode of 50 nm thickness has a sheet resistance of 2.09 Ω □−1 and work function of 3.67 eV. The study demonstrates that the low sintering temperature and work function of the printed film, together with its high conductivity and stability, mean that it is well suited for use as an OLED cathode and that it paves the way for fully printed flexible devices.

A novel porous adhesion material for digital inkjet printing with absorbency for eco-solvent ink and removable adhesion has been successfully prepared by a simple, robust and cost-effective method. There was no traditional emulsifier with low molecular weight adopted in the poly(n-butyl acrylates) emulsion for the preparation of the porous material. Due to the properties of this reactive emulsifier, there was no free emulsifier left after the polymerization, thereby reducing the drawbacks associated with traditional emulsifiers. The porous material possesses high shear strength, moderate peel strength and low tack properties suitable for adhesion and could be removable many times, which offered a new method for recycling. Since the novel porous material can be utilized many times and have potential for recycling, we believe that this material would be environmentally friendly. Additionally, the absorbency of the eco-solvent ink created a suitable platform for digital inkjet printing based on the novel porous material, with resistance to different atmospheres, like acid, base, oxidant, and many organic solvents.

We described a low-cost method for rapid prototyping of a microfluidic paper-based analytical device by inkjet printing of permanent marker ink. After the evaporation of ink solvent is printed onto the paper, hydrophobic resin remains and forms hydrophobic barriers for microfluidic flow and analysis.

In this study, a convenient and facile direct printing method is developed to fabricate patterned silver nanowire (AgNW) thin films. An aqueous silver nanowire (AgNW) ink was first formulated and inkjet printed on flexible substrates with precisely controlled AgNW density per unit area. With a mesh grid structure, the printed heater showed high electrical conductivity and transparency up to 90%. From infrared thermography, a steady-state temperature up to 100 °C was observed uniformly over the printed mesh grid heater with only 4 volts of applied voltage. With precise control on local resistances via AgNW density variation, a gradient heater was designed and printed directly to provide a temperature gradient of up to 10 °C cm−1. When printed on thin polyethylene terephthalate (PET) sheets, the printed heater can have a fast response time within 3 s due to the thermal insulating nature of PET. The printed heaters on PET also showed great mechanical stability and the resistances remained almost the same after 1000 bending cycles.

Self-propelling microjets with multimodal chemical and magnetic controls for motion were prepared from printed waste papers coated with MnO2 nanoparticles. Because the magnetic remote control was infused from the ferromagnetic coating of the printer ink, the nanoparticles decomposed peroxide fuel to induce locomotion by ejecting oxygen bubbles through a microjet. The paper microjets could be loaded with fluorescent rhodamine 6G (R6G), a model payload, before being remotely guided through an external magnetic field inside a fluidic environment. The reported methodology provides an economic, scalable, and biodegradable scheme for the design and development of bubble-propelled microengines, which are capable of directed locomotion.

Microfluidic technology has provided innovative solutions to numerous problems, but the cost of designing and fabricating microfluidic channels is impeding its expansion. In this work, Shrinky-Dink thermoplastic sheets are used to create multilayered complex templates for microfluidic channels. We used inkjet and laserjet printers to raise a predetermined microchannel geometry by depositing several layers of ink for each feature consecutively. We achieved feature heights over 100 μm, which were measured and compared with surface profilometry. Templates closest to the target geometry were then used to create microfluidic devices from soft-lithography with the molds as a template. These microfluidic devices were in turn used to fabricate polymer microfibers using the microfluidic focusing approach to demonstrate the potential that this process has for microfluidic applications. Finally, an economic analysis was conducted to compare the price of common microfluidic template manufacturing methods. We showed that multilayer microchannels can be created significantly quicker and cheaper than current methods for design prototyping and point-of-care applications in the biomedical area.

Pioneering products in wearable technologies, such as Apple Watch, Google Glass or Nike smart sneakers, are leading a new trend in electronic devices. However, the fast developing field of wearable electronics urgently demands lightweight and flexible/bendable energy supplying devices. Here, we present thin, lightweight and flexible dye-sensitized solar cells (DSSCs) using three different kinds of TiO2 nanostructures grown on Ti meshes as photoanodes. The flexible DSSCs based on hierarchical anatase TiO2 nanowire arrays exhibit a higher power conversion efficiency (1.76%) than those based on TiO2 nanotube arrays (1.52%) or TiO2 nanowire arrays (0.85%). This enhancement can be attributed to (1) the large surface area and (2) the low recombination rate of electrons and the redox electrolyte. Moreover, commercial ink has been identified as a promising alternative to fabricate a flexible counter electrode and the corresponding DSSCs achieve a considerable conversion efficiency of 1.59%. The as-fabricated mesh based DSSC retains 88% of its PCE after bending for 300 cycles, demonstrating its good flexibility and fatigue resistance. In addition, the as-fabricated sealed DSSCs have been integrated to light LEDs, which demonstrates that our flexible DSSCs are promising candidates for wearable/flexible energy supplying devices in everyday applications.

A biodegradable polyvinyl alcohol and silver nanowires (AgNWs) have been mixed together with a simple one-step blending method to form a hybrid electrical compositor. Super flexible and highly conductive electrical compositors were successfully developed with an AgNWs content of 80%, in which hundreds, even thousands of AgNWs stacked into a “Chrysanthemum petal” order to exhibit high electrical conductivity of 17 390 S cm−1. The high conductivity corresponded to the formation of a large amount of electrically conductive networks and channels. The conductively electrical compositor can be made into various shapes and can be used on any substrate with different curved surfaces because the compositor ink is so stable and can be stored for a long time without other additives. The compositor is expected to have great potential application in flexible electronics, especially in those fields associated with biology, medicine, food, and life.

We developed a method for direct imprinting of thermally reduced Ag nanoparticles via deformation-driven ink injection to yield high-performance metal grid transparent conductors (TCs). A grid patterned mold was created to have a macroscale cavity by designing a “reservoir” that captured outgoing ink and injected the captured ink into the grid patterned mold cavity by a roof deformation. The ink supply from the reservoir contributed to not only improving the ink filling, but also decreasing the linewidth of the grid patterned mold cavity due to a sidewall deformation on the liquid film. The metal grid TCs fabricated using the reservoir-assisted mold performed better than the metal grids prepared using the typical mold in terms of the sheet resistance (4.7 vs. 12.6 Ω sq−1) and transmittance at 550 nm (93.5 vs. 90.7%), respectively. The metal grid TCs were embedded into large-scale, flexible, and transparent films, which showed a reasonable electromechanical stability under repeated bending. The metal grid embedded TCs were fabricated for application in touch screen panels. Our approach provides a new route for fabrication of high-performance, solution-processed micro/nanoscale metal grid TCs and hybrid TCs based on Ag nanowires, graphene, or carbon nanotubes for use in a variety of next-generation flexible optoelectronic devices.

A robust and simple strategy of microcontact printing is provided to fabricate micro-patterned polydopamine (PDA) films with tunable morphology achieved by altering the concentration of PDA “ink” solution. Photoactive sites on the surface of patterned PDA films allow the further growth of polymer brushes by self-initiated photografting and photopolymerization (SIPGP) endowing the bio-inspired PDA films with various functionalities.

A low-cost and Mo(S,Se)2-free superstrate-type device structure is reported for the first time with the tunable band gap Cu2ZnSn(S1−xSex)4 nanocrystals. Using a facile hot-injection approach with only oleylamine reagent for synthesizing Cu2ZnSn(S1−xSex)4 nanocrystals with varied Se to (S + Se) ratio, the role of Se in Cu2ZnSn(S1−xSex)4 nanocrystals during the sulfurization step is systematically investigated. The loss of Sn is suppressed and the grain size is enlarged when the Se in Cu2ZnSn(S1−xSex)4 nanocrystals is replaced by S during the sulfurization. As a proof-of-concept, our superstrate-type architecture without using any binder in the ink exhibits Voc and FF comparable to the typical substrate-type device structure, in addition to its advantage of low cost.

This paper describes a new method for the fabrication of microfluidic paper-based analytical devices (μPADs) by inkjet printing alone. Microfluidic structures are patterned within less than 5 min on the surface of untreated filter paper by printing a hydrophobic UV curable acrylate composition made of non-volatile and not readily flammable compounds. After ink penetration into the paper and UV curing for 60 s, hydrophobic barriers are formed. Microfluidic channels as narrow as 272 ± 19 μm are achieved. Printed patterns retain their aqueous liquid guiding functionality for at least 6 months when stored at room temperature and for at least 72 h at 50 °C. Printing a thin uniform film on the top of the paper allows the creation of protective layers, resulting in “tunnel-like” sections of microfluidic channels entirely surrounded by inkjet printed hydrophobic barriers. Finally, the same inkjet printer is used to print reagents necessary for colorimetric sensing, which is demonstrated in the example of an enzymatic H2O2 sensor. The detection limit of the μPAD for aqueous H2O2 is 14.4 μM when applying colorimetric data processing. The only equipment required for the entire μPAD fabrication process is an off-the-shelf inkjet printer and a UV light source. This is the first application of standard printing technology for the fully integrated fabrication (microfluidic pattern, back cover, variable pattern depth, enclosed microfluidic structures, biosensor) of entire μPADs.

The optimisation of vapour-grown carbon nanofibres (VGCNFs) dispersed in the biopolymer gellan gum (GG) and its usage as an ink for the direct writing of conducting networks are reported. Sonication optimisation showed that dispersing 10 mg per mL VGCNFs required 3 mg per mL GG solution and 4 minutes of low energy probe sonication. Free-standing films prepared by evaporative casting were found to exhibit electrical conductivity values of up to 35 ± 2 S cm−1. It is demonstrated that sonolysis has a detrimental effect on electrical conductivity. The dispersions were easily modified to allow for direct writing of conducting networks on paper using a commercial fountain pen. The electrical characteristics of these direct written electrodes (on paper) improved with increasing number of layers. The written electrodes on paper were used to connect a battery to a light emitting diode to demonstrate that they can be used in simple devices.

Low concentrations of metallic nanoparticle inks often produce a coffee-ring effect, thereby resulting in high electrical resistance in inkjet-printed lines. The coffee-ring effect is due to a convection flow of ink droplets and can be overcome by reducing the flow. Here we report the formation of absorption layers of ink vehicles on pristine polyimide films and fabrication of convex-shaped lines without the coffee-ring effect even if a low concentration of commercially available ink is used. The coated layers increased the ink concentration and prevented a convection flow of ink droplets. As a result, the electrical resistance of the inkjet-printed lines on polymer-coated polyimide films (8 Ω) was improved threefold over that of lines printed on pristine polyimide films (24 Ω). This is a similar improvement to inkjet-printed lines that were heated gradually (7 Ω), which is one of the methods that can reduce convection flow. Durability tests were conducted and electrical resistance was measured on inkjet-printed lines on polymer-coated polyimide films. Even under harsh environments, the lines showed excellent electrical performance, and they can easily be integrated into practical applications.

A detailed analysis of microcontact printing on different sized silica particles using polyelectrolyte ink is presented including controlled patch geometries., This publication demonstrates the abilities of a precise and straightforward microcontact printing approach for the preparation of patchy silica particles. In a broad particle size range, it is possible to finely tune the number and parameters of three-dimensional patches like diameter and thickness using only polyethyleneimine ink, poly(dimethoxysilane) as stamp material and a suitable release solvent.

Health concerns as a result of harmful UV-rays drive the development of UV-sensors of different kinds. In this research, a UV-responsive smart textile is produced by inkjet printing and UV-LED curing of a specifically designed photochromic ink on PET fabric. This paper focuses on tuning and characterizing the colour performance of a photochromic dye embedded in a UV-curable ink resin. The influence of industrial fabrication parameters on the crosslinking density of the UV-resin and hence on the colour kinetics is investigated. A lower crosslinking density of the UV-resin increases the kinetic switching speed of the photochromic dye molecules upon isomerization. By introducing an extended kinetic model, which defines rate constants kcolouration, kdecay and kdecolouration, the colour performance of photochromic textiles can be predicted. Fabrication parameters present a flexible and fast alternative to polymer conjugation to control kinetics of photochromic dyes in a resin. In particular, industrial fabrication parameters during printing and curing of the photochromic ink are used to set the colour yield, colouration/decolouration rates and the durability, which are important characteristics towards the development of a UV-sensor for smart textile applications.

Earth abundant Cu2ZnSnS4 nanoparticle inks were deposited on molybdenum foil substrates and subsequently converted to high quality thin film Cu2ZnSn(S,Se)4 photovoltaic absorbers. Integration of these absorbers within a thin film solar cell device structure yields a solar energy conversion efficiency which is comparable to identical devices processed on rigid glass substrates. Importantly, this is only achieved when a thin layer of molybdenum is first applied directly to the foil. The layer limits the formation of a thick Mo(S,Se)x layer resulting in a substantially reduced series resistance.

The performance of polymer electrolyte fuel cells decisively depends on the structure and processes in membrane electrode assemblies and their components, particularly the catalyst layers. The structural building blocks of catalyst layers are formed during the processing and application of catalyst inks. Accelerating the structural characterization at the ink stage is thus crucial to expedite further advances in catalyst layer design and fabrication. In this context, deep learning algorithms based on deep convolutional neural networks (ConvNets) can automate the processing of the complex and multi-scale structural features of ink imaging data. This article presents the first application of ConvNets for the high throughput screening of transmission electron microscopy images at the ink stage. Results indicate the importance of model pre-training and data augmentation that works on multiple scales in training robust and accurate classification pipelines.