We demonstrate the fabrication, by exclusive means of inkjet-printing, of capacitive relative humidity sensors on flexible, plastic substrate. These sensors can be successfully used for the measurement of relative-humidity in both air and common soil. We also show that the same technique may be used for the fabrication of the same type of sensors on the surface of the leaves of Elægnus Ebbingei (silverberry).Our results demonstrate the suitability of leaves as substrate for printed electronics and pave the way to the next generation of sensors to be used in fields such as agriculture and flower farming.

We summarize the advantages and disadvantages of some of the most commonly used bioinks. We have probed the mechanical and cytotoxicity properties of Cellink and designed our own bioink from gelatin and Xanthan gum.

Age-related macular degeneration (AMD), a retinal degenerative disease that results in a continuous degeneration of photoreceptors in the retina, which eventually leads to complete blindness. One approach to combat AMD is through the use of artificially implantable photodetectors that are physically placed on the retina. Interestingly, 2D materials such as photosensitive and semiconducting molybdenum disulfide (MoS2) and electrically conducting graphene have recently received tremendous promise due to their unique photonic and optoelectronic properties and their potential in various types of micro and nano-devices. In this study, a highly biocompatible 2D graphene-MoS2 photodetectors on a flexible polyimide substrate were designed, fabricated using inkjet printing to form photosensitive pixels and tested as a function of photo intensity and strain. The inkjet printed 2D heterostructure devices were photoresponsive and the photocurrent scaled proportionally with the incident light intensity, exhibiting a photoresponsivity R ∼ 0.30 A/W at room temperature. The strain-dependent measurements of photocurrent with bending showed a photocurrent of Iph ∼ 1.16 μA with strain levels for curvature up to ∼ 0.262 cm-1. Inkjet printed graphene and MoS2 inks were also characterized using techniques such as Raman Spectroscopy, Photoluminescence (PL) and Scanning Electron Microscopy (SEM).

In this paper, we will discuss stability and reliability requirements of organic electronic devices and evaluate different encapsulation approaches enabling stable organic ultra-thin and stretchable devices. We highlight the differences in requirements and encapsulation approaches for applications, including organic light emitting diode (OLED) displays, OLED lighting, photovoltaics, and sensors. Stability and reliability requirements addressed in this paper cover light management, mechanical characteristics, chemical compatibility, form factors, and durability. While flexible organic electronic devices have already been demonstrated and commercialized, so far only prototypes of ultra-thin and stretchable devices have been demonstrated. The technological progress is promising and by identifying the gaps between prototyping and product realization, we intend to stimulate further research and development in this area.

In this work, a printable tungsten disulfide (WS2) based ink is developed from readily available WS2 powder (0.6 µm average particle size), and an ink-jet printing based deposition method for a tungsten disulfide film is presented. WS2 flake coverage and bulk electrical characteristics under three different irradiance conditions are examined and discussed. Presence of excitons in the absorbance of the inks is performed by optical UV-Vis spectrometry. Metrics using the A exciton peak generated by the few-layered flakes are used to calculate the average flake lateral dimensions, the concentration of WS2 in the inks after size selection and filtering, as well as the average monolayer count of the flakes. After printing, scanning electron microscopy is used to confirm average flake lateral size and average flake area coverage, while an atomic force microscope is used to confirm flake thickness.

New routes in additive devices fabrication techniques and advances in printable materials are required to meet the ever increasing demands for low-cost and large-area flexible electronics. In particular, perovskite-based materials have gained an appeal due to their unique optoelectronics and ferroelectrics properties, which may replace p-n junction in semiconductor devices. Metal-organic methylammonium lead trihalide perovskite formulations have been extensively studied in the last few years as promising materials for use in printed electronics, which do not require high temperatures or vacuum environment, contrary to conventional semiconductor fabrication techniques. In this work, digital inkjet-printing in ambient atmosphere is proposed as a deposition pathway for the fabrication of perovskite active layers in photodetector and thin-film photovoltaic device architectures. The device architecture containing a printed perovskite active layer sandwiched between TiO2 and Spiro-OMeTAD as electron and hole transport layers, respectively, as well as layer-on-layer fabrication and responsivity spectra of the perovskite-based device are presented.

Recent strategy in the electronics sector is to ascertain the ways to make cheap, flexible and environmentally friendly electronic devices. The 3D inkjet printing technology is based on the Additive Manufacturing concept and it is with no doubt capable of revolutionising the whole system of manufacturing electronic devices including: material selection; design and fabrication steps and device configuration and architecture. Thus, 3D inkjet printing technology (IJP) is not only one of the most promising technologies to reduce the harmful radiation/ heat generation but also achieve reductions in manufacturing cost. Here, we explore the potential of 3D – inkjet printing technology to provide an innovative approach for electronic devices in especially information storage elements by seeking to manufacture and characterise state-of-art fully inkjet printed two terminal electronic memory devices. In this work, ink-jettable materials (Ag and PEDOT:PSS) were printed by a piezoelectric Epson Stylus P50 inkjet printing machine on a flexible substrate. All components of the memory cells of a simple metal/active layer/metal structure were deposited via inkjet printing. The quality of the printed layers was first assessed by Nikon LABOPHOT-2 optical microscope, fitted with Nikon Camera DS-Fi1. Furthermore, an in-depth electrical characterisation of the fabricated memory cells was carried out using HP4140B picoammeter.

Inkjet printing, of the researched techniques for printing of hydrogels, gives perhaps the best potential control over the shape and composition of the final hydrogel. It is, however, fundamentally limited by the low viscosity of the printed ink, which means that crosslinking of the hydrogel must take place after printing. This can be particularly problematic for hydrogels as the slow diffusion of the crosslinking species through the gel results in very slow vertical printing speeds, leading to dehydration of the gel and (if simultaneously deposited) cell death. Previous attempts to overcome this limitation have involved the sequential printing of alternating layers to reduce the diffusion distance of reactive species. In this work we demonstrate an alternative approach where the crosslinker and gelator are printed so that they collide with each other before impinging upon the substrate, thereby facilitating hydrogel synthesis and patterning in a single step. Using a model system based upon sodium alginate and calcium chloride a series of 3D structures are demonstrated, with vertical printing speeds significantly faster than previous work. The droplet collision is shown to increase advective mixing before impact, reducing the time taken for gelation to occur, and improving definition of printed patterns. With the facile addition of more printing inks, this approach also enables spatially varied composition of the hydrogel, and work towards this will be discussed.

Bioprinting promises to create three-dimensional in vitro models to study pathological states and possible new therapies, and in the future, to produce complex tissue and organ replacements. This article will describe the recent advances in bioprinting technologies to engineer artificial tissues and organs by controlling spatial heterogeneity of chemical and physical properties of scaffolds and, at the same time, the cellular composition and spatial arrangement. Despite significant technological improvements in recent years, the positioning at the micrometric level and the switching of different cell types and biomaterials remain a challenge, which limits the development of resilient vascular, neural, and lymphatic networks for metabolites, signaling, and waste transport, and thus limits the development of thick and clinically relevant engineered vascularized tissues.

We demonstrate that Additive Manufacturing (3D printing) is a viable approach to rapidly prototype personalised fins for surfboards. Surfing is an iconic sport that is extremely popular in coastal regions around the world. We use computer aided design and 3D printing of a wide range of composite materials to print fins for surfboards, e.g. ABS, carbon fibre, fibre glass and amorphous thermoplastic poly(etherimide) resins. The mechanical characteristics of our 3D printed fins were found to be comparable to commercial fins. Computational fluid dynamics was employed to calculate longitudinal (drag) and tangential (turning) forces, which are important for surfboard maneuverability, stability and speed. A commercial tracking system was used to evaluate the performance of 3D printed fins under real-world conditions (i.e. surfing waves). These data showed that the surfing performance of surfboards with 3D printed fins is similar to that of surfboards with commercial fins.

Stretchable electronics represent an emerging class of devices that can be compressed, twisted and conform to very complicated shapes. The mechanical and electrical compliances of the technology promise to open up applications for healthcare, energy and entertainment purposes. However, advancement in the field has been hindered by material related constraints. Moreover, the current microfabrication facilities are optimized for rigid substrates such as silicon, which have significant different properties compared to elastomers. In this paper, four categories of enabling technologies for stretchable electronics commercialization are critically reviewed, namely: the novel design of stretchable structures, use of non-conventional materials, state-of-art printing techniques and also the patterning of electrodes or metal interconnects via conventional manufacturing techniques.

Active inkjet materials are invoked in the fabrication of optoelectronic devices. These types of multilayer assemblies contain a variety of commercially available ink formulations. It is envisioned that a dielectric SU-8 material can be used in a FET-like structure to form an interlayer between conductive silver and semi-conductive MWCNT-doped PEDOT:PSS ink layers. These printed structures may be fabricated onto a polyimide based flexible substrate, for instance. These structures are a starting point for offering valuable information on layer-on-layer printing interactions and interface problematics within a complete inkjet device fabrication.

Polymer nanocomposites (PNC) include a copolymer or polymer which has nanoparticles dispersed in the polymer matrix at the nano-level. One of the most common types of polymer nanocomposites contain smectic clays as the nanoparticles. These clay minerals increase the mechanical properties of standard polymers and improve barrier properties. For optimum barrier properties, Layer-by-Layer assembly (LbL) is one of the most effective methods for depositing thin films. LbL methods however, are quite tedious and produce large quantities of waste. A newly discovered phenomenon of self-assembled polymer nanocomposites utilizes entropic forces to drive the assembly to spontaneously form a larger nanostructured film. This approach allows polymers and nanoparticles with high particle loadings to be mixed, and create the super gas barrier films. We have developed a coating technique which can be employed to make self-assembled gas barrier films via inkjet printing. This technique is industrially scalable and efficient. This is because it does not need any rinsing step and drying steps as required in LbL. The influence of different polymers Polyvinylpyrrolidone (PVP) and Poly (acrylic acid) PAA with Montmorillonite (MMT) nanoclay solutions on Polyethylene terephthalate (PET) substrate is examined to study their effectiveness as a gas barrier film. The results showing the excellent oxygen barrier behavior of a combination of PVP and MMT Nano clay nanocomposite with high transparency. These high barrier gas nanocomposite films are good candidates for a variety of food packaging applications.

Industrial ultrafast lasers are a key component of many new industrial manufacturing processes. The virtually athermal nature of the laser–matter interaction process enables high-quality material processing for many different materials with feature size reaching into the nanometer scale. Advances in laser average power and beam-delivery technology have significantly improved the throughput and productivity of real-life industrial and medical applications. In this article, we present key examples of laser processing, including drilling, cutting, and surface processing. In particular, we describe how ultrafast lasers can improve vision in patients, extend battery lifetime, improve the efficiency of solar cells and infrared detectors, or be applied in the printing or microelectronics industries. These examples demonstrate how further developments rely on a combination of laser technology, beam handling and delivery, and laser–matter interaction processes.

2D materials have shown to be the next step in semiconductor use and device manufacturing that can allow us to reduce the size of most electronics. One of the novel ways to obtain 2D materials is through liquid exfoliation, in which these materials can be obtained by dispersing the smallest possible particles in different solvents. Once obtained, the solutions can be used to manufacture devices via different processes, one of which is inkjet printing. This process relies in selecting “jettable” fluids, which need to have the necessary combination of viscosity and surface energy or “wettability”. In this work we have modified the viscosities and surface energies of five solvents: IPA (Isopropanol), NMP (N-methyl – 2 pyrrolidone), DMA (Dimethylacetamide), DMF (Dimethylformamide) and a mixture of Cyclohexanone / Terpineol 7:3. We have found an avenue to tailor the viscosity of these solvents though the addition of Ethyl Cellulose (EC), where the viscosity has been increased by up to 15 times at an EC concentration of 6%. For inkjet printing, ideally a viscosity of 4 – 10 cP is recommended, which we have been able to achieve with all of the solvents studied. It has been found that the different solvents present different susceptibilities to the EC addition, with DMA and DMF being the least sensitive to the EC addition. We have also studied the change in the drop dynamics and interactions of the 2D solutions with the substrate. Through this analysis we have found solvents that appear to be attractive for inkjet printing of MoS2 and graphite.

Nano-inkjet printing using an Electrohydrodynamic's (EHD) pulsed cone-jet approach has the potential to bring affordable additive manufacturing to the micro and nanoscale. Ink technology is a major limitation of current EHD techniques. Specifically, most EHD printing processes print either nanoparticles or polymers. The materials are structurally weak and often have poor electrical or mechanical properties. For example, printing nanoparticles effectively creates a cluster of nanoparticles that must be sintered to create a continuous material. To address these issues, we have been adapting reactive inks to work with an EHD pulsed cone-jet. Specifically, we demonstrate that silver micron-scale structures can be printed using an EHD pulsed cone-jet regime. These inks produce solid structures without sintering steps and with good electrical properties.1,2 This work shows that reactive ink chemistries can be combined with EHD printing to produce fine-resolution features consisting of solid metal without an annealing step.

Fabrication methods and performance characteristics of spiral stretchable interconnects fabricated using drop-on-demand printing of silver reactive inks are discussed. This work details ink optimization, device fabrication, and device characterization while demonstrating the potential applications for reactive inks and new design strategies in stretchable electronics. Devices were printed with an ethanol stabilized silver diamine reactive ink and cycled to 160 % over 100 cycles with less than 10% increase in electrical resistance. Maximum deformation before failure was measured at 180% elongation. A novel method for fabrication of a stretchable electronics device has been studied and verified.

Three-dimensional powder printing (3DP) is attractive for the direct fabrication of bioceramic implants and scaffolds from a computer aided design file for bone tissue engineering by localized deposition of a reactive binder liquid onto thin powder layers. This article reviews recent findings on novel material developments for the three-dimensional (3D) printing process using either sintering regimes or cement setting reactions. Customized ceramic implants can be fabricated by 3DP using computer tomography data obtained from a patient, whereas further drug modification of such implants can be achieved either in situ or post-printing. The excellent biological in vitro and in vivo behavior of 3D-printed bioceramics together with processing at ambient conditions may give the opportunity to directly produce cell-seeded patient-specific implants for accelerated and enhanced bone regeneration in the future.

Inkjet printing of various nanoparticle inks, made from silver or copper nanoparticles, and its transformation into solid functional patterns is of high interest in the field of printed electronics. Liquid materials can be deposited as defined patterns in selected areas with micrometer precision. To convert these printed liquid films, consisting of solvents, additives and nanoparticles, into solid functional patterns a post-treatment is required. To this date, many investigations report on various sintering techniques to achieve e.g. high conductivity from the printed conductive materials.

Direct thermal sintering (via furnace or hotplate) requires high temperatures, which makes it not suitable for sensitive polymeric substrates. The novel method of intense pulsed light (IPL) sintering opens the window of opportunity to convert liquid or dried metal layers into solid functional layers within milliseconds without damaging the thermally fragile polymeric substrate.

In this work we present and analyze the application of the IPL sintering on inkjet printed silver patterns on various flexible substrates, like Poly(ethylene naphthalate) (PEN), Poly(ethylene terephthalate) (PET), Polyimide (PI) foils and paper.

A high dependency of the electrical and structural performance of the printed silver layers on the base substrate was observed when flashing with the IPL technique. Flashing parameters were varied and the resulting sheet resistance is presented.

With the analytical comparison of optical and electrical results, the flashing settings could be adapted to achieve highly conductive inkjet printed silver patterns on flexible substrates, when compared to other thermal sintering techniques. Furthermore the first integration of this post treatment methodology into semi-industrial roll-2-roll processing was successfully performed and will be demonstrated.

P3HT: PCBM nanoparticle based inks were fabricated using the miniemulsion technique [1]. The nanoparticles were characterized for their size using a quasi-elastic light scattering technique. The average diameter of P3HT:PCBM nanoparticles was found to be 52nm. The blending of the P3HT and the PCBM was tested using UV-Vis absorbance and fluorescence spectroscopy – it was found that the blend ratio of the nanoparticle can be controlled by varying the individual concentrations of the P3HT and PCBM in chloroform ("the oil phase") of the miniemulsions. Finally the P3HT:PCBM nanoparticle inks were inkjet printed onto PEDOT:PSS coated ITO substrates to form the active layer of the organic photovoltaic cell. Aluminum cathodes were evaporated onto the printed nanoparticle active layer film to form functioning OPVs. The best power conversion efficiency for one of these devices was 0.07%.