With the outbreak of new respiratory viruses and high mortality rates of pulmonary diseases, physiologically relevant models of human respiratory system are urgently needed to study disease pathogenesis, drug efficacy, and pharmaceutics. In this paper, a 3D alveolar barrier model fabricated by printing four human alveolar cell lines, namely, type I and II alveolar cells (NCI-H1703 and NCI-H441), lung fibroblasts (MRC5), and lung microvascular endothelial cells (HULEC-5a) is presented. Automated high-resolution deposition of alveolar cells by drop-on-demand inkjet printing enables to fabricate a three-layered alveolar barrier model with an unprecedented thickness of ≈10 µm. The results show that the 3D structured model better recapitulate the structure, morphologies, and functions of the lung tissue, compared not only to a conventional 2D cell culture model, as expected, but also a 3D non-structured model of a homogeneous mixture of the alveolar cells and collagen. Finally, it is demonstrated that this thin multilayered model reproduce practical tissue-level responses to influenza infection. Drop-on-demand inkjet-printing is an enabling technology for customization, scalable manufacturing, and standardization of their size and growth, and it is believed that this 3D alveolar barrier model can be used as an alternative to traditional test models for pathological and pharmaceutical applications.
Poly(4-vinylphenol) (PVP) is a promising gate dielectric material for organic field-effect transistors (OFETs) and circuits fabricated on plastic substrates. Thermal cross-linking of PVP with a cross-linker, such as poly(melamine- co-formaldehyde) methylated (PMF), at a high temperature (above 170 °C) is widely considered an effective method to remove residual hydroxyl groups that induce polarization effects in the dielectric bulk. However, the threshold voltage shift in transfer characteristics is still observed for an OFET with a PVP-PMF dielectric when it is operated at a slow gate voltage sweep rate. The present study examines the cause of the undesired hysteresis phenomenon and suggests a route to enable a reliable operation. We systematically investigate the effect of the PVP-PMF weight ratio and their annealing temperature on the transfer characteristics of OFETs. We discover that the size of the hysteresis is closely related to the concentration of nonhydrogen-bonded hydroxyl groups in the dielectric bulk and this is controlled by the weight ratio. At a ratio of 0.5:1, a complete elimination of hysteresis was observed irrespective of the annealing temperature. We finally demonstrate a highly reliable operation of small-molecule-based OFETs fabricated on a plastic substrate at a low temperature.
A nonvolatile memory thin film transistor (TFT) is an essential building block in all electronic applications for calculation and identification. In particular, organic memory TFTs using bilayered polymer electrets have attracted significant attention due to excellent mechanical flexibility and fast operating speed. However, the data retention characteristics over an extended period of time remains a major reliability issue for nonvolatile memory devices. Here, the enhancement of data retention in flexible and printed organic memory TFTs by introducing a phase‐separated tunneling layer is demonstrated. The tunneling layer is formed during an active layer printing process with a blend ink of small‐molecule organic semiconductor and polystyrene insulator. The effect of the dielectric tunneling layer on data retention characteristics is systematically investigated. The printed nonvolatile memory devices with the phase‐separated tunneling layer exhibit significantly improved data retention time of over 10 years, validating the feasibility of applying flexible memory into wearable electronics and smart Internet‐of‐Things devices.
Even though the fundamental benefits of the staggered bottom-gate top-contact geometry in organic thin-film transistors (TFTs) have been fully demonstrated for enhancing the charge injection efficiency, most printed organic TFTs with inkjet-printed source/drain electrodes have only been fabricated in bottom-contact configurations, probably due to the difficulty of printing with metal-nanoparticle ink on soluble organic semiconductor (OSC) without film deformation/dissolution. Here, we present the printing process and the electrical characteristics of inkjet-printed top contact OSC in bottom-gate TFTs. We first fabricated polymer bottom-gate TFTs by printing in two different top- and bottom-contact configurations. The physical carrier mobility of the two TFTs was extracted from a gated-contact organic TFT model to exclude the effect of geometric contact resistance RC. When compared to assess the OSC film damage from the printing metallization, the two mobility values were almost identical. This result indicates that the metal nanoparticle ink used in this work formed a top metal contact on the OSC film without significant chemical damage. Furthermore, the printed top-contact TFT exhibited I–V characteristics almost identical to those of a thermally evaporated Ag top-contact TFT. This study suggests the possibility of inkjet-printed top metal contacts for organic thin-film devices such as transistors, solar cells, and diodes.
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