Tunable Organic Active Neural Probe Enabling Near-Sensor Signal Processing.

Neural recording systems have significantly progressed to provide an advanced understanding and treatment for neurological diseases. Flexible transistor-based active neural probes exhibit great potential in electrophysiology applications due to their intrinsic amplification capability and tissue-compliant nature. However, most current active neural probes exhibit bulky back-end connectivity since the output is current, and the development of an integrated circuit for voltage output is crucial for near-sensor signal processing at the abiotic/biotic interface. Here, inkjet-printed organic voltage amplifiers are presented by monolithically integrating organic electrochemical transistors and thin-film polymer resistors on a single, highly flexible substrate for in vivo brain activity recording. Additive inkjet printing enables the seamless integration of multiple active and passive components on the somatosensory cortex, leading to significant noise reduction over the externally connected typical configuration. It also facilitates fine-tuning of the voltage amplification and frequency properties. The organic voltage amplifiers are validated as electrocorticography devices in a rat in vivo model, showing their ability to record local field potentials in an experimental model of spontaneous and epileptiform activity. These results bring organic active neural probes to the forefront in applications where efficient sensory data processing is performed at sensor endpoints.

3D Inkjet-Bioprinted Lung-on-a-Chip.

There is an urgent need for physiologically relevant and customizable biochip models of human lung tissue to provide a niche for lung disease modeling and drug efficacy. Although various lung-on-a-chips have been developed, the conventional fabrication method has been limited in reconstituting a very thin and multilayered architecture and spatial arrangements of multiple cell types in a microfluidic device. To overcome these limitations, we developed a physiologically relevant human alveolar lung-on-a-chip model, effectively integrated with an inkjet-printed, micron-thick, and three-layered tissue. After bioprinting lung tissues inside four culture inserts layer-by-layer, the inserts are implanted into a biochip that supplies a flow of culture medium. This modular implantation procedure enables the formation of a lung-on-a-chip to facilitate the culture of 3D-structured inkjet-bioprinted lung models under perfusion at the air-liquid interface. The bioprinted models cultured on the chip maintained their structure with three layers of tens of micrometers and achieved a tight junction in the epithelial layer, the critical properties of an alveolar barrier. The upregulation of genes involved in the essential functions of alveoli was also confirmed in our model. Our culture insert-mountable organ-on-a-chip is a versatile platform that can be applied to various organ models by implanting and replacing culture inserts. It is amenable to mass production and the development of customized models through the convergence with bioprinting technology.

Sonochemical Degradation of Gelatin Methacryloyl to Control Viscoelasticity for Inkjet Bioprinting.

Inkjet printing enables the mimicry of the microenvironment of natural complex tissues by patterning cells and hydrogels at a high resolution. However, the polymer content of an inkjet-printable bioink is limited as it leads to strong viscoelasticity in the inkjet nozzle. Here it is demonstrated that sonochemical treatment controls the viscoelasticity of a gelatin methacryloyl (GelMA) based bioink by shortening the length of polymer chains without causing chemical destruction of the methacryloyl groups. The rheological properties of treated GelMA inks are evaluated by a piezo-axial vibrator over a wide range of frequencies between 10 and 10 000 Hz. This approach enables to effectively increase the maximum printable polymer concentration from 3% to 10%. Then it is studied how the sonochemical treatment effectively controls the microstructure and mechanical properties of GelMA hydrogel constructs after crosslinking while maintaining its fluid properties within the printable range. The control of mechanical properties of GelMA hydrogels can lead fibroblasts more spreading on the hydrogels. A 3D cell-laden multilayered hydrogel constructs containing layers with different physical properties is fabrictated by using high-resolution inkjet printing. The sonochemical treatment delivers a new path to inkjet bioprinting to build microarchitectures with various physical properties by expanding the range of applicable bioinks.

Dual-gate thin film transistor lactate sensors operating in the subthreshold regime.

Organic thin-film transistors (TFTs) with an electrochemically functionalized sensing gate are promising platforms for wearable health-monitoring technologies because they are light, flexible, and cheap. Achieving both high sensitivity and low power is highly demanding for portable or wearable devices. In this work, we present flexible printed dual-gate (DG) organic TFTs operating in the subthreshold regime with ultralow power and high sensitivity. The subthreshold operation of the gate-modulated TFT-based sensors not only increases the sensitivity but also reduces the power consumption. The DG configuration has deeper depletion and stronger accumulation, thereby further making the subthreshold slope sharper. We integrate an enzymatic lactate-sensing extended-gate electrode into the printed DG TFT and achieve exceptionally high sensitivity (0.77) and ultralow static power consumption (10 nW). Our sensors are successfully demonstrated in physiological lactate monitoring with human saliva. The accuracy of the DG TFT sensing system is as good as that of a high-cost conventional assay. The developed platform can be readily extended to various materials and technologies for high performance wearable sensing applications.

Cationic Iridium(III) Complexes with Benzothiophene-Quinoline Ligands for Deep-Red Light-Emitting Electrochemical Cells.

Three new cationic cyclometalated iridium(III) complexes equipped with differently substituted benzo[b]thiophen-2-ylquinoline cyclometalating ligands and with a sterically demanding tert-butyl-substituted 2,2'-bipyridine ancillary ligand were synthesized and structurally characterized by NMR and X-ray diffraction techniques. To tune the electronic properties of such complexes, the quinoline moiety of the cyclometalating ligands was kept pristine or equipped with electron-withdrawing phenyl and -CF3 substituents, leading to complexes 1, 2, and 3, respectively. A complete electrochemical and photophysical investigation, supported by density functional theory calculations, permits a deep understanding of their electronic properties. The emission of all complexes arises from ligand-centered triplet states in the spectral range between 625 and 950 nm, with excited-state lifetimes between 2.10 and 6.32 µs at 298 K. The unsubstituted complex (1) exhibits the most blue-shifted emission in polymeric matrix at 298 K (λmax = 667 nm, photoluminescence quantum yield (PLQY) = 0.25 and τ = 5.32 µs). The phenyl-substituted complex (2) displays the highest photoluminescent quantum yields (up to 0.30 in polymeric matrix), while the CF3-substituted counterpart (3) shows the most red-shifted emission, peaking at approx. 720 nm, but with lower quantum yields (e.g., 0.10 in polymeric matrix at 298 K). Complexes 1 and 2 were tested in single-layer nondoped light-emitting electrochemical cells (LEECs), using a nozzle-printing technique; both devices display deep-red electroluminescence with an external quantum efficiency close to 20%.

Transfer-Tattoo-Like Cell-Sheet Delivery Induced by Interfacial Cell Migration.

A direct transfer of a cell sheet from a culture surface to a target tissue is introduced. Commercially available, flexible parylene is used as the culture surface, and it is proposed that the UV-treated parylene offers adequate and intermediate levels of cell adhesiveness for both the stable cell attachment during culture and for the efficient cell transfer to a target surface. The versatility of this cell-transfer process is demonstrated with various cell types, including MRC-5, HDFn, HULEC-5a, MC3T3-E1, A549, C2C12 cells, and MDCK-II cells. The novel cell-sheet engineering is based on a mechanism of interfacial cell migration between two surfaces with different adhesion preferences. Monitoring of cytoskeletal dynamics and drug treatments during the cell-transfer process reveals that the interfacial cell migration occurs by utilizing the existing transmembrane proteins on the cell surface to bind to the targeted surface. The re-establishment and reversal of cell polarity after the transfer process are also identified. Its unique capabilities of 3D multilayer stacking, freeform design, and curved surface application are demonstrated. Finally, the therapeutic potential of the cell-sheet delivery system is demonstrated by applying it to cutaneous wound healing and skin-tissue regeneration in mice models.

3D pulmonary fibrosis model for anti-fibrotic drug discovery by inkjet-bioprinting.

Pulmonary fibrosis (PF) is known as a chronic and irreversible disease characterized by excessive extracellular matrix accumulation and lung architecture changes. Large efforts have been made to develop prospective treatments and study the etiology of pulmonary fibrotic diseases utilizing animal models and spherical organoids. As part of these efforts, we created an all-inkjet-printed three-dimensional (3D) alveolar barrier model that can be used for anti-fibrotic drug discovery. Then, we developed a PF model by treating the 3D alveolar barrier with pro-fibrotic cytokine and confirmed that it is suitable for the fibrosis model by observing changes in structural deposition, pulmonary function, epithelial-mesenchymal transition, and fibrosis markers. The model was tested with two approved anti-fibrotic drugs, and we could observe that the symptoms in the disease model were alleviated. Consequently, structural abnormalities and changes in mRNA expression were found in the induced fibrosis model, which were shown to be recovered in all drug treatment groups. The all-inkjet-printed alveolar barrier model was reproducible for disease onset and therapeutic effects in the human body. This finding emphasized that thein vitroartificial tissue with faithfully implemented 3D microstructures using bioprinting technology may be employed as a novel testing platform and disease model to evaluate potential drug efficacy.

Use of a 3D inkjet-printed model to access dust particle toxicology in the human alveolar barrier.

Fine dust particles in the air travel into our body via the airway tract and cause severe respiratory diseases. Thus, the analysis of the effects of dust particles on the respiratory system has been receiving significant research interest. However, most studies on the toxicity of dust particles involve two-dimensional (2D) cell cultures, animal models, and epidemiology. Here, we inkjet-printed a three-dimensional (3D) alveolar barrier model to study how dust particles cause respiratory diseases. The three-layered in vitro model was exposed to A2 fine test dust with varying concentrations and exposure durations. The results highlighted the destruction of the tissue architecture along with apoptosis in the bioprinted alveolar barrier. The damage at the cellular level induced an increase in the amount of pro-inflammatory cytokines secreted, followed by triggering of the signal transduction pathway and activation of transcription factors. As a consequence of the release of cytokines, the extracellular matrix was degraded, which led to the collapse of the cell structure, loss of cell polarity, and a decrease in barrier tightness. Further, the pulmonary surfactant protein-related genes in the dust-treated alveolar tissue were investigated to evaluate the possible role of dust particles in pulmonary surfactant dysfunction. This study demonstrated the use of 3D-printed tissue model to evaluate the physiological impact of fine dust particles on cytotoxicity, alveolar barrier rigidity, and surfactant secretion of an alveolar barrier.

Effect of Aronia Extract on Collagen Synthesis in Human Skin Cell and Dermal Equivalent.

The regulation of collagen synthesis, which occurs in fibroblasts in the dermal layer, is a key process in dermis regeneration and skin reconstruction. Herein, we investigated whether Aronia melanocarpa extract affects the human skin condition. We focused on type I collagen synthesis using two different types of model systems: a monolayer of cells and a bioprinted 3D dermal equivalent. The Aronia extract showed no cytotoxicity and increased cell proliferation in neonatal human dermal fibroblasts. Treatment with Aronia extract increased the transcription of COL1A1 mRNA in direct proportion to the extract concentration without causing a decrease in COL1A1 mRNA degradation. Additionally, the Aronia extract inhibited the expression of MMP1 and MMP3, and an increase in type I collagen was observed along with a decrease in MMP1 protein. We also fabricated dermal equivalents from type I collagen (the major component of the dermis) and dermal fibroblasts by bioprinting. In the 3D dermis model, the compressive modulus directly affected by collagen synthesis increased in direct proportion to the Aronia extract concentration, and expression levels of MMP1 and MMP3 decreased in exactly inverse proportion to its concentration. The findings that the Aronia extract increases synthesis of type I collagen and decreases MMP1 and MMP3 expression suggest that this extract may be useful for the treatment of damaged or aged skin.

Printable inks and deformable electronic array devices.

Deformable printed electronic array devices are expected to revolutionize next-generation electronics. However, although remarkable technological advances in printable inks and deformable electronic array devices have recently been achieved, technical challenges remain to commercialize these technologies. In this review article a brief introduction to printing methods highlighting significant research studies on ink formation for conductors, semiconductors, and insulators is provided, and the structural design and successful printing strategies of deformable electronic array devices are described. Successful device demonstrations are presented in the applications of passive- and active-matrix array devices. Finally, perspectives and technological challenges to be achieved are pointed out to print practically available deformable devices.

The design of an inkjet drive waveform using machine learning.

A drive waveform, which needs to be optimized with ink's fluid properties, is critical to reliable inkjet printing. A generally adopted rule of thumb for its design is mostly dependent on time-consuming and repetitive manual manipulation of its parameters. This work presents a closed-loop machine learning approach to designing an optimal drive waveform for satellite-free inkjet printing at a target velocity. Each of the representative 11 model inks with different fluid properties was ink-jetted with 1100 distinct waveform designs. The high-speed images of their jetting behaviors were acquired and the big datasets of the resulting drop formation and velocity were extracted from the jetting images. Five machine learning models were examined and compared to predict the characteristics of jetting behavior. Among a variety of machine learning models, Multi-layer Perceptron affords the highest prediction accuracy. A closed-loop prediction algorithm that determined the optimal set of waveform parameters for satellite-free drop formation at a target velocity and employed the most superior learning model was established. The proposed method was confirmed through the printing of an unknown model ink with a recommended waveform.

Spatiotemporal Measurement of Arterial Pulse Waves Enabled by Wearable Active-Matrix Pressure Sensor Arrays.

Wearable pressure sensors have demonstrated great potential in detecting pulse pressure waves on the skin for the noninvasive and continuous diagnosis of cardiac conditions. However, difficulties lie in positioning conventional single-point sensors on an invisible arterial line, thereby preventing the detection of adequate signal amplitude for accurate pulse wave analysis. Herein, we introduce the spatiotemporal measurements of arterial pulse waves using wearable active-matrix pressure sensors to obtain optimal pulse waveforms. We fabricate thin-film transistor (TFT) arrays with high yield and uniformity using inkjet printing where array sizes can be customizable and integrate them with highly sensitive piezoresistive sheets. We maximize the pressure sensitivity (16.8 kPa-1) and achieve low power consumption (101 nW) simultaneously by strategically modulating the TFT operation voltage. The sensor array creates a spatiotemporal pulse wave map on the wrist. The map presents the positional dependence of pulse amplitudes, which allows the positioning of the arterial line to accurately extract the augmentation index, a parameter for assessing arterial stiffness. The device overcomes the positional inaccuracy of conventional single-point sensors, and therefore, it can be used for medical applications such as arterial catheter injection or the diagnosis of cardiovascular disease in daily life.

Layout-to-Bitmap Conversion and Design Rules for Inkjet-Printed Large-Scale Integrated Circuits.

Digital inkjet printing (IJP) can greatly reduce the manufacturing cost and waste of flexible large-area electronics by adding micro-fine patterns onto plastic foils. Advanced system design using IJP has been limited by the lack of an electronic design automation (EDA) approach. An EDA approach based on a vector-based layout drawing requires parameterized IJP design rules. This study proposes a layout-to-bitmap (L2B) conversion procedure and line-based design rules that leverage the existing circuit layout EDA tools for advanced IJP designs. The L2B conversion is accomplished by optimizing the parameters of the horizontal and vertical lines by varying the drop spacings and platen temperatures. Next, the line-based layouts are converted to bitmap files which are used as IJP input data for printing multiple metal layers. This study systematically investigated the development of an IJP process employing Ag nanoparticles. The physical characteristics of the proposed process were evaluated based on theories concerning inkjet-printed bead formation. The design rules for fabricating printed thin-film transistor (TFT) circuits were documented. Documentation is the first step in creating an IJP process design kit for advanced electronics design. Using the optimized L2B conversion procedure and the design rules, a 10 × 10 array of printed organic TFTs was fabricated to demonstrate the reliability of the developed process. Additionally, the fabricated printed organic TFTs indicated that the proposed process could be extended to large-scale system designs.

Dual-pulse photoactivated atomic force microscopy.

Photoactivated atomic force microscopy (pAFM), which integrates light excitation and mechanical detection of the deflections of a cantilever tip, has become a widely used tool for probing nanoscale structures. Raising the illuminating laser power is an obvious way to boost the signal-to-noise ratio of pAFM, but strong laser power can damage both the sample and cantilever tip. Here, we demonstrate a dual-pulse pAFM (DP-pAFM) that avoids this problem by using two laser pulses with a time delay. The first laser heats the light absorber and alters the local Grüneisen parameter value, and the second laser boosts the mechanical vibration within the thermal relaxation time. Using this technique, we successfully mapped the optical structures of small-molecule semiconductor films. Of particular interest, DP-pAFM clearly visualized nanoscale cracks in organic semiconductor films, which create crucial problems for small-molecule semiconductors. DP-pAFM opens a promising new optical avenue for studying complex nanoscale phenomena in various research fields.

Homogenization of a reaction diffusion equation can explain influenza A virus load data.

We study the influence of spatial heterogeneity on the antiviral activity of mouse embryonic fibroblasts (MEF) infected with influenza A. MEF of type Ube1L-/- are composed of two distinct sub-populations, the strong type that sustains a strong viral infection and the weak type, sustaining a weak viral load. We present new data on the virus load infection of Ube1L-/-, which have been micro-printed in a checker board pattern of different sizes of the inner squares. Surprisingly, the total viral load at one day after inoculation significantly depends on the sizes of the inner squares. We explain this observation by using a reaction diffusion model and we show that mathematical homogenization can explain the observed inhomogeneities. If the individual patches are large, then the growth rate and the carrying capacity will be the arithmetic means of the patches. For finer and finer patches the average growth rate is still the arithmetic mean, however, the carrying capacity uses the harmonic mean. While fitting the PDE to the experimental data, we also predict that a discrepancy in virus load would be unobservable after only half a day. Furthermore, we predict the viral load in different inner squares that had not been measured in our experiment and the travelling distance the virions can reach after one day.

Printed Organic Light-Emitting Diodes on Fabric with Roll-to-Roll Sputtered ITO Anode and Poly(vinyl alcohol) Planarization Layer.

Electronic textiles, which are a combination of fabrics and electronics, can help realize wearable electronic devices by changing the rigidity of these textiles. We demonstrate organic light-emitting diodes (OLEDs) by directly printing the emitting material on fabric substrates using the nozzle-printing technique. Printing the emitting material directly on a fabric substrate with a rough surface is difficult. To address this, we introduce a planarization layer by using a synthesized 3.5 wt % poly(vinyl alcohol) (PVA) solution. The sputtered ITO anode with the thermally annealed PVA planarization layer on a fabric substrate achieves a low sheet resistance in the range of 60-80 Ω/sq, whereas the ITO electrode without a PVA layer exhibits high sheet resistance values of 10-25 kΩ/sq. This result is because the thermally annealed PVA layer on the fabric surface has a uniform surface morphology and a water contact angle as high as 96°, thus acting as a protective layer with a waterproofing effect; in contrast, the water is completely absorbed on the rough surface without a PVA layer. The fabric-based OLEDs with a thermally annealed PVA layer exhibit a lower turn-on voltage of 3 V and higher luminance values of 5346 cd/m2 at 8 V compared with the devices without a PVA layer (7 V and 3622 cd/m2) at 18 V. These fabric-based OLEDs with a PVA planarization layer can be produced by the nozzle-printing process and can achieve selective patterning as well as direct printing of the emitting material and ITO sputtering on a fabric substrate; furthermore, they emit well even when it bent into a circle with a radius of 1 cm.

All-Inkjet-Printed 3D Alveolar Barrier Model with Physiologically Relevant Microarchitecture.

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.

Sea urchin repelling Tannin- FeIII complex coating for ocean macroalgal afforestation.

Intense seaweed grazing by sea urchins has destroyed kelp forests and accelerated the transformation of these forests into barren areas known as urchin barrens. Once the sea urchins occupy the barren ground, it becomes more challenging to restore the kelp forests. Although phlorotannin, a primary herbivore defense chemical secreted by kelp, has been reported to discourage feeding activities of marine herbivores but the direct application of naturally extracted phlorotannin does not effectively repel sea urchins. In this study, we applied a simple and green Tannin-FeIII (TA-FeIII) coating on substrates as a sea urchin repellent using a cheap, ecofriendly tannin (TA) obtained from biomass as an alternative to phlorotannin. In a model aquarium experiment, most of the sea urchins (Anthocidaris crassispina) in the tank evaded the TA-FeIII-coated substrates. In field tests with 300 sea urchins, the majority of sea urchins could not crawl over the TA-FeIII-coated rope for more than 2 h in contrast to the control group. Hence, the safety, cost-effectiveness, and scalability of the TA-FeIII coating make it a practical candidate to protect the kelp ecosystem from sea urchins.

Creation of bladder assembloids mimicking tissue regeneration and cancer.

Current organoid models are limited by their inability to mimic mature organ architecture and associated tissue microenvironments1,2. Here we create multilayer bladder 'assembloids' by reconstituting tissue stem cells with stromal components to represent an organized architecture with an epithelium surrounding stroma and an outer muscle layer. These assembloids exhibit characteristics of mature adult bladders in cell composition and gene expression at the single-cell transcriptome level, and recapitulate in vivo tissue dynamics of regenerative responses to injury. We also develop malignant counterpart tumour assembloids to recapitulate the in vivo pathophysiological features of urothelial carcinoma. Using the genetically manipulated tumour-assembloid platform, we identify tumoural FOXA1, induced by stromal bone morphogenetic protein (BMP), as a master pioneer factor that drives enhancer reprogramming for the determination of tumour phenotype, suggesting the importance of the FOXA1-BMP-hedgehog signalling feedback axis between tumour and stroma in the control of tumour plasticity.

Author Correction: Freeform micropatterning of living cells into cell culture medium using direct inkjet printing.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.