Surface Functionalization of 3D-Printed Scaffolds with Seed-Assisted Hydrothermally Grown ZnO Nanoarrays for Bone Tissue Engineering.

Bioactive metal-based nanostructures, particularly zinc oxide (ZnO), are promising materials for bone tissue engineering. However, integrating them into 3D-printed polymers using traditional blending methods reduces the cell performance. Alternative surface deposition techniques often require extreme conditions that are unsuitable for polymers. To address these issues, we propose a metal-assisted hydrothermal synthesis method to modify 3D printed polycaprolactone (PCL) scaffolds with ZnO nanoparticles (NPs), facilitating the growth of ZnO nanoarrays (NAs) at a low-temperature (55 °C). Physicochemical characterizations revealed that the ZnO NPs form both physical and chemical bonds with the PCL surface; chemical bonding occurs between the carboxylate groups of PCL and Zn(OH)2 during seed deposition and hydrothermal synthesis. The ZnO NPs and NAs grown for a longer time (18 h) on the surface of PCL scaffolds exhibit significant proliferation and early differentiation of osteoblast-like cells. The proposed method is suitable for the surface modification of thermally degradable polymers, opening up new possibilities for the deposition of diverse metals.

Mesoporous K-doped NiCo2O4 derived from a Prussian blue analog: high-yielding synthesis and assessment as oxygen evolution reaction catalyst.

The conversion and storage of clean renewable energy can be achieved using water splitting. However, water splitting exhibits sluggish kinetics because of the high overpotentials of the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) and should therefore be promoted by OER and/or HER electrocatalysts. As the kinetic barrier of the former reaction exceeds that of the latter, high-performance OER catalysts are highly sought after. Herein, K-doped NiCo2O4 (HK-NCO) was hydrothermally prepared from a Prussian blue analog with a metal-organic framework structure and assessed as an OER catalyst. Extensive K doping increased the number of active oxygen vacancies and changed their intrinsic properties (e.g., binding energy), thus increasing conductivity. As a result, HK-NCO exhibited a Tafel slope of 49.9 mV dec-1 and a low overpotential of 292 mV at 10 mA cm-2, outperforming a commercial OER catalyst (Ir) and thus holding great promise as a component of high-performance electrode materials for metal-oxide batteries and supercapacitors.

Planar ultrasonic transducer based on a metasurface piezoelectric ring array for subwavelength acoustic focusing in water.

The development of a new ultrasonic transducer capable of improved focusing performance has become a necessity to overcome the limitations of conventional ultrasonic transducer technology. In this study, we designed and optimized a metasurface piezoelectric ring device, and using multiphysics finite element analysis, we examined the performance of a planar ultrasonic transducer consisting of this device, a matching layer, a backing layer, and housing in producing a needle-like subwavelength focusing beam in water. For practical experiments, a metasurface piezoelectric ring device was fabricated using a laser ablation process. Subsequently, using a pulse-echo test, we found that the - 6 dB bandwidth of a planar ultrasonic transducer with a center frequency of 1.0 MHz was 37.5%. In addition, the results of an ultrasonic-focusing performance test showed that the full width at half-maximum of the axial subwavelength focusing beam was 0.78λ, and the full lateral width at half-maximum of the subwavelength lateral focusing beam was 7.03λ at a distance of 10.89λ. The needle-like focused ultrasonic beam technology implemented with a piezoelectric ring array based new planar ultrasound transducer is expected to be used in high-resolution imaging devices or medical ultrasound focusing devices in the future.

High-Density Patterned Array Bonding through Void-Free Divinyl Siloxane Bis-Benzocyclobutene Bonding Process.

Divinylsiloxane-bis-benzocyclobutene (DVS-BCB) has attracted significant attention as an intermediate bonding material, owing to its excellent properties. However, its applications are limited, due to damage to peripheral devices at high curing temperatures and unoptimized compressive pressure. Therefore, it is necessary to explore the compressive pressure condition for DVS-BCB bonding. This study demonstrates an optimization process for void-free DVS-BCB bonding. The process for obtaining void-free DVS-BCB bonding is a vacuum condition of 0.03 Torr, compressive pressure of 0.6 N/mm2, and curing temperature of 250 °C for 1 h. Herein, we define two factors affecting the DVS-BCB bonding quality through the DVS-BCB bonding mechanism. For strong DVS-BCB bonding, void-free and high-density chemical bonds are required. Therefore, we observed the DVS-BCB bonding under various compressive pressure conditions at a relatively low temperature (250 °C). The presence of voids and high-density crosslinking density was examined through near-infrared confocal laser microscopy and Fourier-transform infrared microscopy. We also evaluated the adhesion of the DVS-BCB bonding, using a universal testing machine. The results suggest that the good adhesion with no voids and high crosslinking density was obtained at the compressive pressure condition of 0.6 N/mm2. We believe that the proposed process will be of great significance for applications in semiconductor and device packaging technologies.

Effects of Curing Temperature on Bending Durability of Inkjet-Printed Flexible Silver Electrode.

Flexible electrodes should have a good mechanical durability and electrical properties under even extreme bending and deformation conditions. We fabricated such an electrode using an inkjet printing system. In addition, annealing was perfo3rmed under curing temperatures of 150, 170, and 190 °C to improve the electrical resistance performance of the electrode. Scanning electron microscopy, X-ray diffraction, nanoindentation, and surface profile measurements were performed to measure and analyze the electrode characteristics and the change in the shape of the coffee ring. The bending deformation behavior of the electrode was predicted by simulations. To confirm the bending durability of the flexible electrode according to different curing temperatures, the bending deformation and electrical resistance were simultaneously tested. It was found that the electrode cured at a temperature of 170 °C could endure 20,185 bending cycles and had the best durability, which was consistent with the predicted simulation results. Moreover, the average specific resistance before the electrode was disconnected was 13.45 µΩ cm, which is similar to the conventional electrode value. These results are expected to increase the durability and life of flexible electrodes, which can be used in flexible electronic devices, sensors, and wearable devices that are subjected to significant bending deformation.

Actuating Voltage Waveform Optimization of Piezoelectric Inkjet Printhead for Suppression of Residual Vibrations.

After a piezoelectric inkjet printhead jets the first droplet, the actuating membrane still vibrates, creating residual vibrations in the ink channel, which can degrade the inkjet printhead performance. For suppressing these vibrations, an optimized actuating voltage waveform with two pulses must be obtained, of which the first pulse is used for jetting and the second pulse is used to suppress the residual vibrations. In this study, the pressure history within the ink channel of a recirculating piezoelectric inkjet printhead was first acquired using lumped element modeling. Then, for suppressing residual vibrations, a bipolar voltage waveform was optimized via analysis of the tuning time (tt), dwell time (td2), rising time (tr2), falling time (tf2), and voltage amplitude of the second pulse. Two voltage waveforms, Waveform 01 and Waveform 02, were optimized thereafter. In Waveform 01, tt=2 µs, td2=2 µs, and tr2 and tf2=1 µswere finalized as the optimal parameters; in the case of another waveform, the optimal parameters of td2, tr2, and tf2 were found to be 4, 1, and 1 µs, respectively. The optimal voltage amplitude of the second pulse was found to be 1/3 the amplitude of the first pulse. On the basis of our analysis, the tuning time in Waveform 01 is the most sensitive parameter, and the performance yielded is even poorer than that yielded by standard waveform, if not optimized. Therefore, the other waveform is recommended for the suppression of residual vibrations.

Formation of high-density CuBi2O4 thin film photocathodes with polyvinylpyrrolidone-metal interaction.

We present a polymer-assisted spin coating process used to fabricate high-density p-type CuBi2O4 (CBO) thin films. Polyvinylpyrrolidone (PVP) is introduced in the precursor solutions in order to promote uniform nucleation of CBO and prevent formation of the secondary phase, such as Bi2O3, by Bi3+ ion hydrolysis. Slow PVP molecule decomposition during the two-step annealing process, with a 1 M/0.5 M (Bi3+/Cu2+) metal ion concentration, enables optimum contact at the CBO/substrate interface by avoiding formation of voids. This resulted in the formation of non-porous, compact CBO thin films. The highest current density of the photoelectrochemical (PEC) oxygen reduction reaction is obtained with non-porous, compact CBO thin films due to unimpeded charge transport through the CBO bulk, as well as across the interface. When combined with silicon, the high-density CBO thin film investigated in this work is expected to provide new PEC tandem cell options to use for solar applications.

Selective shape control of cerium oxide nanocrystals for photocatalytic and chemical sensing effect.

In this study, we report the precise shape control of crystalline cerium oxide, whose morphology changes between nanorods and nanoparticles in a short time. The proposed synthetic route of cerium oxide nanorods was highly dependent on the reaction time, and 10 min was determined to be the optimum synthetic condition. The cerium oxide nanorods were further converted into nanoparticles by the spontaneous assembly of cerium oxide nanoparticles into nanorods. The transmission electron microscopy results showed that the synthesized nanorods grew with high crystallinity along the 〈110〉 direction. The cerium oxide nanorods have been proven to be very efficient electron mediators for use as excellent photocatalytic materials and highly sensitive chemical sensors. The chemical sensor fabricated on a carbon paper substrate showed the high sensitivity of 1.81 µA mM-1 cm-2 and the detection limit of 6.4 µM with the correlation coefficient of 0.950.

Growth Mechanism of Highly Crystalline CdS Spheres with Grainy Surfaces.

Owing to its excellent optical and electronic properties, CdS has increasingly received considerable attention as a promising III-V semiconductor material. We report on the growth mechanism of CdS spheres with high crystallinity, uniform size distribution, and grainy surfaces under hydrothermal conditions. By controlling the reaction time, temperature, and pH, CdS with various morphologies and size distributions could be synthesized. The analysis of the time evolution of the morphology and size of the CdS particles provided good indications on the growth mechanism. In addition, the effects of the temperature and pH on the formation and size of the CdS spherical particles were studied to understand the reaction mechanism. The characterization of the physicochemical properties of the synthesized samples by scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and Raman spectroscopy is presented.

Facile fabrication of a cerium oxide nanorod.

Nanorods are one-dimensional structures that possess interesting physical and electrical properties and have potential applications in various areas. Cerium oxide, a very abundant rare earth element, is widely utilized in catalysts of exhaust systems, chemical abrasives, electrical devices, oxidant semiconductor devices, UV adsorbents, and fluorescence emitting materials. Shape control is important for controlling the overall shape and quality of the nanorod during synthesis. However, most of the shape control studies of cerium oxide nanomaterials in the literature have been performed under high temperature and high pressure conditions, which impede industrial mass production. In this study, we describe a facile synthesis method for producing Ce(OH)3 nanorods with different diameters through the application of the common ion effect principle using NH+, Cl-, and OH- ions. The resulting Ce(OH)3 rods were dried to produce the corresponding cerium oxide products. Consequently, a one-pot reaction under mild conditions allowed for the production of high-quality nanorods after much shorter reaction times, with the additional natural release of counter ions under reaction equilibrium. The shape and physicochemical properties were characterized using various analytical methods, including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and Raman spectroscopy.

Growth mechanism of cubic MgO granule via common ion effect.

MgO is a typical wide bandgap insulator with its excellent thermodynamic stability, low dielectric constant, and low refractive index for growing various thin film materials. For this application, it is worth developing and understanding suitable growth method for MgO nanostructure. In this study, cubic MgCO3 have been successfully prepared via hydrolysis control of magnesium salt and alkaline solution with common ions to form nanoflake assembly. An optimum hydrothermal process and its shape evolution of cubic MgCO3 and MgO granules are analyzed. The physicochemical properties of the obtained samples are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier Transform InfraRed (FT-IR) to show high purity and structural uniformity of magnesium compounds.