Soft lithographic patterned architectures in dye sensitized solar cells

Arrays of periodic surface features were patterned on mesoporous Nb2O5 and TiO2 films by soft-lithographic techniques to construct photonic crystal (PC) structures on the back side of the oxide. The patterned oxide films were integrated into dye-sensitized solar cells (DSSCs) and their performance was evaluated relative to flat (unpatterned) counterparts. The PC structure on niobium oxide surfaces caused large changes in optical characteristics, particularly in the blue wavelength regime. The incident photon-to-current conversion efficiency (IPCE) of patterned niobium oxide anodes exhibited a relative enhancement over the entire wavelength range corresponding to the higher absorption in optical measurements. However, the effect of surface PC structures on the optical response of the TiO2 is different from that of the Nb2O5 photoanode. The enhancement of light harvesting efficiency (LHE) is not obviously due to the higher thickness and larger dye loading than Nb2O5 films. However, patterned TiO2 samples exhibited higher global efficiency than the flat reference, although there was no notable change in LHE. It was hypothesized that surface PC structures changed the de-trapping rate from trap states based on the simulated reflection behavior near the surface of the PC structure, and that in turn, enhances charge collection efficiency. A cubic array of rectangular ITO posts (5´5´6.5μm, 10μm period) were fabricated on FTO coated glass in order to reduce the distance between charge generation points in the mesoporous TiO2 film and the transparent conductive oxide (TCO) layer in an effort to enhance charge collection in the DSSCs. In spite of the decrease in optical transmission due to the tall ITO structures, DSSCs with patterned ITO exhibited increased photocurrent by 12~18% to the reference DSSCs with identical volume of sensitized TiO2. However, DSSCs with patterned ITO substructures showed deterioration in the open circuit voltage (Voc), fill factor, and global efficiency. Electrochemical impedance spectroscopy (EIS) showed that DSSCs with patterned ITO exhibited faster recombination rates leading to the decline in Voc,, fill factor, and global efficiency. We conclude that a barrier coating to suppress back electron transfer to the electrolyte should be conformally applied in order to take full advantage of the patterned ITO substructure.Doctor of Philosoph

Biodegradable Metallic Glass for Stretchable Transient Electronics

Biodegradable electronics are disposable green devices whose constituents decompose into harmless byproducts, leaving no residual waste and minimally invasive medical implants requiring no removal surgery. Stretchable and flexible form factors are essential in biointegrated electronic applications for conformal integration with soft and expandable skins, tissues, and organs. Here a fully biodegradable MgZnCa metallic glass (MG) film is proposed for intrinsically stretchable electrodes with a high yield limit exploiting the advantages of amorphous phases with no crystalline defects. The irregular dissolution behavior of this amorphous alloy regarding electrical conductivity and morphology is investigated in aqueous solutions with different ion species. The MgZnCa MG nanofilm shows high elastic strain (approximate to 2.6% in the nano-tensile test) and offers enhanced stretchability (approximate to 115% when combined with serpentine geometry). The fatigue resistance in repeatable stretching also improves owing to the wide range of the elastic strain limit. Electronic components including the capacitor, inductor, diode, and transistor using the MgZnCa MG electrode support its integrability to transient electronic devices. The biodegradable triboelectric nanogenerator of MgZnCa MG operates stably over 50 000 cycles and its fatigue resistant applications in mechanical energy harvesting are verified. In vitro cell toxicity and in vivo inflammation tests demonstrate the biocompatibility in biointegrated use

Regulation of cell locomotion by nanosecond-laser-induced hydroxyapatite patterning

Hydroxyapatite, an essential mineral in human bones composed mainly of calcium and phosphorus, is widely used to coat bone graft and implant surfaces for enhanced biocompatibility and bone formation. For a strong implant–bone bond, the bone-forming cells must not only adhere to the implant surface but also move to the surface requiring bone formation. However, strong adhesion tends to inhibit cell migration on the surface of hydroxyapatite. Herein, a cell migration highway pattern that can promote cell migration was prepared using a nanosecond laser on hydroxyapatite coating. The developed surface promoted bone-forming cell movement compared with the unpatterned hydroxyapatite surface, and the cell adhesion and movement speed could be controlled by adjusting the pattern width. Live-cell microscopy, cell tracking, and serum protein analysis revealed the fundamental principle of this phenomenon. These findings are applicable to hydroxyapatite-coated biomaterials and can be implemented easily by laser patterning without complicated processes. The cell migration highway can promote and control cell movement while maintaining the existing advantages of hydroxyapatite coatings. Furthermore, it can be applied to the surface treatment of not only implant materials directly bonded to bone but also various implanted biomaterials implanted that require cell movement control

Spatiotemporal Distribution of Mesoporous Silica Nanoparticles in Tissue-Mimicking Collagen Using Lab-on-a-Chip Technology for Drug Carrier Diffusivity Evaluation

As injected drugs finally diffuse to the target cells, a quantitative understanding of the diffusion behavior of drug molecules or drug carriers is essential for the determination of their efficacy or optimal doses. Here, we propose a method for determining the diffusivity (D, diffusion coefficient) of drug carriers in tissue-mimicking collagen in the lab-on-a-chip (LOC) platform and predict their spatiotemporal distribution using the calculated D. By controlling the concentrations of fluorescent mesoporous silica nanoparticles (MSNs) in each channel, the diffusion of fluorescent MSNs was induced and fluorescence gradients in collagen were produced and captured as images. The D of the MSNs by size was obtained by fitting the fluorescence profiles to the solution of Fick's second law. The D of MSNs varied by size from 2.98 x 10-10 m2/s (MSNs of 10 nm) to 1.14 x 10-11 m2/s (MSNs of 1 mu m). The spatiotemporal profiles of MSNs were calculated using the obtained D, and it was demonstrated that the concentration of MSNs with a size > 200 nm at 100 mu m from the gel-liquid interface will remain < 50% of that in the vessel-mimicking channel even after 3 h. As the analysis and prediction procedures based on fluorescence profile image processing and a least-squares fit to the solution are relatively simple, our results can be extended to various studies to narrow the gap between in vitro tests and animal experiments in drug or particle transport research through the calculation of the diffusion coefficient of drug candidates before animal experiments and might replace some parts of animal experiments of drug delivery studies.N

Improvement of Yttrium Oxyfluoride Coating with Modified Precursor Solution for Laser-Induced Hydrothermal Synthesis

© 2022 by the authors. Licensee MDPI, Basel, Switzerland.In the semiconductor manufacturing process, the inner walls of the equipment are coated with yttrium-based oxides for etch resistance against plasma exposure. Yttrium oxyfluoride (YOF) particle synthesis and coating methods have been actively studied owing to their high erosion resistance compared to Y2O3 and Al2O3. Owing to the formation of a rough and porous coating layer by thermal spray-coating, the coating layer disintegrates, as the etching process has been conducted for a long time. Laser-induced synthesis and coating technology offer several advantages, including simplified process steps, ease of handling, and formation of a dense coating layer on the target ma-terial. In this study, YOF was coated on an aluminum substrate using a modified precursor solution. The NaF and HMTA were added to the precursor solution, resulting in enhanced synthetic reactivity and stabilizing the oxides. The material coated on the surface was analyzed based on the characteristics of composition, chemical bonding, and phase identification. We found that the coating properties can be improved by using an appropriate combination of modified precursor solutions and laser parameters. Therefore, the findings in this study are expected to be utilized in the field of coating technology.N

Conceptual Study for Tissue-Regenerative Biodegradable Magnesium Implant Integrated with Nitric Oxide-Releasing Nanofibers

The excessive initial corrosion rate of Mg is a critical limitation in the clinical application of biodegradable Mg implants because the device loses its fixation strength before the fractured bone heals. This study suggests a new approach to overcome this hurdle by accelerating tissue regeneration instead of delaying the implant biodegradation. As angiogenesis is an essential process in early bone regeneration, a Mg implant coated with electrospun nanofibers containing nitric oxide (NO), which physiologically promotes angiogenesis, is designed. The integrated device enables adjustable amounts of NO to be stored on the NO donor-conjugated nanofiber coating, stably delivered, and released to the fractured bone tissue near the implanted sites. An in vitro corrosion test reveals no adverse effect of the released NO on the corrosion behavior of the Mg implant. Simultaneously, the optimal concentration level of NO released from the implant significantly enhances tube network formation of human umbilical vein endothelial cells without any cytotoxicity problem. This indicates that angiogenesis can be accelerated by combining NO-releasing nanofibers with a Mg implant. With its proven feasibility, the proposed approach could be a novel solution for the initial stability problem of biodegradable Mg implants, leading to successful bone fixation

A new corrosion-inhibiting strategy for biodegradable magnesium: reduced nicotinamide adenine dinucleotide (NADH)

Abstract Utilization of biodegradable metals in biomedical fields is emerging because it avoids high-risk and uneconomic secondary surgeries for removing implantable devices. Mg and its alloys are considered optimum materials for biodegradable implantable devices because of their high biocompatibility; however, their excessive and uncontrollable biodegradation is a difficult challenge to overcome. Here, we present a novel method of inhibiting Mg biodegradation by utilizing reduced nicotinamide adenine dinucleotide (NADH), an endogenous cofactor present in all living cells. Incorporating NADH significantly increases Mg corrosion resistance by promoting the formation of thick and dense protective layers. The unique mechanism by which NADH enables corrosion inhibition was discovered by combined microscopic and spectroscopic analyses. NADH is initially self-adsorbed onto the surface of Mg oxide layers, preventing Cl− ions from dissolving Mg oxides, and later recruits Ca2+ ions to form stable Ca-P protective layers. Furthermore, stability of NADH as a corrosion inhibitor of Mg under physiological conditions were confirmed using cell tests. Moreover, excellent cell adhesion and viability to Mg treated with NADH shows the feasibility of introduction of NADH to Mg-based implantable system. Our strategy using NADH suggests an interesting new way of delaying the degradation of Mg and demonstrates potential roles for biomolecules in the engineering the biodegradability of metals

Biomimetic hydrogel blanket for conserving and recovering intrinsic cell properties

Abstract Background Cells in the human body experience different growth environments and conditions, such as compressive pressure and oxygen concentrations, depending on the type and location of the tissue. Thus, a culture device that emulates the environment inside the body is required to study cells outside the body. Methods A blanket-type cell culture device (Direct Contact Pressing: DCP) was fabricated with an alginate-based hydrogel. Changes in cell morphology due to DCP pressure were observed using a phase contrast microscope. The changes in the oxygen permeability and pressure according to the hydrogel concentration of DCP were analyzed. To compare the effects of DCP with normal or artificial hypoxic cultures, cells were divided based on the culture technique: normal culture, DCP culture device, and artificial hypoxic environment. Changes in phenotype, genes, and glycosaminoglycan amounts according to each environment were evaluated. Based on this, the mechanism of each culture environment on the intrinsic properties of conserving chondrocytes was suggested. Results Chondrocytes live under pressure from the surrounding collagen tissue and experience a hypoxic environment because collagen inhibits oxygen permeability. By culturing the chondrocytes in a DCP environment, the capability of DCP to produce a low-oxygen and physical pressure environment was verified. When human primary chondrocytes, which require pressure and a low-oxygen environment during culture to maintain their innate properties, were cultured using the hydrogel blanket, the original shapes and properties of the chondrocytes were maintained. The intrinsic properties could be recovered even in aged cells that had lost their original cell properties. Conclusions A DCP culture method using a biomimetic hydrogel blanket provides cells with an adjustable physical pressure and a low-oxygen environment. Through this technique, we could maintain the original cellular phenotypes and intrinsic properties of human primary chondrocytes. The results of this study can be applied to other cells that require special pressure and oxygen concentration control to maintain their intrinsic properties. Additionally, this technique has the potential to be applied to the re-differentiation of cells that have lost their original properties