Transparent, Flexible, Conformal Capacitive Pressure Sensors with Nanoparticles.

The fundamental challenge in designing transparent pressure sensors is the ideal combination of high optical transparency and high pressure sensitivity. Satisfying these competing demands is commonly achieved by a compromise between the transparency and usage of a patterned dielectric surface, which increases pressure sensitivity, but decreases transparency. Herein, a design strategy for fabricating high-transparency and high-sensitivity capacitive pressure sensors is proposed, which relies on the multiple states of nanoparticle dispersity resulting in enhanced surface roughness and light transmittance. We utilize two nanoparticle dispersion states on a surface: (i) homogeneous dispersion, where each nanoparticle (≈500 nm) with a size comparable to the visible light wavelength has low light scattering; and (ii) heterogeneous dispersion, where aggregated nanoparticles form a micrometer-sized feature, increasing pressure sensitivity. This approach is experimentally verified using a nanoparticle-dispersed polymer composite, which has high pressure sensitivity (1.0 kPa-1 ), and demonstrates excellent transparency (>95%). We demonstrate that the integration of nanoparticle-dispersed capacitor elements into an array readily yields a real-time pressure monitoring application and a fully functional touch device capable of acting as a pressure sensor-based input device, thereby opening up new avenues to establish processing techniques that are effective on the nanoscale yet applicable to macroscopic processing.

Investigation on achieving super-resolution by solid immersion lens based STED microscopy.

The feasibility of stimulated emission depletion (STED) microscopy using a solid immersion lens was investigated. First, the theoretical feasibility of the considered system is discussed based on a vectorial field algorithm that uses a stratified medium composed of a SIL air-gap and test sample. Using the simulation, we verified that evanescent waves with much higher spatial frequencies corresponding to the high numerical aperture in the air-gap can be utilized to achieve a higher resolution than a confocal fluorescent image without a depletion beam. The simulated expectation was supported by actual imaging on two types of samples: fluorescent beads with a 20 nm diameter and an actin sample with a filamentous structure. The lateral resolution of the system was determined to be 34 nm via the imaging results on the nano-beads. The system was quite promising for achieving nano-scale surface imaging of biological samples; an even higher resolution was achieved by adjusting the wavelength and the intensity of the depletion beam.

Stable water splitting using photoelectrodes with a cryogelated overlayer.

Hydrogen production techniques based on solar-water splitting have emerged as carbon-free energy systems. Many researchers have developed highly efficient thin-film photoelectrochemical (PEC) devices made of low-cost and earth-abundant materials. However, solar water splitting systems suffer from short lifetimes due to catalyst instability that is attributed to both chemical dissolution and mechanical stress produced by hydrogen bubbles. A recent study found that the nanoporous hydrogel could prevent the structural degradation of the PEC devices. In this study, we investigate the protection mechanism of the hydrogel-based overlayer by engineering its porous structure using the cryogelation technique. Tests for cryogel overlayers with varied pore structures, such as disconnected micropores, interconnected micropores, and surface macropores, reveal that the hydrogen gas trapped in the cryogel protector reduce shear stress at the catalyst surface by providing bubble nucleation sites. The cryogelated overlayer effectively preserves the uniformly distributed platinum catalyst particles on the device surface for over 200 h. Our finding can help establish semi-permanent photoelectrochemical devices to realize a carbon-free society.

Tissue-Adhesive Chondroitin Sulfate Hydrogel for Cartilage Reconstruction.

Chondroitin sulfate (CS), the main component of cartilage extracellular matrix, has attracted attention as a biomaterial for cartilage tissue engineering. However, current CS hydrogel systems still have limitations for application in successful cartilage tissue engineering owing to their unsuitable degradation kinetics, insufficient mechanical similarity, and lack of integration with the native cartilage tissue. In this study, using mussel adhesive-inspired catechol chemistry, we developed a functional CS hydrogel that exhibits tunable physical and mechanical properties as well as excellent tissue adhesion for efficient integration with native tissues. Various properties of the developed catechol-functionalized CS (CS-CA) hydrogel, including swelling, degradation, mechanical properties, and adhesiveness, could be tailored by varying the conjugation ratio of the catechol group to the CS backbone and the concentration of the CS-CA conjugates. CS-CA hydrogels exhibited significantly increased modulus (∼10 kPa) and superior adhesive properties (∼3 N) over conventional CS hydrogels (∼hundreds Pa and ∼0.05 N). In addition, CS-CA hydrogels incorporating decellularized cartilage tissue dice promoted the chondrogenic differentiation of human adipose-derived mesenchymal stem cells by providing a cartilage-like microenvironment. Finally, the transplantation of autologous cartilage dice using tissue-adhesive CS-CA hydrogels enhanced cartilage integration with host tissue and neo-cartilage formation owing to favorable physical, mechanical, and biological properties for cartilage formation. In conclusion, our study demonstrated the potential utility of the CS-CA hydrogel system in cartilage tissue reconstruction.

Osteoconductive hybrid hyaluronic acid hydrogel patch for effective bone formation.

Bio-inspired adhesive hydrogels have been applied to cell and drug delivery systems to address various tissue defects and disorders. However, adhesive hydrogels functionalized with phenolic moieties often lack osteoconductive capacity and mechanical properties for bone regeneration. In this study, we utilized the versatile chemical interactions of phenolic moieties to overcome such limitations in bone tissue engineering efforts. Highly osteoconductive hybrid hydrogel patches were fabricated by incorporating inorganic minerals, hydroxyapatite (HAP), or whitlockite (WKT), into pyrogallol-conjugated hyaluronic acid (HA-PG). The hybrid HA-PG patches exhibited improved mechanical strength and reinforced structural/physical properties owing to additional intermolecular complexation between oxidized PG moieties and ions released from inorganic particles. The sustained release of bone morphogenetic protein-2 (BMP-2) from hybrid patches was prolonged by combination of the inherent nucleophilic affinity of oxidized PG and electrostatic interactions between inorganic particles and BMP-2. With increased osteoconductivity, hybrid patches with HAP or WKT enhanced the osteogenic differentiation of human stem cells while also promoting new bone formation in a critical-sized calvarial defect. Our study demonstrates a translational potential of phenolic adhesive hydrogels engineered with inorganic minerals for orthopedic applications.

Determination of the molecular assembly of actin and actin-binding proteins using photoluminescence.

Actin, the most abundant protein in cells, polymerizes into filaments that play key roles in many cellular dynamics. To understand cell dynamics and functions, it is essential to examine the cytoskeleton structure organized by actin and actin-binding proteins. Here, we pave the way for determining the molecular assembly of the actin cytoskeleton using direct photonic in situ analysis, providing the photoluminescence characteristics of actin as a function of filament length and bundling, without labeling. In experiments for monomeric and filamentous actin reconstituted in vitro, structural forms of actin are identified from the peak positions and intensities of photoluminescence. Actin monomers exhibited small intensity emission peaks at 334 nm, whereas filamentous and bundled actin showed a shifted peak at 323 nm with higher intensity. The peak shift was found to be proportional to the length of the actin filament. With probing structural change of actin in various cells in vivo, our study provides an efficient and precise analytical in situ tool to examine the cytoskeleton structure. It will be beneficial for elucidating the mechanism of various cellular functions such as cell migration, differentiation, cytokinesis and adhesion. Furthermore, our technique can be applied to detect the alterations in the cell cytoskeleton that can occur during many pathological processes.

High-resolution acoustophoretic 3D cell patterning to construct functional collateral cylindroids for ischemia therapy.

The fabrication of functional tissues is essential for clinical applications such as disease treatment and drug discovery. Recent studies have revealed that the mechanical environments of tissues, determined by geometric cell patterns, material composition, or mechanical properties, play critical roles in ensuring proper tissue function. Here, we propose an acoustophoretic technique using surface acoustic waves to fabricate therapeutic vascular tissue containing a three-dimensional collateral distribution of vessels. Co-aligned human umbilical vein endothelial cells and human adipose stem cells that are arranged in a biodegradable catechol-conjugated hyaluronic acid hydrogel exhibit enhanced cell-cell contacts, gene expression, and secretion of angiogenic and anti-inflammatory paracrine factors. The therapeutic effects of the fabricated vessel constructs are demonstrated in experiments using an ischemia mouse model by exhibiting the remarkable recovery of damaged tissue. Our study can be referenced to fabricate various types of artificial tissues that mimic the original functions as well as structures.

Micropatterned Pyramidal Ionic Gels for Sensing Broad-Range Pressures with High Sensitivity.

The development of pressure sensors that are effective over a broad range of pressures is crucial for the future development of electronic skin applicable to the detection of a wide pressure range from acoustic wave to dynamic human motion. Here, we present flexible capacitive pressure sensors that incorporate micropatterned pyramidal ionic gels to enable ultrasensitive pressure detection. Our devices show superior pressure-sensing performance, with a broad sensing range from a few pascals up to 50 kPa, with fast response times of <20 ms and a low operating voltage of 0.25 V. Since high-dielectric-constant ionic gels were employed as constituent sensing materials, an unprecedented sensitivity of 41 kPa-1 in the low-pressure regime of <400 Pa could be realized in the context of a metal-insulator-metal platform. This broad-range capacitive pressure sensor allows for the efficient detection of pressure from a variety of sources, including sound waves, a lightweight object, jugular venous pulses, radial artery pulses, and human finger touch. This platform offers a simple, robust approach to low-cost, scalable device design, enabling practical applications of electronic skin.