A Dynamic Ultrasound Phantom with Tissue-Mimicking Mechanical and Acoustic Properties.

Tissue-mimicking phantoms are valuable tools that aid in improving the equipment and training available to medical professionals. However, current phantoms possess limited utility due to their inability to precisely simulate multiple physical properties simultaneously, which is crucial for achieving a system understanding of dynamic human tissues. In this work, novel materials design and fabrication processes to produce various tissue-mimicking materials (TMMs) for skin, adipose, muscle, and soft tissue at a human scale are developed. Target properties (Young's modulus, density, speed of sound, and acoustic attenuation) are first defined for each TMM based on literature. Each TMM recipe is developed, associated mechanical and acoustic properties are characterized, and the TMMs are confirmed to have comparable mechanical and acoustic properties with the corresponding human tissues. Furthermore, a novel sacrificial core to fabricate a hollow, ellipsoid-shaped bladder phantom complete with inlet and outlet tubes, which allow liquids to flow through and expand this phantom, is adopted. This dynamic bladder phantom with realistic mechanical and acoustic properties to human tissues in combination with the developed skin, soft tissue, and subcutaneous adipose tissue TMMs, culminates in a human scale torso tank and electro-mechanical system that can be systematically utilized for characterizing various medical imaging devices.

An Emerging Era: Conformable Ultrasound Electronics.

Conformable electronics are regarded as the next generation of personal healthcare monitoring and remote diagnosis devices. In recent years, piezoelectric-based conformable ultrasound electronics (cUSE) have been intensively studied due to their unique capabilities, including nonradiative monitoring, soft tissue imaging, deep signal decoding, wireless power transfer, portability, and compatibility. This review provides a comprehensive understanding of cUSE for use in biomedical and healthcare monitoring systems and a summary of their recent advancements. Following an introduction to the fundamentals of piezoelectrics and ultrasound transducers, the critical parameters for transducer design are discussed. Next, five types of cUSE with their advantages and limitations are highlighted, and the fabrication of cUSE using advanced technologies is discussed. In addition, the working function, acoustic performance, and accomplishments in various applications are thoroughly summarized. It is noted that application considerations must be given to the tradeoffs between material selection, manufacturing processes, acoustic performance, mechanical integrity, and the entire integrated system. Finally, current challenges and directions for the development of cUSE are highlighted, and research flow is provided as the roadmap for future research. In conclusion, these advances in the fields of piezoelectric materials, ultrasound transducers, and conformable electronics spark an emerging era of biomedicine and personal healthcare.

Interfacial Delamination at Multilayer Thin Films in Semiconductor Devices.

With the evolution of semiconducting industries, thermomechanical failure induced in a multilayered structure with a high aspect ratio during manufacturing and operation has become one of the critical reliability issues. In this work, the effect of thermomechanical stress on the failure of multilayered thin films on Si substrates was studied using analytical calculations and various thermomechanical tests. The residual stress induced during material processing was calculated based on plate bending theory. The calculations enabled the prediction of the weakest region of failure in the thin films. To verify our prediction, additional thermomechanical stress was applied to induce cracking and interfacial delamination by various tests. We assumed that, when accumulated thermomechanical-residual and externally applied mechanical stress becomes larger than a critical value the thin-film cracking or interfacial delamination will occur. The test results agreed well with the prediction based on the analytical calculation in that the film with maximum tensile residual stress is the most vulnerable to failure. These results will provide useful analytical and experimental prediction tools for the failure of multilayered thin films in the device design stage.

Intrinsically stretchable organic light-emitting diodes.

Soft and conformable optoelectronic devices for wearable and implantable electronics require mechanical stretchability. However, very few researches have been done for intrinsically stretchable light-emitting diodes. Here, we present an intrinsically stretchable organic light-emitting diode, whose constituent materials are all highly stretchable. The resulting intrinsically stretchable organic light-emitting diode can emit light when exposed to strains as large as 80%. The turn-on voltage is as low as 8 V, and the maximum luminance, which is a summation of the luminance values from both the anode and cathode sides, is 4400 cd m-2 It can also survive repeated stretching cycles up to 200 times, and small stretching to 50% is shown to substantially enhance its light-emitting efficiency.

Water Passivation of Perovskite Nanocrystals Enables Air-Stable Intrinsically Stretchable Color-Conversion Layers for Stretchable Displays.

Conventional organic light-emitting devices without an encapsulation layer are susceptible to degradation when exposed to air, so realization of air-stable intrinsically-stretchable display is a great challenge because the protection of the devices against penetration of moisture and oxygen is even more difficult under stretching. An air-stable intrinsically-stretchable display that is composed of an intrinsically-stretchable electroluminescent device (SELD) integrated with a stretchable color-conversion layer (SCCL) that contains perovskite nanocrystals (PeNCs) is proposed. PeNCs normally decay when exposed to air, but they become resistant to this decay when dispersed in a stretchable elastomer matrix; this change is a result of a compatibility between capping ligands and the elastomer matrix. Counterintuitively, the moisture can efficiently passivate surface defects of PeNCs, to yield significant increases in both photoluminescence intensity and lifetime. A display that can be stretched up to 180% is demonstrated; it is composed of an air-stable SCCL that down-converts the SELD's blue emission and reemits it as green. The work elucidates the basis of moisture-assisted surface passivation of PeNCs and provides a promising strategy to improve the quantum efficiency of PeNCs with the aid of moisture, which allows PeNCs to be applied for air-stable stretchable displays.

Organic Radical-Linked Covalent Triazine Framework with Paramagnetic Behavior.

The production of multifunctional pure organic materials that combine different sizes of pores and a large number of electron spins is highly desirable due to their potential applications as polarizers for dynamic nuclear polarization-nuclear magnetic resonance and as catalysts and magnetic separation media. Here, we report a polychlorotriphenylmethyl radical-linked covalent triazine framework (PTMR-CTF). Two different sizes of micropores were established by N2 sorption and the presence of unpaired electrons (carbon radicals) by electron spin resonance and superconducting quantum interference device-vibrating sample magnetometer analyses. Magnetization measurements demonstrate that this material exhibits spin-half paramagnetism with a spin concentration of ∼2.63 × 1023 spins/mol. We also determined the microscopic origin of the magnetic moments in PTMR-CTF by investigating its spin density and electronic structure using density functional theory calculations.

Wearable, Luminescent Oxygen Sensor for Transcutaneous Oxygen Monitoring.

We present a new concept for a wearable oxygen (O2) sensor for transcutaneous O2 pressure (tcpO2) monitoring by combining the technologies of luminescent gas sensing and wearable devices. O2 monitoring has been exhaustively studied given its central role in diagnosing various diseases. The ability to quantify the physiological distribution and real-time dynamics of O2 from the subcellular to the macroscopic level is required to fully understand mechanisms associated with both normal physiological and pathological conditions. Despite its profound biological and clinical importance, few effective methods exist for noninvasively quantifying O2 in a physiological setting. The wearable sensor developed here consists of three components: a luminescent sensing film attached onto skin by a carbon tape, an organic light-emitting diode (OLED) as a light source, and an organic photodiode (OPD) as a light detector. All the components are solution-processable and integrated on a plane in a bandage-like configuration. To verify the performance, tcpO2 variations by pressure-induced occlusion were measured in the lower arm and a thumb by the wearable sensor, and the results were comparable to those measured by a commercial instrument. In addition to its flexibility, other features of this sensor render it a potential low-cost solution for the simultaneous monitoring of tcpO2 in any part of a body.

Highly Conformable, Transparent Electrodes for Epidermal Electronics.

We present a highly conformable, stretchable, and transparent electrode for application in epidermal electronics based on polydimethylsiloxane (PDMS) and Ag nanowire (AgNW) networks. With the addition of a small amount of a commercially available nonionic surfactant, Triton X, PDMS became highly adhesive and mechanically compliant, key factors for the development of conformable and stretchable substrates. The polar functional groups present in Triton X interacted with the Pt catalyst present in the PDMS curing agent, thereby hindering the cross-linking reaction of PDMS and modulating the mechanical properties of the polymer. Due to the strong interactions that occur between the polar functional groups of Triton X and AgNWs, AgNWs were effectively embedded in the adhesive PDMS (a-PDMS) matrix, and the highly enhanced conformability, mechanical stretchability, and transparency of the a-PDMS matrix were maintained in the resulting AgNW-embedded a-PDMS matrix. Finally, wearable strain and electrocardiogram (ECG) sensors were fabricated from the AgNW-embedded a-PDMS. The a-PDMS-based strain and ECG sensors exhibited significantly improved sensing performances compared with those of the bare PDMS-based sensors because of the better stretchability and conformability to the skin of the former sensors.

Novel Patterning Method for Nanomaterials and Its Application to Flexible Organic Light-Emitting Diodes.

We present a simple, low-cost, and scalable method to form various patterns of nanomaterials with different dimensions and shapes using capillary and centrifugal forces. The desired patterns were formed on the surfaces of poly(dimethylsiloxane) (PDMS) stamps, and the PDMS stamps were conformally contacted with the surfaces of flexible polymer substrates. Solutions of nanomaterials, such as metal nanowires and nanoparticles, were then drop-casted at one open end of the microchannels formed at the interface of the polymer substrate and PDMS stamp. The nanomaterial solutions penetrated the microchannels due to capillary force interactions between the surfaces and the fluid. The solvents of the nanomaterial solutions exfiltrated from the entrance of microchannels because of the coffee ring effect. Then, the solvent remaining in the microchannels was discharged by applying a centrifugal force by spinning the polymer substrate/PDMS stamp system. Because of the synergistic effect of the capillary force, coffee ring effect, and centrifugal force, uniform patterns of the nanomaterials with clearly defined edges were formed for a variety of pattern shapes and substrates. Furthermore, the direct patterning approach resulted in a significant reduction in the amount of wasted materials. Finally, flexible organic light-emitting diodes were successfully fabricated on the finely patterned nanowire electrodes.

Wearable and Transparent Capacitive Strain Sensor with High Sensitivity Based on Patterned Ag Nanowire Networks.

In this study, a transparent and stretchable thin-film capacitive strain sensor based on patterned Ag nanowire networks (AgNWs) was successfully fabricated. The AgNWs were patterned using a capillary force lithography (CFL) method and were embedded onto the surface of the polydimethylsiloxane substrate. The strain (ε) sensitivity of the capacitive strain sensor was controlled and enhanced by patterning the AgNWs into electrodes with an interdigitated shape. The interdigitated capacitive strain sensor (ICSS) is expected to have -1.57 gauge factor (GF) at 30% ε by calculation, which is much higher than the sensitivity of typical parallel-plate-type capacitive strain sensors. Because of the interdigitated pattern of the electrodes, the GF of the ICSS was increased up to -2.0. The ICSS had no hysteresis behavior up to ε values of 15% and showed stable ε sensing performance during the repeated stretching test at ε values of 10% for 1000 cycles. Furthermore, there was no cross talk between ε and pressure sensing in the AgNW-based ICSS, which was found to be insensitive to externally applied pressure. The ICSS was then used to detect the finger and wrist muscle motions of the human body to simulate its application to large and small ε sensing.

Facile Synthesis of F-TiO2/TiOF2 Mixture by High-Thermal Direct Fluorination and Its Photocatalytic Evaluation.

In this study, the mixture of F-TiO2/TiOF2 has been easily synthesized using titanium (IV) isopropoxide (TTIP) as titanium source by direct fluorination at high temperature according to different partial pressure of fluorine gas. The morphological properties and crystalline of thermally fluorinated photocatalysts were investigated using scanning electron microscope (SEM) and X-ray diffraction (XRD). Chemical composition and optical properties of thermally fluorinated photocatalysts were analyzed by X-ray Photoelectron Spectroscopy (XPS) and Photoluminescence (PL) spectrometer. The phase of F-TiO2/TiOF2 mixture was generated with different proportion by high-thermal direct fluorination. With the increase of the fluorine partial pressure, the proportion of cubic-shaped TiOF2 increased in comparison with globular-shaped TiO2. Also, the degradation rate constant of thermally fluorinated photocatalysts exhibited approximately 70 times more than that of TiO2, which were not treated fluorine gas. It is attributable to the increase of the surface hydroxyl group content and oxygen vacancies.

Foldable Transparent Substrates with Embedded Electrodes for Flexible Electronics.

We present highly flexible transparent electrodes composed of silver nanowire (AgNW) networks and silica aerogels embedded into UV-curable adhesive photopolymers (APPs). Because the aerogels have an extremely high surface-to-volume ratio, the enhanced van der Waals forces of the aerogel surfaces result in more AgNWs being uniformly coated onto a release substrate and embedded into the APP when mixed with an AgNW solution at a fixed concentration. The uniform distribution of the embedded composite electrodes of AgNWs and aerogels was verified by the Joule heating test. The APP with the composite electrodes has a lower sheet resistance (Rs) and a better mechanical stability compared with APP without aerogels. The APP with the embedded electrodes is a freestanding flexible substrate and can be used as an electrode coating on a polymer substrate, such as polydimethylsiloxane and polyethylene terephthalate. On the basis of the bending test results, the APPs with composite electrodes were sufficiently flexible to withstand a 1 mm bending radius (rb) and could be foldable with a slight change in Rs. Organic light emitting diodes were successfully fabricated on the APP with the composite electrodes, indicating the strong potential of the proposed flexible TEs for application as highly flexible transparent conductive substrates.

Rational design of a structural framework with potential use to develop chemical reagents that target and modulate multiple facets of Alzheimer's disease.

Alzheimer's disease (AD) is characterized by multiple, intertwined pathological features, including amyloid-ß (Aß) aggregation, metal ion dyshomeostasis, and oxidative stress. We report a novel compound (ML) prototype of a rationally designed molecule obtained by integrating structural elements for Aß aggregation control, metal chelation, reactive oxygen species (ROS) regulation, and antioxidant activity within a single molecule. Chemical, biochemical, ion mobility mass spectrometric, and NMR studies indicate that the compound ML targets metal-free and metal-bound Aß (metal-Aß) species, suppresses Aß aggregation in vitro, and diminishes toxicity induced by Aß and metal-treated Aß in living cells. Comparison of ML to its structural moieties (i.e., 4-(dimethylamino)phenol (DAP) and (8-aminoquinolin-2-yl)methanol (1)) for reactivity with Aß and metal-Aß suggests the synergy of incorporating structural components for both metal chelation and Aß interaction. Moreover, ML is water-soluble and potentially brain permeable, as well as regulates the formation and presence of free radicals. Overall, we demonstrate that a rational structure-based design strategy can generate a small molecule that can target and modulate multiple factors, providing a new tool to uncover and address AD complexity.

Zinc sensors with lower binding affinities for cellular imaging.

Zinc sensors based on 2,3-dipicolylamine (DPA) and quinoline have been synthesized. They fluoresced in the presence of Zn(2+) and remained fluorescent when other metal ions were present. Fluorescence enhancement of the sensors was not seen for most other metal ions. In vitro studies with fibroblasts showed fluorescence when sensor and Zn(2+) were present. As seen by single crystal X-ray analysis, four nitrogens from the sensor bind to Zn(2+). These new sensors have lower binding constants than the pentadentate sensors based on 2,2-DPA.

Terminal and internal olefin epoxidation with cobalt(II) as the catalyst: evidence for an active oxidant Co(II)-acylperoxo species.

A simple catalytic system that uses commercially available cobalt(II) perchlorate as the catalyst and 3-chloroperoxybenzoic acid as the oxidant was found to be very effective in the epoxidation of a variety of olefins with high product selectivity under mild experimental conditions. More challenging targets such as terminal aliphatic olefins were also efficiently and selectively oxidized to the corresponding epoxides. This catalytic system features a nearly nonradical-type and highly stereospecific epoxidation of aliphatic olefin, fast conversion, and high yields. Olefin epoxidation by this catalytic system is proposed to involve a new reactive Co(II)-OOC(O)R species, based on evidence from H(2)(18)O-exchange experiments, the use of peroxyphenylacetic acid as a mechanistic probe, reactivity and Hammett studies, EPR, and ESI-mass spectrometric investigation. However, the O-O bond of a Co(II)-acylperoxo intermediate (Co(II)-OOC(O)R) was found to be cleaved both heterolytically and homolytically if there is no substrate.

Salicylimine-based fluorescent chemosensor for aluminum ions and application to bioimaging.

In this study, an assay to quantify the presence of aluminum ions using a salicylimine-based receptor was developed utilizing turn-on fluorescence enhancement. Upon treatment with aluminum ions, the fluorescence of the sensor was enhanced at 510 nm due to formation of a 1:1 complex between the chemosensor and the aluminum ions at room temperature. As the concentration of Al(3+) was increased, the fluorescence gradually increased. Other metal ions, such as Na(+), Ag(+), K(+), Ca(2+), Mg(2+), Hg(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Pb(2+), Cr(3+), Fe(3+), and In(3+), had no such significant effect on the fluorescence. In addition, we show that the probe could be used to map intracellular Al(3+) distribution in live cells by confocal microscopy.

Amide-based nonheme cobalt(III) olefin epoxidation catalyst: partition of multiple active oxidants Co(V)=O, Co(IV)=O, and Co(III)-OO(O)CR.

A mononuclear nonheme cobalt(III) complex of a tetradentate ligand containing two deprotonated amide moieties, [Co(bpc)Cl(2)][Et(4)N] (1; H(2)bpc = 4,5-dichloro-1,2-bis(2-pyridine-2-carboxamido)benzene), was prepared and then characterized by elemental analysis, IR, UV/Vis, and EPR spectroscopy, and X-ray crystallography. This nonheme Co(III) complex catalyzes olefin epoxidation upon treatment with meta-chloroperbenzoic acid. It is proposed that complex 1 shows partitioning between the heterolytic and homolytic cleavage of an O-O bond to afford Co(V)=O (3) and Co(IV)=O (4) intermediates, proposed to be responsible for the stereospecific olefin epoxidation and radical-type oxidations, respectively. Moreover, under extreme conditions, in which the concentration of an active substrate is very high, the Co-OOC(O)R (2) species is a possible reactive species for epoxidation. Furthermore, partitioning between heterolysis and homolysis of the O-O bond of the intermediate 2 might be very sensitive to the nature of the solvent, and the O-O bond of the Co-OOC(O)R species might proceed predominantly by heterolytic cleavage, even in the presence of small amounts of protic solvent, to produce a discrete Co(V) O intermediate as the dominant reactive species. Evidence for these multiple active oxidants was derived from product analysis, the use of peroxyphenylacetic acid as the peracid, and EPR measurements. The results suggest that a less accessible Co(V)=O moiety can form in a system in which the supporting chelate ligand comprises a mixture of neutral and anionic nitrogen donors.

Possibility of skin epithelial cell transdifferentiation in tracheal reconstruction.

In tissue engineering, injured tissue is normally reconstructed with cells obtained from that tissue itself. However, it is difficult to obtain cells for reconstruction of the trachea because of its shape and limited accessibility. Therefore, other cell sources having similar form and function or stem cells are used for tracheal reconstruction. In a previous study, we used autologous skin epithelial cells and successfully reconstructed canine tracheas. We found that the tracheal epithelial layer was completely covered with ciliated cells, which is a remarkable finding because skin and tracheal epithelial cells originate from different germinal layers and have very different forms. In this study, to elucidate the origin of the ciliated cells, we identified the stem cell contents of skin epithelial cells on primary culture, marked the skin epithelial cells with PKH26 dye, and transplanted them onto canine tracheas. After 5 months, we identified PKH26 fluorescence on the tracheal epithelial layers, especially over the tracheal cartilages. Consequently, we demonstrated that transplanted autologous skin epithelial stem cells can remain viable on the trachea for a few months and can transdifferentiate into tracheal epithelial cells and chondrocytes.

Assessing the activity and diversity of fumarate-fed denitrifying bacteria by performing field single-well push-pull tests.

In situ biological denitrification has been proposed as an important metabolic activity in the remediation of nitrate-contaminated groundwater. In this study, the effects of fumarate, an electron donor for biological denitrification, on the in situ denitrifying activity were determined by using three types of single-well push-pull tests; transport, biostimulation and activity tests. During the tests, changes in microbial community composition were also investigated using denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes. Transport test demonstrated that non-reactive tracer and biologically reactive solutes behaved similarly. A biostimulation test was conducted to stimulate the denitrifying activities of native microorganisms, which were monitored by detecting the simultaneous production of CO(2) and drastic degradations of both nitrate and fumarate after the injection of fumarate as an electron donor and/or carbon source, with nitrate as an electron acceptor. A phylogenetic analysis suggested that the taxonomic affiliation of the dominant species before biostimulation was γ-Proteobacteria, including Acinetobacter species and Pseudomonas fluorescens, while the dominant species after biostimulation were affiliated with ß-Proteobacteria, cytophaga-Flavobacterium-Bacteroides and high G+C gram-positive bacteria. These results suggest that the analyses of groundwater samples using a combination of single well push pull tests with DGGE can be applied to investigate the activity, diversity and composition shift of denitrifying bacteria in a nitrate-contaminated aquifer.

Factors affecting tissue culture and transplantation using omentum.

In tissue engineering, a stable tissue layer and blood vessels are required for complete tissue formation, to provide structural strength and thickness and to supply oxygen and various nutrients. However, this has not been achieved using in vitro tissue-engineered culture techniques, thus many tissue engineering studies of trachea, bladder, and intestine reconstruction have used omentum. However, many factors critical to cell culture and transplantation using omentum have not yet been studied. For these reasons, we conducted a study of artificial trachea reconstruction in dogs using a poly(lactic-co-glycolic acid) (PLGA) porous scaffold, polypropylene prosthesis, and PKH26-labeled cells. We analyzed factors affecting tissue-engineered reconstruction using omentum, such as cell distribution and formation of cell layer and stability of transplant shape on omentum. As a result, we classified failure factors for tissue-engineered application of omentum and suggested three considerations for effective use of omentum in tissue engineering. Our observations may aid in the design and execution of future studies of omentum usage in tissue engineering.