Neuronal innervation regulates the secretion of neurotrophic myokines and exosomes from skeletal muscle.

Myokines and exosomes, originating from skeletal muscle, are shown to play a significant role in maintaining brain homeostasis. While exercise has been reported to promote muscle secretion, little is known about the effects of neuronal innervation and activity on the yield and molecular composition of biologically active molecules from muscle. As neuromuscular diseases and disabilities associated with denervation impact muscle metabolism, we hypothesize that neuronal innervation and firing may play a pivotal role in regulating secretion activities of skeletal muscles. We examined this hypothesis using an engineered neuromuscular tissue model consisting of skeletal muscles innervated by motor neurons. The innervated muscles displayed elevated expression of mRNAs encoding neurotrophic myokines, such as interleukin-6, brain-derived neurotrophic factor, and FDNC5, as well as the mRNA of peroxisome-proliferator-activated receptor γ coactivator 1α, a key regulator of muscle metabolism. Upon glutamate stimulation, the innervated muscles secreted higher levels of irisin and exosomes containing more diverse neurotrophic microRNAs than neuron-free muscles. Consequently, biological factors secreted by innervated muscles enhanced branching, axonal transport, and, ultimately, spontaneous network activities of primary hippocampal neurons in vitro. Overall, these results reveal the importance of neuronal innervation in modulating muscle-derived factors that promote neuronal function and suggest that the engineered neuromuscular tissue model holds significant promise as a platform for producing neurotrophic molecules.

Nanoscale surface coatings and topographies for neural interfaces.

With the lack of minimally invasive tools for probing neuronal systems across spatiotemporal scales, understanding the working mechanism of the nervous system and limited assessments available are imperative to prevent or treat neurological disorders. In particular, nanoengineered neural interfaces can provide a solution to this technological barrier. This review covers recent surface engineering approaches, including nanoscale surface coatings, and a range of topographies from the microscale to the nanoscale, primarily focusing on neural-interfaced biosystems. Specifically, the immobilization of bioactive molecules to fertilize the neural cell lineage, topographical engineering to induce mechanotransduction in neural cells, and enhanced cell-chip coupling using three-dimensional structured surfaces are highlighted. Advances in neural interface design will help us understand the nervous system, thereby achieving the effective treatments for neurological disorders. STATEMENT OF SIGNIFICANCE: • This review focuses on designing bioactive neural interface with a nanoscale chemical modification and topographical engineering at multiscale perspective. • Versatile nanoscale surface coatings and topographies for neural interface are summarized. • Recent advances in bioactive materials applicable for neural cell culture, electrophysiological sensing, and neural implants are reviewed.

Particle Separation in a Microchannel with a T-Shaped Cross-Section Using Co-Flow of Newtonian and Viscoelastic Fluids.

In this study, we investigated the particle separation phenomenon in a microchannel with a T-shaped cross-section, a unique design detailed in our previous study. Utilizing a co-flow system within this T-shaped microchannel, we examined two types of flow configuration: one where a Newtonian fluid served as the inner fluid and a viscoelastic fluid as the outer fluid (Newtonian/viscoelastic), and another where both the inner and outer fluids were Newtonian fluids (Newtonian/Newtonian). We introduced a mixture of three differently sized particles into the microchannel through the outer fluid and observed that the co-flow of Newtonian/viscoelastic fluids effectively separated particles based on their size compared with Newtonian/Newtonian fluids. In this context, we evaluated and compared the particle separation efficiency, recovery rate, and enrichment factor across both co-flow configurations. The Newtonian/viscoelastic co-flow system demonstrated a superior efficiency and recovery ratio when compared with the Newtonian/Newtonian system. Additionally, we assessed the influence of the flow rate ratio between the inner and outer fluids on particle separation within each co-flow system. Our results indicated that increasing the flow rate ratio enhanced the separation efficiency, particularly in the Newtonian/viscoelastic co-flow configuration. Consequently, this study substantiates the potential of utilizing a Newtonian/viscoelastic co-flow system in a T-shaped straight microchannel for the simultaneous separation of three differently sized particles.

Streamlined Specimen Purification for Rapid COVID-19 Diagnosis Using Positively Charged Polymer Thin Film-Coated Surfaces and Chamber Digital PCR.

The ongoing coronavirus disease 2019 (COVID-19) pandemic demands rapid and straightforward diagnostic tools to prevent early-stage viral transmission. Although nasopharyngeal swabs are a widely used patient sample collection method for diagnosing COVID-19, using these samples for diagnosis without RNA extraction increases the risk of obtaining false-positive and -negative results. Thus, multiple purification steps are necessary, which are time-consuming, generate significant waste, and result in substantial sample loss. To address these issues, we developed surface-modified polymerase chain reaction (PCR) tubes using the tertiary aminated polymer poly(2-dimethylaminomethylstyrene) (pDMAMS) via initiated chemical vapor deposition. Introducing the clinical samples into the pDMAMS-coated tubes resulted in approximately 100% RNA capture efficiency within 25 min, which occurred through electrostatic interactions between the positively charged pDMAMS surface and the negatively charged RNA. The captured RNA is then detected via chamber digital PCR, enabling a sensitive, accurate, and rapid diagnosis. Our platform provides a simple and efficient RNA extraction and detection strategy that allows detection from 22 nasopharyngeal swabs and 21 saliva specimens with 0% false negatives. The proposed method can facilitate the diagnosis of COVID-19 and contribute to the prevention of early-stage transmission.

Hierarchical Topography with Tunable Micro- and Nanoarchitectonics for Highly Enhanced Cardiomyocyte Maturation via Multi-Scale Mechanotransduction.

Enhancing cardiomyocyte (CM) maturation by topographical cues is a critical issue in cardiac tissue engineering. Thus far, single-scale topographies with a broad range of feature shapes and dimensions have been utilized including grooves, pillars, and fibers. This study reports for the first time a hierarchical structure composed of nano-pillars (nPs) on micro-wrinkles (µWs) for effective maturation of CMs. Through capillary force lithography followed by a wrinkling process, vast size ranges of topographies are fabricated, and the responses of CMs are systematically investigated. Maturation of CMs on the hierarchical structures is highly enhanced compared to a single-scale topography: cardiac differentiation of H9C2s (rat cardiomyocytes) on the hierarchical topography is ≈ 2.8 and ≈ 1.9 times higher than those consisting of single-scale µWs and nPs. Both nPs and µWs have important roles in cardiac maturation, and the aspect ratio (height/diameter) of the nPs and the wavelength of the µWs are important in CM maturation. This enhancement is caused by strong focal adhesion and nucleus mediated mechanotransduction of CMs from the confinement effects of the different wavelengths of µWs and the cellular membrane protrusion on the nPs. This study demonstrates how a large family of hierarchical structures is used for cardiac maturation.

Monodisperse Micro-Droplet Generation in Microfluidic Channel with Asymmetric Cross-Sectional Shape.

Micro-droplets are widely used in the fields of chemical and biological research, such as drug delivery, material synthesis, point-of-care diagnostics, and digital PCR. Droplet-based microfluidics has many advantages, such as small reagent consumption, fast reaction time, and independent control of each droplet. Therefore, various micro-droplet generation methods have been proposed, including T-junction breakup, capillary flow-focusing, planar flow-focusing, step emulsification, and high aspect (height-to-width) ratio confinement. In this study, we propose a microfluidic device for generating monodisperse micro-droplets, the microfluidic channel of which has an asymmetric cross-sectional shape and high hypotenuse-to-width ratio (HTWR). It was fabricated using basic MEMS processes, such as photolithography, anisotropic wet etching of Si, and polydimethylsiloxane (PDMS) molding. Due to the geometric similarity of a Si channel and a PDMS mold, both of which were created through the anisotropic etching process of a single crystal Si, the microfluidic channel with the asymmetric cross-sectional shape and high HTWR was easily realized. The effects of HTWR of channels on the size and uniformity of generated micro-droplets were investigated. The monodisperse micro-droplets were generated as the HTWR of the asymmetric channel was over 3.5. In addition, it was found that the flow direction of the oil solution (continuous phase) affected the size of micro-droplets due to the asymmetric channel structures. Two kinds of monodisperse droplets with different sizes were successfully generated for a wider range of flow rates using the asymmetric channel structure in the developed microfluidic device.

Square microchannel enables to focus and orient ellipsoidal Euglena gracilis cells by two-dimensional acoustic standing wave.

Flow cytometry has become an indispensable tool for counting, analyzing, and sorting large cell populations in biological research and medical practice. Unfortunately, it has limitations in the analysis of non-spherically shaped cells due to the variation of their alignment with respect to the flow direction and, hence, the optical interrogation axis, resulting in unreliable cell analysis. Here, we present a simple on-chip acoustofluidic method to fix the orientation of ellipsoidal cells and focus them into a single, aligned stream. Specifically, by generating acoustic standing waves inside a 100 ⋅ 100 µm square-shaped microchannel, we successfully aligned and focused up to 97.7% of a population of Euglena gracilis (an ellipsoidal shaped microalgal species) cells in the center of the microchannel with high precision at a volume rate of 25 to 200 µL min-1. Uniform positioning of ellipsoidal cells is essential for making flow cytometry applicable to the investigation of a greater variety of cell populations and is expected to be beneficial for ecological studies and aquaculture.

Inertia-Acoustophoresis Hybrid Microfluidic Device for Rapid and Efficient Cell Separation.

In this paper, we proposed an integrated microfluidic device that could demonstrate the non-contact, label-free separation of particles and cells through the combination of inertial microfluidics and acoustophoresis. The proposed device integrated two microfluidic chips which were a PDMS channel chip on top of the silicon-based acoustofluidic chip. The PDMS chip worked by prefocusing the particles/cells through inducing the inertial force of the channel structure. The connected acoustofluidic chips separated particles based on their size through an acoustic radiation force. In the serpentine-shaped PDMS chip, particles formed two lines focusing in the channel, and a trifugal-shaped acoustofluidic chip displaced and separated particles, in which larger particles focused on the central channel and smaller ones moved to the side channels. The simultaneous fluidic works allowed high-efficiency particle separation. Using this novel acoustofluidic device with an inertial microchannel, the separation of particles and cells based on their size was presented and analyzed, and the efficiency of the device was shown. The device demonstrated excellent separation performance with a high recovery ratio (up to 96.3%), separation efficiency (up to 99%), and high volume rate (>100 µL/min). Our results showed that integrated devices could be a viable alternative to current cell separation based on their low cost, reduced sample consumption and high throughput capability.

Particle Focusing in a Straight Microchannel with Non-Rectangular Cross-Section.

Recently, studies on particle behavior under Newtonian and non-Newtonian fluids in microchannel have attracted considerable attention because particles and cells of interest can be manipulated and separated from biological samples without any external force. In this paper, two kinds of microchannels with non-rectangular cross-section were fabricated using basic MEMS processes (photolithography, reactive ion etching and anisotropy wet etching), plasma bonding and self-alignment between two PDMS structures. They were used to achieve the experiments for inertial and elasto-inertial particle focusing under Newtonian and non-Newtonian fluids. The particle behavior was compared and investigated for different flow rates and particle size in the microchannel with rhombic and equilateral hexagonal cross section. We also investigated the influence of Newtonian fluid and viscoelastic fluid on particle migration in both microchannels through the numerical simulation. The experimental results showed the multi-line particle focusing in Newtonian fluid over a wide range of flow rates, but the single-line particle focusing was formed in the centerline under non-Newtonian fluid. The tighter particle focusing appeared under non-Newtonian fluid in the microchannel with equilateral hexagonal cross-section than in the microchannel with rhombic cross section because of the effect of an obtuse angle. It revealed that particles suspended in the channel are likely to drift toward a channel center due to a negative net elasto-inertial force throughout the cross-sectional area. Simulation results support the present experimental observation that the viscoelastic fluid in the microchannel with rhombic and equilateral hexagonal cross-section significantly influences on the particle migration toward the channel center owing to coupled effect of inertia and elasticity.

High-Aspect-Ratio Microfluidic Channel with Parallelogram Cross-Section for Monodisperse Droplet Generation.

Droplet-based microfluidics has been widely used as a potent high-throughput platform due to various advantages, such as a small volume of reagent consumption, massive production of droplets, fast reaction time, and independent control of each droplet. Therefore, droplet microfluidic systems demand the reliable generation of droplets with precise and effective control over their size and distribution, which is critically important for various applications in the fields of chemical analysis, material synthesis, lab-on-a-chip, cell research, diagnostic test, and so on. In this study, we propose a microfluidic device with a high-aspect-ratio (HAR) channel, which has a parallelogram cross-section, for generating monodisperse droplets. The HAR channel was fabricated using simple and cheap MEMS processes, such as photolithography, anisotropic wet etching, and PDMS molding, without expensive equipment. In addition, the parallelogram cross-section channel structure, regarded as a difficult shape to implement in previous fabrication methods, was easily formed by the self-alignment between the silicon channel and the PDMS mold, both of which were created from a single crystal silicon through an anisotropic etching process. We investigated the effects of the cross-sectional shape (parallelogram vs. rectangle) and height-to-width ratio of microfluidic channels on the size and uniformity of generated droplets. Using the developed HAR channel with the parallelogram cross-section, we successfully obtained smaller monodisperse droplets for a wider range of flow rates, compared with a previously reported HAR channel with a rectangular cross-section.

A Super-Boosted Hybrid Plasmonic Upconversion Process for Photodetection at 1550 nm Wavelength.

A super-boosted hybrid plasmonic upconversion (UC) architecture comprising a hierarchical plasmonic upconversion (HPU) film and a polymeric microlens array (MLA) film is proposed for efficient photodetection at a wavelength of 1550 nm. Plasmonic metasurfaces and Au core-satellite nanoassembly (CSNA) films can strongly induce a more effective plasmonic effect by providing numerous hot spots in an intense local electromagnetic field up to wavelengths exceeding 1550 nm. Hence, significant UC emission enhancement is realized via the amplified plasmonic coupling of an HPU film comprising an Au CSNA and UC nanoparticles. Furthermore, an MLA polymer film is synergistically coupled with the HPU film, thereby focusing the incident near-infrared light in the micrometer region, including the plasmonic nanostructure area. Consequently, the plasmonic effect super-boosted by microfocusing the incident light, significantly lowers the detectable power limit of a device, resulting in superior sensitivity and responsivity at weak excitation powers. Finally, a triple-cation perovskite-based photodetector coupled with the hybrid plasmonic UC film exhibits the excellent values of responsivity and detectivity of 9.80 A W-1 and 8.22 × 1012 Jones at a weak power density of ≈0.03 mW cm-2 , respectively, demonstrating that the device performance is enhanced by more than 104 magnitudes over a reference sample.

A Versatile Surface Modification Method via Vapor-phase Deposited Functional Polymer Films for Biomedical Device Applications.

For last two decades, the demand for precisely engineered three-dimensional structures has increased continuously for the developments of biomaterials. With the recent advances in micro- and nano-fabrication techniques, various devices with complex surface geometries have been devised and produced in the pharmaceutical and medical fields for various biomedical applications including drug delivery and biosensors. These advanced biomaterials have been designed to mimic the natural environments of tissues more closely and to enhance the performance for their corresponding biomedical applications. One of the important aspects in the rational design of biomaterials is how to configure the surface of the biomedical devices for better control of the chemical and physical properties of the bioactive surfaces without compromising their bulk characteristics. In this viewpoint, it of critical importance to secure a versatile method to modify the surface of various biomedical devices. Recently, a vapor phase method, termed initiated chemical vapor deposition (iCVD) has emerged as damage-free method highly beneficial for the conformal deposition of various functional polymer films onto many kinds of micro- and nano-structured surfaces without restrictions on the substrate material or geometry, which is not trivial to achieve by conventional solution-based surface functionalization methods. With proper structural design, the functional polymer thin film via iCVD can impart required functionality to the biomaterial surfaces while maintaining the fine structure thereon. We believe the iCVD technique can be not only a valuable approach towards fundamental cell-material studies, but also of great importance as a platform technology to extend to other prospective biomaterial designs and material interface modifications for biomedical applications.

Heparin-mediated electrostatic immobilization of bFGF via functional polymer films for enhanced self-renewal of human neural stem cells.

Preserving the self-renewal capability of undifferentiated human neural stem cells (hNSCs) is one of the crucial prerequisites for efficient hNSC-based regenerative medicine. Considering that basic fibroblast growth factor (bFGF) is one of the key contributing factors in maintaining the self-renewal property of hNSCs, the bioactivity and stability of bFGF in the hNSC culture should be regulated carefully. In this study, we developed a functional polymer film of poly(glycidyl methacrylate (GMA)-co-N,N-dimethylaminoethyl methacrylate (DMAEMA)) (coGD, or p(GMA-co-DMAEMA)) via initiated chemical vapor deposition (iCVD), which facilitated a stable, electrostatic adsorption of heparin and subsequent immobilization of bFGF. The bFGF-immobilized coGD surface substantially enhanced the proliferation rate and neurosphere forming ability of hNSCs compared to tissue culture plate (TCP). The expression of the stemness markers of hNSCs such as NESTIN and SOX-2 was also upregulated prominently on the coGD surface. Also, the hNSCs cultured on the coGD surface showed enhanced neurogenesis upon spontaneous differentiation. The immobilized bFGF on the coGD surface stimulated the expression of bFGF receptors and subsequently activated the mitogen-activated protein kinase (MAPK) pathway, attributed to the increase in self-renewal property of hNSCs. Our results indicate that the coGD surface allowed in situ heparin-mediated bFGF immobilization, which served as a robust platform to generate hNSC neurospheres with enhanced self-renewal and differentiation capabilities and thereby will prompt an advance in the field of therapeutics of neurodegenerative diseases.

Particle Focusing under Newtonian and Viscoelastic Flow in a Straight Rhombic Microchannel.

Particle behavior in viscoelastic fluids has attracted considerable attention in recent years. In viscoelastic fluids, as opposed to Newtonian fluids, particle focusing can be simply realized in a microchannel without any external forces or complex structures. In this study, a polydimethylsiloxane (PDMS) microchannel with a rhombic cross-sectional shape was fabricated to experimentally investigate the behavior of inertial and elasto-inertial particles. Particle migration and behavior in Newtonian and non-Newtonian fluids were compared with respect to the flow rate and particle size to investigate their effect on the particle focusing position and focusing width. The PDMS rhombic microchannel was fabricated using basic microelectromechanical systems (MEMS) processes. The experimental results showed that single-line particle focusing was formed along the centerline of the microchannel in the non-Newtonian fluid, unlike the double-line particle focusing in the Newtonian fluid over a wide range of flow rates. Numerical simulation using the same flow conditions as in the experiments revealed that the particles suspended in the channel tend to drift toward the center of the channel owing to the negative net force throughout the cross-sectional area. This supports the experimental observation that the viscoelastic fluid in the rhombic microchannel significantly influences particle migration toward the channel center without any external force owing to coupling between the inertia and elasticity.

Electrothermal soft manipulator enabling safe transport and handling of thin cell/tissue sheets and bioelectronic devices.

"Living" cell sheets or bioelectronic chips have great potentials to improve the quality of diagnostics and therapies. However, handling these thin and delicate materials remains a grand challenge because the external force applied for gripping and releasing can easily deform or damage the materials. This study presents a soft manipulator that can manipulate and transport cell/tissue sheets and ultrathin wearable biosensing devices seamlessly by recapitulating how a cephalopod's suction cup works. The soft manipulator consists of an ultrafast thermo-responsive, microchanneled hydrogel layer with tissue-like softness and an electric heater layer. The electric current to the manipulator drives microchannels of the gel to shrink/expand and results in a pressure change through the microchannels. The manipulator can lift/detach an object within 10 s and can be used repeatedly over 50 times. This soft manipulator would be highly useful for safe and reliable assembly and implantation of therapeutic cell/tissue sheets and biosensing devices.

A Surface-Tailoring Method for Rapid Non-Thermosensitive Cell-Sheet Engineering via Functional Polymer Coatings.

Cell sheet engineering, a technique utilizing a monolayer cell sheet, has recently emerged as a promising technology for scaffold-free tissue engineering. In contrast to conventional tissue-engineering approaches, the cell sheet technology allows cell harvest as a continuous cell sheet with intact extracellular matrix proteins and cell-cell junction, which facilitates cell transplantation without any other artificial biomaterials. A facile, non-thermoresponsive method is demonstrated for a rapid but highly reliable platform for cell-sheet engineering. The developed method exploits the precise modulation of cell-substrate interactions by controlling the surface energy of the substrate via a series of functional polymer coatings to enable prompt cell sheet harvesting within 100 s. The engineered surface can trigger an intrinsic cellular response upon the depletion of divalent cations, leading to spontaneous cell sheet detachment under physiological conditions (pH 7.4 and 37 °C) in a non-thermoresponsive manner. Additionally, the therapeutic potential of the cell sheet is successfully demonstrated by the transplantation of multilayered cell sheets into mouse models of diabetic wounds and ischemia. These findings highlight the ability of the developed surface for non-thermoresponsive cell sheet engineering to serve as a robust platform for regenerative medicine and provide significant breakthroughs in cell sheet technology.

Three-Dimensional Spheroid Culture on Polymer-Coated Surface Potentiate Stem Cell Functions via Enhanced Cell-Extracellular Matrix Interactions.

The aggregation of mesenchymal stem cells (MSCs) into three-dimensional (3D) spheroids has emerged as a promising therapeutic candidate for the treatment of a variety of diseases. In spite of the numerous 3D culture methods suggested recently for MSC spheroid generation, it is still elusive to fully reflect real stem cell niches; this effort majorly suffers from a lack of cell-extracellular matrix (ECM) interactions within the 3D spheroids. In this study, we develop a simple but versatile method for generating human MSC (hMSC) spheroids by culturing the cells on a functional polymer film surface, poly(2,4,6,8-tetravinyl-2,4,6,8-tetramethyl cyclotetrasiloxane) (pV4D4). Interestingly, the pV4D4-coated surface allows a dynamic cell adhesion to the polymer surface while developing the formation of 3D spheroids. The corresponding mechanotransduction promotes the expression of the endogenous ECM and, in turn, results in a remarkable improvement in self-renewal abilities, pro-angiogenic potency, and multilineage differentiation capabilities. This observation highlights the significance of our method compared to the conventional spheroid-generating methods in terms of recreating the ECM-rich microenvironment. We believe the developed surface can serve as a versatile but reliable method for stem cell-based tissue engineering and regenerative medicine.

Polymer-Coated Surface as an Enzyme-Free Culture Platform to Improve Human Mesenchymal Stem Cell (hMSC) Characteristics in Extended Passaging.

For efficient therapeutic use of human mesenchymal stem cells (hMSCs), maximizing their self-renewal performance and multipotency must be fully retained. However, conventional trypsin-based cell passaging methods are known to damage the attached cells to be detached because of the inherent corrosive nature of trypsin, and continuous passaging substantially degrades the self-renewal and differentiation capacity of hMSCs. Therefore, it is imperative to secure a damage-free passaging method that supports cell growth as well as their stem cell function. Here, an enzyme-free cell detachment method using a poly(ethylene glycol dimethacrylate) (pEGDMA)-coated surface is developed, which allows for reduced integrin-dependent cell adhesion. Cell detachment can be facilitated simply by treating the plated cells on the pEGDMA surface with Ca2+ and Mg2+-depleted DPBS. Spontaneous cell detachment occurs within 10 min with the full retention of the cell viability and proliferation ability of hMSCs. Especially, the detachment method can minimize the surface protein damage of hMSCs compared to the conventional trypsin treatment and preserve the self-renewal property and differentiation capacity even with an increased passage number over 10. The developed enzyme-free detachment method using the pEGDMA-coated surface is highly promising for a culture platform to broaden its application to the field of tissue engineering and regenerative medicine.

Facile Fabrication of High-Definition Hierarchical Wrinkle Structures for Investigating the Geometry-Sensitive Fate Commitment of Human Neural Stem Cells.

As neural stem cells (NSCs) interact with biophysical cues from their niche during development, it is important to understand the biomolecular mechanism of how the NSCs process these biophysical cues to regulate their behaviors. In particular, anisotropic geometric cues in micro-/nanoscale have been utilized to investigate the biophysical effect of the structure on NSCs behaviors. Here, a series of new nanoscale anisotropic wrinkle structures with the a range of wavelength scales (from 50 nm to 37 µm) was developed to demonstrate the effect of the anisotropic nanostructure on the fate commitment of NSCs. Intriguingly, two distinct characteristic length scales promoted the neurogenesis. Each wavelength scale showed a striking variation in terms of dependency on the directionality of the structures, suggesting the existence of at least two different ways in the processing of anisotropic geometries for neurogenesis. Furthermore, the combined effect of the two distinctive length scales was observed by employing hierarchical multiscale wrinkle structures with two characteristic neurogenesis-promoting wavelengths. Taken together, the wrinkle structure system developed in this study can serve as an effective platform to advance the understanding of how cells sense anisotropic geometries for their specific cellular behaviors. Furthermore, this could provide clues for improving nerve regeneration system of stem cell therapies.

Stimulus-Responsive Anti-Oxidizing Drug Crystals and their Ecological Implication.

Various antioxidants are being used to neutralize the harmful effects of reactive oxygen species (ROS) overproduced in diseased tissues and contaminated environments. Polymer-directed crystallization of antioxidants has attracted attention as a way to control drug efficacy through molecular dissolution. However, most recrystallized antioxidants undertake continuous dissolution independent of the ROS level, thus causing side-effects. This study demonstrates a unique method to assemble antioxidant crystals that modulate their dissolution rate in response to the ROS level. We hypothesized that antioxidants recrystallized using a ROS-labile polymer would be triggered to dissolve when the ROS level increases. We examined this hypothesis by using catechin as a model antioxidant. Catechin was recrystallized using polyethylenimine cross-linked with ROS-labile diselanediylbis-(ethane-2,1-diyl)-diacrylate. Catechin crystallized with the ROS-labile polymer displays accelerated dissolution proportional to the H2 O2 concentration. The ROS-responsive catechin crystals protect vascular cells from oxidative insults by activating intracellular glutathione peroxidase expression and, in turn, inhibiting an increase in the intracellular oxidative stress. In addition, ROS-responsive catechin crystals alleviate changes in the heart rate of Daphnia magna in oxidative media. We propose that the results of this study would be broadly useful for improving the therapeutic efficacy of a broad array of drug compounds.