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New environmental policies and initiatives increasingly drive firms to develop sustainable technologies, yet it is unclear why firms often decide not to capture value from the technologies that they create. We argue that the under-implementation of environmental technologies can be explained by the concept of institutional decoupling, which suggests that organizations may engage in symbolic actions without necessarily taking the risk of implementing a new technology in a less established market when there is no decisive evidence of its commercial viability. Focusing on the Korean Green Certification Program, a government-initiated review system for environmental technologies, we find that the timing of certification is a key source of variation in the implementation of certified technologies. Our findings also show that the main effect is conditioned by performance feedback and niche density—the factors that shape a firm's risk perceptions. Implications for organization studies, sustainable innovation, and environmental policies are discussed. • Firms often develop sustainable technologies and obtain formal certifications. • However, the degree to which they actually implement certified technologies varies. • We show that the timing of obtaining certification is a key factor of variation. • The timing effects are also conditioned by a firm's risk perceptions. [ABSTRACT FROM AUTHOR]

Extracellular vesicles (EVs), such as exosomes, are nano-sized vesicles derived from endocytic membranes and contain biomolecules such as proteins, lipids, RNAs, and DNAs for the transfer of signals to recipient cells, playing significant roles in cell-to-cell communication. Discovery of exosomes has attracted attention for possible use as next generation therapies in clinical applications; however, several studies suggest that cells secrete exosomes that perform as mediators in the tumor niche and play several roles in tumorigenesis, angiogenesis, and metastasis. Recently, stem cell-derived exosomes have been suggested as a desirable source for regenerative medicine due to their roles in the promotion of angiogenesis via migratory and proliferative mechanisms. This review is aimed at demonstrating the present knowledge of stem cell-derived exosomes and cell-engineered nanovesicles (CNVs) as proliferative, migratory, and anti-senescent therapeutic biomaterial for use in tissue regeneration; wound healing and anti-ageing are explained. We conclude this review by discussing the future perspectives of stem cell-derived exosomes and CNVs as a platform in therapeutic strategies for treatment of wound damage and skin aging. [ABSTRACT FROM AUTHOR]

Stem cells secrete numerous paracrine factors, such as cytokines, growth factors, and extracellular vesicles. As a kind of extracellular vesicle (EV), exosomes produced in the endosomal compartment of eukaryotic cells have recently emerged as a biomedical material for regenerative medicine, because they contain many valuable contents that are derived from the host cells, and can stably deliver those contents to other recipient cells. Although we have previously demonstrated the beneficial effects of human induced potent stem cell-derived exosomes (iPSC-Exo) on the aging of skin fibroblasts, low production yield has remained an obstacle for clinical applications. In this study, we generated cell-engineered nanovesicles (CENVs) by serial extrusion of human iPSCs through membrane filters with diminishing pore sizes, and explored whether the iPSC-CENV ameliorates physiological alterations of human dermal fibroblasts (HDFs) that occur by natural senescence. The iPSC-CENV exhibited similar characteristics to the iPSC-Exo, while the production yield was drastically increased compared to that of iPSC-derived EVs, including exosomes. The proliferation and migration of both young and senescent HDFs were stimulated by the treatment with iPSC-CENVs. In addition, it was revealed that the iPSC-CNEV restored senescence-related alterations of gene expression. Treatment with iPSC-CENVs significantly reduced the activity of senescence-associated-β-galactosidase (SA-β-Gal) in senescent HDFs, as well as suppressing the elevated expression of p53 and p21, key factors involved in cell cycle arrest, apoptosis, and cellular senescence signaling pathways. Taken together, these results suggest that iPSC-CENV could provide an excellent alternative to iPSC-exo, and be exploited as a resource for the treatment of signs of skin aging. [ABSTRACT FROM AUTHOR]

CRISPR/Cas9 system has served a new insight in genome editing of eukaryotes, including human cells. In this system, delivery of Cas9 nuclease with guide RNA has been central challenge in developing safe and efficient techniques. The viral delivery of genes encoding these two components i.e. Cas9 and guide RNA may cause unexpected integration of the DNA sequence into the host cell genome, and lead to potential safety problems such as tumorigenesis. Herein, we report that the Cas9 protein can be directly delivered into the human cells through fusion with 30Kc19, a cell-penetrating and protein-stabilizing protein originating from silkworm. The 30Kc19-conjugated Cas9 (30Kc19-Cas9) showed higher stability than native Cas9 for thermal and chemical-induced inactivation in DNA-cleavable activity. In addition, it was demonstrated that 30Kc19-Cas9 was efficiently delivered into human cells and resulted in targeted gene disruption with single guide RNA by showing gene expression and site-specific mutations in the genome. With the advantages of efficient delivery in addition to the enhancement of Cas9 stability, this method is expected to provide a versatile strategy to advance non-viral and clinically-feasible genome editing for in vivo applications. [ABSTRACT FROM AUTHOR]

In proton exchange membrane fuel cells (PEMFCs), securing sufficient hydration in perfluorosulfonic acid (PFSA) membrane is considered an indicator of performance and durability. Here, we present a straightforward yet effective strategy that sandwiches the nanoporous carbon nanotube (CNT) sheet between the cathodic gas diffusion backing layer (GDBL) and bipolar plate (BP) of a conventional membrane electrode assembly (MEA). CNT sheets are synthesized through the cost-effective direct spinning method. The carbon source, winding rates, and the number of layers are varied to tailor the thickness and nanoporous morphology of the CNT sheets (5, 15, and 30 μm). CNT interlayer MEAs are evaluated for their performance in various temperature and relative humidity (RH), ranges of 80–120 °C and 25–100% RH. With these nanoporous CNT sheets, reactants disperse homogeneously, enhancing membrane hydration and interfacial contact, thereby fulfilling superior performance compared to conventional under entire conditions. Among CNT interlayers, the 30 μm records a 115.4% enhanced peak power density (0.28 W cm−2) and 89.2% extended durability (∼187 h) than conventional under 120 °C and 25% RH. Our strategy delivers a broader perspective of PEMFCs and other fuel cell types based on their ease of production and reproducibility. [Display omitted] • Nanoporous CNT functional interlayers were prepared by direct spinning. • CNT interlayer notably boosts the performance of PEFMCs under all test conditions. • CNT interlayer also achieves 89.2% extended durability of PEMFCs. • These promising boosting mechanisms were demonstrated and optimized. [ABSTRACT FROM AUTHOR]

Summary: An ultrathin layer composed of carbon nanotubes (CNTs) was deposited on the cathodic catalyst layer to boost performance of polymer electrolyte membrane fuel cell (PEMFC) under low to mid relative humidity (RH) conditions. The CNT‐deposited layer (CDL) was formed without modifying the PEMFC components. To investigate the behavior of water and reactants at the inner interface of the membrane electrode assembly (MEA), we characterized the morphology of the CDL (contact angle, pore size distribution, specific surface area, field emission scanning electron microscopy, and energy dispersive spectroscopy images). The CDL in PEMFCs was used as a contributor to enhance the membrane hydration. Thereby performances have been significantly enhanced. Additionally, the three‐dimensional nanostructure of the CDL expanded the active area by uniform dispersion of the reactants. The polarization curves of the conventional MEA and MEA with CDL were evaluated under diverse RH (100%, 70%, 50%, and 30% RH). In the low to mid RH conditions, the maximum power densities were increased by 29.7% (70% RH), 26.6% (50% RH), and 25.5% (30% RH) compared with the conventional MEA. Especially, the maximum power density of the MEA with CDL (0.547 W/cm2 at 70% RH) was higher than that of the conventional MEA (0.482 W/cm2 at 100% RH). Thus, MEA with CDL demonstrated excellent performance enhancement under low to mid RH conditions. [ABSTRACT FROM AUTHOR]

A novel method for replenishing platinum catalysts on an electrolyte membrane of polymer electrolyte membrane fuel cell (PEMFC) is studied. The method injects electrocatalyst‐supplementing ink into a pre‐assembled fuel cell in a simple and non‐destructive manner. For replenishing, straightforward catalyst‐replenishment equipment and corresponding protocol are proposed. The protocol consists of injection, penetration, and purge processes. As a feasibility study, the method is performed on fuel cells with pristine membranes. Target fuel cells for this study include a membrane‐assembled cell without catalyst layers (CLs) (Cell 1) and a cell assembled with a membrane‐coated cathodic CL (Cell 2). An open‐circuit voltage of 0.804 V in Cell 1 and a current of 77 mA in Cell 2 are measured, as supported through electrochemical impedance spectroscopy. Results of energy‐dispersive X‐ray spectroscopy and X‐ray photoelectron spectroscopy also support the presence of platinum catalysts. [ABSTRACT FROM AUTHOR]

In this study, water removal is observed through a transparent fuel cell, and the relationships between it and the responses of voltage and impedance are analyzed. The water flows in the channel are accompanied by voltage soaring. For all studied cases, water flow appearances increase as GDL flooding is induced by supplying more vapor; for example, under a stoichiometry ratio of 2.0, the number of water flow appearances is 0, 3, and 25 for 1800 s as relative humidity increase to 30, 50, and 100%. The average voltage is calculated, and a positive relationship between it and the frequency of water flows is determined. The results reveal that frequent flooding-induced water removal could be one strategy to enhance fuel cell performance. [Display omitted] • The transparent PEMFC is fabricated for observation of water flows at channels. • The water flows appear with every fluctuation of the voltage jump and impedance drop. • GDL flooding induced by more supplied vapor results in frequent water removal from porous electrode. • The performance is enhanced due to frequent voltage recoveries under flooding inducing operation. [ABSTRACT FROM AUTHOR]

Water management is essential to achieve guaranteed performance and durability of polymer electrolyte membrane fuel cells (PEMFCs), and to this end, accurate prognostics and health monitoring should be performed. In this study, we introduce high-frequency resistance (HFR) fluctuations as a parameter to accurately detect the flooding of PEMFCs. Low-frequency resistance (LFR), which is used for diagnosing flooding, is compared with HFR. Under the state of gradual flooding, severe flooding, and flooding mitigation, HFR shows a dynamic response of gradual increase, sharp rise, and decrease, respectively. Conversely, LFR does not respond to gradual flooding and flooding mitigation but only increases rapidly under severe flooding. According to current fluctuations, the reliability of the LFR and HFR fluctuations is evaluated and found to be 77.2 and 100%, respectively. In addition, the LFR and HFR fluctuations precede the current variations by an average of 0.927 s and 3.01 s, respectively. Experimental results demonstrate that HFR is more effective than LFR and current variations for real-time flooding diagnosis because of its high accuracy and fast response. In future work, dynamic HFR fluctuations can be used to simultaneously diagnose flooding and membrane dehydration. [Display omitted] • High-frequency resistance for analyzing real-time flooding diagnosis in fuel cell. • Dynamic HFR response was observed in various stages of flooding. • Detection accuracy of HFR was 100%. • HFR fluctuations caused by flooding preceded the current change on average by 3.01 s. • Flooding can be diagnosed by HFR even when condensation occurs in fuel cell. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNT) based nanoporous layer contacting the catalyst layer in polymer electrolyte membrane fuel cells (PEMFCs) is investigated. Nanoporous CNT-5, CNT-15, and CNT-40 sheets are prepared via direct spinning method with thicknesses is 5, 15, and 40 μm, respectively. The ethanol-derived CNT-5 possess sparse pore networks, whereas CNT-15 and CNT-40 derived from acetone exhibit fine networks, and CNT-15 and CNT-40 differ only in thickness. The CNTs are employed as either standalone nanoporous layer or as an additional layer with carbon-black microporous layer (MPL). Scanning electron microscopy and sessile drop method are utilized for CNT characterization. Current-voltage polarization curve and electrochemical impedance spectroscopy are recorded for the PEMFC characterization. The best performance is obtained when CNT-15 is adopted as an additional nanoporous layer with MPL in the dry operation. The current densities at a cell voltage of 0.6 V are 0.454 and 0.743 A cm−2 in dry and wet operations, respectively, corresponding to an increase of 28.5% and 57.1%, respectively, compared to carbon-black MPL. Enhancements in water management and reaction kinetics lead to this performance increase. In particular, the enhanced water storage and expulsion are benefits differentiated from employing CNT as the single nanoporous layer. [Display omitted] ∙ CNT-based nanoporous layers were employed to GDL of PEMFC. ∙CNTs were fabricated via cost-effective direct spinning method. ∙Additional nanoporous layer (w/ MPL) increased current density by 57% (at 0.6 V). ∙Mitigated charge transfer and ohmic resistances led to performance enhancements. ∙The correlation between the quality of CNT and fuel cell performance was subpar. [ABSTRACT FROM AUTHOR]

3D-printed flexible flow-field plates are employed in this study to realize a bendable polymer electrolyte membrane fuel cell (PEMFC). The prepared bendable PEMFC consists of a membrane electrode assembly (MEA), current collectors, and flow-field plates. The performance of the fuel cell is measured in the flat and bent positions. Polarization curves and impedance plots are analyzed to assess the fuel cell performance. A peak power density of 87.1 mW cm−2 is obtained for the fuel cell with the maximum bending, while a power density of 30.2 mW cm−2 is obtained in the flat position. The enhanced performance is attributed to the compressive stress applied to the reaction sites of the MEA during bending of the fuel cell. The compressive stress is calculated using finite element analysis (FEA). According to the FEA results, the compressive stress occurring at the MEA intensifies as the curvature of the fuel cell increases, resulting in significantly decreased ohmic and charge transfer resistances. The successfully realized bendable fuel cell with 3D-printed flexible flow-field plates exhibits flexibility, decent performance, and a simple structure. It is also competitive in terms of the cost of manufacturing owing to the use of 3D printing. [Display omitted] • A bendable PEMFC was realized with flexible flow-field plates. • Flexible flow-field plates were fabricated by 3D printing. • Performance of the bendable fuel cell was evaluated both in flat and bent positions. • FEA was performed to investigate compressive stress that occurred by bending. • The bendable fuel cell can operate for more than 12 h with bent shape. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) sheet was sandwiched between the cathodic GDBL and a bipolar plate of polymer electrolyte membrane fuel cells (PEMFCs). The CNT sheets were synthesized through the direct spinning method and investigated their morphological characteristics. The electrochemical performances of MEA with CNT interlayer were measured via polarizations, iR-free, and electrochemical impedance spectra (EIS) compared to the conventional MEA under elevating backpressure. The performance of the MEA with CNT interlayer at 1.0 bar g was enhanced by 91.8% (364 mW cm−2 at 0.7 V), which was higher than the peak power density improvement of 13.0% (850 mW cm−2 at 0.48 V). We also identified that corresponding ohmic and charge-transfer resistances were reduced. Especially, the ohmic resistance was decreased by up to 42.2% with increasing operating pressure compared to the conventional MEA due to better hydration and interfacial contact. Notwithstanding that the performance was ameliorated with increased pressure, we found that the mass transport loss tends to become more sensitive at the high current density region, and thus optimum operating conditions were proposed. We concluded that the CNT sheet as a functional interlayer would be advantageous in improving the performance of commercialized PEMFCs. [Display omitted] • CNT sheet was sandwiched between cathodic GDBL and bipolar plate in PEMFCs. • CNT sheets were synthesized through the direct spinning method. • Power density at typical operating voltage enhanced 91.8% (364 mW cm−2 at 0.7 V). • Ohmic resistance was reduced by up to 42.2% with increasing operating pressure. [ABSTRACT FROM AUTHOR]

• PEMFCs with 0.3, 0.5, and 1.0 mm-thick flow channels/ribs are tested. • The effect by increasing operating pressure in different channels is investigated. • Diffusion of reactants by varying channels and pressure are investigated. • Non-dimensional flow characteristics are investigated based on Sh, Re and Sc. Variation in performance of polymer electrolyte membrane fuel cells (PEMFCs) is analyzed, focusing on operating pressure and change in the width of the flow channels. At 0 bar, the maximum power densities are 431, 569, and 799 mW/cm2 with the width of 1.0, 0.5, and 0.3 mm, and at 3.0 bar, the maximum power densities are enhanced to 650, 829, and 914 mW/cm2, respectively. A pair of bipolar plates having the largest width exhibit the highest effect of the pressurized operation, and thus the most considerable change rate in maximum power density (50.8%). To investigate the diffusion phenomenon in the flow channels, a correlation is derived by introducing non-dimensional parameters. The dimensionless number associated with vertical diffusion, Sherwood number, decreases with lessening the width of flow channels and increasing the operating pressure, and diffusion characteristics of PEMFCs are generalized through Sherwood number correlation consisting of Reynolds and Schmidt number. Polymer electrolyte membrane fuel cell; Electrochemical impedance spectroscopy; Flow channel; Diffusion; Sherwood number [Display omitted] [ABSTRACT FROM AUTHOR]

Polymer electrolyte membrane fuel cells were analyzed to investigate changes in the structure of the flow field and operating conditions. The cell performance, which was controlled by adjusting the width of the cathodic channel, improved as the backpressure increases. With the anodic and cathodic flow channels mismatched, the maximum power densities at 3.0 bar for a narrow cathodic channel were 1115 and 1024 mW/cm2, and those for a wide cathodic channel were 959 and 868 mW/cm2, respectively. The diffusion characteristics were investigated using the non-dimensional numbers Re (Reynolds), Sc (Schmidt), and Sh (Sherwood) to confirm the improvement of mass transport. The narrower the channel or the higher the operating pressure, the larger Re was and the smaller Sc and Sh became. In particular, the wider the anodic channel, the larger the value of Sh. [ABSTRACT FROM AUTHOR]