Distortion-Free Stretchable Light-Emitting Diodes via Imperceptible Microwrinkles

Stretchable organic light-emitting diodes (OLEDs) have been considered as a promising technology for next-generation free-form and wearable displays. However, an approach to ensure both high device performance and high resolution has not yet been suggested. While introducing a wrinkled structure in the active pixel areas is a decent method, the formation of out-of-plane macroscopic wrinkles having a wavelength of a few hundred mu m has caused distortion in the shape of the pixel, which is a critical drawback for a matrix-configured display demanding a sharp pixel definition. Herein, microwrinkled OLEDs are fabricated to define a distortion-free pixel by direct deposition of OLEDs on biaxially prestretched elastomeric substrate, being feasible by a low-temperature-based solution process. The total thickness of the device can be significantly reduced up to 350 nm, producing the imperceptible microwrinkles having a wavelength under 20 mu m. The microwrinkled OLEDs show a luminance over 8000 cd m(-2) and maximum current efficiency of 7.76 cd A(-1), which is comparable to the device without wrinkled structure. Finally, a stretchable 4 x 4 OLED pixel array with a microwrinkled structure is demonstrated showing sharply defined square-patterned emission, proving the potential in the future high-resolution stretchable display.N

Comprehensive Analysis Reveals Dynamic and Evolutionary Plasticity of Rab GTPases and Membrane Traffic in Tetrahymena thermophila

Cellular sophistication is not exclusive to multicellular organisms, and unicellular eukaryotes can resemble differentiated animal cells in their complex network of membrane-bound structures. These comparisons can be illuminated by genome-wide surveys of key gene families. We report a systematic analysis of Rabs in a complex unicellular Ciliate, including gene prediction and phylogenetic clustering, expression profiling based on public data, and Green Fluorescent Protein (GFP) tagging. Rabs are monomeric GTPases that regulate membrane traffic. Because Rabs act as compartment-specific determinants, the number of Rabs in an organism reflects intracellular complexity. The Tetrahymena Rab family is similar in size to that in humans and includes both expansions in conserved Rab clades as well as many divergent Rabs. Importantly, more than 90% of Rabs are expressed concurrently in growing cells, while only a small subset appears specialized for other conditions. By localizing most Rabs in living cells, we could assign the majority to specific compartments. These results validated most phylogenetic assignments, but also indicated that some sequence-conserved Rabs were co-opted for novel functions. Our survey uncovered a rare example of a nuclear Rab and substantiated the existence of a previously unrecognized core Rab clade in eukaryotes. Strikingly, several functionally conserved pathways or structures were found to be associated entirely with divergent Rabs. These pathways may have permitted rapid evolution of the associated Rabs or may have arisen independently in diverse lineages and then converged. Thus, characterizing entire gene families can provide insight into the evolutionary flexibility of fundamental cellular pathways

Rediscovery of poly(ethylene glycol)s as a cryoprotectant for mesenchymal stem cells

Abstract Background A medium containing dimethyl sulfoxide (DMSO) (10% v/v) is most widely used for cell cryopreservation at –196 °C. However, residual DMSO consistently raises concerns because of its toxicity; thus, its complete removal process is required. Method As biocompatible polymers approved by the Food and Drug Administration for various biomedical applications for humans, poly(ethylene glycol)s (PEGs) with various molecular weights (400, 600, 1 K, 1.5 K, 5 K, 10 K, and 20 K Da) were studied as a cryoprotectant of mesenchymal stem cells (MSCs). Considering the cell permeability difference of PEGs depending on their molecular weight, the cells were preincubated for 0 h (no incubation), 2 h, and 4 h at 37 °C in the presence of PEGs at 10 wt.% before cryopreservation at –196 °C for 7 days. Then, cell recovery was assayed. Results We found that low molecular weight PEGs (400 and 600 Da) exhibit excellent cryoprotecting properties by 2 h preincubation, whereas intermediate molecular weight PEGs (1 K, 1.5 K, and 5 K Da) exhibit their cryoprotecting properties without preincubation. High molecular weight PEGs (10 K and 20 K Da) were ineffective as cryoprotectants for MSCs. Studies on ice recrystallization inhibition (IRI), ice nucleation inhibition (INI), membrane stabilization, and intracellular transport of PEGs suggest that low molecular weight PEGs (400 and 600 Da) exhibit excellent intracellular transport properties, and thus the internalized PEGs during preincubation contribute to the cryoprotection. Intermediate molecular weight PEGs (1 K, 1.5 K, and 5 K Da) worked by extracellular PEGs through IRI, INI, as well as partly internalized PEGs. High molecular weight PEGs (10 K and 20 K Da) killed the cells during preincubation and were ineffective as cryoprotectants. Conclusions PEGs can be used as cryoprotectants. However, the detailed procedures, including preincubation, should consider the effect of the molecular weight of PEGs. The recovered cells well proliferated and underwent osteo/chondro/adipogenic differentiation similar to the MSCs recovered from the traditional DMSO 10% system. Graphical Abstrac

Poly(Ethylene Glycol)-Poly(l-Alanine)/Hyaluronic Acid Complex as a 3D Platform for Understanding Cancer Cell Migration in the Tumor Microenvironment

Cancer progression and migration in the tumor microenvironment are related to cell types and three-dimensional (3D) matrices. Therefore, developing biomimetic tumor models, including co-culture systems and a tunable 3D matrix, could play an essential role in understanding the cancer environment. Here, multicellular spheroids using human adipose-derived mesenchymal stem cells (hADSCs) and breast cancer cells (MDA-MB-231) within the 3D matrix were used as a tumor microenvironment (TME) mimicking platform. The amphiphilic peptide block copolymer and hyaluronic acid (HA) formed a self-assembled structure, which provides a biocompatible 3D environment for the cells. Multicellular spheroids were formed on the optimized plate and were observed as cell migration from a spheroid within a 3D matrix, such as the invasive and metastatic cancer of TME. This study suggests a new 3D platform using polymer complexes and the importance of tumor complexities, including various cell types and microenvironments

Phase Transition of the PLGA-g-PEG Copolymer Aqueous Solutions

The aqueous solution of poly(lactic acid-co-glycolic acid)-g-poly(ethylene glycol) becomes a gel as the temperature increases. The sol-to-gel transition temperature can be controlled from 15 to 45 °C by varying the number of poly(ethylene glycol) grafts and the composition of the polymer. In addition, hysteresis between heating and cooling cycles could be controlled by adding poly(ethylene glycol) with different molecular weights as an additive. To prove the hypothesis of micellar aggregation for the sol-to-gel transition and the change in hydration status for the gel-to-sol transition, several experiments were performed. Small-angle neutron scattering and Raman spectroscopy sensitively detected the sol-to-gel transition, because it involves aggregation of the scattering particle of micelles. IR and 13C NMR showed that little change in hydration status is involved during the sol-to-gel transition, whereas significant change in hydration status is involved in the gel-to-sol transition. The intrinsic viscosity of the PEG showed that more significant dehydration can occur when PEG is attached to the hydrophobic group. On the basis of the experiments above, PEG dehydration is the major driving force for the phase change of the PLGA-g-PEG aqueous solution. At the sol-to-gel transition temperature, partial dehydration of the PEG induces the micellar aggregation while keeping the core−shell structure. However, at the gel-to-sol transition, dehydration of the PEG is so significant that the core−shell structure is broken and macroscopic phase separation occurs. These phenomena were associated with changes in the carbonyl stretching and ether bending modes in the IR spectra.This work was supported by the Intramural Research Grant of Ewha Womans University, the Ministry of Science and Technology (MOST) of Korea, Korea Science and Engineering Foundation (KOSEF) (Grant RO1-2002-000- 00274-0), and Battelle Independent Research & Development fund. Pacific Northwest National Laboratory is operated by Battelle Memorial Institute for the U.S. Department of Energy under contract DE-AC06-76RLO 1830