Densification in transparent SiO2 glasses prepared by spark plasma sintering.

Recently, spark plasma sintering (SPS) has become an attractive method for the preparation of solid-state ceramics. As SPS is a pressure-assisted low-temperature process, it is important to examine the effects of temperature and pressure on the structural properties of the prepared samples. In the present study, we examined the correlation between the preparation conditions and the physical and structural properties of SiO2 glasses prepared by SPS. Compared with the conventional SiO2 glass, the SPS-SiO2 glasses exhibit a higher density and elastic modulus, but a lower-height first sharp diffraction peak of the X-ray total structure factor. Micro-Raman and micro-IR spectra suggest the formation of heterogeneous regions at the interface between the SiO2 powders and graphite die. Considering the defect formation observed in optical absorption spectra, reduction reaction mainly affects the densification of SPS-SiO2 glass. Hence, the reaction at the interface is important for tailoring the structure and physical properties of solid-state materials prepared by the SPS technique.

Tracer diffusion coefficients of Li+ ions in c-axis oriented LixCoO2 thin films measured by secondary ion mass spectrometry.

Lithium diffusion is a key factor in determining the charge/discharge rate of Li-ion batteries. Herein, we study the tracer diffusion coefficient (D*) of lithium ions in the c-axis oriented LiCoO2 thin film using secondary ion mass spectrometry (SIMS). We applied a step-isotope-exchange method to determine D* in the Li-extracted LixCoO2. The observed values of D* ranged from 2 × 10-12 to 3 × 10-17 cm2 s-1 depending on the compositions in the range of 0.4 < x < 1.0. Approaching the stoichiometric composition (x = 1.0), D* decreases steeply to the minimum, which can be explained by the vacancy diffusion mechanism. Electrochemically determined diffusion coefficients corrected by thermodynamic factors are found to be in good agreement with D* determined by our method, over a wide range of compositions. The c-axis diffusion was explained by the migration of Li+ ions from one layer to another through additional diffusion channels, such as antiphase boundaries and a pair of Li antisite and oxygen vacancies in cobalt oxide layers.

Photocatalytic hydrogen generation of monolithic porous titanium oxide-based glass-ceramics.

A large relative surface area is crucial for high catalytic activity. Monolithic catalysts are important catalytic materials because of minimal self-degradation. Regarding large surface area catalysts, the glass-ceramics (GCs) with high formability, obtained by heat-treatment of the precursor glass, are plausible candidates. This study examines the photocatalytic behaviour of porous GCs obtained after acid leaching of MgO-TiO2-P2O5 GCs. After heat-treatment, anatase TiO2 was precipitated along with other phases. The diffraction intensity ratio between anatase and other phases was the maximum for a heat-treatment temperature of 900 °C. After acid leaching of the GCs, the relative surface area decreased with increasing TiO2 fraction; the surface area was also affected by the sample morphology. H2 generation was observed from porous GCs, while GCs without etching exhibited approximately zero activity. Thus, it was demonstrated that high surface area and prevention of the reduction reaction to Ti(III) are important for tailoring monolithic photocatalytic materials.

Efficient Adhesion Culture of Human Pluripotent Stem Cells Using Laminin Fragments in an Uncoated Manner.

We describe highly effective adhesion culture of human pluripotent stem cells (hPSCs) using laminin fragments without precoating. Culture substrates have been generally thought to exert a cell adhesion effect when they are precoated onto culture vessels. However, simple addition of laminin fragments to a cell suspension during passaging accelerated the adhesion of single dissociated hPSCs onto culture vessels that were not precoated with any culture substrate. Interestingly, similar to conventional precoating, the uncoated addition of laminin fragments supported robust adhesion of single hPSCs and maximum adhesion at a much lower concentration compared with precoating. Similar to precoating laminin fragments, hPSCs seeded with uncoated laminin fragments grew well without cell detachment and maintained pluripotency after continuous subculture. We tested other culture substrates, including full-length laminin and vitronectin, to support hPSC adhesion in the uncoated manner, but only laminin fragments had the potential for application in the uncoated manner. This cost-effective and time-efficient method may contribute to expansion of culture of hPSCs and accelerate the development of regenerative medicine using hPSCs.

Slow Cooling Cryopreservation Optimized to Human Pluripotent Stem Cells.

Human pluripotent stem cells (hPSCs) have the potential for unlimited expansion and differentiation into cells that form all three germ layers. Cryopreservation is one of the key processes for successful applications of hPSCs, because it allows semi-permanent preservation of cells and their easy transportation. Most animal cell lines, including mouse embryonic stem cells, are standardly cryopreserved by slow cooling; however, hPSCs have been difficult to preserve and their cell viability has been extremely low whenever cryopreservation has been attempted.Here, we investigate the reasons for failure of slow cooling in hPSC cryopreservation. Cryopreservation involves a series of steps and is not a straightforward process. Cells may die due to various reasons during cryopreservation. Indeed, hPSCs preserved by traditional methods often suffer necrosis during the freeze-thawing stages, and the colony state of hPSCs prior to cryopreservation is a major factor contributing to cell death.It has now become possible to cryopreserve hPSCs using conventional cryopreservation methods without any specific equipment. This review summarizes the advances in this area and discusses the optimization of slow cooling cryopreservation for hPSC storage.

Modification of the Interface Nanostructure and Magnetic Properties in Nd-Fe-B Thin Films.

The effects of Nd2Fe14B grain size and Nd coating on the coercivity in sputter-deposited Nd-Fe-B/Nd thin films have been investigated in order to gain an insight into the coercivity mechanism of Nd-Fe-B magnets. Highly textured Nd2Fe14B particles were grown successfully on the MgO(100) single-crystal substrate with the Mo underlayer. As the Nd-Fe-B layer thickness t NFB was decreased from 70 to 5 nm, the coercivity H c increased gradually from 6.5 to 16 kOe. By depositing the Nd overlayer onto these films and post-annealing at 500 °C, the H c value further increased from 17.5 kOe (t NFB=70 nm) to 26.2 kOe (t NFB=5 nm). The amount of H c increase by the combination of the Nd coating and post-annealing was about 10 kOe irrespective of the t NFB value. These results therefore suggest an independence of size and interface effects on the coercivity of Nd-Fe-B magnets.

Local coordination state of rare earth in eutectic scintillators for neutron detector applications.

Atomic distribution in phosphors for neutron detection has not been fully elucidated, although their ionization efficiency is strongly dependent on the state of the rare earth in the matrix. In this work, we examine optical properties of Eu-doped 80LiF-20CaF2 eutectics for neutron detector applications based on the Eu distribution. At low concentrations, aggregation of Eu cations is observed, whereas homogeneous atomic dispersion in the CaF2 layer, to substitute Ca(2+) ions, is observed in the eutectics at high concentrations. Eu LIII edge X-ray absorption fine structure (XAFS) analysis suggests that neutron responses do not depend on the amount of Eu(2+) ions. However, transparency, which depends on an ordered lamellar structure, is found to be important for a high light yield in neutron detection. The results confirm the effectiveness of the basic idea concerning the separation of radiation absorbers and activators in particle radiation scintillation and present potential for further improvement of novel bulk detectors.

Pockels effect of silicate glass-ceramics: Observation of optical modulation in Mach-Zehnder system.

Silicate glass has been used for long time because of its advantages from material's viewpoint. In this paper, we report the observation of Pockels effect by Mach-Zehnder interferometer in polycrystalline ceramics made from a ternary silicate glass via crystallization due to heat-treatment, i.e., glass-ceramics. Since the silicate system is employed as the precursor, merits of glass material are fully utilized to fabricate the optical device component, in addition to that of functional crystalline material, leading us to provide an electro-optic device, which is introducible into glass-fiber network.

100-nm-sized magnetic domain reversal by the magneto-electric effect in self-assembled BiFeO3/CoFe2O4 bilayer films.

A (001)-epitaxial-BiFeO3/CoFe2O4 bilayer was grown by self-assembly on SrTiO3 (100) substrates by just coating a mixture precursor solution. The thickness ratio of the bilayer could be controlled by adjusting the composition ratio. For example, a BiFeOx:CoFe2Ox = 4:1 (namely Bi4CoFe6Ox) mixture solution could make a total thickness of 110 nm divided into 85-nm-thick BiFeO3 and 25-nm-thick CoFe2O4. Self-assembly of the bilayer occurred because the perovskite BiFeO3 better matched the lattice constant (misfit approximately 1%) and crystal symmetry of the perovskite SrTiO3 than the spinel CoFe2O4 (misfit approximately 7%). The magnetic domains of the hard magnet CoFe2O4 were switched by the polarization change of BiFeO3 due to an applied vertical voltage, and the switched magnetic domain size was approximately 100 nm in diameter. These results suggest that self-assembled BiFeO3/CoFe2O4 bilayers are interesting in voltage driven nonvolatile memory with a low manufacturing cost.

Efficient and scalable culture of single dissociated human pluripotent stem cells using recombinant E8 fragments of human laminin isoforms.

This unit describes a protocol for efficient expansion of human pluripotent stem cells (hPSCs). A key feature of this method is subculture of hPSCs by single-cell dissociation passaging on substrates coated with recombinant E8 fragments of human laminin isoforms (LM-E8s). LM-E8s, provide superior adhesion over intact laminin isoforms and Matrigel. Single hPSCs seeded on LM-E8s show accelerated migration and rapid reconstruction of clusters, resulting in robust survival and proliferation. This protocol yields 200-fold more hPSCs than conventional subculture methods in 1 month of culture. Furthermore, this protocol can be easily adapted to most hPSC lines in combination with the use of various xeno-free, defined culture media, and large-scale expansion of hPSCs is easily achievable to facilitate the practical applications of hPSCs.

Cryopreservation of human pluripotent stem cells: a general protocol.

Cryopreservation is an essential technique to preserve stem cells, semipermanently sustaining their potentials. There are two main approaches of cryopreservation for human pluripotent stem cells (hPSCs). The first is the vitrification, which involves instantaneous freeze and thaw of hPSCs. The second is the conventional slow-cooling method and a rapid thaw. Both cryopreservation protocols have been standardized and optimized to yield high survivability of hPSCs.

Optimization of slow cooling cryopreservation for human pluripotent stem cells.

Human pluripotent stem cells (hPSCs) have the potential for unlimited expansion and differentiation into cell types of all three germ layers. Cryopreservation is a key process for successful application of hPSCs. However, the current conventional method leads to poor recovery of hPSCs after thawing. Here, we demonstrate a highly efficient recovery method for hPSC cryopreservation by slow freezing and single-cell dissociation. After confirming hPSC survivability after freeze-thawing, we found that hPSCs that were freeze-thawed as colonies showed markedly decreased survival, whereas freeze-thawed single hPSCs retained the majority of their viability. These observations indicated that hPSCs should be cryopreserved as single cells. Freeze-thawed single hPSCs efficiently adhered and survived in the absence of a ROCK inhibitor by optimization of the seeding density. The high recovery rate enabled conventional colony passaging for subculture within 3 days post-thawing. The improved method was also adapted to a xeno-free culture system. Moreover, the cell recovery postcryopreservation was highly supported by coating culture surfaces with human laminin-521 that promotes adhesion of dissociated single hPSCs. This simplified but highly efficient cryopreservation method allows easy handling of cells and bulk storage of high-quality hPSCs.

Laminin E8 fragments support efficient adhesion and expansion of dissociated human pluripotent stem cells.

Human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) have the potential to provide an infinite source of tissues for regenerative medicine. Although defined xeno-free media have been developed, culture conditions for reliable propagation of hESCs still require considerable improvement. Here we show that recombinant E8 fragments of laminin isoforms (LM-E8s), which are the minimum fragments conferring integrin-binding activity, promote greater adhesion of hESCs and hiPSCs than do Matrigel and intact laminin isoforms. Furthermore, LM-E8s sustain long-term self-renewal of hESCs and hiPSCs in defined xeno-free media with dissociated cell passaging. We successfully maintained three hESC and two hiPSC lines on LM-E8s in three defined media for 10 passages. hESCs maintained high level expression of pluripotency markers, had a normal karyotype after 30 passages and could differentiate into all three germ layers. This culture system allows robust proliferation of hESCs and hiPSCs for therapeutic applications.

Comparison of defined culture systems for feeder cell free propagation of human embryonic stem cells.

There are many reports of defined culture systems for the propagation of human embryonic stem cells in the absence of feeder cell support, but no previous study has undertaken a multi-laboratory comparison of these diverse methodologies. In this study, five separate laboratories, each with experience in human embryonic stem cell culture, used a panel of ten embryonic stem cell lines (including WA09 as an index cell line common to all laboratories) to assess eight cell culture methods, with propagation in the presence of Knockout Serum Replacer, FGF-2, and mouse embryonic fibroblast feeder cell layers serving as a positive control. The cultures were assessed for up to ten passages for attachment, death, and differentiated morphology by phase contrast microscopy, for growth by serial cell counts, and for maintenance of stem cell surface marker expression by flow cytometry. Of the eight culture systems, only the control and those based on two commercial media, mTeSR1 and STEMPRO, supported maintenance of most cell lines for ten passages. Cultures grown in the remaining media failed before this point due to lack of attachment, cell death, or overt cell differentiation. Possible explanations for relative success of the commercial formulations in this study, and the lack of success with other formulations from academic groups compared to previously published results, include: the complex combination of growth factors present in the commercial preparations; improved development, manufacture, and quality control in the commercial products; differences in epigenetic adaptation to culture in vitro between different ES cell lines grown in different laboratories.

Recombinant human laminin isoforms can support the undifferentiated growth of human embryonic stem cells.

Human embryonic stem cells (hESCs) are thought to be a promising cell source for cell transplantation therapy. For such a clinical application, the hESCs should be manipulated using appropriate and qualified materials. In this study, we examined the efficacy of recombinant human laminin (rhLM) isoforms on the undifferentiated growth of hESCs. We first determined the major integrins expressed on the hESCs to reveal the preference of the hESCs for rhLMs, and found that the hESCs mainly expressed integrin alpha6beta1, which binds predominantly to laminin-111, -332 and -511/-521. When the hESCs were seeded onto rhLMs, the cells indeed adhered markedly to rhLM-332, and to rhLM-511 and rhLM-111 to a lesser extent. The hESCs proliferated on these three rhLMs for several passages while preserving their pluripotency. These results show that rhLM-111, -332, and -511 are good substrates to expand undifferentiated hESCs due to their high affinity to integrin alpha6beta1 expressed on hESCs.

Cryopreservation of mouse adipose tissue-derived stem/progenitor cells.

Adipose tissue-derived stem/progenitor cells (ASCs) have been reported to differentiate not only into mesodermal cells such as osteoblasts, chondorocytes, and adipocytes, but also to endodermal cells such as hepatocytes and insulin-expressing cells. These stem/progenitor cells are expected to be used for variety of regenerative therapies. This study demonstrates the viability and the adipo/osteogenic potential of cryopreserved ASCs using seven cryopreservation solutions, including 10% DMSO, Cell Freezing Medium-DMSO, Cell Freezing Medium-Glycerol, Cell Banker 1, Cell Banker 1+, Cell Banker 2, and CP-1. ASCs were obtained from mouse subcutaneous adipose tissue. The viability of the cryopreserved ASCs was over 90% with Cell Banker 2 preservation, approximately 90% with Cell Banker 1, Cell Banker 1+, or CP-1 preservation, and less than 80% for 10% DMSO, Cell Freezing Medium-DMSO, or Cell Freezing Medium-Glycerol preservation. No difference in the adipo/osteogenic potential was found between cells with or without cryopreservation in Cell Banker 2. These data suggests that Cell Banker 2 is the most effective cryopreservation solution for ASCs and that cryopreserved as well as noncryopreserved ASCs could be applied for regenerative medicine.

Recombinant sendai virus-mediated gene transfer to adipose tissue-derived stem cells (ASCs).

Adipose tissue-derived stem cells (ASCs) are expected to have clinical applications as well as other stem cells, because ASCs can be obtained safely from adult donors and used in autologous therapies without concern about rejection and the need for immunosuppression. However, the use of gene transfer with Sendai virus (SeV) vectors, which can efficiently introduce foreign genes without toxicity into several cells, with ASCs has not yet been investigated. This study documents on the use of SeV vectors for gene transfer to ASCs. The dose-dependent GFP expression of ASCs transfected with SeV vectors after 48 h of culture at 37 degrees C was first evaluated. Next, the cellular toxicity of ASCs transfected with SeV vectors was verified. In addition, SeV vectors were compared with adenovirus (AdV) vectors. Finally, the time-dependent GFP expression of ASCs transfected with SeV vectors was evaluated. The results showed that transfection of ASCs with SeV vectors results in more efficient expression of transgene (GFP expression) in the ASCs than with AdV vectors after 48 h of culture at 37 degrees C. Moreover, while the transfection of ASCs with AdV vectors at high MOIs was cytotoxic (a lot of transfected cells died) that of ASCs with SeV vectors at high MOIs was not necessarily cytotoxic. In addition, the preservation of multilineage ASCs transfected with SeV was observed. In conclusion, this is the first report describing the successful use of SeV-mediated gene transfer in ASCs, and the results indicate that SeV may thus provide advantages with respect to safety issues in gene therapy.

Isolation of two human fibroblastic cell populations with multiple but distinct potential of mesenchymal differentiation by ceiling culture of mature fat cells from subcutaneous adipose tissue.

Adipose tissue is a source of adult multipotent stem cells that can differentiate along mesenchymal lineage. When mature fat cells obtained from human subcutaneous adipose tissue were maintained with attachment to the ceiling surface of culture flasks filled with medium, two fibroblastic cell populations appeared at the ceiling and the bottom surface. Both populations were positive to CD13, CD90, and CD105, moderately positive to CD9, CD166, and CD54, negative to CD31. CD34, CD66b, CD106, and CD117, exhibited potential of unlimited proliferation, and differentiated along mesenchymal lineage to produce adipocytes, osteoblasts, and chondrocytes. The population that appeared at the ceiling surface showed higher potential of adipogenic differentiation. These observations showed that the cells tightly attached to mature fat cells can generate two fibroblastic cell populations with multiple but distinct potential of differentiation. Since enough number of both populations for clinical transplantation can be easily obtained by maintaining fat cells from a small amount of subcutaneous adipose tissue, this method has an advantage in preparing autologous cells for patients needing repair of damaged tissues by reconstructive therapy.