Verification of Therapeutic Effect through Accelerator Mass Spectrometry-Based Single Cell Level Quantification of hESC-Endothelial Cells Distributed into an Ischemic Model.

As the potential of pluripotent stem cell-derived differentiated cells has been demonstrated in regenerative medicine, differentiated vascular endothelial cells (ECs) are emerging as a therapeutic agent for the cardiovascular system. To verify the therapeutic efficacy of differentiated ECs in an ischemic model, human embryonic stem cells (hESCs) are induced as EC lineage and produce high-purity ECs through fluorescence-activated cell sorting (FACS). When hESC-ECs are transplanted into a hindlimb ischemic model, it is confirmed that blood flow and muscle regeneration are further improved by creating new blood vessels together with autologous ECs than the primary cell as cord blood endothelial progenitor cells (CB-EPCs). In addition, previously reported studies show the detection of transplanted cells engrafted in blood vessels through various tracking methods, but fail to provide accurate quantitative values over time. In this study, it is demonstrated that hESC-ECs are engrafted approximately sevenfold more than CB-EPCs by using an accelerator mass spectrometry (AMS)-based cell tracking technology that can perform quantification at the single cell level. An accurate quantification index is suggested. It has never been reported in in vivo kinetics of hESC-ECs that can act as therapeutic agents.

In vivo tracking of 14C thymidine labeled mesenchymal stem cells using ultra-sensitive accelerator mass spectrometry.

Despite the tremendous advancements made in cell tracking, in vivo imaging and volumetric analysis, it remains difficult to accurately quantify the number of infused cells following stem cell therapy, especially at the single cell level, mainly due to the sensitivity of cells. In this study, we demonstrate the utility of both liquid scintillator counter (LSC) and accelerator mass spectrometry (AMS) in investigating the distribution and quantification of radioisotope labeled adipocyte derived mesenchymal stem cells (AD-MSCs) at the single cell level after intravenous (IV) transplantation. We first show the incorporation of 14C-thymidine (5 nCi/ml, 24.2 ng/ml) into AD-MSCs without affecting key biological characteristics. These cells were then utilized to track and quantify the distribution of AD-MSCs delivered through the tail vein by AMS, revealing the number of AD-MSCs existing within different organs per mg and per organ at different time points. Notably, the results show that this highly sensitive approach can quantify one cell per mg which effectively means that AD-MSCs can be detected in various tissues at the single cell level. While the significance of these cells is yet to be elucidated, we show that it is possible to accurately depict the pattern of distribution and quantify AD-MSCs in living tissue. This approach can serve to incrementally build profiles of biodistribution for stem cells such as MSCs which is essential for both research and therapeutic purposes.

Full range dielectric characteristics of calcium copper titanate thin films prepared by continuous composition-spread sputtering.

Perovskite CaCu3Ti4O12 has drawn a great deal of attention for various electronic applications due to its giant dielectric property as well as a strong stability in a wide range of temperature. In this paper, we use an off-axis continuous composition-spread (CCS) sputtering method to investigate the full range dielectric characteristics of calcium copper titanate thin films. The film compositions are continuously distributed by deposition from two targets of CaTiO3 and CuTiO3. A slightly Ca-deficient, Cu- and Ti-rich film, which has a 0.9:3.2:4.3 ratio for Ca:Cu:Ti, demonstrated the best performance by showing a dielectric constant of 781 at 100 kHz. On the other hand, all other films far away from the CaCu3Ti4O12 composition showed suppressed dielectric properties. Analyses by X-ray photon spectroscopy, micro-Raman microscopy, transmission electron microscopy, and Rutherford backscattering spectroscopy reveal that there are three possible origins for such superior performance at off stoichiometric thin films: (1) bulk doping by excessive Cu and Ti ions, (2) chemically modified grain boundary, and (3) the lowered electrode-sample interface resistance. Our result will provide a new insight into engineering the dielectric properties using off-stoichiometric synthesis.

Silicon nanodisk array design for effective light trapping in ultrathin c-Si.

The use of ultrathin c-Si (crystalline silicon) wafers thinner than 20 µm for solar cells is a very promising approach to realize dramatic reduction in cell cost. However, the ultrathin c-Si requires highly effective light trapping to compensate optical absorption reduction. Conventional texturing in micron scale is hardly applicable to the ultrathin c-Si wafers; thus, nano scale texturing is demanded. In general, nanotexturing is inevitably accompanied by surface area enlargements, which must be minimized in order to suppress surface recombination of minority carriers. In this study, we demonstrate using optical simulations that periodic c-Si nanodisk arrays of short heights less than 200 nm and optimal periods are very useful in terms of light trapping in the ultrathin c-Si wafers while low surface area enlargements are maintained. Double side texturing with the nanodisk arrays leads to over 90% of the Lambertian absorption limit while the surface area enlargement is kept below 1.5.

The effects of nitrogen bonding on hardness of AIN/CrN multilayer hard coatings.

AIN/CrN multilayer hard coatings with various bilayer thicknesses were fabricated by a reactive sputtering process. The microstructural and mechanical characterizations of multilayer coatings were investigated through transmission electron microscope (TEM) observations and the hardness measurements by nano indentation. In particular, the variation of chemical bonding states of the bilayer nitrides was elucidated by near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Many broken nitrogen bonds were formed by decreasing the bilayer thickness of AIN/CrN multilayer coatings. Existence of optimum AIN/CrN multilayer coatings thickness for maximum hardness could be explained by the competition of softening by the formation of broken nitrogen bonds and strengthening induced by decreasing bilayer thickness.

Hardness and nitrogen bonding structure of AlxTi1-xN/CrN multilayer hard coating.

AlxTi1-xN/CrN multilayer coatings were fabricated by magnetron sputtering and those hardness variations were studied by observing the crack propagation and measuring the chemical bonding state of nitrides by Ti addition. While AlN/CrN multilayer shown stair-like crack propagation, AlxTi1-xN/CrN multilayer illustrated straight crack propagation. Most interestingly, Ti addition induced more broken nitrogen bonds in the nitride multilayers, leading to the reduction of hardness. However, the hardness of Al0.25Ti0.75N/CrN multilayer, having high Ti contents, increased by the formation of many Ti-N bond again instead of Al-N bond. From these results, we found that linear crack propagation behavior was dominated by broken nitrogen bonds in the AlxTi1-xN/CrN multilayer coatings.