Abstract Owing to the advantages of integration and being magnet-free and light-weight, the switched-capacitor-convertor plays an increasing role compared to traditional transformer in some specific power supply systems. However, the high output impedance and switching loss largely reduces its power efficiency, due to imperfect topology and transistors. Herein, we propose a fractal-design based switched-capacitor-convertors with characteristics including high conversion efficiency, minimum output impedance, and electrostatic voltage applicability. As a double-function output power management system for triboelectric nanogenerators, it delivers over 67 times charge boosting and 954 W m −2 power density in pulse mode, and achieves over 94% total energy transfer efficiency in constant mode. The establishment of the fractal-design switched-capacitor-convertors provides significant guidance for the development of power management toward multi-functional output for numerous applications. The successful demonstration in triboelectric nanogenerators also declares its great potential in electric vehicles, DC micro-grids etc.
Fatty acid synthase (FASN) is overexpressed in a variety of human cancers, and may be involved in cancer metastasis. Hence, the strategies targeted on FASN may have therapeutic potential for treating cancer metastasis.The aim of this study is to investigate the correlation of FASN expression with metastasis in human osteosarcoma.Human osteosarcoma cell lines U2-OS and osteosarcoma biopsy specimens were employed in this study. The expression of FASN protein in osteosarcoma specimens was detected by IHC (immunohistochemistry) and the relationship with metastasis was analyzed. We performed the cerulenin, an inhibitor of FASN, to inhibit FASN expression in U2-OS cells. Western blot and RT-PCR were performed to investigate the expression of FASN in U2-OS cells. Cells mobility was detected by wound healing and Transwell assays.Results showed that the FASN expression level in the cases with pulmonary metastases was significantly higher than in those without metastasis. In vitro, the invasion and migration of U2-OS cells were suppressed by inhibiting FASN. Our findings suggested that FASN may be involved in osteosarcoma metastasis.
The process of in situ tumors developing into malignant tumors and exhibiting invasive behavior is extremely complicated . From a biophysical point of view, it is a phase change process affected by many factors, including cell-to-cell, cell-to-chemical material, cell-to-environment interaction, etc . In this study, we constructed spheroids based on green fluorescence metastatic breast cancer cells MDA-MB-231 to simulate malignant tumors in vitro , while constructed a three-dimensional (3D) biochip to simulate a micro-environment for the growth and invasion of spheroids. In the experiment, the 3D spheroid was implanted into the chip, and the oriented collagen fibers controlled by collagen concentration and injection rate could guide the MDA-MB-231 cells in the spheroid to undergo directional invasion. The experiment showed that the oriented fibers greatly accelerated the invasion speed of MDA-MB-231 cells compared with the traditional uniform tumor micro-environment, namely obvious invasive branches appeared on the spheroids within 24 hours. In order to analyze this interesting phenomenon, we have developed a quantitative analyzing approach to explore strong angle correlation between the orientation of collagen fibers and invasive direction of cancer cell. The results showed that the oriented collagen fibers produced by the chip can greatly stimulate the invasion potential of cancer cells. This biochip is not only conducive to modeling cancer cell metastasis and studying cell invasion mechanisms, but also has the potential to build a quantitative evaluation platform that can be used in future chemical drug treatments.
Cell migration is an indispensable physiological and pathological process for normal tissue development and cancer metastasis, which is greatly regulated by intracellular signal pathways and extracellular microenvironment (ECM). However, there is a lack of adequate tools to analyze the time-varying cell migration characteristics because of the effects of some factors, i.e., the ECM including the time-dependent local stiffness due to microstructural remodeling by migrating cells. Here, we develop an approach to derive the time-dependent motility parameters from cellular trajectories, based on the time-varying persistent random walk model. In particular, we employ the wavelet denoising and wavelet transform to investigate cell migration velocities and obtain the wavelet power spectrum. The time-dependent motility parameters are subsequently derived via Lorentzian power spectrum. Our analysis shows that the combination of wavelet denoising, wavelet transform and Lorentzian power spectrum provides a powerful tool to derive accurately the time-dependent motility parameters, which reflects the time-varying microenvironment characteristics to some extent.
Mesh networks are a kind of very important network topologies in massively multiprocessor parallel systems. With the continuous increasing in network size, routing algorithm in large size networks with faults has become unavoidable. This paper mainly focuses on fault tolerant routing algorithm on mesh networks. Based on the concept of k submesh, this paper proposes two simple routing algorithms for mesh networks. The algorithms are distributed and local information based. Authors apply probabilistic analysis on the fault tolerance of above routing algorithms. Suppose each node has an independent failure probability, it is able to derive the probability that the routing algorithms successfully return a fault free routing path. For example, authors formally prove that as long as the node failure probability is bounded by 1.87%, the routing algorithms succeed in finding a fault free routing path with probability at least 99%. The routing algorithms run in liner time. Simulation results show that the length of the routing paths constructed by the algorithms is very close to the optimal length.
A microchamber array with composite ECM device enables the construction of a more realistic model for investigating cancer migration mechanisms and has potential to serve as a platform for personalized medicine screening.
Traditional cancer researches focus on the analyses of the mice biopsy in order to understand the formation of cancer and the stage of cancer development. In contrast to in vivo experiments, in vitro investigation of cancer cells provides the flexible manipulation of the experimental parameters and the real time observation of the growth and reproduction of cancer cells, thus has been developing rapidly. However, further studies have demonstrated that cells' behavior in a two-dimensional (2D) environment, e.g. Petri dish, is dramatically different from that in a three-dimensional (3D) environment. Therefore, with assistance of bio-microfluidic chips, 3D bio-printing, direct femtosecond laser writing technology and UV curing hydrogel technology, an increasing number of 3D models have been developed to investigate the behaviors of cancer cells in vitro. Nevertheless, the existing technology is also facing the contradiction between accuracy and speed requirements, as well as the biocompatibility and biodegradability of scaffold materials in use. In this paper, we first summarize and compare present 2D models, e. g. Agar Plate and Boyden Assay, and the developing 3D models in vitro experimental approaches as mentioned above, and discuss the merits of these fabricating technologies. Then we focus on the recent progress and achievements of 3D bio-techniques, especially the successful applications in probing the invasion behaviors of cancer cells. Though significant progress has been made from 2D to 3D approaches and these in vitro experimental models are becoming more flawless in simulating the in vivo environment of cells, the following challenges remain: 1) biocompatible material with the appropriate mechanic properties simulating the environment in vivo; 2) the viability of cells in the complex 3D model with of biomaterial, especially during the laser or UV-assisted gelation of hydrogels; 3) the speed and resolution of the present 3D fabrication technologies; 4) the in situ observation and control of cells. Nevertheless, with the development of 3D bio-technologies, breakthroughs can be expected in solving those problems, and thus will guide the 3D experimental models for the invasion of cancer cells in next few years. This will eventually help people in the war towards cancers, and at the same time provide new experimental approaches for other relevant researches in the interdisciplinary fields of biology, physics, chemistry, materials and engineering.
Performance of triboelectric nanogenerators is limited by low and unstable charge density on tribo-layers. An external-charge pumping method was recently developed and presents a promising and efficient strategy towards high-output triboelectric nanogenerators. However, integratibility and charge accumulation efficiency of the system is rather low. Inspired by the historical development of electromagnetic generators, here, we propose and realize a self-charge excitation triboelectric nanogenerator system towards high and stable output in analogy to the principle of traditional magnetic excitation generators. By rational design of the voltage-multiplying circuits, the completed external and self-charge excitation modes with stable and tailorable output over 1.25 mC m-2 in contact-separation mode have been realized in ambient condition. The realization of the charge excitation system in this work may provide a promising strategy for achieving high-output triboelectric nanogenerators towards practical applications.
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