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16. Characterization of brain tissue : dynamic mechanical testing and viscoelastic modelling

Author

Li, Weiqi

Subjects
Q Science (General)
Abstract

Brain tissue is vulnerable and sensitive, predisposed to potential damage under various conditions of mechanical loading. The studies in this thesis aimed to investigate the viscoelastic properties of brain tissue under various loading conditions and develop viscoelastic models to capture the tissue behaviour. The mechanical properties of brain tissue were quantified using dynamic mechanical analysis (DMA) where a sinusoidally varying displacement was applied to specimens and the viscoelastic properties were obtained under different testing protocols. The regional and directional properties of brain tissue were quantitatively measured at physiological and injurious loading conditions. The compressive properties of brain tissue were studied under time and frequency domains with the same physical conditions. The theory of viscoelasticity was applied to estimate the prediction of viscoelastic response through Finite Element models. Further, the effect of large strain to mechanical behaviour of brain tissue was investigated. This thesis found brain tissue to have showed frequency dependent-viscoelastic properties. The compressive dynamic properties of brain tissue were heterogenous for regions and affected by indenter size and indentation depth. The results demonstrate the feasibility of deriving time-domain viscoelastic parameters from frequency-dependent compressive data for biological tissue. Applications of the brain viscoelastic properties presented in this thesis include the diagnosis of brain injury and fabrication of biomaterials to replicate brain tissue.

Published
2022

29. Protective Effect of Black Rice-Derived Cyanidin-3-O-β-Glucoside on Lipopolysaccharide-Induced Inflammatory Injury in Human Monocyte Cell Line THP-1

Author

YA Fuli, LI Weiqi, MA Yongjie, ZHOU Xinyu, WU Chunting, HUANG Xinhui

Subjects
anthocyanins, cyanidin-3-o-β-glucoside, lipopolysaccharide, monocytes, inflammatory injury, Food processing and manufacture, TP368-456
Abstract

Monocyte-mediated inflammatory responses play a key role in the progression of atherosclerosis. Anthocyanins are polyphenolic flavonoids that are abundant in various dark-colored vegetables, fruits and cereals, which possess a wide range of biological activities. Cyanidin-3-O-β-glucoside (Cy-3-g) is an important anthocyanin monomer. The current study aimed to explore the effects of black rice-derived Cy-3-g on lipopolysaccharide (LPS)-induced inflammatory responses in Tohoku hospital pediatrics-1 (THP-1) as well as its possible mechanism of action. Crude anthocyanins from black rice were obtained by extraction with ethanol-hydrochloric acid solution and macroporous resin adsorption and purified by medium-pressure liquid chromatography with UV detection. Cy-3-g with a purity greater than 96.5% was obtained. THP-1 monocytes were sequentially incubated with different concentrations (0, 0.1, 0.25 and 0.5 μg/mL) Cy-3-g for 4 h, and LPS (50 ng/mL) for additional 48 h. The levels of interleukin (IL)-1β, IL-6, IL-8, IL-10 and tumor necrosis factor (TNF)-α in the culture were determined by enzyme-linked immunosorbent assay (ELISA), and the mRNA expression levels of the genes encoding IL-1β, IL-6, IL-8, IL-10, TNF-α, Toll-like receptor 4 (TLR4) and nuclear factor kappa B (NF-κB) p65 were measured by quantitative polymerase chain reaction (PCR). Moreover, the protein expression levels of TLR4, NF-κB p65 and inhibitor of NF-κB (IκBα) were detected by Western blot. The LPS-induced increase in the relative mRNA expression levels and release levels of IL-1β, IL-6 and TNF-α in THP-1 cells was significantly inhibited by all concentrations of Cy-3-g tested (P 0.05). Cy-3-g at 0.25 and 0.50 μg/mL significantly inhibited the mRNA and protein expression of TLR4 and NF-κB p65 (P 0.05). Black rice-derived Cy-3-g exerts a protective effect on LPS-induced inflammatory injury of THP-1 monocytes possibly through down-regulating the TLR4/NF-κB signaling pathway.

Published
2023
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43. Identification of intrinsic defects and hydrogen passivation in InP using hybrid functional.

Author

Liu, Jinhong, Song, Yang, Xu, Xiaodong, Li, Weiqi, Yang, Jianqun, and Li, Xingji

Subjects
PASSIVATION, ELECTRON traps, FERMI level, ELECTRON mobility, ELECTRON capture
Abstract

Indium phosphide is widely used in electronics and photovoltaic devices due to its high electro-optical conversion efficiency, high electron mobility, and good radiation resistance. Defects are the main limitation for the performance of InP devices. In this work, based on hybrid functional with finite size correction, electronic properties of intrinsic and H-related defects have been investigated in InP. We found that PIn defect is the most stable intrinsic defect with the lowest formation energy. Defect signals detected experimentally are defined by our calculated results. Experimentally observed electron traps with the energy level of EC −0.66 eV and EC −0.68 eV are ascribed to the transition level ɛ(−1/−2) and ɛ(−2/−3) of In vacancies. The hydrogenated vacancies in InP have been systematically reported in the present work. Formation energies of H-related defects indicate that hydrogen atoms prefer to bind to In vacancy than P vacancy. The formation energy of In vacancy decreases with the addition of H, while that of P vacancy increases. For hydrogenated In vacancies, it captures fewer electrons than bare In vacancies when the Fermi level is close to CBM. Especially for the VIn −3H structure, it is 0 charge state in all Fermi levels so that it will not tend to capture electron or hole. Our work is helpful to explain experimental phenomena and radiation-induced damages and improve the performance of InP devices. [ABSTRACT FROM AUTHOR]

Published
2023
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