Crack mechanism and experimental verification on straightening of AZ31B magnesium alloy plate.

When plates with edge cracks in the rolling process is straightened by cyclic tensile and compressive stress, the tip of edge crack always accompanied by stress concentration, which leads to crack propagation. In this paper, damage parameters are imported into the plate straightening model based on determining the GTN damage parameters of magnesium alloy materials by inverse finite element calibration method, the influence of different straightening process schemes and prefabricated V-shaped crack geometry on crack growth is analyzed through the way of the combination of simulation and straightening experiment. The results show that the peak values of equivalent stress and equivalent strain under each straightening roll appear at the crack tip. The value of longitudinal stress and equivalent stain decrease with the distance to crack tip becomes larger. The peak value of longitudinal stress appears when the crack circumferential angle is about 100°, and the crack tip is easy to form crack propagation; when the plate passes roll 2 and roll 4, the equivalent stress and strain concentration at the crack tip are most obvious; when the reduction reaches a certain degree, the void volume fraction (VVF) reaches the VVF of the material breaking; with the increase of the entrance reduction, the number of VVF at the crack tip which reaches the material fracture increases, and the length of crack propagation increases; the stress concentration at the tip of V-shaped crack with large length-width ratio is obvious, and the VVF is more likely to reach the VVF at the time of material fracture, crack initiates and propagates easily.

Design and fabrication of an integrated 3D dynamic multicellular liver-on-a-chip and its application in hepatotoxicity screening.

Nowadays, major methods of in vitro hepatotoxicity research are still based on traditional static two- or three-dimensional cell culture, although these means could investigate some toxic chemicals induced hepatotoxicity, but most of these toxicities failed to reappear in human, at least not in similar or calculable dose level. These failures may cause by the monoculture of only hepatocytes, ignored the signal communication to other non-parenchymal cells in liver tissue, also other complex microenvironment such as endothelial barrier, shear stress and other factors which were really existed in vivo but absent here, final leading to a low reliability of experimental results. In this study, a three-dimensional dynamic multi-cellular liver-on-a-chip device (3D-DMLoC) was developed to reproduce the microenvironment of in vivo liver tissue, including the simulation of hepatic sinusoid, perisinusoidal space and continuous liquid perfusion, hepatocytes could gather to some 3D cell spheroids in this chip. The perfusion could bring a real-time exchange of chemicals, nutrients, metabolites, supply suitable oxygen and a weak shear stress. The pressure and oxygen distribution inner the chip were simulated and evaluated by COMSOL Multiphysics software. HepaRG were co-cultured with HUVEC for 7 days in this chip, expression of hepatic polarization protein ZO-1 and MRP2, liver function factors ALB, UREA and CYP450s were almost all higher than in traditional static culture. Several drugs and heavy metal ions induced hepatotoxicity were then investigated, LDH released from hepatocyte spheroids in mostly 3D-DMLoC groups were higher than same-dosed 2D group, indicated the spheroids were more sensibility to the toxins. The hepatoxicity might be induced by acute hepatocytes injury according to the ratios of secreted AST/ALT contents. In conclusion, a liver-on-a-chip device was successfully developed and verified for better reproducing the in vivo physiological microenvironment of liver. It could be applied for easily, efficiently, and accurately screening the potential hepatotoxic chemicals in future.

Design and fabrication of a liver-on-a-chip platform for convenient, highly efficient, and safe in situ perfusion culture of 3D hepatic spheroids.

Spheroid-based three-dimensional (3D) liver culture models, offering a desirable biomimetic microenvironment, are useful for recapitulating liver functions in vitro. However, a user-friendly, robust and specially optimized method has not been well developed for a convenient, highly efficient, and safe in situ perfusion culture of spheroid-based 3D liver models. Here, we have developed a biomimetic and reversibly assembled liver-on-a-chip (3D-LOC) platform and presented a proof of concept for long-term perfusion culture of 3D human HepG2/C3A spheroids for building a 3D liver spheroid model. On the basis of a fast and reversible seal of concave microwell-based PDMS-membrane-PDMS sandwich multilayer chips, it enables a high-throughput and parallel perfusion culture of 1080 cell spheroids in a high mass transfer and low fluid shear stress biomimetic microenvironment as well as allowing the convenient collection and analysis of the cell spheroids. In terms of reducing spheroid loss and maintaining cell morphology and viability in long-term perfusion culture, the cell spheroids in the 3D-LOC were more safe and efficient. Notably, the polarisation, liver-specific functions, and metabolic activity of the cell spheroids in 3D-LOC were also remarkably improved and exhibited better long-term maintenance over conventional perfusion methods. Additionally, a robust micromilling method that incorporates secondary PDMS coating techniques (SPCs) for fabricating V-shaped concave microwells was also developed. The V-shaped concave microwell arrays exhibited a higher distribution density and aperture ratio, making it easy to form large-scale and uniform-sized cell spheroids with minimum cell loss. In summary, the proposed 3D-LOC could provide a convenient and robust solution for the long-term safe perfusion culture of hepatic spheroids and be beneficial for a variety of potential applications including development of bio-artificial livers, disease modeling, and drug toxicity screening.