Ming-Chun Zhao

Low absorbed energy ductile dimple fracture in lower shelf region in an ultrafine grained ferrite/cementite steel

The curve of absorbed energyvs test temperature for an ultrafine grained ferrite/cementite steel showed a transition from an upper shelf energy to a lower shelf energy,i.e., a transition from an energy-absorbent ductile mode to an energy-absorbent brittle mode. Some dense and small-sized dimples were observed in the lower shelf region. A significant and consistent difference existed between ductile-to-brittle transition temperature and impact energy transition temperature, that is, low absorbed energy but undergoing a ductile dimple fracture at a certain low temperature.

Rare Earth Element Yttrium Modified Mg-Al-Zn Alloy: Microstructure, Degradation Properties and Hardness

The overly-fast degradation rates of magnesium-based alloys in the biological environment have limited their applications as biodegradable bone implants. In this study, rare earth element yttrium (Y) was introduced into AZ61 magnesium alloy (Mg-6Al-1Zn wt %) to control the degradation rate by laser rapid melting. The results showed that the degradation rate of AZ61 magnesium alloy was slowed down by adding Y. This was attributed to the reduction of Mg17Al12 phase and the formation of Al2Y phase that has a more active potential, which decreased galvanic corrosion resulting from its coupling with the anodic matrix phase. Meanwhile, the hardness increased as Y contents increased due to the uniform distribution of the Al2Y and Mg17Al12 phases. However, as the Y contents increased further, the formation of excessive Al2Y phase resulted in the increasing of degradation rate and the decreasing of hardness due to its agglomeration.

Mechanical reinforcement of bioceramics scaffolds via fracture energy dissipation induced by sliding action of MoS2 nanoplatelets

The inherent brittleness of bioceramics restricts their applications in load bearing implant, although they possess good biocompatibility and bioactivity. In this study, molybdenum disulfide nanoplatelets (MSNPs) were used to reinforce bioceramics (Mg2SiO4/CaSiO3) scaffolds fabricated by selective laser sintering (SLS). The fracture mode of scaffolds was transformed from transgranular to mixed trans- and intergranular. It could be explained that MSNPs could slide easily due to their weak interlayer van der Waals interactions and provide elastic deformation due to their high elastic modulus. Such sliding action and elastic deformation synergistically induced crack bridging, crack deflection, pull-out and break of MSNPs. Those effects effectively increased the fracture energy dissipation and strain capacity as well as changed the fracture mode, contributing to high fracture toughness and compression strength. Additionally, the scaffolds with MSNPs not only formed a bioactive apatite layer in simulated body fluid, but also supported cell adhesion and proliferation.

Biodegradation Resistance and Bioactivity of Hydroxyapatite Enhanced Mg-Zn Composites via Selective Laser Melting

Mg-Zn alloys have attracted great attention as implant biomaterials due to their biodegradability and biomechanical compatibility. However, their clinical application was limited due to the too rapid degradation. In the study, hydroxyapatite (HA) was incorporated into Mg-Zn alloy via selective laser melting. Results showed that the degradation rate slowed down due to the decrease of grain size and the formation of protective layer of bone-like apatite. Moreover, the grain size continually decreased with increasing HA content, which was attributed to the heterogeneous nucleation and increased number of nucleation particles in the process of solidification. At the same time, the amount of bone-like apatite increased because HA could provide favorable areas for apatite nucleation. Besides, HA also enhanced the hardness due to the fine grain strengthening and second phase strengthening. However, some pores occurred owing to the agglomerate of HA when its content was excessive, which decreased the biodegradation resistance. These results demonstrated that the Mg-Zn/HA composites were potential implant biomaterials.

Corrosion of AZ91 - Influence of the β-Phase Morphology

The influence of the microstructure, particularly the morphology of the β phase, on the corrosion of Mg alloys has been studied using AZ91 as a model alloy and compared with the corrosion of pure magnesium, used as a standard for comparison. The concentration of the impurity element Fe was below the limit evaluated from theoretical phase diagram construction. Corrosion was measured using hydrogen evolution measurements and some polarization measurements. Corrosion behaviour was characterized for four different microstructures produced by heat treatment of as-cast AZ91: namely (i) as-cast, (ii) homogenization anneal (for 5h and 10h at 380°C), (iii) solid solution and (iv) solution treated and aged. The influence of microstructure can be understood from the interaction of the following three factors: (i) the surface films, (ii) micro-galvanic corrosion acceleration dependant on the amount and distribution of the second phase (the  phase in AZ91) and (iii) the second phase can act as a corrosion barrier and hinder corrosion propagation in the matrix, if the second phase is in the form of a continuous network. It is expected that these factors are important for all multi-phase Mg alloys because all known second phases have corrosion potentials more positive than that of the -phase. The electrochemical measurements did not give good values for the corrosion rate in agreement with the literature.

16 High salt promotes systemic lupus erythematosus by TET2-induced dna demethylation and driving the differentiation of TFH cells

Background and Aims Systemic lupus erythematosus (SLE) is an autoimmune disorder that is characterised by the presence of autoantibodies and immune dysregulation. The pathogenesis of SLE has not been elucidated. The induction of epigenetic changes by environmental factors such as diet may also be relevant. A high-salt diet is considered an important contributor to cardiovascular and renal diseases, and recent research has indicated that a high-salt diet can induce autoimmunity. Methods In this study, the effects of high salt on various immune cells and in MLR/lpr mice were observed, and the underlying mechanisms were investigated by flow cytometry, high-throughput sequencing, DNA methylation map, ChIP-QPCR. Results In this study, high salt (sodium chloride, NaCl), under physiological conditions, was demonstrated to increase the differentiation of Tfh. A high-salt diet markedly increased lupus features in MRL/lpr mice. The mechanism is NaCl-induced DNA demethylation via the recruitment of the hydroxytransferase Ten-Eleven Translocation 2 (TET2). Gene silencing of TET2 obviously diminished NaCl-induced Tfh cell polarisation in vitro. In addition, the gene expression of sh2d1a, map3k1, spn and stat5b was enhanced after NaCl treatment, consistent with the findings in lupus CD4+T cells. However, only spn was directly regulated by TET2, and spn was not the sole target for NaCl. Conclusions High-salt treatment promotes SLE in mice and the underlying mechanism might be NaCl enhancing Tfh cell differentiation by TET2 inducing global and gene specific DNA demethylation. Our findings not only explain the epigenetic mechanisms of high-salt induced autoimmunity but also provide an attractive molecular target for intervention strategies of SLE.