Customized heat treatment process enabled excellent mechanical properties in wire arc additively manufactured Mg-RE-Zn-Zr alloys

Customized heat treatment is essential for enhancing the mechanical properties of additively manufactured metallic materials,especially for alloys with complex phase constituents and heterogenous microstructure.However,the interrelated evolutions of different microstructure features make it difficult to establish optimal heat treatment processes.Herein,we proposed a method for customized heat treatment process exploration and establishment to overcome this challenge for such kind of alloys,and a wire arc additively manufactured(WAAM)Mg-Gd-Y-Zn-Zr alloy with layered heterostructure was used for feasibility verification.Through this method,the optimal microstructures(fine grain,controllable amount of long period stacking ordered(LPSO)structure and nano-scaleβ'precipitates)and the corresponding customized heat treatment processes(520°C/30 min+200°C/48 h)were obtained to achieve a good combination of a high strength of 364 MPa and a considerable elongation of 6.2%,which surpassed those of other state-of-the-art WAAM-processed Mg alloys.Furthermore,we evidenced that the favorable effect of the undeformed LPSO structures on the mechanical properties was emphasized only when the nano-scaleβ'precipitates were present.It is believed that the findings promote the application of magnesium alloy workpieces and help to establish customized heat treatment processes for additively manufactured materials.

Additive manufacturing of magnesium and its alloys: process-formabilitymicrostructure-performance relationship and underlying mechanism

Magnesium and its alloys,as a promising class of materials,is popular in lightweight application and biomedical implants due to their low density and good biocompatibility.Additive manufacturing(AM)of Mg and its alloys is of growing interest in academia and industry.The domain-by-domain localized forming characteristics of AM leads to unique microstructures and performances of AM-process Mg and its alloys,which are different from those of traditionally manufactured counterparts.However,the intrinsic mechanisms still remain unclear and need to be in-depth explored.Therefore,this work aims to discuss and analyze the possible underlying mechanisms regarding defect appearance and elimination,microstructure formation and evolution,and performance improvement,based on presenting a comprehensive and systematic review on the relationship between process parameters,forming quality,microstructure characteristics and resultant performances.Lastly,some key perspectives requiring focus for further progression are highlighted to promote development of AM-processed Mg and its alloys and accelerate their industrialization.

Enhanced strength-ductility synergy in a wire and arc additively manufactured Mg alloy via tuning interlayer dwell time

Strength-ductility trade-off is a common issue in Mg alloys. This work proposed that a synergistic enhancement of strength and ductility could be achieved through tuning interlayer dwell time(IDT) in the wire and arc additive manufacturing(WAAM) process of Mg alloy.The thermal couples were used to monitor the thermal history during the WAAM process. Additionally, the effect of different IDTs on the microstructure characteristics and resultant mechanical properties of WAAM-processed Mg alloy thin-wall were investigated. The results showed that the stable temperature of the thin-wall component could reach 290 ℃ at IDT=0s, indicating that the thermal accumulation effect was remarkable. Consequently, unimodal coarse grains with an average size of 39.6 μm were generated, and the resultant room-temperature tensile property was poor. With the IDT extended to 60s, the thermal input and thermal dissipation reached a balance, and the stable temperature was only 170 ℃, closing to the initial temperature of the substrate. A refined grain structure with bimodal size distribution was obtained. The remelting zone had fine grains with the size of 15.2 μm, while the arc zone owned coarse grains with the size of 24.5 μm.The alternatively distributed coarse and fine grains lead to the elimination of strength-ductility trade-off. The ultimate tensile strength and elongation of the samples at IDT=60s are increased by 20.6 and 75.0% of those samples at IDT=0s, respectively. The findings will facilitate the development of additive manufacturing processes for advanced Mg alloys.

D-二聚体/纤维蛋白原比值对急性冠脉综合征的诊断价值

目的 探讨D-二聚体/纤维蛋白原比值对急性冠脉综合征的诊断价值。方法 收集2018年1月~2019年9月在本院就诊的并接受冠状动脉造影检查的患者150例。根据冠状动脉造影结果,将其分为A组(急性心肌梗死(AMI)组)、B组(稳定型心绞痛(SAP)组)、C组(不稳定型心绞痛(UAP)组),每组各50例。通过对D-二聚体、纤维蛋白原、D/F比值3项指标检测,评价对ACS诊断的应用价值。结果 D-二聚体、纤维蛋白原的水平:A组最高,其次是C组、B组,组间差异有统计学意义(P<0.01);D/F比值C组水平最高,其次是A组、B组,组间差异有统计学意义(P<0.01)。结论 D-二聚体、纤维蛋白原、D/F比值指标对ACS的诊断具有重要价值,其中D/F比值诊断价值最高。

Hypoxic response elements and Tet-On advanced double-controlled systems regulate hVEGF_(165) and angiopoietin-1 gene expression in vitro

Angiogenesis in ischemic tissue is a complex and multi-gene event. In the study, we constructed hypoxic re-sponse elements （HRE） and the Tet-On advanced double-controlled systems and investigated their effects on the expression of hVEGF165 and angiopoietin-1 （Ang-1） genes in rat cardiomyocytes exposed to hypoxia and pharma-cologic induction. We infected neonatal rat cardiomyocytes with recombinant rAAV-rtTA-Rs-M2/rAAV-TRE-Tight-Ang-1 and rAAV-9HRE- hVEGF165. Our results indicated that the viral titer was 1×1012 vg /mL and the viral purity exceeded 98%. hVEGF165 expression was induced by hypoxia, but not by normoxia （P 0.001）. Ang-1 expression was evident under doxycycline induction, but undetectable without doxycycline induction （P 0.001）. Immunofluorescence staining showed that positively stained hVEGF165 and Ang-1 protein appeared only under both hypoxia and doxycycline induction. We demonstrate here that HRE and the recombinant Tet-On advanced double gene-controlled systems sensitively regulate the expression of hVEGF165 and Ang-1 genes in an altered oxygen environment and under pharmacological induction in vitro.

Pigment epithelium derived factor(PEDF)prevents methyl methacrylate monomer-induced cytotoxicity in H9c2 cells

Acrylic bone cements are currently the most frequently and extensively used materials in orthopedic implant treatment. However, adverse effects have been described of acrylic bone cement on the cardiovascular system. In the present study, we examined the cytotoxicity of bone cement ingredient methyl methacrylate（MMA） to cardiomyocytes and the potential detoxifying effect of pigment epithelium-derived factor（PEDF） in H9c2 cells.We found that high concentration of MM A（〉 120 mmol/L） led to necrotic cell death in H9c2 cells. However, MMA at low concentrations（30-90 mmol/L） caused apoptosis. Pretreatment of PEDF prevented MMA-induced cytotoxicity. In addition, PEDF enhanced total superoxide dismutase activities, and decreased MMA-induced production of malonaldehyde. Furthermore, MMA-induced downregulation of Akt activity was suppressed by PEDF.PEDF also increased the levels of peroxisome proliferator activated receptor gamma（PPARγ）and lysophosphatidic acids（LPA） through PEDF receptor. These results indicated that PEDF inhibited MMA-induced cytotoxicity through attenuating oxidative stress, activating the phosphatidylinositol 3-kinase（PI3K）/Akt pathway and/or PEDF receptorLPA-PPARy pathways in H9c2 cells. PEDF may be explored as a candidate therapeutic agent for alleviating bone cement implantation syndrome during orthopedic surgery.

How many proteins interacting with symbiosis receptor-like kinase （SymRK） involved in nodulation？

Nodule formation is a tightly regulated process that integrates specific signal exchange and coordinated activation of developmental mechanisms to synchronize bacte-rial infection and organ development. Symbiosis receptor kinase （SymRK） is indispensable for symbiotic signal transduction of root nodule symbiosis （RNS） upon stimulation of root cells by microbial signaling molecules. But the protein turnover model of SymRK and the way for nodulation factor signals downstream transduction from SymRK are not clear. Over the past years, a number of proteins interacting with SymRK which required for root nodule symbiosis have been identified. Here we summarized structures and functions of these pro-teins, and concluded that major challenge would be revealing relations between them and the regulation mechanisms of SymRK in nodulation.

Developing guanine base editors for G-to-T editing in rice

Single nucleotide polymorphisms (SNPs) are widely present and related to desirable agronomic traits in crops.clustered regularly interspaced palindromic repeats(CRISPR)/CRISPR-associated nuclease 9 (Cas9)-mediated base editors have been frequently used to correct defective alleles and create novel alleles by artificial evolution for rapid crop genetic improvement (Ma et al.,2021).

Adsorption and desorption of herbicide monosulfuron-ester in Chinese soils

Monosulfuron-ester is a new,low rate,sulfonylurea herbicide that is being promoted for annual broadleaf and gramineal weed control;however,there is a lack of published information on its behavior in soils.The adsorption and desorption of monosulfuronester by seven type soils were measured using a batch equilibrium technique.The results showed that the Freundlich equation fitted its adsorption and desorption well,and the Freundlich constant values （K f-ads ） ranged from 0.88 to 5.66.Adsorption isotherms were nonlinear with 1/n f-ads values 1.Soil pH,organic matter （OM）,and clay content were the main factors influencing its adsorption and desorption.Adsorption and desorption were negatively correlated with pH 4.0–8.0 while positively correlated with OM and clay content.The adsorption of monosulfuron-ester was mainly a physical process,because its free energy （？G） in seven soils was less than 40 kJ/mol.Monosulfuron-ester adsorption by three soils increased with increasing CaCl 2 concentration using CaCl 2 as a background electrolyte.Monosulfuron-ester desorption was hysteretic in all tested soils.

Transformation of japonica rice with RHL gene and salt tolerance of the transgenic rice plant

Overexpression of the yeast HAL2 gene increases salt tolerance of yeast and plant. Rice HAL2-like (RHL) gene was introduced into a japonica rice cultivar HJ19 with Agrobacterium tumefaciens-mediated transformation. Transgenic plants in R0 generation were selected on the principle of GUS-positive, RHL gene PCR-positive and normal growth. Hygromycin-resistant plants of some transgenic lines in R1 generation increased salt tolerance during the seedling and booting stage, being less damaged in the cy-tomembrane and stronger in leaf tissue viability under salt stress during booting period. Southern analysis of transgenic lines tolerant to salt in R1 generation showed that the RHL gene expression cassette had been successfully integrated into rice genome. Moreover, gene engineering breeding methodology and really salt-tolerant rice cultivar were discussed.

Suppression of LjBAK1-mediated immunity by SymRK promotes rhizobial infection in Lotus japonicus.

An important question in biology is how organisms can associate with different microbes that pose no threat (commensals), pose a severe threat (pathogens) and those that are beneficial (symbionts). The root nodule symbiosis serves as important model system to address such questions in the context of plant-microbe interactions. It is now generally accepted that rhizobia have the abilities to actively suppress host immune responses during the infection process, analogous to the way in which plant pathogens can evade immune recognition. However, much remains to be elucidated with regard to the mechanisms by which the host recognizes the rhizobia as pathogens and how, subsequently, these pathways are suppressed to allow establishment of the nitrogen fixing symbiosis. In this study, we found that SymRK (Symbiosis Receptor-like Kinase) is required for rhizobial suppression of plant innate immunity in Lotus japonicus. SymRK associates with LjBAK1 (BRASSINOSTEROID INSENSITIVE 1-Associated receptor Kinase 1), a well characterized, positive regulator of plant innate immunity, and directly inhibits LjBAK1 kinase activity. Rhizobial inoculation enhances the association between SymRK and LjBAK1 in planta. LjBAK1 is required to regulate plant innate immunity and plays a negative role in mediating rhizobial infection in L. japonicus. The data indicate that the protein complex of SymRK-LjBAK1 serves as an intersection point between rhizobial symbiotic signaling pathways and innate immunity pathways, which provides an evidence that rhizobia might actively suppress the host's ability to mount a defense response in the legume-rhizobium symbiosis.

An MAP kinase interacts with LHK1 and regulates nodule organogenesis in Lotus japonicus

Symbiosis receptor-like kinase(SymRK) is a key protein mediating the legume-Rhizobium symbiosis.Our previous work has identified an MAP kinase kinase,SIP2,as a SymRK-interacting protein to positively regulate nodule organogenesis in Lotus japonicus,suggesting that an MAPK cascade might be involved in Rhizobium-legume symbiosis.In this study,LjMPK6 was identified as a phosphorylation target of SIP2.Stable transgenic L.japonicus with RNAi silencing of LjMPK6 decreased the numbers of nodule primordia(NP) and nodule,while plants overexpressing LjMPK6 increased the numbers of nodule,infection threads(ITs),and NP,indicating that LjMPK6 plays a positive role in nodulation.LjMPK6 could interact with a cytokinin receptor,LHK1 both in vivo and in vitro.LjMPK6 was shown to compete with LHP1 to bind to the receiver domain(RD) of LHK1 and to downregulate the expression of two LjACS(1-aminocyclopropane-1-carboxylic acid synthase) genes and ethylene levels during nodulation.This study demonstrated an important role of LjMPK6 in regulation of nodule organogenesis and ethylene production in L.japonicus.

A C3HC4-type RING finger protein regulates rhizobial infection and nodule organogenesis in Lotus japonicus

During the establishment of rhizobia-legume symbiosis, the cytokinin receptor LHK1 （Lotus Histidine Kinase 1） is essential for nodule formation. However, the mechanism by which cytokinin signaling regulates symbiosis remains largely unknown. In this study, an LHK1-interacting protein, LjCZF% was identified and further characterized. LjCZF1 is a C3HC4-type RiNG finger protein that is highly conserved in plants. LjCZF1 specifically interacted with LHK1 in yeast two-hybrid, in vitro pull-down and co-immunoprecipitation assays conducted in tobacco. Phosphomimetic mutation of the potential threonine （T167D） phosphorylation site enhanced the interaction between LjCZF1 and LHK1, whereas phosphorylation mutation （T167A） eliminated this interaction. Transcript abundance of LjCZF1 was up-regulated significantly after inoculation with rhizobia. The LORE1 insertion mutant and clustered regularly interspaced short palindromic repeats （CRISPR）/CRISPR- associated protein 9-mediated knockout mutant Lotus japonicus plants demonstrated significantly reduced number of infection threads and nodules. In contrast, plants over-expressing LjCZF1 exhibited increased numbers of infection threads and nodules. Collectively, these data support the notion that LjCZF1 is a positive regulator of symbiotic nodulation, possibly through interaction with LH K1.