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• WE43 magnesium alloy fabricated by laser powder bed fusion was treated by high temperature oxidation (HTO) to inhibit degradation. • HTO increased surface wettability, hardness and abrasive resistance. • HTO slightly decreased strength and significantly increased ductility. • HTO increased cytocompatibility, hemocompatibility and osteogenesis. • Influence mechanism of HTO on mechanical properties and biocompatibility was clarified. Laser powder bed fusion (L-PBF) has been used to fabricate biodegradable Mg implants of WE43 alloy, but the degradation is too fast compared with the term bone reconstruction. Previous studies show that high temperature oxidation (HTO) can successfully inhibit the degradation of WE43 alloy. In this work, the influence of HTO on L -PBF samples of WE43 alloy was investigated regarding tensile, compressive, and abrasive resistance, as well as in vitro cytotoxicity, cell proliferation, hemolysis, and osteogenesis. Compared with the as-built L -PBF samples, HTO increased grain size and grain texture, stabilized and coarsened precipitates, and caused discontinuous static recrystallization in the matrix. The oxide layer at the surface of the HTO samples improved surface roughness, hydrophilia, hardness, and abrasive resistance. The tensile strength decreased slightly from 292 to 265 MPa, while the elongation substantially increased from 10.97% to 16.58% after HTO. The in vitro cell viability, cell proliferation, hemolysis, and osteogenic effect were considerably enhanced due to the improvement of surface quality and the initial inhibition of excessive Mg2+ releasement. Overall, HTO is of great benefit to the surface performance, ductility, and biocompatibility of WE43 alloy fabricated by L -PBF for biodegradable applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Reconstruction of subarticular bone defects is an intractable challenge in orthopedics. The simultaneous repair of cancellous defects, fractures, and cartilage damage is an ideal surgical outcome. 3D printed porous anatomical WE43 (magnesium with 4 wt% yttrium and 3 wt% rare earths) scaffolds have many advantages for repairing such bone defects, including good biocompatibility, appropriate mechanical strength, customizable shape and structure, and biodegradability. In a previous investigation, we successfully enhanced the corrosion resistance of WE43 samples via high temperature oxidation (HTO). In the present study, we explored the feasibility and effectiveness of HTO-treated 3D printed porous anatomical WE43 scaffolds for repairing the cancellous bone defects accompanied by split fractures via in vitro and in vivoexperiments. After HTO treatment, a dense oxidation layer mainly composed of Y2O3and Nd2O3formed on the surface of scaffolds. In addition, the majority of the grains were equiaxed, with an average grain size of 7.4 μm. Cell and rabbit experiments confirmed the non-cytotoxicity and biocompatibility of the HTO-treated WE43 scaffolds. After the implantation of scaffolds inside bone defects, their porous structures could be maintained for more than 12 weeks without penetration and for more than 6 weeks with penetration. During the postoperative follow-up period for up to 48 weeks, radiographic examinations and histological analysis revealed that abundant bone gradually regenerated along with scaffold degradation, and stable osseointegration formed between new bone and scaffold residues. MRI images further demonstrated no evidence of any obvious damage to the cartilage, ligaments, or menisci, confirming the absence of traumatic osteoarthritis. Moreover, finite element analysis and biomechanical tests further verified that the scaffolds was conducive to a uniform mechanical distribution. In conclusion, applying the HTO-treated 3D printed porous anatomical WE43 scaffolds exhibited favorable repairing effects for subarticular cancellous bone defects, possessing great potential for clinical application.

The effects of pore size in additively manufactured biodegradable porous magnesium on the mechanical properties and biodegradation of the scaffolds as well as new bone formation have rarely been reported. In this work, we found that high temperature oxidation improves the corrosion resistance of magnesium scaffold. And the effects of pore size on the mechanical characteristics and biodegradation of scaffolds, as well as new bone formation, were investigated using magnesium scaffolds with three different pore sizes, namely, 500, 800, and 1400 μm (P500, P800, and P1400). We discovered that the mechanical characteristics of the P500 group were much better than those of the other two groups. In vitroand in vivoinvestigations showed that WE43 magnesium alloy scaffolds supported the survival of mesenchymal stem cells and did not cause any local toxicity. Due to their larger specific surface area, the scaffolds in the P500 group released more magnesium ions within reasonable range and improved the osteogenic differentiation of bone mesenchymal stem cells compared with the other two scaffolds. In a rabbit femoral condyle defect model, the P500 group demonstrated unique performance in promoting new bone formation, indicating its great potential for use in bone defect regeneration therapy.

Laser powder bed fusion (L-PBF) of magnesium (Mg) alloy porous scaffolds is expected to solve the dual challenges from customized structures and biodegradable functions required for repairing bone defects. However, one of the key technical difficulties lies in the poor L-PBF process performance of Mg, contributed by the high susceptibility to oxidation, vaporization, thermal expansion, and powder attachment etc. This work investigated the influence of L-PBF energy input and scanning strategy on the formation quality of porous scaffolds by using WE43 powder, and characterized the microstructure, mechanical properties, biocompatibility, biodegradation and osteogenic effect of the as-built WE43 porous scaffolds. With the customized energy input and scanning strategy, the relative density of struts reached over 99.5%, and the geometrical error between the designed and the fabricated porosity declined to below 10%. Massive secondary phases including intermetallic precipitates and oxides were observed. The compressive strength (4.37–23.49 MPa) and elastic modulus (154.40–873.02 MPa) were comparable to those of cancellous bone. Good biocompatibility was observed by in vitrocell viability and in vivoimplantation. The biodegradation of as-built porous scaffolds promoted the osteogenic effect, but the structural integrity devastated after 12 h by the immersion tests in Hank's solution and after 4 weeks by the implantation in rabbits' femur, indicating an excessively rapid degradation rate.

The influence of pure Al, Al-Si and Zn-Al weld fillers on microstructure and mechanical properties was investigated during lap laser welding-brazing of Al to Cu. Al4.2Cu3.2Zn0.7IMC layer and plate-like Al2Cu phase were observed at Al/Cu interface with pure Al and Al-Si weld fillers. Microcrack was easy to generate in Al2Cu phase decreasing the joint strength. When the Zn-Al weld filler was adopted, the formation of Al2Cu brittle phase was limited by low Al content and the CuZn and CuZn5IMC layers were observed at Al/Cu interface. According to the chemical potential, the diffusivity of Cu atoms in Zn-Al weld filler was much lower than that of pure Al and Al-Si weld fillers, which prevented from the formation of coppery phases near the Al/Cu interface. Si atoms tended to concentrate at Al/Cu interface. It played a role in obstructing the diffusion of Cu atoms, enhancing the Al/Cu joint strength to some extent. According to nanoindentation result, the mechanical property of the formed phases (CuZn and CuZn5) in the case of Zn-Al weld filler was better than that formed with pure Al and Al-Si weld fillers such as Al2Cu and Al4.2Cu3.2Zn0.7. The highest tensile strength was 148 MPa with Zn-Al weld filler.

The thermal effect and the light output of a laser crystal under different pumping depths were reported., Based on the thermal model of a single-ended pumped Tm:YAP crystal, the thermal stress coupled model used Comsol to theoretically calculate the effect of changing the pump spot size and pump depth on crystal heat distribution and stress distribution. The experimental results showed that the laser output power first increased and then decreased with increasing pump spot size. As the depth of focus increased, the laser output power first increased and then decreased. The experimental results were consistent with the theoretical simulation results. The theory of pump spot radius and depth of focus in this paper provided an effective simulation method for mitigating thermal effects, and provided theoretical supports for laser crystals to obtain higher laser output power.

Disc brakes have been applied in various automobiles widely and their braking performance has vitally important effects on the safe operation of automobiles. Although numerous researches have been conducted to find out the influential law and mechanism of working condition parameters like braking pressure, initial braking speed, and interface temperature on braking performance of disc brakes, the influence of magnetic field is seldom taken into consideration. In this paper, based on the novel automotive frictional-magnetic compound disc brake, the influential law of magnetic field on braking performance was investigated deeply. First, braking simulation tests of disc brakes were carried out, and then dynamic variation laws and mechanisms of braking torque and interface temperature were discussed. Furthermore, some parameters including average braking torque, trend coefficient and fluctuation coefficient of braking torque, average temperature, maximum temperature rise, and the time corresponding to the maximum temperature rise were extracted to characterize the braking performance of disc brakes. Finally, the influential law and mechanism of excitation voltage on braking performance were analyzed through braking simulation tests and surface topography analysis of friction material. It is concluded that the performance of frictional-magnetic compound disc brake is prior to common brake. Magnetic field is greatly beneficial for improving the braking performance of frictional-magnetic compound disc brake.

A fiber laser welding-brazing procedure has been developed for joining AZ31B magnesium alloy to Cu-Ni coated Ti-6Al-4V titanium sheet using AZ92D filler wire. The effect of the interlayer arrangements (AZ31B/Ni-Cu/Ti-6Al-4V and AZ31B/Cu-Ni/Ti-6Al-4V) on appearance, interfacial reaction and mechanical properties were investigated at different heat input. It was found that the feasibility of this process depends strongly on the pre-existing Cu-Ni layer on the Ti surface that promotes wetting of the AZ92 filler. Within the range of 1200–1600 W, defect free joints in both interlayer arrangements. Depending on the interlayer arrangements chosen, different reactions layers formed inside the joint region. Nevertheless, at optimum heat input (1400 W), Ti2Ni mingled with Ti3Al interfacial reaction products was produced along the fusion zone (FZ)-Ti brazed interface in both interlayer arrangements. The tensile-shear fracture load of the joints produced at the optimum laser power reached a maximum value of 2016.5 N for AZ31B/Ni-Cu/Ti-6Al-4V and 2014.6 N for AZ31B/Cu-Ni/Ti-6Al-4V, representing an efficiency of 71% compared to AZ31B alloy. Under suitable heat input, the joints failed at the fusion zone of the AZ31B base metal. In contrast, incomplete brazing or large volume of intermetallics at the brazed interface resulted in interfacial failure at lower/higher heat input.

•Join Mg and Ni-coated Ti using laser heat-conduction welding process.•Influence of laser power on welding quality and interfacial reaction was investigated.•A bidirectional elemental diffusion mechanism was clarified based on numerical simulation.•Joint strength and fracture mode were associated with interfacial bonding and weld defects.

The immiscible and nonreactive characteristics of Mg/Ti dissimilar metals restrict the metallurgical bonding and reliable joining of them. To solve this problem, the Al interlayer between Mg/Ti was added. The Mg/Ti joint without addition of Al interlayer could not be welded, while relatively acceptable appearance was obtained when adding Al interlayer. The interfacial reaction was improved with the assistance of Al interlayer resulting in metallurgical bonding at the interface. The TiAl3phase formed at the direct laser irradiation zone. Note that the interfacial reaction layer increased little with the increasing thickness of Al interlayer. The interfacial reaction layer was mainly restricted by dissolution of Ti element. Temperature field and thermodynamic calculation assisted to prove the interfacial reaction at the fusion zone/Ti interface and the formation of TiAl3. The tensile-shear testing indicated that the maximum tensile-shear force could reach 2230 N/cm (about 81% of that of AZ31B Mg alloy base metal) when the laser power was 2300 W and the thickness of added Al interlayer was 0.05 mm. The tensile-shear force decreased when network structure of Mg17Al12precipitated in the weld zone. The fracture path changed from fusion zone/Ti to Mg fusion line when the thickness of Al interlayer exceeded 0.12 mm.

ABSTRACTMany symbiotic Epichloëspecies are seed-transmitted in their grass hosts. For a detailed investigation of Epichloë festucaecolonization throughout the life cycle of its host, the authors transformed strain Fl1 with a fungal-active gene for enhanced cyan-fluorescent protein (eCFP), introduced it into perennial ryegrass (Lolium perenne), and used confocal microscopy to track its growth in the shoot apex, floral primordium, floral organs, seeds, and seedlings. Hyphae intercellularly colonized leaf sheaths, blades, true stems, and leaf primordia, and among floral primordia the endophyte exhibited different levels of colonization. In preanthesis florets, E. festucaecolonized the pistil and stamen, but not pollen grains, and ramified throughout the ovule nucellus, but not the integument or embryo sac. Generally, only a single hypha was observed extended from the ovary placenta into the ovule. Within 4 d after anthesis, fungal hyphae had ramified throughout the developing seed and embryo. As the embryo matured, fungal hyphae became abundant between the testa and aleurone layer, and around the shoot apex and radical of the embryonic axis. During germination, hyphae accumulated in the mesocotyl and invaded the newly formed shoot apex near the meristem. In this host-fungus symbiosis, transmission to seedlings averaged 41% in 2010 and 76% in 2011. Each year, the frequency of ovary infection was similar to the frequency of infecting embryos and seedlings, indicating that colonization of the ovary and embryo was required for seed transmission.

Red clover (Trifolium pratenseL.) is an important forage legume in the United States. Improving forage quality and biomass yield is an important goal of forage breeding programs. Plant development, particularly the transition from vegetative to reproductive growth, is an important factor affecting biomass accumulation and forage quality. Thus, genetic manipulation of genes that regulate the transition from the vegetative to reproductive phase can be an efficient strategy for genetic improvement of red clover. One such gene is miR156, a microRNA gene that serves as a master regulator of vegetative phase change in land plants. We report here the development of transgenic red clover plants overexpressing the maize Corngrass1gene encoding two tandem miR156s. The transgenic plants displayed striking phenotypic changes compared with the wild‐type plants, including the increased number of shoots, delayed flowering, enhanced forage yield, and improved forage quality. These results suggest that manipulating miR156 or its target genes is a potential tool for genetic improvement of forage legumes.

Summary:Phenolic formaldehyde (PF) resins are attractive due to their excellent performances such as high temperature resistance, thermal abrasion, and high yield of carbon conversion. In this communication, PF resin‐based composite hollow spheres were fabricated by in situ favorable absorption and catalytic crosslinking of PF resin within sulfonated polystyrene gel layers of the hollow sphere templates at low temperature. The composite hollow spheres were achieved in one step, avoiding traditional removal of template cores. The intact shell was tuned from double‐layered to single‐layered. Carbon hollow spheres with porous shell were derived by carbonization of the PF composite hollow spheres. Metal/carbon composite hollow spheres were further synthesized by the incorporation of metal within the porous shell, which would be a promising material for catalysis. TEM image of carbon double‐shelled hollow spheres after the PF composite spheres are calcined at 800 °C for 2 h in nitrogen. TEM image of carbon double‐shelled hollow spheres after the PF composite spheres are calcined at 800 °C for 2 h in nitrogen.

Paraformaldehyde was end-capped with acetyl groups and was applied as a crosslinking agent for a bismaleimide (BMI)-modified novolac resin system. The processibility of the resin system containing 5 wt % crosslinking agent still met the need for resin transfer molding (RTM), whereas the thermomechanical properties of crosslinked resin improved significantly. The composites based on the resin system and woven glass fabric showed better flexural strength, modulus, and higher retention rates at 200 and 300°C than that based on a resin system without acetyl-capped paraformaldehyde. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1265–1271, 2002

A thermosetting resin system for resin-transfer molding based on novolak and bismaleimide (BMI) was developed. The novolak resin was allylated and BMI was used as the curing agent, and allyl phenyl ether, as the diluent. The viscosity–temperature curve and the viscosity–time curve were used to characterize the processing property of the resin system. The resin system had a long pot life at the injection temperature. Based on the DSC data, a regime for the curing and postcuring cycles was established. The cured resin showed outstanding heat resistance and good flexural properties. Composites based on the resin system and woven glass fabric were fabricated using RTM technology. The composites showed very good flexural properties at room temperature and high retention rates at 200 and 300°C. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 83: 1651–1657, 2002