Microstructure and mechanical properties of nickel-based superalloy fabricated by laser powder-bed fusion using recycled powders

Evaluating the recyclability of powders in additive manufacturing has been a long-term challenge.In this study,the microstructure and mechanical properties of a nickel-based superalloy fabricated by laser powder-bed fusion(LPBF)using recycled powders were investigated.Re-melted powder surfaces,satellite particles,and deformed powders were found in the recycled powders,combined with a high-oxygencontent surface layer.The increasing oxygen content led to the formation of high-density oxide inclusions;moreover,printing-induced cracks widely occurred and mainly formed along the grain boundaries in the as-built LPBF nickel-based superalloys fabricated using recycled powders.A little change in the Si or Mn content did not increase the hot cracking susceptibility(HCS)of the printed parts.The changing aspect ratio and the surface damage of the recycled powders might contribute to increasing the crack density.Moreover,the configuration of cracks in the as-built parts led to anisotropic mechanical properties,mainly resulting in extremely low ductility vertical to the building direction,and the cracks mainly propagated along the cellular boundary owing to the existence of a brittle precipitation phase.

Chronic Exposure to Hypoxia Inhibits Myelinogenesis and Causes Motor Coordination Deficits in Adult Mice

Exposure to chronic hypoxia is considered to be a risk factor for deficits in brain function in adults,but the underlying mechanisms remain largely unknown.Since active myelinogenesis persists in the adult central nervous system,here we aimed to investigate the impact of chronic hypoxia on myelination and the related functional consequences in adult mice.Using a transgenic approach to label newly-generated myelin sheaths(NG2-CreER^(TM);Tau-mGFP),we found that myelinogenesis was highly active in most brain regions,such as the motor cortex and corpus callosum.After exposure to hypoxia(10%oxygen)12 h per day for 4 weeks,myelinogenesis was largely inhibited in the 4-month old brain and the mice displayed motor coordination deficits revealed by the beam-walking test.To determine the relationship between the inhibited myelination and functional impairment,we induced oligoden-droglia-specific deletion of the transcription factor 01ig2 by tamoxifen(NG2-CreER^(TM);Tau-mGFP;Olig2 fl/fl)in adult mice to mimic the decreased myelinogenesis caused by hypoxia.The deletion of OHg2 inhibited myelinogenesis and consequently impaired motor coordination,suggesting that myelinogenesis is required for motor function in adult mice.To understand whether enhancing myelination could protect brain functions against hypoxia,we treated hypoxic mice with the myelination-enhancing drug-clemastine,which resulted in enhanced myelogenesis and improved motor coordination.Taken together,our data indicate that chronic hypoxia inhibits myelinogenesis and causes functional deficits in the brain and that enhancing myelinogenesis protects brain functions against hypoxia-related deficits.

Dicer Deletion in Astrocytes Inhibits Oligodendroglial Differentiation and Myelination

Increasing evidence has shown that astrocytes are implicated in regulating oligodendrocyte myelination,but the underlying mechanisms remain largely unknown.To understand whether microRNAs in astrocytes function in regulating oligodendroglial differentiation and myelination in the developing and adult CNS,we generated inducible astrocyte-specific Dicer conditional knockout mice(hGFAP-CreERT;Dicer fl/fl).By using a reporter mouse line(mT/mG),we confirmed that hGFAP-CreERT drives an efficient and astrocyte-specific recombination in the developing CNS,upon tamoxifen treatment from postnatal day 3(P3)to P7.The Dicer deletion in astrocytes resulted in inhibited oligodendroglial differentiation and myelination in the developing CNS of Dicer cKO mice at P10 and P14,and did not alter the densities of neurons or axons,indicating that Dicer in astrocytes is required for oligodendrocyte myelination.Consequently,the Dicer deletion in astrocytes at P3 resulted in impaired spatial memory and motor coordination at the age of 9 weeks.To understand whether Dicer in astrocytes is also required for remyelination,we induced Dicer deletion in 3-month-old mice and then injected lysolecithin into the corpus callosum to induce demyelination.The Dicer deletion in astrocytes blocked remyelination in the corpus callosum 14 days after induced demyelination.Together,our results indicate that Dicer in astrocytes is required for oligodendroglia myelination in both the developing and adult CNS.

Improving native human sperm freezing protection by using a modified vitrification method

Slow freezing is the most commonly used technique for the cryopreservation of spermatozoa in clinical practice.However,it has been shown to have a negative impact on sperm function and structure.Vitrification as a successful alternative method has been proved to have better protective effects on human embryos,but vitrification of spermatozoa is still subject to low recovery rates.In this study,a modified vitrification method for native spermatozoa was developed.A total of 28 semen samples were included;each sample was divided into three equal parts and assigned to fresh,slow freezing,and vitrification groups.Sperm vitality,motility,morphology,DNA integrity,and acrosome reaction were assessed for each of the groups.The results showed that vitrification achieves better results for several sperm protection parameters than slow freezing;vitrification achieves a higher recovery rate(P<0.05),motility(P<0.05),morphology(P<0.05),and curve line velocity(P<0.05)than slow freezing.Furthermore,DNA fragmentation was decreased(P<0.05)and better acrosome protection(P<0.05)was exhibited in the spermatozoa after vitrification.Principal component analysis of all sperm parameters revealed that the vitrification cluster was closer to the fresh cluster,indicating that spermatozoa are better preserved through vitrification.In conclusion,while both slow freezing and vitrification have negative effects on sperm function and structure,the vitrification protocol described here had a relatively better recovery rate(65.8%)and showed improved preservation of several sperm quality parameters compared with slow freezing.