Hole density dependent magnetic structure and anisotropy in Fe-pnictide superconductor

The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabilized magnetic structure evolves with increasing hole doping level.Namely,the stripe antiferromagnetic phase dominates at zero doping,while magnetic structures with more antiferromagnetic linking numbers such as the staggered tetramer,staggered trimer,and staggered dimer phases become energetically favorable as the hole density increases.At a certain doping level,energy degeneracy of different magnetic structures appears,indicating strong magnetic frustration and magnetic fluctuations in the system.We suggest that the magnetic competition induced by the hole doping may explain the fast decrease of the Neel temperature TNand the moderately suppressed magnetic moment in the hole doped Fe-pnicitides.Moreover,our results show a sign reversal of the kinetic energy anisotropy as the magnetic ground state evolves,which may be the mechanism behind the puzzling sign reversal of the in-plane resistivity anisotropy in hole-doped Fe-pnicitides.

Graphene oxide-composited chitosan scaffold contributes to functional recovery of injured spinal cord in rats

The study illustrates that graphene oxide nanosheets can endow materials with continuous electrical conductivity for up to 4 weeks. Conductive nerve scaffolds can bridge a sciatic nerve injury and guide the growth of neurons;however, whether the scaffolds can be used for the repair of spinal cord nerve injuries remains to be explored. In this study, a conductive graphene oxide composited chitosan scaffold was fabricated by genipin crosslinking and lyophilization. The prepared chitosan-graphene oxide scaffold presented a porous structure with an inner diameter of 18–87 μm, and a conductivity that reached 2.83 mS/cm because of good distribution of the graphene oxide nanosheets, which could be degraded by peroxidase. The chitosan-graphene oxide scaffold was transplanted into a T9 total resected rat spinal cord. The results show that the chitosan-graphene oxide scaffold induces nerve cells to grow into the pores between chitosan molecular chains, inducing angiogenesis in regenerated tissue, and promote neuron migration and neural tissue regeneration in the pores of the scaffold, thereby promoting the repair of damaged nerve tissue. The behavioral and electrophysiological results suggest that the chitosan-graphene oxide scaffold could significantly restore the neurological function of rats. Moreover, the functional recovery of rats treated with chitosangraphene oxide scaffold was better than that treated with chitosan scaffold. The results show that graphene oxide could have a positive role in the recovery of neurological function after spinal cord injury by promoting the degradation of the scaffold, adhesion, and migration of nerve cells to the scaffold. This study was approved by the Ethics Committee of Animal Research at the First Affiliated Hospital of Third Military Medical University(Army Medical University)(approval No. AMUWEC20191327) on August 30, 2019.

Conducting polypyrrole in tissue engineering applications

Polypyrrole （PPy）, the earliest prepared conducting polymer, has good biocompatibility, easy synthesis and flexibility in processing. Compared with metal and inorganic materials, doped PPy has better mechanical match with live tissue, resulting in its many applications in biomedical field. This mini-review presents some information on specific PPy properties for tissue engineering applications, including its synthesis, doping, bio-modiflcation. Although some challenges and unanswered problems still remain, PPy as novel biomaterial has promoted the development tissue engineering for its clinical application in the future.

Electrophoretic deposition of Al_(2)O_(3)/ZrO_(2) layer with controllable thickness in ethanol medium

ZrO_(2) toughened Al_(2)O_(3)(Al_(2)O_(3)/ZrO_(2))ceramic layers with required thickness were prepared by electrophoretic deposition(EPD)method using ethanol suspensions with stabilizing agent of polyethyleneimine(PEI)under constant-voltage mode in this paper.The deposition of Al_(2)O_(3)/ZrO_(2) ceramic powders occurred on the titanium alloy cathode.A stable suspension with 1wt% PEI in ethanol at pH 5 was prepared in terms of the zeta potential and sedimentation of the suspension.The effects of the suspension concentration,applied voltage,deposition time and processing method of titanium alloy cathode on the coating thickness and morphology were investigated.The deposition layers on titanium alloys with smooth surfaces and thickness of 0.35–1.2 mm could be obtained by adjusting the aforementioned parameters.In addition,after being sintered at 1500℃ for 3 h in air atmosphere,ZrO_(2) toughened Al_(2)O_(3) ceramic layers became smooth and dense.