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The less-than-ideal cell infiltration resulting from inherently small pore size limits the application of electrospinning scaffold in tissue engineering and regeneration medicine. The present study aims to develop a porogenic method which can significantly increase pore size in electrospinning scaffold and enhance cell migration. With this method, composite scaffolds consisting of poly( -caprolactone) (PCL) fibers and poly(ethylene oxide) (PEO) microparticles were prepared by simultaneously electrospinning and electrospraying. Removal of the PEO microparticles from the composites generated large pores. In vitro culture of NIH3T3 cells and in vivo subcutaneous implantation both demonstrated that the porogenic scaffolds markedly facilitated cell infiltration. With the same technique, vascular grafts with alternative dense and loose layers were prepared by turning on or off electrospraying PEO. SEM showed that there was no a clear delamination between the loose and dense layers. The mechanical strength and burst pressure of these vascular grafts could meet the requirements of vascular implantation. In conclusion, electrospinning PCL fibers with electrospraying PEO microparticles may be an effective and controllable method to increase pore size in electrospinning scaffold and provides a useful tool for the fabrication of vascular grafts that meets the need of blood vessel replacement.

Developing metal-free catalysts for oxygen reduction reaction (ORR) is a great challenge in the development of fuel cells. Nitrogen and sulfur codoped carbon with remarkably high nitrogen content up to 13.00 at % was successfully fabricated by pyrolysis of homogeneous mixture of exfoliated graphitic flakes and ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bimi][Tf2N]). The exfoliated graphite flakes served as a structure-directing substance as well as additional carbon source in the fabrication. It was demonstrated that the use of graphite flakes increased the nitrogen doping level, optimized the composition of active nitrogen configurations, and enlarged the specific surface area of the catalysts. Electrochemical characterizations revealed that the N and S codoped carbon fabricated by this method exhibited superior catalytic activities toward ORR under both acidic and alkaline conditions. Particularly in alkaline solution, the current catalyst compared favorably to the conventional 20 wt % Pt/C catalyst via four-electron transfer pathway with better ORR selectivity. The excellent catalytic activity was mainly ascribed to high nitrogen doping content, appropriate constitution of active nitrogen configurations, large specific surface area, and synergistic effect of N and S codoping.

Tortuosity factor τ of the solid phase is an important parameter for the accurate prediction of SOFC electrode conductivity. This work investigates the effect of computational domain on τ. The results show that a computational domain with cross section area of 15d*15d (d: particle diameter) is necessary for the calculation of τ when 15% deviation is allowed. The result also validates that the anisotropic property of τ shown in the previous literatures is caused by the insufficient sample size. This study builds a framework for the further study of τ.

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