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Because of the inherent appearance similar to the natural extracellular matrix, ultrafine fibrous membranes prepared via electrospinning exhibit widespread applications, especially in the biomedical area. Extensional modifications of coaxial and emulsion electrospinning have drawn much attention in preparation of core/shell fibers for applications as tissue engineering scaffolds and controlled delivery systems for bioactive substances. Due to incorporation of multi-components in the electrospun core/ shell fibers, the process of coaxial and emulsion electrospinning became more susceptible. The theories have not been fully understood. A series of investigations were carried out evaluating the systematic and processing parameters. This paper reviews advantages and potentials of electrospun core/shell fibers as well as factors influencing their formation on the basis of our research and new progress. core/shell fibers, coaxial electrospinning, emulsion electrospinning, controlled delivery, tissue engineering

Porous scaffolds with graded pores are crucial to osteochondral regeneration. In this study, a technique combining solution casting with gelatin-microsphere template leaching has been developed to produce poly(L-lactide-co-glycolide) (PLGA) scaffolds with graded pores. The traditional emulsification and solvent extraction method was improved by using the gradient ethanol/water solutions to extract water to prepare gelatin microspheres with a smooth surface without the use of any surfactant. Gelatin microspheres with different diameters were in sequence put into a custom-made cylindrical Teflon mold and bonded together to obtain gelatin-microsphere templates. By using the gelatin-microsphere templates as porogen, PLGA scaffolds with graded pore size across the cylindrical axis were prepared. The porosity of the scaffold was as high as 95%. The pore size effect on osteoblasts was studied. The results showed that the graded scaffolds possessed good biocompatibility for osteoblast growth. During the 14 days culture, the cell proliferation of all the three pore layers displayed the trend of increasing. The proliferation rate of the large pore layer was lower than the other two layers. However, the difference of alkaline phosphatase activity on the three pore layers was not statistically significant. We assumed that it was probably because of the hydrophobicity and the short culture time. It was demonstrated that gradient ethanol/water solutions provided a simple way to prepared gelatin microspheres. The graded scaffolds would provide potential application for osteochondral regeneration.

The hexagonal boron nitride (h-BN) nanosheets have been used as nanofillers to improve the barrier properties of the waterborne epoxy (WEP) coatings. However, the h-BN nanosheets tend to agglomerate, which limits their anticorrosion applications. In this paper, the h-BN/polyaniline (h-BN/PANI) nanocomposites were prepared by the in situ polymerization of aniline on the surfaces of the h-BN nanosheets, which were further used to improve the anticorrosion performance of the WEP coatings. The structures of the as-prepared h-BN/PANI nanocomposites were investigated by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The anticorrosion performances of the coatings were evaluated by electrochemical impedance spectroscopy. After immersion in 3.5 wt % NaCl solution for 28 days, the macro-morphologies and elemental changes of the substrate surfaces were analyzed by a 3D digital microscope and an energy-dispersive spectroscope, respectively. The results showed that the WEP coatings with the h-BN/PANI nanocomposites, especially that with 2 wt % h-BN/PANI nanocomposites, exhibited remarkably reinforced anticorrosion performance compared to the pure WEP coating. For the WEP coating, the coating with 1 wt % PANI, and the coating with 1 wt % h-BN, the substrates have been completely corroded. However, there was no obvious corrosion region for the coating containing 2 wt % h-BN/PANI nanocomposites. The superior anticorrosion performance of the coatings with h-BN/PANI nanocomposites was mainly attributed to the synergistic effect of the well-dispersed h-BN/PANI nanocomposites as the physical barrier and PANI as the corrosion inhibitor in this system.