In this article, a tubular vascular tissue engineering scaffold with core-shell structured fibers was produced by coaxial electrospinning at an appropriate flow rate ratio between the inner and outer solution. PCL was selected as the core to provide the mechanical property and integrity to the scaffold while collagen was used as the shell to improve the attachment and proliferation of vascular cells due to its excellent biocompatibility. The fine core-shell structured fibers were demonstrated by scanning electron microscope and transmission electron microscope observations. Subsequently, the collagen shell was crosslinked by genipin and further bound with heparin. The crosslinking process was confirmed by the increasing of tensile strength, swelling ratio and thermogravimetric analysis measurements while the surface heparin content was characterized by means of a UV-spectrophotometer and activated partial thromboplastin time tests. Furthermore, the mechanical properties such as stitch strength and bursting pressure of the as-prepared scaffold were measured. Moreover, the biocompatibility of the scaffold was evaluated by cytotoxicity investigation with L929 cells via MTT assay. Endothelial cell adhesion assessments were conducted to reveal the possibility of the formation of an endothelial cell layer on the scaffold surface, while the ability of smooth muscle cell penetration into the scaffold wall was also assessed by confocal laser scanning microscopy. The as-prepared core-shell structured scaffold showed promising potential for use in vascular tissue engineering.

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Using different Ziegler-Natta catalysts, we have prepared two samples of isotactic polypropylene with similar molecular weight and average isotacticity, but different stereo defect distributions. The influence of ultrasonic irradiation on the conformation and crystallization behavior of those samples were investigated by differential scanning calorimetry, wide angle X ray diffraction and Fourier transform infrared spectros copy. The ultrasonic treatment induced a decrease in the degree of crystalline perfection and a wider distri bution range of the crystalline perfection of polypropylene. Meanwhile, the crystal particles pack looser and the crystallite size decreased under the influence of ultrasonic irradiation. On the conformation aspect, the molecular movement in polypropylene became more intensive, the molecular entanglement was reduced when ultrasound was applied. Moreover, it was found that the uniformity of stereo defect distribution also played important role in determining the conformation and crystallization behavior of polypropylene sam ples irradiated by ultrasound.

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Compared with polypseudorotaxanes (PPRs) formed from the self-assembly of β-cyclodextrins (β-CDs) with poly­(propylene glycol) (PPG) and γ-CDs with poly­(N-isopropylacrylamide) (PNIPAAm), the ratio of the inner cavity size of β-CD to the cross-sectional area of PNIPAAm appears not appropriate for their self-assembly. For a better understanding of the possibility of β-CDs including PNIPAAm and the crystal structure of PPRs formed therefrom, the PNIPAAm homo- and copolymers were subjected to self-assembly with β-CDs in an aqueous solution at room temperature. The results revealed that when β-CDs meet thicker PNIPAAms, the self-assembly takes place, not only giving rise to PPRs by a manner of main-chain inclusion complexation but also presenting the PPRs a matched over-fit crystal structure different from those of either a matched tight-fit β-CD–PPG PPR or a mismatched over-fit γ-CD–PNIPAAm PPR. This is most likely due to the thicker PNIPAAm adapting its unfavorable main-chain cross-sectional area to fit into the cavity of β-CDs by changing the side-chain conformations. Based on the X-ray diffraction patterns, a monoclinic crystal system was created from these PPRs and the unit cell parameters calculated were as follows: a = 15.3 Å, b = 10.3 Å, and c = 21.2 Å; β = 110.3°; and space group P2. It suggested that this matched over-fit crystal structure would possess a Mosaic crystal structure rather than a typical channel-like one.