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A biodegradable poly(ε-caprolactone) (PCL) was synthesized by ring-opening polymerization of ε-caprolactone catalyzed by Sn(Oct)2/BDO, followed by the heparin conjugation using EDC/NHS chemistry. The structure of the heparin-PCL conjugate was characterized by (1)H-NMR and GPC. The results of static contact angle and water uptake ratio measurements also confirmed the conjugation of heparin with the polyester. Its in vitro anticoagulation time was substantially extended, as evidenced by activated partial thromboplastin time (APTT) testing. Afterwards the conjugate was electrospun into small-diameter tubular scaffolds and loaded with Fibroblast Growth Factor 2 (FGF2) in aqueous solution. The loading efficiency was assayed by enzyme-linked immunosorbent assay (ELISA); the results indicated that the conjugate holds a higher loading efficiency than the blank polyester. The viability of released FGF2 was evaluated by MTT and cell adhesion tests. The amount and morphology of cells were significantly improved after FGF2 loading onto the electrospun heparin-PCL vascular scaffolds.

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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.

Poly(ε-caprolactone) (PCL) was conjugated with heparin and fabricated into nonwoven tubular scaffold by electrospinning. The dynamic contact angle analysis revealed the hydrophilicity improvement due to heparin concentrating on the conjugate surface. The microbicinchoninic acid and quartz crystal microbalance measurements implied that the conjugate can significantly reduce the absorption of plasma protein, such as albumin and fibrinogen, indicative of the good blood biocompatibility. As evidenced by Enzyme Linked Immunosorbent Assay, the electrospun conjugate scaffolds possessed a higher loading capability of vascular endothelial growth factor (VEGF) than that of the blank PCL in aqueous solution via static interaction. The viability of loaded VEGF was evaluated by cell culture and adhesion tests. The amount and morphology of cells were substantially improved after VEGF was loaded into scaffolds exhibiting excellent cell biocompatibility. To assess the in vivo biocompatibility, a tubular scaffold (L = 4 cm, D = 2 mm) was transplanted into dog's femoral artery. The scaffold patency was inspected by carotid artery angiography 4 weeks after implantation. The explanted scaffold was also investigated by histological analysis including hematoxyline eosin, Millere Masson (collagen and elastin), and von Kossa (calcium) stain. Furthermore, von Willebrand factor immunohistochemical stain was performed to examine the formation of endothelial layer. The conjugate shows the potential to be used as scaffold materials in vascular tissue engineering.

Aim: Recent studies have demonstrated that mesenchymal stem cells (MSCs) can differentiate into endothelial cells. The effect of shear stress on MSC differentiation is incompletely understood, and most studies have been based on two-dimensional systems. We used a model of tissue-engineered vascular grafts (TEVGs) to investigate the effects of shear stress on MSC differentiation. Methods: MSCs were isolated from canine bone marrow. The TEVG was constructed by seeding MSCs onto poly-ε-caprolactone and lactic acid (PCLA) scaffolds and subjecting them to shear stress provided by a pulsatile bioreactor for four days (two days at 1 dyne/cm 2 to 15 dyne/cm 2 and two days at 15 dyne/cm 2 ). Results: Shear stress significantly increased the expression of endothelial cell markers, such as platelet-endothelial cell adhesion molecule-1 (PECAM-1), VE-cadherin, and CD34, at both the mRNA and protein levels as compared with static control cells. Protein levels of alpha-smooth muscle actin (α-SMA) and calponin were substantially reduced in shear stresscultured cells. There was no significant change in the expression of α-SMA, smooth muscle myosin heavy chain (SMMHC) or calponin at the mRNA level. Conclusion: Shear stress upregulated the expression of endothelial cell-related markers and downregulated smooth muscle-related markers in canine MSCs. This study may serve as a basis for further investigation of the effects of shear stress on MSC differentiation in TEVGs.

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New kinds of thermosensitive and supramolecular structured hydrogels were synthesized via copolymerization of N-isopropylacrylamide (NIPA) with photocurable and biodegradable polypseudorotaxanes as cross-linkers under UV irradiation. The polypseudorotaxanes were prepared by supramolecular self-assemblies of R-cyclodextrins threaded onto amphiphilic LA-PEG-LA copolymers end-capped with methacryloyl groups. The structure of the hydrogels was characterized in detail with FTIR, 1 H NMR, XRD, DSC, and TGA techniques. The analytical results have demonstrated that the channel-type crystalline structure of inclusion complexes (ICs) remains in as-obtained hydrogels. Their swelling behavior was measured gravimetrically in the temperature range from 22 to 67 °C. It was observed that the crosslinked hydrogel made of only the macromer guest shows also thermosensitive. However, this stimuliresponsive property disappears when R-CDs are threaded onto the polymeric backbone and reappears when PNIPA blocks are introduced. The theromsensitivity of these hydrogels could be modulated by changing the PNIPA content as well as the R-CD to macromer ratio.