Surface modification and endothelialization of vascular biomaterials are common approaches that are used to both resist the nonspecific adhesion of proteins and improve the hemocompatibility and long-term patency of artificial vascular grafts. Surface modification of vascular grafts using hydrophilic poly(ethylene glycol), zwitterionic polymers, heparin or other bioactive molecules can efficiently enhance hemocompatibility, and consequently prevent thrombosis on artificial vascular grafts. However, these modified surfaces may be excessively hydrophilic, which limits initial vascular endothelial cell adhesion and formation of a confluent endothelial lining. Therefore, the improvement of endothelialization on these grafts by chemical modification with specific peptides and genes is now arousing more and more interest. Several active peptides, such as RGD, CAG, REDV and YIGSR, can be specifically recognized by endothelial cells. Consequently, graft surfaces that are modified by these peptides can exhibit targeting selectivity for the adhesion of endothelial cells, and genes can be delivered by targeting carriers to specific tissues to enhance the promotion and regeneration of blood vessels. These methods could effectively accelerate selective endothelial cell recruitment and functional endothelialization. In this review, recent developments in the surface modification and endothelialization of biomaterials in vascular tissue engineering are summarized. Both gene engineering and targeting ligand immobilization are promising methods to improve the clinical outcome of artificial vascular grafts.

A new amphiphilic BF -azadipyrromethene (aza-BODIPY) dye 1 has been synthesized using a Cu -catalyzed "click" reaction. For this dye, two self-assembly pathways that lead to different type of J-aggregates with distinct near-infrared optical properties have been discovered. The metastable off-pathway product displays a broad, structureless absorption band while the thermodynamically stable on-pathway aggregate exhibits the characteristic spectral features of a J-aggregate, that is, red-shifted intense absorption band with significantly narrowed linewidth. The morphology and structure of the aggregates were studied by atomic force microscopy, transmission and scanning electron microscopy. The aggregation processes of 1 were investigated by temperature- and concentration-dependent UV/Vis spectroscopy and evaluated by models for cooperative self-assembly.

A novel organic-inorganic hybrid with two polyhedral oligosilsesquioxane (POSS) nanoparticles covalently attached to perylene diimide (PDI) via a rigid 1,4-phenylene linkage (POSS-PDI-POSS) was designed and synthesized to examine the effect of bulky and well-defined nanoparticle side chains on the self-assembly behavior of PDI derivatives. The molecules were self-assembled directly by slow evaporation of a cast drop from solution in tetrahydrofuran to give rise to uniform crystalline nanobelts with dimensions typically of 0.2 mm × 1 µm × 50 nm. The phase behavior and crystal structure of the sample were then elucidated via a combination of different experimental techniques such as differential scanning calorimetry (DSC), wideangle X-ray diffraction (WAXD), selected area electron diffraction (SAED) in transmission electron microscopy (TEM), polarized light microscopy, and atomic force microscopy. One-dimensional (1D) WAXD and DSC revealed that only one crystalline phase exists. Based on the 2D WAXD fiber pattern obtained from the oriented POSS-PDI-POSS samples, the crystalline structure was determined to be a triclinic unit cell with dimensions of a ) 6.577 nm, b ) 5.213 nm, c ) 1.107 nm, R ) 93.26°, β ) 94.85°, and γ ) 92.73°, which was confirmed by SAED experiments on the single crystals with different crystal zone orientations. The detailed molecular conformational analysis indicated that the steric hindrance of the POSS nanoparticles covalently attached to PDI via a rigid 1,4-phenylene linkage makes it difficult to achieve a continuous stacking of PDIs. Instead, the molecules dimerized to maximize the π-π interaction. The dimers then became the building blocks and packed themselves into the unit cell. This strong tendency for dimerization was supported by concentration-dependent ultraviolet/visible absorption spectra, florescence spectra, and tandem mass spectroscopy with traveling wave ion mobility separation. The combined SAED and TEM results showed that the c*-axis of the crystal is along the elongated direction of the single-crystal nanobelt and the normal direction of the π-π stacking is along the a*-axis. A crystal structure with six dimers as one supramolecular motif in one unit cell was proposed to account for the unusually large unit cell dimensions. The complex structure could be attributed to the longitudinal, transverse, and slightly rotational offsets between the PDIs in the dimers and interdigitated neighboring dimers due probably to both electrostatic interactions and steric demands. The molecular packing scheme in the crystal was simulated using Cerius 2 software, and the resulting diffraction data agreed well with the experimental results. The rationale for such 1D nanostructured morphology formation is also discussed.

Nowadays, gene transfer technology has been widely used to promote endothelialization of artificial vascular grafts. However, the lack of gene vectors with low cytotoxicity and targeting function still remains a pressing challenge. Herein, polyethylenimine (PEI, 1.8 kDa or 10 kDa) was conjugated to an amphiphilic and biodegradable diblock copolymer poly(ethylene glycol)-b-poly(lactide-co-glycolide) (mPEG-b-PLGA) to prepare mPEG-b-PLGA-g-PEI copolymers with the aim to develop gene vectors with low cytotoxicity while high transfection efficiency. The micelles were prepared from mPEG-b-PLGA-g-PEI copolymers by self-assembly method. Furthermore, Cys-Arg-Glu-Asp-Val-Trp (CREDVW) peptide was linked to micelle surface to enable the micelles with special recognition for endothelial cells (ECs). In addition, pEGFP-ZNF580 plasmids were condensed into these CREDVW-linked micelles to enhance the proliferation of ECs. These CREDVW-linked micelle/pEGFP-ZNF580 complexes exhibited low cytotoxicity by MTT assay. The cell transfection results demonstrated that pEGFP-ZNF580 could be transferred into ECs efficiently by these micelles. The results of Western blot analysis showed that the relative ZNF580 protein level in transfected ECs increased to 76.9%. The rapid migration of transfected ECs can be verified by wound healing assay. These results indicated that CREDVW-linked micelles could be a suitable gene transfer vector with low cytotoxicity and high transfection efficiency, which has great potential for rapid endothelialization of artificial blood vessels.

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An aza‐BODIPY dye 1 bearing two hydrophobic fan‐shaped tridodecyloxybenzamide pendants through 1,2,3‐triazole linkages was synthesized by a click reaction and characterized. 1H NMR studies indicated that dye 1 exhibited variable conformations through intramolecular H‐bonding interaction, which is beneficial for the polymorphism of aggregation. The thermodynamic, structural, and kinetic aspect of the supramolecular polymerization of dye 1 was investigated by UV/Vis absorption spectroscopy, IR spectroscopy, AFM, TEM, and SEM. Biphasic aggregation pathways of dye 1, leads to the formation of off‐pathway, metastable Agg. I and thermodynamically stable Agg. II with distinct H‐aggregation spectra and nanoscale morphology. The living manner of the supramolecular polymerization of dye 1 was demonstrated in seeded polymerization experiments with temperature‐modulated successive cooling–heating cycles.

Poly­(octamethylene carbonate) (POMC), as the eighth member of the newly developed biodegradable aliphatic polycarbonate family, demonstrates a reversible crystal–crystal transition, which is highly similar to Brill transition extensively studied in the nylon family. With the dipole–dipole interaction in POMC much weaker than the hydrogen bonding, POMC exhibits its “Brill transition” temperature at around 42 °C, much lower than nylons. The two crystalline structures of POMC at below and above the transition temperature can be identified. The transition of POMC is largely associated with the reversible conformation change of methylene sequences from trans-dominated at low temperatures to trans/gauche coexistence at high temperatures.