Jin-lei Wang

Identification of Surface Structures on 3C-SiC Nanocrystals with Hydrogen and Hydroxyl Bonding by Photoluminescence

SiC nanocrystals (NCs) exhibit unique surface chemistry and possess special properties. This provides the opportunity to design suitable surface structures by terminating the surface dangling bonds with different atoms thereby boding well for practical applications. In this article, we report the photoluminescence properties of 3C-SiC NCs in water suspensions with different pH values. Besides a blue band stemming from the quantum confinement effect, the 3C-SiC NCs show an additional photoluminescence band at 510 nm when the excitation wavelengths are longer than 350 nm. Its intensity relative to the blue band increases with the excitation wavelength. The 510 nm band appears only in acidic suspensions but not in alkaline ones. Fourier transform infrared, X-ray photoelectron spectroscopy, and X-ray absorption near-edge structure analyses clearly reveal that the 3C-SiC NCs in the water suspension have Si-H and Si-OH bonds on their surface, implying that water molecules only react with a Si-terminated surface. First-principle calculations suggest that the additional 510 nm band arises from structures induced by H(+) and OH(-) dissociated from water and attached to Si dimers on the modified (001) Si-terminated portion of the NCs. The size requirement is consistent with the observation that the 510 nm band can only be observed when the excitation wavelengths are relatively large, that is, excitation of bigger NCs.

Intracellular pathways and nuclear localization signal peptide-mediated gene transfection by cationic polymeric nanovectors

Polyethylenimine (PEI) - based polymers are promising cationic nanovectors. A good understanding of the mechanism by which cationic polymers/DNA complexes are internalized and delivered to nuclei helps to identify which transport steps may be manipulated in order to improve the transfection efficiency. In this work, cell internalization and trafficking of PEI-CyD (PC) composed of β-cyclodextrin (β-CyD) and polyethylenimine (PEI, Mw 600) are studied. The results show that the PC transfected DNA is internalized by binding membrane-associated proteoglycans. The endocytic pathway of the PC particles is caveolae- and clathrin-dependent with both pathways converging to the lysosome. The intracellular fate of the PC provides visual evidence that it can escape from the lysosome. Lysosomal inhibition with chloroquine has no effect on PC mediated transfection implying that blocking the lysosomal traffic does not improve transfection. To improve the nuclear delivery of PC transfected DNA, nuclear localization signal (NLS) peptides are chosen to conjugate and combine with the PC. Compared to PC/pDNA, PC-NLS/pDNA, and PC/pDNA/NLS can effectively improve gene transfection in dividing and non-dividing cells.

Zwitterionic polycarboxybetaine coating functionalized with REDV peptide to improve selectivity for endothelial cells.

Surface immobilization of bioactive molecules has been a promising strategy to develop in situ endothelialization for cardiovascular implants. With the aim to construct endothelial cell specific coating with low fouling property, zwitterionic carboxybetaine methacrylate and butyl methacrylate were copolymerized as coating materials, spin-coated onto substrates, and immobilized with endothelial cell selective peptide Arg-Glu-Asp-Val (REDV) through functionalization of carboxy groups in carboxybetaine by NHS/EDC chemistry. Experimental results proved that carboxybetaine-REDV coating maintained desirable antifouling ability and fine hemocompatibility. Separate culture and coculture of HUVECs (human umbilical vein endothelial cells) with HUASMCs (human umbilical artery smooth muscle cells) showed that the coating was able to enhance the competitive growth of endothelial cells while limiting the adhesion, proliferation, and migration of smooth muscle cells. The existence of zwitterionic carboxybetaine helps to screen undesirable adsorption of platelets, and its nonspecific resistance to smooth muscle cells contributes to the realization of endothelial cell selectivity.

A strategy on constructing core collections by least distance stepwise sampling

A strategy was proposed for constructing core collections by least distance stepwise sampling (LDSS) based on genotypic values. In each procedure of cluster, the sampling is performed in the subgroup with the least distance in the dendrogram during constructing a core collection. Mean difference percentage (MD), variance difference percentage (VD), coincidence rate of range (CR) and variable rate of coefficient of variation (VR) were used to evaluate the representativeness of core collections constructed by this strategy. A cotton germplasm collection of 1,547 accessions with 18 quantitative traits was used to construct core collections. Genotypic values of all quantitative traits of the cotton collection were unbiasedly predicted based on mixed linear model approach. By three sampling percentages (10, 20 and 30%), four genetic distances (city block distance, Euclidean distance, standardized Euclidean distance and Mahalanobis distance) combining four hierarchical cluster methods (nearest distance method, furthest distance method, unweighted pair-group average method and Ward’s method) were adopted to evaluate the property of this strategy. Simulations were conducted in order to draw consistent, stable and reproducible results. The principal components analysis was performed to validate this strategy. The results showed that core collections constructed by LDSS strategy had a good representativeness of the initial collection. As compared to the control strategy (stepwise clusters with random sampling strategy), LDSS strategy could construct more representative core collections. For LDSS strategy, cluster methods did not need to be considered because all hierarchical cluster methods could give same results completely. The results also suggested that standardized Euclidean distance was an appropriate genetic distance for constructing core collections in this strategy.

Glycerol-Bonded 3C-SiC Nanocrystal Solid Films Exhibiting Broad and Stable Violet to Blue-Green Emission

We have produced glycerol-bonded 3C-SiC nanocrystal (NC) films, which when excited by photons of different wavelengths, produce strong and tunable violet to blue-green (360-540 nm) emission as a result of the quantum confinement effects rendered by the 3C-SiC NCs. The emission is so intense that the emission spots are visible to the naked eyes. The light emission is very stable and even after storing in air for more than six months, no intensity degradation can be observed. X-ray photoelectron spectroscopy and absorption fine structure measurements indicate that the Si-terminated NC surfaces are completely bonded to glycerol molecules. Calculations of geometry optimization and electron structures based on the density functional theory for 3C-SiC NCs with attached glycerol molecules show that these molecules are bonded on the NCs causing strong surface structural change, while the isolated levels in the conduction band of the bare 3C-SiC NCs are replaced with quasi-continuous bands that provide continuous tunability of the emitted light by changing the frequencies of exciting laser. As an application, we demonstrate the potential of using 3C-SiC NCs to fabricate full-color emitting solid films by incorporating porous silicon.

Direct Adhesion of Endothelial Cells to Bioinspired Poly(dopamine) Coating Through Endogenous Fibronectin and Integrin α5β1

Mussel-inspired poly(dopamine) (PDA) coating is proven to be a simple, versatile, and effective strategy to promote cell adhesion onto various substrates. In this study, the initial adhesive behavior of human umbilical vein endothelial cells (HUVECs) is evaluated on a PDA coating under serum-free conditions. It is found that HUVECs can attach directly to and spread with well-organized cytoskeleton and fibrillar adhesions on the PDA surface, whereas cells adhere poorly to and barely spread on the control polycaprolactone surface. Endogenous fibronectin and α5 β1 integrin are found to be involved in the cell adhesion process. These findings will lead to a better understanding of interactions between cells and PDA coating, paving the way for the further development of PDA.

Facile fabrication of robust superhydrophobic multilayered film based on bioinspired poly(dopamine)-modified carbon nanotubes

Thin organic films containing carbon nanotubes (CNTs) have received increasing attention in many fields. In this study, a robust thin superhydrophobic film has been created by using layer-by-layer assembly of the carbon nanotubes wrapped by poly(dopamine) (CNT@PDA) and poly(ethyleneimine) (PEI). UV-vis spectroscopy, ellipsometry, and quartz crystal microbalance with dissipation (QCM-D) measurements confirmed that the sequential deposition of PEI and CNT@PDA resulted in a linear growth of the (PEI-CNT@PDA) film. This thin film contained as much as 77 wt% CNTs. Moreover, a very stable and flexible free-standing (PEI-CNT@PDA) film could be obtained by employing cellulose acetate (CA) as a sacrificial layer. The film could even withstand ultrasonication in saturated SDS aqueous solution for 30 min. SEM observations indicated that the ultrathin film consisted of nanoscale interpenetrating networks of entangled CNTs and exhibited a very rough surface morphology. The (PEI-CNT@PDA) film turned superhydrophobic after being coated with a low-surface-energy compound. The superhydrophobic films showed excellent resistance against the adhesion of both platelets and Escherichia coli (E. coli). The (PEI-CNT@PDA) films and the proposed methodology may find applications in the area of medical devices to reduce device-associated thrombosis and infection.

Surface-mediated functional gene delivery: an effective strategy for enhancing competitiveness of endothelial cells over smooth muscle cells.

The non-biorecognition of general biomaterials and inherent biospecificity of biological systems pose key challenges to the optimal functions of medical devices. In this study, we constructed the surface-mediated functional gene delivery through layer-by-layer self-assembly of protamine sulfate (PrS) and plasmid DNA encoding hepatocyte growth factor (HGF), aiming at specific enhancing endothelial cells (EC) compeititiveness over smooth muscle cells (SMC). Characterizations of the (PrS/HGF-pDNA) multilayered films present the linear buildup with homogeneous and flat topographical feature. The amount of DNA can be easily controlled. By using these multilayered films, both human umbilical vein endothelial cells (HUVEC) and human umbilical artery smooth muscle cells (HUASMC) can be directly transfected when they contact with the multilayered films. On transfection, increasing secretion of HGF has been detected in both HUVEC and HUASMC culture, which leads to selective promotion of HUVEC proliferation. In the co-culture experiment, we also exhibit the promoted and hindered growth of HUVEC and HUASMC, respectively, which could be attributed to the inverse influence of HUVEC on HUASMC. These results collectively demonstrate that our system can be served as a powerful tool for enhancing competitiveness of EC over SMC, which opens perspectives for the regulation of intercellular competitiveness in the field of interventional therapy.

Cucurbit[8]uril supramolecular assembly for positively charged ultrathin films as nanocontainers.

The design of positively charged ultrathin films for surface modification is of crucial importance for biomedical applications. Herein, we report the layer-by-layer assembly of pure positively charged ultrathin films based on the host-guest interaction of cucurbit[8]uril (CB[8]). Two positively charged poly(ethylenimine)s (PEI) functionalized with guest moieties methyl viologen (MV) and indole (ID) were alternately assembled with the formation of CB[8] ternary complex under basic conditions. The growth of the (PEI-MV@CB[8]/PEI-ID) films was monitored by spectroscopic ellipsometry and quartz crystal microbalance. The morphology and structure of the films were characterized by scanning electron microscopy and UV-vis spectroscopy, respectively. These positively charged (PEI-MV@CB[8]/PEI-ID) films were very stable in the pH range from 4 to 9 but disassembled immediately when subjected to a competitive guest adamantylamine. Finally, the films were successfully employed as nanocontainers for DNA loading and subsequent directing the transfection of the adhered cells.

Characteristics and anticoagulation behavior of polyethylene terephthalate modified by C2H2 plasma immersion ion implantation-deposition

Acetylene (C2H2) plasma immersion ion implantation-deposition (PIII-D) is conducted on polyethylene terephthalate (PET) to improve its blood compatibility. The structural and physicochemical properties of the modified surface are characterized by, Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and static contact angle measurement. Atomic force microscopy discloses that the average roughness (Ra) of film surface decreases from 58.9 nm to 11.4 nm after C2H2 PIII-D treats PET. Attenuated total reflection Fourier transform infrared spectroscopy shows that the specfic adsorption peaks for PET decrease after ion implantation and deposition. Raman spectroscopy indicates that a thin amorphous polymerlike carbon (PLC) film is formed in the PET. The effects of the surface modification on the chemical bonding of C, H, and O are examined by XPS and the results show that the ratio of sp3 C–C to sp2 C=C is 0.25. After C2H2 PIII-D, the polar component γp of surface energy increases from 2.4 mN/m to 12.3 mN/...