Electrochemical Decarboxylative Cross-Coupling with Nucleophiles.

Decarboxylative cross-coupling reactions are powerful tools for carbon-heteroatom bonds formation, but typically require pre-activated carboxylic acids as substrates or heteroelectrophiles as functional groups. Herein, we present an electrochemical decarboxylative cross-coupling of carboxylic acids with structurally diverse fluorine, alcohol, H2O, acid, and amine as nucleophiles. This strategy takes advantage of the ready availability of these building blocks from commercial libraries, as well as the mild and oxidant-free conditions provided by electrochemical system. This reaction demonstrates good functional-group tolerance and its utility in late-stage functionalization.

Enzyme stability in polymer hydrogel-enzyme hybrid nanocarrier containing phosphorylcholine group.

Enzymes are biological catalysts with good biocompatibility and high efficiency and have been widely used in many fields, such as wastewater treatment, biosensors, and the medical industry. However, their inherently low stability under conditions of practical use limits further applications. Zwitterionic polymers possessing a pair of oppositely charged groups in their repeating units can increase protein stability because of their good biocompatibility and high water content. In this study, zwitterionic copolymer nanogels comprising poly(2-methacryloyloxyethyl phosphorylcholine (MPC)-co-methacrylic acid-N-hydroxy succinimide ester (MNHS)) (PMS) were synthesized via reversible addition-fragmentation chain-transfer polymerization (RAFT). ß-Galactosidase (ß-gal) was post-modified within zwitterionic polymer nanogels with a covalently-bound spacer and the activity was compared with that of directly immobilized ß-gal and free ß-gal. Compared with direct immobilization, covalent immobilization with a spacer could reduce the structural change of ß-gal, as confirmed by the circular dichroism spectra. Although the activity of ß-gal decreased after immobilization, the hybrids of the ß-gal immobilized nanogels, termed hybrid nanogel-enzymes, demonstrated superior stability compared to the free enzymes. The hybrid nanogel-enzymes maintained their function against inactivation by organic solvents and proteinases owing to their high water content, anti-biofouling properties, and limited mass transfer. They can also withstand protein aggregation at high temperatures and maintain their activity. Compared to direct immobilization, immobilization with a spacer resulted in a dramatic increase in the enzyme activity and a slight decrease in the stability. These results indicate that polymer nanogels containing phosphorylcholine units are promising materials for enzyme immobilization, expanding the scope of enzyme applications.

Electrochemical Oxidation Enables Regioselective 1,3-Hydroxyfunctionalization of Cyclopropanes.

The direct construction of 1,3-hydroxyfunctionalized molecules is still a significant challenge, as they can currently be obtained through multiple synthetic steps. Herein, we report a general and efficient 1,3-hydroxyfunctionalization of arylcyclopropanes by electrochemical oxidation with a strategic choice of nucleophiles and H2O. 1,3-Amino alcohols, 1,3-alkynyl alcohols, 1,3-hydroxyesters, and 1,3-halo alcohols are achieved with high levels of chemo- and regio-selectivity, opening a new dimension for 1,3-difunctionalization reaction.

Synthesis of Benzylic Alcohols by Decarboxylative Hydroxylation.

Herein, we demonstrate an efficient method for the decarboxylative hydroxylation of carboxylic acids with silver(I) as the catalyst and cerium ammonium nitrate as the oxidant and its utility in chemoselective late-stage functionalization of natural products and drug molecules. The chemoselectivity of this protocol arises from a benzylic nitrate intermediate that retards further oxidation and is hydrolyzed to the final benzylic alcohol product. Mechanistic investigation reveals that the facile oxidation of silver carboxylate affords silver(II) species as an intermediate oxidant responsible for decarboxylation.

Glutathione-Sensitive Silicon Nanowire Arrays for Gene Transfection.

Ingenious surface modification strategies and special topological morphologies endow the biomaterial interface with excellent ability to regulate the cell fate. In this work, a gene delivery platform based on glutathione-sensitive silicon nanowire arrays (SiNWAs) is developed, exhibiting good transfection efficiency of several cell types. Briefly, the surface of SiNWAs is grafted of PEICBA, a branched cationic polymer cross-linked by disulfide bonds (SN-PEICBA). When the cells adhere to the platform surface, silicon nanowires penetrate into the cells and the high concentration of reduced glutathione (GSH) in cytoplasm breaks the disulfide bonds (S-S) in PEICBA. The plasmid DNA preloaded on the cationic polymers is successfully delivered to the nuclei through the nonlysosomal pathway. Cells harvested from the SN-PEICBA show high retention of viability and the platform surface can be reused though S-S replacement for at least three times. In general, our platform is a creative combination of intracellular responsive strategy and surface morphology, which has great potential for auxiliary use in ex vivo cell-based therapies and various biomedical applications.

One-step preparation of gold nanovectors using folate modified polyethylenimine and their use in target-specific gene transfection.

Gene transfection, as an effective treatment for inherited and acquired life threatening diseases caused by genetic deficiencies and abnormalities, has evolved as a promising therapeutic strategy for cancer and other intractable diseases. Non-target-specific vectors will affect normal cells as well as pathogenic cells, resulting in a relative decrease in transfection efficiency and unnecessary cytotoxicity. In the present work, gold nanoparticles (AuNPs) functionalized with folate (FA)-modified polyethylenimine (PEI-FA) were prepared by a single step method (without additional reducing agent) for targeted gene transfection in tumor cells. Moreover, an improved compound vector system was developed by mixing PEI-AuNPs and PEI-FA-AuNPs. It was shown that the compound vector system not only greatly increased transfection efficiency in HeLa cells, but also reduced cytotoxicity. By comparison, the transfection efficiency in L929 cells lacking folate receptor, was clearly lower than in tumor cells. The specific gene transfection of HeLa cells using this vector system could be clearly observed by confocal laser scanning microscopy in a co-culture system of HeLa cells and L929 cells. This transfection system with high-efficiency, high-specificity and low-toxicity appears to have potential in targeted cancer treatment and drug delivery.

Small addition of Zn2+ in Ca2+@DNA results in elevated gene transfection by aminated PGMA-modified silicon nanowire arrays.

Gene therapy, a promising and effective treatment, has ignited new hope in overcoming difficult-to-cure diseases. The key question in gene therapy is how to efficiently and safely deliver exogenous nucleic acids into the nuclei of target cells. To achieve stable, efficient and safe gene transfer and to ensure efficiency of gene transfer into cell nuclei, a zinc ion-assisted gene delivery nanosystem was proposed in the present study by loading a low concentration of Zn2+ in Ca2+@DNA nanoparticles on ethanolamine-functionalized poly(glycidyl methacrylate) (PGEA)-modified SiNWAs (Zn2+/Ca2+@DNA + SN-PGEA). The results showed that with the help of Zn ions, this composite nanosystem could promote more DNA in the cell nuclei and thus dramatically increased the transfection efficiency by as much as 7-fold. The nanosystem with 0.2 mM Zn2+, 100 mM Ca2+ and PGEA modification on SiNWAs displayed the highest transfection efficiency and good biocompatibility. This new composite nanosystem will have great potential in gene transfection for biomedical research.

A Comprehensive Method for Accurate Strain Distribution Measurement of Cell Substrate Subjected to Large Deformation.

Cell mechanical stretching in vitro is a fundamental technique commonly used in cardiovascular mechanobiology research. Accordingly, it is crucial to measure the accurate strain field of cell substrate under different strains. Digital image correlation (DIC) is a widely used measurement technique, which is able to obtain the accurate displacement and strain distribution. However, the traditional DIC algorithm used in digital image correlation engine (DICe) cannot obtain accurate result when utilized in large strain measurement. In this paper, an improved method aiming to acquire accurate strain distribution of substrate in large deformation was proposed, to evaluate the effect and accuracy, based on numerical experiments. The results showed that this method was effective and highly accurate. Then, we carried out uniaxial substrate stretching experiments and applied our method to measure strain distribution of the substrate. The proposed method could obtain accurate strain distribution of substrate film during large stretching, which would allow researchers to adequately describe the response of cells to different strains of substrate.

[Development of Automatic Preparation Device of Sclerosing Foam Based on Tessari Method].

Based on the principle of manual preparation of sclerosing foam with Tessari method,using the analysis of user requirements and combining it with theory of mechanics,we designed an automatic equipment.The device could be used to replace the manual operation,and could overcome the shortcomings of manual sclerosing foam preparation,such as the difficulty in controlling of pushing speed and stroke and poor reproducibility.This automatic device has the functions of adjustable pushing speed,pushing frequency,pushing stroke and is suitable for a variety of different types of syringes.It can not only provide quantitative parameters for the study of foam properties,but also be used for the standardization of clinical sclerosing foam.The experimental study on"the effect of pushing speed on the stability of foam"was carried out with using the device,and the experimental results were quite satisfactory.

Physiological pulsatile flow culture conditions to generate functional endothelium on a sulfated silk fibroin nanofibrous scaffold.

Many studies have demonstrated that in vitro shear stress conditioning of endothelial cell-seeded small-diameter vascular grafts can improve cell retention and function. However, the laminar flow and pulsatile flow conditions which are commonly used in vascular tissue engineering and hemodynamic studies are quite different from the actual physiological pulsatile flow which is pulsatile in nature with typical pressure and flow waveforms. The actual physiological pulsatile flow leading to temporal and spatial variations of the wall shear stress may result in different phenotypes and functions of ECs. Thus, the aim of this study is to find out the best in vitro dynamic culture conditions to generate functional endothelium on sulfated silk fibroin nanofibrous scaffolds for small-diameter vascular tissue engineering. Rat aortic endothelial cells (RAECs) were seeded on sulfated silk fibroin nanofibrous scaffolds and cultured under three different patterns of flow conditioning, e.g., steady laminar flow (SLF), sinusoidal flow (SF), or physiological pulsatile flow (PPF) representative of a typical femoral distal pulse wave in vivo for up to 24 h. Cell morphology, cytoskeleton alignment, fibronectin assembly, apoptosis, and retention on the scaffolds were investigated and were compared between three different patterns of flow conditioning. The results showed that ECs responded differentially to different exposure time and different flow patterns. The actual PPF conditioning demonstrated excellent EC retention on sulfated silk fibroin scaffolds in comparison with SLF and SF, in addition to the alignment of cells in the direction of fluid flow, the formation of denser and regular F-actin microfilament bundles in the same direction, the assembly of thicker and highly crosslinked fibronectin, and the significant inhibition of cell apoptosis. Therefore, the actual PPF conditioning might contribute importantly to the generation of functional endothelium on a sulfated silk fibroin nanofibrous scaffold and thereby yield a thromboresistant luminal surface.

Hydrostatic pressures promote initial osteodifferentiation with ERK1/2 not p38 MAPK signaling involved.

Mechanical stress has been considered to be an important factor in bone remodeling and recent publications have shown that mechanical stress can regulate the direction of stem cell differentiation. The exact mechanobiological effects of pressure on initial osteodifferentiation of mesenchymal stem cells (MSCs) have not been determined. These mechanobiological mechanisms may be important both in biological responses during orthodontic tooth movement and in the development of new mechanobiological strategies for bone tissue engineering. We investigated the effects of static (23 kPa) or dynamic (10-36 kPa and at 0.25 Hz frequency) pressure on MSCs during the initial process of osteoblastic differentiation following treatment with dexamethasone, beta-glycerophosphate and ascorbic acid (for 0, 3, and 7 days, respectively). The following parameters were analyzed in the ALPase activity, mRNA level of osteogenesis-related transcription factors (Runx2, Osterix, Msx2, and Dlx5), and phosphorylation of ERK1/2 and p38 MAPK. The results showed that exposure to either dynamic or static pressure induced initial osteodifferentiation of MSCs. Particularly both types of pressure strongly stimulated the expression of osteogenesis-related factors of totally undifferentiated MSCs. ERK signaling participated in early osteodifferentiation and played a positive but non-critical role in mechanotransduction, whereas p38 MAPK was not involved in this process. Furthermore, the undifferentiated MSCs were highly sensitive to pressure exposure; whereas after osteoinduction MSCs reacted to pressure in a lower response state. The findings should lead to further studies to unveil the complex initial biological mechanisms of bone remodeling and regeneration upon mechanical stimuli.