Po-Da Hong

Solvent effects on aggregation behavior of polyvinyl alcohol solutions

Abstract The present study elucidates the effects of solvent quality and polymer concentration on the aggregation behavior of polyvinyl alcohol (PVA) solutions from the dilute solution to semi-dilute solution regions. Combination of the results in static and dynamic light scattering indicates that in dilute solution the thermodynamic driving forces primarily dominate the dynamic behavior of PVA/N-methylpyrrolidone (PVA/NMP) solution. In contrast with PVA/water solution, the hydrodynamic interaction would dominate the dynamic behavior of the solution. The concentration dependence on the dynamic behavior of semi-dilute solution has also been studied through DLS measurement. For PVA/water solutions, the hydrodynamic correlation length of fast mode has a concentration dependence given by ξD=[η]C−0.42, and the value of exponent is close to the predicted value from scaling theory in the marginal solvent. On the other hand, for PVA/NMP solutions the value of exponent is close to the predicted value from the scaling theory in good solvent limit: −0.75. However, contrary to the expectation, the gelation behavior could not occur in PVA/water solutions at the same condition of gelation in PVA/NMP solution even though the affinity of water to PVA is much lower than that of NMP. In this work, we considered that the PVA/NMP solution might possess a character that could form a homogeneous network structure. The intermolecular associations must play a dominant role as soon as the chains start to overlap in PVA/NMP solution. On the other hand, combining the DLS result with our previous work, the gelation of PVA/NMP solutions is considered due to complex formation in the transient network junctions, i.e. the formation of molecular complex is crucial to the physical gelation in a good solvent system.

Solvent effect on structural change of poly(vinyl alcohol) physical gels

In this study, the relationship between the polymer-solvent interaction and the network structure of poly(vinyl alcohol) (PVA) gels prepared with organic solvents such as N-methylpyrrolidone (NMP) and ethylene glycol (EG) are investi- gated. The values of the intrinsic viscosity (h) and Huggins constant k* of dilute PVA solutions indicate that the attractive interaction between PVA and NMP is higher than that between PVA and EG. The X-ray result shows that PVA-EG gels have a (101) diffraction peak of PVA crystal that appeared at about 2uA 197, while PVA-NMP gels only show a broad amorphous scattering peak. On the other hand, Fourier transform infrared results of PVA/EG gels also clearly show an intense peak at 1141 cm 01 due to the crystalline absorption. The results of H 1 pulsed nuclear magnetic resonance show that the spin-spin relaxation time, T s and T l, respectively, related to the poly- mer-rich and polymer-poor components decrease, and the fractional amount of the polymer-rich component, f s , increases, while that of the polymer-poor component, f l , decreases with an increase in the concentration of polymer. At a given concentration, the value of f s in the PVA-EG gel is larger than that in the PVA-NMP one. These facts indicate that the crystallinity in the PVA-EG gel is higher than that in the PVA- NMP gel, implying that the aggregation of PVA chains is much easier in the poor solvent, EG, than in the good solvent, NMP. The structural change with aging time in the PVA-EG gel is very remarkable because of the significant syneresis, indicating that the opaque PVA-EG gel with higher crystallinity has a comparatively heteroge- neous and unstable network structure than the PVA-NMP gel does. q 1998 John Wiley &

Engineering three-dimensional collagen-IKVAV matrix to mimic neural microenvironment.

Engineering the cellular microenvironment has great potential to create a platform technology toward engineering of tissue and organs. This study aims to engineer a neural microenvironment through fabrication of three-dimensional (3D) engineered collagen matrixes mimicking in-vivo-like conditions. Collagen was chemically modified with a pentapeptide epitope consisting of isoleucine-lysine-valine-alanine-valine (IKVAV) to mimic laminin structure supports of the neural extracellular matrix (ECM). Three-dimensional collagen matrixes with and without IKVAV peptide modification were fabricated by freeze-drying technology and chemical cross-linking with glutaraldehyde. Structural information of 3D collagen matrixes indicated interconnected pores structure with an average pore size of 180 μm. Our results indicated that culture of dorsal root ganglion (DRG) cells in 3D collagen matrix was greatly influenced by 3D culture method and significantly enhanced with engineered collagen matrix conjugated with IKVAV peptide. It may be concluded that an appropriate 3D culture of neurons enables DRG to positively improve the cellular fate toward further acceleration in tissue regeneration.

Effect of rigid amorphous phase on glass transition behavior of poly(trimethylene terephthalate)

Abstract In this work, a three-phase model consisting of crystalline, mobile amorphous and rigid amorphous phases (RAP) was used to describe the structural formation of poly(trimethylene terephthalate) (PTT) at various crystallization conditions. The variation in thickness and fraction of each phase was studied on both crystallization temperature T c and crystallization time t c effects from differential scanning calorimetry and small angle X-ray scattering analyzes. The results showed that the rigid amorphous fraction and thickness of PTT increased with increasing T c . Meanwhile, there is no remarkable change in crystalline fraction and thickness, and long period. A characteristic length ξ a for cooperative motion of polymer chains in amorphous phase was determined from the variation in glass transition interval using dynamic mechanical analysis. The change in this length scale of glass transition was considered to be correlated with the variation in the thickness of rigid and mobile amorphous phases. The T g of PTT increases and the relaxation peak becomes broader at high temperature flank with T c . These facts are considered due to that the RAP formation leads to the suppression of cooperative motion for amorphous chains.

Polysaccharide gene transfection agents

Gene delivery is a promising technique that involves in vitro or in vivo introduction of exogenous genes into cells for experimental and therapeutic purposes. Successful gene delivery depends on the development of effective and safe delivery vectors. Two main delivery systems, viral and non-viral gene carriers, are currently deployed for gene therapy. While most current gene therapy clinical trials are based on viral approaches, non-viral gene medicines have also emerged as potentially safe and effective for the treatment of a wide variety of genetic and acquired diseases. Non-viral technologies consist of plasmid-based expression systems containing a gene associated with the synthetic gene delivery vector. Polysaccharides compile a large family of heterogenic sequences of monomers with various applications and several advantages as gene delivery agents. This chapter, compiles the recent progress in polysaccharide based gene delivery, it also provides an overview and recent developments of polysaccharide employed for in vitro and in vivo delivery of therapeutically important nucleotides, e.g. plasmid DNA and small interfering RNA.

Influence of charge on FITC-BSA-loaded chondroitin sulfate-chitosan nanoparticles upon cell uptake in human Caco-2 cell monolayers

Background and methods Chondroitin sulfate-chitosan (ChS-CS) nanoparticles and positively and negatively charged fluorescein isothiocyanate-conjugated bovine serum albumin (FITC-BSA)-loaded ChS-CS nanoparticles were prepared and characterized. The properties of ChS-CS nanoparticles, including cellular uptake, cytotoxicity, and transepithelial transport, as well as findings on field emission-scanning electron microscopy, transmission electron microscopy, and confocal laser scanning microscopy were evaluated in human epithelial colorectal adenocarcinoma (Caco-2) fibroblasts. ChS-CS nanoparticles with a mean particle size of 250 nm and zeta potentials ranging from −30 to +18 mV were prepared using an ionic gelation method. Results Standard cell viability assays demonstrated that cells incubated with ChS-CS and FITC-BSA-loaded ChS-CS nanoparticles remained more than 95% viable at particle concentrations up to 0.1 mg/mL. Endocytosis of nanoparticles was confirmed by confocal laser scanning microscopy and measured by flow cytometry. Ex vivo transepithelial transport studies using Caco-2 cells indicated that the nanoparticles were effectively transported into Caco-2 cells via endocytosis. The uptake of positively charged FITC-BSA-loaded ChS-CS nanoparticles across the epithelial membrane was more efficient than that of the negatively charged nanoparticles. Conclusion The ChS-CS nanoparticles fabricated in this study were effectively endocytosed by Caco-2 fibroblasts without significant cytotoxicity at high nanoparticle concentrations. ChS-CS nanoparticles represent a potential novel delivery system for the transport of hydrophilic macromolecules.

Competition between Phase Separation and Crystallization in a PCL/PEG Polymer Blend Captured by Synchronized SAXS, WAXS, and DSC

We conducted simultaneous, small-angle, X-ray scattering/differential scanning calorimetry (SAXS/ DSC) and simultaneous, wide-angle, X-ray scattering (WAXS)/DSC measurements for a polymer blend of poly(ε-caprolactone)/poly(ethylene glycol) (PCL/PEG). The time-dependent SAXS/DSC and WAXS/DSC results, measured while the system was quenched below the melting temperature of PCL from a melting state, revealed the competitive behavior between liquid-liquid phase separation and crystallization in the polymer blend. The time-dependent structural evolution extracted from the SAXS/WAXS/DSC results can be characterized by the following four stages in the PCL crystallization process: the induction (I), nucleation (II), growth (III), and late (IV) stages. The influence of the liquid-liquid phase separation on the crystallization of PCL was also observed by phase-contrast microscope and polarized microscope with 1/4λ compensator.

Development of 3D in vitro platform technology to engineer mesenchymal stem cells

This study aims to develop a three-dimensional in vitro culture system to genetically engineer mesenchymal stem cells (MSC) to express bone morphogenic protein-2. We employed nanofabrication technologies borrowed from the spinning industry, such as electrospinning, to mass-produce identical building blocks in a variety of shapes and sizes to fabricate electrospun nanofiber sheets comprised of composites of poly (glycolic acid) and collagen. Homogenous nanoparticles of cationic biodegradable natural polymer were formed by simple mixing of an aqueous solution of plasmid DNA encoded bone morphogenic protein-2 with the same volume of cationic polysaccharide, dextran-spermine. Rat bone marrow MSC were cultured on electrospun nanofiber sheets comprised of composites of poly (glycolic acid) and collagen prior to the incorporation of the nanoparticles into the nanofiber sheets. Bone morphogenic protein-2 was significantly detected in MSC cultured on nanofiber sheets incorporated with nanoparticles after 2 days compared with MSC cultured on nanofiber sheets incorporated with naked plasmid DNA. We conclude that the incorporation of nanoparticles into nanofiber sheets is a very promising strategy to genetically engineer MSC and can be used for further applications in regenerative medicine therapy.

Drawing of poly(vinyl alcohol) gel films

Abstract The drawability and physical properties of dried poly(vinyl alcohol) (PVA) gel films prepared from N-methylpyrrolidone (NMP) and ethyleneglycol (EG) solutions were compared. X-ray diffraction and differential scanning calorimetry showed that PVA/EG gels had higher values of crystallinity than PVA/NMP gels. The drawability of dried PVA/NMP gels was higher than that of PVA/EG gels at all drawing temperatures. Although the maximum draw ratio of dried PVA/NMP gel films increased with molecular weight, the extent of the increase is much less than in the case of polyethylene gel films, partly because the highest molecular weight available in this study was lower than in the case of ultra-high-molecular weight polyethylene. The highest draw ratio achieved was about 28 × for a dried PVA/NMP (DP = 14400, 2 wt%) gel film and its tensile strength and modulus were 1 GPa and 30 GPa, respectively. The αc relaxation temperature (Tαc) of PVA shifted to high temperature with increasing draw ratio, approaching the melting point, while the second-order crystal transition point remained at 120°C. This implies that the αc relaxation is related to molecular motion in the crystal-amorphous boundary.

Cationized dextran nanoparticle-encapsulated CXCR4-siRNA enhanced correlation between CXCR4 expression and serum alkaline phosphatase in a mouse model of colorectal cancer

Purpose: The failure of colorectal cancer treatments is partly due to overexpression of CXCR4 by tumor cells, which plays a critical role in cell metastasis. Moreover, serum alkaline phosphatase (ALP) levels are frequently elevated in patients with metastatic colorectal cancer. A polysaccharide, dextran, was chosen as the vector of siRNA. Spermine was conjugated to oxidized dextran by reductive amination process to obtain cationized dextran, so-called dextran-spermine, in order to prepare CXCR4-siRNAs/dextran-spermine nanoparticles. The fabricated nanoparticles were used in order to investigate whether downregulation of CXCR4 expression could affect serum ALP in mouse models of colorectal cancer. Methods: Colorectal cancer was established in BALB/C mice following injection of mouse colon carcinoma cells CT.26WT through the tail vein. CXCR4 siRNA for two sites of the target gene was administered following injection of naked siRNA or siRNA encapsulated into nanoparticles. Results: In vivo animal data revealed that CXCR4 silencing by dextran-spermine nanoparticles significantly downregulated CXCR4 expression compared with naked CXCR4 siRNA. Furthermore, there was correlation between CXCR4 expression and serum ALP. Conclusion: CXCR4 siRNA/dextran-spermine nanoparticles appear to be highly effective, and may be suitable for further in vivo applications. Further research evaluation will be needed to determine the effect of CXCR4 silencing on serum ALP levels, which may be a useful marker to predict liver metastasis in colorectal cancer.