Chao-Ming Shih

Tuning of Lower Critical Solution Temperature (LCST) of Poly(N-Isopropylacrylamide-co-Acrylic acid) Hydrogels

Temperature-responsive hydrogel with a lower critical solution temperature (LCST) close to human body temperature was prepared. Crosslinked N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) copolymer networks were synthesized at various monomer ratios in the presence of ammonium persulfate (APS), N,N′-methylenebisacrylamide (NMBA) and N,N,N′,N′-tetramethylethylenediamine (TEMED) via a redox polymerization method. The resulting hydrogels possessed thermo- and pH-responsive characteristics. They were characterized in terms of swelling ratio, volume change, water uptake and diffusivity, water vapor uptake and diffusivity, and phase transition temperature. The water liquid and vapor diffusion coefficients for all the synthesized hydrogels were higher than the literature data, implying higher rates for drug release. The LCST of the hydrogel increased with higher AAc content in the copolymer. The gel containing 1.8% AAc exhibited an LCST similar to human body temperature, demonstrating a potential use in drug controlled release and biomedical applications.

In vitro biocompatibility of magnetic thermo-responsive nanohydrogel particles of poly(N-isopropylacrylamide-co-acrylic acid) with Fe3O4 cores: effect of particle size and chemical composition.

Biocompatibility is a critical factor in the design and development of candidate materials for biomedical use. This paper reports on the in vitro biocompatibility of magnetic stimuli-sensitive nanohydrogel particles composed of magnetite cores in poly(N-isopropylacrylamide-co-acrylic acid) shells referred to Fe(3)O(4)/P(NIPAAm-co-AAc). The AAc concentration and polymerization time were varied to fabricate magnetic nanoparticles with various AAc levels (1.80-2.37%) and particle sizes (74-213 nm). The P(NIPAAm-co-AAc) shell exhibited thermo-sensitive properties and the Fe(3)O(4) core constituted 2.25-4.10% of the particles by weight. After a 2-day incubation of L929 cells with extract media that had been conditioned with various test samples, the cellular responses were monitored in terms of cell viability and growth. The Live/Dead assays showed that high levels of cellular viability (97.3-98.1%) were observed in all groups, indicating that none of the nanoparticles were cytotoxic. However, the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymetho-xyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assays demonstrated that the activity of mitochondrial dehydrogenase varied significantly in cultures exposed to different magnetic nanohydrogel particles. The murine fibroblasts exposed to the NIP-(AAc5.1-Fe)-2 sample, which contained the highest AAc content and largest particle sizes, were the least metabolically active. In contrast, the activity levels in the cultures treated with the low AAc content and small size particles (NIP-(AAc2.6-Fe)-1) were not significantly different from those in the control group. Our findings suggest that smaller magnetic stimuli-sensitive nanohydrogel particles with a lower AAc content may have little inhibitory impact on cell proliferation. Overall, the in vitro biocompatibilities of the nanoparticles depend on the chemical composition and size of the Fe(3)O(4)/P(NIPAAm-co-AAc) particles.

Correlation between free-volume properties and pervaporative flux of polyurethane-zeolite composites on organic solvent mixtures.

Micron-sized zeolite particles were incorporated into a polyurethane (PU) matrix to prepare ethylbenzene-selective membranes. The resulting composite membranes were used in the pervaporation (PV) of ethylbenzene/styrene (EB/ST) mixtures. The sorption, diffusion, and PV permeation behaviors as a result of zeolite addition were elucidated. Zeolite is less chemically compatible with organic solvents than PU and the PU-zeolite composites, which exhibited suppressed solvent solubilities compared with pristine PU. However, these membranes favor EB transport by diffusion selectivity. The diffusivity and permeation flux increases in parallel with the enlarged radius of the free-volume hole size (R(4) increasing from 3.46 to 3.64 Å using positron annihilation lifetime spectroscopy analysis) by increasing the zeolite content from 0 to 23%. The enlarged free volume at a zeolite loading of 23% promoted pure solvent diffusivities by 10% higher than that of the unfilled film. During the PV operation on the EB/ST mixture, a significant diffusion-coupling was observed, and the permeant diffusion coefficients from the binary mixture exceeded the pure solvent diffusivity. The permeation flux was greatly improved (up to 0.72 kg/m(2)·h) by zeolite addition without any detrimental effect on the separation efficiency.

Drug permeation behavior through thermo- and pH-responsive polycarbonate-g-poly(N-isopropylacrylamide-co-acrylic acid) composites

Poly(N-isopropylacrylamide-co-acrylic acid) hydrogel was grafted onto track-etched polycarbonate (PC) films using the free-radical polymerization method to prepare thermo-sensitive micro-porous films. Differential scanning calorimeter analysis was used to determine the lower critical solution temperature for the hydrogels. Thermo-gravimetric analysis was used to determine the thermal stability of the PC–hydrogel composite films. The composite films were characterized using Fourier transform-infrared spectra, scanning electron microscope, and effective pore diameters derived from water permeability data. 4-Acetamidophenol, citric acid, KCl, and methyl orange were used as the model drugs. For neutral drugs, the larger molecules exhibited lower permeability but higher on–off ratio than smaller ones. The strong electrolyte model molecules (KCl) exhibited depressed permeability due to enlarged hydrated ion sizes. The acidic (citric acid) model solution promoted gel shrinkage, resulting in increased drug permeability and on–off ratio.

Electrolyte design and optimization on for dye sensitized solar cells: Response surface analysis and simulation

In this study, the affects of electrolyte composition on photovoltaic parameters in dye-sensitized solar cells (DSSCs) are analyzed using response surface methodology. We have obtained the relationship of the electrolyte conductivity, tri-iodide diffusivity, and DSSC efficiency based on LiI, I2, and PMII concentrations in the electrolyte. With the optimal concentration of PMII at 1.4 M, LiI 0 M, and I2 at 0.1 M, we could reach the highest electrolyte conductivity of 28.86 mS/cm (only 0.45% in error between predicted and experimental data). When PMII at 1.4 M, LiI 0 M and I2 at 0.02 M, the predicted optimal cell efficiency was 8.41%, which was validated with an experimental value of 7.9% (with an error of 6.5%).