Pitt Supaphol

Drug-loaded electrospun mats of poly(vinyl alcohol) fibres and their release characteristics of four model drugs

Mats of PVA nanofibres were successfully prepared by the electrospinning process and were developed as carriers of drugs for a transdermal drug delivery system. Four types of non-steroidal anti-inflammatory drug with varying water solubility property, i.e. sodium salicylate (freely soluble in water), diclofenac sodium (sparingly soluble in water), naproxen (NAP), and indomethacin (IND) (both insoluble in water), were selected as model drugs. The morphological appearance of the drug-loaded electrospun PVA mats depended on the nature of the model drugs. The 1H-nuclear magnetic resonance results confirmed that the electrospinning process did not affect the chemical integrity of the drugs. Thermal properties of the drug-loaded electrospun PVA mats were analysed by differential scanning calorimetry and thermogravimetric analysis. The molecular weight of the model drugs played a major role on both the rate and the total amount of drugs released from the as-prepared drug-loaded electrospun PVA mats, with the rate and the total amount of the drugs released decreasing with increasing molecular weight of the drugs. Lastly, the drug-loaded electrospun PVA mats exhibited much better release characteristics of the model drugs than drug-loaded as-cast films.

PREPARATION AND ADSORPTION BEHAVIOR OF AMINATED ELECTROSPUN POLYACRYLONITRILE NANOFIBER MATS FOR HEAVY METAL ION REMOVAL

Polyacrylonitrile (PAN) nanofiber mats were prepared by electrospinning and they were further modified to contain amidino diethylenediamine chelating groups on their surface via heterogeneous reaction with diethylenetriamine (DETA). The obtained aminated PAN (APAN) nanofiber mats were evaluated for their chelating property with four types of metal ions, namely Cu(II), Ag(I), Fe(II), and Pb(II) ions. The amounts of the metal ions adsorbed onto the APAN nanofiber mats were influenced by the initial pH and the initial concentration of the metal ion solutions. Increasing the contact time also resulted in a monotonous increase in the adsorbed amounts of the metal ions, which finally reached equilibria at about 10 h for Cu(II) ions and about 5 h for Ag(I), Fe(II), and Pb(II) ions. The maximal adsorption capacities of the metal ions on the APAN nanofiber mats, as calculated from the Langmuir model, were 150.6, 155.5, 116.5, and 60.6 mg g(-1), respectively. Lastly, the spent APAN nanofiber mats could be facilely regenerated with a hydrochloric acid (HCl) aqueous solution.

Extraction and electrospinning of gelatin from fish skin

Ultra-fine gelatin fibers were successfully fabricated by electrospinning from the solutions of Nile tilapia (Oreochromis niloticus) skin-extracted gelatin in either acetic acid or formic acid aqueous solutions. The extracted gelatin contained 7.3% moisture, 89.4% protein, 0.3% lipid, and 0.4% ash contents (on the basis of wet weight), while the bloom gel strength, the shear viscosity, and the pH values were 328 g, 17.8 mPa s, and 5.0, respectively. Both the acid concentration and the concentration of the gelatin solutions strongly influenced the properties of the as-prepared solutions and the obtained gelatin fibers. At low acid concentrations (i.e., 15% (w/v) extracted gelatin solutions in 10 and 20% (v/v) acetic acid solvents or 10-60% (v/v) formic acid solvents), a combination between smooth and beaded fibers was observed. At low concentrations of the gelatin solutions in either 40% (v/v) acetic acid solvent or 80% (v/v) formic acid solvent (i.e., 5-11%, w/v), either discrete beads or beaded fibers were obtained, while, at higher concentrations (i.e., 14-29%, w/v), only smooth or a combination of smooth and beaded fibers were obtained. The average diameters of the obtained fibers, regardless of the types of the acid solvents used, ranged between 109 and 761 nm. Lastly, cross-linking of the obtained gelatin fiber mats with glutaraldehyde vapor caused slight shrinkage from their original dimension, and the cross-linked gelatin fiber mats became stiffer.

Aliphatic Lipid Substitution on 2 kDa Polyethylenimine Improves Plasmid Delivery and Transgene Expression

This study was conducted in order to develop amphiphilic, low molecular weight polymeric carriers for nonviral gene delivery. Caprylic, myristic, palmitic, stearic, oleic and linoleic acids were grafted onto the 2 kDa polyethylenimine (PEI) and properties critical for gene delivery were investigated using 293T and bone marrow stromal cells. The extent of lipid substitution on the polymers was controlled by the lipid:PEI feed ratio during the synthesis. The toxicity of the native and lipid-substituted 2 kDa PEI was relatively lower than the 25 kDa PEI, although lipid substitution generally increased the toxicity of the polymers in vitro. Lipid substitution reduced the ability of the polymers to complex DNA, as well as the stability of final complexes, as measured by heparin-induced dissociation. Once fully complexed to a plasmid DNA, however, the lipid-substituted polymers increased the plasmid DNA delivery to the cells. In 293T cells, the lipid-substituted polymers displayed a transfection ability that was equivalent to highly effective 25 kDa PEI, but without the toxic effect associated with the latter polymer. Among the lipids explored, no particular lipid emerged as the ideal substituent for transgene expression, although linoleic acid appeared to be superior to other lipid substituents. No correlation was evident between the level of substitution and DNA delivery efficiency of the polymers, and as little as 1 lipid substitution per PEI was effective in transforming the ineffective 2 kDa PEI into an effective carrier. The current structure-function studies are providing important clues about the properties critical for gene delivery and providing carriers effective for nonviral plasmid delivery.

Isothermal melt- and cold-crystallization kinetics and subsequent melting behavior in syndiotactic polypropylene: a differential scanning calorimetry study

The isothermal melt- and cold-crystallization kinetics and subsequent melting behavior of syndiotactic polypropylene ( s-PP) were investigated using differential scanning calorimetry (DSC). The overall crystallization kinetics was determined by directly fitting the experimental data to the Avrami and Malkin macrokinetic models using a non-linear multi-variable regression program. When plotted as a function of crystallization temperature, the overall crystallization rate parameters for melt-crystallization process exhibited an unmistakable double bell-shaped curve, while those for cold-crystallization process showed the typical bell-shaped curve. Comparison of the overall crystallization rate parameters obtained for both melt- and cold-crystallization processes indicated that crystallization from the glassy state proceeded at a much greater rate than that from the melt state. Melting of samples isothermally crystallized at low and moderate crystallization temperatures exhibited multiple-melting phenomenon. Determination of the equilibrium melting temperature according to the “linear” and “non-linear” Hoffman‐Weeks extrapolative methods provided values of ca. 145 and 182 8C, respectively. q 2000 Elsevier Science Ltd. All rights reserved.

Non-isothermal melt crystallization kinetics for poly(trimethylene terephthalate)/poly(butylene terephthalate) blends

Abstract Various macrokinetic models, namely the Avrami, Ozawa, and Ziabicki models, were applied to describe the non-isothermal melt crystallization process of poly(trimethylene terephthalate) (PTT), poly(butylene terephthalate) (PBT), and their blends. Both the Avrami and the Ozawa models were found to describe the experimental data fairly well. Among the blend compositions studied, Ziabicki’s kinetic crystallizability parameter was found to decrease with increasing PTT content. The effective energy barrier for non-isothermal crystallization process of these blends, analyzed based on the differential iso-conversional method of Friedman, was found to be an increasing function of the relative degree of melt conversion. Within the relative degree of melt conversion range of less than ca. 0.5, the effective energy barrier was found to increase with increasing PTT content.

Nonisothermal melt-crystallization kinetics for three linear aromatic polyesters

Abstract The kinetics of nonisothermal crystallization of three different types of linear aromatic polyester, namely poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT), which are different in their number of methylene groups (i.e. 2, 3, and 4 for PET, PTT, and PBT, respectively), was investigated using differential scanning calorimetry (DSC). Analysis of the data was carried out based on the Avrami, Tobin, Ozawa, and Ziabicki models. It was found that the Avrami model provided a more satisfactorily good fit to the experimental data for these polyesters than did the Tobin model. The Ozawa model was found to describe the experimental data fairly well. The Ziabicki’s kinetic crystallizability parameter G for these polyesters was found to be of the following order: PBT>PTT>PET. The effective energy barrier for nonisothermal crystallization process of these polyesters, determined by the Friedman method, was found to be an increase function with the relative degree of crystallinity.

Thermal, crystallization, and rheological characteristics of poly(trimethylene terephthalate)/poly(butylene terephthalate) blends

Abstract Blends of poly(trimethylene terephthalate) (PTT) and poly(butylene terephthalate) (PBT) were miscible in all of the blend compositions studied, as evidenced by an observed single and composition-dependent glass transition temperature for each blend composition. The variation of the glass transition temperature with the blend composition was well predicted by the Gordon–Taylor equation, with fitting parameter being ca. 6.9. The cold crystallization (peak) temperature was found to increase, while the melt crystallization (peak) temperature was found to decrease, with increasing PTT content. The subsequent melting behavior for these blends (after cold crystallization) showed the melting point depression behavior, in that the melting (peak) temperature for each component was lowered with increasing content of the other component. During crystallization, the pure components crystallized simultaneously to form their own crystals. The blend having 60 percent by weight of PTT showed the lowest apparent degree of crystallinity. The steady shear viscosities for the pure components and the blends showed slight decrease with increasing shear rate (within the shear rate range of 0.25–25 s−1), with those of the blends lying in between those of the pure components.

Crystalline memory effects in isothermal crystallization of syndiotactic polypropylene

Isothermal crystallization behavior after partial or complete melting of syndiotactic polypropylene was investigated by differential scanning calorimetry (DSC). On partial melting, the total concentration of predetermined nuclei was found to decrease with increasing fusion temperature and increasing time period that the sample spent at a specific fusion temperature. A significant effect of the rate of heating to the fusion temperature was also observed. On complete melting, the total concentration of predetermined nuclei was found to approach a constant value, which is the concentration of infusible heterogeneous nuclei (e.g., impurities, catalyst residues) present originally in the sample. At a specific fusion temperature, the concentration of predetermined athermal nuclei was found to decrease exponentially with the time period spent in the melt.

Nonisothermal bulk crystallization and subsequent melting behavior of syndiotactic polypropylenes: Crystallization from the melt state

Various macrokinetic models, namely, the Avrami, the Tobin, and the Ozawa models, were applied to describe the crystallization process of syndiotactic polypropylene (s-PP) under nonisothermal conditions. Both Avrami and Tobin models were shown to provide a fair description of the experimental data. The Avrami exponent na was found to range from 2.4 to 5.3, while the Tobin exponent nt was found to range from 3.1 to 6.7. The Ozawa model was found to describe the nonisothermal crystallization kinetics of s-PP very well. The Ziabickis kinetic crystallizability, suggesting the crystallization ability of polymers from the melt when cooled at a unit cooling rate, was also evaluated and was found to range from 0.93 to 1.40°C s−1. The energy barrier for nonisothermal crystallization, based on the Augis–Bennett method, was found to range from −78.6 to −108.1 kJ mol−1.