Jumi Yun

Fluorination of electrospun hydrogel fibers for a controlled release drug delivery system

Electrospinning and fluorination were carried out in order to obtain a controlled release drug delivery system to solve the problem of both an initial burst of the drug and a limited release time. Poly(vinyl alcohol) was electrospun with Procion Blue as a model drug and heat treated in order to obtain cross-linked hydrogel fibers. Two different kinds of electrospun fibers of thin and thick diameters were obtained by controlling the electrospinning conditions. Thin fibers offer more available sites than thick fibers for surface modification during fluorination. Fluorination was conducted to control the release period by introducing hydrophobic functional groups on the surface of fibers. With an increase in the reaction pressure of the fluorine gas hydrophobic C-F and C-F(2) bonds were more effectively introduced. Over-fluorination of the fibers at higher reaction pressures of fluorine gas led to the introduction of C-F(2) bonds, which made the surface of the fibers hydrophobic and resulted in a decrease in their swelling potential. When C-F bonds were generated the initial drug burst decreased dramatically and total release time increased significantly, by a factor of approximately 6.7 times.

Preparation and Characteristics of Conducting Polymer-Coated MWCNTs as Electromagnetic Interference Shielding Materials

The conducting polymer-coated multi-walled carbon nanotubes (MWCNTs) were prepared by template polymerization of aniline and pyrrole on the surface of MWCNTs in order to develop the novel electromagnetic interference (EMI) shielding materials. The conducting polymer phases formed on the surface of MWCNTs were confirmed by field emission-scanning electron microscopy and field emission-transmission electron microscopy. Both permittivity and permeability were significantly improved for the conducting polymer-coated MWCNTs due to the intrinsic electrical properties of MWCNTs and the conducting properties of coated polymers. The electromagnetic waves were effectively absorbed based on the permittivity nature of conducting polymer and MWCNTs preventing the secondary interference from reflecting the electromagnetic waves. The highly improved EMI shielding efficiency was also obtained for the conducting polymer-coated MWCNTs showing the synergistic effects by combining MWCNTs and the conducting polymers.

Erratum to: Electromagnetic interference shielding effects of polyaniline-coated multi-wall carbon nanotubes/maghemite nanocomposites

Highly conductive nanocomposites were prepared by in situ polymerization of polyaniline (PANi) and multi-walled carbon nanotubes (MWCNTs) as electromagnetic interference shielding materials. γ-Fe2O3 nanoparticles were also incorporated in the nanocomposites to improve the ferromagnetic properties. SEM and TEM images showed the uniformly coated PANi on the surface of MWCNTs and γ-Fe2O3. XRD peaks also confirmed the presence of MWCNT and γ-Fe2O3 in the nanocomposites. The nanocomposites showed significant improvement in permittivity, permeability, and electromagnetic interference shielding efficiency due to the conductive effect of MWCNTs and the magnetic effect of γ-Fe2O3. The electromagnetic interference shielding efficiency of nanocomposites increased up to 34.1 dB due to the synergetic effect of reflection and absorption of electromagnetic interference by MWCNTs and γ-Fe2O3 additives.

Improvement in ammonia gas sensing behavior by polypyrrole/multi-walled carbon nanotubes composites

Polypyrrole (PPy)/multi-walled carbon nanotubes (MWCNTs) composites were prepared by in situ polymerization of pyrrole on the surface of MWCNTs templates to improve the ammonia gas sensing properties. PPy morphologies, formed on the surface of MWCNTs, were investigated by field emission scanning electron microscopy. The thermal stabilities of the PPy/MWCNTs composites were improved as the content of MWCNTs increased due to the higher thermal stability of the MWCNTs. PPy/MWCNTs composites showed synergistic effects in improving the ammonia gas sensing properties, attributed to the combination of efficient electron transfer between PPy/MWCNTs composites and ammonia gas, and the reproducible electrical resistance variation on PPy during the gas sensing process.

Preparation and characteristics of conducting polymer-coated multiwalled carbon nanotubes for a gas sensor

Conducting polymer-coated multiwalled carbon nanotubes (MWCNTs) were prepared by template polymerization in order to enhance their gas sensitivity. This investigation of the conducting polymer phases that formed on the surface of the MWCNTs is based on field-emission scanning electron microscopy images. The thermal stability of the conduct - ing polymer-coated MWCNTs was significantly improved by the high thermal stability of MWCNTs. The synergistic effects of the conducting polymer-coated MWCNTs improve the gas-sensing properties. MWCNTs coated with polyaniline uniformly show outstanding improvement in gas sensitivity to NH3 due to the synergistic combination of efficient adsorp - tion of NH3 gas and variation in the conduction of electrons.

Dual-responsive release behavior of pH-sensitive PVA/PAAc hydrogels containing temperature-sensitive PVA/PNIPAAm microcapsules

Both temperature and pH responsive drug delivery system was prepared by combining temperature-sensitive poly(vinyl alcohol) (PVA)/poly(N-isopropylacrylamide) (PNIPAAm) microcapsules and pH-sensitive PVA/poly(acrylic acid) (PAAc) hydrogels. The release of drug from the composite hydrogels increased as the pH increased due to the repulsion among the carboxylate anions in the PVA/PAAc hydrogels. The release of drug from the composite hydrogels also increased as the temperature decreased due to the higher hydrophilicity generated below the lower critical solution temperature of PNIPAAm. The compression moduli of composite hydrogels increased with increasing the content of PVA/PNIPAAm microcapsules. The biocompatibility of composite hydrogels was confirmed by the cytotoxicity test.

Controlled Release Behavior of Temperature Responsive Composite Hydrogel Containing Activated Carbon

The composites of temperature-sensitive hydrogel and activated carbons were prepared in order to improve both the mechanical strength of hydrogel matrix and the loading capacity of drug in a hydrogel drug delivery system. The swelling of composite hydrogel was varied depending on the temperature. Both the swelling and the release behavior of the composite hydrogel were varied depending on the kind of activated carbon. The release behavior showed the high efficiency which is important for practical applications. Keywords : Drug delivery system, Controlled release, Temperature-sensitive hydrogel, Activated carbon, Mechanical property

Improvement in transdermal drug delivery performance by graphite oxide/temperature-responsive hydrogel composites with micro heater.

Transdermal drug delivery system (TDDS) was prepared with temperature-responsive hydrogel. The graphite was oxidized and incorporated into hydrogel matrix to improve the thermal response of hydrogel. The micro heater was fabricated to control the temperature precisely by adopting a joule heating method. The drug in hydrogel was delivered through a hairless mouse skin by controlling temperature. The efficiency of drug delivery was improved obviously by incorporation of graphite oxide due to the excellent thermal conductivity and the increased interfacial affinity between graphite oxide and hydrogel matrix. The fabricated micro heater was effective in controlling the temperature over lower critical solution temperature of hydrogel precisely with a small voltage less than 1 V. The cell viability test on graphite oxide composite hydrogel showed enough safety for using as a transdermal drug delivery patch. The performance of TDDS could be improved noticeably based on temperature-responsive hydrogel, thermally conductive graphite oxide, and efficient micro heater.

Effect of graphite oxide on photodegradation behavior of poly(vinyl alcohol)/graphite oxide composite hydrogels

Poly(vinyl alcohol) (PVA) composites with various graphite oxide (GO) contents (0 to 10 wt%) were prepared by sonicating the mixture of PVA and GO, followed by crosslinking with glutaraldehyde. GO was pre-treated with oxyfluorination (O 2:F2 = 8:2) in order to mod- ify the surface of GO to allow it to carry hydrophilic functional groups. PVA/GO compos- ite hydrogels were characterized by scanning electron microscopy and Fourier-transform infrared spectrometer (FT-IR). The morphology of the PVA/GO composite hydrogels and the variations in soluble gel portion were investigated under various GO contents and UV irradiation doses. The variation in the chemical structure of photo degraded PVA/GO com- posite hydrogels was studied by FT-IR. The photochemical stability of PVA/GO composite hydrogels under UV irradiation was found to improve noticeably with increasing content of uniformly dispersed GO.

Electro-responsive Transdermal Drug Release of MWCNT/PVA Nanocomposite Hydrogels

Multi-walled carbon nanotube (MWCNT)/poly(vinyl alcohol) (PVA) nanocomposite hydrogels were prepared by freezingthawing method for the electro-responsive transdermal drug delivery. MWCNTs were used as the functional ingredient to improve both mechanical and electrical properties of MWCNT/PVA nanocomposite hydrogels. The morphology of nanocomposites revealed the uniform distribution of MWCNTs and the good interfacial contact. The compression moduli of hydrogel matrices increased greatly from 40 to 1500 kPa by forming MWCNT/PVA nanocomposites. The swelling ratio of MWCNT/PVA nanocomposites decreased as the content of MWCNTs increased under no electric voltage applied. However, the swelling ratio of MWCNT/PVA nanocomposites increased as the content of MWCNTs increased under electric voltage applied and the applied electric voltage increased. The drug was released in the electro-responsive manner through the skin due to the electro-sensitive swelling characteristics of MWCNT/PVA nanocomposite hydrogels.