Jeong Hyun Yeum

Antimicrobial polyethyleneimine-silver nanoparticles in a stable colloidal dispersion

Excellent colloidal stability and antimicrobial activity are important parameters for silver nanoparticles (AgNPs) in a range of biomedical applications. In this study, polyethyleneimine (PEI)-capped silver nanoparticles (PEI-AgNPs) were synthesized in the presence of sodium borohydride (NaBH(4)) and PEI at room temperature. The PEI-AgNPs had a positive zeta potential of approximately +49 mV, and formed a stable nanocolloid against agglomeration due to electrostatic repulsion. The particle size and hydrodynamic cluster size showed significant correlations with the amount of PEI and NaBH(4). PEI-AgNPs and even PEI showed excellent antimicrobial activity against Staphylococus aureus and Klebsiella pneumoniae. The cytotoxic effects of PEI and PEI-AgNPs were confirmed by an evaluation of the cell viability. The results suggest that the amount of PEI should be minimized to the level that maintains the stability of PEI-AgNPs in a colloidal dispersion.

Electrospun novel super-absorbent based on polysaccharide–polyvinyl alcohol–montmorillonite clay nanocomposites

A novel super-absorbent material was fabricated by electrospinning the natural polysaccharide pullulan (PULL) with polyvinyl alcohol (PVA) and montmorillonite (MMT) clay to form nonwoven webs, which were then heat treated. Transmission electron microscopy (TEM) micrographs, X-ray diffraction (XRD) patterns, and Fourier transform infrared (FTIR) analysis of the novel super-absorbent nanofibers suggest the coexistence of PULL, PVA, and MMT through the exfoliation of MMT layers in the super-absorbent nanofiber composite. The heat-treated PULL/PVA/MMT webs loaded with 5 wt% MMT electrospun nanofibers exhibited a water absorbency of 143.42 g g(-1) in distilled water and a water absorbency of 39.75 g g(-1) in a 0.9 wt% NaCl solution. Under extremely dry conditions, the PULL/PVA/MMT webs exhibited the ability to retain 43% distilled water and 38% saline water after being exposed to the atmosphere for one week. The heat treatment improved the crystallinity of the electrospun PULL/PVA/MMT super-absorbent webs and thus made the webs highly stable in aqueous environments. Overall, the addition of MMT resulted in improved thermal stability and mechanical properties and increased the water absorbency of the PULL/PVA/MMT composite.

Preparation and characterization of MRI-active gadolinium nanocomposite particles for neutron capture therapy

We demonstrate the synthesis and characteristics of MRI-active Gd2O3 core/SiO2 shell/poly(2-methacryloyloxyethyl phosphorylcholine) corona composite nanoparticles (Gd2O3@SiO2@PMPC NPs). The prepared NPs have a number of attractive features in cancer diagnosis and neutron capture therapy (NCT): biocompatibility, colloidal stability, low cytotoxicity, nucleus affinity, passive targeting, etc. Monodisperse and highly crystalline Gd2O3 NPs were prepared using a polyol protocol to control the average particle size and surface properties. The Gd2O3 NPs were then functionalized with SiO2 and a biomimetic layer of PMPC, to achieve reduced toxicity and enhanced nucleus affinity, for use as an MRI-active Gd-NCT agent. The size of the NPs was tailored to be from 50 to 100 nm for passive accumulation in tumor tissue through loosened capillary vessels. The morphologies and structures of Gd2O3, Gd2O3@SiO2–Br, and Gd2O3@SiO2@PMPC NPs were studied by FT-IR, XRD, HR-TEM, and TGA. In vitro cytotoxicity was investigated with three kinds of normal and cancer cells, and in vitro and in vivo MRI analyses were performed to confirm the contrast ability, accumulation, and sustentation of NPs in tumor tissues.

Effect of pullulan/poly(vinyl alcohol) blend system on the montmorillonite structure with property characterization of electrospun pullulan/poly(vinyl alcohol)/montmorillonite nanofibers

Nanofibers of the composite of pullulan (PULL), poly(vinyl alcohol) (PVA), and montmorillonite clay (MMT) were prepared using electrospinning method in aqueous solutions. Pullulan is an interesting natural polymer for many of its merits and good properties. Because of biocompatibility and non-toxicity of PVA, it could be used in numerous fields. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA) were done to characterize the PULL/PVA/MMT nanofibers morphology and properties. XRD patterns and FTIR data demonstrated that there were good interactions between PULL and PVA caused by possibly hydrogen bonds. Moreover, XRD data and TEM images indicated that intercalated and exfoliated MMT nanoplatelets can be obtained within the PULL/PVA/MMT nanofibers depending on the PULL/PVA blend ratios. Furthermore, the thermal stability and mechanical property (tensile strength) of PULL/PVA/MMT nanofibers could be enhanced more by exfoliated MMT nanoplatelets than intercalated structures of that nanoplatelets.

Structures and physical properties of graphene/PVDF nanocomposite films prepared by solution-mixing and melt-compression

We have manufactured poly(vinylidene fluoride) (PVDF)-based nanocomposite films with different graphene contents of 0.1∼10.0 wt% by ultrasonicated solution-mixing and melt-compression. As a reinforcing nanofiller, graphene sheets are prepared by rapid thermal expansion of graphite oxide, which are from the oxidation of natural graphite flakes. Graphene sheets are characterized to be well exfoliated and dispersed in the nanocomposite films. X-ray diffraction data confirm that the α-phase crystals of PVDF are dominantly developed in the nanocomposite films during the meltcrystallization. DSC cooling thermograms show that the graphene sheets serve as nucleating agents for the PVDF α-form crystals. Thermal stability of the nanocomposite films under oxygen gas atmosphere is noticeably improved, specifically for the nanocomposite with 1.0 wt% graphene. Electrical volume resistivity of the nanocomposite films is substantially decreased from ∼1014 to ∼106 W cm, especially at a critical graphene content between 1.0 and 3.0 wt%. In addition, mechanical storage modulus is highly improved with increasing the graphene content in the nanocomposite films. The increment of the storage modulus for the nanocomposite film at 30 °C with increasing the graphene content is analyzed by adopting the theoretical model proposed by Halpin and Tsai.

Novel Poly(vinyl alcohol)/Clay Nanocomposite Microspheres via Suspension Polymerization and Saponification

Poly(vinyl alcohol) (PVA)/montmorillonite (MMT) clay nanocomposite microspheres were synthesized through suspension polymerization followed by the heterogeneous saponification for the first time. The effects of MMT on the saponification rate of poly(vinyl acetate) (PVAc) microspheres were studied. It was found that the saponification rate of PVAc significantly increased in the presence of MMT particles. The molecular weight of extracted PVA from the PVA/MMT was lower than that of pure PVA synthesized under similar conditions. TGA, TEM and XRD measurements illustrated that the clay platelets were intercalated in the polymer matrix.

Preparation of poly(vinyl acetate)/clay and poly(vinyl acetate)/poly(vinyl alcohol)/clay microspheres

Poly(vinyl acetate) (PVAc)/poly(vinyl alcohol)(PVA)/montmorillonite (MMT) clay nanocomposite microspheres with a core/shell structure have been developed via a suspension polymerization approach. In order to prepare the PVAc/MMT and PVAc/PVA/MMT nanocomposite microspheres, which are promising precursor of PVA/MMT nanocomposite microspheres, suspension polymerization of vinyl acetate with organophilic MMT and heterogeneous saponification were conducted. A quaternary ammonium salt, cetyltrimethylammonium bromide, was mixed with the MMT in the monomer phase prior to the suspension polymerization. The rate of conversion decreased with an increase in MMT concentration. The incorporation of MMT into the PVAc was verified by FT-IR spectroscopy. Organic vinyl acetate monomers were intercalated into the interlayer regions of organophilic clay hosts and followed by suspension polymerization. Partially saponified PVA/MMT nanocomposite microspheres with a core/shell structure were successfully prepared by heterogeneous saponification.

Aroma finishing of PET fabrics with PVAc nanoparticles containing lavender oil

A durable aroma finishing for PET fabric was carried out by adopting poly(vinyl acetate) (PVAc) nanoparticles containing lavender oil (LO) in core. Relatively small size of PVAc nanoparticles (ca. 244 nm of mean particle diameter) was expected to resist the frictional destruction of the particles, which is frequently observed in cases of microcapsules. PVAc nanoparticles containing LO in core were prepared by emulsification-diffusion method and their application as an aroma releasing agent for PET fabrics was assessed through the observation of releasing profiles of LO in ethanol for experimental acceleration. Melamine-formaldehyde (MF) microcapsules containing LO were also prepared and treated on fabrics for comparison. PVAc nanoparticles treated on PET fabric showed higher initial releasing amount, which was ascribed to the enhanced surface area. After 2 days of releasing, PET fabric treated with PVAc nanoparticles showed slower and more stable releasing profile and reached about 12 ppm of cumulative release after 16 days, which was under two thirds of that with MF microcapsules. PVAc nanoparticles can be used as an agent for durable aroma finishing of PET fabrics.

Graphene oxide-coated guided bone regeneration membranes with enhanced osteogenesis: Spectroscopic analysis and animal study

ABSTRACT Guided bone regeneration (GBR) is a technique where a barrier membrane is placed over the bone defect to prevent cell growth from the connective tissue and epithelium. Titanium (Ti) has excellent mechanical properties and is one of the most frequently used materials in implant dentistry. This study examined how graphene oxide (GO)-coated Ti (GO-Ti) membranes can enhance the osteogenesis of MC3T3-E1 preosteoblasts and promote new bone formation for potential applications to GBR. The physicochemical properties of GO-Ti membranes were characterized by atomic force microscopy, Raman spectroscopy, X-ray diffraction, and contact angle measurements. The cellular behaviors of MC3T3-E1 preosteoblasts on GO-Ti membranes were examined by cell counting kit-8 and alkaline phosphatase (ALP) activity assays. The effects of GO-Ti membranes on bone regeneration were evaluated by implanting them into rat calvarial defects. GO was coated uniformly on Ti substrates, which allowed a decrease in surface roughness and contact. GO-Ti membranes stimulated significantly ALP activity without interfering with their proliferation. Furthermore, GO-Ti membranes enhanced new bone formation significantly in full-thickness calvarial defects without inflammatory responses. Therefore, this suggests that GO-Ti membranes can be applied effectively to GBR because these graphene-coated Ti membranes have potent effects on stimulating osteogenic differentiation and exhibit superior bioactivity.

Effect of montmorillonite on wettability and microstructure properties of zein/montmorillonite nanocomposite nanofiber mats

Zein is a hydrophobic protein produced from maize and has great potential in a number of industrial applications such as food, food coating and food packaging. The objectives of this study are to determine the effects of montmorillonite on the wettability and microstructure properties of zein/montmorillonite nanocomposite nanofiber mats fabricated by the electrospinning technique in ethyl alcohol aqueous solution. The zein/montmorillonite nanofiber mats were characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis and contact angle measurements. This study shows that the introduction of montmorillonite resulted in the improvement of the thermal stability and hydrophilicity for the zein matrix. X-ray diffraction patterns and transmission electron microscopy micrographs suggest the coexistence of intercalated montmorillonite layers over the examined montmorillonite contents. Since montmorillonite is a hydrophilic clay, its addition can be used not only to produce nanomaterials with the already known improved properties but also to enhance the hydrophilicity of material.