Yun Ok Kang

Electrospinning of polysaccharides for regenerative medicine.

Electrospinning techniques enable the production of continuous fibers with dimensions on the scale of nanometers from a wide range of natural and synthetic polymers. The number of recent studies regarding electrospun polysaccharides and their derivatives, which are potentially useful for regenerative medicine, is increasing dramatically. However, difficulties regarding the processibility of the polysaccharides (e.g., poor solubility and high surface tension) have limited their application. In this review, we summarize the characteristics of various polysaccharides such as alginate, cellulose, chitin, chitosan, hyaluronic acid, starch, dextran, and heparin, which are either currently being used or have potential to be used for electrospinning. The recent progress of nanofiber matrices electrospun from polysaccharides and their biomedical applications in tissue engineering, wound dressings, drug delivery, and enzyme immobilization are discussed.

Chitosan-coated poly(vinyl alcohol) nanofibers for wound dressings

A PVA nanofibrous matrix was prepared by electrospinning an aqueous 10 wt % PVA solution. The mean diameter of the PVA nanofibers electrospun from the PVA aqueous solution was 240 nm. The water resistance of the as-spun PVA nanofibrous matrix was improved by physically crosslinking the PVA nanofibers by heat treatment at 150 degrees C for 10 min, which were found to be the optimal heat treatment conditions determined from chemical and morphological considerations. In addition, the heat-treated PVA (H-PVA) nanofibrous matrix was coated with a chitosan solution to construct biomimetic nanofibrous wound dressings. The chitosan-coated PVA (C-PVA) nanofibrous matrix showed less hydrophilic and better tensile properties than the H-PVA nanofibrous matrix. The effect of the chitosan coating on open wound healing in a mouse was examined. The C-PVA and H-PVA nanofibrous matrices showed faster wound healing than the control. The histological examination and mechanical stability revealed the C-PVA nanofibrous matrix to be more effective as a wound-healing accelerator in the early stages of wound healing than the H-PVA nanofibrous matrix.

Epidermal cellular response to poly(vinyl alcohol) nanofibers containing silver nanoparticles.

A heat-treated PVA nanofibrous matrix containing silver (Ag) was prepared by electrospinning an aqueous 10 wt% PVA solution and followed by heat treatment at 150 degrees C for 10 min. The average diameter of the as-spun and heat-treated PVA nanofibers was 330 nm. The heat-treated PVA nanofibrous matrix containing Ag was irradiated with UV light to transform the Ag ions in the nanofibrous matrix into Ag nanoparticles. The in vitro cytotoxicity of the Ag ions and/or nanoparticles on normal human epidermal keratinocytes (NHEK) and fibroblasts (NHEF) cultures was examined. The PVA nanofibrous matrix containing Ag showed slightly higher level of attachment and spreading in the early stage culture (1 h) than the PVA nanofibers without Ag (control). However, compared with the PVA nanofibers without Ag, the heat-treated and UV-irradiated PVA nanofibers, containing mainly Ag ions and nanoparticles, respectively, showed reduced cell attachment and spreading. This shows that both Ag ions and Ag nanoparticles are cytotoxic to NHEK and NHEF. There was no significant difference in cytotoxicity to NHEK and NHEF between Ag ions and Ag nanoparticles. NHEF appeared to be more sensitive to Ag ions or particles than NHEK. In addition, the residual nitrate ions (NO3(-)) in the PVA nanofibers had an adverse effect on the culture of both cells.

Antimicrobial Silver Chloride Nanoparticles Stabilized with Chitosan Oligomer for the Healing of Burns

Recently, numerous compounds have been studied in order to develop antibacterial agents, which can prevent colonized wounds from infection, and assist the wound healing. For this purpose, novel silver chloride nanoparticles stabilized with chitosan oligomer (CHI-AgCl NPs) were synthesized to investigate the influence of antibacterial chitosan oligomer (CHI) exerted by the silver chloride nanoparticles (AgCl NPs) on burn wound healing in a rat model. The CHI-AgCl NPs had a spherical morphology with a mean diameter of 42 ± 15 nm. The burn wound healing of CHI-AgCl NPs ointment was compared with untreated group, Vaseline ointment, and chitosan ointment group. The burn wound treated with CHI-AgCl NPs ointment was completely healed by 14 treatment days, and was similar to normal skin. Particularly, the regenerated collagen density became the highest in the CHI-AgCl NPs ointment group. The CHI-AgCl NPs ointment is considered a suitable healing agent for burn wounds, due to dual antibacterial activity of the AgCl NPs and CHI.

Photocatalytic activities of cellulose-based nanofibers with different silver phases: Silver ions and nanoparticles

Cellulose acetate (CA) nanofibers with 5 wt% AgNO3 were fabricated by electrospinning. The Ag ions in as-spun CA nanofibers were photo-reduced to Ag nanoparticles (NPs) using a UV irradiation, and the UV-irradiated CA nanofibers were then transformed to cellulose nanofibers containing Ag NPs by deacetylation reaction. The size and content of Ag NPs in CA fibers was further increased under the deacetylation condition. The catalytic activity of the CA and cellulose nanofibers with different Ag ions/NPs ratios was examined by two model reactions; photodegradation reaction of methylene blue (MB) and chemiluminescent (CL) reaction of luminol. The Ag ions played an important role as a reducing catalyst of MB, whereas the Ag NPs are more effective than Ag ions in the CL reaction. Therefore, the CA and cellulose nanofibrous matrices with Ag ions or NPs have diverse potential applications as catalytic membranes for sensing to specific chemicals.

Formation of Ag Nanoparticles in PVA Solution and Catalytic Activity of Their Electrospun PVA Nanofibers

Ag nanoparticles (NPs) were prepared by chemical reduction based on green synthesis in an aqueous poly(vinyl alcohol) (PVA) solution with different temperatures and pHs. The PVA and maltose were used as stabilizing and reducing agents, respectively. Silver nitrate (AgNO3) precursor for Ag NPs was also used by 1 wt% on the base of the weight of PVA. The formation of Ag NPs was examined by UV-Vis spectrophotometer, and their size was measured by transmission electron microscopy (TEM), and nanoparticle size analyzer (NPSA). The formation rate of Ag NPs in the PVA solution increased with increasing temperature and pH, whereas the size of Ag NPs stabilized with PVA increased with increasing temperature, or with decreasing pH. Subsequently, the PVA nanofibrous matrix containing Ag NPs was prepared, by electrospinning PVA solution with Ag NPs, and followed by heat treatment. The morphology and crystalline structure of PVA nanofibers with Ag NPs was observed with field emission scanning electron microscopy (FE-SEM), and X-ray diffractometer (XRD), respectively. From the degradation reaction of methylene blue (MB) using PVA nanofibers web and film, it was found that the catalytic activity of PVA matrices with Ag NPs was strongly dependent on the surface area of the PVA matrices.

Functional cellulose-based nanofibers with catalytic activity: Effect of Ag content and Ag phase

The cellulose acetate nanofibers containing Ag ions [CA(as-spun)] were fabricated by electrospinning a CA solution with 0-5wt% AgNO3. The CA(as-spun) was UV-irradiated to produce CA nanofibers containing Ag ions/nanopaticles (NPs) [CA(UV)], and the CA(UV) was deacetylated to cellulose nanofibers with Ag NPs [CA(UV+DA)]. When the CA(UV) was deacetylated with KOH/ethanol solution, the number and size of the Ag NPs were further increased. During the deacetylation reaction, residual Ag(+) ions in the CA(UV) seemed to be reduced by hydroxide anions in KOH/ethanol solution and Ag NPs seemed to be diffused and aggregated further in the cellulose nanofibers. The catalytic activity of cellulose-based nanofibers with different Ag contents or phases was investigated using a reduction of methylene blue (MB) as a model reaction. From a model reaction, Ag ions played an important role as a reducing catalyst of MB.

Composite Nonwoven of Meltblown/Electrospun Polyurethane

Transdermal drug delivery system has various merits compared to oral drug delivery system. Polyurethane nonwovens have been attracted as backing materials for patch and wound dressing, as they have superior stretchability and breathablility to films. The previous works on thermoplastic polyurethane nonwovens were mainly focused on the effects of meltblow processing parameters rather than pore, through which the infection can be occurred. It is critical to reduce the pore size without sacrificing the air permeability. In this study, we developed polyurethane composite nonwovens by combining the meltblowing and electrospinning processes. The composite nonwoven showed less than of mean pore diameter with maintaining the air permeability. The load-elongation curve showed excellent adhesion between the meltblown and the electrospun layers even at large elongation. The excellent pore properties and stretchability of the composite nonwoven can be very useful for patch backing materials.

Characterization of Nanofibrous and Microfibrous Web Fabricated Using Polyurethane-Impregnated Poly(trimethylene terephthalate)

Abstract: Poly(trimethylene terephthalate) (PTT), a semi-crystalline polyester, has been used in many applicationsbecause of its good dyeability and good mechanical properties such as elasticity. Sorona (DuPont) and Corterra (ShellChemicals) are some trade names of PTT. We describe herein a PTT nanofibrous web fabricated by electrospinning,which is a simple technique for generating nanofibers from a polymer solution and a melt. PTT pellets were dissolvedin 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) followed by electrospinning to yield PTT nanofibers with an average diam-eter of 900±97 nm. Then, the PTT nanofibrous web was impregnated with a polyurethane (PU) solution. The resultingmaterial had better mechanical properties and also displayed a lower water contact angle than the PTT nanofibersbecause a relatively hydrophilic PU was coated onto the PTT nanofibrous web. Additionally, the pilling property of thePU-impregnated PTT nanofibrous web was enhanced by the induced welding among the PTT nanofibers because of PUimpregnation. The air permeability of the PTT nanofibrous web was evaluated both before and after PU-impregnation.The results indicated that the PU-impregnated PTT nanofibrous web could be used in various industrial applications.Keywords: poly(trimethylene terephthalate), polyurethane coating, electrospinning, nanofiber, microfiber