Hyoun-Hyang Park

Tunable omnidirectional reflection bands and defect modes of a one-dimensional photonic band gap structure with liquid crystals

We have theoretically investigated the tunability of the omnidirectional reflection band (ORB) of a one-dimensional (1D) photonic crystal (PC) consisting of alternating isotropic dielectric and nematic liquid crystal layers by an external electric field. The width of the ORB becomes wide as the external voltage increases, but the center frequency is changed little. The frequency of the defect mode created by inserting a layer of liquid crystals into a 1D dielectric PC is also found to be tunable by the application of external voltage. These properties can be applied to tunable optical filters or optical switches.

Influence of the delivery systems using a microneedle array on the permeation of a hydrophilic molecule, calcein

Despite the advantages of drug delivery through the skin, such as easy accessibility, convenience, prolonged therapy, avoidance of the liver first-pass metabolism and a large surface area, transdermal drug delivery is only used with a small subset of drugs because most compounds cannot cross the skin at therapeutically useful rates. Recently, a new concept was introduced known as microneedles and these could be pierced to effectively deliver drugs using micron-sized needles in a minimally invasive and painless manner. In this study, biocompatible polycarbonate (PC) microneedle arrays with various depths (200 and 500 microm) and densities (45, 99 and 154 ea/cm2) were fabricated using a micro-mechanical process. The skin permeability of a hydrophilic molecule, calcein (622.5D), was examined according to the delivery systems of microneedle, drug loading, depth of the PC microneedle, and density of the PC microneedle. The skin permeability of calcein was the highest when the calcein gel was applied to the skin with the 500 microm-depth PC microneedle, simultaneously. In addition, the skin permeability of calcein was the highest when 0.1g of calcein gel was coupled to the 500 microm-depth PC microneedle (154 ea/cm2) as well as longer microneedles and larger density of microneedles. Taken together, this study suggests that a biocompatible PC microneedle might be a suitable tool for transdermal drug delivery system of hydrophilic molecules with the possible applications to macromolecules such as proteins and peptides.

A novel fabrication process for out-of-plane microneedle sheets of biocompatible polymer

This paper presents a novel process for fabricating out-of-plane microneedle sheets of biocompatible polymer using in-plane microneedles. This process comprises four steps: (1) fabrication of in-plane microneedles using inclined UV lithography and electroforming, (2) conversion of the in-plane microneedles to an out-of-plane microneedle array, (3) fabrication of a negative PDMS mold and (4) fabrication of out-of-plane microneedle sheets of biocompatible polymer by hot embossing. The in-plane microneedles are fabricated with a sharp tip for low insertion forces and are made long to ensure sufficient penetration depth. The in-plane microneedles are converted into an out-of-plane microneedle array to increase the needle density. The negative mold is fabricated for mass-production using a polymer molding technique. The final out-of-plane microneedle sheets are produced using polycarbonate for biocompatibility by employing the hot embossing process. The height of the fabricated needles ranges from 500 to 1500 µm, and the distance between the needles is 500 to 2000 µm. The radii of curvature are approximately 2 µm, while the tip angles are in the range of 39–56°. Most of the geometrical characteristics of the out-of-plane microneedles can be freely controlled for real life applications such as drug delivery, cosmetic delivery and mesotherapy. Since it is also possible to mass-produce the microneedles, this novel process holds sufficient potential for applications in industrial fields.

In vitro characterization of the invasiveness of polymer microneedle against skin

The micro-sized needles could pierce the skin to deliver drugs effectively in a minimally invasive and painless manner. However, there are only a few reports that identify the invasiveness and painlessness of microneedle (MN), and in vitro characterization studies were conducted to examine the invasiveness of MN in experimental animals and healthy volunteers. First, a fluorescent molecule was applied to show the skin holes according to the application time of MN and then the whitening effect in UV-exposed hairless rats was observed using reflectance spectroscopy according to the application time of MN. The extent of skin irritation by the application time of MN in healthy volunteers was determined from the value of skin redness. Regardless of MN application time, skin redness occurred and then disappeared 30 min after removal of MN; this phenomenon was insignificant with the application time of MN. Thus, if the MN was applied, a skin hole appeared, skin redness was observed and then the skin redness disappeared 30 min after removal of MN. Taken together, polymer MN might be a suitable tool for safe transdermal drug delivery of small molecules.

Effect of microneedle on the pharmacokinetics of ketoprofen from its transdermal formulations

Non-invasive transdermal delivery using microneedle arrays was recently introduced to deliver a variety of large and hydrophilic compounds into the skin, including proteins and DNA. In this study, a microneedle array was applied to the delivery of a hydrophobic drug, ketoprofen, to determine if transdermal delivery in rats can be improved without the need for permeation enhancers. The ability of a microneedle to increase the skin permeability of ketoprofen was tested using the following procedure. A microneedle array was inserted into the lower back skin of a rat using a clip for 10 min. Subsequently, 24 mg/kg of a ketoprofen gel was loaded on the same site where the microneedle had been applied. Simultaneously, the microneedle was coated with 24 mg/kg of a ketoprofen gel, and inserted into the skin using a clip for 10 min. As a negative control experiment, only 24 mg/kg of the ketoprofen gel was applied to the shaved lower back of a rat. Blood samples were taken at the indicated times. The plasma concentration (Cp) was obtained as a function of time (t), and the pharmacokinetic parameters were calculated using the BE program. The group loaded with the microneedle coated with ketoprofen gel showed a 1.86-fold and 2.86-fold increase in the AUC and Cmax compared with the ketoprofen gel alone group. These results suggest that a microneedle can be an ideal tool for transdermal delivery products.

Effect of applying modes of the polymer microneedle- roller on the permeation of l-ascorbic acid in rats

Despite the advantages of drug delivery through skin, transdermal drug delivery is only used with a small subset of drugs because most compounds cannot cross the skin at therapeutically useful rates. Recently, a new concept known as microneedle was introduced and could be used to pierce effectively to deliver drugs using micron-sized needles in a minimally invasive and painless manner. In this study, the polymer microneedle-roller was fabricated so that it can be applied into the permeation of l-ascorbic acid. Moreover, a recent publication suggested the possibility of ascorbic acid 2-phosphate as a hair restorer; hence, this study was carried out to check the effect of l-ascorbic acid itself on the hair growing rate in rats according to the presence of various application frequencies of the polymer microneedle-roller. When the polymer microneedle-roller was applied nine times with four directions into rat’s shaved skin, the permeation of l-ascorbic acid increased by 10.54-fold compared to that of the absence of the polymer microneedle-roller. The histological examination revealed that the skin pretreated with various application frequencies of the polymer microneedle-roller had more transport pathways. The faster hair growing phenomenon was observed in the presence of polymer microneedle-roller compared to the absence of the polymer microneedle-roller.

Density measurement of particles in rf silane plasmas by the multipass laser extinction method

Measurement of the time evolution of the particle number density was investigated in rf silane plasmas by using the multipass laser extinction method. A He–Ne laser beam underwent multiple reflections on one horizontal plane of the plasma. The extinction signal increased in proportion to the beam pass numbers. A 1011cm−3 density of 8nm radius particles was measured at 10s in a 32mTorr and 50W discharge using nine passes. The primary particle density was obtained by comparing the measured particle sizes with the calculated sizes from the light extinction signals and the Brownian free molecule coagulation model.

Charge dependence of nano-particle growth in silane plasmas under UV irradiation

The controlled generation of nano-particles has been an important issue for the nano-structure formation in processing plasmas. We observed that the particle growth under UV irradiation was enhanced due to electric charge reduction of the particles, suggesting that the variation of particle charges could be a control parameter for the particle growth. The particle growth variation by UV irradiation is well described by the particle coagulation model with time- dependent particle charges in consideration, where predator particles grow by adsorbing a few nanometer-sized proto-particles.

An indirect electric field-induced control in directional migration of rat mesenchymal stem cells

We present the efficacy of an indirect E-field on the directional migration of rat mesenchymal stem cell (MSC). To avoid current flow through culture media and cell, E-fields were generated without exposing electrodes directly to the cell media. MSC migration was observed during wound closure in presence of indirect E-field. MSC migration depended on the E-field strength and occurs predominantly in the anodal direction. Indirect E-field therapy proved as tentative tool for controlled cell movement and healing.

Efficacy of an AC sinusoidal electric field for apoptosis induction in lung carcinoma cells (A549)

An AC sinusoidal electric field was applied to lung carcinoma cells for the induction of apoptosis. The occurrence of apoptosis was determined by analysis of Annexin V/PI and DNA fragmentation. Additional evidence of apoptosis was confirmed by caspase-3 cleavage and disruption of mitochondrial membrane potential. These results demonstrated that the expression of apoptosis can be controlled by varying the magnitude and the duration of the field, and that the application of an AC electric field can stimulate the apoptosis via mitochondria-mediated pathway.