Papers by Author: John M. Rhee

Abstract: We developed the successive roller type of microneedle system without pain to improve the permeation of drug through the skin barrier. The permeation rates of FITC-ovalbumin (OVA, MW: 45,000g/mole), FITC-insulin (MW: 5,733 g/mole) and FITC-bufexamac (MW: 227.37 g/mole) as model drugs were determined by modified Franz diffusion cells using the microneedle device with four times treatment. The average penetration fluxes of FITC- OVA, FITC-insulin and FITC-bufexamac were steeply increased from 13.4 to 83.3, 10.1 to 110.6 and 11.9 to 242.6 pmol/cm2 with treatment for 12 hrs, respectively. The lower the molecular weight of the drugs, the more the permeation flux investigated. In conclusion, we confirmed the possibility of the application for transdermal delivery of the larger molecular drugs as protein using the designed microneedle treatment device.

Abstract: The double-layered microspheres play an important role in controlling drug delivery for pharmaceutical application, because of the low initial burst compared with single-layered spheres and targetable delivery to specific organ. But it has drawback in loading drug and controlling size. In this study, we developed double-layered spheres using relatively simple oil-in-water (O/W) solvent evaporation method using bovine serum albumin (BSA) as water-soluble protein and poly(D,L-lactide-co-glycolide) (PLGA). BSA/PLGA double-layered microspheres were fabricated using O/W solvent evaporation method and investigated the specific character of double-layered microspheres according to the kind of surfactants. In SEM observation, double layered microsphere had spherical shape and smooth surface without pores. And the double layered microsphere using O/W solvent evaporation method was transparency because of slow evaporation of solvent. In fluorescent observation, we observed the fluorescent core in the double-walled spheres composed of FITC-BSA and PLGA using fluorescent observation. In the case of polyvinylalcohol as emulsifier, the yield was better than gelatin. As decreased concentration of PLGA, the size of double-layered microspheres deceased.

Abstract: In order to application for the tissue engineered intervertebral disc (IVD), we designed the synthetic/natural hybrid scaffolds with poly(lactide-co-glycolide) (PLGA) and small intestine submucosa (SIS). SIS has been widely used as a biomaterial because SIS consists of various collagens and cytokines. SIS, however, possesses disadvantages such as their weak mechanical properties and uncontrolled degradation. Novel composite scaffolds of PLGA/SIS were manufactured by simple immersion method of PLGA scaffolds in SIS solution under vacuum. Then SIS was crosslinked. Also, PLGA scaffolds and SIS sponges were manufactured by solvent casting/salt leaching and freeze-dried methods, respectively. We evaluated pore structure, porosity, water absorption ability and cell viability of three types of scaffolds for the application of IVD.

Abstract: Recently, it has been studied tissue engineered technique as novel approaches for treatment of the degenerative intervertebral disc (IVD). We designed the hybrid type of IVD mimicked scaffolds with poly(lactide-co-glycolide) (PLGA) and methoxypoly(ethyleneglycol)- poly(
-caprolactone) (MPEG-PCL) diblock copolymers in order to application for the tissue engineered IVD. The MPEG-PCL solutions formed a gel-to-sol phase transitions as the temperature was increasesd. MPEG-PCL diblock copolymers were prepared by ring opening polymerization, and then nucleus pulposus (NP) cell was impregnated. Also, in order to restore annulus fibrosus (AF), we fabricated PLGA scaffold by solvent casting/salt leaching method. We confirmed disc cell function in manufactured scaffold through MTT assay in vitro and gross morphology and special staining in vivo for the possibility of the application of tissue engineering techniques.

Abstract: This study was designed to investigate the influence of demineralized bone particles (DBP)/PLGA hybrid scaffold on angiogenesis and osteogenesis in a calvarial defect model. DBP/PLGA scaffolds were manufactured by solvent casting/salt leaching method, and each scaffold contained 0, 10, 20, 40, and 80 wt% DBP of PLGA, respectively. A total of 34 rats were operated and bicortical holes were placed on their calvaria. The defects were filled with different ratio DBP/PLGA scaffolds. After 3, 7, 14, and 28 days, specimens were taken and, histologic, immunohistologic and RT-PCR analyses were carried out concerning number of vessels and density of regenerated bone, and angiogenic activation. On days 7, in all experimental groups, bone formation occurred in a direction from defected margin of calvarium to center of implanted scaffold and new vessel formation took place in front of the osteogenic regeneration front. We found that the 20 and 40 wt% DBP/PLGA scaffold was superior in its ability to regenerate new bone, induced more intensive formation of microvasculature and expressed in a higher level of osteocalcin mRNA than other groups.

Abstract: Electrochemical double layer capacitors (EDLCs) are promising high power energy sources for many different applications where high power density, high cycle efficiency and long cycle life are needed. However, because the energy density of EDLCs is small compared to that of rechargeable batteries one needs to increase the capacitance of EDLCs. The nanofiber diameters range from 50 nm to 400 nm, depending on the concentration of polymer solution types, tip-to-collector distance, applied voltage, and viscosity of the solution. The main advantage of the electrospinning process is that it is a simple means to prepare continuous fibers with unusually large surface to volume ratios and pore structure surfaces. So, feature of nanofiber webs are the high specific surface area developed by creating pores on the nanofiber surface. In this work, the multiwalled carbon nanotubes embedded polyacrylonitrile solutions in N,N-dimethylformamide (DMF) were electrospun to be webs consisting of 350 nm ultrafine nanofibers, which were used to produce a series of activated carbon nanofibers with developed mesoporosity and high electrical conductivity through stabilization, carbonization-activation processes.