Biomedical subjects

Kyekyoon Kevin Kim

Publications and source records attributed to Kyekyoon Kevin Kim.

4 recordsLinked to original sources

PubMed2005

In vitro degradation of polyanhydride/polyester core-shell double-wall microspheres.

Double-wall microspheres (DWMS), comprising distinct polymer core and shell phases, are useful and interesting for controlled-release drug delivery. In particular, the presence of a surface-eroding polymer core may be expected to limit water penetration and, therefore, delay degradation of the core phase and drug release. In this study, solid microspheres and DWMS were fabricated using a surface-eroding polymer (poly[1,6-bis(p-carboxyphenoxy)hexane]; PCPH) and a bulk-eroding polymer (poly(D,L-lactide-co-glycolide); PLG). Erosion of the particles was observed by optical and electron microscopy, while polymer degradation was followed by gel permeation chromatography, during incubation in buffer at 37 degrees C. Degradation and erosion were very different depending on which polymer formed the particle shell. Nevertheless, the relatively thin (approximately 5 microm) PCPH shells could not prevent water penetration, and the PLG cores completely eroded by 6 weeks of incubation.

Chromatography, Gel↗

PubMed2005

Small-molecule release from poly(D,L-lactide)/poly(D,L-lactide-co-glycolide) composite microparticles.

Addition of biodegradable polymer shells surrounding polymeric, drug-loaded microparticles offers the opportunity to control drug release rates. A novel fabrication method was used to produce microparticles with precise control of particle diameter and the thickness of the polymer shell. The effect of shell thickness on release of a model drug, piroxicam, has been clearly shown for 2- to 15-microm thick shells of poly(D,L-lactide) (PDLL) surrounding a poly(D,L-lactide-co-glycolide) (PLG) core and compared to pure PLG microspheres loaded with piroxicam. Furthermore, the core-shell microparticles are compared to microspheres containing blended polymers in the same mass ratios to demonstrate the importance of the core-shell morphology. Combining PDLL(PLG) microcapsules of different shell thicknesses allows nearly constant release rates to be attained for a period of 6 weeks.

Chemistry, Pharmaceutical↗

PubMed2004

Microsphere size, precipitation kinetics and drug distribution control drug release from biodegradable polyanhydride microspheres.

A thorough understanding of the factors affecting drug release mechanisms from surface-erodible polymer devices is critical to the design of optimal delivery systems. Poly(sebacic anhydride) (PSA) microspheres were loaded with three model drug compounds (rhodamine B, p-nitroaniline and piroxicam) with a range of polarities (water solubilities). The drug release profiles from monodisperse particles of three different sizes were compared to release from polydisperse microspheres. Each of the model drugs exhibited different release mechanisms. Drug distribution within the polymer was investigated by laser scanning confocal microscopy and scanning electron microscopy. Rhodamine, the most hydrophilic compound investigated, was localized strongly toward the microsphere surface, while the much more hydrophobic compound, piroxicam, distributed more evenly. Furthermore, all three compounds were most uniformly distributed in the smallest microspheres, most likely due to the competing effects of drug diffusion out of the nascent polymer droplets and the precipitation of polymer upon solvent extraction, which effectively "traps" the drug in the polymer matrix. The differing drug distributions were manifested in the drug release profiles. Rhodamine was released very quickly independent of microsphere size. Thus, extended release profiles may not be obtainable if the drug strongly redistributes in the microspheres. The release of p-nitroaniline was more prolonged, but still showed little dependence on microsphere size. Hence, when water-soluble drugs are encapsulated with hydrophobic polymers, it may be difficult to tailor release profiles by controlling microsphere size. The piroxicam-loaded microspheres exhibit the most interesting release profiles, showing that release duration can be increased by decreasing microsphere size, resulting in a more uniform drug distribution.

Anhydrides↗

PubMed2004

Controlling surface nano-structure using flow-limited field-injection electrostatic spraying (FFESS) of poly(D,L-lactide-co-glycolide).

Improved control of surface micro- and nano-structure may lead to enhanced performance of degradable biomedical devices such as surgical dressings, vascular grafts, tissue engineering scaffolds, sutures, and structures for guided tissue regeneration. An electrohydrodynamic method called flow-limited field-injection electrostatic spraying (FFESS) has been developed as an improved technique for the controlled deposition of polymeric material. Injecting charge using a nano-sharpened tungsten needle in a process called field ionization can efficiently induce an ionic state in a solution of poly(D,L-lactide-co-glycolide) increasing its capacity to carry charge. As a result, sprays have been produced that are finer and more precisely controlled than sprays produced by conventional electrospraying techniques, which employ hypodermic needles as the spray nozzle. Here, the effect of FFESS variables including applied voltage, polymer solution flow rate, and solvent properties (surface tension, viscosity, vapor pressure) on spray performance have been qualitatively evaluated. Under certain conditions, increasing the applied voltage produced an increasingly rough surface morphology. Similarly, by reducing solvent surface tension and increasing solvent vapor pressure, more distinct surface structures could be formed including uniform nanoparticles. Working ranges of the important parameters for the production of specific structure types such as smooth or porous surfaces, non-woven or melded fibers, and distinct or melded nanoparticles have been defined. FFESS technology provides a simple yet powerful technique for fabricating biomedical devices with a precisely defined nano-structure potentially capable of utilizing a broad range of biocompatible polymeric materials.

Biocompatible Materials↗