• Polymer(Korea)
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• v.29 no.3
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• pp.282-287
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• 2005

A novel ice particle leaching method for fabrication of porous and biodegradable PLGA scaffold has been proposed for the application to tissue engineering. After uniform mixing of poly(L-lactide-co-glycolide) (PLGA) and bovine serum albumin-fluorescein isothiocyanate (FITC-BSA), the FITC-BSA loaded scaffold was fabricated by adding various ratio of ice particle. The release profiles of FITC-BSA were examined using pH 7.4 PBS for 28 days at $37^{circ}$. The release amount was determined by fluorescence intensity by using the fluorescence spectrophotometer and the morphological change of the scaffolds was observed by scanning electron microscope. The release initial burst of BSA containing scaffolds was lower than that of simple dipping scaffolds resulting in constant release aspect. Although the BSA concentration increased. the initial burst was not increased. As a result of this study, it can be suggested that ice particle leaching method for the tissue engineered scaffold miff be very useful and it is possible to impregnate with water soluble factors like cytokine. We suggest that ice particle leaching method may be useful to tissue engineered organ regeneration.

• Polymer(Korea)
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• v.31 no.3
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• pp.201-205
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• 2007

Biodegradable polymers such as polylactide, polyglycolide and poly (lactide- co-glycolide) (PLGA) have been extensively investigated because of easily controlled drug release rate, completely degradable materials without the toxic by-product, and good biocompatibility. But, according to the bulk erosion property of PLGA in vitro test, it had the disadvantage that first-order release reduced releasing amount slowly after excessive initial burst. In this study we used PLGA powder obtained through recrystallization to revise bulk erosion property of PLGA. The PLGA used in this study was prepared by vacuum drying method and to estimate release profiles of BCNU loaded PLGA wafer. We also evaluated the release profile of drug with the water soluble additive. It was found that the drug loaded PLGA recrystallized by vacuum drying method exhibited the initial burst and the constant rate of drug release compared to that prepared by a conventional method.

• Polymer(Korea)
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• v.32 no.3
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• pp.199-205
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• 2008

In this study, we fabricated poly (lactide-co-glycolide) (PLGA) scaffold modified with small intestinal submucosa (SIS) as a drug delivery matrix of bioactive molecules. SIS derived from the submucosa layer of porcine intestine has been widely used as biomaterial because of low immune response. PLGA scaffold was prepared by the method of solvent casting/salt leaching. Novel composite scaffolds of SIS/PLGA were manufactured by simple immersion method of PLGA scaffold in SIS solution under vacuum. SEM observation shows that PLGA and SIS/PLGA scaffolds have interconnective and open pores. Especially, SIS/PLGA scaffold showed that micro-sponge of SIS with interconnected pore structures were formed in the pores of PLGA scaffold. In order to assay release profile of proteins, we manufactured FITC conjugated BSA loaded PLGA and SIS/PLGA scaffold. And the release amount was identified by fluorescence intensity using the fluorescence spectrophotometer. The initial burst of BSA containing SIS/PLGA scaffolds was lower than that of PLGA scaffolds resulting in constant release. And release of BSA in SIS/PLGA scaffold was fast and incremental because of the increased content of BSA. In conclusion, we confirmed that penetrated SIS solution prevented the initial burst of BSA and PLGA modified with SIS scaffold is useful as protein carriers with controlled release pattern.

• Polymer(Korea)
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• v.33 no.1
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• pp.7-12
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• 2009

PLGA microspheres have been known as an injectable system for tissue engineering. The purpose of this study was to investigate the condition of emulsion formation and cell adhesion on the microsphere surface. BSA-loaded PLGA microsphere was fabricated by oil-in-water (O/W) and water-in-oil-in-water (W/O/W) solvent evaporation method. Sodium alginate was dissolved in water phase to control initial burst release and to improve lag time by PLGA bulk degradation. In addition, the morphology of cells attached on the micro spheres was studied using a scanning electron microscopy (SEM). Cellular proliferation behavior of human disc cells cultivated on PLGA micro spheres was analyzed using a MTT assay. MTT assay revealed that the cells can attach and proliferate on PLGA microspheres. According to these results, we concluded that BSA -loaded alginate/PLGA microspheres can be used as an injectable system for tissue engineering application.

• Macromolecular Research
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• v.17 no.10
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• pp.734-738
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• 2009

Biodegradable, pH-sensitive, glycol chitosan (GC) hydrogels were prepared using divinyl adipate (DVA) as a crosslinker and acetic acid as a catalyst. DVA has highly reactive double vinyl ester groups and GC contains a high density of hydroxyl groups, with two in every glucosamine unit. The transesterification reaction between vinyl esters and hydroxyl groups produced crosslinked GC hydrogels. The initial crosslinking reaction was monitored by measuring the viscosity of the reaction mixture. When DVA was added to the GC solution and heated to $50^{\circ}C$, the viscosity of the GC solution gradually increased, implying a crosslinking reaction and hydrogel formation. A new peak from the ester group was observed in the FTIR spectra of the GC hydrogels, confirming the crosslinking reaction. The synthesized GC hydrogel showed pH-dependent water absorbency, mainly due to the presence of amine groups ($-NH_2$) at the C-2 position of the glucosamine unit of GC. The water absorbency greatly increased at acidic pH and slightly decreased at alkaline pH. The GC hydrogel gradually degraded in $37^{\circ}C$ water due to hydrolysis of the ester bonds, which were intermolecular crosslinking sites. A red dye, 5-carboxyltetramethyl-rhodamine (CTMR), was entrapped in the GC hydrogels as a model compound. CTMR was released from GC hydrogels in two steps: an initial burst release mainly due to desorption and diffusion, and a second sustained release possibly due to gradual degradation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.5
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• pp.383-390
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• 2013

The reduction of the maximum acceleration which causes shock for a missile is very important to prevent abnormal operation of a missile and decrease size and cost of missile components. Because the maximum acceleration created by operation of an ejection gas generator occurs in the initial ejection stage, the design parameters which affect initial ejection stage were examined. The igniter and the nozzle closure were selected as design parameters of a gas generator. The maximum acceleration created by the gas generator was examined experimentally by changing of the design parameters. Finally the reduction effect of the maximum acceleration was compared quantitatively by static fire test of a gas generator. The maximum acceleration of the best model which was applied to each optimal design parameter was about 68% reduced than that of the reference model.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.4
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• pp.67-75
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• 2009

Multi-layered video coding that provides scalability across the visual content has emerged for easily adaptive service over current heterogeneous network. However, the network is still error prone environment so that video service may suffer packet loss or erroneous decoding of the video. Especially distortion caused by the burst error may propagate to several pictures until intra refreshing, which will raise a terrific degradation of picture quality. To overcome the problem at terminal independently, we propose a new error concealment algorithm for the multi-layered video coding. The proposed method uses the similarity of between layers in the multi-layered video coding and POCS (Projections Onto Convex Sets) which is a powerful error concealment tool, but heavily dependent on initial values. To find adequate initial value which can reduce iteration times as well as achieve high performance, we took consideration into both features of layered approach coding and the correlation in neighbor blocks. The simulation results show that the proposed concealment method works well.

• Biomaterials and Biomechanics in Bioengineering
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• v.1 no.1
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• pp.13-25
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• 2014

In the current study, a drug-eluting stent coated with biodegradable polymers and sirolimus was developed by using an ultrasonic nanocoater and characterized in aspects of surface smoothness and coating thickness. In addition, in vitro release profiles of sirolimus by changing top coating layer with different biodegradable polymers were investigated. Smooth surfaces with variable thickness could be fabricated by optimizing polymer concentration, flow rate, nozzle-tip distance, gas pressure, various solvents and ultrasonic power. Smooth surface could be generated by using volatile solvents (acetone, chloroform, and methylene chloride) or post-treating with solvent vapor. Coating thickness could be controlled by varying injection volume or polymer concentration, and higher concentration could reduce the coating time while obtaining the same thickness. The thickness measurement was the most effectively performed by a conventional cutting method among three different methods that were investigated in this study. Release profiles of sirolimus were effectively controlled by changing polymers for top layer. PLGA made the release rate 3 times faster than PDLLA and PLLA and all top layers prevented burst release at the initial phase of profiles. Our results will provide useful and informative knowledge for developing drug-eluting stents, especially coated with biodegradable polymers.

• KSBB Journal
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• v.23 no.5
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• pp.408-412
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• 2008

The rosiglitazone loaded poly (lactide-co-glycolide) (PLGA) nanoparticles (NPs) were prepared by the emulsion-evaporation method and optimized for particle size and entrapment efficiency. The optimized particles were 140-180 nm in size with narrow size distribution and 80% entrapment efficiency at 1% w/w initial drug loading when prepared with 1-3% w/v of PVA as a surfactant. These particulate carriers exhibited controlled in vitro release of rosiglitazone for 36 hrs at a nearly constant rate after 4 hrs release. In conclusion, these results indicate that PLGA NPs have greater potential for oral delivery of rosiglitazone.

• Biomolecules & Therapeutics
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• v.22 no.2
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• pp.161-165
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• 2014

The main purpose of this study was to develop a novel, in situ gel system for sustained delivery of ranitidine hydrochloride. Ranitidine in situ gels at 0.2%, 0.5%, and 1.0% gellan gum concentration (w/v) were prepared, respectively, and characterized in terms of preparation, viscosity and in vitro release. The viscosity of the gellan gum formulations in solution increased with increasing concentrations of gellan gum. In vitro study showed that the release of ranitidine from these gels was characterized by an initial phase of high release (burst effect) and translated to the second phase of moderate release. Single photon emission computing tomography technique was used to evaluate the stomach residence time of gel containing $^{99m}Tc$ tracer. The animal experiment suggested in situ gel had feasibility of forming gels in stomach and sustained the ranitidine release from the gels over the period of at least 8 h. In conclusion, the in situ gel system is a promising approach for the oral delivery of ranitidine for the therapeutic effects improvement.