• Journal of Pharmaceutical Investigation
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• v.30 no.4
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• pp.253-258
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• 2000

In order to design the oral vaccine delivery system, we prepared the alginate micro spheres containing GFP (green fluorescent protein) as a model drug by spray method. To optimize the preparation conditions of microspheres, we investigated the effects of various parameters including nozzle pressure, nozzle opening angle, and concentrations of sodium alginate and calcium chloride. The prepared microspheres were evaluated by measuring their sizes, loading efficiency, and morphology. The particle size of microspheres was affected by the concentration of sodium alginate and calcium chloride, nozzle pressure, and nozzle opening angle. As the concentration of sodium alginate increased, GFP loading efficiency and particles size of microsphere also increased. However, it was observed to be difficult to spray the sodium alginate solution with concentration greater than 1.5% (w/v), due to high viscosity. The pressure over $3\;kgf/cm^2$ didn't affect the size of particles. As a result, the spraying method enabled us to prepare microspheres for oral vaccine delivery system. In this study, microspheres prepared with 1% (w/v) sodium alginate had greater loading efficiency and better spherical shape.

• Macromolecular Research
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• v.8 no.2
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• pp.80-88
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• 2000

Biodegradable microspheres were prepared with poly(L-lactide-co-glycolide) (PLGA, 75 : 25 by mole ratio) by an oil/oil solvent evaporation method for the sustained release of anti-AIDS virus agent, AZT The microspheres of relatively narrow size distribution (7.6$\pm$ 3.8 ㎛) were obtained by controlling the fabrication conditions. The shape of microspheres prepared was smooth and spherical. The efficiency of AZT loading into the PLGA microsphere was over 93% compared to that below 15% for microspheres by a conventional water/oil/water method. The effects of Preparation conditions on the morphology and in vitro AZT release pattern were investigated. in vitro release studies showed that different release pattern and release rates could be achieved by simply modifying factors in the fabrication conditions such as the type and amount of surfactant, initial amount of loaded drug, the temperature of solvent evaporation, and so on. PLCA microspheres prepared by 5% of initial drug loading, 1.0% (w/w) of surfactant concentration, and 25$\^{C}$ of solvent evaporation temperature were free from initial burst effect and a near-zero order sustained release was observed. Possible mechanisms of the near-zero order sustained release for our system have been proposed.

• Radiation Oncology Journal
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• v.12 no.3
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• pp.295-300
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• 1994

It was the purpose of present study to develop a new thermoseed for heating deep-seated tumors and assessment of the effect of magnetic control on thermoseeds. Aqueous suspension of iron micro spheres (Ferropolysaccharide) was injected directly into the VX-2 hepatoma and heated with 1.2 MHz inductive radiofrequency unit. Aqueous thermoseed suspension was delivered to the tumor by simple percutaneous injection. The limitation of the thermoseed heating method is the positional change of thermoseed particles in the tumor after implantation. The thermoseed particles could enter the systemic blood circulation and cause a severe embolization of a critical organ. To minimize this limitation, we have used the magnetic control after loading the thermoseed in the tumor, W hen ferropolysaccharides were exposed to a strong magnetic field, they magnetized and subsequently exerted a magnetic force on each other, forming larger aggregates of particles. The size of aggregated Particles were too big to enter the systemic blood circulation. Thus, unlike other thermoseed method, we hold the thermoseed particles stationary in the tumor. The temperature of the injected site and immediate vicinity elevated by $4-5^{\circ}C$. The temperature of the surrounding normal hepatic tissue elevated by $1-2^{circ}C$ only. The heating effect within the tumor was variable depending on the density of ferromagnetic aqueous suspension. Our results suggest that inductive heating of tumor injected with ferropolysaccharide solution offers the possibility of effective heat delivery to the defined tumor volume, which is difficult to heat with other heating devices.

• Macromolecular Research
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• v.13 no.3
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• pp.187-193
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• 2005

The TEMPO-mediated living free-radical bulk and dispersion polymerization of styrene in the presence of camphorsulfonic acid (CSA) are investigated. In the absence of TEMPO and CSA in the bulk polymerization, a conversion of $93\%$ is achieved within 6 hr of polymerization. When only TEMPO is involved in this polymerization, the pseudo-living free-radical polymerization is well achieved, however, the polymerization rate becomes quite slow. This retardation of the polymerization rate is solved by the addition of a low concentration of CSA. In the TEMPO-mediated dispersion polymerization in the presence of CSA, similar trends in the conversion, kinetics, and PDI are observed as those observed in the case of bulk polymerization. When only TEMPO is used in the dispersion polymerization, the resulting particle size becomes quite broad, due to the prolonged polymerization time. However, when a 1.0 molar ratio of CSA to TEMPO is added to the TEMPO-mediated dispersion polymerization, fairly mono-disperse PS microspheres having an average size of 5.83 $\mu$m and a CV of 3.4$\%$ are successfully obtained, due to the narrow molecular weight distribution of the intermediate oligomers and shortening of the polymerization time. This result indicates that the addition of CSA to the TEMPO-mediated bulk and the use of dispersion polymerization not only shortens the polymerization time, but also greatly improves the uniformity of the microspheres.

• Journal of Pharmaceutical Investigation
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• v.38 no.1
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• pp.63-72
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• 2008

Meloxicam-loaded microspheres were prepared with poly(D,L-lactic acid)(PLA) by a solvent-emulsion evaporation method. The morphology, particle size, drug loading capacity, drug entrapment efficiency (EE) and release patterns of drug were investigated in vitro. Various batches of micro spheres with different size and drug content were obtained by changing the ratio of meloxicam to $PLA^{\circ}{\AE}s$ with different molecular weight, PLA concentration in the dispersed phase and stirring rate. Meloxicam crystals on microsphere surface, which were released rapidly and could act as a loading dose, were observed with increasing drug content. The release rate was increased with increase in drug contents and decrease in the molecular weight of PLA. Microspheres prepared with smaller molecular weight produced faster drug release rate. The release rate of meloxicam for long-acting injectable delivery system in vitro, which would aid in predicting in vivo release profile, could be controlled by properly optimizing various factors affecting characteristics of microspheres. Blood concentration-time profile of meloxicam after intramuscular injection of meloxicam-loaded microspheres in rabbits showed possibility of long term application of this system in clinical settings.

• Computers and Concrete
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• v.28 no.5
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• pp.521-532
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• 2021

Present paper focuses on the modeling of size effect on the compressive strength of normal concrete with the application of Discrete Element Method (DEM). Test specimens with different size and shape were cast and uniaxial compressive strength test was performed on each sample. Five different concrete mixes were used, all belonging to a different normal strength concrete class (C20/25, C30/37, C35/45, C45/55, and C50/60). The numerical simulations were carried out by using the PFC 5 software, which applies rigid spheres and contacts between them to model the material. DEM modeling of size effect could be advantageous because the development of micro-cracks in the material can be observed and the failure mode can be visualized. The series of experiments were repeated with the model after calibration. The relationship of the parallel bond strength of the contacts and the laboratory compressive strength test was analyzed by aiming to determine a relation between the compressive strength and the bond strength of different sized models. An equation was derived based on Bazant's size effect law to estimate the parallel bond strength of differently sized specimens. The parameters of the equation were optimized based on measurement data using nonlinear least-squares method with SSE (sum of squared errors) objective function. The laboratory test results showed a good agreement with the literature data (compressive strength is decreasing with the increase of the size of the specimen regardless of the shape). The derived estimation models showed strong correlation with the measurement data. The results indicated that the size effect is stronger on concretes with lower strength class due to the higher level of inhomogeneity of the material. It was observed that size effect is more significant on cube specimens than on cylinder samples, which can be caused by the side ratios of the specimens and the size of the purely compressed zone. A limit value for the minimum size of DE model for cubes and cylinder was determined, above which the size effect on compressive strength can be neglected within the investigated size range. The relationship of model size (particle number) and computational time was analyzed and a method to decrease the computational time (number of iterations) of material genesis is proposed.

• Journal of the Korean Geographical Society
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• v.43 no.6
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• pp.894-913
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• 2008

This study examines scale issues in the contemporary feminist migration literature. Scale appears as important, yet poorly understood concept in this field of study. The increasing attention to the feminization of migration requires not only gendered, but also scalar-sensitive approaches. Feminists criticize the conventional approach to the migration as a gender-blind approach that privileges national scale around which migration processes are organized. Claiming multiscalar and interscalar analyses, they propose investigations ranging from macro to micro processes which include globalized gendered division of labor, transnational family networks, and reproduction which takes place in and through the bodies and homes of migrant women. The migrant women, the major actors in recent transnational migration, cross various borders: the national boundaries and the public and private divides, in particular. This crossover can unsettle patriarchal gender relations which have been established based on the physical and symbolic division of nation-states and public/private spheres. Blurring these divisions accompanies social construction of various scales. The transnational family networks of migrant women, for example, show the construction of a transnational scale by migrant women as well as globalization from below. This paper points out misunderstandings of scale in the feminist migration literature and attempts to fill the gaps by introducing the meanings and implications of scales developed mostly by feminist geographers. In so doing, it promotes the interdisciplinary communication.

• Polymer(Korea)
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• v.33 no.1
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• pp.26-32
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• 2009

The aim of this research was to prepare microparticulate systems based on poly (lactide-co-glycolide)(PLGA) for the local release of ipriflavone in order to reduce bone loss. We developed the IP loaded PLGA microspheres using relatively simple oil-in-water(O/W) solvent evaporation method. HPLC was used to perform the in vitro release test of IP and morphology of cell attached on the micro-spheres was investigated using SEM. Cytotoxicity was assayed by cell counting kit-8 (CCK-8) test. Osteogenic differential cells were analyzed by ALP activity. Through RT-PCR analysis, we observed osteocalcin, ALP, and Type I collagen mRNA expression. The release of IP in vitro was more prolonged over 42 days and IP/PLGA microspheres showed the improvement on the cell proliferation, ALP activity and RT-PCR comparing with control (only PLGA). This initial research will be used to direct future work involved in developing this composite injectable bone tissue engineering system.