Sung Wook Choi

Fabrication of a BMP-2-immobilized porous microsphere modified by heparin for bone tissue engineering.

The purpose of this study was to fabricate BMP-2-immobilized porous poly(lactide-co-glycolide) (PLGA) microspheres (PMS) modified with heparin for bone regeneration. A fluidic device was used to fabricate PMS and the fabricated PMS was modified with heparin-dopamine (Hep-DOPA). Bone morphogenic protein-2 (BMP-2) was immobilized on the heparinized PMS (Hep-PMS) via electrostatic interactions. Both PMS and modified PMS were characterized using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). MG-63 cell activity on PMS and modified PMS were assessed via alkaline phosphatase (ALP) activity, calcium deposition, and osteocalcin and osteopontin mRNA expression. Immobilized Hep-DOPA and BMP-2 on PMS were demonstrated by XPS analysis. BMP-2-immobilized Hep-PMS provided significantly higher ALP activity, calcium deposition, and osteocalcin and osteopontin mRNA expression compared to PMS alone. These results suggest that BMP-2-immobilized Hep-PMS effectively improves MG-63 cell activity. In conclusion, BMP-2-immobilized Hep-PMS can be used to effectively regenerate bone defects.

Synthesis and characterization of PEO–PCL–PEO triblock copolymers: Effects of the PCL chain length on the physical property of W1/O/W2 multiple emulsions

A series of poly(ethylene glycol)-block-poly(epsilon-caprolactone)-block-poly(ethylene glycol) (PEO-PCL-PEO) triblock copolymers were prepared and then used for the investigation of the effects of the ratio of epsilon-caprolactone to poly(ethylene glycol) (i.e., [CL]/[EO]) on the physical properties of water-in-oil-in-water (W(1)/O/W(2)) multiple emulsions containing a model reagent, ascorbic acid-2-glucoside (AA2G). In the synthesis, the [CL]/[EO] was varied from 0.11 to 0.31. The molecular weights and compositions of PEO-PCL-PEO were determined by GPC and (1)H NMR analyses. Thermal behavior and crystal formation were studied by DSC, XRD, FT-IR, and polarized optical microscopy (POM). Aggregate behavior of PEO-PCL-PEO was confirmed by DLS, UV, and (1)H NMR. Morphology and relative stiffness of the W(1)/O/W(2) multiple emulsions in the presence of PEO-PCL-PEO were studied by confocal laser scanning microscopy (CLSM) and rheometer. Variation in the [CL]/[EO] significantly affects the crystalline temperature and spherulite morphology of PEO-PCL-PEO. As the [CL]/[EO] increases, the CMCs of PEO-PCL-PEO decreases and the slope of aggregate size reduction against the copolymer concentration becomes steeper except for the lowest [CL]/[EO] value of PEO-PCL-PEO (i.e., P-222). P-222 significantly increases the viscosity of continuous (W(2)) phase, which implies the copolymer would exist in the W(2) phase. On the other hand, the triblock copolymers with relatively high [CL]/[EO] ratios mainly contribute to the size reduction of multiple emulsions and the formation of a firm wall structure. The particle size of the multiple emulsion decreases and the elastic modulus increased as [CL]/[EO] increases, confirmed by microscopic and rheometric analyses.

Effect of lactoferrin-impregnated porous poly(lactide-co-glycolide) (PLGA) microspheres on osteogenic differentiation of rabbit adipose-derived stem cells (rADSCs).

The aim of this study was to develop lactoferrin (LF)-impregnated porous poly(lactide-co-glycolide) (PLGA) microspheres (PMs) to induce osteogenic differentiation of rabbit adipose-derived stem cells (rADSCs). Porous PLGA PMs were fabricated by a fluidic device and their surfaces were modified with heparin-dopamine (Hep-DOPA). Then, LF (100μg, 500μg, and 1000μg) was impregnated on the surface of heparinized PMs (Hep-PMs) via electrostatic interactions to yield LF-impregnated PMs. PMs and modified PMs were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Osteogenic differentiation of rADSCs on PMs and modified PMs was demonstrated by alkaline phosphatase (ALP) activity, calcium deposition, and mRNA expression of osteocalcin and osteopontin. Successful immobilization of Hep-DOPA and LF on the surface of PMs was confirmed by XPS analysis. LF-impregnated PMs generated significantly greater ALP activity, calcium deposition, and mRNA expression of osteocalcin and osteopontin compared with PMs. These results suggested that LF-impregnated PMs effectively induced osteogenic differentiation of rADSCs.

A facile method for the preparation of monodisperse beads with uniform pore sizes for cell culture

This paper describes a facile method for the preparation of porous gelatin beads with uniform pore sizes using a simple fluidic device and their application as supporting materials for cell culture. An aqueous gelatin droplet containing many uniform toluene droplets, produced in the fluidic device, is dropped into liquid nitrogen for instant freezing and the small toluene droplets evolve into pores in the gelatin beads after removal of toluene and then freeze-drying. The porous gelatin beads exhibit a uniform pore size and monodisperse diameter as well as large open pores at the surface. Fluorescence microscopy images of fibroblast-loaded gelatin beads confirm the attachment and proliferation of the cells throughout the porous gelatin beads.

Effects of surface characteristics on non-specific agglutination in latex immunoagglutination antibody assay

Abstract To monitor the non-specific agglutination (NSA) in latex immunoagglutination assay, antigen-coated structured latex particles, which have carboxyl and sulphonate groups as hydrophilic domains, were tested for an antibody assay. Sulphonated particles showed NSA in high antibody concentrations, where no surface antigen left to match with. This was further justified with the more stable highly sulphonated particles, which showed higher degree of NSA. It can therefore be confirmed that sulphonate groups cause (or at least promote) NSA, while carboxyl groups do not. Surface coverage over 17% was not fully utilized for antigen–antibody reaction, due to the prozone effect. The difference in sensitivity of particles was explained in terms of our new explanations on the governing interactions of protein adsorption.

Uniform tricalcium phosphate beads with an open porous structure for tissue engineering

Uniform tricalcium phosphate (TCP) porous beads with micro and macro pore sizes were fabricated using a simple fluidic device. For micro-porous TCP beads, an aqueous gelatin mixture containing TCP powder was introduced as the discontinuous phase into the fluidic device, where a toluene phase served as the continuous phase. The resulting aqueous TCP droplets were instantly frozen at -20°C and freeze-dried, followed by calcination at 1200°C. An oil-in-water-in-oil (O/W/O) emulsion templating method was employed to fabricate macro-porous TCP beads. An oil-in-water (O/W) emulsion was introduced into the fluidic device as the discontinuous phase with all other experimental conditions the same as for the micro-porous TCP beads. Uniform macro-porous TCP beads with a highly porous structure were finally obtained after freeze-drying and calcination. Large pore size and good interconnectivity of the macro-porous TCP beads were confirmed by scanning electron microscopy and porosimetry. In addition, penetration of host tissue into the macro-pores of the TCP beads was demonstrated by subcutaneously implanting the two types of porous TCP beads into mice and histologically analyzing stained sections at 1-4 weeks post implantation. The macro-porous TCP beads with a highly open porous structure could potentially be used as an injectable material for bone tissue engineering.

Synthesis and characterization of multifunctional Fe3O4/poly(fluorescein O-methacrylate) core/shell nanoparticles.

Multifunctional fluorescent and superparamagnetic Fe(3)O(4)/poly(fluorescein O-methacrylate) [Fe(3)O(4)/poly(FMA)] nanoparticles with core/shell structure were synthesized via surface-initiated polymerization. First, polymerizable double bonds were introduced onto the surface of Fe(3)O(4) nanoparticles via ligand exchange and a condensation reaction. A fluorescent monomer, FMA, was then polymerized to the double bonds at the surface via free-radical polymerization, leading to form a fluorescent polymer shell around the superparamagnetic Fe(3)O(4) core. The resultant Fe(3)O(4)/poly(FMA) nanoparticles were characterized by Fourier transform infrared, nuclear magnetic resonance, and X-ray diffraction spectroscopy to confirm the reactions. Transmission electron microscopy images showed that the Fe(3)O(4)/poly(FMA) nanoparticles have a spherical and monodisperse core/shell morphology. Photoluminescence spectroscopy and superconducting quantum interference device magnetometer analyses confirmed that the Fe(3)O(4)/poly(FMA) nanoparticles exhibited fluorescent and superparamagnetic properties, respectively. In addition, we demonstrated the potential bioimaging application of the Fe(3)O(4)/poly(FMA) nanoparticles by visualizing the cellular uptake of the nanoparticles into A549 lung cancer cells.

Core-shell Poly(D,L-Lactide-co-glycolide)/Poly(ethyl 2-cyanoacrylate) Microparticles with Doxorubicin to Reduce Initial Burst Release

Monodispersed microparticles with a poly(d,l-lactide-co-glycolide) (PLGA) core and a poly(ethyl 2-cyanoacrylate) (PE2CA) shell were prepared by Shirasu porous glass (SPG) membrane emulsification to reduce the initial burst release of doxorubicin (DOX). Solution mixtures with different weight ratios of PLGA polymer and E2CA monomer were permeated under pressure through an SPG membrane with 1.9 ώm pore size into a continuous water phase with sodium lauryl sulfate as a surfactant. Core-shell structured microparticles were formed by the mechanism of anionic interfacial polymerization of E2CA and precipitation of both polymers. The average diameter of the resulting microparticles with various PLGA:E2CA ratios ranged from 1.42 to 2.73 ώm. The morphology and core-shell structure of the microparticles were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The DOX release profiles revealed that the microparticles with an equivalent PLGA:E2CA weight ratio of 1:1 exhibited the optimal condition to reduce the initial burst of DOX. The initial release rate of DOX was dependent on the PLGA:E2CA ratio, and was minimized at a 1:1 ratio.

Effect of electrostatic repulsive force on the permeate flux and flux modeling in the microfiltration of negatively charged microspheres

Abstract A study on the permeate flux was performed in a stirred cell filled with monodispersed carboxylated microspheres (polystyrene/polymethacrylic acid, PS/PMAA), to investigate the effects of surface charge (the number density of surface carboxyl group, Nc; 0.45, 5.94, 9.14, and 10.25 nm−2) and the stirrer speed (300, 400, and 600 rpm) under constant transmembrane pressure. The permeate flux was found to be dependent on the surface charge, the ionic strength, and the stirrer speed. The permeate flux was proportional to the surface charge of microspheres and inversely proportional to the ionic strength because of electrostatic repulsive interaction and steric hindrance. The cake porosity was estimated by Kozeny–Carman equation from the steady-state permeate flux data. Experimental data elucidated that the cake porosity was extended from 0.211 to 3.04 upon the introduction of carboxyl group on the microsphere surface, leading to the high permeate flux. Consequently, resistance-in-series model was employed for the modeling of the permeate flux and showed a good agreement with the experimental results.

Preparation of poly(NIPAAm)-Pluronic F68 as a thermosensitive surfactant for a controlled drug release

This paper describes the synthesis of thermosensitive surfactants by polymerizing N-isopropylacrylamide (NIPAAm) into the Pluronic F68 surfactant and their application for a controlled drug release. Poly(NIPAAm)-Pluronic surfactants with different lengths of the NIPAAm block were synthesized by activating two hydroxyl groups of poly(ethylene oxide) (PEO) at the end of Pluronic F68 using cerium ammonium nitrate (CAN, redox initiator), followed by adding the NIPAAm monomer into a reactor. The resultant poly(NIPAAm)-Pluronic surfactants were characterized by FT-IR and gel filtration chromatography (GPC). It was observed that their critical micellar concentrations increased with an increase in the length of the poly(NIPAAm) block. In addition, poly(D,L-lactide-co-glycolide) (PLGA) microparticles was prepared by an oil-in-water emulsion and solvent evaporation method using the poly(NIPAAm)-Pluronic surfactants in an aqueous continuous phase. At 37°C, nile red (model dye) was released from the PLGA microparticles in a more sustained manner when the length of poly(NIPAAm) was longer due to a thicker layer of shrunken poly(NIPAAm) at the surface of the microparticles.