Dong June Chung

Thermal behaviour of poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) tri-block copolymers

Thermal behavior of poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) tri-block copolymers with different block lengths is examined. Thermal behavior of specimens crystallized under the isothermal and dynamic condition are characterized by DSC. Also WAXD and SAXS are employed to investigate the structure. Depending on the relative length of each block, tri-block copolymers can be classified into three groups: PCL dominant crystallization; PEG dominant crystallization; and the competing case. When the crystallization of PEG and PCL are competing, the crystallization of each block shows strong dependency on the thermal hystory of crystallization, leading to multiple melting and crystallization peaks. Also, the typical micro-phase separation of block copolymers seems to play an important role, competing with crystallization, especially under the dynamic crystallization condition.

Effect of the structure of chain extenders on the dynamic mechanical behaviour of polyurethane

The dynamic mechanical behaviors of polyurethanes with different types of non-linear chain extenders are compared with those of corresponding linear chain extender. The Tg of the soft segment matrix showed much variation depending on the type of the chain extenders. The use of non-linear chain extender results in at least 30°C shift toward the higher temperature compared with the sample with 1,4-butanediol. The softening temperature of the hard segment domains is dependent on the detailed structure of the chain extender. Cyclic chain extender and some chain extenders with pendent groups showed a quite significant increase in the softening temperature and well-developed rubbery plateau regions. In tan δ peaks, the peak representing the soft segment matrix becomes much sharper and larger when non-linear chain extenders are employed.

In vitro and in vivo Application of PLGA Nanofiber for Artificial Blood Vessel

Poly(lactic-co-glycolic acid) (PLGA) tubes (5 mm in diameter) were fabricated using an electro spinning method and used as a scaffold for artificial blood vessels through the hybridization of smooth muscle cells (SMCs) and endothelial cells (ECs) differentiated from canine bone marrow under previously reported conditions. The potential clinical applications of these artificial blood vessels were investigated using a canine model. From the results, the tubular-type PLGA scaffolds for artificial blood vessels showed good mechanical strength, and the duallayered blood vessels showed acceptable hybridization behavior with ECs and SMCs. The artificial blood vessels were implanted and substituted for an artery in an adult dog over a 3-week period. The hybridized blood vessels showed neointimal formation with good patency. However, the control vessel (unhybridized vessel) was occluded during the early stages of implantation. These results suggest a shortcut for the development of small diameter, tubular-type, nanofiber blood vessels using a biodegradable material (PLGA).

Cellular-uptake behavior of polymer nanoparticles into consideration of biosafety

Nanoparticles have tremendous potential in cancer prevention, detection and augmenting existing treatments. They can target tumors, carry imaging capability to document the presence of tumors, sense pathophysiological defects in tumor cells, deliver therapeutic genes or drugs based on the tumor characteristics, respond to external triggers to release an appropriate agent, document the tumor response, and identify the residual tumor cells. Nanoparticles < 30 nanometers in diameter show unexpected and unique properties. Furthermore, particles < 5 nanometers in size can easily penetrate cells as well as living tissues and organs. This study evaluated the safety of nano materials in a living body and the relationship between the living tissue and synthetic nano materials by examining thein-vitro cytotoxicity of poly(lactic-co-glycolic) acid (PLGA) nano-spheres and fluorescein isothiocynate(FITC)-labeled dendrimers as polymeric nanoparticles. PLGA was chosen because it has been used extensively for biodegradable nanoparticles on account of its outstanding bio-compatibility and its acceptance as an FDA approved material. The dendrimer was chosen because it can carry a molecule that recognizes cancer cells, a therapeutic agent that can kill those cells, and a molecule that recognizes the signals of cell death. Cytotoxicity in L929 mouse fibroblasts was monitored using MTT assay. Microscopic observations were also carried out to observe cell growth. All assays yielded meaningful results and the PLGA nanoparticles showed less cytotoxicity than the dendrimer. These nanoparticles ranged in size from 10 to 100 nm according to microscopy and spectroscopic methods.

Preparation and Properties of PEG-Modified PHEMA Hydrogel and the Morphological Effect

ConclusionsNovel HEMA based hydrogels modified by a PEG graft were prepared by the crosslinking polymerization of HEMA in the presence of a methacryloyl PEG macromer with different chain length. The increasing degree of swelling and the decreasing surface contact angle highlight the increasing hydrophilic nature of the gels modified by incorporating PEG. The PEG modified PHEMA gels had a porous network structure with pore sizes ranging from submicron to tens of microns, which changed according to composition. From the cytotoxicity test, the modified gel was found to be non-toxic and biocompatible. This material might applicable as a material for controlled drug delivery and as a gel scaffold in tissue engineering.

Controlled Release Behavior of Bioactive Molecules from Photo-Reactive Hyaluronic Acid-Alginate Scaffolds

There are three important components in tissue engineering: the cells, signaling factors (cytokines and growth factors), and scaffolds. To obtain finely engineered tissue, all three components should perform their individual functions and be fully integrated with each other. For the past few years, we have studied the characteristics of photodimerizable HA (CHA)/alginate (CA) composite materials. CHA/CA complex hydrogels, which were irradiated under UV light and then treated with calcium ions, were found to have good biocompatibility, mechanical properties and water resistance for implantable tissue scaffolds. In this study, we introduced a cell growth factor (basic fibroblast growth factor; bFGF) into the CHA/CA scaffolds and studied its release behavior. We also introduced tetracycline hydrochloride and flurbiprofen into the same scaffolds as model activation factors and evaluated their release behaviors from the scaffolds. The drug release rate from the materials was influenced by various parameters, such as the degree of crosslinking, the crosslinker type, the physico-chemical properties of the drug, and the amount of the drug in the polymer. The results indicated that the negatively charged CHA/CA composite materials showed sustained release behavior and that HA has a particularly strong negative charge, making it attractive toward tetracycline hydrochloride and bFGF, but repulsive toward flurbiprofen.

Peripheral berve regeneration through nerve conduit composed of alginate-collagen-chitosan

Although the peripheral nerve system has a relatively good regenerating capacity compared to the central nerve system, peripheral nerve repair remains a clinical challenge as restoration of normal nerve function is highly variable. Synthetic tubular nerve conduits were designed as an alternative repair method in order to replace the need for an isograft. These nerve conduits guide regenerating axons from the proximal toward the distal end, maintain within growth-promoting molecules released by the nerve stumps, and protect regenerating axons from infiltrating scar tissue. In this work, we prepared cinnamoylated alginate (CA)-collagen-chitosan nerve conduit using the lyophilization method to generate a controllable parallel channel in the center and then investigated its influence on peripheral nerve regeneration in an animal study. At 12 weeks after implantation, histological study showed that tissue cable was continuously bridging the gap of the sciatic nerve in all rats. Our newly developed nerve conduit is a promising tool for use in peripheral nerve regeneration and provides a suitable experimental model for future clinical application.

In situ sodium alginate-hyaluronic acid hydrogel coating method for clinical applications

A novel synthetic method is reported to prepare HAAL hydrogels derived from hyaluronic acid (HA) and sodium alginate (AL) with different compositions (ranging from 1:1 to 1:5) through ionic and covalent crosslinking is reported in this study. The synthesized hydrogels were characterized by FTIR spectroscopy. Surface morphology and equilibrium swelling behavior of the hydrogels were also examined. In an MTT assay, the hydrogel extracts were found to be non-cytotoxic to L929 mouse fibroblasts. The blood compatibility of the synthesized hydrogels was assayed with a platelet adhesion test, and was comparable with that of medical-grade polyurethane (PU, Pellethane®). HAAL hydrogels with recombinant human epidermal growth factor (rh-EGF) exhibited enhanced cell proliferation and adhesion (human L929 fibroblast). These characteristics demonstrate that HAAL hydrogels treated using this in situ coating method have potential for usage in various clinical applications.

Synthesis of pH-responsive and adhesive super-absorbent hydrogel through bulk polymerization

AbstractSodium acrylate (AANa) and hydroxyethyl methacrylate (HEMA) were synthesized by bulk polymerization technique to achieve a pH-responsive, super-absorbent hydrogel (SHG) copolymer. The synthesized copolymer was confirmed by FTIR spectroscopy. The pH responsive behavior of the SHG with different monomer ratios of HEMA and AA was investigated, and the SHG showed significant swelling properties at pH 7. The hydrogels were evaluated for the influences of crosslinking agent content, changes in the surface/cross-sectional morphology according to the degree of crosslinking, the water-absorbing properties of swellable SHG, and the adhesion properties to other polymer surfaces. The SHG hydrogel also exhibited good biocompatibility, low cytotoxicity, and high cell viability. The synthesized SHG hydrogel could be used for wound dressing materials in clinical applications requiring high absorption capacity when body fluids are heavily secreted from a wound site. Poly(AA-co-HEMA) hydrogels (SHG) may also have potential uses in biomedical applications such as wound healing and tissue engineering.

Biodegradable and Elastomeric Poly(glycerol sebacate) as a Coating Material for Nitinol Bare Stent

We synthesized and evaluated biodegradable and elastomeric polyesters (poly(glycerol sebacate) (PGS)) using polycondensation between glycerol and sebacic acid to form a cross-linked network structure without using exogenous catalysts. Synthesized materials possess good mechanical properties, elasticity, and surface erosion biodegradation behavior. The tensile strength of the PGS was as high as 0.28 ± 0.004 MPa, and Youngs modulus was 0.122 ± 0.0003 MPa. Elongation was as high as 237.8 ± 0.64%, and repeated elongation behavior was also observed to at least three times the original length without rupture. The water-in-air contact angles of the PGS surfaces were about 60°. We also analyzed the properties of an electrospray coating of biodegradable PGS on a nitinol stent for the purpose of enhancing long-term patency for the therapeutic treatment of varicose veins disease. The surface morphology and thickness of coating layer could be controlled by adjusting the electrospraying conditions and solution parameters.