Jung Woog Shin

Nanoaggregate of thermosensitive chitosan-Pluronic for sustained release of hydrophobic drug

A thermo-sensitive chitosan-Pluronic copolymer (CP) was prepared by grafting mono-carboxyl Pluronic onto the chitosan using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and N-hydroxysuccinimide (NHS). Indomethacin (IMC)-loaded nanoaggregate (NA) was prepared using the synthesized CP by the direct dissolution method. The critical aggregate concentration (CAC), hydrodynamic size and surface morphology of the prepared CP nanoaggregate (CPNA) were characterized by fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM), respectively. The resulting CAC and the average diameter of CPNA were about 0.31 g/l and 120 nm, indicating high structural stability of CPNA and size favorable for intravenous delivery of drugs. In vitro release test of the IMC encapsulated into CPNA showed sustained release rate of IMC as compared with that from Pluronic micelle. Therefore, we can conclude that our CPNA can be a novel type of superior drug carrier for sustained delivery of hydrophobic drugs.

Nano-hydroxyapatite/poly ϵ-caprolactone composite 3D scaffolds for mastoid obliteration

The aim of this study is to evaluate the use of our nano-HA/PCL composite 3D scaffolds as graft materials for mastoid cavity obliteration in an animal model. Nano-HA particles were synthesized by chemical precipitation technique and mixed them with PCL solution to make composite paste. 3D scaffolds were fabricated by a paste extruding deposition process. The nano-HA/PCL 3D scaffolds showed good in vivo bone regeneration behaviour in a rabbit model after 4 and 8 week implantation. To characterize the 3D scaffolds as a grafting material for mastoid obliteration, mastoid cavities were introduced in rats and implanted the scaffolds. After two week implantation, histological examination showed good tissue ingrowth and new bone formation behaviour. It can be argued that our nano-HA/PCL composite 3D scaffold is a promising alternative material for mastoid obliteration.

In Vitro Evaluation of Poly ε-Caprolactone/Hydroxyapatite Composite as Scaffolds for Bone Tissue Engineering with Human Bone Marrow Stromal Cells

This study evaluated the potential of the PCL (poly -caprolactone)/HA(Hydroxyapatite) composite materials as a scaffold for bone regeneration. For this, we fabricated scaffolds utilizing salt leaching method. The PCL/HA composite scaffolds were prepared with various HA contents (20wt%, 40wt%, 60 wt %). To ensure the potential for the scaffolds, porosity tests were conducted along with SEM observations. The porosity decreased with the increase of the contents of HA particles. The porosity of the composite with the highest contents of HA was still adoptable (~85%). In addition, the PCL/HA composite scaffolds were evaluated for their ability of osteogenic differentiation with human bone marrow stromal cell (hBMSC) in vitro. Alkaline phosphatase (ALP) activity, markers for osteoblastic differentiation, and total protein contents were evaluated in hBMSCs following 14 days of cultivation. The addition of HA particles enhanced proliferation of hBMSC during the test. Also, the differentiation ability of the cells was increased as HA particles were added. In this study, we concluded that PCL/HA composite scaffolds has great potential as a scaffold for bone tissue engineering.

Evaluation of Bonding Stress for the Newly Suggested Bone Cement: Comparison with Currently Used PMMA through Animal Studies

PMMA remains the most popular material of bone cement for orthopaedic surgeries. However, conventional PMMA bone cement still has some problems. For this, we suggested new composite material (BBC) consisting of hydroxyapatite (45%), chitosan (10%) and PMMA. The purpose of this study was to evaluate the bonding stress at the interface of PMMA with additives and host bone using a rabbit model. After 6, 12 weeks of operation, the bonding stresses were evaluated by measuring shear stress through push-out test. The results of the tests showed that after 6 weeks the shear stress of the BBC was 2.65±0.29MPa and the PMMA was 1.21±0.31MPa (p<0.05). However, after 12 weeks, there were no significant differences between BBC and conventional PMMA bone cement. In SEM analysis, bone surface of BBC showed higher roughness than that of conventional PMMA bone cement after push-out test. From the study we conducted, addition of HA particles and chitosan to conventional PMMA bone cement showed promising results. The BBC has clinical potential of bone substitutes replacing conventional PMMA.

Acellular matrix of bovine pericardium bound with L-arginine

Surface immobilization of bioactive molecules onto natural tissues has been interestingly studied for the development of new functional matrices for the replacement of lost or malfunctioning tissues. In this study, an acellular matrix of bovine pericardium (ABP) was chemically modified by the direct coupling of L-arginine after glutaraldehyde (GA) cross-linking. The effects of L-arginine coupling on durability and calcification were investigated and the biocompatibility was evaluated in vitro and in vivo. A four-step detergent and enzymatic extraction process has been utilized to remove cellular components from fresh bovine pericardium (BP). Microscopic observation confirmed that nearly all cellular constituents are removed. Thermal and mechanical properties showed that the durability of L-arginine-treated matrices increased as compared with control ABP and GA-treated ABP. Resistance to collagenase digestion revealed that modified matrices have greater resistance to enzyme digestion than control ABP and GA-treated ABP. The in vivo calcification study demonstrated much less calcium deposition on L-arginine-treated ABP than GA-treated one. In vitro cell viability results showed that ABP modified with L-arginine leads to a significant increase in attachment of human dermal fibroblasts. The obtained results attest to the usefulness of L-arginine-treated ABP matrices for cardiovascular bioprostheses.

Characterization of PCL/HA Composite Scaffolds for Bone Tissue Engineering

Porous and bioactive composite scaffolds based on poly ε-caprolactone(PCL) and hydroxyapatite(HA) were successfully fabricated by solvent casting and salt leaching method. The scaffolds have interconnected pore structure with pore size ranging from 10μm to 500μm. The pore size of PCL scaffold and PCL/HA scaffold were similar to that of the salt particles. The pore walls became thick and the small pores on the surface of macropores were formed as the HA increased. MTT assay showed that HA content did not affect initial cell attachment in both PCL scaffolds and PCL/HA scaffolds. The osteoblasts proliferated in both scaffolds, but the cell number was higher in the PCL/HA composite scaffolds. It was found that the incorporation of hydroxyapatite enhances bone cell proliferation rather than initial cell attachment in PCL/HA composite scaffolds. The results suggest that the PCL/HA composite scaffolds have a potential for the bone tissue engineering applications.

Biodegradable Porous PCL/HA Scaffolds for Bone Tissue Engineering

Poly ε-caprolactone(PCL)/hydroxyapatite(HA) composite scaffolds were fabricated by particulate leaching and freeze drying routes with different HA content. Porosity was decreased with HA addition, while mean pore size was maintained at around porogen size regardless of HA content. Compressive modulus was increased with increasing HA content. In this study, the optimum content of HA was around 40% in weight against PCL to obtain the highest compressive modulus with keeping porosity above 85%. HA apparently enhanced proliferation of osteoblast-like MG63 cells in PCL/HA composite scaffolds. Typical adhesion, migration and aggregation procedure of MG63 cells were found on PCL, while spreading morphology only was found on HA even at the early stage of adhesion without migration or aggregation.

A Tissue Engineering Based Approach to Regeneration of Intervertebral Disc

Thermosensitive scaffold was suggested for the partial replacement of nucleus in degenerated intervertebral disc with a minimally invasive surgical procedure. Biocompatible and thermosensitive scaffolds were prepared by coupling reaction of Pluronic with chitosan and it was inserted in degenerative spinal motion segments. To confirm the regeneration of degenerative discs and subsequent structural stability, cell proliferation and morphological changes were evaluated using relaxation time, quantity of DNA and histological examination. As a result, inserted group showed higher relaxation time, reduced the decrement of DNA contents, and accumulated GAG amount. The results confirmed the potential of thermosensitive scaffolds and minimally invasive surgical procedure for the regeneration of degenerative discs.

Synthesis and characterization of X-ray nanophosphors using solution-combustion

We investigated nanophosphor materials that exhibit high resolution and emission efficiency for use in X-ray medical imaging. Rare-earth phosphor material has long been used due to its high atomic number and emission efficiency, but these materials tend to exhibit lower resolution and emission efficiency when manufactured in bulk. In this study, we synthesized nanometer-scale phosphors of Gd2O3:Eu and Y2O3:Eu using the solution-combustion method, and we evaluated the dependence of the optical properties of these nanophosphors on europium concentration and synthesis atmosphere. The nanophosphors were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and photoluminescence (PL) spectroscopy. Characterization of the optical properties revealed that both Gd2O3:Eu and Y2O3:Eu exhibited peak emission intensity at 611 nm, which corresponded to that for commercial bulk phosphors. These results imply that manufacturing nanophosphors can achieve thin and compact displays that have enhanced performance, and that improvements in emission efficiency of nanophosphors could reduce the required patient dose for medical imaging.

The design of hybrid x-ray detector using quantum size effect

Group 2?6 compounds (e.g., CdTe, CdS, CdSe) are utilized as photoconductors at the bulk level but manufactured as phosphors at the nano-level. Each of these uses has strengths and weaknesses. Here we attempted to fuse the two uses to maximize the strengths of each by using only one compound. We invented an X-ray detector that could function at two different levels -as a photoconductor in the bulk state and as a phosphor at the nano-scale- by hybridizing two different kinds of layer from one compound. This system operates as follows. First, an X-ray is converted to light on the luminescence layer, after which the light is received on the photoconductor layer. This light has the exact wavelength range required on the photoconductor. The quantum size effect refers to the impact of changes in the electronic energy level density according to the size of the crystal in a nano-particle on its optical and electrical characteristics. On account of this effect, two different kinds of layer from one compound can be used by regulating its size. Thus, by controlling the particle size and changing the emission wavelength, the most appropriate absorption wavelength for a photoconductor in the bulk state can be emitted from the nano-phosphor. The conversion efficiency in the hybrid structure is apparently superior to that in the bulk-state single layer. In conclusion, the electrical and optical characteristics of the proposed hybrid structure are superior to those of a conventional structure. These findings confirm the feasibility of a hybrid structure based on the quantum size effect.