Papers by Author: Sung Su Chun

Abstract: A collagen material was chemically grafted on hydroxyapatite (HA) to enhance bone cell attachment because the collagen is a major constituent of connective tissues and has been regarded as one of the most excellent coating materials for bone bonding. First, HA disks were prepared with 12mm diameter and 1mm thickness. And then collagen (type I) was immobilbized on the HA surface using a 3-APTES coupling agent on HA disk surfaces. MC3T3-E1 osteoblasts were seeded on the collagen-grafted and non-grated HA disks and cultured for 4 hrs to evaluate the cell adhesion on the HA discs. The Attached cell morphology on discs was observed with a fluorescent optical microscopy (FOM) and a scanning electron microscopy (SEM). The osteoblasts on the collagen-grafted sample were more spread than those on the non-grafted sample. It is believed that collagen-grafted HA surface provides suitable sites for cell attaching due to the high biocompatibility of collagen.

Abstract: β-tricalcium phosphate (TCP) ceramic nanofibers via electrospinning route have been produced using β-TCP sol, which was prepared by the mixing of calcium nitrate tetrahydrate and triethyl phosphate as Ca sand P precursors, respectively. The as-prepared sol was tightly caped and aged in a drying oven at 90 °C for 16 hrs. The aged sol was evaporated in opened containers at 35 °C to reach a proper value of viscosity (100 cPs). Viscous solution was prepared by the mixing of β-TCP sol and high-molecular weight PVP to obtain appropriate viscosity for electrospinning. The mixed solution of β-TCP and PVP with various ratios were vigorously mixed using hot plate/stirrer for 24 hrs and then electrospun. The as-electrospun β-TCP nanofibers were dried in a drying oven at 60°C for 12 hrs and then heat-treated at 500, 600, 700 and 800 °C at 1°C/min heating rate in air. Surface morphology and phase identification of as-spun and heat-treated β-TCP nanofibers were studied. The results have shown that ratio between PVP and β-TCP sol and heat-treatment conditions significantly affected the crystalline phase and morphology of β-TCP nanofibers.

Abstract: Bioresorbable calcium metaphosphate (CMP) nanofibers were produced by an electrospinning technique. In order to produce the nanofibers, CMP sol was prepared by the mixing of two precursors, such as calcium nitrate tetrahydrate (Ca[NO3]⋅4H2O) and triethyl phosphate (TEP, [C2H5O]3PO), using methyl alcohol as a solvent. The Ca/P ratio of the mixture was set to be 0.50 to produce stoichiometric CMP sol. At least 5 hrs of pre-hydrolysis of phosphorus precursor were required to obtain β-CMP phase. Viscous solutions for the electrospinning were made by the mixing of CMP sol and high-molecular weight polymeric solution at various ratios. The ratio of CMP sol and polymer solution was controlled to obtain an appropriate viscosity for the electrospinning. As-electrospun CMP nanofibers were dried in a drying oven at 70°C for 24 hrs and then heat-treated at various temperatures at a ramp of 1°C/min in air for 1hr. The as-electrospun and heat-treated CMP nanofibers were characterized using X-ray analysis, FT-IR, TG-DTA and SEM techniques. The results showed that the preparation of CMP sol, mixed solution properties, and heat-treatment condition of as-electrospun nanofibers significantly affect the spinability and surface morphology of the CMP nanofibers.

Abstract: Biphasic calcium phosphate powders (BCP) of hydroxyapatite (HA) and tricalcium phosphate (β-TCP) with the various ratio of HA to β-TCP were prepared by utilizing mechanochemical synthesis. Calcium hydrogen-phosphate dihydrate (brushite, CaHPO4⋅2H2O) and calcium carbonate (calcite, CaCO3) powders have been chosen as the starting materials. The original Ca/P ratio of CaHPO4⋅2H2O - CaCO3 batch was set to be 1.67. A mixture of starting materials was milled using a planetary mill (ZrO2 jar and balls) with water for 3, 4, 5, 6 and 7 hrs. The XRD study of calcined powders was conducted for phase identification and for HA/β-TCP ratio as well. The phases of the calcined powders were HA and β-TCP, and the HA/β-TCP ratio varied with the milling time. The mass fraction of HA and β-TCP phases was calculated from the XRD intensities of HA and β-TCP. The ratio of the mixture milled for 4 hrs and calcined at 900°C was 85(HA):15(β-TCP) (BCP 85/15) and the content of β-TCP increased with the milling time. It is believed defective HA powder formed at relatively short period of milling time (less than 3 hrs The research revealed that nanocrystalline BCP powders could be synthesized by an employment of a medium-high energy mechanical activation at room temperatures (~25°C) without any preliminary chemical processing.

Abstract: Degradation characteristics of calcium metaphosphate (CMP) ceramics substituted by 5, 10, 15, 20 mol% of NaPO3 and KPO3, respectively, was evaluated in revised simulated body fluid (R-SBF) by measuring the weight change, flexural strength, crystalline phases, and surface morphology with immersion period. The weight loss of CMP substituted by KPO3 was significantly higher than that of CMP substituted by NaPO3. The weight loss in the KCa(PO3)3–CMP samples was due to the dissolution of KCa(PO3)3 phase. The flexural strength of NaCa(PO3)3–CMP samples increased, however, that of KCa(PO3)3–CMP samples decreased significantly due to the dissolution of KCa(PO3) phase with immersion period. The dissolution of KCa(PO3)3 phase formed a pore structure in KCa(PO3)3–CMP samples.