Papers by Author: Chang Kuk You

Abstract: Beta-tricalcium phosphate(β-TCP) coating layer is known to be resorbed much faster than hydroxyapatite(HA), however, there has been no report to explain the exact reason of these results. Eighty titanium discs, coated with HA(n=40) or β-TCP(n=40) by dip and spin coating method, were divided into 2 subgroups respectively; Dissolution(D, n=20) and osteoclast culture(C, n=20). The coated discs in D group were immersed in the cell culture media for 5 days, whereas, in C group, osteoclasts were seeded on the specimens and cultured for 5 days. After simple dissolution test, β-TCP coating layer showed much more cracks and denudation as compared to HA. In osteoclast culture group, mean area fraction of resorption pits in HA-C group was 11.62%, which was significantly higher than that of 0.73% in β-TCP-C group(p=0.001). In conclusion, the resorption mechanisms of HA and β-TCP coating layers were different each other in vitro study. The coated β-TCP was degraded mainly by dissolution and separation from implant, on the other hand, the HA coating layer was resorbed by osteoclastic activity.

Abstract: Recently, nanomaterials have received considerable attention because of their potential applications in the biomedical field. In the present study, we investigated the effects of nano-sized calcium metaphosphate (CMP) particles (50 nm) compared with micro-sized CMP particles (200-500 nm and 10 μm) on the proliferation and osteoblastic differentiation of human bone marrow stem cells (BMSCs). BMSCs were challenged with CMP particles with different sizes for 3, 5, and 7 days. An analysis of the proliferation revealed that the nano-sized CMP particles (50 nm) stimulated the proliferation of BMSCs up to 27.79% compared to the untreated control. This stimulatory effect of the nano-sized CMP particle was dose-dependent. CMP particles appeared to adhere on the surface of BMSCs but this did not cause distinguishable morphological changes. Moreover, all CMP particles (50 nm to 10 μm) were capable of stimulating an osteoblastic differentiation of BMSCs as accessed by alkaline phosphatase (ALP) and von Kossa stainings. Further molecular analysis revealed that all the CMP particles induced an expression of osteoblast-related genes such as osteocalcin (OC) and collagen I (Col I). Taken together, our data demonstrate that nano-sized CMP particles have the potential to stimulate the proliferation and osteoblastic differentiation of BMSCs.

Abstract: OH groups on hydroxyapatite (HA) and calcium metaphosphate (CMP) were evaluated by grafting tetraethyl orthosilicate (TEOS) and 3-aminopropyltriethyloxysilane (3-APTES) which can bond covalently with OH group of ceramic biomaterials. The prepared HA and CMP disks were soaked in pH 2 and 5 of acidic water and ethanol solution respectively, where pH change of each solution was measured during soaking of samples. After grafting TEOS and 3-APTES on HA and CMP disks, samples were ultrasonically cleaned in distilled water and soaked in pH 5 of ethanol solution, and pH measurement was carried out in the same manner. The pH value of HA and CMP in aqueous solution at pH 2 increased with time continuously, resulting from dissolution of HA and CMP by acidic condition on surface. At pH 5 in aqueous solution, it was the same though the pH increase was smaller. In case of ethanol at pH 5 with HA, though pH value went up slightly, the curve became saturated with time, while there was no change in pH with CMP. After grafting TEOS and 3-APTES, pH values were stabilized with few changes, indicating that there was no direct chemical reaction between the acidic media and the surface of samples due to covalently grafted TEOS and 3-APTES layer. In conclusion, it was confirmed that OH group on the surface of HA was crystallographic and chemical one rather than physically adsorbed one by grafting TEOS or 3-APTES and it will serve an effective binding site for calcium and phosphate ions, or minerals.

Abstract: As a part of the effort to develop a suitable scaffold for tissue-engineered bone regeneration, we modified calcium metaphosphate (CMP) ceramic with Na20 and evaluated its efficiency as a scaffold. We incorporate 5% Na20 into pure CMP and prepare for an average pore size of 250 or 450 µm average pore sizes. The incorporation of 5% Na2O caused reduced compressive strength and there was no change in biodegradability. The in vitro cellular attachment and proliferation rate, however, were slightly improved. The 5% Na2O-incorporated macroporous CMP ceramic-cell constructs treated with Emdogain induced ectopic bone formation more effectively than those without Emdogain treatment. These results suggest that the incorporation of 5% Na2O into pure CMP is not effective for improving the physical characteristics of pure CMP but it is positive for improving the cellular reaction and osteogenic effect with the addition of Emdogain.

Abstract: Grit-blasting using bioactive HA and biodegradable CMP followed by acid etching was done. The apatite formation of prepared Ti samples was evaluated by immersion in R-SBF. And cell viability, proliferation, and differentiation were conducted using MTT assay and ALP staining. In RSBF immersion tests, non-etched HA-blasted samples showed the faster apatite-like formation than other samples. Acid etched and non-etched HA-blasted samples showed better cell viability and proliferation compared to CMP-blasted samples after 1 and 3 days. And the cell differentiation of non-etched HA-blasted samples was better compared to etched ones, and etched and non-etched CMP-blasted samples.

Abstract: Grit blasting using bioactive HA and biodegradable CMP followed by acid etching has been done. HNO3 and H3PO4 were used for the etching solution by controlling the concentration and etching time to know the effect on the surface chemistry and morphology of the Ti implant. Characterization of samples was done by using SEM, EDX and surface profilometer. The contents of residues on Ti surface decreased with increasing acid concentration and etching time. It was observed that the acidic etching rate of HA grits on Ti surface was faster than that of CMP grits. And HNO3 etched more rapidly the HA and CMP grits on Ti surface, compared to H3PO4. Therefore, the surface roughness of dental implants can be controlled by having appropriate combination of acid concentration and etching time.

Abstract: Five kinds of gypsums, (1) CaSO4•2H2O (caldium sulfate dihydrate; CSD), (2) CaSO4•1/2H2O (calcium sulfate hemihydrate; CSH), (3) CaSO4 (calcium sulfate anhydrite; CSA), (4) CSH200 (CSH heat-treated at 200°C after self-hardening), and (5) CSH600 (CSH heat-treated at 600°C after self-hardening) were used as candidates for coating materials on calcium metaphosphate (CMP) scaffod to control degradation rate of CMP and to extend degradation limit. The disks of CSD, CSH, CSA, CSH 200, and CSH600 were prepared by self-hardening after mixing with water, where CSH200 and CSH600 were heat-treated at 200°C and 600°C, respectively. In order to control fast resorption rate of gypsum, CMP-CSA composites were prepared with different CSA contents such as 0, 5, 10, 20, 30, 50, and 70 vol% and heat-treated at 900°C for 4 hours. The degradation rates of various gypsums were evaluated in revised simulated body fluid (r-SBF) for 1, 3, 7, and 21 days, respectively. Degradation rate of each specimen was measured in terms of weight loss change with time and degraded surface morphology was examined by SEM. All kinds of gypsums were transformd into CSD after self-hardening with water. Most of gypsums were degraded by 35~60 wt% at 7 days and by 70~99 wt% at 21 days of soaking in SBF. In the group of CMP-CSA composites, the degree of degradation of them was considerably retarded compared to that of five pure gypsums. The surface morphology showed elongated needle-like crystals during the degradation with time.

Abstract: Surface morphology and degradation behavior of mechanically mixed and chemically precipitated biphasic calcium phosphate (M-BCP and P-BCP) were compared. For the M-BCP powder, commercial HA and TCP powders were used. In order to prepare P-BCP powder, precipitation method was used. The particle size of P-BCP was smaller than that of M-BCP. The disk-type specimens of each powder were prepared for the morphology comparison and degradation test. The surface morphology of sintered samples was porous in M-BCP and dense in P-BCP. The degradation test was conducted in the revised simulated body fluid (R-SBF) for 1, 7, and 21 days. Surface morphology and degradation rate of two samples were different. The weight gain in both samples increased linearly with immersion period due to apatite-like layer formation. However, the weight gain in M-BCP was much higher than that in P-BCP. The weight gain was related to the surface morphology and degradation with immersion period.

Abstract: As a part of the efforts to develop a suitable scaffold optimizing bone regeneration that has similar physical properties to bone, we modified calcium metaphosphate (CMP) ceramics with K2O and evaluated their efficiency as a scaffold for tissue engineered bone tissue regeneration. Macroporous CMP ceramics modified by incorporation of 5% K2O to improve biodegradability were prepared to have 250 and 450 µm average pore sizes, respectively. The modified CMP ceramics were cultured with mouse primary calvarial osteoblastic cells in osteogenic media for 2 weeks and these cell-CMP ceramic constructs with or without Emdogain treatment were implanted in the SCID mice subcutaneous pouches. After 1, 2, and 3 weeks, the degree of ectopic bone formation was evaluated. The modified macroporous CMP ceramic-cell constructs treated with Emdogain induced ectopic bone formation, whereas the modified CMP ceramic-cell constructs without Emdogain treatment induced no ectopic bone formation. This result suggests that the Emdogain treatment on cell-scaffold constructs for tissue engineered bone regeneration may be effective for osteogenic activation of attached cells.

Abstract: Electrophoretic deposition was used for HA coating on dental implants with different coating thickness. The HA coating thickness was examined in terms of applied voltage and time, and powder concentration in suspension. Nano-size HA and SiO2-CaO-P2O5-B2O3 bioglass powders were synthesized by sol-gel method. Polyvinyl alcohol (3 wt%) as a binder was resolved in ethyl alcohol, then, nano HA powder was dispersed ultrasonically in the mixture for 15 min and pH was adjusted with HNO3 for positive charging on particle. Titanium substrate was held on cathode and counter electrode was platinum. HA with 0.5 % and 0.03 % of powder concentration was deposited electrophoretically at 10~20 V for 1~20 minutes. The thickness of as-deposited HA layer decreased from nearly 80 µm (0.5 %, 20 V, 10 min) to 4~5 µm (0.03%, 10V, 1 min) as powder concentration, applied voltage and time decreased, respectively. The surface of HA coating layer deposited in lower powder concentration showed much more homogeneous and relatively dense morphology, in contrast, the surface in thick suspension became rough or porous and was easily spalled. In a co-deposition of HA and bioglass, co-deposited glass played an important role in increasing bonding strength between coating layer and substrate. It is believed that electrophoretic deposition method can be one of alternatives for relatively thin and easy HA coating.