Papers by Author: Ho Yeon Song

Abstract: Calcium phosphate bone substitutes are widely used for providing support for the in-growth of hard tissue in various medical applications (e.g., dental, orthopedic). Recently, research involving bone substitutes with interconnected open pore structures has focused on improving the mechanical properties of the substitutes and modifying their surfaces with proteins (e.g., collagen, bone morphogenetic protein) to induce early bone formation. In particular, it is highly desirable to develop a functional gradient-structured bone substitute that has the potential to control the bioresoption rate. A porous BCP scaffold was fabricated by the sponge replica method using a PU sponge. The sponge was dip coated three times followed by oven drying, burning out, and microwave sintering. Several approaches were used to fabricate a functional gradient scaffold. TCP was synthesized using the sol-gel process, and it infiltrated into the pore channel that formed after the burning out of the PU sponge. X-ray diffraction analysis characterized the phase identification of the BCP scaffold. Microstructures of the composites were observed using scanning electron microscopy.

Abstract: The HAp-(t-ZrO2) ceramic composites with mimetic osteon microstructures were fabricated to investigate the technical feasibility of fabricating natural bone mimetics by a combination of multi-extrusion and rolling processes. The HAp and graphite powders were mixed with ethylene vinyl acetate and stearic acid using a shear mixer, and the mixture was extruded by the multi-extrusion process to create filaments. A HAp sheet was prepared by a rolling process. The HAp filaments and carbon filaments were arranged one by one on the HAp sheet, and the system was rolled to form a mimetic osteon microstructure. Burning out and sintering processes were performed for removal of the organic binder and graphite and for densification. The pore diameter and core of the mimetic osteon microstructure were approximately 50μm and 150μm, respectively. The porosity and bending strength were approximately 60% and 177MPa, respectively in the sample sintered at 1450°C.

Abstract: Calcium phosphate ceramics such as hydroxy apatite (HA), β-tricalcium phosphate (β-TCP) and bicalcium phosphate (BCP) have been used as a bone graft biomaterial because of their good biocompatibility and similarity of chemical composition to natural bones. To increase the mechanical and osteoconductive properties, the granules and spongy type porous bone graft substitutes were prepared by fibrous monolithic process and polyurethane foam replica methods, respectively. The pore sizes obtained using these approaches ranged between 100-600 µm. The cytotoxicity, cellular proliferation, differentiation and ECM deposition on the bone graft substitutes were observed by SEM and confocal microscopy. Moreover, the scaffolds were implanted in the rabbit femur. New bone formation and biodegradation of bone graft were observed through follow-up X-ray, micro-CT analysis and histological findings. After several months (2, 3, 6, 12 and 24 months) of implantation, new bone formation and ingrowths were observed in defect sites of the animal by CaP ceramics and 2 to 3 times higher bone ingrowths were confirmed than that of the normal trabecular bones in terms of total bone volume (BV).

Abstract: The continuously porous t-ZrO2 bodies were fabricated by the extrusion process. The average pore size of the 2nd passed samples was about 260μm in diameter. The maximum bending strength value was about 177MPa. For the evaluation of their biocompatibility, human osteoblast like MG-63 cells and osteoclast like Raw 264.7 cells were cultured on the top surface of the porous t-ZrO2 bodies. The osteoblast cells were grown with spindle shape, condensed circular growth and three-dimensional network type. In contrast, the osteoclast cells appeared with pebble stone structure.

Abstract: Using microwave synthesized HAp nano powder and polymethyl methacrylate (PMMA) as a pore-forming agent, the porous biphasic calcium phosphate (BCP) ceramics were fabricated depending on the sintering temperature. The synthesized HAp powders was about 70-90 nm in diameter. In the porous sintered bodies, the pores having 150-180 μm were homogeneously dispersed in the BCP matrix. Some amounts of pores interconnected due the necking of PMMA powders which will increase the osteoconductivity and ingrowth of bone-tissues while using as a bone substrate. As the sintering temperature increased, the relative density increased and showed the maximum value of 79.6%. From the SBF experiment, the maximum resorption of Ca2+ ion was observed in the sample sintered at 1000°C.