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Suncheon, South Korea

Seo D.S.,Jeonnam Technopark | Hwang K.H.,Gyeongsang National University | Lee J.K.,Chosun University
Applied Mechanics and Materials | Year: 2012

This work describes dissolution and related mechanical weakening of phase-pure and dense hydroxyapatite (HA) in distilled water of pH 7.4. Phase-pure HA powder has been synthesized by a wet precipitation method. After uniaxial and cold isostatic pressing, and sintering at 1200°C, dense HA with 98% above of the theoretical density has been obtained. The results show that HA powder has stoichiometric composition with a Ca/P ratio 1.67 ± 0.02. Even after extended exposure for 10 h, no second phases, such as tricalcium phosphate (TCP) and calcium oxide can be observed. Although the HA is supposed to be stable in liquid environment, surface dissolution appears specifically at material's grain boundaries after immersion for 7 days. Following further immersion to 14 days, grain boundary dissolution progresses interior to the bulk following these paths. This dissolving behavior generates HA particles, disintegrates dense microstructure and at least forms micron-scale cavity. Mechanical property of the HA has been also affected. Fracture toughness (KIc) of the HA sintered body is approximately 1.0 MPa•m1/2. It drastically decreases to almost half of the initial value due to the severe surface dissolution. © (2012) Trans Tech Publications, Switzerland. Source


Seo D.S.,Jeonnam Technopark | Lee J.K.,Chosun University | Hwang K.H.,Gyeongsang National University
Journal of Nanoscience and Nanotechnology | Year: 2015

Hydroxyapatite (HA) is widely used as a bioactive ceramics as it forms a chemical bond with bone. However, the drawback to using this material is its inferior mechanical properties. In this research, surface corrosion and disintegration of nanoscaled HA in a dog were studied, and the mechanism by which phase-pure HA dissolved in vivo was investigated. Biological properties of HA in vivo are affected by the grain-boundary dissolution followed by a surface corrosion and microstructural disintegration. This kind of dissolution process, apparently evidenced at the grain boundary, causes particle generation, which indicates that both long-term bone in-growth and mechanical properties can dramatically deteriorate. Implant dissolution by osteoclasts in vivo is also observed on the surface of hydroxyapatite. Implant surface showed an aggressive corrosion by an osteoclast resorption. Severe and deeper dissolution underwent close to osteoclast resulting in formation of smaller and more round particle shape. Copyright © 2015 American Scientific Publishers All rights reserved. Source


Seo D.S.,Jeonnam Technopark | Chae H.C.,Chosun University | Lee J.K.,Chosun University
Journal of Nanoscience and Nanotechnology | Year: 2015

Hydroxyapatite coatings were fabricated on zirconia substrates by a room temperature spray process and were investigated with regards to their microstructure, composition and dissolution in water. An initial hydroxyapatite powder was prepared by heat treatment of bovine-bone derived powder at 1100°C for 2 h, while dense zirconia substrates were fabricated by pressing 3Y-TZP powder and sintering it at 1350°C for 2 h. Room temperature spray coating was performed using a slit nozzle in a low pressure-chamber with a controlled coating time. The phase composition of the resultant hydroxyapatite coatings was similar to that of the starting powder, however, the grain size of the hydroxyapatite particles was reduced to about 100 nm due to their formation by particle impaction and fracture. All areas of the coating had a similar morphology, consisting of reticulated structure with a high surface roughness. The hydroxyapatite coating layer exhibited biostability in a stimulated body fluid, with no severe dissolution being observed during in vitro experimentation. Copyright © 2015 American Scientific Publishers All rights reserved. Source


Seo D.S.,Jeonnam Technopark | Lee J.K.,Chosun University | Hwang K.H.,Korea University | Hahn B.D.,Korea Institute of Materials Science | Yoon S.Y.,Korea University
Journal of Nanoscience and Nanotechnology | Year: 2015

Three types of raw materials were used for the fabrication of hydroxyapatite coatings by using the room temperature spraying method and their influence on the microstructure and in vitro characteristics were investigated. Starting hydroxyapatite powders for coatings on titanium substrate were prepared by a heat treatment at 1100°C for 2h of bovine bone, bone ash, and commercial hydroxyapatite powders. The phase compositions and Ca/P ratios of the thre hydroxyapatite coatings were similar to those of the raw materials without de composition or formation of a new phase. All hydroxyapatite coatings showed a honeycomb structure, but their surface microstructures revealed different features in regards to surface morphology and roughness, based on the staring materials. All coatings consisted of nano-sized grains and had dense microstructure. Inferred from in vitro experiments in pure water, all coatings have a good dissolution-resistance and biostability in water. Copyright © 2015 American Scientific Publishers All rights reserved. Source


Seo D.S.,Jeonnam Technopark | Hwang K.H.,Gyeongsang National University | Yoon S.Y.,Pusan National University | Lee J.K.,Chosun University
Journal of Ceramic Processing Research | Year: 2012

Hydroxyapatite compacts were fabricated by pressureless- and hot-pressing of natural powders recycled from pig bones and their sintered property and biostability investigated. Organics of bone were removed by soaking the bones in a NaOH solution. An organic-free hydroxyapatite powder was obtained by calcination of dried bones and milling by an attritor. Porous hydroxyapatite compacts were fabricated by pressureless-sintering which was carried out at a temperature of 1100°C for 1 h in a humid atmosphere. Dense hydroxyapatite compacts were prepared by hot-pressing at 1000°C for 0.5 h under a pressure of 30 MPa in an Ar atmosphere. Almost the detectable peaks in the calcined powder were identical to hydroxyapatite with a small peak of MgO. Sintered hydroxyapatite compacts have a density of 77% by pressureless-sintering and 95% by hotpressing. An immersion test in buffered water revealed that there was no clear evidence of dissolution for the hot-pressed hydroxyapatite compacts derived from recycled pig bones. By comparison with an extensive dissolution on the surface of an artificial hydroxyapatite compact in buffered water, the hydroxyapatite compacts recycled from pig bones have a superior biostability for in vitro tests. Source

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