Biomedical subjects

Hyun-Min Kim

Publications and source records attributed to Hyun-Min Kim.

21 records · Page 2Linked to original sources

PubMed2002

Apatite-forming ability of CaO-containing titania.

It was recently shown that titanium metal and its alloys spontaneously form a bonelike apatite layer on their surfaces in the living body and bond to the bone through the apatite layer, when the sodium ions are incorporated into titanium oxide layer of their surfaces by chemical and heat treatments. It is expected that their apatite-forming ability, and hence their bone-bonding ability, could be enhanced, if the calcium ions are incorporated into their surface titanium oxide layers instead of the sodium ions, because the calcium ions released from their surface layers can increase the ionic activity product of the apatite of the surrounding fluid more effectively than the sodium ions. In the present study, in order to investigate the effect of incorporation of the calcium ions into the titanium oxide layer on its apatite-forming ability, apatite-forming abilities of titania gels which have different CaO contents and subjected to different heat treatments were examined in a simulated body fluid with ion concentrations nearly equal to those of the human blood plasma. It was found that CaO-containing gels do not form the apatite on their surfaces as far as they take an amorphous phase in spite of the fact that they release larger amounts of the calcium ions with increasing CaO contents of the gels. They form the apatite when they take an anatase-like structure even though they do not contain CaO. These results indicate that a specific structure of the titanium oxide is more important for the apatite nucleation than the magnitude of the ionic activity products of the apatite in the surrounding fluid.

Apatites↗

PubMed2002

Apatite formation on zirconium metal treated with aqueous NaOH.

Previous studies by the authors have shown that titanium metal, titanium alloys and tantalum metal which were subjected to aqueous NaOH solution and subsequent heat treatments form an apatite surface layer upon immersion in a simulated body fluid (SBF) with ion concentrations nearly equal to those in human blood plasma. These metals form the apatite surface layer even in living body, and bond to living bone through the apatite layer. In the present study, the apatite-forming ability of NaOH-treated zirconium metal in SBF has been investigated. A hydrated zirconia gel layer was formed on the surface of the zirconium metal on exposure to 1-15 M NaOH aqueous solutions at 95 degrees C for 24h. It was observed that the metals treated in NaOH aqueous solutions with concentrations above 5 M form an apatite layer on their surface in SBF. This indicates that the Zr-OH group of the zirconia gel induces apatite nucleation. The present study points to the possibility of obtaining bioactive zirconium after treatment by NaOH.

Apatites↗

PubMed2002

Mechanism of bonelike apatite formation on bioactive tantalum metal in a simulated body fluid.

Development of tantalum metal with bone-bonding ability is paid much attention because of its attractive features such as high fracture toughness, high workability and its achievement on clinical usage. Formation of bonelike apatite is an essential prerequisite for artificial materials to make direct bond to living bone. The apatite formation can be assessed in vitro using a simulated body fluid (SBF) that has almost equal compositions of inorganic ions to human blood plasma. The present authors previously showed that the apatite formation on tantalum metal in SBF was remarkably accelerated by treatment with NaOH aqueous solution and subsequent firing at 300 degrees C, while untreated tantalum metal spontaneously forms the apatite after a long soaking period. The purpose of the present study is to clarify the reason why the NaOH and heat treatments accelerate the apatite formation on tantalum metal. X-ray photoelectron spectroscopy was used to analyze changes in surface structure of the tantalum metal at an initial stage after immersion in SBF. Untreated tantalum metal had tantalum oxide passive layer on its surface, while amorphous sodium tantalate was formed on the surface of the tantalum metal by the NaOH and heat treatments. After soaking in SBF, the untreated tantalum metal sluggishly formed small amount of Ta-OH groups by a hydration of the tantalum oxide passive layer on its surface. In contrast, the treated tantalum metal rapidly formed Ta-OH groups by exchange of Na+ ion in the amorphous sodium tantalate on its surface with H3O+ ion in SBF. Both the formed Ta-OH groups combined with Ca2+ ion to form a kind of calcium tantalate, and then with phosphate ion, followed by combination with large amount of Ca2+ ions and phosphate ions to build up apatite layer. The formation rate of Ta-OH groups on the treated tantalum metal predominates the following process including adsorption of Ca2+ ion and phosphate ion on the surface. It is concluded that the acceleration of the apatite nucleation on the tantalum metal in SBF by the NaOH and heat treatments was attributed to the fast formation of Ta-OH group, followed by combination of the Ta-OH groups with Ca2+ and phosphate ions.

Apatites↗