氏名　Achariya Rakngram
学位の種類　博士（工学）
学位記番号　博甲第480号
学位授与の日付　平成20年8月31日
学位論文題目　Study on High Reliable Hydroxyapatite Coating on Titanium Substrate　（チタン基材への高信頼性ハイドロキシアパタイトコーティングに関する研究）
論文審査委員
　主査　教授　武藤睦治
　副査　教授　植松敬三
　副査　教授　岡崎正和
　副査　准教授　宮下幸雄
　副査　産学融合特任講師　大塚雄市

• 論文目次
• 論文要旨
• 論文審査の結果の要旨

［平成20（2008）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

Chapter 1.
　Introductuion　p.1
　1.1　The need for biomaterials　p.2
　1.2　Type of Biomaterals and its propaties　p.5
　1.3　Metallic implant materials　p.7
　1.4　Ceramic implant materials　p.20
　1.5　Calcium Phosphate Coating Deposition Processes　p.29
　1.6　Scope of present work　p.36
　REFERENCES　p.38
Chapter 2.
　Biomimetic process of hydroxyapatite formation on commercially pure titunium and Ti-6Al-4V
　Abstract　p.45
　2.1　Introduction　p.46
　2.2　Experimental procedure　p.47
　2.3　Results and Discussion　p.49
　2.4　Conclusion　p.62
　REFERENCES　p.64
Chapter 3.
　Electrochemical depositions of calcium phosphate film on commercially pure titanium and Ti-6Al-4V
　Abstract　p.66
　3.1　Introduction　p.67
　3.2　Experimental procedures　p.68
　3.3　Results and Discussion　p.71
　3.4　Conclusion　p.86
Chapter 4.
　Plasma sprayed HAp Top coat with Ti and HAp/Ti bond coats layer on commercially pure titanium
　Abstract　p.89
　4.1　Introduction　p.90
　4.2　Experimental procedure　p.91
　4.3　Results and Discussion　p.96
　4.4　Conclusion　p.107
　REFERENCES　p.108
Chapter 5.
　Conclusion　p.111
　5.1　General Conclusion　p.112
　5.2　Recommendations for further work　p.117
Appendix A　p.119
　Simulated body fluid preparation　p.119

In recent years, the development of new materials for the effective repair of the skeletal system is an outstanding goal of biomaterials science. Biomaterials are needed to alleviate pain and restore function to diseased or damaged part of the body. A major contributor to the need for “spare parts” for the body is the progressive deterioration of tissue with age. However, it is still in doubt whether the implant materials can survive and still possess their function in the body for the remaining years of the patient’s life; that is about 20 years at least. This requirement of survivability should be realized under conditions of use that are severe to all kind of implant materials－metals, polymers, and ceramics: corrosive saline solution at 36.5℃　under variable multiaxial, cyclical mechanical loads. Since metallic and ceramic implants are good to use as implant materials in most part of the body especially in bone or other load bearing. The strength and other mechanical properties can be obtained from metals and the biocompatibility of materials can be obtained from ceramic implant materials. In order to produce implant materials with longer survivability for various kinds of applications, the controlled thickness－thin, medium thick, and thick coating－suitable to each application of implant materials would be also required.

Chapter 1 Introduction: Biomaterials as well as basic properties and requirements of the materials which are used as implant materials have been introduced. General properties of metallic and ceramic implant materials including the fabrication processes of ceramic coating on metal substrate have been described. Scope and propose of the present study have also been presented.

Chapter 2 Biomimetic process of hydroxyapatite formation on commercially pure titanium and Ti-6A1-4V: The biomimetic process was applied to prepare a thin film of hydroxyapatite on cp-Ti and Ti-6A1-4V: The surface modifications of the substrates were done by alkali and ca-rich solution treatment before apatite precipitation in r-SBF. HAp thin layer formed on the substrate within a week. A scratch test, used to evaluate the adhesive strength of the HAp layer, showed that the HAp layer was not scraped off until the applied load reached 26N.

Chapter 3 Electrochemical depositions of calcium phosphate film on commercially pure titanium and Ti-6A1-4V: The electrochemical depositions of medium-thick calcium phosphate film on cp-Ti and Ti-6A1-4V in two types of types of electrolytes, mono-calcium phosphate monohydrate （MCPM） based aqueous solution and supersaturated calcium phosphate solution （SCPS）, were carried out by the cathodic polarization at 3mA/cm2 for 45 min. The major phase appeared in the were DCPD co-existed with OCP with the thickness of 45-55 μm in average. After soaking in r-SBF, the amorphous bone-like apatite became a single phase in the coating. From the scratch test, the highest critical load of 87.2N was obtained. The critical load was decreased almost 50% for all of the specimens after apatite precipitation in r-SBF.

Chapter 4 Plasma sprayed HAp Top coat with Ti and HAp/Ti bond coats layer on commercially pure titanium: The thick coating of HAp with three different type of bond coats were done in this chapter. Commercially pure titanium substrate surfaces were modified by Al2O3 grit powder and then with HAp/Ti mixed powders at room temperature by using sand and wet blasting machines, respectively. Then plasma spraying with Ti powders or HAp/Ti mixed powders was carried out as a bond coating layer. The hydroxyapatite top coat was sprayed with 100 μm thickness, subsequently. Tension-tension and compression-compression fatigue testing were carried out to evaluate the adhesive strength of the coating layers. Degree of the damage was successfully evaluated by the acoustic emission from the specimen during testing.

Chapter 5 Conclusion: the general conclusions with the new finding of the current work were summarized. Recommendation for further work was also presented.

　本論文は、「Study on High Reliable Hydroxyapatite Coating on Titanium Substrate（チタン基材への高信頼性ハイドロキシアパタイトコーティングに関する研究）」と題し、5章より構成されている。
　第1章「Introduction」では、生体材料に要求される諸特性について述べるとともに、金属基材上への生体適合皮膜の生成の現状と問題点について述べるとともに、本研究の目的と範囲を述べている。
　第2章「Biomimetic process of hydroxyapatite formation on commercially pure titanium and Ti-6A1-4V」では、アルカリ溶液およびCa高濃度溶液処理によるカルシュウムタイタネイド皮膜生成後に擬似体液中でハイドロキシアパタイト膜への置換を行う、新たに開発した生体擬似プロセスに基づく、チタン基材への薄膜生成に関して述べており、1週間以内にハイドロキシアパタイト皮膜の生成が可能であり、きわめて高い密着強度を示すことを明らかにしている。
　第3章「Electrochemical depositions of calcium phosphate film on commercially pure titanium and Ti-6A1-4V」では、2種類の電界溶液（mono-calcium phosphate monohydrate 水溶液およびsupersaturated calcium phosphate（溶液）を用いて、3mA/cm2という低電流密度で陰極分解することにより、チタン基板上に45-55μmの厚さのカルシウムフォスフェイトの成膜が可能であることを示し、この膜を擬似体液に浸漬することにより骨と同成分のハイドロキシアパタイト膜へと置換することができることを示している。さらに、スクラッチ試験による密着強度もきわめて高いことを明らかにしている。
　第4章「Plasma sprayed HAp top coat with Ti and HAp/Ti bond coat layer on commercially pure titanium」では、100μm程度の厚膜の生成に実用されているプラズマ溶射手法の問題点である低密着強度を改善するため、チタン基材とハイドロキシアパタイト・トップコートの間に、TiならびにTi/HApのボンドコートを導入したプラズマ溶射法を提案し、Ti/HAp混合粉末を用いたボンドコートが最も優れた密着性を示し、皮膜材の疲労試験により、過激な運動で骨が受ける荷重以上の負荷を長期間にわたりの繰り返しを与えた場合でも、損傷を生じないことを明らかにしている。
　第5章「Conclusion」では、本論文で得られた結論を要約するとともに、本論文に基づき、今後の展開についても論じている。
　よって、本論文は工学上及び工業上貢献するところが大きく、博士（工学）の学位論文として十分な価値を有するものと認める。