刘宣勇
论文题目：等离子喷涂生物活性硅灰石涂层研究
作者简介：刘宣勇，男，1974年03月出生，1999年03月师从于中国科学院上海硅酸盐研究所丁传贤教授，于2002年08月获博士学位。
摘
要
采用等离子喷涂技术在钛合金表面沉积生物活性陶瓷涂层是改善钛合金骨替换材料生物学性能的常用手段。等离子喷涂HA涂层和生物活性玻璃涂层已被广泛研究和应用，它们都具有良好的生物活性和生物相容性。但由于它们与钛合金基体的热膨胀系数不匹配，导致与基体的结合强度较低，临床应用仍然受到一定的限制。
硅灰石陶瓷具有同生物活性玻璃类似的化学组成以及与钛合金相近的热膨胀系数。与生物活性玻璃类似的组成保证了硅灰石具有良好的生物活性；相近的热膨胀系数使硅灰石涂层能与钛合金基体牢固的结合。但这方面的研究工作尚未见文献报导。
本论文采用等离子喷涂技术，将硅灰石陶瓷沉积于钛合金基体表面，制备了硅灰石涂层，对涂层的工艺、结构和性能作了研究。在此基础上，又制备了硅灰石/TiO2复合涂层、硅灰石/ZrO2复合涂层和硅酸二钙涂层，并研究了它们的结构和性能。
本文取得的主要结果有：
1．利用等离子喷涂技术，将天然硅灰石粉末进行球化，能得到球化效果良好、粒径分布均匀、流动性好、可供喷涂的原料。由球化粉末制得的涂层具有粗糙的表面和较少的裂纹，与Ti-6Al-4V基体的结合强度值可达42.8 MPa，远高于现有生物活性涂层与钛合金的结合强度。
2．等离子喷涂硅灰石涂层的显微结构和相组成都存在不均匀性。涂层的主晶相是三斜晶系的硅灰石晶体（TC），涂层中也存在少量的CaO和SiO2晶体以及玻璃相。硅灰石晶体中还存在层错缺陷。涂层中的玻璃相区域与硅灰石晶体紧密相邻，在玻璃相区域中能观察到纳米微晶的存在。
3．等离子喷涂硅灰石涂层经模拟体液浸泡后，涂层表面与体液反应生成碳酸磷灰石（CHA）。其过程是：涂层中的Ca2+与体液中的H+交换，使体液中的Ca2+浓度、pH值升高，相应的体液中磷灰石的离子活度积也升高，同时涂层表面形成富硅层，为磷灰石成核提供位置，使磷灰石很快在其表面成核。在溶液中的碳酸根参与下，晶化形成的是多晶碳酸磷灰石层，其组成与人体骨骼中的主要无机成分一致。形成的磷灰石是纳米级微晶，局部的团簇有一定的择优取向。碳酸磷灰石的形成证明，硅灰石涂层具有优良的生物活性。
4．成骨细胞能在等离子喷涂硅灰石涂层表面生存并增殖。硅灰石涂层在培养液中的溶解产物能激活成骨细胞的基因表达和表型分化。成骨细胞培养实验结果充分表明了等离子喷涂硅灰石涂层具有良好细胞相容性和骨形成能力。
5．硅灰石/TiO2复合涂层（W3T7和W7T3）与Ti-6Al-4V基体的结合强度超过30 MPa。模拟体液浸泡试验显示，TiO2可抑制硅灰石涂层的降解和消溶，碳酸磷灰石能在W7T3涂层表面形成，但不能在W3T7涂层表面形成，这表明W7T3涂层具有良好的生物活性。成骨细胞能在W7T3涂层表面生存并增殖，意味着此种涂层具有良好的细胞相容性和骨形成能力。
6．硅灰石/ZrO2复合涂层（W3Z7和W7Z3）与Ti-6Al-4V基体的结合强度高于30 MPa。模拟体液浸泡试验显示，ZrO2可抑制硅灰石涂层的降解和消溶，碳酸磷灰石能在W3Z7和W7Z3涂层表面形成，这表明它们具有良好的生物活性。成骨细胞能在W3Z7和W7Z3涂层表面生存并增殖，意味着它们都具有良好的细胞相容性和骨形成能力。
7．等离子喷涂硅酸二钙涂层与Ti-6Al-4V基体结合强度较高，其值可达38.9 MPa。硅酸二钙涂层浸泡在模拟体液中两天后，表面被致密的球形磷灰石晶体（CHA）覆盖，在磷灰石层之下可观察到明显的富硅层。随着浸泡时间延长，表面的磷灰石层逐渐增厚。上述结果表明，硅酸二钙涂层具有优良的生物活性。成骨细胞能在硅酸二钙涂层表面生存并增殖，迅速攀附并覆盖涂层表面，这表明等离子喷涂硅酸二钙涂层具有良好的细胞相容性和骨形成能力。
从以上结果中可以看出，等离子喷涂硅灰石涂层、硅酸二钙涂层以及W7T3、W3Z7、W7Z3三种复合涂层都具有良好的生物活性又与钛合金基体有较高的结合强度，是较有应用前途的骨替换候选材料。
关键词:
等离子喷涂，硅灰石涂层，硅酸二钙涂层，生物活性，生物相容性
Abstract
Bioceramic-coated Ti alloys by plasma spraying is a common means to improve the bioactivity and biocompatibility of Ti alloy bone grafts. Plasma sprayed HA and bioglass coatings with good bioactivity and biocompatibility possess low bond strength onto Ti alloy substrate because of the mismatch of the thermal expansion coefficient between the coating and the substrate, which limits their application in clinic.
The composition of wollastonite is similar to that of the bioactive glass, which suggests good bioactivity and biocompatibility of wollastonite. In addition, the thermal expansion coefficient of wollastonite is close to that of Ti alloys. It indicates that wollastonite coating is tightly bonding to Ti alloy substrate. However, wollastonite-coated Ti alloys for biomedical application has hardly been reported.
In the thesis, wollastonite coatings are deposited onto Ti alloys by plasma spraying. The process, structures and properties of wollastonite coating are examined. In order to improve the properties of wollastonite coating, the wollastonite/TiO2 and wollastonite/ZrO2 composite coatings and dicalcium silicate coating are also prepared and studied.
Results obtained are described as follows:
1. Spheroidized wollastonite powder is prepared by plasma spraying natural wollastonite powder into water. The spheroidized powder presents a sphere-like morphology, uniform distribution of particle size and good flowability, which is necessary for plasma spraying. The coating produced with the spheroidized wollastonite powder possesses rough surface and few microcracks, its bond strength to Ti-6Al-4V substrate is up to about 42.8 MPa.
2. The plasma sprayed wollastonite coating is not homogeneous. Some pores and microcracks existed in the coatings. The primary crystalline phase of the coating is triclinic structure wollastonite. Some crystalline wollastonite grains with dislocation are also observed in the coating. Glassy phase, tridymite (SiO2) and CaO are also found in the coating. Some nanocrystals formed in glassy phase are detected by TEM.
3. The carbonate-containing hydroxyapatite (CHA) layer is formed on the surface of plasma sprayed wollastonite coatings soaked in SBF solution and possessed preferential orientation of the CHA crystals. Prior to the formation of the CHA layer, silica-rich layer is formed on the surface of plasma sprayed wollastonite coating soaked in SBF solution. The formation mechanism of apatite on the plasma sprayed wollastonite coatings in SBF solution was explained in terms of the ionic exchange between H+ within SBF solution and Ca2+ in the coating, which resulted in the increase in [Ca2+], pH value and ionic activity product (IP) of apatite in SBF solution and provided a specific surface with lower interface energy against apatite. This caused the decrease in the free energy to the formation of apatite nuclei. The formation of CHA layer on the coating surface indicates wollastonite coating possesses good bioactivity.
4. Osteoblasts survive and proliferate on the surface of wollastonite coating. The ionic dissolution products of wollastonite coating in culturing medium can activate gene express and phenotype differentiation of osteoblast. The results indicate plasma sprayed wollastonite coatings possess good cytocompatibility and osteogenic potential.
5. The bond strengths of wollastonite/TiO2 composite coatings (W3T7 and W7T3) to Ti-6Al-4V substrate are higher than 30MPa. The SBF test shows that TiO2 in coating decreases the dissolution of wollastonite coating, CHA layer is formed on the surface of W7T3 coatings and not on the surface of W3T7 coating, which indicates that W7T3 coatings possesses good bioactivity. Osteoblasts survive and proliferate on the surface of W7T3 coating, which indicates that W7T3 coating possesses good cytocompatibility and osteogenic potential.
6. The bond strengths of wollastonite/ZrO2 composite coatings (W3Z7 and W7Z3) to Ti-6Al-4V substrate are higher than 30MPa. The SBF test shows that ZrO2 in coating decreases the dissolution of wollastonite coating, CHA layer is formed on the surface of W7Z3 and W3Z7 coatings, which indicates that they possesses good bioactivity. Osteoblasts survive and proliferate on the surfaces of W7Z3 and W3Z7 coatings, which indicates that they possess good cytocompatibility and osteogenic potential.
7. Plasma sprayed dicalcium silicate bond tightly to Ti-6Al-4V substrate, its bond strength is up to 38.9 MPa. A dense CHA layer is formed on the surface of dicalcium silicate coating soaked in SBF solution for 2 days. A silica-rich layer is also observed between the CHA layer and the coating. With an increase in the immersion time, the CHA layer gradually become thicker. The results obtained indicate that the plasma sprayed dicalcium silicate coating possesses good bioactivity. Osteoblasts survive and proliferate on the surface of plasma sprayed dicalcium silicate coatings, which indicates that it possesses good cytocompatibility and osteogenic potential.
KEYWORDS:
Plasma spraying, wollastonite coating, dicalcium silicate coating, bioactivity, biocompatibility
