鈦金屬及其合金是極具潛力且運用極廣的生醫材料，由於其擁有高比強度、優異機械性質、耐蝕性、及良好的生物相容性，使得鈦合金常應用於牙科植體與生醫器材，然而現今鈦合金已無法完全符合生醫的臨床要求，因此為了提高其機械、化學及生物相容性能，需研發新的鈦合金材料與進行其表面性質改良以增進其功能性。目前新型生醫鈦合金研究，主要朝向提升鈦合金強度及增加其耐蝕性，並避免其植入人體時會釋出有毒金屬離子的機會。在前期研究中發現鈦合金裡添加銅元素可析出Ti2Cu來阻擋差排，並與錫元素結合可產生強化效果，文獻中亦指出鈦合金添加5~7wt.%銅元素會有最佳的耐蝕性與機械性質。隨後在眾多的鈣磷系骨水泥(CPC)中，發現氫氧基磷灰石(HA)是最接近人體骨骼成分的生醫陶瓷材料，其具有極佳的生物相容性及誘骨性，甚至可以直接與人體骨骼結合，使其在近年來相當被看好的骨骼植入材料。基於此，本文結合此兩者的優勢，希望能開發出更符合臨床醫療所需的人工植體。
本文主要內容包含三部份，分別敘述如下：
(1)第一部份研究主要是利用微弧氧化法(MAO)，將濃度0.15M的醋酸鈣(CA)與0.06M的磷酸二氫鈉(SDP)之混和電解溶液直接在Ti7Cu5Sn合金表面，製備成富含鈣磷化合物的骨水泥生物陶瓷鍍層與氫氧基磷灰石。實驗條件為分別施加250、300、350伏特的直流電壓、而電流密度皆為3A/cm2，在Ti7Cu5Sn合金基材上並持續30分鐘，從上述樣品的表面SEM照片結果發現，MAO反應後之鍍層具有微弧氧化作用典型的微孔、粗糙表面，且隨著施加電壓升高，導致微孔大小、鍍層厚度、微硬度及表面粗糙度都隨之增加，這些性質皆有助於細胞的附著與增長。另從鍍層橫節面的SEM照片可得知，依結構可約略劃分為兩層，包含外部較厚的疏鬆層與內部較薄的緊實層，並由各電壓條件下之SEM照片，確認鍍層皆與基材緊密結合無縫隙。其次，由表面EDS成分分析結果得知，此三種電壓下之MAO鍍層皆含有鈦、銅、錫、鈣、磷等元素，並顯示電解液經過高電壓可與基材之熔融態電漿相結合。當電壓條件350伏特時，其鍍層表面之鈣磷莫耳比為1.72，已相當接近正常人體骨骼之鈣磷比1.67。另從橫截面的EDS元素分佈圖，可將鍍層依成分細分為三層，分別為含鈣磷化合物的骨水泥外層、含有氧化鈦及鈣磷化合物的混和中間層及高濃度的氧化鈦內層。最後，由XRD繞射圖可確認，(a)電壓為250伏特條件下，鍍層表面主要由鈣磷鹽類骨水泥的二鈣磷酸鹽(CaHPO4・2H2O，DCPD)、金紅石(Rutile)、銳鈦礦(Anatase)、及鈦酸鈣(CaTiO3)等組成。(b)電壓升至350伏特時，出現了更多鈣磷類的化合物如焦磷酸鈣(Ca2P2O7)、磷酸鈣((Ca3(PO4)2)及焦磷酸鈦(TiP2O7)。其中在250伏特的二鈣磷酸鹽繞射峰，升壓至300伏特時轉相成焦磷酸鈣，達到350伏特時更轉相成氫氧基磷灰石結晶，故電壓提高可增強氫氧基磷灰石結晶的純化。
(2)第二部分為添加濃度0.03M氫氧化鍶((Sr(OH)2・8H2O))溶液，於濃度0.15M的醋酸鈣與0.06M的磷酸二氫鈉之混和電解溶液。由於人體骨骼中已有大量的鍶存在，添加鍶可應用於促進骨細胞分化，抑制骨吸收，降低骨質流失的速率，並可治療骨質疏鬆症。再者鍶元素與鈣元素之化學性質相似，鍶元素會取代氫氧基磷灰石化合物中鈣元素的位置。由含鍶的鍍層樣品SEM照片發現，其表面物理性質如表面微孔洞大小、鍍層厚度、硬度及粗糙度等趨勢皆與不含鍶之鍍層特性一致呈現正相關特性。在350伏特條件下，表面散布更多微細小孔洞，此微細小孔洞可促進細胞的附著與增生。其中厚度與微硬度與250伏特條件下相較，更可提升51.4%與9.5%。另各電壓條件下之橫節面SEM照片，可確認鍍層皆與基材緊密結合無縫隙，而不含鍶之MAO鍍層依照結構亦可分為緻密與疏鬆內外兩層。其次，由表面EDS成分分析結果得知，此三種電壓下之MAO鍍層皆含有鈦、銅、錫、鈣、磷、鍶等元素。當電壓條件250伏特時，其鍍層表面之鈣磷莫耳比為1.97，已超過正常人體骨骼之鈣磷比，顯示添加鍶可幫助提高鍍層表面的鈣磷含量，這可歸功於鍶元素可幫助導電所致。另從橫截面的EDS元素分佈圖可確認鍶元素已經成功地結合於鍍層中。最後，經由XRD圖可更加證實樣品的鍍層膜已有效的轉相為含鍶元素的氫氧基磷灰石(Sr-HA)，即使在低電壓250伏特的情況下，也能成功的製備出含鍶的氫氧基磷灰石。
(3)第三部分研究最後由電化學動態極化法(PD)結果，得知Ti7Cu5Sn合金基材，因為有相當緻密的氧化膜，其腐蝕電位為-127.7mV，然而經過微弧後的不含鍶鍍層之腐蝕電位仍然低於基材，其原因為鍍層中之大量鈣磷化合物及氫氧基磷灰石結晶，並隨著電壓升高至350伏特，會提高其腐蝕電位與減小其腐蝕電流，其腐蝕電位與腐蝕電流效果增益分別可達58.5%與70.0%，這是由於高電壓會形成較厚的鍍層與較好的HA結晶，可以提供保護，減少腐蝕速率。再者，添加鍶元素鍍層的腐蝕電位與腐蝕電流趨勢，也跟未添加鍶樣品的趨勢一致，甚至在電壓250伏特與300伏特時，添加鍶元素鍍層其腐蝕電位更高，腐蝕電流更小，與未添加鍶元素之鍍層相比，在300伏特時，其腐蝕電位、腐蝕電流分別改善達7.6%與33.2%。此外由電化學阻抗頻譜（EIS），可非破壞性的深入研究鍍層之內部各層基本性質，其實驗數據可由Zview模擬軟體分析得知，MAO鍍層符合三層的電路元件模擬，更呼應前面EDS元素分佈圖的三層成分模型。再依三層的電路元件模擬參數發現相同電壓下，內層之阻抗值最高、中間次之、外層之阻抗為最低，這是由於外層之孔洞較多質地也較疏鬆，內層質地最緻密也無孔洞出現造成。進一步在不同電壓情況下，比較外層阻抗值，發現越高電壓下阻抗越低，這是由於高電壓造成較粗大的孔洞、質地較疏鬆及較薄的高品質氫氧基磷灰石結晶層。
綜合上述的結果，可知樣品製備在微弧氧化過程，電壓350伏特、表面電流密度3A/cm2及30分鐘的條件下，可以成功地製備高品質、高抗腐蝕性及的高純度的氫氧基磷灰石結晶鍍層，並得知較高的外加電壓可提高表面的結晶品質、較好的細胞附著表面及提高抗腐蝕能力。

Titanium (Ti) and its alloys have highly potential and are wildly used for biomaterials due to their high specific strength, excellent mechanical properties, better corrosion resistance, and good biocompatibility. Therefore, Ti alloys are often used in dental implants and biomedical equipment. However, the properties of Ti alloys cannot fully comply with the biomedical and clinical requirements nowadays. To improve the mechanical behavior, chemical behavior and biocompatibility of Ti alloys, a new Ti alloy should be developed so that its surface properties can be improved and its functionality can be enhanced. Currently, the study on new biomedical Ti alloy mainly focuses on the topic of strength lifting, corrosion resistance increase, and exemption from the release of toxic metal ions while it is implanted into the human body. In the previous studies, it was found that the adding Cu ions in Ti alloy facilitate to separate out Ti2Cu compound to block dislocations and combine with Sn ions so that the effect can be strengthened. It was also found that the best corrosion resistance and mechanical properties appear when 5～7wt.% of Cu element is added. Subsequently, hydroxyapatite (HA) was found to be the biomedical ceramic material with the most similarity to the human skeleton composition among many calcium phosphate cements (CPC). In recent years, HA has been recognized as the popular material for the bone implant due to its excellent biocompatibility, osteoconductivity and the ability to connect with human bones directly. Based on these reasons, this paper aims to combine the advantages of both alloys to develop an implant that meets the requirement of clinic more.
This paper mainly includes three parts as follows:
(1) First part :
The 0.15M electrolyte containing of calcium acetate (CA) and 0.06M of sodium dihydrogen phosphate (SDP) are used to directly produce the Ca/P-rich bioceramic coatings and HA on the surface of Ti7Cu5Sn alloy by the micro-arc oxidation (MAO) method. The experimental conditions with voltages of 250, 300, 350 V, and current density of 3A/cm2 are applied on the Ti7Cu5Sn substrate for 30 minutes. From the SEM images of the above samples, it is found that the coatings have the typical type of porous and rough surface after processing MAO method. In addition, the average pore size, coating thickness, micro hardness and surface roughness are increasing with the increase of applied voltage. These properties help cells attach and grow on the coating surfaces. It also found that the MAO coatings can be roughly divided into two layers, the outer oxide layer (thick and porous layer) and the inner oxide layer (thin and impact layer) from the cross-section SEM images. It is also found that the coating and alloys are closely integrated without any gaps from the SEM images with various voltages. Furthermore, the analysis on the EDS surface shows that MAO for all three voltages coatings contain Ti, Cu, Sn, Ca and P elements, and verifies that Ca、P ions in electrolyte can combine with the molten plasma of alloys by applying higher voltage. With the voltage of 350 V, the Ca/P ratio of the surface coating is 1.72 and very close to that of natural human bone acalcium (1.67). Furthermore, from the cross section of the EDS element distribution pattern, the MAO coating can be subdivided into three layers, the outer layer containing Ca/P compound of CPC, the mixture middle layer containing Ca/P compound and TiO2 oxide, and the inner layer with high concentrations of TiO2 oxide. Finally, the XRD diffraction is facilitated to verify: (a) With the voltage of 250 V, the coating is mainly composed of dicalcium phosphate dihydrate (CaHPO4・2H2O, DCPD), rutile, anatase, and calcium titanate (CaTiO3) of calcium phosphate bone cements. (b) With the increase of voltage to 350 V, more calcium phosphate compounds, such as calcium pyrophosphate (Ca2P2O7), Tricalcium phosphate ((Ca3(PO4)2) and titanium pyrophosphate (TiP2O7) are emerged. Especially, the DCPD phase will transform into calcium pyrophosphate phase by applying voltages from 250 V to 300 V. The calcium pyrophosphate phase will further transform into HA when the voltage reaches 350 V. Therefore, the increasing voltage is advantageous to improve the purification of crystal HA.
(2) Second part:
A solution of 0.03M strontium hydroxide ((Sr(OH) 2・8H2O)) is added to the mixture solution containing 0.15M CA and 0.06M SDP to produce Sr-HA. There are a large amount of strontium (Sr) elements existing in the natural human bones. Sr is beneficial to promote bone cell differentiation, inhibit bone resorption, reduce bone loss rate, and treat osteoporosis. Moreover, the chemical properties of Sr are similar with those of Ca. Therefore, Sr is eligible to replace the position of Ca in HA. From the surface SEM image of Sr-HA coatings, it is found that all trends of physical properties, such as average pores size, coating thickness, micro-hardness and roughness, are the same as those of HA and show positive correlation. At 350 V, there are more tiny micro-holes spreading over the coating surfaces. These tiny holes can promote cell attachment and proliferation. Especially, the thickness and micro-hardness at 350 V are improved about 51.4% and 9.5% compared to the case of 250 V. Besides, from the SEM images, r-HA coatings are found to closely integrate with the alloys without any gaps between coating and alloys. The Sr-HA coatings can also be roughly divided into two layers, the outer porous layer and inner dense layer. Next, the surface EDS analysis shows that MAO coatings contain Ti, Cu, Sn, Ca, P and Sr elements at all three voltage levels. At 250 V, the Ca/P ratio of the Sr-HA coating surface is 1.97 and higher than that of the normal human bone. It indicates that the Sr addition can raise the Ca/P ratio of Sr-HA coating due to Sr’s high conductivity. In addition, the EDS line scan of cross-section coating verifies the successful merge of Sr with coating. Finally, it can be further confirmed that coating had been successfully transferred into Sr-HA through XRD pattern, even in the case of low voltage (250 V).
(3) The third part:
By the electrochemical dynamic polarization method (PD), the corrosion potential of Ti7Cu5Sn alloy is obtained to be -127.7mV due to the dense oxide film on its surface. However, the corrosion potential of HA coatings is still lower than that of Ti7Cu5Sn since there are numerous calcium phosphate compound and HA in the coatings. The corrosion potential becomes higher and the corrosion current becomes lower with the increase of applied voltage to 350 V. The gains of corrosion potential and corrosion current applied from 250 V to 350 V are 58.5％and 70.0％, respectively. Therefore, the high applied voltage facilitates to form thicker coatings and better HA crystals to provide protection and reduce the corrosion rate. Furthermore, the trend of corrosion potential and corrosion current for Sr-HA coatings is the same as that of HA with increasing applied voltage. Sr-HA even has higher corrosion potential and lower corrosion current compared to HA at voltage of 250V and 300 V, in which the corrosion potential and corrosion current have been improved 7.6% and 33.2% at 300 V, respectively..
Moreover, a non-destructive study is available to investigate the basic properties of the inner layers of coating by EIS test, and the experiment results can be analyzed by Zview simulation software. The MAO coatings conform the simulation model of three circuit layers and coincide the three component layers of EDS line scan. According to the parameters fitted by the model of three circuit layers, it is found that the inner layer has the highest impedance resistance at the same voltage because it is the most dense oxide layer and has no holes appearance. Thus the outer layer has the lowest impedance resistance at the same voltage because it has many holes and is looser. Furthermore, the impedance resistance of the outer layer is investigated at different applied voltages. It is found that the outer layer has lower impedance resistance at high applied voltage due to bigger hole, looser texture and thinner HA layer
In conclusion, the sample preparation condition with applied voltage of 350 V, current density of 3A/cm2, and oxide time of 30 minutes can successfully produce high quality, high corrosion resistance and high purity HA coating by MAO method. It is also known that the higher applied voltage ensures higher surface quality, better cell attachment and stronger corrosion resistance.

References
[1]R. Bothe, L. Beaton, and H. Davenport, "Reaction of bone to multiple metallic implants," Surg Gynecol Obstet, vol. 71, pp. 598-602, 1940.
[2]S. Izman, A. Shah, E. Nazim, M. Hassan, M. Anwar, M. R. Abdul-Kadir, et al., Surface modification techniques for biomedical grade of titanium alloys: Oxidation, carburization and ion implantation processes: INTECH Open Access Publisher, 2012.
[3]M. Metikoš-Huković, E. Tkalčec, A. Kwokal, and J. Piljac, "An in vitro study of Ti and Ti-alloys coated with sol–gel derived hydroxyapatite coatings," Surface and Coatings Technology, vol. 165, pp. 40-50, 2003.
[4]W.-H. Song, Y.-K. Jun, Y. Han, and S.-H. Hong, "Biomimetic apatite coatings on micro-arc oxidized titania," Biomaterials, vol. 25, pp. 3341-3349, 2004.
[5]K. Venkateswarlu, N. Rameshbabu, A. C. Bose, V. Muthupandi, S. Subramanian, D. MubarakAli, et al., "Fabrication of corrosion resistant, bioactive and antibacterial silver substituted hydroxyapatite/titania composite coating on Cp Ti," Ceramics International, vol. 38, pp. 731-740, 2012.
[6]J. Li, "Behaviour of titanium and titania-based ceramics in vitro and in vivo," Biomaterials, vol. 14, pp. 229-232, 1993.
[7]X. Shi, L. Xu, and Q. Wang, "Porous TiO 2 film prepared by micro-arc oxidation and its electrochemical behaviors in Hank's solution," Surface and Coatings Technology, vol. 205, pp. 1730-1735, 2010.
[8]A. Yerokhin, A. Shatrov, V. Samsonov, P. Shashkov, A. Pilkington, A. Leyland, et al., "Oxide ceramic coatings on aluminium alloys produced by a pulsed bipolar plasma electrolytic oxidation process," Surface and Coatings Technology, vol. 199, pp. 150-157, 2005.
[9]Y. Gu, C.-f. Chen, S. Bandopadhyay, C. Ning, Y. Zhang, and Y. Guo, "Corrosion mechanism and model of pulsed DC microarc oxidation treated AZ31 alloy in simulated body fluid," Applied Surface Science, vol. 258, pp. 6116-6126, 2012.
[10]W.-C. Gu, G.-H. Lv, H. Chen, G.-L. Chen, W.-R. Feng, and S.-Z. Yang, "Characterisation of ceramic coatings produced by plasma electrolytic oxidation of aluminum alloy," Materials Science and Engineering: A, vol. 447, pp. 158-162, 2007.
[11]X. Sun, M. Nouri, Y. Wang, and D. Li, "Corrosive wear resistance of Mg–Al–Zn alloys with alloyed yttrium," Wear, vol. 302, pp. 1624-1632, 2013.
[12]S. Bruni, M. Martinesi, M. Stio, C. Treves, T. Bacci, and F. Borgioli, "Effects of surface treatment of Ti–6Al–4V titanium alloy on biocompatibility in cultured human umbilical vein endothelial cells," Acta Biomaterialia, vol. 1, pp. 223-234, 2005.
[13]S. Rao, T. Ushida, T. Tateishi, Y. Okazaki, and S. Asao, "Effect of Ti, Al, and V ions on the relative growth rate of fibroblasts (L929) and osteoblasts (MC3T3-E1) cells," Bio-medical materials and engineering, vol. 6, pp. 79-86, 1995.
[14]P. Zatta, D. Drago, S. Bolognin, and S. L. Sensi, "Alzheimer's disease, metal ions and metal homeostatic therapy," Trends in Pharmacological Sciences, vol. 30, pp. 346-355, 2009.
[15]L. Tsao, "Effect of Sn addition on the corrosion behavior of Ti–7Cu–Sn cast alloys for biomedical applications," Materials Science and Engineering: C, vol. 46, pp. 246-252, 2015.
[16]L. Tsao, R. Wu, M. Wu, C. Huang, and R. Chen, "Formation of ultrafine structure in as cast Ti7CuXSn alloys," Materials Science and Technology, vol. 29, pp. 1529-1536, 2013.
[17]S. Shadanbaz and G. J. Dias, "Calcium phosphate coatings on magnesium alloys for biomedical applications: a review," Acta Biomaterialia, vol. 8, pp. 20-30, 2012.
[18]K. Sanosh, M.-C. Chu, A. Balakrishnan, Y.-J. Lee, T. Kim, and S.-J. Cho, "Synthesis of nano hydroxyapatite powder that simulate teeth particle morphology and composition," Current Applied Physics, vol. 9, pp. 1459-1462, 2009.
[19]M. Long and H. Rack, "Titanium alloys in total joint replacement—a materials science perspective," Biomaterials, vol. 19, pp. 1621-1639, 1998.
[20]X. Liu, P. K. Chu, and C. Ding, "Surface modification of titanium, titanium alloys, and related materials for biomedical applications," Materials Science and Engineering: R: Reports, vol. 47, pp. 49-121, 2004.
[21]J. Polmear, "Titanium alloys," Light alloys, 1981.
[22]D. Eylon, R. R. Boyer, and D. A. Koss, "Beta Titanium Alloys in the 1990's," Warrendale, PA (United States); Minerals, Metals and Materials Society1993.
[23]R. L. Buly, M. H. Huo, E. Salvati, W. Brien, and M. Bansal, "Titanium wear debris in failed cemented total hip arthroplasty: an analysis of 71 cases," The Journal of arthroplasty, vol. 7, pp. 315-323, 1992.
[24]M. Semlitsch, F. Staub, and H. Weber, "Titanium-Aluminium-Niobium Alloy, Development for Biocompatible, High Strength Surgical Implants-Titan-Aluminium-Niob-Legierung, entwickelt für körperverträgliche, hochfeste Implantate in der Chirurgie," Biomedizinische Technik/Biomedical Engineering, vol. 30, pp. 334-339, 1985.
[25]K. K. Wang, L. J. Gustavson, and J. H. Dumbleton, "Microstructure and properties of a new beta titanium alloy, Ti-12Mo-6Zr-2Fe, developed for surgical implants," ASTM SPECIAL TECHNICAL PUBLICATION, vol. 1272, pp. 76-87, 1996.
[26]A. K. Mishra and J. Davidson, "Ti--13 Nb--13 Zr: a New Low Modulus, High Strength, Corrosion Resistant Near-Beta Alloy for Orthopaedic Implants," Beta Titanium Alloys in the 1990's, pp. 61-72, 1993.
[27]L. D. Zardiackas, D. W. Mitchell, and J. A. Disegi, "" Characterization of ti-15Mo Beta Titanium Alloy for Orthopaedic," Medical Applications of Titanium and Its Alloys: The Material and Biological Issues, p. 60, 1996.
[28]K. Wang, "The use of titanium for medical applications in the USA," Materials Science and Engineering: A, vol. 213, pp. 134-137, 1996.
[29]W. E. Brown and L. C. Chow, "Dental restorative cement pastes," ed: Google Patents, 1990.
[30]A. A. Mirtchi, J. Lemaitre, and N. Terao, "Calcium phosphate cements: Study of the β-tricalcium phosphate—monocalcium phosphate system," Biomaterials, vol. 10, pp. 475-480, 1989.
[31]S. Patel, "Optimising calcium phosphate cement formulations to widen clinical applications," University of Birmingham, 2011.
[32]M. Mhaede, F. Pastorek, and B. Hadzima, "Influence of shot peening on corrosion properties of biocompatible magnesium alloy AZ31 coated by dicalcium phosphate dihydrate (DCPD)," Materials Science and Engineering: C, vol. 39, pp. 330-335, 2014.
[33]K. de Groot, Bioceramics of calcium phosphate: CRC, 1983.
[34]S. Hulbert, J. Bokros, L. Hench, J. Wilson, and G. Heimke, "Ceramics in clinical applications, past, present and future," High Tech Ceramics.(Part A), pp. 189-213, 1986.
[35]T. Jinno, S. K. Kirk, S. Morita, and V. M. Goldberg, "Effects of calcium ion implantation on osseointegration of surface-blasted titanium alloy femoral implants in a canine total hip arthroplasty model," The Journal of arthroplasty, vol. 19, pp. 102-109, 2004.
[36]J.-W. Park, J.-H. Jang, C. S. Lee, and T. Hanawa, "Osteoconductivity of hydrophilic microstructured titanium implants with phosphate ion chemistry," Acta biomaterialia, vol. 5, pp. 2311-2321, 2009.
[37]D. Farlay, G. Boivin, G. Panczer, A. Lalande, and P. J. Meunier, "Long‐Term Strontium Ranelate Administration in Monkeys Preserves Characteristics of Bone Mineral Crystals and Degree of Mineralization of Bone," Journal of Bone and Mineral Research, vol. 20, pp. 1569-1578, 2005.
[38]J. Christoffersen, M. R. Christoffersen, N. Kolthoff, and O. Bärenholdt, "Effects of strontium ions on growth and dissolution of hydroxyapatite and on bone mineral detection," Bone, vol. 20, pp. 47-54, 1997.
[39]L. Snizhko, A. Yerokhin, A. Pilkington, N. Gurevina, D. Misnyankin, A. Leyland, et al., "Anodic processes in plasma electrolytic oxidation of aluminium in alkaline solutions," Electrochimica Acta, vol. 49, pp. 2085-2095, 2004.
[40]G. Chen, Z. Wang, H. Bai, J. Li, and H. Cai, "A preliminary study on investigating the attachment of soft tissue onto micro-arc oxidized titanium alloy implants," Biomedical materials, vol. 4, p. 015017, 2009.
[41]B. Groessner-Schreiber and R. S. Tuan, "Enhanced extracellular matrix production and mineralization by osteoblasts cultured on titanium surfaces in vitro," Journal of cell science, vol. 101, pp. 209-217, 1992.
[42]Z. Yao, L. Li, and Z. Jiang, "Adjustment of the ratio of Ca/P in the ceramic coating on Mg alloy by plasma electrolytic oxidation," Applied Surface Science, vol. 255, pp. 6724-6728, 2009.
[43]Y. Wang, T. Lei, B. Jiang, and L. Guo, "Growth, microstructure and mechanical properties of microarc oxidation coatings on titanium alloy in phosphate-containing solution," Applied surface science, vol. 233, pp. 258-267, 2004.
[44]D. Wei, Y. Zhou, and H. Guo, "Characterization and properties of microarc oxidized coatings containing Si, Ca and Na on titanium," Ceramics International, vol. 37, pp. 1761-1768, 2011.
[45]J. Sun, Y. Han, and X. Huang, "Hydroxyapatite coatings prepared by micro-arc oxidation in Ca-and P-containing electrolyte," Surface and coatings technology, vol. 201, pp. 5655-5658, 2007.
[46]K. Qiu, X. J. Zhao, C. X. Wan, C. S. Zhao, and Y. W. Chen, "Effect of strontium ions on the growth of ROS17/2.8 cells on porous calcium polyphosphate scaffolds," Biomaterials, vol. 27, pp. 1277-1286, 2006.
[47]C. Wu, Y. Ramaswamy, D. Kwik, and H. Zreiqat, "The effect of strontium incorporation into CaSiO 3 ceramics on their physical and biological properties," Biomaterials, vol. 28, pp. 3171-3181, 2007.
[48]Z. Li, W. Lam, C. Yang, B. Xu, G. Ni, S. Abbah, et al., "Chemical composition, crystal size and lattice structural changes after incorporation of strontium into biomimetic apatite," Biomaterials, vol. 28, pp. 1452-1460, 2007.
[49]M. Grynpas and P. Marie, "Effects of low doses of strontium on bone quality and quantity in rats," Bone, vol. 11, pp. 313-319, 1990.
[50]K. Nan, T. Wu, J. Chen, S. Jiang, Y. Huang, and G. Pei, "Strontium doped hydroxyapatite film formed by micro-arc oxidation," Materials Science and Engineering: C, vol. 29, pp. 1554-1558, 2009.
[51]J. Yan, J. F. Sun, P. K. Chu, Y. Han, and Y. M. Zhang, "Bone integration capability of a series of strontium‐containing hydroxyapatite coatings formed by micro‐arc oxidation," Journal of Biomedical Materials Research Part A, vol. 101, pp. 2465-2480, 2013.
[52]Y. Han, J. Zhou, S. Lu, and L. Zhang, "Enhanced osteoblast functions of narrow interligand spaced Sr-HA nano-fibers/rods grown on microporous titania coatings," RSC Advances, vol. 3, pp. 11169-11184, 2013.
[53]A. Yanovska, V. Kuznetsov, A. Stanislavov, S. Danilchenko, and L. Sukhodub, "Calcium–phosphate coatings obtained biomimetically on magnesium substrates under low magnetic field," Applied Surface Science, vol. 258, pp. 8577-8584, 2012.
[54]Q. Zhao, X. Guo, X. Dang, J. Hao, J. Lai, and K. Wang, "Preparation and properties of composite MAO/ECD coatings on magnesium alloy," Colloids and Surfaces B: Biointerfaces, vol. 102, pp. 321-326, 2013.
[55]Y. Huang, Y. Yan, X. Pang, Q. Ding, and S. Han, "Bioactivity and corrosion properties of gelatin-containing and strontium-doped calcium phosphate composite coating," Applied Surface Science, vol. 282, pp. 583-589, 2013.
[56]L. Benea, E. Mardare-Danaila, M. Mardare, and J.-P. Celis, "Preparation of titanium oxide and hydroxyapatite on Ti–6Al–4V alloy surface and electrochemical behaviour in bio-simulated fluid solution," Corrosion Science, vol. 80, pp. 331-338, 2014.
[57]M. Montazeri, C. Dehghanian, M. Shokouhfar, and A. Baradaran, "Investigation of the voltage and time effects on the formation of hydroxyapatite-containing titania prepared by plasma electrolytic oxidation on Ti–6Al–4V alloy and its corrosion behavior," Applied Surface Science, vol. 257, pp. 7268-7275, 2011.
[58]G. Argade, S. Panigrahi, and R. Mishra, "Effects of grain size on the corrosion resistance of wrought magnesium alloys containing neodymium," Corrosion Science, vol. 58, pp. 145-151, 2012.
[59]H. S. Kim, S. J. Yoo, J. W. Ahn, D. H. Kim, and W. J. Kim, "Ultrafine grained titanium sheets with high strength and high corrosion resistance," Materials Science and Engineering: A, vol. 528, pp. 8479-8485, 2011.