純鎂上製備生物可降解性二水磷酸氫鈣皮膜以及其在人工體液內之腐蝕行為

Fabrication of biodegradable DCPD coating on pure magnesium and its corrosion behavior in simulated body fluid

蘇恆佳(Heng-Chia Su)

指導教授 ： 林招松

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.10190

摘要

鎂合金近十年來在生物醫用材料受到重視，相較於傳統鈍態金屬植入物如不鏽鋼、鈦合金、鈷鉻鉬合金等，鎂合金具有無毒性、生物相容性、可降解性、不需經二次手術取出等優勢，是第三代生物醫療材料中具應用潛力的材料。但未經處理的鎂合金在人體環境中腐蝕速率過快，必須經適當處理提升抗蝕性。

本研究著重在純鎂表面製作一層具生物活性的二水磷酸氫鈣皮膜來降低在模擬人工體液中的腐蝕速率。文獻指出，二水磷酸氫鈣皮膜具有一定程度的保護性，植入後能與人體骨頭組織緊密結合並促進骨細胞成長，具有良好的生物相容性及生物活性。製程選用化成的方式，將商業用純鎂浸泡在含0.152 M硝酸鈣以及0.217 M磷酸二氫銨之酸性化成液中數分鐘後取出，進行表面形貌、橫截面觀察(SEM)、成分分析(EDX、XPS、XRD)。抗腐蝕性則以電化學(EIS、極化曲線)與析氫試驗量測，來判斷在模擬人工體液中的腐蝕速率以及腐蝕形貌。並以實驗數據來推測皮膜組成及皮膜生成的反應機構。

結果顯示在未添加硝酸鈉化成液中，40℃反應下之化成皮膜披覆最均勻且無脫水裂紋，有最佳的抗蝕性。此外，在40℃之化成液中額外添加不同濃度的硝酸鈉，可加速化成初期皮膜披覆在表面的速度。在化成液中額外添加硝酸鈉可產生較緻密、孔隙率較低的皮膜。在本實驗中，硝酸鈉添加的量為0.8、1.6、3.2以及6.4 mM，在0.8 mM至3.2 mM的區間中，皮膜在模擬人工體液內的腐蝕電流密度隨添加量增加而降低，直到6.4 mM此趨勢消失，3.2 mM之皮膜有最低的腐蝕電流密度。在析氫試驗中，所有參數的皮膜在前兩天析氫量較少，第三天析氫量大幅上升，推測皮膜已有局部崩解的現象，在前四天內析氫量的趨勢和電化學趨勢相同，研究以皮膜成長機制討論加入硝酸鈉後皮膜抗蝕性提升之原因。

關鍵字

純鎂 ； 磷酸鈣鹽化成處理 ； 生物活性 ； 生物可降解 ； 抗蝕性

並列摘要

Magnesium and its alloys have become increasingly important in the biomedical field for the last decade. Comparing to the traditional bioinert implants such as stainless steels, titanium alloys and cobalt-chromium-molybdem alloys, magnesium and its alloys have some advantages including biocompatibility, biodegradability, non-toxicity, signifying them as one of the potential biodegradable implants. However, magnesium and its alloys corrode rapidly in the physiological environment. Surface modification is thus essential to enhance the corrosion resistance of magnesium alloys.

Dicalcium phosphate (DCPD) coating can provide some degrees of protection from corrosion in the simulated body fluid and stimulate the attachment and differentiation of bone cells. The present study employed chemical conversion coating method to fabricate bioactive DCPD coating on pure magnesium. The conversion solution was mainly composed of 0.152 M calcium nitrate and 0.217 M ammonium dihydrogen phosphate. After immersion in the conversion solution for several min., the DCPD-coated magnesium was characterized by SEM/EDS and its corrosion resistance was evaluated by polarization curves, EIS, and hydrogen evolution measurement in simulated body fluid (Hank balanced salt solution, HBSS).

The results show that the DCPD coating formed in the conversion solution free of sodium nitrate at 40℃ is homogeneous and crack-free. The presence of sodium nitrate (0.8 ~ 6.4 mM) in the solution at 40℃ accelerates the nucleation of DCPD. The resulting coating thus has lower porosity and better corrosion resistance than that formed in the absent of sodium nitrate. Moreover, the coating formed in the solution with the addition of 3.2 mM sodium nitrate exhibits the lowest porosity and the smallest corrosion current density. The DCPD-coated magnesium underwent lower amounts of hydrogen evolution than the bare magnesium during the first two-day immersion in HBSS. A marked increase in hydrogen evolution was observed after three days of immersion, suggesting that the DCPD coating had been attacked locally. The amount of hydrogen evolved during the first four-day of immersion was consistent with the electrochemical characterization results. Finally, how the presence of sodium nitrate affects the formation and corrosion resistance of the DCPD coating on magnesium is discussed in detail.

並列關鍵字

pure magnesium ； calcium phosphate conversion coating ； bioactive ； biodegradable ； corrosion resistance

參考文獻

9. 黃莉婷, 特定單脈衝電磁場與植物性雌激素對蝕骨細胞分化機轉之探討, in 中原大學醫學工程學系碩士論文. 2004年6月. p. 9-18.

1. Song, Y., D. Shan, R. Chen, F. Zhang, and E.-H. Han, A novel phosphate conversion film on Mg–8.8 Li alloy. Surface and Coatings Technology, 2009. 203(9): p. 1107-1113.

2. Song, Y., D. Shan, R. Chen, F. Zhang, and E.-H. Han, Formation mechanism of phosphate conversion film on Mg–8.8 Li alloy. Corrosion Science, 2009. 51(1): p. 62-69.

3. Witte, F., The history of biodegradable magnesium implants: a review. Acta Biomater, 2010. 6(5): p. 1680-92.

4. Heublein, B., R. Rohde, V. Kaese, M. Niemeyer, W. Hartung, and A. Haverich, Biocorrosion of magnesium alloys: a new principle in cardiovascular implant technology? Heart, 2003. 89(6): p. 651-656.