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Electrolytic Deposition of Bioceramics on Metallic Implants at Room Temperature
|關鍵字:||Electrolytic deposition;電解沈積;Zirconia coating;Hydroxyapatite;Calcium phosphate coating;Co-Cr-Mo alloy;Titanium;氧化鋯塗層;氫氧基磷灰石;磷酸鈣塗層;Co-Cr-Mo合金;鈦||出版社:||材料工程學研究所||摘要:||
在0.0625 M ZrO(NO3)2溶液(pH = 2.2)中，使用電流密度2 mA/cm2能夠在ASTM F-75 Co-Cr-Mo合金上電解沉積得到Zr(OH)4膠體(gel)。經過350-700 oC空氣中熱處理120 min後，藉由在Hank’s溶液中電化學極化，與超高分子量聚乙烯(ultra-high molecular-weight polyethylene, UHMWPE)在負載應力50 MPa下磨耗試驗、刮痕試驗、表面型態觀察、與XRD分析評估被覆ZrO2的試片，被覆ZrO2的試片經500oC熱處理120 min後具有良好的附著力、較低的UHMWPE磨耗損耗、與在Hank’s溶液中有較高的保護電位，在350oC £ T £ 400oC熱處理能得到平行試片的單斜(monoclinic) ( 1 1)擇優取向(preferred orientation)，T ³ 500oC能得到正方(tetragonal)結構的ZrO2，在T ³ 700oC則得到隨機取向(random orientation)的單斜結構與正方結構的混合結構。
磷酸鈣(calcium phosphate)陶瓷，尤其是氫氧基磷灰石(hydroxyapatite, HA)由於絕佳的生物相容性(biocompatibility)而廣受矚目，並已臨床應用在骨科與牙科中，在製備HA塗層的方法中，電化學沉積法是一較新穎並具有潛力的方法，然而，文獻指出的電化學製程均控制在較高的溫度，本研究成功地在室溫下沉積均勻的HA塗層於鈦表面，XRD的結果顯示在低電流密度(1和5 mA/cm2)下沉積所得的塗層主要成分為DCPD (dicalcium phosphate dihydrate, CaHPO4·2H2O)，在電流密度10 mA/cm2以上能夠得到HA結構，且其經100-600 oC熱處理1 hr後仍維持相穩定，經700oC熱處理後部分HA相轉換成b-TCP成為雙相磷酸鈣(biphasic calcium phosphate)塗層，刮痕試驗顯示HA塗層能夠承受106.3 MPa的剪應力(shear stress)而不被刮落，其附著力優於較高溫度下沉積的HA塗層，HA塗層具有緻密的內層與粗糙的表面型態，其可能較滿足植入材料的要求與適合骨組織的貼附(attachment)。
鈦與電解沉積的HA及DCPD塗層在37 oC模擬體液(Hank’s溶液)中浸泡1、7、14、和30天，藉由表面型態，成分，和晶體結構分析探討其浸泡行為，DCPD塗層快速溶解且HA相在其表面析出，重量和HA的繞射強度隨浸泡時間而增加，HA和熱處理的HA塗層經過浸泡後較具結晶性與隨機取向，首先在被覆HA的試片表面析出的HA相是隨機取向(random orientation)，隨著(1 1 2)面漸漸析出後造成2q在31.5-32.5o間的寬化的(broaden)繞射峰，此寬化的繞射峰亦顯示析出的HA相為低結晶性或由微小的晶體所組成，SEM照片觀察到大量的HA小顆粒析出在塗層表面，因此HA塗層在浸泡於Hank’s溶液時，扮演新生HA相的先驅物(precursor)的重要角色，在細胞培養評估中，細胞能在HA和熱處理的HA塗層表面伸展良好，並且在500oC熱處理的HA上所觀察到的細胞數量最多，G-292細胞在500oC熱處理的HA上呈現較高的酸性磷酸酯脢(acid phosphatase)活性，且在HA和500oC熱處理的HA上呈現相近的鹼性磷酸酯脢(alkaline phosphatase)活性，因此，HA塗層經500oC熱處理後具有較佳結晶性、在模擬體液中穩定、並且在細胞培養評估中較具相容性。
An electrolytic Zr(OH)4 gel has been coated on ASTM F-75 Co-Cr-Mo alloy specimens in 0.0625 M ZrO(NO3)2 solution with pH = 2.2 at a current density of 2 mA/cm2. After heating at 350-700oC for 120 min in air, the ZrO2-coated specimen was evaluated by electrochemical polarization in Hank's solution, wear tests with UHMWPE (Ultra-high molecular-weight polyethylene) under a load stress of 50 MPa, scratch tests, surface morphology observations, and XRD analysis. The ZrO2-coated specimen heated at 500oC for 120 min revealed a good adhesion of 610 MPa on Co-Cr-Mo substrate, a lower wear loss of UHMWPE and a higher protection potential than the uncoated specimen in Hank's solution. A monoclinic structure with ( 1 1) preferred orientation parallel to the sheet plane was detected at 350oC £ T £ 400oC and a tetragonal structure of ZrO2 was detected at T ³ 500oC. Then a monoclinic structure with random orientation and a tetragonal structure were mixed at T ³ 700oC.
Calcium phosphate (CaP) ceramics, especially hydroxyapatite (HA), have received much attention and have been clinically applied in orthopaedics and dentistry due to their excellent biocompatibility. Among several methods for preparing hydroxyapatite (HA) coating, electrochemical deposition is a relatively new and possible process. However, documented electrochemical processes were conducted at elevated temperature. In this study, uniform HA coatings have been directly deposited on titanium at room temperature. XRD results demonstrated that dicalcium phosphate dihydrate (CaHPO4×2H2O, DCPD) was the main component of the coating deposited at lower current densities (1 and 5 mA/cm2). HA structure was obtained at current density above 10 mA/cm2 and remained stable after heat treatment at 100-600oC for 1 hr. Part of HA phase was transformed into b-TCP and became a biphasic calcium phosphate coating after heating at 700oC. Scratch tests showed that HA coating was not scraped off until a shear stress of 106.3 MPa. Coatings deposited at room temperature exhibited stronger adhesion than those at elevated temperature. HA coating revealed a dense inner layer and rough surface morphology which could fulfill the requisition of implant materials and be adequate to the attachment of bone tissue.
The immersion behaviors of titanium and electrolytic hydroxyapatite (HA) and dicalcium phosphate dihydrate (DCPD) coatings were investigated in the simulated physiological fluid (Hank's solution) at 37oC for 1, 7, 14, and 30 days for evaluation of changes in morphology, composition, and crystal structure. The specimens were characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy before and after immersion. The mass variations of the specimens and the pH values of the solutions were measured for understanding the immersion behavior. DCPD coating dissolved rapidly and subsequently HA phase precipitated on the surface. The weight and the intensity of HA increased with immersion time. HA and heated HA coatings became more crystalline and random orientated after immersion. The primary HA phase precipitated on the surface of HA coated specimen was random orientation. The (1 1 2) plane precipitated gradually and caused a broaden peak between 2q of 31.5-32.5o. The broaden diffraction peaks also indicate the precipitated HA phase is poor crystalline or composed of small crystals. A lot of small precipitated HA granular particles can be observed on the coatings in the SEM photographs. The electrolytic HA coating played as a significant precursor in the precipitation process of newly formed HA phase in Hank's solution. In the cell culture evaluation, cells spread out well on the surface of HA and heated HA coatings according to SEM observation. The amount of cells grown on HA coated specimen after heated at 500oC was greater than that of the other specimens. G-292 cells also presented a higher acid phosphatase activity on HA coating heated at 500oC and similar alkaline phosphatase activity on HA and heated at 500oC specimens. Therefore, HA coating after heating at 500oC with more crystalline was stable in simulated body fluid and presented better biocompatible in cell culture evaluation.
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