Hydroxyapatite coating on a titanium metal substrate by a discharging method in modified artificial body fluid

PURPOSE: The aim of this study was to evaluate the formation of a hydroxyapatite coating on titanium plate by discharging in typical and modified artificial body fluids. MATERIALS AND METHODS: Japanese Industrial Standard Grade 2 titanium plates were used as specimens. Discharging was performed on the specimens in each solution, and the surface topography of each coating was observed with a scanning electron microscope. The Ca/P atomic ratio and surface characterization of each coating were evaluated by x-ray photoelectron spectroscopy, and crystal phases of each coating were analyzed by Fourier transform infrared spectroscopy and x-ray diffraction. RESULTS: Tricalcium phosphate formed on the titanium surface in a 1.5 Ca/P solution with high ion concentrations of calcium (2.5 mmol/L) and phosphorous (1.67 mmol/L). Crystalline HA was formed on the titanium surface in a 1.5 Ca/P solution (Hanks' balanced salt solution without organic molecules) with low ion concentrations of calcium (1.26 mmol/L) and phosphorus (0.83 mmol/L). DISCUSSION: A solution containing organic pH buffer was insufficient to form stable coatings on the titanium surface. Coating properties strongly depended on the Ca/P chemical ratio of the applied solution. A Ca/P ratio of 1.5 was appropriate for preparing a calcium phosphate coating on a titanium surface, whereas a Ca/P ratio of 2.5 was excessively high. CONCLUSION: These findings suggest that Hanks' balanced salt solution without organic molecules is the most suitable solution for forming crystalline hydroxyapatite coatings on titanium surfaces by the discharging method.     

A methodological study for the analysis of apatite-coated dental implants retrieved from humans

The stability of thermally processed hydroxyapatite coatings for oral and orthopedic bioprostheses has been questioned. Information on the chemical changes, which occur with hydroxyapatite biomaterials post-implantation in humans, is lacking. The purpose of this investigation was to begin to examine post-implantation surface changes of hydroxyapatite-coated implants using scanning electron microscopy (SEM), x-ray microanalysis (EDAX), Fourier transform infrared spectroscopy (FTIR), and x-ray diffraction (XRD). Three retrieved dental implant specimens from humans following clinical failure due to peri-implantitis were examined. Unimplanted cylinders served as controls. Clinically, the retrieved specimens were all enveloped by a fibrous tissue capsule with bone present at the apical extent of the implant. SEM analysis showed that the retrieved surfaces were coated with both calcified and proteinaceous deposits. EDAX scans of the retrieved specimens demonstrated evidence of hydroxyapatite coating loss reflected by increasing titanium and aluminum signals. Other foreign ions such as sodium, chloride, sulfur, silica, and magnesium were detected. XRD of the control specimens showed that the samples were predominantly apatite; however, two peaks were detected in the diffraction pattern, which are not characteristic of hydroxyapatite, indicating that small amounts of one or more other crystalline phases were also present. The retrieved specimens showed slightly larger average crystal size relative to the control sample material, and the non-apatite lines were not present. FTIR evaluation of the retrieved specimens revealed the incorporation of carbonate and organic matrix on or into the hydroxyapatite. Narrowing of and increased detail in the phosphate peaks indicated an increase in average crystal size and/or perfection relative to the controls, as did the XRD results. Based on these results, we conclude that chemical changes may occur within the coating, with the incorporation of carbonate and concomitant reduction in hydroxyapatite coating thickness. Thermodynamic dissolution-reprecipitation of the coating itself and subsequent surface insult by bacterial and local inflammatory components may be involved with these changes.     

Characterization of hydroxyapatite films obtained by pulsed-laser deposition on Ti and Ti-6AL-4v substrates.

OBJECTIVES: Pulsed-laser deposition (PLD) is a development process to obtain hydroxyapatite (HA) thin film. It is an alternative to hydroxyapatite deposition techniques usually employed to cover orthopaedic or dental titanium implant surfaces. The aim of this study is to find out the characteristic ratio for Ca/P (1.66) deposit on titanium implant with the PLD process. METHODS: In a preliminary study, the coating parameters of pure and highly crystalline HA on Ti or Ti-6Al-4V substrates were verified by analysing the deposit by Rutherford backscattering spectroscopy (RBS). Ablation parameters to reach a stoichiometric hydroxyapatite composition (ideal Ca/P atomic ratio) and to control the growth of crystalline phases were: 575 degrees C for the substrate temperature, 0.4 mbar H2O vapour pressure in the ablation chamber, the target substrate distance was 40 mm and the deposition time was 120 min. In a second part, the film properties were analysed by means of XRD, SEM, AFM. The coating adhesion of the HA to the substrate was determined with a micro scratch tester. RESULTS: The analysed HA thin films showed a perfect crystallized and textured deposit. Sample observation and surface quality analysis demonstrated a surface roughness and adhesion of the films to the substrates compatible with biological applications. SIGNIFICANCE: These results suggest that pulsed-laser deposition is a suitable technique to obtain crystalline and adherent hydroxyapatite films on Ti or Ti-6Al-4V substrates. The quality of the HA deposit with the PLD process could be an interesting option for coating dental implant.     

应用IBAD方法制备纯钛表面多孔TCP／HA涂层材料的微观分析

目的:为了改善钛种植体的生物相容性,对纯钛表面沉积多孔磷酸三钙/羟基磷灰石(Tricalciumphosphate/hydroxyapatite,TCP/HA)复合涂层材料的表面结构和化学成分进行分析,并与沉积羟基磷灰石(Hydroxyapatite,HA)的钛表面进行对比。方法:用离子束辅助沉积方法(Ionbeamassisteddeposition,IBAD)在纯钛表面沉积HA和TCP/HA涂层材料,通过扫描电镜(Scanningelectronmicroscope,SEM)、原子力显微镜(Atomicforcemicroscopy,AFM)、X射线能谱分析(EnergydispersiveX-rayanalysis,EDX)以及X射线衍射(X-raydiffraction,XRD)技术,检测两种涂层材料表面的微观形态和化学成分,并进行比较。结果:SEM和AFM显示TCP/HA涂层材料表面存在多孔结构,表面化学成分分析显示TCP/HA涂层的钙磷比低于HA,XRD证实TCP/HA涂层内同时存在TCP和HA两种化合物。结论:用IBAD方法在纯钛表面成功地沉积了具有多孔结构的TCP/HA复合涂层材料,该涂层材料和基体材料的结合牢固,改善了基体材料的生物相容性,是一种有应用前景的种植体表面涂层材料。     

Long-term bone response to titanium implants coated with thin radiofrequent magnetron-sputtered hydroxyapatite in rabbits

PURPOSE: The present study was designed to investigate the long-term bone response around machined screw-type uncoated and calcium phosphate (CaP) -coated commercially pure titanium implants. MATERIALS AND METHODS: Using a magnetron sputtering technique, implants with a CaP coating similar in composition and CaP ratio to hydroxyapatite were produced. Heat treatment was subsequently used to increase the crystallinity of the coatings. Four types of coatings (0.1 and 2.0 microm amorphous and 0.1 and 2.0 microm crystalline) were manufactured; uncoated implants served as a control. Three hundred twenty implants (64 of each type) were randomly placed in the tibial cortical and trabecular femoral bones of 40 rabbits. The rabbits were sacrificed 9 months after implant placement. RESULTS: Histomorphometric evaluation carried out on ground sections revealed that the crystalline CaP coatings achieved the highest bone-implant contact in both tibiae and femora compared with amorphous CaP-coated and uncoated titanium. DISCUSSION: The present study suggests that submicron crystalline hydroxyapatite coating adds bioactive properties to titanium oral implants. CONCLUSION: An ultra-thin, 0.1-microm crystalline CaP coating can elicit and maintain an improved long-term bone response compared to amorphous coated or uncoated Ti implants, without any adverse tissue reactions.     

钛表面掺镓羟基磷灰石涂层的合成和性能表征

目的:钛表面制备含镓羟基磷灰石(Ga-HA)涂层并研究其理化性能。方法:溶胶-凝胶法制备Ga-HA,浸润-提拉法制备涂层并煅烧。SEM检测涂层表面形貌,FTIR、XRD分析其基团结构,拉伸试验检测其结合强度,AAS检测镓、钙离子释放浓度。结果:Ga-HA的结晶度高于HA。体外释放实验结果显示煅烧后涂层钙、镓离子释放量减少。讨论:镓的掺入使HA结晶度增强但未改变其主要晶相结构;镓的掺入有助于减缓涂层的降解,为Ga-HA涂层在骨质疏松患者的临床应用提供了基础。     

钛表面载银HA-TCP溶胶凝胶涂层的制备及其抗菌性的研究

目的：用溶胶凝胶法在钛表面制备载银HA-TCP涂层，并观察其抗菌性能。方法：采用溶胶凝胶法将Ag^＋导入HA-TCP溶胶，并在钛表面涂层。用X射线衍射（XRD）和傅立叶变换红外光谱（FTIR）对涂层结构进行表征分析，用X射线能谱（EDS）分析涂层表面元素构成和分布，用扫描电镜（SEM）观察涂层表面形貌。观察涂层对牙龈卟啉单胞菌P.g、具核梭杆菌F.n、伴放线放线杆菌A-a的生长抑制作用，并计算抗菌率。结果：载银HA-TCP溶胶在钛表面涂层均匀，由大量的亚微米及细微的介孔组成。XRD检测出HA、钛、锐钛矿和β-TCP的衍射峰；FTIR分析涂层含有OH^-．PO4^3-及CO3^2-的特征吸收峰。EDS检测发现钙、磷、钛、碳、氧和银在涂层表面的分布。与对照组比较，载银HA-TCP涂层对牙龈卟啉单胞菌P.g、具核梭杆菌F.n、伴放线放线杆菌A.a具有明显的抗菌效果。结论：本试验在钛表面涂覆载银HA-TCP溶胶，使钛植入体获得了具有生物活性及抗菌性的仿生涂层。     

含锌碳磷灰石的溶胶凝胶法制备及性能表征

目的通过溶胶凝胶法制备含锌的碳磷灰石（Zn- CHA）涂层材料,并探讨锌离子取代反应对羟磷灰石物理化学性质的影响。方法实验制备了锌离子取代量和钙磷比不相同的两组样本,其中钙足量组样本的钙磷比为1.67,锌离子取代4%的钙离子;钙不足量组的钙磷比小于1.67,锌离子取代8%的钙离子。采用X射线衍射仪（XRD）、傅立叶变换红外光谱仪（FTIR）对样本的物相结构和化学组成进行分析研究,并采用扫描电镜观察样本的表面形貌。此外,还采用原子吸收分光光度计（AAS）对样本的溶解特性与锌离子的关系进行研究。结果X射线衍射分析表明样本中含有羟磷灰石相,傅立叶变换红外光谱分析结果表明样本为碳磷灰石,溶解实验表明钙不足量组和钙足量组样本中分别存在锌离子整合到羟磷灰石晶格内和吸附在羟磷灰石晶体表面两种情况。结论研究表明含锌的碳磷灰石能够通过简单的溶胶凝胶法制备获得。     

In vivo evaluation of the trabecular bone behavior to porous electrostatic spray deposition-derived calcium phosphate coatings

OBJECTIVES: Electrostatic spray deposition (ESD) is a new technique to deposit calcium phosphate (CaP) coatings. The aim of the present study was to evaluate the bone behavior of ESD CaP-coated implants with various degrees of crystallinities in the trabecular bone of the femoral condyle of goats. MATERIAL AND METHODS: Using the ESD technique, thin porous CaP coatings were deposited on tapered, conical, screw-shaped titanium implants. Three different heat-treatments were applied, resulting in amorphous CaP (400 degrees C, ESD1), crystalline carbonate apatite (500 degrees C, ESD2), and crystalline carbonated hydroxyapatite (700 degrees C, ESD3). Implants were inserted into the trabecular bone of the femoral condyles of goats for 12 weeks, and titanium (Ti) implants served as controls. RESULTS: The results showed that ESD-derived coatings are osteocompatible. Histomorphometrical analysis showed that the application of a CaP coating resulted in more bone contact along the press-fit area of the implant compared with the Ti implants. Moreover, the percentage bone contact of the ESD3-coated implants was increased, compared with the Ti control group. Regarding the other coatings, no differences were found compared with the control group. CONCLUSION: Crystalline carbonated hydroxyapatite ESD-coated implants positively influenced the biological performance compared with Ti control implants.     

纯钛种植体表面纳米含氟磷灰石涂层的构建和表征

目的：在纯钛表面构建纳米含氟磷灰石涂层并进行性能表征。方法：采用溶胶凝胶法在纯钛表面构建纳米级含氟磷灰石涂层，用X线衍射、X线光电子能谱、扫描电镜和溶解度测试表征其晶体结构、化学组成、表面形貌、厚度以及化学稳定性；用体外成骨细胞培养评价其生物活性。结果：该涂层具有良好的晶体结构和均匀的纳米级表面形貌，化学稳定性理想。体外成骨细胞培养显示其具有良好的生物活性。结论：本实验构建的涂层具有良好的性能和应用前景。     

Surface analysis and effects on interfacial bone microhardness of collagen-coated titanium implants: a rabbit model

PURPOSE: The aim of this study was to evaluate the surface chemistry and the microhardness at the implant-bone interface using a recently developed collagen-coated titanium implant in a short-term rabbit model. MATERIALS AND METHODS: Surface chemistry was evaluated by x-ray photoelectron spectroscopy (XPS), while in vivo studies involved 4-week implants mid-diaphysis in the lateral femurs of adult male rabbits. After conventional embedding and evaluation of histologic sections, the resinembedded blocks containing the implanted screws were used to measure bone hardness by means of an indentation test. RESULTS: Decomposition of the C1s peak obtained by XPS analysis confirmed that surface-immobilized collagen retained all the molecular features of the control, nonimmobilized reference. As to microhardness measurement, newly formed bone at the collagen-coated-implant/bone interface was significantly harder than bone at the interface of the uncoated control implant and bone. DISCUSSION: These results suggested that collagen coating significantly improves bone maturation and mineralization at the interface in comparison with uncoated commercially pure titanium. Surface modification of titanium implants by collagen coating has recently been discussed as a promising approach to the biochemical modification of implant surfaces. The present results support previous histologic findings and demonstrated that the biomolecular layer linked over the titanium implant can increase the bone healing rate, at least in this animal model. CONCLUSIONS: The present microhardness measurement at the bone-implant interface showed that collagen coating can significantly improve bone maturation and mineralization at the interface in comparison with uncoated commercially pure titanium, confirming and substantiating previous findings by histomorphometric measurements from the same model.     

Influence of post-deposition heating time and the presence of water vapor on sputter-coated calcium phosphate crystallinity

Extensive research suggested that calcium phosphate (CaP) coatings on titanium implants are essential for early bone response. However, the characterization of CaP crystallinity and the means to control coating crystallinity are not well-established. In this study, the effect of a 400 degrees C heat treatment for 1, 2, or 4 hours, and in the presence or absence of water vapor, on CaP crystallinity was investigated. Scanning electron microscopy indicated dense as-sputtered coatings. Increase in coating crystallinity was observed to be consistent with the increasing number of PO(4) peaks observed as a result of different heat treatments. In addition, x-ray diffraction analyses indicated amorphous as-sputtered coatings, whereas crystalline CaP coatings in the range of 0-85% were observed after different post-deposition heat treatments. It was concluded that the presence of water vapor and post-deposition heat treatment time significantly affect the crystallinity of CaP coatings, which may ultimately affect bone healing.     

Characterization and dissolution behavior of sputtered calcium phosphate coatings after different postdeposition heat treatment temperatures

There is a lack of correlation between specific properties of hydroxyapatite coating surfaces, osseointegration processes, and implant success. The aim of this study was to evaluate the relationship between well-characterized structural and chemical properties of radio-frequency sputtered calcium phosphate (CaP) coatings and their dissolution behavior. Sputtered CaP coatings were evaluated as-sputtered (non-heat treated) or after 1 hour of postsputter heat treatments at 400 degrees C or 600 degrees C. All coatings were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and contact angle measurement. The dissolution behavior of CaP coatings in the presence and absence of proteins was also investigated. It was observed from this study that as-sputtered CaP coatings were amorphous. The 400 degrees C heat-treated CaP coatings exhibited low crystallinity (1.9% +/- 0.4%), whereas the 600 degrees C heat-treated CaP coatings were highly crystalline (67.0% +/- 2.4%). The increase of Ca/P ratio, PO4/HPO4 ratio, and the number of PO4 peaks were observed to be consistent with the increase in heating temperature and the degrees of coating crystallinity. Phosphorus ions released from CaP coatings decreased with the increase of crystallinity of CaP coatings. In addition, immersion of CaP coatings in media containing proteins resulted in an increase in P ions released as compared with coatings immersed in media without proteins. It was concluded that the degree of CaP coating crystallinity can be controlled by varying the postdeposition heat-treatment temperature. It was also concluded that, aside from coating crystallinity, dissolution and reprecipitation of the coatings can be controlled by knowing the presence of proteins in the media and PO4/HPO4 ratio within the coatings.     

微弧氧化联合溶胶-凝胶工艺制备钛表面复合生物涂层的研究

目的探讨微弧氧化联合溶胶-凝胶工艺制备钛表面复合生物涂层。方法钛片根据表面处理工艺不同分为5组:对照组,MAO(微弧氧化组),MAO+Sol/gel(微弧氧化+溶胶-凝胶组),MAO+Sol/gel-LowZn(微弧氧化+溶胶-凝胶低锌组),MAO+Sol/gel-HighZn(微弧氧化+溶胶-凝胶高锌组)。利用扫描电镜(SEM)观察涂层表面形貌,X射线能谱分析仪(EDX)和X射线衍射仪(XRD)分析元素分布和成分,测厚仪测量涂层厚度;粗糙度测试仪测量表面粗糙度。结果 SEM下可见MAO组钛表面粗糙多孔,联合溶胶-凝胶处理后,钛表面更加平整紧密,EDX得出MAO+Sol/gel组钙磷元素的质量百分比分别为25.00%和15.49%,MAO+Sol/gel-Low Zn组和MAO+Sol/gel-High Zn组钙、磷、锌元素的质量百分比分别为22.87%、15.01%、1.82%与18.66%、15.60%、7.45%,XRD得出MAO+Sol/gel组、MAO+Sol/gel-Low Zn组和MAO+Sol/gel-High Zn组均可见特征性羟基磷灰石(HA)峰和Ca3(PO4)2峰,MAO+Sol/gel-High Zn组表面涂层厚度最高(10.40±0.49)μm(P<0.05),MAO+Sol/gel组表面粗糙度最高(1.17±0.10)μm(P<0.05)。结论应用微弧氧化联合溶胶-凝胶工艺,可在钛金属表面制备出HA涂层,并通过调节溶胶凝胶中Zn(NO3)2·6H2O的含量,制备出HA和不同含量锌离子的复合生物涂层。经过两种不同工艺联合处理后,钛表面涂层厚度逐渐增加,而粗糙度随着溶胶凝胶中锌离子的增加逐渐降低。     

Dissolution kinetics of calcium phosphate coatings

Plasma spray and high velocity oxy-fuel (HVOF) techniques produce coatings with varying composition and amounts of amorphous and crystalline phases. For coatings containing greater amorphous phases, a higher release of calcium ions is evident when samples are placed in Hank's calcium-free balanced salt solutions. Calcium is released from the amorphous phases in the coating, a conclusion that is supported by x-ray powder diffraction (XRD) results. Ion beam sputtering and RF magnetron sputtering under lower energy conditions produce amorphous coatings that will dissolve in a very short time period. When heat treated, crystalline phases are produced in the coatings. Heat-treated coatings are significantly more stable than the amorphous coatings. The dissolution rates of both amorphous and crystalline coatings produced by RF magnetron sputtering have been measured under constant solution conditions at pH 6.50. No reprecipitation is possible under these conditions. The amorphous coating dissolved at a significantly higher rate than the heat-treated coating. Reprecipitation of calcium phosphate onto amorphous coatings is possible in a physiological pH solution. Under these conditions, the dissolution rate of the amorphous coating is four times slower than at the pH 6.50 conditions.     

Hydroxyapatite-electroplated cp-titanium implant and its bone integration potentiality: an in vivo study

PURPOSE: This study was designed to precipitate hydroxyapatite coating on the surface of commercially pure titanium (cpTi) implants using an electroplating technique. After characterization of the hydroxyapatite coating, the bone-implant interface and bone integration of both cpTi and hydroxyapatite-coated implants were assessed. MATERIALS: Twenty implants were divided equally into 2 main groups (n = 10). Ten cpTi implants were utilized as received, while the others were hydroxyapatite coated and then sterilized. The implants of both groups were inserted in the tibiae of New Zealand rabbits. The purity and crystallinity of the hydroxyapatite coat were characterized using x-ray diffraction. A scanning electron microscope examined the grain morphology. Profilometer evaluated the surface texture before and after sterilization. Histological examination using a scanning electron microscope was performed to qualify osseointegration of the regenerated bone and measure the gap distance at the bone-implant interface. RESULTS: Pure crystalline hydroxyapatite precipitate of thickness (range 69-78 microm) and rough surface (2.7 +/- 0.2 microm) compared to smooth cpTi (1.3 +/- 0.5 microm). The gamma-radiation sterilization resulted in finer grains and insignificant smoother surface. Histological examination of the cpTi implant exhibited less bone regeneration with few and less dense bone trabeculae, and gap distance was significantly high (1.29 +/- 0.51 microm). Meanwhile, the hydroxyapatite-coated implant showed a recognizable amount of bone regeneration with more and denser bone trabeculae, and gap distance ranged from 0 to 1.32 microm. CONCLUSIONS: The employed technique provided a thin and uniform pure crystalline hydroxyapatite coating. The characterization of the precipitated film is promising for clinically successful long-term bone fixation.     

牙种植体纳米含氟羟基磷灰石涂层材料制备实验研究

目的 探讨用溶胶-凝胶法制备出的纳米含氟羟基磷灰石（nFHA）材料用于纯钛表面涂覆的理论依据。方法 本实验于2010年1-5月在中南大学粉末冶金研究院完成。采用溶胶-凝胶法制备nFHA和羟基磷灰石（HA）材料,通过X线衍射（XRD）、透射电镜（TEM）表征其物相组成及颗粒大小,扫描电镜（SEM）观察涂层在纯钛表面形貌。结果 XRD检测结果显示,运用溶胶-凝胶法可制备出nFHA材料,氟离子进入HA晶体中,以nFHA固溶体形式存在。TEM显示,nFHA晶体呈短棒状,粒径大部分在100 nm以下,符合纳米级别。SEM显示,热处理后的nFHA涂层,为多孔形貌,相互形成穿通结构,颗粒均匀分布,无明显裂纹。结论 （1） 采用溶胶-凝胶法可制备出nFHA涂层材料;（2） nFHA较HA在钛基表面涂层可形成更佳的孔隙结构。     

Mandibular bone response to plasma-sprayed coatings of hydroxyapatite

Sintered hydroxyapatite ceramic particles can be applied as a coating on a titanium substrate using a plasma-spraying technique. The biological and mechanical properties of implants with such a coating were studied in the mandible of a dog. The results indicated that a very strong and direct bonding between the hydroxyapatite coating and the mandibular bone developed. The shear strength of the bone/ceramic interface was higher than the interfacial strength between ceramic and titanium substrate. From the radiologic, macroscopic, and microscopic observations it was concluded that the biological properties of plasma-sprayed coatings of hydroxyapatite are the same as those of sintered hydroxyapatite ceramic. As a result of mechanical failure of the coherence of the hydroxyapatite particles at the outer layer of the coating, free particles of hydroxyapatite were observed in the surrounding bone tissue.     

In vivo evaluation of hydroxyapatite coatings of different crystallinities

PURPOSE: The influence of calcium phosphate (CaP) and hydroxyapatite (HA) crystallinity on bone-implant osseointegration is not well established. In this study, the effect of HA crystallinity and coating method on bone-implant osseointegration was investigated using a rat tibia model. MATERIALS AND METHODS: HA coatings 1 to 5 microm thick were produced using a supersonic particle acceleration (SPA) technology. The HA crystallinities used for this study were weight ratios of 30%, 50%, 70%, and 90%. A total of 128 HA-coated implants were placed into the tibiae of 64 male Sprague-Dawley rats. Bone-implant interfaces were evaluated using histology and push-out strength testing at 3 and 9 weeks after implantation. RESULTS: The 70% crystalline coatings exhibited significantly greater interfacial strength (5 implants/time point/treatment) than the 30%, 50%, and 90% crystalline coatings at 3 and 9 weeks following implantation. The implants with coatings of 70% crystallinity also had the greatest bone contact length. In addition, the HA coatings produced with SPA demonstrated greater interfacial strength and bone contact length than plasma-sprayed HA coatings (except for the HA coating with 30% crystallinity). DISCUSSION: HA coatings of different crystallinities exhibited different dissolution and re-precipitation properties which may enhance early bone formation and bone bonding. CONCLUSIONS: This study suggested that coating crystallinity and coating methods can influence the bone-implant interface.