Micromorphological effect of calcium phosphate coating on compatibility of magnesium alloy with osteoblast

Abstract

Octacalcium phosphate (OCP) and hydroxyapatite (HAp) coatings were developed to control the degradation speed and to improve the biocompatibility of biodegradable magnesium alloys. Osteoblast MG-63 was cultured directly on OCP- and HAp-coated Mg-3Al-1Zn (wt%, AZ31) alloy (OCP- and HAp-AZ31) to evaluate cell compatibility. Cell proliferation was remarkably improved with OCP and HAp coatings which reduced the corrosion and prevented the H₂O₂ generation on Mg alloy substrate. OCP-AZ31 showed sparse distribution of living cell colonies and dead cells. HAp-AZ31 showed dense and homogeneous distribution of living cells, with dead cells localized over and around corrosion pits, some of which were formed underneath the coating. These results demonstrated that cells were dead due to changes in the local environment, and it is necessary to evaluate the local biocompatibility of magnesium alloys. Cell density on HAp-AZ31 was higher than that on OCP-AZ31 although there was not a significant difference in the amount of Mg ions released in medium between OCP- and HAp-AZ31. The outer layer of OCP and HAp coatings consisted of plate-like crystal with a thickness of around 0.1 μm and rod-like crystals with a diameter of around 0.1 μm, respectively, which grew from a continuous inner layer. Osteoblasts formed focal contacts on the tips of plate-like OCP and rod-like HAp crystals, with heights of 2–5 μm. The spacing between OCP tips of 0.8–1.1 μm was wider than that between HAp tips of 0.2–0.3 μm. These results demonstrated that cell proliferation depended on the micromorphology of the coatings which governed spacing of focal contacts. Consequently, HAp coating is suitable for improving cell compatibility and bone-forming ability of the Mg alloy.     

Ribbon-like and rod-like hydroxyapatite crystals deposited on titanium surface with electrochemical method

Homogeneous coatings were attained by electrochemical method in electrolytes containing Ca²⁺ and PO₄³⁻ ions with Ca/P ratio being 1.67. SEM observation showed that the hydroxyapatite (HAp,Ca₁₀(PO₄)₆(OH)₂) crystals prepared with higher concentration electrolyte (4 × 10^− 2 M Ca²⁺) are ribbon-like with thickness of nanometer size, a morphology seldom reported previously. In an electrolyte of lower concentration (6 × 10^− 4 M Ca²⁺), the HAp crystals formed are rod-like with a hexagonal cross section and diameter of about 70–80 nm. XRD patterns and IR spectra confirmed that the coatings consist of HAp crystals. TEM micrographs and SAD indicated that the longitude direction for both ribbon-like and rod-like crystal is [002], and the flat surface of the ribbon is (110). HRTEM showed that the ribbon-like crystal is a mixture of HAp and octacalcium phosphate (OCP, Ca₈H₂(PO₄)₆.5H₂O).     

In vitro cytocompatibility and corrosion resistance of zinc-doped hydroxyapatite coatings on a titanium substrate

To improve biocompatibility and corrosion resistance during the initial implantation stage, zinc-substituted hydroxyapatite (ZnHAp) coating was fabricated on pure titanium by the electrolytic deposition method. The morphology, microstructure and chemical composition of the coating were investigated by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis and Fourier transform infrared spectroscopy. The prepared ZnHAp crystals were calcium deficient and were carbonated owing to the incorporation of some Zn²⁺. This incorporation of Zn²⁺ into the HAp significantly reduced porosity and caused the coating to become noticeably denser. In addition, the Zn²⁺ ions were homogeneously distributed in the coating. The potentiodynamic polarisation test revealed that the ZnHAp-coated surface showed superior corrosion resistance over that of the HAp-coated surface and bare Ti. The in vitro bioactivity was evaluated in a simulated body fluid, which revealed that the ZnHAp coating can rapidly induce bone-like apatite formation of nuclear and growth features. In addition, the cell response tests showed that the MC3T3-E1 cells on the ZnHAp coating clearly enhanced the in vitro cytocompatibility of Ti compared with the same cells on HAp coating. ZnHAp coating was thus beneficial for improving biocompatibility.     

A study of the process and kinetics of electrochemical deposition and the hydrothermal synthesis of hydroxyapatite coatings

Hydroxyapatite (HAp) coatings were prepared using electrochemical deposition and post-hydrothermal synthesis. The composition and morphology of coatings at each processing step was studied through the application of scanning electron microscopy (SEM), X-ray diffraction (XRD) and infra-red spectroscopy (IR). The mechanism and kinetics of hydrothermal synthesis were considered in particular, and the influnce of the temperature and time on the HAp formation rate was also investigated. The results show that the electrochemical deposition coatings are composed of CaHPO₄2H₂O crystals which are converted into needle-like HAp crystals after post-hydrothermal treatment. The HAp content of the coatings increases with the treatment temperature and time. The synthesis rate also increases with the pH value of the water. The formation of HAp coatings is considered to be a combination of several reactions. An Arrhenius relationship was found between the HAp formation rate and the temperature, and an apparent activation energy of 94.4 KJ/mol was obtained by calculation. © 2000 Kluwer Academic Publishers     

Electrolytic deposition of magnesium-substituted hydroxyapatite crystals on titanium substrate

Electrolytic deposition of magnesium-substituted hydroxyapatite (Mg-HAp) coatings on titanium was investigated and Mg-HAp crystals with up to 2 wt.% Mg²⁺ were deposited in electrolytes with various Mg²⁺ concentration. The incorporation of Mg substantially changed the morphology of the HAp crystals and decreased the crystal size and crystallinity of the HAp. The similarity with natural dentin and bone in composition and the increased specific surface of the Mg-HAp coatings on the Ti substrates were believed to benefit the bioactivity and the drug-carrying properties of the coatings.     

钛合金表面电泳沉积法制备YSZ/HAp纳米复合涂层

采用电泳沉积法在钛合金基体上制备了YSZ/HAp纳米复合涂层,用场发射扫描电镜、X射线衍射和能量散射谱对复合涂层HAp外层的表面形貌和晶相、复合涂层的断面形貌及元素组成分布进行分析研究,通过粘结-拉伸实验测定了涂层与基体的结合强度.结果表明YSZ/HAp纳米复合涂层与钛合金基体的结合强度明显高于HAp单一涂层与钛合金基体的结合强度,说明YSZ/HAp的复合缓和了HAp涂层与钛合金基体之间的热膨胀系数失配现象,改善了涂层与基体之间的结合.     

电化学沉积法制备和表征锌掺杂羟基磷灰石涂层

采用电化学沉积法在纯钛金属表面沉积锌掺杂羟基磷灰石涂层并进行表征。SEM及XRD等方法检测发现：溶液中未加入锌时,沉积得到结晶度很高的截面为规则六边形的棒状羟基磷灰石晶体,直径平均约90nm;加入锌后,锌能够抑制羟基磷灰石的结晶过程及形貌转变,同时晶体尺寸明显减小。电解液中掺入的锌含量极值为20mol%,因为当锌含量超过20%时,钛基体表面会沉积无定形的胶状锌钙磷酸盐。XRD精细扫描实验计算得出：当电解液中锌含量低于10mol%时,羟基磷灰石的晶格常数a随锌含量增加而减小,c随锌含量增加而增大;当电解液中锌含量高于10%时,晶格常数a随锌含量增加而增大,c随锌含量增加而减小。     

Biomimetic synthesis of enamel-like hydroxyapatite on self-assembled monolayers

Hydroxyapatite (HAp) crystals mimicking tooth enamel in chemical composition and morphology were formed on sulfonic-terminated self-assembled monolayer (SAM) in 1.5SBF with F⁻ at 50 °C for 7 days. F⁻ ions showed a marked effect on the composition and morphology of deposited HAp crystals. In the absence of F⁻ ions, HAp containing CO₃²⁻ were formed on SAM, and worm-like crystals of 200–300 nm in length aggregated to form a spherical morphology. When F⁻ was added, HAp crystals containing both CO₃²⁻ and F⁻ were formed on SAM. Needle-shaped crystals of high aspect ratio and 1–2 μm in length grew elongated along the c-axial direction. In addition, these needle-shaped crystals grew in bundles, mimicking HAp crystals in tooth enamel. After the process of ripening, the needles in bundle grew to large size of up to 10 μm in length, and still kept no crystal–crystal fusion like enamel HAp crystals. The formation of enamel-like HAp can be attributed to the substitute of F⁻ for OH⁻ by disturbing the normal progress of HAp formation on SAM. The results suggest potential applications in preparing a novel dental material by a simple method.     

Characterisation, corrosion resistance and in vitro bioactivity of manganese-doped hydroxyapatite films electrodeposited on titanium

This work elucidated the corrosion resistance and in vitro bioactivity of electroplated manganese-doped hydroxyapatite (MnHAp) film on NaOH-treated titanium (Ti). The NaOH treatment process was performed on Ti surface to enhance the adhesion of the MnHAp coating on Ti. Scanning electron microscopy images showed that the MnHAp coating had needle-like apatite crystals, and the approximately 10 μm thick layer was denser than HAp. Energy-dispersive X-ray spectroscopy analysis revealed that the MnHAp crystals were Ca-deficient and the Mn/P molar ratio was 0.048. X-ray diffraction confirmed the presence of single-phase MnHAp, which was aligned vertically to the substrate. Fourier transform infrared spectroscopy indicated the presence of phosphate bands ranging from 500 to 650 and 900 to 1,100 cm^?1, and a hydroxyl band at 3,571 cm^?1, which was characteristic of HAp. Bond strength test revealed that adhesion for the MnHAp coating was more enhanced than that of the HAp coating. Potentiodynamic polarisation test showed that the MnHAp-coated surface exhibited superior corrosion resistance over the HAp single-coated surface. Bioactivity test conducted by immersing the coatings in simulated body fluid showed that MnHAp coating can rapidly induce bone-like apatite nucleation and growth. Osteoblast cellular tests revealed that the MnHAp coating was better at improving the in vitro biocompatibility of Ti than the HAp coating.     

含柠檬酸根电解液中钛表面电解沉积羟基磷灰石晶体的动力学过程

在含0.6mmol/L Ca2+离子和0.36mmol/L H2PO4-离子的电解液中加入2.4mmol/L柠檬酸根离子进行钛表面阴极电沉积.结果表明柠檬酸根离子延长了HA晶体的形核孕育期,并且晶体形貌由规则的六棱柱变化为细尖锥状.通过沉积电流,涂层增重,晶形变化等规律对整个沉积过程做出阶段性划分(吸附期、孕育期、爆发生长期、次层生长期和平衡期),并对各阶段的微观过程生长机理进行了探讨,尝试建立了含柠檬酸根电解液中电解沉积HA晶体的生长模型.     

有机小分子调控下的羟基磷灰石的合成

以甘氨酸和乙二胺为模型分子,在中性条件下采用水热法,研究有机小分子对羟基磷灰石(HAP)晶体生长形貌的影响。采用透射电子显微镜(TEM)、X射线衍射仪(XRD)和傅里叶变换红外光谱仪(FTIR)分析了合成产物的形貌、结构和组成。实验结果表明,甘氨酸诱导合成的HAP呈六方棒状,长500～2000nm,直径为50～100nm;在乙二胺的诱导下合成了长100～250nm、宽30～50nm的片状HAP晶体。对照空白实验可知,小分子上的极性基团通过静电吸附或分子占位显著影响HAP的形貌。     

Effect of suspension stability on electrophoretic deposition of hydroxyapatite coatings

In order to prepare densely packed hydroxyapatite (HAp) coating onto titanium substrate through electrophoretic deposition (EPD), it is highly desirable to produce stable HAp suspension. In this study, nano-HAp particles prepared by hydrothermal method were employed for EPD. The stability of HAp suspensions in various primary aliphatic alcohols (C1–C4) has been studied by measurement of sedimentation tests and electricity conductivity. Furthermore, to make a stable suspension, a dispersant [triethanolamine (TEA)] was added. Maximum stability is observed for the suspension containing n-butanol as the dispersion medium and TEA as the dispersant. The HAp coating deposited in this suspension was observed to be a crack-free and densely packed coating through scanning electron microscopy examination. The shear strength and nano-indention tests have confirmed the good adhesion between the coating and the substrate.     

Effect of urea on formation of hydroxyapatite through double-step hydrothermal processing

The effect of urea on the formation of hydroxyapatite (HAp) was studied by employing the double-step hydrothermal processing of a powder mixture of beta-tricalcium phosphate (β-TCP) and dicalcium phosphate dihydrate (DCPD). Co-existence of urea was found to sustain morphology of HAp crystals in the compacts under an initial concentration of 2 mol dm^-3 and less. Homogenous morphology of needle-like crystals was observed on the compacts carbonated owing to decomposition of urea. Carbonate ions (CO₃^2-) was found to be substituted in both the phosphate and hydroxide sites of HAp lattice. The synthesized HAp was calcium deficient, as it had a Ca/P atomic ratio of 1.62 and the phase was identified as calcium deficient hydroxyapatite (CDHA). The release of CO₃^2- ions from urea during the hydrothermal treatment determined the morphology of the CDHA in the compacts. The usage of urea in the morphological control of carbonate-substituted HAp (CHAp) employing the double-step hydrothermal method is established.     

Mechanical and photocatalytic properties of hydroxyapatite/titania nanocomposites prepared by combined high gravity and hydrothermal process

Hydroxyapatite/titania nanocomposites of different ratios have been successfully synthesized by combined high gravity and hydrothermal methods. SEM and TEM observations showed that small spheres of TiO₂, identified as anatase crystals of 10–15 nm, were deposited on HAp rod-like crystals. EDAX analysis confirmed the presence of Ca, P, Ti and O. X-ray diffraction patterns indicated the presence of hydroxyapatite and anatase phase. More number of anatase peaks appeared in the XRD patterns with higher colloidal concentration of TiO₂ in the HAp/TiO₂ compound. Mechanical stability of the HAp/TiO₂ nanocomposites was determined by reinforcing them with high molecular weight polyethylene (HMWPE) and the tensile strength of the samples was analyzed. Photocatalytic activity of the HAp/TiO₂ particles was examined by decomposition of methyl orange (MO). The results showed that photocatalytic properties of HAp/TiO₂ composites are more effective than that of individual HAp and TiO₂ which implied that the HAp improved the photocatalytic activity of well known photocatalyst TiO₂.     

Effect of Additives on the Morphology of the Hydrated Product and Physical Properties of a Calcium Phosphate Cement

The morphology of a hydrated calcium phosphate cement （CPC） doped with several normally used additives was investigated by scanning electron microscopy （SEM） and the compressive strength of the cement was determined in this study. The hydrated products of CPC without additives was rod-like hydroxyapatite （HA） grains with around 2-5 μm in length and 100 nm in width. The addition of Sr obviously decreased the crystal size of the rod-like grains. CPCs containing carbonate, collagen and gelatin showed flake-like crystal morphology. Crylic acid-containing CPC presented flocculus-like structure. And malic acid-containing CPC exhibited oriented flake-like structure. The X-ray diffraction （XRD） analysis showed that the additives used in this study did not alter the hydration products of the cement. The compressive strength tests indicated that the compressive strength of the cement with rod-like morphology HA crystals was much higher than that of the cement with flake-like morphology HA crystals, and the cement with oriented flake-like morphology HA crystals exhibited the poorest compressive strength.     

In-vitro bioactivity,biocorrosion and antibacterial activity of silicon integrated hydroxyapatite/chitosan composite coating on 316 L stainless steel implants

A simple and effective ultrasonication method was applied for the preparation of 0, 0.4, 0.8, 1.0 and 1.6 wt% silicon substituted hydroxyapatite (HAp) (SH). The Ca/P ratio of the synthesised SH nanoparticles were in the range of 1.58–1.70. Morphological changes were noticed in HAp with respect to the amount of Si from 0 to 1.6 wt%. The morphology of the particles changed from spherical shape to rod-like morphology with respect to the amount of Si which was confirmed using transmission electron microscopy. X-ray diffraction studies confirm the formation of phase pure SH nanoparticles without any secondary phase. Chitosan (CTS) blended SH nanocomposites coating on surgical grade 316 L stainless steel (316 L SS) implant was made by spin coating technique. The surface of the coated implant was characterised using scanning electron microscopy which confirms the uniform coating without cracks and pores. The increased corrosion resistance of the 1.6 wt% of SH/CTS-coated SS implant in the simulated body fluid (SBF) indicates the long-term biostability of SH composite-coated ceramics in vitro than the 0 wt% SH/CTS. The testing of SH/CTS nanocomposites with gram-positive and gram-negative bacterial strains confirms that the antibacterial ability improves with the higher substitution of Si. In addition, formation of bone-like apatite layer on the SH/CTS-coated implant in SBF was studied through SEM analysis and it confirms the ability to increase the HAp formation on the surface of 1.0 wt% SH/CTS-coated 316 L SS implant.     

Influence of fluorine substitution on the morphology and structure of hydroxyapatite nanocrystals prepared by hydrothermal method

Hydroxyapatite (HAp) nanocrystals with different levels of fluorine substitution (P/F = 0, 6, 4 and 2) on the OH sites were produced via hydrothermal method. The fluorine substitution was found to alter the morphology of crystals appreciably. The aspect ratio and the crystallinity of HAp crystals increased with increasing fluorine substitution. The presence of broad ring and hallow ring patterns in electron diffraction suggests the low-crystalline nature of HAp crystals. With increasing fluorine substitution, the diffraction patterns exhibited discrete rings and numerous diffraction spots, implying the increased crystallinity. Raman spectra from the HAp nanoparticles also support the less-crystalline nature of the pristine HAp and the enhanced crystallization by fluorine substitution. In HAp crystals processed with no fluorine substitution, surface energy and planar Ca²⁺ density are less sensitive to the crystallographic orientation because of its low-crystalline nature, favoring equi-axed or slightly elongated particles. The addition of fluorine apparently increased the crystallinity, enhancing the orientation dependent growth and accordingly the aspect ratio. Osteoblast proliferation was observed to be enhanced by fluorine substitution in HAp. In vitro biological data support that the excellent osteoblastic cell viability and functional activity of the fluoridated apatite.     

Corrosion resistance and antibacterial effects of hydroxyapatite coating induced by polyacrylic acid and gentamicin sulfate on magnesium alloy

Magnesium(Mg)alloys have attracted considerable research attention as potential biocompatible implant materials.However,the major barriers to the extended use of such medical devices are the possibility of high corrosion rate and implantassociated infections.To solve them,a novel polyacrylic acid(PAA)/gentamicin sulfate(GS)-hydroxyapatite(HAp)coating was synthesized by a one-step hydrothermal deposition method.Characteristics of functional coatings were investigated by SEM,FTIR and XRD.Corrosion properties of samples were evaluated by electrochemical and hydrogen evolution tests.Antibacterial activities of the coatings against Staphylococcus aureus(S.aureus)were measured by the plate-counting method.Results showed that the as-prepared HAp coating with dense and flawless morphologies could not only enhance the corrosion resistance of Mg alloys,but also improve the adhesion strength between the HAp coating and the substrate.In addition,the induction of the apatite coating during immersion confirmed the excellent mineralization ability of the HAp coating.Moreover,the obtained HAp coati ng possessed antibacterial properties and could prolong the release of GS.Thus,the PAA/GS-HAp coated Mg alloy could serve as a better candidate for biomedical applications with good anti-corrosion and antibacterial properties.     

沉积电压对Hap-PAM生物涂层结构及性能的影响

为了提高生物惰性材料C/C的生物活性以及C/C基体与生物活性材料羟基磷灰石(HAp)的结合强度, 以丙烯酰胺单体(AM)和声化学制备的纳米HAp为原料, 异丙醇为分散介质, 采用水热电泳聚合沉积法在C/C复合材料表面制备了羟基磷灰石-聚丙烯酰胺(HAp-PAM)生物复合涂层。用XRD、 TEM、 SEM、 FTIR、 力学性能测试等手段对涂层的相组成、 官能团、 断面的微观形貌及结合强度进行了测试和表征, 研究了水热沉积电压对复合涂层结构和性能的影响。结果表明: 随着沉积电压的升高, 涂层中HAp的衍射峰呈现先增强后减小的趋势, PAM的衍射峰逐渐消失; 涂层的结合强度随着电压的升高先增强后减小。沉积电压为150 V时, 涂层的致密性和均匀性达到最佳, 涂层的厚度以及涂层与基体的结合强度分别达到最大值25 μm 和19 MPa。      

Effects of deposition temperature and chemical composition on the ZnO crystal growth on the surface of Pd catalyst through electroless chemical reaction

Zinc oxide (ZnO) was site-selectively grown on the palladium (Pd) catalyst through the electroless deposition process under mild conditions, and the effects of deposition temperature and chemical composition on the ZnO crystal growth were investigated. ZnO crystals were synthesized on the UV-patterned Pd catalysts in the aqueous solutions of various dimethylamine borane (DMAB)/Zn(NO₃)₂ ratio at 30–70 °C. The site-selective deposition was confirmed by X-ray photoelectron spectroscopy (XPS) data and elemental maps of Pd, Zn and oxygen in energy-filtering transmission electron microscopy (EFTEM), and the crystal morphology was observed by scanning electron microscopy (SEM). A strong near band emission at around 390 nm and a weak green emission at around 470 nm were observed in the photoluminescence (PL) spectrum. The ZnO crystals were grown in the following three steps: (1) ZnO fibrils were generated on the Pd catalysts and became sphere-like particles, (2) hexagonal wurtzite crystals initiated to grow from the sphere-like particles, and (3) the crystals grew in two directions—longitudinal and lateral growths giving rod-type or needle-type hexagonal crystals. It was found that longitudinal growth rate increased with increasing deposition temperature or DMAB/Zn(NO₃)₂ ratio.