Biomimetic Hydroxyapatite Coating on Metal Implants

The combination of the high mechanical strength of metals with the osteoconductive properties of calcium phosphates make hydroxyapatite coatings on titanium implants widely used in orthopedic surgery. However, the most popular coating method, plasma spraying, exhibits some important drawbacks: the inability to cover porous implants and to incorporate biologically active agents, delamination, and particle release. The aim of this study was to elaborate a dense, strong, and thick calcium-phosphate coating on titanium and porous-tantalum implants using a two-step biomimetic procedure. In the first step, the implants were soaked in a solution that was 5 times more concentrated than regular simulated body fluid (SBF-A solution). A thin but uniform amorphous calcium-phosphate coating was deposited on the metal. Then, the implants were immersed in the SBF-B solution, which had a similar composition as the SBF-A solution, but with decreased contents of crystal growth inhibitors (i.e., Mg²⁺ and HCO₃⁻). This resulted in the fast precipitation of a 30 μm thick crystalline calcium-phosphate coating. The pH of the SBF-B solution and the thickness of the crystalline coating layer were studied as a function of time. The Fourier transform infrared spectra and X-ray diffraction patterns showed that this new coating closely resembles bone mineral. Our biomimetic coating should facilitate rapid bone formation around the implant, reducing therewith the patient's recovery time after surgery.     

羟基磷灰石涂层的生物仿生法研究进展

羟基磷灰石的生物复合涂层具有很高的外科应用价值.制备羟基磷灰石复合材料的方法有很多种,其中仿生法模仿了自然界生理磷灰石的矿化机制,在类似于人体组织内环境条件的水溶液中自然沉积出磷灰石层.仿生法具有许多其它方法无可比拟的优越性.本文对近年来文献报道中出现的生物仿生法进行了综述,阐述了各种仿生法中包括对基体进行预处理使其表面官能团化,再将基体在模拟体液中浸泡从而使磷灰石自然沉积的模拟生物矿化的4个阶段的工艺过程及其仿生机理.     

通过仿生法在纯镁表面制备羟基磷灰石涂层的研究

在纯镁表面自组装单分子层,用CaCl2和K2HPO4溶液对其进行预钙化处理,将处理过的纯镁试样浸泡于钙磷饱和溶液,仿生沉积得到羟基磷灰石涂层。利用X射线衍射和扫描电子显微镜对形成的涂层进行表征。试验结果表明,6天后即在镁基体表面得到了均匀致密、以羟基磷灰石（HA）为主晶相的羽毛状涂层。     

Interconnected Hydroxyapatite Nanofibers in the Biomimetic Coating of a Bioinert Ceramic Substrate

A bioinert ceramic substrate, α-Al₂O₃, has been coated with hydroxyapatite (HAp) by the biomimetic route using simulated body fluid (SBF) solution at room temperature. The substrate was incubated at 37°C in SBF for 6 days with a periodic replacement with freshly prepared SBF at 48-h intervals. After 6 days, continuous nanofiber-like structures of HAp (5–35 μm in length, 0.05 μm diameter) were obtained, connecting the intra- and interglobular clusters, within the coated mineral layer on the substrate surface. This is a unique and new observation, and this phenomenon has been demonstrated by a simple fractal growth model.     

Biomolecular Template-Induced Biomimetic Coating of Hydroxyapatite on an SS 316 L Substrate

Bone, a natural composite, comprises non-stoichiometric calcium hydroxyapatite (HAp) precipitated in a controlled reaction environment of a highly aligned, anisotropic organic template (type I collagen) that leads to its exotic tensile and compressive strength. It differs from stoichiometric hydroxyapatite in composition, crystallinity, and other physical and mechanical properties. In the present study, functionalized biomolecular template-induced precipitation of HAp on an SS 316 L substrate following biomimetic route exhibits distinct alterations in crystal growth and geometry, which in turn indicates the potential of the process to develop a non-stoichiometric HAp coating on metal implants.     

Synthesis of a Hydroxyapatite/Collagen/Chondroitin Sulfate Nanocomposite by a Novel Precipitation Method

A hydroxyapatite/collagen/chondroitin sulfate nanocomposite that partly mimicked the composition of cartilage was synthesized through a novel precipitation method, using a calcium hydroxide suspension and phosphoric acid solutions that contained several mixing ratios of type II collagen (Col) and chondroitin sulfate (ChS). The precipitates were shaped and consolidated via filter pressing and subsequent cold isostatic pressing, respectively. A preferential alignment of the crystallographic c -axis of the hydroxyapatite nanocrystals along the longitudinal direction of the Col and ChS mixture was observed. The fracture strength and Vickers hardness of the nanocomposites were in the ranges of 35–50 and 119–219 MPa, respectively. This nanocomposite may be applicable for use as a bone substitute, because of its potential capability of bone remodeling through endochondral ossification.     

Apatite Coating on Organic Polymers by a Biomimetic Process

Dense and uniform layers of a biologically active carbonate-containing hydroxyapatite can be formed on various kinds of organic polymers by the following biomimetic method. First, a substrate is set in contact with particles of CaO–SiO₂-based glass soaked in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma for forming the apatite nuclei on the substrate. Second, the substrate is soaked in another solution highly supersaturated with respect to the apatite, e.g, with ion concentrations 1.5 times those of SBF (1.5SBF) for making the apatite nuclei grow on the substrate in situ. The induction period for the apatite nucleation, which is defined as the time of the first treatment required for forming enough of the apatite nuclei to make the continuous layer after the second treatment, was almost 24 h for most of the examined polymers. The adhesive strength of the formed apatite layer to the polymers was as high as 3 to 4 M Pa for poly(ethylene terephthalate), poly-ether sulfone, and poly (vinyl alcohol) hydrogel. This type of apatite–organic polymer composite is expected to be useful for repairing not only living hard tissues but also soft ones.     

固相离子交换法制备碳酸羟基磷灰石涂层的研究

通过涂覆-烧结法在氧化铝(Al2O3)基体上制备羟基磷灰石(HA)/氟羟基磷灰石(FHA)双层涂层,然后采用固相离子交换法在湿CO2气氛中对HA表层进行碳酸化处理。XRD、FTIR和SEM测试结果表明:FHA中间层能有效地抑制HA与Al2O3的反应,湿CO2气氛中的湿气有利于分解相的恢复,而碳酸根能进入到表面涂层结构内部,形成A型替代为主的碳酸羟基磷灰石(CHA)。所获得的双层涂层具有多孔粗糙的表面,但与Al2O3基体结合紧密。     

Hydroxyapatite Mineralization on the Calcium Chloride Blended Polyurethane Nanofiber via Biomimetic Method

Polyurethane nanofibers containing calcium chloride (CaCl2) were prepared via an electrospinning technique for the biomedical applications. Polyurethane nanofibers with different concentration of CaCl2 were electrospun, and their bioactivity evaluation was conducted by incubating in biomimetic simulated body fluid (SBF) solution. The morphology, structure and thermal properties of the polyurethane/CaCl2 composite nanofibers were characterized by means of scanning electron microscopy (SEM), field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetry. SEM images revealed that the CaCl2 salt incorporated homogeneously to form well-oriented nanofibers with smooth surface and uniform diameters along their lengths. The SBF incubation test confirmed the formation of apatite-like materials, exhibiting enhanced bioactive behavior of the polyurethane/CaCl2 composite nanofibers. This study demonstrated that the electrospun polyurethane containing CaCl2 composite nanofibers enhanced the in vitro bioactivity and supports the growth of apatite-like materials.     

Hydroxyapatite Mineralization on the Calcium Chloride Blended Polyurethane Nanofiber via Biomimetic Method

Polyurethane nanofibers containing calcium chloride (CaCl₂) were prepared via an electrospinning technique for the biomedical applications. Polyurethane nanofibers with different concentration of CaCl₂ were electrospun, and their bioactivity evaluation was conducted by incubating in biomimetic simulated body fluid (SBF) solution. The morphology, structure and thermal properties of the polyurethane/CaCl₂ composite nanofibers were characterized by means of scanning electron microscopy (SEM), field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetry. SEM images revealed that the CaCl₂ salt incorporated homogeneously to form well-oriented nanofibers with smooth surface and uniform diameters along their lengths. The SBF incubation test confirmed the formation of apatite-like materials, exhibiting enhanced bioactive behavior of the polyurethane/CaCl₂ composite nanofibers. This study demonstrated that the electrospun polyurethane containing CaCl₂ composite nanofibers enhanced the in vitro bioactivity and supports the growth of apatite-like materials.     

溶胶凝胶法制备羟基磷灰石/TiO2复合生物活性涂层的研究

通过溶胶凝胶法在纯钛基体上制备了羟基磷灰石/TiO2复合生物活性涂层.HA可以提高钛基的生物活性,TiO2可以提高涂层与基体的物理、化学相容性和结合强度.HA和TiO2溶胶由前驱体制得,按不同物质的量比直接混合两种溶胶来制备复合溶胶.使用XRD、SEM研究了不同温度下热处理后涂层的组成和结构.实验结果表明HA的结晶度和晶粒随着温度的升高而提高和变大;涂层表面为连续多孔结构.粘结拉伸结果表明复合涂层与基体结合良好,较纯HA涂层与基体的结合强度有较大提高.复合涂层试样于SBF中浸泡2d、7d和14d的SEM分析结果表明复合涂层表面的磷灰石形成量较高.电位动力学曲线分析表明复合涂层可以提高基体的耐蚀性.     

Hydroxyapatite Coating on Titanium Substrate by the Sol-Gel Process

Hydroxyapatite coatings on titanium were attempted by a sol-gel process combined with conventional heat treatment and with UV irradiation at ambient temperature after dipping/ withdrawing a substrate into/from the sol. X-ray diffraction data showed that a coating film prepared by heat treatment was amorphous and crystallized in Ca₅(PO₄)₃(OH) at a temperature of 773–973 K. The infrared spectra for coating films that have been prepared by heat treatment at a temperature of 573–873 K were in fair agreement with those for a coating film prepared by UV irradiation. After ethylene oxide sterilization, the cytotoxicity of coating film decreased with increasing irradiation time in UV irradiation, whereas it decreased with increasing temperature in conventional heat treatment. In comparisons between ethylene oxide sterilization and autoclave sterilization, the coating film sterilized by autoclave had much lower cytotoxicity than that sterilized by ethylene oxide. Furthermore, an animal test in the transfemoral drill hole on a rat for 4 weeks was examined using an implant prepared by heat treatment and autoclave sterilization. The sol-gel-coated titanium had slightly higher bone apposition than uncoated titanium as a control material.     

Dense Nanostructured Hydroxyapatite Coating on Titanium by Aerosol Deposition

In order to improve biocompatibility of Ti metal substrates, 1-μm-thick nanostructured hydroxyapatite (HAp) coatings were deposited on the substrates through aerosol deposition, which sprays HAp powder with an average particle size of 3.2 μm at room temperature in vacuum. The original HAp particles were fractured into nanoscale fragments to form highly dense coating during the deposition process. Density of the HAp coating was 98.5% theoretical density (TD). Transmission electron microscopy observation revealed that the as-deposited coating consisted of HAp crystallites with average grain size of 16.2 nm and amorphous phase. Tensile adhesion strength between the coating and the substrate was 30.5±1.2 MPa. Annealing up to 500°C in air increased crystallinity and grain size in the coating without any delamination or crack according to X-ray diffraction analysis and electron microscopy. MTS assay and alkaline phosphatase activity measurements with MC3T3-E1 preosteoblast cell revealed that the biocompatibility was greatly improved by postdeposition heat treatment at 400°C in air due to well-crystallized HAp with average grain size of 29.3 nm. However, further heat treatment at 500°C deteriorated biocompatibility due to rapid growth of HAp grains to average size of 99 nm. Cross section of the coating on a commercially available Ti dental implant revealed full coverage of the surface with HAp.     

羟基磷灰石涂层的制备

本文以五氧化二磷、无水乙醇、硝酸钙为原料,通过溶胶-凝胶法制备羟基磷石灰涂层。选用2mm/s的速度浸渍提拉载玻片,在载玻片上进行涂膜,经60℃干燥后在650℃烧结保温3h,可在载玻片上得到羟基磷灰石涂层。研究结果表明:制备溶胶合适的配比为Ca(NO3)22·4H2O:P2O5(摩尔比)=10:3,即Ca/P原子比=5:3(约等于1.67)。     

纳米晶种涂层法合成Silicalite-1沸石膜

用纳米晶种涂层二次生长成膜法在大孔a-Al2O3(孔径4~6 mm)陶瓷管上合成Silicalite-1沸石膜. 用X射线衍射(XRD)和扫描电镜(SEM)表征分析了沸石膜的形态,并通过单组分气体渗透实验对合成膜管的渗透性能进行了测试. 结果表明,合成的Silicalite-1沸石膜连续、互生,看不出晶间孔;沸石膜层厚8~10 mm;常温常压下H2/N2的理想分离系数为3.9,超过其努森扩散值3.74,H2/C3H8的理想分离系数为19.1,远大于其Knudsen扩散比值4.69,且H2的渗透率达到1.43′10-6 mol/(m2×s×Pa). 气体分离数据表明,该膜没有明显的缺陷存在.     

Hydroxyapatite Coating on Thermally Oxidized Titanium Substrates

Titanium substrates were oxidized in oxygen or air at temperatures of 600°–800°C, then immersed in solutions of 2.0m M – 20.7m M CaCl₂ and 1.2m M –12.4m M KH₂PO₄ for aging periods of 0.5–10 d. The titanium surface was successfully coated with hydroxyapatite (HAP) when the substrates were oxidized in oxygen gas at 610°C for 1 h and then aged in a solution of 2.00m M Ca²⁺ and 1.20m M PO₄³⁻. The Ca/P ratio of the surface coating increased toward its stoichiometric HAP value (return 10/6) as the aging time increased; the Ca/P ratio attained a value of 1.66 after 10 d.     

羟基磷灰石生物陶瓷涂层制备方法评述

根据医用生物陶瓷羟基为磷灰石及医用金属材料的生物，力学特性，本文认为在金属基体表面涂覆羟基磷灰石是综合金属材料及生物陶瓷材料各自优越性阳有希望的途径这一。评述了羟基磷灰石涂层的制备方法，论证了较为优化的涂层结构。     

Processing and Performance of Hydroxyapatite/Fluorapatite Double Layer Coating on Zirconia by the Powder Slurry Method

A hydroxyapatite/fluorapatite (HA/FA) double layer was coated on ZrO₂ by a powder slurry method. The FA layer between the HA layer and the ZrO₂ substrate was effective in suppressing the reaction between HA and ZrO₂. The rheological properties of the slurry and the thermal treatment conditions were optimized. Addition of small amounts of tri-ethyl phosphate dispersant and polyvinylbutyral binder (up to 5 wt%) was effective in reducing the slurry viscosity, even at high loadings of HA powder. Each layer (HA, FA) was deposited on ZrO₂ repeatedly to induce a uniform layer, and the final heat treatment was carried out above 1200°C to consolidate the coating layer. During this process, without the FA-intermediate layer, a severe reaction between HA and ZrO₂ occurred to form tri-calcium phosphate and CaZrO₃ products. However, the presence of the FA layer between HA and ZrO₂ effectively suppressed the reaction up to 1300°C. The obtained HA/FA double coating layer was micro-porous and relatively rough, but was firmly adhered to the ZrO₂ substrate, having a bonding strength of approximately 25 MPa after heat treatment above 1200°C. The osteoblast-like cells cultured on the HA/FA coating layer spread and proliferated favorably, having a cell proliferation rate comparable to that of a plastic control and HA bulk ceramic.     

Microheterogeneous Collagen Model on the Basis of a Chromatographic Study on Hydroxyapatite Columns

Abstract

Earlier, on the basis of experimental chromatograms of collagen obtained on hydroxyapatite columns, a microheterogeneous collagen model with fluctuating primary structures around a mean structure was proposed. In this paper this model is examined in detail on the basis of a new chromatographic theory. Good fits were obtained between theory and experiment. It was estimated that the probability, π, that aspartic and glutamic residues exist at correct positions on the three α collagen peptide chains is about 0.8. The following conclusions were derived at the same time: (a) the energy of adsorption, ?, for a carboxyl group of collagen on to a crystal site of hydroxyapatite is 0.7 kcal/mol. (b) The replusive interaction energy, [Etilde], for one of collagen molecules with another on the crystal surface is 3 kcal/mol when these make maximum contact. (c) The square-root, h', of the area on the collegen surface where a carboxyl group can move freely (around the mean position) is 2.5-3.5 Å. (d) It is likely that a considerable adsorption of phosphate ions from the buffer occurs on the collagen surface adsorbed on the hydroxyapatite surface. The experimental values obtained in (a)–(c) are all reasonable ones; this strongly supports the microheterogeneous model itself. It is suggested that the ambiguous primary structure arises at a translational level of biosynthesis.     

电泳沉积磷灰石生物陶瓷涂层的研究进展

羟基磷灰石(HA)生物涂层材料是最有发展前途的生物硬组织替代材料之一.电泳沉积具有装置简单,操作方便,非线性,沉积温度低等特点,可以解决传统HA生物陶瓷涂层制备工艺上的各种不足.文中探讨了电泳沉积的各种工艺影响因素,综合介绍了国内外有关电泳沉积HA复合(梯度)生物涂层和电泳沉积与其它方法复合制备HA生物涂层的研究报道,进而提出了相应的设想和展望.