Antibacterial and bioactive calcium titanate layers formed on Ti metal and its alloys

An antibacterial and bioactive titanium (Ti)-based material was developed for use as a bone substitute under load-bearing conditions. As previously reported, Ti metal was successively subjected to NaOH, CaCl₂, heat, and water treatments to form a calcium-deficient calcium titanate layer on its surface. When placed in a simulated body fluid (SBF), this bioactive Ti formed an apatite layer on its surface and tightly bonded to bones in the body. To address concerns regarding deep infection during orthopedic surgery, Ag⁺ ions were incorporated on the surface of this bioactive Ti metal to impart antibacterial properties. Ti metal was first soaked in a 5 M NaOH solution to form a 1 μm-thick sodium hydrogen titanate layer on the surface and then in a 100 mM CaCl₂ solution to form a calcium hydrogen titanate layer via replacement of the Na⁺ ions with Ca²⁺ ions. The Ti material was subsequently heated at 600 °C for 1 h to transform the calcium hydrogen titanate into calcium titanate. This heat-treated titanium metal was then soaked in 0.01–10 mM AgNO₃ solutions at 80 °C for 24 h. As a result, 0.1–0.82 at.% Ag⁺ ions and a small amount of H₃O⁺ ions were incorporated into the surface calcium titanate layers. The resultant products formed apatite on their surface in an SBF, released 0.35–3.24 ppm Ag⁺ ion into the fetal bovine serum within 24 h, and exhibited a strong antibacterial effect against Staphylococcus aureus. These results suggest that the present Ti metals should exhibit strong antibacterial properties in the living body in addition to tightly bonding to the surrounding bone through the apatite layer that forms on their surfaces in the body.     

Surface modification of a Ti–7.5Mo alloy using NaOH treatment and Bioglass® coating

The objective of this study was to propose a surface modification for a low-modulus Ti–7.5Mo alloy to initiate the formation of hydroxyapatite (HA) during in vitro bioactivity tests in simulated body fluid (SBF). Specimens of commercially pure titanium (c.p. Ti) and Ti–7.5Mo were initially immersed in a 15 M NaOH solution at 60°C for 24 h, resulting in the formation of a porous network structure composed of sodium titanate (Na₂Ti₅O₁₁). Afterwards, bioactive Bioglass^® particles were deposited on the surface of NaOH-treated c.p. Ti and Ti–7.5Mo. The specimens were then immersed in SBF at 37°C for 1, 7 and 28 days, respectively. The apatite-forming ability of the NaOH-treated and Bioglass^®-coated Ti–7.5Mo was higher than that of the c.p. Ti under the same condition. The X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) results indicated that the deposited amounts of calcium phosphate were much greater for the surface-treated Ti–7.5Mo than for the c.p. Ti, a finding attributable to or correlated with the higher pH value of the SBF containing surface-treated Ti–7.5Mo. Moreover, in the surface-treated Ti–7.5Mo, the pH value of the SBF approached a peak of 7.66 on the first day. A combination of NaOH treatment and subsequent Bioglass^® coating was successfully used to initiate in vitro HA formation in the surface of the Ti–7.5Mo alloy.     

Solid-phase interaction in the hydroxyapatite/titanium heterostructures upon high-temperature annealing in air and argon

Samples of 100- and 500-nm-thick hydroxyapatite films on titanium were investigated using scanning electron microscopy, electron probe X-ray microanalysis, and X-ray powder diffraction. The films were prepared by high-frequency magnetron sputtering of a target in an argon atmosphere (1 × 10^?1 Pa) at a magnetron power density of 40–70 W/cm². These conditions provided growth of films at a rate as high as 0.7 nm/s. It was demonstrated that the hydroxyapatite film annealed in argon is characterized by deep pores that have diameters ranging from 0.3 to 8.0 µm and are uniformly distributed throughout the film surface. The electron probe X-ray microanalysis confirmed the presence of all elements (Ti, O, Ca, P) under investigation, except for hydrogen, in the samples of the films. For biologically compatible hydroxyapatite, the optimum ratio Ca : P ? 1.5–1.7 was achieved in the hydroxyapatite/titanium system with a 500-nm-thick hydroxyapatite layer upon annealing in argon at a temperature of 1050°C for 30 min. It was established that the hydroxyapatite/titanium system contains intermediate phases, including calcium titanate CaTiO₃, which proved the interaction of hydroxyapatite with titanium.     

HOPG片电化学沉积羟基磷灰石初探

为探索羟基磷灰石(HA)在含碳基体上电化学沉积,采用了高定向裂解石墨(HOPG)片这一具有原子级平整表面的导电材料作为阴极材料,探索了电沉积时间、溶液pH值及溶液浓度对沉积层成分和形貌的影响,利用TEM、SEM、AFM、EDS及XRD等进行了表征分析,并初步探讨了羟基磷灰石电沉积机理。结果表明电解液初始pH值为5和钙离子浓度低于0.007mol/L时有利于促进HA的生长,并且可以形成单层片状结构,得到比较规整完善的多孔状单层HA涂层。而延长电沉积和陈化时间则有助于缺钙型HA垂直于基底表面生长,并促进钙磷比增加,形成缺钙性HA。研究将为电沉积羟基磷灰石的应用提供必要的理论和实验支持。     

Growth of hydrophobic TiO2 on wood surface using a hydrothermal method

Hydrophobic titanium dioxide (TiO₂) was successfully grown on a wood surface using a hydrothermal method. Energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and water contact angle (WCA) were employed to characterize the features of grown TiO₂ and its hydrophobicity. EDS, XRD, and FTIR proved that anatase TiO₂ chemically bonded to the wood surface through the combination of hydrogen groups during the hydrothermal process. The values of WCAs manifested that the hydrophobicity of the treated wood was mainly dependent on specific reaction conditions, especially on reaction pH value and hydrothermal temperature. The highest WCA reached 154° when the hydrothermal temperature was 130 °C. The treated wood thus possessed a superhydrophobic surface.     

Hydrothermal precipitation of hydroxyapatite on anodic titanium oxide films containing Ca and P

Highly-crystallized hydroxyapatite (HA) can be precipitated during heat treatment in high-pressure steam at 300 °C on an anodic titanium oxide film containing Ca and P (AOFCP), which has been electrochemically formed on a titanium substrate prior to the hydrothermal treatment. Factors affecting the precipitation, such as a percentage of distilled water in the autoclave and additives in the AOFCP, were evaluated by scanning electron microscopy. Ca²⁺ and PO^3– ₄ ions were leached from the AOFCP into a water layer covering the film surface, and nucleate HA heterogeneously on the porous TiO₂ matrix of the AOFCP which was made by the ion leaching. The morphology of the precipitated crystals was significantly affected by the water volume ratio because the concentrations of the Ca²⁺ and PO₄ ^3– ions varied depending on the thickness of the water layer. The amount of the precipitation decreased on the AOFCP which was formed in the solution containing a small amount of Mg²⁺ ions or formed on Ti-6Al-4V alloy instead of titanium.     

Surface modification of natural and synthetic hydroxyapatites powders by grafting polypyrrole

The modification of hydroxyapatite surface by grafting polypyrrole has been investigated with two hydroxyapatites (HA) powders. One is natural derived from bovine bone, it was prepared by calcination at 750 °C. The other is synthetic synthesized by the sol–gel method using Ca(NO₃)₂·4H₂O and P₂O₅. The presence of (C₄H₃N) _n polymeric fragment bound to HA surface was evidenced by infrared analysis. X-ray powder analysis has shown that the apatite structure remains unchanged during the surface modification. The thermogravimetric analysis has shown that the weight loss exhibited by HA increased from 8.7 to 47.8 and from 18.3 to 42.8 wt% for natural hydroxyapatite (NHA)/polypyrrole and synthetic hydroxyapatite (SHA)/polypyrrole, respectively, as the pyrrole solution concentration increased from 5 to 15 wt%. Grafting of polypyrrole on HA surface caused an increase in specific surface area up to 113 m²/g for SHA and up to 107 m²/g for NHA aged in 15 wt% pyrrole solution (HA/15Pyrrole). According to the results found for these two apatites, a mechanism of surface modification was proposed for the formation of N–H hydrogen bonds as the result of a reaction between the C₄H₅N organic reagent and OH^? ions of the HA.     

Effects of titanium surface modifications on bonding behavior of hydroxyapatite ceramics and titanium by hydrothermal hot-pressing

In order to improve the interface strength in the bonded body of hydroxyapatite (HA) ceramics and Ti disks prepared by a hydrothermal hot-pressing (HHP) method, the effects of Ti surface modification on the bonding behavior were investigated. The reaction layer composed of titanium dioxide and sodium titanate was formed on the Ti surface using a 5 M NaOH solution with the objective of increasing the interface strength between the Ti substrate and HA ceramics to be formed by the HHP method. Three conditions with different temperature and treatment times were tested to modify the Ti surface. A mixture of calcium hydrogen phosphate dihydrate and calcium hydroxide was used as a starting powder material for solidifying HA. Solidification of HA and its bonding with Ti were achieved simultaneously by using the HHP method at the low temperature as low as 323 K. 3-point bending tests were conducted to obtain an estimate of the interface fracture toughness of HA/Ti. The Ti surface modification conducted at 323 K for 2 h using the hydrothermal NaOH solution was shown to be most effective among the three conditions tested. The hydrothermal Ti surface modification enabled us to increase significantly the interface fracture toughness. The enhancement of the interface fracture toughness was possibly due to the presence of anatase formed on the Ti surface and the good adhesion in the bioactive layer.     

Sol-gel derived hydroxyapatite coatings on titanium substrate

Biomaterials, in particular those used for orthopaedic prostheses, consist of a metallic substrate, exhibiting excellent mechanical properties, coated with a ceramic layer, which guarantees resistance to the corrosion and an elevated bioactivity. In this paper the preparation of sol-gel films of hydroxyapatite, HA (Ca₁₀(PO₄)₆(OH)₂), on titanium substrate is described. The samples were obtained through the dip-coating method, starting from a colloidal suspension of hydroxyapatite. In order to increase the adhesion between the HA film and the metallic substrate, the same substrate has been preliminarily coated either with titanium oxide, TiO₂ (in the anatase or rutile phase), or calcium titanate, CaTiO₃ (perovskite). Also these latter films have been deposited from a sol-gel solution. The characterization of the films through XRD, SEM, and AFM gave good results for the crystallinity of the deposited HA; for what concerns the sample morphology, the films turned out to be homogeneous and crack-free.     

钛网表面含hBMP-2的复合涂层制备及hBMP-2的释放研究

为提高骨接合钛网的骨整合性和生物活性, 本研究采用碱热处理法在钛网表面构建出具有多孔结构的钛酸盐纳米纤维, 利用电化学沉积技术在钛酸盐纳米纤维表面制备磷酸钙涂层, 并采用不同方法将人骨形态发生蛋白(hBMP-2)引入涂层, 制备了三种含hBMP-2分子的复合涂层(TmhB、TmHedhB和TmHhBed)。实验对各复合涂层的表面形貌、化学成分、相组成和hBMP-2的含量与释放性能进行了表征。研究发现: 各涂层都具有多孔纤维结构, TmHedhB和TmHhBed中的磷酸钙相为羟基磷灰石(HA), 呈“串珠”状包裹在钛酸盐纳米纤维表面, “串珠”状HA的引入促进了复合涂层对hBMP-2的吸附。电化学共沉积技术在钛酸盐纳米纤维表面制备的HA/hBMP-2复合涂层中hBMP-2的含量最大, 达886 ng/mg, 在6~48 h内具有明显的hBMP-2缓释性能。     

Interfacial titanium oxide between hydroxyapatite and TiAlFe substrate

The interface between nano-crystalline hydroxyapatite (HA) thin films and a titanium alloy (Ti5Al2.5Fe) has been studied by means of Fourier transform infrared spectrophotometry and X-ray diffraction at grazing incidence. The HA thin films were deposited by radio-frequency magnetron sputtering in low pressure dry argon on substrates kept at low temperature or heated at 550 °C. The effect of film treatment by sputtering and annealing in humid air, as a simple, effective way of restoring the crystallinity and stoichiometry of the HA bulk, was studied in correlation with the development of a titanium oxide layer at the film-substrate interface. An interfacial TiO₂ film grew at the interface during annealing in moist air, while a TiO₂ layer diffused into the HA films when directly sputtered at 550 °C. The formation of an interfacial titanium oxide layer was inhibited by the insertion of a crystalline TiN buffer interlayer between the substrate and the HA film. Separately, the mechanical characteristics of the different HA films were monitored by nanoindentation to find out how they had been affected.     

Hydroxyapatite coating of titanium by biomimetic method

The biomimetic method was used in order to deposit, on titanium substrates, an hydroxyapatite (HA) coating. The bioactive HA layer was obtained by using, in the first stage of the process, a glass having the composition 2.5CaO2SiO₂ different from the one proposed for the application of the biomimetic method. This glass can be obtained via sol–gel, a method that allows one to obtain, easily, very pure products. The growth of HA crystals was confirmed by Fourier transform infrared, SEM, EDS and X-ray photoelectron spectroscopy (XPS) results. The experimental results suggest that, as reported in the literature for other supports, the silicate ions released from the glass in the first stage bind themselves to the titanium support. In particular, from XPS analysis it is evident that the titanium substrate is well covered by a calcium phosphate layer of the type of HA.     

Pulsed laser deposition of hydroxyapatite on titanium substrate with titania interlayer

Pulsed laser deposition (PLD) has been used to deposit hydroxyapatite (HA) ceramic over titanium substrate with an interlayer of titania. PLD has been identified as a potential candidate for bioceramic coatings over metallic substrates to be used as orthopedic and dental implants because of better process control and preservation of phase identity of the coating component. However, direct deposition of hydroxyapatite on titanium at elevated temperature results in the formation of natural oxide layer along with some perovskites like calcium titanate at the interface. This leads to easy debonding of ceramic layer from the metal and thereby affecting the adhesion strength. In the present study, adherent and stable HA coating over Ti6Al4V was achieved with the help of an interlayer of titania. The interlayer was made to a submicron level and HA was deposited consecutively to a thickness of around one micron by exposing to laser ablation at a substrate temperature of 400°C. The deposited phase was identified to be phase pure HA by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and inductively coupled plasma spectrometry. The mechanical behavior of coating evaluated by scratch test indicates that the adhesion strength of HA coating was improved with the presence of titania interlayer.     

Sol–gel derived hydroxyapatite/titania biocoatings on titanium substrate

A simple sol–gel method was successfully developed for a hydroxyapatite (HA)/TiO₂ double layer deposition on a pure titanium substrate. Phase formation, surface morphology, and interfacial microstructure were investigated by differential scanning calorimetry analysis (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The TiO₂ layer was coated by a spin coating method at a speed of 1500 rpm for 15 s, followed by a heat treatment at 560 °C for 20 min. The HA film was subsequently spin coated on the outer surface at the same speed and then heat-treated at difference temperatures. Results indicated that the HA phase began to crystallize after a heat treatment at 580 °C; and the crystallinity increased obviously at a temperature of 780 °C. The HA film showed a porous structure and a thickness of 5–7 μm after the heat treatment at 780 °C. SEM observations revealed no delamination and crack at the interfaces of HA/TiO₂ and TiO₂/Ti. The HA film with a porous structure is expected to be more susceptible to the natural remodeling processes when it is implanted in a living body.     

In situ synthesis of hydroxyapatite-grafted titanium nanotube composite

ABSTRACT

The present study is an investigation to demonstrate the effectiveness of in situ approach in the synthesis of hydroxyapatite-grafted titanium nanotube composite (HA-TNT). This method involves combining the process of HA sol–gel and rapid breakdown anodisation of titanium in a novel solution consisting of NaCl and N₃PO₄. This new synthesis approach produced a uniform dispersion of Anatase and Rutile phases of TiO₂ nanotubes with minimal agglomeration in the matrix of crystalline HA. The characterisation of homogenised HA-TNT composite was investigated via field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM) and X-ray diffraction (XRD). FESEM and TEM images indicated the nanostructure of composite with TiO₂ nanotube diameter of approximately 10 nm. XRD and EDS analyses confirmed the formation of HA crystalline with the Ca/P ratio of 1.58 and formation of Anatase and Rutile phase of TiO₂ nanotubes.     

酸-水热法辅以水热温度对钛材生物活性的影响

为提高医用钛材的生物活性,通过酸-水热复合法在其表面设计并制备了TiO_2纳米棒,探讨水热温度对钛表面TiO_2纳米棒形成的影响,然后对试样进行模拟体液生物活性实验,采用扫描电子显微镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)分析手段研究了钛表面生成产物的形貌、元素组成和物相组成.结果表明:随着水热温度的增加,二氧化钛层的表面形貌发生改变,从片状到棒状,之后纳米棒发生团聚;试样中金红石相和锐钛矿相的衍射峰强度随水热温度的增加而增强;水热温度为130℃时,钛表面可以形成尺寸均匀、长度基本一致的TiO_2纳米棒,其厚度、长度和直径分别为2.5μm、150 nm和10 nm,且纳米棒是由锐钛矿型和金红石型TiO_2的混合相组成.模拟体液生物活性实验后,水热处理后材料表面有富含Ca、P的羟基磷灰石生成,而羟基磷灰石的形成主要与纳米棒的形成和膜层的厚度有关.其中,水热温度为130℃时形成的纳米棒结构较好,膜层较厚,其表面诱导磷灰石沉积的含量最多,具有较好的生物活性.     

Coating of hydroxyapatite on various substrates via hydrothermal reactions of Ca(edta)2- and phosphate

Hydroxyapatite was coated on various substrates such as 12 mol % ceria-doped tetragonal zirconia (12Ce-TZP), 3 mol % yttria-doped tetragonal zirconia (3Y-TZP), alumina, monetite coated titanium (Ti/CaHPO₄) and calcium titanate coated titanium (Ti/CaTiO₃) via hydrothermal reactions of Ca(edta)^2- and 0.05 M NaH₂PO₄ at initial pH 6 and 160–200 °C for 0.5–6 h. Rod-like particles of hydroxyapatite precipitated to form film on the substrates above 160 °C. The morphology of the film changed significantly depending on the characteristics of substrate, i.e. hydroxyapatite entirely coated the surfaces of 12Ce-TZP, Ti/CaHPO₄ and Ti/CaTiO₃ plates, but sparsely deposited on 3Y-TZP and Al₂O₃ plates. Film thickness increased with time (ca. 20 and 90 m on 12Ce-TZP plates for 0.5 and 6 h, respectively, at pH 6 and 200 °C). The adhesive strength of the film for the substrate was in the order, 12Ce-TZP/hydroxyapatite(28 MPa) > Ti/CaTiO₃/hydroxyapatite (22 MPa) > Ti/CaHPO₄/hydroxyapatite (9 MPa). © 2001 Kluwer Academic Publishers     

Synthesis of titanium dioxide nanotubes via one-step dynamic hydrothermal process

Titanium dioxide (TiO₂) nanotubes were synthesized via one-step dynamic hydrothermal process from commercial TiO₂ powder. The effects of NaOH concentration, reaction time, reaction temperature, stirring process and washing on the morphology, and the exchange ions of the nanotubes were investigated. The morphology of the nanotubes was characterized in detail with transmission electron microscopy and scanning electron microscope. In the dynamic hydrothermal process, stirring can reduce the reaction time of transformation from particles to nanotubes. The nanotubes were formed when the expected reaction temperature reached to 130 °C. Energy dispersive X-ray analysis was used to determine the exchange of sodium ions and protons in washing process. The Na⁺ ions attached in the nanotubes were removed completely by HCl aqueous solution and deionized water treatments. X-ray diffraction patterns showed the titanate phase of the as-synthesized sample and anatase phase of TiO₂ nanotubes after calcination process at 400 °C for 2 h.     

Formation of bioactive functionally graded structure on Ti-6Al-4V alloy by chemical surface treatment

An Al- and V-free sodium titanate hydrogel layer with a graded structure where the sodium titanate gradually decreases toward the interior, was formed on the surface of Ti-6Al-4V alloy, when the alloy was exposed to 5M NaOH solution at 60 °C for 24 h. This gel layer was transformed into an amorphous sodium titanate layer without giving considerable change in the graded structure, except a little increase in the depth of the oxygen distribution by a heat treatment at 600 °C for 1 h. The sodium titanate layer formed Ti-OH groups on its surface by exchanging its Na⁺ ion with H₃O⁺ ion in simulated body fluid when soaked in the fluid, and thus formed Ti-OH groups induced the apatite nucleation. The apatite layer also formed a graded structure toward the substrate. The strong bond of the apatite layer to the substrate was attributed to this graded structure.     

XPS study of the process of apatite formation on bioactive Ti—6Al—4V alloy in simulated body fluid

Bioactive Ti—6Al—4V alloy, which spontaneously forms a bonelike apatite layer on its surface in the body and bonds to living bone through this apatite layer, can be prepared by producing an amorphous sodium titanate on its surface by NaOH and heat treatments. In this study, the process of apatite formation on the bioactive Ti—6Al—4V alloy was investigated in vitro, by analyzing its surface with X-ray photoelectron spectroscopy as a function of soaking time in a simulated body fluid 4SBF). Thin-film X-ray diffractometry of the alloy surface and atomic emission spectroscopy of the fluid were also performed complementarily. It was found that immediately after immersion in the SBF,the alloy exchanged Na¹ ions from the surface sodium titanate with H₃O¹ ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after their formation,incorporated the calcium ions in the fluid to form calcium titanate. The calcium titanate thereafter incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate, which was later crystallized into bonelike apatite. This process of apatite formation on the alloy was the same as on the pure titanium metal, because the alloy formed the sodium titanate free of Al and V by the NaOH and heat treatments. The initial formation of the calcium titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania dissociated from the Ti-OH groups with the positively charged calcium ions in the fluid. The calcium titanate is postulated to gain a positive charge and interact with the negatively charged phosphate ions in the fluid to form amorphous calcium phosphate, which eventually stabilizes into crystalline apatite.