The order of calcium and phosphate ion deposition on chemically treated titanium surfaces soaked in aqueous solution

Layer-by-layer self-assembly of PLL/CPP-ACP multilayer on SLA titanium surface: Enhancing osseointegration and antibacterial activity in vitro and in vivo

Dental Implants are expected to possess both excellent osteointegration and antibacterial activity because poor osseointegration and infection are two major causes of titanium implant failure. In this study, we constructed layer-by-layer self-assembly films consisting of anionic casein phosphopeptides-amorphous calcium phosphate (CPP-ACP) and cationic poly (L-lysine) (PLL) on sandblasted and acid etched (SLA) titanium surfaces and evaluated their osseointegration and antibacterial performance in vitro and in vivo. The surface properties were examined, including microstructure, elemental composition, wettability, and Ca2+ ion release. The impact the surfaces had on the adhesion, proliferation and differentiation abilities of MC3T3-E1 cells were investigated, as well as the material's antibacterial performance after exposure to the oral microorganisms such as Porphyromonas gingivalis (P. g) and Actinobacillus actinomycetemcomitans (A. a). For the in vivo studies, SLA and Ti (PLL/CA-3.0)10 implants were inserted into the extraction socket immediately after extracting the rabbit mandibular anterior teeth with or without exposure to mixed bacteria solution (P. g & A. a). Three rabbits in each group were sacrificed to collect samples at 2, 4, and 6 weeks of post-implantation, respectively. Radiographic and histomorphometry examinations were performed to evaluate the implant osseointegration. The modified titanium surfaces were successfully prepared and appeared as a compact nano-structure with high hydrophilicity. In particular, the Ti (PLL/CA-3.0)10 surface was able to continuously release Ca2+ ions. From the in vitro and in vivo studies, the modified titanium surfaces expressed enhanced osteogenic and antibacterial properties. Hence, the PLL/CPP-ACP multilayer coating on titanium surfaces was constructed via a layer-by-layer self-assembly technology, possibly improving the biofunctionalization of Ti-based dental implants.

Mechanistic studies of biomineralisation on silver incorporated anatase TiO2

Here we report silver incorporated anatase TiO₂ developed on Ti metal by H₂O₂-AgNO₃ and heat treatment to have faster biomineralisation or apatite-forming ability in simulated body fluid (SBF). Apatite-forming ability has been investigated concerning heat treatment temperatures ranges, 400-800 °C and duration of soaking period in SBF. The apatite formation showed an increasing trend with increase in the heat treatment temperatures up to 600 °C and beyond that the Ti metal lost this ability. XRD as wells as Raman results of such chemical and heat-treated Ti metal at different temperatures further correlates the apatite nucleation directly in relation with that of anatase to rutile TiO₂ formation. Further, a time dependent apatite mineralisation study by XPS revealed simultaneous calcium and phosphate deposition at the early stage of soaking in SBF. Therefore, the apatite nucleation in the present chemically treated Ti metal depends on the crystalline phase of TiO₂ formed by H₂O₂ and heat treatment along with Ag⁺ ion release.

Biodegradable/biocompatible coated metal implants for orthopedic applications

Biocompatible metals have been suggested as revolutionary biomaterials for bone-grafting therapies. Although metals and their alloys are widely and successfully used in producing biomedical implants due to their good mechanical properties and corrosion resistance, they have a lack in bioactivity. Therefore coating of the metal surface with calcium phosphates (CaP) is a benign way to achieve well bioactivity and get controlled corrosion properties. The biocompatibility and bioactivity calcium phosphates (CaP) in bone growth were guided them to biomedical treatment of bone defects and fractures. Many techniques have been used for fabrication of CaP coatings on metal substrates such as magnesium and titanium. The present review will focus on the synthesis of CaP and their relative forms using different techniques especially electrochemical techniques. The latter has always been known of its unique way of optimizing the process parameters that led to a control in the structure and characteristics of the produced materials.

Mineralization of a superficially porous microsphere scaffold via plasma modification

Novel porous mineralization layers were obtained on scaffolds. The plasma process could enhance the bonding force between apatite and the substrate surface.

Micro-topography and reactivity of implant surfaces: an in vitro study in simulated body fluid (SBF)

The creation of micro-textured dental implant surfaces possessing a stimulating activity represents a challenge in implant dentistry; particularly, the formation of a thin, biologically active, calcium-phosphate layer on their surface could help to strengthen the bond to the surrounding bone. The aim of the present study was to characterize in terms of macrostructure, micro-topography and reactivity in simulated body fluid (SBF), the surface of titanium (Ti) implants blasted with TiO2 particles, acid etched with hydrofluoric acid, and activated with Ca and Mg-containing nanoparticles. Sandblasted and acid-etched implants were analyzed by ESEM-EDX (environmental scanning electron microscope with energy dispersive X-ray system) to study the micromorphology of the surface and to perform elemental X-ray microanalysis (microchemical analyses) and element mapping. ESEM-EDX analyses were performed at time 0 and after a 28-day soaking period in SBF Hank's balanced salt solution (HBSS) following ISO 23317 (implants for surgery—in vitro evaluation for apatite-forming ability of implant materials). Microchemical analyses (weight % and atomic %) and element mapping were carried out to evaluate the relative element content, element distribution, and calcium/phosphorus (Ca/P) atomic ratio. Raman spectroscopy was used to assess the possible presence of impurities due to manufacturing and to investigate the phases formed upon HBSS soaking. Micro-morphological analyses showed a micro-textured, highly rough surface with microgrooves. Microchemical analyses showed compositional differences among the apical, middle, and distal thirds. The micro-Raman analyses of the as-received implant showed the presence of amorphous Ti oxide and traces of anatase, calcite, and a carbonaceous material derived from the decomposition of an organic component of lipidic nature (presumably used as lubricant). A uniform layer of Ca-poor calcium phosphates (CaPs) (Ca/P ratio <1.47) was observed after soaking in HBSS; the detection of the 961 cm⁻¹ Raman band confirms this finding. These implants showed a micro-textured surface supporting the formation of CaPs when immersed in SBF. These properties may likely favor bone anchorage and healing by stimulation of mineralizing cells.

Surface controlled calcium phosphate formation on three-dimensional bacterial cellulose-based nanofibers

Studies on the early calcium phosphate (Ca-P) formation on nanosized substrates may allow us to understand the biomineralization mechanisms at the molecular level. In this work, in situ formation of Ca-P minerals on bacterial cellulose (BC)-based nanofibers was investigated, for the first time, using the X-ray absorption near-edge structure (XANES) spectroscopy. In addition, the influence of the surface coating of nanofibers on the formation of Ca-P minerals was determined. Combined with XRD analysis, XANES results revealed that the nascent precursor was ACP (amorphous calcium phosphate) which was converted to TCP (β-tricalcium phosphate), then OCP (octacalcium phosphate), and finally to HAP (hydroxyapatite) when phosphorylated BC nanofibers were the templates. However, the formation of nascent precursor and its transformation process varied depending on the nature of the coating material on nanofibrous templates. These results provide new insights into basic mechanisms of mineralization and can lead to the development of novel bioinspired nanostructured materials.

Biomineralization studies on cellulose membrane exposed to biological fluids of Anodonta cygnea

The present work proposes to analyse the results obtained under in vitro conditions where cellulose artificial membranes were incubated with biological fluids from the freshwater bivalve Anodonta cygnea. The membranes were mounted between two half 'Ussing chambers' with different composition solutions in order to simulate epithelial surfaces separating organic fluid compartments. The membrane surfaces were submitted to two synthetic calcium and phosphate solutions on opposite sides, at pH 6.0, 7.0 or 9.0 during a period of 6 hours. Additional assays were accomplished mixing these solutions with haemolymph or extrapallial fluid from A. cygnea, only on the calcium side. A selective ion movement, mainly dependent on the membrane pore size and/or cationic affinity, occurred with higher permeability for calcium ions to the opposite phosphate chamber supported by calcium diffusion forces across the cellulose membrane. In general, this promoted a more intense mineral precipitation on the phosphate membrane surface. A strong deposition of calcium phosphate mineral was observed at pH 9.0 as a primary layer with a homogeneous microstructure, being totally absent at pH 6.0. The membrane showed an additional crystal phase at pH 7.0 exhibiting a very particular hexagonal or cuttlebone shape, mainly on the phosphate surface. When organic fluids of A. cygnea were included, these crystal forms presented a high tendency to aggregate under rosaceous shapes, also predominantly in the phosphate side. The cellulose membrane was permeable to small organic molecules that diffused from the calcium towards the phosphate side. In the calcium side, very few similar crystals were observed. The presence of organic matrix from A. cygnea fluids induced a preliminary apatite-brushite crystal polymorphism. So, the present results suggest that cellulose membranes can be used as surrogates of biological epithelia with preferential ionic diffusion from the calcium to the phosphate side where the main mineral precipitation events occurred. Additionally, the organic fluids from freshwater bivalves should be also thoroughly researched in the applied biomedical field, as mineral nucleators and crystal modulators on biosynthetic systems.

Conformation change of bovine serum albumin induced by bioactive titanium metals and its effects on cell behaviors

The conformation change of bovine serum albumin (BSA) induced by bioactive titanium surfaces, including acid-alkali-treated titanium (AA-Ti) and alkali-heat-treated titanium (AH-Ti), was studied, and its effects on the activity of MC3T3-E1 cell were evaluated. Pure titanium metal (P-Ti) was used as control. The AA-Ti could adsorb more BSA on its surface than AH-Ti and P-Ti. The α-helix part of the protein adsorbed on P-Ti has weakly decreased compared with native BSA, and it dramatically decreased on AA-Ti and AH-Ti. The β-sheet segment of proteins adsorbed on P-Ti and AH-Ti had obviously increased. Much more tryptophan residues were exposed after the protein conformation changed when it interacted with AH-Ti, and some tryptophan residues were enveloped after it interacted with AA-Ti and P-Ti. AA-Ti has more tryptophan residues enveloped than P-Ti. All titanium surfaces induced tyrosine residues exposed, especially for the P-Ti. The higher ratio of COO(-)/NH3(+) for the proteins on P-Ti and AA-Ti indicated an orientation of proteins on P-Ti and AA-Ti, which makes more COO(-) exposed. The lower ratio of COO(-)/NH3(+) on AH-Ti indicates that more NH3(+) is exposed on its surface. The cell proliferation ability on different treated titanium surfaces coated with BSA followed by the order: P-Ti > AA-Ti > AH-Ti, which indicated that the protein conformation change on different bioactive titanium surfaces has great effect on the cell activity. Our results showed that the different biological response of bioactive titanium metals might depend on the protein conformation change induced by the surface structure.

Micropatterned TiO₂ nanotube surfaces for site-selective nucleation of hydroxyapatite from simulated body fluid

TiO₂ nanotube layers can provide greatly enhanced kinetics for hydroxyapatite formation from simulated body fluid compared with smooth, compact TiO₂ surfaces. In the present work we show how this contrast in reactivity can be used to create highly defined lateral microstructures where bone-like hydroxyapatite can be deposited with very high selectivity. For this we used a photolithographic approach to produce micropatterned TiO₂ nanotube layers surrounded by compact oxide that were then immersed in a simulated body fluid (SBF) solution. Not only the tubular vs. flat geometry but also the finding that compact oxides created in phosphate electrolytes in particular suppress apatite deposition are crucial for a very high reactivity contrast. Overall the results show the feasibility of stimulating hydroxyapatite deposition at surface locations where needed or desired. This provides a valuable tool for biomedical device design.

Anti-inflammatory properties of bioactive titanium metals

Anti-inflammatory properties of bioactive titanium metals prepared by anodic oxidation (AO-Ti) and alkali-heat (AH-Ti) treatments were studied by bacterial adhesion test and myeloperoxidase (MPO) activity assay methods. The bioactivities of the metals were also evaluated by apatite formation ability and osteoblasts culture experiments. Both metals could induce apatite formation and support osteoblasts proliferation. At the condition with normal incandescent light shine, both bioactive titanium metals had antibacterial adhesion properties compared with the titanium metal without treatment. The MPO activity assay proved that they both showed anti-inflammatory properties in vivo. The bioactive AO-Ti had better anti-inflammatory properties than the AH-Ti. It indicated that it is possible to optimize the anti-inflammatory properties of the bioactive titanium metals by different preparation methods.

Cathodic alkaline treatment of zirconium to give the ability to form calcium phosphate

The cathodic polarization technique to form an alkaline environment on a zirconium (Zr) surface, discussed in the present study, is unique, and gives the ability to form calcium phosphate in a simulated body fluid to Zr; on the other hand, many previous studies have been conducted using immersion in alkaline solutions. In this study, two discrete techniques were investigated. Zr was cathodically polarized in an electrolyte without calcium and phosphate ions, and Zr was cathodically polarized in another electrolyte containing calcium and phosphate ions, Hanks' solution, to directly form a calcium phosphate layer. The surface was characterized using X-ray photoelectron spectroscopy, and the performance of the material was evaluated by immersion in Hanks' solution. As a result, the ability to form calcium phosphate in Hanks' solution was given by cathodic polarization in the Na(2)SO(4) solution containing H(2)O(2). In addition, a cathodic potential under -1.5 V(SCE) is required to form hydroxyapatite directly in Hanks' solution. This research clearly reveals useful surface modification techniques giving the ability to form calcium phosphate in a simulated body fluid by cathodic polarization.

Influence of calcium ion deposition on apatite-inducing ability of porous titanium for biomedical applications

In the present study, the influence of calcium ion deposition on the apatite-inducing ability of porous titanium (Ti) was investigated in a modified simulated body fluid (m-SBF). Calcium hydroxide (Ca(OH)(2)) solutions with five degrees of saturation were used to hydrothermally deposit Ca ions on porous Ti with a porosity of 80%. Apatite-inducing ability of the Ca-ion-deposited porous Ti was evaluated by soaking them in m-SBF for up to 14 days. Scanning electron microscopy (SEM) and X-ray diffractometry (XRD) confirmed that a thin layer of calcium titanate (CaTiO(3))/calcium oxide (CaO) mixture with a nanostructured porous network was produced on porous Ti substrates after hydrothermal treatment at 200 degrees C for 8 h. X-ray photoelectron spectroscopy results demonstrated that the content of the Ca ions deposited on Ti and the thickness of the CaTiO(3)/CaO layer increased with increasing saturation degree of the Ca(OH)(2) solution. The thickest (over 10 nm) CaTiO(3)/CaO layer with the highest Ca content was achieved on the Ti treated in an oversaturated Ca(OH)(2) solution (0.2 M). SEM, XRD, transmission electron microscopy and Fourier transformed infrared spectroscopy analysis indicated that the porous Ti samples deposited with the highest content of Ca ions exhibited the best apatite-inducing ability, producing a dense and complete carbonated apatite coating after a 14 day soaking in m-SBF. The present study illustrated the validity of using Ca ion deposition as a pre-treatment to endow desirable apatite-inducing ability of porous Ti for bone tissue engineering applications.

Accelerated Bonelike Apatite Growth on Porous Polymer/Ceramic Composite Scaffolds in Vitro

Although biodegradable polymer/ceramic composite scaffolds can overcome the limitations of conventional ceramic bone substitutes, the osteogenic potential of these scaffolds needs to be further enhanced for efficient bone tissue engineering. In this study, bonelike apatite was efficiently coated onto the scaffold surface by using polymer/ceramic composite scaffolds instead of polymer scaffolds and by using an accelerated biomimetic process to enhance the osteogenic potential of the scaffold. The creation of bonelike, apatite-coated polymer scaffold was achieved by incubating the scaffolds in simulated body fluid (SBF). The apatite growth on porous poly(D,L-lactic-co-glycolic acid)/nanohydroxyapatite (PLGA/ HA) composite scaffolds was significantly faster than on porous PLGA scaffolds. In addition, the distribution of coated apatite was more uniform on PLGA/HA scaffolds than on PLGA scaffolds. After a 5-day incubation period, the mass of apatite coated onto PLGA/HA scaffolds incubated in 5 x SBF was 2.3-fold higher than PLGA/HA scaffolds incubated in 1 x SBF. Furthermore, when the scaffolds were incubated in 5 x SBF for 5 days, the mass of apatite coated onto PLGA/HA scaffolds was 4.5-fold higher than PLGA scaffolds. These results indicate that the biomimetic apatite coating can be accelerated by using a polymer/ceramic composite scaffold and concentrated SBF. When seeded with osteoblasts, the apatite-coated PLGA/HA scaffolds exhibited significantly higher cell growth, alkaline phosphatase activity, and mineralization in vitro compared to the apatite-coated PLGA scaffolds. Therefore, the apatite-coated PLGA/HA scaffolds may provide enhanced osteogenic potential when used as scaffold for bone tissue engineering.

Nucleation and growth of calcium phosphate on amine-, carboxyl- and hydroxyl-silane self-assembled monolayers

Upon implantation, calcium phosphate (Ca-P) surfaces form on materials that are bone bioactive. In this study, the evolving surface characteristics associated with calcium phosphate precipitation are modeled using self-assembled monolayers (SAMs), in a one-step nucleation process. SAMs were used to create amine (-NH2), carboxyl (-COOH) and hydroxyl (-OH) functionalized surfaces by grafting 3-aminopropyltriethoxysilane, 3-triethoxysilylpropyl succinic anhydride and glycidoxypropyl tri-methoxysilane, respectively, onto oxidized silicon wafers. The SAM surfaces were characterized using ellipsometry to establish the presence of grafted molecules. On the surfaces incubated in simulated physiological fluids for 7 days, the thickness of Ca-P layer grew slowly over the first few hours, increasing strongly between 1 and 5 days and then slowed down again. FTIR showed the dependence of calcium phosphate morphology on the type of surface groups, with stronger P-O bands seen on the OH-terminated surface. SEM analysis showed dispersed Ca-P precipitates on the -COOH and -OH terminated surfaces after 1 day immersion. After 7 days, all SAM surfaces were covered with uniformly dispersed and denser Ca-P precipitates. The underlying Ca-P layer showed cracks on the -NH2-terminated surface. Rutherford backscattering spectrometry (RBS) data analysis confirmed that Ca/P ratio is in excellent agreement with the theoretical value of 1.67 for hydroxyapatite. X-ray diffraction (XRD) analysis also showed evidence of apatite formation on all the surfaces, with stronger evidence on the -OH-terminated surface. Highly porous Ca-P precipitates were observed on the SAM surfaces portrayed by the AFM scans with nanoscale RMS roughness. Thus, using highly controlled surface chemistry, under physiological conditions, in vitro, this study demonstrates that a hydroxylated surface enhances Ca-P nucleation and growth relative to other surfaces, thereby supporting the concept of its beneficial effect on bone tissue formation and growth.

Characterization of surface modified Ti-6Al-7Nb alloy

In the last years different types of surface modifications were developed with the aim of improving the osteointegration ability of titanium alloys. The chemical composition, crystallographic structure and morphology of a surface layer can be modified in order to obtain a better interaction between the implant, the cells and the organic fluids. The final goal is to obtain a more efficient bone growth also in critical clinical cases. In the present paper were reported several data about the characterization of the Ti-6Al-7Nb alloy treated by two innovative surface treatments. They consist of blasting, followed by a two step chemical etching and heat treatment performed in air or in vacuum. TEM, XRD and SEM investigations were performed in order to assess the structure and morphology of the modified surfaces. The surface chemical composition was investigated by XPS ad AES analyses. The ability to interact with physiological fluids was tested by immersion of the treated materials in an acellular simulated body fluid (SBF). Metal ion concentration analyses of the fluid and SEM observations of the samples were performed after different times of soaking. The mechanical characterization involved scratch and fatigue tests. The surface of treated samples shows chemical, structural and morphological modifications. The passivation pre-treatment has influence on the surface modification. The treated samples evidenced a quite low metal ion release and interact with SBF solution, showing a moderate bioactivity. A relevant decrease in fatigue strength was observed on modified samples.

New chemical treatment for bioactive titanium alloy with high corrosion resistance

It was recently claimed that titanium metal and its alloys can bond to the living bone, without being coated by apatite (VPS coatings), but by being chemically and heat-treated. The bioactivity of treated titanium is of interest because of the opportunity to obtain orthopaedic or dental implants presenting, at the same time, high toughness, strength and fatigue resistance as well as bone-bonding ability. The bioactive behaviour of the treated implants is due to the presence of a modified surface, which, during soaking in body fluid, promotes the precipitation of apatite. The apatite formed is strongly bonded to the substrate and promotes living bone bonding. In this work were characterised samples of Ti-6Al-7Nb alloy with surfaces presenting a different chemical and mechanical state. The aim of the research was twofold. The first objective was to characterise chemically and heat-treated samples with different surface topography, in order to define the best conditions for osteogenic integration. The second aim was to assess the corrosion behaviour of the bioactive implants, because they expose a microporous and quite thin modified surface layer. No-treated and passivated samples, with a surface state closed to that nowadays used on implants, were used as reference. The surface structure, morphology, electrochemical behaviour and bioactivity of the different samples were assessed by means of XRD, SEM-EDS, anodic polarizations, open circuit measurements and in-vitro tests. Results evidence that it is possible to modify the surface of the Ti-6Al-7Nb alloy in order to obtain the formation of a bioactive layer and that the substrate roughness influences the characteristics of the surface layer formed. It was also evidenced that the as treated surfaces present inadequate corrosion behaviour, so a new two-step chemical treatment has been developed in order to obtain a bioactive material with good corrosion resistance.

Influence of surface self-modification in Ringer's solution on the passive behavior of titanium

The influence of the spontaneous surface modification of titanium by exposure to Ringer's solution at open-circuit conditions on the passive behavior was studied. The electrochemical behavior of Ti was compared in a simple NaCl and in Ringer's physiological solution. Potentiodynamic polarization curves show significantly higher passive current densities in Ringer's solution as compared with the simple saline solution. Furthermore, impedance spectra measured at the open-circuit potential as a function of time indicate that in saline solution a long-term exposure over some days leads to a strong increase of the protectiveness of the passive film. This improvement of the passive behavior cannot be observed in Ringer's solution, but a strong modification of the passive film/electrolyte interface can be seen in the impedance spectra. The changes in the impedance spectra can be correlated with the results observed by surface characterization regarding the morphology (scanning electron microscopy) and chemical composition of the surface (X-ray photoelectron spectroscopy). In agreement with previous work by others, a spontaneous modification of the surface of Ti by Ca and P species was observed. The composition of the Ca/P precipitates changes as a function of time, indicating a slow formation of a hydroxyapatite-like deposit layer on the surface. The results of the present work indicate that the formation of the outer Ca-P deposit layer on the passive Ti surface (which is beneficial for the biological performance) hinders the normal aging of the passive TiO(2). Even though the protectiveness of the passive film can be considered as high also in Ringer's solution, significantly higher passive dissolution rates (i.e., higher metal-ion release) for Ti exposed to Ringer's solution can be expected as compared with a simple saline solution.

Preparation of bioactive titanium metal via anodic oxidation treatment

Titania with specific structures of anatase and rutile was found to induce apatite formation in vitro. In this study, anodic oxidation in H(2)SO(4) solution, which could form anatase and rutile on titanium metal surface by conditioning the process, was employed to modify the structure and bioactivity of biomedical titanium. After the titanium metal was subjected to anodic oxidation treatment, thin film X-ray diffraction and scanning electron microscopy results showed the titanium metals surfaces were covered by porous titania of anatase and/or rutile. In simulated body fluid (SBF), the titanium anodically oxidized under the conditions with spark-discharge could induce apatite formation on its surface. The induction period of apatite formation was decreased with increasing amount of either anatase or rutile by conditioning the anodic oxidation. After the titanium metal, anodically oxidized under the conditions without spark-discharge, was subjected to heat treatment at 600 degrees C for 1 h, it could also induce apatite formation in SBF because the amount of anatase and/or rutile was increased by the heat treatment. Our results showed that induction of apatite-forming ability on titanium metal could be attained by anodic oxidation conjoined with heat treatment. So it was believed that anodic oxidation in H(2)SO(4) solution was an effective way to prepare bioactive titanium.

Nucleation and growth of apatite on chemically treated titanium alloy: an electrochemical impedance spectroscopy study

Bone-like apatite formed on the surface of Ti6Al4V pretreated with NaOH solution after having been immersed in simulated body fluid (SBF), while no apatite formed on the surface of untreated Ti6Al4V. In the present study, electrochemical impedance spectroscopy (EIS) measurement was used to investigate the nucleation and growth of apatite on chemically treated Ti6Al4V immersed in the SBF solution, and the difference between the behaviors of treated and untreated Ti6Al4V. Appropriate equivalent circuit models were constructed to describe the nucleation and growth of apatite, and thin oxide film formed on the surface of untreated Ti6Al4V. It was found that EIS is a useful method for investigating the nucleation and growth of bone-like apatite on Ti6Al4V pretreated with NaOH solution.

Electrochemically assisted deposition of thin calcium phosphate coatings at near-physiological pH and temperature

An electrochemical method for the deposition of calcium phosphate phases on titanium surfaces using the galvanostatic mode is presented. Deposition was performed in a (Ca(2+) / H(x)PO(4) ((3-x)-))-containing electrolyte near physiological conditions with regard to pH (6.4) and temperature (36 degrees C). Cathodic alkalization leads first to the formation of a thin homogeneous layer that shows a nanoscale surface topography of alternating wall-like elevations and channels. It is thought that these channels in the calcium phosphate prelayer are formed as pathways for hydroxyl ions and hydrogen. Upon this layer, spheres of amorphous calcium phosphate (ACP) are formed as indicated by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy. According to transmission electron microscopy images, these spheres consist of small clusters of calcium phosphate (approximately 30 nm) and can grow up to 300 nm in diameter. Characteristic for this ACP is a high water content as seen by FTIR. As a function of current density, the ACP is then transformed into crystalline hydroxyapatite (HAP), which was identified using FTIR and X-ray diffraction. The morphology of the HAP crystals can be described as needles with dimensions of <500-nm length and <60-nm width. By choice of different electrochemical parameters, a homogeneous coating of either ACP, HAP, or the intermediate phase can be achieved, as shown in a kinetic phase diagram, thus allowing the formation of coatings with different properties in solubility and morphology.

Calcium and phosphate adsorption as initial steps of apatite nucleation on sol-gel-prepared titania surface

Titania powders have been prepared by the sol-gel route from Ti (IV) ethoxide under acidic conditions. Adsorption experiments of calcium and phosphate ions on gel-derived titania suspensions were performed to suggest a likely initial step of apatite growth on its surface. Experiments were performed as a function of time and pH at 37 degrees C with and without NaCl present in the suspensions. Also, zeta (zeta) potential experiments were performed to determine the kind of calcium adsorption. Results suggest that, apparently, calcium and phosphate adsorption can act as two different initial steps for apatite growth.

The effect of Ca/P concentration and temperature of simulated body fluid on the growth of hydroxyapatite coating on alkali-treated 316L stainless steel

316L-SS is one of the important materials both in orthopaedics and dentistry for bone screw/plate, intra-medullary rod, fixation wire, HIP joint, and knee joint. However, the biocompatibility and bone-bonding ability troubled researches for years. In the study, a simple chemical method was tried so as to establish and induce a bioactive HA layer on the surface of 316L stainless steel. When the metallic substrates treated with 10 M NaOH aqueous solution and subsequently heated at 600 degrees C, a thin sodium chromium oxide layer was formed on the surfaces as the linking layer for HA and 316L-SS. After 316L-SS treated with alkali solution, it would soak into a simulated body fluid with higher concentration of calcium and phosphorous ions to increase the possibility of nucleation of HA. However, the iron oxide and iron chromium oxides were formed on the surface when calcium and phosphorous ions increased. This resulted in loosening the HA layer. When the alkali-treated 316L-SS was soaked into SBF at a temperature of 80 degrees C, it could form a dense and uniform bone-like hydroxyapatite layer on the surface. In the research, the mechanism of the formation of sodium chromium oxide and HA would also be described by the analysis of X-ray diffractometer, scanning electron microscope, energy-dispersion spectrophotometer, and Fourier transformation infrared.

The role of surface functional groups in calcium phosphate nucleation on titanium foil: a self-assembled monolayer technique

Surface functional groups play important roles in nucleating calcium phosphate deposition on surgical titanium implants. In this study, various functional groups were introduced onto the surface of commercially pure titanium foils using a self-assembled monolayer (SAM) technique. An organic silane, 7-oct-1-enyltrichlorosilane (OETS) was used and -OH, -PO4H2, -COOH groups were derived from its unsaturated double bond. Ti foils were first oxidized in concentrated H2SO4/H2O2. ESCA and contact angle measurements were used to characterize the SAM surfaces and confirm the presence of various functional groups. A fast calcium phosphate deposition experiment was carried out by mixing Ca2+- and (PO4)(3-)-containing solutions in the presence of the surface-modified Ti samples at pH 7.4 at room temperature in order to verify the nucleating abilities of these functional groups. SEM, Raman spectroscopy, XRD and ATR-FTIR results showed that poorly crystallized hydroxyapatite (HA) can be deposited on the SAM surfaces with -PO4H2 and -COOH functional groups, but not onto the SAM with -CH=CH2 and -OH. -PO4H2 exhibited a stronger nucleating ability than that of -COOH. The oxidized Ti sample also showed some calcium phosphate deposition but to a lesser extent as compared to SAM surfaces with -PO4H2 and -COOH. The pre-deposited HA can rapidly induce biomimetic apatite layer formation after immersion in 1.5 SBF for 18 h regardless of the amount of pre-deposited HA. The results suggested that the pre-deposition of HA onto these functionalized SAM surfaces might be an effective and fast way to prepare biomimetic apatite coatings on surgical implants.

Bonelike apatite growth on hydroxyapatite-gelatin sponges from simulated body fluid

In vitro bioactivity of gelatin sponges and hydroxyapatite-enriched gelatin sponges was tested through evaluation of the variations in their composition and morphology after soaking in simulated body fluid (1.5) for periods up to 21 days at 37 degrees C. The presence of hydroxyapatite inside the sponges promotes the deposition of bonelike apatite crystals. The deposits are laid down as spherical aggregates, with mean diameters increasing from about 1-2 microm, after 4 days of soaking in simulated body fluid solution, up to about 3.5 microm in the samples soaked for 21 days. Simultaneously, the relative amount of inorganic phase increases up to about 56% wt, leading to a composite material with a composition quite close to that of bone tissue. The inorganic phase is a poor crystalline carbonated apatite similar to trabecular bone apatite.

Carbonate apatite coating on titanium induced rapidly by precalcification

Chemical treatments have been thought to be promised methods for improving bioactivity of titanium. In this work, the effect of precalcification with boiling saturated Ca(OH)2 solution on bioactivation of titanium was investigated. After precalcification and soaking in supersaturated Ca-P solution (SCP), calcium phosphate rapidly precipitated onto the surfaces of titanium, and after only three days an uniform apatite layer was found up to thickness of a few micrometers. The observation using scanning electron microscopy (SEM) showed that the coating was composed of a number of small crystal grains. The investigation by X-ray energy dispersion spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) indicated that the coating was Ca-deficient carbonate apatite. Based on the analyses for the surfaces and SCP, a mechanism of precipitation of apatite was proposed in thermal dynamics and kinetics.

TEM-EDX study of mechanism of bonelike apatite formation on bioactive titanium metal in simulated body fluid

Bioactive titanium metal, which forms a bonelike apatite layer on its surface in the body and bonds to the bone through the apatite layer, can be prepared by NaOH and heat treatments to form an amorphous sodium titanate layer on the metal. In the present study, the mechanism of apatite formation on the bioactive titanium metal has been investigated in vitro. The metal surface was examined using transmission electron microscopy and energy dispersive X-ray spectrometry as a function of the soaking time in a simulated body fluid (SBF) and complemented with atomic emission spectroscopy analysis of the fluid. It was found that, immediately after immersion in the SBF, the metal exchanged Na(+) ions from the surface sodium titanate with H(3)O(+) ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after they were formed, incorporated the calcium ions in the fluid to form an amorphous calcium titanate. After a long soaking time, the amorphous calcium titanate incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate with a low Ca/P atomic ratio of 1.40. The amorphous calcium phosphate thereafter converted into bonelike crystalline apatite with a Ca/P ratio of 1.65, which is equal to the value of bone mineral. The initial formation of the amorphous calcium titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania, which are dissociated from the Ti-OH groups, with the positively charged calcium ions in the fluid. The amorphous calcium titanate is speculated to gain a positive charge and to interact with the negatively charged phosphate ions in the fluid to form the amorphous calcium phosphate, which eventually stabilizes into bonelike crystalline apatite.

An X-ray photoelectron spectroscopy study of the process of apatite formation on bioactive titanium metal

Bioactive titanium metal, prepared by treatment with NaOH followed by an annealing stage to form a sodium titanate layer with a graded structure on its surface, forms a biologically active bone-like apatite layer on its surface in the body, and bonds to bone through this apatite layer. In this study, process of apatite formation on the bioactive titanium metal in a simulated body fluid was investigated using X-ray photoelectron spectroscopy. The bioactive titanium metal formed Ti-OH groups soon after soaking in the simulated body fluid, via the exchange of the Na(+) ions in the sodium titanate on its surface with H(3)O(+) ions in the fluid. The Ti-OH groups on the metal combined with the calcium ions in the fluid immediately to form a calcium titanate. After a long period, the calcium titanate on the metal took the phosphate ions as well as the calcium ions in the fluid to form the apatite nuclei. The apatite nuclei then proceeded to grow by consuming the calcium and phosphate ions in the fluid. These results indicate that the Ti-OH groups formed on the metal induce the apatite nucleation indirectly, by forming a calcium titanate. The initial formation mechanism of the calcium titanate may be attributable to the electrostatic interaction of the negatively charged Ti-OH groups with the positively charged calcium ions.

In vitro bioactivity of aerosol-gel deposited TiO(2) thin coatings

Bioactive, pure, and Ca- or P-doped TiO(2) thin coatings on Ti metal and Si wafers were prepared by the aerosol-gel technique. The coatings were characterized by X-ray photoelectron spectroscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. Bioactivity was determined in vitro in a simulated body fluid and was shown to be fully comparable to sol gel-derived TiO(2) coatings prepared by dip-coating. However, the formation rate of carbonate containing apatite decreased with increasing dopant concentration, which was related to changes in chemical composition and topology of the coatings.