Preparation of bioactive Ti and its alloys via simple chemical surface treatment

Apatite-forming ability of titanium in terms of pH of the exposed solution

In order to elucidate the main factor governing the capacity for apatite formation of titanium (Ti), Ti was exposed to HCl or NaOH solutions with different pH values ranging from approximately 0 to 14 and then heat-treated at 600°C. Apatite formed on the metal surface in a simulated body fluid, when Ti was exposed to solutions with a pH less than 1.1 or higher than 13.6, while no apatite formed upon exposure to solutions with an intermediate pH value. The apatite formation on Ti exposed to strongly acidic or alkaline solutions is attributed to the magnitude of the positive or negative surface charge, respectively, while the absence of apatite formation at an intermediate pH is attributed to its neutral surface charge. The positive or negative surface charge was produced by the effect of either the acidic or alkaline ions on Ti, respectively. It is predicted from the present results that the bone bonding of Ti depends upon the pH of the solution to which it is exposed, i.e. Ti forms a bone-like apatite on its surface in the living body and bonds to living bone through the apatite layer upon heat treatment after exposure to a strongly acidic or alkaline solution.

Laminin Coating Promotes Calcium Phosphate Precipitation on Titanium Discs in vitro

Objectives

The objective of this study was to investigate the effect of a laminin coating on calcium phosphate precipitation on three potentially bioactive titanium surfaces in simulated body fluid.

Material and Methods

Blasted titanium discs were prepared by alkali and heat treatment (AH), anodic oxidation (AO) or hydroxyapatite coating (HA) and subsequently coated with laminin. A laminin coated blasted surface (B) served as a positive control while a blasted non coated (B-) served as a negative control. Surface morphology was examined by Scanning Electron Microscopy (SEM). The analysis of the precipitated calcium and phosphorous was performed by Energy Dispersive X-ray Spectroscopy (EDX).

Results

The thickness of the laminin coating was estimated at 26 Å by ellipsometry. Interferometry revealed that the coating process did not affect any of the tested topographical parameters on µm level when comparing B to B-. After 2 weeks of incubation in SBF, the alkali-heat treated discs displayed the highest calcium phosphate deposition and the B group showed higher levels of calcium phosphate than the B- group.

Conclusions

Our results suggest that laminin may have the potential to be used as a coating agent in order to enhance the osseoinductive performance of biomaterial surfaces, with the protein molecules possibly functioning as nucleation centres for apatite formation. Nevertheless, in vivo studies are required in order to clarify the longevity of the coating and its performance in the complex biological environment.

Bone integration capability of alkali- and heat-treated nanobimorphic Ti-15Mo-5Zr-3Al

The role of nanofeatured titanium surfaces in a number of aspects of in vivo bone-implant integration, and, in particular, their potential advantages over microfeatured titanium surfaces, as well as their specific contribution to osteoconductivity, is largely unknown. This study reports the creation of a unique nanobimorphic titanium surface comprised of nanotrabecular and nanotuft-like structures and determines how the addition of this nanofeature to a microroughened surface affects bone-implant integration. Machined surfaces without microroughness, sandblasted microroughened surfaces, and micro-nano hybrid surfaces created by sandblasting and alkali and heat treatment of Ti-15Mo-5Zr-3Al alloy were subjected to biomechanical, interfacial and histological analyses in a rat model. The presence of microroughness enabled accelerated establishment of biomechanical implant fixation in the early stages of healing compared to the non-microroughened surfaces; however, it did not increase the implant fixation at the late stages of healing. The addition of nanobimorphic features to the microroughened surfaces further increased the implant fixation by as much as 60-100% over the healing time. Bone area within 50 μm of the implant surface, but not beyond this distance, was significantly increased by the presence of nanobimorphic features. Although the percentage of bone-implant contact was also significantly increased by the addition of nanobimorphic features, the greatest improvement was found in the soft tissue intervention between the bone and the implant, which was reduced from >30% to <5%. Mineralized tissue densely deposited with calcium-binding globular proteins was observed in an extensive area of nanobimorphic surfaces after biomechanical testing. This study clearly demonstrates the nanofeature-enhanced osteoconductivity of titanium by an alkali- and heat-treated nanobimorphic surface compared to that by microfeatured surfaces, which results not only in an acceleration but also an improvement of bone-implant integration. The identified biological parameters that successfully detect the advantages of nanofeatures over microfeatures will be useful in evaluating new implant surfaces in future studies.

Biomimetic calcium phosphate coating on Ti-7.5Mo alloy for dental application

Titanium and its alloys have been used as bone-replacement implants due to their excellent corrosion resistance and biocompatibility. However, a titanium coating is a bioinert material and cannot bond chemically to bone tissue. The objective of this work was to evaluate the influence of alkaline treatment and heat treatment on the formation of calcium phosphate layer on the surface of a Ti-7.5Mo alloy after soaking in simulated body fluid (SBF). Thirty six titanium alloy plates were assigned into two groups. For group I, samples were immersed in a 5.0-M NaOH aqueous solution at 80°C for 72 h, washed with distilled water and dried at 40°C for 24 h. For group II, after the alkaline treatment, samples were heat-treated at 600°C for 1 h in an electrical furnace in air. Then, all samples were immersed in SBF for 7 or 14 days to allow the formation of a calcium phosphate coating on the surface. The surfaces were characterized using SEM, EDS, AFM and contact angle measurements.

In vitro Evaluation of Calcium Phosphate Precipitation on Possibly Bioactive Titanium Surfaces in the Presence of Laminin

Objectives

The aim of the present study was to evaluate calcium phosphate precipitation and the amount of precipitated protein on three potentially bioactive surfaces when adding laminin in simulated body fluid.

Material and Methods

Blasted titanium discs were prepared by three different techniques claimed to provide bioactivity: alkali and heat treatment (AH), anodic oxidation (AO) or hydroxyapatite coating (HA). A blasted surface incubated in laminin-containing simulated body fuid served as a positive control (B) while a blasted surface incubated in non laminin-containing simulated body fuid served as a negative control (B-). The immersion time was 1 hour, 24 hours, 72 hours and 1 week. Surface topography was investigated by interferometry and morphology by Scanning Electron Microscopy (SEM). Analysis of the precipitated calcium and phosphorous was performed by Energy Dispersive X-ray Spectroscopy (EDX) and the adsorbed laminin was quantified by iodine (¹²⁵I) labeling.

Results

SEM demonstrated that all specimens except for the negative control were totally covered with calcium phosphate (CaP) after 1 week. EDX revealed that B- demonstrated lower sum of Ca and P levels compared to the other groups after 1 week. Iodine labeling demonstrated that laminin precipitated in a similar manner on the possibly bioactive surfaces as on the positive control surface.

Conclusions

Our results indicate that laminin precipitates equally on all tested titanium surfaces and may function as a nucleation center thus locally elevating the calcium concentration. Nevertheless further studies are required to clarify the role of laminin in the interaction of biomaterials with the host bone tissue.

Biomimetic fibronectin/mineral and osteogenic growth peptide/mineral composites synthesized on calcium phosphate thin films

Composites of fibronectin/mineral and osteogenic growth peptide/mineral were synthesized on calcium phosphate coated substrates immersed in Dulbecco's phosphate-buffered saline solution containing biomolecules. The kinetics of coprecipitation for two biomolecules was similar, and the biomolecules participated in the formation of the crystal latticework and influenced the mineral structure and composition.

A nitrogen doped TiO2 layer on Ti metal for the enhanced formation of apatite

Biomedical titanium metals subjected to gas under precisely regulated oxygen partial pressures (P(O2)) from 10(-18) to 10(5) Pa at 973 K for 1 h were soaked in a simulated body fluid (SBF), whose ion concentrations were nearly equal to those of human blood plasma, at 36.5°C for up to 7 days. The effect of oxygen partial pressures on apatite formation was assessed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) measurements. After heating, the weight of the oxide layer (mainly TiO(2)) formed on the titanium metal was found to increase with increased oxygen partial pressure. Nitrogen (N)-doped TiO(2) (Interstitial N) was formed under a P(O2) of 10(-14) Pa. At lower P(O2) (10(-18) Pa), only a titanium nitride layer (TiN and Ti(2)N) was formed. After soaking in SBF, apatite was detected on heat-treated titanium metal samples. The most apatite was formed, based on the growth rate calculated from the apatite coverage ratio, on the titanium metal heated under a P(O2) of 10(-14) Pa, followed by the sample heated under a P(O2) of 10 and 10(4) Pa (in N(2)). The titanium metal heated under a P(O2) of 10(5) Pa (in O(2)) experienced far less apatite formation than the former three titanium samples. Similarly, very little weight change was observed for the titanium metal heated under a P(O2) of 10(-18) Pa (in N(2)). During the experimental observation period (5 days, 36.5°C, SBF), the following relationship held: The growth rate of apatite decreased in the order P(O2) of 10(-14) Pa > P(O2) of 10 Pa ≥ P(O2) of 10(4) Pa > P(O2) of 10(5) Pa > > P(O2) of 10(-18) Pa. These results suggest that N-doped TiO(2) (Interstitial N) strongly induces apatite formation but samples coated only with titanium nitride do not. Thus, controlling the formation of N-doped TiO(2) is expected to improve the bioactivity of biomedical titanium metal.

Surface mineralization of Ti6Al4V substrates with calcium apatites for the retention and local delivery of recombinant human bone morphogenetic protein-2

Titanium alloys are prevalently used as orthopedic prosthetics. Inadequate bone-implant interactions can lead to premature prosthetic loosening and implant failure. Local delivery of osteogenic therapeutics promoting osteointegration of the implant is an attractive strategy to address this clinical challenge. Given the affinity of calcium apatites for bone matrix proteins we hypothesize that titanium alloys surface mineralized with calcium apatites should be explored for the retention and local delivery of osteogenic recombinant human bone morphogenetic protein-2 (rhBMP-2). Using a heterogeneous surface nucleation and growth process driven by the gradual pH elevation of an acidic solution of hydroxyapatite via thermal decomposition of urea, Ti6Al4V substrates were surface mineralized with calcium apatite domains exhibiting good affinity for the substrate. The microstructures, size and surface coverage of the mineral domains as a function of the in vitro mineralization conditions were examined by light and scanning electron microscopy and the surface calcium ion content quantified. An optimal mineralization condition was identified to rapidly (<10h) achieve surface mineral coverage far superior to those accomplished by week long incubation in simulated body fluids. In vitro retention-release profiles of rhBMP-2 from the mineralized and unmineralized Ti6Al4V, determined by an enzyme-linked immunosorbent assay, supported a higher degree of retention of rhBMP-2 on the mineralized substrate. The rhBMP-2 retained on the mineralized substrate after 24h incubation in phosphate-buffered saline remained bioactive, as indicated by its ability to induce osteogenic transdifferentiation of C2C12 myoblasts attached to the substrate. This mineralization technique could also be applied to the surface mineralization of calcium apatites on dense tantalum and titanium and porous titanium substrates.

Nanostructured positively charged bioactive TiO2 layer formed on Ti metal by NaOH, acid and heat treatments

Nanometer-scale roughness was generated on the surface of titanium (Ti) metal by NaOH treatment and remained after subsequent acid treatment with HCl, HNO(3) or H(2)SO(4) solution, as long as the acid concentration was not high. It also remained after heat treatment. Sodium hydrogen titanate produced by NaOH treatment was transformed into hydrogen titanate after subsequent acid treatment as long as the acid concentration was not high. The hydrogen titanate was then transformed into titanium oxide (TiO(2)) of anatase and rutile by heat treatment. Treated Ti metals exhibited high apatite-forming abilities in a simulated body fluid especially when the acid concentration was greater than 10 mM, irrespective of the type of acid solutions used. This high apatite-forming ability was maintained in humid environments for long periods. The high apatite-forming ability was attributed to the positive surface charge that formed on the TiO(2) layer and not to the surface roughness or a specific crystalline phase. This positively charged TiO(2) induced apatite formation by first selectively adsorbing negatively charged phosphate ions followed by positively charged calcium ions. Apatite formation is expected on the surfaces of such treated Ti metals after short periods, even in living systems. The bonding of metal to living bone is also expected to take place through this apatite layer.

Enhanced bone-integration capability of alkali- and heat-treated nanopolymorphic titanium in micro-to-nanoscale hierarchy

This study introduces nanopolymorphic features of alkali- and heat-treated titanium surfaces, comprising of tuft-like, plate-like, and nodular structures that are smaller than 100 nm and determines whether and how the addition of these nanofeatures to a microroughened titanium surface affects bone-implant integration. A comprehensive assessment of biomechanical, interfacial, and histological analyses in a rat model was performed for machined surfaces without microroughness, sandblasted-microroughened surfaces, and micro-nano hybrid surfaces created by sandblasting and alkali and heat treatment. The microroughened surface accelerated the establishment of implant biomechanical fixation at the early healing stage compared with the non-microroughened surface but did not increase the implant fixation at the late healing stage. The addition of the nanopolymorphic features to the microroughened surface further increased implant fixation throughout the healing time. The area of the new bone within 50 μm proximity of the implant surfaces, which was increased 2-3-fold using microroughened surfaces, was further increased 2-fold using nanopolymorphic surfaces. In contrast, the bone area in a 50-200 μm zone was not influenced by either microroughened or nanopolymorphic surfaces. The percentage of bone-implant contact, which was increased 4-5-fold, using microroughened surfaces, was further increased substantially by over 2-fold throughout the healing period. The percentage of soft tissue intervention between bone and implant surfaces, which was reduced to half by microroughened surfaces, was additionally reduced by the nanopolymorphic surfaces to between one-third and one-fourth, resulting in only 5-7% soft tissue intervention compared with 60-75% for the non-microroughened surface. Thus, using an exemplary alkali- and heat-treated nanopolymorphic surface, this study identified critical parameters necessary to describe the process and consequences of bone-implant integration, for which nanofeatures have specific and substantial roles beyond those of microfeatures. Nanofeature-enhanced osteoconductivity, which resulted in both the acceleration and elevation of bone-implant integration, has clearly been demonstrated.

Synthesis of bio-functionalized three-dimensional titania nanofibrous structures using femtosecond laser ablation

The primary objective of current tissue regeneration research is to synthesize nano-based platforms that can induce guided, controlled, and rapid healing. Titanium nanotubes have been extensively considered as a new biomaterial for biosensors, implants, cell growth, tissue engineering, and drug delivery systems. However, due to their one-dimensional structure and chemical inertness, cell adhesion to nanotubes is poor. Therefore, further surface modification is required to enhance nanotube-cell interaction. Although there have been a considerable number of studies on growing titanium nanotubes, synthesizing a three-dimensional (3-D) nano-architecture which can act as a growth support platform for bone and stem cells has not been reported so far. Therefore, we present a novel technique to synthesize and grow 3-D titania interwoven nanofibrous structures on a titanium substrate using femtosecond laser irradiation under ambient conditions. This surface architecture incorporate the functions of 3-D nano-scaled topography and modified chemical properties to improve osseointegration while at the same time leaving space to deliver other functional agents. The results indicate that laser pulse repetition can control the density and pore size of engineered nanofibrous structures. In vitro experiments reveal that the titania nanofibrous architecture possesses excellent bioactivity and can induce rapid, uniform, and controllable bone-like apatite precipitation once immersed in simulated body fluid (SBF). This approach to synthesizing 3-D titania nanofibrous structures suggests considerable promise for the promotion of Ti interfacial properties to develop new functional biomaterials for various biomedical applications.

Surface modifications of magnesium alloys for biomedical applications

In recent years, research on magnesium (Mg) alloys had increased significantly for hard tissue replacement and stent application due to their outstanding advantages. Firstly, Mg alloys have mechanical properties similar to bone which avoid stress shielding. Secondly, they are biocompatible essential to the human metabolism as a factor for many enzymes. In addition, main degradation product Mg is an essential trace element for human enzymes. The most important reason is they are perfectly biodegradable in the body fluid. However, extremely high degradation rate, resulting in too rapid loss of mechanical strength in chloride containing environments limits their applications. Engineered artificial biomaterials with appropriate mechanical properties, surface chemistry, and surface topography are in a great demand. As the interaction between the cells and tissues with biomaterials at the tissue--implant interface is a surface phenomenon; surface properties play a major role in determining both the biological response to implants and the material response to the physiological condition. Therefore, the ability to modify the surface properties while preserve the bulk properties is important, and surface modification to form a hard, biocompatible and corrosion resistant modified layer have always been an interesting topic in biomaterials field. In this article, attempts are made to give an overview of the current research and development status of surface modification technologies of Mg alloys for biomedical materials research. Further, the advantages/disadvantages of the different methods and with regard to the most promising method for Mg alloys are discussed. Finally, the scientific challenges are proposed based on own research and the work of other scientists.

Preparation of bioactive Ti-15Zr-4Nb-4Ta alloy from HCl and heat treatments after an NaOH treatment

Ti-15Zr-4Nb-4Ta alloy does not contain any cytotoxic elements and has a high mechanical strength. Water or HCl and heat treatments were applied to this alloy after NaOH treatment to form a bioactive titanium oxide layer with a nanometer scale roughness on its surface. The nanometer scale roughness was formed on the surface after the first NaOH treatment and remained, even after a subsequent water or HCl and heat treatment. A layer that was mainly composed of anatase was formed on the surface after the heat treatment. Thus, the treated alloy showed a high apatite-forming ability in an SBF, as well as a high scratch resistance. Its high apatite-forming ability was attributed to its positive surface charge. The same alloy subjected to a heat treatment without a water or HCl treatment after the NaOH treatment did not show an apatite-forming ability. This was attributed to a too slow release rate of sodium ions from the surface in an SBF. Ti-15Zr-4Nb-4Ta alloy samples subjected to a water or HCl and heat treatment after the NaOH treatment are expected to be useful as orthopedic and dental implants, since they can form an apatite layer on their surface in a living body and bond to living bone through this apatite layer.

Bone bonding bioactivity of Ti metal and Ti-Zr-Nb-Ta alloys with Ca ions incorporated on their surfaces by simple chemical and heat treatments

Ti15Zr4Nb4Ta and Ti29Nb13Ta4.6Zr, which do not contain the potentially cytotoxic elements V and Al, represent a new generation of alloys with improved corrosion resistance, mechanical properties, and cytocompatibility. Recently it has become possible for the apatite forming ability of these alloys to be ascertained by treatment with alkali, CaCl2, heat, and water (ACaHW). In order to confirm the actual in vivo bioactivity of commercially pure titanium (cp-Ti) and these alloys after subjecting them to ACaHW treatment at different temperatures, the bone bonding strength of implants made from these materials was evaluated. The failure load between implant and bone was measured for treated and untreated plates at 4, 8, 16, and 26 weeks after implantation in rabbit tibia. The untreated implants showed almost no bonding, whereas all treated implants showed successful bonding by 4 weeks, and the failure load subsequently increased with time. This suggests that a simple and economical ACaHW treatment could successfully be used to impart bone bonding bioactivity to Ti metal and Ti-Zr-Nb-Ta alloys in vivo. In particular, implants heat treated at 700 °C exhibited significantly greater bone bonding strength, as well as augmented in vitro apatite formation, in comparison with those treated at 600 °C. Thus, with this improved bioactive treatment process these advantageous Ti-Zr-Nb-Ta alloys can serve as useful candidates for orthopedic devices.

Bioactive Ti metal analogous to human cancellous bone: Fabrication by selective laser melting and chemical treatments

Selective laser melting (SLM) is a useful technique for preparing three-dimensional porous bodies with complicated internal structures directly from titanium (Ti) powders without any intermediate processing steps, with the products being expected to be useful as a bone substitute. In this study the necessary SLM processing conditions to obtain a dense product, such as the laser power, scanning speed, and hatching pattern, were investigated using a Ti powder of less than 45 μm particle size. The results show that a fully dense plate thinner than 1.8 mm was obtained when the laser power to scanning speed ratio was greater than 0.5 and the hatch spacing was less than the laser diameter, with a 30 μm thick powder layer. Porous Ti metals with structures analogous to human cancellous bone were fabricated and the compressive strength measured. The compressive strength was in the range 35-120 MPa when the porosity was in the range 75-55%. Porous Ti metals fabricated by SLM were heat-treated at 1300 °C for 1h in an argon gas atmosphere to smooth the surface. Such prepared specimens were subjected to NaOH, HCl, and heat treatment to provide bioactivity. Field emission scanning electron micrographs showed that fine networks of titanium oxide were formed over the whole surface of the porous body. These treated porous bodies formed bone-like apatite on their surfaces in a simulated body fluid within 3 days. In vivo studies showed that new bone penetrated into the pores and directly bonded to the walls within 12 weeks after implantation into the femur of Japanese white rabbits. The percentage bone affinity indices of the chemical- and heat-treated porous bodies were significantly higher than that of untreated implants.

Fast Formation of Biomimetic Ca-P Coatings on Ti6Al4V

The aim of this study was to accelerate the formation of biomimetic Calcium-Phosphate (Ca-P) coatings on Ti6Al4V by using a 5 times more concentrated Simulated Body Fluid (SBFx5) than the regular SBF. The production of SBFx5 was possible by decreasing the pH of the solution to approximately 6 with CO2 gas. The release of this mildly acidic gas allowed the formation of a Ca-P film after 4h of immersion at pH=6.8. The structure of this coating was an amorphous carbonated Ca-P. In addition, our experiments showed that the presence of Mg2+ was absolutely necessary for the Ca-P coating formation on Ti6Al4V substrate. Mg2+ is a crystal growth inhibitor and favored the heterogeneous nucleation. Furthermore, depth profile X-Ray Photoelectron Spectroscopy showed that Ca-P nucleation on the passive Titanium oxide (TiO2) passive layer was initiated by Ca2+ and Mg2+. The attachment of this Ca-P coating resulted probably from chemical bonds such as P-O-Ti and Ca-O-Ti. Ca was more present at the coating/substrate interface than P. Thereby Ca-O-Ti seems to be favored.

Mechanism of Apatite Formation on Bioactive Titanium Metal

The present authors previously showed that titanium metal, which was exposed to 5.OMNaOH solution at 60°C for 24 h and heat-treated at 600°C for 1 h, spontaneously forms a bonelike apatite layer on its surface in the living body, and tightly bonds to the bone through the apatite layer. In the present study, mechanism of the apatite formation on the bioactive titanium metal was investigated in an acellular simulated body fluid (SBF). A thin sodium titanate layer was formed on the surface of the titanium metal by the NaOH and heat treatments. The sodium titanate layer released Na+ ions via exchange with H3O+ ions in SBF, to form a lot of Ti-OH groups on its surface. The Ti-OH groups first combined with Ca2+ ions in SBF, and then later with PO43- ions to form the apatite. Titania and Na2O-TiO2 gels prepared by a sol-gel method as model substances of the sodium titanate layer on the surface of the titanium metal showed that Ti-OH groups of anatase structure are effective for the apatite nucleation, whereas those of amorphous structure and Na2Ti5O11 crystal are not effective.

Effect of heat treatments on apatite-forming ability of NaOH- and HCl-treated titanium metal

Titanium (Ti) metal was soaked in HCl solution after NaOH treatment and then subjected to heat treatments at different temperatures. Their apatite-forming abilities in a simulated body fluid (SBF) were discussed in terms of their surface structures and properties. The nanometer scale roughness formed on Ti metal after NaOH treatment remained after the HCl treatment and a subsequent heat treatment below 700°C. Hydrogen titanate was formed on Ti metal from an HCl treatment after NaOH treatment, and this was converted into titanium oxide of anatase and rutile phases by a subsequent heat treatment above 500°C. The scratch resistance of the surface layer increased with the formation of the titanium oxide after a heat treatment up to 700°C, and then decreased with increasing temperature. The Ti metal with a titanium oxide layer formed on its surface showed a high apatite-forming ability in SBF when the heat treatment temperature was in the range 500-700°C. The high apatite-forming ability was attributed to the positive surface charge in an SBF. These positive surface charges were ascribed to the presence of chloride ions, which were adsorbed on the surfaces and dissociated in the SBF to give an acid environment.

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.

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.

Preparation of superhydrophilic microrough titanium implant surfaces by alkali treatment

A new strategy to render intrinsically hydrophobic microrough titanium implant surfaces superhydrophilic is reported, which is based on a rapid treatment with diluted aqueous sodium hydroxide solutions. The physicochemical characterization and protein interaction of the resulting superhydrophilic implant surfaces are presented. The superhydrophilicity of alkali treated microrough titanium substrates was mainly attributed to deprotonation and ion exchange processes in combination with a strong enhancement of wettability due to the roughness of the used substrates. Albeit these minor and mostly reversible chemical changes qualitative and quantitative differences between the protein adsorption on untreated and alkali treated microrough titanium substrates were detected. These differences in protein adsorption might account for the enhanced osseointegrative potential of superhydrophilic alkali treated microrough implant surfaces. The presented alkali treatment protocol represents a new clinically applicable route to superhydrophilic microrough titanium substrates by rendering the implant surface superhydrophilic "in situ of implantation".

Preparation of bioactive Ti metal surface enriched with calcium ions by chemical treatment

A calcium solution treatment was applied to a NaOH-treated titanium metal to give it bioactivity, scratch resistance and moisture resistance. The titanium metal was soaked in a 5 M NaOH solution and then a 100 mM CaCl(2) solution to incorporate Ca(2+) ions into the titanium metal surface by ion exchange. This treated titanium metal was subsequently heated at 600 degrees C and soaked in hot water at 80 degrees C. The NaOH treatment incorporated approximately 5 at.% Na(+) ions into the Ti metal surface. These Na(+) ions were completely replaced by Ca(2+) ions by the CaCl(2) treatment. The number of Ca(2+) ions remained even after subsequent heat and water treatments. Although the NaOH-CaCl(2)-treated titanium metal showed slightly higher apatite-forming ability in a simulated body fluid than the NaOH-treated titanium metal, it lost its apatite-forming ability during the heat treatment. However, subsequent water or autoclave treatment restored the apatite-forming ability of the NaOH-CaCl(2)-heat-treated titanium metal. Although the apatite-forming ability of the NaOH-heat-treated titanium metal decreased dramatically when it was kept at high humidity, that of NaOH-CaCl(2)-heat-water-treated titanium metal was maintained even in the humid environment. The heat treatment increased the critical scratch resistance of the surface layer of the NaOH-CaCl(2)-treated titanium metal remarkably, and it did not deteriorate on subsequent water treatment.

Tissue-engineered ligament: implant constructs for tooth replacement

AIM

A tissue-engineered periodontal ligament (PDL) around implants would represent an important new therapeutic tool to replace lost teeth. The PDL is the key to tooth anchoring; it connects tooth root and alveolar bone, and it sustains bone formation.

MATERIALS AND METHODS

Cells were isolated from PDL and cultured in a bioreactor on titanium pins. After the formation of multiple cellular layers, pins were implanted in enlarged dental alveolae.

MAIN OUTCOME MEASURES

Cell-covered implants integrated without adverse effects, and induced bone in their vicinity.

RESULTS

A histological examination of a dog model revealed that cells were arranged in a typical ligament-like fashion. In human patients, product safety was ascertained for 6-60 months. Probing and motility assessments suggested that the implants were well integrated with mechanical properties similar to those of teeth. Radiographs demonstrated the regeneration of deficient alveolar bone, the development of a lamina dura adjacent to a mineral-devoid space around the implant and implant migration in an intact bone structure.

CONCLUSIONS

New tissue consistent with PDL developed on the surface of dental implants after implantation. This proof-of-principal investigation demonstrates the application of ligament-anchored implants, which have potential advantages over osseointegrated oral implants.

Biomimetic apatite formation on calcium phosphate-coated titanium in Dulbecco's phosphate-buffered saline solution containing CaCl(2) with and without fibronectin

Calcium phosphate (CaP) thin films with different degrees of crystallinity were coated on the surfaces of commercially pure titanium by electron beam evaporation. The details of apatite nucleation and growth on the coating layer were investigated in Dulbecco's phosphate-buffered saline solutions containing calcium chloride (DPBS) or DPBS with fibronectin (DPBSF). The surfaces of the samples were examined by field emission scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The concentrations of fibronectin and calcium ions (Ca(2+)) were monitored by the bicinchoninic acid method (BCA) and use of a calcium assay kit (DICA-500), respectively. Apatite initially formed at the fastest rate on the CaP-coated samples with the lowest degree of crystallinity and reached the maximum Ca(2+) concentration after immersion in DPBS solution for 15min. After 15min the concentration of Ca(2+) decreased with the growth of apatite on the coating layers. For all the samples the maximum Ca(2+) concentration in the DPBS solutions decreased with increasing crystallinity and immersion time to reach the maximum concentration increased. The presence of fibronectin in the DPBS solutions delayed the formation and affected the morphology of the apatite. Fibronectin incorporated into apatite deposited on the surface of titanium did not affect its biological activity in terms of promoting osteoblast adhesion.

Enhancement of octacalcium phosphate deposition on a titanium surface activated by electron cyclotron resonance plasma oxidation

The present study was designed to investigate whether the formation of octacalcium phosphate (OCP) is accelerated on titanium (Ti) surface by an electron cyclotron resonance (ECR) plasma oxidation at various pressures and temperatures. X-ray diffraction (XRD) of Ti-oxidized substrates showed that the rutile TiO(2) phase on its surfaces appeared at 300 degrees C and was crystallized when the oxidation temperature increased up to 600 degrees C. The thickness of TiO(2) film on the substrates increased progressively as the temperature increased. The oxidized Ti surfaces were soaked in calcium and phosphate solutions supersaturated with respect to both hydroxyapatite (HA) and OCP but slightly supersaturated with dicalcium phosphate dihydrate (DCPD). OCP crystals with a blade-like morphology were deposited as the primary crystalline phase on Ti substrates, while DCPD was included as a minor constituent. The amount of OCP deposition was maximized under 0.015 Pa in 300 degrees C. On the other hand, the oxidation temperature did not show a significant effect on the deposit in the range examined. The phase conversion from OCP to HA, determined by XRD, was demonstrated to occur even at 1 day and to advance until 7 days by immersing the Ti substrate with the deposit in simulated body fluid at 37 degrees C. The present results suggest that ECR plasma oxidation could be used to improve a Ti surface regarding its bioactivity due to the enhancement of osteoconductive OCP deposition.

Biomimetic coatings for bone tissue engineering of critical-sized defects

The repair of critical-sized bone defects is still challenging in the fields of implantology, maxillofacial surgery and orthopaedics. Current therapies such as autografts and allografts are associated with various limitations. Cytokine-based bone tissue engineering has been attracting increasing attention. Bone-inducing agents have been locally injected to stimulate the native bone-formation activity, but without much success. The reason is that these drugs must be delivered slowly and at a low concentration to be effective. This then mimics the natural method of cytokine release. For this purpose, a suitable vehicle was developed, the so-called biomimetic coating, which can be deposited on metal implants as well as on biomaterials. Materials that are currently used to fill bony defects cannot by themselves trigger bone formation. Therefore, biological functionalization of such materials by the biomimetic method resulted in a novel biomimetic coating onto different biomaterials. Bone morphogenetic protein 2 (BMP-2)-incorporated biomimetic coating can be a solution for a large bone defect repair in the fields of dental implantology, maxillofacial surgery and orthopaedics. Here, we review the performance of the biomimetic coating both in vitro and in vivo.

Positively charged bioactive Ti metal prepared by simple chemical and heat treatments

A highly bioactive bone-bonding Ti metal was obtained when Ti metal was simply heat-treated after a common acid treatment. This bone-bonding property was ascribed to the formation of apatite on the Ti metal in a body environment. The formation of apatite on the Ti metal was induced neither by its surface roughness nor by the rutile phase precipitated on its surface, but by its positively charged surface. The surface of the Ti metal was positively charged because acid groups were adsorbed on titanium hydride formed on the Ti metal by the acid treatment, and remained even after the titanium hydride was transformed into titanium oxide by the subsequent heat treatment. These results provide a new principle based on a positively charged surface for obtaining bioactive materials.

A novel method for local administration of strontium from implant surfaces

This study proves that a film of Strontianite (SrCO(3)) successfully can be formed on a bioactive surface of sodium titanate when exposed to a strontium acetate solution. This Strontianite film is believed to enable local release of strontium ions from implant surfaces and thus stimulate bone formation in vivo. Depending on the method, different types of films were achieved with different release rates of strontium ions, and the results points at the possibility to tailor the rate and amount of strontium that is to be released from the surface. Strontium has earlier been shown to be highly involved in the formation of new bone as it stimulates the replication of osteoblasts and decreases the activity of osteoclasts. The benefit of strontium has for example been proved in studies where the number of vertebral compression fractures in osteoporotic persons was drastically reduced in patients receiving therapeutical doses of strontium. Therefore, it is here suggested that the bone healing process around an implant may be improved if strontium is administered locally at the site of the implant. The films described in this paper were produced by a simple immersion process where alkali treated titanium was exposed to an aqueous solution containing strontium acetate. By heating the samples at different times during the process, different release rates of strontium ions were achieved when the samples were exposed to simulated body fluid. The strontium containing films also promoted precipitation of bone like apatite when exposed to a simulated body fluid.

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 degrees C for 24 h, resulting in the formation of a porous network structure composed of sodium titanate (Na(2)Ti(5)O(11)). 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 degrees 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.

Bone response of Mg ion-implanted clinical implants with the plasma source ion implantation method

OBJECTIVES

This study examined the bone response of magnesium (Mg) ion-implanted implants produced using a plasma source ion implantation method.

MATERIALS AND METHODS

The surface characteristics were evaluated by scanning electron microscopy, Auger electron spectroscopy, X-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy. The screw-type titanium implants were treated with resorbable blasting media (RBM) and divided into one control group (RBM implants) and three test groups (Mg ion-implanted implants with different retained Mg doses). Twenty-four implants from each group were placed into the tibiae of 24 New Zealand white rabbits. After allowing 6 weeks for healing, the removal torque (RTQ) was measured and the implants were subjected to histomorphometric analysis.

RESULTS

The surface roughness and surface morphology of the test groups were similar. The Mg ion-implanted implants with a 2.3 x 10(15) ions/cm(2) retained dose showed a significantly higher RTQ than the other implants. Histomorphometric analysis indicated that the bone contact of this group was superior to the other groups.

CONCLUSION

The bone response of Mg ion-implanted implant showed results superior or similar to an RBM-treated implant. The optimal Mg ion concentration that induced the strongest osseointegration was approximately 9%.

Cell response of titanium implant with a roughened surface containing titanium hydride: an in vitro study

PURPOSE

The purpose of this study was to investigate the effect of surface chemistry of a sandblasted and acid-etched implant (with and without titanium hydride [TiH(2)]) on cell attachment, proliferation, and differentiation of preosteoblasts (MC3T3-E1).

MATERIALS AND METHODS

Sandblasted and dual acid-etched titanium discs comprised the test group, whereas sandblasted, acid-etched, and heat-treated discs comprised the control group. Both groups' discs were sent for surface characterization. MC3T3-E1 cells were cultured on these 2 groups' discs, and then cell attachment, cell proliferation, and cell differentiation were analyzed.

RESULTS

Scanning electron microscope analysis showed that the titanium discs in the 2 groups shared the same surface topography; however, x-ray diffraction examination showed that the TiH(2) diffractions only appeared in the test group. Cell attachment and cell proliferation were much better in the test group than in the control group at all time points investigated (P < .05). The expressions of alkaline phosphatase and osteocalcin were significantly higher in the test group than in the control group for both protein and transcription level at every time point (P < .05 or P < .01).

CONCLUSIONS

These results suggested that surface chemistry played a significant role in cell response to the sandblasted and acid-etched surface and the presence of TiH(2) might promote the attachment, proliferation, and differentiation of preosteoblasts.

In vitro cellular response and in vivo primary osteointegration of electrochemically modified titanium

Anodic spark deposition (ASD) is an attractive technique for improving the implant-bone interface that can be applied to titanium and titanium alloys. This technique produces a surface with microporous morphology and an oxide layer enriched with calcium and phosphorus. The aim of the present study was to investigate the biological response in vitro using primary human osteoblasts as a cellular model and the osteogenic primary response in vivo within a short experimental time frame (2 and 4 weeks) in an animal model (rabbit). Responses were assessed by comparing the new electrochemical biomimetic treatments to an acid-etching treatment as control. The in vitro biological response was characterized by cell morphology, adhesion, proliferation activity and cell metabolic activity. A complete assessment of osteogenic activity in vivo was achieved by estimating static and dynamic histomorphometric parameters at several time points within the considered time frame. The in vitro study showed enhanced osteoblast adhesion and higher metabolic activity for the ASD-treated surfaces during the first days after seeding compared to the control titanium. For the ASD surfaces, the histomorphometry indicated a higher mineral apposition rate within 2 weeks and a more extended bone activation within the first week after surgery, leading to more extensive bone-implant contact after 2 weeks. In conclusion, the ASD surface treatments enhanced the biological response in vitro, promoting an early osteoblast adhesion, and the osteointegrative properties in vivo, accelerating the primary osteogenic response.

Laser cladding of bioactive glass coatings

Laser cladding by powder injection has been used to produce bioactive glass coatings on titanium alloy (Ti6Al4V) substrates. Bioactive glass compositions alternative to 45S5 Bioglass were demonstrated to exhibit a gradual wetting angle-temperature evolution and therefore a more homogeneous deposition of the coating over the substrate was achieved. Among the different compositions studied, the S520 bioactive glass showed smoother wetting angle-temperature behavior and was successfully used as precursor material to produce bioactive coatings. Coatings processed using a Nd:YAG laser presented calcium silicate crystallization at the surface, with a uniform composition along the coating cross-section, and no significant dilution of the titanium alloy was observed. These coatings maintain similar bioactivity to that of the precursor material as demonstrated by immersion in simulated body fluid.

Apatite-forming ability of Ti-15Zr-4Nb-4Ta alloy induced by calcium solution treatment

Ti-15Zr-4Nb-4Ta alloy free from cytotoxic elements shows high mechanical strength and high corrosion resistance. However, simple NaOH and heat treatments cannot induce its ability to form apatite in the body environment. In the present study, this alloy was found to exhibit high apatite-forming ability when it was treated with NaOH and CaCl(2) solutions, and then subjected to heat and hot water treatments to form calcium titanate, rutile, and anatase on its surface. Its high apatite-forming ability was maintained even in 95% relative humidity at 80 degrees C after 1 week. The surface layer of the treated alloy had scratch resistance high enough for handling hard surgical devices. Thus, the treated alloy is believed to be useful for orthopedic and dental implants.