Enhancement of bone-bonding strengths of titanium alloy implants by alkali and heat treatments

Mechanistic insights into the spontaneous induction of bone formation

The grand discovery of morphogens, or "form-generating substances", revealed that tissue morphogenesis is initiated by soluble molecular signals or morphogens primarily belonging to the transforming growth factor-β (TGF-β) supergene family. The regenerative potential of bone rests on its extracellular matrix, which is the repository of several morphogens that tightly control cellular differentiating pathways, cellular matrix deposition and remodeling. Alluringly, the matrix also contains specific factors transferred from the heterotopic implanted bone matrices initiating "Tissue Induction", as provocatively described in Nature in 1945. Later, it was found that selected genes and gene products of the TGF-β supergene family singly, synchronously, and synergistically mastermind the induction of bone formation. This review describes the phenomenon of the spontaneous and/or intrinsic osteoinductivity of calcium phosphate-based biomaterials and titanium' constructs without the applications of soluble osteogenetic molecular signals. The review shows the spontaneous induction of bone formation initiated by Ca++ activating stem cell differentiation and up-regulation of bone morphogenetic proteins genes. Expressed gene products are embedded into the concavities of the calcium phosphate-based substrata, initiating bone formation as a secondary response. Pure titanium's substrata do not initiate the spontaneous induction of bone formation. The induction of bone is solely dependent on acid, alkali and heat treatments to form apatite layers on the treated titanium surfaces. The induction of bone formation is achieved exclusively by apatite-based biomaterial surfaces. The hydroxyapatite, in its various forms and geometric configurations, finely tunes the induction of bone formation in heterotopic sites. Cellular differentiation by fine-tuning of the cellular molecular machinery is initiated by specific geometric modularity of the hydroxyapatite substrata that push cellular buttons that start the ripple-like cascade of "Tissue Induction", generating newly formed ossicles with bone marrow in heterotopic extraskeletal sites. The highlighted mechanistic insights into the spontaneous induction of bone formation are a research platform invocating selected molecular elements to construct the induction of bone formation.

Understanding and optimizing the antibacterial functions of anodized nano-engineered titanium implants

Nanoscale surface modification of titanium-based orthopaedic and dental implants is routinely applied to augment bioactivity, however, as is the case with other cells, bacterial adhesion is increased on nano-rough surfaces. Electrochemically anodized Ti implants with titania nanotubes (TNTs) have been proposed as an ideal implant surface with desirable bioactivity and local drug release functions to target various conditions. However, a comprehensive state of the art overview of why and how such TNTs-Ti implants acquire antibacterial functions, and an in-depth knowledge of how topography, chemistry and local elution of potent antibiotic agents influence such functions has not been reported. This review discusses and details the application of nano-engineered Ti implants modified with TNTs for maximum local antibacterial functions, deciphering the interdependence of various characteristics and the fine-tuning of different parameters to minimize cytotoxicity. An ideal implant surface should cater simultaneously to ossoeintegration (and soft-tissue integration for dental implants), immunomodulation and antibacterial functions. We also evaluate the effectiveness and challenges associated with such synergistic functions from modified TNTs-implants. Particular focus is placed on the metallic and semi-metallic modification of TNTs towards enabling bactericidal properties, which is often dose dependent. Additionally, there are concerns over the cytotoxicity of these therapies. In that light, research challenges in this domain and expectations from the next generation of customizable antibacterial TNTs implants towards clinical translation are critically evaluated. STATEMENT OF SIGNIFICANCE: One of the major causes of titanium orthopaedic/dental implant failure is bacterial colonization and infection, which results in complete implant failure and the need for revision surgery and re-implantation. Using advanced nanotechnology, controlled nanotopographies have been fabricated on Ti implants, for instance anodized nanotubes, which can accommodate and locally elute potent antibiotic agents. In this pioneering review, we shine light on the topographical, chemical and therapeutic aspects of antibacterial nanotubes towards achieving desirable tailored antibacterial efficacy without cytotoxicity concerns. This interdisciplinary review will appeal to researchers from the wider scientific community interested in biomaterials science, structure and function, and will provide an improved understanding of controlling bacterial infection around nano-engineered implants, aimed at bridging the gap between research and clinics.

In vitro evaluation of NaOCl-mediated functionalization of biologically aged titanium surfaces

The aim of this study was to evaluate the NaOCl-mediated biofunctionalization of titanium surfaces. Titanium disks stored for 2 weeks were immersed in 5% NaOCl solution for 24 h. A disk immersed in distilled water for 24 h was used as a control. X-ray photoelectron spectrometer assay of the titanium surface after NaOCl treatment demonstrated that organic contaminants containing carbon and nitrogen were removed and the number of hydroxyl groups increased. The NaOCl treatment substantially converted the titanium surface to superhydrophilic status (θ<5°), which resulted in an increased number of attached cells and enhanced cell spreading on the NaOCl-treated surfaces. These results indicate that biofunctionalization of the biologically degraded titanium surfaces can be achieved by chemical surface treatment with 5% NaOCl. The mechanism for desorption of strongly adsorbed organic molecules with polar groups such as amino and aldehyde groups from titanium surfaces by ClO^- was elucidated.

Simulated body fluid and the novel bioactive materials derived from it

Professor Larry Hench first reported that certain glasses are able to spontaneously bond to living bone in 1970. This discovery stimulated research into new kinds of bone-bonding materials. However, there were no guiding principles for this purpose, and many animals were sacrificed in the effort to establish them. The present authors proposed in 1991 that the bone-bonding capacity of a material could be evaluated by examining apatite formation on its surface in an acellular simulated body fluid (SBF), without the need of performing any animal experiments. Various kinds of novel bone-bonding bioactive materials based on Ti metal and its alloys with a number of different functions have been developed using SBF. Some of these have entered clinical use as important bone-repairing materials. Without the method of SBF evaluation, these novel materials would not have been developed. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 968-977, 2019.

The Surface Anodization of Titanium Dental Implants Improves Blood Clot Formation Followed by Osseointegration

The anodization of titanium dental implant influences the biologic processes of osseointegration. 34 grit-blasted and acid-etched titanium specimens were used to evaluate micro- and nano-roughness (Ra), contact angle (θ) and blood clot extension (bce). 17 samples were anodized (test) while the remaining were used as control. The bce, was measured using 10 µL of human blood left in contact with titanium for 5 min at room temperature. The micro- and nano-scale Ra were measured under CLSM and AFM, respectively, while the θ was analyzed using the sessile drop technique. The bone-implant contact (BIC) rate was measured on two narrow implants retrieved for fracture. bce was 42.5 (±22) for test and 26.6% (±13)% for control group (p = 0.049). The micro-Ra was 6.0 (±1.5) for the test and 5.8 (±1.8) µm for control group (p > 0.05). The θ was 98.5° (±18.7°) for test and 103° (±15.2°) for control group (p > 0.05). The nano-Ra was 286 (±40) for the test and 226 (±40) nm for control group (p < 0.05). The BIC rate was 52.5 (±2.1) for test and 34.5% (±2.1%) for control implant (p = 0.014). (Conclusions) The titanium anodized surface significantly increases blood clot retention, significantly increases nano-roughness, and favors osseointegration. When placing dental implants in poor bone quality sites or with immediate loading protocol anodized Ti6Al4V dental implants should be preferred.

Novel bioactive materials developed by simulated body fluid evaluation: Surface-modified Ti metal and its alloys

Until the discovery of the bone-bonding activity of Bioglass by Hench et al. in the early 1970s, it had not been demonstrated that a synthetic material could bond to living bone without eliciting a foreign body reaction. Since then, various kinds of materials based on calcium phosphate, such as sintered hydroxyapatite and β-tricalcium phosphate have also been shown to bond to living bone. Until the discovery of the bone-bonding activity of Ti metal formed with a sodium titanate surface layer by the present authors in 1996, it had not been shown that a metallic material could bond to living bone. Since then, various kinds of surface-modified Ti metal and its alloys have been found to bond to living bone. Until the discovery of the osteoinduction of porous hydroxyapatite by Yamasaki in 1990, it was unknown whether a synthetic material could induce bone formation even in muscle tissue. Since then, various kinds of porous calcium phosphate ceramics have been shown to induce osteoinduction. Until the discovery of osteoinduction induced by a porous Ti metal formed with a titanium oxide surface layer by Fujibayashi et al. in 2004, it had been unclear whether porous metals would be able to induce osteoinduction. These novel bioactive materials have been developed by systematic research into the apatite formation that occurs on surface-modified Ti metal and its related materials in an acellular simulated body fluid (SBF) having ion concentrations almost equal to those of human blood plasma. Some of the novel bioactive materials based on Ti metal are already in clinical use or clinical trials, such as artificial hip joints and spinal fusion devices. In the present paper, we review how these novel bioactive materials based on Ti metal have been developed based on an evaluation of apatite formation in SBF. Without the SBF evaluation, these novel bioactive materials would most likely never have been developed.

STATEMENT OF SIGNIFICANCE

On the basis of systematic study of apatite formation on a material in a simulated body fluid, various kinds of novel bioactive materials possessing not only bone-bonding activity and but also various other functions such as bone growth promotion, antibacterial activity and osteoinduction have been developed. Some of them are already successfully applied to clinical applications or trials for artificial hip joints and spinal fusion devices. It is shown in the present paper how these novel bioactive materials have been developed.

New Ti-Alloys and Surface Modifications to Improve the Mechanical Properties and the Biological Response to Orthopedic and Dental Implants: A Review

Titanium implants are widely used in the orthopedic and dentistry fields for many decades, for joint arthroplasties, spinal and maxillofacial reconstructions, and dental prostheses. However, despite the quite satisfactory survival rates failures still exist. New Ti-alloys and surface treatments have been developed, in an attempt to overcome those failures. This review provides information about new Ti-alloys that provide better mechanical properties to the implants, such as superelasticity, mechanical strength, and corrosion resistance. Furthermore, in vitro and in vivo studies, which investigate the biocompatibility and cytotoxicity of these new biomaterials, are introduced. In addition, data regarding the bioactivity of new surface treatments and surface topographies on Ti-implants is provided. The aim of this paper is to discuss the current trends, advantages, and disadvantages of new titanium-based biomaterials, fabricated to enhance the quality of life of many patients around the world.

In vivo study of the early bone-bonding ability of Ti meshes formed with calcium titanate via chemical treatments

Alkali and heat (AH) treatment forming sodium titanate has been shown to connect bioinert Ti metal and bone tissue. Artificial joints treated with this method have achieved extensive clinical application. Recently a new chemical treatment of Alkali-Calcium-Heat-Water (ACaHW) treatment forming calcium titanate was proposed. Notably, the apatite-forming ability of this treatment is greater than that of AH treatment, as verified in vitro. However, the early bone-bonding abilities of the two treatments have not been compared in vivo. To simulate clinical application, we treated a commercially pure Ti (Cp-Ti) mesh implant with AH or ACaHW. Then, using mechanical and histological methods, we compared the bone-bonding abilities of the two treatments early during the implantation process (2-4 weeks); untreated Cp-Ti mesh was used as a control. Because the mesh structure might influence bone-bonding ability, we compared these bonding abilities with values obtained at 4 and 8 weeks using a Cp-Ti implant with a plate structure. In the mesh group, histological comparisons at 2 and 3 weeks indicated that ACaHW treatment resulted in a bone-bonding ability similar to that of AH treatment; ACaHW exhibited a greater bonding ability than AH at 4 weeks. However, in tests of the plate group at later time points, such differences were not apparent. The results obtained here indicate that during the early stage of embedment, ACaHW treatment of Cp-Ti mesh implants yields a higher bone-bonding ability than AH treatment, thus providing a positive reference for future clinical applications.

Growth of Novel Ceramic Layers on Metals via Chemical and Heat Treatments for Inducing Various Biological Functions

The present authors' systematic studies on growth of novel ceramic layers on Ti metal and its alloys by chemical and heat treatments for inducing bone-bonding bioactivity and some other biological functions are reviewed. Ti metal formed an apatite on its surface in a simulated body fluid, when heat-treated after exposure to strong acid solutions to form rutile surface layer, or to strong alkali solutions to form sodium titanate surface layer. Both types of Ti metal tightly bonded to the living bone. The alkali and heat treatment was applied to the surface Ti metal of an artificial hip joint and successfully used in the clinic since 2007. The acid and heat treatments was applied to porous Ti metal to induce osteoconductivity as well as osteoinductivity. The resulting product was successfully used in clinical trials for spinal fusion devices. For the Ti-based alloys, the alkali and heat treatment was little modified to form calcium titanate surface layer. Bone-growth promoting Mg, Sr, and Zn ions as well as the antibacterial Ag ion were successfully incorporated into the calcium titanate layer.

Bioactive titanate layers formed on titanium and its alloys by simple chemical and heat treatments

To reveal general principles for obtaining bone-bonding bioactive metallic titanium, Ti metal was heat-treated after exposure to a solution with different pH. The material formed an apatite layer at its surface in simulated body fluid when heat-treated after exposure to a strong acid or alkali solution, because it formed a positively charged titanium oxide and negatively charged sodium titanate film on its surface, respectively. Such treated these Ti metals tightly bonded to living bone. Porous Ti metal heat-treated after exposure to an acidic solution exhibited not only osteoconductive, but also osteoinductive behavior. Porous Ti metal exposed to an alkaline solution also exhibits osteoconductivity as well as osteoinductivity, if it was subsequently subjected to acid and heat treatments. These acid and heat treatments were not effective for most Ti-based alloys. However, even those alloys exhibited apatite formation when they were subjected to acid and heat treatment after a NaOH treatment, since the alloying elements were removed from the surface by the latter. The NaOH and heat treatments were also not effective for Ti-Zr-Nb-Ta alloys. These alloys displayed apatite formation when subjected to CaCl₂ treatment after NaOH treatment, forming Ca-deficient calcium titanate at their surfaces after subsequent heat and hot water treatments. The bioactive Ti metal subjected to NaOH and heat treatments has been clinically used as an artificial hip joint material in Japan since 2007. A porous Ti metal subjected to NaOH, HCl and heat treatments has successfully undergone clinical trials as a spinal fusion device.

Spine interbody implants: material selection and modification, functionalization and bioactivation of surfaces to improve osseointegration

The clinical outcome of lumbar spinal fusion is correlated with achievement of bony fusion. Improving interbody implant bone on-growth and in-growth may enhance fusion, limiting pseudoarthrosis, stress shielding, subsidence and implant failure. Polyetheretherketone (PEEK) and titanium (Ti) are commonly selected for interbody spacer construction. Although these materials have desirable biocompatibility and mechanical properties, they require further modification to support osseointegration. Reports of extensive research on this topic are available in biomaterial-centric published reports; however, there are few clinical studies concerning surface modification of interbody spinal implants. The current article focuses on surface modifications aimed at fostering osseointegration from a clinician's point of view. Surface modification of Ti by creating rougher surfaces, modifying its surface topography (macro and nano), physical and chemical treatment and creating a porous material with high interconnectivity can improve its osseointegrative potential and bioactivity. Coating the surface with osteoconductive materials like hydroxyapatite (HA) can improve osseointegration. Because PEEK spacers are relatively inert, creating a composite by adding Ti or osteoconductive materials like HA can improve osseointegration. In addition, PEEK may be coated with Ti, effectively bio-activating the coating.

Bone bonding ability of a chemically and thermally treated low elastic modulus Ti alloy: gum metal

The gum metal with composition Ti-36Nb-2Ta-3Zr-0.3O, is free from cytotoxic elements and exhibits a low elastic modulus as well as high mechanical strength. We have previously demonstrated that this gum metal, once subjected to a series of surface treatments--immersion in 1 M NaOH (alkali treatment) and then 100 mM CaCl2, before heating at 700 °C (sample: ACaH-GM), with an optional final hot water immersion (sample: ACaHW-GM)--has apatite-forming ability in simulated body fluid. To confirm the in vivo bioactivity of these treated alloys, failure loads between implants and bone at 4, 8, 16, and 26 weeks after implantation in rabbits' tibiae were measured for untreated gum metal (UT-GM), ACaH-GM and ACaHW-GM, as well as pure titanium plates after alkali and heat treatment (AH-Ti). The ACaH-GM and UT-GM plates showed almost no bonding, whereas ACaHW-GM and AH-Ti plates showed successful bonding by 4 weeks, and their failure loads subsequently increased with time. The histological findings showed a large amount of new bone in contact with the surface of ACaHW-GM and AH-Ti plates, suggesting that the ACaHW treatment could impart bone-bonding bioactivity to a gum metal in vivo. Thus, with this improved bioactive treatment, these advantageous gum metals become useful candidates for orthopedic and dental devices.

Is the bone-bonding ability of a cementless total hip prosthesis enhanced by alkaline and heat treatments?

BACKGROUND

Cementless total hip arthroplasty (THA) implants using alkaline and heat treatments were developed to enhance bone bonding. Although bone-bonding ability of the alkali- and heat-treated titanium surface has been demonstrated in animal studies, it remains unknown whether it enhances or provides durable bone bonding in humans.

QUESTIONS/PURPOSES

We therefore (1) determined long-term survivorship, function, and radiographic signs of failure of fixation of alkali- and heat-treated THA implants; and (2) histologically examined their bone-bonding ability in two human retrievals.

METHODS

We retrospectively reviewed 58 patients who underwent 70 primary THAs, of whom 67 were available for minimum followup of 8 years (average, 10 years; range, 8-12 years). Survival rate was calculated. Hip function was evaluated using the Japan Orthopaedic Association (JOA) hip scores, and radiographic signs of implant failure were determined from anteroposterior radiographs. Two retrieved implants were investigated histologically.

RESULTS

Using revision for any reason as the end point, the overall survival rate was 98% (95% confidence interval, 96%-100%) at 10 years. The patients' average JOA hip scores improved from 47 points preoperatively to 91 points at the time of the last followup. No implant had radiographic signs of loosening. Histologically we observed bone in the pores 2 weeks after implantation in one specimen and apparently direct bonding between bone and the titanium surface in its deep pores 8 years after implantation.

CONCLUSIONS

Cementless THA implants with alkaline and heat treatments showed a high survival rate. Further study is required to determine whether the treatment enhances direct bone bonding.

Fabrication and characterization of porous Ti-7.5Mo alloy scaffolds for biomedical applications

Porous titanium and titanium alloys are promising scaffolds for bone tissue engineering, since they have the potential to provide new bone tissue ingrowth abilities and low elastic modulus to match that of natural bone. In the present study, porous Ti-7.5Mo alloy scaffolds with various porosities from 30 to 75 % were successfully prepared through a space-holder sintering method. The yield strength and elastic modulus of a Ti-7.5Mo scaffold with a porosity of 50 % are 127 MPa and 4.2 GPa, respectively, being relatively comparable to the reported mechanical properties of natural bone. In addition, the porous Ti-7.5Mo alloy exhibited improved apatite-forming abilities after pretreatment (with NaOH or NaOH + water) and subsequent immersion in simulated body fluid (SBF) at 37 °C. After soaking in an SBF solution for 21 days, a dense apatite layer covered the inner and outer surfaces of the pretreated porous Ti-7.5Mo substrates, thereby providing favorable bioactive conditions for bone bonding and growth. The preliminary cell culturing result revealed that the porous Ti-7.5Mo alloy supported cell attachment.

Formation of a bioactive calcium titanate layer on gum metal by chemical treatment

The so-called gum metal with the composition Ti-36Nb-2Ta-3Zr-0.3O is free from cytotoxic elements and exhibits a low elastic modulus as well as high mechanical strength. In the present study, it was shown that this alloy exhibited a high capacity for apatite formation in a simulated body fluid when subjected to 1 M NaOH treatment, 100 mM CaCl(2) treatment, heat treatment at 700°C, and then hot water treatment. The high apatite formation was attributed to the CaTi(2)O(5) which was precipitated on its surface, and found to be maintained even in a humid environment over a long period. The treated surface exhibited high scratch resistance, which is likely to be useful in clinical applications. The surface treatment had little effect on the unique mechanical properties described above. These results show that gum metal subjected to the present surface treatments exhibits a high potential for bone-bonding, which will be useful in orthopedic and dental implants.

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.

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.

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.

Tissue-response to calcium-bonded titanium surface

Our previous study demonstrated that calcium-bonded titanium surface (Ca-Ti) can be obtained by hydrothermal reaction between titanium (Ti) and CaCl(2) and that bone-apatite like formation was observed after immersion in simulated body fluid. The purpose of the study was to determine the in vivo response to Ca-Ti surface using a rodent tibia model. Cylinders of commercially pure Ti were divided into three groups: (1) untreated group; (2) NaOH+hTi group: soaked in 5 mol/L NaOH solution at 60 degrees C then heated at 400 degrees C for 1 h; and (3) Ca-Ti group: hydrothermally treated in the presence of 10 mmol/L CaCl(2) at 200 degrees C for 24 h. The cylinders implanted in surgically created defects in tibias of 8-week old male Wistar rats were retrieved after 1, 2, and 4 weeks. Histomorphometric evaluations were made on stained decalcified thin sections. Results showed that at 1, 2, and 4 week after implantation, respectively, bone contact was 55.2 +/- 16.4%, 88.1 +/- 9.9%, and 96.1 +/- 4.8% for Ca-Ti implants, 5.7 +/- 5.3%, 19.9 +/- 1.2%, 57.4 +/- 4.8% for untreated; and 27.2 +/- 0.7%, 70.9 +/- 7.7%, and 96.0 +/- 5.1% for NaOH+hTi implants. These results suggest that hydrothermal treatment with CaCl(2) provides a bioactive Ca-Ti bonded surface that allows bone formation greater than that obtained with NaOH+heat treated Ti surfaces.

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.

Novel Bioactive Titanate Layers Formed on Ti Metal and Its Alloys by Chemical Treatments

Sodium titanate formed on Ti metal by NaOH and heat treatments induces apatite formation on its surface in a body environment and bonds to living bone. These treatments have been applied to porous Ti metal in artificial hip joints, and have been used clinically in Japan since 2007. Calcium titanate formed on Ti-15Zr-4Nb-4Ta alloy by NaOH, CaCl₂, heat, and water treatments induces apatite formation on its surface in a body environment. Titanium oxide formed on porous Ti metal by NaOH, HCl, and heat treatments exhibits osteoinductivity as well as osteoconductivity. This is now under clinical tests for application to a spinal fusion device.

Effect of CaCl₂ hydrothermal treatment on the bone bond strength and osteoconductivity of Ti-0.5Pt and Ti-6Al-4V-0.5Pt alloy implants

To achieve osteoconductivity, Ti-0.5Pt and Ti-6Al-4V-0.5Pt alloys were hydrothermally treated at 200 degrees C in 10 mmol/l CaCl(2) aqueous solution for 24 h (HT-treatment). We conducted histological investigations of the HT-treated materials by using Wistar strain rats (SD rats) to evaluate the usefulness of the treatment. To measure the bone bond strength, the specimens were implanted in the tibia of SD rats, and a pull-out test was conducted. From the early postoperative stages, direct bone contact was obtained for the HT-treated implants. Within 1-4 weeks of implantation, the bone contact ratios and bone bond strengths of the HT-treated implants were higher than those of the non-treated implants. The Ti-0.5Pt and Ti-6Al-4V-0.5Pt alloys with HT-treatment showed the potential to develop a new implant with a high bone bond strength and rapid osteoconduction.

Bone formation on apatite-coated titanium with incorporated BMP-2/heparin in vivo

OBJECTIVE

The objective of this study was to investigate whether the in vivo osteoinductive activity of an implant material is enhanced by covering the surface of apatite with incorporated bone morphogenetic protein 2 (BMP-2) and heparin which maintains the activity of BMP-2.

STUDY DESIGN

Titanium implants were alkaline treated, heat activated, and soaked in stimulated body fluid with or without BMP-2/heparin to coat the apatite around them. Treated implant bars were then implanted in rat tibiae. After 3 weeks, nondecalcified sections were prepared and the new bone formation around the implants was examined.

RESULTS

A greater amount of bone formed on the apatite-coated implants containing BMP-2/heparin than on apatite-coated implants containing BMP, with >or=3 microg/mL heparin. Apatite-coated titanium implants with BMP-2/heparin had significantly enhanced new endosteal bone formation, with increases vertically (134%) and horizontally (124%).

CONCLUSIONS

Bone formation was stimulated around the apatite-covered titanium coated with BMP-2/heparin, which may be useful in improving implant therapy.

Apatite formation on alkaline-treated dense TiO2 coatings deposited using the solution precursor plasma spray process

A dense titania (TiO2) coating was deposited from an ethanol-based solution containing titanium isopropoxide using the solution precursor plasma spray (SPPS) process. XRD and Raman spectrum analyses confirmed that the coating is exclusively composed of rutile TiO2. SEM micrographs show the as-sprayed coating is dense with a uniform thickness and there are no coarse splat boundaries. The as-sprayed coating was chemically treated in 5M NaOH solution at 80 degrees C for 48 h. The bioactivity of as-sprayed and alkaline-treated coatings was investigated by immersing the coatings in simulated body fluid (SBF) for 14-28 days, respectively. After 28 days immersion, there is a complete layer of carbonate-containing apatite formed on the alkaline-treated TiO2 coating surface, but none formed on the as-sprayed coating.

Effect of hot water and heat treatment on the apatite-forming ability of titania films formed on titanium metal via anodic oxidation in acetic acid solutions

Titanium and its alloys have been widely used for orthopedic implants because of their good biocompatibility. We have previously shown that the crystalline titania layers formed on the surface of titanium metal via anodic oxidation can induce apatite formation in simulated body fluid, whereas amorphous titania layers do not possess apatite-forming ability. In this study, hot water and heat treatments were applied to transform the titania layers from an amorphous structure into a crystalline structure after titanium metal had been anodized in acetic acid solution. The apatite-forming ability of titania layers subjected to the above treatments in simulated body fluid was investigated. The XRD and SEM results indicated hot water and/or heat treatment could greatly transform the crystal structure of titania layers from an amorphous structure into anatase, or a mixture of anatase and rutile. The abundance of Ti-OH groups formed by hot water treatment could contribute to apatite formation on the surface of titanium metals, and subsequent heat treatment would enhance the bond strength between the apatite layers and the titanium substrates. Thus, bioactive titanium metals could be prepared via anodic oxidation and subsequent hot water and heat treatment that would be suitable for applications under load-bearing conditions.

Surface modification of organic polymers with bioactive titanium oxide without the aid of a silane-coupling agent

Polyethylene (PE), polyethylene terephthalate (PET), ethylene-vinyl alcohol copolymer (EVOH), and poly(epsilon-caprolactam) (Nylon 6) were successfully modified with a thin crystalline titanium oxide layer on their surfaces by a simple dipping into a titanium alkoxide solution and a subsequent soak in hot HCl solution, without the aid of a silane-coupling agent. The surface modified polymers formed a bone-like apatite layer in a simulated body fluid (SBF) within a period of 2 days. PE, PET, and Nylon 6 formed an apatite layer faster and had a higher adhesive strength to the apatite. Three-dimensional fabrics with open spaces in various sizes containing such surface modified polymer fibers are expected to be useful as bone substitutes, since they may be able to form apatite on their constituent fibers in the living body, and thus, integrate with living bone.

Mechanical properties and apatite forming ability of TiO2 nanoparticles/high density polyethylene composite: Effect of filler content

Composite materials consisting of TiO(2) nanoparticles and high-density polyethylene (HDPE), designated hereafter as TiO(2)/HDPE, were prepared by a kneading and forming process. The effect of TiO(2) content on the mechanical properties and apatite forming ability of these materials was studied. Increased TiO(2) content resulted in an increase in bending strength, yield strength, Young's modulus and compressive strength (bending strength = 68 MPa, yield strength = 54 MPa, Young's modulus = 7 GPa, and compressive strength = 82 MPa) at 50 vol% TiO(2). The composite with 50 vol% TiO(2) shows a similar strength and Young's modulus to human cortical bone. The TiO(2)/HDPE composites with different TiO(2) contents were soaked at 36.5 degrees C for up to 14 days in a simulated body fluid (SBF) whose ion concentrations were nearly equal to those of human blood plasma. The apatite forming ability, which is indicative of bioactivity, increased with TiO(2) content. Little apatite formation was observed for the TiO(2)/HDPE composite with 20 vol% content. However, in the case of 40 vol% TiO(2) content and higher, the apatite layers were formed on the surface of the composites within 7 days. The most potent TiO(2) content for a bone-repairing material was 50 vol%, judging from the mechanical and biological results. This kind of bioactive material with similar mechanical properties to human cortical bone is expected to be useful as a load bearing bone substitute in areas such as the vertebra and cranium.

Formation of bone-like apatite on organic polymers treated with a silane-coupling agent and a titania solution

Polyethylene terephthalate (PET), ethylene-vinyl alcohol copolymer (EVOH) and Nylon 6 in plate form were treated with silane-coupling agents, a titanium alkoxide-alcohol solution and a hot HCl solution to form a thin crystalline titanium oxide layer. When placed in a simulated body fluid with ion concentrations nearly equal to those of the human blood plasma, nanosized bone-like apatite formed uniformly on the surfaces of these treated polymers: within 2 days for PET and Nylon 6, and 7 days for EVOH. This indicates that such titania-modified polymers might form bone-like apatite in the living body, and bond to living bone through this apatite layer. Three-dimensional fabrics of these polymer fibers, with open spaces in various sizes, are expected to be useful as bone substitutes, as they will be integrated with the natural bone.

Mechanical properties and osteoconductivity of porous bioactive titanium

Porous bioactive titanium implants (porosity of 40%) were produced by a plasma-spray method and subsequent chemical and thermal treatments of immersion in a 5M aqueous NaOH solution at 60 degrees C for 24 h, immersion in distilled water at 40 degrees C for 48 h, and heating to 600 degrees C for 1 h. Compression strength and bending strength were 280 MPa (0.2% offset yield strength 85.2 MPa) and 101 MPa, respectively. For in vivo analysis, bioactive and nontreated porous titanium cylinders were implanted into 6mm diameter holes in rabbit femoral condyles. The percentage of bone-implant contact (affinity index) of the bioactive implants (BGs) was significantly larger than for the nontreated implants (CGs) at all postimplantation times (13.5 versus 10.5, 16.7 versus 12.7, 17.7 versus 10.2, 19.1 versus 7.8 at 2, 4, 8 and 16 weeks, respectively). The percentage of bone area ingrowth showed a significant increase with the BGs, whereas with the CGs it appeared to decrease after 4 weeks (10.7 versus 9.9, 12.3 versus 13.1, 15.2 versus 9.8, 20.6 versus 8.7 at 2, 4, 8 and 16 weeks, respectively). These results suggest that porous bioactive titanium has sufficient mechanical properties and biocompatibility for clinical use under load-bearing conditions.

Quantitative evaluation of the fibrin clot extension on different implant surfaces: an in vitro study

The aim of the present study was a quantitative evaluation of the in vitro fibrin clot extension on different implant surfaces. Forty-five disk-shaped commercially pure Grade 2 titanium samples with three different surface topographies (machined, DPS, and Plus) were used in the present study. For the quantitative evaluation of the fibrin clot, 30 specimens were used (10 per group); human whole blood was employed. Venous blood was drawn from three healthy adult volunteers, and 0.2 mL were immediately dropped onto the surface of each specimen. Contact time was 5 min at room temperature; then the samples were rinsed with saline solution and fixed in a buffered solution of glutaraldehyde and paraformaldehyde. Samples were washed again with buffer and dehydrated in an ascending alcohol series. Specimens belonging to all groups were observed under SEM at a magnification of 1000x. From each sample, 50 random micrographs were collected in .tif format with an N x M 1024 x 768 grid of pixels. Quantitative analysis of fibrin clot extension showed the following results: in machined samples fibrin clot extension was 345987.2 +/- 63747.7 pixels(2) (mean +/- SD), in DPS samples fibrin clot extension was 375930.9 +/- 54726.86 pixels(2) (mean +/- SD), and in Plus samples, fibrin clot extension was 612333.6 +/- 46268.42 pixels(2) (mean +/- SD). With ANOVA it was possible to find that there were significant differences among the groups. The Tukey test revealed that the extension of the fibrin clot of Plus samples was statistically higher compared to both machined and DPS samples. The results of this in vitro study indicate that there is a correlation between implant surface morphology and fibrin clot extension. Improvement in surface microtexture complexity seems to determine the formation of a more extensive and three dimensionally complex fibrin scaffold. Further investigations are necessary to explain in more detail the mechanisms that regulate the fibrin clot formation on different implant surfaces.

Comparative study of osteoconduction on micromachined and alkali-treated titanium alloy surfaces in vitro and in vivo

This study sought to evaluate osteoconduction of Ti-6Al-4V surfaces under various conditions, including micro-patterned, alkali-treated, micro-patterned plus alkali-treated, and surfaces without any treatment as the control. The through-mask electrochemical micromachining (EMM) was used to fabricate micro-hole arrays on the titanium alloy surface. In vitro calcium phosphate formation on titanium surfaces was in static and dynamic simulated body fluid (SBF). In vivo comparison was conducted in the medullary cavity of dog femur using the implant cages which could provide the same physiological environment for specimens with different surface conditions. In vitro experiments indicate good conduction of calcium phosphate on the alkali-treated surfaces, and also better calcium phosphate deposition on the micro-hole surface than on the flat surfaces in dynamic SBF. In vivo experiments confirm the beneficial effect of alkaline treatment on osteoconduction. The results of in vivo experiments also indicate a synergistic effect of the alkaline treatment and the topographic pattern on osteoconduction.

Biocompatibility of β-stabilizing elements of titanium alloys

In comparison to the presently used alpha + beta titanium alloys for biomedical applications, beta-titanium alloys have many advantageous mechanical properties, such as an improved wear resistance, a high elasticity and an excellent cold and hot formability. This will promote their future increased application as materials for orthopaedic joint replacements. Not all elements with beta-stabilizing properties in titanium alloys are suitable for biomaterial applications-corrosion and wear processes cause a release of these alloying elements to the surrounding tissue. In this investigation, the biocompability of alloying elements for beta- and near beta-titanium alloys was tested in order to estimate their suitability for biomaterial components. Titanium (grade 2) and the implant steel X2CrNiMo18153 (AISI 316 L) were tested as reference materials. The investigation included the corrosion properties of the elements, proliferation, mitochondrial activity, cell morphology and the size of MC3T3-E1 cells and GM7373 cells after 7 days incubation in direct contact with polished slices of the metals. The statistical significance was considered by Weir-test and Lord-test (alpha = 0.05). The biocompatibility range of the investigated metals is (decreasing biocompatibility): niobium-tantalum, titanium, zirconium-aluminium-316 L-molybdenum.

Surface potential change in bioactive titanium metal during the process of apatite formation in simulated body fluid

Bioactive titanium metal can be prepared by NaOH and heat treatments that present the metal with a graded bioactive surface layer of amorphous sodium titanate. This study used laser electrophoresis together with transmission electron microscopy (TEM) and energy-dispersive X-ray microanalysis (EDX) to relate the surface potential change of the bioactive titanium metal with its surface structural change in simulated body fluid (SBF). The surface potential of the metal was highly negative immediately after immersion in SBF. With increasing soaking time, the surface potential increased, revealing a maximum positive value, and then decreased to a constant negative value. TEM-EDX showed that immediately after immersion in SBF, the metal surface formed Ti-OH groups by exchanging Na(+) ions in the surface sodium titanate with H3O(+) ions in the fluid. Thereafter, with increasing soaking time the metal surface formed an amorphous calcium titanate, then an amorphous calcium phosphate, and, finally, apatite with bone-like composition and structure. These results indicate that the process of apatite formation on bioactive titanium metal is initiated by the formation of Ti-OH groups with negative charges that interact with calcium ions with positive charges to form calcium titanate. The calcium titanate gains a positive charge and later interacts with phosphate ions with negative charges, forming amorphous calcium phosphate. The amorphous calcium phosphate eventually transforms and stabilizes into bone-like crystalline apatite with a negative charge.

Effects on instruments of the World Health Organization-recommended protocols for decontamination after possible exposure to transmissible spongiform encephalopathy-contaminated tissue

It has been recommended by the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) that rigorous decontamination protocols be used on surgical instruments that have been exposed to tissue possibly contaminated with Creutzfeldt-Jakob disease (CJD). This study was designed to examine the effects of these protocols on various types of surgical instruments. The most important conclusions are: (1) autoclaving in 1N NaOH will cause darkening of some instruments; (2) soaking in 1N NaOH at room temperature damages carbon steel but not stainless steel or titanium; (3) soaking in chlorine bleach will badly corrode gold-plated instruments and will damage some, but not all, stainless-steel instruments, especially welded and soldered joints. Damage became apparent after the first exposure and therefore long tests are not necessary to establish which instruments will be damaged.

Biology of alkali- and heat-treated titanium implants

In cementless fixation systems, surface character is an important factor. Alkali and heat treatments of titanium metal have been shown to produce strong bonding to bone and a higher ongrowth rate. In this study we examined the effect of alkali and heat treatments on titanium rods in an intramedullary rabbit femur model, in regard to the cementless hip stem. The implant rods were 5 mm in diameter and 25 mm in length. Half of the implants were immersed in 5 mol/L sodium hydroxide solution and heated at 600 degrees C for 1 h (AH implants), and the other half were untreated (CL implants). The rods were implanted into the distal femur of the rabbits; AH implants into the left femur and CL implants into the right. The bone-implant interfaces were evaluated at 3, 6, and 12 weeks after implantation. Pull-out tests showed that the AH implants had a significantly higher bonding strength to bone than the CL implants at each time point. As postoperative time elapsed, histological examination revealed that new bone formed on the surface of both types of implants, but significantly more bone made direct contact with the surface of the AH implants. At 12 weeks, approximately 56% of the whole surface of the AH implants was covered with the bone. In conclusion, alkali- and heat-treated titanium offers strong bone bonding and a high affinity to bone as opposed to a conventional mechanical interlocking mechanism. Alkali and heat treatments of titanium may be suitable surface treatments for cementless joint replacement implants.

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.

Apatite-forming ability of carboxyl group-containing polymer gels in a simulated body fluid

Carboxymethylated chitin, gellan gum, and curdlan gels were soaked in a simulated body fluid (SBF) having ion concentrations nearly equal to those of human blood plasma. Some of the gels had been soaked in a saturated Ca(OH)(2) solution, while others had not. The carboxymethylated chitin and gellan gum gels have carboxyl groups, while the curdlan gel has hydroxyl groups. None of the gels formed apatite on their surfaces in the SBF when they had not been subjected to the Ca(OH)(2) treatment, whereas the carboxymethylated chitin and gellan gum gels formed apatite on their surfaces when they had been subjected to the Ca(OH)(2) treatment. The curdlan gel did not form an apatite deposit even after the Ca(OH)(2) treatment. Apatite formation on the carboxymethylated chitin and gellan gum gels was attributed to the catalytic effect of their carboxyl groups for apatite nucleation, and acceleration of apatite nucleation from released Ca(2+) ions. This result provides a guiding principle for obtaining apatite-organic polymer fiber composites. This composite is expected to have an analogous structure to that of natural bone.