Formation and characterization of anodic titanium oxide films containing Ca and P

Preparation and properties of composite MAO/ECD coatings on magnesium alloy

Magnesium alloys are potential biodegradable implants because of their outstanding biological performance and biodegradability in the bioenvironment. However, the rapid corrosion of magnesium and its alloys in human body fluids or blood plasma limits their clinical application. In the present work, we first fabricated porous micro-arc oxidation (MAO) coatings containing Ca/P on the magnesium alloy substrate by conducting MAO in the electrolyte containing calcium gluconate. Subsequently, hydroxyapatite (HA) coatings were prepared using electrochemical deposition (ECD) on the MAO coatings. Finally, a MAO/ECD composite coating was successfully fabricated on the magnesium alloy. The phase, morphology and composition of the biological coatings were monitored with X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy, and corrosion resistance was evaluated by means of electrochemical methods in a simulated body fluid. The experimental results indicated that the formation of HA-containing composite coatings on magnesium alloy effectively decreases its corrosion rate and more importantly endows it with a potential bioactivity. We believe that the combined use of MAO and ECD to modify magnesium alloys would make them more attractive for clinical applications.

Electrically polarized micro-arc oxidized TiO2 coatings with enhanced surface hydrophilicity

The use of micro-arc oxidation titania (MAO TiO2) coatings to modify titanium surfaces improves the biocompatibility of implant surfaces. To obtain hydrophilic MAO TiO2 coating surfaces electric polarization, which induces surface electric fields in the materials and produces surface charges, was performed in this study. Electric polarization of the MAO TiO2 coatings was confirmed by measuring the thermally stimulated depolarization current. After electric polarization treatment the MAO TiO2 coatings did not exhibit any obvious changes in surface roughness, morphology, or phase components. X-ray photoelectron spectroscopy results indicated that electric polarization resulted in oxidation of the cathodic-faced surfaces and reduction of the anodic-faced surfaces. This result suggests that the existence of a concentration gradient of oxide ions/oxygen vacancies produced the stored space charge in the coatings. Reduction of the deionized water contact angle on the polarized MAO TiO2 surfaces was maintained for longer periods compared with the non-polarized surface. Our study demonstrated that metastable electric fields across the MAO TiO2 coating produced by electric polarization made it durably wettable by reducing the interfacial surface tension between the material and water.

Innovative antimicrobial coating of titanium implants with iodine

BACKGROUND

Postoperative infection associated with implants remains a serious complication in orthopedic surgery. Several biomaterial surface treatments have been proposed as a means of reducing the incidence of implant-associated infections. In this study, a clinical trial was performed using an iodine-supported titanium that suppresses the microbial activities.

METHODS

A total of 222 patients with postoperative infection or compromised status were treated using iodine-supported titanium implants. The mean age of the patients was 49.4 years (range 5-85 years). One hundred twenty-seven patients were male and 95 were female. In 158 patients, iodine-supported implants were used to prevent infection, such as compromised hosts and conditions, and in 64 patients to treat active infection. White blood cell (WBCs) and C-reactive protein (CRP) levels were measured pre- and postoperatively in all patients. To confirm whether iodine from the implant affected physiological functions, thyroid hormone levels in the blood were examined. Both examinations were conducted sequentially for a year. Radiological evaluations were performed regularly after the operation. The chronological changes of the iodine amount were evaluated using half pins removed after completion of external fixation.

RESULTS

The mean follow-up period was 18.4 months (range 3-44 months). Acute infection developed in three tumor cases among the 158 patients on preventive therapy. All three recovered without removal of the implants. Infection was cured in all 64 patients with infection. Median WBC levels were in the normal range, and median CRP levels returned to <0.5 within 4 weeks after surgery. Abnormalities of thyroid gland function were not detected. None of the patients experienced loosening of the implants. There were two patients with mechanical implant failure, which was treated by re-implantation. Excellent bone ingrowth and ongrowth were found around all hip and tumor prostheses. One year later, the amount of iodine on external fixation pins remained about 20-30%.

CONCLUSIONS

Iodine-supported titanium implants can be very effective for preventing and treating infections after orthopedic surgery. Cytotoxicity and adverse effects were not detected.

Antibacterial effect and cytocompatibility of nano-structured TiO2 film containing Cl

The aim of this study was to investigate the antibacterial effect and cytocompatibility of a nano-structured TiO2 film that contained Cl and had been coated onto commercially pure titanium. First, we prepared nano-structured TiO2 by anodization with hydrofluoric acid. Then, to confer an antibacterial effect, we performed a second anodization with NaCl solutions of different concentrations (0.5 M, 1 M, 2 M). The morphology, composition, and wettability of the surface were investigated by SEM, EDS, and a video contact angle measuring system. The antibacterial effect was evaluated by film adhesion method. And cytotoxicity was determined by the viability of MG-63 cells in a MTT assay. The SEM and EDS results showed that the TiO2 nano-structure containing Cl had successfully formed after the second anodization. The contact angle analysis showed that the anodized titanium had a hydrophilic character. The results of this in vitro investigation demonstrated that the TiO2 nano-structure film anodized in 1 M NaCl had an antibacterial effect and good cell compatibility.

In vitro antibacterial activity and cytocompatibility of bismuth doped micro-arc oxidized titanium

Chemical manipulations of the implant surface produce a bactericidal feature to prevent infections around dental implants. Despite the successful use of bismuth against mucosal and dermis infections, the antibacterial effect of bismuth in the oral cavity remains under investigation. The aim of this study was to evaluate the antibacterial activities of bismuth compounds against Actinobacillus actinomycetemcomitans, Staphylococcus mutans, and methicillin-resistant Staphylococcus aureus (MRSA), and to investigate the antimicrobial effects of bismuth doped micro-arc oxidation (MAO) titanium via an agar diffusion test. Cell viability, alkaline phosphatase activity, and mineralization level of MG63 osteoblast-like cells seeded on the coatings were evaluated at 1, 7, and 14 days. The results demonstrate that bismuth nitrate possess superior antibacterial activity when compared with bismuth acetate, bismuth subgallate, and silver nitrate. The bismuth doped MAO coating (contained 6.2 atomic percentage bismuth) had good biological affinities to the MG63 cells and showed a higher antibacterial efficacy against Actinobacillus actinomycetemcomitans and MRSA, where the reduction rates of colony numbers is higher than that of the control group by 1.5 and 1.9 times, respectively. These in vitro evaluations demonstrate that titanium implants with bismuth on the surface may be useful for better infection control.

A multi-scaled hybrid orthopedic implant: bone ECM-shaped Sr-HA nanofibers on the microporous walls of a macroporous titanium scaffold

We report here, for the first time, a novel multi-scaled hybrid orthopedic implant material consisting of a macroporous Ti scaffold, whose macropores' walls have a microporous titania layer which is fully covered with nanofibers of Sr-doped hydroxyapatite (Sr-HA). The microporous titania layer is formed on and within the Ti scaffold by micro-arc oxidation, which firmly binds to the Ti substrate and contains Ca2+, Sr2+ and PO4(3-) ions. It is then hydrothermally treated to form Sr-HA nanofibers. During the hydrothermal treatment, Sr-HA nanoprisms nucleate from Ca0.5Sr0.5TiO3 pre-formed on the TiO2 and grow in length to nanofibers at the expense of Ca2+, Sr2+ and PO4(3-) ions that migrate from the TiO2. These Sr-HA nanofibers construct a network structure similar to the hierarchical organization of bone extracellular matrix (ECM), and the resulting nanofibrous surface displays a firm adhesion to substrate, superhydrophilicity and apatite-inducing ability. The induced apatite prefers to nucleate on the basal-faceted surfaces of Sr-HA nanofibers. The nanofiber-walled scaffold has a great potential for load-bearing orthotopic use.

An innovative technique to simply fabricate ZrO₂-HA-TiO₂ nanostructured layers

For the first time, ZrO₂-HA-TiO₂ layers were synthesized through EPD-Enhanced MAO (EEMAO) technique in only one step where no supplementary treatment was required. SEM, XRD, EDX, and XPS techniques were employed to propose a correlation between the growth parameters and the physical and chemical properties of the layers. The layers revealed a porous structure where applying higher voltages and/or utilizing higher concentrated electrolytes resulted in formation of wider pores and increasing the zirconium concentration in the layers; meanwhile, prolonging the growth time had the same effects. The layers mainly consisted of anatase, hydroxyapatite, monoclinic ZrO₂, and tetragonal ZrO₂ phases. Increasing the voltage, electrolyte concentration, and time, hydroxyapatite as well as tetragonal ZrO₂ was decomposed to α-TCP, monoclinic ZrO₂, and ZrO. The nanosized zirconia particles (d = 20-60 nm) were further accumulated on the vicinity of the layers when thicker electrolytes were utilized or higher voltages were applied. Emphasizing on the chemical and electrochemical foundations, a probable formation mechanism was finally put forward.

Spectral and physical properties of electrochemically formed colored layers on titanium covered with clearcoats

We present the application and characterization of two commercial polymer clearcoats to electrochemically formed colored passive layers on titanium with the aim of providing physical protection required in many of titanium's applications, while allowing the unique appearance of the colored layers to show through. Thin layers of an acrylic automotive clearcoat (∼3.5 μm thick) and an epoxy marine clearcoat (∼6.5 μm thick) are applied to the colored titanium surfaces using spin coating, and are found to slightly modify their visual properties, while maintaining their bright, well-defined sparkling colors. Both clearcoats are found to significantly reduce the surface roughness, thereby reducing potential wear from friction and the adhesion of fine dirt particles. They are also found to notably decrease the wetting properties of colored titanium, furthering its protection against damage from ambient and aqueous media. The clearcoats show the ability to protect colored titanium from physical and chemical damage, with the automotive clearcoat exhibiting superior adhesion. Our electrochemical coloring technique combined with the application of clearcoats creates a new and unique system that does not rely solely on a polymer coating for its colorful appearance and protection against corrosion.

Antibacterial iodine-supported titanium implants

Deep infection remains a serious complication in orthopedic implant surgery. In order to reduce the incidence of implant-associated infections, several biomaterial surface treatments have been proposed. This study focused on evaluating the antibacterial activity of iodine-supported titanium (Ti-I(2)) and its impact on post-implant infection, as well as determining the potential suitability of Ti-I(2) as a biomaterial. External fixation pins were used in this experiment as trial implants because of the ease of making the septic models. The antibacterial activity of the metal was measured using a modification of the Japanese Industrial Standards method. Activity was evaluated by exposing the implants to Staphylococcus aureus or Escherichia coli and comparing reaction of pathogens to Ti-I(2) vs. stainless steel and titanium controls. Ti-I(2) clearly inhibited bacterial colonization more than the control metals. In addition, cytocompatibility was assessed by counting the number of colonies that formed on the metals. The three metals showed the same amount of fibroblast colony formation. Japanese white rabbits were used as an in vivo model. Three pins were inserted into both femora of six rabbits for histological analysis. Pin sites were inspected and graded for infection and inflammation. Fewer signs of infection and inflammatory changes were observed in conjunction with the Ti-I(2) pins. Furthermore, osteoconductivity of the implant was evaluated with osteoid formation surface of the pin. Consecutive bone formation was observed around the Ti-I(2) and titanium pins, while little osteoid formation was found around the stainless steel pins. These findings suggest that Ti-I(2) has antimicrobial activity and exhibits cytocompatibility. Therefore, Ti-I(2) substantially reduces the incidence of implant infection and shows particular promise as a biomaterial.

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.

Enhanced cell integration to titanium alloy by surface treatment with microarc oxidation: a pilot study

Microarc oxidation (MAO) is a surface treatment that provides nanoporous pits, and thick oxide layers, and incorporates calcium and phosphorus into the coating layer of titanium alloy. We presumed such modification on the surface of titanium alloy by MAO would improve the ability of cementless stems to osseointegrate. We therefore compared the in vitro ability of cells to adhere to MAOed titanium alloy to that of two different types of surface modifications: machined and grit-blasted. We performed energy-dispersive x-ray spectroscopy and scanned electron microscopy investigations to assess the structure and morphology of the surfaces. Biologic and morphologic responses to osteoblast cell lines (SaOS-2) were then examined by measuring cell proliferation, cell differentiation (alkaline phosphatase activity), and alpha v beta 3 integrin. The cell proliferation rate, alkaline phosphatase activity, and cell adhesion in the MAO group increased in comparison to those in the machined and grit-blasted groups. The osteoblast cell lines of the MAO group were also homogeneously spread on the surface, strongly adhered, and well differentiated when compared to the other groups. This method could be a reasonable option for treating the surfaces of titanium alloy for better osseointegration.

Formation of hydroxyapatite within porous TiO(2) layer by micro-arc oxidation coupled with electrophoretic deposition

Micro-arc oxidation (MAO) is commonly used to modify the surface of Ti-based medical implants with a bioactive and porous titanium oxide (TiO(2)) layer. This study reports a novel method of incorporating hydroxyapatite (HA) within the TiO(2) layer by coupling MAO with an electrophoretic deposition (EPD) process. A HA-incorporated, porous TiO(2) layer was produced successfully on the Ti substrate using the EPD-coupled MAO treatment, as confirmed by electron microscopy observations. Addition of ethanol to the electrolyte solution containing the fine HA particles was essential to reduce the level of gaseous emission on the anode, which obstructs the attachment of HA particles. In vitro cellular assays showed that the incorporation of HA significantly improved the osteoblastic activity on the coating layer.

Preparation of Bioactive Hydroxyapatite on Pure Titanium

In this study, a hydroxyapatite (HA) was coated on a pure titanium surface by means of a complex oxidation and hydrothermal treatment. First an anodic oxidation was done on the titanium plates, followed by micro-arc oxidation. The HA-coated specimens and pure titanium specimens were immersed in SLB for 1, 5, and 10 days, respectively, to study their electrochemical behavior. The corrosion currents of HA-coated specimens were less than pure titanium specimens. This indicated that HA coating prevented surface metal ions of the implant from dissolving, thereby, reducing the tissue toxicity. The cytotoxic effect on fibroblasts L929 cells was measured by cell counting after being seeded for 2, 4, 8, 12, and 24 h. The number of surface cell attachments on the HA-coated specimens was much greater than on pure titanium specimens. The morphology of the cells on the HA coating had normal shapes and spread well with some cells climbing onto surface pores while cells on the pure titanium were oval shaped. The results confirm that the cell compatibility on HA-coated ion titanium surfaces is much better than pure titanium.

Transmission electron microscopy of coatings formed by plasma electrolytic oxidation of titanium

Transmission electron microscopy and supporting film analyses are used to investigate the changes in composition, morphology and structure of coatings formed on titanium during DC plasma electrolytic oxidation in a calcium- and phosphorus-containing electrolyte. The coatings are of potential interest as bioactive surfaces. The initial barrier film, of mixed amorphous and nanocrystalline structure, formed below the sparking voltage of 180 V, incorporates small amounts of phosphorus and calcium species, with phosphorus confined to the outer approximately 63% of the coating thickness. On commencement of sparking, calcium- and phosphorus-rich amorphous material forms at the coating surface, with local heating promoting crystallization in underlying and adjacent anodic titania. The amorphous material thickens with increased treatment time, comprising almost the whole of the approximately 5.7-microm-thick coating formed at 340 V. At this stage, the coating is approximately 4.4 times thicker than the oxidized titanium, with a near-surface composition of about 12 at.% Ti, 58 at.% O, 19 at.% P and 11 at.% Ca. Further, the amount of titanium consumed in forming the coating is similar to that calculated from the anodizing charge, although there may be non-Faradaic contributions to the coating growth.

Histomorphometry and stability analysis of early loaded implants with two different surface conditions in beagle dogs

STATEMENT OF PROBLEM

Despite an improved bone reactions of Mg-incorporated implants in the animals, little yet has been carried out by the experimental investigations in functional loading conditions.

PURPOSE

This study investigated the clinical and histologic parameters of osseointegrated Mg-incorporated implants in early loading conditions.

MATERIAL AND METHODS

A total of 36 solid screw implants (diameter 3.75 mm, length 10 mm) were placed in the mandibles of 6 beagle dogs. Test groups included 18 Mg-incorporated implants. Turned titanium implants served as control. Gold crowns were inserted 4 weeks after implant placement and the dogs were immediately put on a food diet. Implants were observed for 10 weeks after loading. Radiographic assessments and stability tests were performed at the time of fixture installation, 2^nd stage surgery, 4 weeks after loading, and 10 weeks after loading. Histological observations and morphometrical measurements were also performed.

RESULTS

Of 36 implants, 33 displayed no discernible mobility, corresponding to successful clinical function. There was no statistically significant difference between test implants and controls in marginal bone levels (P = .46) and RFA values. The mean BIC% in the Mg-implants was 54.5 ± 8.4%. The mean BIC% in the turned implant was 45.3 ± 12.2%. These differences between the Mg-implant and control implant were statistically significant (P = .005).

CONCLUSIONS

The anodized, Mg-incorporated implant demonstrated significantly more bone-to-implant contact (BIC) in early loading conditions.

CLINICAL IMPLICATIONS

The results of this study in beagle dogs suggest the possibility of achieving predictable stability of early loaded free-standing dental implants with Mg-incorporated surface.

A preliminary study on investigating the attachment of soft tissue onto micro-arc oxidized titanium alloy implants

Intraosseous transcutaneous amputation prostheses (ITAP) rely on the integrity of the soft tissue-implant interface as a barrier to exogenous agents, and in the prevention of avulsion and marsupilization. This experimental work aimed at the in vivo evaluation of soft tissue attachment to Ti alloy (Ti6Al4V) transcutaneous custom-made screws treated by a micro-arc oxidation (MAO) method. Prior to implantation, the surface of the MAO treated implants was analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD). The experimental model comprised implantation of 16 transcutaneous screws (two groups: MAO and machined (control); total eight implants/group) in the medial aspect of the left tibia of eight female goats. The animals were euthanized at eight weeks and the samples harvested and processed for histological and histomorphometrical analysis of soft tissue attachment to the implant surface. Significant higher soft tissue attachment was observed in the MAO-modified group compared to the control. The in vivo data indicated that MAO-modified Ti alloy could be a useful biomaterial for tissue engineering and benefit applications where bone-anchored transcutaneous implants are used.

UV-enhanced bioactivity and cell response of micro-arc oxidized titania coatings

Using ultraviolet (UV) irradiation of micro-arc oxidized (MAO) titania coating in distilled water for 0.5 and 2h, we have achieved an enhanced bioactivity and cell response to titania surface. The MAO coating appears porous and predominantly consists of nanocrystallized anatase TiO(2). Compared with the MAO coating, the UV-irradiated coatings do not exhibit any obvious change in surface roughness, morphology, grain size and phase component; however, they have more abundant basic Ti-OH groups and become more hydrophilic because the water contact angle decreases significantly from 17.9+/-0.8 degrees to 0 degrees . In simulated body fluid (SBF), bonelike apatite-forming ability is significantly stronger on the UV-irradiated coatings than the MAO coating. SaOS-2 human osteoblast-like cell attachment, proliferation and alkaline phosphatase of the cell are greater on the UV-irradiated coatings relative to the MAO coating. UV irradiation of titania results in the conversion of Ti(4+) to Ti(3+) and the generation of oxygen vacancies, which could react with the absorbed water to form basic Ti-OH groups. The enhanced bioactivity and cell response of the UV-irradiated coatings are proven to result from abundant Ti-OH groups on the coating surfaces. After storing the UV-irradiated coatings in the dark for two weeks, the basic Ti-OH groups on the coatings slightly decrease in amount and can induce apatite formation after a short period of SBF immersion, and show relative long-term stability.

Nanocrystallized SrHA/SrHA-SrTiO(3)/SrTiO(3)-TiO(2) multilayer coatings formed by micro-arc oxidation for photocatalytic application

Novel photocatalytic coatings containing strontium hydroxyapatite (SrHA), strontium titanate (SrTiO(3)), and TiO(2) were formed by micro-arc oxidation (MAO) in an aqueous electrolyte containing strontium acetate and β-glycerophosphate disodium at 530 V for 0.1-5 min. The structure evolution of the coatings was investigated as a function of processing time, and the photocatalytic activity of the coatings was evaluated by measuring the decomposition rate of methyl orange under ultraviolet irradiation. During the MAO processing of the coatings, it was observed that some granules appeared in the electrolyte adjacent to the anode and they increased in amount as the processing time was prolonged. The obtained results show that the granules are amorphous and poorly crystallized SrHA with negative charges. The coating prepared for 5 min presents a microporous structure of SrHA/SrHA-SrTiO(3)/SrTiO(3)-TiO(2) multilayers, in which the SrHA outermost layer and the SrHA-SrTiO(3) intermediate layer are nanocrystallized. It is suggested that formation of the granules, electro-migration of the granules onto the pre-formed layer, and crystallization of the adhered granules are possible mechanisms for the formation of a SrHA/SrHA-SrTiO(3)/SrTiO(3)-TiO(2) multilayer coating. This coating shows much higher photocatalytic decomposition efficiency relative to the MAO-formed TiO(2) coating, and is expected to have an important photocatalytic application.

A novel multiphase anodic spark deposition coating for the improvement of orthopedic implant osseointegration: an experimental study in cortical bone of sheep

The effect of a new three-step anodic spark deposition process, labeled TiSpark, including two consecutive treatments performed first in a P solution and second in Ca solution, followed by an additional alkali etching step, was investigated for the improvement of osseointegration of commercial grade 2 titanium, machined (Ti) or Al(2)O(3) sandblasted (Ti-SA), cylindrical implants (12 mm in length and 4 mm in diameter) in cortical bone of 12 adult sheep. Histomorphometric and microhardness measurements were carried out at each experimental time (4, 8, and 12 weeks) to quantify the bone-to-implant contact around the implants as well as the newly bone hardness and bone maturation index. TiSpark treated surfaces were covered by a thick layer of crystalline anatase TiO(2) and by a further Ca/P layer. Bone tissue extends and grows on the surface of the TiSpark treated implants without any fibrous tissue, enhancing the short-term osseointegration properties of implant. Bone mineralization rate was also influenced by the chemical composition of implants and sandblasted materials presented the lowest bone maturation rate at the interface. Data suggests that the TiSpark treatment produces a modification of the Ti surface, which presents good bioactivity and may be suitable for achieving a stable implant osseointegration.

Biomimetic coating of compound titania and hydroxyapatite on titanium

The modification on the titanium implant surface is an effective method to improve the biocompatibility of titanium. This article describes efforts to improve implant biocompatibility by applying titania and hydroxyapatite to form a three-layer coating on the titanium surface. This three-layer coating is made up of HA as the top layer (formed by hydrothermal treatment), porous TiO2 as the middle layer (formed by micro-arc oxidation) and a dense TiO2 film as the inner layer (formed by preanodic oxidation). The physicochemical characteristics, cell behavior and in vivo studies were assessed. The physicochemical characteristics were investigated using scanning electron micoscopy observation, fibronectin and laminin adsorption, corrosion test and X-ray diffraction analysis. Cell behavior included morphology observation with scanning electron microscopy (SEM), number count with methylthiazol tetrazolium (MTT) assay and Alkaline phosphatase (ALP, a representative enzyme of osteoblastic differentiation) activity of osteoblast-like MC3T3-E1 cells. In study in vivo the specimens were embedded in skull wound for repair. By the analysis of experiments, the titanium coated with this three-layer coating has been proved to have excellent corrosion resistance and good biocompatibility, which can promote cell proliferation and bone formation. So this modified titanium is an improved alternative to untreated titanium for bone repair applications.

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.

Calcium phosphate-based coatings on titanium and its alloys

Use of titanium as biomaterial is possible because of its very favorable biocompatibility with living tissue. Titanium implants having calcium phosphate coatings on their surface show good fixation to the bone. This review covers briefly the requirements of typical biomaterials and narrowly focuses on the works on titanium. Calcium phosphate ceramics for use in implants are introduced and various methods of producing calcium phosphate coating on titanium substrates are elaborated. Advantages and disadvantages of each type of coating from the view point of process simplicity, cost-effectiveness, stability of the coatings, coating integration with the bone, cell behavior, and so forth are highlighted. Taking into account all these factors, the efficient method(s) of producing these coatings are indicated finally.