Hard Tissue Replacement Materials Research Articles

Effect of Cu content on the mechanical, corrosion and antibacterial properties of porous NiTi-xCu alloys for biomedical application

Porous NiTi alloys are widely used as hard tissue replacement materials due to their excellent corrosion resistance and biocompatibility. However, the lack of antibacterial ability may lead to bacterial infection after surgery. Therefore, enhancing the antibacterial ability of porous NiTi alloys by incorporating Cu is of significant value. In this paper, porous NiTi-xCu alloys (x = 0, 0.5, 1, 1.5 at%) were prepared via powder metallurgy and the influence of Cu content on their properties were investigated. The results demonstrate that the compressive strength and antibacterial activity of the alloys increase with increasing Cu content. The NiTi-1.5Cu sample exhibits the highest compressive strength of 48.7 MPa and antibacterial rate of 99.6 %. Furthermore, the addition of Cu improves the corrosion resistance of the alloys, and the NiTi-1Cu specimen exhibits the lowest corrosion rate of 0.123 mm year−1. It is concluded that the incorporation of Cu effectively enhances the compressive strength, corrosion resistance and antibacterial properties of the porous NiTi alloys, making them promising candidates for hard tissue replacement applications.

Mechanical properties evaluation of metacarpophalangeal joint prosthesis with new titanium-nickel memory alloy: a cadaver study

ObjectiveNi-Ti memory alloys are unusual materials for hard-tissue replacement because of their unique superelasticity, good biocompatibility, high strength, low specific gravity, low magnetism, wear resistance, corrosion resistance and fatigue resistance. The current study aims to evaluate its mechanical properties and provide biomechanical basis for the clinical application of the prosthesis.MethodsTen adult metacarpophalangeal joint specimens were randomly divided into a prosthesis group (n = 5, underwent metacarpophalangeal joint prosthesis) and a control group (n = 5, underwent sham operation). Firstly, the axial compression strength was tested with BOSE material testing machine to evaluate its biomechanical strength. Secondly, these specimens were tested for strain changes using BOSE material testing machine and GOM non-contact optical strain measurement system to evaluate the stress changes. Thirdly, fatigue test was performed between groups. Lastly, the mechanical wear of the metacarpophalangeal joint prosthesis was tested with ETK5510 material testing machine to study its mechanical properties.ResultsAxial compression stiffness in the prosthesis group was greater than that in the control group in terms of 30 ° and 60 ° flexion positions (P < 0.05). There was no statistically significant difference between two groups with regards to axial compression stiffness and stress change test (P > 0.05). In the fatigue wear test, the mean mass loss in the prosthesis group’s prosthesis was 17.2 mg and 17.619 mm3, respectively. The mean volume wear rate was 0.12%. There was no statistically significant difference in the maximum pull-out force of the metacarpal, phalangeal, and polymer polyethylene pads between the prosthesis group and the control group specimens.ConclusionsNi-Ti memory alloy metacarpophalangeal joint prosthesis conforms to the biomechanical characteristics of metacarpophalangeal joints without implants, and the fatigue strength can fully meet the needs of metacarpophalangeal joint activities after joint replacement.

A Comprehensive Review on Novel Graphene‐Hydroxyapatite Nanocomposites For Potential Bioimplant Applications

AbstractThe advancements in medical treatment necessitated the development of advanced bio‐implant materials for hard tissue replacement and bone regeneration. Hydroxyapatite (HA), an extreme bioresorbable material having physicochemical similarities with natural bone, seems to be a good bioimplant. Still, the ineffective mechanical properties, viz. fracture toughness, wear resistance, and tensile strength, restrict its practical utility in bioimplants. Recently, graphene‐HA nanocomposites have been explored for potential bioimplant applications ascribed to their superior biocompatibility, bioactivity, osteoconductivity, and enhanced mechanical properties. The huge surface area with a two‐dimensional sheet structure facilitates graphene's strong integration with HA, thus enhancing mechanical properties. These enhanced mechanical properties of graphene‐HA nanocomposite are chiefly attributed to the pull‐out, ridge growth, crack deflection, and grain bridging characteristics exhibited by graphene filler in the HA matrix. Further, graphene is neutral and biocompatible, thus improving the graphene‐HA nanocomposite‘s biocompatibility. These qualities made this nanocomposite a rising star among bio‐ceramic implant materials. This review presents the current scenario on the synthesis and mechanical and biological properties of graphene‐hydroxyapatite nanocomposite, which seems to be a propitious material for implants in orthopaedic applications.

Study on the osteogenesis of rat mesenchymal stem cells and the long-term antibacterial activity of Staphylococcus epidermidis on the surface of silver-rich TiN/Ag modified titanium alloy.

The main causes of failure of orthopedic implants are infection and poor bone ingrowth. Surface modification of the implants to allow for long-term antibacterial and osteogenic functions is an effective solution to prevent failure of the implants. We developed silver-rich TiN/Ag nano-multilayers on the surface of titanium alloy with different doses of Ag+ . The antibacterial stability and osteogenesis of the silver-rich surface were determined by evaluating the adhesion and proliferation of Staphylococcus epidermidis, and the adhesion, proliferation, alkaline phosphatase activity, extracellular matrix mineralization, and the expression level of genes involved in osteogenic differentiation of rat bone mesenchymal stem cells (BMSCs). The results demonstrated that the antibacterial rates (Ra) of 5 × 1016 -Ag, 1 × 1017 -Ag, 5 × 1017 -Ag, and 1 × 1018 -Ag were respectively 46.21%, 85.66%, 94.99%, 98.48%, and 99.99%. After subcutaneous implantation in rats or immersion in phosphate buffered saline for up to 12 weeks, the silver-rich surface of the titanium alloy showed long-term stable inhibition of Staphylococcus epidermidis. Furthermore, in vitro and in vivo studies indicated that the Ag-implanted titanium did not show apparent cytotoxicity and that lower Ag+ implanted groups (5 × 1016 -Ag, 1 × 1017 -Ag) had better viability and biological safety when compared with higher Ag+ implanted groups. In addition, when compared with the Ti6Al4V-group, all Ag-implanted groups exhibited enhanced osteogenic indicators in rat BMSCs. Regarding osteogenic indicators, the surfaces of the 5 × 1017 -Ag group had better osteogenic effects than those of other groups. Therefore, the proper dose of Ag+ implanted TiN/Ag nano-multilayers may be one of the options for the hard tissue replacement materials with antibacterial activity and osteogenic functions.

Phase field simulation of spinodal decomposition in Zr–Nb alloys for implant materials

Zirconium (Zr)-based alloys, a new class of hard-tissue replacement materials, show lower strength compared to traditional medical metal materials such as stainless steel, cobalt alloy, and Ti-6Al-4V alloys, which may lead to premature fracture of the implant. Spinodal decomposition can increase the strength greatly without an increase in the elastic modulus of the alloy. In this study, a phase field method based on the Cahn–Hilliard equation was applied to the simulation of the spinodal decomposition in Zr–Nb alloys. The spinodal region on the Zr–Nb phase diagram was calculated by the phase field method by considering the interfacial energy and elastic strain energy contribution to the total Gibbs free energy. Furthermore, the effects of the Nb content and heat-treatment temperature on the morphology, amplitude, and volume fraction of the decomposition phases are discussed. Simulation results indicate that the morphology of the β′ phase is interconnected and regular with a preferential alignment in the ⟨110⟩ direction to reduce the strain energy, which may restrict the spinodal decomposition of the alloys. The two droplet phases merge, which can be attributed to the reduction in the elastic strain energy. The phase decomposition rate increases with an increase in aging temperature, but the aging temperature has only a small influence on the final volume fraction of the β′ phase.

Novel niobium and silver toughened hydroxyapatite nanocomposites with enhanced mechanical and biological properties for load-bearing bone implants

An ideal load-bearing implant material for hard tissue replacement requires a combination of excellent mechanical properties and biological functions. However, such combination can hardly be achieved by monolithic bioceramics or metals. To this end, by combining the individual characteristic advantages of hydroxyapatite (HA), niobium (Nb) and silver (Ag), we have developed novel Nb and Ag co-reinforced HA nanocomposites by high energy ball milling (HEBM) and spark plasma sintering (SPS). The fabricated HA–20Nb and HA–15Nb–5Ag (wt%) show nanocomposite microstructure with metallic reinforcements uniformly dispersed in the HA matrix. The formation of a nanothick Ca4Nb2O9 transition layer at the interfaces of HA/Nb enables high interface strength between the reinforcements and the HA matrix. Addition of Nb or Nb–Ag could significantly increase the compressive strength and fracture toughness of HA. In vitro and in vivo evaluations further show that addition of Nb could promote osteoblast proliferation, increase the osteogenic differentiation and enhance the osteointegration ability. Incorporation of Ag could remarkably increase the antibacterial activity both against Gram-positive organism Staphylococcus aureus and Gram-negative organism Escherichia coli. Thus, the developed new nanocomposites can bridge the gap between the mechanical and biofunctional requirements for load-bearing bone implants.

Combined Optimized Effect of a Highly Self-Organized Nanosubstrate and an Electric Field on Osteoblast Bone Cells Activity.

The effect of an electric field within specific intensity limits on the activity of human cells has been previously investigated. However, there are a considerable number of factors that influence the in vitro development of cell populations. In biocompatibility studies, the nature of the substrate and its topography are decisive in osteoblasts bone cells development. Further on, electrical field stimulation may activate biochemical paths that contribute to a faster, more effective self-adjustment and proliferation of specific cell types on various nanosubstrates. Within the present research, an electrical stimulation device has been manufactured and optimum values of parameters that led to enhanced osteoblasts activity, with respect to the alkaline phosphatase and total protein levels, have been found. Homogeneous electric field distribution induced by a highly organized titanium dioxide nanotubes substrate had an optimum effect on cell response. Specific substrate topography in combination with appropriate electrical stimulation enhanced osteoblasts bone cells capacity to self-adjust the levels of their specific biomarkers. The findings are of importance in the future design and development of new advanced orthopaedic materials for hard tissue replacement.

Biomedical Porous Shape Memory Alloys for Hard-Tissue Replacement Materials.

Porous shape memory alloys (SMAs), including NiTi and Ni-free Ti-based alloys, are unusual materials for hard-tissue replacements because of their unique superelasticity (SE), good biocompatibility, and low elastic modulus. However, the Ni ion releasing for porous NiTi SMAs in physiological conditions and relatively low SE for porous Ni-free SMAs have delayed their clinic applications as implantable materials. The present article reviews recent research progresses on porous NiTi and Ni-free SMAs for hard-tissue replacements, focusing on two specific topics: (i) synthesis of porous SMAs with optimal porous structure, microstructure, mechanical, and biological properties; and, (ii) surface modifications that are designed to create bio-inert or bio-active surfaces with low Ni releasing and high biocompatibility for porous NiTi SMAs. With the advances of preparation technique, the porous SMAs can be tailored to satisfied porous structure with porosity ranging from 30% to 85% and different pore sizes. In addition, they can exhibit an elastic modulus of 0.4–15 GPa and SE of more than 2.5%, as well as good cell and tissue biocompatibility. As a result, porous SMAs had already been used in maxillofacial repairing, teeth root replacement, and cervical and lumbar vertebral implantation. Based on current research progresses, possible future directions are discussed for “property-pore structure” relationship and surface modification investigations, which could lead to optimized porous biomedical SMAs. We believe that porous SMAs with optimal porous structure and a bioactive surface layer are the most competitive candidate for short-term and long-term hard-tissue replacement materials.

Changes in the Mechanical Properties of Ti Samples with TiN and TiN/TiO2 Coatings Deposited by Different PVD Methods

The metallic implants represent a major class of the hard tissue replacement materials. In order to enhance the surface properties of the titanium alloys multicomponent coatings containing ceramic phases are employed to improve the tribological performance, corrosion resistance and biocompatibility. The mechanical properties (elastic modulus, necking region, loss of adhesion) of arc PVD TiN and TiN/TiO2 coatings deposited on unalloyed Ti (99 wt. %) foil were examined by nanoindentation, uniaxial tensile test while applying a new approach - using thermal imaging camera during the test. The hardness of the TiN coating reached values of 9649 MPa and 67 GPa, while that of the TiN/TiO2 was lowered down to 8774 MPa and 58.5 GPa which low values are closer to that of the cortical bone. The mechanical behavior of TiN/TiO2 coated material characterized it as a more plastic system indicating a good deformability while the TiN displayed more fragile behavior. There were no signs of loss of adhesion or loss of coating integrity up to maximum load for all tested TiN and TiN/TiO2 coated samples. The thermal analysis proves that the coated samples show lower thermal conductivity, which is very important for the performance of an endosseous dental implant for example.

Divalent ion encapsulated nano titania on Ti metal as a bioactive surface with enhanced protein adsorption

A novel approach on incorporation of divalent species such as Mg, Ca and Sr into the titania nanostructures formed on Ti metal surface and their comparative study on enhancement of bioactivity, protein adsorption and cell compatibility is reported. When treated with hydrogen peroxide, Ti metal forms hydrogen titanate. On subsequent treatment with Mg or Ca or Sr nitrate solutions, respective ions are incorporated into hydrogen titanate layer, and heat treatment leads to titania decorated with these ions. The resultant heat-treated samples when soaked in simulated body fluid form bone-like apatite which indicates the present surface modification enhances the bioactivity. Further, enhanced protein adsorption in bovine serum albumin is an indication of suitability of these divalent species to form chelate compounds with amino acids, and Ca containing titania nanostructure favours more protein adsorption compared to the others. Cytocompatibility studies using MG-63, human osteosarcoma cell lines shows these divalent ion containing titania nanostructure favours the cell attachment and did not show any cytotoxicity. Bioactivity, enhanced protein adsorption along with cytocompatibility clearly indicates such surface modification approach to be useful to design hard tissue replacement materials in orthopaedic and dental field.

Controlled electrophoretic deposition of HAp/β-TCP composite coatings on piranha treated 316L SS for enhanced mechanical and biological properties

Hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) bioactive materials have been used as individual coatings on steel implants employed in the fields of orthopedics and dentistry due to their excellent properties, which foster effective healing of the repair site. However, slow dissolution of HAp and fairly little fast dissolution of β-TCP present a major obstacle for such applications and this leads to the focus on the investigation of a mixture of HAp and β-TCP composite that forms biphasic calcium phosphate (BCP). The BCP coatings were achieved by thickness controlled electrophoretic deposition on piranha treated 316L SS. This method is well controlled and the anticipated dissolution rate could be attained with faster formation of new bone at the implant site, when compared to the individual HAp or β-TCP coating. The structural, functional, morphological and elemental composition of the coatings were characterized by using various analytical techniques. The BCP coating has been shown to have a role in obstructing the corrosion to a greater extent when in contact with SBF solution. The BCP coating also shows excellent in vitro and mechanical properties and osteoblasts cellular tests revealed that the coating was more effective in improving biocompatibility. This makes it an ideal candidate material for hard tissue replacement.

Enhanced osteogenesis on titanium implants by UVB photofunctionalization of hydrothermally grown TiO₂ coatings.

Even though Ti-based implants are the most used materials for hard tissue replacement, they may present lack of osseointegration on the long term, due to their inertness. Hydrothermal treatment (HT) is a useful technique for the synthesis of firmly attached, highly crystalline coatings made of anatase titanium dioxide (TiO2), providing favorable nanoroughness and higher exposed surface area, as well as greater hydrophilicity, compared to the native amorphous oxide on pristine titanium. The hydrophilicity drops even more by photofunctionalization of the nanostructured TiO2-anatase coatings under UV light. Human mesenchymal stem cells exhibited a good response to the combination of the positive surface characteristics, especially in respect to the UVB pre-irradiation. The results showed that the cells were not harmed in terms of viability; even more, they were encouraged to differentiate in osteoblasts and to become osteogenically active, as confirmed by the calcium ion uptake and the formation of well-mineralized, bone-like nodule structures. In addition, the enrichment of hydroxyl groups on the HT-surfaces by UVB photofunctionalization accelerated the cell differentiation process and greatly improved the osteogenesis in comparison with the nonirradiated samples. The optimal surface characteristics of the HT-anatase coatings as well as the high potentiality of the photo-induced hydrophilicity, which was reached during a relatively short pre-irradiation time (5 h) with UVB light, can be correlated with better osseointegration ability in vivo; among the samples, the superior biological behavior of the roughest and most hydrophilic HT coating makes it a good candidate for further studies and applications.

Solution combustion synthesis and characterization of strontium substituted hydroxyapatite nanocrystals

In the present study, synthesis of monophasic Sr-HAp nanocrystals using a single step Solution Combustion Synthesis (SCS) process is reported. Effects of important process parameters on the formation of monophasic Sr-HAp nanocrystals were investigated to optimize the process for cost effective synthesis. X-ray Diffraction (XRD) and transmission electron microscopy (TEM) studies of as-synthesized powders (Sr ranging from 0 to 30%) revealed close packed hexagonal structure, with individual primary particle sizes ranging from 15 to 70nm length and 5±1nm diameter. Scanning Electron Microscopy (SEM) studies showed that Sr substitution in HAp increased the aspect (L/D) ratio of primary nanorod and reduced the secondary agglomerate coarsening. Fourier Transform-Infrared (FTIR) and Energy Dispersive Spectroscopy (EDS) studies confirmed the presence of appropriate concentrations of phosphates and hydroxyl groups along with small amounts of carbonates in the as-synthesized Sr-HAp. Differential Scanning Calorimetry (DSC) studies up to 400°C and XRD patterns of powders calcined at 1100°C proved that Sr addition in HAp enhances the stability by suppressing the phase transformation during further consolidation. In effect, nano Sr-HAp powders synthesized using SCS process resembled the structural and chemical nature of bone mineral and could be used as a possible candidate material for hard tissue replacement and drug delivery systems.

β-Type Zr–Nb–Ti biomedical materials with high plasticity and low modulus for hard tissue replacements

In order to develop new biomedical materials for hard tissue replacements, Zr–20Nb–xTi (x=0, 3, 7, 11 and 15) alloys with required properties were designed and prepared by using the vacuum arc melting method for the first time. Phase analysis and microstructural observation showed that all the as cast samples consisted of equiaxed β-Zr phase. The mechanical properties and fracture behaviors of the Zr–20Nb–xTi alloys have been analyzed. It is found that these alloys exhibit high plasticity, moderate compressive strength (1044–1325MPa) and yield stress (854–1080MPa), high elastic energy (12–20MJ/m3) and low Young's modulus (28–31GPa). This good combination of mechanical properties makes them potential biomedical materials for hard tissue replacement.

Development of a surface roughness model in end milling of nHAP using PCD insert

Similar physical properties with human bone make hydroxyapatite (HAP) a suitable bioceramic material for hard tissue replacement in the fields of orthopedics and dentistry. Before being used in the human body, HAP needs to be machined to the required shape and dimensions with minimal surface roughness. This study investigates the machinability of fully dense nano-crystalline hydroxyapatite (nHAP) bioceramic in milling operations using polycrystalline diamond insert (PCD). The focus is on the effects of various machining conditions on surface roughness. The first order and second order surface roughness models for the end milling of nHAP is developed using response surface methodology (RSM), relating surface roughness to the cutting parameters: cutting speed, feed, and depth of cut. Based on the experimental results, it is found that cutting parameters have significant effect on surface roughness. For the ranges used in this study, a low feed (0.002mm/rev) results in a smooth surface, and the middle depth of cut (0.5mm) should be avoided. The final results show that the combination of cutting speed v=92m/min, feed f=0.002mm/rev, and depth of cut ap=1.6mm gives a minimum surface roughness of 0.64μm. In addition, it is proven that milling of nHAP is feasible for the fabrication of implants.

Structure and mechanical performance of in situ synthesized hydroxyapatite/polyetheretherketone nanocomposite materials

Nano-hydroxyapatite (HA) particles were prepared by a sol–gel method and polyetheretherketone (PEEK) composite materials containing a various amount of lab-prepared HA fillers had been successfully synthesized via an in situ synthesis process. The materials structure was characterized by infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy and the mechanical performance was investigated by a tensile strength test. The tensile strength of HA/PEEK composites reaches an optimal 108 MPa at 6.1% HA content. The composites with HA content below 17.4% exhibit a plastic break mode, while a brittle break mode above 17.4%. The results exhibit that the strong bonding between hydroxyapatite fillers and PEEK matrix has been achieved. And it was proved that this strong bonding may be mainly attributed to the physical factors, such as mechanical interlock between PEEK molecules and HA surface. The study clearly demonstrates that in situ synthesized HA/PEEK composite materials have the potential for use as an alternative material for hard tissue replacement.

Multifunctionality of Perovskites BaTiO3 and CaTiO3 in a Composite with Hydroxyapatite as Orthopedic Implant Materials

In the present article, the multifunctional behavior of perovskites BaTiO3 and CaTiO3 has been studied for their potential orthopedic applications. The biocompatibility and electrical conductivity properties of HA-40 wt%BaTiO3 (25.9 vol% BaTiO3) and HA-40 wt% CaTiO3 (35.3 wt% CaTiO3) composites were investigated to verify its suitability as hard tissue replacement materials. L929 mouse fibroblasts and Human osteoblasts (SaOS2) cells were used to study the cell adhesion and proliferation behavior on the composite surfaces. It has been observed that the developed composites are biocompatible and the conductivity and dielectric behavior of the composite is comparable to dry human bone.

Effect of water aging on the apatite formation of a low-modulus Ti–7.5Mo alloy treated with aqueous NaOH

The objective of this experiment was to develop biomimetic calcium phosphate coatings on low-modulus Ti–7.5Mo substrates treated with NaOH aqueous solutions and subsequent water aging before soaking them in simulated body fluid (SBF). Specimens of commercially pure titanium (c.p. Ti) and Ti–7.5Mo were initially treated with 5 M NaOH at 60 °C for 24 h, resulting in the formation of a porous network structure composed of sodium titanate (Na2Ti5O11). Afterward, the specimens were aged in distilled water at 80 °C for 12, 24, or 48 h, and subsequently immersed in 1.5SBF at 37 °C for either 1 or 13 days. The calcium phosphate-forming abilities of the c.p. Ti and Ti–7.5Mo achieved by a single NaOH treatment were low, but were significantly increased by the water aging. The amount of calcium phosphate deposited on the Ti–7.5Mo after NaOH treatment and subsequent water aging for 12 or 24 h was much greater than other conditions. The calcium phosphate-coated Ti–7.5Mo has strong potential as an artificial bone substitute or in other hard tissue-replacement materials with heavy load-bearing requirements due to a favorable combination of bioactivity, low elastic modulus, and low processing costs.

Formation of calcium phosphates on low-modulus Ti–7.5Mo alloy by acid and alkali treatments

This study investigated the hydroxyapatite (HA) coating on metal implants in order to enhance their bioactive properties. In this study, HA coatings were formed on the surfaces of commercially pure titanium (c.p. Ti) and Ti–7.5Mo which were acid-etched and subsequently alkali-treated before samples were soaked in simulated body fluid (SBF). Specimens of c.p. Ti and Ti–7.5Mo were etched in either H3PO4 or HCl, and subsequently treated in NaOH. The surfaces of acid-etched c.p. Ti showed a porous structure, whereas those of acid-etched Ti–7.5Mo showed some grinding marks, but no porosity. After subsequent alkali treatment in NaOH, the surfaces of both the c.p. Ti and Ti–7.5Mo substrates exhibited microporous network structures. The specimens were then immersed in SBF at 37 °C for 28 days. Apatite began to deposit on acid-etched and NaOH-treated Ti–7.5Mo within 1 day after immersion in the SBF. After 28 days of immersion in the SBF, a dense and uniform layer was produced on the surfaces of all samples. The HA formation rate was the highest for HCl and NaOH-pretreated samples, and the results of EDS and XRD showed that much more intensive peaks of HA appear on the specimens of HCl and NaOH-treated Ti–7.5Mo than on any other sample. Thus, this method of apatite coating Ti–7.5Mo appears to be promising for artificial bone substitutes or other hard tissue replacement materials with heavy load-bearing applications due to their desirable combination of bioactivity, low elastic modulus, and low processing costs.

Surface modification of a low-modulus Ti–7.5Mo alloy treated with aqueous NaOH

A new α″ phase Ti–7.5Mo alloy with a lower elastic modulus had been developed for biomedical applications. This Ti–7.5Mo alloy also exhibits an even better strength/modulus combination and excellent corrosion resistance. However, titanium alloys doesn't bond directly to living bone. In the present study, bioactive coatings on commercially pure titanium (c.p. Ti) and Ti–7.5Mo were prepared by a simple chemical technique. Specimens of c.p. Ti and Ti–7.5Mo were initially immersed in a 5, 10 or 15 M NaOH solution at 60 °C for 24 h, resulting in the formation of a porous network structure composed of sodium titanate (Na 2Ti 5O 11). X-ray diffraction (XRD) results indicated that the intensity of the sodium titanate peak increased with an increasing NaOH concentration. The specimens were then immersed in simulated body fluid (SBF) at 37 °C for 3, 7 and 28 days, respectively. The apatite-forming ability of alkali-treated Ti–7.5Mo was higher than that of alkali-treated c.p. Ti on exposure to 5, 10 or 15 M NaOH aqueous solutions. The XRD results also indicated that the deposited amounts of calcium phosphate were much greater for alkali-treated Ti–7.5Mo than for alkali-treated c.p. Ti. The average thickness of calcium phosphate layer of 15 M NaOH-treated Ti–7.5Mo after immersion in SBF for 28 days was about 15 μm. The alkali treatment of Ti–7.5Mo by NaOH aqueous solutions can be anticipated to be promising artificial bone substitutes or other hard tissue replacement materials for heavy load-bearing applications due to their wonderful combination of bioactivity, low elastic modulus and low processing costs.