Porous Titanium Samples Research Articles

Three-dimensional real structure-based finite element analysis of mechanical behavior for porous titanium manufactured by a space holder method

In this study, porous titanium samples were manufactured by a space holder method with sodium chloride. Each porous titanium sample contained two types of pores based on their sizes: macropores and micropores. Macropores were those emerged from removing the space holder, whereas micropores were voids created during powder compaction. The porous titanium exhibited low elastic modulus close to that of the human bone. Computed tomography (CT) was employed to examine the porous structure of the Ti samples. The CT results were then used in finite element simulations for analysis of the mechanical behavior of the porous titanium. The CT-based finite element model was found to give better results compared to the unit-cell finite element model in terms of agreement with the experimental data. The CT model combined with the strain hardening behavior of Ti having micropores prescribed to the matrix allowed for accurate predictions of elastic modulus, yield strength, and flow stress. These results signify the importance of taking into account pores at different scales as well as their morphology and distribution at least at macroscale.

Titanium Substrate Surfaces Coated with Hydroxyapatite by Magnetron Sputtering

The deposition of hydroxyapatite coatings on titanium via sputtering techniques has been quite studied on commercial dense substrates, for use as a biomaterial. In this work, porous titanium samples produced by powder metallurgy and commercially dense titanium sheet, used as control, were used as substrates. The coatings were deposited by radio frequency magnetron sputtering using a hydroxyapatite target in argon atmosphere with different deposition times. Samples characterization was performed by Optical Microscopy, Scanning Electron Microscopy/Energy Dispersive Spectroscopy and low-angle X-ray Diffraction. Hydroxyapatite coating depositions were obtained on both titanium substrates. The results indicated the potential of this methodology for titanium substrates with homogeneous hydroxyapatite coatings.

Structure, composition and morphology of bioactive titanate layer on porous titanium surfaces

A bioactive coating was produced on pore surfaces of porous titanium samples by an amendatory alkali-heat treatment method. Porous titanium was prepared by powder metallurgy and its porosity and average size were 45% and 135 μm, respectively. Coating morphology, coating structure and phase constituents were examined by SEM, XPS and XRD. It was found that a micro-network structure with sizes of <200 nm mainly composed of bioactive sodium titanate and rutile phases of TiO2 covered the interior and exterior of porous titanium cells, and redundant Ca ion was detected in the titanate layer. The concentration distribution of Ti, O, Ca and Na in the coating showed a compositional gradient from the intermediate layer toward the outer surface. These compositional gradients indicate that the coating bonded to Ti substrate without a distinct interface. After immersion into the SBF solution for 3 days, a bone-like carbonate–hydroxylapatite showing a good biocompatibility was detected on the coating surface. And the redundant Ca advanced the bioactivity of the coating. Thus, the present modification is expected to allow the use of the bioactive porous titanium as artificial bones even under load-bearing conditions.

Space holder 방법으로 제조된 다공질 타이타늄의 기계적 성질에 대한 Computed-Tomography를 이용한 유한요소해석

In this study, porous titanium samples were manufactured by space holder methods using two kinds of urea and sodium chloride space holders. Three-dimensional pore structures were obtained by a computed-tomography (CT) technique and utilized for finite element analysis in order to investigate the mechanical properties. The CT-based finite element analyses were in better agreement with the experimental results than unit cell model-based analyses. Both the experimental and CT-based results showed the same tendency that the elastic modulus decreased with increasing the porosities. The total porosity of the bulk body plays a key role in determining the elastic modulus of porous materials.

Effects of sintering temperature on morphology and mechanical characteristics of 3D printed porous titanium used as dental implant

Porous titanium samples were manufactured using the 3D printing and sintering method in order to determine the effects of final sintering temperature on morphology and mechanical properties. Cylindrical samples were printed and split into groups according to a final sintering temperature (FST). Irregular geometry samples were also printed and split into groups according to their FST. The cylindrical samples were used to determine part shrinkage, in compressive tests to provide stress-strain data, in microCT scans to provide internal morphology data and for optical microscopy to determine surface morphology. All of the samples were used in microhardness testing to establish the hardness. Below 1100°C FST, shrinkage was in the region of 20% but increased to approximately 30% by a FST of 1300°C. Porosity varied from a maximum of approximately 65% at the surface to the region of 30% internally. Between 97 and 99% of the internal porosity is interconnected. Average pore size varied between 24μm at the surface and 19μm internally. Sample hardness increased to in excess of 300HV0.05 with increasing FST while samples with an FST of below 1250°C produced an elastic–brittle stress/strain curve and samples above this displayed elastic–plastic behaviour. Yield strength increased significantly through the range of sintering temperatures while the Young's modulus remained fairly consistent.

Mechanical Properties and Bioactive Surface Modification via Alkali-Heat Treatment of Porous Titanium for Biomedical Applications

Porous titanium with relative density from 0.4 to 0.64 was prepared by powder metallurgy. The porous structures were examined by scanning electron microscopy and phase constituents were analysed by X-ray diffraction. Mechanical properties of the porous titanium were investigated using a compressive test. To enhance the bioactivity of the alloy surface, alkali-heat treatment was used to modify the surface. Results indicate that the elastic modulus and plateau stress of the porous titanium samples both as-sintered and alkali and heat treatment decrease with decreasing relative density. And the relationship between relative yield stress and elastic modulus with relative density of porous titanium after alkali and heat treatment are agreement with that of as-sintered porous titanium. After alkali-heat treatment, a bioactive Na2Ti5O11 layer formed on the surface of the pre-treated porous titanium. A reduction in the number and severity of this bioactive deposition was observed with the decrease in relative density of porous titanium because of the increasing surface area. In a word, The mechanical properties of the porous titanium can be tailored to match those of human bone, therefore, these bioactive porous titanium have the potential to be a bioactive implant material.

Study of Sol-Gel/Powder Metallurgy Technique for Processing Titanium Parts

The powder metallurgy processing of titanium devices for biomedical applications has complex steps. In order to introduce a new processing route, this work studied a sol-gel technique combined with powder metallurgy for producing porous titanium samples. The process involves the mixture of titanium powders with sodium alginate suspension, which undergoes reticulation by calcium salt solution contact, forming a titanium/calcium alginate hydrogel in granule shape. Later, the hydrogel granules were dried and sintered in a high vacuum furnace for titanium particles consolidation and calcium alginate removal. The samples characterization was performed by scanning electron microscopy, optical microscopy, metallographic analysis, semi-quantitative X-ray fluorescence spectroscopy and X-ray diffraction. The results showed that the methodology used is adequate for producing porous titanium parts, since the samples presented no contamination, a uniform shape, particle consolidation and interconnected porosity. The research continues aiming to obtain samples with different bulk morphology, like, discs or bars for surgical implant applications.

Comparison of Porosity Measurement Techniques for Porous Titanium Scaffolds Evaluation

Porous titanium has been used for grafts and implant coatings as it allows the mechanical interlocking of the pores and bone. Evaluation of porous scaffolds for bone regeneration is essential for their manufacture. Porosity, pore size, pore shape and pore homogeneity are parameters that influence strongly the mechanical strength and biological functionality. In this study, porous titanium samples were manufactured by powder metallurgy by using pure titanium powders mixed with a pore former. The quantification of the porosity parameters was assessed in this work by geometric method and gamma-ray transmission, the non-destructive techniques and metallographic images processing, a destructive technique. Qualitative evaluation of pore morphology and surface topography were performed by scanning electron microscopy and optical microscopy. The results obtained and the effectiveness of the techniques used were compared in order to select those most suitable for characterization of porous titanium scaffolds.

Highly porous titanium scaffolds for orthopaedic applications

For many years, the solid metals and their alloys have been widely used for fabrication of the implants replacing hard human tissues or their functions. To improve fixation of solid implants to the surrounding bone tissues, the materials with porous structures have been introduced. By tissue ingrowing into a porous structure of metallic implant, the bonding between the implant and the bone has been obtained. Substantial pore interconnectivity, in metallic implants, allows extensive body fluid transport through the porous implant. This can provoke bone tissue ingrowth, consequently, leading to the development of highly porous metallic implants, which could be used as scaffolds in bone tissue engineering. The goal of this study was to develop and then investigate properties of highly porous titanium structures received from powder metallurgy process. The properties of porous titanium samples, such as microstructure, porosity, Young's modulus, strength, together with permeability and corrosion resistance were investigated. Porous titanium scaffolds with nonhomogeneous distribution of interconnected pores with pore size in the range up to 600 μm in diameter and a total porosity in the range up to 75% were developed. The relatively high permeability was observed for samples with highest values of porosity. Comparing to cast titanium, the porous titanium was low resistant to corrosion. The mechanical parameters of the investigated samples were similar to those for cancellous bone. The development of high-porous titanium material shows high potential to be modern material for creating a 3D structure for bone regeneration and implant fixation.

Porous titanium for biomedical applications: An experimental study on rabbits

The aim of this study was to carry out an in vivo assessment of bone ingrowth in two different types of porous titanium -the first being completely porous, and the second with a porous surface and dense nucleus, manufactured by powder metallurgy- and to evaluate their mechanical properties. Ten scaffolds from each group were submitted to metallographic analysis and compression tests. Next, two scaffolds of each type were inserted into 14 rabbits, which were sacrificed 8 weeks after surgery. The samples were submitted for histological examination. Metallographic analysis revealed interconnected pores, and the average interconnected pore diameter was about 360 mm, with 36% total porosity. The totally porous titanium samples and the titanium samples with porous surface and dense nucleus showed an average compressive strength of 16.19 MPa and 69.27 MPa, respectively. After 8 weeks, the animals showed bone ingrowth, even into the most internal pores. The pore morphology was effective in permitting bone ingrowth in both groups. Titanium scaffolds with a porous surface and dense nucleus showed the best mechanical properties and most adequate interface.

Fabrication of biomimetic apatite coating on porous titanium and their osteointegration in femurs of dogs

In the present study, porous titanium with three-dimensionally interconnected pores and a porosity of 74.3 ± 3.8% was made by a slurry foaming method. After being pretreated with acid–alkali or alkali–heat method and then immersed into a supersaturated calcium phosphate solution to form a biomimetic apatite coating on the surface, the porous titanium samples were hemi-transcortically implanted into the femurs of dogs for two months. The experimental results showed that the surface apatite coatings deposited on acid–alkali and alkali–heat treated porous titanium had different morphology and thickness. However, histological and histomorphometric analysis confirmed that both types of apatite-coated implants had excellent osteointegration with host bone, and their osteoconduction had also no significant difference. This study proved that both acid–alkali and alkali–heat treatments might have the same efficiency in activating porous titanium, and the apatite-coated porous titanium could be potential to be used in clinic.

Mechanical properties of powder titanium at different production stages. III. Contact formation in powder titanium based on examination of mechanical properties in sintering

The mechanical properties of porous titanium samples in vacuum sintering are analyzed. The effect of porosity and initial powder size on conductivity, static and dynamic elastic moduli, ultimate strength, and strain to failure is examined for sintering temperatures between 300 and 1200°C. The quality of contact in materials in different structural states is subjected to a comparative analysis.

Characterization of CaP Coating Deposited on Porous Titanium

Synthetic Hydroxyapatite (HA) has been used as coating in order to enhance biocompatibility of titanium implants. Osseointegration at the implant-bone interface can be positively affected by the presence of HA coating and other biocompatible calcium phosphates (CaP) deposited on titanium implants, due to the high biocompatibility of these bioceramics. The biomimetic process is based on the nucleation and growth of a bioceramic film onto a substrate immersed in a body fluid solution (SBF) and it can be applied to deposit CaP coatings onto metallic substrates. The present work presents results on the characterization by SEM of CaP coating deposited on porous titanium samples by a biomimetic process.

Porosity Characterization of Sintered Titanium Scaffolds for Surgical Implants

Porosity and pore size are critical features for biomaterial scaffolds as they play an essential role in bone formation and bone ingrowth in vivo. Therefore, techniques for scaffolds evaluation are of great importance for their design and processing. Porous titanium has been used for grafts and implant coatings as it allows the mechanical interlocking of the pores and bone. In this study, porous titanium samples were manufactured by powder metallurgy. The porosity quantification was assessed by optical quantitative metallographic analysis, and non-destructive gamma-ray transmission and X-ray microtomography techniques, in order to compare their efficacy for porosity evaluation. Pore morphology and surface topography were characterized via scanning electron microscopy. These techniques have demonstrated to be suitable for titanium scaffolds evaluation, and micro-CT was the one that allowed the three-dimensional porosity assessment.

Evaluation of Biomimetic Solution for Coating Powder Metallurgy Porous Titanium Samples

In order to improve implant-bone attachment, porous titanium has been used to achieve the ingrowth of bone tissue within the porous structure. Although this biomaterial has shown efficient bone adhesion for orthopedic and dental implants, the ideal surface must have chemical bonds at the implant-bone interface. In this work, samples of pure porous titanium were produced by powder metallurgy technique and submitted to biomimetic process in order to evaluate the material’s bioactivity and to enhance its osteoconductivity. The samples were immersed in modified simulated body fluid (mSBF) which induces the nucleation and growth of a calcium phosphate bioactive film and a chemical bond with titanium. SEM, EDX and FTIR analyses showed that a calcium phosphate deposition occurred without the need of pre-treatments to increase the surface bioactivity. As a result, this research revealed the potential for obtaining a bonelike apatite film on this porous titanium by biomimetic method.

Corrosion Resistance Evaluation of Porous Titanium with Biomimetic Coatings

In this work, porous titanium samples processed by powder metallurgy and coated with biomimetic coatings, obtained during different periods of immersion in a simulated body fluid (SBF), were tested for corrosion resistance in a phosphate buffer solution (PBS). Uncoated samples were also tested for comparison. The corrosion resistance of both types of titanium samples was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarisation curves. The electrochemical results indicated the formation of a surface film on the porous Ti samples with immersion in the SBF solution and this biomimetic film increased their corrosion resistance. This film helps osteointegration besides increasing corrosion resistance.

Acoustical and Poromechanical Characterisation of Titanium Scaffolds for Biomedical Applications

Abstract: Biocompatible materials are designed so as to mimic biological materials such as bone as closely as possible. As regards the mechanical aspect of bone replacement materials, a certain stiffness and strength are mandatory to effectively carry the loads imposed on the skeleton. In this paper, porous titanium with different porosities, produced on the basis of metal powder and space holder components, is investigated as bone replacement material. For the determination of mechanical properties, i.e. strength of dense and porous titanium samples, two kinds of experiments were performed – uniaxial and triaxial tests. The triaxial tests were of poromechanical nature, i.e. oil was employed to induce the same pressure both at the lateral surfaces of the cylindrical samples and inside the pores. The stiffness properties were revealed by acoustic (ultrasonic) tests. Different frequencies give access to different stiffness components (stiffness tensor components related to high‐frequency‐induced bulk waves versus Young's moduli related to low‐frequency‐induced bar waves), at different observation scales; namely, the observation scale the dense titanium with around 100 μm characteristic length (characterised through the high frequencies) versus that of the porous material with a few millimetres of characteristic length (characterised through the low frequencies). Finally, the experimental results were used to develop and validate a poro‐micromechanical model for porous titanium, which quantifies material stiffness and strength from its porosity and (in the case of the aforementioned triaxial tests) its pore pressurisation state.

Study of Calcium Phosphate Deposition on Porous Titanium Samples

Surgical implant coatings and grafts for tissue replacement have been made by porous surface materials to improve the implant to bone attachment. In this work, porous titanium samples were produced via powder metallurgy techniques and submitted to the biomimetic process in order to enhance its osteoconductivity. This process allows a nucleation and growth of a calcium phosphate film which makes a chemical bond with titanium. Therefore, it avoids the looseness of this film from substrate. The samples were chemically treated, heat treated at different temperatures and soaked into a modified body fluid solution (mSBF) during periods of 2 and 7 days. Samples with and without pretreatments and not soaked in mSBF were used as controls. SEM and EDX analyses detected a calcium phosphate phase on the sample surfaces treated at 400°C and 600°C and soaked in mSBF for 2 and 7 days. The results demonstrated the potential of the methodology applied for obtaining a bonelike apatite film on porous titanium samples processed by powder metallurgy.

Effects of Pore Morphology and Bone Ingrowth on Mechanical Properties of Microporous Titanium as an Orthopaedic Implant Material

Successful bone formation which leads to functional osseointegration is determined by the local mechanical environment around bone-interfacing implants. In this work, a novel porous titanium material is developed and tested and then impact of porosity on mechanical properties as a function of bone ingrowth is studied numerically. A superplastic foaming technique is used to produce CP-Ti material with rounded, interconnected pores of 50% porosity; the pore size and morphology is particularly suitable for bone ingrowth. In order to understand the structure-property relations for this new material, a numerical simulation is performed to study the effect of the porous microstructure and bone ingrowth on the mechanical properties. Using ABAQUS, we create two-dimensional representative microstructures for fully porous samples, as well as samples with partial and full bone ingrowth. We then use the finite element method to predict the macroscopic mechanical properties of the foam, e.g., overall Young's modulus and yield stress, as well as the local stress and strain pattern of both the titanium foam and bone inclusions. The strain-stress curve, stress concentrations and stress shielding caused by the bone-implant modulus mismatch are examined for different microstructures in both elastic and plastic region. The results are compared with experimental data from the porous titanium samples. Based on the finite element predictions, bone ingrowth is predicted to dramatically reduce stress concentrations around the pores. It is shown that the morphology of the implants will influence both macroscopic properties (such as modulus) and localized behavior (such as stress concentrations). Therefore, these studies provide a methodology for the optimal design of porous titanium as an implant material.