Papers by Keyword: Porous Titanium

Abstract: As a new type of material combined with special structure and function, the porous titanium was prepared through vacuum distillation and sintering process, by which the titanium powder was used as raw material, magnesium particles and its powder as space holder, anhydrous ethanol as binder. The porosity of porous titanium obtained by this method is between 35% and 75% and its opening ratio runs up to 95%. The experimental result showed that magnesium existed in the compacted precursor was evaporated rapidly in vacuum when temperature reached 750°C and removed completely within 20 minutes. The suitable sintering temperature was between 1050°C and 1250°C, but the porosity of porous titanium decreased from 76.2% to 61.3% with temperature elevated. The precursor uniformity was improved by addition of anhydrous ethanol and its formability and density was also done by addition of magnesium powder. The relative density of precursor increased from 82% to 98% with magnesium powder volume fraction varied from 30 vol.% to 80 vol.%.

Abstract: Relationship between the macroscopic and local strains of porous metals is examined by microstructural observation. Open-cell porous titanium with 60% porosity was compressed up to 30% macroscopic strain at room temperature. Open-cell porous nickel with 95% porosity was compressed up to 40% macroscopic strain at room temperature. Local strains in cell walls of both porous titanium and nickel were evaluated by electron backscatter diffraction (EBSD). Absolute value of the local strain increased with increasing the macroscopic strain and it is smaller than that of macroscopic strain. In addition, the value of the local strain at the cell junctions was larger than that of the center of cell struts.

Abstract: Nowadays, the development of materials with gradient porosity is an important aim for many applications, especially in the field of bone tissue replacement. This research work shows the design and manufacture of a simple and economical device to process Ti cylinders with elongated and high interconnected porosity by freeze-casting techniques. The influence of the vessel material on the internal lamellar structure of the porous Ti samples is also studied. The device has been validated with: (i) a thermal gradient from-10 °C at the cold surface to 20 °C at the hot surface; and (ii) a cylindrical vessel with 12 mm diameter of alumina or Teflon. These working conditions have allowed maintaining the freezing conditions during the full process (alumina vessel: 30 minutes; Teflon vessel: 3 hours). After the solidification of the Ti aqueous suspension, the ice is sublimated (24 hours at-50 °C and 0.070 mbar). Then, the resulting powder is sintered (1150 °C for 5 h at high vacuum ~ 10^-5 mbar), obtaining the porous Ti sample with the final structural strength. Finally, a detailed study of the most relevant porosity features is performed: porosity ratio and interconnectivity degree by Archimedes’ method, and size and shape of the pores by image analysis at three different zones along the longitudinal cross section. The results indicate the viability of the device to enhance the directional freezing and thus, the elongated porosity. Teflon vessel present the best results, with an average porosity ratio and porosity size of 39.5 % and 123.3 μm, respectively. This suggests an optimal biomechanical and bifunctional balance of this porous material.

Abstract: Commercially pure titanium (cp Ti) is typically accepted as one of the best in vitro and in vivo bone replacement biomaterial, due to its excellent balance between biomechanical and biofunctional properties. In that context, the aim of this work is to prove the hypothesis of a simultaneous solution to certain specific limitations of cpTi, which can often compromise the reliability of implants: (i) stress-shielding phenomenon, and (ii) a deficient biointerface with bone, which reduces the osseointegration. Porous samples of cp Ti, grade IV, were obtained by space-holder technique (50 vol.% NH₄HCO₃, 800 MPa, at 1250 oC during 2h, under high vacuum), to produce a good balance between Young ́s Modulus and yield strength. Different types of porous samples were manufactured by considering different size particles ranges of NH₄HCO₃: 100-200μm, 250-355μm and 355-500μm. Afterwards, they were coated with a PEEK/45S5 bioactive glass composite by electrophoretic deposition, to be finally sintered at 350oC for 1h. The coatings homogeneity, infiltration efficiency, adhesion and cracking, were studied in order to establish correlations with processing conditions (time of deposition, applied voltage, composition, concentration and stability of the colloidal suspension). Detailed structural characterization of the coatings was performed (SEM and XRD), besides the contact angle and contact profilometry testing. Additional mechanical and chemical insights were achieved by evaluating both the tribo-mechanical (instrumented microindentation and micro-scratch testing) and electrochemical behaviors (potentiodynamic polarization and in vitro corrosion tests in SBF). All these results allowed us to determine the optimal balance of properties for a porous substrate (space holder of 250-355μm) with a coating obtained for 65 V, 2 min, 6 mm (distance between electrodes), 10 g/L bioactive glass and 20 g/l PEEK. The high adhesion estimated between the bioactive/biopolymer coatings and the porous titanium substrates (excellent infiltration) suggest that this new biocomposite is a good candidate for load-bearing applications.

Abstract: The paper gives a short review of P/M routes which were developed or adapted by the authors for the net-shape manufacturing of titanium implants. Special attention is paid to the production of highly porous bone implants, where the porosity is achieved by the application of temporary space holder particles, which are removed before or during sintering by decomposition or dissolution. In this case, shaping was done either by machining of powder compacts in the green and sintered state or by metal injection moulding (MIM). The challenges of these shaping technologies and current solutions are discussed. To complete the review, two promising new technologies for the net-shape production of highly porous titanium implants, the replica technique and additive manufacturing are briefly introduced.

Abstract: The manufacture of graded materials has gained an enormous interest during the last decade due to the diversity of industrial and biological materials systems that require or are actually designed to implement that criterion; those natural or artificial materials offer multiple possibilities of applications. In this work, a novel uniaxial and sequential compaction device has been successfully designed and fabricated, in order to obtain samples with three different layers; this new device is suitable for both conventional and non-conventional powder metallurgy (PM) techniques. In addition, this device allowed us to use different combinations of powders and space-holder particles, irrespective of their nature, sizes, morphologies and proportions. It has no restriction about applying different compaction pressures for every layer, which may result in increasing or decreasing porosity. This compaction device is especially powerful if the aim is obtaining samples with radial graded porosity for biomedical applications (replacement of cortical bone involved in different joints and dental restorations) and nuclear applications (mimicking burnt used nuclear fuel). Specifically in this work, different samples with radial graded porosity were fabricated and then microstructurally and mechanically characterized: i) Commercially pure titanium (CP Ti) samples, starting from blends CP Ti with 20 vol.%, 40 vol.% and 60 vol.% of Sodium Chloride (NaCl) as space holder, which were placed in core, intermediate and external layers, respectively; processing conditions were 800 MPa of compaction pressure and 1250 °C for 2h in high vacuum of sintering; and ii) CeO₂ samples, starting from blends CeO₂ with 0.5 vol.%, 3.0 vol.% and 7.5 vol.% of Ethylene Bis Stearamide (EBS) as space holder, which were placed in core, intermediate and external layers, respectively; processing conditions were 460 MPa in external layer and 700 MPa in core and intermediate layers of compaction pressure, and 1700 °C during 4h in static air of sintering. This new device has proved to have unique advantages for solving problems of structural integrity in conventional PM manufacturing in a simple, economic and reproducible way.

Abstract: Porous titanium samples of cp Ti grade IV were obtained by space-holder technique (50%vol of NH₄HCO₃, 800 MPa, 1250 oC during 2h in high vacuum), producing a good balance between stiffness and mechanical strength. The samples were coated with chitosan/45S5 bioactive glass composite by electrophoretic deposition. Homogeneity, infiltration efficiency, and coatings integrity (cracking and adhesion) were evaluated in order to establish correlations with processing parameters. SEM, FTIR, and contact profilometry were performed for detailed characterization of the coatings; and micro-mechanical properties (P-h curves and scratch testing) were set-up as well. Optimum EPD parameters were 25V, 7 min and suspension containing 0.5 g/L chitosan and 1.5 g/L BG a titanium structure with pore sizes greater than 200 μm are required.

Abstract: This paper investigates the properties of Ti scaffolds with a porosity of 73%. In the processing route, a new space holder material was applied - saccharose, commonly known as table sugar. Porous Ti was made by the dissolution of sugar crystals from the Ti-sugar green compact and final sintering of the remaining Ti scaffold. The sintered scaffolds showed uniform pore distribution. The pores had polyhedral shape and their dimensions reached 1 mm. The scaffolds were made and investigated with respect to possible medical applications. After all processing stages, the surface was oxidized and showed average wettability with the lowest wetting angle of 81.5^o, which was strongly correlated with the condition of the surface. The chemical etching in an HF solution resulted in a strong wettability improvement. Due to very high porosity, the compression strength (1.48 MPa) and Young’s modulus (33.7 MPa) of the scaffolds were relatively low.

Abstract: In this article, the layered deposition method is adopted to prepare the collagen/hydroxyapatite (COL/HA) composite coating. The morphology and elements of the COL/HA composite coating are observed using a scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS), the optical density (O.D.) values are obtained by MTT assay to assess the cellular viabilityof composite coating. The experimental results showed that the addition of collagen not only improve the bonding strength of composite coating and porous titanium substrate, but also combine the osteoconduction of inorganic coating HA and the osteoinduction of organic coating COL, effectively enhance the cellular adhesion, proliferation and differentiation. The cellular viability cultured in COL/HA composite coating is much higher than the pure HA modified coating.

Abstract: The role of pores structure in porous titanium with helical pores was studied. The results showed that porosity of porous titanium depends on diameter of titanium fiber (d₁), screw diameter (d₂) and screw pitch (d₃). With the increase of titanium fiber diameter, the decrease of screw diameter and screw pitch, the porosity of porous titanium decreases. Compressive yield strength and Young’s modulus increase with the decrease of porosity, and the final functional expression of compressive yield strength and Young’s modulus depending on porosity was given.