Hydroxyapatite/titania sol-gel coatings on titanium-zirconium alloy for biomedical applications

A simple sol–gel method was developed for hydroxyapatite/titania (HA/TiO2) coatings on non-toxic titanium–zirconium (TiZr) alloy for biomedical applications. The HA/TiO2-coated TiZr alloy displayed excellent bioactivity when soaked in a simulated body fluid (SBF) for an appropriate period. Differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy-energy dispersive spectrometry were used to characterize the phase transformations and the surface structures and to assess the in vitro tests. The HA/TiO2 layers were spin-coated on the surface of TiZr alloy at a speed of 3000 rpm for 15 s, followed by a heat treatment at 600 °C for 20 min in an argon atmosphere sequentially. The TiO2 layer exhibited a cracked surface and an anatase structure and the HA layer displayed a uniform dense structure. Both the TiO2 and HA layers were 25 μm thick, and the total thickness of the HA/TiO2 coatings was 50 μm. The TiZr alloy after the above HA/TiO2 coatings displayed excellent bone-like apatite-forming ability when soaked in SBF and can be anticipated to be a promising load-bearing implant material.

Porous titanium with porosity gradients for biomedical applications

Highly porous titanium and titanium alloys with an open cell structure are promising implant materials due to their low elastic modulus, excellent bioactivity, biocompatibility and the ability for bone regeneration. However, the mechanical strength of the porous titanium decreases dramatically with increasing porosity, which is a prerequisite for the ingrowth of new bone tissues and vascularization. In the present study, porous titanium with porosity gradients, i.e. solid core with highly porous outer shell was successfully fabricated using a powder metallurgy approach. Satisfactory mechanical properties derived from the solid core and osseointegration capacity derived from the outer shell can be achieved simultaneously through the design of the porosity gradients of the porous titanium. The outer shell of porous titanium exhibited a porous architecture very close to
that of natural bone, i.e. a porosity of 70% and pore size distribution in the range of 200 - 500 μm. The peak stress and the elastic modulus of the porous titanium with a porosity gradient (an overall porosity 63%) under compression were approximately 152 MPa and 4 GPa, respectively. These
properties are very close to those of natural bone. For comparison, porous titanium with a uniform porosity of 63% was also prepared and haracterised in the present study. The peak stress and the elastic modulus were 109 MPa and 4 GPa, respectively. The topography of the porous titanium
affected the mechanical properties significantly.

Preparation and characterisation of new titanium based alloys for orthopaedic and dental applications

Various types of titanium alloys with high strength and low elastic modulus and, at the same time, vanadium and aluminium free have been developed as surgical biomaterials in recent years. Moreover, porous metals are promising hard tissue implants in orthopaedic and dentistry, where they mimic the porous structure and the low elastic modulus of natural bone. In the present study, new biocompatible Ti-based alloy foams with approximate relative densities of 0.4, in which Sn and Nb were added as alloying metals, were synthesised through powder metallurgy method.
The new alloys were prepared by mechanical alloying and subsequently sintered at high temperature using a vacuum furnace. The characteristics and the processability of the ball milled powders and the new porous titanium-based alloys were characterised by X-ray diffraction, optical
microscopy and scanning electron microscopy .The mechanical properties of the new titanium alloys were examined by Vickers microhardness measurements and compression testing.

Processing and mechanical properties of porous titanium-niobium shape memory alloy for biomedical applications

Ti-26 at.%Nb (hereafter Ti-26Nb) alloy foams were fabricated by space-holder sintering process. The porous structures of the foams were characterized by scanning electron microscopy (SEM). The mechanical properties of the Ti-26Nb foam samples were investigated using compressive test. Results indicate that mechanical properties of Ti-26Nb foam samples are influenced by foam porosity. The plateau stresses and elastic moduli of the foams under compression decrease with the increase of their porosities. The plateau stresses and elastic moduli are measured to be from 10~200 MPa and 0.4~5.0 GPa for the Ti-26Nb foam samples with porosities ranged from 80~50 %, respectively.

Sol-gel derived hydroxyapatite/titania biocoatings on titanium substrate

A simple sol–gel method was successfully developed for a hydroxyapatite (HA)/TiO₂ double layer deposition on a pure titanium substrate. Phase formation, surface morphology, and interfacial microstructure were investigated by differential scanning calorimetry analysis (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The TiO₂ layer was coated by a spin coating method at a speed of 1500 rpm for 15 s, followed by a heat treatment at 560 °C for 20 min. The HA film was subsequently spin coated on the outer surface at the same speed and then heat-treated at difference temperatures. Results indicated that the HA phase began to crystallize after a heat treatment at 580 °C; and the crystallinity increased obviously at a temperature of 780 °C. The HA film showed a porous structure and a thickness of 5–7 μm after the heat treatment at 780 °C. SEM observations revealed no delamination and crack at the interfaces of HA/TiO₂ and TiO₂/Ti. The HA film with a porous structure is expected to be more susceptible to the natural remodeling processes when it is implanted in a living body.

Cracking and blowout in an aluminium high-pressure die casting die

Die cracking and metal blowout have been identified as problems in production of the structural sump, a high pressure die cast aluminium part, at Ford's Geelong manufacturing plant. Visual inspection, thermography and strain measurements have been performed and results are consistent with the view that cracking and blowout are caused by excessive stresses and deflections, respectively, generated by bending of the sliding cores. Models are being developed for finite element simulation of the stresses and deflections in the die during production, with a view to eliminating the aforementioned problems.

Squeeze pin implementation in a high pressure die casting

This paper discusses the implementation of hydraulically operated squeeze pins to reduce porosity formation in cast aluminium bearing caps. Two complete sets are cast in an eight-cavity die with a 2000t cold chamber high pressure die casting machine. The initial die configuration used a sliding core assembly with stationary pins to core a through hole in a thick section of the front cam caps. This configuration resulted in high post machining scrap rates, primarily due to porosity associated with solidification shrinkage. Replacement of the sliding core assembly with a squeeze pin unit substantially reduced shrinkage porosity in the critical region, with consequent reductions in the scrap rate. The squeeze pins are actuated 1.5s after the piston reaches the high shot changeover position, but can be successfully engaged between I and 3.5 seconds after high shot changeover. Density measurements and visual inspection confirmed the substantial improvement in porosity levels in the critical region of the castings.

Integrated optimization system for high pressure die casting processes

High pressure die casting (HPDC) is a versatile process for producing engineered metal parts by forcing molten metal under high pressure into reusable steel dies. However there are a large number of attributes involved which contribute to the complexity of the process. A novel integrated approach is developed to optimize the high pressure die casting processes. The die temperature profiles will be studied with infrared thermograph technology and the internal cooling system will be optimized to provide even cooling to the components and the die. The heat stored in the die and the components is studied with image processing. Based on the geometrical profile of the components, cooling channels can be redesigned to improve the cooling efficiency while the cooling time is reduced. This will not only significantly improve the quality of the castings but also improve the productivity of the process.

A life cycle inventory of aluminium die casting

As part of an ongoing project, a life cycle inventory (LCI) of aluminium high pressure die casting (HPDC) has been collected. This has been conducted from the view of an individual product and also the entire process. The objective of the study was to analyse the process and suggest changes to reduce environmental impacts. One modem aluminium high pressure die casting plant located in Victoria, Australia was evaluated and modelled. Site specific data on energy and materials was gathered and the process was modelled using a typical automotive component. The paper also presents our experience and methodology used in this inventory data collection process from the real industry for LCA purposes. The inventory data collected itself reveals that the HPDC process is energy intensive and as such the major emissions were from the use of natural gas fired furnaces and from the brown coal derived electricity. It is also found the large environmental benefits of using secondary aluminium over primary aluminium in the HPDC process. A detailed LCA is being cal1ied out based on the inventory obtained.

Apatite-inducing ability of titanium oxide layer on titanium surface : the effect of surface energy

In the present study, pure titanium (Ti) plates were firstly treated to form various types of oxide layers on the surface and then were immersed into simulated body fluid (SBF) to evaluate the apatite-forming ability. The surface morphology and roughness of the different oxide layers were measured by atomic force microscopy (AFM), and the surface energies were determined based on the Owens–Wendt (OW) methods. It was found that Ti samples after alkali heat (AH) treatment achieved the best apatite formation after soaking in SBF for three weeks, compared with those without treatment, thermal or H₂O₂ oxidation. Furthermore, contact angle measurement revealed that the oxide layer on the alkali heat treated Ti samples possessed the highest surface energy. The results indicate that the apatite-inducing ability of a titanium oxide layer links to its surface energy. Apatite nucleation is easier on a surface with a higher surface energy.

Simulation of three-point bending test of titanium foam for biomedical applications

Using Titanium (Ti) foam as an implant material is a new approach for biomedical applications and it is important to understand the mechanical behaviors of this new foam material. In the present study, the bending of the Ti foam has been simulated and compared against recently published data [1]. FE Analysis has been performed by Abaqus software. Stiffness and Yield strength of foams between 50% (cortical bone) to 80% (cancellous bone) porosity range were considered. This study showed that crushable foam material model in Abaqus, which has developed primarily for Aluminum (Al) foam alloys, is also valid for Ti Foam before any crack or damage occurs in the sample.

Photo-catalysis of red wine stains using titanium dioxide sol-gel coatings on wool fabrics

This paper investigated the use of titanium dioxide sol-gel coatings to photo-catalyse red wine stains on wool fabrics. Coatings were produced by the hydrolysis and condensation of titanium butoxide (Ti(OC4H9)4) on the surface of wool fabrics after pad application. Coatings were partially converted to the anatase form of titanium dioxide by prolonged immersion in boiling water. The coating presence was confirmed using scanning electron microscopy, UVspectrophotometry and atomic force microscopy. Coated samples were measured for photo-catalytic activity by degrading red wine stains from the surface of the coated fabric. The level of photocatalysis was determined for each of the coating systems after 168 hours. Red wine stains were photo-catalysed and level of staining was reduced from the UV exposed surface of the coated wool fabric.