So the first year of the project has come to an end and this article summarises the main outcomes of the research work carried out during this time. The main focus of the first years’ work was to set up the process cycle for the experiments and to analyse the results to confirm the possibility of achieving mechanically superior compositions of Ti and Au while sustaining the excellent biocompatibility of the individual elements.
The project started with placing an order for 2 inch circular Ti and Au targets. A optimal balance between price and efficient thickness of the Au target was the main factor in making this decision. With targets in place, a series of calibration runs were performed at different sputtering power and Ar gas flow to understand the sputtering rates of the individual targets. Meanwhile, the Ti substrates were processed to achieve the required surface finish and features. The prepared substrates were loaded into the deposition chamber and thin films with six different Ti:Au ratios were developed to study the effect of composition on the mechanical and biocompatibility of the deposited coatings.
Nanoindentation characterization techniques were specifically selected to study the mechanical features like hardness and elastic modulus and the Alamar blue assay based cytotoxicity test was selected to assess the biocompatibility of the deposited thin films. Other characterization techniques were employed to corelate the mechanical and biomedical properties with the chemical composition of thin films. Scanning electron microscopy (SEM) was performed to analyse the morphological changes, X ray diffraction (XRD) for structural, Energy dispersive X ray spectroscopy (EDXS) for elemental composition and Atomic force microscopy (AFM) for surface characterization.
Ti-Au thin films were found to be extremely biocompatible right across the range from 100% Ti to 100%Au, even when extract preparation was subjected to shaking to encourage ion leaching into the prepared extract. The main reason for cell viability value above 90% for all the films is that these films adhere very well to the films and no ions leach in the extract as shown by the extremely low ion concentration observed when tested in ICPOEMS technique. XRD results show that when deposited at room temperature, the films develop quasi amorphous Ti-Au intermetallic at intermediate Au composition of 25-53 at%. Similarly, AFM and SEM imaging show that in the composition range of 25-53 at%. Au, the film roughness and size of surface features coming from these quasi amorphous Ti-Au intermetallic particles are very small compared to other Au rich films where crystalline Au particles start to grow. It is expected that by depositing at higher temperature or heat treating at higher temperature, these quasi amorphous Ti-Au intermetallic states can be encouraged to develop into specific crystalline phases which are known to exhibit enhanced mechanical properties like hardness and elastic modulus.
Therefore, these results form the basis for the next stage of research which aims to develop crystalline Ti-Au intermetallic of higher mechanical hardness by depositing these film compositions at deposition temperatures higher than 400˚C.
Follow our research journey to learn more about the effect of process parameters like deposition temperature and deposition pressure on the mechanical properties of Ti-Au thin films...
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