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Title: Application of Biocompatible thin organic coatings to improve tribology of Ti6Al4V Alloy
Keywords: Tribology, Ti6Al4V, Polymer, UHMWPE, SAM
Issue Date: 28-Sep-2011
Citation: BHARAT PANJWANI (2011-09-28). Application of Biocompatible thin organic coatings to improve tribology of Ti6Al4V Alloy. ScholarBank@NUS Repository.
Abstract: Titanium and its alloys have been extensively used in many biomedical and industrial applications due to their high specific strength with acceptable elastic modulus, corrosion resistance and biocompatibility. However, high coefficient of friction and low wear resistance of titanium and its alloys limit their usage in some applications. To improve the tribological properties of titanium and its alloys, various surface modifications, coatings and treatments have been explored. In spite of these developments, there is still a need to further investigate effective solutions to improve tribological properties of titanium and its alloys. In this thesis, application of thin organic coatings to improve tribology of titanium and its alloys has been explored with emphasis on biomedical applications. Ti6Al4V alloy, a commonly used titanium alloy, has been chosen as substrate material in the studies of this thesis. In the first study, ultra-high molecular weight polyethylene (UHMWPE) polymer thin film (thickness of 19.6?2.0 ?m) was coated onto substrate using dip-coating method. Physical characterizations (contact angle, thickness measurement, Field emission-scanning electron microscopy (FE-SEM) morphology and atomic force microscopy (AFM) imaging), biocompatibility test (cytotoxicity) and chemical characterizations (Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS)) were carried out for the obtained UHMWPE coating. Tribological characterization of this coating was carried out using 4 mm diameter silicon nitride ball counterface in a ball-on-disk tribometer for different normal loads (0.5, 1.0, 2.0 and 4.0 N) and rotational speeds (200 and 400 rpm). This coating exhibited low friction coefficient (0.15) and high wear life (> 96,000 cycles) for the tested conditions. Perfluoropolyether (PFPE) overcoat on UHMWPE coating further increased the wear resistance of coating as tested at even higher rotational speed (1000 rpm). UHMWPE coatings (with and without PFPE overcoat) meet the requirements of cytotoxicity test using the ISO 10993-5 elution method. Due to their low surface energy, wear resistance and noncytotoxic nature, the thin coatings of UHMWPE and UHMWPE/PFPE can find various applications in biomedical implants and devices. Despite having suitable properties for biomedical applications, higher thickness of UHMWPE and UHMWPE/PFPE coatings may prevent their usage in micro-electro-mechanical systems (MEMS) biomedical applications. In the second study of this thesis, 3-glycidoxypropyltrimethoxy silane (GPTMS) self-assembled monolayers (SAMs) with PFPE overcoat has been deposited onto substrate. For comparison, PFPE coating has also been formed onto same substrate. Ti6Al4V alloy specimens with PFPE overcoat and GPTMS/PFPE composite coating showed low coefficient of friction and high wear durability as tested at 0.2 N normal load and rotational speed of 200 rpm. The wear durability of the obtained GPTMS/PFPE coating is much higher than that for only PFPE coating. Obtained coatings were also characterized by contact angle measurement, AFM imaging and XPS analysis. Formed PFPE and GPTMS/PFPE coatings are biocompatible in nature. Due to the combination of hydrophobicity, low friction coefficient, high wear resistance and noncytotoxicity, these coatings can find usage in biomedical applications where low coating thickness may be crucial. Molecular thickness (< 4 nm) of these coatings is particularly advantageous for their applications in biomedical MEMS devices.
Appears in Collections:Master's Theses (Open)

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