CHAPTER 1
INTRODUCTION
This section basically provides research background, problem statements, objectives and scope of this research.
1.1 Research Background
There are tremendous materials such as ceramic, glasses, metallic and polymeric biomaterials are used for medical purposes. The metallic substrate such as Ti-6Al-4V
usually used in medical implants due to its excellent biocompatibility properties, excellent corrosion resistance in body fluid and strength to weight ratio advantage. For
hard tissue replacements, Ti-6Al-4V is the most excellent biomaterials because of the ideal recipe for implanted alloy included low elastic modulus, low stress shielding, good
wear resistance, high mechanical strength and fatique resistance Thirugnanam, 2009.
Further studies showed that the release of both vanadium and aluminum ions from the alloys may cause long-term health problems, such as peripheral neuropathy,
osteomalacia, and Alzheimer diseases S. Rao et al., 1996 . However, the effect of metal release and corrosion in vivo due to titanium accumulation in tissues adjacent to
the implant. In addition, these metal implants may lose and even separate from the surrounding tissues during implantation Aziz et al., 2001. Titanium material is bioinert
which have slower abilities to bond to bone and to guide bone growth as compared to the other biomaterials with bioactive properties such as Hydroxyapatite HA or
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Chitosan CTS. Titanium does not have surface properties similar to the bone tissue. This weakness should be improved by producing bioceramic coating on the surface
Dudek, 2009.
Hydroxyapatite HA is the most popular bioactive ceramic materials used in medical. It is a ceramic material that possesses exceptional biocompatibility and bioactivity
properties with respect to bone cells and tissues, due to its similarity with the hard tissues of the body Ferrazz et al., 2004. HA has been widely used as a bulk implant
material in non-load bearing areas of the body Curran et al., 2011. Although HA has excellent biocompatibility properties, it is limited in use due to its low strength and
brittle nature Prokopiew et al., 2006. The main reason of this loss in mechanical properties of HA is decomposition of HA into some calcium phosphate phases such as
tricalcium phosphate TCP and even tetra-calcium phosphate TTCP Mobasherpour et al., 2009. Calcium phosphate phases are brittle and have weaker strength. Hence, HA
can be used only for applications in which an insignificant magnitude of stress needs to be borne Thomas et al., 1980. Attempts to overcome these disadvantages have been
made by using HA as a surface coating on bioinert metallic substrates such as titanium, Ti-6Al-4V, and stainless steel 3I6L Yip et al., 1997. Nonetheless, most of the reports
demonstrated that bonding strength between HA surface coating and titanium substrate was not high enough for the requirement of clinical application. The main difficulty
encountered is the sintering of the HA coating. As high temperatures result in degradation of the metal substrate and the thermal decomposition of HA, sintering
temperatures ideally should be below 1000 °C under which HA is difficult to be fully densified Wei et al., 2005.
One way to improve the low strength of pure HA coatings is to form a composite coating by reinforcing HA coating with a strong secondary phase such as CTS Xiu
Feng Xiao et al., 2005. It is expected that the incorporation of CTS particles as reinforcement within the coating will improve the bonding strength between the coating
and the substrate. An alternative solution is to develop a composite composed of CTS 2
powder and HA. The coating has been applied extensively for metallic prostheses with the aim of improving bone apposition Kaya et al., 2008 and implant obsession, well as
reducing curative time Sun et al., 2001.
Numerous methods of surface coating techniques have been established to deposit HACTS based coatings on to Ti-6Al-4V. These methods range from the conventional
press-and sinter method to more elegant approaches such as sputtering Yoshinari et al., 1997, electrophoretic deposition Kaya et al., 2008, and plasma spraying Cheng et al.,
1997. However, further investigation revealed that HA coatings are rather more soluble than expected in vivo or in vitro simulated physiological conditions, that may result in
loose or even failure of the implant after long time of implantation. It has been reported that although the early fixation is good for HA coated implants, but the high dissolution
rate of HA coating in biological environment does show detrimental effect and eventually leads to the failure of the implant Gineste et al., 1999. In this study,
HACTS composite powder was mechanically mixed with ball milled for 4 hours. Designed clamp was used for support the deposition of HACTS powder onto Ti-6Al-4V
substrate in a tube furnace. The HACTS composite layer on Ti-6Al-4V substrate were characterized physically and mechanically behavior using X-Ray Diffraction XRD,
Scanning Electron Microscopy SEM, Energy-dispersive X-ray EDX and Vickers Microhardness.
1.2 Problem Statement
