Biomedical Engineering Reference
In-Depth Information
Titanium materials are resistant to corrosion because of the stable
passivity of the surface oxide ilm. Apart from that, titanium and
titanium alloys are generally regarded to have good biocompatibility,
although there are reports that show the accumulation of titanium
in tissues adjacent to the implant, signifying metal release and
corrosion
in vivo
[2,17]. In addition, these metal implants may
loosen and even separate from the surrounding tissues during
implantation [16, 18, 29]. Titanium and titanium-based alloys
have relatively poor tribological properties because of their low
hardness [17].
One of the methods that allow the change of biological properties
of Ti alloys is to produce a composite, which will exhibit the favorable
mechanical properties of titanium, excellent biocompatibility
and bioactivity of ceramic. The main ceramics, used in medicine
are hydroxyapatite, silica, or bioglass [3]. Hydroxyapatite (HA,
Ca
10
(PO
4
)
6
(OH)
2
) shows good biocompatibility because of its
chemical and crystallographic structure being similar to that of
living bone. HA has porous nature and is bioactive, which means that
after some time it is partially resorbed and replaced by natural bone
[32]. Besides, HA has the ability to form strong chemical bonds with
natural bone. Unfortunately, the HA cannot be used for load bearing
applications, due to its poor mechanical properties with regard to
natural bone. The ceramic coating on the titanium, improves the
surface bioactivity, but often lakes off as a result of poor ceramic/
metal interface bonding, which may cause the surgery to fail [1, 33].
For this reason, the nanocomposite materials containing titanium
and ceramic as a reinforced phase are promising alternatives to
conventional materials, because they can potentially be designed to
match the properties of bone tissue in order to enhance patients'
quantity of life [4−7, 27].
Earlier, microcrystalline Ti-20 vol% HA composite with a relative
density of 97.86% was fabricated by a hot pressing technique [27].
The phase constitution of Ti-20 vol% HA composite is similar to
that of HA-based composite with Ti and HA as the predominant
phases. Elastic modulus and Vicker's hardness of Ti-20 vol% HA
composite are 102.6 and 3.41 GPa, respectively. Additionally, the
osteointegration ability of the composite is better than that of
pure titanium, especially in the early stage after the implantation,
which may be due to the presence of HA ceramic in the Ti-matrix
composite [27].
