Biomedical Engineering Reference
In-Depth Information
Blood haemolysis of various ceramic powders, alumina, i.e. Al
3
O
2
, zir-
conium oxide/yttrium oxide ZrO
2
/Y
2
O
3
, silicon carbide SiC, aluminum nitride
AIN, boron carbide B
4
C, boron nitride BN, titanium diboride TiB
2
, titanium
carbide TiC, titanium nitride TiN was investigated according to ISO/TR 7405-
1984 (F) by Dion et al. (1993b). Test results indicated that most of the ceramic
powders produced almost no haemolytic activity.
Alumina is the most used bioceramic in orthopaedics because of its
mechanical (high hardness, low friction and wear) and biological (inertness to
the in vivo) properties. Polycrystalline Al
3
O
2
with an UHMWPE is accepted as
the best combination of biomaterials for total hip prosthesis (Kumta, 2006). This
combination has also been used for double-pivot bearings of centrifugal blood
pump (Takami et al., 1997, 1998). The study analysed the materials in vitro and
in vivo (systemic toxicity, sensitization, cytotoxicity, mutagenicity, direct
contact haemolysis and thrombogenicity). The results indicated that both Al
3
O
2
and UHMWPE are suitable for bearings of blood pumps.
8.5 Modifications of biomaterials to enhance
haemocompatibility and biocompatibility
Any implanted biomaterial cardiac device is a foreign material for human body
and it can cause complications such as thrombosis and infections (see Section
8.3). Biomaterials trigger the defence mechanism of the body when the material
comes into contact with tissue and blood. Therefore, surface modification of any
biomaterial is considered to be inevitable for cardiac devices. Different methods
have been investigated for modifying blood-contacting surfaces in order to
reduce these complications (Klee and HÈker, 1999). These methods are either
forming a biological layer or coating of organic/inorganic material on
biomaterial surface without changing the mechanical properties.
Current blood contacting surfaces are categorized into three sections as
smooth surfaces, textured surfaces and biolized surfaces (Nos et al., 1996).
This section draws heavily on the most used surface coatings with respect to
commercial cardiac devices. These coatings include titanium nitride (TiN)
(inorganic), DLC (inorganic), 2-methacryloyloxyethyl phosphorylcholine
(MPC) (organic), heparin (bioactive) and textured (bioactive).
TiN coatings (inorganic)
TiN, which is a refractory ceramic coating and corrosion resistant, has been used
in many left VADs (LVAD) because of its mechanical characteristics (Sin et al.,
2009). Its mechanical properties make it an excellent tribological coating.
Physical or chemical vapour deposition methods are used for TiN coating on a
bulk material. Its blood compatibility behaviour makes it a preferred coating for
heart valves and heart assist devices (Dion et al., 1992). Dion et al. (1993d)
