Biomedical Engineering Reference
In-Depth Information
ance expected when the same biomaterial is used for low flow rate circulatory
device is different from that for a high flow rate device. The FDA regulates and
approves the medical devices only within certain clinical applications instead of
a biomaterial itself for biocompatibility. More details related to the preparation
and testing of biomaterials are given in Section 8.6.
In order to investigate the biomaterial used for artificial hearts, one must
define the blood±material
interaction phenomena and its complications
accordingly.
8.3.1 Complications of VADs
Protein adsorption
Plasma protein adsorption is the first reaction when blood interfaces with an
artificial surface. It usually starts in a few seconds after blood±surface inter-
action. It simply means that the dissolved matters in a solution, especially
proteins, adsorb on to the surface of the foreign substance. Primarily, protein
deposition to the surface does not always indicate body's response to the
material but rather large amount of proteins simply cause adhesion to the surface
(LeDuc and Wang, 2006). The influence on the blood cells by adhesive protein
has been a matter of concern. This problem has made a direct challenge to
developers to modify artificial surfaces in order to reduce protein adsorption,
and hence prevent damaging blood cells. However, controlled protein adsorption
can be usefull due to the formation of a thin natural surface to interact with
blood. Studies of protein absorption to different materials are mentioned in the
next subsections.
Thromboembolism
One of the complications of cardiac devices is thrombosis, to be considered
during cardiac device in vivo testing (see Section 8.7). Thrombosis is the
formation of thrombus in a vessel, which can cause death. Platelet adhesion and
aggregation cause thrombus formation on artificial surfaces and this formation
contains aggregated platelets, red cells, fibrins and other cellular elements.
￿ ￿ ￿ ￿ ￿
Platelets
Platelets are blood cells, approximately 2±4m in diameter, which are respon-
sible for blood clotting during bleeding. Adhesion, release and aggregation are
the main reactions of platelets to vessel wall damages. One way of reducing
platelet adhesion is the reduction of surface energy which can be controlled by a
surface of hydrophilic and/or hydrophobic domains (Klee and HÈker, 1999).
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