Biomedical Engineering Reference
In-Depth Information
Butter et al. [94] comment that in tests, it showed no difference from the controls. However,
the works published indicated that DLC is a promising biomaterial for heart valve applica-
tions, and it is known that much research work is under progress on this topic. Furthermore,
DLC-coated stents can be permanently inserted into an artery that will assist to open the
artery through which the blood can flow through it. Cardiovascular implantation of stents
is becoming famous and rapidly used worldwide, although it has several shortcomings such
as restenosis and occlusion. Moreover, arterial stents can induce platelet activation and may
initiate thrombosis by shear forces on the flow and by platelet adhesion to the metal. Alanazi
et al. [115] evaluated in vitro the performance of stents coated with DLC. Growth arrays
using smooth muscle cells and endothelial cells evidenced that DLC did not affect prolifera-
tion rates and no cytotoxic effects were observed. Flow cytometric analyses showed no sig-
nificant changes in mean channel fluorescence intensity for the structural antigens CD41a
and CD42b. On the other hand, contrast expression of the activation-dependent antigens
CD62p and CD63 increased significantly in uncoated compared with DLC-coated stents.
Release of metal ions into the bloodstream is a matter of concern, and Alanazi et al. [115]
used atomic adsorption spectrometry to detect a significant release of nickel and chromium
ions into human plasma over 4 days from uncoated stents. Similar results were obtained
by inductively coupled plasma mass spectrometry analysis, and in this case, the release of
metal ions from DLC coated stents was “virtually undetectable.” From these observations,
the authors concluded that the coating of intracoronary stents with DLC may contribute to
a reduction in thrombogenicity and consecutively in the incidence of acute occlusion and
restenosis in vivo. Furthermore, in vitro tests were performed by coating the catheters with
a mixture of Ag and DLC, and the results confirmed the efficacy of this coating for local
freedom from bacterial infection. DLC coatings on segmented polyurethane were tested for
blood compatibility by McLaughlin et al. [116], and it was shown that they could be superior
to an excellent nonthrombogenic polymer, 2-hydroxyethyl methacrylate, during the experi-
ments performed in a parallel flow chamber. Finally, the authors concluded that greater
attention should be paid to DLC for use in the medical field.
DLC-Coated Guide Wires
Guide wires are often used to introduce stents, catheters and other medical devices inside
the human body. In practice, a good guide wire should possess high flexibility, low coef-
ficient of friction, inertness, and biocompatibility. In the past decade, it is customary to use
stainless steel as a guide wire material. Stainless steel is often coated with polytetrafluo-
roethylene or silicon to improve the lubricity or to lower the friction. Nevertheless, these
coatings have serious shortcomings such as poor adhesion and less stability with stainless
steel causing the release of coated materials. In principle, the guide wires should not have
any implant trauma or harm the wall of the vessels during its insertion alongside the
path of the vessels. Furthermore, studies were also performed to coat guide wires with
DLC, and their stability, lubrication, and hemocompatibility were evaluated [117, 118]. The
results are supportive of the fact that DLC containing suitable elements is capable of being
used as guide wires. However, care must be taken to negate its delamination and spalla-
tion during winding of the guide wires.
Other Biomedical Applications of Diamond
To minimize the problem of biofilm formation, Elinson et al. [119] applied a thin layer
of DLC over soft contact lenses. Furthermore, from their experiments, they confirmed
© 2011 by Taylor & Francis Group, LLC
