Biomedical Engineering Reference
In-Depth Information
(nickel-titanium shape memory alloy) stents coated with a-C:H was made for endovas-
cular treatment of superficial femoral artery occlusive disease [185]. Primary results of
this investigation showed a 100% patency rate 12 months after intervention. However,
another clinical test in the year 2004 reported that a-C:H coating does not provide signifi-
cant improvements over uncoated stainless steel stents [186]. A random study of the hemo-
compatibility of a-C:H coated stainless steel stents was made by comparing them with
uncoated stents during the treatment of coronary artery disease in 347 patients. After 6
months' implantation, it was observed that the binary restenosis is 31.8% for a-C:H coated
stents and 35.9% for stainless steel stents, while the major adverse cardiac effect is 30.5%
for a-C:H coated stainless steel stents and 32.7% for uncoated ones.
Some of the amorphous carbon coatings have been incorporated into commercial stents
or related products. The Cardio Carbon Company Limited has two amorphous carbon-
coated titanium implants: Angelini Lamina-lo
TM
(mechanical heart valve) and Angelini
Valvuloplasty
TM
ring that is used for heart valve repairs. Plasmachem of Germany pro-
duces a stent coated with 50 nm of amorphous carbon, marketed under the trade name
BioDiamond Stent
TM
. They use a plasma-induced cold deposition technique to coat amor-
phous carbon on stainless steel 316L stents. The company PHYTIS sells amorphous
carbon-coated stents on which they report a reduced rate of restenosis due to the amor-
phous carbon coating and that target revascularization has been necessary in only 3.27%
of the lesions treated. Another company, Sorin Biomedica of Italy, produces heart valves
and stents (Carbonstent
TM
) which are coated by approximately 0.5
μ
m thick Carboilm
TM
.
This coating is produced by PVD from a carbon target, and the company states that
Carboilm
TM
has a turbostratic structure equivalent to that of pyrolytic carbon. In one clini-
cal study, 165 Carbonstents
TM
were used in 129 coronary lesions of 110 patients [187]. At
the 1-month follow-up, there were no sign of stent thrombosis or any other major adverse
cardiac events. In another clinical study, the Carbonstent
TM
was implanted in 112 patients
with 132 de novo lesions [188]. The 6-month angiographic follow-up was obtained in 108
patients (96%) (127 lesions); the angiographic restenosis rate was a low 11%.
Other Biomedical Applications
An amorphous carbon coated centrifugal ventricular blood pump device (made by
SunMedical Technology Research Corporation, Nagano, Japan) was implanted in calves.
Without any postoperative anticoagulation, only minor evidence of thrombosis was found
on the amorphous carbon coated surfaces after explantation [189].
Hydrogenated amorphous carbon coatings have been investigated for oral implants
[190-193]. It was observed that the RF-PECVD deposited a-C:H layers showed significant
biointegration and resistance to saliva and other oral cavity elements [190]. Ion beam plated
a-C:H films on orthodontic nitinol arch wires reduce the Ni ions release to a great extent
[191-193]. The growth rate of Sa3 squamous carcinoma cells is also higher on coated wires
[193].
There were studies on coating guide wires with amorphous carbon, and investigations
of the films' lubrication, stability, and hemocompatible properties were addressed [194-
196]. It was observed that a-C:H coated guide wires exhibited a lower coefficient of fric-
tion, better adhesion with stainless steel, higher hardness, and better hemocompatibility
than other coatings, such as PTFE [195]. Si and F have been incorporated in a-C:H film to
improve adhesion with the substrate and stability during guide wire windings. Use of
an a-Si:H interlayer has increased the substrate adhesion significantly, while Si doping in
FCVA deposited ta-C was reported to reduce film cracking [194]. Lubrication properties
