Biomedical Engineering Reference
In-Depth Information
CH
3
-(CH-CH
2
)
m
-(C-CH
2
)
n
-(CH-CH
2
)
m
-
CH
3
FIGURE 6.4
Chemical structure of SIBS.
(Fishell et al., 2009). Unlike the CYPHER stent, TAXUS stent retains at least 90% of the drug
on the polymer after elution of the initial 10% during the first few months.
Fluoropolymer
The XIENCE™ V Everolimus-eluting coronary stent system (XIENCE V or XIENCE V
EECSS) is a device/drug combination product consisting of either the MULTI-LINK
VISION
®
Coronary Stent System or the Multi-Link Mini Vision
®
Coronary Stent System
coated with a formulation containing Everolimus as the active ingredient, embedded in
a nonerodible polymer. The stent has a reference diameter of 2.5-4.0 mm and is used to
treat lesions 28 mm in length or smaller, marketed under the names of XIENCE V Rapid-
Exchange EECSS and XIENCE V over-the-wire EECSS. The stent material is a medical-grade
L605 cobalt chromium (CoCr) alloy with a design strut thickness of 81 µm (Nakazawa et
al., 2009). The usable length of the delivery system is 143 cm for both (rapid exchange and
over-the-wire) delivery systems. The drug Everolimus is a novel, semisynthetic macrolide
immunosuppressant, synthesized by chemical modification of rapamycin (sirolimus). The
molecular formula of Everolimus is C
53
H
83
NO
14
with a molecular weight of 958.224 g/mol.
The nonerodible polymer is loaded with 100
μ
g/cm
2
of Everolimus and has a maximum
nominal drug content of 181
μ
g on the stent (4.0 × 28 mm).
The inactive ingredients comprise PBMA (Figure 6.3), a polymer that adheres to the
stent and acts as the drug coating, and poly(vinylidene luoride-
co
-hexaluoropropylene)
(PVDF-HFP) (Figure 6.5) as the stent matrix layer containing Everolimus. PVDF-HFP is a
nonerodible semicrystalline random copolymer with an
M
w
of 254,000-293,000 Da. This
copolymer is mixed with Everolimus (83%:17% w/w polymer/Everolimus) and applied to
the entire PBMA-coated stent surface as a conformal coating. The drug is loaded at a den-
sity of 100
μ
g/cm
2
for all product sizes. No topcoat layer is used.
Phospholipid Polymer
The Endeavor
®
Zotarolimus-Eluting Coronary Stent on an over-the-wire or Multi-
Exchange
®
II (MX2) stent delivery system is a device/drug combination product with a
reference diameter of 2.5-3.5 mm that is used to treat lesions of 27 mm in length or smaller.
The stent material is an F-562 CoCr alloy with a design strut thickness of 91
μ
m (Nakazawa
et al., 2009). The drug delivery system consists of a PC coating in a conformal layer with
Zotarolimus at a density of 1.6
μ
g/mm
2
(Udipi et al., 2007). Zotarolimus, also named ABT-
H F F F
-(C-C)
m
-(C-C)
n
-
F
H
F
CF
3
FIGURE 6.5
Chemical structure of (PVDF-HFP).
