Biomedical Engineering Reference
In-Depth Information
Active agent
O
N
S
C
S
Binding agent
NH
NH
O
O
O
O
P
P
O
O
O
O
P
P
Coordination layer
O
O
O
O
Metal stent surface
FIGURE 6.17
Phosphorylcholine-based copolymers used for drug release coatings.
Multiple-Layer Reservoir
The Cordis CYPHER Sirolimus stent has a matrix coating consisting of three layers: the
primer Parylene C layer (2
μ
m thick), the matrix/drug layer, and the matrix only topcoat
layer (Figure 6.18). After coating with Parylene C, the matrix/drug layer, which is 10
μ
m
thick, is applied, onto which a drug-free 0.6-
μ
m layer of PBMA is added, which minimizes
the burst release (Acharya and Park, 2006).
In experiments reported by Morice et al. (2002), a prolonged release of sirolimus demon-
strated from a three-layer system, with 80% being released over 30 days through a drug-
free polymer top coat.
Top coat
PBMA (0.6 µm)
Matrix/drug
PEVA/PBMA with Sirolimus (10 µm)
Primer coat
Parylene C (2 µm)
316 Stainless steel stent, Bx velocity 140 µm
Core
FIGURE 6.18
Three-layer structure of the CYPHER sirolimus delivery system.
