Biomedical Engineering Reference
In-Depth Information
coatings. Without preparing additional architecture for asymmetrical coating, the first
generation of DES has a continuous layer of the drug/matrix coating covering the whole
stent surface. The strut thickness of the DES varies with the mechanical properties of the
stent material. The fully absorbable PLLA and biocorrosive magnesium stents have the
largest strut thicknesses, ranging from 150 to 240
μ
m. Stainless steel stents have median
strut thicknesses ranging from 110 to 140
μ
m. Finally, CoCr alloy stents, the strongest stent
platform material, have strut thicknesses ranging from 60 to 90
μ
m. The stent structure can
be defined as luminal (interior) and abluminal (exterior) surfaces (Figure 6.10b). The ablu-
minal surface is against the wall of the blood vessel and the luminal surface is in contact
with the flow of the bloodstream.
The third basic structure is the combination of holes and hinges (Kukreja et al., 2008).
The intra-built holes are used to load drugs either with or without matrix materials. The
housing structure for holes is much stronger than the hinge structure. The flexibility of
the stent is a function of the ductility of the hinge structure without deformation of the
holes, preventing the matrix from extruding out. Figure 6.11a shows the hole-and-hinge
structure of the CoStar stent.
The fourth basic structure is the intra-built deep grooves for drug loading, such as in
the Janus stent (Figure 6.11b) (Acharya and Park, 2006). The grooves are cut on the ablu-
minal surface of the stent. Drugs are loaded in these cavities and delivered directly to the
contacting vessel wall. No drugs are directly eluted into the bloodstream. Both holes and
(a)
Schematic of bare
metal express stent
Schematic of TAXUS
express stent with
matrix/drug coating
(b)
Abluminal
Abluminal
Metal strut
Luminal
Width
FIGURE 6.10
Tubular and rectangular structures of bare metal stent. (Reproduced with permission from HMP Communi-
cations LLC. Chadwick, D.R.,
Cath. Lab. Dig.
, 14, 1.1, 2006.) (a) Express stent with and without coating. (b) Cross
section of tubular and rectangular structures.
