Page 322 - Biodegradable Polyesters

300 12 Biodegradable Polyesters Polymer–Polymer Composites

Coronary arteries

(a) (b) Plaque build-up
Figure 12.1 Position of coronary arteries (a) and progression of plaque buildup within a
coronary artery (b). Images adapted from Ref. [3].

(a) (b) (c) (d) (e)

Figure 12.2 Stenting procedure: (a) catheter (d) stent deployment, and (e) stented ves-
insertion, (b) balloon expansion, (c) inser- sel. Images adapted from Ref. [3]. Copyright
tion of catheter with stent mounted on the Medmovie.com. All rights reserved.
end after removal of the balloon catheter,

12.2
Stenting Development

12.2.1
Bare Metal Stents

The first stents were relatively simple in nature when compared with stents of
today and were primarily made of medical grade stainless steel [4] (316l stainless
steel) and less commonly of cobalt–chromium or nickel–titanium alloys. Stents
of this nature fit into the category of “bare metal stents” (BMSs). Although stain-
less steel has excellent mechanical properties, it contains small amounts of nickel,
molybdenum, and manganese to which some people are allergic [5], thus height-
ening the risk of restenosis (i.e., re-narrowing of the vessel) in some patients [6].
Restenosis occurs via an inflammatory reaction at the stented site of the vessel
which causes smooth muscle cells to migrate to the surface of the inner wall of
the vessel and proliferate. This proliferation (i.e., multiplication and spreading) of
the cells is what causes the vessel to re-narrow [7]. Furthermore, blood platelets
(also known as thrombocytes) have a tendency to stick to BMSs which can cause