Biomedical Engineering Reference
In-Depth Information
re-stenosis, which results mainly from over-proliferation of vascular SMCs and
production of extracellular matrix. The limitations exhibited by bare metal
stents have led to the search for new stent materials, designs, surface treatments
and coatings to improve the performance of
the device,
in particular,
attenuation of the rate of in-stent re-stenosis.
Stainless steel is by far the most common currently approved material or
stent technology due to its excellent mechanical properties. There are five basic
types of stent configuration—coil, helical spiral, woven (braided or knitted),
ring (individual or sequential) and cell (closed or opened). The devices differ
slightly in strut pattern, width, length, diameter, inter-unit connections,
geometry, flexibility, radial strength, radiopacity, surface area coverage, metal
content, metal composition and/or their delivery system.
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These differing
characteristics appear to profoundly influence both thrombosis and re-stenosis
rates. In order to enhance biocompatibility, therapeutic compounds have been
introduced to the device surface in so-called drug eluting stent (DES) tech-
nology. Despite this advance a number of problems have become evident in
several studies such as the uncontrolled release of drug, lack of clinical evidence
with respect to the reduction of NIH, and disadvantageous generation of
debris.
Finally, we mention the strategy of re-endothelialization of stent surfaces in
order to generate a 'natural' environment.
101,102
This approach represents an
interesting adjunct to the usual philosophy for cell-surface studies outlined
above in the sense that, in this case, cells on a surface are being employed to
enhance biocompatibility. Earlier work involved simple seeding with cells prior
to and after implantation, but this approach can lead to cell loss. Recently, the
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Figure 2.17
Strategy for surface attachment of endothelial progenitor cells via
oriented Fab fragment of antibody. Fragment is a selective binder for cell
surface protein.
