Principles of Clinical and Engineering Integration in Hemocompatibility - Biomaterials Science: An Integrated Clinical and Engineering Approach - page 19

follow-ups. No residual stent prosthesis in the area should be present once
biodegradability is completed. No potential adverse reactions with the
coronary artery should take place. Vasomotion restoration of the artery is
necessary [1, 27, 51-62].
Should Cardiac Stents Be Biodegradable/Bioabsorbable?
Overview
The injured vessel, after percutaneous coronary intervention, can necessitate
scaffolding. There has not been a consensus about the necessary time for
such a scaffolding. Current DESs have demonstrated their capacity in pro-
viding scaffolding for injured vessels and limiting in-stent restenosis.
Typical permanent polymers used in sirolimus- and paclitaxel-eluting stents
include poly(ethylene-co-vinyl acetate), poly(n-butyl-methacrylate), and
poly(styrene-b-isobutylene-b-styrene) [17-21, 60, 65].
There have been long-term safety concerns about the permanent nature
of the stent material and polymers. Several noteworthy adverse effects that
occur with DES include delayed healing, endothelial dysfunction, chronic
arterial-wall inflammation, impaired neointimal formation, and late-
acquired stent malapposition [9-15, 64]. In addition, particularly serious
concerns are late and very late stent thrombosis, which appear long after
stent deployment. These can lead to severe clinical outcomes, including
death [2, 47, 48, 50-60, 64, 65].
The durable polymers used in DES have been shown to provoke an inflam-
matory response in animals, such as giant cell infiltration around the stent
struts, and progressive granulomatous and eosinophilic reactions. These
reactions can increase beyond the first year. Chronic inflammation may
decrease efficacy [60, 64-66]. Reports of increased rate of endothelial dys-
function after DES implantation compared with bare-metal stent (BMS)
implantation have given impetus to considering biodegradable and bioab-
sorbable options for cardiac stents [2, 16-21, 57-60].
Moreover, these effects can increase the incidence of very late stent throm-
bosis, a rare event, after DES implantation [16-21]. In addition, delayed loss of
anti-restenotic efficacy has also been observed with the early DES technolo-
gies [22, 23]. Chronic arterial-wall inflammation and endothelial dysfunction
may be associated with the increased rate of target vessel revascularization
at a late stage, which has been found particularly in patients with complex
lesions, including those with diabetes [24, 25].
Among the biodegradable polymers implemented, polylactic acid, poly-
glycolide, and poly(D,L-lactic-co-glycolic acid) are particularly common.
These can be completely metabolized as they break into monomers, water,
and carbon dioxide. Stents with these biodegradable polymers have anti-
proliferative agents as eluting agents, which include sirolimus, tacrolimus,
biolimus, and paclitaxel [27, 51-60].