Biomedical Engineering Reference
In-Depth Information
phosphorylcholine (PC) based polymer (Lewis, et al. , 2002). The coating is
a synthetic copy of the outer layer head groups of the predominant lipid of
the red blood cell membrane, and has been shown to impart a high degree
of haemo-compatibility once bound to implant surfaces (Whelan et al. ,
2000; Malik et al. , 2001; Lewis et al. , 2002). Clinical studies have confi rmed
that PC coating of stents reduces thrombogenicity and some studies have
demonstrated a lower restenosis rate, particularly when used for small
vessel lesions (Beaudry et al. , 2001; Grenadier et al. , 2002; Shinozaki et al. ,
2005). PC coatings have also been exploited as a means of drug delivery
including Zotarolimus from the Endeavour ® stent produced by Medtronic
Inc. (Minneapolis, MN). The application of drug eluting stents will be dis-
cussed more fully later in this chapter.
In another application of PC, the Trilayer stainless steel-tantalum-
stainless steel PC coated stent (the TriMaxx launched by Abbott Vascular
in 2005) has been developed. This stent contains two outer layers of 316L
stainless steel and a thin inner layer of tantalum to provide greater strength
and thus allow the reduction of stent thickness combined with the biocom-
patibility benefi ts of the PC. TriMaxx have been shown to be safely deployed
for the treatment on de novo coronary lesions with six month clinical and
angiographic results comparable to those seen with other bare metal stents
(Abizaid et al. , 2007).
Polyzene-F, a negatively charged, high molecular weight polymer
(poly[bis(trifl uoromethoxy) phosphazene]) that displays biocompatible,
anti-infl ammatory and bacterial resistance properties when applied to a
range of materials has been exploited for use on Co-Cr stents. Animal
studies have demonstrated that Polyzene-F coated stents provided effec-
tive control of in-stent restenosis compared with drug eluting stents, and
demonstrated favourable thromboresistance and low infl ammation
(Radeleff et al. , 2008). More recently, the fi rst human trials of a prospec-
tive, single-centre study to evaluate the short-, mid- and long-term safety
and effi cacy of a Co-Cr stent with nanothin, Polyzene-F (CATANIA
stent, CeloNova Biosciences, Newnan, GA, USA) have been reported
(Tamburino et al. , 2009). The results showed the coated stent possesed
excellent safety profi les in the early and mid-term and a high level of effi -
cacy in the treatment of de novo coronary lesions of a complex popula-
tion. At the 12 month follow-up reported at a presentation at the 21 st
International Symposium on Endovascular Therapy in January 2009, none
of the 55 patients recruited experienced stent thrombosis and the coating
was reported as 'highly biocompatible', easily placed, resistant to platelet
adhesion and mechanically sound, resulting in low rates of binary angio-
graphic restenosis (6.8%). It remains to be seen whether Polyzene-F
coated stents will provide a viable alternative to bare metal and drug
eluting stents.
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