[Thesis]. Manchester, UK: The University of Manchester; 2019.
Coronary artery disease is the leading cardiovascular related death worldwide. The
mainstay therapeutic intervention is either coronary artery bypass grafting or endovascular
approaches, inserting a metallic scaffold to maintain the opened state of the vessel.
There are many scaffolds currently available and under development, with bare metal
stents being first designed followed by drug eluting stents which are now commonly
used. This necessitates the use of dual anti-platelet therapy to evade thrombosis.
Bare metal stents pose a significant risk of in-stent restenosis followed by late
stent thrombosis risk caused by the drug eluting stent. Importantly, drug eluting
stents have significantly decreased the incidence of in-stent restenosis. Consequently,
there remains the need to develop a complication-free stent, and thus we propose combining
the structural strength of metallic stents, bare metal stents, with the surface characteristics
of graphene to promote vessel healing and prevent complications. Graphene is a mono
layered sheet of hexagonal structured carbon atoms, and has been hailed as the Ă˘wonderĂ˘
material across many disciplines. We aim to incorporate many of the desirable qualities
of graphene and graphene oxide; strong, flexible, anti-corrosive, smooth, biocompatible,
antibacterial, into a coronary stent coating in order to alleviate some of the complications
of currently available stents.
Graphene was prepared by liquid phase exfoliation using a stabilising agent known
as 1-pyrene sulfonic acid sodium salt while graphene oxide was prepared by HummerĂ˘s
exfoliation method. The quality of the dispersions were characterised using a range
of techniques, particularly Raman spectroscopy and atomic force microscopy. Dip-coating,
with applied bias and spray coating techniques were tested to select the optimal method
of graphene/graphene oxide coating of bare metal stents. The selected technique was
then investigated further to optimise coating to achieve thin, uniform and maximal
coverage of the stent. Human coronary artery endothelial cell growth was investigated
in vitro by incubation with the coated stents for durations of one and eight days
(n=3). Following this, stents coated with graphene and graphene oxide underwent ex
vivo incubation on porcine aortic tissue for a period of 14 days in order to determine
the formation of neointimal hyperplasia. Following 14 days, visualisation by scanning
electron microscopy was performed as well as MillerĂ˘s staining and immunohistochemistry
for endothelial cells.
Spray coating was selected at a spray distance of 10cm and 400Ă‚ÂµL at 0.4 mgmL-1 concentration
to spray the stents for a duration of 60-80 minutes. Enhanced human coronary artery
endothelial cell growth was observed from day one to day eight, on the graphene coated
stents when compared to uncoated stents and graphene oxide coated stent. Porcine coronary
and aortic tissue culture demonstrated no significant difference in neointimal thickness
between any of the coated/uncoated bare metal stent groups. Graphene and graphene
oxide were not inferior to uncoated bare metal stents in neointimal thickness. There
were no endothelial cells present after 14 days of aortic tissue culture, even though
endothelial cells were present before tissue culture.
Graphene coating prototype of coronary artery bare metal stents was achieved by spray
coating. Graphene coating supported enhanced viability and growth of human coronary
artery endothelial cells. Ex vivo study of neointimal hyperplasia in the porcine aortic
tissue revealed no benefit of graphene coating in reducing neointimal thickness.