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Page 2 of 15 Qiu et al. Vessel Plus 2018;2:12 I http://dx.doi.org/10.20517/2574-1209.2018.13

drug-eluting stents (DESs) which were firstly approved by Food and Drug Administration (FDA) of USA in
2002. DESs are coated with non-degradable polymer embedded with anti-proliferative drugs, to avoid the
occurrence of in-stent restenosis (ISR) which represents a major drawback of bare metal stents (BMSs) .
[2]
Although the use of DESs can substantially reduce the ISR rates, especially in high-risk patients (lowered by
74%), other clinical problems arise, particularly the increase of late stent thrombosis (ST, with a mortality
rate of about 45%) after implantation of DESs . The development of deadly ST is concertedly facilitated
[3,4]
by hypersensitivity to the permanent presence of alloy and by incomplete repair of the endothelium at the
site of vascular wall injury due to the anti-proliferative drug coatings . Also, the presence of permanent
[5]
stent could cause the increasing risk of strut fracture and failure under complicated loading and corrosive
conditions, leading to heart attack or failure, unstable angina and other clinical complications in patients .
[6]
To overcome these issues, it becomes mandatory to develop next-generation bioresorbable stents (BRSs) to
replace metallic ones. Biodegradable polymers have attracted the most interests for manufacturing BRSs .
[7-9]
Fully expandable biodegradable polymeric stents provide the mechanical support to the vessel wall with
appropriate radial strength, to prevent mechanical recoil after immediate implantation. When arterial
remodelling achieves a relatively stable phase at 6 months, the mechanical support is no more required. As
a result, stents are supposed to be designed to dissolve after 6 months in human body, leaving behind the
intact vessel with no pro-inflammatory substances or obstacles . During the process, the biodegradable
[10]
polymers gradually soften, thus allowing a smooth transfer of the load from the stent to the healing artery,
and eventually removing the significantly high stresses induced to the stented artery.

Earlier development of polymeric BRSs includes the Igaki-Tamai stent (Kyoto Medical Planning Co. Ltd,
Japan), the Abbott BVS vascular drug-eluting stent (Abbott Vascular, Santa Clara, California, USA) and the
REVA stent (Reva Medical, San Diego, California, USA) . The Igaki-Tamai stent, made of poly-L-lactic acid
[8,9]
(PLLA), has a zig-zag design with straight connective struts. It was the first fully biodegradable polymeric
stent ever implanted in humans, and degraded over 18 to 24 months with good performance . The Abbott
[8]
BVS stent has a bioresorbable polymer backbone of PLLA, incorporated with a polymer coating of poly-
DL-lactic acid (PDLLA) containing and controlling the release of the anti-proliferative drug. The BVS 1.0
has out-of-phase sinusoidal rings connected either directly or by straight bridging struts. The first in-man
study of BVS 1.0 stents not only highlighted the efficacy and safety of using a biodegradable scaffold, but also
provided vital data that help develop the BVS 1.1 stent which has in-phase sinusoidal rings connected by
straight bridging struts, which can provide radial support for a longer period of time . This is also the case
[9]
for REVA stent, which is made of absorbable tyrosine-derived polycarbonate polymer and has a distinctive
slide-and-lock design. The preclinical trials of REVA stents have led to the development of the second-
generation REZOLVE bioresorbable stent with a helical design .
[9]
Development of next-generation polymeric BRSs still faces many challenges and unsolved issues, such as
stent material and design, mechanical support, in vivo performance, biodegradation rate and manufacturing
process. One of the major uncertainties for polymeric BRSs is the effective control of mechanical properties
during the biodegradation process. It is very important for BRSs to relieve symptoms immediately and also
offer mechanical support for an appropriate period of times. Currently, there is a critical shortage of such
data and information, severely limiting the application and further development of BRSs. Designers must
use a trial-and-error approach to work out the appropriate material formulation and geometrical parameters
of BRSs that can sustain mechanical loads during the degradation process. As an evidence, the concept of
a biodegradable polymeric stent dates back to the 1980s, yet currently there are no designs with the FDA
approval on the market. Abbott BVS PLLA stent, also named as ABSORB, is a first-of-its-kind device used
initially in Europe and parts of Asia Pacific and Latin America to treat arteries with mild restenosis. To
promote clinical application at a large scale or even to replace metallic stents, the mechanical performance
of BRSs needs to be thoroughly investigated and quantitatively characterised, especially over the full period