Page 236 - IJB-9-2

International Journal of Bioprinting Coronary and peripheral artery disease. State of the art.

also be known as “elastic memory.” Self-expandable stents of the VS right after balloon deflation. Cumulative recoil
are fabricated in their expanded shape (final shape) and is also used to evaluate the performance of VS, which is
subsequently crimped into the delivery system (catheter). the difference between the diameter of VS during balloon
Apart from self-expandability, these stents should also inflation and the diameter of the stent lumen 24 h after
possess low elastic modulus and high yield stress for large implantation. The recoil behavior of a medical device can
elastic strains. The elastic modulus measures the resistance be predicted by quantifying its elastic modulus: the higher
of the material to elastic deformation. Low moduli materials the elastic modulus, the lower the stent recoil .
[28]
stretch a lot when pulled, then recovering their original Stent thrombosis is an acute thrombotic occlusion
shape. The elastic strain is the amount of deformation of a of a coronary VS. Although it may be clinically silent,
material that is fully recovered upon removal of the stress stent thrombosis is usually associated to acute coronary
without any residual plastic deformation. Recovery elastic syndrome symptoms. With respect to stenting in PAS, the
deformations around 10% are considered large elastic thrombotic events can also happen, though later in time.
strains and thus suitable for the manufacturing of stents. Even if the highest risk falls into the first month after stent
The major part of self-expandable stents are made from implantation, thrombosis could also happen years after
braiding, knitting or tubing . implantation, especially for permanent and peripheral
[28]
Radial strength is the strength needed to compress VS. Another occlusion of VS happens after neointimal
a material (a VS in this particular case). Proper radial proliferation, which progressively narrows the stent lumen,
strength of VS is of great importance because it will representing a long-term side effect (6–12 months after
[30]
determine the permanence of the stent in position and implantation and depending on the type of VS) . In this
its ability to maintain the vessel properly open (patency), case, the most frequent sign is the appearance of anginal
which is of special importance in PAD. That is, a VS must symptoms (in coronary) or claudication/ischemic(in
[31]
possess enough radial strength to hold the vessel and to peripheral) symptoms . Antiproliferative drugs such as
prevent migration of the medical device. On the contrary, sirolimus, everolimus or paclitaxel are of great usefulness
excessive radial strength may lead to vessel overexpansion, in the prevention of this side effect, especially when locally
causing endothelial injury, inflammatory reaction, and released from DES.
rupture/deformation risk (pseudoaneurysm, dissection). The evolution of the VS, the implantation procedure
According to Lachowitzer, the “structural design of the and the prophylactic treatment (typically involving the
device plays the largest role in a device’s radial strength and use of two antiplatelet drugs) have allowed for a reduction
stiffness” . Briefly, the wider and more open the structure in the thrombosis incidence, though it is still a matter of
[27]
of the VS, the lower the radial strength. concern in this type of interventions. Moreover, Modi
An optimal VS must possess optimal axial flexibility et al. have reported that there was no significant difference
and radial rigidity to guarantee the stent patency. The between the rate of stent thrombosis between bare-metal
greater the radial stiffness of the medical device, the stents and eluting drug stents, and only the timing of the
[31]
greater the pressure exerted over the vascular wall, thus event varies . Generally, thrombosis is more likely caused
guaranteeing blood flow. On the other hand, the higher by DES, whereas BMS are more associated to in-stent
the axial flexibility, the better the stent adaptation and restenosis events. Nonetheless, it is challenging to separate
deformation to the human body curvatures and less damage both cases, since they are related to each other in terms of the
to the vascular walls. Solving these two contradictory and pathological mechanisms. According to Reejhsinghani and
coexisting problems of axial flexibility and radial rigidity is Lofti, delayed arterial healing following DES implantation
one of the main challenges in the design of stents. is characterized by a lack of complete re-endothelialization
and persistence of fibrin when compared with BMS, and
VS recoil is defined as the difference between this delayed healing is the primary substrate underlying all
the minimum diameter of the crimped stent (before cases of late DES thrombosis . Since polymer-coatings
[32]
implantation) and the minimal luminal diameter of the are commonly applied in DES to control drug release, any
stent after implantation (once expanded). Consequently, hypersensitivity to these ingredients could improve the
recoil stent events affect the lumen diameter and thus risk of thrombosis. Once again, the geometry of the stent
the expansion of the stent. This modification could lead plays an important role, since it has been demonstrated
to malposition and restenosis. The VS, which is able to that thick-strutted stents possess higher thrombotic
maintain its initial expansion diameter, would have lower risk than thin-strutted VS ; therefore, it is necessary to
[33]
recoil value and better stent patency in the long term . optimize not only the manufacturing, the composition and
[29]
Acute recoil is defined as the difference between the the implantation strategy, but also the structural design of
maximum diameter of inflated balloon and the diameter the medical device.

Volume 9 Issue 2 (2023) 228 https://doi.org/10.18063/ijb.v9i2.664