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Biocompatible materials for cardiovascular stents: A Review

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Abstract

One of the most common interventions performed today is intravascular stenting. A stent is a small tubular device placed into a blood vessel to hold it open. This review covers various aspects of stents from how it is placed into the vessel (e.g. the coronary artery) to the biocompatible materials used (e.g. metal). Mechanical considerations are also being discussed as well as comparison between self-expanding stents and drug eluting stents versus resorbable stents. Other latest research are also covered such as a 'smart stent monitor' based on sensors providing real-time feedback.
Biocompatible materials for cardiovascular stents
Yann Blake
17334432
4Bio5: Biomechanics module supervised by Dr. David Hoey
Department of Mechanical and Manufacturing Engineering
Trinity College Dublin
December 2020
Abstract
One of the most common interventions performed today is intravascular stenting. A stent is a small
tubular device placed into a blood vessel to hold it open. This review covers various aspects of stents from
how it is placed into the vessel (e.g. the coronary artery) to the biocompatible materials used (e.g. metal).
Mechanical considerations are also being discussed as well as comparison between self-expanding stents
and drug eluting stents versus resorbable stents. Other latest research are also covered such as a ’smart
stent monitor’ based on sensors providing real-time feedback.
Contents
1 Introduction 2
1.1 Thevarietyofstents........................................ 2
1.2 Cardiovascular diseases and the need for Stents . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Arteries and Stents Mechanics 3
2.1 FromArteriesstudiestoStents.................................. 3
2.2 Mechanical considerations for Stent design . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Influence of biocompatible materials on stent performances 4
4 Perspectives of improvement 5
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Yann Blake Biocompatible materials for cardiovascular stents
1 Introduction
Biomaterials are increasingly used in numerous
medical applications such as the treatment of cardio-
vascular diseases. These are natural or synthetic ma-
terials suitable to be introduced into living tissues and
designed to interface with specific biological systems.
Biomaterials’ desired effects includes treatment, aug-
mentation or replacement of biological functions. Ar-
tificial heart medical devices and joints implants are
some concrete applications of that.[1, 2] Another im-
portant application where biomaterials are necessary
is intravascular stenting. The Global Vascular Stent
Market is indeed expected to grow significantly in
the upcoming years with the increasing demand for
minimally invasive surgeries, the rise of patients with
cardiovascular diseases and overall the aging of the
population.[3]
1.1 The variety of stents
Stents are small medical tubes inserted in the body
to maintain open an obstructed hollow organ or pas-
sageway (more accurately a lumen - which is the cav-
ity within a tube) such as a blood vessel.[4] These
are woven (interlaced at right angles), knitted (in-
terlocking loops) or braided (several parts woven to-
gether) cylindrical mesh structure made of biocom-
patible materials usually metals or plastics such as
stainless steel, nitrol or chrome-cobalt alloy.[5] Once
placed in the blood vessel, often an artery, the stents
are expected to restore the flow of the fluid -in this
case- blood. Traditional stents are expected to stay
in place and last over the long-term. Other types of
stent however may have different expected duration:
dissolving or biodegradable stents.[6]
Stents have also other applications than extend-
ing obstructed blood vessels: these have also been
tested for microvascular anastomosis surgery. Mi-
crovascular anastomosis is the formation of a connec-
tion between two normally distinct very small blood
vessels performed under a surgical microscope. It
was observed that using a dissolvable stent during
this process achieved faster repair of the blood ves-
sels and less dilation at the point of surgery.[7] In
addition to these fully dissolvable stents, other stents
have been designed to only allow a part of it to dis-
solve. An expandable stent having a dissolvable por-
tion may have an application in arterial intersections
where an aneurysm is formed (abnormal bubble of
blood formed adjacent to the blood vessel where the
walls had a weak spot). In this case, the stent would be
expected to close the aneurysm sac, at the neck point -
in the axis of the blood vessel walls. On the other side,
the dissolvable portion would be in contact with an ac-
tivating agent to allow the intersecting blood vessel to
flow normally.[8] Dissolvable stents are also used in
other lumen such as in the urinary tract[9]
Different stent types based on new materials,
methods or solutions now exist. The latest innovations
focus on coated, resorbable, and drug-eluting stents.
The desired improvements include the release of bi-
ological active agents able to control adhesion to the
lumen walls, cell differentiation, or vessel tissue de-
velopment. These new stents also provide new physi-
cal–chemical properties and degradation rate. Despite
the extensive progress in the research for new stents
which will be discussed in this review, no ideal stent
yet exists.[10]
1.2 Cardiovascular diseases and the
need for Stents
As it was mentioned, stents are often used to open
some obstructed lumen, especially blood vessels. Let
us then look into reasons why these blood vessels may
be obstructed.
The heart is the key organ which keeps blood con-
tinually circulating throughout the body. Arteries are
the blood vessels which supply oxygen-rich blood
to the entire organism. Arteries have much higher
pressure than vein blood vessels. The arteries sup-
plying blood to the heart are referred to as coronary
arteries. Sometimes, coronary arteries become nar-
row due to plaque deposits or other phenomena. The
plaque deposits consist of an accumulation of cells,
fats, excess of cholesterol, other lipids, calcium, cel-
lular debris and other substances. The narrowing of
these vessels which is called atherosclerosis is pre-
cisely what the stents try to compensate. Atheroscle-
rosis not only occurs in coronary arteries but in many
other sites of complex blood vessel geometry: ab-
dominal aorta, iliacs (near the abdomens), femorals
(in the legs), popliteals (knees), carotids (neck), and
cerebrals (brain).[11, 12] Atherosclerosis is a com-
mon disorder of the arteries and an important cause
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Yann Blake Biocompatible materials for cardiovascular stents
of Cardiovascular diseases (i.e. heart failure, stroke,
high blood pressure and peripheral artery disease -
similar to coronary artery disease but excluding the
heart and the brain).[13]
The incidence of Atherosclerosis varies from 23%
to 74% in various studies,[14, 15, 16, 17, 18] and it is
reported to be the responsible for more than 25% of
deaths on the Indian subcontinent.[18] These figures
clearly demonstrate the importance in understanding,
extending research and treating this condition.
Atherosclerosis is detected via electrocardiogram,
ultrasound, computerized tomography (CT) scan or
magnetic resonance angiography (MRA). Once the
point of return is passed and prevention strategies
would not work anymore, treatments become nec-
essary. Angioplasty is the most common treatment
which consists of opening up the obstructed vessel
using a small flexible plastic tube or catherer with a
’balloon’ at the end. The balloon is inflated which
widens the vessel (Figure 1). The plastic tube is often
inserted from femoral artery where a small cut allows
it to be inserted. Stent implantation usually occurs at
the same time.
2 Arteries and Stents Mechanics
2.1 From Arteries studies to Stents
In order to understand the mechanics of Arteries it
is essential to understand their structure. Arteries like
all blood vessels are made of three distinct layers also
called tunicae. The first, tunica intima lines the inside
walls and is very thin. It is a semipermeable mem-
brane with various roles such as pressure regulation
facilitator. When it comes to mechanical modelling, it
is often neglected because of its small thickness. The
second, tunica media is made of smooth muscle cells
embedded in an extracellular plexus of elastin and col-
lagen and an aqueous ground substance. The third and
outermost layer is the tunica adventitia which consists
of a dense network of collagen fibers with scattered fi-
broblasts, elastin and nerves. It appears to serve as a
protective layer which prevents rupture of the vessel
when an increase in pressure occurs, since fibers grad-
ually straighten in these conditions.[3]
On the perspective of mechanical behaviors of
blood vessels, many observations have been made
through various research. The presence of resid-
ual stresses both in axial and circumferential direc-
tions was reported. Residual stresses appear to be
related to the remodeling of the blood vessel wall
which occurs when stress changes.[19] Luminal part
(the innermost) is reported to be under compression
while the outermost under tension which benefits to
growth and remodeling of the vessels. Other char-
acteristics include: anisotropy under load-free con-
figuration (due to different tissue properties); incom-
pressibility (due to the high water content); viscoelas-
tic response of the tissues; hysteresis (dependence
on history) under cyclic loads; stress relaxation after
sustained deformation; pseudoelastic (behaving dif-
ferently in loading and unloading). It is also ob-
served that aged arteries are stiffer than younger ar-
teries due to fracture of the elastic laminae (mem-
brane) caused with fatigue in the tunica media -
and due to cross linking among collagen fibers in
the tunica adventitia during remodeling process.[3]
Figure 1: Process of Stent im-
plantation with angioplasty [3]
Beyond the
mechanics of ar-
teries mentioned,
there are a num-
ber of deforma-
tions these ves-
sels undergo when
subjected to me-
chanical forces -
be it from internal
blood flow, con-
tiguous tissue teth-
ering or implanted
devices such as
stents. Muscu-
loskeletal motions
are also widely
studied through
magnetic reso-
nance angiogra-
phy imaging to
show how these
strongly impact
arterial deforma-
tions: twisting,
shortening and bending angles are observed. These
deformations are more significant in older patients
due to loss of arterial elasticity. In addition to in vivo
Page 3
Yann Blake Biocompatible materials for cardiovascular stents
observations many biomechanical models on twist-
ing, kinking or tortuosity deformations using finite
elements methods are used to theoretically predict pa-
rameters such as critical loads. Similarly, 3D-model
algorithms showed that fracture mechanism on the
stent may occur in situations of compression or move-
ment of the blood vessels in supine and fetal positions
(of the patient) where maximum hip and knee flexion
happen.[20, 21] Many others papers report on mod-
eling algorithms among which the study of physical
forces on stented and non-stented femoropopliteal
arteries (commonly subject to Atherosclerosis) in pa-
tients with peripheral arterial disease based on differ-
ent leg positions.[22, 23] All these findings provide
an essential ground to understand the mechanical be-
haviors of stents and thus the requirements when de-
signing them.
2.2 Mechanical considerations for Stent
design
Mechanical behaviour of balloon-expandable
stents (also called expanding stents) have been stud-
ied by Dumoulin et al.[24] The metallic P308 Pal-
maz stent with diamond-shaped cells (once expanded)
and made of stainless-steel was tested through several
models. One important challenge to deal with when
designing these stents is the recoil phenomena.[25]
Stent recoil refers to the percentage by which the di-
ameter of the stent decreases between its expanded
diameter (from the angioplasty) to its relaxed diam-
eter (either following angioplasty or over the long-
term).[26] That is an aspect where stent design firms
often focus on with additional connectors on the more
proximal end of the stent for more axial strength; or
with wider peaks which focus strain to reduce re-
coil as well as other connector (to the lumen walls)
design innovation.[27] Pattern of cells and thickness
appeared to also provide less recoil and foreshorten-
ing and better flexibility.[28] From Dumoulin et al.’s
models it was highlighted that not only expansion and
intrinsic recoil is correlated with the stent shape but
also its mechanical properties and the external stresses
in that location - which leads to most stents being de-
signed 10 to 15 percent larger than the targeted blood
vessel. Their crushing modelling showed that buck-
ling is a critical issue in stent design. Comparison
between coated stents (with self-adhesive foil to fa-
cilitate embedding to lumen walls) and bare stents
showed no change in stiffness. Palmaz stents have
the advantage of high radial strength which is recom-
mended for highly resistant plaque obstructions (se-
vere Atherosclerosis) - but its plastic nature makes it
less suitable for pulsating or compressing blood ves-
sel sites, with higher permanent collapse risks. Al-
ternatively, these locations would require purely elas-
tic stents allowing reversible deformations and thus
avoiding collapse.[24]
3 Influence of biocompatible ma-
terials on stent performances
Let us extend on the advantages between balloon-
expandable stents which Palmaz belongs to and other
types of stents, as well as comparing the various bio-
compatible materials used.
Before recoil even becomes a challenge, the ease
of deploying the stent is essential as well as its re-
sistance to dislodgement. For metallic stent such as
the Palmaz, it requires a higher yield point value or
lower modulus of elasticity. Stainless steel which is
widely used achieves moderately well for yield point
and radial force. However the modulus of elasticity
(200 GPa) is not low, which can only be compen-
sated with design shapes. Another metal used, Niti-
nol (Nickel titanium alloy) is more complex in that
regards. The nickel-to-titanium ratio and the high-
temperature heat treatment influences the thermal
memory and the temperature at which the crystalline
structure changes - which consequently changes the
material flexibility and malleability. Ideally, high flex-
ibility and malleability are desired when the stent is
inserted in the implantation system (tube) at room
temperature. Then, low flexibilitity with high rigid-
ity (achieved with austenite crystalline structure) is
desired when the stent is released in the blood ves-
sel at around 30 degrees Celsius. These key tem-
perature points therefore play a major role in stent
performances for the nitinol material, unlike stainless
steel. Dyet et al. demonstrate two distinct groups
of metallic stents in terms of mechanical properties:
those affected by their construction and those directly
affected by the metal properties. Overall they con-
sider high radial strength, high radio-opacity, elas-
ticity, flexibility, good trackability as being the ideal
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Yann Blake Biocompatible materials for cardiovascular stents
properties of a stent ; although none of the stents
they tested or researched on (in 2000) met these cri-
teria. The necessity of assessment of metal fatigue is
also stated, since several incidents of stents breaking
up occurred when submitted to repeated flexing.[29]
Since 2000, many other biocompatible materials ap-
peared and were widely tested.
Resorbable stent also called biodegradable stent
which are manufactured from a material capable of
dissolving or being absorbed in the organism, are be-
coming increasingly popular since these avoid many
risks and long-term issues - permanent stents bring.
A zinc-copper biodegradable metal stent developed
by Zhou et al. in 2019 achieved less intrinsic elas-
tic recoil than standard stainless steel stents; better
trackability (less push force when passing through
curved vessels thus reducing mechanical stimulation
on them). Their stent also facilitates the recovery
of vascular pulsatility (difference between blood sys-
tolic and diastolic velocities).[30] Choubey et al. per-
formed Finite element analysis to compare predicted
Von-Mises Tress, recoil, Fracture point, Ultimate Ten-
sile strength and factor of safety for seven stent ma-
terials: Stainless Steel 316L, Cobalt Chromium L-
605 Stent, biodegradable Stent (PCL), Nitinol Stent
(Austenite), Elgiloy Stent, Tantalum Stent, Cobalt
Chromium. Biodegradable stents made of polycapro-
lactone (PCL) polymer had the most significant recoil
making it less ideal than the other materials. Its Ulti-
mate Tensile strength was also the lowest. Tantalum
(a transition metal) achieved poor performances too.
Overall Cobalt Chromium L-605 and Nitinol (with
good corrosion resistance) have the best balance and
make better material for stent.[31] Other research sup-
port the use of cobalt-chromium stent.[32] Biodegrad-
able stints remain at the center of innovation, in addi-
tion to zinc-copper or PCL, some use Fe–Mn alloys.
[33]
Drug eluting stents are another important seg-
ment of research, improving standard or coated stents.
Stent coatings can control biocompatibility, degrada-
tion rate, protein adsorption, and adequate formation
of endothelial tissue. These are parameters making
stents perfom better. Coating materials are either or-
ganic polymers, biological components or inorganic
coatings (e.g. nitrides). Drug eluting stents aim to
reduce the overproduction of tissue in the stent site
which would cause obstruction again. Antiprolifera-
tive substances ’drugs’ are therefore used such as pa-
clitaxel or limus.[10]
4 Perspectives of improvement
In 2020, researchers from ETH Zurich devel-
oped a high-level precision, biocompatible and 3D-
printable micro-robot which delivers drug in the or-
ganism through the blood vessels. They are now in-
vestigating the use of such micro-robots for imple-
mentation of surgical tools especially stents.[34] The
same university also introduced a new technology
based on ’4-D printing’ which allows stents to be up
to forty times smaller than existing ones.[35]
To alert potential recoil, pressure monitors placed
on the stent - at both ends - have been developed
which informs the patient or doctor when there is a
drop in blood pressure across the stent. The informa-
tion is transmitted wirelessly to a reader placed on the
body close to the stent site. These inexpensive small
scale technologies aim to better monitor the evolution
of the stents over time.[36, 37, 38]
When it comes to the blood vessel conditions
(such as atherosclerosis) in the coronary artery, sev-
eral research show opposing findings, conclusions and
recommendations between stenting or bypass surgery.
Some research demonstrate that coronary artery by-
pass surgery may be the best treatment option for the
majority of patients having more than one blocked
heart artery instead of placing stents. This high-
lights the need for further research and improve-
ment of stents which may allow patients to avoid
open heart surgery while obtaining the same treatment
performance.[39]
The motivations of innovation is often to over-
come the current limitations of stents, such as resteno-
sis (the recurrence of narrowing of a blood ves-
sel, sometimes from recoil), or inflammation and
thrombosis (formation of blood clot) at the stent
site. Other characteristics are also often desired such
as biodegradability and some mechanical parameters
based on the targeted blood vessel. Finding the ideal
design and material doesn’t suffice, when biocompat-
ibility remains the most important constraint when
designing a stent. Promising stent solutions are cur-
rently in development, the numerous stent patents
filled in recent years can testify this.[10] Clinical trials
and market approval requests from companies have
also been rising.[35]
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Yann Blake Biocompatible materials for cardiovascular stents
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Further Reading
[A]Khalilimeybodi, A., Khoei, A.A. and Sharif-Kashani, B., 2019. Future Balloon-Expandable Stents: High
or Low-Strength Materials?. Cardiovascular Engineering and Technology, pp.1-17.
[B]Beier, S., Ormiston, J., Webster, M., Cater, J., Norris, S., Medrano-Gracia, P., Young, A. and Cowan, B.,
2016. Hemodynamics in idealized stented coronary arteries: important stent design considerations. Annals
of biomedical engineering, 44(2), pp.315-329.
[C]Olivier F Bertrand, Rajender Sipehia, Rosaire Mongrain, Josep Rod´
es, Jean-Claude Tardif, Luc Bilodeau,
Gilles Cˆ
ot´
e, Martial G Bourassa, Biocompatibility aspects of new stent technology, Journal of the American
Page 8
Yann Blake Biocompatible materials for cardiovascular stents
College of Cardiology, Volume 32, Issue 3, 1998, Pages 562-571,
[D]Wenwang Wu, Xiaoke Song, Jun Liang, Re Xia, Guian Qian, Daining Fang, Mechanical properties of
anti-tetrachiral auxetic stents, Composite Structures, Volume 185, 2018, Pages 381-392,
Page 9
... Coronary artery disease (CAD), in particular, is the third most common cause of mortality worldwide, imposing a major health and economic burden on most developed nations [6][7][8][9][10][11]. CAD is characterized by the narrowing of the artery due to plaque deposits beneath the endothelium. Cells, fats, calcium, cellular debris, and other substances may accumulate in these deposits, starting a cascade of events-diminished blood vessel artery lumen, restricted blood flow, and inadequate nutrients and oxygen supply to the cardiac muscle-that can eventually cause myocardial infarction or transient cerebral ischemic attacks and stroke [12][13][14][15][16][17]. ...
... To restore normal blood flow and avoid the other critical consequences of vessel narrowing, special devices called stents can be inserted into the affected vessel using fluoroscopic and/or endoscopic guidance [13,14]. This procedure is minimally invasive compared to open cardiac surgery and is associated with lower mortality and morbidity in the long term and better outcomes in critically ill patients in the short term [15]. ...
... Therefore, cardiovascular stents are life-saving devices, rightfully included in the top ten medical breakthroughs of our century [18]. From a constructive point of view, stents are small, complex, cylindrically shaped hollow structures formed into a sequential ring construction comprising a series of struts and connecting elements [13,15,19]. The way that stents work relies on their design, which helps keep the path of human arteries through the body open [20,21]. ...
Article
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One of the leading causes of morbidity and mortality worldwide is coronary artery disease, a condition characterized by the narrowing of the artery due to plaque deposits. The standard of care for treating this disease is the introduction of a stent at the lesion site. This life-saving tubular device ensures vessel support, keeping the blood-flow path open so that the cardiac muscle receives its vital nutrients and oxygen supply. Several generations of stents have been iteratively developed towards improving patient outcomes and diminishing adverse side effects following the implanting procedure. Moving from bare-metal stents to drug-eluting stents, and recently reaching bioresorbable stents, this research field is under continuous development. To keep up with how stent technology has advanced in the past few decades, this paper reviews the evolution of these devices, focusing on how they can be further optimized towards creating an ideal vascular scaffold.
... Stents are another area where hybrid biomaterials are used. (2) The researchers are also trying to precisely assess the fate of these cells after their implantation, as well as their exact contribution in the reconstruction of the tissue compared to cells of the host tissue. They use imaging techniques (microscopy, MRI, etc.) for this. ...
Article
Biomaterials are present in the implants used daily in orthopedic surgery, which can be placed temporarily (osteosynthesis material or bone replacement products) or permanently (joint prostheses). In all cases, they must withstand the various mechanical and biological stresses caused by their implantation in living tissue. This is subject to a marketing authorization procedure which requires the EEC marking. The biomaterial of which an implant is made is one of its fundamental characteristics, as is its shape and the nature of its friction torque for arthroplasties. These biomaterials are characterized by three essential criteria: their biocompatibility, their resistance to corrosion and their mechanical properties. In this review, several examples, particularly cardiovascular with artificial heart and stents are discussed. Different types of biomaterials are also detailed.
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Even though scientific studies of smart stents are extensive, current smart stents focus on pressure sensors. This paper presents a novel implantable biocompatible smart stent for monitoring eventual restenosis. The device is comprised of a metal mesh structure, a biocompatible and adaptable envelope, and pair-operated ultrasonic sensors for restenosis monitoring through flow velocity. Aside from continuous monitoring of restenosis post-implantation, it is also important to evaluate whether the stent design itself causes complications such as restenosis or thrombosis. Therefore, computational fluid dynamic (CFD) analysis before and after stent implantation were carried out as well as finite element analysis (FEA). The proposed smart stent was put in the descending thoracic section of a virtually reconstructed aorta that comes from a computed tomography (CT) scan. Blood flow velocity showed that after stent implantation, there is not liquid retention or vortex generation. In addition, blood pressures after stent implantation were within the normal blood pressure values. The stress and the factor of safety (FOS) analysis showed that the stress values reached by the stent are very far from the yield strength limit of the materials and that the stent is stiff enough to support the applied loads exported from the CFD results.
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Cardiovascular diseases are the most distributed cause of death worldwide. Stenting of arteries as a percutaneous transluminal angioplasty procedure became a promising minimally invasive therapy based on re-opening narrowed arteries by stent insertion. In order to improve and optimize this method, many research groups are focusing on designing new or improving existent stents. Since the beginning of the stent development in 1986, starting with bare-metal stents (BMS), these devices have been continuously enhanced by applying new materials, developing stent coatings based on inorganic and organic compounds including drugs, nanoparticles or biological components such as genes and cells, as well as adapting stent designs with different fabrication technologies. Drug eluting stents (DES) have been developed to overcome the main shortcomings of BMS or coated stents. Coatings are mainly applied to control biocompatibility, degradation rate, protein adsorption, and allow adequate endothelialization in order to ensure better clinical outcome of BMS, reducing restenosis and thrombosis. As coating materials (i) organic polymers: polyurethanes, poly(ε-caprolactone), styrene-b-isobutylene-b-styrene, polyhydroxybutyrates, poly(lactide-co-glycolide), and phosphoryl choline; (ii) biological components: vascular endothelial growth factor (VEGF) and anti-CD34 antibody and (iii) inorganic coatings: noble metals, wide class of oxides, nitrides, silicide and carbide, hydroxyapatite, diamond-like carbon, and others are used. DES were developed to reduce the tissue hyperplasia and in-stent restenosis utilizing antiproliferative substances like paclitaxel, limus (siro-, zotaro-, evero-, bio-, amphi-, tacro-limus), ABT‐578, tyrphostin AGL‐2043, genes, etc. The innovative solutions aim at overcoming the main limitations of the stent technology, such as in-stent restenosis and stent thrombosis, while maintaining the prime requirements on biocompatibility, biodegradability, and mechanical behavior. This paper provides an overview of the existing stent types, their functionality, materials, and manufacturing conditions demonstrating the still huge potential for the development of promising stent solutions.
Article
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Despite the multitude of stents implanted annually worldwide, the most common complication called in-stent restenosis still poses a significant risk to patients. Here, a “smart” stent equipped with microscale sensors and wireless interface is developed to enable continuous monitoring of restenosis through the implanted stent. This electrically active stent functions as a radiofrequency wireless pressure transducer to track local hemodynamic changes upon a renarrowing condition. The smart stent is devised and constructed to fulfill both engineering and clinical requirements while proving its compatibility with the standard angioplasty procedure. Prototypes pass testing through assembly on balloon catheters withstanding crimping forces of >100 N and balloon expansion pressure up to 16 atm, and show wireless sensing with a resolution of 12.4 mmHg. In a swine model, this device demonstrates wireless detection of blood clot formation, as well as real-time tracking of local blood pressure change over a range of 108 mmHg that well covers the range involved in human. The demonstrated results are expected to greatly advance smart stent technology toward its clinical practice.
Article
The effectiveness of cardiovascular stenting procedure depends on the crimping and expansion characteristics of a stent, influenced by its design parameters. In this study, CoCr stents are fabricated, crimped on a tri-folded balloon, and expanded using manual inflation device. Similarly, in the finite element model, a tri-folded balloon is used to expand the stent. The length and diameter are measured to evaluate the radial strength, recoil, foreshortening, and dogboning. The simulation and experimental results match satisfactorily. The validated FE model can be used with confidence to optimize future stent designs, thus reducing the number of testing and product development time.
Article
Purpose: Recent progress in material science allows researchers to use novel materials with enhanced capabilities like optimum biodegradability, higher strength, and flexibility in the design of coronary stents. Considering the wide range of mechanical properties of existing and newfangled materials, finding the influence of variations in mechanical properties of stent materials is critical for developing a practical design. Methods: The sensitivity of stent functional characteristics to variations in its material plastic properties is obtained through FEM modeling. Balloon-expandable coronary stent designs: Absorb BVS, and Xience are examined for artificial and commercial polymeric, and metallic materials, respectively. Standard tests including (1) the crimping process followed by stent implantation in an atherosclerotic artery and (2) the three-point bending test, have been simulated according to ASTM standards. Results: In Absorb BVS, materials with higher yield stress than PLLA have similar residual deflection and maximum bending force to PLLA, which is not the case for Xience stent and Co-Cr. Moreover, elevated yield stress significantly reduces stent flexibility only in Xience stent. For both stents, with different degree of influence, an increase in yield or ultimate stress improves stent radial strength and stiffness and reduces arterial stress and plastic strain of stent, which consequently enhances the stent mechanical performance. Contrarily, yield or ultimate stress elevation increases stent recoil which adversely affects stent performance. Conclusion: Using high-strength materials has a double-edged sword effect on the stent performance and existing uncertainty in the precise estimate of stent mechanical properties adversely affects the reliability of numerical models' predictions.
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The mechanical properties of artery stent are of key importance to the mechanical integrity and biomechanical performance reliability of stent-plaque-artery system. In this paper, making use of auxetic deformation features of chiral structures and mechanical benefits of structural hierarchy, two types of innovative chiral stents with auxetic properties are proposed: (a) anti-tetrachiral stent with circular and elliptical nodes; (b) hierarchical anti-tetrachiral stents with circular and elliptical nodes. Firstly, the in-plane mechanical properties of anti-tetrachiral structures are investigated theoretically, and uniaxial tensile experiments are performed for verification; Secondly, design procedures of anti-tetrachiral stent and hierarchical anti-tetrachiral stent with circular and elliptical nodes are elaborated. Effects of stent geometrical parameters on the tensile mechanical behaviors of these stents are studied with finite element analysis (FEA). It is found that the mechanical behaviors of anti-tetrachiral stent can be tailored through adjusting the levels of hierarchical structures and unit cell design parameters. Finally, the deformation of anti-tetrachiral and hierarchical anti-tetrachiral stents during stenting process are investigated with FEA. It is found that the proposed anti-tetrachiral and hierarchical anti-tetrachiral stents exhibit remarkable radial expanding abilities while maintaining axial stability, thus show promising performances for practical clinical applications.
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The incidence of coronary heart disease has markedly increased in India over the past few years. Ischemic heart disease, the largest cause of morbidity and mortality in the developed and developing countries today is overwhelmingly contributed by atherosclerosis. The study highlights the impact of atherosclerotic lesions in the population of Rajkot district. We studied atherosclerotic lesions in coronary arteries in cases subjected to autopsy in last 4 years, to grade and to evaluate the atheromatous plaques; and to assess the cases of myocardial infarction amongst them. The study comprises dissected specimens of heart in total 360 cases subjected for autopsy. The vessels were examined for the presence of atherosclerotic lesions which were graded according to American Heart Association and examined for evidence of myocardial infarction. The study comprises the cases in age group between 20 to 80 years. Commonest type of atherosclerosis seen was grade-4. Left Anterior Descending Coronary was most commonly involved artery. Myocardial infarction was the cause of death in 35 cases (9.72%) The data obtained may form a baseline for the forthcoming studies.
Chapter
The number of 3D textile applications in medicine is rapidly increasing as new technology and procedures are introduced in health care. A first estimate of current medical applications of both general and 3D textiles is presented based on the medical devices classification system established by the US Food and Drug Administration. The textile specifics for these applications are covered from a textile technique perspective where the different 3D weaving as well as knitting, braiding and non-woven techniques are described and how their properties they can contribute in medical applications. In addition, emerging opportunities based on smart textiles as part of textile systems are described on a general level. The strong application areas of 3D medical textiles, i.e. wound management, vascular grafting and scaffolding for tissue engineering are covered in detail both from the medical and textiles perspective. Finally, some future lines of development are suggested and a short discussion on how new 3D textiles applications can be developed in close cooperation between the textile industry and the health care sector is presented.