TITLE OF THE INVENTION
AN IMPROVED BIORESORBABLE POLYMERIC VASCULAR STENT DEVICE
FIELD OF THE INVENTION
The present invention relates to an improved bioresorbable polymeric vascular device.
Particularly, the present invention relates to bioresorbable expandable medical devices such as
stents for supporting and maintaining the patency of a body lumen. The invention relates to stent
design made of bioresorbable and biocompatible polymer which fits within the body lumen
namely blood vessels and is useful in treating various cardiovascular disorders like
atherosclerosis, restenosis or cannanlicular obstructions. It also relates to delivering the drug via
stent scaffold to adjacent vessel wall which leads to uniform distribution of drug particles within
the polymeric stent scaffold. It also relates to bioresorbable stent which remains radio-opaque till
the scaffold disappears completely from the lumen.
BACKGROUND AND PRIOR ART OF THE INVENTION
A stent is a medical device which serves as internal scaffold to increase or maintain the
lumen of a body conduit. Stents have been widely used for coronary diseases, tracheobronchial
obstruction; in oesophagus and gastrointestinal tract and in urology. Metallic coronary stents are
widely used for treatment of arterial dissection, elastic recoil, and intimal hyperplasia following
percutaneous transluminal coronary angioplasty. Metal based stents permanently remain in the
patient’s body. They can induce endothelial dysfunction and inflammation which may further
precipitate medical complications such as Late Stent Thrombosis (LST) and need for prolonged
anti-platelet therapy. Currently metallic drug eluting stents are used for treating coronary artery
disease. These stents are permanent implants and restrict natural healing process and Vasomotion
resulting in long term (more than 5 years post implantation) complications such as Very Late
Stent Thrombosis. The risk of stent thrombosis due to metallic stents has not been overcome by
even drug eluting stents. Rather, vascular lumen remodeling and expansion is prevented by use
of such stents.
Restenosis is mainly caused by early constrictive remodeling (vessel shrinkage) and to
some extent by hyperplastic healing response. Preventing constrictive remodeling can therefore,
limit stent associated restenosis. Bioresorbable stents overcome this limitation. They support a
body conduit only during its healing process- usually 2 -3 years, leaving behind a normal,
healthy artery free of any foreign body. With time, the mechanical load is transferred to the
surrounding vessels and stent mass and strength decreases. During this process, it gradually loses
its radial strength and ability to resist constrictive remodeling forces long before it is fully
absorbed. Moreover, they allow longer term drug delivery to the vessel wall from an internal
reservoir, which in turn eliminates the need for a second surgery to remove the device.
Nonetheless, technological challenges are associated with developing a stent from a
bioresorbable polymer. It should have sufficient radial strength, also known as hoop or
circumferential strength and rigidity to withstand radial compressive forces. The stent should
prevent negative vessel remodelling and avoid stent deformity/strut fractures. It should have
minimum recoil and should be sufficiently flexible to allow from crimping and expansion.
However, thickness of struts and long term creep are drawbacks associated with polymeric based
stents.
A number of polymeric stents have been designed with varying geometries, linear or
curved strut shapes (like diamond shaped cells, W-shaped cells, hour-glass shaped cells,
parallelogram or quadrilateral shaped regions, bow-tie shaped cells, opposing M-shaped
elements), and varying shapes of inter-linking bars like S, H, I, O, V to overcome the
disadvantages associated with metallic stents. Few documents disclose a stent design which
provides movement freedom i.e. while twisting and expanding. Few documents discloses a stent
design which provides better radial rigidity, vessel coverage by allowing side branch access,
reduced fore shortening, more flexibility. It provides better scaffolding per unit area of vessel
wall to be supported.
Few documents describe an axially-radially nested stent that maintains expanded size and
resist recoil due to the slide and lock design. Such a locking mechanism has also been disclosed in
Few documents, whereby the locking mechanism secures the stent in crimped state onto a carrier
module so that it stays immobilized for deployment. Another locking stent having multiple locking
points has been disclosed in US patent publication number US 2004/0249442 Al wherein the interconnecting
elements of the stents are interlocked in one or the other position.
However, currently manufactured polymeric stents do not adequately provide sufficient
tailoring of the properties of the material forming the stent t and obtain the desired mechanical
behavior of the device under clinically relevant in-vivo loading conditions. Moreover, the size of
the stent scaffold for preventing restenosis depends on the vessel to be treated. There is a need to
design and manufacture a vascular stent of various sizes (i.e. lengths and diameters) that can
meet both clinical and mechanical requirements of the stent.
OBJECTIVES OF THE PROPOSED INVENTION
The primary objective of the present invention is to provide an improved stent dvice
which overcome the above-said drawbacks of the existing stent device.
Another objective of the present invention to provide an improved stent design with
desired flexibility and strength which supports the vessel wall with a uniform force.
Yet another objective of the present invention to provide a stent which is made up of
bioresorbable polymer whereby the crystal orientation allows more radial rigidity.
BRIEF/DESCRIPTION OF DRAWINGS/FIGURES
Further aspects and advantages of the present invention will be readily understood from the
following detailed description with reference to the accompanying drawings. Reference numerals
have been used to refer to identical or similar functionally similar elements. The figures together
with a detailed description below, are incorporated in and form part of the specification, and
serve to further illustrate the aspects and explain various principles and advantages, in
accordance with the present invention wherein:
FIG. 1 depicts an improved stent device according to one of the aspect of the present invention.
FIG. 2 (a to d) depicts a computer simulation illustration depicting a partial view of an aspect of
a bioresorbable medical device depicting scaffold strut segments
FIG. 3 depicts a flattened view of a portion of exemplary stent pattern
FIG. 4 depicts a portion of stent pattern from FIG. 3
FIG. 5 depicts another portion of stent pattern from FIG. 3
Skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and
have not necessarily been drawn to scale. For example, the dimensions of some of the elements
in the drawings may be exaggerated relative to other elements to help to improve understanding
of aspects of the present invention.
DESCRIPTION OF DRAWINGS/FIGURES
FIG. 2 (a) and FIG. 2(c) show the finite element simulation for crimped and expanded
profile of the stent and the movement of the struts and links during the same. FIG. 2 (b) and FIG.
2 (d) represent the recoil of the stent during crimping and expansion respectively. Struts
arrangements are optimized for minimum contact in crimping and minimum recoil.
FIG. 3 depicts an exemplary stent pattern 100 for use with embodiment of a polymeric
tube. The stent pattern 100 is shown in a flattened condition in order to have a clear view. A
radially expandable stent is formed when this flattened portion of the stent pattern 100 is molded
in a cylindrical form.
As depicted in FIG. 3, stent pattern 100 includes a plurality of cylindrical rings 302 with
each ring including a plurality of amoebic (irregular) shaped cells 304. Any number of rings 302
can be included in the stent pattern 100 depending upon the length of the stent pattern which is
desired. For reference, line A-A represents the longitudinal axis of a stent using the pattern
depicted in FIG. 3.
Amoebic shaped cells 304 are formed of two struts 305 and 306 lying opposite to other
two struts 307 and 308. Struts 305 and 308 are S-shaped while struts 306 and 307 are N-shaped.
The arrangement of the struts is such that struts with same shape lie diagonally opposite to each
other. S-shaped strut comprises two diagonal linear bar arms 309 and 310, and three short linear
bar arms 311, 312 and 313. N-shaped struts comprises two diagonal linear arms 314 and 315,
and one short linear bar arm 316 which connects the two diagonal linear arms 314 and 315 via
curved bar elements 317 and 318.
The stent pattern 100 further includes interlinking arm 319 that is perpendicular to the
line A-A. They connect the intersection of bar arms 305 and 306, and 307 and 308. Moreover,
they connect cylindrical ring 304 with adjacent cylindrical ring 304. The inter-linking elements
are two question-marks being joined at their linear ends 320.
Another embodiment of stent pattern 100 can also be described as comprised of
interconnected W-shaped elements 321. Embodiments of the stent depicted in the FIG. 4 above
can include any number of circumferentially aligned W-shaped elements. Each W-shaped
element is formed of one S-shaped strut 305 and one N-shaped strut 306. . It comprises of three
peaks 322,323, 324 and two depressions 325 and 326. The point of junction of these two struts
links one W-shaped element with opposing W-shaped element by interlinking arm 319. This
point of junction corresponds to one of the depressions 325 of W-shaped element 321. A valley
327 is formed when the inter-linking arm 319 connects two opposing W-shaped elements 321 at
the junction point 325.
Another embodiment of the present invention states that interlinking arm 319 connects
two opposing Y-shaped elements 328. As shown in FIG 5, Y-shaped elements have one long
diagonal arm, two short straight arms one of which is connecting the interlinking arm 319.
DESCRIPTION OF PROPOSED INVENTION
While the invention is susceptible to various modifications and alternative forms, specific aspect
thereof has been shown by way of example in the drawings and will be described in detail below.
It should be understood, however that it is not intended to limit the invention to the particular
forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and
alternative falling within the spirit and the scope of the invention as defined by the appended
claims.
The Applicants would like to mention that the drawings are drawn to show only those specific
details that are pertinent to understanding the aspects of the present invention so as not to
obscure the disclosure with details that will be readily apparent to those of ordinary skill in the
art having benefit of the description herein.
The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a
non-exclusive inclusion, such that a system, device that comprises a list of components does not
include only those components but may include other components not expressly listed or
inherent to such system or device. In other words, one or more elements in a system or device
proceeded by “comprises… a” does not, without more constraints, preclude the existence of
other elements or additional elements in the system or device.
In the following description of the aspects of the invention, reference is made to the
accompanying drawings that form part hereof and in which are shown by way of illustration
specific aspects in which the invention may be practiced. The aspects are described in sufficient
details to enable those skilled in the art to practice the invention, and it is to be understood that
other aspects may be utilized and that changes may be made without departing from the scope of
the present invention. The following description is, therefore, not to be taken in a limiting sense,
and the scope of the present invention is defined only be the appended claims.
Accordingly, the proposed invention relates to an improved stent device comprising a plurality of
irregular W-shape segments having three peaks and two depressions that is repeated
circumferentially to form a ring and thereafter the ring is repeated along the length up to
predetermined distance, and subsequently manipulated helically; link shown in Fig3., the said
stent device consisting of 2 Y-shaped turning point and one fixed point and the link 319;.element
described as 319 rotates about the fixed point in opposite direction in crimping and expansion to
serve as a lock to reduce recoil; rotating link used for longitudinal stretching; two struts opening
opposite at the peaks of Y-shaped element 328; helical aligned W-shaped elements 321; Element
319 for flexibility.
Another aspect of the present invention, wherein the said stent design results in fore lengthening
on expansion.
Yet another aspect of the present invention, wherein the said stent is manufactured via injection
molding technique.
Yet another aspect of the present invention, wherein the said stent is manufactured from
bioresorbable polymers
Yet another aspect of the present invention, wherein the said bioresorbable polymer is
‘breathable’ i.e. the orientation of the crystals of the polymer are such that it stretches on
expansion and thus provides radial rigidity.
Yet another aspect of the present invention, wherein the said stent is saturated with a drug and/or
radio-opaque solution using nano cellular technology. The process can be carried out during
injection molding procedure or when the stent is ‘hot’ after the procedure.

ADVANTAGES OF THE INVENTION
1. The first advantage of the present invention to provide an improved stent design with desired
flexibility and strength which supports the vessel wall with a uniform force.
2. Another advantage of the present invention to provide a stent which is made up of
bioresorbable polymer whereby the crystal orientation allows more radial rigidity.
3. Yet another advantage of the present invention to provide a stent which remains radio-opaque
throughout the life of the bioresorbable stent and gradually elutes a drug into the vessel wall.
The inventors have been working to develop the invention, so that advantage can be
achieved in an economical, practical, and facile manner. While preferred aspects and example
configurations have been shown and described, it is to be understood that various further
modifications and additional configurations will be apparent to those skilled in the art. It is
intended that the specific embodiments and configurations herein disclosed are illustrative of
the preferred nature of the invention, and should not be interpreted as limitations on the scope
of the invention.