U.S. patent application number 16/000804 was filed with the patent office on 2018-10-04 for scaffolds having radiopaque markers.
The applicant listed for this patent is Abbott Cardiovascular Systems Inc.. Invention is credited to Joan Bei, Annie Liu, Stephen Pacetti, Karen Wang.
Application Number | 20180280165 16/000804 |
Document ID | / |
Family ID | 55911034 |
Filed Date | 2018-10-04 |
United States Patent
Application |
20180280165 |
Kind Code |
A1 |
Pacetti; Stephen ; et
al. |
October 4, 2018 |
SCAFFOLDS HAVING RADIOPAQUE MARKERS
Abstract
A scaffold includes a radiopaque marker connected to a strut.
The marker is retained within the strut by one or more of a
mechanical interference fit, a polymer coating or melt, and/or by
friction. The marker can take the form of a bead, rivet or snap-in
marker, or a tube deformed when attached to the strut. The strut is
made from a tube. The strut has a thickness of about 100
microns.
Inventors: |
Pacetti; Stephen; (San Jose,
CA) ; Bei; Joan; (Palo Alto, CA) ; Wang;
Karen; (Cupertino, CA) ; Liu; Annie;
(Cupertino, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Abbott Cardiovascular Systems Inc. |
Santa Clara |
CA |
US |
|
|
Family ID: |
55911034 |
Appl. No.: |
16/000804 |
Filed: |
June 5, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14620096 |
Feb 11, 2015 |
9999527 |
|
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16000804 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 2210/0071 20130101;
A61F 2240/001 20130101; A61F 2/915 20130101; A61L 31/18 20130101;
A61F 2/82 20130101; A61L 31/04 20130101; A61F 2002/91575 20130101;
A61F 2002/91533 20130101; A61F 2250/0098 20130101; A61F 2210/0004
20130101 |
International
Class: |
A61F 2/82 20130101
A61F002/82; A61F 2/915 20130101 A61F002/915; A61L 31/04 20060101
A61L031/04; A61L 31/18 20060101 A61L031/18 |
Claims
1. A method for making a medical device, comprising: providing a
polymer scaffold including a strut having a hole formed in the
strut, wherein the hole has a length, a width, and a hole opening
located on a first side and a second side of the strut; and using a
rivet comprising a radiopaque material and having a head and a
shank, wherein a diameter of the head is greater than a diameter of
the shank, the shank includes a tail and a medial portion, and the
shank's medial portion is between the tail and the head; attaching
the rivet to the scaffold including placing the shank into the
hole; and deforming the tail, whereupon the deformed tail has a
width that exceeds the hole width.
2-3. (canceled)
4. The method of claim 1, wherein the first side and the second
side are a luminal side and an abluminal side, respectively, of the
hole opening, wherein the head is placed at the luminal side and
held in place by a mandrel disposed within a bore of the scaffold,
and the tail extends from the abluminal side of the hole opening,
and the deforming step includes compressing the rivet between a
roller or a pin applied to the tail at the abluminal side, and a
surface of the mandrel applied to the head at the luminal side of
the opening.
5-7. (canceled)
8. The method of claim 1, wherein the marker has an undeformed
length L measured from the head to the tail and before the
deforming step, a deformed length L' measured from the head to the
deformed tail, the strut has a thickness t, and wherein the marker
lengths L, L' and strut thickness t are related as
1.2.ltoreq.L/t.ltoreq.1.8 and 1.1.ltoreq.(L'/t).ltoreq.1.5.
9. The method of claim 1, wherein the scaffold comprises a polymer
having a glass transition temperature (TG), and the scaffold is
heated 0-20 degrees above TG when the shank is placed in the
hole.
10. The method of claim 1, wherein the polymeric scaffold comprises
a polymer having a glass transition temperature (TG), and the
scaffold is heated 0-20 degrees above TG after the shank is placed
in the hole.
11. The method of claim 1, wherein the radiopaque material is
platinum, platinum/iridium alloy, iridium, tantalum, palladium,
tungsten, niobium, zirconium, iron, zinc, magnesium, or manganese,
or their alloys.
12-20. (canceled)
21. The method of claim 1, wherein the scaffold is made from a
polymer comprising poly(L-lactide), wherein the scaffold has a wall
thickness between 80 and 120 microns, and wherein following the
deforming step a distance measured from the head to the deformed
tail is between 100 microns and 150 microns.
22. The method of claim 1, wherein the hole width is a diameter and
the deformed tail width is a greater than the diameter of the
hole.
23. The method of claim 1, wherein the hole diameter is about the
same as the shank diameter before the deforming step.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to bioresorbable scaffolds;
more particularly, this invention relates to bioresorbable
scaffolds for treating an anatomical lumen of the body.
Description of the State of the Art
[0002] Radially expandable endoprostheses are artificial devices
adapted to be implanted in an anatomical lumen. An "anatomical
lumen" refers to a cavity, or duct, of a tubular organ such as a
blood vessel, urinary tract, and bile duct. Stents are examples of
endoprostheses that are generally cylindrical in shape and function
to hold open and sometimes expand a segment of an anatomical lumen.
Stents are often used in the treatment of atherosclerotic stenosis
in blood vessels. "Stenosis" refers to a narrowing or constriction
of the diameter of a bodily passage or orifice. In such treatments,
stents reinforce the walls of the blood vessel and prevent
restenosis following angioplasty in the vascular system.
"Restenosis" refers to the reoccurrence of stenosis in a blood
vessel or heart valve after it has been treated (as by balloon
angioplasty, stenting, or valvuloplasty) with apparent success.
[0003] The treatment of a diseased site or lesion with a stent
involves both delivery and deployment of the stent. "Delivery"
refers to introducing and transporting the stent through an
anatomical lumen to a desired treatment site, such as a lesion.
"Deployment" corresponds to expansion of the stent within the lumen
at the treatment region. Delivery and deployment of a stent are
accomplished by positioning the stent about one end of a catheter,
inserting the end of the catheter through the skin into the
anatomical lumen, advancing the catheter in the anatomical lumen to
a desired treatment location, expanding the stent at the treatment
location, and removing the catheter from the lumen.
[0004] The following terminology is used. When reference is made to
a "stent", this term will refer to a permanent structure, usually
comprised of a metal or metal alloy, generally speaking, while a
scaffold will refer to a structure comprising a bioresorbable
polymer, or other resorbable material such as an erodible metal,
and capable of radially supporting a vessel for a limited period of
time, e.g., 3, 6 or 12 months following implantation. It is
understood, however, that the art sometimes uses the term "stent"
when referring to either type of structure.
[0005] Scaffolds and stents traditionally fall into two general
categories--balloon expanded and self-expanding. The later type
expands (at least partially) to a deployed or expanded state within
a vessel when a radial restraint is removed, while the former
relies on an externally-applied force to configure it from a
crimped or stowed state to the deployed or expanded state.
[0006] Self-expanding stents are designed to expand significantly
when a radial restraint is removed such that a balloon is often not
needed to deploy the stent. Self-expanding stents do not undergo,
or undergo relatively no plastic or inelastic deformation when
stowed in a sheath or expanded within a lumen (with or without an
assisting balloon). Balloon expanded stents or scaffolds, by
contrast, undergo a significant plastic or inelastic deformation
when both crimped and later deployed by a balloon.
[0007] In the case of a balloon expandable stent, the stent is
mounted about a balloon portion of a balloon catheter. The stent is
compressed or crimped onto the balloon. Crimping may be achieved by
use of an iris-type or other form of crimper, such as the crimping
machine disclosed and illustrated in US 2012/0042501. A significant
amount of plastic or inelastic deformation occurs both when the
balloon expandable stent or scaffold is crimped and later deployed
by a balloon. At the treatment site within the lumen, the stent is
expanded by inflating the balloon.
[0008] The stent must be able to satisfy a number of basic,
functional requirements. The stent (or scaffold) must be capable of
sustaining radial compressive forces as it supports walls of a
vessel. Therefore, a stent must possess adequate radial strength.
After deployment, the stent must adequately maintain its size and
shape throughout its service life despite the various forces that
may come to bear on it. In particular, the stent must adequately
maintain a vessel at a prescribed diameter for a desired treatment
time despite these forces. The treatment time may correspond to the
time required for the vessel walls to remodel, after which the
stent is no longer needed.
[0009] Examples of bioresorbable polymer scaffolds include those
described in U.S. Pat. No. 8,002,817 to Limon, U.S. Pat. No.
8,303,644 to Lord, and U.S. Pat. No. 8,388,673 to Yang. FIG. 1
shows a distal region of a bioresorbable polymer scaffold designed
for delivery through anatomical lumen using a catheter and
plastically expanded using a balloon. The scaffold has a
cylindrical shape having a central axis 2 and includes a pattern of
interconnecting structural elements, which will be called bar arms
or struts 4. Axis 2 extends through the center of the cylindrical
shape formed by the struts 4. The stresses involved during
compression and deployment are generally distributed throughout the
struts 4 but are focused at the bending elements, crowns or strut
junctions. Struts 4 include a series of ring struts 6 that are
connected to each other at crowns 8. Ring struts 6 and crowns 8
form sinusoidal rings 5. Rings 5 are arranged longitudinally and
centered on an axis 2. Struts 4 also include link struts 9 that
connect rings 5 to each other. Rings 5 and link struts 9
collectively form a tubular scaffold 10 having axis 2 represent a
bore or longitudinal axis of the scaffold 10. Ring 5d is located at
a distal end of the scaffold. Crown 8 form smaller angles when the
scaffold 10 is crimped to a balloon and larger angles when
plastically expanded by the balloon. After deployment, the scaffold
is subjected to static and cyclic compressive loads from
surrounding tissue. Rings 5 are configured to maintain the
scaffold's radially expanded state after deployment.
[0010] Scaffolds may be made from a biodegradable, bioabsorbable,
bioresorbable, or bioerodable polymer. The terms biodegradable,
bioabsorbable, bioresorbable, biosoluble or bioerodable refer to
the property of a material or stent to degrade, absorb, resorb, or
erode away from an implant site. Scaffolds may also be constructed
of bioerodible metals and alloys. The scaffold, as opposed to a
durable metal stent, is intended to remain in the body for only a
limited period of time. In many treatment applications, the
presence of a stent in a body may be necessary for a limited period
of time until its intended function of, for example, maintaining
vascular patency and/or drug delivery is accomplished. Moreover, it
has been shown that biodegradable scaffolds allow for improved
healing of the anatomical lumen as compared to metal stents, which
may lead to a reduced incidence of late stage thrombosis. In these
cases, there is a desire to treat a vessel using a polymer
scaffold, in particular a bioabsorable or bioresorbable polymer
scaffold, as opposed to a metal stent, so that the prosthesis's
presence in the vessel is temporary.
[0011] Polymeric materials considered for use as a polymeric
scaffold, e.g. poly(L-lactide) ("PLLA"),
poly(D,L-lactide-co-glycolide) ("PLGA"),
poly(D-lactide-co-glycolide) or poly(L-lactide-co-D-lactide)
("PLLA-co-PDLA") with less than 10% D-lactide,
poly(L-lactide-co-caprolactone), poly(caprolactone), PLLD/PDLA
stereo complex, and blends of the aforementioned polymers may be
described, through comparison with a metallic material used to form
a stent, in some of the following ways. Polymeric materials
typically possess a lower strength to volume ratio compared to
metals, which means more material is needed to provide an
equivalent mechanical property. Therefore, struts must be made
thicker and wider to have the required strength for a stent to
support lumen walls at a desired radius. The scaffold made from
such polymers also tends to be brittle or have limited fracture
toughness. The anisotropic and rate-dependent inelastic properties
(i.e., strength/stiffness of the material varies depending upon the
rate at which the material is deformed, in addition to the
temperature, degree of hydration, thermal history) inherent in the
material, only compound this complexity in working with a polymer,
particularly, bioresorbable polymers such as PLLA or PLGA.
[0012] One additional challenge with using a bioresorbable polymer
(and polymers generally composed of carbon, hydrogen, oxygen, and
nitrogen) for a scaffold structure is that the material is
radiolucent with no radiopacity. Bioresorbable polymers tend to
have x-ray absorption similar to body tissue. A known way to
address the problem is to attach radiopaque markers to structural
elements of the scaffold, such as a strut, bar arm or link. For
example, FIG. 1 shows a link element 9d connecting a distal end
ring 5d to an adjacent ring 5. The link element 9d has a pair of
holes. Each of the holes holds a radiopaque marker 11. There are
challenges to the use of the markers 11 with the scaffold 10.
[0013] There needs to be a reliable way of attaching the markers 11
to the link element 9d so that the markers 11 will not separate
from the scaffold during a processing step like crimping the
scaffold to a balloon or when the scaffold is balloon-expanded from
the crimped state. These two events--crimping and balloon
expansion--are particularly problematic for marker adherence to the
scaffold because both events induce significant plastic deformation
in the scaffold body. If this deformation causes significant out of
plane or irregular deformation of struts supporting, or near to
markers the marker can dislodge (e.g., if the strut holding the
marker is twisted or bent during crimping the marker can fall out
of its hole). A scaffold with radiopaque markers and methods for
attaching the marker to a scaffold body is discussed in
US20070156230.
[0014] There is a continuing need to improve upon the reliability
of radiopaque marker securement to a scaffold; and there is also a
need to improve upon methods of attaching radiopaque markers to
meet demands for scaffold patterns or structure that render prior
methods of marker attachment in adequate or unreliable.
SUMMARY OF THE INVENTION
[0015] What is disclosed are scaffolds having radiopaque markers
and methods for attaching radiopaque markers to a strut, link or
bar arm of a polymeric scaffold.
[0016] According to one aspect markers are re-shaped to facilitate
a better retention within a marker hole. Examples include a marker
shaped as a tube or rivet.
[0017] According to another aspect a hole for retaining the marker
is re-shaped to better secure the marker in the hole. Examples
include holes having polygonal shapes or holes having grooves.
[0018] According to another aspect of the invention a scaffold
structure for holding a marker and method for making the same
addresses a need to maintain a low profile for struts exposed in
the bloodstream, while ensuring the marker will be securely held in
the strut. Low profiles for struts mean thinner struts or thinner
portions of struts. The desire for low profiles addresses the
degree thrombogenicity of the scaffold, which can be influenced by
a strut thickness overall and/or protrusion from a strut surface.
Blood compatibility, also known as hemocompatibility or
thromboresistance, is a desired property for scaffolds and stents.
The adverse event of scaffold thrombosis, while a very low
frequency event, carries with it a high incidence of morbidity and
mortality. To mitigate the risk of thrombosis, dual anti-platelet
therapy is administered with all coronary scaffold and stent
implantation. This is to reduce thrombus formation due to the
procedure, vessel injury, and the implant itself. Scaffolds and
stents are foreign bodies and they all have some degree of
thrombogenicity. The thrombogenicity of a scaffold refers to its
propensity to form thrombus and this is due to several factors,
including strut thickness, strut width, strut shape, total scaffold
surface area, scaffold pattern, scaffold length, scaffold diameter,
surface roughness and surface chemistry. Some of these factors are
interrelated. Low strut profile also leads to less neointimal
proliferation as the neointima will proliferate to the degree
necessary to cover the strut. As such coverage is a necessary step
to complete healing. Thinner struts are believed to endothelialize
and heal more rapidly.
[0019] Markers attached to a scaffold having thinner struts,
however, may not hold as reliably as a scaffold having thicker
struts since there is less surface contact area between the strut
and marker. Embodiments of invention address this need. According
to another aspect a thickness of the marker and strut is kept below
threshold values while reliably retaining the marker in the
hole.
[0020] According to other aspects of the invention, there is a
scaffold, medical device, method for making such a scaffold, method
of attaching a marker to a strut or bar arm of a scaffold, or
method for assembly of a medical device comprising such a scaffold
having one or more, or any combination of the following things (1)
through (19): [0021] (1) A method to reduce the thrombogenicity, or
a scaffold having reduced thrombogenicity, the scaffold comprising
a strut, the strut including a strut thickness and a marker
attached to the strut, wherein the strut has a thickness (t) and
the marker has a length (L, as measured from abluminal to luminal
surface portions) and is held in the strut, the marker including a
portion that can protrude outward from an abluminal and/or luminal
surface of the strut, wherein the marker length (L) and
strut/link/bar arm thickness (t) are related as follows:
1.2.ltoreq.(L/t).ltoreq.1.8; 1.1.ltoreq.(L'/t).ltoreq.1.5;
1.0.ltoreq.(L/t).ltoreq.1.8; and/or 1.0.ltoreq.(L'/t).ltoreq.1.5,
where L is an undeformed length (e.g., rivet, tube), L' is a
deformed length (e.g. a rivet, coating or snap-in marker between
abluminal and luminal surfaces). [0022] (2) A scaffold comprising a
bar arm, link or strut having a hole holding a marker, or a method
for making the same according to one or more, or any combination of
features described for a Concept A through Concept G infra and with
reference to illustrative examples shown in FIGS. 3A-3C, FIGS. 4A,
4B, 5A and 5B, FIGS. 6A and 6B, FIG. 6C, FIGS. 7A-7B, FIGS. 8A-8C,
FIGS. 9A-9C, FIGS. 10A-10B, FIGS. 11A-11B, FIGS. 12A-12B and FIGS.
13A-13B, respectively. [0023] (3) An aspect ratio (AR) of strut
width (w) to wall thickness (t) (AR=w/t) is between 0.5 to 2.0, 0.5
to 1.5, 0.7 to 1.5, 0.7 to 1.3, 0.9 to 1.5, 0.9 to 1.2, 1.0 to 1.5,
1.5 to 2.0, or 2.0 to 3.0; [0024] (4) A scaffold comprising a
strut, link and/or bar arm including a marker secured to the strut,
link and/or bar arm according to any of Concept A, Concept B,
Concept C, Concept D, Concept E, Concept F or Concept G-type
markers. [0025] (5) A scaffold comprising a deformed marker secured
to a strut, bar arm and/or link, wherein the marker is a rivet,
snap-fit, irregularly-shaped, tube or spherical marker before the
marker is deformed. [0026] (6) A marker having a head and a tail
such as a rivet, hollow tube, solid tube, polygonal, oblate
spheroid, and/or spherical body. The marker is secured to a strut,
bar arm, link and/or connector. [0027] (7) A combined bump (luminal
side plus abluminal side, and referring to a portion of a marker
and/or polymer at the marker) is no more than a strut or link
thickness, e.g., no more than 100 or 85 microns, so that the length
at the marker is at most twice a strut or bar arm thickness at the
marker. [0028] (8) A combined bump (luminal side plus abluminal
side, and referring to a portion of a marker and/or polymer at the
marker) is at least 10-50% more than a thickness of a strut or bar
arm at the marker. [0029] (9) A wall thickness for a scaffold
(pre-crimp diameter of 3 to 5 mm) is less than 150 microns, less
than 140 microns, less than 130 microns, about 100 micron, 80 to
100 microns, 80 to 120 microns, 90 to 100 microns, 90 to 110
microns, 110 to 120 microns, or 95 to 105 microns. More preferably
a wall thickness is between 80 and 100 microns, and more preferably
between 85 and 95 microns; and [0030] (10) A wall thickness for a
scaffold (pre-crimp diameter of 7 to 10 mm) is less than 280
microns, less than 260 microns, less than 240 microns, about 190
micron, 149 to 186 microns, 149 to 220 microns, 170 to 190 microns,
170 to 210 microns, 210 to 220 microns. More preferably a wall
thickness is between 150 and 190 microns for a scaffold having an
outer diameter of 7, 8 or 9 mm. [0031] (11) A polymeric scaffold is
heated about 0-20 degrees above its Tg during or after marker
placement. [0032] (12) The radiopaque marker is comprised of
platinum, platinum/iridium alloy, iridium, tantalum, palladium,
tungsten, niobium, zirconium, iron, zinc, magnesium, manganese or
their alloys. [0033] (13) A method for making a medical device,
comprising: providing a polymer scaffold including a strut having a
hole formed in the strut, wherein the hole has a length and a
width; and providing a radiopaque marker having a first end, second
end, and medial portions; and attaching the marker to the scaffold
including placing the marker into the hole; wherein when the marker
is attached to the scaffold the medial portion is disposed in the
hole and the marker is retained in the hole at least partially by
one or both of the first and second ends. [0034] (14) The method of
(6) according to one or more, or any combination of the following
things: wherein the attaching step includes deforming at least one
of the first and second ends such that the deformed end has a width
greater than the hole width; wherein the marker is a rivet having a
head and tail, and wherein the tail is the deformed end; wherein
the rivet head is placed on a luminal side of the strut and held in
place by a mandrel, and the tail disposed on the abluminal strut
side is deformed by a roller or pin; wherein the marker is a tube
and both the first and second ends are deformed to have a width
greater than the hole width; wherein the attaching step includes
using a tool having jaws forming points to engage the tube ends,
wherein the jaws deform the ends; wherein the marker is a snap-fit
marker; wherein the marker has an undeformed length (L), a deformed
length (L'), and the strut has a thickness (t), and the marker
lengths and strut thickness are related as follows:
1.2.ltoreq.(L/t).ltoreq.1.8; 1.1.ltoreq.(L'/t).ltoreq.1.5; and/or
wherein the marker has an undeformed length (L), a deformed length
(L'), and the strut has a thickness (t), and the marker lengths and
strut thickness are related as follows:
1.0.ltoreq.(L/t).ltoreq.1.8; and 1.0.ltoreq.(L'/t).ltoreq.1.5.
[0035] (15) A method for making a medical device, comprising:
providing a polymer scaffold including a strut; making a grooved
hole in the strut including forming at least one groove in a wall
of the hole; and attaching a radiopaque marker to the scaffold
including placing the marker into the grooved hole. [0036] (16) The
method of (8) according to one or more, or any combination of the
following things: wherein the grooved hole has vertical grooves
extending generally parallel to a bore axis of the hole; wherein
the grooved hole has one or more spiral grooves; wherein the
grooved hole is a tapped hole having between about 2 to 6 threads
per 100 microns; wherein the grooved hole is an annular hole
disposed between upper and lower rims of the hole; wherein the
making the grooved hole includes using a laser and reflector to
etch the annular hole; wherein the hole is polygonal hole; wherein
the hole elliptical; further comprising applying a polymer melt or
coating to the hole and marker, whereby the polymer becomes
disposed between gaps between the at least one groove and marker.
[0037] (17) A method, comprising: providing a scaffold made from a
polymer tube, the scaffold having a network of elements including a
strut; providing a hole in the strut or link, wherein the hole
extends from an abluminal surface to a luminal surface of the
strut; disposing a radiopaque marker at least partially within the
hole; and applying a coating comprising a polymer to the luminal
and abluminal surfaces; wherein a thickness measured between
abluminal and luminal surfaces of the coating nearby to the marker
(tc) is related to a length (L) measured between abluminal and
luminal surfaces of the coating at the marker as
0.8.ltoreq.(L/tc).ltoreq.1.8. [0038] (18) The method of (10)
according to one or more, or any combination of the following
things: wherein t is about 100 microns; and/or wherein the marker
height (L), the marker is secured to a strut, the strut thickness
is t, and 1.1.ltoreq.(L/t).ltoreq.1.5. [0039] (19) A medical
device, comprising: a scaffold made from a polymer tube, the
scaffold having a network of elements including a strut or link; a
hole formed in the strut or link, wherein the hole extends from the
abluminal surface to the luminal surface; a radiopaque marker at
least partially disposed within the hole; and a coating comprising
a polymer on the luminal and abluminal surfaces; wherein a
thickness measured between abluminal and luminal surfaces of the
coating adjacent the marker (tc) is related to a length (L)
measured between abluminal and luminal surfaces of the coating at
the marker as 1.1.ltoreq.(L/tc).ltoreq.1.5.
INCORPORATION BY REFERENCE
[0040] All publications and patent applications mentioned in the
present specification are herein incorporated by reference to the
same extent as if each individual publication or patent application
was specifically and individually indicated to be incorporated by
reference. To the extent there are any inconsistent usages of words
and/or phrases between an incorporated publication or patent and
the present specification, these words and/or phrases will have a
meaning that is consistent with the manner in which they are used
in the present specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1 is a perspective view of a portion of a prior art
scaffold. The scaffold is shown in a crimped state (balloon not
shown).
[0042] FIG. 2 is a top partial view of a scaffold showing a link
connecting adjacent rings. The link includes holes for holding
markers.
[0043] FIG. 2A is a partial side-cross sectional view of the link
of FIG. 2 taken at section IIA-IIA with a spherical marker being
placed in the hole.
[0044] FIG. 2B shows the link of FIG. 2A after the marker is placed
in the hole.
[0045] FIG. 3A shows a first embodiment of sealing layers of a
polymer applied to abluminal and luminal surfaces of a marker
strut.
[0046] FIG. 3B shows a second embodiment of sealing layers of a
polymer applied to abluminal and luminal surfaces of a marker
strut.
[0047] FIG. 3C shows a third embodiment of sealing layers of a
polymer applied to abluminal and luminal surfaces of a marker
strut.
[0048] FIG. 4A is a top view of a polygonal, four-sided marker hole
without an inserted marker.
[0049] FIG. 4B is a top view of the polygonal, four-sided marker
hole of FIG. 4A with an inserted marker.
[0050] FIG. 5A is a top view of a polygonal, six-sided marker hole
without an inserted marker.
[0051] FIG. 5B is a top view of the polygonal, six-sided marker
hole of FIG. 5A with an inserted marker.
[0052] FIG. 6A is a top view of a marker hole with grooves, without
an inserted marker.
[0053] FIG. 6B is a top view of the marker hole of FIG. 6A, with an
inserted marker.
[0054] FIG. 6C is a side cross-sectional view of a link with marker
hole having grooves according to another embodiment.
[0055] FIG. 7A is a cross sectional view of the marker according to
any of the embodiments of FIGS. 4A, 4B, 5A and 5B, where FIG. 7A
shows the marker hole and marker without a polymer coating.
[0056] FIG. 7B is a cross sectional view of the marker according to
any of the embodiments of FIGS. 4A, 4B, 5A and 5B, where FIG. 7B
shows the marker hole and marker with a polymer coating.
[0057] FIG. 8A is a partial side-cross sectional view of a link
according to another embodiment. A spherical marker is being placed
in a hole of the link.
[0058] FIG. 8B shows the link of FIG. 8A after the marker is placed
in the hole.
[0059] FIG. 8C shows a method for making the hole of FIG. 8A.
[0060] FIGS. 9A and 9B show a side and top view, respectively, of a
marker according to another embodiment.
[0061] FIG. 9C is a cross-sectional view of a link having a hole
and the marker of FIG. 9A embedded in the hole.
[0062] FIGS. 10A and 10B are cross-sectional views of a link and
marker and method of attaching the marker to the link according to
another embodiment.
[0063] FIGS. 11A and 11B are cross-sectional views of a link and
marker and method of attaching the marker to the link according to
another embodiment.
[0064] FIGS. 12A and 12B are cross-sectional views of a link and
marker and method of attaching the marker to the link according to
another embodiment.
[0065] FIGS. 13A and 13B are cross-sectional views of a link and
marker and method of attaching the marker to the link according to
another embodiment.
DETAILED DESCRIPTION
[0066] In the description like reference numbers appearing in the
drawings and description designate corresponding or like elements
among the different views.
[0067] For purposes of this disclosure, the following terms and
definitions apply:
[0068] The terms "about," "approximately," "generally," or
"substantially" mean 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, 1.5%, 1%,
between 1-2%, 1-3%, or 0.5%-5% less or more than, less than, or
more than a stated value, a range or each endpoint of a stated
range, or a one-sigma, two-sigma, three-sigma variation from a
stated mean or expected value (Gaussian distribution). For example,
d1 about d2 means d1 is 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, 1.5%,
1%, 0% or between 1-2%, 1-3%, 1-5%, or 0.5%-5% different from d2.
If d1 is a mean value, then d2 is about d1 means d2 is within a
one-sigma, two-sigma, or three-sigma variance or standard deviation
from d1.
[0069] It is understood that any numerical value, range, or either
range endpoint (including, e.g., "approximately none", "about
none", "about all", etc.) preceded by the word "about,"
"approximately," "generally," or "substantially" in this disclosure
also describes or discloses the same numerical value, range, or
either range endpoint not preceded by the word "about,"
"approximately," "generally," or "substantially."
[0070] A "stent" means a permanent, durable or non-degrading
structure, usually comprised of a non-degrading metal or metal
alloy structure, generally speaking, while a "scaffold" means a
temporary structure comprising a bioresorbable or biodegradable
polymer, metal, alloy or combination thereof and capable of
radially supporting a vessel for a limited period of time, e.g., 3,
6 or 12 months following implantation. It is understood, however,
that the art sometimes uses the term "stent" when referring to
either type of structure.
[0071] "Inflated diameter" or "expanded diameter" refers to the
inner diameter or the outer diameter the scaffold attains when its
supporting balloon is inflated to expand the scaffold from its
crimped configuration to implant the scaffold within a vessel. The
inflated diameter may refer to a post-dilation balloon diameter
which is beyond the nominal balloon diameter, e.g., a 6.5 mm
balloon (i.e., a balloon having a 6.5 mm nominal diameter when
inflated to a nominal balloon pressure such as 6 times atmospheric
pressure) has about a 7.4 mm post-dilation diameter, or a 6.0 mm
balloon has about a 6.5 mm post-dilation diameter. The nominal to
post dilation ratios for a balloon may range from 1.05 to 1.15
(i.e., a post-dilation diameter may be 5% to 15% greater than a
nominal inflated balloon diameter). The scaffold diameter, after
attaining an inflated diameter by balloon pressure, will to some
degree decrease in diameter due to recoil effects related primarily
to, any or all of, the manner in which the scaffold was fabricated
and processed, the scaffold material and the scaffold design.
[0072] When reference is made to a diameter it shall mean the inner
diameter or the outer diameter, unless stated or implied otherwise
given the context of the description.
[0073] When reference is made to a scaffold strut, it also applies
to a link or bar arm.
[0074] "Post-dilation diameter" (PDD) of a scaffold refers to the
inner diameter of the scaffold after being increased to its
expanded diameter and the balloon removed from the patient's
vasculature. The PDD accounts for the effects of recoil. For
example, an acute PDD refers to the scaffold diameter that accounts
for an acute recoil in the scaffold.
[0075] A "pre-crimp diameter" means an outer diameter (OD) of a
tube from which the scaffold was made (e.g., the scaffold is cut
from a dip coated, injection molded, extruded, radially expanded,
die drawn, and/or annealed tube) or the scaffold before it is
crimped to a balloon. Similarly, a "crimped diameter" means the OD
of the scaffold when crimped to a balloon. The "pre-crimp diameter"
can be about 2 to 2.5, 2 to 2.3, 2.3, 2, 2.5, 3.0 times greater
than the crimped diameter and about 0.9, 1.0, 1.1, 1.3 and about
1-1.5 times higher than an expanded diameter, the nominal balloon
diameter, or post-dilation diameter. Crimping, for purposes of this
disclosure, means a diameter reduction of a scaffold characterized
by a significant plastic deformation, i.e., more than 10%, or more
than 50% of the diameter reduction is attributed to plastic
deformation, such as at a crown in the case of a stent or scaffold
that has an undulating ring pattern, e.g., FIG. 1. When the
scaffold is deployed or expanded by the balloon, the inflated
balloon plastically deforms the scaffold from its crimped diameter.
Methods for crimping scaffolds made according to the disclosure are
described in US20130255853.
[0076] Bioresorbable scaffolds comprised of biodegradable polyester
polymers are radiolucent. In order to provide for fluoroscopic
visualization, radiopaque markers are placed on the scaffold. For
example, the scaffold described in U.S. Pat. No. 8,388,673 ('673
patent) has two platinum markers 206 secured at each end of the
scaffold 200, as shown in FIG. 2 of the '673 patent.
[0077] FIG. 2 is a top planar view of a portion of a polymer
scaffold, e.g., a polymer scaffold having a pattern of rings
interconnected by links as in the case of the '673 patent
embodiments. There is a link strut 20 extending between rings 5d, 5
in FIG. 2. The strut 20 has formed left and right structures or
strut portions 21b, 21a, respectively, for holding a radiopaque
marker. The markers are retainable in holes 22 formed by the
structures 21a, 21b. The surface 22a corresponds to an abluminal
surface of the scaffold. An example of a corresponding scaffold
structure having the link 20 is described in FIGS. 2, 5A-5D, 6A-6E
and col. 9, line 3 through col. 14, line 17 of the '673 patent. The
embodiments of a scaffold having a marker-holding link structure or
method for making the same according to this disclosure in some
embodiments include the embodiments of a scaffold pattern according
to FIGS. 2, 5A-5D, 6A-6E and col. 9, line 3 through col. 14, line
17 of the '673 patent.
[0078] One method for marker placement forces a spherical-like body
into a cylindrical hole. This process is illustrated by FIGS. 2A
and 2B. Shown in cross-section is the hole 22 and surrounding
structure of the link portion 21a as seen from Section IIa-IIa in
FIG. 2. The hole 22 extends through the entire thickness (t) of the
strut portion 21a and the hole 22 has an about constant diameter
(d) from the luminal surface 22b to the abluminal surface 22a. A
generally spherical marker 25 is force-fit into the hole 22 to
produce the marker 25' in the hole 22 illustrated in FIG. 2B. The
spherical marker 25 has a volume about equal to, less than or
greater than the volume of the open space defined by the plane of
the abluminal surface 22a, the plane of the luminal surface 22b and
the generally cylindrical walls 24 of the hole 22. The spherical
body is reshaped into body 25' by the walls 24 and a tool. The
deformed shape 25' may be achieved by using one or two rollers
pressed against the sphere 25 when it is disposed within the hole
22. The rollers (not shown) are pressed against each side of the
marker 25 to produce the deformed marker 25' structure shown in
FIG. 2B. Alternatively, the marker 25 may be held on a tip of a
magnetized, or vacuum mandrel and pressed (from the abluminal
surface 22a side) into the hole 22 while a non-compliant flat
surface is pressed into the marker from the luminal side 22b.
Referring to FIG. 2B, the marker 25' has an abluminal surface 25a
that is about flush with surface 22a and luminal surface 25b that
is about flush with surface 22b. Methods for placing the marker 25
in the hole 22 are discussed in US20070156230.
[0079] According to one example, the hole 22 has a hole diameter
(d) of 233.7 .mu.m and an average initial spherical marker size
(Johnson-Matthey marker beads) of 236.7 .mu.m. The thickness (t) is
157.5 microns and hole 22 volume is t.times..pi.d.sup.2=6.76E6
.mu.m.sup.3. The average spherical volume size is 6.94E6
.mu.m.sup.3. Hence, in this embodiment when the spherical marker 25
is press-fit into the hole 22, the marker 25 is deformed from a
generally spherical shape into more of a cylindrical shape. In some
embodiments an average volume size for the marker 25 may be only
slightly larger in volume (3%) than a hole 22 volume. Larger beads
presumably stretch the marker brim while smaller beads will contact
the walls 24 when deformed, but do not fill the hole 22 volume
completely. As would be understood, the about flush with the
luminal and abluminal surfaces accounts for the variances in marker
25 volume size from the manufacturer and volume size variances of
the hole 22 volume.
[0080] TABLE 1 contains a theoretical volume of an average
spherical platinum marker 25 relative to that of the hole 22 for a
Scaffold A and a Scaffold B.
TABLE-US-00001 TABLE 1 Marker and Hole Dimensions Strut Thickness
Marker Hole Average Marker Idealized Marker Average Marker Scaffold
(.mu.m) Diameter (.mu.m) Diameter (.mu.m) Hole Volume (.mu.m.sup.3)
Volume (.mu.m.sup.3) A 157.5 233.7 236.7 6.76E6 6.94E6 B 100 241.3
236.7 4.57E6 6.94E6
[0081] The larger the marker volume is relative to the hole volume,
the more the marker brim or space 22 must increase in size if the
marker 25' will be flush with the surfaces 22a, 22b. Otherwise, if
the volume for the hole 22 does not increase marker material would
be left protruding above and/or below the hole 22.
[0082] With respect to the different thickness struts of Scaffold A
and Scaffold B (TABLE 1) it will be appreciated that an acceptable
marker 25 fitting method and/or structure for Scaffold A (thick
struts) may not be acceptable for Scaffold B (thin struts). It may
be necessary to change the volume and/or shape size of the hole
and/or marker, and/or method of attachment of the marker to a hole
when a strut thickness is reduced in size, e.g., when there is an
about 37% reduction in strut thickness.
[0083] There are several dimensional parameters that result in a
physical interaction between the strut walls 24 and marker 25
surface sufficient to keep the marker in the hole 25 during
scaffold manipulations, such as drug coating, crimping and scaffold
expansion. Factors (1)-(3) that affect the physical securement of
the marker 25' in the hole 22 include: [0084] (1) The interference
fit between the marker 25' and the inside surface or brim 24 of the
marker hole 22. This fit is a function of [0085] The total contact
area between the marker 25' and the polymer walls or brim 24.
[0086] The residual stresses in the marker brim 24 polymer and 25'
that results in a compressive or hoop stress between the marker
brim 24 and marker 25'. [0087] (2) The roughness of the marker 25'
surface and surface of the brim 24, or coefficient of static
friction between the contacting marker and wall surfaces. [0088]
(3) Where a drug-polymer coating is applied (not shown in FIG. 2B),
the gluing-in effect of the drug/polymer coating. The contribution
of this coating to marker 25' retention comes down to the fracture
strength of the coating on the abluminal or luminal surfaces 22a,
22b as the coating must fracture through its thickness on either
side for the marker 25' to become dislodged.
[0089] With respect to factor (3), in some embodiments an
Everolimus/PDLLA coating is applied after the marker 25' is fit in
place. This type of coating can seal in the marker 25. However, an
Everolimus/PDLLA coating tends to be thin (e.g., 3 microns on the
abluminal surface 22a and 1 micron on the luminal surface 22b),
which limits it's out of plane shear strength resisting dislodgment
of the marker from the hole.
[0090] In some embodiments a polymer strut, bar arm and/or link has
a thickness about, or less than about 100 microns, which is less
than the wall thickness for known scaffolds cut from tubes. There
are several desirable properties or capabilities that follow from a
reduction in wall thickness for a scaffold strut; for example, a
reduction from the Scaffold A wall thickness to Scaffold B wall
thickness. The advantages of using the reduced wall thickness
include a lower profile and hence better deliverability, reduced
acute thrombogenicity, and potentially better healing. In some
embodiments the Scaffold B (100 micron wall thickness) has a
pattern of rings interconnected by struts as disclosed in the '673
patent.
[0091] In some embodiments it is desirable to use the same size
marker 25 for Scaffold B as with Scaffold A, so that there is no
difference, or reduction, in radiopacity between the two scaffold
types. Reducing the strut thickness, while keeping the marker hole
22 the same size can however result in the marker protruding above
and/or below the strut surfaces due to the reduced hole volume. It
may be desirable to keep the abluminal and luminal surfaces 25a,
25b of the marker 25' flush with corresponding surfaces 22a, 22b
for Scaffold B, in which case the hole 22 diameter (d) may be
increased to partially account for the reduced hole volume
resulting from the thinner strut. This is shown in TABLE 1 for
Scaffold B, which has a hole diameter greater than the hole
diameter for Scaffold A.
[0092] With respect to Factor (1) it will be appreciated that the
substantially frictional force relied on to resist dislodgement of
the marker 25' from the hole 22 reduces as the strut thickness is
reduced. When using a fixed sized marker of constant volume, and
assuming the marker fills a cylindrical hole, the contact area
between the marker and hole sidewall may be expressed in terms of a
marker volume and strut thickness, as in EQ. 1.
A=2 (.pi.tV).sup.1/2 (EQ. 1) [0093] Where [0094] A=Contact area
between marker hole sidewall and marker [0095] t=Strut thickness
[0096] V=marker volume
[0097] EQ. 1 shows that in a limiting case of the strut 21a
thickness becoming very thin (t.fwdarw.0), the marker 25' becomes
more and more like a thin disc, which would have minimal mechanical
interaction with the wall 24. Hence the frictional forces between
the marker 25' and wall 24 decreases because the contact area is
reduced. Comparing Scaffold A with Scaffold B, the marker 25'
retention force in the hole 22 therefore becomes worse due to the
about 37% reduction in strut thickness. Indeed, it may be expected
that the Factor A (frictional) forces that hold the marker 25' in
the hole reduce by about 20%, which 20% reduction is the surface
area reduction of the walls 24 when the strut thickness is reduced
by the about 37% (Scaffold A.fwdarw.Scaffold B). This assumes the
coefficients of static friction and level of residual hoop stress
are otherwise unchanged between Scaffold A and B.
[0098] According to another aspect of the disclosure there are
embodiments of a strut having a hole for holding a radiopaque
marker and methods for securing a marker to a strut. The
embodiments address the ongoing need for having a more secure
attachment of a marker to a polymer strut. In preferred embodiments
the polymer strut has a thickness, or a scaffold comprising the
strut is cut from a tube having a wall thickness less than about
160 .mu.m or 150 .mu.m, a wall thickness of about 100 .mu.m or a
wall thickness less than 100 .mu.m and while retaining the same
size marker as a strut having a thickness between 150-160 .mu.m, so
that the radiopacity of the scaffold does not change.
[0099] An improved securement of a marker to a hole according to
the disclosure includes embodiments having one or more of the
following Concepts A through G: [0100] A. Following marker
insertion a sealing biodegradable polymer is applied to secure the
marker in place (Concept A). [0101] B. The strut hole is made in an
irregular shape to increase an adhesive and mechanical locking
effect of a scaffold coating (Concept B). [0102] C. The marker has
roughened surfaces to increase the coefficient of friction between
the polymer walls and marker (Concept C). [0103] D. The holes are
made concave to increase the contact area and/or to provide a
mechanical engagement between the marker and the hole (Concept D).
[0104] E. Radiopaque markers shaped like, or usable as rivets are
attached to the hole (Concept E). [0105] F. Polygonal or Irregular
markers (Concept F). [0106] G. Snap-in markers (Concept G).
[0107] A. Addition of a Sealing Biodegradable Polymer After Marker
Insertion, but Before Drug Spray
[0108] According to Concept A, sealing layers of polymer 30 are
applied to the abluminal and/or luminal surfaces 22a, 22b of the
strut 21a near the marker 25' and luminal and abluminal surfaces
25a, 25b surfaces of the marker 25' as shown in FIGS. 3A-3C. The
amount of sealing polymer 30 applied on the marker 25 may be
significant but without creating an unsatisfactory bump or
protrusion on the abluminal or luminal surfaces. To increase the
available space for the sealing polymer (without reducing the
marker size or creating a large bump on the surface) the hole 22
may be made wider, so that the marker 25 when pressed and deformed
into the hole 22 is recessed from the abluminal surface 22a and/or
abluminal surface 22b. This is shown in FIGS. 3B and 3C. In FIG. 3B
the marker 25' is recessed from the side 22a but flush with 22b. In
FIG. 3C the marker 25' is recessed on both surfaces.
[0109] The sealing polymer 30 may be applied in different ways. One
approach is to apply a small amount of solution consisting of a
biodegradable polymer dissolved in solvent. This can be done with a
fine needle attached to a micro-syringe pump dispenser. The
solution could be applied to both the abluminal and luminal
surfaces of the marker and marker brim portions of the hole 22
(FIGS. 3A-3C). Suitable polymers include poly(L-lactide) ("PLLA"),
poly(D,L-lactide-co-glycolide) ("PLGA"),
poly(D-lactide-co-glycolide), poly(D,L-lactide) ("PDLLA")
poly(L-lactide-co-caprolactone) ("PLLA-PCL") and other
bioresorbable polymers. Solvents include chloroform, acetone,
trichloroethylene, 2-butanone, cyclopentanone, ethyl acetate, and
cyclohexanone.
[0110] Alternatively, the sealing polymer may be applied in a
molten state. As compared to the solvent application embodiment of
the sealing polymer, a polymer applied in the molten state may
produce a more sizable bump or protrusion on the abluminal and/or
luminal surface 22a, 22b. While avoidance of bumps on these
surfaces is generally of concern, small bumps or protrusions are
acceptable if they are less than the strut thickness. For example,
in some embodiments the bump is less than about 100 microns, or
about 85 microns (combined bumps on luminal and abluminal sides).
Thus the length of the marker (L' or L) may be up to about 100 or
85 microns higher than the strut thickness, as in a strut thickness
of about 100 or 85 microns.
[0111] B. Use of a Polygonal or Irregular Marker Hole to Improve
Adhesive Effect of Coating
[0112] According to Concept B, the marker hole 22 is modified to
increase the adhesive effect of a drug/polymer coating on
increasing the marker retention. If larger gaps are made between
the marker 25 and wall 24 of the hole 22 more of the coating can
become disposed between the marker 25' and wall 24 of the hole 22.
The presence of the coating in this area (in addition to having
coating extending over the surfaces 22a, 25a, 22b and 25a) can help
to secure the marker 25 in the hole because the surface area
contact among the coating, wall 24 and marker 25 is increased.
Essentially, the coating disposed within the gaps between the wall
24 and marker 25 can perform more as an adhesive. In addition, the
coating filling in around the deformed marker bead can improve
retention via mechanical interlocking. Gaps can be made by forming
the hole with rectangular, hexagonal or more generally polygonal
sides as opposed to a round hole. When a spherical marker 25 is
pressed into a hole having these types of walls there will be gaps
at each wall corner.
[0113] FIGS. 4A and 4B show modified marker-holding strut portions
31a, 31b before and after, respectively, a marker 25 is pressed
into each hole 32 of the strut portions 31a, 31b. The holes 32 are
formed as rectangular holes. Since there are four sides 34 to a
rectangular, there are four corners to the hole 32. As can be
appreciated from FIG. 4B there are four gaps 33 between the hole
walls 34 and the bead 25'. The gaps 33 are present at each wall
corner of the rectangular hole 32.
[0114] FIGS. 5A and 5B show modified marker-holding strut portions
41a, 41b before and after, respectively, a marker 25 is pressed
into each hole 42 of the strut portions 41a, 41b. The holes 42 are
formed as hexagonal holes. Since there are six sides 44 to a
hexagon, there are six corners to the hole 42. As can be
appreciated from FIG. 5B there is at least one and up to six gaps
43 between the hole walls 44 and the marker 25'.
[0115] Referring to FIGS. 7A and 7B there is shown cross-sectional
side-views of the holes 32 and 42 with the marker 25' in the hole.
The view of FIG. 7A is taken from section VIIa-VIIa in FIGS. 4B and
5B. As shown there is the gap 33, 43 present at the corner, which
provides space for the polymer coating 32 (FIG. 7B) to lodged when
the coating is applied to the scaffold. The coating 32 is disposed
between the surface of the marker 25' and wall 34, 44 of the hole
32, 42 combined with the coating disposed on the luminal and/or
abluminal surfaces 32a, 32b, 42a, 42b. The polymer coating 32 shown
in FIG. 7B may be a drug-polymer coating or polymer coating applied
by spraying, or a molten polymer applied to the brim of the hole 22
and over the marker 25'.
[0116] C. Roughened Wall Surfaces
[0117] FIGS. 6A and 6B show modified marker-holding strut portions
51a, 51b before and after, respectively, a marker 25' is pressed
into each hole 52 of the strut portions 51a, 51b. The holes 52 are
formed as bearclaw holes or holes having grooves 54 formed through
the thickness and along the perimeter of the hole. The grooves 54
may be formed using a laser directed down into the hole and moved
circumferentially about the perimeter to cut out the grooves 54.
Each of the grooves 54 can serve as a gap that fills up with a
coating or molten polymer 32 to form an adhesive binding surfaces
of the marker 25' to walls of the hole 52, in the same way as the
embodiments of FIGS. 4A, 4B, 5A and 5B where the binding occurs at
wall corners 33, 43.
[0118] Grooves may be formed as spiral grooves as opposed to
grooves that extend straight down (i.e., into the paper in FIGS.
6A-6B). Spiral grooves may be formed by a tapping tool such as a
finely threaded drill bit or screw (about 1, 2, 3, 4, 5 or 4-10
threads per 100 microns). This structure is shown in FIG. 6C where
a strut portion 51a' having an abluminal surface 52a' and hole 52'
is tapped to produce one or more spiral grooves surface 54'. The
hole 52' may have 2 to 10 threads per 100 microns, or a groove may
have a pitch of about 10, 20, 30 or 50 microns.
[0119] Any combination of the Concept B and Concept C embodiments
are contemplated. A hole may be polygonal such as rectangular,
square or hexagonal with the grooves formed on walls. There may be
1, 2, 3, 4, 5-10, a plurality or grooves, grooves every 10, 20, 45,
or 10-30 degrees about the perimeter of the hole. "Grooves" refers
to either straight grooves (FIG. 6A-6B) or spiral grooves or
threading (FIG. 6C). The grooves may be formed in a polygonal hole
(e.g., square, rectangular, hexagonal) or elliptical hole (e.g., a
circular hole).
[0120] D. Marker Having Concave walls
[0121] According to Concept D, a marker hole has a concave surface
between upper and lower rims to hold a marker in place. Referring
to FIGS. 8A-8B, there is shown a strut portion 61a having an
abluminal and luminal surface 62a, 62b respectively and a hole 62
to receive the marker 25, as shown. The wall 64 of the hole is
cylindrical, like in the FIG. 2A embodiment, except that the wall
64 includes an annular and concave surface (or groove) formed about
the perimeter. The (groove) surface 64c located between the upper
and lower edges of the hole 62 is between an optional upper and
lower rim 64a, 64b of the hole 62. The rims 64a, 64b help retain
the marker 25 in the hole 62. According to this embodiment a hole
has a pseudo-mechanical interlock feature provided by the annular
groove 64c. Referring to FIG. 8B the deformed marker 25' has a
portion 26a generally taking the shape of the annular groove 64c
having a concave shape, or displacing into the space defined by
this part of the wall when the marker is forced into the hole. The
rims 64a, 64b, and the convex shape of 25' nested into concave
annular groove 64c, resist dislodgment of the marker 25' from the
hole 62. As can be appreciated from FIG. 8B the marker 25' would
have to deform before it dislodges from the hole 62. Because the
marker 25' must deform to dislodge from the hole 62, the hole 62
having the annular groove 64c between upper and lower rims 64a, 64b
provides a mechanical interlock. In contrast to other embodiments,
the structure shown in FIG. 8B need not rely primarily or solely on
friction and/or an adhesive/coating to secure the marker in
place.
[0122] FIG. 8C illustrates a method for making the hole 62
according to Concept D using a laser 200 reflected off a reflective
surface 204 of a reflector tool or reflector 202. The reflector 202
is frustoconical and is configured to extend up through the
untapped hole 20. The reflector 202 is pressed and held against the
luminal surface 62b to hold it in place. The reflective surface 204
is arranged at an angle of between 20 to 60 degrees with respect to
the untapped wall of the hole 20. The surface 204 is arranged so
that laser light impacts the wall 64c' at about a right angle as
shown. The laser 200 is directed onto the surface 204, which
reflects the light towards the wall and causes the laser energy to
etch-out the groove. The laser is traced (or scanned) about the
perimeter of the hole 20 to make the annular groove shown in FIG.
8A. The laser would trace a circle on the reflector 202, just
inside the edges of the marker hole 20. The groove thickness (i.e.,
distance between the upper and lower rims 64a, 64b) can be up to
about 60% to 80% and/or between about 20% to 50% of the strut
thickness.
[0123] In the embodiments, the reflectors 202 having surface 204
can have a frustoconical part for each of the paired holes (FIG.
2), or instead have a set of hemispheres or cones for a set of
marker holes An alternative laser reflector would be one which does
not protrude into the marker bead hole but which presents a concave
surface pressed up against the bottom of the hole with edges at
surface 62b. A laser beam imping on this surface would be reflected
against the opposite wall of hole 20. In another embodiment, the
annular groove may instead be formed by a pin having an oblate
spheroid shaped at its tip. The tip of the pin is forced into the
hole 20 so that the tip sits within the hole. The hole is deformed
to have an annular groove as shown in FIG. 8A. Then the marker 25
is pressed into the hole 62 to take a similar shape as in FIG.
8B.
[0124] E. Radiopaque Markers as Rivets
[0125] According to Concept E, a marker shaped as a rivet is used
in place of the spherical marker 25. FIGS. 9A and 9B show
respective side and top views of the marker 27 shaped as a rivet.
The head 28 may include the abluminal surface 27a or luminal
surface 27b of the rivet 27. In the drawings, the head 28 includes
the abluminal surface 27a. It may be preferred to the have the head
28 be the luminal surface portion of the rivet 27 for assembly
purposes, since then the scaffold may be placed over a mandrel and
the tail portion of the rivet deformed by a tool (e.g., a pin)
applied externally to the scaffold abluminal surface. The rivet 27
has a head diameter d1 and the shank 27c diameter d2 is about equal
to the hole 22 diameter. The head 28 has a height of h2, which is
about the amount the head 28 will extend beyond the abluminal
surface 22a of the strut portion 21a. While not desirable, it may
be an acceptable protrusion for a head 28 that does not extend more
than about 25 microns, or from about 5 to 10 microns up to about 25
microns from the abluminal surface 22a, or a head that extends by
an amount no more than about 25% of the strut thickness. The same
extent of protrusion beyond the luminal surface 22b may be
tolerated for the deformed tail of the rivet.
[0126] Referring to FIG. 9C there is shown the rivet in the hole
22. The deformed tail 27b' secures the rivet 27 in the hole 22. The
overall height h1 is preferably not more than about 40% or about
10%-40% greater than the strut thickness (t) and the tail height is
about the same as, or within 5 to 200 microns in dimension compared
to the head height h2.
[0127] The rivet 27 may be attached to the hole 22 of the strut
portion 21a by first inserting the rivet 27 into the hole 22 from
the bore side of the scaffold so that the head 28 rests on the
luminal surface 22b of the strut portion 21a. The scaffold is then
slipped over a tight fitting mandrel. With the mandrel surface
pressed against the head 28 a tool (e.g., a pin) is used to deform
the tail 27b to produce the deformed tail 27b' in FIG. 9C. In some
embodiments, the rivet 27 may be first inserted into the hole 22
from the abluminal side so that head 28 rests on the abluminal
surface 22a of the strut potion 21a. With the head 28 held in place
by a tool or flat surface applied against the abluminal surface,
the tail 27b is deformed by a tool, pin, or mandrel which is
inserted into the bore or threaded through the scaffold pattern
from an adjacent position on the abluminal surface. In some
embodiments the rivet 27 may be a solid body (FIG. 9A-9B) or a
hollow body, e.g., the shank is a hollow tube and the opening
extends through the head 28 of the rivet.
[0128] In some embodiments a rivet is a hollow or solid cylindrical
tube and devoid of a pre-made head 28. In these embodiments the
tube (solid or hollow) may be first fit within the hole then a
pinch tool used to form the head and tail portions of the
rivet.
[0129] Referring to FIGS. 10A-10B and 11A-11B there is shown
embodiments for securing a marker using a starting cylindrical tube
hollow (tube 65) or solid (tube 75), respectively.
[0130] Referring to FIGS. 10A-10B there is an attachment of a
marker shaped as a hollow tube 65 placed into the strut portion 21a
hole and deformed using a pinching tool 60. FIG. 10B shows the
deformed marker 65'. The tube 65 has an inside cylindrical surface
67 and outer diameter that is about, or slightly greater than the
hole 22 diameter. The tube has an undeformed length about equal to
about 10%-40%, or 40%-80% greater than the strut thickness (t). The
deformed tube/rivet has a deformed length (h2) of about 10-50%
greater than the strut thickness and/or an undeformed length (h3)
of about 15% to 70% greater than the strut thickness (t).
[0131] The pinching tool 60 includes an upper arm 60a and lower arm
60b. The deforming faces of the two arms 60a, 60b are the same. The
face includes a deforming face 62a, 62b respectively shaped as an
apex,point, hemisphere or convex surface, so that when pressed into
the tube the end portions extending above the strut surface 22a,
22b respectively will be pushed outwardly, as shown in FIG. 10B.
The arm's flattening surface 63a, 63b flattens the material against
the strut surface. As can be appreciated from the drawings the
deformed ends 65a', 65b' of the deformed tube 65' resemble the
faces of the deforming faces 63a, 63b.
[0132] Referring to FIGS. 11A-11B there is an attachment of a
marker shaped as a solid tube 75 placed into the strut portion 21a
hole and deformed using a pinching tool 70. FIG. 11B shows the
deformed marker 75'. The tube has an undeformed length about equal
to about 10%-40%, or 40%-80% greater than the strut thickness (t).
The deformed tube/rivet has a deformed length (h2) of about 10-50%
greater than the strut thickness and/or an undeformed length (h3)
of about 15% to 70% greater than the strut thickness (t).
[0133] The pinching tool 70 includes an upper arm 70a and lower arm
70b. The deforming faces of the two arms 70a, 70b are the same. The
faces include a deforming face 72a for arm 70a and deforming face
72b for arm 70b, both of which may be shaped with an apex, point,
hemisphere, or convex surface, so that when pressed into the tube
the end portions extending above the strut surface 22a, 22b
respectively will be pushed outwardly, as shown in FIG. 11B. The
arm's flattening surface 73a, 73b flattens the material against the
strut surface. As can be appreciated from the drawings the deformed
ends 75a', 75b' of the deformed tube 75' resemble the faces of the
deforming faces 73a, 72a, 73b, and 73a.
[0134] F. Use of a Polygonal or Irregular Marker Shape
[0135] According to Concept F, an irregular-shaped marker having
protruding edges is placed in a lased hole prior to a thermal
process that shrinks the lased hole. Polymeric bioresorbable
scaffolds may be laser cut from a tube. This thin wall, precision
tubing can be fabricated by extrusion and expansion processes that
include stretch blow molding. The tubing resulting from such
processes is formed by deformation of the polymer, which can result
in residual stresses remaining in the tube. Heating the tube above
its glass transition temperature (Tg) releases these stresses and
can be used advantageously to shrink features such as lased marker
bead holes to increase securement of a previously placed radiopaque
marker. In an alternative embodiment, the temperature of the
scaffold is raised above the Tg of the tube material and the marker
placed into the softer, heated polymer. This allows the polymer to
become more compliant, or flow and thus allow a marker,
particularly an irregularly shaped marker, to interact with the
polymer surfaces to a greater degree, thereby raising the
frictional forces and/or forming a mechanical fit, depending on the
marker type used.
[0136] Referring to FIG. 12A and 12B there is shown an irregularly
shaped marker 85 placed in the hole 22 of the strut portion 21a.
The hole 22 may be at ambient temperature or at an elevated
temperature (about 0-20 Degrees C above the Tg of the strut
material). Alternately, the hole 22 is heated above the Tg after
the marker is inserted. The marker 85 has bumps, edges, corners or
burrs 81 over its surface that when placed in the hole 22 deforms
the hole, as illustrated in FIG. 12B. The engagement between the
marker 85 and hole may form a mechanical interlock. For a marker
with cylindrical symmetry, a degree of roughness can be defined as
the maximum and minimum distances in terms of radius from the
markers cylindrical axis (e.g., difference between inner and out
diameter as a maximum degree of roughness, or % of inner or outer
diameter). For the marker 85 this distance from max to min may be
between 5 to 50% of the maximum marker diameter The marker may have
a flower, star or polygonal shape to produce the same effect. When
placed in the hole 22 the hole 22 deforms. The marker 85 may or may
not deform, depending on the temperature of hole 22 and the
hardness of the marker material.
[0137] G. Snap-In Marker
[0138] According to Concept G, a snap-in marker is used. Referring
to FIGS. 13A and 13B there is shown a marker 95 having a preformed
head 98 and tail 92. The shank 95c of the marker has an extent
about equal to that the hole 22, which in this case is a diameter.
The length of the shank is about, slightly less, or slightly more
than the strut thickness. In other embodiments the marker 95 may be
rectangular, hexagonal or polygonal for fitting into the holes
shown in FIGS. 4A, 5A, 6A or 6C. The distance between abluminal
surface 95a and luminal surface 95b in FIG. 13B satisfies
inequality IE.2 or IE.4, defined below.
[0139] Platinum, and especially platinum/iridium alloys, are
stronger than polymeric materials because they are metals. Many
assembly and securement process use snap-fit parts where the
tolerances and shapes are designed to hold parts together without
fasteners. The main feature of the marker 95 is the head 98 and
tail 92 having an enlarged diameter over the shank 95c part. There
could be formed on portions 98 and 92 round ridges, or more wedge
shaped features. When pressed in, the polymer will deform
preferentially allowing the tail 92 or head 98 to pass through, or
imbed within the hole to become partially or fully recessed within
the hole 22. When the tail 92 or head 98 passes completely through
hole 22, the polymer surface 22a or 22b will snap under marker
feature 98 or 92, securing it and preventing movement in either
direction.
[0140] With respect to any of Concepts A through G, the marker
material may be platinum, platinum/iridium alloy, iridium,
tantalum, palladium, tungsten, niobium, zirconium, or alloys
thereof. The marker material may also be of biodegradable metals
such as iron, zinc, magnesium, manganese or their alloys.
[0141] For some embodiments included under Concept A (e.g., the
embodiments shown in FIGS. 3A-3C); some embodiments included under
Concept E (e.g., the embodiments shown in FIGS. 9A-9C, 10A-10B and
11A-11B); and some embodiments included under Concept G (e.g., the
embodiments shown in FIGS. 13A-13B) the following inequalities
IE.1-IE.4 apply:
t.times.(1.2).ltoreq.L.ltoreq.t.times.(1.8) or
1.2.ltoreq.(L/t).ltoreq.1.8 IE.1
t.times.(1.1).ltoreq.L'.ltoreq.t.times.(1.5) or
1.1.ltoreq.(L'/t).ltoreq.1.5 IE.2
t.times.(1.0).ltoreq.L.ltoreq.t.times.(1.8) or
1.0.ltoreq.(L/t).ltoreq.1.8 IE.3
t.times.(1.0).ltoreq.L'.ltoreq.t.times.(1.5) or
1.0.ltoreq.(L'/t).ltoreq.1.5 IE.4
[0142] Where: [0143] t is the average strut, bar arm or link
thickness, or wall thickness of the tube from which the scaffold
was made. The thickness t may vary between about 80 to 150 microns,
80 to 120 microns, 80 to 110 microns, 80 to 100 microns, or the
thickness may be about 100 microns, or the thickness may be up to
130 or 140 microns; [0144] L is an undeformed length of the marker
(Concept E); and [0145] L' is a deformed length of the marker
(measured from the abluminal surface portion to the luminal surface
portion for Concept E), length of the marker (Concept G), or
distance between abluminal and luminal surfaces of a coating and/or
polymer fill (Concept A).
[0146] Exemplary values for t are about 80 microns to 120 microns,
or about 100 microns and L' or L being between about 100 microns
and 150 microns.
[0147] The relations IE.1, IE.2, IE.3 and IE.4 reflect a need to
maintain a low profile for struts exposed in the bloodstream, while
ensuring the marker will be securely held in the strut. The concern
addressed here is the degree thrombogenicity of the scaffold, which
can be influenced by a strut thickness overall and/or protrusion
from a strut surface. Blood compatibility, also known as
hemocompatibility or thromboresistance, is a desired property for
scaffolds and stents. The adverse event of scaffold thrombosis,
while a very low frequency event, carries with it a high incidence
of morbidity and mortality. To mitigate the risk of thrombosis,
dual anti-platelet therapy is administered with all coronary
scaffold and stent implantation. This is to reduce thrombus
formation due to the procedure, vessel injury, and the implant
itself. Scaffolds and stents are foreign bodies and they all have
some degree of thrombogenicity. The thrombogenicity of a scaffold
refers to its propensity to form thrombus and this is due to
several factors, including strut thickness, strut width, strut
shape, total scaffold surface area, scaffold pattern, scaffold
length, scaffold diameter, surface roughness and surface chemistry.
Some of these factors are interrelated. The effect of strut
thickness on acute thrombogenicity has been documented and studied
both in vivo and in silico.
[0148] The above description of illustrated embodiments of the
invention, including what is described in the Abstract, is not
intended to be exhaustive or to limit the invention to the precise
forms disclosed. While specific embodiments of, and examples for,
the invention are described herein for illustrative purposes,
various modifications are possible within the scope of the
invention, as those skilled in the relevant art will recognize.
[0149] These modifications can be made to the invention in light of
the above detailed description. The terms used in claims should not
be construed to limit the invention to the specific embodiments
disclosed in the specification.
* * * * *