U.S. patent application number 10/756721 was filed with the patent office on 2005-06-09 for medical devices.
Invention is credited to Devens, Douglas A. JR., Zoromski, Michele.
Application Number | 20050124976 10/756721 |
Document ID | / |
Family ID | 34633622 |
Filed Date | 2005-06-09 |
United States Patent
Application |
20050124976 |
Kind Code |
A1 |
Devens, Douglas A. JR. ; et
al. |
June 9, 2005 |
Medical devices
Abstract
Medical devices and methods of making the devices are described.
In some embodiments, the devices include multiple layers, and one
or more layers can include a nanocomposite material.
Inventors: |
Devens, Douglas A. JR.; (St.
Paul, MN) ; Zoromski, Michele; (Minneapolis,
MN) |
Correspondence
Address: |
FISH & RICHARDSON PC
225 FRANKLIN ST
BOSTON
MA
02110
US
|
Family ID: |
34633622 |
Appl. No.: |
10/756721 |
Filed: |
January 13, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10756721 |
Jan 13, 2004 |
|
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10728079 |
Dec 4, 2003 |
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Current U.S.
Class: |
604/523 ;
138/137; 264/634 |
Current CPC
Class: |
Y10T 428/1393 20150115;
B32B 27/32 20130101; A61M 25/1006 20130101; B32B 1/08 20130101;
B32B 27/20 20130101; A61M 25/1029 20130101; A61M 25/0045 20130101;
B32B 27/08 20130101; B32B 2535/00 20130101; B32B 2307/542 20130101;
B32B 2597/00 20130101 |
Class at
Publication: |
604/523 ;
264/634; 138/137 |
International
Class: |
A61M 025/00 |
Claims
What is claimed is:
1. A co-extruded medical tube, comprising: a first layer; and a
second layer disposed radially inwardly of the first layer, wherein
the first and second layers have different compositions, and one of
the layers comprises a nanocomposite material and has a viscosity
between 25% and 120% of a viscosity of the other layer as measured
at a shear rate of 1 s.sup.-1 and a temperature of 220.degree.
C.
2. The medical tube of claim 1, wherein the second layer is bonded
directly to the first layer.
3. The medical tube of claim 1, wherein the first layer is the
outermost layer of the co-extruded tube.
4. The medical tube of claim 1, further comprising a third layer
having a different composition than the second layer, the third
layer having a viscosity greater than a viscosity of the second
layer as measured at a shear rate of 1 s.sup.-1 and a temperature
of 220.degree. C.
5. The medical tube of claim 4, wherein the composition of the
third layer is different that the composition of the first
layer.
6. The medical tube of claim 5, wherein the third layer is the
innermost layer.
7. The medical tube of claim 1, wherein the composition of the
first layer is a nanocomposite.
8. The medical tube of claim 1, wherein the composition of the
second layer is a non-nanocomposite.
9. The medical tube of claim 1, wherein the first and second layer
has a thickness uniformity of 80% or greater around the
circumference of the medical tube.
10. A co-extruded medical tube comprising: a first layer comprising
a nanocomposite material having a first viscosity; and a second
layer comprising a second material and having a second viscosity,
wherein the first viscosity is from about 25% to about 120% of the
second viscosity as measured at a shear rate less than about 1
s.sup.-1 and a temperature of about 60.degree. C. to about
120.degree. C. above a flow temperature of a highest flow
temperature material that is co-extruded.
11. The medical tube of claim 10, wherein the shear rate has a
value of about 0.1 s.sup.-1.
12. The medical tube of claim 10, wherein the temperature is
220.degree. C.
13. The medical tube of claim 1 further comprising a third
co-extruded layer comprising a third material having a third
viscosity that varies with shear rate, wherein the second viscosity
is from about 5% to about 35% of the third viscosity as measured at
a shear rate less than about 1 s.sup.-1 and a temperature of about
60.degree. C. to about 120.degree. C. above a flow temperature of a
highest flow temperature material that is co-extruded.
14. The medical tube of claim 10, wherein the second material
comprises Plexar.RTM. PX380, a modified polyolefin.
15. The medical tube of claim 13, wherein the third material
comprises Marlex.RTM., a high density polyethylene.
16. The medical tube of claim 10, wherein the first layer comprises
at least about 30% of a cross-sectional area of the medical
tube.
17. The medical tube of claim 10, wherein the second layer
comprises at least about 5% of a cross-sectional area of the
medical tube.
18. The medical tube of claim 13, wherein the third layer comprises
at least about 10% of the medical device.
19. The medical tube of claim 10, wherein the first layer and the
second layer are coextensively co-extruded.
20. The medical tube of claim 10, wherein the first layer and the
second layer are intermittently co-extruded.
21. A medical device comprising: a tubular body comprising a
plurality of co-extruded layers, wherein a viscosity of a first
layer is from about 25% to about 120% of a second viscosity of an
adjacent layer as measured at a shear rate less than about 1
s.sup.-1 and a temperature of about 60.degree. C. to about
120.degree. C. above a flow temperature of a highest flow
temperature material that is co-extruded.
22. The medical device of claim 21, wherein the shear rate is below
about 0.1 s.sup.-1.
23. The medical device of claim 21, wherein at least one of the
plurality of co-extruded layers comprises a nanocomposite
material.
24. The medical device of claim 21, wherein the plurality of
co-extruded layers comprises an outer nanocomposite layer, a middle
layer, and an inner layer.
25. The medical device of claim 24, wherein the middle layer
comprises Plexar.RTM. PX380, a modified polyolefin.
26. The medical device of claim 24, wherein the inner layer
comprises Marlex.RTM., a high density polyethylene.
27. A method of manufacturing a device including a first layer and
a second layer, the method comprising: selecting a shear rate at or
below about 1 s.sup.-1; selecting a temperature; selecting a
material for the second layer, the material having a viscosity
value at the shear rate and the temperature; selecting a
nanocomposite material for the first layer that has a viscosity
within about 20% to about 125% of the viscosity value of the
material for the second layer; and co-extruding the first and
second layers.
28. The method of claim 27, wherein the device is a medical
device.
29. The method of claim 27, wherein the shear rate is below about
0.5 s.sup.-1.
30. The method of claim 27, wherein the shear rate is about0.1
s.sup.-1.
31. The method of claim 27, wherein the temperature is about
60.degree. C. to about 120.degree. C. above a flow temperature of a
highest flow temperature material co-extruded.
32. A tubular member comprising: a first layer and a second layer
co-extruded with the first layer, wherein one of the layers
comprises a nanocomposite material, and one of the layers comprises
a thickness that varies by less than about 20% from a mean value of
thickness, the thickness being measured at four points per
cross-sectional cut made at ten random, non-consecutive locations
along a production length of the tubular member.
33. The tubular member of claim 32, wherein the thickness varies by
less than 15% from the mean value of thickness.
34. The tubular member of claim 32, wherein the thickness varies by
less than 10% from the mean value of thickness.
35. The tubular member of claim 32, wherein the first layer has a
first thickness that varies less than about 20% from a mean value
of thickness for the first layer and the second layer has a second
thickness that varies less than about 20% from a mean value of
thickness for the second layer.
36. The tubular member of claim 33, wherein the tubular member
further comprises a third layer.
37. A method of making a medical device, the method comprising:
forming a tubular member, the tubular member comprising a first
layer and a second layer co-extruded with the first layer, wherein
one of the layers comprises a nanocomposite material, and one of
the layers comprises a thickness that varies by less than about 20%
from a mean value of thickness, the thickness being measured at
four points per cross-sectional cut made at ten random,
non-consecutive locations along a production length of the tubular
member; and incorporating a portion of the tubular member as a
component of the medical device.
38. The method of claim 37, wherein the medical device is a
catheter.
39. The method of claim 37, wherein the medical device is a
balloon-catheter.
40. The method of claim 37, wherein the thickness varies by less
than 15% from the mean value of thickness.
41. The method of claim 37, wherein the thickness varies by less
than 10% from the mean value of thickness.
42. The method of claim 37, wherein the device is a stent delivery
system, and the tubular member is a catheter or a sheath.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part application of
and claims priority to U.S. application Ser. No. 10/728,079, filed
on Dec. 4, 2003, hereby incorporated by reference in its
entirety.
TECHNICAL FIELD
[0002] The invention relates to medical devices, such as, for
example, medical tubing, guide wires, catheters, and balloon
catheters, and methods of making the devices.
BACKGROUND
[0003] Intravascular medical devices, such as guide wires,
catheters, and medical tubing, allow physicians to perform a
medical procedure, such as balloon angioplasty or delivery of an
endoprosthesis, e.g., a stent. In some cases, a device is inserted
into a patient's vascular system at a convenient site and
subsequently delivered, e.g., pushed, through the vascular system
to a target site. The path that the device takes through the
vascular system to the target site can be relatively tortuous, for
example, requiring the device to change direction frequently.
[0004] In some circumstances, it is desirable for the device to
have relatively good flexibility so that it can track along the
tortuous path. At the same time, the device preferably has good
pushability so that forces applied proximally to the device can be
transmitted distally to deliver the device.
SUMMARY
[0005] The invention relates to medical devices, such as, for
example, catheters, stents, and medical tubing.
[0006] In one aspect, the invention features a co-extruded medical
tube including a first layer, and a second layer disposed radially
inwardly of the first layer, wherein the first and second layers
have different compositions, and one of the layers has a
nanocomposite material and has a viscosity between 25% and 120% of
a viscosity of the other layer as measured at a shear rate of
1s.sup.-1 and a temperature of 220.degree. C.
[0007] Embodiments may include one or more of the following
features. The second layer is bonded directly to the first layer.
The first layer is the outermost layer of the co-extruded tube. The
composition of the first layer is a nanocomposite. The composition
of the second layer is a non-nanocomposite. The first and second
layer have a thickness uniformity of 80% or greater around the
circumference of the medical tube.
[0008] The medical tube can further include a third layer, e.g.,
one having a different composition than the second layer. The third
layer can have a viscosity greater than a viscosity of the second
layer as measured at a shear rate of 1 s.sup.-1 and a temperature
of 220.degree. C. The composition of the third layer can be
different than the composition of the first layer. The third layer
can be the innermost layer.
[0009] In another aspect, the invention features a co-extruded
medical tube including a first layer having a nanocomposite
material having a first viscosity, and a second layer having a
second material and having a second viscosity. The first viscosity
is from about 25% to about 120% of the second viscosity as measured
at a shear rate less than about 1 s.sup.-1 and a temperature of
about 60.degree. C. to about 120.degree. C. above a flow
temperature of a highest flow temperature material that is
co-extruded.
[0010] Embodiments may include one or more of the following
features. The shear rate has a value of about 0.1 s.sup.-1. The
temperature is about 220.degree. C. The second material includes
Plexar.RTM. PX380, a modified polyolefin. The first layer is at
least about 30% of a cross-sectional area of the medical tube. The
second layer is at least about 5% of a cross-sectional area of the
medical tube.
[0011] The medical tube can further include a third co-extruded
layer having a third material having a third viscosity that varies
with shear rate. The second viscosity can be from about 5% to about
35% of the third viscosity as measured at a shear rate less than
about 1 s.sup.-1 and a temperature of about 60.degree. C. to about
120.degree. C. above a flow temperature of a highest flow
temperature material that is co-extruded. The third material can
include Marlex.RTM., a high density polyethylene. The third layer
can be at least about 10% of the medical device.
[0012] The first layer and the second layer can be coextensively
co-extruded or intermittently co-extruded.
[0013] In another aspect, the invention features a medical device
including a tubular body having a plurality of co-extruded layers,
wherein a viscosity of a first layer is from about 25% to about
120% of a second viscosity of an adjacent layer. The viscosity is
measured at a shear rate less than about 1 s.sup.-1 and a
temperature of about 60.degree. C. to about 120.degree. C. above a
flow temperature of a highest flow temperature material that is
co-extruded.
[0014] Embodiments may include one or more of the following
features. The shear rate is below about 0.1 s.sup.-1. At least one
of the plurality of co-extruded layers includes a nanocomposite
material. The plurality of co-extruded layers includes an outer
nanocomposite layer, a middle layer, and an inner layer. The middle
layer includes Plexar.RTM. PX380, a modified polyolefin, and/or the
inner layer includes Marlex.RTM., a high density polyethylene.
[0015] In another aspect, the invention features a method of
manufacturing a device including, a first layer and a second layer.
The method includes selecting a shear rate at or below about 1
s.sup.-1, selecting a temperature, selecting a material for the
second layer, the material having a viscosity value at the shear
rate and the temperature, selecting a nanocomposite material for
the first layer that has a viscosity within about 20% to about 125%
of the viscosity value of the material for the second layer, and
co-extruding the first and second layers.
[0016] Embodiments may include one or more of the following
features. The device is a medical device. The shear rate is below
about 0.5 s.sup.-1, e.g., about 0.1 s.sup.-1. The temperature is
about 60.degree. C. to about 120.degree. C. above a flow
temperature of a highest flow temperature material co-extruded.
[0017] In another aspect, the invention features a tubular member
including a first layer and a second layer co-extruded with the
first layer, wherein one of the layers has a nanocomposite
material, and one of the layers has a thickness that varies by less
than about 20% from a mean value of thickness. The thickness is
measured at four points per cross-sectional cut made at ten random,
non-consecutive locations along a production length of the tubular
member.
[0018] Embodiments may include one or more of the following
features. The thickness varies by less than about 15% (e.g., less
than about 10%) from the mean value of thickness. The first layer
has a first thickness that varies less than about 20% from a mean
value of thickness for the first layer, and the second layer has a
second thickness that varies less than about 20% from a mean value
of thickness for the second layer. The tubular member further
includes a third layer.
[0019] In another aspect, the invention features a method of making
a medical device. The method includes forming a tubular member
having a first layer and a second layer co-extruded with the first
layer, and incorporating a portion of the tubular member as a
component of the medical device. One of the layers has a
nanocomposite material, and one of the layers has a thickness that
varies by less than about 20% from a mean value of thickness. The
thickness is measured at four points per cross-sectional cut made
at ten random, non-consecutive locations along a production length
of the tubular member.
[0020] Embodiments may include one or more of the following
features. The medical device can be, for example, a catheter or a
balloon-catheter. The thickness can vary by less than about 15%
(e.g., less than about 10%) from the mean value of thickness.
[0021] Embodiments may have one or more of the following
advantages. The medical device can have two or more layers that
together provide relatively good flexibility so that the medical
device can track along tortuous path within a patient's body. At
the same time, the two or more layers of the medical device provide
good pushability so that forces applied proximally to the device
can be transmitted distally to deliver the device. For example, at
least one of the layers of the medical device includes a
nanocomposite material that increases the stiffness of the medical
device such that the medical device can be advanced through a
patient's body without kinking and/or buckling. A medical device
including a layer having nanocomposite material can be formed to
have concentric multiple layers with high quality interfaces. As a
result, the medical device has a relatively smooth interior
surface, which does not interfere with guide wire movement and
hence pushability of the medical device. As a further result, the
multiple concentric layers reduce the likelihood of forming weak
spots (e.g., spot that are deficient in strength) in the medical
device. A medical device including multiple layers wherein at least
one of the layers includes nanocomposite materials can be extruded
economically, that is, scrap material is reduced because devices
with concentric multiple layers can be consistently produced.
[0022] Other aspects, features and advantages of the invention will
be apparent from the description of the preferred embodiments and
from the claims.
DESCRIPTION OF DRAWINGS
[0023] FIG. 1 is an illustration of a portion of a balloon catheter
system.
[0024] FIG. 2A is a cross-sectional view of a tube of the balloon
catheter system of FIG. 1, taken along line 2A-2A.
[0025] FIG. 2B is a cross-sectional view of a tube of a balloon
catheter system that has non-uniform co-extruded layers.
[0026] FIG. 3 is a plot of viscosity versus shear rate for several
nanocomposite and pure polymer materials. The viscosity
measurements in this plot were measured at a temperature of
220.degree. C.
[0027] FIG. 4A is a perspective view of an exemplary cross-head
device. FIG. 4B is an exploded view of the cross-head device of
FIG. 4A.
[0028] FIG. 5A is a side view of an exemplary retainer nut used
within the cross-head device of FIG. 4A. FIG. 5B is a top view of
the retainer nut of FIG. 5A. FIG. 5C is a cross-sectional view of
the retainer nut taken along line 5C-5C in FIG. 5B.
[0029] FIG. 6 is a cross-sectional view of a multilayer tube.
[0030] FIG. 7 is a cross-sectional view of a multilayer tube.
[0031] FIG. 8A is a cross-sectional side view of a portion of a
stent delivery system. FIG. 8B is an enlarged view of region A in
FIG. 8A. FIG. 8C is an enlarged view of region B in FIG. 8A.
DETAILED DESCRIPTION
[0032] Referring to FIG. 1, a balloon catheter system 10 includes a
catheter 12 and an inflatable balloon 14 carried by the catheter.
Catheter 12 includes an outer shaft 16 and an inner shaft 18
defining a lumen 19. Shafts 16 and 18 are concentric and define an
annular lumen 20 between them. During use, catheter system 10 can
be delivered to a treatment area (e.g., a coronary artery) by
passing lumen 19 over a guide wire 22 emplaced in the body, and
pushing the catheter system to the treatment area. Balloon 14 can
then be inflated or deflated by delivering or withdrawing a fluid
(such as a liquid or a gas) through annular lumen 20. Examples of
balloon catheter systems are described in U.S. Pat. Nos. 5,19 5,969
and 5,270,086, and exemplified by the Maverick(&
single-operator exchange system and over-the-wire systems,
available from Boston Scientific Scimed, Maple Grove, Minn.
[0033] Referring to FIG. 2A, inner shaft 18 has multiple,
co-extruded polymer layers 24, 26, 28. Inner layer 28 is made of a
high radial strength, low friction polymer (e.g., high density
polyethylene) that minimizes the likelihood of collapse of the
catheter 12 during balloon inflation and, at the same time,
facilitates movement of the catheter over guide wire 22. Middle
layer 26 is made of a polymer (e.g., a modified polyolefin) that
enhances bonding between inner layer 28 and outer layer 24. Outer
layer 24 enhances the pushability of the catheter 12, and is
typically relatively stiff as compared to the inner and middle
layers 28, 26, respectively. At least one of the layers, e.g. the
outer layer 24, is made out of a nanocomposite material. The
nanocomposite material can include nanosized (e.g., 1000 nm to 1
nm) particles (such as clay, glass, or carbon particles) dispersed
within a polymer matrix (such as a polyamide available as Nylon
12.RTM. from DuPont deNemours & Co, Wilmington, Del.). The
addition of the nanosized particles enhances the mechanical
properties, such as the stiffness of the polymer.
[0034] As illustrated in FIG. 2A, the uniformity of the co-extruded
layers is maintained. The thickness of the layers is substantially
constant around the circumference of catheter 12 and adjacent
layers are separated by an interface. The high precision with which
layers 24, 26, 28 can be formed means that inner shaft 18 can be
formed accurately and consistently, which in turn, can enhance the
performance and manufacture of catheter system 10 (e.g. by reducing
scrap). Referring to FIG. 2B, in a non-uniform co-extrusion, one
polymer layer blends into adjacent layers on occasion. The
irregularity of this co-extrusion affects the performance of the
catheter by, e.g., modifying the flexibility and kink-resistance of
the tube, varying its inner or outer diameter, and/or exposing an
outer polymer layer to the guide wire lumen, which could be
non-optimal for low friction sliding over a guide wire. In
embodiments, the precision of the co-extrusion can be such that the
layers have a thickness uniformity of about 80% or greater (e.g.,
equal to or greater than 85%, equal to or greater than 90%, or
equal to or greater than 95%) around the circumference over a
length of a catheter that is 60 centimeters or greater.
[0035] The precision of the co-extrusion of a three-layered tube
including a nanocomposite material is controlled by selecting
combinations of materials that are compatible under certain shear
rate characteristics. In some embodiments, the nanocomposite
material is selected to have viscosities, under certain shear rate
characteristics, that are compatible with materials used to form
middle layer 26 (i.e., the layer used to bind the inner layer to
the outer layer). For example, the nanocomposite material can have
a viscosity that is within about 25% to about 120% of the viscosity
of the middle layer as measured at a shear rate at or below 1
s.sup.-1 and a temperature of 220.degree. C. That is, the viscosity
of the nanocomposite material can be greater than or equal to about
25%, greater than or equal to about 30%, greater than or equal to
about 35%, greater than or equal to about 40%, greater than or
equal to about 45%, greater than or equal to about 50%, greater
than or equal to about 55%, greater than or equal to about 60%,
greater than or equal to about 65%, greater than or equal to about
70%, greater than or equal to about 75%, greater than or equal to
about 80%, greater than or equal to about 85%, greater than or
equal to about 90%, greater than or equal to about 95%, greater
than or equal to about 100%, greater than or equal to about 105%,
greater than or equal to about 110%, greater than or equal to about
115% of the middle layer 26; and/or equal to or less than 120%,
equal to or less than 115%, equal to or less than 110%, equal to or
less than 105%, equal to or less than 100%, equal to or less than
95%, equal to or less than 90%, equal to or less than 85%, equal to
or less than 80%, equal to or less than 75%, equal to or less than
70%, equal to or less than 65%, equal to or less than 60%, equal to
or less than 55%, equal to or less than 50%, equal to or less than
45%, equal to or less than 40%, equal to or less than 35%, equal to
or less than 30% of the middle layer 26.
[0036] Referring to FIG. 3, in embodiments, the nanocomposite
material exhibits a viscosity profile as a function of shear rate
in which the viscosity tends toward a maximum. Certain
nanocomposite materials, such as Foster nanocomposite formula
number 05293-B01 available from Foster Compounding, Dayville, Conn.
and RTP formula number 0299 FX 83107F available from RTP Company,
Winona, Minn., have a viscosity profile that tends toward infinity
at a low shear rate. Other nanocomposite materials have a viscosity
profile that tends towards a maximum viscosity at low shear rate
values (e.g., Ube Nano-PA 12 formula number 3030C2 available from
Ube Industries, Ube America Inc., New York, N.Y. and RTP formula
number 0299 FX 83107C available from RTP Company, Winona, Minn.),
which is more common to pure polymers and are typically more
compatible with other materials for precision co-extrusion.
[0037] Materials used to form the middle layer 26 have viscosities
that are lower than viscosities of materials used in the inner
layer 28 at low shear rates (e.g., at or below 1 s.sup.-1). In
certain embodiments, the middle layer 26 has a viscosity that is 5%
to 35% of the viscosity of the inner layer 28. For example, the
viscosity of middle layer 26 can be greater than or equal to about
5%, greater than or equal to about 10%, greater than or equal to
about 15%, greater than or equal to about 20%, greater than or
equal to about 25%, greater than or equal to about 30% of inner
layer 28; and/or less than or equal to about 35%, less than or
equal to about 30%, less than or equal to about 25%, less than or
equal to about 20%, less than or equal to about 15%, less than or
equal to about 10% of the inner layer 28. It is believed that a
lower viscosity material aids in the co-extrusion of a higher
viscosity material by acting as a lubricant to minimize frictional
forces along the extrusion channel. For example, in oil pipelines,
water (a low viscosity material) is commonly used to aid the flow
of oil (a high viscosity material) through the pipe. As a result of
using a middle layer with a lower viscosity than the inner layer,
flow within a co-extrusion device is increased, thereby further
increasing the likelihood of precision co-extrusion.
[0038] The viscosity of a material can be experimentally determined
by capillary or parallel plate rheometry. In capillary rheometry, a
material (e.g., a polymer or a nanocomposite) is placed within a
capillary rheometer (e.g., Kayness Incorporated, Galaxy V, Model
1802) at about room temperature. The capillary rheometer is heated
to a target temperature about 80.degree. C. above the flow
temperature of the material, and held at the target temperature for
about 10 minutes. The flow temperature is the temperature at which
the material transforms from a solid state to a liquid state, for
example the melt temperature for crystalline polymers and the glass
transition temperature for non-crystalline polymers. The flow
temperature of the material can be determined by differential
scanning calorimetry (DSC) (e.g., using a Thermal Analysis Model
2920). In cases in which DSC reveals more than one flow
temperature, such as when the material includes a blend of
polymers, the highest of the flow temperatures is used as the flow
temperature of the material in heating the rheometer. Next, the
material is extruded using a pressure at which the shear rate has a
constant value, such as 100 s.sup.-1. The rheometer then calculates
and reports the viscosity of the material at the selected constant
shear rate in accordance with ASTM 3835-96.
[0039] The viscosity of a material can also be measured using a
parallel plate rheometer (i.e., dynamic shear measurement) using a
method described by ASTM D4065-95 (Vol. 8.02) and ASTM D4440-95a
(Vol. 8.03). The data line measured using the parallel plate
rheometer is fit using either the Power Law Model or the Ellis
Model, depending upon the rhelogogical characteristics of the
polymer being measured. To compute the viscosity, the data is
transformed using the Cox-Merz rule to steady viscosity
calculations, such as those produce by a capillary rheometer. The
Cox-Merz rule is described in detail on p. 150 of Dynamics of
Polymer Liquids, Vol. 1, 2.sup.nd Edition, by Bird et al.,
published by John Wiley and Sons, New York, as well as on pages 619
-622 of the Journal of Polymer Science, Vol. 28, 1958. As indicated
above, viscosity can be measured by either capillary or parallel
plate rheometry. To the extent values by the two techniques are not
in agreement, it is typically sufficient that one or the other
provides a viscosity value that satisfies the relationship for high
precision extrusions, as discussed above. While either technique
can be used to measure viscosity, typically, viscosity measurements
at low shear rates (below about 1 s.sup.-1) are measured using the
parallel plate method.
[0040] After the materials for each layer are selected based on
their material properties (e.g., stiffness or lubricity) and good
combination of shear viscosities at a low shear rate, the materials
are used to form a co-extruded product, e.g., a tube. For example,
a tube can be prepared by using an extrusion apparatus such as, for
example, one having a cross-head, such as cross-head 100 shown in
FIGS. 4A and 4B and exemplified by a cross-head device manufactured
by GENCA (St. Petersburg, Fla.), model number B 1 Tri Die. To aid
in attachment (i.e., less time to assemble and disassemble) of
cross-head 100 to an extruder such as, for example, an extruder
commercially available from C W Brabender, South Hackensack, N.J.,
a retainer nut 105 formed from 440C stainless steel, as shown in
FIGS. 5A, 5B, and 5C was used. Illustrative examples, including
process parameters, for making a co-extruded product are provided
below. Other illustrative examples of process parameters,
techniques and apparatus for extruding a three-layered tube can be
found in U.S. Pat. No. 6,165,166 issued to Samuelson et al., U.S.
Pat. No. 6,319,228 issued to Kastenhofer, and U.S. Pat. No.
6,464,683 issued to Samuelson et al., the disclosures of which are
hereby incorporated by reference.
[0041] In some embodiments, melt pumps are used to modulate the
feed rate or flow of polymers in the crosshead. Exemplary melt
pumps are described in International Application Publication
Number, WO 01/32398, entitled "Method and Apparatus for Extruding
Catheter Tubing", the disclosure of which is hereby incorporated by
reference. In certain embodiments servo-controlled valves are used
to modulate the feed rate or flow of polymers in the crosshead.
Exemplary servo-controlled valves are described in U.S. Pat. No.
3,752,617 issued to Burlis et al, the disclosure of which is hereby
incorporated by reference.
[0042] By screening the materials for certain combinations of shear
viscosities at low shear rates, the co-extruded product can be
formed having well-defined features. In embodiments in which the
co-extruded product is a tube, the tube has a radial cross section
with good concentricity, e.g., the thickness of each layer is
accurate and precise. Referring to FIGS. 6 and 7, the concentricity
of the tube can be determined by examining the radial cross section
of the tube, and measuring the thickness of each layer (as shown,
three layers) along four equally spaced directions (FIG. 6) or
eight equally spaced directions (FIG. 7). The thickness can be
measured, for example, using a microscope (e.g., a Toolscope
microscope model number MM-40/2, available from Nikon, Melville,
N.Y.) and a digital caliper or a micrometer. The layers are
considered concentric when the thickness of each layer varies by no
more than about 20% (e.g., less than or equal to about 15%, 10%, or
5%) from a mean value of thickness measured around its
circumference for a sampling over the length of a production run. A
sampling over the length of a production run is conducted by
selecting 10 or more (e.g., 10, 15, or 20) random, non-consecutive
points along a production run length (e.g., 1000 feet) and
measuring the thickness of each layer at each of the 10 points.
[0043] The co-extruded concentric inner tube can then be
incorporated into catheter system 10. For example, inner tube 18
can be attached to balloon 14 using an adhesive or a weld, such as,
for example, a radio-frequency weld or a laser weld. Catheter
system 10 can be used, for example, for angioplasty and/or to
deliver an endoprosthesis, such as a stent.
[0044] Turning now to the materials for the layers, as indicated
above, in certain embodiments, one (or more) layers of the
co-extruded product includes a nanocomposite material. The
nanocomposite material can include a polymer matrix having
dispersed therein nanosized (e.g., 1000 nm to 1 nm) particles that
enhance the properties (e.g., strength and stiffness) of the
polymer. Examples of nanocomposite materials include Ube Nano-PA12
(formula number #3030C2, available from Ube Industries, Ube America
Inc., New York, N.Y.); RTP formula number 0299 FX 83017C,
(available from RTP Company, Winona, Minn.). Other examples of
nanocomposite materials are described in U.S. application No.
2003/0065355. In certain embodiments, the nanocomposite material
has a shear viscosity of about 500 to about 15,000 Pa-s (e.g.,
about 500 to about 2,500 Pa-s) at a shear rate of or below 1
s.sup.-1 (e.g. 1 s.sup.-1, 0.5 s.sup.-1, 0.1 s.sup.-1) at about
380.degree. F. to about 450.degree. F.
[0045] The particles in the nanocomposite material can be synthetic
or natural. Examples of particles include phyllosilicates,
including clays and micas (that may optionally be intercalated
and/or exfoliated) such as montmorillonite (mmt), hectorites,
hydrotalcites, vermiculite, and laponite; monomeric silicates such
as polyhedral oligomeric silsequioxanes (POSS) including various
functionalized POSS and polymerized POSS; single and multi walled
carbon and ceramic nanotubes, nanowires and nanofibers including
single and multi walled fullerene nanotubes, silica nanogels, and
alumina nanofibers; metal and metal oxide powders including
aluminum oxide, titanium oxide, tungsten oxide, tantalum oxide,
zirconium oxide, gold (Au), silver (Ag), platinum (Pt) and magnetic
or paramagnetic powders such as neodynium iron boron,
superparamagnectic ferrite oxide or superparamagnetic maghemite;
organic materials, including temperature sensitive polymers such as
polyvinylpyrrolidone and n-isopropylacrylamide copolymers or
blends, and poloxamer. Biodegradable polymers may also be used, may
be magnetized, if desired, and include for example,
poly(lactic)acid, polysaccharide, and polyalkycyanoacrylate. A
nanocomposite material can include a mixture of two or more
different particle s, in any combination. A nanocomposite material
can include, for example, about 0.1 to about 10 weight percent of
particles.
[0046] Exemplary polymer matrix materials for a nanocomposite
material include thermoplastics and thermosets. Examples of
thermoplastics include, for example, polyolefins, polyamides, such
as nylon 12, nylon 11, nylon 6/12, nylon 6, and nylon 66,
polyesters, polyethers, polyurethanes, polyureas, polyvinyls,
polyacrylics, fluoropolymers, copolymers and block copolymers
thereof, such as block copolymers of polyether and polyamide, e.g.,
Pebax.RTM.; and mixtures thereof. Examples of thermosets include
clastomers such as EPDM, epichlorohydrin, nitrile butadiene
elastomers, silicones, etc. Conventional thermosets such as
expoxies, isocyanates, etc., can also be used. Biocompatible
thermosets, for example, biodegradable polycaprolactone,
poly(dimethylsiloxane) containing polyurethanes and ureas, and
polysiloxanes, may also be used. One or more of these materials can
be used in the nanocomposite material, in any combination.
[0047] Other embodiments of nancomposite materials are described in
Parsonage et al., U.S. patent application Publication 2003/0093107,
hereby incorporated by reference in its entirety. For example, the
nanocomposite materials can be functionalizers to enhance the
properties of the materials and/or to enhance compatibility between
layers. The nanocomposite materials can include one ore more
coupling or compatibilizing agents.
[0048] One or more non-nanocomposite polymers, e.g., pure polymers,
can be used in the other layers of the co-extruded product. In
embodiments, one or more layers include a high density
polyethylene, such as Marlex.RTM. 4903 available from Chevron
Phillips Chemical Company, Woodlands, Tex. In embodiments, one or
more layers can include a modified polyolefin, such as a maleic
anhydride polyolefin available as Plexar.RTM. PX380 from Equistar
Chemical Company, Newark, N.J.). In certain embodiments, one or
more layers can contain one or more nylons. Examples of nylons
include aliphatic nylons, such as Nylon 11 (Elf Atochem), Nylon 6
(Allied Signal), Nylon 6/10 (BASF), Nylon 6/12 (Ashley Polymers)
and Nylon 12. Additional examples of nylons include aromatic
nylons, such as GRIVORY.RTM. (EMS) and Nylon MXD-6. Other nylons
and/or combinations of nylons can be used.
[0049] In some embodiments, one or more layers can contain a liquid
crystal polymer (LCP) (e.g., a composite material having the LCP
incorporated therein). Examples of LCPs include polyester(s),
polyamide(s) and/or their copolymers, such as VECTRA.RTM. A
(Ticona), VECTRA.RTM. B (Ticona) and VECTRA.RTM. LKX (Ticona)
(e.g., VECTRA.RTM. LKX 1111 (Ticona)). Other LCPs and/or
combinations of LCPs can be used.
[0050] In certain embodiments, an adhesion enhancing material can
be incorporated into one or more material layers. An adhesion
enhancing material can be used, for example, to enhance the
adhesion between adjacent layers. Examples of adhesion enhancing
materials include epoxy or anhydride modified polyolefins, such as
LOTADER.RTM. (Elf Atochem) and KODAR.RTM. PETG (Eastman Kodak). An
adhesion enhancing material can be added to a material (e.g., a
composition containing one or more polymers) prior to extrusion
(described below). For example, in embodiments in which alternate
layers are formed of PET and PBT, PETG can be added to the PET
before extrusion.
[0051] The amount of adhesion enhancing material can vary depending
upon the intended use. In some embodiments, a sufficient amount of
adhesion enhancing material(s) are included in the material so that
the adhesion enhancing material(s) makes up at least about 0.5
percent of the resulting mixture that forms the layer (e.g., at
least about one percent, at least about five percent, at least
about 10 percent) and/or at most about 20 percent of the resulting
mixture that forms the layer (e.g., at most about 15 percent, at
most about 12 percent, at most about 10 percent).
[0052] In certain embodiments, the adhesion between one or more
adjacent layers can vary as layer thickness is varied. Generally,
embodiments can provide adhesion between one or more (e.g., all)
layers in a medical device (e.g., a tube). For example, one or more
(e.g., all) layers in a medical device (e.g., a tube) can
demonstrate good adhesion when flexed, deflated and/or inflated. In
some embodiments, a medical device (e.g., a tube) can show good
flexibility and/or adhesion (e.g., when one or more layers are
relatively thin).
[0053] In some embodiments, a compatibilizing material can be
incorporated into one or more material layers. The compatibilizing
material can be designed, for example, to modify one or more phase
boundaries of the LCP(s) and one or more of the other polymer(s)
(e.g., thermoplastic polymer(s)) and/or to enhance adhesion between
the LCPs and one or more of the other polymer(s). The
compatibilizing material can also be designed to enhance adhesion
between nanocomposites material and the polymer(s). The
compatibilizing material can be a copolymer, such as a block
copolymer, including moieties of at least two different chemical
structures, respectively providing compatibility with an LCP and
one or more other polymers in the mixture. The compatibilizing
material can be a reactive polymer that reacts with the LCP and/or
one or more other polymers in the mixture. The compatibilizing
material can be a catalyst that promotes a reaction between the LCP
and one or more other polymers in the mixture. Other
compatibilizing materials can be used. Combinations of
compatibilizing materials can be used.
[0054] Examples of compatibilizing materials include copolyester
elastomers, ethylene unsaturated ester copolymers, such as
ethylene-maleic anhydride copolymers, copolymers of ethylene and a
carboxylic acid or acid derivative, such as ethylene-methyl
acrylate copolymers, polyolefins or ethylene-unsaturated ester
copolymers grafted with functional monomers, such as
ethylene-methyl acrylate copolymers, copolymers of ethylene and a
carboxylic acid or acid derivative, such as ethylene-methyl
acrylate maleic anhydride terpolymers, terpolymers of ethylene,
unsaturated ester and a carboxylic acid or acid derivative, such as
ethylene-methyl acrylate-methacrylic acid terpolymers, maleic acid
grafted styrene-ethylene-butadiene-styrene block copolymers, and
acrylic acid elastomers, such as acrylic rubbers. Similar polymers
containing epoxy functional groups, for instance derived from
glycidyl methylacrylate (e.g.,
alkyl(meth)acrylate-ethylene-glycidyl (meth)acrylate polymers) can
be used. Monomeric copolymers can be used. PETG can be used.
Examples of compatibilizing materials include HYTREL.RTM. HTR-6108,
POLYBOND(.RTM. 3009 (BP Chemicals), SP 2205 (Chevron), DS 1328/60
(Chevron), LOTADER(.RTM. 2400, ESCOR(.RTM. ATX-320, ESCOR.RTM.
ATX-325, VAMAC.RTM.G G1 and LOTADER.RTM. AX8660. In certain
embodiments, a compatibilizing material (e.g., PETG) can be mixed
with one or more polymers (e.g., an LCP-containing material) prior
to extrusion.
[0055] While certain polymers and polymer combinations are
discussed above, other polymers and polymer combinations can also
be used. Other polymers include, for example, elastomers such as
thermoplastic elastomers and engineering thermoplastic elastomers,
such as polybutylene terephthalate-polyethene glycol block
copolymers, which are available, for example, as HYTREL.RTM.. These
are discussed in Hamilton U.S. Pat. No. 5,797,877, the entire
content of which is incorporated herein by reference. Other
polymers include polyurethenes. Other polymers include copolymers
such as ABS (acrylonitrile-butadiene-styrene), ABS/nylon,
ABS/-polyvinyl chloride (PVC), ABS/polycarbonate, acrylonitrile
copolymer, polyacrylamide, polyacrylate and polyacrylsulfone,
polyesters such as polyethylene terephthalate (PET), polybutylene
terephthalate (PBT), polyethylene naphthalate (PEN), liquid crystal
polymer (LCP), polyester/polycaprolactone and
polyester/polyadipate; and high melt temperature polyethers
including polyetheretherketone (PEEK), polyethersulfone (PES),
polyetherimide (PEI) and polyetherketone (PEK), polymenthylpentene,
polyphenylene ether, polyphenylene sulfide, and styrene
acrylonitrile (SAN), ethylene, propylene ethylene vinylacetate and
ethylene vinyl alcohol (EVA), various ionomers, polyethylene type
I-IV, polyolefins, polyurethane, polyvinyl chloride, and
polysiloxanes (silicones). Those with low to medium melt
temperatures include fluorocarbons such as polychlorotriethylene
(CTFE), poly[ethylene-co-chlorotrifluoroethylene] (ECTFE) copolymer
ethylene tetrafluoroethylene (ETFE), copolymer tetrafluoroethylene
and hexafluoropropylene (FEP), perfluoroalkane (PFA) and
poly[vinylidene fluoride] (PVDF).
OTHER EMBODIMENTS
[0056] Inner tube 18 can include any number of layers (e.g., two
layers, three layers, four layers, five layers, six layers or
more). Preferably, the viscosity (measured at a shear rate of about
1 s.sup.-1 or less and a temperature of 220.degree. C.) of a
nanocomposite layer is between about 25% and 120% a viscosity
(measured at a shear rate of about 1 s.sup.-1 or less and a
temperature of 220.degree. C.) of an adjacent layer (i.e.,
contacting layer such as middle layer 26, as shown in FIG. 2D).
[0057] Any one or more of the layers can be formed from one or more
nanocomposites materials, in any combination. The layers can be
coextensive or intermittent. For example, one or more layers of
material can terminate along the length of the medical device, and
optionally, extend again, spaced from where the layer terminated.
One or more layers can have variable thickness. Embodiments of
tubes having intermittent layer(s) and/or layer(s) of variable
thickness are described in U.S. Ser. No. 10/645,014, entitled
"Multilayer Medical Devices" and filed on Aug. 21, 2003, hereby
incorporated by reference.
[0058] In other embodiments, the co-extruded tube and/or the
methods described herein can be used to form other medical devices.
For example, a co-extruded tube can be used to manufacture a
medical balloon. The balloon can be made using a blow molding
process in which the tube (e.g., inner shaft 18) is placed (e.g.,
centered) in a preheated balloon mold, and air is introduced into
the tube to maintain the patency of the tube lumen. After soaking
at a predetermined temperature and time, the tube is stretched for
a predetermined distance at a predetermined time, rate, and
temperature. The pressure inside the tube is then sufficiently
increased to radially expand the tube inside the mold to form the
balloon. The formed balloon can be heat treated, for example, to
enhance folding memory, and/or folded into a predetermined profile.
The balloon can then be attached to a catheter to form a balloon
catheter. Illustrative methods of forming a balloon from a tube are
described in, for example, commonly-assigned U.S. Ser. No.
10/263,225, filed Oct. 2, 2002, and entitled "Medical Balloon";
Anderson U.S. Pat. No. 6,120,364; Wang U.S. Pat. No. 5,714,110; and
Noddin U.S. Pat. No. 4,963,313, all hereby incorporated by
reference in their entirety.
[0059] The co-extruded tube described above can be formed into a
guide wire, e.g., a polymer guide wire. Methods of making a guide
wire, including one having good pushability is described in U.S.
Pat. No. 5,951,494, hereby incorporated by reference in its
entirety.
[0060] The co-extruded tube can be used as a synthetic vascular
graft. The graft can be used to replace a damaged or dysfunctional
body vessel (e.g., at the site of an aneurysm or an occlusion), to
bypass or divert blood flow around a damaged region, or to create a
shunt between an artery and a vein (e.g., for multiple needle
access for hemodialysis access). Vascular grafts are described, for
example, in U.S. Pat. No. 5,320,100.
[0061] The co-extruded tube can be used as a graft in a
stent-graft, or a covered stent. The graft can include a
nanocomposite layer for strength, and another layer carrying a
drug.
[0062] The co-extruded tube can be sized and shaped to form a
variety of catheters. Examples of catheters include guide catheters
(e.g., as described in U.S. Pat. No. 6,595,952), tumor ablation
catheters, aneurysm catheters, urology catheters, and perfusion
catheters (e.g., as described in U.S. Pat. No. 6,503,224). The tube
can be formed into an introducer sheath or a restraining sheath for
a stent delivery system, for example, as described in U.S. Pat. No.
6,488,694. The catheters can include one or more nanocomposite
layers for strength, and one or more layers carrying a marker for
fluoroscopic, ultrasound, and/or magnetic resonance detection, as
described, for example, in commonly assigned U.S. Ser. No.
10/390,202, filed Mar. 17, 2003.
[0063] Referring to FIG. 8A, a stent delivery system 110 includes
an inner catheter 112 and a retractable sheath 114. Inner catheter
112 is a tube having a lumen 116 sized for delivery over a
guidewire. A stent 118 is carried on a distal portion of inner
catheter 112. Sheath 114 covers stent 118 during delivery and can
be retracted to expose the stent for expansion at a treatment
location within a body lumen such as a blood vessel. Inner catheter
112 and sheath 114 are coextruded members having at least two
layers. Referring particularly to FIG. 8B, the inner catheter
includes an inner layer 120 and an outer layer 122. Inner layer 120
is formed of a relatively low friction polymer to facilitate
delivery over a guidewire. Outer layer 122 includes a nanocomposite
material. Referring particularly to FIG. 8C, sheath 114 also
includes an inner layer 124 and an outer layer 126. Inner layer 124
is a low friction polymer that facilitates sliding motion over the
stent during retraction of the sheath. Outer layer 126 includes a
nanocomposite material. Examples of nanocomposite materials include
polyamide 12, e.g., Nylon 12-based materials such as the RTP
formulations described above. High dimensional uniformity of the
nanocomposite-containing coextruded catheter and sheath facilitates
smooth delivery over the guidewire and sheath retraction. In
embodiments, only the sheath or the inner catheter includes a
nanocomposite material. A suitable stent is a self expanding or
balloon expandable stent. In the case of a balloon expandable
stent, the stent is carried over a balloon mounted on the inner
catheter. Further discussion of a delivery system for a
self-expanding stent is described in Raeder-Devens et al., US
2003/0050686, the entire contents of which is hereby incorporated
by reference.
[0064] The following examples are illustrative and not intended to
be limiting.
EXAMPLE I
[0065] A tube having three concentric layers (inner layer, middle
layer, and outer layer) was co-extruded using cross-head 100 (FIGS.
4A-4B) in combination with an extrusion line that included three
extruders arranged upstream of cross-head 100. Materials for the
inner and outer layers were fed from the inner and outer extruders
into respective gear pumps melt filters. The middle layer material
was fed from the middle extruder into a melt filter. From the
respective melt filters, the materials were each fed into separate
adapters that fed into the cross-head 100. After extrusion of the
three-layered tube from cross-head 100, the tube passed into a
water tank about 6 feet long to cool the tube. After cooling, the
tube was passed through an air wipe that removed water from the
tube. The tube was pulled through the tank and the air wipe with a
puller that regulated line speed. Subsequent to cooling and drying,
the puller fed the tube into a cutter that cut the tube to a
desired length.
[0066] The tube included an Ube Nano-PA 12, formula number
.multidot.3030C2 (a nanocomposite material) outer layer, a
Plexar.RTM. PX380 (a maleic anhydride polyolefin) middle layer, and
a Marlex.RTM. 4903 (a high density polyethylene) inner layer. The
materials selected for the outer, middle and inner layers were
selected to provide high precision co-extrusion. In accordance with
the selection criteria described above, the viscosity of the outer
layer (the nanocomposite layer) at a shear rate of 1 s.sup.-1 and a
temperature of 220.degree. C. was 2,750 Pa-s, which is within 25%
to 120% of the viscosity value of the middle layer at 1 s.sup.-1
and 220.degree. C., 3,500 Pa-s), as shown in FIG. 4. In addition,
the viscosity of the middle layer at a shear rate of 1 s.sup.-1 and
a temperature of 220.degree. C. (3,500 Pa-s) was within 5% to 35%
of the viscosity of the inner layer at 1 s.sup.-1 and 220.degree.
C. (10,500 Pa-s), as shown in FIG. 4. In this example, the inner
layer and the outer layer have different rheological properties
(i.e., the inner layer has a viscosity that is at least three times
5 greater than the viscosity of the outer layer at a shear rate or
below about 1 s.sup.-1 and a temperature of 220.degree. C.) The
tube was co-extruded using the process temperatures and equipment
shown in Table 1.
1TABLE 1 Extruder Screw Feed Zone 1 Zone 2 Zone 3 Clamp Material
Diameter Temp. Temp. Temp. Temp. Temp. Screen Marlex .RTM. 3/4"
70.degree. F. 345.degree. F. 365.degree. F. 385.degree. F.
420.degree. F. 60/100/60 4903 meter Plexar .RTM. 1/2" 70.degree. F.
370.degree. F. 380.degree. F. 410.degree. F. 420.degree. F. None
PX380 meter Ube 3/4" 70.degree. F. 350.degree. F. 375.degree. F.
395.degree. F. 395.degree. F. 60/100/60 Nano- meter PA 12 Melt Heat
Barrel Melt Pump Inlet Pressure pump Pump Speed Clamp Filter
Adapter Pressure (psi) (cc/rev) Temp (rpm) Temp. Filter Temp. Temp
(psi) Marlex .RTM. 1400 0.16 420.degree. F. 3.1 420.degree. F. 55
420.degree. F. 420.degree. F. 2300 4903 micron Plexar .RTM. 1300
None None None None 55 420.degree. F. 420.degree. F. 1600 PX380
micron Ube 1500 0.16 395.degree. F. 4.9 395.degree. F. 10
395.degree. F. 395.degree. F. 1725 Nano- micron PA 12
[0067] Using a 0.048 inch die and a 0.032 inch mandrel/tip the
shape of the tube at the exit of cross-head 100 was formed. The
line speed was about 37 feet per minute and the gap between the
cross-head 100 and the water tank was {fraction (5/16)}". The
temperature of cross-head 100 was 420.degree. F. during extrusion.
The air pressure was about 11 inches of water.
[0068] Each layer in the co-extruded tube was well-defined as
viewed in cross-section with concentricity of the layers determined
from four measurements equally distributed around the
circumference. The outer layer formed about 53.6% of the
cross-sectional area, the inner layer formed about 32.1% of the
cross-sectional area, and the middle layer formed about 14.3% of
the cross-sectional area. Calculated over the sampling (i.e.,
thickness measurements taken at 10 randomly selected,
non-consecutive cross-sections over 1000 feet of product), the
average wall thickness of the outer layer was 0.0015 inches, with a
standard deviation of 3.0675.times.10.sup.-5 inches over the
duration of the run. The minimum value measured for the outer layer
was 0.0015 inches and the maximum value measure for the outer layer
was 0.0016 inches. The average wall thickness of the middle layer
was 0.0004 inches, with a standard deviation of
4.0593.times.10.sup.-5 inches over the duration of the run. The
minimum value measured for the middle layer was 0.0003 inches and
the maximum value measure for the middle layer was 0.0005 inches.
The average wall thickness of the inner layer was 0.0009 inches,
with a standard deviation of 7.0949.times.10.sup.-5 inches over the
duration of the run. The minimum value measured for the inner layer
was 0.0008 inches and the maximum value measure for the inner layer
was 0.0010 inches.
EXAMPLE II
[0069] A tube having three concentric layers was co-extruded using
the cross-head and extrusion line described in Example I. The outer
layer of the tube was formed of RTP formula number 0299 FX 83107C
(a nanocomposites material), a middle tie layer formed of
Plexar.RTM. PX380 (a modified polyolefin), and an inner layer
formed of Marlex.RTM. 4903 (a high density polyethylene). The
materials for each of the layers were selected in accordance with
the high precision co-extrusion criteria described above. For
example, as shown in FIG. 4, at a shear rate of 1 s.sup.-1 and a
temperature of 220.degree. C., RTP formula number 0299 FX 83107C
has a viscosity of 1,200 Pa-s, which is within 25% to 120% of the
viscosity of Plexar.RTM. PX380 at the same low shear rate and
temperature, 3,500 Pa-s.
[0070] The tube was co-extruded using the process temperatures and
equipment shown in Table 2.
2TABLE 2 Extruder Screw Feed Zone 1 Zone 2 Zone 3 Clamp Material
Diameter Temp. Temp. Temp. Temp. Temp. Screen Marlex .RTM. 3/4"
90.degree. F. 380.degree. F. 400.degree. F. 410.degree. F.
420.degree. F. 60/100/60 4903 meter Plexar .RTM. 1/2" 77.degree. F.
345.degree. F. 365.degree. F. 385.degree. F. 420.degree. F. None
PX380 meter RTP, 0299 3/4" 90.degree. F. 335.degree. F. 350.degree.
F. 375.degree. F. 385.degree. F. 60/100/60 FX 83107C meter Melt
Heat Barrel Melt Pump Inlet Pressure pump Pump Speed Clamp Filter
Adapter Pressure (psi) (cc/rev) Temp. (rpm) Temp. Filter Temp. Temp
(psi) Marlex .RTM. 1650 0.16 420.degree. F. 3.0 420.degree. F. 55
420.degree. F. 420.degree. F. 1650 4903 micron Plexar .RTM. 1000
None None None None 55 410.degree. F. 410.degree. F. 1070 PX380
micron RTP, 0299 1600 0.16 385.degree. F. 5.0 385.degree. F. 10
395.degree. F. 385.degree. F. 1060 FX 83107C micron
[0071] Using a 0.042 inch die and a 0.028 inch mandrel/tip the
shape of the tube at the exit of cross-head 100 was formed. The
line speed was about 39 feet per minute and the gap between the
cross-head 100 and the water tank was 1/4". The temperature of
cross-head 100 was 410.degree. F. during extrusion. The air
pressure was about 17 inches of water.
[0072] Each layer in the co-extruded tube was well-defined as
viewed in cross-section with concentricity of the layers determined
from four measurements equally distributed around the
circumference. The outer layer formed about 50% of the
cross-sectional area, the inner layer formed about 32.1 % of the
cross-sectional area, and the middle layer formed about 17.9% of
the cross-sectional area. Calculated over the sampling, the average
wall thickness of the outer layer was 0.0014 inches, with a
standard deviation of 3.5404.times.10.sup.-5 inches over the
duration of the run. The minimum value measured for the outer layer
was 0.0014 inches and the maximum value measure for the outer layer
was 0.0015 inches. The average wall thickness of the middle layer
was 0.0005 inches, with a standard deviation of
3.9000.times.10.sup.-5 inches over the duration of the run. The
minimum value measured for the middle layer was 0.0004 inches and
the maximum value measure for the middle layer was 0.0005 inches.
The average wall thickness of the inner layer was 0.0009 inches,
with a standard deviation of 4.5177.times.10.sup.-5 inches over the
duration of the run. The minimum value measured for the inner layer
was 0.0009 inches and the maximum value measure for the inner layer
was 0.0010 inches.
[0073] With regard to Examples I and II, in other embodiments, tube
can be formed to have a cross-sectional area that is composed of at
least 30% of outer layer 24, at least 5% of middle layer 26, and at
least 10% of inner layer 28.
[0074] All of the features disclosed herein may be combined in any
combination. Each feature disclosed may be replaced by an
alternative feature serving the same, equivalent, or similar
purpose. Thus, unless expressly stated otherwise, each feature
disclosed is only an example of a generic series of equivalent or
similar features.
[0075] All publications, applications, and patents referred to in
this application are herein incorporated by reference to the same
extent as if each individual publication or patent was specifically
and individually indicated to be incorporated by reference in their
entirety.
[0076] Other embodiments are within the claims.
* * * * *