U.S. patent application number 11/482814 was filed with the patent office on 2007-11-01 for biocompatible self-lubricating polymer compositions and their use in medical and surgical devices.
Invention is credited to Xiaoping Guo, Richard E. Stehr.
Application Number | 20070254000 11/482814 |
Document ID | / |
Family ID | 38648587 |
Filed Date | 2007-11-01 |
United States Patent
Application |
20070254000 |
Kind Code |
A1 |
Guo; Xiaoping ; et
al. |
November 1, 2007 |
Biocompatible self-lubricating polymer compositions and their use
in medical and surgical devices
Abstract
The invention comprises self-lubricating polymer compositions
that are especially useful in medical devices and valves and
gaskets of medical devices. In a preferred embodiment, the polymer
compositions comprise a thermosetting or thermoplastic silicone
elastomer in combination with a lubricity enhancing
polyfluoropolyether fluid or hydrocarbon-based synthetic oil. In
other preferred embodiments, the polymer compositions contain only
biocompatible components. The improved anti-friction properties of
the self-lubricating polymers can be demonstrated over a course of
insertion and withdrawal cycles, where conventional polymers have
changing and mostly increasing force required for each insertion
and withdrawal, while the polymer compositions of the invention
remain stable.
Inventors: |
Guo; Xiaoping; (Eden
Prairie, MN) ; Stehr; Richard E.; (Stillwater,
MN) |
Correspondence
Address: |
WILEY REIN LLP
1776 K. STREET N.W.
WASHINGTON
DC
20006
US
|
Family ID: |
38648587 |
Appl. No.: |
11/482814 |
Filed: |
July 10, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60795593 |
Apr 28, 2006 |
|
|
|
Current U.S.
Class: |
424/422 ;
604/500 |
Current CPC
Class: |
A61M 2025/0048 20130101;
A61M 2025/006 20130101; A61M 2025/0062 20130101; A61M 25/00
20130101; A61L 29/049 20130101; A61L 29/049 20130101; A61M 25/0021
20130101; C08L 83/04 20130101 |
Class at
Publication: |
424/422 ;
604/500 |
International
Class: |
A61M 31/00 20060101
A61M031/00 |
Claims
1. A biocompatible, self-lubricating polymer composition comprising
a silicone elastomer and about 1 to about 20 parts per hundred by
weight (phr) of a lubricity enhancing PFPE or hydrocarbon based
synthetic oils.
2. The self-lubricating polymer composition of claim 1, wherein the
silicone elastomer is selected from one or more silicone resins
having a durometer hardness from about 10 to about 90 on the Shore
A scale.
3. The self-lubricating polymer composition of claim 1, wherein the
PFPE synthetic oil is present at about 4 to about 20 phr.
4. The self-lubricating polymer composition of claim 2, wherein the
PFPE synthetic oil is present at about 4 to about 20 phr.
5. The self-lubricating polymer composition of claim 1, wherein the
PFPE synthetic oil is present at about 4 to about 6 phr.
6. The self-lubricating polymer composition of claim 2, wherein the
PFPE synthetic oil is present at about 4 to about 6 phr.
7. The self-lubricating polymer composition of claim 1, further
comprising a biocompatible, solid lubricant micropowder.
8. The self-lubricating polymer composition of claim 1, wherein the
silicone elastomer is a methylvinyl silicone elastomer and has a
durometer hardness of about 30 to about 40 in the Shore A
scale.
9. The self-lubricating polymer composition of claim 8, wherein the
PFPE synthetic oil is present at about 4 to about 6 phr.
10. The self-lubricating polymer composition of claim 8, further
comprising a biocompatible, solid lubricant micropowder.
11. A medical or surgical device having a receiving area for
inserting or withdrawing, the receiving area having a seal
comprising a self-lubricating polymer composition, the polymer
composition comprising a silicone elastomer and one or more of a
biocompatible solid lubricant at about 0.1 to 20 phr and a
biocompatible liquid lubricant at about 0.1 to 20 phr.
12. The medical or surgical device of claim 11, wherein the
silicone elastomer has a durometer hardness from about 10 to about
90 on the Shore A scale.
13. The medical or surgical device of claim 12, wherein the
silicone elastomer is a methylvinyl silicone elastomer and has
durometer hardness from about 20 to about 40 on the Shore A
scale.
14. The medical or surgical device of claim 11, wherein the polymer
composition comprises PFPE synthetic oil.
15. The medical or surgical device of claim 14, wherein the PFPE
synthetic oil is present at about 4 to about 10 phr.
16. The medical or surgical device of claim 14, wherein the PFPE
synthetic oil is present at about 4 to about 6 phr.
17. The medical or surgical device of claim 15, wherein the polymer
composition contains no solid lubricant.
18. The medical or surgical device of claim 16, wherein the polymer
composition contains no solid lubricant.
19. The medical or surgical device of claim 11, wherein the polymer
composition comprises a solid lubricant micropowder at about 0.1 to
20 phr.
20. A gasket or seal for a biomedical device comprising a
self-lubricating polymer composition comprising a silicone
elastomer and about 1 to about 20 parts per hundred by weight (phr)
of a lubricity enhancing polyfluoropolyether fluid or
hydrocarbon-based synthetic oil.
21. The gasket or seal of claim 20, wherein the silicone elastomer
is selected from one or more silicone resins having a durometer
hardness from about 10 to about 90 on the Shore A scale.
22. The gasket or seal of claim 20, wherein the silicone elastomer
is a methylvinyl silicone elastomer and has a durometer hardness of
about 20 to about 40 in the Shore A scale.
23. The gasket or seal of claim 20, wherein the lubricity enhancing
oil comprises PFPE synthetic oil and where PFPE is present at about
4 to about 10 phr.
24. The gasket or seal of claim 22, wherein the lubricity enhancing
oil comprises PFPE synthetic oil and where PFPE is present at about
4 to about 10 phr.
25. The gasket or seal of claim 20, wherein the lubricity enhancing
oil comprises PFPE synthetic oil and where PFPE is present at about
4 to about 10 phr.
26. The gasket or seal of claim 22, wherein the lubricity enhancing
oil comprises PFPE synthetic oil and where PFPE is present at about
4 to about 10 phr.
27. The gasket or seal of claim 20, further comprising a
biocompatible, solid lubricant micropowder.
28. The gasket or seal of claim 22, further comprising a
biocompatible, solid lubricant micropowder.
29. A method of producing a biocompatible self-lubricating polymer
for use in a medical or surgical device, comprising mixing a
silicone elastomer or silicone elastomer blend having a durometer
hardness of about 10 to about 90 on the Shore A scale with one or
more liquid lubricants having a surface energy of about 10 to about
20 dyne/cm, and setting the mixture into a desired shape or mold
for a selected medical or surgical device of part thereof.
30. The method of claim 29, wherein the liquid lubricant is PFPE
synthetic oil and PFPE is present at about 4 to about 10 phr.
31. The method of claim 29, wherein the liquid lubricant is PFPE
synthetic oil and PFPE is present at about 4 to about 6 phr.
32. The method of claim 29, wherein the silicone elastomer is a
methylvinyl silicone elastomer and has a durometer hardness of
about 30 to about 40 on the Shore A scale.
33. The method of claim 29, wherein the medical or surgical device
is a tube having an outside diameter from about 5 mm to about 2 mm
and an inside diameter of about 3.5 mm to about 1.5 mm.
34. The method of claim 29, wherein the medical or surgical device
is an introducer.
35. The method of claim 29, wherein the medical or surgical device
is a hemostasis valve.
36. The method of claim 29, further comprising adding a
biocompatible, solid lubricant micropowder to the mixture of
silicone elastomer or blend and one or more liquid lubricants.
37. The method of claim 29, wherein the polymer is used in the
production of a receiving area for medical or surgical device or
part thereof.
38. The method of claim 26, wherein the receiving area for medical
or surgical device or part thereof is formed into a dynamic
seal.
39. The method of claim 29, wherein the receiving area for medical
or surgical device or part thereof is formed into a semidynamic
seal.
40. The method of claim 29, wherein the medical or surgical device
is a catheter.
41. The method of claim 29, wherein the polymer is used in the
production of a sheath, tube or tubing, whereby the tube, sheath or
tubing comprises at least about 10% or more of the self-lubricating
polymer over its insertion length or receiving length.
42. A medical or surgical device made from the method of claim
37.
43. A medical or surgical device incorporating a sheath, tube or
tubing made from the method of claim 41.
44. A biocompatible self-lubricating polymer composition comprising
a silicone elastomer and about 1 to about 20 phr of a biocompatible
lubricant composition comprising one or more of a
polyfluoropolyether synthetic oil, a polytetrafluoroethylene
synthetic oil, a hydrocarbon-based synthetic oil, a low molecular
weight polytetrafluoroethylene powder, a titanium dioxide
micropowder, a molybdenum disulfide micropowder, a graphite
micropowder, a baron nitride micropowder, or a porous
micropowder.
45. The self-lubricating polymer composition of claim 44, wherein
the silicone elastomer is selected from one or more silicone resins
having a durometer hardness from about 10 to about 90 on the Shore
A scale.
46. The self-lubricating polymer composition of claim 44, wherein
the lubricant composition comprises PFPE synthetic oil.
47. The self-lubricating polymer composition of claim 46, wherein
PFPE is present at about 4 to about 10 phr.
48. The self-lubricating polymer composition of claim 47, wherein
the PFPE synthetic oil is present at about 4 to about 6 phr.
49. The self-lubricating polymer composition of claim 44, wherein
the lubricant composition consists essentially of PFPE synthetic
oil.
50. The self-lubricating polymer composition of claim 49, wherein
the PFPE synthetic oil is present at about 1 to about 10 phr.
51. The self-lubricating polymer composition of claim 50, wherein
the PFPE is present at about 4 to 10 phr.
52. The self-lubricating polymer composition of claim 44, wherein
the silicone elastomer is a thermosetting or thermoplastic silicone
elastomer.
53. The self-lubricating polymer composition of claim 52, wherein
the silicone elastomer is a methylvinyl silicone elastomer.
54. The self-lubricating polymer composition of claim 46, wherein
the silicone elastomer is a methylvinyl silicone elastomer.
55. The self-lubricating polymer composition of claim 49, wherein
the silicone elastomer is a methylvinyl silicone elastomer.
56. The self-lubricating polymer composition of claim 50, wherein
the silicone elastomer is a methylvinyl silicone elastomer.
Description
[0001] This application claims priority benefit of U.S. provisional
application 60/795,593 filed on Apr. 28, 2006, the entire contents
of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to polymer compositions with enhanced
anti-friction properties for use in medical applications and
medical devices. The polymer compositions have reduced friction
characteristics and can be implemented in tubing, gaskets, valves,
and in a variety of insertion devices and other devices used in
procedures to introduce objects into the body, for example.
INTRODUCTION, RELATED ART AND BACKGROUND TO THE INVENTION
[0003] A growing number of surgical or medical procedures employ
devices and kits that rely on inserting a device or tube through a
sealed valve or apparatus. For example, catheters and guides are
typically inserted through a sterile valve to introduce fluids,
intraluminal devices and many other instruments into the body or
into the lumen of a blood vessel. In fact, various surgical kits
now include valves and devices to assist in the simultaneous,
sterile insertion of multiple elements into vessels or elsewhere in
the body. To operate properly, the valves must be capable of
accepting different sized elements, be sufficiently pliable and/or
elastic to maintain a seal during manipulation, and allow the user
to effectively introduce and remove devices under sufficient
control to avoid damage to vessels or other body tissue. However,
pliable or flexible polymers tend to cause a degree of friction
when an element is inserted or withdrawn into or through them.
During medical or surgical procedures, this friction is undesirable
and may lead to a lack of control and require forceful insertion or
withdrawal. Some kits and procedures even require multiple
guidewire and catheter exchange steps, for example, which
exacerbates the insertion and withdrawal problems. The sealed or
sealable valves used must also prevent the introduction of air into
a blood vessel and/or contamination of body tissue during insertion
and withdrawal. Because of these and other requirements, the safe
insertion and withdrawal, as well as the related forces used to
insert and withdraw, has become a problem with many devices and
kits used today. To attempt to alleviate this problem, silicone oil
is customarily used to externally lubricate the valves and devices.
During a medical procedure, this lubricant can be wiped away or
lose its effectiveness after even a single insertion and withdrawal
action.
[0004] A high performance hemostasis valve has recently been
described that can be sealed effectively to prevent leaks and
contamination and which is capable of accepting various catheters
having a variety of diameters (see, for example, U.S. Pat. No.
6,632,200). As described below, the inventors' improvements on this
and many other devices, which in part addresses the friction
problem during insertion and withdrawal noted above, includes a
self-lubricating polymer composition that effectively allows
elements to slide in and out of valves, other devices, tubes, or
through tissue in a more controlled and easier manner. Accordingly,
the use of the self-lubricating polymer compositions of the
invention improves the performance and use of a variety of medical
and surgical devices and kits. In addition, the polymer
compositions can be used to improve basic catheter and tubing
applications, or wherever one material slides over or across
another material in a sealed or sealable device, valve, or
gasket.
SUMMARY OF THE INVENTION
[0005] In one aspect, the invention addresses the use of a
self-lubricating polymer composition to make at least a part of or
element to a medical or surgical device, or a kit comprising such
medical or surgical devices. In some applications, it is desirable
for these polymers to be flexible enough to form a sufficient seal
around the surface of any element inserted into it and/or in
contact with it during the course of using the device. For example,
the self-lubricating polymer can be used as a gasket at or around
the insertion site of a guide or catheter. Similarly, the guide or
catheter itself can be made of, or at least partially made of, the
self-lubricating polymer.
[0006] In a general aspect, the invention addresses the use of a
polymer material at a semidynamic seal, such as where one part
moves along, slides over, or contacts another part or element in
the practice or use of a medical or surgical device, and/or at a
dynamic seal, where two or more parts similarly contact or move
against each other. Various gaskets, valves, covers and other
sealing structures can be used in medical and surgical devices to
produce a semidynamic or dynamic seal. Thus, any of the existing
and/or future sealing structures can be improved through the use of
the polymer compositions of the invention.
[0007] In another general aspect, the invention provides
self-lubricating or enhanced lubricity polymer compositions for use
in medical and surgical devices and related applications. The term
lubricity is used in the conventional sense of a lubricating
characteristic that effectively reduces friction between rubbing or
contact surfaces. Lubricity can be most important in conditions of
boundary lubrication and/or for continuously maintaining a low
surface-energy and/or to effectively repel body fluids and the
resulting drag forces on contact surfaces. By increasing the
lubricity of the polymer material used, the degree of deformation
can be limited for a particular structure to form or maintain a
leak-proof seal, while the force needed to slide over or through
the structure is reduced. A preferred example of a self-lubricating
polymer composition comprises a biocompatible elastomer, and
especially preferred is a biocompatible silicone elastomer. Other
biocompatible blends of elastomers and/or thermoplastic polymers
can also be used, as known in the art. The self-lubricating
compositions also comprise one or more lubricants, such as
synthetic oils and/or solid lubricants. Preferred synthetic oil
lubricants are polyfluoropolyether (PFPE) synthetic oils,
polytetrafluoroethylene (PTFE) synthetic oils, and
hydrocarbon-based synthetic oils, namely co-oligomers of ethylene
and olefins. Preferred solid lubricants include low molecular
weight polytetrafluoroethylene powders, titanium dioxide
micropowders, molybdenum disulfide micropowders, graphite
micropowders or flakes, and baron nitride micropowders and the
like. Any combination of these lubricants and others available
and/or used in the art for biocompatible materials can be selected,
and preferred combinations are given in the Examples.
[0008] As noted above, the self-lubricating polymer compositions
can be used to produce one or more parts or elements in a medical
or surgical device. In one preferred example, the part or element
can comprise all or part of an insertion device or a receiving area
for an inserted device or other elongated medical device.
Typically, a receiving area employs a gasket or seal, which can
readily and/or repeatedly permit passage of one or more devices,
optionally of varying diameters. The gasket or seal or other
receiving area is comprised of the polymer composition of the
invention and thus has improved lubricity characteristics, for
example with respect to a reduction in insertion and withdrawal
forces compared to other materials and/or a reduction in the
fluctuation of frictional forces during repeated or regular use.
The receiving area can also be or comprise a centering orifice for
inserting a device, which functions to position or center the
inserted device into a particular region. Furthermore, multilayered
structures may also be used, wherein at least one layer comprises a
self-lubricating composition of the invention, preferably a layer
in contact with another component or against which frictional
forces are generated during use. In a preferred example, the outer
layer of an inserting device and/or the inner layer of a receiving
area, such as a gasket, sheath or seal, comprises a biocompatible
self-lubricating composition of the invention. In addition, various
lengths of the inserting device or receiving area can comprise a
self-lubricating polymer composition of the invention, anywhere
from the entire insertion length, to less than 10% of the insertion
length, to only the tip or inserting end of the insertion device,
and even intermittent or non-contiguous sections covering a desired
percentage of the insertion length can be used. Thus, a
multilayered tube or sheath can be made and used, and one of skill
in the art is familiar with molding and co-extrusion processes, for
example, for producing these parts of medical devices.
[0009] Accordingly, it is one object of the invention to provide a
medical or surgical device that comprises a receiving area and/or
insertion device made at least in part of a self-lubricating
polymer composition. The parts, elements, biomedical, medical or
surgical devices that contain the receiving areas or comprise
insertion devices can thus exhibit improved anti-friction
performance in the ease with which insertion and withdrawal of
elongated elements or parts occurs and in the maintenance of
adequate sealing characteristics to avoid or substantially avoid
leakage of fluids, blood, or the flow of air during use. It is an
additional object to provide a biocompatible polymer for use in
biomedical applications, including human, veterinary, and
biomedical research fields, wherein a self-lubricating polymer of
the invention provides an improved lubricity surface for inserting
into or withdrawing from or out of a variety of devices or body
tissues.
[0010] Other objects, features, details, utilities, and advantages
of the present invention will be apparent from the following more
particular written description of various embodiments and examples
of the invention, as further illustrated in the accompanying
drawings and defined in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 depicts a cross-sectional view of preferred cardiac
catheter device comprising hub 10 containing a hemostasis valve as
exemplary receiving area, a stopcock assembly 12, a guidewire 20,
and a catheter sheath or shaft 30 extending into the lumen of a
vessel. The valve receiving area comprises a gasket or seal made of
a self-lubricating polymer of the invention primarily comprising a
silicone elastomer and a synthetic oil. The forces required to
introduce, manipulate, control, and/or withdraw the catheter device
are substantially less than those when a conventional elastomer
without modification is used for the gasket or seal.
[0012] FIG. 2 depicts a close-up, cross-sectional view of an
inserting device 200 inserted into a hemostasis valve, where
various parts or elements of the valve can be made of the
self-lubricating polymer of the invention. For example, sheath 100
(on its inner and/or outer surface) and gasket area 200 can both be
composed of the self-lubricating polymer compositions of the
invention to improve performance, such as anti-friction and sealing
performance.
[0013] FIG. 3 is a radial, cross-sectional view of a catheter
sheath or shaft 120 passing through the gasket 43 of a valve, for
example, similarly, any tubing used in or inserted into a body
tissue can be made of a self-lubricating polymer composition of the
invention.
[0014] FIG. 4 shows exemplary results of an insertion and
withdrawal cycle performed on a hemostasis valve produced from the
formulation in Example 1. Each spike represents the forces measured
in one of fourteen insertion/withdrawal cycles, and the ten
separate lines represent one of ten different catheters inserted
into the same hemostasis valve. Even after the unusually large
number of insertions and withdrawals for a single hemostasis valve,
the forces through each cycle are maintained at an acceptable
level, at about 0.3 lbs on average, and within an advantageously
small variance in the range of measured force.
[0015] FIG. 5 shows the results of 96 insertion/withdrawal cycles
of two different catheters through a conventional hemostasis valve
made of unmodified silicone elastomers with external lubricating
oil as typically used. The increasing forces after about ten
insertion/withdrawal cycles is the result of lubricating oils being
removed or wiped off the contacting surfaces. The changes in
forces, from about 0.05 lbs to about 0.6 lbs, represent
dramatically different forces that would be required to insert and
withdraw. Except for cycles 4-10, the forces vary from nearly every
cycle to the next.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION
[0016] Throughout this disclosure, applicants refer to texts,
patent documents, and other sources of information. One skilled in
the art can use the entire contents of any of the cited sources of
information to make and use aspects of this invention. Each and
every cited source of information is specifically incorporated
herein by reference in its entirety. Portions of these sources may
be included in this document as allowed or required. However, the
meaning of any term or phrase specifically defined or explained in
this disclosure shall not be modified by the content of any of the
sources.
[0017] The headings (such as "Introduction" and "Brief Summary")
used are intended only for general organization of topics within
the disclosure of the invention and are not intended to limit the
disclosure of the invention or any aspect of it. In particular,
subject matter disclosed in the "Introduction" includes aspects of
technology within the scope of the invention and thus may not
constitute background art. Subject matter disclosed in the "Brief
Summary" is not an exhaustive or complete disclosure of the entire
scope of the invention or any particular embodiment.
[0018] As used herein, the words "preferred," "preferentially," and
"preferably" refer to embodiments of the invention that afford
certain benefits, under certain circumstances. However, other
embodiments may also be preferred, under the same or other
circumstances. Furthermore, the recitation of one or more preferred
embodiments does not imply that other embodiments are not useful
and is not intended to exclude other embodiments from the scope of
the invention and no disclaimer of other embodiments should be
inferred from the discussion of a preferred embodiment or a figure
showing a preferred embodiment. In fact, the nature of the polymer
compositions of the invention allow one of skill in the art to make
and use the invention on any medical or surgical device available
or contemplated.
[0019] The phrases "self-lubricating polymer composition,"
"self-lubricating composition," and "polymer composition of the
invention" all refer to a composition comprising a biocompatible
polymer or blend of polymers and a biocompatible lubricant. In
preferred embodiments, the composition is composed of polymer
compounds that have not previously been used together, or in a
particular ratio or ratios, for use in a medical, surgical, or
biomedical device.
[0020] The invention relates to the new, successful development of
various self-lubricating polymer compositions, and especially
silicone elastomer compositions, which can be used to make a
variety of medical and surgical devices and thereby minimize
friction forces during use while maintaining sufficient sealing
characteristics. In one aspect, particular surfaces or elements of
devices comprise a self-lubricating polymer of the invention. The
medical devices of preferred interest include, but are not limited
to, hemostasis valves of a variety of types including those for
cardiac catheters, medical tubing, sheaths and gaskets used in
valves and insertion devices, ultrasound catheters, and similar
devices.
[0021] In one general sense and without any intention to limit the
scope to any particular explanation or mechanism for how it works,
the invention provides a lubrication system for a polymer material,
preferably a silicone elastomer material, through physical
modifications of the polymer matrix. Parts or components of a
medical device can thus be made to exhibit an improved surface
lubricity and result in low friction forces during use or in
medical procedures, providing advantages by at least improving the
ease of use and/or comfort to a patient. Thus, it is one object of
this invention to provide a self-lubrication mechanism for a
surface or polymer matrix, such as a silicone elastomer matrix,
such that any medical or surgical device made from the polymer
matrix can release or spontaneously release embedded lubricant from
the matrix or onto a contact surface(s) when the device is used.
Accordingly, contact surface lubricity and the resulting lowered
frictional forces during use can be reliably maintained throughout
a procedure. Another object is to provide a lubrication system for
a silicone elastomer that is biocompatible and can be used with a
variety of medical and surgical devices and parts or elements
thereof. Further, the lubrication and anti-friction performance
characteristics are not degraded but can actually be enhanced by
contact with blood, tissue, or medical fluids.
[0022] In preferred embodiments, the polymer compositions of the
invention are designed to act like a matrix that allows the
lubricant contained within to continuously migrate to the surface
of the part or device made of the polymer. In effect, the lubricant
is driven to the surface as the friction forces of the insertion
and withdrawal cycles move the lubricant or wipe the lubricant
away. After manufacture, the surface of the polymer composition is
essentially primed with lubricant. As this lubricant is used during
insertion and withdrawal cycles, the lubricant in the matrix
migrates to replace the surface lubricant. The result is a constant
friction force throughout the insertion and withdrawal cycles. Any
of the polymer resins discussed here or in the Examples can form an
effective matrix for migration of lubricant. In addition, solid
porous silica powder or similar powders can optionally be added to
increase the amount of lubricant contained in the matrix.
[0023] A number of polymers have been suggested as self-lubricating
in a variety of applications, including: polyethylene;
polyetherimide; polypropylene; polyetheretherketone (PEEK);
polytetrafluoroethylene (PTFE) or Teflon (DuPont, Wilmington,
Del.); Ultra High Molecular Weight (UHMW) polyethylene;
polyoxymethylene or Delrin (DuPont, Wilmington, Del.);
polyamide-imide (PAI) or TORLON (Solvay Advance Polymers,
Alpharetta, Ga.); polyoxymethylene (POM), acetal resin, or Delrin
(DuPont, Wilmington, Del.); and polyvinylidene fluoride or Kynar
(Atochem Corporation). Some of these polymers do not possess the
combination of flexibility and lubricity desired for the medical
and surgical device applications noted herein. However, these
polymers may be modified with similar methods of the invention and
used to produce catheters and sheaths, for example, having improved
anti-friction properties. Furthermore, the preferred polymer
compositions of this invention are biocompatible, such as
biocompatible thermosetting silicone elastomers and thermoplastic
silicone elastomers.
[0024] In designing or selecting an acceptable or optimum polymer
or blend of polymers for a particular device or part thereof, a
method of the invention can take into account the matrix-controlled
lubricant release mechanism. To optimize this mechanism or make it
effective for a particular use, one can modify raw polymer
compositions. In one example, a silicone elastomer resin can be
cured with either organic peroxide crosslinking or, especially, by
addition of a curing agent such as silicon hydride (SiH) and
platinum as catalyst. In the latter approach, one can use liquid
and/or solid lubricants, and preferably lubricants that are highly
non-polar and chemically inert. The chemical inert characteristics
can be important in avoiding combinations that interfere with a
curing agent. The lubricants can also have low surface energies
that are compatible with the polymer or blends used and, in the
case of the silicone elastomers, can be about 20 mN/m (or dyne/cm).
One or more lubricants with surface energies below 20 dyne/cm can
be selected for use, as explained below and in the Examples.
Furthermore, the percentage of lubricant used and the amount
available during the insertion and withdrawal use can be changed to
arrive at a desirable level for the anti-friction function for a
particular part or medical device or method contemplated. One of
skill in the art is familiar with varying the amount of lubricants
and with additional compounds or additives, such as porous silica
powders and the like, for increasing the amount of lubricant that
can effectively create an anti-friction polymer composition or
material.
[0025] In one method of producing the polymer compositions of the
invention, the one or more lubricants are incorporated into the raw
polymer or blend, such as the raw, gum-like silicone elastomer
resin, with a two-roller mill compounding process as known in the
art. After sufficient compounding to thoroughly mix the components,
the lubricants are well dispersed into the matrix or occupy
molecular pores within the matrix. To make a medical device part or
element, the compounded polymer composition is molded, extruded or
shaped and cured. In the case of a silicone elastomer, it is molded
into shape and thermally cured. The curing process will create
elastomeric, chemical crosslinks, which effectively trap the one or
more lubricants in the polymer matrix. One can also consider the
water repellency of non-polar lubricants and a lubricant
concentration gradient from the center to the surface of the part.
The limited chemical compatibility between the non-polar silicone
elastomer and the non-polar lubricants, for example, can
synergistically control the release of the lubricants to the
surface. One of skill in the art is familiar with methods to
produce concentration gradients.
[0026] Since silicone elastomers are one of the commonly used
biomaterials in the medical device industry, the examples here and
the preferred embodiments include silicone elastomers. However, the
invention is not limited to the use of silicone elastomers or any
particular polymer for that matter.
[0027] Silicone elastomers possess high coefficients of friction
and relatively lack lubricity characteristics, which leads to
patient discomfort and potential tissue trauma during medical
procedures. The high friction forces generated during the insertion
and withdrawal of catheters through an introducer containing a
silicone elastomer, such as a hemostasis valve, have routinely
challenged the medical devices industry. In practice, a hemostasis
valve is externally lubricated with silicone oil during
manufacture. During use, silicone oil is quickly removed by the
insertion and withdrawal actions and, therefore, the lubricating
effect from the silicone oil is quickly lost. As a result, the
frictional forces are extremely inconsistent during a medical
procedure and begin to vary from the first insertion. At the
beginning of a procedure, the friction forces are relatively low
due to the effect of the externally added silicone oil, while in
the midst of a procedure the forces jump to an extremely high level
as the oil dissipates, is removed or rubbed off. This can influence
the physician's use and control of the device.
[0028] In the past, the industry has attempted to modify either
hemostasis valve design (such as in various design found in patent
documents U.S. Pat. Nos. 6,776,774; 6,723,073; 6,702,255;
6,632,200; 5,807,350; and 5,782,817) or the silicone elastomer
materials by adding so-called solid lubricity enhancing additives,
including bismuth oxychloride, PTFE powder, titanium dioxide,
graphite, (see for example U.S. Pat. No. 5,562,632). Despite these
attempts, none of hemostasis valves on the market provide constant
performance and low friction forces.
[0029] As a preferred example of the improvements possible under
this invention, the performance of hemostasis valve as shown in
U.S. Pat. No. 6,632,200 and 6,551,283 can be improved by
incorporating the self-lubricating polymer composition at various
parts. A silicone elastomer is selected as well as liquid
lubricants and/or solid lubricant additives. The liquid lubricants
have low surface energies compared to the silicone elastomer or
blend selected and this better ensures the partial solubility and
compatibility of the liquid lubricant into the matrix of the
silicone elastomer. By adjusting the lubricant used based upon the
surface energy, an optimum release characteristic from the
resulting cured polymer matrix and/or a controllable release rate
can be found. For example, incorporating a solid lubricant or
additional solid lubricant enhances the surface abrasive
resistance, surface smoothness, and/or tear strength. Preferred
liquid lubricants are polyfluoropolyether synthetic oils and
hydrocarbon-based synthetic oils, while preferred solid lubricants
are low molecular weight polytetrafluoroethylene powders, titanium
dioxide, and baron nitrides. Both the liquid and solid lubricants
are preferably chemically inert, devoid of chemical reactivity for
the polymer or blend and curing agent used, and are preferably
non-polar. This prevents them from interfering in the curing
process. To increase the incorporation of a high or sufficient
amount of synthetic oils or lubricants into the polymer matrix, a
porous filler, such as porous silica, can optionally be added.
[0030] Generally, the self-lubricating polymer compositions of
silicone elastomers contain 0.1 to 20 phr (part Per Hundredth Resin
by weight) liquid lubricants and/or 0 to 20 phr solid lubricants.
However, various preferred ranges of liquid and/or solid lubricant
concentrations can be selected for use, including 1-20 phr, 1-5
phr, 3-5 phr, 3-6 phr, 4-6 phr, 3-10 phr, 1-10 phr, 1-15 phr, 5-15
phr, 8-10 phr, 10-20 phr, 15-20, and 5-10 phr, for example, can be
used for either or both of the solid and liquid lubricant, alone or
in combination. By selecting a fluid-like lubricant that has
similar surface energy to that of the cured silicone elastomer but
is chemically-inert, one of skill in the art can be better assured
that the lubricant can be effectively contained in the molecular
pores of the cured matrix due to surface tension. At the same time,
the lubricants do not interfere with the chemical reaction of
curing. Therefore, after curing, the fluid-like lubricant can be
released under friction forces, preferably with continuous
migration driven by the concentration gradient existing from the
bulk material to the surface.
[0031] The following are some examples of the preferred
self-lubricating polymers of silicone elastomers of the invention
in which polyfluoropolyether (PFPE) or perfluoroalkylether
synthetic oil (having surface energies of 18 to 20 mN/m or dyne/cm)
are used as liquid lubricants. In addition or alternatively, boron
nitride or low molecular weight polytetrafluoroethylene (PTFE)
micropowders may be used as solid lubricants to adjust
anti-friction or abrasion resistance and/or tear strength.
[0032] A preferred example of a medical device or part thereof to
demonstrate the improved anti-friction characteristics of the
polymer compositions of the invention is a hemostasis valve. The
valve may be reliably used with a wide variety of diameters for an
inserting device, up to about 9 F (3 mm) catheters and down to
guidewires of about 0.014 in. (0.35 mm). A hollow tube can also be
used, as in a molded 8 F introducer that can also be used as a
catheter for various purposes.
ILLUSTRATIVE EXAMPLES
[0033] Together with a mixture comprised of the appropriate tubing
or gasket body materials, a combination of the silicone elastomer
and lubricant, such as PFPE, is placed in a previously-heated mold
and is then heated to a temperature of about 130 to 200 degrees C.,
preferably at a molding clamping pressure of about 0.5 to 25 MPa,
and preferably for a processing time of about 1 to 20 minutes, to
obtain the finished product. The silicone rubber or elastomer
selected may be one with a particular Durometer hardness (for
example, the "Shore A scale" which, for the purposes of this
invention, includes similar or any comparable hardness scale for
polymer compositions as known in the art). For example, anywhere
between about 10 durometer to about 90 durometer can be used. The
combined elastomer/lubricant polymers can then be evaluated on
certain valve body designs having differing diameters. Insertion
force measurements and leakage can then be conducted. An optimal
polymer combination can be thus selected for any particular
combination of medical device parts or elements, such as a catheter
and hemostasis valve, valves or gaskets and various introducers,
such as steerable introducers or Swartze introducers, and similar
parts of functional parts of medical and biological devices.
Usually, the insertion force is desired to be low and no leakage
present.
[0034] The components of the polymer composition can also be varied
to optimize hardness, weight, and thickness, and one skilled in the
art is familiar with selecting silicone elastomers, for example,
that can result in a final product having a desirable or optimal
ranges for any or all of these characteristics. In one embodiment,
any of the Elastosil or Silastic series of liquid silicone rubber
can be selected. The methylvinyl silicone resin Silastic Q7-4735 is
used in the examples below, but many other resins can be selected
and similarly used, as noted above, including Silastic Q7-4720.
Example 1
[0035] A silicone elastomer resin based upon methylvinyl silicone
(Silastic Q7-4735) is selected as the polymer matrix. A liquid
lubricant, PFPE synthetic oil, is used at 5 parts per hundred of
rubber (phr). The components are mixed using a two-roller mill. The
resulting compound is transfer-molded into the gaskets of a
hemostasis valve, as noted above, and then post-cured at 150
degrees C. for 2 hours.
Example 2
[0036] The same polymer resin as Example 1, but a liquid lubricant
(PFPE synthetic oil) is used at 10 phr.
Example 3
[0037] The same polymer resin as Example 1, but a solid lubricant
(low molecular weight PTFE micropowder) is used at 3 phr, and a
liquid lubricant (PFPE synthetic oil) is used at 5 phr.
Example 4
[0038] The same polymer resin as Example 1, but a solid lubricant
(low molecular weight PTFE micropowder) is used at 8 phr, and a
liquid lubricant (polyfluoroalkylether synthetic oil) is used at 8
phr.
Example 5
[0039] The same polymer resin as Example 1, but a solid lubricant
(boron nitride micropowder) is used at 5 phr, and a liquid
lubricant (polyfluoroalkylether synthetic oil) is used at 10
phr.
Example 6
[0040] A thermoplastic silicone elastomer, Geniomer 200, is
selected as the resin, a solid lubricant (low molecular weight PTFE
micropowder) is used at 3 phr, and a liquid lubricant
(polyfluoroalkyl ether synthetic oil) is used at 8 phr. The
ingredients are mixed into a self-lubricating polymer composition
using a solvent or melt compound approach, as known in the art. The
resulting composition is then injection molded into a hemostasis
gasket as noted above.
Example 7
[0041] The utility of the self-lubricating polymer compositions and
the parts or elements made from them can be tested under cyclic
insertion conditions at constant forces. Unlike currently available
products, the insertion forces are very stable at about 0.25 lbs
during one hundred insertion cycles, even when five different 6F
catheters are used. In comparison, the insertion forces vary from
0.1 to 0.6 lbs during the parallel tests using currently available
materials.
[0042] As shown in FIG. 4, the repeated insertion and withdrawal
cycles of the self-lubricating polymer of Example 1 show very
little changes in forces measured over the 14 cycles. Even when new
catheters are used on the same hemostasis gasket, the forces remain
constant. Thus, the self-lubricating polymers of the invention
allow a greatly improved consistency in the insertion and
withdrawal processes. Comparing to the FIG. 5 results of a
conventional polymer and hemostasis gasket, the forces vary over
the entire period of the experiment and there is a dramatic and
fairly constant increase in required forces at about cycle 10,
presumably when the externally applied lubricant is no longer
effective.
[0043] The reduction in friction forces can be demonstrated in a
method that is illustrated in FIG. 1, in which a catheter is
inserted into the blood vessel through an introducer that has a
hemostasis value contained in its hub. The lubricant releasing from
the self-lubricating polymer composition of the hemostasis valve
effectively self-lubricates the contact surfaces between the
catheter and hemostasis valve, leading to the reduction in the
friction forces and/or substantially constant and predictable
friction forces.
[0044] Although various embodiments of this invention have been
described above with a certain degree of particularity, or with
reference to one or more individual embodiments, those skilled in
the art could make numerous alterations to the disclosed
embodiments without departing from the spirit or scope of this
invention. It is intended that all matter contained in the above
description and shown in the accompanying drawings shall be
interpreted as illustrative only of particular embodiments and not
limiting. All directional references (e.g., proximal, distal,
upper, lower, upward, downward, left, right, lateral, front, back,
top, bottom, above, below, vertical, horizontal, clockwise, and
counterclockwise) are only used for identification purposes to aid
the reader's understanding of the present invention, and do not
create limitations, particularly as to the position, orientation,
or use of the invention. Connection references (e.g., attached,
coupled, connected, and joined) are to be construed broadly and may
include intermediate members between a collection of elements and
relative movement between elements unless otherwise indicated. As
such, connection references do not necessarily infer that two
elements are directly connected and in fixed relation to each
other. It is intended that all matter contained in the above
description or shown in the accompanying drawings shall be
interpreted as illustrative only and not limiting. Changes in
detail or structure may be made without departing from the basic
elements of the invention as defined in the following claims. The
invention is not limited to any particular embodiment or example
given here. Instead, one of skill in the art can use the
information and concepts described to devise many other embodiments
beyond those given specifically here.
* * * * *