U.S. patent application number 10/992563 was filed with the patent office on 2005-04-07 for treatment of bioprosthetic tissues to mitigate post implantation calcification.
Invention is credited to Carpentier, Alain F., Carpentier, Sophie M..
Application Number | 20050071926 10/992563 |
Document ID | / |
Family ID | 21905086 |
Filed Date | 2005-04-07 |
United States Patent
Application |
20050071926 |
Kind Code |
A1 |
Carpentier, Sophie M. ; et
al. |
April 7, 2005 |
Treatment of bioprosthetic tissues to mitigate post implantation
calcification
Abstract
Bioprosthetic tissues are treated by immersing or otherwise
contacting fixed, unfixed or partially fixed tissue with a
glutaraldehyde solution that has previously been heat-treated or pH
adjusted prior to its contact with the tissue. The prior heat
treating or pH adjustment of the glutaraldehyde solution causes its
free aldehyde concentration to decrease by about 25% or more,
preferably by as much as 50%, and allows a "stabilized"
glutaraldehyde solution to be obtained at the desired concentration
and pH for an optimal fixation of the tissue at high or low
temperature. This treatment results in a decrease in the tissue's
propensity to calcify after being implanted within the body of a
human or animal patient. The heat-treated or pH adjusted
glutaraldehyde solution may, in some cases, also be used as a
terminal sterilization solution such that the
calcification-decreasing treatment with the previously treated
glutaraldehyde and a terminal sterilization may be carried out
simultaneously and/or in a single container.
Inventors: |
Carpentier, Sophie M.;
(Paris, FR) ; Carpentier, Alain F.; (Paris,
FR) |
Correspondence
Address: |
EDWARDS LIFESCIENCES CORPORATION
ONE EDWARDS WAY
IRVINE
CA
92614
US
|
Family ID: |
21905086 |
Appl. No.: |
10/992563 |
Filed: |
November 18, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10992563 |
Nov 18, 2004 |
|
|
|
10039367 |
Jan 3, 2002 |
|
|
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Current U.S.
Class: |
8/94.11 |
Current CPC
Class: |
B65B 63/08 20130101;
A61L 27/3604 20130101; A61L 27/3687 20130101; A61L 2400/02
20130101 |
Class at
Publication: |
008/094.11 |
International
Class: |
A61F 002/06 |
Claims
What is claimed is:
1. A method for mitigating post-implantation calcification of a
bioprosthetic implant material, said method comprising the steps
of: providing a solution selected from the group consisting of a
glutaraldehyde solution and a physiologic solution; adjusting the
pH of the solution to a pH in the range of about 5.0 to 7.0;
contacting a quantity of biological tissue that contains connective
tissue protein with the pH-adjusted solution; and heating the
solution and the tissue to a heat treating temperature in the range
of about 30.degree. C. to 70.degree. C. for a period of time.
2. The method of claim 1, wherein the heat treating temperature is
in the range of about 40.degree. C. to 60.degree. C.
3. The method of claim 1, wherein the heat treating temperature is
about 50.degree. C..+-.5.degree. C.
4. The method of claim 1, wherein the period of time is between
about one hour and six months.
5. The method of claim 1, wherein the period of time is between
about one day and two months.
6. The method of claim 1, wherein the period of time is between
about 5 days to 10 days.
7. The method of claim 1, wherein the period of time is about 7
days.
8. The method of claim 1, wherein the pH of the solution is
adjusted to about 6.0.
9. The method of claim 1, wherein the pH of the solution is
adjusted by heating the solution to a pre-heat temperature for a
pre-heat period.
10. The method of claim 9, wherein the pre-heat temperature is
between 60-80.degree. C.
11. The method of claim 10, wherein the pre-heat temperature is
about 70.degree. C..+-.5.degree. C.
12. The method of claim 1, wherein the pH of the solution is
adjusted without heating the solution.
13. The method of claim 12, wherein the pH of the solution is
adjusted to about 6.0.
14. The method of claim 13 wherein the heat treating temperature is
about 50.degree. C..+-.520 C.
15. The method of claim 13 wherein the period of time is between
about 5 days to 10 days.
16. The method of claim 1, wherein the solution is aqueous
glutaraldehyde buffered to a starting pH, wherein the step of
adjusting comprises lowering the pH.
17. The method of claim 16, wherein the starting pH is between
about 7.2 to 7.8.
18. A method for mitigating post-implantation calcification of a
bioprosthetic heart valve, said method comprising the steps of:
harvesting desired biological tissue from a human cadaver or animal
donor, and preparing the tissue by trimming to size and washing
with a suitable washing solution; exposing the tissue to a fixation
process to form cross-linkages in the tissue to obtain fixed
tissue; providing a solution selected from the group consisting of
a glutaraldehyde solution and a physiologic solution and adjusting
the pH of the solution to between about 5.0 and 7.0; immersing the
fixed tissue in the solution; heating the solution and the fixed
tissue to a heat treating temperature in the range of about
30.degree. C. to 70.degree. C. for a period of time; and assembling
the heat treated and fixed tissue with non-biological components to
form a bioprosthetic heart valve.
19. The method of claim 18, wherein the heat treating temperature
is in the range of about 40.degree. C. to 60.degree. C.
20. The method of claim 19, wherein the heat treating temperature
is about 50.degree. C..+-.5.degree. C.
21. The method of claim 18, wherein the period of time is between
about one day and two months.
22. The method of claim 18, wherein the period of time is between
about 5 days to 10 days.
23. The method of claim 18, wherein the period of time is about 7
days.
24. The method of claim 18, wherein the pH of the solution is
adjusted to about 6.0.
25. The method of claim 18, further including, after the tissue has
been fixed and heat treated, and prior to assembly into a heart
valve, subjecting the fixed tissue to a first bioburden reduction
process including: contacting the fixed tissue with a mixture
containing: i) a crosslinking agent, ii) a denaturing agent and
iii) a surfactant.
26. The method of claim 25, further including, after assembling the
heart valve, subjecting the fixed tissue to a second bioburden
reduction process including: contacting the fixed tissue with a
mixture containing: i) a crosslinking agent, ii) a denaturing agent
and iii) a surfactant.
27. The method of claim 26, wherein the second bioburden reduction
process is done at a temperature of about 37.degree. C. for a
period of time longer than the first bioburden reduction
process.
28. The method of claim 27, further including storing the heart
valve in a solution of glutaraldehyde.
29. The method of claim 18, wherein the solution is aqueous
glutaraldehyde buffered to a starting pH, wherein the step of
adjusting comprises lowering the pH.
30. The method of claim 29, wherein the starting pH is between
about 7.2 to 7.8.
Description
RELATED APPLICATION
[0001] The present application is a divisional of Ser. No.
10/039,367, filed Jan. 3, 2002, which application is expressly
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention pertains generally to biomaterials and more
particularly to methods for mitigating the post-implantation
calcification of bioprosthetic materials and the bioprosthetic
devices and articles produced by such methods.
BACKGROUND OF THE INVENTION
[0003] Implantable biological tissues can be formed of human
tissues preserved by freezing (i.e., cryopreserving) the so called
homograft tissues, or of animal tissues preserved by chemically
fixing (i.e., tanning) the so called bioprosthesis (Carpentier,
Biological Tissues in Heart Valve Replacement, Butterworth (1972),
Ionescu editor). The type of biological tissues used as
bioprostheses include cardiac valves, blood vessels, skin, dura
mater, pericardium, small intestinal submucosa ("SIS tissue"),
ligaments and tendons. These biological tissues typically contain
connective tissue proteins (i.e., collagen and elastin) that act as
the supportive framework of the tissue. The pliability or rigidity
of each biological tissue is largely determined by the relative
amounts of collagen and elastin present within the tissue and/or by
the physical structure and configuration of its connective tissue
framework. Collagen is the most abundant connective tissue protein
present in most tissues. Each collagen molecule is made up of three
(3) polypeptide chains intertwined in a coiled helical
configuration.
[0004] The techniques used for chemical fixation of biological
tissues typically involve the exposure of the biological tissue to
one or more chemical fixatives (i.e., tanning agents) that form
cross-linkages between the polypeptide chains within a given
collagen molecule (i.e., intramolecular crosslinkages), or between
adjacent collagen molecules (i.e., intermolecular
crosslinkages).
[0005] Examples of chemical fixative agents that have been utilized
to cross-link collagenous biological tissues include: formaldehyde,
glutaraldehyde, dialdehyde starch, hexamethylene diisocyanate and
certain polyepoxy compounds. Of the various chemical fixatives
available, glutaraldehyde has been the most widely used since the
discovery of its antiimmunological and antidegenerative effects by
Dr. Carpentier in 1968. See Carpentier, A., J. Thorac.
Cardiovascular Surgery, 58: 467-69 (1969). In addition,
glutaraldehyde is one of the most efficient sterilization agents.
Glutaraldehyde is used as the fixative and the sterilant for many
commercially available bioprosthetic products, such as porcine
bioprosthetic heart valves (e.g., the Carpentier-Edwards.RTM.
stented porcine Bioprosthesis), bovine pericardial heart valves
(e.g., Carpentier-Edwards.RTM. Pericardial Bioprosthesis) and
stentless porcine aortic valves (e.g., Edwards PRIMA Plus.RTM.
Stentless Aortic Bioprosthesis), all manufactured and sold by
Edwards Lifesciences LLC, Irvine, Calif.
[0006] One problem associated with the implantation of many
bioprosthetic materials is that the connective tissue proteins
(i.e., collagen and elastin) within these materials can become
calcified following implantation within the body. Such
calcification can result in undesirable stiffening or degradation
of the bioprosthesis. Two (2) types of calcification--intrinsic and
extrinsic--are known to occur in fixed collagenous bioprostheses.
Intrinsic calcification follows the adsorption by the tissue of
lipoproteins and calcium binding proteins. Extrinsic calcification
follows the adhesion of cells (e.g., platelets) to the
bioprosthesis and leads to the development of calcium
phosphate-containing surface plaques on the bioprosthesis.
[0007] The factors that affect the rate at which fixed tissue
bioprostheses undergo calcification have not been fully elucidated.
However, factors thought to influence the rate of calcification
include the patient's age, the existence of metabolic disorders
(i.e., hypercalcemia, diabetes, etc.), dietary factors, the
presence of infection, parenteral calcium administration,
dehydration, in situ distortion of the bioprosthesis (e.g.,
mechanical stress), inadequate anticoagulation therapy during the
initial period following surgical implantation and immunologic
host-tissue responses.
[0008] Various techniques have heretofore been proposed for
mitigating the in situ calcification of glutaraldehyde-fixed
bioprostheses or for otherwise improving the glutaraldehyde
fixation process. Included among these are the methods described in
U.S. Pat. No. 4,729,139 (Nashef) entitled Selective Incorporation
of a Polymer into Implantable Biological Tissue to Inhibit
Calcification; U.S. Pat. No. 4,885,005 (Nashef et al.) entitled
Surfactant Treatment of Implantable Biological Tissue To Inhibit
Calcification; U.S. Pat. No. 4,648,881 (Carpentier et al.) entitled
Implantable Biological Tissue and Process For Preparation Thereof;
U.S. Pat. No. 4,976,733 (Girardot) entitled Prevention of
Prosthesis Calcification; U.S. Pat. No. 4,120,649 (Schechter)
entitled Transplants; U.S. Pat. No. 5,002,566 (Carpentier) entitled
Calcification Mitigation of Bioprosthetic Implants; EP 103947A2
(Pollock et al.) entitled Method For Inhibiting Mineralization of
Natural Tissue During Implantation, and U.S. Pat. No. 5,215,541
(Nashef et al.) entitled Surfactant Treatment of Implantable
Biological Tissue to Inhibit Calcification. Recently a new
technique of calcium mitigation by high temperature fixation of the
tissue in glutaraldehyde has been developed and was described in
U.S. Pat. No. 5,931,969 (Carpentier et al.) entitled Methods And
Apparatus For Treating Biological Tissue To Mitigate Calcification.
Although some of these techniques have proven to be efficient in
reducing calcification, there remains a need in the art for further
improvements of the existing techniques or for the development of
new calcification-mitigating techniques to lessen the propensity
for post-implantation calcification of fixed bioprosthetic
tissues.
SUMMARY OF THE INVENTION
[0009] The present invention provides methods for treating tissue
to inhibit post implant calcification whereby fixed, unfixed or
partially fixed tissue is immersed in or otherwise contacted with a
pre-treated glutaraldehyde solution. In a preferred embodiment of
the present invention, the glutaraldehyde solution is heat-treated
prior to its contact with the tissue. Preferably, the
glutaraldehyde solution is heated to a first temperature for a
first period of time. The temperature of the glutaraldehyde
solution is then adjusted to a second temperature (preferably lower
than the first temperature), before contacting the bioprosthetic
tissue.
[0010] The first temperature to which the glutaraldehyde solution
is heated is sufficiently high, and is maintained for sufficiently
long, to cause the free aldehyde content and pH of the
glutaraldehyde solution to fall by a predetermined amount.
Preferably, the prior heat treating of the glutaraldehyde solution
causes the free aldehyde concentration of the solution to decrease
by about 25%, preferably by about 50%. The glutaraldehyde solution
may be buffered so that the pH is initially in the range of about
7.2 to 7.8, preferably about 7.4. After the heating has been
carried out, the pH of the solution will typically have fallen to
approximately 5.0 to 7.0, preferably 6.0. Due to the preheating of
the glutaraldehyde solution, the solution does not significantly
change its chemical characteristics when used to treat the tissue
later in the procedure.
[0011] In a preferred embodiment, the glutaraldehyde solution is
heated to a first temperature of at least 20.degree. C., but
preferably not more than 90.degree. C. More preferably, the
glutaraldehyde solution is heated to a temperature between about
60.degree. C. to 80.degree. C., and most preferably about
70.degree. C..+-.5.degree. C. The glutaraldehyde solution may
become somewhat yellow in color during this heat-treatment step.
The time period during which the first temperature must be
maintained will typically vary inversely with the first temperature
(i.e., lower temperatures will require a longer period of time to
cause a decrease in free aldehyde content and/or a fall in pH).
Preferably, the glutaraldehyde is heated to the first temperature
for a period of time between about one hour and six months, and
more preferably about 1 day to 2 months. Thereafter, the solution
is filtered and adjusted to a second temperature before adding the
tissue. Preferably, this second temperature may be in the range of
about 30.degree. C. to 70.degree. C., preferably about
40-60.degree. C., and more preferably about 50.degree.
C..+-.5.degree. C.
[0012] In another embodiment of the present invention,
glutaraldehyde solution is not heat treated but the pH of the
glutaraldehyde solution is adjusted to a pH within the range of
about 5.0 to 7.0, and preferably to about 6.0. The pretreated
glutaraldehyde solution, whether by preheating or pH adjustment, is
then used to treat the tissue, preferably at a temperature in the
range of about 30.degree. C. to 70.degree. C., more preferably at a
temperature between about 40.degree. C. to 60.degree. C., and most
preferably, at a temperature of about 50.degree. C..+-.5.degree. C.
In a preferred embodiment, the tissue is treated for a period of
time between about one hour to six months, and more preferably for
about one day to two months. For example, at a temperature of about
50.degree. C., the preferred period of time is between about 5 days
to 10 days, and most preferably, for about seven days.
[0013] The heat-treated or pH adjusted glutaraldehyde solution may,
in some cases, also be used as a terminal sterilization solution
such that the calcification-decreasing treatment with previously
treated glutaraldehyde and a terminal sterilization may be carried
out simultaneously with the same solution and/or in a single
container.
[0014] The heat-treated glutaraldehyde solutions may also contain
other chemicals to enhance its efficacy, such as surfactants (e.g.,
Tween.RTM. 80), alcohol (e.g., ethanol) and/or aldehydes (e.g.,
formaldehyde).
[0015] In another embodiment of the method of the present
invention, the tissue is heat treated in a preheated solution other
than glutaraldehyde, for example, any other fixative solution or a
surfactant solution (e.g., Tween.RTM. 80 with or without ethanol
and/or formaldehyde), or a physiologic solution (e.g., saline or a
balanced salt solution). The preheating of the solution is carried
out at a temperature between about 20.degree. C. to 90.degree. C.,
more preferably between about 37.degree. C. and 60.degree. C., and
most preferably about 45.degree. C., for one hour to six months,
preferably one day to two months. In the preheated solution, the
tissue is heat treated between about 30.degree. C. and 70.degree.
C., and more preferably about 50.degree. C., for about one day to
two months. In another embodiment, the tissue is heat treated in a
non-preheat treated physiologic solution wherein the pH has been
adjusted between 5.0 and 7.0, preferably 6.0.
[0016] The method of the present invention results in a decrease in
the tissue's propensity to calcify after being implanted within the
body of a human or animal patient. Prior to, concurrently with, or
after undergoing treatment with the pre-treated glutaraldehyde, the
tissue may be chemically fixed by exposing the tissue to one or
more chemical fixatives or cryopreserved by freezing the tissue in
accordance with well known techniques.
[0017] Further in accordance with the invention, there are provided
bioprosthetic devices or articles that are formed, wholly or
partially, of tissue that has been treated in accordance with the
various embodiments of the method of the present invention.
Examples of biological tissues of human or animal origin which may
be used in bioprosthetic devices or articles of the present
invention include, but are not necessarily limited to: heart
valves; venous valves; blood vessels; ureter; tendon; dura mater;
skin; pericardium; cartilage (e.g., meniscus); ligament; bone;
intestine (e.g., intestinal wall); small intestinal submucosa ("SIS
tissue"), and periostium.
[0018] Further in accordance with the present invention, there are
provided methods for treating diseases and disorders of mammalian
patients, by implanting bioprosthetic materials that have undergone
the calcification mitigating treatment of the various embodiments
of the method of the present invention. Such treatment methods
include, but are not limited to, a) the surgical replacement of
diseased heart valves with bioprosthetic heart valves that have
been treated with glutaraldehyde in accordance with the present
invention, b) the repair or bypassing of blood vessels by
implanting biological vascular grafts that have been treated with
glutaraldehyde in accordance with the present invention, c) the
surgical replacement or repair of torn or deficient ligaments by
implanting bioprosthetic ligaments that have been treated with
glutaraldehyde in accordance with the present invention and, d) the
repair, reconstruction, reformation, enhancement, bulking,
ingrowth, reconstruction or regeneration of native tissues by
implanting one or more biopolymeric or bioprosthetic tissue
scaffolds that have been treated with glutaraldehyde in accordance
with the present invention (e.g., tissue engineering with a natural
tissue or biopolymeric scaffold).
[0019] Still further in accordance with this invention, the various
embodiments of the method of mitigating post-implantation
calcification of bioprosthetic tissues offer significant advantages
over previous practices wherein glutaraldehyde was heated in the
presence of the tissue, as the present invention allows the
desirable features of the heat treatment to be achieved prior to
any contact between the glutaraldehyde solution and the tissue, and
also allows the temperature of the glutaraldehyde solution to be
lowered to about 30.degree. C. to 70.degree. C., preferably about
40.degree. C. to 60.degree. C., or most preferably at about
50.degree. C. prior to any contact with the tissue. This lessens
the potential for untoward or undesirable reactions to the
bioprosthetic tissue due to exposure to high free aldehyde
concentrations and/or long term heat treatment at temperatures
above 60.degree. C. It also allows for treatment of the tissue
within realistic manufacturing time frames.
[0020] Still further in accordance with this invention, the method
of preheating the solution, and/or heating the tissue, offer better
sterilization of both the solution and the tissue at the different
stages of the manufacturing process, including the terminal stage.
Further aspects and advantages of the present invention will become
apparent to those skilled in the relevant art, upon reading and
understanding the "Description of Exemplary Embodiments" set forth
herebelow.
BRIEF DESCRIPTION OF THE DRAWING
[0021] FIG. 1 is a flow diagram of one embodiment of the method for
mitigating calcification of a bioprosthetic material, in accordance
with the present invention.
[0022] FIG. 2 is a flow diagram of another embodiment of the method
for preparing a bioprosthetic device in accordance with the method
of the present invention.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0023] The following examples are provided for the purpose of
describing and illustrating a few exemplary embodiments of the
invention only. One skilled in the art will recognize that other
embodiments of the invention are possible, but are not described in
detail here. Thus, these examples are not intended to limit the
scope of the invention in any way.
[0024] It has previously been reported that cross-linked
bioprosthetic tissue post-treated in 0.625% glutaraldehyde
phosphate solution for 2 months at 50.degree. C., with fluid
movement (e.g., shaking), exhibited less calcification in the rat
subcutaneous and rabbit intramuscular implant models than control
cross-linked bioprosthetic tissue fixed in 0.625% glutaraldehyde
phosphate solution under typical conditions (i.e., room temperature
for 1-14 days). See 66 Ann. Thoracic Surgery 264-6 (1998). Tissues
treated under these conditions exhibited a characteristic tan to
brown appearance. The heated 0.625% glutaraldehyde phosphate
solution also darkened to an amber-brown color and the aldehyde
concentration within that solution dropped to about 0.3%.
[0025] Since the above publication, the Applicant has discovered
that it is advantageous to conduct the heating step on the
glutaraldehyde solution prior to its contact with the tissue. The
heat-treated glutaraldehyde may then be cooled to a lower
temperature and the tissue may then be added to the cooled
glutaraldehyde solution under conditions of reduced severity,
greater convenience, or both (e.g., shorter time, lower
temperature, or both). By heat-treating the glutaraldehyde solution
in the absence of the tissue, higher temperatures, concentrations
or both can be used during the heat-treating process without
risking or causing any adverse effect on the tissue. In another
embodiment, the glutaraldehyde solution can be buffered by
adjusting the pH of the solution to within a range of about 5.0 to
7.0, preferably about 6.0. Applicants have found that the buffered
glutaraldehyde solution has a similar, although slightly less,
advantageous effect as the heat-treated glutaraldehyde
solution.
[0026] The mechanism by which the heat-treated glutaraldehyde
mitigates post-implantation calcification is not presently known
with certainty. However, Applicants postulate that this
calcification mitigating effect is due at least in part to the
leaching of lipoproteins and calcium binding proteins and in part
to the formation of a calcification mitigating chemical or moiety
within the glutaraldehyde solution that acts to limit or inhibit
the fixation of calcium into the tissue, either by way of a
physical barrier effect (i.e., by retarding diffusion at the
boundary layer) and/or by chemically modifying the structure and
the surface charge of the tissue and thus its affinity to attract
calcium ions. Heat-treated glutaraldehyde can also be used to
enhance sterilization by leaving the tissue in the heat-treated
glutaraldehyde or by heating the tissue within the previously heat
treated glutaraldehyde solution to temperatures between about
37.degree. C. and 60.degree. C.
[0027] A. General Method for Mitigating Calcification of
Bioprosthetic Material
[0028] FIG. 1 is a flow diagram that generally illustrates one
embodiment of the method of the present invention. As shown in FIG.
1, the first step of the process is to heat treat glutaraldehyde
solution in the absence of tissue. It will be appreciated that the
concentration of glutaraldehyde in the starting solution may be
varied. Thereafter, the solution concentration may be adjusted, if
desired, prior to addition of the tissue. It is believed that
glutaraldehyde concentrations of as little as 0.1% and as much as
25% or more may be used during the heat-treating step. Reduced
glutaraldehyde concentrations of 0.6% to 2.5% have, to date, been
successfully obtained and used by Applicant, and those skilled in
the art will recognize that higher or lower concentrations of
glutaraldehyde may indeed prove to be advantageous during the
heat-treating step of the process. The preferred concentration for
use during the heat-treating step (FIG. 1) is 1.0-2.0%. This
heat-treating of the glutaraldehyde may be accomplished by heating
of the solution until the free aldehyde content of the solution has
fallen about 25% or more and remains stable at that level (e.g., a
solution of 1.8% falls to about 0.6% or less). Initially, the
solution containing glutaraldehyde may be buffered to a pH of 7.4
with a phosphate buffer, a non-phosphate buffer such as a HEPES
buffer, or other suitable buffered solutions, and, in such cases,
heating of the solution to cause the free aldehyde content to fall
will also cause the pH of the solution to fall. In another
embodiment of the present invention, rather than heat treating the
glutaraldehyde solution, the pH may be adjusted from 7.4 to a pH
within the range of about 5.0 to 7.0, preferably 6.0.
[0029] The heat-treating of the glutaraldehyde may be accomplished
by any suitable means. In this example, the glutaraldehyde is
pre-heated to and maintained at a temperature between about
20-90.degree. C., preferably between about 60.degree. C.-80.degree.
C., and most preferably 70.degree. C..+-.5.degree. C. for a
sufficient period of time to cause the free aldehyde concentration
to decrease by at least 25% and to stabilize at a pH of
approximately 6.0 (i.e., the pH of 6.0 corresponds to a free
aldehyde concentration of about 0.3-0.7%). Depending on the
temperature used, the step of heat treating the glutaraldehyde may
take anywhere from one hour to six months or more depending on the
temperature used. The preferred method is to heat the
glutaraldehyde solution to approximately 70.degree. C..+-.5.degree.
C., for approximately 1 day to 2 months or until the desired fall
of at least 25% or more in free aldehyde concentration and a pH of
approximately 6.0, are observed.
[0030] After the heat-treatment of the glutaraldehyde has been
completed the solution is cooled to a second temperature that does
not cause damage to the tissue (e.g., about 30.degree. C. to
70.degree. C., preferably about 40.degree. C. to 60.degree. C., or
most preferably at about 50.degree. C.). An unfixed,
partially-fixed, or fixed tissue is then contacted with the
heat-treated glutaraldehyde. Tissue that has been "fully fixed" in
this regard means that the tissue has been fixed to an extent
suitable for use as an implant, while "partially fixed" means that
the tissue has been fixed to some extent short of being fully
fixed. This tissue treatment step is preferably accomplished by
immersing fixed, partially fixed or unfixed tissue in the
heat-treated glutaraldehyde solution while maintaining the solution
at about 30.degree. C. to 70.degree. C., preferably about
40.degree. C. to 60.degree. C., or most preferably at about
50.degree. C. It is preferable that the pH of the solution be left
at about 6.0 prior to placement of the tissue within the solution.
Thereafter, the temperature of the solution is maintained at
approximately 50.degree. C. with the tissue immersed in the
solution to allow the heat-treated glutaraldehyde solution to
interact with or modify the tissue. The tissue's susceptibility to
post-implant calcification will be significantly reduced after
immersion for as little as one hour to as much as six months or
more (depending primarily on the temperature used), but typically
occurs within 1 to 15 days at 50.degree. C.
[0031] In another embodiment of the method of the present
invention, the tissue may be heat treated in a surfactant solution
(e.g., Tween.RTM. 80 with or without ethanol and/or formaldehyde)
or in a physiologic solution (e.g. saline or a balanced salt
solution) at a temperature between about 37.degree. C. and
60.degree. C., preferably about 45.degree. C., for about one hour
to six months, preferably about one to 15 days, and then heat
treated in a glutaraldehyde solution as described above.
[0032] Prior to, concurrently with or after the tissue treatment
step, the tissue may be cryopreserved or otherwise preserved, i.e.
by fixation.
[0033] B. An Example of a Method for Manufacturing a Fixed
Heterologous Heart Valve Bioprosthesis Having Mitigated Propensity
for Post-Implantation Calcification
[0034] FIG. 2 is a flow diagram of a specific process for
manufacturing a bioprosthetic device, such as a stented or
stentless porcine heart valve or bovine pericardial heart valve of
the type referred to herein. The following is a description of the
exemplary process shown in FIG. 2.
[0035] 1. Heat-Treating of Glutaraldehyde
[0036] Prepare Glutaraldehyde Solution
[0037] Initially, an aqueous solution of 1.8% by weight
glutaraldehyde is prepared in a clean, inert vessel (e.g., a vessel
made of stainless steel, plastic or borosilicate glass) and such
solution is then buffered to the pH of approximately 7.4 by adding
phosphate buffered saline solution.
[0038] Preheat Glutaraldehyde Solution in Absence of Tissue
[0039] The glutaraldehyde in the solution is then preheated. Such
preheating of the glutaraldehyde is accomplished by heating of the
solution to about 70.degree. C..+-.5.degree. C. and maintaining
such temperature until the pH of the solution falls to
approximately 6.0. At this point, the color of the solution can be
colorless to golden or brown. The fall of the solution pH to 6.0
and the accompanying change in color to golden or brown indicates
that the preheating treatment has been completed. This preheating
step is typically completed after 1-14 days, preferably 6-8 days,
of maintaining the solution at the 70.degree. C..+-.5.degree. C.
temperature. Higher temperatures ranging up to approximately
90.degree. C. may be used, and the use of such higher temperatures
will typically speed the desired fall in free aldehyde
concentration and accompanying change in pH (e.g., a solution
having a starting pH adjusted to 7.4 will fall to a pH of about 6.0
after approximately 1-3 days at 90.degree. C.). Lower temperatures,
ranging downward to approximately 20.degree. C., may also be used,
and the use of such lower temperatures will typically cause the
desired free aldehyde content and pH changes to take longer. After
the heat treatment of the solution has been carried out the
solution is filtered.
[0040] Optional Neutralization of pH of Heat-Treated Glutaraldehyde
Solution
[0041] After the glutaraldehyde has been heat-treated, the solution
is allowed to cool to about 50.degree. C. and its pH may be
adjusted at step 24 back to approximately 7.4 by adding phosphate
buffered saline or some other suitable buffer.
[0042] 2. Harvesting, Preparation and Fixation of Tissue
[0043] Harvesting/Preparation of Biological Tissue
[0044] The desired biological tissue is harvested from a human
cadaver or animal donor, and prepared for subsequent fixation and
treatment. The tissue is typically harvested by surgical cutting or
removal from its host animal. Thereafter, it is typically trimmed
or cut to size and washed with sterile water, basic salt solution,
saline or other suitable washing solution.
[0045] Fixation of Biological Tissue
[0046] The biological tissue may be fixed prior to, during or after
its treatment with the heat-treated glutaraldehyde. In this
example, the tissue is fixed prior to undergoing the treatment with
heat-treated glutaraldehyde. This fixation is carried out by
immersing the tissue in a solution of 0.625% by weight
glutaraldehyde buffered to a pH of approximately 7.4 by a suitable
buffer such as a phosphate buffer, for 1-14 days at ambient
temperature. In order to enhance fixation or sterilization other
chemical compounds such as surfactants (e.g. Tween.RTM. 80) and/or
ethanol and/or formaldehyde can be added to the glutaraldehyde. It
will be appreciated, however, that various other fixatives may be
used, such as aldehydes (e.g., formaldehyde, glutaraldehyde,
dialdehyde starch) or polyglycidyl ethers (e.g., Denacol 810), or
heterologous bifunctional or multifunctional crosslinkers.
[0047] Rinsing of Tissue
[0048] After it has been removed from the fixative solution, the
tissue is thoroughly rinsed with saline solution, basic salt
solution or free glutaraldehyde solution or some other suitable
washing solution.
[0049] 3. Treatment of Tissue with Heat-Treated Glutaraldehyde to
Mitigate Post-Implantation Calcification
[0050] Immersion of Tissue in Heat-Treated Glutaraldehyde
Solution
[0051] After the fixed tissue has been rinsed, it is treated with
the pre-heat treated glutaraldehyde solution. The pre-heat treated
glutaraldehyde solution is placed in a vessel such as a stainless
steel bath, cooled to and maintained at preferably 50.degree.
C..+-.5.degree. C. The fixed/rinsed tissue is then immersed in the
heat-treated glutaraldehyde solution and the solution is
continually maintained at 50.degree. C..+-.5.degree. C. with the
tissue immersed in the solution with or without fluid movement. The
tissue's susceptibility to post-implant calcification will be
significantly reduced after immersion for as little as one hour to
as much as six months or more (depending primarily on the
temperature used), but typically occurs within 6 to 8 days at
50.degree. C..+-.5.degree.. Thereafter, the tissue is removed from
the solution. The tissue is typically brown in color at this
time.
[0052] Rinsing of Tissue
[0053] After it has been removed from the heat-treated
glutaraldehyde solution, the tissue is thoroughly rinsed with
saline solution, basic salt solution or some other suitable washing
solution.
[0054] 4. Poststerilization, Assembly/Fabrication and Storage of
Bioprosthesis
[0055] First Bioburden Reduction (BREP I)
[0056] After the tissue has been fixed, treated with the
heat-treated glutaraldehyde and rinsed, it is subjected to a first
bioburden reduction treatment immersed in or otherwise contacted
with a mixture containing i) a crosslinking agent, ii) a denaturing
agent and iii) a surfactant (i.e., a CDS solution). One preferred
CDS solution (described in U.S. Pat. No. 4,885,005 and U.S. Pat.
No. 4,648,881) is a mixture of i) formaldehyde, ii) ethanol and ii)
surfactant (e.g., Tween.RTM. 80 surfactant, available from ICI
Americas, Brantford, Ontario). Such preferred CDS solution may also
be referred to by the acronym "FETS" and has a preferred
formulation as follows:
[0057] Formaldehyde 4.0..+-.. 0.4% by weight
[0058] Ethanol 22.0..+-..2.2% by weight
[0059] Tween.RTM. 80 1.2..+-..0.2% by weight
[0060] The tissue is preferably immersed in the CDS solution for 2
hours to 7 days and typically about 2 hours. During this immersion
period, the CDS solution is maintained at a temperature of
4-50.degree. C., and preferably at about 20-37.degree. C.
[0061] Those skilled in the art will appreciate that various
alternative chemical compounds or solutions may be substituted for
each component of the CDS solution, as follows:
[0062] Potential Alternative Crosslinking Agents
[0063] A. Aldehydes: formaldehyde, glutaraldehyde,
paraformaldehyde, glyceraldehyde, glyoxal acetaldehyde or
acrolein
[0064] B. Epoxides: any of the various Denacols and their
individual reactive species, including mono, di, tri, and
multi-functionalized epoxides
[0065] C. Carbodiimides
[0066] D. Mixed multifunctional molecules (e.g. aldehyde-epoxide
combination)
[0067] Potential Alternative Denaturing Agents
[0068] A. Alcohols/Solvents: e.g., ethanol, isopropyl alcohol
[0069] B. Acidified Ethers: e.g., sulfuric acid/ether mixture,
acetone, ethers of small alkyl size (methyl, ethyl, etc. but
probably not beyond butyl)
[0070] C. Ketones: e.g., methyl ethyl ketone (MEK)
[0071] D. Commercial Solvent Systems: e.g., Genesolve..TM.. (Allied
Signal, Inc., Morristown, N.J.)
[0072] E. Glycols: glycerol ethylene glycol, polyethylene glycol,
low molecular weight carbowax
[0073] F. Chaotropic Agents: e.g., urea, guanidine hydrochloride,
guanidine thiocyanate, potassium iodide
[0074] G. High Concentration Salt Solutions: e.g., lithium
chloride, sodium chloride, cesium chloride.
[0075] Potential Alternative Surfactants
[0076] (these surfactant compounds can be used individually or in
mixtures such as deoxycholate/Triton or commercially-available
mixtures such as Micro-80/90.)
[0077] A. Anionic Surfactants: e.g., esters of lauric acid,
including but not limited to sodium laurel sulfate (also called
sodium dodecyl sulfate)
[0078] B. Alkyl sulfonic acid salts: e.g., 1-decanesulfonic acid
sodium salt
[0079] C. Non-ionic compounds: e.g., compounds based on the
polyoxyethylene ether structures, including Triton X-100, 114, 405,
N-101 (available commercially from Sigma Chemical, St. Louis, Mo.)
and related structures; Pluronic and Tetronic surfactants
(available commercially from BASF Chemicals, Mount Olive, N.J.)
[0080] D. Alkylated Phenoxypolyethoxy Alcohols: e.g., NP40, Nonidet
P40, Igepal, CA630, hydrolyzed/functionalized animal and plant
compounds including Tween.RTM. 80, Tween.RTM. 20,
octyl-derivatives, octyl b-glucoside, octyl b-thioglucopyranoside,
deoxycholate and derivatives thereof, zwitterionic compounds,
3-([cholamidopropyl]-dimethyl amino)-1-propanesulfonate (CHAPS),
3-([cholamidopropyl]-dimethyl amino)-2-hydroxy-1-propanesulfonat-e
(CHAPSO) (available from Pierce Biotec Company, Rockford,
Ill.).
[0081] Fabrication/Assembly
[0082] After the first bioburden reduction has been completed, the
tissue maybe again rinsed with a suitable rinsing solution such as
isotonic saline or 0.625% glutaraldehyde and transported into a
clean room or aseptic environment. Thereafter, the tissue may be
further trimmed or shaped (if necessary) and attached to or
assembled with any non-biological components (e.g., stents, frames,
suture rings, conduits, segments of polyester mesh to prevent
suture tear-through, etc.) to form the desired bioprosthetic
device. Examples of bioprosthetic devices that are assembled of
both biological tissue and non-biological components include
stented porcine bioprosthetic heart valves (e.g., the
Carpentier-Edwards.RTM. Bioprosthesis), and bovine pericardial
heart valves (e.g., Carpentier-Edwards.RTM. Pericardial
Bioprosthesis), stentless porcine aortic valves that incorporate
fabric reinforcements (e.g., Edwards PRIMA Plus.RTM. Stentless
Aortic Bioprosthesis), and conduit valves for bio-mechanical
ventricular assist devices (e.g., the Novacor N-100PC model), all
available from Edwards Lifesciences LLC, Irvine, Calif.
[0083] Second Bioburden Reduction (BREP II)
[0084] After the bioprosthesis has been fabricated and assembled it
is subjected to a second bioburden reduction that is essentially a
repeat of the first bioburden reduction described above, however,
in this second bioburden reduction step, the solution is preferably
maintained at about 37.degree. C. for approximately 2 hours to 10
days, preferably about 9 hours.
[0085] Terminal Heating and Storage
[0086] After completion of the second bioburden reduction, the
tissue (or bioprosthesis) is rinsed with a suitable rinsing
solution (such as isotonic saline or 0.625% glutaraldehyde
solution) and then placed in a terminal solution for storage and
sterilization. The preferred terminal solution is a glutaraldehyde
solution having a concentration of about 0.2 to 1.0% by weight
glutaraldehyde, and most preferably about 0.625% by weight
glutaraldehyde. This solution has a strong sterilizing effect that
can be enhanced by a terminal heating of the solution.
[0087] In this terminal sterilization step, the tissue (or
bioprosthesis) is immersed in or contacted with the terminal
solution and heated for a period of time sufficient to ensure
sterility of the bioprosthesis until the time of implantation. The
period of heating varies depending upon the temperature utilized,
i.e., the lower the temperature the longer the period of time. For
example, from 1 or 2 hours to 1 month for temperatures between
about 50.degree. C. and 20.degree. C., respectively. Preferably,
the period of time is 1 to 6 days at 37.degree. C. or 6 hours to 2
days at 50.degree. C., but one of skill in the art will recognize
that these temperature or time values can be modified within the
scope of the invention.
[0088] In order to avoid additional transfer and manipulation, the
terminal heating is preferably carried out in the sealed storage
container or package in which the bioprosthesis will be shipped and
stored until the time of implantation. The tissue (or
bioprosthesis) is aseptically deposited in the storage container
that has been pre-filled with the 0.625% glutaraldehyde aqueous
solution buffered to a pH of 7.4 with sodium hydroxide, such that
the tissue (or bioprosthesis) is fully immersed in the buffered
glutaraldehyde solution. Thereafter, the container is sealed and
placed at room temperature for at least 7 days, or in an oven at
37.degree. C. for 24 hours, or at 50.degree. C. for 6 hours to
enhance the sterilization power of glutaraldehyde. Thereafter, the
container is cooled to room temperature and shipped to the hospital
or other location(s) where it is stored until the time of use of
the bioprosthesis.
[0089] In another embodiment, the terminal heating is carried out
before placing the tissue or bioprosthesis in the storage
container.
[0090] In some cases, glutaraldehyde that has been heat-treated in
accordance with this invention may be used as the terminal solution
and, in such cases, it may be possible to shorten or completely
eliminate the previous step of immersing the tissue in previously
heat-treated glutaraldehyde, opting instead to accomplish some or
all of the treatment of the tissue by heat-treated glutaraldehyde
until the last step of storage, i.e., concurrently with the
terminal sterilization step.
[0091] While the foregoing is a complete description of the
preferred embodiments of the invention, various alternatives,
modifications, and equivalents may be used. Moreover, it will be
obvious that certain other modifications may be practiced within
the scope of the appended claims.
* * * * *