U.S. patent application number 09/520665 was filed with the patent office on 2001-11-29 for copolymers of tyrosine-based polyarylates and poly(alkylene oxides).
Invention is credited to Kohn, Joachim B., Yu, Chun.
Application Number | 20010046505 09/520665 |
Document ID | / |
Family ID | 27617403 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046505 |
Kind Code |
A1 |
Kohn, Joachim B. ; et
al. |
November 29, 2001 |
Copolymers of tyrosine-based polyarylates and poly(alkylene
oxides)
Abstract
Implantable medical devices and drug delivery implants
containing polyarylate random block copolymers are disclosed, along
with methods for drug delivery and for preventing the formation of
adhesions between injured tissues employing the polyarylate random
block copolymers.
Inventors: |
Kohn, Joachim B.; (Highland
Park, NJ) ; Yu, Chun; (Piscataway, NJ) |
Correspondence
Address: |
Synnestvedt & Lechner
Peter J Butch III Esquire
2600 Aramark Tower
1101 Market Street
Philadelphia
PA
19107
US
|
Family ID: |
27617403 |
Appl. No.: |
09/520665 |
Filed: |
March 7, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09520665 |
Mar 7, 2000 |
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09085571 |
May 27, 1998 |
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6048521 |
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09085571 |
May 27, 1998 |
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PCT/US96/19098 |
Nov 27, 1996 |
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PCT/US96/19098 |
Nov 27, 1996 |
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09056050 |
Apr 7, 1998 |
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6120491 |
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60064656 |
Nov 7, 1997 |
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Current U.S.
Class: |
424/400 |
Current CPC
Class: |
C08G 63/6858 20130101;
A61L 27/34 20130101; A61L 31/06 20130101; C08G 63/6856 20130101;
A61L 31/06 20130101; A61L 27/18 20130101; A61L 27/34 20130101; A61K
9/204 20130101; C07K 14/001 20130101; C08G 64/1641 20130101; A61L
31/148 20130101; C08L 69/00 20130101; A61L 31/10 20130101; C08L
69/00 20130101; C08L 69/00 20130101; A61L 17/10 20130101; C08L
69/00 20130101; C08G 64/045 20130101; A61K 38/00 20130101; C08G
69/44 20130101; C08G 64/12 20130101; C08G 63/672 20130101; C08G
69/10 20130101; C08G 64/183 20130101; A61L 27/18 20130101; A61L
31/10 20130101 |
Class at
Publication: |
424/400 |
International
Class: |
A61K 009/00 |
Claims
What is claimed is
1. An implantable medical device comprising a polyarylate,
polymerized as a random block copolymer of a dicarboxylic acid with
both a tyrosine-derived diphenol and a poly(alkylene oxide),
wherein an equimolar combined quantity of said diphenol and said
poly(alkylene oxide) is reacted with said dicarboxylic acid in a
molar ratio of said diphenol to said poly(alkylene oxide) between
about 1:99 and about 99:1; and wherein said dicarboxylic acid has
the structure: 4in which R is selected from the group consisting of
saturated and unsaturated, substituted and unsubstituted alkyl,
aryl and alkylaryl groups containing up to 18 carbon atoms; said
tyrosine derived diphenol has the structure: 5in which R.sub.1 is
--CH.dbd.CH-- or (--CH.sub.2--).sub.j, wherein j is zero or an
integer from one to eight, and R.sub.2 is selected from the group
consisting of straight and branched alkyl and alkylaryl groups
containing up to 18 carbon atoms and optionally containing at least
one ether linkage and derivatives of biologically and
pharmaceutically active compounds covalently bonded to said
diphenol; and said poly(alkylene oxide) has the
structure:(--O--R.sub.3--).sub.yin which each R.sub.3 is
independently an alkylene group containing up to 4 carbon atoms and
y is an integer between about 5 and about 3000.
2. The implantable medical device of claim 1, wherein the surface
of said device is coated with said random block copolymer.
3. The implantable medical device of claim 1, comprising a
biologically or physiologically active compound in combination with
said random block copolymer, wherein said active compound is
present in an amount sufficient for therapeutically effective
site-specific or systemic drug delivery.
4. The implantable medical device of claim 3, wherein said
biologically or physiologically active compound is covalently
bonded to said copolymer.
5. An implantable medical device in the form of a sheet consisting
essentially of a polyarylate, polymerized as a random block
copolymer of a dicarboxylic acid with both a tyrosine-derived
diphenol and a poly(alkylene oxide), wherein an equimolar combined
quantity of said diphenol and said poly(alkylene oxide) is reacted
with said dicarboxylic acid in a molar ratio of said diphenol to
said poly(alkylene oxide) between about 1:99 and about 99:1; and
wherein said dicarboxylic acid has the structure: 6in which R is
selected from the group consisting of saturated and unsaturated,
substituted and unsubstituted alkyl, aryl and alkylaryl groups
containing up to 18 carbon atoms; said tyrosine-derived diphenol
has the structure: 7in which R.sub.1 is --CH.dbd.CH-- or
(--CH.sub.2--).sub.j, wherein j is zero or an integer from one to
eight, and R.sub.2 is selected from the group consisting of
straight and branched alkyl and alkylaryl groups containing up to
18 carbon atoms and optionally containing at least one ether
linkage and derivatives of biologically and pharmaceutically active
compounds covalently bonded to said diphenol; and said
poly(alkylene oxide) has the structure:(--O--R.sub.3--).sub.yin
which each R.sub.3 is independently an alkylene group containing up
to 4 carbon atoms and y is an integer between about 5 and about
3000. for use as a barrier for surgical adhesion prevention.
6. A method for site-specific or systemic drug delivery comprising
implanting in the body of a patient in need thereof an implantable
drug delivery device comprising a therapeutically effective amount
of a biologically or physiologically active compound in combination
with a polyarylate, polymerized as a random block copolymer of a
dicarboxylic acid with both a tyrosine-derived diphenol and a
poly(alkylene oxide), wherein an equimolar combined quantity of
said diphenol and said poly(alkylene oxide) is reacted with said
dicarboxylic acid in a molar ratio of said diphenol to said
poly(alkylene oxide) between about 1:99 and about 99:1; and wherein
said dicarboxylic acid has the structure: 8in which R is selected
from the group consisting of saturated and unsaturated, substituted
and unsubstituted alkyl, aryl and alkylaryl groups containing up to
18 carbon atoms; said tyrosine-derived diphenol has the structure:
9in which R.sub.1 is --CH.dbd.CH-- or (--CH.sub.2--).sub.j, wherein
j is zero or an integer from one to eight, and R.sub.2 is selected
from the group consisting of straight and branched alkyl and
alkylaryl groups containing up to 18 carbon atoms and optionally
containing at least one ether linkage and derivatives of
biologically and pharmaceutically active compounds covalently
bonded to said diphenol; and said poly(alkylene oxide) has the
structure:(--O--R.sub.3--).sub.yin which each R.sub.3 is
independently an alkylene group containing up to 4 carbon atoms and
y is an integer between about 5 and about 3000.
7. The method of claim 6, wherein said biologically or
physiologically active compound is covalently bonded to said
copolymer.
8. A method for preventing the formation of adhesions between
injured tissues comprising inserting as a barrier between said
injured tissues a sheet consisting essentially of a polyarylate,
polymerized as a random block copolymer of a dicarboxylic acid with
both a tyrosine-derived diphenol and a poly(alkylene oxide),
wherein an equimolar combined quantity of said diphenol and said
poly(alkylene oxide) is reacted with said dicarboxylic acid in a
molar ratio of said diphenol to said poly(alkylene oxide) between
about 1:99 and about 99:1; and wherein said dicarboxylic acid has
the structure: 10in which R is selected from the group consisting
of saturated and unsaturated, substituted and unsubstituted alkyl,
aryl and alkylaryl groups containing up to 18 carbon atoms; said
tyrosine-derived diphenol has the structure: 11in which R.sub.1 is
--CH.dbd.CH-- or (--CH.sub.2--).sub.j, wherein j is zero or an
integer from one to eight, and R.sub.2 is selected from the group
consisting of straight and branched alkyl and alkylaryl groups
containing up to 18 carbon atoms and optionally containing at least
one ether linkage and derivatives of biologically and
pharmaceutically active compounds covalently bonded to said
diphenol; and said poly(alkylene oxide) has the
structure:(--O--R.sub.3--).sub.yin which each R.sub.3 is
independently an alkylene group containing up to 4 carbon atoms and
y is an integer between about 5 and about 3000.
9. The controlled drug delivery system comprising a biologically or
pharmaceutically active compound physically coated with a random
block copolymer having the formula: 12wherein R.sub.1 is
--CH.dbd.CH-- or (--CH.sub.2--).sub.j, in which j is zero or an
integer from one to eight; R.sub.2 is selected from the group
consisting of straight and branched alkyl and alkylaryl groups
containing up to 18 carbon atoms and optionally containing at least
one ether linkage, and derivatives of biologically and
physiologically active compounds covalently bonded to said
copolymer; each R.sub.3 is independently an alkylene group
containing up to 4 carbon atoms; A is selected from the group
consisting of: 13wherein R.sub.8 is selected from the group
consisting of saturated and unsaturated, substituted and
unsubstituted alkyl, aryl and alkylaryl groups containing up to 18
carbon atoms; y is between about 5 and about 3000; and f is the
percent molar fraction of alkylene oxide in said copolymer and
ranges between about 1 and about 99 mole percent.
10. A controlled drug delivery system comprising a random block
copolymer having the formula: 14wherein R.sub.1 is --CH.dbd.CH-- or
(--CH.sub.2--).sub.j, in which j is zero or an integer from one to
eight; R.sub.2 is selected from the group consisting of straight
and branched alkyl and alkylaryl groups containing up to 18 carbon
atoms and optionally containing at least one ether linkage, and
derivatives of biologically and physiologically active compounds
covalently bonded to said copolymer; each R.sub.3 is independently
an alkylene group containing up to 4 carbon atoms; A is selected
from the group consisting of: 15wherein R.sub.8 is selected from
the group consisting of saturated and unsaturated, substituted and
unsubstituted alkyl, aryl and alkylaryl groups containing up to 18
carbon atoms; y is between about 5 and about 3000; and f is the
percent molar fraction of alkylene oxide in said copolymer and
ranges between about 1 and about 99 mole percent. Physically add
mixed with a biologically or pharmaceutically active compound.
11. A controlled drug delivery system comprising a biologically or
pharmaceutically active compound physically embedded or dispersed
into a polymeric matrix formed from a random block copolymer having
the formula: 16wherein R.sub.1 is --CH.dbd.CH-- or
(--CH.sub.2--).sub.j, in which j is zero or an integer from one to
eight; R.sub.2 is selected from the group consisting of straight
and branched alkyl and alkylaryl groups containing up to 18 carbon
atoms and optionally containing at least one ether linkage, and
derivatives of biologically and physiologically active compounds
covalently bonded to said copolymer; each R.sub.3 is independently
an alkylene group containing up to 4 carbon atoms; A is selected
from the group consisting of: 17wherein R.sub.8 is selected from
the group consisting of saturated and unsaturated, substituted and
unsubstituted alkyl, aryl and alkylaryl groups containing up to 18
carbon atoms; y is between about 5 and about 3000; and f is the
percent molar fraction of alkylene oxide in said copolymer and
ranges between about 1 and about 99 mole percent.
12. A method of regulating cellular attachment, migration and
proliferation on a polymeric substrate, comprising contacting
living cells, tissues or biological fluids containing living cells
with a random block copolymer having the formula: 18wherein R.sub.1
is --CH.dbd.CH-- or (--CH.sub.2--).sub.j, in which j is zero or an
integer from one to eight; R.sub.2 is selected from the group
consisting of straight and branched alkyl and alkylaryl groups
containing up to 18 carbon atoms and optionally containing at least
one ether linkage, and derivatives of biologically and
physiologically active compounds covalently bonded to said
copolymer; each R.sub.3 is independently an alkylene group
containing up to 4 carbon atoms; A is selected from the group
consisting of: 19wherein R.sub.8 is selected from the group
consisting of saturated and unsaturated, substituted and
unsubstituted alkyl, aryl and alkylaryl groups containing up to 18
carbon atoms; y is between about 5 and about 3000; and f is the
percent molar fraction of alkylene oxide in said copolymer and
ranges between about 1 and about 99 mole percent.
13. The method of claim 12, wherein said polymer is in the form of
a coating on a medical implant.
14. The method of claim 12, wherein said polymer is in the form of
a film.
15. The method of claim 12, wherein said polymer is in the form of
a polymeric tissue scaffold.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the priority benefit under 35
U.S.C. .sctn.120 of the Nov. 27, 1996 International filing date of
co-pending PCT Application No. PCT/US 96/19098, designating the
United States, which in turn claims the priority benefit under 35
U.S.C. .sctn.120 from the Nov. 27, 1995 filing date of U.S. patent
application Ser. No. 08/562,842, now U.S. Pat. No. 5,658,995. The
disclosures of the PCT Application and U.S. Pat. No. 5,658,995 are
incorporated herein by reference. The present application also
claims priority benefit of U.S. Provisional Application Ser. Nos.
60/064,905 filed Nov. 7, 1997 and 60/081,502 filed Apr. 13, 1998,
the disclosures of both of which are also incorporated herein by
reference thereto. This application also claims priority benefit of
U.S. patent application Ser. No. 09/056,050 filed Apr. 7, 1998,
which, in turn, claims the priority benefit of U.S. Provisional
Patent Ser. No. 60/064,656 filed on Nov. 7, 1997. The disclosures
of both the aforementioned standard U.S. patent application and the
U.S. provisional patent application from which it claims priority
benefit are also incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to copolymers of
tyrosine-based polycarbonates and poly(alkylene oxide) and to
methods of synthesizing such polymers.
[0003] Linear aromatic polycarbonates derived from diphenols such
as bisphenol-A represent an important class of condensation
polymers. Such polycarbonates are strong, tough, high melting
materials. They are well-known in the literature and are
commercially produced in large quantities.
[0004] The early investigations on block copolymers of
poly(bisphenol-A carbonate) and poly(alkylene oxide) started in
1961 and were conducted by the groups of Merrill and Goldberg.
Merrill, J. Polym. Sci., 55, 343-52 (1961) for the first time
introduced poly(alkylene oxide) blocks into poly(bisphenol-A
carbonate). Merrill described the interfacial copolymerization of
poly(bisphenol-A carbonate) (dissolved in methylene chloride) and
poly(alkylene oxide) bischloroformate (dissolved in aqueous sodium
hydroxide). The presence of flexible blocks of poly(alkylene oxide)
promoted the crystallization of the polycarbonate, which resulted
in flexible polymers with high melting points. Later on, Goldberg,
J. Polym. Sci., Part C, 4, 707-30 (1964) reported more work on
block copolymers of poly(bisphenol-A carbonate) and poly(ethylene
oxide). The incorporation of flexible, polar, water soluble block
segments into the rigid, linear, aromatic polycarbonate chains
produced elastomers with unusual thermal and plastic properties. In
particular Goldberg described the use of poly(ethylene oxide) as a
comonomer with bisphenol-A. The synthesis was based on the reaction
of phosgene with the mixture of monomers in pyridine followed by
purification of the copolymer by precipitation in isopropanol.
Copolymers were studied for structure-property correlations as a
function of poly(ethylene oxide) molecular weight and copolymer
composition. Remarkable strength and snappy elasticity were
observed at poly(ethylene oxide) block concentration greater than 3
mole-%. These thermoplastic elastomers also exhibited high
softening temperatures (>180.degree. C.) and tensile elongations
up to about 700%. Both glass transition temperature and softening
temperature varied linearly with the molar ratio of poly(ethylene
oxide). The early studies established that these copolymers are
good elastomers, but no medical applications were considered.
[0005] Later on, Tanisugi et al., Polym. J., 17(3), 499-508 (1985);
Tanisugi et al., Polym. J., 16(8), 633-40 (1984); Tanisugi et al.,
Polym. J., 17(8), 909-18(1984); Suzuki et al., Polym. J., 16(2),
129-38 (1983); and Suzuki et al., Polym. J., 15(1), 15-23 (1982)
reported detailed studies of mechanical relaxation, morphology,
water sorption, swelling, and the diffusion of water and ethanol
vapors through membranes made from the copolymers.
[0006] Mandenius et al., Biomaterials, 12(4), 369-73 (1991)
reported plasma protein absorption of the copolymer, compared to
polysulphone, polyamide and polyacrylonitrile as membranes for
blood purification. Adhesion of platelets onto Langmuir and solvent
cast films of the copolymers was also reported by Cho et al., J.
Biomed. Mat. Res., 27, 199-206 (1993). The use of copolymers of
poly(bisphenol-A carbonate) and poly(alkylene oxide) as
hemodialysis membrane or plasma separator was disclosed in U.S.
Pat. Nos. 4,308,145 and 5,084,173 and in EP 46,817; DE 2,713,283;
DE 2,932,737 and DE 2,932,761.
[0007] Heretofore, block copolymers of polycarbonates and
poly(alkylene oxide) have not been studied as medical implantation
materials. Although an extensive search of the literature revealed
no studies of in vitro or in vivo degradation, one of ordinary
skill in the art would not expect that the currently known block
copolymers of poly(bisphenol-A carbonate) and poly(alkylene oxide)
would degrade under physiological conditions at rates suitable for
the formulation of degradable implants.
[0008] U.S. Pat. Nos. 5,198,507 and 5,216,115 disclosed
tyrosine-derived diphenolic monomers, the chemical structure of
which was designed to be particularly useful in the polymerization
of polycarbonates, polyiminocarbonates and polyarylates. The
resulting polymers are useful as degradable polymers in general,
and as tissue compatible bioerodible materials for biomedical uses
in particular. The suitability of these polymers for this end-use
application is the result of their derivation from naturally
occurring metabolites, in particular, the amino acid
L-tyrosine.
[0009] Tyrosine-based polycarbonates are strong, tough, hydrophobic
materials that degrade slowly under physiological conditions. For
many medical applications such as drug delivery, non-thrombogenic
coatings, vascular grafts, wound treatment, artificial skin,
relatively soft materials are needed that are more hydrophilic and
degrade faster than the available tyrosine-based
polycarbonates.
SUMMARY OF THE INVENTION
[0010] In this invention, the introduction of poly(alkylene oxide)
segments into the backbone of tyrosine-based polycarbonates was
found to lead to softer, more hydrophilic polymers that exhibited
significantly increased rates of degradation. Since the previously
known block copolymers of poly(bisphenol-A carbonate) and
poly(alkylene oxide) apparently do not degrade appreciably under
physiological conditions, the finding was unexpected that the
incorporation of poly(alkylene oxide) into tyrosine-based
polycarbonate significantly increased the rate of degradation.
Furthermore, the disclosed copolymers of tyrosine-based
polycarbonate and poly(ethylene oxide) have an alkyl ester pendent
chain at each monomeric repeat unit. This pendent chain is an
unprecedented structural feature among the currently known block
copolymers of poly(bisphenol A carbonate) and poly(alkylene oxide).
As shown in more detail below, variation in the length of the
pendent chain can be used to fine-tune the polymer properties.
Studies of this kind are known in the literature for other polymer
systems, but have not been performed for block copolymers of
poly(bisphenol A carbonate) and poly(alkylene oxide). In addition,
the presence of a carboxylic acid containing pendent chain can
facilitate the attachment of biologically or pharmaceutically
active moieties to the polymer backbone. This, too, is an
unprecedented feature among the previously known copolymers of
bisphenol-A and poly(alkylene oxide).
[0011] Therefore, according to one aspect of the present invention,
a random block copolymer of a tyrosine-derived diphenol monomer and
a poly(alkylene oxide) is provided having the structure of Formula
I: 1
[0012] wherein R.sub.1 is --CH.dbd.CH-- or (--CH.sub.2--).sub.j, in
which j is zero or an integer from one to eight;
[0013] R.sub.2 is selected from straight and branched alkyl and
alkylaryl groups containing up to 18 carbon atoms and optionally
containing at least one ether linkage and derivatives of
biologically and pharmaceutically active compounds covalently
bonded to the copolymer;
[0014] each R.sub.3 is independently selected from alkylene groups
containing from 1 up to 4 carbon atoms;
[0015] y is between about 5 and about 3000; and
[0016] f is the percent molar fraction of alkylene oxide in the
copolymer, and ranges between about 1 and about 99 mole
percent.
[0017] Another important phenomena that was observed for the
copolymers is the temperature dependent inverse phase transition of
the polymer gel or the polymer solution in aqueous solvents.
Inverse temperature transitions have been observed for several
natural and synthetic polymer systems such as proteins and
protein-based polymers as described by Urry, Tissue Engineering:
Current Perspectives (Boston Birkhauser, New York), 199-206,
poly(acrylic acid) derived copolymers as described by Annaka et
al., Nature, 355, 430-32(1992); Tanaka et al., Phys. Rev. Lett.,
45(20), 1636-39(1980) and Hirokawa et al., J. Chem. Phys., 81(12),
6379-80(1984), and poly(ethylene glycol)-poly(propylene glycol)
copolymers as described by Armstrong et al., Macromol. Reports,
A31(suppl. 6&7), 1299-306(1994). Polymer gels and solutions of
these polymers are known to undergo continuous or discontinous
volume change upon changes in temperature, solvent composition, pH
or ionic composition. The driving forces for the phase change can
be attractive or repulsive electrostatic interactions, hydrogen
bonding or hydrophobic effects.
[0018] For nonionic synthetic polymers such as protein-based
bioelastic materials, poly(N-isopropylacrylamide) and poly(ethylene
glycol)-poly(propylene glycol) copolymers, as well as the
copolymers of the present invention, the driving force of phase
transition is the combination of hydrogen bonding and hydrophobic
effect. As the temperature increases, the gels of these polymers
undergo a phase transition from a swollen to a collapsed state,
while polymer solutions precipitate at certain temperature or
within certain temperature ranges. These polymers, including the
copolymers of the present invention, and especially those that
undergo a phase transition at about 30-40.degree. C. on heating can
be used as biomaterials for drug release and clinical implantation
materials. Specific applications include the prevention of
adhesions and tissue reconstruction.
[0019] Therefore, the present invention also includes implantable
medical devices containing the random block copolymers of the
present invention. In one embodiment of the present invention, the
copolymers are combined with a quantity of a biologically or
pharmaceutically active compound sufficient for therapeutically
effective site-specific or systemic drug delivery as described by
Gutowska et al., J. Biomater. Res., 29, 811-21 (1995) and Hoffman,
J. Controlled Release, 6, 297-305 (1987). In another embodiment of
the present invention, the copolymer is in the form of a sheet or a
coating applied to exposed injured tissue for use as a barrier for
the prevention of surgical adhesions as described by Urry et al.,
Mat. Res. Soc. Symp. Proc., 292, 253-64 (1993).
[0020] Furthermore, another aspect of the present invention
provides a method for site-specific or systemic drug delivery by
implanting in the body of a patient in need thereof an implantable
drug delivery device containing a therapeutically effective amount
of a biologically or physiologically active compound in combination
with the random block copolymer of the present invention. Yet
another aspect of the present invention provides a method for
preventing the formation of adhesions between injured tissues by
inserting as a barrier between the injured tissues a sheet or a
coating of the random block copolymer of the present invention.
[0021] As noted above, the tyrosine-derived diphenol monomers are
also useful in the polymerization of polyarylates. The introduction
of poly(alkylene oxide) segments into the backbone of
tyrosine-based polyarylates would also be expected to lead to
softer, more hydrophilic polymers with significantly increased
rates of degradation. Therefore, according to still yet another
aspect of the present invention, aliphatic and aromatic
polyarylates are provided, polymerized as random block copolymers
of a dicarboxylic acid with a tyrosine-derived diphenol and a
poly(alkylene oxide), wherein an equimolar combined quantity of the
diphenol and the poly(alkylene oxide) is reacted with a
dicarboxylic acid in a molar ratio of the diphenol to the
poly(alkylene oxide) between about 1:99 and about 99:1;
[0022] wherein the tyrosine-derived diphenol has the structure of
Formula II: 2
[0023] in which R.sub.1 and R.sub.2 are the same as described above
with respect to Formula I;
[0024] the dicarboxylic acid has the structure of Formula III:
3
[0025] in which R is selected from saturated and unsaturated,
substituted and unsubstituted alkyl, aryl and alkylaryl groups
containing up to 18 carbon atoms; and
[0026] the poly(alkylene oxide) has the structure of Formula
IV:
(--O--R.sub.3--).sub.y (IV)
[0027] in which each R.sub.3 is independently selected from
alkylene groups containing up to 4 carbon atoms and y is between
about 5 and about 3000.
[0028] The random block copolymers of the present invention
suitable for use as implantable medical devices, or in methods for
site-specific or systemic drug delivery, or in methods for
preventing the formation of adhesions between injured tissues
include the polyarylates of the present invention.
[0029] Copolymers based on tyrosine-derived diphenols and
poly(alkylene oxide) represent a new group of nonionic polymers
that show inverse temperature transitions. These copolymers contain
natural amino acids as building blocks, are degradable under
physiological conditions, and have been shown to be biocompatible.
By changing the tyrosine-derived diphenol, the poly(alkylene oxide)
and the ratio of the two components, the copolymers can be designed
and synthesized to exhibit desired transition temperatures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 depicts the glass transition temperatures of poly(DTE
co PEG.sub.1,000 carbonates) (O), poly(DTB co PEG.sub.1,000
carbonates) (.DELTA.) and poly(DTH co PEG.sub.1,000 carbonates)
(.diamond.) of the present invention having different PEG contents
and in comparison to corresponding polycarbonate homopolymers;
[0031] FIG. 2 depicts the water uptake of poly(DTE co 5%
PEG.sub.1,000 carbonate) (o), poly(DTE co 15% PEG.sub.1,000
carbonate) (.diamond.) and poly(DTE co 30% PEG.sub.1,000 carbonate)
(.DELTA.) measured as a function of incubation time at 37.degree.
C. in phosphate buffered saline;
[0032] FIG. 3 depicts the pNA release from poly(DTB carbonate) (O),
poly(DTB co 1% PEG.sub.1,000 carbonate) (.DELTA.) and poly(DTB co 5
% PEG.sub.1,000 carbonate) (.diamond.) microspheres measured as a
function of incubation time at 37.degree. C. in phosphate
buffer;
[0033] FIG. 4 depicts the FITC-dextran released from microspheres
made of poly(DTB carbonate) (.DELTA.), poly(DTB co 1% PEG.sub.1,000
carbonate) (.diamond.) and poly(DTB co 5% PEG.sub.1,000 carbonate)
(O) as a function of incubation time at 37.degree. C. in phosphate
buffered saline;
[0034] FIG. 5 depicts the molecular weight retention of
poly(bisphenol-A co 5% PEG.sub.1,000 carbonate) (.DELTA.), poly(DTE
co 5% PEG.sub.1,000 carbonate) (.diamond.) and poly(DTE co 30%
PEG.sub.1,000 carbonate) (O) as a function of incubation time at
37.degree. C. in phosphate buffered saline; and
[0035] FIG. 6 depicts a turbidity curve for poly(DTE co 70%
PEG.sub.1,000 carbonate) in water at 500 nm.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0036] The above-defined polymers of Formula I are random block
copolymers of the above-defined tyrosine-derived diphenols of
Formula II with the above-defined poly(alkylene oxide) of Formula
IV. The defined units of tyrosine-derived diphenols and
poly(alkylene oxide) do not imply the presence of defined blocks
within the structure of Formula I. The percent molar fraction of
alkylene oxide, f, in the copolymer may range between about 1 and
about 99 mole percent, with a molar fraction of alkylene oxide
between about 5 and about 95 mole percent being preferred. The mole
percent of alkylene oxide may vary over the entire range, with
polymers having levels of alkylene oxide higher than 5 mole percent
being resistant to cell attachment. Polymers with levels higher
than 70 mole percent are water soluble. Polymers with any level of
alkylene oxide are useful, in drug delivery, with water-soluble
compositions being preferred for drug-targeting applications.
[0037] The diphenols shown in Formula II are described in
co-pending and commonly owned U.S. patent application Ser. No.
08/414,339 filed Mar. 31, 1995. The disclosure of this patent is
incorporated herein by reference.
[0038] In Formula II, and thus consequently in Formula I, R.sub.1
is preferably --CH.sub.2--CH.sub.2-- and R.sub.2 is preferably a
straight chain ethyl, butyl, hexyl or octyl group. R.sub.2 may
contain at least one ether linkage. When R.sub.1 is
--CH.sub.2--CH.sub.2--, the diphenol compound of Formula I is
referred to as a desaminotyrosyl-tyrosine alkyl ester. The most
preferred member of the group of desaminotyrosyl-tyrosine alkyl
esters is the hexyl ester, referred to as desaminotyrosyl-tyrosine
hexyl ester or DTH.
[0039] The diphenol compounds may be prepared as described in the
above-referenced U.S. patent application Ser. No. 08/1414,339. The
method described in U.S. Pat. No. 5,099,060 may also be employed,
and is incorporated herein by reference.
[0040] The poly(alkylene oxide) shown in Formula IV can be any
commonly used alkylene oxide known in the art, as is preferably a
poly(ethylene oxide), poly(propylene oxide) or poly(tetra methylene
oxide). Poly(alkylene oxide) blocks containing ethylene oxide,
propylene oxide or tetramethylene oxide units in various
combinations are also possible constituents within the context of
the current invention.
[0041] The poly(alkylene oxide) is most preferably a poly(ethylene
oxide) in which y of Formula IV is between about 20 and about 200.
More preferred embodiments are obtained when poly(ethylene oxide)
blocks with a molecular weight of about 1,000 to about 20,000 g/mol
are used. For these preferred embodiments, in the structure of
Formula IV, both R.sub.3 groups are hydrogen and y has values from
about 22 to about 220. A value for y ranging between about 22 and
about 182 is even more preferred.
[0042] The random block copolymers of Formula I may be prepared by
the conventional methods for polymerizing diphenols into
polycarbonates described in the aforementioned U.S. Pat. No.
5,099,060, which methods are also incorporated herein by reference.
This involves the reaction of the desired ratio of tyrosine-derived
diphenol and poly(alkylene oxide) with phosgene or phosgene
precursors (e.g., diphosgene or triphosgene) in the presence of a
catalyst. Thus, the copolymers of Formula I may be prepared by
interfacial polycondensation, polycondensation in a homogeneous
phase or by transesterification. The suitable processes, associated
catalysts and solvents are known in the art and are taught in
Schnell, Chemistry and Physics of Polycarbonates, (Interscience,
New York 1964), the teachings of which are also incorporated herein
by reference. One of ordinary sill in the art will be able to
extend the disclosed techniques to the random block
copolymerization of a tyrosine-derived diphenol with a
poly(alkylene oxide) without undue experimentation.
[0043] The random block copolymers of Formula I have weight-average
molecular weights above about 20,000 daltons, and preferably above
about 30,000 daltons. The number-average molecular weights of the
random block copolymers of Formula I are above about 10,000
daltons, and preferably above about 20,000 daltons. Molecular
weight determinations are calculated from gel permeation
chromatography relative to polystyrene standards without further
correction.
[0044] As disclosed above, R.sub.2 of the random block copolymer of
Formula I and the tyrosine-derived diphenol of Formula II can be a
derivative of a biologically or pharmaceutically active compound
covalently bonded to the copolymer or diphenol. R.sub.2 is
covalently bonded to the copolymer or diphenol by means of an amide
bond when in the underivatized biologically or pharmaceutically
active compound a primary or secondary amine is present at the
position of the amide bond in the derivative. R.sub.2 is covalently
bonded to the copolymer or diphenol by means of an ester bond when
in the underivatized biologically or pharmaceutically active
compound a primary hydroxyl is present at the position of the ester
bond in the derivative. The biologically or pharmaceutically active
compound may also be derivatized at a ketone, aldehyde or
carboxylic acid group with a linkage moiety that is covalently
bonded to the copolymer or diphenol by means of an amide or ester
bond.
[0045] Examples of biologically or pharmaceutically active
compounds suitable for use with the present invention include
acyclovir, cephradine, malphalen, procaine, ephedrine, adriamycin,
daunomycin, plumbagin, atropine, quinine, digoxin, quinidine,
biologically active peptides, chlorin e.sub.6, cephradine,
cephalothin, melphalan, penicillin V, aspirin, nicotinic acid,
chemodeoxycholic acid, chlorambucil, and the like. The compounds
are covalently bonded to the copolymer or diphenol by methods well
understood by those of ordinary skill in the art. Drug delivery
compounds may also be formed by physically blending the
biologically or pharmaceutically active compound to be delivered
with the random block copolymers of the present invention using
conventional techniques well-known to those of ordinary skill in
the art.
[0046] The tyrosine-derived diphenol compounds of Formula II and
the poly(alkylene oxide) of Formula IV may also be reacted
according to the method disclosed by U.S. Pat. No. 5,216,115 to
form polyarylates, the disclosure of which is hereby incorporated
by reference thereto. As disclosed by U.S. Pat. No. 5,216,115, the
diphenol compounds are reacted with the aliphatic or aromatic
dicarboxylic acids of Formula III in a carbodiimide mediated direct
polyesterification using 4-(dimethylamino)pyridinium-p-toluene
sulfonate (DPTS) as a catalyst to form aliphatic or aromatic
polyarylates. Random block copolymers with poly(alkylene oxide) may
be formed by substituting poly(alkylene oxide) for the tyrosine
derived diphenol compound in an amount effective to provide the
desired ratio of diphenol to poly(alkylene oxide) in the random
block copolymer.
[0047] The random block copolymers of the present invention, both
polycarbonate and polyarylates, can be worked up by known methods
commonly employed in the field of synthetic polymers to produce a
variety of useful articles with valuable physical and chemical
properties, all derived from tissue-compatible monomers. The useful
articles can be shaped by conventional polymer-forming techniques
such as extrusion, compression molding, injection molding, solvent
casting, spin casting, and the like. Shaped articles prepared from
the polymers are useful, inter alia, as degradable biomaterials for
medical implant applications. Such applications include the use of
the shaped articles as vascular grafts and stents, bone plates,
sutures, implantable sensors, barriers for surgical adhesion
prevention, implantable drug delivery devices, scaffolds for tissue
regeneration, and other therapeutic aids and articles which
decompose harmlessly within a known period of time. The polymers
can also be formed as a coating on the surface of implants by
conventional dipping or spray coating techniques to prevent the
formation of adhesions on the implant.
[0048] Implantable articles formed from the random block copolymers
of the present invention must be sterile. Sterility is readily
accomplished by conventional methods such as irradiation or
treatment with gases or heat.
[0049] The following non-limiting examples set forth hereinbelow
illustrate certain aspects of the invention. All parts and
percentages are by weight unless otherwise noted and all
temperatures are in degrees Celsius.
[0050] MATERIALS AND METHODS
[0051] Materials
[0052] L-Tyrosine, thionyl chloride, pyridine, methylene chloride,
tetrahydrofuran (THF), ethanol, butanol, hexanol, octanol,
3-(4-hydroxy-phenyl)propionic acid (desaminotyrosine, Dat),
dicyclohexyl carbodiimide (DCC), and hydroxybenzotriazole (HOBt)
were obtained from Aldrich, phosgene (solution in toluene) was
obtained from Fluka. All solvents were of HPLC grade and were used
as received.
[0053] Spin Casting
[0054] The bottom glass slide of dual chamber units (#177380, Nunc,
Inc.) was spin cast first with a styrene silane copolymer solution
(2.5% w/v in ethyl acetate), as described by Ertel et al., J.
Biomat. Sci. Polym. Edn., 3, 163-83 (1991), which served as a
coupling agent, and then with the polymer solution (2% w/v in
methylene chloride) for 30 s at 800 rpm. The coated slides were
dried under vacuum for one week prior to cell culture.
Poly(bisphenol-A carbonate) was similarly spin cast and included as
a control in the cell growth studies.
[0055] Compression Molding
[0056] Thin polymer films were prepared by compression molding.
Processing temperature was 30-35.degree. C. above Tg for each
polymer. To minimize polymer adhesion to the metal plates of the
mold, two teflon sheets were added between the polymer and metal
plates of the mold.
[0057] Spectroscopy
[0058] FT-IR spectra were recorded on a Matson Cygnus 100
spectrometer. Polymer samples were dissolved in methylene chloride
and films were cast directly onto NaCl plates. All spectra were
collected after 16 scans at 2 cm.sup.-1 resolution. UV/Vis spectra
were recorded on a Perkin-Elmer Lambda 3B spectrophotometer. NMR
spectra of polymer solutions in deuterated chloroform were recorded
on a Varian VXR-200 spectrometer (64 scans).
[0059] Gel Permeation Chromatography (GPC)
[0060] The chromatographic system consisted of a Perkin-Elmer Model
410 pump, a Waters Model 410 RI detector, and a PE-Nelson Model
2600 computerized data station. Two PL-gel GPC columns (pore size
10.sup.5 and 10.sup.3 .ANG.) were operated in series at a flow rate
of 1 ml/min using THF. Molecular weights were calculated relative
to polystyrene standards without further correction.
[0061] Thermal Analysis
[0062] The glass transition temperature (T.sub.g) was determined by
differential scanning calorimetry (DSC) on a DuPont 910 DSC
instrument calibrated with indium. Each specimen was subjected to
two consecutive DSC scans. After the first run the specimen was
quenched with liquid nitrogen and the second scan was performed
immediately thereafter. T.sub.gwas determined in the second DSC
scan as the midpoint. The heating rate for all polymers was
10.degree. C./min and the average sample size was 10 mg.
[0063] Water Uptake
[0064] A piece of copolymer (15-20 mg) was cut from a film
incubated in PBS at 37.degree. C., and wiped to remove water on the
surface of the sample. Water content (WC in %) was determined by
thermogravimetric analysis (TGA) on a DuPont 951 TGA instrument at
a heating rate of 10.degree. C./min and was reported as percentage
weight lost below 200.degree. C. Water uptake was calculated as
WC/(1-WC).
[0065] Hydrolytic Degradation Studies
[0066] Samples were cut from compression molded films and incubated
at 37.degree. C in phosphate buffer saline (0.1 M, pH 7.4) (PBS)
containing 200 mg/L of sodium azide to inhibit bacterial growth.
The degradation process was followed by recording weekly the
changes in the molecular weight of the polymer. Results are the
average of two separate specimens per polymer.
[0067] Microsphere Processing
[0068] Microspheres were prepared by solvent evaporation as
described by Mathiowitz et al., J. App Polym. Sci., 35, 755-74
(1988). 0.05 g of copolymer was dissolved in 1 mL of methylene
chloride. The polymer solution was injected into 50 mL of an
aqueous solution of poly(vinyl alcohol) (PVA) in a 150 mL beaker
with 3 baffles. The mixture was stirred by a overhead stirrer with
a propeller at 1300 rpm. After 4 h of stirring, the microspheres
were collected by membrane filtration and washed 6 times with water
to remove as much PVA as possible. Then the microspheres were dried
to constant weight under high vacuum.
[0069] Drug Loading and Release
[0070] p-Nitroaniline (pNA) was dissolved in the polymer solution
followed by microsphere formation as described above. pNA loading
was determined by UV spectroscopy (.lambda.=380 nm) after complete
dissolution of an exactly weighed amount of microspheres in
methylene chloride.
[0071] FITC-dextrans were dissolved in 50 ml of water and dispersed
in the polymer solution by sonication (w/o/w method) followed by
microsphere formation as described above. To determine the
FITC-dextran loading, the microspheres were dissolved in methylene
chloride and the FITC-dextran was extracted into aqueous phosphate
buffer solution (0.1 M, pH 7.4) followed by florescence
spectrophotometry (excitation: 495 nm, emission: 520 nm).
[0072] An exactly weighed amount of pNA or FITC-dextran loaded
microspheres were placed in an exactly measured volume of phosphate
buffer solution (0.1 M, pH 7.4) at 37.degree. C. in a water shaker
bath. The amount of pNA or FITC-dextran released into the buffer
solution was determined as described above.
[0073] Cell Growth
[0074] Fetal rat lung fibroblasts (#CCL192, American Tissue Culture
Collection) were grown in Ryan Red medium with 50 mg/ml sodium
ascorbate and 10% fetal calf serum as described by Poiani et al.,
Amino Acids, 4, 237-48 (1993) and Ryan et al., Tiss. Cult. Meth.,
10, 3-5 (1986). For polymer evaluation, the dual chamber units
(#177380, Nunc, Inc.) were spin cast first with a styrene silane
copolymer solution (2.5% w/v in ethyl acetate), which served as a
coupling agent, and then with the polymer solution of interest.
Unmodified plastic (#177429, Nunc) and glass dual chamber units
(#177380, Nunc) served as controls and were used as received. Prior
to cell seeding, all surfaces were incubated for 3 hours with PBS
containing 5 % penicillin-streptomycin. Cells from passage 5 were
subsequently seeded at a density of 10.sup.4 cells/cm.sup.2. After
1 or 5 days of incubation, the cells were gently rinsed with PBS,
and trypsinized from 3 separate chambers. The suspension was
counted 4 times in a hemocytometer.
[0075] Measurement of Inverse Temperature Transition
[0076] The detection of inverse phase transition is based on the
increase in turbidity as the initial soluble polymerprecipitates
upon heating. The increase in turbidity is monitored by visible
spectroscopy as described below.
[0077] Polymer solutions: Optical Density (OD) measurements for
0.05% (w/v) polymer aqueous solutions were performed at 500 nm on a
diode array spectrophotomer (Hewlett Packard, Model 8452-A) with a
water-jacketed cell holder coupled with a refrigerated circulating
bath (Neslab, model RTE-8). Temperature was manually controlled at
rates of 0.5.degree. C./min. and monitored by a microprocessor
thermometer (Omega, model HH22). The initial breaking point in the
resulting optical density versus temperature curve was taken as the
onset of the temperature of transition.
[0078] Nomenclature
[0079] Copolymer structure and composition is represented in the
following way: in poly(DTX co fPEG.sub.Mw carbonate), X relates to
the length of the alkyl ester pendent chain. In the examples
described below E (ethyl), B (butyl), and H (hexyl) were used. The
percent molar fraction of poly(ethylene oxide) content in the
copolymer is represented by the letter f. In the samples listed
below, the value of f was varied from 1 to 70 mole%. M.sub.w
represents the average molecular weight of the PEG blocks used in
the synthesis of the copolymer. Thus, Poly (DTE co 5% PEG.sub.1,000
carbonate) refers to a copolymer prepared from the ethyl ester of
desaminotyrosyl-tyrosine, and 5 mole % of PEG blocks having an
average molecular weight of 1000 g/mol.
EXAMPLES
Example 1
[0080] Poly(DTE co 5% PEG.sub.1,000 carbonate) was synthesized as
follows:
[0081] 10.85 g of DTE (30.4 mmole) and 1.57 g of PEG.sub.1,000
(1.59 mmole) were placed into a 250 ml flask. Then 60 ml of dry
methylene chloride and 9.6 ml of anhydrous pyridine were added. At
room temperature, 20.6 ml of a 1.93 M solution of phosgene in
toluene was added slowly to the solution with overhead stirring
during 90 minutes. 180 ml THF was added to dilute the reaction
mixture. The copolymer was precipitated by slowly adding the
mixture into 2400 ml of ethyl ether. The copolymer was redissolved
in 220 ml THF (5% w/v solution) and reprecipitated by slowly adding
the polymer solution into 2200 ml of water.
[0082] 10.8 g of a white copolymer was obtained. As determined by
GPC using THF as the solvent, the copolymer has a weight average
molecular weight of 127,000 daltons, a number average molecular
weight of 84,000 daltons and a polydispersity of 1.5.
Example 2
[0083] Poly(DTE co 30% PEG.sub.1,000 carbonate) was synthesized as
follows:
[0084] 5.23 g of DTE (14.6 mmole) and 6.20 g of PEG.sub.1,000 (6.27
mmole) were placed into a 250 ml flask. Then 60 ml of dry methylene
chloride and 6.7 ml of anhydrous pyridine were added. At room
temperature, 13.5 ml of a 1.93 M solution of phosgene in toluene
was added slowly to the solution with overhead stirring during 90
minutes. 180 ml THF was added to dilute the reaction mixture. The
copolymer was precipitated by slowly adding the mixture into 2400
ml of ethyl ether. The copolymer was redissolved in 200 ml THF (5%
w/v solution) and reprecipitated by slowly adding the polymer
solution into 2000 ml of water.
[0085] 8.9 g of a white copolymer was obtained. As determined by
GPC using THF as the solvent, the copolymer has a weight average
molecular weight of 41,000 daltons, a number average molecular
weight of 31,000 daltons and a polydispersity of 1.3.
Example 3
[0086] Poly(DTO co 5% PEG.sub.1,000 carbonate) was synthesized as
follows:
[0087] 9.23 g of DTO (20.9 mmole) and 1.09 g of PEG.sub.1,000 (1.1
mmole) were placed into a 250 ml flask. Then 50 ml of dry methylene
chloride and 7.0 ml of anhydrous pyridine were added. At room
temperature, 14.3 ml of a 1.93 M solution of phosgene in toluene
was added slowly to the solution with overhead stirring during 90
minutes. 150 ml ThF was added to dilute the reaction mixture. The
copolymer was precipitated by slowly adding the mixture into 2000
ml of ethyl ether. The copolymer was redissolved in 200 ml THF (5%
w/v solution) and reprecipitated by slowly adding the polymer
solution into 2000 ml of water.
[0088] 9.1 g of a white copolymer was obtained. As determined by
GPC using ThF as the solvent, the copolymer has a weight average
molecular weight of 32,000 daltons, a number average molecular
weight of 13,000 daltons and a polydispersity of 2.5.
Example 4
[0089] Poly(DTE co 0.262% PEG.sub.20,000 carbonate) was synthesized
as follows:
[0090] 10.24 g of DTE (28.6 mmole) and 1.5 g of PEG.sub.20,000
(0.075 mmole) were placed into a 250 ml flask. Then 60 ml of dry
methylene chloride and 8.7 ml of anhydrous pyridine were added. At
room temperature 18.6 ml of a 1.93 M solution of phosgene in
toluene was added slowly to the solution with overhead stirring
during 90 minutes. 180 ml THF was added to dilute the reaction
mixture. The copolymer was precipitated by slowly adding the
mixture into 2400 ml of ethyl ether. The copolymer was redissolved
in 220 ml THF (5% w/v solution) and reprecipitated by slowly adding
the polymer solution into 2200 ml of water.
[0091] 10.1 g of a white copolymer was obtained. As determined by
GPC using THF as the solvent, the copolymer has a weight average
molecular weight of 178,000 daltons, a number average molecular
weight of 84,000 daltons and a polydispersity of 2.1.
Example 5
[0092] Poly(DTE co 70% PEG.sub.1,000 carbonate) is water soluble,
so in the final purification step, isopropanol was used instead of
water:
[0093] 1.29 g of DTE (3.60 mmole) and 8.31 g of PEG.sub.1,000 (8.40
mmole) were placed into a 250 ml flask. Then 50 ml of dry methylene
chloride and 3.6 ml of anhydrous pyridine were added. At room
temperature, 7.8 ml of a 1.93 M solution of phosgene in toluene was
added slowly to the solution with overhead stirring during 90
minutes. 150 ml THE was added to dilute the reaction mixture. The
copolymer was precipitated by slowly adding the mixture into 2000
ml of ethyl ether. The copolymer was redissolved in 70 ml THF (5%
w/v solution) and reprecipitated by slowly adding the polymer
solution into 700 ml of isopropanol.
[0094] 6.4 g of a white copolymer was obtained. As determined by
GPC using THF as the solvent, the copolymer has a weight average
molecular weight of 47,000 daltons, a number average molecular
weight of 37,000 daltons and a polydispersity of 1.3.
[0095] Poly(DTB co 1% PEG.sub.1,000 carbonate), Poly(DTB co 5%
PEG.sub.1,000 carbonate), Poly(DTB co 10% PEG.sub.1,000 carbonate),
Poly(DTH co co 1% PEG.sub.1,000 carbonate), Poly(DTH co 5%
PEG.sub.1,000 carbonate), Poly(DTH co 10% PEG.sub.1,000 carbonate),
Poly(DTH co 20% PEG.sub.1,000 carbonate) and poly(bisphenol-A co 5%
PEG.sub.1,000 carbonate) were synthesized by similar methods and
used for different studies.
Polymer Characterization
[0096] Glass transition temperature
[0097] Copolymers were prepared according to the examples given
above. The glass transition temperature (T.sub.g) of these
copolymers and their corresponding polycarbonate homopolymers were
measured (FIG. 1). In each series of copolymers, T.sub.gof the
copolymers decreased as the molar fraction of PEG.sub.1,000
increased.
[0098] Mechanical Properties
[0099] Tensile modulus: The dry specimens of poly(DTE co 5%
PEG.sub.1,000 carbonate) had tensile modulus of 1.3 Gpa, which is
comparable to all tyrosine-derived polycarbonates which have
tensile modulus within a range of 1.2-1.6 Gpa. See Ertel et al., J.
Biomed. Mater. Res., 28, 919-930 (1994). After 24 h of incubation,
the specimens had 10% of water uptake, and the tensile modulus
dropped to 0.58 Gpa.
[0100] Tensile strength at yield and break: The combination of PEG
into the backbone of the tyrosine derived polymer had a profound
effect on the tensile strength and ductility of the polymer. While
poly(DTE carbonate) was very brittle and failed without yielding
after 4% elongation (See the aforementioned Ertel et. al., J.
Biomed. Mater. Res., 28, 919-930 (1994)), the poly(DTE co 5%
PEG.sub.1,000 carbonate) did manage to elongate up to 153% before
failing. The tensile strength at yield was 41 MPa, at break was 22
MPa. The incubated copolymer became extremely ductile. Film
specimens yielded after 6% elongation and failed after up to 650%
elongation. The tensile strength at yield was 15 MPa, at break was
19 MPa.
[0101] Water Uptake
[0102] The amount of water taken up by thin, compression molded
films of poly(DTE co PEG.sub.1,000 carbonates) was determined as
described in the experimental section. The compression molded test
specimens contained 5 mol %, 15 mol %, or 30 mol % of PEG. Over a 5
h period, poly(DTE co 5% PEG.sub.1,000 carbonate) reached an
equilibrium water uptake of 10%. For poly(DTE co 15% PEG.sub.1,000
carbonate), the equilibrium water uptake after 1 h was 25%. For
poly(DTE co 30% PEG.sub.1,000 carbonate) the equilibrium water
uptake after only 1 h was 92%. The rate of water uptake and the
equilibrium water content increased as the molar fraction of
poly(ethylene oxide) increased (FIG. 2). At poly(ethylene oxide)
contents above 20%, the copolymers behave increasingly like
hydrogels.
[0103] Microsphere Formation and Drug Release
[0104] The formation of microspheres was studied using poly(DTB co
PEG.sub.1,000 carbonates). The homopolymer, poly(DTB carbonate) was
included in the studies as control. Next, microspheres were
formulated containing either pNA or FITC-dextran. These compounds
are useful models for low molecular weight hydrophobic drugs and
high molecular weight hydrophilic drugs respectively. As a general
rule, microspheres could only be isolated when the PEG content was
below 10%. Above that value, microspheres formed initially, but
tended to adhere to each other and formed a gum-like precipitate
during work up. Thus, free flowing microspheres were formed for the
poly(DTB carbonate) and for poly(DTB co 1% PEG.sub.1,000 carbonate)
and poly(DTB co 5% PEG.sub.1000 carbonate). For poly(DTB co10%
PEG.sub.1,000 carbonate), no microspheres could be isolated.
[0105] It was an unexpected finding that the presence of even very
small molar fractions of poly(alkylene oxide) had a significant
effect on the drug release rate. This is illustrated in FIG. 3,
showing the cumulative release of pNA from the series of copolymers
of DTB and PEG.sub.1000.
[0106] The release of FITC-dextran from microspheres made of the
homopolymers was extremely slow. The typical release profile for
FTIC-dextran from the homopolymers was characterized by a short
burst effect followed by a very long lag period during which no
further FITC-dextran was released from the microspheres. Including
1 to 5% of PEG.sub.1,000 in the polymer composition led to a
significant increase in the amount of FITC-dextran that was rapidly
released from the microspheres (FIG. 4). Thus, the disclosed
copolymers can assist in the formulation of controlled drug release
systems for hydrophilic, high molecular weight drugs.
[0107] Degradation in Vitro
[0108] Degradation study was performed for two poly(DTE co
PEG.sub.1,000 carbonates) with poly(bisphenol-A co 5% PEG.sub.1,000
carbonate) as control. After one day of incubation in buffer at
37.degree. C., thin film specimens of all copolymers had adsorbed
water and reached saturation. Contrary to the industrially used
very slowly degrading poly(bisphenol-A co PEG carbonates) the
tyrosine-derived poly(DTX co PEG carbonates) degraded fast under
physiological conditions in vitro, as demonstrated by GPC.
[0109] The changes in the molecular weight over time were followed
for all three polymers. When the changes were plotted as percent
molecular weight retention vs. time, all three polymers had similar
degradation profiles, shown for poly(bisphenol-A co 5%
PEG.sub.1,000 carbonate), poly(DTE co 5% PEG.sub.1,000 carbonate)
and poly(DET co. 30% PEG.sub.1,000 carbonate) in FIG. 5. During
nine weeks of observation, poly(bisphenol-A co 5% PEG.sub.1,000
carbonate) lost only about 15% of its molecular weight while
poly(DTE co 5% PEG.sub.1,000 carbonate) and poly(DTE co 30%
PEG.sub.1,000 carbonate) lost about 60% and 75% of their molecular
weight.
[0110] Inverse Temperature Transition
[0111] FIG. 6 illustrates the inverse temperature transition for
poly(DTE Co 70% PEG.sub.1,000 carbonate). This polymer is initially
in solution as shown by its low absorbence at 500 nm. Upon heating,
the polymer precipitates, as indicated by the increasing
absorbance. In this particular case, the phase transition starts at
57.+-.1.degree. C.
[0112] Cell Growth
[0113] The interactions of the polymer with living cells provides
important information about possible medical applications. In vitro
studies of cell growth also provide an indication of the possible
cytotoxicity of a polymer. Such studies are recognized as the first
screening tests in the biocompatibility evaluation of medical
implant materials according to the FDA Tripartide Biocompatibility
guidelines.
[0114] Cell growth and spreading decreased as the molar fraction of
PEG present in the copolymer increased (Table I). This can be
explained by reduced cellular attachment due to the high mobility
of the PEG block on the polymer surface. An alternative explanation
is based on the general tendency of PEG to prevent the adsorption
of proteins onto surfaces. Thus, when PEG is part of the polymer
structure, less proteins may be adsorbed to the polymer surface
which, in turn, reduces the ability of cells to attach to the
surface. It was an unexpected finding that as little as 5% of
PEG.sub.1,000 in the copolymer was sufficient to eliminate almost
completely the ability of rat lung fibroblasts cells to attach and
grow on the copolymer surfaces. The unattached cells float in the
medium and aggregate to each other. Viability tests using trypan
blue and calcein AM show that these cells remain viable even after
5 days. This demonstrated that the copolymers are
non-cytotoxic.
1TABLE I Cell Attachment And Proliferation On Surfaces Of
Copolymers Attachment Proliferation PEG Copolymer (.times. 100
cell/cm.sup.2) Diphenol Mole % PEG 1 day 5 days DTE 0 46 .+-. 13
596 .+-. 100 5 8 .+-. 8 46 .+-. 14 15 4 .+-. 5 11 .+-. 10 30 3 .+-.
5 11 .+-. 10 DTB 0 56 .+-. 17 401 .+-. 79 1 50 .+-. 14 163 .+-. 40
5 16 .+-. 10 18 .+-. 13 10 9 .+-. 9 7 .+-. 7 DTH 0 32 .+-. 10 268
.+-. 46 1 52 .+-. 31 275 .+-. 71 5 9 .+-. 11 3 .+-. 7 10 9 .+-. 11
11 .+-. 14 Control surfaces glass 50 .+-. 16 555 .+-. 91 poly(BPA
carbonate) 17 .+-. 10 123 .+-. 37
[0115] The foregoing examples and description of the preferred
embodiment should be taken as illustrating, rather than as
limiting, the present invention as defined by the claims. As will
be readily appreciated, numerous variations and combinations of the
features set forth above can be utilized without departing from the
present invention as set forth in the claims. Such variations are
not regarded as a departure from the spirit and scope of the
invention, and all such modifications are intended to be included
within the scope of the following claims.
* * * * *