CA2165890A1

CA2165890A1 - Crosslinked acidic polysaccharides and their uses

Info

Publication number: CA2165890A1
Application number: CA 2165890
Authority: CA
Inventors: Tuyen T. Nguyen
Original assignee: Hercules LLC
Current assignee: Hercules LLC
Priority date: 1994-12-22
Filing date: 1995-12-21
Publication date: 1996-06-23
Also published as: BR9505996A; AU697534B2; JPH08253504A; KR960022568A; CN1131675A; EP0718312A3; AR000523A1; EP0718312A2; US5690961A; AU4063495A; MX9600065A; PL312026A1

Abstract

Acidic polysaccharides crosslinked by reaction with di- or polyanhydrides. The use of anhydride-crosslinked hyaluronic acid as a treatment for arthritis, as a drug delivery vehicle, to reduce the incidence of post-operative adhesion formation, to promote the healing of chronic wounds and ulcers, and as a component of cosmetic formulations.

Description

2 1 ~

This invention relateQ to acidic polysaccharideQ
crosslinked by reaction with di- or polyanhydrides, and preferably hyaluronic acid crosslinked with dianhydrides.
The crosslinked hyaluronic acid may be used as a treatment for arthritis, as a drug deli~ery vehicle, to reduce the incidence of p~Qt-operat~ve adhesion formation, to promote the healing of chronic wound-Q and ulcers, and as a component of cosmetic formulationQ.
The synovial fluid found in m~mm~lian joints functions as a lubricant and shock absorber. The most important component of the synovial fluid is sodium hyaluronate, which makes the greatest contribution to the m~rh~n~cal properties of the fluid. ~yaluronic acid is a naturally occurring high molecular weight glycosaminoglycan having a repeating disaccharide unit of D-glucuronic acid and N-acetylglucosamino-2-acetamido-2-deso~y-D-glucose joined by a ~1-3 glucosidic bond. The disaccharides are joined to form an unbranched, uncrosslinked polys~cch~ride chain by ~1~4 glucosidic bonds. In addition to its presence in synovial fluids, hyaluronic acid occur-Q in cell coats, pericellular gels, the e~tracellular matris substance of connective tissues of vertebrates, the vitreous humor of the eye, human umbilical cord tissue, rooster combs and in some bacteria.

Q

In healthy synovial fluid, the molecular weight of the sodium hyaluronate is very high, ranging from 1,600,000 to 10,900,000. Because the molecular weight is so high, even d lute solutions e~hibit significant viscoelastic properties. In typical human synovial fluid the concentration of sodium hyaluronate is about 0.3%.
During inflammation of a joint caused by osteo- or rheumatoid arthritis both the molecular weight of hyaluronic acid and its concentration are reduced. This lowering of molecular weight decreases the ability of synovial fluid to act as a shock absorber, and thus the fluid does not provide adequate protection for the cartilage of the joint. In the case of advanced arthri~is ~e cartilage is corroded away, leading to pain when t~e joint is in m~tion (see for e~ample, "The Merck Manual of Diagnosis and Therapy-16th Edition", p 1338-42).
Relatively ~ derate ~ lecular weight sodium hyaluronate has been used successfully as a supplemental synovial fluid in the leg joint of race horses (Balazs et al., J. Equine Vet. Sci., p. 217-228, 1985). ~owever human synovial fluid contains substantially higher molecular weight sodium hyaluronate than that of horse~.
Solutions of sodium hyaluronate also have been tested as supplemental synovial fluid for human osteoarthritic joints by injection into the joints. Treatment of arthritis by injection of sodium hyaluronate has been disclosed by 2~

Weiss et al., Semin. Arthriti~ Rheum., 11, p. 143, (1981);
Nakimi et al., J. Clin. phArmrol. Therapy Tosicology, 20, p.
501, (1982); Greco~ ro et al., Pharmatherapeutica, 5, p.
137, (1987) and Briganiti et al., Clinical Trials Journal, 24, p. 333, (1987). ~owever, the ~ st recent evaluations of such proce~ures in~icate that intra-articular injections of sodium hyaluronate solutions do not perform mea3urably differently from placeboq (Dahlberg et al., in "Arthritis &
Rheumatism" 37, p.521, 1994). Brown et al. in Esp. Physiol.
_ , p.125, (1991), showed that the half-life of hyaluronic acid injected in a joint i-~ only about 13 hour~. Dahlberg, vide supra, ha~ pointed out that a 13 hour half-life i~
short for therapeutic value.
One of the causes for the high rate of loss of sodium hyaluronate from the synovial cavity i-Q the degradation of the molecule by enzymes and hydrosy radicals. Enzymes such as hyaluronidase, glucuronidase and glucosidase are found in the human body (A.J. Bollet, J. Biological Chem., 238, p. 3522, 1963). The most active enzyme is hyaluronidase, which CUtQ sodium hyaluronate along the backbone. The other two enzymes attack the polymer from the end~.
~ydro~y radical~ come from two ~ources. The primary source is white blood cells, where macrophage-~ and neutrophils release santhine perosidase and other enzymes to form supero~ide anion, hydrogen pero~ide and hypochlorite, which upon breakdown form hydro~y radical. Another source ~1fi~

for hydrosy radical i5 the reduction of osygen by reducing agents in the presence of iron. A comm~n reducing agent in the body is ascorbic acid. Oxygen i~ reduced by iron(II) to form superoxide anion, which then reacts with iron (III) to form hydrogen peroside. ~ydrogen peroside i~ reduced to hydrosy radical.
Increasing the molecular weight of sodium hyaluronate by cross~ ng has been accomplished in a number of ways.
Sakurai et al. in U.S. Patent No. 4,716,224, disclo~e crosslinked hyaluronic acid or salts thereof prepared by crosslinking hya~ur~nic acid or itQ salt~ with a polyfunctional epoxide. The cro~ e~ compo~ition~ are stated to be resistant to hyaluronidase enzyme and possibly to be useful in treatment of arthritis and a~ a component of cosmetics. In U.S. Patent No. 4,863,907 Sakurai et al.
disclose crosslinked glycosaminoglycan or salt~ thereof, prepared by crosslinking a glycosaminoglycan or a salt thereof with a polyfunctional eposy compound. The crosslinked compositions are stated to have escellent resistance to glycosidase enzyme and to be useful in medical deviceQ, ophth~lmologic drug-~ and cosmRticQ.
~uang et al., in European Patent Application No. 0 507 604 A2, disclose ionically crosslinked carbosyl-cont~;ning polysaccharides where the cross~ ing agent is a compound possessing a trivalent cation. The compositions are stated 2 ~

to be useful in preventing po~t-operati~e adhesion formation following surgery.
Malson et al., in U.S. Patent No. 4,716,154 disclose crosslinking hyaluronic acid with bi- or polyfunctional eposideQ or their corre~ponding halohydrinQ, epihalohydrins or halides, and divinyl sulfone. The croQ~linked materials are said to be useful a-~ substitutes for ~itreous humor of the eye. Malson et al., in U.S. Patent No. 4,772,419 also disclose crosslinking hyaluronic acid with polyfunctional eposide Q .
In U.S. Patent No. 4,957,744 della Valle et al.
disclose crosslinked esters of hyaluronic acid prepared by esterifying the carbosyl groups of hyaluronic acid with polyhydric alcohols. It is proposed that the crosslinked material~ be used aq therapeutic agentQ, e.g. as drugs for treatment of arthriti~, and a~ ingredient~ of cosmRtic formulations.
Balazs et al., in U.S. Patent Nos. 4,582,865, 4,605,691 and 4,636,524, disclose crosslinking of hyaluronic acid and its ~alts, and of other polysaccharides, by reaction with divinylsulfone. In U.S. Patent Nos. 5,128,326 and 4,582,865, Balazs et al. disclose crosslinking hyaluronic acid with formaldehyde, eposide~, polyaziridyl compound-~ and di~inyl sulfone. In U.S. Patent No. 4,713,448 Balaz~ et al.
disclose chemically m~difying hyaluronic acid by reaction with aldehydes such as formaldehyde, glutaraldehyde and ~ 658~

glyosal, and teach the possibility that crosslin~;ng ha-Q
occurred. In U.S. Patent Nos. 4,582,865, 4,605,691, 4,636,524, 5,128,326, 4,582,865 and 4,713,448 the uses disclosed for the productQ are cosmetic formulations and drug delivery systemQ.
In U.S. Patent No. 5,356,883 Ruo et al. disclose crosslinking hyaluronic acid by reaction with biscarbodiimides. The hydrogelQ that are produced are taught to have utility as biocompatible gel, film~ or sponges.
This invention pertainQ to crosQlin~e~ compo-Qitions comprising linked polysaccharideQ cont~ining acidic groups or their salts, wherein at leaQt one hydrosyl group of each linked polysaccharide is esterified with a carbosyl group contained in a polycarbosylic acid cont~; n; ng at least four carbosyl group~, and at least two carbosyl group~ of the polycarbosylic acid are esterified with hydrosyl groups of the polysaccharides. A novel feature of the cro~-Qlinked compo-Qitions is the ester linkage formed from hydrosyl groupQ on the polysaccharide and the tetracarbosylic acid.
In a preferred ~m~o~im~ he ~olysAccha-i~e comprises hyaluronic acid or a salt of hyaluronic acid; the polycarbosylic acid iQ a tetracarbosylic acid, and the crosslinked composition ha~ substantially greater resistance to the enzyme hyaluronidase and to hydrosy radicalQ than hyaluronic acid or its sodium salt.

In another embodiment the invention pertain~ to a mRthod for crosslinking a polysaccharide cont~ining acidic groups which comprises reacting the polysaccharide with a d-- or polyanhydride.
In another embodiment the invention also pertains to pharmaceutical composition~ for treating m~mm~l ian arthritis, for preventing post-operative adhesion formation and for promoting the healing of chronic wounds, comprising as the active com~onent the crosslinked hyaluronic acid of this invention, or it~ pharmaceutically acceptable salts.
In a further em~odLment the i~ention pertains to drug delivery systems and cosmetic composition-~ compri~ing the crosslinked hyaluronic acid of this invention.
In yet another embodiment the invention pertains to methods for treating m~mm~l ian arthritis, reducing the incidence of post-operative adhesion formation and promoting the healing of chronic wound~ and ulcer~ comprising injecting or applying an effec~ive ~mou~ of a pharmaceutical composition comprising as the active component the crosslinke~ hyaluronic acid of this invention, or its pharmaceutically acceptable salts.
The crosslinked compositions of thi~ invention comprise linked polysaccharides containing acidic groups or their salts, wherein at least one hydrosyl group of each linked polysaccharide is esterified with a carbo~yl group contained in a polycarbo~ylic acid containing at least four carboxyl '~:1 65~q~

groups, and at least two carbo~yl groups of the polycarbosylic acid are esterified with hydroxyl groups of the polysaccharides.
The preferred acidic groups comprise at least one member selected from the group con isting of carbosyl, sulfate, sulfite and phosphate. The most preferred acidic group is the carbosyl group.
Preferred polysaccharides for use in this invention comprise those selected from the group consisting of hyaluronic acid, chondroitin sulfate, keratan sulfate, dermatan sulfate, heparan sulfate, heparin, carbosymethyl cellulose, pectin, alginic acid, polygalacturonic acid, polymannuronic acid, polyglucuronic acid and carrageenan.
The m~st preferred is hyaluronic acid.
The preferred salts in the operation of this invention comprise salts of an Al k~li or ~ 1 i ne earth metal, aluminum or ammonium. The ~ st preferred salt is a salt of sodium.
The preferred polycarbosylic acids of this invention are tetracarbosylic acids, which comprise members selected from the group consisting of:

HOOC~Y--COOH HOOC--N--~--N H

where Yl is a tetravalent organic radical selected from the group consisting of aliphatic, aromatic, cycloaliphatic, heterocyclic and polymeric radical~, and where Y 2 iS a divalent organic radical selected from the group consisting of aliphatic, aromatic, cycloaliphatic, heterocyclic and polymeric radicals.
Preferably Yl is selected from the group consisting of 1,2,3,4-tetrasubstituted benzene, 1,2,4,5-tetrasubstituted benzene, 1,2,5,6-tetrasubstituted naphthalene, 1,2,4,5-tetrasubstituted naphthalene, 1,2,6,7-tetrasubstituted naphthalene, 1,2,7,8-tetrasubstituted naphthalene, 2,3,6,7-tetrasubstituted naphthalene, 1,4,5,8-tetrasubstituted naphthalene, 2,3,2',3'-tetrasubstituted biphenyl, 3,4,2',3'-tetrasubstituted biphenyl, 3,4,3',4'-tetrasubstituted biphenyl, 1,2,3,4-tetrasubstituted anthracene, 1,2,5,6-tetrasubstituted anthracene, 1,2,6,7-te~r~subs~ituted anthracene, 1,2,7,8-tetrasubstituted anthracene, 2,3,6,7-tetrasubstituted anthracene, 1,2,3,4-tetrasubstituted phenanthrene, 1,2,7,8-tetrasubstituted phenanthrene, 1,2,6,7-tetrasubstituted phenanthrene, 1,2,5,6-tetrasubstituted phenanthrene, 2,3,6,7-tetrasubstituted phenanthrene, 1,8,9,10-tetrasubstituted phenanthrene, 3,4,9,10-tetrasubstituted perylene, 2,3,5,6-tetrasubstituted pyrazine, 2,3,4,5-tetrasubstituted thiophene, 2,3,4,5-tetrasubstituted pyrrolidine, ~6~

~R~ ~R~ ~rR~

\~
where R comprises linear, branched, or cyclic alkyl, aryl, -O-, -S-, -SO 2-, -CO-, -COO-, -NR 1-, -CONR1-, -COS-, -N=N-, -N (O) =N-, -CR 2R3-, -C~I2-, -CHR2-, -R~-, -SiR2R3-, -OSiR2R3O-, -POR2-, -POR2O- and -A-X-B-;
where R1 is hydrogen or C1-C5 alkyli where R2, R3 and R~, which can be the same or different, are linear or cyclic alkyl, ary~, substituted aryl, perfluoroalkyl and perfluoroaryl;
where R5 is hydrogen, alkyl, aryl, or aralkyli where A and B, which can be the same or different, are -O-, -S-, -CO-, -SO 2-, -SO-, -POR 2- ~ -POR20-, -SiR2R3-, -CON~R2-, -CON~-, -NR 1- and -N~-; and where X is an oligomer of a polyalkylene ether, polyalkylene thioether, polyaryl ether, polyester, polybutadiene, polyarylether sulfone, polyetherimide, polyamide, polyamic acid, polyamide imide, polyimide, polyalkyl phenol, polyphenol, polyamine, polysilo~ane, polyvinyl alcohol, polyurethane, polyurea and polycarbonate.
Y2 is preferably selected from the group consisting of polyethers, polythioethers, polyesters, polyamides, 9 ~

polyimides, polyamic acid~, polyamide ;~;des, polysulfor.es, polyhydantoins, polyamineQ, polyurethane~, polyurea~, polysilosanes, tetracarbonate~ and polybutadiene.
Esemplary tetracarbosylic acid~ are 3,4,3',4'-benzophenone tetracarbosylic acid, 2,3,6,7-naphthalene tetracarbo~ylic acid, 1,4,5,8-naphthalene tetracarboxylic acid, 1,2,4,5-naphthalene tetracarbosylic acid, 1,2,5,6-naphthalene tetracarbosylic acid, 3,4,3'4'-diphenyl tetracarbosylic acid, 2,3,2',3'-diphenyl tetracarbosylic acid, 2,2-bis(3,4-dicarbosyphenyl)propane, 3,4,9,10-perylene tetracarboxylic acid, bis(3,4-dicarbosyphenyl)ether, 1,1-bis(2,3-dicarbosyphenyl)ethane, bis(3,4-dicarbosyphenyl)methane, decahydronaphthalene-1,4,5,8-tetracarbosylic acid, 4,8-dimethyl-1,2,3,4,5,6,7-hesahydronaphthalene-1,2,5,6-tetracarbosylic acid, pyromellitic acid, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid, cyclopentane tetracarbosylic acid, pyrrolidine-2,3,4,5-tetracarbo~ylic acid, pyrazine-2,3,5,6-tetracarbosylic acid, thiophene-2,3,4,5-tetracarbosylic acid, ethylenediamine tetraacetic acid, diethylenetriamine pentaacetic acid, 4,4-sulfonyldiphthalic acid and 1-(3,4-dicarbo~yphenyl~ 3,3-trime~hylindane-5,6(6,7)-dicarbosylic acid, 2,2'-bis(2,3-dicarbosyphenyl)propane, 1,1'-bis(3,4-dicarbosyphenyl)ethane, 1-(3'4-dicarbosyphenyl~-3-methylindane-5,6(6,7)-dicarbosylic acid, 3,4-dicarbosy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid, 216~g~

l-methyl-3,4-dicarbosy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid, 3,4,9,10-perylene tetracarboxylic acid, 1,8,9,10-phenanthrene tetr~carboxylic acid, 2,6-~.chloronaphthalene-1,4,5,8-tetrac~rho-ylic acid, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic acid, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic acid, 2,3,3',4'-benzophenone tetracarbosylic acid, 2,3,2',3'-benzophenone tetracarboxylic acid, 4,4'-oxodiphthalic acid, 3,3'-osodiphthalic acid, 4,4'-thiodiphthalic acid, 3,3'-thiodiphthalic acid and 2,3,5,6-bicyclo(2,2,2)octane tetracarboxylic acid.
The most preferred tetracarboxylic acids are pyromellitic acid and 3,4,3',4'-benzophenone tetracarboxylic acid.
Operable polycarboxylic acids having more than four carboxyl groups comprise members selected from the group consisting of styrene/maleic acid copolymers, alkyl vinyl ether/maleic acid copolymers and:

R~R'm--A--R"--(COOHh~ p where n is 2 or 3, m is 0 or 1, p i-Q 2 to about 100,000, R
is aryl or saturated or unsaturated C l-ClOO000 alkyl, R' is aryl or saturated or unsaturated C l-ClO alkyl, R" is aryl or saturated or unsaturated C 2-C30 alkyl and A is:

2:1~58~

o o o~
where R is aryl or saturated or un-Qaturated C 1-C~O alkyl.
It has been found that when the crosslinked composition is derived from hyaluronic acid or its salts, the crosslinked composition has subQtantially greater resistance to ~egrada~ion cau~ed by hydro~y radical or enzyme~, in particular hyaluronida-~e, than does hyaluronic acid itself or its salts.
For esample, when an aqueou~ solution of sodium hyaluronate was treated with the enzyme hyaluronidase, the time it took to reduce the viscosity to one-half of the viscosity measured at 10 minute-~ (the visco~ity half-life) was only 0.5 hours. ~owever, when the test was carried out under the same conditions on a crosslinked composition of this invention where the polysaccharide was hyaluronic acid and the tetracarbosylic acid was pyLv",ellitic acid or 3,4,3',4'-benzophenone tetracarbosylic acid, the viscosity half-life waq 34 hours or 30 hours respectively.
In the tests for degradation by hydrosy radical the hydro~y radicals were generated by reaction of ferric chloride with ascorbic acid as described by Wong et al.
Inorganic Biochemistry, 14, p. 127 (1981). In a typical test the viscosity half-life was 0.9 hours for hyaluronic 8~

acid. When the same test waQ carried out under the same condition~ on a crosslinked compo~ition of this invention wherein the polysaccharide was hyaluronic acid and the tetracarbosylic acid waQ ~y~o ~llitic acid or 3,4,3',4'-benzophenone tetracarbosylic acid, the viscosity half-life was 24 hours or 6 hour~ respectively.
In another embodiment, the invention pertain~ to a method for crosslin~ing the acidic polysaccharides or their salts, comprising reacting the polysaccharides with a di- or polyanhydride, where polyanhydride~ are defined to mean those anydrides cont~i n i ng more than two anhydride groups per molecule.
The dianhydrides operable in the method of this invention comprise member-~ of the group ~elected from:

o o 0~ ~,0 where Yl is a tetravalent organic radical selected from the group consisting of aliphatic, aromatic, cycloaliphatic, heterocyclic and polymeric radicals, and where Y 2 iS a di~alent orga~ic ~adical ~elected from the group consiQting of aliphatic, aromatic, cycloaliphatic, heterocyclic and polymeric radical~.
Preferably Yl is selected from the group consisting of 1,2,3,4-tetrasubstituted benzene, 1,2,4,5-tetrasubstituted ~-1. 6~g ~

benzene, 1,2,5,6-tetrasubstituted naphthalene, 1,2,4,5-tetrasubstituted naphthalene, 1,2,6,7-tetrasubstituted naphthalene, 1,2,7,8-tetrasub~tituted naphthalene, 2,3,6,7-tetrasubstituted naphthalene, 1,4,5,8-tetrasubstituted naphthalene, 2,3,2',3'-tetrasubstituted biphenyl, 3,4,2',3'-tetrasubstituted biphenyl, 3,4,3',4'-tetrasubstituted ~iphenyl, 1,2,3,4-tetrasubstituted anthracene, 1,2,5,6-tetrasubstituted anthracene, 1,~,6,7-tetrasubstituted anthracene, 1,2,7,8-tetrasubstituted anthracene, 2,3,6,7-tetrasubstituted anthracene, 1,2,3,4-tetra~ubstituted phenanthrene, 1,2,7,8-tetrasubstituted phenanthrene, 1,2,6,7-tetrasubstituted phenanthrene, 1,2,5,6-tetrasubstituted phen~nthrene, 2,~S)~-tetrasubstituted phenanthrene, 1,8,9,10-tetrasubstituted phenanthrene, 3,4,9,10-tetrasubstituted perylene, 2,3,5,6-tetrasubstituted pyrazine, 2,3,4,5-tetrasubstituted thiophene, 2,3,4,5-tetrasubstituted pyrrolidine, ~R~ ~R~ ~R~

where R comprises linear, branched, or cyclic alkyl, aryl, -O-, -S-, -SO 2-, -CO-~ -COO-, -NRl-~ -CONRl-, -COS-, -N=N-, -N(O)=N-, -CR2R3-, -C~2-, -C~R2-, -~4- ~ -SiR2R3 -OSiR2R3O-, -POR2-, -POR2O- and -A-X-B-;
where Rl i~ hydrogen or C l-C5 alkyl;
where R2, R3 and R~, which can be the .Qame or different, are linear or cyclic alkyl, aryl, substituted aryl, perfluoroalkyl and perfluoroaryl;
where R 5 is hydrogen, alkyl, aryl, or aralkyli where A and B, which can be the same or different, are -O-, -S-, -CO-, -SO 2- / -SO-, -POR2-, -POR2O-, -SiR2R3-, -CONHR2-, -CONH-, -NR,- and -N~-; and where X is an oligomer of a polyalkylene ether, polyalkylene thioether, polyaryl ether, polyester, polybutadiene, polyarylether sulfone, polyetherimide, polyamide, polyamic acid, polyamide imide, polyimide, polyalkyl phenol, polyphenol, polyamine, polysilosane, polyvinyl alcohol, polyurethane, polyurea and polycarbonate.
Y2 is preferably selected from the group consisting of polyethers, p~ly~hioe~hers, polyesters~ polyamides, polyimides, polyamic acids, polyamide imideq, polysulfones, polyhydantoins, polyamine.Q, polyurethanes, polyurea~, polysilosanes, tetracarbonates and polybutadiene.
The dianhydrides are preferably selected from the group consisting of 3,4,3',4'-benzophenone tetracarbosylic acid dianhydride, 2,3,6,7-naphthalene tetracarbosylic acid dianhydride, 1,4,5,8-naphthalene tetracarbosylic acid dianhydride, 1,2,4,5-naphthalene tetracarbosylic acid 2 1 ~

dianhydride, 1,2,5,6-naphthalene tetracarbosylic acid dianhydride, 3,4,3',4'-diphenyl tetracarbosylic acid dianhydride, 2,3,2',3'-diphenyl tetracarbosylic acid dianhydride, 2,2-bis(3,4-dicarbosyphenyl)propane dianhydride, 3,4,9,10-perylene tetracarbosylic acid dianhydride, bis(3,4-dic~rbosyphenyl)ether dianhydride, 1,1-bis(2,3-dicarbosyphenyl~ethane dianhydride, bis(3,4-dicarbo~yphenyl)methane dianhydride, decahydronaphthalene-1,4,5,8-tetracarbosylic acid dianhydride, 4,8-dimethyl-1,2,3,4,5,6,7-hesahydronaphthalene-1,2,5,6-tetracarboxylic acid dianhydride, ~y~o-l~llitic acid dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, cyclopentane tetracarbo~ylic acid dianhydride, pyrrolidine-2,3,~,5-tetrac~r~o~yli~ acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, thiophene-2,3,4,5-tetracarboxylic acid dianhydride, ethylenediamine tetraacetic acid dianhydride, diethylenetriamine pentaacetic acid dianhydride, 4,4-sulfonyldiphthalic acid dianhydride, 2,2'-bis(2,3-dicarbosyphenyl)propane dianhydride, 1-(3,4-dicarboxyphenyl)-1,3,3-trimethylindane-5,6(6,7)-dicarbosylic acid dianhydride, 1,1'-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1-(3'4-dicarboxyphenyl)-3-methylindane-5,6(6,7)-dicarboxylic acid dianhydride, 3,4-dicarbo~y-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid 2 ~ ~x~

di~nhydride, 1-methyl-3,4-dicarbosy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid dianhydride, 3,4,9,10-perylene tetracarboxylic acid dianhydride, 1,8,9,10-phenanthrene tetracarboxylic acid dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetr~rho-ylic acid dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetr~rho~ylic acid dianhydr~e J 2,3,~6,7-te~rach~o~on~pht~e~e-1,~,5,8-tetracarboxylic acid dianhydride, 2,3,3',4'-benzophenone tetracarboxylic acid, 2,3,2',3'-benzophenone tetra~arboxylic acid dianhydride, 4,4'-osodiphthalic a~id dianhydride, 3,3'-oxodiphthalic acid dianhydride, 4,4'-thiodiphthalic acid dianhydride, 3,3'-thiodiphthalic acid dianhydride and 2,3,5,6-bicyclo(2,2,2)octane tetracarboxylic acid dianhydride.
The most preferred dianhydrides are ~y~Oll~llitic acid dianhydride and 3,4,3',4'-benzophenone tetracarboxylic acid dianhydride.
Polyanhydride~ operable in carrying out the method of this invention are member~ selected from the group consisting of styrene/maleic anhydride copolymers, alkyl vinyl ether/maleic anhydride copolymer~ and:

R--R'm--A--R~\O

;COOH~

8~

where where n i~ 0 or 1, m i~ 0 or 1, p iQ 2 to about 100,000, R i-~ aryl or qaturated or unsaturated C 1-ClOO,OOO
alkyl, R' is aryl or saturated or unsaturated C 1-ClO alkyl, R" is aryl or saturated or unQaturated ~ 2-C30 alkyl and A is:

o o -- or --N
0~
where R i Q aryl or saturated or unsaturated C 1-ClO alkyl.
The ~ st preferred polyanhydrides are obtained by reacting ~ nomeric or polymeric polyols or polyamineq with an escess of dianhydride, wherein the number of equivalents of anhydride i~ at lea~t twice that of the number of equivalent-~ of hydrosyl or amine contained in the polyol or polyamine, or by reacting monomeric or polymeric polyols or polyamines with an e~cess of monoanhydride also cont~i n ing an acyl halide, wherein the number of equivalents of anhydride plu~ acyl halide i5 at least twice that of the number of equivalent~ of hydrosyl or amine contained in the polyol or polyamine.
Because anhydride functionality i~ readily hydrolyzable in water, it is preferred that the reaction of the di- or polyanhydrides with polysaccharide be carried out in a polar, aprotic solvent. Preferred solvents are N-methyl pyrrolidinone, N-ethyl pyrrolidinone, N-cyclohesyl 2.~5g~

pyrrolidinone, 4-methyl morpholine N-oside, dimethyl formamide, sulfolane and dimethyl sulfoside.
Salts of the acidic polysaccharides may not be soluble in the preferred solvents. In particular, the sodium salt of hyaluronic acid is not soluble in the preferred solvents, and so it is generally convenient for the purpose of this embodiment to convert the sodium salt to a tetraalkyl amn~nium salt to increase solubility. After the crosslinking reaction of the tetraalkyl ammonium salt and the dianhydride, the product can then be converted back to the sodium form by ion eschange.
In the crosslin~ing reaction the ratio of di- or polyanhydride to polysaccharide is most readily espressed in terms of the equivalents of anhydride contained in the di-or polyanhydride per equivalent of repeating unit in the polysaccharide. For the purpose of the invention the ratio is from about 0.05 to about 4 equivalent~ of anhydride per equivalent of repeating unit. A preferred ratio is from about 0.08 to about 2, and the most preferred ratio from about 0.4 to a~o~t 1.6.
In still other embodiments the invention pertains to pharmaceutical compositions for treating m~mm~lian arthritis, for preventing post-operative adhesions and for promoting the healing of chronic wounds and ulcer~. The active component of these pharmaceutical compositions comprises crosslinked hyaluronic acid, or a ph~rmAceutically 8~G

acceptable salt of crosslinked hyaluronic acid, wherein at least one hydrosyl group of each linked hyaluronic acid is esterified with a carbosyl group contained in a polycarbosylic acid cont~i ni ng at least four carbosyl groups, and at least two carbosyl groups of the polycarbosylic acid are esterified with hydrosyl groups of the hyaluronic acid.
Pharmaceutically acceptable salt~ are preferably salts of an alkali or alkaline earth metal, aluminum or amn~nium.
The most preferred pharmaceutically acceptable salt is sodium.
The methods and compositions of this invention can be used to prevent post-operative adhesions in any ~nim~l that is susceptible to unwanted a & esion formation following surgery. The method and composition~ are used to prevent adhesions from developing in mAmmAl Q ~ preferably human beings. They are useful in all types of surgery where it is desired to inhibit the formation of post-surgical adhesions, e.g., ab~omin~l surgery, gynecological surgery, thoracic surgery, orthopedic surgery, neurological surgery and ophthAlm~logical surgery.
The adhesion preventative may be ~m;n;stered to the site of surgical trauma by any convenient mode such as, for example, by lavage, by coating directly on the site in a gel, cream, film or foam, or by any other convenient method.
The administration of the adhesion preventative can occur at ~6~

any time before significant wound healing has occurred. It is preferred to a~mi ni Qter it at the conclusion of surgery, just prior to closing of the wound. However, in some cases it may be desirable to administer the preventative continually over a period of time. An effective amount of adhesion preventative is an amount necessary to affect a reduction in the incidence of post-operative surgical adhes~on~. Preferably, the amount should be enough to coat the entire area exposed to the surgical trauma, and if desired an additional amount sufficient to coat body tissue adjacent to the area of trauma. The effective amount can be readily determined empirically.
The compositions of this invention can also be used to promote the healing of chronic wounds, e.g. burns, and ulcers, e.g. diabetes foot ulcers in mAmmAls, in particular, human beings. Hyaluronic acid retainQ ~ isture and also has angiogenesis characteristics that make it useful for this application. When utilized for wound healing the compositions may be used alone in aqueous solution, preferably physiological saline solution, or the solutions may be combined with wound healing drugs and other water soluble polymers. They may be A~mi ni stered to the site of the wound or ulcer by any convenient m~de such as, for example, by lavage, by coating directly on the site in a gel, cream, film or foam, by impregnation in a hAn~Age or wound dressing that iQ applied to wound or ulcer, or by any 8~0 other convenient method. An effective amcunt to promote healing is enough to coat the entire area of the wound or ulcer and if desired an additional amount sufficient to coat body tissue adjacent to the wound or ulcer. The effective amount can be readily dete-mi~ed empirically. A typical anhydride-crosslinked hyaluronic acid may contain as other ingredients water-soluble polymers, antibiotics, ~mmunosuppressant~ and pain reducer~.
In the application of the crosslinked hyaluronic acid of this invention to the treatment of arthritis in m~mn~ls, in particular human beings, the crosslinked hyaluronic acid is usually dissolved in physiological saline to a sufficient Yiscosity to pa-~s throu~h an injection needle, not m~re than about 50,000 cps, preferably about 5,000 to about 30,000 cps. The treatment solution is then injected into the diseased joint.
A typical knee joint synovial fluid supplementation injection procedure is similar to one described by Miller et al. in J. Bone and Joint Surgery, 40, p.636 (1985). A
sterile solution, 2.5 ml, of the sodium salt of anhydride-crosslinked hyaluronic acid (concentration of crosslinked hyaluronic acid 10 mg/ml) in buffered saline (sodium chloride 8.5 mg/ml, dibasic sodium phosphate 0.537 mg/ml, sodium dihydrogen phosphate 0.016 mg/ml) is slowly drawn into a syringe to ensure the absence of air pockets. The knee is then prepared for injection by cleaning with soap, ~6~D

wiping with cetyl trimethylamm~nium bromide and painting with tincture of iodine. The ~olution i~ injected into a synovium cavity through a premarked triangular arc at the lateral side of the joint bound by the tibial plateau, the edge of the ligamentum patellae, and the curve of the lateral femoral condyle. Local anaesthesia may be used prior to injection. In certain cases knee aspiration with the buffered saline solution may be needed prior to the synovial fluid supplementation injection. Such a procedure is described by Dahlberg et al. in Arthritis ~ Rheumatism, 37, 1994, page 521.
The injectable solution may contain materials in addition to the crosslinked hyaluronic acid. These include water soluble polymers such a~ chondroitin sulfate, dermatan sulfate, and/or a phospholipid to improve the lubricity of the solution. Anesthetic~, anti-inflammatory reagents, antibiotics, antibacterials, cytotosin~ and sugar~ may be added also.
Anhydride-crosslinked hyaluronic acid may be used a-Q a drug delivery system. The crosslinked hyaluronic acid forms a molecular cage in which ~ lecule~ with pharmacological activity can be dispersed. The substance~ contained in the cage are delivered into the environment by diffusion. The drug molecule, or mi~ture of drug ~ lecules, may be covalently or non-covalently bonded to the hyaluronic acid.
The covalent bonding can be via attachment to the carbosylic ~6s~q~

-2~-acid or hydrosyl groups of the hyaluronic acid moieties.
The gels, film_, threads, particles or sponges of anhydride-crosslinked hyaluronic acid may be placed, sprayed, ingested, injected or implanted at the location where the contained pharmacological substance iQ needed. These substances may be therapeutic drugs (such as anesthetics, analgesics, anti-inflammatories, diuretics, antagonists, antibiotics~ hoDmones, antirheumatics, adrenergic agonists, cytostaticQ, antihypertensive~ or immunosuppressant agents), growth factors, enzymes or cellular anti-adhesion compounds.
The crosslinked hyaluronic acid of this invention can also function aQ a component of cosm~tics for topical uses.
Because hyaluronic acid has been.shown to hold ~ isture under low relative humidity conditionQ and yield a pleasant and smooth feeling at high relative humiditieQ, it has been used aQ a m~isturizer in cosmetic formulationQ. The crosslinked hyaluronic acid of thi-Q invention will provide similar effects. Mistures of crosslinked hyaluronic acid with other low cost water-soluble polymers such as carbo~ymethyl cellulose, pectin, alginate, soy protein, casein and gelatin may also be em~loyed.
Natural e~tractQ of plant sources, such as cactus aloe vera, mesquite, m, tricaria ch~m~milla, tumeric, carrot, jojoba, rose and others, may be blended into a cosmetic formulation cont~ g crosslinked hyaluronic acid. Alpha hydro~y acids such as lactic and hydro~y ethanoic may be 2 1 ~

added to the formulation to improve the plasticity of the skin.
A typical anti-aging cosmetic composition is:
2-hydro~yethanoic acid, 7%, propyleno glycol, 15%, crosslinked hyaluronic acid solution (1 g/100 ml), 1%, water, 60% and ethyl alcohol, 17%, where all percentages are by weight.
A formulation for facial soft gel is: aqueous slurry of carbo2ymethyl cellulose (3 g/100 ml), 25%, aqueous solutlon of triethanolamine (10 g/100 ml), 11%, Methyl Gluceth-10, 5%, crosslinked hyaluronic acid aqueous solution (1 g/100 ml), 1%, perfume and preservatives, 1%, water, 57%, where all percentages are be weig~t.
A typical essential skin moisturizer composition is hydro2yethyl cellulose, 0.5%, Methyl Gluceth-10, 2%, glycerin, 2%, cros-~linked hyaluronic acid aqueous solution (1 g/100 ml), 1%, water, 94%, preservatives and perfume, 0.5%, where all percentages are by weight.
The invention is illustrated by the following E2amples, which are provided for the purpose of representation, and are not to be construed as limiting the scope of the invention. All parts and percentages in the e2amples are by weight unless otherwise specified.
E2ample 1 The example describes the preparation of a methyltricaprylylamm~nium salt of hyaluronic acid.

~ ~5'~9Q

To a solution of 10 g of sodium hyaluronate (fermentation product, Chisso Corporation, Chiba, Japan) in 1000 ml of water wa~ added a solution of 50 g. of methyltricaprylylammonium chloride (Ali~uat 336, Aldrich Chemical, Milwaukee, Wi~con~in) in 50 ml of acetone. The mi~ture wa~ stirred overnight, and then the rubbery precipitate was filtered, washed with water and acetone, and then dried in vacuo overnight. It waQ again soaked in 500 ml of acetone for 7 hours and dried in vacuo overnight to yield 46.9 g of rubbery material.
Example~ 2-9 These e~ample~ deQcribe crosslinking of the methyltricaprylylammonium salt of hyaluronic acid with dianhydrides.
The product of E~ample 1, 2.0 g (0.46 meq of repeating unit), wa~ dissolved in 100 ml of N-methylpyrrolidinone. To this solution was added a dianhydride, and then the misture was tumble-stirred for 16 hours. The dianhydride~ utilized were ethylenediamine tetraacetic acid dianhydride (EDTAA), diethylenetriamine pe~taacetic acid dianhydride (DETPAA), 3,4,3',4'-benzophenone ~etracar~o~ylic acid dianhydride (BTDA~ and 4,4'o~odiphthalic acid dianhydride (OPDA).
E~amples 2 and 3 are control~ utilizing no anhydride.
The data in Table 1 show the gelation at the end of the 16 hour stirring period, demonstrating the crosslinking of 5~a the methyltricaprylylammonium salt of hyaluronic acid. The viscositieq are Brookfield visco-qitie~.

EYampl~Initial Anhydrid~ Anhydrid~ Anhydrid~ Final No.Vi~co~ity Amo~nt, g Amcunt,Visco~ity I1i -le~ (cp~) 2 2375 --- 0.00 --- 1505 3 2300 --- 0.00 --- 1555 4 2365 EDTAA 0.10 0.39 gelled 2340 EDTAA 0.15 0.59 gelled 6 2345 DETPAA 0.10 0.28 gelled 7 2300 DETPAA 0.15 0.42 gelled 8 2100 2TDA 0.10 0.3~ gelled 9 2165 OPDA 0.10 0.32 gelled E~amples 10-17 These e~ampleq describe conversion of the crosslinked mRthyltricaprylylammonium saltQ of hyaluronic acid prepared in E~ampleq 4-9 to the corresponding sodium saltq.
To the solutionQ of cros~linked methyltricaprylyl-amo~nium saltQ of hyaluronic acid (E~amples 4-9) in N-methylpyrrQli~inone at 1~ ~C wa~ added a ~olution of 1 g of salt in 50 ml of water. The resulting mixtures were stirred for 10 minutes, and then 10 ml of acetone waQ added. After 20 minuteq the resulting precipitates were filtered, washed with S0 ml of 4/1 acetone/water five timeq, washed three timeq with 30 ml potionQ of acetone and then dried in a vacuum oven until a constant weight was obtained. The resulting material~ were redissolved in 100 ml of phosphate buffered saline water (p~=7.4), and then the viscosities of the resulting solutions were measured. The data are in Table 2.
The substantial increase in viscosity found in Esamples 12 and 16 and formation of -~ubstantial amount-~ of gel in Examples 13-15 and 17 indicate the crosslinked nature of the material.

0EYample No.Cro~slinked galtgodium galt, Viscosity of 0.4 Aq.Solution (cps) Control, no 25 crossl in~ing 11 Control, no 26 crossl~ n~ ~ ng 12 E~ample 4 640 13 EYample 559 + in oluble gels 14 Exampl- 622 + insolubl~ gels EYample 726 + insoluble gel~
16 EYampl- 8 199 17 Example 911 + insoluble gels . E~ample 18 ThiQ e~ample illustrates the resistance of the anhydride-crosslinked hyaluronic acid to degradation by hyaluronidase.
Sample~ of hyaluronic acid crosslinked by reaction with pyromellitic acid dianhydride (PMDA) or a mi~ture of PMDA
and BTDA (1/1 by weight) were prepared by the method~ of 9 ~

E~ample-~ 1-17. They were tested and evaluated according to the following procedure.
To a 100 ml aqueous Qolution of sodium salt of crosslinked hyaluronate (0.4% wt/vol, buffered at pH 7.4) was added 1 ml of a solution of hyaluronidase ~EC 3.2.1.35;
type I-S, from bovine testes, lyophilized, 290 units/mg, Sigma Chemical, St. Louis, Mo.) with the concentration of 290 units/ml waQ added. The mi~ture was sh~en for about 10 seconds, and then the first viscosity (Brookfield) was measured after 10 minutes. The viscosity wa~ then monitored for a period of time. The viscosity at 10 minutes was considered to be 100~. The degradation resistance of the sample was assessed by measuring the time required to reduce the viscosity to 50% of the 10 minute value ~viscosity half-life). The control (E~ample 18A) con~i~ted of sodium hyaluronate. The results are in Table 3.

Table 3 ~yaluronidase Te~t of Anhydride-cro~slinked ~yaluronic Acid EYample Number Dianhydride Visco~ity ~alf-Life 18A -~ - 0.5 hours ~ 65~

E~am~le 19 This e~ample illu-QtrateQ the resiQtance of the anhydride-crosslinked hyaluronic acid to degradation by hydro~y radicals as generated by the reaction of ascorbic acid with ferric chloride.
Samples of hyaluronic acid cros~linked with PMDA and 3TDA ~ere pre~ared by the methods of E~amples 1-17. They were tested and evaluated according to the following procedure.
To a 100 ml aqueous solution of sodium salt of crosslinked hyaluronate (0.4% wt/vol, buffered at p~ 7.4) 1 ml of a 0.34 M ferric chloride solution and 1 ml of 0.18 M
ascorbic acid solution were added. The mi~ture was s~ken for about 10 seconds, and then the first viscosity (Brookfield) was measured after 10 minutes. The viscosity at this point was considered to be 100%. The degradation resistance of the sample was assessed by mRasuring the time required to reduce the viscosity to 50% of the 10 minute value (viscosity half-life). The control (E~ample l9A) consisted of sodium hyaluronate. The resultQ are in Table 4.

~ ~ 6 ~

Table 4 Ferric Chloride/A~corbic Acid Test of Anhydride-Cros~linked Hyaluronic Acid Example Number Dianhydride Viscosity Half-Life l9A -------- 0.9 hours Example 20 This e~ample describes crosslinking the methyltricaprylylammonium salt of hyaluronic acid with a polyanhydride.
The polyanhydride:

CH9CH2C--CH2~

was prepared by mi~ing a solution of 0.1 g (1 meq) of 1,2,4,5-benzene tetracarbo~ylic acid dianhydride and 0.020 g (0.45 meq) of 2-ethyl-2-hydro~ymethyl-1,3-propane diol in 10 ml of N-mRthylpyrrolidinone. The solution of the polyanhydride wa.~ then added to a solution of 0.7 g of the 2~ 6~q product of Esample 1 in 100 ml of N-methylpyrrolidinone.
After 1 hour, the ~olution became a dispersed gel with visible gel particle~.
Esample 21 This esample describes crossli n~i ng the methyltricaprylylammonium salt of hyaluronic acid with a polyanhydride.
The polyanhydride:

CH3CH~C~H2~[~

was prepared by mising a solution of 0.1 g (1 meq) of trimellitic anhydride acid chloride, 0.1 g (0.45 meq) of 2-ethyl-2-hydrorymethyl-1,3-propane diol and O.07 g of triethylamine in 10 ml of N-methylpyrrolidinone. The solution of the polyanhydride was then added to a solution of O.7 g of the product of Esample 1 in 100 ml of N-methylpyrrolidinone. After 1 hour, the solution became a dispersed gel with visible gel particles.
While the invention has been described with respect to specific embodiments, it should be understood that they are ~1~5~q~

not intended to be limiting and that many variations and modifications are pos~ible without departing from the scope of this invention.

Claims

1. A crosslinked composition comprising linked polysaccharides containing acidic groups or their salts, wherein at least one hydroxyl group of each linked polysaccharide is esterified with a carboxyl group contained in a polycarboxylic acid having at least four carboxyl groups, and wherein at least two carboxyl groups of the polycarboxylic acid are esterified with hydroxyl groups of the polysaccharides.

2. The crosslinked composition of claim 1 wherein the polysaccharide comprises hyaluronic acid.

3. The crosslinked composition of claim 1 wherein the polysaccharide comprises the sodium salt of hyaluronic acid.

4. The crosslinked composition of any of the previous claims wherein the tetracarboxylic acid comprises at least one member selected from the group consisting of 3,4,3',4'-benzophenone tetracarboxylic acid, 2,3,6,7-naphthalene tetracarboxylic acid, 1,4,5,8-naphthalene tetracarboxylic acid, 1,2,4,5-naphthalene tetracarboxylic acid, 1,2,5,6-naphthalene tetracarboxylic acid, 3,4,3'4'-diphenyl tetracarboxylic acid, 2,3,2',3'-diphenyl tetracarboxylic acid, 2,2-bis(3,4-dicarboxyphenyl)propane, 3,4,9,10-perylene tetracarboxylic acid, bis(3,4-dicarboxyphenyl)ether, 1,1-bis(2,3-dicarboxyphenyl)ethane, bis(3,4-dicarboxyphenyl)methane, decahydronaphthalene-1,4,5,8-tetracarboxylic acid, 4,8-dimethyl-1,2,3,4,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic acid, pyromellitic acid, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid, cyclopentane tetracarboxylic acid, pyrrolidine-2,3,4,5-tetracarboxylic acid, pyrazine-2,3,5,6-tetracarboxylic acid, thiophene-2,3,4,5-tetracarboxylic acid, ethylenediamine tetraacetic acid, diethylenetriamine pentaacetic acid, 4,4-sulfonyldiphthalic acid and 1-(3,4-dicarboxyphenyl)-1,3,3-trimethylindane-5,6(6,7)-dicarboxylic acid, 2,2'-bis(2,3-dicarboxyphenyl)propane, 1,1'-bis(3,4-dicarboxyphenyl)ethane, 1-(3'4-dicarboxyphenyl)-3-methylindane-5,6(6,7)-dicarboxylic acid, 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid, 1-methyl-3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid, 3,4,9,10-perylene tetracarboxylic acid, 1,8,9,10-phenanthrene tetracarboxylic acid, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic acid, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic acid, 2,3,3',4'-benzophenone tetracarboxylic acid, 2,3,2',3'-benzophenone tetracarboxylic acid, 4,4'-oxodiphthalic acid, 3,3'-oxodiphthalic acid, 4,4'-thiodiphthalic acid, 3,3'-thiodiphthalic acid and 2,3,5,6-bicyclo(2,2,2)octane tetracarboxylic acid.

5. The crosslinked composition of claims 1, 2 or 3 wherein the polycarboxylic acid containing more than four carboxyls comprises a member selected from the group consisting of styrene/maleic acid copolymers, alkyl vinyl ether/maleic acid copolymers and:

where n is 2 or 3, m is 0 or 1, p is 2 to about 100,000, R
is aryl or saturated or unsaturated C 1-C100,000 alkyl, R' is aryl or saturated or unsaturated C 1-C10 alkyl, R" is aryl or saturated or unsaturated C 2-C30 alkyl and A is:

, , , or where R''' is aryl or saturated or unsaturated C 1-C10 alkyl.

6. The crosslinked composition of claims 2 or 3 wherein the crosslinked composition has substantially greater resistance to the enzyme hyaluronidase than does hyaluronic acid or its salts.

7. The crosslinked composition of claims 2 or 3 wherein the crosslinked composition has substantially greater resistance to hydroxy radicals than does hyaluronic acid or its salts.

8. A method for crosslinking polysaccharides containing acidic groups or their salts, comprising reacting said polysaccharide with a di- or polyanhydride.

9. The method of claim 8 wherein the acidic groups comprise at least one member selected from the group consisting of carboxyl, sulfate, sulfite and phosphate.

10. The method of claim 8 wherein the polysaccharide comprises a member selected from the group consisting of hyaluronic acid, chondroitin sulfate, keratan sulfate, dermatan sulfate, heparan sulfate, heparin, carboxymethyl cellulose, pectin, alginic acid, polygalacturonic acid, polymannuronic acid, polyglucuronic acid and carrageenan.

11. The method of claim 8 wherein the polysaccharide comprises hyaluronic acid.

12. The method of claim 8 wherein the polysaccharide comprises a salt of hyaluronic acid.

13. The method of claim 12 wherein the salt of hyaluronic acid comprises a sodium salt.

14. The method of claim 12 wherein the salt of hyaluronic acid comprises a tetraalkylammonium salt.

15. The method of claims 8, 9, 10, 11, 12, 13 or 14 wherein the dianhydride is a member selected from the group consisting of:

and where Y1 is a tetravalent organic radical selected from the group consisting of aliphatic, aromatic, cycloaliphatic, heterocyclic and polymeric radicals, and where Y2 is a divalent organic radical selected from the group consisting of aliphatic, aromatic, cycloaliphatic, heterocyclic and polymeric radicals.

16. The method of claim 15 wherein the dianhydride comprises a member selected from the group consisting of 3,4,3',4'-benzophenone tetracarboxylic acid dianhydride, 2,3,6,7-naphthalene tetracarboxylic acid dianhydride, 1,4,5,8-naphthalene tetracarboxylic acid dianhydride, 1,2,4,5-naphthalene tetracarboxylic acid dianhydride, 1,2,5,6-naphthalene tetracarboxylic acid dianhydride, 3,4,3',4'-diphenyl tetracarboxylic acid dianhydride, 2,3,2',3'-diphenyl tetracarboxylic acid dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 3,4,9,10-perylene tetracarboxylic acid dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, decahydronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 4,8-dimethyl-1,2,3,4,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic acid dianhydride, pyromellitic acid dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, cyclopentane tetracarboxylic acid dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, thiophene-2,3,4,5-tetracarboxylic acid dianhydride, ethylenediamine tetraacetic acid dianhydride, diethylenetriamine pentaacetic acid dianhydride, 4,4-sulfonyldiphthalic acid dianhydride, 2,2'-bis(2,3-dicarboxyphenyl)propane dianhydride, 1-(3,4-dicarboxyphenyl)-1,3,3-trimethylindane-5,6(6,7)-dicarboxylic acid dianhydride, 1,1'-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1-(3'4-dicarboxyphenyl)-3-methylindane-5,6(6,7)-dicarboxylic acid dianhydride, 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid dianhydride, 1-methyl-3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid dianhydride, 3,4,9,10-perylene tetracarboxylic acid dianhydride, 1,8,9,10-phenanthrene tetracarboxylic acid dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,3,3',4'-benzophenone tetracarboxylic acid, 2,3,2',3'-benzophenone tetracarboxylic acid dianhydride, 4,4'-oxodiphthalic acid dianhydride, 3,3'-oxodiphthalic acid dianhydride, 4,4'-thiodiphthalic acid dianhydride, 3,3'-thiodiphthalic acid dianhydride and 2,3,5,6-bicyclo(2,2,2)octane tetracarboxylic acid dianhydride.

17. The method of claims 8, 9, 10, 11, 12, 13 or 14 wherein the polyanhydride is a member selected from the group consisting of styrene/maleic anhydride copolymers, alkyl vinyl ether/maleic anhydride copolymers and:

where where n is 0 or 1, m is 0 or 1, p is 2 to about 100,000, R is aryl or saturated or unsaturated C 1-C100,000 alkyl, R' is aryl or saturated or unsaturated C 1-C30 alkyl, R" is aryl or saturated or unsaturated C 2-C30 alkyl and A is:

, , , or where R''' is aryl or saturated or unsaturated C 1-C10 alkyl.

18. The method of claims 8-17 wherein the equivalents of anhydride in the di- or polyanhydride per equivalent of repeating unit in the polysaccharide is from about 0.05 to about 4.