Inter and/or intramolecular cross-linked esters of acid polysaccharides are disclosed in which a part or all of the carboxy groups are esterified with hydroxyl groups of the same molecule and/or of different molecules of the acid polysaccharide. These inner cross-linked esters of polysaccharide acids are useful in the field of biodegradable plastic materials, to manufacture sanitary and surgical articles, in the cosmetic and pharmaceutical fields, in the food industry and in many other industrial fields.

SUMMARY 
The present invention concerns inter and/or intramolecular esters of acid 
polysaccharides containing carboxy functions, in which a part or all of 
such functions are esterified with hydroxyl groups of the same molecule 
and/or of different molecules of the acid polysaccharide, thus forming 
lactone or intermolecular ester bonds. These "inner" esters of 
polysaccharide acids, in which there is no intervention by OH groups of 
other alcohols, can also be defined as "auto-crosslinked polysaccharides", 
since the formation of a mono- or polymolecular cross-link is the 
consequence of the abovementioned internal esterification. Hereafter, the 
new compounds of the present invention will be referred to by this 
definition. The adjective "cross-linked" refers to the crosswise 
connections between the carboxyls and hydroxyls of the polysaccharide 
molecules. 
The new inner esters can be total or partial, depending on whether all or 
only part of the carboxy functions are esterified in the above manner. In 
the partial inner esters, further carboxy functions can be either totally 
or partially esterified with monovalent or polyvalent alcohols, thus 
forming "external" ester groups, and in the partial esters of both these 
ester groups the non-esterified carboxy functions may be free or salified 
with metals or organic bases. 
DETAILED DESCRIPTION OF THE INVENTION 
Esterification between different polysaccharide molecules consequently 
increases their molecular weight, which can be roughly doubled or 
multiplied according to the number of molecules involved in the 
crosslinking. The degree of "polymerization" varies according to the 
conditions used in the preparation procedure described hereafter, such as 
temperature, reaction duration, but it may likewise depend on the 
polysaccharide to be crosslinked. Even though it is impossible to 
ascertain the ratio between the two types of ester bonds, an approximate 
representation can be made on the basis of the molecular weight, this 
being proportional to the number of molecules of the polysaccharide 
aggregate of the abovesaid bonds of intermolecular inner esters. 
Particularly important are the crosslinked products of the present 
invention, resulting from the fusion of two or three polysaccharide 
molecules, and products varying in their degree of "polymerization" in 
these terms. They can be obtained for example by means of the procedure 
used in the illustrative Examples. 
The invention also concerns the use of the new inner esters, for example in 
the field of biodegradable plastic materials, to manufacture sanitary and 
surgical articles, in the cosmetic and pharmaceutical fields, in the food 
industry and in many other industrial fields. 
Acid polysaccharides containing carboxy functions which serve as the basic 
starting materials to the new inner esters of the present invention are 
all those already known and described in literature, such as the natural 
ones of animal or vegetable origin, and synthetic derivatives of the same, 
but above all hyaluronic acid, alginic acid, carboxymethylcellulose, 
carboxymethyl starch (also referred to as "carboxymethylamide") and 
carboxymethylchitin. Also the external partial esters of acidic 
polysaccharides, such as those of hyaluronic acid and alginic acid, may 
serve as starting compounds. The partial esters of carboxymethylcellulose, 
of carboxymethylamide and carboxymethylchitin which can be used as 
starting materials are described in co-pending U.S. application Ser. No. 
350,920, entitled "New Polysaccharide Esters", which is hereby 
incorporated by reference, was filed on the same day as the present 
application and is based upon Italian patent application No. 47963A/88. 
These partial esters can also be obtained according to the general 
preparation procedure for carboxy polysaccharide esters described in the 
European patent application No. 86305233.8 (Pub. No. 0216453, published on 
Apr. 1, 1987). As starting material it is also possible to use molecular 
fractions of the abovesaid acidic polysaccharides as well as their partial 
esters. 
The specific use of the new esters can be determined and depends upon the 
overall degree of esterification, inner and possibly external, that is the 
number of esterified carboxy functions, and also the number of salified 
groups, as well as the degree of aggregation ("polymerization") of the 
molecules involved in the process of esterification. These indeed are the 
factors which determine the solubility of the product and its 
viscous-elastic properties. Thus, for example, the total esters are 
practically insoluble in aqueous liquids and are suitable, due to their 
molecular structure, for use in the manufacture of plastic materials and 
as additives for such materials. The esters with medium or low degrees of 
esterification and their salts with inorganic or organic bases are more or 
less soluble in aqueous conditions and are suitable for the preparation of 
gels destined for various uses, in the cosmetic and pharmaceutical fields 
and in the medical-sanitary field in general. 
The autocross-linked products of the present invention may possess all the 
carboxy functions in the form of an inner ester, or only an aliquot part 
of the same. In these partial inner esters the percentage of "cross-links" 
varies preferably between 1 and 60%, and especially between 5 and 30% of 
the number of carboxy groups in the acidic polysaccharides. 
The new inner esters of the present invention have become available because 
of the discovery of an original chemical procedure which is based on the 
activation of the carboxy groups by the addition of substances capable of 
inducing such activation. The unstable intermediate products obtained from 
the activation reaction separate spontaneously, either after the addition 
of catalysts and/or following a rise in temperature, forming the above 
mentioned inner ester bonds with hydroxyls of the same or other 
polysaccharide molecule. According to the degree of inner esterification 
desired, either all or an aliquot part of the carboxy functions are 
activated (the aliquot part being obtained by using an excess of 
activating substances or by suitable dosing methods). 
The carboxy groups to be converted into inner ester groups can be activated 
starting from polysaccharides containing free carboxy groups, or, 
preferably, from polysaccharides containing salified carboxy groups, for 
example metal salts, preferably alkaline or alkaline earth metals, and 
above all with quaternary amonium salts, such as those descried hereafter. 
Salts with organic bases such as amines can however also be used as 
starting substances. 
Methods for the activation of free or salified carboxy groups are per se 
known, particularly in the field of peptide synthesis, and those skilled 
in the art can easily determine which method is the most suitable, 
especially whether or not to use the starting substances in their free or 
salified form. Activation methods per se known for peptide synthesis 
procedures and useful in the preparation procedures of the present 
invention are described, for example, in Bodanszky, M., In search of new 
methods in peptide synthesis, Int. J. Peptide Protein Res. 25, 1985, 
449-474; and Gross, E. et al., The Peptides, Analysis Synthesis, Biology, 
Academic Press, Inc., 1979, Vol. 1, Chapter 2. According to such 
procedures, a carboxyl component is activated, that is, a carboxyl 
component is converted to a reactive form. Such activation typically 
involves a reaction between an acid and an activating agent according to 
the scheme: 
##STR1## 
wherein X is an electron withdrawing moiety. Most activated derivatives of 
carboxylic acids, therefore, are mixed anhydrides, including in the broad 
sense also acid azides and acid chlorides which can be considered mixed 
anhydrides of hydrazoic acid and HCl as the activating agents. In 
addition, activation of a carboxyl component can be accomplished by the 
formation of intermediate "activated esters". These "activated esters" can 
be of various types, but particularly useful "activated esters" are those 
prepared by use of dicyclohexylcarbodiimide, p-nitrophenyl esters, 
trichlorophenyl esters, pentachlorophenyl esters, and O-acyl derivatives 
of hydroxylamines, particularly esters of N-hydroxysuccinimide. 
All of these various types of activation procedures are useful in the 
preparation of the cross-linked carboxy polysaccharides of the invention, 
as all of these procedures can be characterized as importantly involving 
the reaction of a carboxyl group with an activating agent which 
essentially results in the formation of a substituent group that is easily 
reactive with a hydroxyl group so as to easily form the inner ester 
bonding characteristic of the products of the invention. The number of 
carboxy functions to be converted into inner esters is in proportion to 
the number of activated carboxy functions and this number depends on the 
quality of the activating agent used. In order to obtain total inner 
esters therefore, an excess of activating agents should be used, while in 
the case of partial esters, the quantity of this agent should be dosed 
according to the degree of esterification desired. 
The carboxy groups which are still free or salified after the cross-linking 
reaction according to the present invention can be exchanged in order to 
obtain opportune salts or can be esterified with the abovementioned 
monovalent or polyvalent alcohols thus obtaining mixed esters, partly 
cross-linked and partly externally esterified. Of course, partial 
esterification with alcohols can be effected before activation of part of 
the carboxy groups and subsequent conversion into inner esters, that is, 
the abovementioned polysaccharide esters can be used as starting 
substances. 
The new procedure for the preparation of cross-linked polysaccharides is 
therefore characterized by treating a polysaccharide, having free or 
salified carboxy groups and possibly also carboxy groups esterified with 
mono- or polyvalent alcohols, with an agent which activates the carboxy 
function, possibly in the presence of an auxiliary agent favouring the 
formation of intermediate activated derivatives and/or a tertiary organic 
or inorganic base, exposing the mixture to heating or irradiation 
(particularly with UV light) and, if desired, esterification with mono- or 
polyvalent alcohols of the carboxy groups still free or salified in the 
polysaccharides thus obtained, and if desired, by salifying free carboxy 
groups or by freeing salified carboxy groups. Of the substances able to 
activate the carboxy group, the conventional ones described in literature 
can be used, for example those usually used in the synthesis of peptides, 
except however those which would have the effect of altering or destroying 
the molecular structure of the starting polysaccharide, such as those used 
for the formation of carboxyl halides. Preferred substances which lead to 
the formation of activated esters are those, such as, carbodiimides, 
dicyclohexylcarbodiimide, benzyl-isopropyl-carbodiimmide, 
benzyl-ethyl-carbodiimmide; ethoxyacetylene; Woodward's reagent 
(N-ethyl-5-phenylisoxazolium-3'-sulfonate), or halogen derivatives from 
aliphatic, cycloaliphatic or aromatic hydrocarbons, or from heterocyclic 
compounds with halogen made mobile by the presence of one or more 
activating groups, such as chloroacetonitryl and especially the salts of 
2-chloro-N-alkypyridine, such as chloride of 2-chloro-N-methyl-pyridine or 
other alkyl derivatives with inferior alkyl groups, such as those with up 
to 6 carbon atoms. In the place of chloride derivatives, other halogen 
derivatives can of course be used, such as bromide derivatives. 
This activation reaction can be carried out in organic solvents, especially 
aprotic solvents such as dialkylsulfoxides, dialkylcarboxylamides, such as 
in particular lower alkyl dialkylsulfoxides, particularly 
dimethylsulfoxide, polymethylene sulfoxides, such as tetramethylene 
sulfoxide, dialkyls or polymethylene sulfones, such as tetramethylene 
sulfone, sulfolane and lower alkyl dialkylamides of lower aliphatic acids 
in which the alkyl groups have a maximum of six carbon atoms, such as 
dimethyl or diethyl formamide or dimethyl or diethyl acetamide. Other 
solvents may also be used, however, and these need not always be aprotic, 
such as alcohols, ethers, ketones, esters, such as lower aliphatic 
dialkyloxyhydrocarbides, such as dimethoxyethane and especially aliphatic 
or heterocyclic alcohols and ketones with a low boiling point, such as 
lower N-alkyl-pyrrolidones, such as N-methylpyrrolidone or 
N-ethyl-pyrrolidone, hexafluoroisopropanol and trifluoroethanol. If 
halogen derivatives are used as carboxyl-activating substances, especially 
in the form of salts, such as the above mentioned 
2-chloro-N-methylpyridinium chloride, it is better to use a metal salt or 
a salt of the organic base of the starting polysaccharide, especially one 
of the quaternary ammonium salts described hereafter, such as tetrabutyl 
ammonium salt. These salts have the special advantage of being very 
soluble in the abovesaid organic solvents in which the crosslinking 
reaction is best effected, thus guaranteeing an excellent yield. It is 
advisable to add to the mixture a substance capable of subtracting acid, 
such as organic bases, carbonates, bicarbonates or alkaline or alkaline 
earth acetates, or organic bases and especially tertiary bases such as 
pyridine and its homologues, such as collidine, or aliphatic amine bases, 
such as triethylamine or N-methyl-piperazine. 
The use of quaternary ammonium salts represents a particularly advantageous 
procedure of the present invention and constitutes one of its main 
objectives. Such ammonium salts are well known and are prepared in the 
same way as other known salts. They derive from alkyls having preferably 
between 1 and 6 carbon atoms. It is preferable to use tetrabutyl ammonium 
salts. One variation in the procedure of the present invention in which 
quaternary ammonium salts are used, consists in reacting an alkaline salt, 
for example sodium or potassium salt, in the presence of catalyzing 
quantity of a quaternary ammonium salt, such as tetrabutylammonium iodide. 
The substances which catalyze activation of the carboxy groups to be added 
to the activating agents are reported in literature and these too are 
preferably bases such as those mentioned previously. Thus, for example, 
when the carboxy groups are activated with isothiazoline salts it is 
preferable to add some triethylamine to the reaction mixture. 
The reaction of formation of activated intermediates, such as and 
especially esters, is carried out at the temperature recommended in 
literature and this temperature can however be varied should circumstances 
require as can be easily determined by one skilled in the art. The 
formation of inner ester bonds can come about within a fairly wide 
temperature range, for example between 0.degree. C. and 150.degree. C., 
preferably room temperature or slightly above, for example between 
20.degree. C. and 75.degree. C. Raising the temperature favours the 
formation of inner ester bonds, as does exposure to radiations of suitable 
wavelength, such as ultraviolet rays. 
In the produced polysaccharide crosslinked products, those remaining free 
carboxy groups or those in the form of salts can be partially or totally 
esterified with mono-or polyvalent alcohols, thus obtaining esters mixed 
with bonds which are in part internal and in part external. The alcohols 
used for this esterification correspond to those dealt with hereafter and 
from which the new mixed esters of the present invention are derived. 
For esterification of the free or salified carboxy groups, known, 
conventional methods may be used, such as reaction between a carboxy salt, 
such as sodium salt, and an etherifying agent or the alcohols themselves 
in the presence of catalyzing substances, such as acid-type 
ion-exchangers. The known etherifying agents described in literature can 
be used, such as especially the esters of various inorganic acids or 
organic sulfonic acids, such as hydrogen acids, that is the hydrocarbyl 
halides such as methyl or ethyl iodide or neutral sulfates or hydrocarbyl 
acids, sulfites, carbonates, silicates, phosphites or hydrocarbyl 
sulphonates, such as methyl-, benzo-, or p-toluolsulfonate or methyl or 
ethyl chlorosulfonate. The reaction can take place in a suitable solvent, 
such as an alcohol, preferably the one corresponding to the alkyl group to 
be introduced into the carboxy group, but also nonpolar solvents such as 
ketones, ethers such as dioxane or aprotic solvents, such as 
dimethylsulfoxide. As a base, it is possible to use for example an 
alkaline or alkaline earth metal hydrate or magnesium or silver oxide or a 
basic salt of one of these metals, such as a carbonate and, of the organic 
bases, a tertiary nitrogenous base, such as pyridine or collidine. Instead 
of the base it is also possible to use a basic ion-exchanger. When 
starting from salts of partial polysaccharide esters, these may also be 
ammonium salts, such as ammonium or substituted ammonium salts. 
According to one chemically original procedure described in the abovesaid 
European patent application No. 86305233.8, the external esters can be 
advantageously prepared by starting with quaternary ammonium salts with an 
etherifying agent in an aprotic solvent, such as dialkylsulfoxides, 
dialkylcarboxylamides, such as in particular lower alkyl dialkylsulfoxides 
with a maximum of 6 carbon atoms, particularly dimethylsulfoxide, and the 
lower alkyl dialkylamides of lower aliphatic acids, such as dimethyl or 
diethyl formamide or dimethyl or diethyl acetamide. Reaction should be 
effected preferably within a temperature range of between about 25.degree. 
C. and 75.degree. C. for example at about 30.degree. C. Esterification is 
effected preferably by gradually adding the etherifying agent to the 
abovesaid ammonium salt dissolved in one of the solvents mentioned, for 
example in dimethylsulfoxide. 
As alkylating agents it is possible to use those mentioned above, 
especially the alkyl halogens. As starting ammonium salts it is preferable 
to use lower ammonium tetraalkylates, since alkyl groups have preferably 
between 1 and 6 carbon atoms. It is best to use tetrabutyl ammonium salt. 
These quaternary ammonium salts can be prepared by reacting a metal salt 
of the acidic polysaccharide, in part internally esterified, preferably 
one of those mentioned above, especially sodium or potassium salt, in 
aqueous solution with a salified sulfonic resin with a quaternary ammonium 
base. The tetralkyl ammonium base of the polysaccharide ester can be 
obtained by freeze-drying the eluate. These starting salts are soluble in 
the above aprotic solvents, so that esterification according to this 
procedure is particularly easy and provides good yields. It is therefore 
only by following this procedure that the number of carboxy groups to be 
esterified can be exactly dosed. 
One variation of this procedure consists in reacting potassium or sodium 
salt, suspended in a suitable solvent, such as dimethylsulfoxide, with a 
suitable alkylating agent in the presence of a catalyzing quantity of a 
quaternary ammonium salt, such as tetrabutyl ammonium iodide. 
In the inner esters obtained according to the new procedure, the carboxy 
groups still left intact can be salified with organic or inorganic bases. 
The choice of bases for the formation of such salts is based on the 
intended use of the product. The inorganic salts are preferably those of 
alkaline metals, such as sodium or potassium salts or ammonium salts, 
cesium salts, salts of alkaline earth metals, such as calcium, magnesium 
or aluminum. 
The salts of organic bases are especially those of aliphatic, araliphatic, 
cycloaliphatic or heterocyclic amines. The ammonium salts of this type may 
derive from therapeutically acceptable, but inactive, amines, or from 
amines with a therapeutic action. Of the former, special consideration 
should be given to aliphatic amines, for example, mono, di and 
trialkylamines, with alkyl groups with a maximum of 18 carbon atoms, or 
arylalkylamines with the same number of carbon atoms in the aliphatic part 
and where aryl means a benzene group possibly substituted by between 1 and 
3 hydroxy groups. As therapeutically acceptable amines, but not active in 
themselves, cyclic amines are very suitable, such as alkylene amines with 
rings of between 4 and 6 carbon atoms, possibly interrupted in the ring by 
heteroatoms, such as oxygen, sulphur and nitrogen, such as piperidine, 
morpholine or piperazine, or may be substituted for example by amino or 
hydroxy functions, as in the case of aminoethanol, ethylene diamine or 
choline. 
Should the crosslinked polysaccharides of the present invention be intended 
for pharmacological and therapeutic uses, their vehicling functions can be 
put to good use (as explained hereafter) for therapeutically active 
amines, preparing the salts of such amines. These salts can therefore 
derive from all basic nitrogenous drugs, such as those of the following 
groups: alkaloids, peptides, phenothiazines, benzodiazepines, 
thioxanthenes, hormones, vitamins, anticonvulsivants, antipsychotics, 
antiemetics, anesthetics, hypnotics, anorexigenics, tranquilizers, muscle 
relaxants, coronary vasodilators, antineoplastics, antibiotics, 
antibacterials, antivirals, antimalarials, carbonic anhydrase inhibitors, 
nonsteroid antiinflammatory agents, vasoconstrictors, cholinergic 
agonists, cholinergic antagonists, adrenergic agonists, adrenergic 
antagonists, narcotic antagonists. 
The salts can be prepared in a manner per se known in the art, for example 
by treating the crosslinked polysaccharide having a certain number of free 
carboxy functions, with the calculated quantity of base. However, salts 
can also be formed by double exchange; for example it is possible to 
obtain alkaline salts, such as sodium salt, treating a solution of 
quaternary ammonium salt of the crosslinked polysaccharide and/or 
partially esterified, with an aqueous solution of alkaline chloride, and 
isolating the alkaline salt present, for example by precipitation with a 
suitable solvent, such as a ketone, for example with acetone. 
The cross-linked polysaccharides of the present invention may use, as 
starting substrate, any natural or synthetic polysaccharide substituted by 
carboxy groups, such as those corresponding to the above starting 
materials for the procedure of the invention. The invention especially 
concerns cross-linked acidic polysaccharides derived from hyaluronic acid, 
from alginic acid, from carboxymethylcellulose, from carboxymethylamide 
and from carboxymethylchitin. 
Hyaluronic acid derivatives are of major importance compared to derivatives 
of other series, due to the biological origin of the starting substrate, 
which permits the new crosslinked substances to be used in pharmaceutics, 
surgery and medicine in general. 
The substrate of hyaluronic acid can be of any origin, such as acids 
extracted from the above natural starting materials, for example from 
cocks' combs. The preparation of these acids is described in literature: 
preferably, purified hyaluronic acids should be used. According to the 
invention, it is preferable to use hyaluronic acids constituting molecular 
fractions of the integral acids obtained directly by extraction of organic 
materials with a wide range of molecular weights, for example between 
90%-80% and 0.2% of the molecular weight of the integral acid, preferably 
between 5% and 0.2%. These fractions can be obtained by various procedures 
described in literature, and that is with hydrolyzing, oxidizing or 
enzymatic chemical agents or physical procedures, for example mechanical 
or irradiation procedures, and often during the same purification 
procedures, primordial extracts may be formed. Separation and purification 
of the molecular fractions obtained comes about by means of known 
techniques, such as by molecular filtration. One purified HY fraction 
suitable to be used according to the invention is for example the one 
known as "noninflammatory-NIF-NaHA sodium hyaluronate", described by 
Balazs in the pamphlet "Healon"--A guide to its use in Ophthalmic 
Surgery--D. Miller & R. Stegmann, eds. John Wiley & Sons N.Y. 81983: p.5. 
Also particularly important as starting materials for the esters of the 
present invention are two purified fractions which can be obtained from 
hyaluronic acid, for example the one extracted from cocks' combs, known by 
the names of "Hyalastine" and "Hyalectin". The fraction Hyalastine has an 
average molecular weight of about 50,000 to 100,000 while the fraction 
Hyalectin has an average molecular weight of about 500,000 to 730,000. One 
combined fraction of these two fractions has also been isolated and 
characterized as having an average molecular weight of between about 
250,000 and about 350,000. This combined fraction can be obtained with a 
yield of 80% of the total hyaluronic acid available in the particular 
starting material, while the fraction Hyalectin can be obtained with a 
yield of 30% and the fraction Hyalastine with a yield of 50% of the 
starting HY. The preparation of these fractions is described in the 
above-mentioned European patent publication No. 0138572A3. 
The alginic acid to be used to prepare new derivatives may be obtained by 
extraction from various natural materials, especially from brown algae 
(Phaecophyceae). The polysaccharide is constituted by chains of 
D-mannuronic acid and L-guluronic acid. The molecular weight is very 
varied, depending on its origin and can be, for instance, between 30,000 
and 200,000. It depends not only on the type of alga used, but also on the 
season in which it was gathered, on the origin and age of the plant. The 
main species of brown algae used to obtain alginic acid are for example 
Macrocystis pyrifera, Laminaria Cloustoni, Laminaria hyperborea, Laminaria 
Flexicaulis, Laminaria digitata, Ascophyllum nodosum and Fucus serratus. 
Alginic acid is found in these algae as a diffuse component of the cell 
walls in the form of a mixture of its various alkaline salts, among which 
features especially sodium salt, a mixture known also as algin. These 
salts are normally extracted in aqueous conditions with a solution of 
sodium carbonate and from this extract alginic acid can be obtained 
directly by precipitation with an acid, for example a mineral acid such as 
hydrochloric acid, or indirectly by first making insoluble calcium salt. 
Alginic acid or alkaline alginates can however by obtained by 
microbiological methods, for example by fermentation with Pseudomonas 
aeruginosa or Pseudomonas putida, Pseudomonas fluorescens or Pseudomonas 
mendocina mutants. Preparation of the various types of alginic acid is 
described in literature. For the purposes of the present invention, 
purified alginic acids should be used. 
Carboxymethyl-derivatives of cellulose, starch and chitin are also useful 
in the present invention and have also been amply described in literature. 
Apart from carboxy polysaccharides themselves, it is possible to use their 
partial esters with mono or polyvalent alcohols as starting materials for 
the preparation of the new cross-linked products of the invention. 
In the cross-linked polysaccharides of the invention which also have 
carboxy functions esterified with monovalent or polyvalent alcohols, 
whether these functions be present in the starting materials of the above 
mentioned procedure, or whether they be introduced at the end of the 
procedure, the alcohols may belong to the aliphatic, araliphatic, 
alicyclic or heterocyclic series. 
The following description concerns the overall view of the above useful 
alcohols, on the understanding that the various groups and single 
compounds should be chosen on the basis of the particular polysaccharide 
substrates and their uses, as illustrated below. Thus, for example, one 
skilled in the art will know which alcohols are to be chosen for the 
cross-linked products intended for therapeutic and sanitary uses and which 
others are more suitable for the cross-linked products for use in the 
alimentary field or in the perfume industry or in the fields of resins and 
textiles. 
Alcohols of the aliphatic series for use as esterifying components are for 
example those with a maximum of 34 carbon atoms, which can be saturated or 
unsaturated and which can possibly also be substituted by other free 
functional or functionally modified groups, such as amino, hydroxyl, 
aldehydo, keto, mercapto, carboxy groups or by groups deriving from these, 
such as hydrocarbyl or dihydrocarbylamino groups (here and hereafter 
meaning by the term "hydrocarbyl" not only monovalent radicals of 
carbohydrates for example type C.sub.n H.sub.2n+1', but also bivalent or 
trivalent radicals, such as "alkylenes" C.sub.n H.sub.2n or "alkylidenes" 
C.sub.n H.sub.2n), ether or ester groups, acetal or ketal groups, 
thioether or thioester groups, and esterified carboxy groups or carbamidic 
and substituted carbamidic groups by one or two hydrocarbyl groups, by 
nitrile groups or halogens. Of the above groups containing hydrocarbyl 
radicals, these should preferably be inferior aliphatic radicals, such as 
alkylic, with a maximum of 6 carbon atoms. Such alcohols may then be 
interupted in the carbon atom chain by heteroatoms, such as atoms of 
oxygen, nitrogen and sulfur. 
It is preferable to choose alcohols substituted with one or two of the 
abovesaid functional groups. Alcohols of the above group to be preferred 
for the purposes of the present invention are those with a maximum of 12 
and especially 6 carbon atoms and in which the hydrocarbyl radicals in the 
abovesaid amino, ether, ester, thioether, thioester, acetal, ketal groups 
represent alkyl groups with a maximum of 4 carbon atoms, and also in the 
esterified carboxy groups or substituted carbamidic groups or hydrocarbyl 
groups are alkyls with the same number of carbon atoms, and in which the 
amino or carbamidic groups may be alkylene amine or alkylene carbamidic 
groups with a maximum of 8 carbon atoms. Of these alcohols special mention 
should be given to those which are saturated and unsubstituted such as 
methyl, ethyl, propyl, isopropyl alcohols, n-butyl alcohol, isobutyl 
alcohol, tert-butyl alcohol, amyl alcohols, pentyl, hexyl, octyl, nonyl 
and dodecyl alcohols and above all those with a linear chain, such as 
n-octyl and n-dodecyl alcohols. Of the substituted alcohols of this group, 
the following should be mentioned: bivalent alcohols such as ethylene 
glycol, propylene glycol, butylene glycol, trivalent alcohols such as 
glycerin, aldehyde alcohols such as tartronic alcohol, carboxy alcohols 
such as lactic acids, for example glycolic acid, malic acid, tartaric 
acids, citric acid, aminoalcohols, such as aminoethanol, aminopropanol, 
n-aminopropanol, n-aminobutanol and their dimethyl and diethyl derivatives 
in the amine function, choline, pyrrolidinylethanol, piperidinylethanol, 
piperazinylethanol and the corresponding derivatives of n-propyl or 
n-butyl alcohols, monothioethyleneglycol and its alkyl derivatives, for 
example the ethyl derivative in the mercapto function. 
Of the higher aliphatic saturated alcohols, the following should be given 
as examples: cetyl alcohol and myricyl alcohol, but of special importance 
for the purposes of the present invention are the higher unsaturated 
alcohols with one or two double bonds, such as especially those contained 
in many essential oils and having affinity with terpenes, such as 
citronellol, geraniol, nerol, nerolidol, linalool, farnesol, phytol. Of 
the lower unsaturated alcohols, the ones to be considered are allyl 
alcohol and propargyl alcohol. 
Of the araliphatic alcohols, special mention should be given to those with 
only one benzene residue and in which the aliphatic chain has a maximum of 
4 carbon atoms and in which the benzene residue may be substituted by 
between 1 and 3 methyl or hydroxy groups or by halogen atoms, especially 
by chlorine, bromine, iodine, and in which the aliphatic chain may be 
substituted by one or more functions chosen from the groups comprising 
free amino groups or mono or dimethyl groups or by pyrrolidine or 
piperidine groups. Of these alcohols special mention should be given to 
benzyl alcohol and phenethyl alcohol. 
Alcohols of the cycloaliphatic or aliphatic cycloaliphatic series may 
derive from mono or polycyclic carbohydrates, may preferably have a 
maximum of 34 carbon atoms, may be unsubstituted and may contain one or 
more substituents, such as those mentioned above for the aliphatic 
alcohols. Of the alcohols derived from single-ringed cyclic carbohydrates, 
special mention should be given to those with a maximum of 12 carbon 
atoms, the rings having preferably between 5 and 7 carbon atoms, which may 
be substituted for example by between one and three lower alkyl groups, 
such as methyl, ethyl, propyl, or isopropyl groups. As alcohols specific 
to this group, cyclohexanol, cyclohexanediol, 1,2,3 cyclohexanetriol and 
1,3,5 cyclohexanetriol (phloroglucitol), inositol, should be mentioned, as 
well as the alcohols deriving from p-menthane, such as carvomenthol, 
menthol, .alpha. and .gamma.-terpineol, 1-terpinenol, 4-terpinenol and 
piperitol, or the mixture of these alcohols as "terpineol", 1,4- and 
1,8-terpin. Of the alcohols deriving from carbohydrates with condensed 
rings, for example those of the thujane, pinane or camphane group, useful 
also are thujanol, sabinol, pinol hydrate, D and L-borneol and D and 
L-isoborneol. 
Aliphatic-cycloaliphatic polycyclic alcohols to be used for the esters of 
the present invention are sterols, cholic acids and steroids, such as the 
sexual hormones and their synthetic analogues, and in particular 
corticosteroids and their derivatives. Thus it is possible to use for 
example: cholesterol, dihydrocholesterol, epidihydrocholesterol, 
coprostanol, epicoprostanol, sitosterol, stigmasterol, ergosterol, cholic 
acid, deoxycholic acid, lithocholic acid, estriol, estradiol, equilenin, 
equilin and their alkyl derivatives, as well as the ethynyl or propynyl 
derivatives in position 17, for example 17-.alpha.-ethynyl-estradiol or 
7-.alpha.-methyl-17-.alpha.-ethynyl-estradiol, pregnenolone, pregnanediol, 
testosterone and its derivatives, such as 17-.alpha.-methyltestosterone, 
1,2-dehydrotestosterone and 17-.alpha.-methyl-1,2-dehydrotestosterone, 
alkynyl derivatives in position 17 of testosterone and 
1,2-dehydrotestosterone, such as 17-.alpha.-ethynyltestosterone, 
17-.alpha.-propynyltestosterone, norgestrel, hydroxyprogesterone, 
corticosterone, deoxycorticosterone, 19-nortestosterone, 
19-nor-17-.alpha.-methyltestosterone and 
19-nor-17-.alpha.-ethynyltestosterone, cortisone, hydrocortisone, 
prednisone, prednisolone, fludrocortisone, dexamethasone, betamethasone, 
paramethasone, flumethasone, fluocinolone, fluprednylidene, clobetasol, 
beclomethasone, aldosterone, desoxycorticosterone, alfaxalone, alfadolone, 
bolasterone. 
Useful esterifying components for the esters of the present invention are 
genins, (aglycons) of cardioactive glycosides, such as digitoxigenin, 
gitoxigenin, digoxigenin, strophanthidin, tigogenin, saponins. 
Other alcohols to be used according to the invention are vitamin alcohols 
such as axerophthol, vitamins D.sub.2 and D.sub.3, aneurine, lactoflavine, 
ascorbic acid, riboflavine, thiamine, pantothenic acid. 
Heterocyclic alcohols may be considered to be derivatives of the abovesaid 
cycloaliphatic or aliphatic-cycloaliphatic alcohols, if their linear or 
cyclic chains are interrupted by one or more, for example between one and 
three ethero atoms chosen from the group formed by --O--, --S--, --N and 
--NH and in these there may be one or more unsaturated bonds for example 
double bonds, particularly between one and three, thus including also 
heterocyclic compounds with aromatic structures. The following are 
specific useful examples: furfuryl alcohol, alkaloids and derivatives such 
as atropine, scopolamine, cinchonine, cinchonidina, quinine, morphine, 
codeine, nalorphine, N-butylscopolammonium bromide, ajmaline; 
phenylethylamines such as ephedrine, isoproterenol, epinephrine; 
phenothiazine drugs such as perphenazine, pipothiazine, carphenazine, 
homofenazine, acetophenazine, fluphenazine, N-hydroxyethylpromethazine 
chloride; thioxanthene drugs such as flupenthizol and clopenthixol; 
anticonvulsivants such as meprophendiol, antipsychotics such as opipramol; 
antiemetics such as oxypendil; analgesics such as carbetidine and 
phenoperidine and methadol; hypnotics such as etodroxizine; anorexics such 
as benzhydrol and diphemethoxidine; mild tranquilizers such as 
hydroxyzine; muscle relaxants such as cinnamedrine, diphylline, 
mephenesin, methocarbamol, chlorphenesin, 2,2-diethyl-1,3-propanediol, 
guaifenesin, idrocilamide; coronary vasodilators such as dipyridamole and 
oxyfedrine; adrenergic blockers such as propanolol, timolol, pindolot, 
bupranolol, atenolol, metoprolol, practolol; antineoplastics such as 
6-azauridine, cytarabine, floxuridine; antibiotics such as 
chloramphenicol, thiamphenicol, erythromycin, oleandomycin, lincomycin; 
antivirals such as idoxuridine; peripheral vasodilators such as 
isonicotinyl alcohol; carbonic anhydrase inhibitors such as sulocarbilate; 
antiasthmatics and antiinflammatories such as tiaramide; sulfamides such 
as 2-p-sulfanylanilinoethanol. While "inner" cross-linking of acid 
polysaccharides alone, without "external" esterification of the carboxy 
groups with alcohols of the aforesaid series, yields products which 
present properties similar to those of the starting products, but with the 
advantages mentioned previously, and may therefore be applied in all the 
fields in which the latter are used; simultaneous "external" 
esterification of the carboxy groups may prove useful in imparting to the 
polysaccharide properties specific to the alcohols themselves. In this 
case the crosslinked products act as a vehicle for the properties of the 
alcohols and in this manner can be put to good use in the pharmaceutical 
and medical fields. Thus, it is possible to prepare drugs containing 
cross-linked products according to the invention and therapeutically 
active alcohols, such as those listed above. Medicaments of this kind 
mainly have a hyaluronic acid base but those based on the other 
polysaccharides mentioned can also be used. 
Salification, too, can have a double purpose, both in the manufacture of 
products in which the intrinsic properties of the basic polysaccharides 
are put to use, and in imparting to these the properties of the salifying 
bases, for example those with therapeutically active bases, for example 
those mentioned above. 
The vehicling of a drug with the new cross-linked products can however also 
be achieved by the simple addition (physical mixture) of a drug and/or of 
a therapeutically active base to the polysaccharide. The present invention 
therefore also includes medicaments containing: 
1. a pharmacologically active substance or an association of 
pharmacologically active substances and 
2. a carrying vehicle comprising a cross-linked product of an acidic 
polysaccharide according to the invention 
Salts may be present in mixtures of this kind, should the following be 
chosen as component: 
1) an organic base. Particularly important are associations of this type in 
which the component 
2) is a cross-linked product having as its base hyaluronic acid or one of 
its esters. 
The abovesaid medicaments may be in solid form, for example as freeze-dried 
powders containing only the two components 1) and 2) as a mixture or 
separately packed and this galenic form is especially suitable for topical 
use. Indeed such medicaments in solid form, on contact with the epithelium 
to be treated, form solutions which are more or less concentrated 
according to the nature of the particular epithelium and with the same 
characteristics as the solutions previously prepared in vitro and 
represent another aspect of the present invention. Such solutions are 
preferably in distilled water or in sterile physiological solutions and 
contain preferably no other pharmaceutical vehicle. The concentrations of 
these solutions may vary greatly, for example between 0.01 and 75%, both 
for the two separate components and for their mixtures. Preference should 
be given to solutions of a pronounced elastic viscous character, for 
example containing from 10% to 100% of the medicament or of each of the 
two components. 
Particularly are medicaments of this type, both in an anhydrous form 
(freeze-dried powder) or as solutions, either concentrated or diluted in 
water or saline, possibly with the addition of additives or auxiliary 
substances, such as particularly disinfectants or mineral salts acting as 
buffer or others, for ophthalmic use, based on cross-linked hyaluronic 
acid. 
Among the medicaments of the type described here, preference should be 
given, as the case may be, to those with a degree of acidity suitable to 
the area in which they are to be applied, that is, with a physiologically 
tolerable pH. The pH may be adjusted by suitably regulating the quantity 
of polysaccharide, of its salts and of any basic or acid substances which 
may be present. 
The degree of cross-linking and esterification depends firstly on the 
properties which are to be obtained in the various fields of application, 
for example a lesser or greater degree of lipophilia or hydrophilia in 
cases of therapeutic application. Usually, a high degree of cross-linking 
and esterification increases the lipophilic character of a substance and 
therefore diminishes its solubility in water. For a therapeutic use of the 
new cross-linked products it is important to regulate the degree of 
esterification in order to ensure, despite good and improved lipophilia 
compared to the basic polysaccharides or their salts, a sufficient degree 
of hydrosolubility. Naturally, the molecular size of the esterifying 
components should be considered, as it usually influences hydrosolubility 
in an inversely proportional manner. 
The new cross-linked products, esterified with therapeutically active 
alcohols and/or salified with therapeutically active bases or the 
abovesaid medicaments containing them, are therapeutically more 
efficacious, and have a greater and/or longer-lasting effect (retard 
effect) as compared to the starting drugs. Particularly important are 
medicaments of this type, based on polysaccharides which are highly 
compatible with the biological environment, such as in the case of 
hyaluronic acid. 
Hyaluronic acid also constitutes however a very important substrate thanks 
to its own pharmaceutical action. The cross-linked products based on this 
polysaccharide, possibly also esterified with therapeutically inactive 
alcohols, have improved stability compared to hyaluronic acid itself and 
its esters. Such cross-linked products can be used for all known 
indications for the above compounds, for example hyaluronic acid itself, 
for example intraarticular injections with a lubricant action. As a result 
of the greater stability of the new cross-linked products with regard to 
hyaluronidase as compared to the free acid and to the esters, its action 
is greatly prolonged. The pharmacologically inert alcohols with which to 
esterify such cross-linked products of hyaluronic acid are preferably 
lower aliphatic alcohols with a maximum of 8 carbon atoms, especially 
saturated monovalent alcohols, such as ethanol, propyl alcohol, isopropyl 
alcohol, and n-butyl alcohol or isobutyl alcohol. 
The cross-linked products based on hyaluronic acid are very suitable for 
cosmetic uses. Of the esters of these cross-linked products, important are 
those deriving from therapeutically inactive alcohols, such as for example 
saturated or unsaturated aliphatic alcohols, for example unsubstituted 
alcohols of this kind with a straight or ramified chain, for example with 
between 1 and 8 carbon atoms, such as those mentioned above. Particularly 
interesting are also unsaturated alcohols, for example with one or more 
double bonds, such as vinyl or allyl alcohols and their condensed 
derivatives, or polyvalent alcohols, such as glycerine. Also useful are 
aliphatic alcohols, for example those derived from cyclopentane or 
cyclohexane and their derivatives substituted by lower alkyl groups, for 
example alkyls with between 1 and 4 carbon atoms, especially by methyl 
groups. Particularly interesting are also esters with cycloaliphatic and 
aliphatic-cycloaliphatic alcohols derived from terpenes, such as those 
mentioned above and from therapeutically active alcohols, and which are 
also useful in cosmetics. 
Extremely important is the use of cross-linked products based on hyaluronic 
acid for the manufacture of sanitary and surgical items. The esters of 
these cross-linked products are preferably those mentioned above for use 
in cosmetics. 
The use of hyaluronic cross-linked products as vehicles for drugs intended 
for topical use is particularly useful in ophthalmology, where a 
particular compatibility is noted between the new products and the corneal 
epithelium, and therefore also excellent tolerability, with no 
sensitization effects. Furthermore, when the medicaments are administered 
in the form of concentrated solutions with elastic-viscous characteristics 
or in solid form, it is possible to obtain, on the corneal epithelium, 
homogenous and stable films which are perfectly transparent and adhering, 
which guarantee prolonged bioavailability of the drug and which therefore 
constitute excellent preparations with a retard effect. Such ophthalmic 
medicaments are particularly valuable in the veterinary field, considering 
that no chemotherapeutic specialities exist in this field, for example, 
veterinary specialities for ocular use containing chemotherapeutic 
components. As a result, preparations intended for humans are normally 
used and these do not always guarantee a specific range of action, nor 
they do allow for the particular conditions in which the treatment must be 
effected. This, for example, is the case of infective 
keratoconjunctivitis, pink eye or IBK, an infection which mainly affects 
cattle, sheep and goats. 
The new cross-linked hyaluronic products and possibly medicaments of the 
type described above which contain them as component 2) may be applied in 
other fields too, and markedly in dermatology and in diseases of the 
mucosa, for example of the mouth. Furthermore, they can be used to obtain 
a systemic effect thanks to transuctaneous absorption, for example in 
suppositories. All these applications are possible both in human and 
veterinary medicine. In human medicine the new medicaments are 
particularly suitable for pediatric use. The present invention includes in 
particular any one of these therapeutic applications. 
Also objects of the present invention are pharmaceutical preparations 
containing one or more cross-linked acidic polysaccharide products as 
defined above or associative medicaments containing them as component 2) 
also mentioned above. Apart from the therapeutically active substance or 
substances, such pharmaceutical preparations also contain the usual 
excipients and may be destined for oral, rectal, parenteral, subcutaneous, 
local or intradermal use. They are therefore in solid or semisolid form, 
for example pills, tablets, gelatinous capsules, capsules, suppositories, 
soft gelatin capsules. For parenteral and subcutaneous uses those forms 
intended for intramuscular or intradermal uses, or suitable for infusions 
or intravenous injections can be used, and can therefore be presented as 
solutions of the active compounds or as freeze-dried powders of the active 
compounds to be mixed with one or more pharmaceutically acceptable 
excipients or diluents, and which are suitable for the above uses being 
osmotically compatible with the physiological fluids. For local use, those 
preparations in the form of sprays should be considered, for example nasal 
sprays, creams and ointments for topical use or sticking plasters 
specially prepared for intradermal administration. Solubility of the 
cross-linked products in organic solvents with low boiling points makes 
them particularly suitable for the manufacture of "sprays". 
The preparations of this invention can be administered to man or animal. 
They contain preferably between 0.01% and 10% of active component for the 
solutions, sprays, ointments and creams and between 1% and 100% and 
preferably between 15% and 50% of active compound for the solid form 
preparations. Dosages to be administered will depend on individual 
diagnoses, on the desired effect and on the chosen administration route. 
The daily dosages of these preparations can be deducted from those already 
used both for the basic polysaccharide (as in the case of hyaluronic acid) 
for the corresponding cures, for example the cure for arthritis, for 
example in man or horse, and for the alcoholic component, in the case of 
esters, or of component 1) in the above medicaments, should these 
components represent the active principal whose action is to be exploited. 
Thus, for example, a cross-linked product of hyaluronic acid esterified 
even partially with cortisone, can be dosed according to its content of 
this steroid and to the usual dosage of the same in the known 
pharmaceutical preparations. 
The preparation of salts according to the invention can be carried out in 
per se known procedures, by bringing into contact solutions either in 
aqueous suspensions or in organic solvents of the two components 1) and 2) 
and possibly of bases or basic salts of the above alkaline or alkaline 
earth metals or magnesium or aluminium in calculated quantities and 
isolating the salts in amorphous anhydrous form according to known 
techniques. It is possible for example to first prepare aqueous solutions 
of the two components 1) and 2), release such components from aqueous 
solutions of their salts with suitable ionic exchangers, mix the two 
solutions at a low temperature, for example between 0.degree. C. and 
20.degree. C., if the salt thus obtained is easily soluble in water it can 
be freeze-dried, while poorly soluble salts may be separated by 
centrifugation or filtration or decantation and possibly subsequently 
dried. 
For these associated medicaments too, dosage is based on that of the active 
principles used singly and may therefore be easily determined by one 
skilled in the art, taking into consideration the dosages recommended for 
corresponding known drugs. In the cosmetic articles according to the 
invention, the cross-linked acidic polysaccharide products and their salts 
are mixed with the excipients commonly used in the art and are for example 
those already listed above for pharmaceutical preparations. Above all, 
creams, ointments, lotions for topical use are used, in which the 
crosslinked polysaccharide or one of its salts can constitute the active 
cosmetic principle, possibly with the addition of other cosmetically 
active principles, such as for example steroids, for example pregnenolone, 
or one of the principles already reported. In such polysaccharides, the 
carboxy groups not used in cross-linking are preferably free or salified 
or are esterified with pharmacologically inactive alcohols, for example 
one of the lower aliphatic alcohols mentioned previously. The cosmetic 
articles can however also contain groups esterified with alcohols which 
have themselves a cosmetic action or an action which is auxiliary to the 
same, such as for example disinfectant substances, sunshields, 
waterproofing or regenerating or antiwrinkle substances or odoriferous 
substances, especially perfumes. Such substances may however also be 
simply mixed with the cross-linked polysaccharide, thus constituting 
cosmetic compositions similar to the medicaments previously described in 
which the pharmaceutically active component 1) is substituted by a 
cosmetological factor. Use of the cosmetic preparations of the present 
invention in the perfume industry represents a great step forward in 
techniques, since it allows slow, constant and protracted release of the 
odorous principles. 
An important object of the present invention is constituted by sanitary and 
surgical articles, by their manufacturing methods and by their use. These 
articles are for example similar to those already known and commercially 
available or described in literature, for example those with a hyaluronic 
acid base, for example inserts or ophthalmic lenses. 
Surgical and sanitary articles of special importance are those which can be 
obtained from appropriate solutions of the cross-linked products in 
organic liquids which are capable of being made into films, sheets and 
threads to be used in surgery as auxiliary or substitutive articles for 
the skin in cases of serious damage to this organ, such as burns, or as 
suture threads in surgery. The invention includes particularly these uses 
and a preparation procedure for these articles consisting in (a) forming a 
solution of the crosslinked polysaccharide or of one of its salts in an 
organic solvent; (b) making this solution into sheet or thread form; and 
(c) removing the organic solvent. 
The formation of a solution of the crosslinked polysaccharide or of one of 
its salts is conducted in a suitable organic solvent, for example a 
ketone, an ester or an aprotic solvent such as an amide of a carboxy acid, 
especially a dialkylamide or of an aliphatic acid with between 1 and 5 
carbon atoms and deriving from alkyl groups with between 1 and 6 carbon 
atoms, and above all from an organic sulfoxide, that is a dialkylsulfoxide 
with alkyl groups with a maximum of 6 carbon atoms, such as especially 
dimethylsulfoxide or diethylsulfoxide and also especially a fluorurate 
solvent with a low boiling point, such as especially 
hexafluoro-isopropanol. 
Removing the organic solvent (c) is conducted by contact with another 
organic or aqueous solvent which must be mixable with the first solvent 
and in which the polysaccharide ester is insoluble, especially a lower 
aliphatic alcohol, for example ethyl alcohol (wet spinning), or, should a 
solvent with a not too high boiling point be used to prepare the solution 
of the polysaccharide derivative, in removing this same solvent by dry 
spinning, that is with a gas current and especially with suitably heated 
nitrogen. Dry-wet spinning can also be used with excellent results. 
Particularly important are threads obtained with cross-linked products with 
a hyaluronic acid base, which can be used for the preparation of lints for 
the medication of wounds and in surgery. The use of such lints has the 
special advantage of being biodegradable to hyaluronic acid in the 
organism, by means of naturally existing enzymes. If cross-linked products 
containing also ester groups are used, these should be chosen from among 
those deriving from therapeutically acceptable alcohols, so that after 
enzymatic scission, apart from hyaluronic acid, innocuous alcohols are 
also formed, such as ethyl alcohol. 
In the preparation of the abovesaid sanitary and surgical articles, it is 
possible also to include to advantage plasticizing materials in order to 
improve their mechanical characteristics, such as in the case of threads, 
to improve their resistance to tangles. Such plasticizers may be for 
example alkaline salts of fatty acids, for example sodium stearate, esters 
of organic acids with a high number of carbon atoms and the like. 
Another application of hyaluronic cross-linked products where their 
biodegradability by esterases present in the organism is exploited, is 
represented by the preparation of capsules for subcutaneous implantation 
of medicaments or microcapsules by injection, for example by subcutaneous 
or intramuscular route. Up till now, for the application of subcutaneous 
medicaments designed to give slow release and therefore a retard effect, 
capsules made of silicon materials have been used, with the disadvantage 
that such capsules tend to migrate within the organism with no possibility 
of recovering them. Clearly, with the new hyaluronic derivatives this 
danger has been eliminated. 
Of great importance is the preparation of microcapsules based on 
cross-linked hyaluronic products, eliminating the problems associated with 
their use, until now very limited for the same reasons as those explained 
above and opening up a vast field of application wherever a retard effect 
by injective route is desired. 
Another application in the fields of medicine and surgery of the 
cross-linked hyaluronic products is represented by the preparation of 
various solid inserts such as plates, discs, sheets, and the like to 
replace those currently in use which are made of metal or synthetic 
plastic material, wherever these inserts are destined for removal after a 
certain period of time. Preparations with an animal collagen base, being 
proteic by nature, often have unpleasant side effects such as inflammation 
or rejection. In the case of cross-linked hyaluronic products, even though 
they are made of animal and not human hyaluronic acid, this danger does 
not exist as there is no incompatibility between the polysaccharides of 
various animal species. 
Another application regards their use in increasing and correcting defects 
in the soft tissues: for a long time now there has been an urgent call for 
safe and effective biomaterials with which to substitute lost or damaged 
soft tissues. Many materials have been used such as paraffin, teflon 
paste, silicone and bovine collagen to replace lost soft tissues. However, 
these materials were associated with undesirable and permanent changes in 
the skin, with in situ migration of implants and negative reactions. For 
this reason there is a constant call in medicine for a versatile 
biomaterial. The cross-linked products of hyaluronic acid may be safely 
used to correct such defects of the soft tissues such as acne scars, 
postsurgical atropic irregularities, Mobs' chemosurgery, lacerated scars 
of the lip and old-age wrinkles. 
Part of the applications in the fields of medicine and surgery of the new 
hyaluronic derivatives according to the present invention are preparations 
made of expanding material, especially in the form of sponges, for the 
medication of wounds or various lesions. 
The above applications of the cross-linked products with a hyaluronic acid 
base represent the ideal solution for those sanitary and surgical articles 
which are intended to be introduced in one way or another into human or 
animal organisms or to be externally applied to the same. It is also 
possible however to make the same articles, using other cross-linked 
polysaccharides according to the invention, such as those mentioned above 
and especially those with an alginic acid base. In the same way, too, the 
cross-linked products are broken down in the organism to give basic 
polysaccharides which are generally well tolerated by the organism with no 
danger of rejection. 
Of the cross-linked alginic acid products, special mention should be given 
to industrial and household uses and articles and alimentary articles and 
their uses. These, especially in the form of cross-linked partial salts, 
possibly further esterified with inert alcohols, such as especially lower 
aliphatic alcohols, for the preparation of gels, which can be widely used 
in the food industry, for the manufacture of ice-creams, puddings and many 
other kinds of sweet foods. Another property of these cross-linked 
products is their capacity for retaining water, because of which they can 
be used for example for the preservation of many frozen foods. A third 
property is their ability to emulsify and to stabilize emulsions. From 
this point of view, too, the alginic cross-linked products are important 
in the food industry, where they serve in the preparation of condiments 
and for the stabilization of many drinks such as beer and fruit juice, 
sauces and syrups. As emulsifiers, alginic cross-linked products can be 
used in the manufacture of polishes, anti-foam agents, lactics and as 
stabilizers in the ceramics and detergent industries. They can also be 
used in the paper industry, to make adhesive products, in textile printing 
and dyeing. 
With regard to the physical, pharmacological and therapeutic properties, 
the substantial equivalence between the acidic polysaccharide cross-linked 
products of the present invention, possibly esterified with the abovesaid 
alcohols, and their salts, such as metal salts, it should be understood 
that the facts previously reported regarding the nonsalified products are 
true also of the salts. 
The present invention also includes modifications in the preparation 
procedure for the new cross-linked products and their salts, in which a 
procedure is interrupted at any one stage or in which a procedure is begun 
with an intermediate compound and the remaining stages are carried out, or 
in which the starting products are formed in situ.