METHOD FOR THE PRODUCTION OF AN ANTIBACTERIAL CHITOS-CONTAINING POLYMER FOR MEDICINAL PURPOSES, IN PARTICULAR FOR WOUND TREATMENT

Description

[0001] The present invention relates to a method for producing a polymer for medical purposes, in particular for wound treatment. The invention also relates to the polymer obtained by the method as such, as well as its use in medicine and in wound dressings.

[0002] Wound dressings with a hydrogel layer are known in the prior art. Such wound dressings can both absorb wound exudate and moisturize the wound, thus accelerating wound healing.

[0003] Wound dressings with an antibacterial component are also known in the prior art. Due to their antibacterial properties, they are used particularly for the treatment of infected wounds.

[0004] Velazquez-Morales et al. ("Polymer electrolytes derived from chitosan / polyether networks"; Electrochimica Acta, Vol. 43, 1998) describe the synthesis of oxypropylated chitosan and its reaction with oligoether-based mono- and diisocyanates. The aim is to improve the film-forming properties of cross-linked polymer electrolytes in order to produce particularly thin polymer films.

[0005] Gandini et al. ("Recent contributions to the preparation of polymers derived from renewable resources"; Journal of Polymers and the Environment, Vol. 10, 2002) address the use of renewable resources as starting materials for polymer synthesis. They disclose the reaction of oxypropylated chitosan with an isocyanate-terminated prepolymer.

[0006] Levi-Polyachenko et al. ("Chitosan wound dressing with hexagonal silver nanoparticles for hyperthermia and enhanced delivery of small molecules"; Colloids and Surfaces B: Biointerfaces, Vol. 142, 2016) reveal a wound dressing that is a dried film consisting of chitosan and silver nanoparticles.

[0007] There is a need to provide new materials for wound dressings based on hydrogels.

[0008] The object of the present invention was to provide a new and improved material for medical purposes. In particular, the object of the present invention was to provide a new and improved material for wound treatment. Various requirements were placed on the material. These requirements were as follows: a) The material should exhibit good antibacterial efficacy. b) The material should not release any antibacterial components. c) The material should be suitable for a wide variety of wound types and enable gentle wound treatment. d) The material should be easy and quick to manufacture. e) The material should not contain any substances toxic to the human or animal body.

[0009] It has been shown that a polymer produced using the following process can fulfill the aforementioned tasks and requirements.

[0010] The present invention is defined in the accompanying claims.

[0011] The polymer according to the invention for use in wound treatment in the sense of a medical indication according to claim 1 and as a component of a wound dressing according to claim 2 is produced by the following steps: i. Providing an isocyanate-terminated prepolymer containing polyalkylene oxide units. ii. Dissolving a chitosan in an aqueous liquid to obtain an aqueous chitosan-containing preparation. iii. Mixing the prepolymer, the aqueous chitosan-containing preparation, and optionally one or more other components to obtain a reaction mixture. iv. Reacting the prepolymer in the reaction mixture to obtain the polymer.

[0012] The proportion of the prepolymer, the chitosan, the aqueous liquid and one or more other components, each based on the total weight of the reaction mixture, is as follows: 5 to 50 wt.% prepolymer, at least 0.4 wt.% chitosan, 40 to 90 wt.% aqueous liquid and 0 to 30 wt.% of one or more other components.

[0013] The order of steps i. and ii. can also be reversed and is not essential to the invention.

[0014] The isocyanate-terminated prepolymer is also referred to simply as the prepolymer in this document. Therefore, whenever the prepolymer is mentioned in this document, it refers, unless otherwise stated, to the isocyanate-terminated prepolymer.

[0015] A characteristic feature of the present invention is that the chitosan is encapsulated within the polymer. This is achieved in particular by allowing the prepolymer in the reaction mixture to react with the chitosan, so that at least a portion of the chitosan, or preferably the entire amount of chitosan, is covalently bound within the polymer. The reaction mechanisms involved are described in more detail below.

[0016] In principle, the polymer according to the invention provides a hydrated polyurethane hydrogel system or a hydrated polyurethane foam system in whose cross-linked polymer structure chitosan is firmly encapsulated, particularly by covalent incorporation. This combines the advantages of hydrogel technology in wound treatment with the antibacterial properties of chitosan in a particularly advantageous manner. The polymer according to the invention can thus create a moist wound environment that supports wound healing by absorbing wound exudate and / or releasing moisture to the wound. It does not adhere to the wound. These properties alone enable effective and gentle treatment of many different wound types. Furthermore, the polymer according to the invention possesses antibacterial efficacy due to its chitosan content, which further enhances its wound-healing potential.It is considered particularly advantageous that the chitosan, as an antibacterial active ingredient, is firmly encapsulated within the polymer structure and consequently is not released. The polymer therefore does not release the chitosan into the wound, which could reduce its antibacterial efficacy. Further advantages of the polymer according to the invention are its simple and rapid production and its good biocompatibility with human and animal tissue.

[0017] In a particularly preferred embodiment of the invention, the prepolymer is branched with at least three arms (in particular, exactly three arms), and the polyalkylene oxide units are formed by polyethylene oxide and / or polypropylene oxide units. In step i above, an isocyanate-terminated prepolymer with at least three arms, containing polyethylene oxide and / or polypropylene oxide units, is thus provided. The weight ratio of ethylene oxide to propylene oxide units can be from 3:1 to 7:1. The polymer can be produced particularly well with such a compound.

[0018] A typical isocyanate-terminated prepolymer according to the aforementioned particularly preferred embodiment is, for example, a three-arm copolymer of ethylene oxide and propylene oxide units, each terminally reacted with a molecule of isophorone diisocyanate. It has a content of reactive isocyanate end groups (NCO groups) of 2.5% to 4.0%, preferably 3.0% to 3.4%, and particularly preferably 3.2%, and a molar ratio of ethylene oxide units to propylene oxide units of 3:1 to 4:1. Such an isocyanate-terminated prepolymer with aliphatic isocyanate groups is commercially available, for example, as Aquapol® < PI-13000-31 (Carpenter; Richmond, USA).

[0019] The following figure illustrates the schematic structure of a three-armed, isocyanate-terminated prepolymer containing polyethylene oxide and polypropylene oxide units (as in Aquapol®). A glycerol molecule forms the center of the prepolymer. The three "arms" of the prepolymer, each with a terminal isocyanate group, are linked to the hydroxyl groups of the glycerol molecule. The glycerol molecule itself is not shown in the figure. It would be located in the right half of the image where the three "arms," ​​schematically represented as wavy lines, meet. The left half of the image shows the chemical structure of one "arm" in more detail.

[0020] Chitosan is available in various molar weights and is typically obtained from chitin by deacetylation. The chitosan can have a molar weight of 50 kDa to 375 kDa, preferably 50 kDa to 310 kDa, and particularly preferably 50 kDa to 190 kDa. A lower molar weight has the advantage of easier solubility. Furthermore, the chitosan can have a degree of deacetylation of at least 50%, preferably at least 60%, more preferably at least 70%, and particularly preferably at least 75%. In particular, the chitosan exhibits a degree of deacetylation of 75% to 85%. Chitosan with a high degree of deacetylation possesses many highly reactive amine groups for rapid conversion of the prepolymer. Accordingly, a chitosan with a molar weight of 50 kDa to 190 kDa and a degree of deacetylation of at least 75%, particularly 75% to 85%, is especially preferred.Such chitosan is commercially available from the company Sigma-Aldrich as "low molecular weight chitosan".

[0021] The aqueous solution typically has an acidic pH, as chitosan would otherwise dissolve poorly or not at all. An aqueous solution has a water content of at least 50% by weight. However, the aqueous solution used here usually has a significantly higher water content, for example, at least 80%, 85%, 90%, or 95% by weight. A pH value is acidic if it is less than 7. The pH value of the aqueous solution can be, for example, 0 to 6, 0 to 5, 0 to 4, 0 to 3, 0 to 2, 0 to 1, 1 to 6, 2 to 6, 3 to 6, 4 to 6, or 5 to 6. The lower the pH value of the aqueous solution, the more chitosan can dissolve. The less acidic the aqueous solution, the better the amine groups of the dissolved chitosan can react with the prepolymer. In particular, the aqueous liquid is diluted hydrochloric acid.

[0022] The aqueous solution is essentially water to which an acid, such as hydrochloric acid, has been added. The amount of acid added depends on the amount of chitosan to be dissolved. Thus, the acid concentration in the solution typically increases with the amount of chitosan to be dissolved. Besides hydrochloric acid, other strong inorganic or organic acids can also be used to dissolve the chitosan. Examples include formic acid, citric acid, acetic acid, lactic acid, phosphoric acid, and propanoic acid. However, inorganic acids are preferred over organic acids in this context because they leave almost no residue in the polymer. The resulting polymers therefore exhibit higher purity. For example, hydrochloric acid leaves only inert chloride ions in the polymer.

[0023] The aqueous liquid may optionally contain other substances besides the acid component. However, in this case, it is specifically intended that the aqueous liquid contains no other substances apart from the acid component. The aqueous liquid then consists of water and the acid component. The claimed dilute hydrochloric acid, in any case, consists of water and hydrochloric acid and has an acidic pH value, which may be selected from one of the aforementioned ranges.

[0024] The aqueous solution is used to dissolve the chitosan. This yields an aqueous, chitosan-containing preparation, which is typically also a liquid. The color and viscosity of the preparation depend on the type and concentration of chitosan. For example, a preparation with 1 wt% chitosan is clear and thin, while a preparation with 4 wt% chitosan is yellowish and highly viscous (based on a low molar weight chitosan).

[0025] The additional components that can be optionally mixed with the prepolymer and the chitosan-containing aqueous preparation in step iii. could, for example, be a humectant or an inorganic salt. This allows the chemical and physical properties of the polymer to be influenced and adapted for the specific application. However, the presence of these additional components is not mandatory, which is why they are listed as optional here. For instance, it may be possible to mix only the prepolymer with the aqueous chitosan-containing preparation to obtain the reaction mixture. The reaction mixture would then consist of the prepolymer and the aqueous chitosan-containing preparation.

[0026] Suitable humectants include ethylene glycol, propylene glycol, PEG300, PEG2000, glycerol, sucrose, or sorbitol. Glycerol is particularly preferred. These humectants can increase the polymer's absorption capacity and reduce its moisture loss.

[0027] Sodium chloride, potassium chloride, magnesium chloride, calcium chloride, or a mixture of at least two of these salts can be used as the inorganic salt. Sodium chloride as the sole salt is particularly preferred. A preferred salt mixture contains sodium chloride, potassium chloride, and calcium chloride. These three salts are also used to prepare Ringer's solution. The inorganic salts can simulate the electrolyte content in wound serum released from a wound. Thus, the polymer provides a particularly wound-healing environment.

[0028] The following areas are provided according to the invention for the production of the antibacterial polymer with covalently bonded chitosan: The proportion of the prepolymer based on the total weight of the reaction mixture is 5 to 50 wt.%. In particular, the proportion of the prepolymer based on the total weight of the reaction mixture is 10 to 50 wt.%.

[0029] The proportion of chitosan, based on the total weight of the reaction mixture, is at least 0.4 wt%. Specifically, the proportion of chitosan, based on the total weight of the reaction mixture, is 0.4 to 5 wt%. The proportion of chitosan, based on the total weight of the reaction mixture, may also be limited to a range of 0.4 to 1.8 wt%.

[0030] The proportion of aqueous liquid based on the total weight of the reaction mixture is 40 to 90 wt.%. In particular, the proportion of aqueous liquid based on the total weight of the reaction mixture is 50 to 90 wt.%.

[0031] The proportion of one or more additional components, based on the total weight of the reaction mixture, is 0 to 30 wt.%. This range of 0 to 30 wt.% refers to the sum of all additional components present.

[0032] The proportions of the prepolymer, the chitosan, the aqueous liquid, and the other components together total 100 wt.%. If no other components are included (i.e., the optional additional components are omitted), the proportions of the prepolymer, the chitosan, and the aqueous liquid together total 100 wt.%.

[0033] Chemically speaking, the polymers proposed here are all hydrogels. A hydrogel is a dispersed system consisting of at least one solid hydrophilic phase and one liquid phase, namely water. The solid phase forms a sponge-like, three-dimensional polymeric network filled with water. However, the external appearance of the polymers can vary depending on the ratio of prepolymer to aqueous liquid in the reaction mixture. Thus, the polymer can exhibit the appearance of a gel, a gel foam, or a foam.

[0034] When the polymer exists as a gel, it contains few or no cavities or cells. The polymer can then form a continuous, discrete layer. As a gel, the polymer can also be transparent. Therefore, when the polymer is in gel form, it exhibits the typical external appearance of hydrogels.

[0035] When the polymer exists as a foam, it is porous and contains numerous open and / or closed cavities or cells. The foam polymer is typically white and opaque, and more voluminous compared to a gel polymer of the same mass. Furthermore, the foam polymer contains a higher solid polymer content and less water than a gel polymer of the same mass.

[0036] The variant of the polymer known as "gel foam" represents a transitional form between gel and foam. "Gel foam" can also be understood as a pre-swollen hydrophilic foam.

[0037] Three alternative embodiments of the invention are described below, in which the aforementioned parameters for the prepolymer and the aqueous liquid are further specified. Due to the different parameters for the prepolymer and the aqueous liquid, the polymers according to these three embodiments differ in their consistency and are present as either a gel, gel foam, or foam.

[0038] Firstly, the proportions of the prepolymer and the aqueous liquid can be chosen as follows: The proportion of the prepolymer based on the total weight of the reaction mixture is 10 to 25 wt.%.

[0039] The proportion of aqueous liquid relative to the total weight of the reaction mixture is 74 to 90 wt.%.

[0040] After the prepolymer is reacted in the reaction mixture, a polymer in gel form is obtained. This gel-like polymer has a high water-release capacity and is therefore particularly well-suited for the treatment of dry wounds.

[0041] Secondly, the proportions of the prepolymer and the aqueous liquid can be chosen as follows: The proportion of the prepolymer based on the total weight of the reaction mixture is 26 to 33 wt.%.

[0042] The proportion of aqueous liquid relative to the total weight of the reaction mixture is 66 to 73 wt.%.

[0043] After the prepolymer reacts in the reaction mixture, a polymer in the gel-to-foam transition state is obtained, which is also referred to as gel foam. The gel foam can both release and absorb a relatively large amount of water and is therefore suitable for treating a wide variety of wound types.

[0044] Thirdly, the proportions of the prepolymer and the aqueous liquid can be chosen as follows: The proportion of the prepolymer based on the total weight of the reaction mixture is 34 to 50 wt.%.

[0045] The proportion of aqueous liquid relative to the total weight of the reaction mixture is 50 to 65 wt.%.

[0046] After the prepolymer is reacted in the reaction mixture, a polymer in the form of a foam is obtained. This foam-like polymer has a high water absorption capacity and is therefore particularly well suited for the treatment of highly exuding wounds.

[0047] In connection with the present invention, it is particularly advantageous if the proportion of chitosan, based on the total weight of the reaction mixture, is at least 0.8 wt.%, in particular 0.8 to 5 wt.% or at least 0.8 to 1.8 wt.%. The polymer then exhibits high antibacterial efficacy and can be produced quickly.

[0048] If a humectant such as glycerol is provided, it may advantageously have a proportion of 10 to 25 wt.%, in particular 15 to 25 wt.%, based on the total weight of the reaction mixture.

[0049] If an inorganic salt such as sodium chloride is provided, it may advantageously have a proportion of 0.1 to 5 wt.%, preferably 0.1 to 3 wt.% and particularly preferably 0.5 to 1.5 wt.% based on the total weight of the reaction mixture.

[0050] During the reaction of the prepolymer, reactions occur involving the isocyanate groups of the prepolymer. This reaction typically begins automatically once the reaction mixture has been prepared. The reaction of the prepolymer within the reaction mixture can be understood as a polymerization process that leads to the formation of the polymer.

[0051] Typically, the conversion of the prepolymer in the reaction mixture is essentially complete. This means that no isocyanate groups toxic to human and animal cells remain in the polymer. Whether the prepolymer has been essentially completely converted in the reaction mixture can be verified, for example, using IR spectroscopy. The absence of an absorption band at 2260 cm⁻¹ for the isocyanate group serves as evidence of complete conversion of the prepolymer.

[0052] The following reactions, in particular, may be involved in the conversion of the prepolymer in the reaction mixture: a) Reaction of an isocyanate group of the prepolymer with an amine group of the chitosan, forming a urea bond. b) Reaction of an isocyanate group of the prepolymer with a hydroxyl group of the chitosan, forming a urethane bond. c) Reaction of an isocyanate group of the prepolymer with a water molecule, converting the isocyanate group into an amine group with the release of carbon dioxide. d) Reaction of an isocyanate group of the prepolymer with an amine group formed according to reaction c), forming a urea bond.

[0053] Reaction a) occurs faster than reaction b), and reaction b) in turn occurs faster than reaction c).

[0054] Which of the reactions a) to d) take place or predominate during the conversion of the prepolymer in the reaction mixture depends, among other things, on the previously mentioned reaction rates and the ratios of prepolymer, chitosan and water.

[0055] In particular, the reactions a) and / or b) mentioned above are involved in the conversion of the prepolymer, so that, as mentioned at the outset, at least a portion of the chitosan, or preferably all of it, is covalently bound to the prepolymer. If only a portion of the chitosan is covalently bound (for example, if little prepolymer and a large amount of chitosan are used), the remaining, non-covalently bound portion of the chitosan is usually also tightly enclosed within the polymer structure and cannot escape from it. This can be due to hydrophilic interactions between the chitosan molecules and the polymer. However, non-covalently bound chitosan can also simply be trapped within the polymer because the chitosan molecules are larger than the "mesh" of the polymer network.

[0056] Whether the prepolymer has reacted with the chitosan according to reaction a) or b) can be determined, for example, using IR spectroscopy. For this purpose, the absorption at 1654 cm⁻¹ (for the urea bond) or 1714 cm⁻¹ (for the urethane bond) in the polymer's IR spectrum can be evaluated. In particular, the covalent incorporation of the chitosan can be identified by a stronger absorption band at 1654 cm⁻¹ (urea bond) compared to a polymer without chitosan.

[0057] The conversion of the prepolymer in the reaction mixture can involve one or more reactions selected from the group comprising reaction a), reaction b), reaction c), and reaction d), whereby at least reaction a) and / or reaction b) are involved in the conversion of the prepolymer. The aforementioned group may also include further reactions involved in the conversion of the prepolymer.

[0058] It may be intended that only the aforementioned reactions a) to d) are involved in the conversion of the prepolymer. In this case, one or more reactions selected from the group consisting of reaction a), reaction b), reaction c), and reaction d) would be involved in the conversion of the prepolymer in the reaction mixture, with at least reaction a) and / or reaction b) participating in the conversion of the prepolymer. The conversion of the prepolymer can be limited to reactions a) to d) if the aqueous liquid consists of water and acid (for example, water and hydrochloric acid, i.e., dilute hydrochloric acid) and the reaction mixture consists of the prepolymer and the aqueous, chitosan-containing preparation.

[0059] Typically, the reaction mixture is designed to contain no amine-terminated prepolymer, particularly no amine-terminated prepolymer containing polyalkylene oxide units. Such amine-terminated prepolymers are commercially available (for example, Jeffamin® < ED-2003; Huntsman, Everberg, Belgium) and are often reacted with isocyanate-terminated prepolymers instead of chitosan in the prior art to obtain hydrogels. However, the present approach involves reacting the isocyanate-terminated prepolymer with chitosan rather than an amine-terminated prepolymer, resulting in a polymer with unexpectedly advantageous properties.

[0060] It can also be advantageous to provide that the reaction mixture contains no other component with an amine group besides chitosan. The reaction mixture can then also be free of the aforementioned amine-terminated prepolymer. If the reaction mixture contains no other component with an amine group besides chitosan, the covalent incorporation of the chitosan into the polymer can be particularly well ensured.

[0061] The polymer was developed for medical use, and in particular for wound treatment. Accordingly, claim 1 claims the use of the polymer in all its embodiments for wound treatment (second medical indication). Building on this, a further medical indication specifically envisages the use of the polymer in all its embodiments for the treatment of infected wounds.

[0062] When the polymer is used in wound treatment, it is typically integrated into a wound dressing. Accordingly, claim 2 also claims a wound dressing incorporating the polymer in all its embodiments. According to the invention, such a wound dressing comprises a backing layer and a wound-contacting layer, wherein the polymer forms the wound-contacting layer. This allows the polymer to best exert its advantageous properties, such as the absorption of wound exudate and the killing of infectious microorganisms contained in the wound exudate. Examples and figures

[0063] The following examples and figures are intended to explain the invention in more detail. Production of the polymers

[0064] Various polymers were produced and their properties were investigated. Table 1lists the composition and consistency of the manufactured polymers consisting of prepolymer, chitosan and dilute hydrochloric acid. Table 1: Composition and consistency of the produced polymers Example number Prepolymer [g] Chitosan [g] HCl [g] Prepolymer / Chitosan / HCl wt% consistency 1 0,6 0,05 4,95 10,71 / 0,89 / 88,39 gel 2 0,6 0,1 4,9 10,71 / 1,79 / 87,50 gel 3 0,8 0,05 4,95 13,79 / 0,86 / 85,34 gel 4 0,8 0,1 4,9 13,79 / 1,72 / 84,48 gel 5 1,0 - 5 16,67 / - / 83,33 gel 6 1,0 0,00625 4,99375 16,67 / 0,1 / 83,23 gel 7 1,0 0,0125 4,9875 16,67 / 0,2 / 83,13 gel 8 1,0 0,025 4,975 16,67 / 0,4 / 82,9 gel 9 1,0 0,05 4,95 16,67 / 0,83 / 82,5 gel 10 1,0 0,1 4,9 16,67 / 1,67 / 81,67 gel 11 1,2 0,05 4,95 19,35 / 0,81 / 79,84 gel 12 1,2 0,1 4,9 19,35 / 1,61 / 79,03 gel 13 1,4 0,05 4,95 21,88 / 0,78 / 77,34 gel 14 1,6 0,05 4,95 24,24 / 0,76 / 75,00 gel 15 1,6 0,1 4,9 24,24 / 1,52 / 74,24 gel 16 1,8 0,05 4,95 26,47 / 0,74 / 72,79 Gel foam 17 2,0 0,05 4,95 28,57 / 0,71 / 70,71 Gel foam 18 2,0 0,1 4,9 28,57 / 1,43 / 70,00 Gel foam 19 2,2 0,05 4,95 30,56 / 0,69 / 68,75 Gel foam 20 2,4 0,05 4,95 32,43 / 0,68 / 66,89 Gel foam 21 2,4 0,1 4,9 32,43 / 1,35 / 66,22 Gel foam 22 2,6 0,05 4,95 34,21 / 0,66 / 65,13 foam 23 2,8 0,05 4,95 35,90 / 0,64 / 63,46 foam 24 2,8 0,1 4,9 35,90 / 1,28 / 62,82 foam 25 3,0 0,05 4,95 37,50 / 0,63 / 61,88 foam 26 3,2 0,05 4,95 39,02 / 0,61 / 60,37 foam 27 3,2 0,1 4,9 39,02 / 1,22 / 59,76 foam 28 3,4 0,05 4,95 40,48 / 0,60 / 58,93 foam 29 3,6 0,05 4,95 41,86 / 0,58 / 57,56 foam 30 3,6 0,1 4,9 41,86 / 1,16 / 56,98 foam 31 3,8 0,05 4,95 43,18 / 0,57 / 56,25 foam 32 4,0 0,05 4,95 44,44 / 0,56 / 55,00 foam 33 4,0 0,1 4,9 44,44 / 1,11 / 54,44 foam 34 4,2 0,05 4,95 45,65 / 0,54 / 53,80 foam 35 4,4 0,05 4,95 46,81 / 0,53 / 52,66 foam 36 4,4 0,1 4,9 46,81 / 1,06 / 52,13 foam 37 4,6 0,05 4,95 47,92 / 0,52 / 51,56 foam 38 4,8 0,05 4,95 48,98 / 0,51 / 50,51 foam 39 4,8 0,1 4,9 48,98 / 1,02 / 50,00 foam 40 5,0 0,05 4,95 50,00 / 0,50 / 49,50 foam

[0065] The production of the polymers will be explained in more detail using example 9: Step 1 (Preparation of the claimed aqueous chitosan-containing preparation): 96 ml of demineralized water and 4 ml of 1 M hydrochloric acid were mixed (claimed aqueous liquid in the form of dilute hydrochloric acid). 1 g of chitosan was added to this liquid and stirred until the chitosan was completely dissolved. Accordingly, the preparation had a chitosan concentration of 1 wt%. Step 2 (Preparation of the claimed reaction mixture): 1 g of prepolymer was mixed with 5 g of the preparation made in Step 1. The resulting reaction mixture therefore consisted of 1 g of prepolymer, 0.05 g of chitosan, and 4.95 g of dilute hydrochloric acid, as shown in Table 1. The proportions of the prepolymer, the chitosan, and the dilute hydrochloric acid, based on the total weight of the reaction mixture, were therefore 16.67 wt%, 0.83 wt%, and 82.5 wt%, respectively.-% (see also column 5 in Table 1, headed "Prepolymer / Chitosan / HCl"). The reaction mixture was placed in a Petri dish. Larger quantities of the reaction mixture were also prepared if several Petri dishes were to be filled or if a Petri dish was to be completely filled with the reaction mixture. Step 3 (Obtaining the Polymer): The reaction mixture was left to stand in the Petri dish until the polymerization process, and thus the conversion of the prepolymer, was complete. The polymerization process was considered complete when the sample had solidified (i.e., reached the gel point) and was no longer sticky on its surface. This could be checked manually on a laboratory scale using a spatula.

[0066] The other examples listed in Table 1 were prepared in a similar manner to Example 9. The differences in the preparation of the other examples were essentially limited to the chitosan concentration of the preparation made in Step 1 and the amount of prepolymer mixed with the chitosan-containing preparation in Step 2. For example, in Example 12, the preparation made in Step 1 contained 2 wt% chitosan. 5 g of this were then mixed with 1.2 g of prepolymer in Step 2 to obtain the reaction mixture. If the chitosan concentration of the preparation made in Step 1 was to be greater than 1 wt%, a larger amount of 1 M hydrochloric acid was generally required to dissolve the chitosan (i.e., the hydrochloric acid concentration in the aqueous solution was then higher). Conversely, if the preparation contained less than 1 wt%, a larger amount of 1 M hydrochloric acid was required to dissolve the chitosan.(If it should contain -% chitosan) a lower concentration of hydrochloric acid could also be used if necessary.

[0067] The following four statements apply to all examples in Table 1. Only the first three statements apply to the examples in Tables 2 and 3. The liquid used to dissolve the chitosan contained only demineralized water and hydrochloric acid. The chitosan had a molar weight of 50 to 190 kDa and a degree of deacetylation of 75 to 85% (Sigma-Aldrich, Steinheim, Germany; product number 448869). The prepolymer was Aquapol® < PI-13000-31 from Carpenter (Richmond, USA). As previously mentioned, this is a three-armed, branched isocyanate-terminated prepolymer containing polyethylene oxide and polypropylene oxide units. The reaction mixture contained only the prepolymer and the aqueous, chitosan-containing preparation.

[0068] Example 5 does not contain chitosan and is therefore not a polymer according to the invention. Example 5 served merely as a control sample.

[0069] The polymers from Table 2 and 3 In addition to prepolymer, chitosan and dilute hydrochloric acid, they contain one or more other components such as a humectant and / or an inorganic salt. Table 2: Composition of polymers with humectant and / or salt Example number Humectant Prepolymer [g] Chitosan [g] HCl [g] Humectant [g] NaCl [g] 41 Ethylene glycol 1,0 0,05 4,95 1,0 - 42 Propylene glycol 1,0 0,05 4,95 1,0 - 43 PEG300 1,0 0,05 4,95 1,0 - 44 PEG2000 1,0 0,05 4,95 1,0 - 45 Glycerol 1,0 0,05 4,95 1,0 - 46 sucrose 1,0 0,05 4,95 1,0 - 47 Sorbitol 1,0 0,05 4,95 1,0 - 48 - 1,0 0,05 4,95 - 0,1 49 Ethylene glycol 1,0 0,05 4,95 1,0 0,1 50 Propylene glycol 1,0 0,05 4,95 1,0 0,1 51 PEG300 1,0 0,05 4,95 1,0 0,1 52 PEG2000 1,0 0,05 4,95 1,0 0,1 53 Glycerol 1,0 0,05 4,95 1,0 0,1 54 sucrose 1,0 0,05 4,95 1,0 0,1 55 Sorbitol 1,0 0,05 4,95 1,0 0,1 Table 3: Composition of the polymers from Table 2 in wt.% (based on the total weight of the reaction mixture) Example number Prepolymer wt.% Chitosan wt% HCl wt.% Humectant wt.% NaCl wt.% 41 - 47 14,29 0,71 70,71 14,29 - 48 16,39 0,82 81,15 - 1,64 49 - 55 14,08 0,70 69,72 14,08 1,41

[0070] Examples 41 to 55 are composed similarly to Example 9. Examples 41 to 47 differ from Example 9 in that they additionally contain a humectant. Unlike Example 9, Example 48 contains an inorganic salt in the form of sodium chloride. Unlike Example 9, Examples 49 to 55 contain both a humectant and an inorganic salt, namely sodium chloride.

[0071] Examples 41 to 55 were prepared in a manner very similar to Example 9. The aqueous, chitosan-containing preparation was prepared as described in Step 1. Subsequently, 1 g of prepolymer, 5 g of the chitosan-containing preparation, and the other components (1 g humectant in Examples 41-47 and 49-55, and 0.1 g sodium chloride in Examples 48-55) were mixed together, poured into a Petri dish, and allowed to solidify. Due to their high water solubility, the humectants and the salt used mixed well with the prepolymer and the chitosan-containing preparation, especially when larger quantities of the reaction mixture were prepared. For example, a larger batch of the reaction mixture for Polymer 53 could be obtained by mixing 10 g of prepolymer, 50 g of chitosan-containing preparation, 10 g of glycerol, and 1 g of sodium chloride (= 10 times the initial batch). consistency of the polymers

[0072] Figures 1 and 2The photographs show selected examples from Table 1. The two figures are intended to illustrate how the polymer can appear as a gel, gel foam, and foam. The example numbers are indicated below the respective samples.

[0073] Table 4 and Table 5 For better clarity, we will again explain the composition and consistency of the examples. Figure 1 or Figure 2 (This information can also be found in Table 1). Table 4: Composition and consistency of the polymers from Figure 1 Example number Prepolymer [g] Chitosan [g] HCl [g] Prepolymer / Chitosan / HCl wt% consistency 1 0,6 0,05 4,95 10,71 / 0,89 / 88,39 gel 3 0,8 0,05 4,95 13,79 / 0,86 / 85,34 gel 9 1,0 0,05 4,95 16,67 / 0,83 / 82,5 gel 11 1,2 0,05 4,95 19,35 / 0,81 / 79,84 gel 13 1,4 0,05 4,95 21,88 / 0,78 / 77,34 gel 14 1,6 0,05 4,95 24,24 / 0,76 / 75,00 gel 16 1,8 0,05 4,95 26,47 / 0,74 / 72,79 Gel foam 17 2,0 0,05 4,95 28,57 / 0,71 / 70,71 Gel foam 19 2,2 0,05 4,95 30,56 / 0,69 / 68,75 Gel foam 20 2,4 0,05 4,95 32,43 / 0,68 / 66,89 Gel foam 22 2,6 0,05 4,95 34,21 / 0,66 / 65,13 foam 23 2,8 0,05 4,95 35,90 / 0,64 / 63,46 foam 25 3,0 0,05 4,95 37,50 / 0,63 / 61,88 foam 26 3,2 0,05 4,95 39,02 / 0,61 / 60,37 foam 28 3,4 0,05 4,95 40,48 / 0,60 / 58,93 foam 29 3,6 0,05 4,95 41,86 / 0,58 / 57,56 foam 31 3,8 0,05 4,95 43,18 / 0,57 / 56,25 foam 32 4,0 0,05 4,95 44,44 / 0,56 / 55,00 foam 34 4,2 0,05 4,95 45,65 / 0,54 / 53,80 foam 35 4,4 0,05 4,95 46,81 / 0,53 / 52,66 foam 37 4,6 0,05 4,95 47,92 / 0,52 / 51,56 foam 38 4,8 0,05 4,95 48,98 / 0,51 / 50,51 foam 40 5,0 0,05 4,95 50,00 / 0,50 / 49,50 foam Table 5: Composition and consistency of the polymers from Figure 2 Example number Prepolymer [g] Chitosan [g] HCl [g] Prepolymer / Chitosan / HCl wt% consistency 2 0,6 0,1 4,9 10,71 / 1,79 / 87,50 gel 4 0,8 0,1 4,9 13,79 / 1,72 / 84,48 gel 10 1,0 0,1 4,9 16,67 / 1,67 / 81,67 gel 12 1,2 0,1 4,9 19,35 / 1,61 / 79,03 gel 15 1,6 0,1 4,9 24,24 / 1,52 / 74,24 gel 18 2,0 0,1 4,9 28,57 / 1,43 / 70,00 Gel foam 21 2,4 0,1 4,9 32,43 / 1,35 / 66,22 Gel foam 24 2,8 0,1 4,9 35,90 / 1,28 / 62,82 foam 27 3,2 0,1 4,9 39,02 / 1,22 / 59,76 foam 30 3,6 0,1 4,9 41,86 / 1,16 / 56,98 foam 33 4,0 0,1 4,9 44,44 / 1,11 / 54,44 foam 36 4,4 0,1 4,9 46,81 / 1,06 / 52,13 foam 39 4,8 0,1 4,9 48,98 / 1,02 / 50,00 foam

[0074] The examples from Figure 1were prepared by mixing a constant amount of the chitosan-containing preparation with a chitosan concentration of 1 wt% with increasing amounts of prepolymer. In contrast, the chitosan concentration in the samples in Figure 2 twice as high, i.e., 2 wt.%.

[0075] The comparison of examples from Figure 1 with the examples from Figure 2 This has shown that the ratio of prepolymer to aqueous liquid, independent of the amount of chitosan used, determines whether a polymer is obtained in the form of a gel, a gel foam, or a foam. The polymer transitions from a gel-like to a foam-like state when the prepolymer concentration in the reaction mixture is increased. Furthermore, it has been shown that chitosan can influence the strength of the resulting polymers. The strength of the polymers can increase when the chitosan content in the reaction mixture increases. Antibacterial efficacy of the polymers

[0076] Selected examples from Table 1 were investigated for their antibacterial efficacy using a soft agar test. For this purpose, a defined concentration of bacteria commonly found in infected wounds was applied to the samples to be tested in soft agar, and the CFU / ml was evaluated after a test period of 24 hours (CFU stands for colony-forming unit).

[0077] The procedure and evaluation of the soft agar test are briefly explained below: The bacterial strain was added to 9 ml of Caso bouillon and incubated at 37°C for 18 to 24 hours. After incubation, the bacterial density of the suspension was 1 x 10⁸ < CFU / ml.

[0078] 100 ml of soft agar were tempered to 45 °C and inoculated with 1 ml of the bacterial suspension.

[0079] Sample pieces measuring 2.5 cm x 2.5 cm were punched out using a die and transferred to empty Petri dishes using sterile tweezers.

[0080] One ml of the inoculated soft agar was applied to the surface of each sample using a pipette, taking care to prevent it from running off. It solidifies at room temperature after approximately 10 minutes.

[0081] Additionally, a control was set up. For this, 1 ml of inoculated soft agar was pipetted into a 50 ml Falcon tube and 3 ml of 1 / 4 strength Ringer's solution was added to prevent the soft agar from drying out.

[0082] The inoculated samples were incubated at 37°C. After a 24-hour test period, 100 ml of Dey-Engley inhibitor was added. For the 0-hour value, 1 ml of the inoculated soft agar was pipetted directly into the Dey-Engley inhibitor. The samples were then treated in an ultrasonic bath for one minute and additionally shaken to release the bacteria into the solution.

[0083] Subsequently, suitable dilution series with Dey-Engley inhibitor were prepared and plated onto Caso plates using a spiral plate system (Eddy Jet, IUL Instruments). After incubation of the plates at 37°C for 18 to 24 hours, the final evaluation was performed (ASTM E2180-01). Each polymer sample and each control was tested three times using the soft agar assay. Geometrisches Mittle der Probe = log x 1 + log x 2 + log x 3 / 3 Geometrisches Mittle der Kontrolle = log xk 1 + log xk 2 + log xk 3 / 3 Log − Stufen Reduktion = Log − Stufe Kontrolle − Log − Stufe Probe

[0084] Figure 3 and Figure 4The results of the soft agar tests for examples 8, 9, and 10, and 1 and 17, respectively, from Table 1 are shown. The antibacterial activity of the samples against up to three different bacterial strains, namely Staphylococcus aureus (DSM No. 346), Klebsiella pneumoniae (DSM No. 789), and Bacillus subtilis (DSM No. 675), was investigated. The dashed line indicates the boundary between a bacteriostatic and a bactericidal effect (values ​​below the line are bacteriostatic, values ​​above the line are bactericidal).

[0085] Table 6 and Table 7 For better clarity, we will again explain the composition and consistency of the examples. Figure 3 or Figure 4 (This information can also be found in Table 1). Table 6: Composition and consistency of the polymers from Figure 3 Example number Prepolymer [g] Chitosan [g] HCl [g] Prepolymer / Chitosan / HCl wt% consistency 8 1,0 0,025 4,975 16,67 / 0,4 / 82,9 gel 9 1,0 0,05 4,95 16,67 / 0,83 / 82,5 gel 10 1,0 0,1 4,9 16,67 / 1,67 / 81,67 gel Table 7: Composition and consistency of the polymers from Figure 4 Example number Prepolymer [g] Chitosan [g] HCl [g] Prepolymer / Chitosan / HCl wt% consistency 1 0,6 0,05 4,95 10,71 / 0,89 / 88,39 gel 17 2,0 0,05 4,95 28,57 / 0,71 / 70,71 Gel foam

[0086] As can be seen from Table 6, the examples from Figure 3 The aim was to create gels with an essentially identical ratio of prepolymer to aqueous liquid, but differing in their chitosan content. The antibacterial activity of different chitosan concentrations, while maintaining otherwise identical polymer properties, was to be compared using these samples.

[0087] The examples from Figure 4 In contrast, the samples have an essentially identical chitosan content but differ in the ratio of prepolymer to aqueous liquid and thus in their consistency (see Table 7). These samples were used to investigate whether the consistency of the polymers significantly influences their antibacterial activity.

[0088] In the soft agar tests, significant antibacterial activity against at least one of the bacterial strains was demonstrated for all samples examined (see Figure 3 Significant antibacterial activity is therefore already present at a chitosan content of 0.4% by weight. Particularly good effects were obtained at a chitosan content of 0.8% by weight.

[0089] Furthermore, it has been shown that the ratio of prepolymer to aqueous liquid can influence the antibacterial activity of the polymers. For example, the antibacterial activity of the gel sample against the bacterial strain Staphylococcus aureus was significantly better than that of the otherwise comparable gel foam sample (see Figure 4 Accordingly, gel polymers are particularly preferred in this case with regard to their antibacterial efficacy. Reaction rate of the polymers

[0090] Table 8This section specifies the composition and reaction rate of examples 6 to 10 from Table 1. The reaction rate refers to the time required for the conversion of the prepolymer, i.e., for the polymerization process. The polymerization process proceeds more rapidly with increasing chitosan concentration. A higher polymerization rate facilitates the fast, cost-effective, and economical production of the polymers. Table 8: Reaction rate (abbreviated as RG) of examples 6 to 10 from Table 1 Example number Prepolymer [g] Chitosan [g] HCl [g] Prepolymer / Chitosan / HCl wt% RG 6 1,0 0,00625 4,99375 16,67 / 0,1 / 83,23 45 min 7 1,0 0,0125 4,9875 16,67 / 0,2 / 83,13 20 min 8 1,0 0,025 4,975 16,67 / 0,4 / 82,9 15 min 9 1,0 0,05 4,95 16,67 / 0,83 / 82,5 10 min 10 1,0 0,1 4,9 16,67 / 1,67 / 81,67 5 min Absorption capacity of the polymers

[0091] Selected examples from Table 1 were investigated with regard to their absorption capacity. To measure the absorption capacity, samples measuring 2.5 cm x 2.5 cm were punched out and weighed. They were then placed in a beaker containing demineralized water for 24 hours and subsequently weighed again. Each sample was tested three times. The absorption capacity is calculated using the following equation and is given in g / g: Absorptionskapazität = Endgewicht − Anfangsgewicht / Anfangsgewicht

[0092] Figure 5 and Figure 6 The results of the absorption tests for selected examples from Table 1 are shown.

[0093] Table 9 and Table 10 For better clarity, we will again explain the composition and consistency of the examples. Figure 5 or Figure 6 (This information can also be found in Table 1). Table 9: Composition and consistency of the polymers from Figure 5 Example number Prepolymer [g] Chitosan [g] HCl [g] Prepolymer / Chitosan / HCl wt% consistency 6 1,0 0,00625 4,99375 16,67 / 0,1 / 83,23 gel 7 1,0 0,0125 4,9875 16,67 / 0,2 / 83,13 gel 8 1,0 0,025 4,975 16,67 / 0,4 / 82,9 gel 9 1,0 0,05 4,95 16,67 / 0,83 / 82,5 gel 10 1,0 0,1 4,9 16,67 / 1,67 / 81,67 gel Table 10: Composition and consistency of the polymers from Figure 6 Example number Prepolymer [g] Chitosan [g] HCl [g] Prepolymer / Chitosan / HCl wt% consistency 1 0,6 0,05 4,95 10,71 / 0,89 / 88,39 gel 9 1,0 0,05 4,95 16,67 / 0,83 / 82,5 gel 17 2,0 0,05 4,95 28,57 / 0,71 / 70,71 Gel foam 25 3,0 0,05 4,95 37,50 / 0,63 / 61,88 foam

[0094] All samples tested showed satisfactory absorption capacities for use in wound therapy. However, if the highest possible absorption capacity is desired with a defined amount of chitosan (for example, when treating highly exuding wounds), gel foam polymers or, in particular, foam polymers may be preferable to gel polymers (see Figure 6 ). Moisture release capacity of polymers

[0095] Selected examples from Table 1 were examined with regard to their moisture release capacity. This test determined how much moisture the polymers could release to filter papers. This can provide an indication of how much moisture the polymers in a wound dressing can release to the wound surface.

[0096] The experimental procedure was as follows: First, round sample pieces with a diameter of 3.5 cm were punched out from the produced polymers.

[0097] Each sample was placed in a Petri dish lined with five sheets of filter paper, the weight of which had been previously determined (initial weight). The diameter of the Petri dish and filter paper was 5 cm. The Petri dishes were covered with lids and additionally sealed with Parafilm to prevent moisture loss. The samples were then left in the sealed Petri dishes at room temperature for 24 hours.

[0098] The Petri dishes were then opened and weighed again without the samples (final weight) to calculate the moisture release capacity in mg / cm². Each sample was tested three times. Feuchtigkeitsabgabekapazität = Endgewicht − Anfangsgewicht × 1000 / A Initial weight: Weight of the Petri dish and filter papers at the start of the experiment ("dry") in g. Final weight: Weight of the Petri dish and filter papers after the experiment ("moistened") in g. A: Area of ​​the sample in cm².

[0099] Figure 7 and Figure 8 The results of the moisture release tests for selected examples from Table 1 are shown. The same examples were selected as previously used in the absorption tests. All samples tested showed satisfactory moisture release capacities for use in wound therapy. However, if the highest possible moisture release capacity is desired with a defined amount of chitosan (for example, when treating dry wounds), the gel polymers may be preferable to the gel foam polymers and the foam polymers (see Figure 8 ). IR spectra of the polymers and the starting materials

[0100] Figure 9Figure 1 shows FT-IR spectra of selected examples from Table 1, as well as of the prepolymer (Aquapol®) and chitosan. The spectra of the following samples are shown in the figure (from top to bottom): chitosan, prepolymer, example 5, example 6, example 7, example 8, example 9, example 10.

[0101] Isocyanate groups, urethane groups, and urea groups lead to absorption bands at 2260 cm⁻¹, 1714 cm⁻¹, and 1654 cm⁻¹, respectively, in the IR spectra. The recorded IR spectra confirm that the synthesized polymers no longer possess isocyanate groups, indicating that complete conversion of the prepolymers has occurred. This makes the polymers well-tolerated by human and animal cells. The ratio of the urethane band to the urea band depends on the polymer composition. The polymers containing chitosan (Examples 6 to 10) exhibit a stronger urea band (at 1654 cm⁻¹) than the polymer without chitosan (Example 5). This is due to the covalent incorporation of chitosan into the polymer, forming additional urea bonds. Wound dressing with polymer

[0102] Figure 10Figure 1 shows a wound dressing with a polymer according to the invention in schematic form. The wound dressing comprises a backing layer 1, which is fully coated with an adhesive layer 2. The backing layer 1 For example, it could be a waterproof, water vapor permeable polyurethane film, which is fully coated with an acrylate adhesive as an adhesive layer. 2 is coated. The back layer 1 It serves as a supporting and covering layer in the wound dressing. The adhesive layer 2 It allows the wound dressing to be attached to the patient's body. Furthermore, the wound dressing includes a wound contact layer. 3, which is formed by the polymer according to the invention. When the wound dressing is attached to the patient's body, the wound contact layer 3 placed directly on the wound. With the wound contact layer 3The wound dressing can absorb wound exudate, release moisture to the wound, and in particular, also exhibit antibacterial activity.

[0103] It is also conceivable that the wound dressing comprises further layers. For example, another absorbent layer could be placed between the adhesive layer 2 and the wound contact layer. 3 They are arranged to increase the absorption capacity of the wound dressing. The absorbent layer can, for example, comprise a hydrophilic polyurethane foam or a non-woven fabric.

[0104] The wound dressing can be produced by applying the polymer in liquid state (i.e., the required reaction mixture) to the back layer. 1 or their adhesive layer 2 It is poured directly onto the wound. The finished wound dressing is then available after the polymer has hardened. Alternatively, the wound contact layer can be... 3also produced in a separate casting mold and then with the back layer 1 over their adhesive layer 2 be connected.

Claims

1. Polymer for use in wound treatment, wherein the polymer is obtainable by a process comprising the steps of i. providing an isocyanate-terminated prepolymer containing polyalkylene oxide units, ii. dissolving a chitosan in an aqueous liquid to obtain an aqueous, chitosan-containing preparation, iii. mixing the prepolymer, the aqueous, chitosan-containing preparation and optionally one or more further components to obtain a reaction mixture, iv. reacting the prepolymer in the reaction mixture to obtain the polymer, wherein - the proportion of the prepolymer based on the total weight of the reaction mixture is 5% to 50% by weight, in particular 10% to 50% by weight, - the proportion of the chitosan based on the total weight of the reaction mixture is at least 0.4% by weight, in particular 0.4% to 5% by weight, - the proportion of the aqueous liquid based on the total weight of the reaction mixture is 40% to 90% by weight, in particular 50% to 90% by weight, and - the proportion of the one or more further components based on the total weight of the reaction mixture is 0% to 30% by weight.

2. Wound dressing, comprising a polymer obtainable by a process comprising the steps of i. providing an isocyanate-terminated prepolymer containing polyalkylene oxide units, ii. dissolving a chitosan in an aqueous liquid to obtain an aqueous, chitosan-containing preparation, iii. mixing the prepolymer, the aqueous, chitosan-containing preparation and optionally one or more further components to obtain a reaction mixture, iv. reacting the prepolymer in the reaction mixture to obtain the polymer, wherein - the proportion of the prepolymer based on the total weight of the reaction mixture is 5% to 50% by weight, in particular 10% to 50% by weight, - the proportion of the chitosan based on the total weight of the reaction mixture is at least 0.4% by weight, in particular 0.4% to 5% by weight, - the proportion of the aqueous liquid based on the total weight of the reaction mixture is 40% to 90% by weight, in particular 50% to 90% by weight, and - the proportion of the one or more further components based on the total weight of the reaction mixture is 0% to 30% by weight, and wherein the wound dressing comprises a backing layer (1) and a wound-contacting layer (3), wherein the polymer forms the wound-contacting layer (3).

3. Polymer or wound dressing according to Claim 1 or 2, wherein the prepolymer has at least three-armed branching and the polyalkylene oxide units are formed by polyethylene oxide units and / or polypropylene oxide units, wherein the weight ratio of ethylene oxide units to propylene oxide units is preferably 3:1 to 7:1.

4. Polymer or wound dressing according to any of the preceding claims, wherein the chitosan - has a molar weight of 50 kDa to 375 kDa, preferably from 50 kDa to 310 kDa and particularly preferably from 50 kDa to 190 kDa and / or - has a degree of deacetylation of at least 50%, preferably of at least 60%, more preferably of at least 70%, particularly preferably of at least 75% and in particular of 75% to 85%.

5. Polymer or wound dressing according to any of the preceding claims, wherein the aqueous liquid has an acidic pH and in particular is dilute hydrochloric acid.

6. Polymer or wound dressing according to any of the preceding claims, wherein a humectant is present as further component, wherein the humectant is preferably ethylene glycol, propylene glycol, PEG300, PEG2000, glycerol, sucrose or sorbitol.

7. Polymer or wound dressing according to any of the preceding claims, wherein an inorganic salt is present as further component, wherein the salt is preferably sodium chloride, potassium chloride, magnesium chloride, calcium chloride or a mixture of at least two of these salts.

8. Polymer or wound dressing according to any of the preceding claims, wherein the polymer is in the form of a gel, a gel foam or a foam.

9. Polymer or wound dressing according to any of the preceding Claims 1 to 8, wherein - the proportion of the prepolymer based on the total weight of the reaction mixture is 10% to 25% by weight, and - the proportion of the aqueous liquid based on the total weight of the reaction mixture is 74% to 90% by weight.

10. Polymer or wound dressing according to any of the preceding Claims 1 to 8, wherein - the proportion of the prepolymer based on the total weight of the reaction mixture is 26% to 33% by weight, and - the proportion of the aqueous liquid based on the total weight of the reaction mixture is 66% to 73% by weight.

11. Polymer or wound dressing according to any of the preceding Claims 1 to 8, wherein - the proportion of the prepolymer based on the total weight of the reaction mixture is 34% to 50% by weight, and - the proportion of the aqueous liquid based on the total weight of the reaction mixture is 50% to 65% by weight.

12. Polymer or wound dressing according to any of the preceding claims, wherein the proportion of the chitosan based on the total weight of the reaction mixture is at least 0.8% by weight, in particular 0.8% to 5% by weight.