EP1469893A1 - Stellate prepolymers for the production of ultra-thin coatings that form hydrogels - Google Patents

Abstract

The invention relates to the use of stellate polymers comprising hydrophilic polymer arms, which bear a reactive functional group R on their free ends, for the production of ultra-thin coatings that form hydrogels. The coatings that form hydrogels thus obtained actively suppress an unspecific protein absorption on surfaces provided with said coating.

Description

Star-shaped prepolymers for the production of ultra-thin, hydrogel-forming coatings

The present invention relates to the use of star-shaped polymers with hydrophilic polymer arms, which carry a reactive functional group R at their free ends, for the production of ultra-thin, hydrogel-forming coatings. The hydrogel-forming coatings obtained in this way effectively suppress non-specific protein absorption on surfaces provided with them.

The specific and non-specific interaction of proteins and cells with artificial surfaces forms the basis of many medical, biochemical and biotechnological applications. To prevent unwanted deposits, also known as biofouling and plaque, and to stimulate a desired cell colonization, it is necessary to prevent non-specific protein and cell adsorption. Since biological systems can actively modify their environment (surfaces) themselves, to reduce non-specific protein and cell adsorption, the cells must be prevented from conditioning their environment by membrane proteins or extracellular matrix proteins in a way that prepares for non-specific cell colonization.

The use of specific adsorption processes for analysis naturally requires the type, quantity and conformation of unspecifically adsorbed molecules to be precisely controlled or, even better, to completely prevent unspecific adsorption. For the detection of biomolecules that are only present in extremely small quantities, it must be ensured that the substances to be detected are not lost through unspecific adsorption on the way to the detection.

The suppression of non-specific protein adsorption and cell colonization in the field of medical technology, e.g. B. with catheters, contact lenses or prostheses is also important. For prostheses and implants, the targeted suppression of non-specific adsorption processes is a prerequisite for specific coupling via the integration of ligands, signal substances and growth factors of molecules and cells, which enables the healing and ingrowth of biological tissue.

Furthermore, the prevention of biological deposits of proteins or bacteria plays an important role in the hygiene area and in keeping surfaces clean that cannot be permanently cleaned without residues. Unwanted, biological deposits on extremely large wetted surfaces such as ship hulls, water basins and the like as well as deposits in inaccessible places, such as large pipe systems, represent a major economic problem. The antipiaque coatings currently used are mostly toxic organometallic compounds or lose their bactericidal action very quickly.

Plaque formation and biofouling therefore represent a considerable economic and ecological burden that has not yet been satisfactorily resolved.

Various polymeric, especially hydrogel-forming, coatings have been proposed to avoid unspecific protein adsorption on surfaces. Hydrogel-forming coatings are coatings that are swollen by water. For example, adsorbate layers made from polyethylene glycol (PEG) reduce subsequent adsorption of proteins from biological media (see, for example: Merrill EW, in Poly (ethylene glycol) Chemistry, publisher JM Harris, p. 199-220, Plenum Press, New York: 1992; C.-G. Gölander, Jamea N. Herron, Cape Lim, P. Claesson, P. Stenius, JD Andrade, in Poly (ethylene glycol) Chemistry, editor JM Harris, Plenum Press, New York: 1992). Polymer surfaces that have been modified with poly (ethylene oxide) to reduce protein adsorption on implant materials have also been intensively investigated in recent years (Paine et al. Macromolecules 1990, 23, p. 3104).

US 5,993,890 describes triblock copolymers which contain a polysaccharide block, e.g. B. a heparin or dextran block and hydrophobic hydrocarbon residues exhibit. The polymers are particularly suitable for preventing protein adsorption on hydrophobic surfaces.

EP 272842 A2 describes coatings with low affinity for proteins, which by applying compositions of hydroxyl-containing polymers, for. B. cellulose derivatives and crosslinking agents, e.g. B. copolymers of acrylic acid and N-methylolacrylamide, on microporous substrates and subsequent crosslinking of the coating.

EP 335308 A2 describes the use of prepolymers made from polyethylene oxide diols and triols, the terminal OH groups of which have been reacted with polyisocyanates, for the production of coatings with low non-specific protein adsorption.

No. 6,087,415 discloses antimicrobial coatings for biomedical articles such as contact lenses, which are produced by coupling polymers containing carboxyl groups to the OH or NH ₂ groups on the surface of the biomedical article.

Furthermore, US Pat. No. 6,150,459 and 6,207,749 propose synthetic comb polymers for this purpose which have a hydrophobic polymer backbone, e.g. B. a polylactide or a polymer derived from methyl methacrylate, and grafted hydrophilic polymer chains, which are preferably derived from polyethylene glycols or polyacrylic acid.

J. Ruhe et al. (Prucker O. and Rühe J. Langmuir 1998, 14 (24), 6893-6898; Macromolecules, 1998, 31 (3), 592-601; Macromolecules, 1998, 31 (3), 602-613.) a coating process in which a surface is first modified with a monolayer of an initiator. This is then used to trigger radical polymerization. The result is very dense layers, whereby the layer thickness can grow up to several hundred nanometers thick. Cruise et al. (Biomaterials 1998, 19, 1287-1294) and and Han et al. (Macromolecules 1997, 30, 6077-6083.0) describe the use of acrylate-terminated prepolymers which have been prepared either from PEG diols or PEG triols for the production of hydrogel layers. To bind to the surface, the acrylate-terminated prepolymer is exposed on a correspondingly pretreated substrate, as a result of which the prepolymer crosslinks to a hydrogel on its own or with acrylate-terminated glycerol triol with the addition of benzene dimethyl ketal. In this way, hydrogel layers with layer thicknesses between 135 μm and 180 μm are obtained. The areas of use for these hydrogel layers are in vivo use, e.g. B. to suppress postoperative adhesion processes, use as a diffusion barrier, for gluing or sealing of tissues, in vivo medication or use as a direct implant, eg. B. in the form of a hydrogel cell suspension, peptide hydrogel or a growth factor hydrogel.

Although the hydrogel-forming coatings known from the prior art reduce the unspecific cell and protein adsorption, the long-term stability of the coatings is often unsatisfactory. In other cases, the barrier effect for proteins is insufficient. In many cases, complicated manufacturing processes for these coatings prevent their wide applicability, especially on irregularly shaped surfaces. There is therefore a need for suitable processes for the production of extremely thin, hydrogel-forming coatings which form reproducibly dense and controllable layers, show a sufficiently high long-term resistance to protein and cell adsorption and can be used universally, that is to say they can be widely used for material coatings. Furthermore, it should be possible to integrate specific, functional molecules into the layers in a defined manner or to anchor them on the surface. Desirably, the coatings in the application fields mentioned should be able to be applied as ultra-thin, molecularly smooth films. It is also desirable to incorporate defined functionalities into these coatings. In addition, the coating process should advantageously also be able to be carried out from aqueous preparations. As far as possible, existing procedures should Ren for the production of the substrates and components by the use of hydrogel coatings are not impaired and the applicability in various fields of application.

It has been found that this object can be achieved by coatings based on cross-linked star-shaped prepolymers which on average have at least four polymer arms A, which are in themselves soluble in water and which carry a reactive functional group R at their free ends, which reacts with a complementary reactive functional group R ¹ or with itself to form bonds.

Accordingly, the present invention relates to the use of star-shaped prepolymers which have on average at least four polymer arms A, which are in themselves soluble in water and carry a reactive functional group R at their free ends, with groups R 'complementary thereto or with them react themselves to form bonds to produce ultra-thin, hydrogel-forming coatings.

The present invention also relates to a method for producing ultra-thin, hydrogel-forming coatings, which is characterized in that

i. a solution of a star-shaped prepolymer which has on average at least four polymer arms A, which are in themselves soluble in water and carry a reactive functional group R at their free ends, applied to the surface to be coated and ii. then carries out a linking reaction between the reactive groups.

A person skilled in the art understands a hydrogel-forming coating to be those coatings which are swollen by water as a result of the intercalation of water molecules in the coating. Star-shaped polymers are understood to mean those polymers which have a plurality of polymer chains bonded to a low-molecular central unit, the low-molecular central unit generally having 4 to 100 skeletal atoms such as C atoms, N atoms or O atoms. Accordingly, the star-shaped polymers used in accordance with the invention can be described by the following general formula I:

Z (ABR) _n (I) where n is an integer with a value of at least 4, e.g. B. 4 to 12, in particular 5 to 12 and especially 6 to 8;

Z stands for a low molecular weight n-valent organic radical as the central unit, which generally has 4 to 100, preferably 5 to 50 framework atoms, in particular 6 to 30 framework atoms. The central unit can have both aliphatic and aromatic groups. It stands for example for one of at least 4-valent alcohol, e.g. B. a 4- to 12-valent, preferably an at least 5-valent, especially a 6- to 8-valent alcohol, e.g. B. pentaerythritol, dipentaerythritol, a sugar alcohol such as erythritol, xylitol, mannitol, sorbitol, maltitol, isomaltulose, isomaltitol, trehalulose, or the like;

A is a hydrophilic polymer chain which as such is water soluble;

B is a chemical bond or a divalent, low molecular weight organic radical preferably having from 1 to 20, preferably 2 to 10 carbon atoms, for example, a C _{2 0} -Cι alkylene group, a phenylene or a naphthylene group or a C ₅ -Cιo-cycloalkylene group, wherein the phenylene, naphthylene and the cycloalkylene group additionally one or more, e.g. B. 1, 2, 3, 4, 5, or 6 substituents, e.g. B. may have alkyl groups with 1 to 4 carbon atoms, alkoxy groups with 1 to 4 carbon atoms or halogen; and R is a reactive group which can react with a complementary reactive functional group R 'or with itself to form bonds.

Reactive groups R in this sense are those which react with nucleophiles in an addition or substitution reaction, e.g. B. isocyanate groups, (meth) acrylic groups, oxirane groups, oxazoline groups, carboxylic acid groups, carboxylic acid ester and carboxylic acid anhydride groups, carboxylic acid and sulfonic acid halide groups, but also the complementary, reacting as nucleophile groups such as alcoholic OH groups, primary and secondary amino groups, thiol groups and the like. So-called active ester groups of the formula - C (0) 0-X, in which X is pentafluorophenyl, pyrrolidin-2,5-dion-1-yl, benzo-1, 2,3-triazol-1-yI, are particularly preferred as examples of carboxylic acid ester groups or a carboxamidine residue.

Also suitable as reactive groups R are free-radically polymerizable C = C double bonds, e.g. B. in addition to the above (meth) acrylic groups also vinyl ether and vinyl ester groups, further activated C = C double bonds, activated C≡C triple bond and N = N double bonds, with allyl groups in the sense of an en reaction or with conjugated diolefin groups react in the sense of a Diels-Alder reaction. Examples of groups which can react with allyl groups in the sense of an en reaction or with dienes in the sense of a Diels-Alder reaction are maleic acid and fumaric acid groups, maleic acid esters and fumaric acid ester groups, cinnamic acid ester groups, propiolic acid (ester) groups, Maleic acid amide and fumaric acid amide groups, maleimide groups, azodicarboxylic acid ester groups and 1, 3,4-triazoline-2,5-dione groups.

In a preferred embodiment, the star-shaped prepolymer has functional groups which are amenable to an addition or substitution reaction by nucleophiles. This also includes groups that react in the sense of a Michael reaction. Examples are in particular isocyanate groups, (meth) acrylic groups (react in the sense of a Michael reaction), oxirane groups or carboxylic ester groups. A particularly preferred embodiment relates to star-shaped prepolymers which have isocyanate groups as reactive groups R.

In another embodiment, the prepolymer has ethylenically unsaturated, free-radically polymerizable double bonds as reactive groups R.

To achieve layers that are as compact as possible, it is necessary that the star-shaped prepolymer has an average of at least 4, e.g. B. 4 to 12, preferably at least 5 and in particular 6 to 8 polymer arms. The number average molecular weight of the polymer arms is preferably in the range from 300 to 3000 g / mol, and in particular in the range from 500 to 2000 g / mol. Accordingly, the star-shaped prepolymer has a number average molecular weight in the range from 2000 to 20,000 g / mol, in particular 2500 to 15000 g / mol.

The molecular weight can be determined in a manner known per se by means of gel permeation chromatography, using commercially available columns, detectors and evaluation software. If the number of end groups per polymer molecule is known, the molecular weight can also be determined by titration of the end groups, in the case of isocyanate groups e.g. B. by reaction with a defined amount of a secondary amine such as dibutylamine and subsequent titration of the excess amine with acid.

Adequate swellability of the coating by water is ensured by the water solubility of the polymer arms A. Adequate swellability of the coating by water is generally guaranteed when the molecular structure, ie. H. at least the type of repeat units, preferably also the molecular weight of the polymer arm, corresponds to a polymer whose solubility in water is at least 1% by weight and preferably at least 5% by weight (at 25 ° C. and 1 bar).

Examples of such polymers with sufficient water solubility are poly-C ₂ -C ₄ -alkylene oxides, polyoxazolines, polyvinyl alcohols, homo- and copolymers which contain at least 50% by weight of copolymerized N-vinylpyrrolidone, homo- and Copolymers which contain at least 30% by weight of hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, acrylamide, methacrylamide, acrylic acid and / or methacrylic acid in copolymerized form, hydroxylated polydienes and the like.

In a preferred embodiment, the polymer arms A are derived from poly-C2-C ₄ -alkylene oxides and are selected in particular from polyethylene oxide, polypropylene oxide and polyethylene oxide / polypropylene oxide copolymers, which can have a block or a statistical arrangement of the repeating units. Star-shaped prepolymers whose polymer arms A are derived from polyethylene oxides or from polyethylene oxide / polypropylene oxide copolymers with a propylene oxide content of not more than 50% are particularly preferred.

The prepolymers used according to the invention are e.g. T. known, e.g. B. from WO 98/20060, US 6,162,862 (polyether star polymers), Chujo Y. et al., Polym. J. 1992, 24 (11), 1301-1306 (star-shaped polyoxazolines), WO 01/55360 (star-shaped polyvinyl alcohols, copolymers containing star-shaped vinylpyrrolidone) or can be prepared by the methods described therein.

The star-shaped prepolymers used in accordance with the invention are generally produced by functionalizing suitable star-shaped prepolymer precursors which already have the prepolymer structure described above, ie at least 4 water-soluble polymer arms, and which each have a functional group R "at the ends of the polymer arms, which can be converted into one of the aforementioned reactive groups R. The groups R "include halogen atoms bonded to aliphatic or aromatic carbon atoms, preferably to a primary aliphatic carbon atom, in particular chlorine, bromine or iodine, to an aliphatic or aromatic and in particular to a primary, aliphatic carbon atom-linked OH groups, thiol groups and NHR ² groups with R ² = hydrogen or -CC ₄ alkyl. Such prepolymer precursors are known from the prior art, for. B. from US 3,865,806, US 5,872,086, US 6,162,862, Polym. J. 1992, 24 (11), 1301-1306, WO 01/55360 and commercially available, e.g. B. in the case of star-shaped poly-C ₂ -C ₄ -alkylene oxides under the trade names VORANOL®, TERRALOX®, SYNALOX® and DOWFAX® from Dow-Chemical Corporation, SORBETH® from Glyco-Chemicals Inc. and GLUCAM® from Amerchol Corp. or can be prepared by known methods in polymer chemistry by polymerizing suitable monomers in the presence of polyfunctional initiators, e.g. B. by "living" polymerization (see: Hsieh, HL; Quirk, RP Anionic polymerization: Principles and Practical Applications, New York, Marcel Dekker, 1996; Matyjaszewski, K. Controlled / Living radical polymerization: Progress in ATRP, NMP, and RAFT, Washington, DC: American Chemical Society, 2000) or in particular in the case of ethylenically unsaturated monomers by atom transfer radical polymerization (ATRP) according to the processes described in WO 98/40415.

The star-shaped prepolymer precursors can in principle be functionalized in analogy to known functionalization processes of the prior art.

For the preparation of prepolymers which carry A amino groups at the ends of the polymer arms, there are particularly suitable starting materials as prepolymer precursors which have A OH groups at the ends of the polymer arms. The conversion of OH groups to amino groups can e.g. B. in analogy to that of Skarzewski, J. et al. Monatsh. Chem. 1983, 114, 1071-1077 method described. To this end, the OH groups in a conventional manner, (z. B. by Organikum, 15th ed., VEB, Berlin 1981 S. 241ff .; J. March, Advanced Organic Synthesis ^3rd ed. S. 382 ff. see also Example 12) with a halogenating agent such as thionyl chloride, sulfuryl chloride, thionyl bromide, phosphorus tribromide, phosphorus oxychloride, oxalyl chloride and the like, optionally in the presence of an auxiliary base such as pyridine or triethylamine, in the corresponding halide, or with methanesulfonyl chloride in the corresponding mesylate. The halogen compound thus obtained, or the mesylate then with an alkali metal azide, preferably in an aprotic polar solvent such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide or N-methylpyrrolidone, into which the corresponding azide is converted. The azide is then converted to the amino compound with hydrogen in the presence of a transition metal catalyst or with a complex hydride such as lithium aluminum hydride.

The preparation of prepolymers which carry oxirane groups at the ends of the polymer arms A can be achieved, for example, by reacting prepolymer precursors which have OH groups at the ends of the polymer arms with glycidyl chloride.

Prepolymers which carry A (meth) acrylic groups at the ends of the polymer arms can be produced, for example, by esterifying prepolymer precursors which carry A OH groups at the ends of the polymer arms with acrylic acid or methacrylic acid or by reacting the OH- Groups with acrylic chloride or with methacryl chloride in analogy to known processes. Alternatively, in prepolymer precursors which carry A NH ₂ groups at the ends of the polymer arms, the NH ₂ groups can be reacted with acrylic acid or methacrylic acid or with their acid chlorides. The preparation of (meth) acrylate-terminated prepolymers can e.g. B. in analogy to that of Cruise et al. Biomaterials_1998, 19, 1287-1294 and Han et al. Macromolecules 1997, 30, 6077-6083 for the modification of polyether diols and triols described methods take place.

Prepolymers which carry thiol groups at the ends of polymer arms A can be prepared, for example, by reacting prepolymer precursors which carry halogen atoms at the ends of polymer arms A with thioacetic acid and subsequent hydrolysis in analogy to that in Houben-Weyl, Methods of Organic Chemistry, Ed. E. Müller, 4th ed., Vol. 9, p. 749, G. Thieme, Stuttgart 1955.

The preparation of prepolymers which carry isocyanate at the ends of the polymer arms A is preferably achieved by adding a low molecular weight diisocyanate. anates to prepolymer precursors which have A OH, SH, or NHR "groups at the ends of the polymer arms (R '= H, or an aliphatic radical). Star-shaped polyols with OH end groups are preferably used.

Both aromatic diisocyanates such as toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, commercially available mixture of toluene-2,4- and -2,6-diisocyanate (TDI), m-phenylene diisocyanate, 3, 3 ^{'diphenyl-4,4'} - biphenylene diisocyanate, 4,4'-biphenylene diisocyanate, 4,4'-

Diphenylmethane diisocyanate, 3,3 ^{'dichloro 4,4'} -biphenylendiisocyanat, cumene-2,4-diisocyanate, 1, 5-naphthalene diisocyanate, p-xylylene diisocyanate, p-

Phenylene diisocyanate, 4-methoxy-1,3-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4-bromo-1,3-phenylene diisocyanate, 4-ethoxy-1,3-phenylene diisocyanate, 2,4-dimethyl-1, 3-phenylene diisocyanate, 5,6-dimethyl-1, 3-phenylene diisocyanate, 2,4-diisocyanatodiphenyl ether, benzidine diisocyanate, 4,6-dimethyl-1, 3-phenylene diisocyanate, 9,10-anthracene diisocyanate, 4,4 ^' -

Diisocyanatodibenzyl, 3,3 ^{'-dimethyl-4,4'-diisocyanatodiphenylmethanes, 2,6-dimethyl-4,4'} -diisocyantodiphenyl, 2,4-diisocyanatostilbene, 3,3'-dimethoxy-4,4 ^'- diisocyantodiphenyl, 1 , 4-anthracene diisocyanate, 2,5-fluoro diisocyanate, 1, 8-naphthalene diisocyanate, 2,6-diisocyanatobenzofuran, as well as aliphatic and cycloaliphatic diisocyanates such as isophorone diisocyanate (IPDI), ethylene diisocyanate, ethylidene diisocyanate, propylene-1,2-di-hexo -1, 2-diisocyanate, cyclohexylene-1, 4-diisocyanate, 1, 6-hexamethylene diisocyanate, 1, 4-

Tetramethylene diisocyanate, 1, 10-decamethylene diisocyanate and methylene dicyclohexyl diisocyanate.

Preference is given to diisocyanates whose isocyanate groups differ in their reactivity, such as toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and a mixture of toluene-2,4- and -2,6-diisocyanate and ice and trans-isophorone.

Star-shaped prepolymers with aliphatic diisocyanate end groups are particularly preferred, in particular those as obtained by adding IPDI to the chain ends of OH-group-terminated star-shaped prepolymer precursors. The star polymers are naturally reacted with the diisocyanate in such a way that a diisocyanate unit is added to each chain end of the star molecules, the second isocyanate group of the diisocyanate remaining free. In this way, each end group of the star molecules is provided with a free isocyanate group via a urethane linkage. Methods for this are described, for example, in US Pat. No. 5,808,131, WO 98/20060 and US 6,162,862 and Bartelink CF et al. J. Polymer Science 2000, 38, 2555-2565.

As a rule, the prepolymer precursor to avoid the formation of multimeric adducts, i. H. Adducts in which two or more prepolymers are linked to one another via diisocyanate units give an excess of the diisocyanate. As a rule, the excess is at least 10 mol%, based on the stoichiometry of the reaction, i.e. H. at least 1.1 moles, preferably at least 2 moles and in particular at least 5 moles of diisocyanate and especially at least 10 moles of diisocyanate are used per mole of functional group in the prepolymer precursor. The reaction is preferably carried out under controlled reaction conditions, i.e. H. the prepolymer precursor is added under reaction conditions so slowly that heating of the reactor contents by more than 20 K is avoided. The prepolymer precursor is preferably reacted with the diisocyanate in the absence of a solvent or diluent.

The reaction can take place in the absence or in the presence of small amounts of conventional catalysts which promote the formation of urethanes. Suitable catalysts are, for example, tertiary amines such as diazabicyclooctane (DABCO) and organotin compounds, e.g. B. DialkyIzinn (IV) salts of aliphatic carboxylic acids such as dibutyltin dilaurate and dibutyltin dioctoate. The amount of catalyst is generally not more than 0.5% by weight, based on the prepolymer precursor, eg. B. 0.01 to 0.5 wt .-%, in particular 0.02 to 0.3 wt .-%. In a preferred procedure, no catalyst is used. The required reaction temperatures naturally depend on the reactivity of the prepolymer precursor used, the diisocyanate, and if used on the type and amount of the catalyst used. It is generally in the range from 20 to 100 ° C. and in particular in the range from 35 to 80 ° C. It goes without saying that the reaction of the prepolymer precursor with the diisocyanate takes place in the absence of moisture (<2000 ppm, preferably <500 ppm).

The reaction mixture thus obtained is generally worked up by distilling off the excess diisocyanate, preferably under reduced pressure. The reaction products obtained predominantly contain the star-shaped prepolymer which has isocyanate groups at the ends of the polymer arms. The proportion of the star-shaped prepolymer is generally at least 70% by weight, preferably at least 80% by weight, of the reaction product. The remaining constituents of the reaction product are essentially dimers and, in small proportions, trimers, which in these quantities are also suitable for producing the coatings according to the invention.

The substrates to be coated with the star-shaped prepolymers according to the invention are in principle not subject to any restrictions. The substrates can have regularly or irregularly shaped, smooth or porous surfaces. Examples of suitable surface materials are oxidic surfaces, e.g. B. silicates such as glass, quartz, silicon dioxide such as in silica gels, or ceramics, further semimetals such as silicon, semiconductor materials, metals and metal alloys such as steel, polymers such as polyvinyl chloride, polyethylene, polymethylpentene, polypropylene, polyester, fluoropolymers (eg Teflon ®), polyamides, polyurethanes, poly (meth) acrylates, blends and composites of the aforementioned materials surfaces, including cellulose and natural fibers such as cotton fibers and wool. The polymers can be woven or non-woven material.

According to the invention, the ultrathin, hydrogel-forming coatings are produced by depositing the star-shaped prepolymers on the layered surface from a solution of the prepolymers by methods known per se and subsequent crosslinking of the reactive groups of the prepolymers. The deposition and crosslinking steps can be repeated if desired. This leads to thicker layers.

Examples of deposition processes are the immersion of the surface to be coated in the solution of the prepolymer and the spin coating - the solution of the prepolymer is applied to the surface to be coated rotating at high speed. It goes without saying that the coating measures are usually carried out under dust-free conditions for the production of ultra-thin coatings.

In the immersion process, the substrates are immersed in a solution of the star polymer in a suitable solvent and then the solution is run off, so that a thin liquid film with the most uniform thickness remains on the substrate. This is then dried. The resulting film thickness depends on the concentration of the star polymer solution. The networking is then triggered.

With spin coating, the substrate, which is initially not rotating, is generally completely wetted with the solution of the star-shaped prepolymer. Subsequently, the substrate to be coated is rotated at high speeds, preferably above 1000 rpm, eg. B. 1000 to 10000 U / min in rotation, the solution is largely spun off and a thin coating film remains on the surface of the substrate. Then networking is also triggered here.

The concentration of the prepolymer in the solution will generally not exceed 100 mg / ml, preferably 50 mg / ml and in particular 20 mg / ml. The concentration is usually at least 0.001 mg / ml, preferably at least 0.005 and in particular at least 0.01 mg / ml. The thickness of the coating can of course be controlled via the concentration, whereby very low concentrations usually lead to monolayers of the star polymers on the coated surfaces.

As a rule, the coating measures are chosen so that the coating thickness (measured by means of ellipsometry according to the method described in Guide to using WVASE 32 ™, JA Woollam Co. Ind., Lincoln NE USA 1998) has a value of 500 nm, preferably 200 nm and in particular does not exceed 100 nm. The process also enables the production of monolayers with thicknesses below 2 nm, e.g. B. 0.5 to 2 nm. For many applications, layer thicknesses in the range from 1 to 100 nm, in particular in the range from 2 to 50 nm, are preferred.

In principle, all solvents are suitable as solvents which have no or only a low reactivity towards the functional groups R of the prepolymer. Among these, those are preferred which have a high vapor pressure and are therefore easy to remove. Preferred solvents are therefore those which have a boiling point below 150 ° C. and preferably below 120 ° C. at normal pressure. Examples of suitable solvents are aprotic solvents, e.g. B. ethers such as tetrahydrofuran (THF), dioxane, diethyl ether, tert-butyl methyl ether, aromatic hydrocarbons such as xylenes and toluene, acetonitrile, propionitrile and mixtures of these solvents. In the case of prepolymers with OH, SH, carboxyl, (meth) acrylic and oxirane groups, protic solvents such as water or alcohols, e.g. B. methanol, ethanol, n-propanol, isopropanol, n-butanol and tert-butanol, and mixtures thereof with aprotic solvents. In the case of prepolymers with isocyanate groups, water and mixtures of water with aprotic solvents are surprisingly suitable in addition to the abovementioned aprotic solvents, since the degradation of the isocyanate groups in the prepolymers presumably takes place comparatively slowly.

The type of networking can be done in different ways. In one embodiment of the invention, the article coated with the uncrosslinked prepolymer will generally be treated with a crosslinking agent.

In principle, all polyfunctional compounds are suitable as crosslinking agents, the functional groups of which react with the functional groups of the prepolymer to form bonds. These functional groups are also referred to below as complementary functional groups R '. Table 1 provides an overview of complementary functional groups R ', the reactive groups R of the prepolymer being indicated in the first row and the groups R' complementary thereto being indicated in the first column:

Table 1: Complementary functional groups

Reactive group isocyanate acrylate / -SH -NH ₂ -OH oxirane

R acrylamide

complementary

Group R '

Isocyanate X * X X X

Acrylate X X X

Acrylamide X X X

-SH X X X

-NH ₂ XXX

-OH X X X

-COOH X

Oxirane X X X

Most active X X

* In the presence of water

Accordingly, one embodiment of the invention relates to a method in which the linking of the reactive groups R is initiated by adding a compound V1 which has at least two reactive groups R 'per molecule which reacts with the reactive groups R of the star-shaped prepolymer to form bonds.

The polyfunctional compounds V1 can be low molecular weight compounds, e.g. B. aliphatic or cycloaliphatic diols, triols and tetraols, e.g. B. ethylene glycol, butanediol, diethylene glycol, triethylene glycol, trimethylolpropane, pentaerythritol and the like, aliphatic or cycloaliphatic diamines, triamines or tetramines, for. Example, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1, 8-diamino-3,6-dioxaoctane, diaminocyclohexane, isophoronediamine and the like, amino alcohols such as ethanolamine, diethanolamine, aliphatic or cycloaliphatic dithonic acids such as tricarboxylic acids or to dicarboxylic acids such as tricarboxylic acids or tricarboxylic acids such as dicarboxylic acids such as tricarboxylic acids Sebacic acid, glutaric acid, adipic acid, phthalic acid, isophthalic acid, or around the aforementioned diisocyanates, depending on the type of reactive groups the prepolymer has. The low-molecular polyfunctional In contrast to the prepolymers, ionic compounds generally have a molecular weight of <500 g / mol.

The polyfunctional compound V1 can already be contained in the solution of the prepolymer which is used for the coating. Then react in the initially formed coating of largely uncrosslinked prepolymers, e.g. B. when drying or when heating the coating, the reactive groups R 'of the crosslinking agent with the reactive groups R of the prepolymer and in this way form a layer of crosslinked prepolymers.

If the reactive groups R of the prepolymer are conjugated dienes, the compound V1 will accordingly have at least two denophilic groups and vice versa. If the prepolymers have reactive groups which undergo an en reaction, the compound V1 will have at least two allylic double bonds. As a rule, in such systems for the production of the coatings, solutions are used which contain both the prepolymer and the compounds V1. The crosslinking then takes place when the primarily obtained coating dries, if appropriate after heating.

In principle, prepolymers are also suitable as polyfunctional compounds V1 which have at least four polymer arms A, which are in themselves soluble in water and have a reactive functional group R 'at their free ends, which react with the reactive groups R of the prepolymer to form bonds. In other words, solutions of at least two different prepolymers can also be used for the process according to the invention, in which one prepolymer has reactive groups R and the other has reactive groups R 'which are complementary thereto. In this way too, a layer of crosslinked prepolymers is obtained.

In another embodiment of the invention, the linking of the reactive groups R is initiated by adding a sufficient amount of a compound V2 which reacts with a part of the reactive groups R to form ver groups R 'reacts, which reacts with the remaining reactive groups R to form bonds. In the case of prepolymers with isocyanate groups, crosslinking can be triggered, for example, by treating the coated article with water, e.g. B. by storage in a damp atmosphere or under water. Here, some of the isocyanate groups react to form amino groups, which in turn react with the remaining isocyanate groups to form bonds, forming a layer of crosslinked prepolymers. The crosslinking agent V2 is therefore water here.

In a further embodiment of the invention, the group R is selected from ethylenically unsaturated, free-radically polymerizable double bonds. In this case, the crosslinking takes place in a thermal or photochemical manner, i. H. by irradiation with UV radiation or with electron radiation. In the case of photochemical crosslinking by UV radiation, suitable photoinitiators will generally be added to the solution of the prepolymer. The type and amount of photoinitiator required to initiate photochemical crosslinking is known to the person skilled in the art from radiation-curing lacquer technology.

In a further embodiment of the invention, a star-shaped prepolymer, preferably as a monolayer, is first applied to the surface to be coated in the manner described above, partial crosslinking of the reactive groups R is optionally carried out and then at least one further star-shaped prepolymer 2 is applied to the surface applied surface treated in this way, which has at least four polymer arms A, which are in themselves soluble in water and have at their free ends a reactive functional group R ', which have a complementary to the reactive groups R of the prepolymer 1 reactivity. If necessary, the remaining reactive groups R 'are then crosslinked again. This process can be repeated one or more times. In this way it is possible to produce multilayer coatings in a targeted manner. This procedure is also referred to below as the layer-by-layer method. The layer-by-layer process can be carried out in a particularly elegant manner with such prepolymers can be realized which have reactive groups R which react with compounds V2 to form reactive groups R 'which have a reactivity which is complementary to the groups R. Examples of groups R are isocyanate groups. In this case, the connection V2 is water. NH ₂ groups then form as complementarily reactive groups R '. If the crosslinking of the first layer with compound V2 is triggered, the coating obtained has free groups R '(for example amino groups) on its surface. These then react with the groups R (for example isocyanate groups) of the prepolymers applied in a second coating process to form bonds. The second coating process is preferably also controlled such that a monolayer of prepolymers is deposited on the first coating. Crosslinking of the second layer by means of compound V2 (for example water) and repetition of this procedure thus allows the production of highly crosslinked, highly ordered layers, in particular if the amount of coating in the individual coating stages has been chosen so that monolayers are obtained.

The coatings can also with mixtures of star-shaped prepolymers and water-soluble polysaccharides such as hyaluronates, heparins, alginates or z. B. dextran. When using prepolymers with functional groups reactive towards OH functions, e.g. B. isocyanate groups then the polysaccharide acts as a crosslinker.

The method according to the invention also allows the targeted incorporation of foreign materials, ie materials that do not form hydrogel-forming coatings, into the coating. These include bioactive materials such as drugs, oligonucleotides, peptides, proteins, signaling substances, growth factors, cells, carbohydrates and lipids, inorganic components such as apatites and hydroxyapatides, quaternary ammonium salt compounds, compounds from bisguanidines, quaternary pyridinium salt compounds, compounds from phosphonium salts, thiazoylbenzimidazoles, sulfonyl compounds, Salicyl compounds or organometallic compounds. The installation is preferably carried out by coadsorption from solutions which contain the prepolymer and the foreign component. In addition, the prepolymers with the bioactive materials mentioned before Sorption are implemented or reacted as a mixture with unmodified prepolymers on the surface. Of course, it is also possible to apply the finished hydrogel coating in a targeted manner by physisorption or chemisorption.

When coating according to the layer-by-layer method, biological components can also be introduced in the form of an intermediate layer that does not completely cover.

For this purpose, it is used that the top layer of the star-shaped prepolymers usually still carry reactive groups, which react specifically with frequently occurring chemical groups of biomolecules even under mild conditions (in aqueous solution, at room temperature). Examples are the reaction of NCO groups on the surface of the polymer layer with alcohol, thiol or amino groups which are present in proteins and peptides, or which can be easily introduced into many biomolecules by methods of the prior art. Another example is the Michael addition of thiol or amino groups to acrylates and acrylamides in the top layer of the coating. Another example is the implementation of activated esters in the top layer of the coating with alcohol or amino groups of the biomolecules.

Examples of suitable biological components which can be introduced into the hydrogel coatings produced by the process according to the invention are medicaments, e.g. B. heparins, antibiotics such as streptomycin, gentomycin, penicillin, neomycin, acriflavin, ampillicin, chitin, chitosan and their derivatives, as well as other bactericidal substances, further growth factors such as BMPs (bone morphogenic proteins), HGHs (human growth hormons), GMCSF (macrophages colony stimulating factors), heparin-binding factors such as FGFs, VGF, TGFs, communication and architecture-mediating signal substances such as BHL, HHL, OHL, DHLs, OHHL, OOHL, ODHL, OdDHL, HBHL, HtDHL and other, integrin-mediating signaling molecules, proteins such as Fibronectin, laminin, vitronectin, collagen, thrombospondin and other adhesion-promoting proteins, me- mechanically or otherwise physically modulated proteins such as stretched fibronectin, adhesion-mediating peptide sequences such as RGD, RGDS, RGDV, RDT, LRGDN, LDV, REDV, IKVAV, YIGSR, PDSGR, DGEA, peptide sequences which differ only by a change in the conformation, e.g. B. cyclic peptide sequences amino acid sequences and oligonucleotides that enable molecular recognition, such as sequences from RNA or DNA, carbohydrates and lipids, such as sugar and long-chain hydrocarbon compounds that allow interaction with the cell membrane, cells or cell assemblies of fibroblasts, osteoblasts, chondrocytes and other cell types, but also pluripotent cell material.

It is often advantageous to pretreat the surface to be coated in such a way that it has an increased number (areal density) of functional groups R 'which can react with the functional groups R of the prepolymer to form bonds.

For this purpose, the surfaces of inert materials will often be chemically activated before coating. This can be done, for example, by treating the surface to be coated with acid or alkali, by oxidation (flaming), by electron radiation or by plasma treatment with an oxygen-containing plasma, as described by P. Chevallier et al. J. Phys. Chem. B 2001, 105 (50), 12490-12497; in JP 09302118 A2; in DE 10011275; or by D. Klee, et al. Adv. Polym. Be. 1999, 149, 1-57.

The surface to be coated can also be treated with compounds which are known to have good adhesion to the surface and which also have functional groups R 'which are complementary to the functional groups R of the star-shaped prepolymer. Suitable groups R ', depending on the reactive group R of the prepolymer: isocyanate, amino, hydroxyl and epoxy groups, furthermore groups which react in the sense of Michael addition, dienophilic groups which enter into Diels-Alder addition reactions, are electron-poor double bonds which react in a Diels-Alder addition or en reaction with allylic double bonds; activated ester groups; oxazoline; as well as vinyl groups and thiols, which specifically undergo free radical addition.

The type of group that causes adhesion to the surface to be coated naturally depends on the chemical nature of the surface to be coated. In the case of oxidic, such as ceramic and glass-like surfaces, as well as in the case of metallic surfaces, compounds which have silane groups, in particular trialkoxysilane groups, have proven useful. Examples of such compounds are trialkoxyaminoalkylsilanes such as triethoxyaminopropylsilane and N [(3-triethoxysilyl) propyl] ethylenediamine, trialkoxyalkyl-3-glycidyl ether silanes such as triethoxypropyl-3-glycidyl ether silane and trialkoxy alkyl mercaptoxy tranhexane triloxiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylalkylsiloxylsiloxylalkylsiloxylalkane such as 1-triethoxysilyl-3-acryloxypropane. Polyoxidic polyammonium groups are also suitable as adhesion-promoting groups for oxidic materials and plastic materials. Examples of such compounds are polyammonium compound with free primary amine groups such as z. B. by J. Scheerder, J.F.J Engbersen, and D.N. Reinhoudt, Recl. Trav. Chim. Pays-Bas 1996, 115 (6), 307-320, and von Decher, Science 1997, 277, 1232-1237 for this purpose.

The aforementioned compounds are preferably applied as a monolayer to the surface to be coated. Such monolayers can be achieved in a manner known per se by treating the surfaces to be coated with dilute solutions of the compounds, for. B. according to the immersion process described above or by means of spin coating. Solvents and concentrations correspond to the information given for the application of the prepolymers. It is often advisable to treat the surfaces with the abovementioned compounds, which are known to have good adhesion to the surface, following activation by flame, by electron radiation or by plasma treatment. The surfaces coated according to this invention swell in direct contact with water, aqueous solutions and moist gases to form very stable hydrogels. In contrast to many hydrogel-forming coatings of the prior art, the coatings are stable even after prolonged contact with aqueous solutions, since the deposits can be removed by simply rinsing with water. The coatings obtained according to the invention effectively prevent the non-specific adsorption of proteins and cells over a long period of time and are superior in this point to the hydrogel coatings of the prior art. Due to their chemical composition, the coatings are biocompatible and non-toxic.

The use of the star-shaped prepolymers with reactive end groups advantageously enables the use of simple coating processes such as immersion, spin coating (rotary spin processes) and in particular a layer-by-layer structure.

The peculiarity of the star-shaped prepolymers with reactive end groups also makes it possible, in a very simple and controlled manner, to produce thin to ultra-thin hydrogel coatings with a layer thickness below 100 nm, preferably below 50 nm and, if desired, below 10 nm. The coatings prevent unspecific protein adsorption and cell adhesion and can thus prevent bacterial colonization. The low thickness of the coating is particularly advantageous since the macroscopic properties and the appearance of the underlying material remain practically unchanged.

The use of star-shaped prepolymers with reactive end groups also makes it possible in a simple manner to produce ordered monolayers and multilayers whose structure and properties such as water absorption, penetrability and flexibility can be set very precisely for the respective application.

The method according to the invention also allows in a unique way, various functions such. B. biological agents, function centers, signal Store substances, growth factors, etc. in the individual hydrogel layers and thus transfer a biofunctional coating to substrates. The suppression of non-specific bacterial colonization can be increased by incorporating bactericides, biological signaling substances and colloidal particles with a diameter preferably below 100 nm. On the other hand, the method according to the invention also opens up the possibility of specifically promoting colonization with specific bacteria and cells by incorporating biological signaling molecules and ligands.

Due to the properties of the coatings obtained according to the invention, the method according to the invention can be used for the production of micro sensors and micro analysis systems, for coating micro cannulas for the introduction of genetic material into cells and of capillary systems in which the adsorption of biological compounds on the capillary surfaces is large Represents a problem and can significantly impair the analytical sensitivity. In other words, the use of star-shaped prepolymers for the production of hydrogel coatings opens up areas of application in which conventional polymers and hydrogels cannot be used or have not been used due to their inadequate protein resistance.

The method according to the invention is also particularly suitable for coating objects which are in direct contact with living matter, such as implants. The coatings can be applied to a wide range of laboratory utensils, medical products and instruments, but also in the semi-technical area to surfaces that must be kept extremely clean, i.e. as free of protein and cells as possible, or that are difficult to access for cleaning steps.

The coatings obtainable according to the invention are also particularly advantageous where only extremely thin coatings are possible. For example, the method according to the invention can be used to produce ultra-thin coatings on the inner walls of hose and tube systems. those who in turn only have a particularly small diameter, e.g. B. in the μm range, have (implantable pump systems, thin catheters, microbiological and genetic engineering laboratory equipment). However, the method according to the invention is also suitable for coating extremely large areas (ship hulls, technical pipe systems, swimming pools, operating theaters, etc.).

FIG. 1 shows the ellipsometrically determined layer thickness of a coating according to the invention as a function of the number of coating processes.

FIG. 2 shows the increase in the thickness of a dried coating according to the invention which is exposed to atmospheric moisture (determined by ellipsometry).

FIG. 3 shows a light micrograph of a glass plate coated according to the invention (thickness of the coating about 50 nm) which had been incubated with a fibroblast suspension.

FIGS. 4a and 4b show light microscopic images of glass platelets which have a coating according to the invention on one half and a polystyrene coating on the other half and which were incubated with a fibroblast suspension.

FIG. 5 shows an optical micrograph of a glass plate which was half coated with a mixture of star prepolymers and dextran (1: 1) and half uncoated and which was incubated with a fibroblast suspension.

The following examples are intended to explain the invention further.

I. Manufacturing examples Six-armed isocyanate-terminated polyethers.

In all cases, a commercially available isophorone diisocyanate was used as the isocyanate (IPDI: 72% ice and 28% trans isomer)

The prepolymer precursors used are commercially available 6-armed polyalkylene ethers (hereinafter referred to as polyols) which have been prepared by anionic ring-opening polymerization from ethylene oxide and / or propylene oxide using sorbitol as the initiator. The polyol used was dried to a residual water content of less than 350 ppm before use. Residues of the alkali metal hydroxide used for the preparation of the polyols were bound by neutralization with phosphoric acid.

In all production examples, the polyol was slowly added via a pump (approx. 80 ml / h), so that the reaction temperature did not deviate from the specified temperature by more than 10 K.

The molecular weight (the number average is given in each case) was determined by gel permeation chromatography at room temperature on three columns connected in series (column 1: Waters μ-Styragel 1000 angstroms, I = 30 cm; column 2: Waters μ-Styragel 100 angstroms, I = 30 cm; column 3: PSS SDV 50 Angstrom, I = 60 cm) using tetrahydrofuran as eluent, a refractometry detector (Waters Rl 2410) and using the evaluation software PSS Win-GPC V 4.02. The elution diagrams were adapted for evaluation on two Gaussian curves, the proportion of bi- / trimer being determined via the area ratios.

The characterization of the end groups of functionalized prepolymers and the functionalization yield, where indicated, were also carried out by elemental analysis (sulfur, nitrogen), by means of IR spectroscopy (v SH, C = 0, NH) or by titration (unreacted OH groups). The unreacted OH groups were determined by reacting the prepolymers with acetic anhydride in pyridine and titrating excess acid (hydrolysis of the unreacted acetic anhydride) with NaOH.

Production example 1:

The polyol used is a 6-arm statistical poly (ethylene / propylene oxide) with an EO / PO ratio of 80/20 with a molecular weight of 3100 g / mol. Before the reaction, 0.05% by weight of phosphoric acid was added to the polyol and the mixture was heated to 80 ° C. in vacuo with stirring.

262 g of IPDI (1.18 mol) were placed in a reactor and heated to 50 ° C. in an inert gas atmosphere. The dried and degassed polyol (50 g, 0.016 mol) was then added slowly (approx. 80 ml / h) using a peristaltic pump. After the addition was complete, the reaction mixture was stirred at 50 ° C for an additional 60 hours. Excess IPDI was completely distilled off at 130 ° C. and a pressure of 0.025 mbar using a thin-layer distillation apparatus.

Production example 2:

The polyol used corresponds to the polyol from Preparation Example 1.

210 g of IPDI (0.94 mol) and 0.06 g (0.1% by weight) of diazabicyclooctane (DABCO) were placed in a reactor and the mixture was heated to 50 ° C. under an inert gas atmosphere. The dried and degassed polyol (58 g, 0.019 mol) was then added slowly (approx. 80 ml / h) using a peristaltic pump. After the addition was complete, the reaction mixture was stirred at 50 ° C. for a further 60 hours. Excess IPDI was distilled off at 130 ° C. and a pressure of 0.025 mbar using a thin-film distillation apparatus. Production Example 3:

The polyol used is a 6-arm statistical poly (ethylene / propylene oxide) with an EO / PO ratio of 80/20 with a molecular weight of 10,000 g / mol. Before the reaction, 0.05% by weight of phosphoric acid was added to the polyol and heated to 80 ° C. in vacuo with stirring.

IPDI (100 g, 0.45 mol) was placed in a reactor and heated to 50 ° C. in a protective gas atmosphere. For this purpose, the dried and degassed polyol (50 g, 0.005 mol) was slowly added with the aid of a peristaltic pump (approx. 80 ml / h). After the addition was complete, the reaction mixture was stirred at 50 ° C for an additional 60 hours. After thin-film distillation (100 ° C., 0.025 mbar), the isocyanate-terminated star prepolymers were obtained.

Production example 4:

The polyol used is a 6-arm polypropylene oxide with a molecular weight of 3000 g / mol. Before the reaction, 0.05% by weight of phosphoric acid was added to the polyol and heated in vacuo at 80 ° C. for 1 h.

480 g (0.154 mol) of the polyol were slowly (80 ml / h) under a protective gas atmosphere with the aid of a peristaltic pump to a vigorously stirred mixture of 840 g IPDI (3.78 mol) and 0.99 which was heated at 50 ° C. g of dibutyltin dilaurate (DBTL). After the addition was complete, the reaction mixture was stirred at 50 ° C for an additional 48 hours. After thin-film distillation (160 ° C, 0.01 mbar), the isocyanate-terminated star prepolymers were obtained.

The prepolymers of Preparation Examples Nos. 5, 6, 7 and 9 were prepared analogously to Preparation Example 1. Analogously to production example 2, the prepolymers of Preparation Examples 8 and 10. The molar ratio of diisocyanate to OH groups in the polyol (NCO / 2 / OH) is shown in Table 2. Table 2 also shows the proportions of monomolecular star-shaped polymers (mono-star) and of bi- and trimolecular reaction products (bi- and tri-stem), as determined by means of gel permeation chromatography.

Production Example 11:

Analogously to preparation example 1, 30 g of a 6-arm statistical poly (ethylene oxide / propylene oxide) with an EO / PO ratio of 80/20 with a number average molecular weight of 12,000 were reacted with 50 g (0.23 mol) of IPDI. After thin-layer distillation (100 ° C / 0.001 mbar), the isocyanate-terminated star prepolymer was obtained.

Table 2: Production examples

Production of star polymers with thiol, acrylate, acrylamide or NH ₂ groups

Production Example 12: Thiol-terminated star polyether

A commercially available 6-arm polyethylene oxide, which had OH groups at the ends of the polyether chains, was brominated with PBr ₃ using a customary method (Mills et al., J. Chem. Soc. Perkin Trans. 2, (4), 697 -706, 1995, see also Tetrahedron 44 (5), 1988, pp. 1553-1558 and Inorg. Chim. Acta 97 (2) 1985, pp. 143-150 and in general J. March, Advances in Organic Synthesis 3rd ed. J. Wiley & Sons, New York 1985, p. 383), whereby a 6-arm polyethylene oxide was obtained which had bromine atoms at the ends of the polyether chains. This was predried in the manner described for Example 1. A solution of 15 eq was then slowly dripped in at 100 ° C. Thioacetic acid in 200 ml ethanol with 15 eq. Ethoxide. After a further 24 h the thioacetate was hydrolyzed with 1 N aqueous HCl. After hydrolysis of the thioacetate obtained as an intermediate, the solution was stirred under nitrogen at 78 ° C. for a further two hours. The desired thiol group-containing product was removed using a thin-layer distillation apparatus with the exclusion of air.

An IR spectrum of the product obtained showed a weak band at 2558 cm ^"1 , which can be assigned to the SH vibration. The elementally determined sulfur content corresponds to a degree of functionalization of 5.1.

Production Example 13: Acrylate-terminated star polyether

A solution of 40 g (12.9 mmol) of the predried polyether used in Preparation 1 in 400 ml of dichloromethane was cooled to 0 ° C. and for several hours with a solution of 465 mmol of pyridine and 465 mmol of acryloyl chloride in 30 ml of dichloromethane added. The reaction solution was at 0 ° C for a further six hours and then stirred for a further 30 h at room temperature. The precipitated salt was filtered off and the filtrate was washed first with dilute hydrochloric acid and then with aqueous sodium hydrogen carbonate solution. The organic phase was dried over magnesium sulfate. The product was precipitated by adding diethyl ether, filtered off and dried in vacuo.

An IR spectrum of the prepolymer showed an intense characteristic band at 1730 cm ^"1 , which can be assigned to the C = 0 vibration. Titrimetric determination of the OH group content showed a degree of functionalization of> 5.

Production Example 14: Amine-terminated star polyether

A saturated solution of 100 g (32.3 mmol) of the predried polyether used in Preparation 1 in 400 ml of dichloromethane was cooled to 0 ° C. under a nitrogen atmosphere. For this purpose, 580 mmol of pyridine were first added very slowly and then 580 mmol of methanesulfonyl chloride. After 24 hours, the precipitate was filtered off and the mesylate formed was precipitated by adding diethyl ether. The mesylate obtained was dissolved in dimethylformamide and stirred with 1.16 mol of sodium azide at 60 ° C. for 24 hours. After cooling, the mixture was diluted with water and extracted with dichloromethane. The organic phase was then dried over magnesium sulfate, the product was precipitated by adding diethyl ether, filtered and the product was dried in vacuo. The resulting polyether functionalized with azide groups was dissolved in dry tetrahydrofuran and the solution was added dropwise to a suspension of 290 mmol LiAIH ₄ in tetrahydrofuran. The mixture was stirred at 60 ° C. for 16 h and, after cooling, 15% sodium hydroxide solution was slowly added until a white granular precipitate formed. It was then filtered through silica. The amine-terminated polyether was precipitated from the solution thus obtained by adding diethyl ether and dried in vacuo. A sharp band at 3310 cm ^"1 can be seen in the IR spectrum of the prepolymer, which is attributable to the NH vibration. The nitrogen content determined by elemental analysis corresponds to a degree of functionalization> 5.

Production Example 15: Acrylamide-terminated star polyether

A solution of 30 g (approx. 9.6 mmol) of the predried amine-terminated polyether from preparation example 14 in 300 ml of toluene was cooled to 0 ° C. under a nitrogen atmosphere and diluted with dichloromethane until a clear solution was obtained. 320 mmol of pyridine were then added, followed by 320 mmol of acryloyl chloride over several hours. After the addition had ended, the mixture was stabilized with BHT, stirred at least for a further 6 hours at 0 ° C. with exclusion of light and concentrated to 200 ml. The precipitated salt was filtered off and the filtrate was poured into 500 ml of cold diethyl ether. This resulted in a solid which was dissolved in 200 ml of distilled water. 10 g of NaCl were added to the solution. The pH was adjusted to 7 by adding 1N NaOH and the neutralized solution was extracted several times with dichloromethane. The organic phases are combined with diethyl ether, a solid precipitating out. This was taken up a second time in dichloromethane, a stabilizer was added and it was again precipitated in 500 ml of cold diethyl ether, filtered off and dried in vacuo. In this way, the star polyether terminated with acrylamide groups was obtained.

A strong band at 1670 cm ^"1 can be seen in the IR spectrum, which can be assigned to the amide EO group. The nitrogen value determined by elemental analysis corresponds to a degree of functionalization> 5.

Production of hydrogel coatings

Glass platelets (floated glass, quartz glass, standard glass) and hydrophilic silicon wafers were used as substrates (Si [100]). The substrates were cleaned in an ultrasonic bath first in acetone, then in Millipore water and then in isopropanol. All substrates were kept in suitable protective containers under a layer of liquid in order to avoid contamination by dust and grease droplets from the air.

The water used was basically desalinated (18 MΩ-cm or better). All solutions were cleaned of dust and particulate contamination with a 0.05 μ filter. Filtered deionized water is also referred to below as Millipore water.

Coatings with the exclusion of water were carried out in a glove box (brown) under an atmosphere with a water content of less than 1 ppm H ₂ O / Q ₂ .

1. Amino functionalization of the substrates

1.1. The cleaned substrates were treated in a plasma system of the TePla 100-E type from Plasma Systeme for 10 minutes in oxygen plasma (pressure: 0.15 mbar). The substrates treated in this way were then stored in deionized water.

For amino functionalization, the substrate surface was first coated with an aminosilian monolayer as a promoter. For this purpose, the sample taken from the water and blown dry with nitrogen was transferred to a glove box. There, the substrates were stored in a 0.4% (v / v) solution of N- (3- (trimethoxysilyl) propyl) ethylenediamine in dry toluene for 16 h, then washed thoroughly with toluene and, before use, in a glove box under a nitrogen atmosphere a filtered nitrogen stream dried.

1.2 Alternatively, the substrates were treated with oxygen under a 40 W UV lamp for 10 min (distance between substrate surface and light source 2 mm) and then placed in Millipore water (MP-H ₂ 0). The sample taken from the MP-H ₂ O and blown dry with nitrogen was then treated as in 1.1 with (trimethoxysilyl) propyl) ethylenediamine.

2. Coating the substrates

All measures were carried out under dust-free conditions (clean room conditions).

2.1 Coating through immersion

General regulation a)

The substrates functionalized according to the instructions under 1.1 are immersed in a solution of the respective prepolymer in dry THF (0.05 mg / ml to 5 mg / ml). The solution is allowed to drain carefully so that a thin liquid film of uniform thickness remains on the substrate. This is dried. The resulting film thickness depends on the concentration of the star polymer solution. The samples are then removed from the glovebox, protected from dust, and reacted in a humid atmosphere. The samples are placed in MP-H2O until use / examination.

General regulation b)

The substrates functionalized according to the instructions under 1.1 are immersed in a freshly prepared solution of the prepolymer (0.005 mg / ml to 20 mg / ml in 1: 1 THF: MP-H ₂ O). The solution is allowed to drain carefully so that a thin liquid film of uniform thickness remains on the substrate, which is dried. After the film has reacted, the samples are placed in MP-H ₂ 0 until use. Table 3 lists tests and resulting layer thicknesses which were obtained by an immersion coating. The layer thicknesses were determined by ellipsometry ("Guide to using WVASE32 ™", JA Woollam Co., Ind., Lincoln, NE, USA, 1998).

Table 3:

Prepolymer concentration regulation solvent layer thickness

Manufacturing [mg / ml] example

No. 3 0.005 b THF / H ₂ 0 1.3 nm

No. 3 0.05 b THF / H ₂ O 3.0 nm

No. 3 0.5 b THF / H ₂ O 4.9 nm

No. 3 1, 0 b THF / H ₂ O 12.0 nm

No. 3 20.0 b THF / H ₂ O 23.0 nm

No. 1 0.05 a THF 4 - 5 Ä

No. 1 2.0 a THF 7 -8 Ä

No. 1 5.0 a THF 9 -10 Ä

2.2 Coating by means of spin coating (rotary spin process) of a thin polymer layer (general rule)

The coating of 1 amine-functionalized substrates produced was carried out using a spin coater (model: WS-400A-6TFM / lite from the company: SPS). For this purpose, the non-rotating, dried substrate is completely wetted with the prepolymer solution (0.05 mg / ml to 5 mg / ml star polymer in THF) before the solution at acceleration level "5" and a final speed of 5000 rpm for 40 Is flung for seconds. The sample is then dry. The substrates coated in this way were stored in the absence of dust overnight at a humidity of 50 to 80%. The samples treated in this way can then be used immediately for the desired application or placed in MP-H ₂ 0 until use. In a variant of the process described above, the amine-functionalized substrate prepared according to 1 is rinsed on the spin coater with rotation (3000 rpm) with salt-free water before the coating is carried out with a freshly prepared water-containing star polymer solution in THF. In this way, better wetting of the substrate and a very thin polymer film are achieved.

The results are summarized in Table 4. The layer thickness was determined ellipsometrically.

Table 4:

Prepolymer concentration layer thickness

Production example [mg / ml]

No. 3 0.005 0.9 nm

No. 3 0.01 3.1 nm

No. 3 0.05 5.4 nm

No. 3 0.1 7.5 nm

No. 3 0.5 11.4 nm

No. 3 1, 0 14.6 nm

No. 3 2.5 15.5 nm

No. 3 5.0 43.2 nm

No. 3 10.0 112.0 nm

No. 3 20.0 211, 2 nm

No. 1 0.5 7 - 9 nm

No. 1 1, 0 12 -13.5 nm

No. 1 2.0 14 -17 nm

Coating layer by layer:

3.1 General regulation for the production of monolayers using spin coating: The substrates functionalized and washed according to point 1 are carefully blown dry on the spin coater in a filtered nitrogen stream. The substrate is slightly warmed with the nitrogen stream preheated to 50 ° C. before a solution of the prepolymer from preparation example 1 (in THF; 0.5 to 5 mg / ml, see 111-1) is spun on with the exclusion of moisture (spin coater) Model: WS-400A-6TFM / lite by the company: PLC, acceleration level "2" and a speed of 1500 rpm). Even before the film has dried completely, the surface of the still rotating substrate is washed several times by applying a drop of anhydrous dichloromethane in order to remove excess prepolymer. The procedure is repeated to achieve a dense monofilm. The sample coated in this way is then crosslinked by placing it in MP-H ₂ O. The procedure is repeated according to the number of monolayers to be applied.

3.2 General regulation for the production of monolayers using immersion:

The substrates pretreated according to point 1 are placed for one hour with exclusion of moisture in a solution of the prepolymer in anhydrous THF. The samples are then washed several times with anhydrous THF to rinse off non-chemically bound prepolymer molecules. The samples are then placed in MP-H 0 for one hour. The sample is dried and then placed in a THF bath to remove water from the coating. The samples are then dried in a dust-free atmosphere or in a filtered nitrogen stream. To apply a further monofilm, this procedure is repeated, starting with immersing the sample in the anhydrous solution of the prepolymer in THF. The samples coated in this way can be used immediately for the desired application or placed in MP-H ₂ 0 until they are used. III. Examination of the polymer films

1. Investigation of the concentration dependence of the thickness of a monolayer:

Silicon wafers manufactured according to the regulation under 11-1. were pretreated, were placed in a solution of the prepolymer from preparation example 1 in anhydrous THF. After immersion, the samples were washed several times with anhydrous THF. After the subsequent one-hour soak in MP-H ₂ 0, they were removed and dried as described under II-3.2. The layer thickness of the hydrogel films obtained was determined by means of ellipsometry. The values are given in Table 5:

Table 5:

The values in Table 5 show that the layer thickness initially increases strongly with increasing concentration of the prepolymer solution and approaches a limit value at high concentration (e.g. 5 mg / ml). It is believed that at low concentrations, due to the lower degree of surface coverage, more NCO groups with reactive groups form covalent bonds on the surface. In contrast, a higher concentration presumably leads to a densely packed adsorbate layer of star molecules with less binding to the surface via the NCO groups. 2. Examination of layer thickness as a function of the number of layers applied:

For this purpose, a monolayer was first prepared as described under 1., using a solution of the prepolymer from Preparation Example 1 in THF with a concentration of 1.0 mg / ml. The substrate coated in this way was then placed in a solution of the same prepolymer in anhydrous THF (concentration 1.0 mg / ml). The sample was then washed several times with anhydrous THF. After the subsequent one-hour soak in MP-H ₂ 0, they were removed and dried as described above. This procedure was repeated a total of five times, the layer thickness being determined by means of ellipsometry after each application of a further layer. The results are shown in Figure 1.

As can be seen from FIG. 1, the layer thickness increases linearly with increasing number of layers, the slope of the compensating line is approximately 4.7 A / layer, which corresponds to the thickness of a monolayer.

3. Determination of the water swelling of a thin hydrogel layer

The swelling behavior was examined by means of ellipsometry on a thin coating. The change in layer thickness, which directly reflects the swelling behavior of the hydrogel layer, was measured in situ.

The samples were pretreated as described under II.-1. After the sample had been dried in a filtered nitrogen stream, a solution of the polymer from Preparation Example 1 (5 mg / ml in dry THF) was spin-coated at a speed of 6000 rpm. (40 sec.) As described under II-2.2. The sample produced in this way was then stored in water for one hour and, after drying in the filtered nitrogen stream, was dried for 30 minutes at 90 ° C./0.1. The dried sample was then exposed to the laboratory atmosphere (20 ° C, 60% relative humidity) exposed and the change in layer thickness caused by water absorption was examined in-situ by means of ellipsometry. The results of the investigation are shown in FIG. 2.

As can be seen from FIG. 2, the layer thickness of the dried sample initially increases continuously as a result of contact with the moist air. After approx. 10 h no further increase in layer thickness can be seen. The total relative increase in layer thickness is approx. 2%, which corresponds to an absolute increase of a few angstroms.

4. Investigation of the adsorption of biopolymers by observing the diffusion of single molecules

Glass slides with a recess as well as cover glasses (d = 170 μm) were used as substrates and initially as under 11-1. described pretreated. The substrates used were then coated with the prepolymer from preparation example 3 in the manner described for N-2.2 (spin coating of a solution of 5 mg / ml prepolymer in dry THF at a speed of 5000 rpm).

The investigation was carried out by means of confocal laser microscopy and by means of confocal fluorescence correlation spectroscopy (FCS) using the fluorescent dye MR 121. The dye was in PBS buffer (140 mM NaCl, 10 mM KCI, 6.4 mM Na ₂ HP0 ₄ x 2H ₂ 0, 2 mM KH ₂ P0 ₄ ) diluted to a concentration of 10 ^"10 M. 120 .mu.l of the solution were pipetted into the approx. 100 .mu.l well of the above-mentioned slide and covered with the 170 .mu.m coated cover glass. For reference an uncoated glass slide and an uncoated cover slip were used.

For confocal laser microscopy, the slide with the sample was positioned with the cover slip down over the microscope objective. By moving the lens, the laser focus was focused about 10 μm above the cover slip in the sample solution.

In this way could the interaction of the dye (MR121), via a- also labeled with the dye oligonucleotides (MR-121 IPs) in solutions of 10 ^{"9 -10"} M ¹⁰ microns in a volume of about 1 ³ directly the glass surface can be observed. In order to observe the conditions directly on the surface, the excitation light of the laser was focused on the glass surface in such a way that the reflection caused by the glass-water transition was maximum. It was found that the labeled oligonucleotides adsorb from the PBS (additionally with 5 mM MgC) solution in the reference and were then no longer freely movable. The individual molecules could then be located on the surface in the microscopic images. In contrast, in the sample space coated according to the invention, the oligonucleotides are free to move - similarly as in solution and cannot be localized as in solution, so that an increased background fluorescence was measured for the entire image.

Confocal fluorescence correlation spectroscopy (FCS) enables the interaction of the dye oligonucleotide (MR 121-IPs) of 10 ^"9 - 10 ^{" 10} M with the surface to be measured quantitatively (see also M. Sauer et al., Anal Chem. 2000, 72, 3717-3724). FCS curves of homogeneous solutions, i.e. all fluorophores behave in the same way and can be described by neglecting tripletters by a sigmoidal fit. Its turning point corresponds to an average diffusion time for the movement of a fluorophore through the detection volume. The higher the mean diffusion time, the less the interaction of the fluorophore with its surroundings or, the higher the diffusion times of the fluorophore, the stronger the adhesion of the labeled molecule on the examined surfaces. This can be used as a quality feature of a non-adhesive coating. If you describe the FCS curve for the sample of MR 121-IP (T30) in the area of the uncoated glass surface (glass, focused on 0 μm) with a sigmoid curve, you get a turning point of approx. 1 second. This indicates a very strong interaction of the dye with the glass surface. In contrast, the FCS curve for a sample of MR 121-IP (T30) on the surface coated according to the invention (hydrogel, focused on 0 μm) has a turning point at 238 μs, which almost corresponds to that of a freely diffusing MR 121-IP. If the detection volume is shifted 4 μm into the solution, no more surface influence can be determined in the case of the glass coated according to the invention. In the case of glass surfaces, it can be seen that the FCS curve (glass, focused on 4 μm) shows a turning point at 23.5 ms, which in turn indicates very clear interactions of the fluorescent-labeled oligonucleotide with the surface. Only when the detection volume has been shifted by 40 μm into the solution do both curves approach the freely moving MR 121-IP. The diffusion times obtained for MR 121-IP (T30) are summarized in Table 6.

Table 6: Average diffusion times of MR 121 on and at different heights above a glass or hydrogel surface

5. Cell adhesion experiments:

The cell adhesion experiments were carried out with GFP-Actin 3T3 fibroblasts (chicken) and MC3T3-E1 osteoblasts (chicken). The cells were stored in 50 ml PMMA cell culture boxes at 37 ° C. and 5% CO ₂ in a steam-saturated atmosphere in an incubator and replicated. The cell media used are standard cell media. For fibroblasts, the cell medium consisted of an aqueous solution of 88 vol% DMEM (Dulbecco's modified eagle's medium, Biochrom KG) with 10 vol% fetal calf serum (FCS, Invitrogen), 1 vol% penecillin solution (penstrep, Sigma), 1 vol% Glutamine (Invitrogen) and 0.5 mg / ml antibiotic, Geneticin (Sigma), while for the osteoblasts the cell medium from an aqueous solution of 94 vol% α-MEM (α-modified eagle's medium) with 5 vol% calf serum (FCS, Invitrogen) and 1 vol% glutamine (Invitrogen) was produced. The cells were split regularly to guarantee maximum growth and to maintain GFP expression.

Adhesion experiments were carried out in sterile PS petri dishes (50 mm diameter). Before the cells were added to the petri dishes, they were removed from the cell culture boxes with 2 ml trypsin per petri dish and then deposited in a centrifuge (10 min. At 1000 rpm) as sediment. Diluted again with medium, the cell suspension was then applied to the substrates using pipettes and then incubated. If the cells adhere to the substrate, they form a uniform layer that can be clearly seen under the light microscope. If the cells cannot attach to the substrate, i.e. the adhesion of the cell to the substrate is suppressed, the cells die and can be recognized as small, round cell clusters on the surface.

In experiment 1, a glass plate coated according to the invention was used as the substrate, which was spin-coated according to the instructions given in II-2.2 with a solution of the prepolymer from preparation example 3 (5.0 mg / ml), one according to 11-1. pretreated glass plate was produced. The thickness of the coating was approximately 50 nm. The sample was then treated with the cell suspension in the manner described above and examined in a light microscope. The results of the investigation are shown in FIG. 3. FIG. 3 shows that the coating is cell-resistant, because the cells have died and can be recognized as small, round cell clusters on the surface. The surface shows no cell growth even after 120 h, which demonstrates the long-term effect and stability of the coating. Similar results can also be found with thinner coatings which have a thickness of approximately 5 nm.

In experiments 2 and 2a, glass plates were used as substrates which had been coated by spin coating according to the instructions given in II-2.2 with a solution of the prepolymer from preparation example 3 (5.0 mg / ml or 1 mg / ml) (d = 15 nm or d = 5 nm). Then one half was coated with polystyrene (1.0 mg / ml or 2.5 mg / ml in THF) by means of dip coating. The sample was then treated with the cell suspension in the manner described above and examined in a light microscope. The results of the investigation are shown in FIGS. 4a and 4b.

FIGS. 4a and 4b show that the cells colonize on the surface treated with polystyrene and die on the surface coated according to the invention.

In experiment 3 glass platelets served as substrate were the one half by dip coating according to the instructions given in 11-2.1 b with a mixture of prepolymers from preparation example 3 (5.0 mg / ml) and dextran dissolved in water (20 mg / ml, d = 30 nm) had been coated. The sample was then treated with the cell suspension in the manner described above and examined in a light microscope. The results of the investigation are shown in FIG. 5.

FIG. 5 shows that the cells colonize on the untreated surface and die on the surface coated according to the invention.

Claims

claims:

1. Use of star-shaped prepolymers which have an average of at least four polymer arms A, which are in themselves soluble in water and carry at their free ends a reactive functional group R, the complementary reactive functional groups R 'or with themselves under Binding can react to produce ultra-thin, hydrogel-forming coatings.

2. Use according to claim 1, characterized in that the reactive group R is selected from isocyanate groups, (meth) acrylic groups, oxirane groups, carboxylic acid ester groups and the reactive group R 'is selected from primary and secondary amino groups, thiol groups, car- boxyl groups and hydroxyl groups.

3. Use according to claim 1, characterized in that the reactive group R is selected from ethylenically unsaturated, free-radically polymerizable double bonds.

4. Use according to one of the preceding claims, wherein the star-shaped prepolymer has on average 6 to 8 polymer arms.

5. Use according to one of the preceding claims, wherein the star-shaped prepolymer has a number average molecular weight in the range from 2000 to 20,000 g / mol.

6. Use according to any one of the preceding claims, wherein the polymer arms have a number average molecular weight in the range from 300 to 3000 g / mol.

7. Use according to one of the preceding claims, wherein the polymer arms A are selected from poly-C ₂ -C ₄ -alkylene oxides, polyoxazolidones, polyvinyl alcohols, homopolymers and copolymers which have at least 50% by weight. % N-vinylpyrrolidone in copolymerized form, homo- and copolymers which contain at least 30% by weight of acrylamide and / or methacrylamide in copolymerized form, homo- and copolymers which contain at least 30% by weight of acrylic acid and / or methacrylic acid in copolymerized form.

8. Use according to claim 7, wherein the polymer arms A are selected from polyethylene oxide, polypropylene oxide and polyethylene oxide / polypropylene oxide block copolymers.

9. Use according to one of the preceding claims, wherein the star-shaped prepolymer is in the form of an aqueous preparation.

10. A process for producing ultra-thin, hydrogel-forming coatings, characterized in that

i. a solution of a star-shaped prepolymer which has on average at least four polymer arms A, which are in themselves soluble in water and carry a reactive functional group R at their free ends, applied to the surface to be coated and ii. then carries out a linking reaction between the reactive groups.

11. The method according to claim 10, characterized in that the amount of prepolymer applied to the surface is selected such that a coating with a thickness of less than 50 nm results.

12. The method according to claim 10 or 11, characterized in that the concentration of prepolymer in the solution is 0.001 mg / ml to 100 mg / ml.

13. The method according to any one of claims 10 to 12, characterized in that the surface to be coated has been pretreated in such a way that an increased number of functional groups R '.

14. The method according to claim 13, characterized in that the surface was treated in an oxygen-containing plasma.

15. The method according to claim 13 or 14, characterized in that the surface has been pretreated with a silane compound which has a functional group R '.

16. The method according to any one of claims 10 to 15, characterized in that the linkage of the reactive groups R is triggered by adding a compound V1, which has at least two reactive groups R 'per molecule, with the reactive groups R of the star-shaped polymer under Bond formation reacts.

17. The method according to any one of claims 10 to 15, characterized in that the linkage of the reactive groups R is triggered by adding a sufficient amount of a compound V2 which reacts with a part of the reactive groups R to form reactive groups R ', which react with the remaining reactive groups R to form bonds.

18. The method according to claim 17, characterized in that the reactive groups R are isocyanate groups and compound V2 water.

19. The method according to claim 10, characterized in that the group R is selected from ethylenically unsaturated, free-radically polymerizable double bonds and the crosslinking is triggered thermally or photochemically.

20. The method according to any one of claims 10 to 16, characterized in that a) first a star-shaped prepolymer 1, which has at least four polymer arms A, which are in themselves soluble in water and have a reactive functional group R at their free ends , applied to the surface to be coated, optionally carrying out a partial crosslinking of the reactive groups R, a coating being obtained which still has reactive groups R on its surface, b) subsequently at least one further star-shaped prepolymer 2 which has at least four polymer arms A. , which are soluble in water per se and have a reactive functional group R 'at their free ends, which react with the reactive groups R of the star-shaped polymer to form bonds, apply to the surface treated in this way, optionally trigger a crosslinking of the groups R' and optionally steps a) and b) one or repeated several times.

21. The method according to claim 17 or 18, characterized in that a) a star-shaped prepolymer 1, which has at least four polymer arms A, which are in themselves soluble in water and have a reactive functional group R at their free ends, on the applying to the surface to be coated, b) adding a sufficient amount of a compound V2 which reacts with part of the reactive groups R to form reactive groups R ', which react with the remaining reactive groups R to form a bond, giving a coating which adheres to its surface has functional groups R ', c) subsequently applying at least one further star-shaped prepolymer 1 to the surface treated in this way and again triggering crosslinking of the groups R by adding a compound V2 and optionally repeating steps b) and c) one or more times.

22. The method according to any one of claims 10 to 21, characterized in that a biologically active material and / or cell material is incorporated into the coating.