DE4002513C1 - Modifying surface of membrane for e.g. dialysis - by coating with mono:functional polymer contg. at least one hydrophilic chain - Google Patents

Abstract

Method comprises coating with at least one monofunctional polymer (I) contg. one or more hydrophilic chains. One end of each chain bonds chemically to the substrate, while the other is at least partially free to move. (I) is e.g. a polymer of formula R1-((X-R3-)k(X-R4-)2)m- R-((R5-X3-)o-(R6-X4-)p)-R2, where R1 and R2 are alkyl, carboxyl, sulphonic acid, sulphonamide, NO2 or quat. ammonium gps., R3-R6 are 1-6C alkyl, (alk)aryl or aralkyl, X is O or S, k and p are 1-400 and n and m are 5-300. USE/ADVANTAGE - In membranes for ultra- and microfiltration, dialysis, osmosis or reverse osmosis of biological fluids and blood. (I) may also be used in enzyme electrodes. Membranes coated with (I) are less likely to become blocked with adsorbed protein.

Description

The invention relates to a method for surface modification of substrates by applying polymers the surface of the substrates.

In the medical and biological fields, both research as well as routine testing liquids, what proteinaceous material as solid particles or contained in dissolved or swollen form, about Membrane separation processes examined or prepared. Similar Systems are used in biotechnological process engineering also worked up via membrane separation processes. Examples for such separation processes using membranes would be about Ultra or microfiltration, dialysis, osmosis or reverse osmosis. In this context it should be mentioned also the numerous enzyme electrodes.

Although the membranes used in these separation processes according to the respective application from different Materials exist and their structure is very are structured differently, but they all have because of their fouling behavior and the related short downtimes only due to limited usability for liquids containing protein. Under fouling a non-specific protein adsorption on the membranes, which drastically reduces their permeability. So  z. B. tried in the filtration of whey, by frequent Backwash the fouling topping on the membranes To keep control. However, this leads to undesirable interruptions of the filtration processor. Sometimes detergents are also used used for backwashing, but for reasons of compatibility is often intolerable.

These fouling problems do not only arise with membrane Separation processes, but z. B. also used in medicine of intra- or extracorpolar blood conductors and catheters, with blood or insulin pumps, with artificial organs, such as B. kidney or heart, as well as heart-lung machines. So wherever foreign surfaces with protein-containing Liquids such as B. blood come into contact. Protein deposition does not only form fouling Layers but through these protein deposits also triggered coagulation processes that lead to thrombosis or lead to embolism.

Protein adsorption on sensor membranes and on membranes sampling from bioreactors falsifies the measurement results and can use the adhesion-promoting layers for cellular Generate deposits and for microbial growth.

Particularly susceptible to protein deposits, especially on the Surfaces, are hydrophobic membranes with poor wettability, such as B. those made of polysulfones or polyvinylidene fluoride. However, the advantage of these polymers is theirs thermal stability, which guarantees that membranes are made of these materials are easy to sterilize.

Since membranes made of hydrophilic polymers, such as. B. from cellulose derivatives, a slightly improved anti-fouling behavior show, attempts have been made to hydrophilize hydrophobic polymers, e.g. B. by adding hydrophilic polymers such as  Polyvinyl acetate or polyvinyl pyrrolidone (PVP) to polyvinylidene fluoride (EP 00 12 557 A1). However, in order to increase hydrophilic To achieve effects, either need such large amounts be added to polyvinylpyrrolidone that the mechanical Resistance of the resulting membranes reduced is, or the polyvinyl acetate is in a second to saponify complex process step.

Attempts had been made to remedy this disadvantage by the PVP through high-energy radiation on PVDF membranes grafted on (A. Niemöller and G. Ellinghorst, Die Angewandte Macromolecular Chemistry 151, No. 2489, 49-67 (1987)). It is however, it is known that grafting is both a technical represents complex process, as well as an uneven Distribution of the grafted polymer leads. By this grafting of PVP on PVDF membranes takes place Hydrophilization (increase in water absorption by 45% by weight), but this effect is very difficult on a certain one adjustable, tight degree of grafting. Will this the opposite effects occur.

The object of the invention is to provide a method with which the surfaces of different substrates Kind of like B. of membranes or medical devices, such as blood lines or catheters, such can be modified and equipped so that their anti Fouling behavior against proteins, microorganisms and Cell fragments are dramatically improved and only minimal Protein deposition on the order of a submolecular Layer arises, but without its physical Properties, such as their stability, disadvantageous to change. This procedure is intended to be independent of Substrate material and regardless of the structure of the substrates be applicable.  

This task is solved by being monofunctional Polymers containing one or more hydrophilic, linear or contain branched chains, with within each chain the hydrophilic character whose hydrophobic predominates, or mixtures of these monofunctional polymers, each via the functional group of the polymers and via reactive groups on the surface of the substrates through chemical bonds the surface of the substrates fixed so that one end of the hydrophilic chains is fixed, and mobility the other end (s) of the hydrophilic chains entirely or partially preserved. Surprisingly, it was found that a drastic improvement in anti-fouling Behavior of substrates such. B. of membranes or medical devices, such as blood lines or catheters, comes when you look at the surface of the substrates in this way modified. The connection of the monofunctional polymers the most varied of surfaces takes place in such a way that the hydrophilic polymer chains with one end to the protective surface to be tied, so that it with "dangle" the other end (s) freely in the solution. Surprisingly was found to be a "turf" of hydrophilic Polymer chains with only one end on the surface the substrates are fixed so that the other end of the hydrophilic polymer chains freely movable in liquids is a drastic reduction in the adsorption of Proteins, microorganisms or cell fragments. Because the hydrophilic polymer chains not only through Adhesive forces, but by real chemical bonds the surface of the substrates are fixed is permanent Coating, d. H. a permanent modification of the Given substrate surfaces. The hydrophilic polymer chains cannot be rinsed off the substrate surface.

Surprisingly, it was found that the protein-repellent Effect of the hydrophilic polymer chains in the manner of  the occupancy density depends on that at high occupancy densities the best effects are achieved. For liquids that contain a certain protein in a dominant amount an adjustment of the chain length possible, because surprisingly it was found that the optimal chain length too depends on the type of protein.

According to the prevailing opinion, adsorption occurs on surfaces of proteins, the accumulation of blood components, the Thrombogenicity, d. H. the tendency to form blood clotting to induce, the less, the more hydrophilic the Surface is d. H. the smaller the measured with water Contact angle is on the surface. Surprisingly found that with a surface modification according to the method according to the invention a reduction in protein adsorption is achieved that is not with the water rim angle is correlated. On the surface of a polyhydrogenmethylsiloxane were according to the invention Grafted polyethylene glycol ether chains and the Adsorption of fibrinogen from a flowing solution (1.5 g / l fibrinogen, 0.1 M NaCl, 0.01 M phosphate buffer; pH = 7; v = 0.5 ml / min with 1 mm feed hose diameter) was examined. It was surprisingly found that with increasing Chain length of the polyethylene glycol ether (formula 6) the amount of protein adsorbed decreased, although between n = 7 and n = 113 both the advancing and retreating contact angles remained almost constant or increased slightly.

Preferred embodiments of the method according to the invention use polymers of the general formulas (1) to (4) or mixtures thereof.

R¹ - [(X¹-R³-) _k - (X²-R⁴-) _l ] _m -R - [(R⁵-X³-) _o - (R⁶-X⁴-) _p ] _n -R² (1)

R¹- (X¹-R³-) _m -R- (R⁴-X²-) _n -R² (2)

R¹ - [(R³-X¹-) _k - (R⁴-X²-) _l ] _n -R² (3)

R- (R³-X¹-) _n -R² (4)

R means the functional group through which the polymers (1) to (4) fixed to the surface of the substrates, R¹ or R² are non-polar, polar non-ionic or ionic Groups with R³ to R⁶ = alkyl (C₁ to C₆), aryl, alkaryl or aralkyl, each linear or branched, X = O or S, and k to p = 1 to 400, preferably n and / or m = 5 to 300. Polymers can be used without restriction of generality of the general formulas (1) to (4), where R¹ or R² z. B. alkyl (substituted or unsubstituted, e.g. Trifluoromethyl), carboxy, sulfonic acid, sulfonamide, Nitro or quaternary ammonium groups can be.

You get particularly good results when you look at polymers Polyether of the general formula (5) used,

R - [(CH₂) _m -O-] _n -R¹ (5)

where R is the functional group through which the Polymers (5) fixed on the surface of the substrates, with R¹ = Alkyl (C₁ to C₆), m = 1-6 and n = 3-300. Such polyethers can e.g. B. polyethylene oxides of the general formula (6) be

R- (CH₂-CH₂-O-) _n -CH₃ (6)

where R again denotes the functional group via which the polymers (6) are fixed on the surface of the substrates, with n = 3-250.

The functional groups R can

be, where R⁷ is a non-hydrolyzable group and R¹³ a group with suitable functionality for the connection to the polymer means Y is a hydrolyzable group, such as B. a halogen, an alkoxy, acyloxy or a Amino group, and q can have the values 0, 1 or 2. With the elimination of the (r) substituent Y, the polymer becomes bound the surface.

Linking the functional groups (R) to the polymers takes place through usual chemical reactions, in which starting e.g. B. from the polymer alcohol (R = OH) the OH group in the functional group R is transferred in which the polymer alcohol e.g. B. with allyl bromide, allyl glycidyl ether, hexamethylene diisocyanate, DMSO plus acetic anhydride, phosgene, cyanuric chloride or 1,1'-carbonyldiimidazole is implemented. This is using the example of polyethylene glycol (PEG) (compare Formula (6)) explained in more detail.

The alcohol is converted into toluene by reaction with sodium generates the alcoholate, which is then mixed with allyl bromide to produce the desired monofunctional polyether (9) results. Analogue the reaction takes place with allyl glycidyl ether.

Suitable PEG's are e.g. B. the following company products Aldrich with the general formula

HO- (CH₂-CH₂-O-) _n -CH₃.

PEG₅₀₀₀ (n = 113), PEG₂₀₀₀ (n = 45), PEG₇₅₀ (n = 16), PEG₅₅₀ (n = 12) and PEG₃₅₀ (n = 7).

With the method according to the invention, the surfaces of all substrates can be modified which have reactive groups on the surface which are capable of reacting with the functional groups (R) of the polymers. Such substrates exist e.g. B. from silicon, from silicate ceramics or from silicate glasses, since these carry on the surface Si-OH groups, with the functional groups (R) of the polymers, such as. B. the R⁷ _q Y _(3-q) Si or the R⁷ _q Y _(3-q) SiR¹³ groups via a condensation reaction, for. B. by splitting off HY, the desired fixation on the surface by chemical bonds.

The same applies analogously to all substrates made of metal (M) which carry on the surface M-OH groups which have formed from the oxide layer MO _x .

For substrates that have no or only very little on the surface surprisingly, few reactive groups found that a coating of the substrates with linear or branched polyhydrogen organosiloxanes the application of the monofunctional polymers for the chemical fixation of the monofunctional polymers necessary reactive groups because the monofunctional Polymers now via the Si-H groups of the polyhydrogenorganosiloxanes chemically on the surface of the substrates can fix. The combination is essential to the invention coating the surface of the substrates with linear or branched polyhydrogen organosiloxanes with the subsequent chemical fixation of the hydrophilic Polymer chains on the surface of the substrates over the Si-H groups of the polyhydrogenorganosiloxanes. Especially advantageous in this embodiment of the invention  The procedure is the fact that the occupancy density of the Surface with the hydrophilic polymer chains now over the Density of the Si-H groups used Can control polyhydrogen organosiloxanes. Depending on Use case you can now use the surface of the substrates a thin or dense "lawn" of hydrophilic Occupy polymer chains.

It can e.g. B. on ceramic materials or on plastics Coatings with polyhydrogenorganosiloxanes with Thicknesses from just a few nanometers to a few micrometers be applied so that a variety of Provide materials with a protein-repellent layer can be. Such polyhydrogen organosiloxane layers adhere particularly well to surfaces with silanol groups, such as B. on glass, quartz or silicon. If necessary etching of the surface required before coating be.

Particularly good results are achieved when using polyhydrogen organosiloxanes of the general formula (7) used

with R⁸ to R¹¹ = alkyl, aryl, aralkyl or alkaryl, R¹² = H, r = 2-∞. The representation of the substituents R ^{11, 12} means that either H atoms (= R 12) or the substituents R ^{11 can} be attached to the silicon atoms in an unspecified manner. The percentage of the H atoms (= R 12) in the sum of the substituents R 11 + R 12 can be varied within a wide range, namely from 1% to 100%. A proportion of 20 to 100% is particularly preferred. In this way, the coverage density of the substrate surface can be controlled with the hydrophilic polymer chains. The values for r can be between 2 and ∞. The spelling "∞" should clarify that the upper limit of the technically possible chain lengths is not known. R can certainly assume values <1000. Examples of such polyhydrogen organosiloxanes are polyhydrogenmethylsiloxanes of the general formula (8), with R¹¹ = CH₃, R¹² = H and r = 1 to ∞.

Commercially available polyhydrogenmethylsiloxanes of the general Formula (8) are e.g. B. the following company products Petrach Systems, where "H%" is the percentage of H means and the values for r are approximate.

Substrates, the surfaces of which by this embodiment of the method according to the invention can be modified e.g. B. from metals, from silicon, from ceramics, from glasses (mineral, organic) or polymers.

The substrates can be coated by dip coating, e.g. B. in vacuum or in an inert gas atmosphere (N₂, Ar or others Noble gases) at 120 ° C. Not tight enough to the Surface bound portions are refluxed by rinsing with an organic solvent, e.g. B. with cyclohexane, away.  

The hydrophilic polymer chains are linked to the polyhydrogenorganosiloxanes in a hydrosylation reaction, e.g. B. with allyl-terminated polymers. The use of platinum catalysts for the addition of silanes or siloxanes with Si-H groups to compounds with olefinic double bonds is known and z. B. in DE-OS 26 46 726 or in DE-PS 31 33 869 described. H₂PtCl₆ · 6H₂O is preferred as the catalyst. The amount of platinum catalyst to be used is 10 ^-4 to 10 ^-6 moles per mole of SiH groups in the siloxane.

Using the example of a coated with polyhydrogenmethylsiloxane (8) Substrate and an allyl-terminated polyethylene glycol (PEG) as a hydrophilic polymer chain is the invention Procedure explained in more detail. You put an excess of the polyethylene glycols provided with the allyl end groups to ensure that those contained in the siloxane React SiH groups as quantitatively as possible. In the Carrying out the reaction will be the allyl-terminated PEG and the catalyst in one with respect to the reactants inert solvents at a temperature just below submitted to its boiling point. The connection of the hydrophilic Polymer chains on those with the polyhydrogenmethylsiloxane coated surfaces then takes place in the above described reaction solution under a nitrogen atmosphere within from 20 to 24 hours at temperatures around 100 ° C. When using a PEG with a molecular weight of 750 D was an occupancy density using the method described in the example of 80%, based on the SiH sites. Contact angle measurements with water showed Polydimethylsiloxane surfaces reduce the Edge angle by approx. 50 ° (advancing edge angle) or approx. 70 ° (Retreat edge angle). If the surface of a slow (laminar) exposed to flowing protein solution is the Protein adsorption on the according to the inventive method  modified surface reduced by a factor of 10 compared to the unmodified polydimethylsiloxane Surface, with a fibrinogen solution (1.5 g / l) by approx Factor 4.

On surfaces on which a polyhydrogen organosiloxane Layer does not adhere well, was surprisingly found that a firm liability can be brought about can, if these surfaces with a very thin (0.1 up to 10 nm) silicon layer. This can e.g. B. by Sputtering (cathode sputtering, ion sputtering), by plasma deposition, by vapor deposition or by chemical deposition from the vapor phase (CVD), starting from silanes or of organosilicon compounds. Sputter layers with great success on the most diverse Applied materials such. B. on ceramic materials, which ensures excellent adhesion of the protein-repellent Layer on various materials achieved can be. The same applies to metals that oxidize easily and their oxides on the surface of the substrates OH groups can form. These can also be done with the above mentioned methods with good results on a wide variety of materials be applied.

In a further embodiment of the method according to the invention, a thin layer of silicon or a metal (M), which is easily oxidized and whose oxide forms OH groups, is applied to the surface of the substrates, before coating with the polyhydrogenorganosiloxanes or before coupling the hydrophilic polymer chains can be applied according to the techniques described above, so that an SiO _x or MO _x layer is initially formed on the surface of the substrates, which then forms Si-OH or M-OH groups on the surface of the substrates. Alternatively, SiO _x or MO _{x can also be used as a} starting point for coating the substrates. The substrates pretreated in this way are then either coated with the polyhydrogenorganosiloxanes to which the hydrophilic polymer chains are then coupled, but the hydrophilic polymer chains are coupled directly to the surface of the substrates pretreated in this way via their functional groups (R), such as, for. B. on the R⁷ _q Y _(3-q) Si or on the R⁷ _y Y _(3-q) SiR¹³ groups, without intermediate coating with polyhydrogen organosiloxanes. In this way, the surfaces of substrates can be modified from almost all materials, since there are a number of methods with which thin layers can be produced on surfaces. So z. B. the surfaces of almost all metallic, ceramic or polymeric substrates can be modified in this way. This embodiment of the method according to the invention is very particularly suitable for modifying polymer membranes, ceramic or metallic membranes, and blood conductors and catheters.

The coating also proved to be particularly advantageous Silicon or with suitable metals and subsequent Coating with polyhydrogenorganosiloxanes, to which then the hydrophilic polymer chains are fixed, or the Coating with silicon or with suitable metals and subsequent fixation of the hydrophilic polymer chains. Essential to the invention is thus the combination of Coating the substrates with silicon or with suitable ones Metals combined with a coating of Polyhydrogenorganosiloxanes and subsequent chemical Fixation of the hydrophilic polymer chains, or the combination coating the substrates with silicon or with suitable metals, and subsequent chemical fixation the hydrophilic polymer chains.  

For metallic substrates, for substrates made of metal oxides and for substrates with a thin metal or metal oxide layer are covered, i.e. with substrates whose The surfaces can be covered with metal OH groups of the hydrophilic polymer chains via coupling reagents take place such. B. on γ-aminopropyl-triethoxysilane ((EtO) ₃Si (CH₂) ₃NH₂), with the elimination of ethanol. The The hydrophilic polymer chains are then linked in the in the present case via the amino group of the coupling reagent and via suitable functional groups (R) of the polymers. in the If the coupling reagent is present, it is also possible to both H atoms of the NH₂ group through hydrophilic polymer chains to replace. This method is particularly well suited for the modification of the surfaces of metals or of Metal oxides. However, since it is also possible to Base layer as an adhesion-promoting thin layer on various Applying materials is another universally applicable embodiment of the invention Given procedure. As a method of application of these metal oxide layers are both the above. method such as sputtering etc., as well as the deposition from organometallic Compounds or from metal hydrides from the Gas phase (CVD = chemical vapor deposition).

In a further embodiment of the method according to the invention the surface of the substrates with functional Provide groups, e.g. B. with amino groups to which then hydrophilic polymer chains via suitable functional groups (R) the polymers are chemically fixed. This equipment the surfaces with functional groups can e.g. B. at Plastics are made by known wet chemical processes or by means of plasma chemical reactions, such as. B. in one N₂ / H₂ low pressure plasma. Further examples are in DE-PS 33 37 763 included. This is a chemically solid, stable Connection of the hydrophilic polymer chains guaranteed. A  Many different materials can be used on the Surface by wet chemical processes, by Plasma deposition, by CVD or by PVD techniques, such as e.g. B. evaporation, ion plating or sputtering, with reactive Groups are provided so that a further scope of the method according to the invention given is.

In a further embodiment of the invention The surface of the substrates is treated with a Polymer layer covered and then the surface of this Polymer layer by wet chemical processes, by CVD Technology, by plasma deposition or by PVD technology with reactive groups, over which then the hydrophilic Polymer chains via their functional groups by chemical Bindings are fixed.

In a further embodiment of the invention Process the surface of the substrates by plasma polymerization covered with a polymer layer, e.g. B. with a polyolefin, a polyfluorocarbon or one Polysiloxane layer, and on the surface of this Polymeric layer located by long-lived radicals Reaction with functional group forming agents, such as e.g. B. with ammonia, reactive groups created. These are in the case of reaction with ammonia H₂N groups. To this reactive groups then become the hydrophilic polymer chains chemically fixed.

With the method according to the invention, membranes can be of the most varied types Be equipped. For microfiltration membranes is due to the low layer thickness of the hydrophilic Polymer chains the pore radius is only slightly reduced, around 8 to 20 nm, which is achieved by using a starting membrane with a slightly larger pore radius  can. For ultrafiltration membranes, their exclusion limit below the molecular weights of the proteins in question is whey z. B. below 20,000, the Separation characteristics also imperceptible due to the equipment influenced with hydrophilic polymer chains, and man can be achieved by using UF membranes with slightly higher Adjust the cut-off characteristic to the exclusion limit. With the Processes according to the invention can also use gas separation membranes, e.g. B. pervaporation membranes can be modified. Further can polymer membranes as well as metal or ceramic membranes be modified with the inventive method. Further Areas of application are hoses and other parts for Sampling systems, pipelines and other (bio) reactor components.

The reduced tendency towards protein adsorption makes that surfaces modified by the process according to the invention also suitable for contact with blood since the inclination for the formation of blood clots (thrombi, emboli) and Deposits from the blood are reduced. Possible applications are blood conductors, such as B. artificial arteries or Veins, blood filters, membranes, tubing and pump inner surfaces in extracorporeal use (artificial kidney, oxygenators), as well as catheters and implants for the temporary or permanent intracorporeal use, such as. B. Blood pumps or insulin pumps.

Another application of the method according to the invention is the provision of column material for the stationary Phase in liquid phase chromatography. So z. B. a protein-neutral material in affinity chromatography can be used as column material to which the as Functional groups grafted to traps will.  

The usability of the method according to the invention is described in the following based on comparative experiments. This will uses a measurement method that shows the time course of the Formation and dissolution of adsorption layers or deposits detected in a flow cell. That’s why Fourier transform infrared method in restricted total reflection applied (FTIR-ATR, ATR = attenuated total reflection). The polymers on which the Protein adsorption is examined as a thin layer according to the inventive method on germanium prisms upset. For the investigations on modified Polysiloxanes (polyhydrogenorganosiloxane + polyether) is used a polydimethylsiloxane (PDMSO) as a reference surface.

The prisms prepared in this way are sequentially in exact Intervals on both sides in contact with laminar flowing Solutions of phosphate buffer, protein, phosphate buffer and distilled water. IR- Spectra recorded. Via the into the neighboring medium The evanescent wave that crosses becomes the toward the detector emerging beam through the optical absorption in the interface area weakened. In this way, for example adsorbed protein over its absorption bands be detected.

Test conditions

Circulating solvent: 0.1 M NaCl + 0.01 M phosphate buffer (pH 7);
Protein solution: 10 ml buffer solution (fibrinogen concentration 1.5 g / l) + 20 µl¹²⁵ iodine-labeled human fibrinogen (1.09 mg / ml, 100 µC / ml, 3.7 MBq, on the calibration date, from Amersham No. IM 53 PG); Flow rate 0.5 ml / min.

Trial evaluation

The ATR measurement provides a superimposition of the spectra of the adsorbent and the adsorbendum (protein from aqueous solution). Difference spectra between the spectra when flowing around with pure phosphate buffer solution and with protein solution are formed for evaluation. The amount of protein adsorbed at a given time is determined by integrating its characteristic absorption bands. (e.g. "Amide II band" around 1550 cm ^-1 ).

To evaluate the band intensities are based on the Lambert-Beers law uses the following relationships:

A - integral absorption (AE * cm ^-1 )
ν₁, ν₂ - absorption range of the IR band concerned
I, I₀ - IR intensity with or without a flow cell
R - reflection coefficient
ε - molar absorption coefficient
c - molar concentration
d _eff - effective optical path length

By plotting these quantities over time, the curves result which show the course of protein adsorption and desorption on prepared surfaces and are shown in FIG. 1.

Fig. 1 shows the surface integrals of the amide II absorption bands as a function of time in the adsorption (0 to 100 min) and desorption (approx 100 to 220 min). Curve 1 describes the protein adsorption on the reference surface (PDMSO), curve 2 on a modified polysiloxane surface (poly- (H) -organosiloxane grafted with PEG₅₀₀₀ chains), and the partial desorption after exchange of the respective solutions.

One shows clearly on the modified surface decreased fibrinogen adsorption.

By using a radioactively labeled protein solution and one in the flow cell opposite the ATR prism inserted germanium platelets, each with the same The IR measuring method was coated by subsequent Determination of the ²² iodine activity of the plate calibrated.

After desorption and drying, it is opened in the flow cell radioactivity remaining on the coated germanium plate measured in a specially shielded γ detector and can be measured with the amide IR after rinsing with N₂ Signal can be compared.

The "irreversible" amount of protein absorbed is under On the basis of the assumption of stoichiometrically identical relationships of labeled and unlabeled protein in the Solution and calculated on the surfaces.

This results in the absorption units used here about 1.6 µg / cm² per unit as a measure of the occupancy density on fibrinogen.

Claims (19)

1. A process for the surface modification of substrates by applying polymers to the surface of the substrates, characterized in that monofunctional polymers which contain one or more hydrophilic, linear or branched chains, the hydrophilic character of each chain predominating their hydrophobic character, or mixtures of these monofunctional polymers, in each case via the functional group of the polymers and via reactive groups on the surface of the substrates by chemical bonds to the surface of the substrates in such a way that one end of the hydrophilic chains is fixed, and the mobility of the other end (n) the hydrophilic chains are wholly or partly preserved. 2. The method according to claim 1, characterized in that polymers of the general formula R¹ - [(X¹-R³-) _k (X²-R⁴-) _l ] _m -R - [(R⁵-X³-) _o - (R⁶- X⁴-) _p ] _n -R² (1) and / orR¹- (X¹-R³-) _m -R- (R⁴-X²-) _n -R² (2) and / orR - [(R³-X¹-) _k - (R⁴-X²-) _l ] _n -R² (3) and / or R- (R³-X¹-) _n -R² (4), where
R is the functional group via which the polymers are fixed on the surface of the substrates, and R¹ or R² are nonpolar, polar nonionic or ionic groups, with R³ to R⁶ = alkyl (C₁ to C₆), aryl, alkaryl or aralkyl, X = O or S, and k to p = 1-400, preferably n, m = 5-300. 3. The method according to claim 2, characterized in that polymers of the general formula (1) to (4) are used,  with R¹, R² = alkyl- (substituted and unsubstituted), Carboxyl, sulfonic acid, sulfonamide, nitro or quaternary Ammonium groups. 4. The method according to claim 2, characterized in that the polymers used are polyethers of the general formula R - [(CH₂) _m -O-] _n -R¹ (5), where
R is the functional group via which the polymers are fixed on the surface of the substrates, with R¹ = alkyl (C₁ is C₆), m = 1-6 and n = 3-300. 5. The method according to claim 4, characterized in that the polymers used are preferably polyethylene oxides of the general formula R- (CH₂-CH₂-O-) _n -CH₃ (6), wherein
R is the functional group by means of which the polymers are fixed on the surface of the substrates, with n = 3-250. 6. The method according to one or more of claims 1 to 5, characterized in that one uses polymers whose functional group R⁷ _q Y _(3-q) Si or R⁷ _q Y _(3-q) Si-R-, where R⁷ is a non-hydrolyzable group and R¹³ is a group with suitable functionality for binding to the polymer, Y is a hydrolyzable group and q can have the values 0, 1 or 2. 7. The method according to one or more of claims 1 to 6, characterized in that the surface of the  Substrates before applying the hydrophilic polymer chains provided with reactive groups or with reactive groups supporting layers to which the polymers are coated their functional group is fixed by chemical bonds will. 8. The method according to one or more of claims 1 to 7, characterized in that a polymer layer the surface of the substrates and that the Surface of the polymer layer by wet chemical methods, through CVD technology (CVD = chemical vapor deposition), through Plasma deposition, by plasma activation or by PVD Provides technology with reactive groups to which the polymers through their functional group through chemical bonds be fixed. 9. The method according to one or more of claims 1 to 7, characterized in that one on the surface of the Substrates by plasma polymerizing a polymer layer and the surface of this polymer layer with reactive groups by putting them on the surface long-lasting radicals created in the polymer layer can react with agents forming functional groups. 10. The method according to claim 9, characterized in that one polyolefin, one on the surface of the substrates Applies polyfluorocarbon or a polysiloxane layer. 11. The method according to claim 7, characterized in that the surface of the substrates with silicon or with a Metal (M), the oxide layer of which can form an OH group, coated so that the substrate surface with Si-OH or is equipped with MOH groups. 12. The method according to claim 11, characterized in that the silicon or the metal is evaporated in vacuo, or  using cathode sputtering or by decomposing silicon or metal compounds according to the CVD technique or by plasma decomposition of silicon or metal compounds onto the surface of the substrates. 13. The method according to claim 7, characterized in that the surface of the substrates with SiO _x or with metal oxides which can form OH groups, coated by known techniques, so that the substrate surface is equipped with Si-OH or with MOH groups becomes. 14. The method according to claim 7, characterized in that the surface of the substrates by wet chemical methods, by CVD technology, by plasma deposition or by Provides PVD technology with reactive groups. 15. The method according to one or more of claims 1 to 7, 11 to 14, characterized in that one before application of the polymers the substrate with linear and / or branched polyhydrogenorganosiloxanes coated, and that the polymers via their functional group and via the Si-H groups of the polyhydrogenorganosiloxanes chemically attached to the Surface of the substrates fixed, and that the occupancy density the surface with the polymers on the density the Si-H groups of the polyhydrogenorganosiloxanes used controls. 16. The method according to claim 15, characterized in that polyhydrogenorganosiloxanes of the general formula used, with R⁸ to R¹¹ = alkyl, aryl, aralkyl or alkaryl, R¹² = H, r = 2-∞, and with a proportion of H atoms (= R¹²) based on the sum of the substituents R¹¹ + R¹² from 1 to 100 %, preferably from 20 to 100%. 17. The method according to one or more of claims 1 to 16, characterized in that the surface of Modified substrates made of metals, of polymers, of Ceramics or mineral glasses. 18. The method according to one or more of claims 1 to 17, characterized in that the surface of membranes modified. 19. Substrates, characterized by a surface modification according to a method according to one or more of the Claims 1 to 18.