METHOD FOR PRODUCING CONDUCTIVE PEDOT:PSS PARTICLES

Description

[0001] The present invention relates to a process for the production of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) particles comprising at least the steps: a) Providing a mixture comprising poly(3,4-ethylenedioxythiophene) and polystyrenesulfonate in a solvent at least comprising water; b) Forming one or more PEDOT:PSS droplets by introducing the mixture from process step a) into an organic solvent A, wherein the aqueous PEDOT:PSS mixture forms the droplet interior and the organic solvent A forms the droplet exterior; c) Contacting the PEDOT:PSS droplets obtained from process step b) with a coagulating solution comprising a curing agent and at least one further solvent B, wherein the density of the coagulating solution is greater than the density of the organic solvent A and less than the density of the aqueous poly(3,4-ethylenedioxythiophene) and polystyrenesulfonate mixture; with curing of the PEDOT:PSS droplets to PEDOT:PSS particles.Furthermore, the present invention discloses spherical PEDOT:PSS particles without further mechanically strengthening substances and the use of the particles, for example, as cell culture microcarriers or suspension electrodes.

[0002] Many industries, such as the food, cosmetics, or pharmaceutical industries, require large quantities of complex biological substances. These substances are typically produced in stirred-tank reactors using cell cultures. Since most vertebrate cells are adherent cells, meaning they require substrates for growth and proliferation, the culture medium is usually supplemented with biocompatible carrier particles. Poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) particles are preferred for this purpose because their size is in the correct micrometer range, their surface structure promotes cell anchoring on the particle surface, their particle density allows them to be suspended in the stirred-tank reactor with low energy input, and they are also biologically compatible.Due to their specific porosity, PEDOT:PSS particles also offer a very high surface-to-volume ratio, which provides the basis for the efficient large-scale production of biological substances. Furthermore, PEDOT:PSS as a material system also exhibits special electrical properties. The particles can provide very fast charge / discharge kinetics and high energy and power densities, as the electrical charge is stored not only in the electronic double layer but also within the polymer matrix. These fundamental properties make the particles promising substrates in energy storage and energy conversion technology.

[0003] Unfortunately, filled or porous PEDOT:PSS particles can currently only be produced in combination with a composite or carrier material, which imparts intrinsically lacking mechanical support and shaping properties to the particles. The synthesis of these stabilized particles requires complex, multi-step processes, which offer insufficient conditions for efficient scale-up and, in the case of hybrid particles, lead to a deterioration of the electrochemical properties of the particles due to the electrically inactive additional material. Furthermore, there are no processes and, accordingly, no commercially available microcarriers based on a single, fully synthetic hydrogel.

[0004] Some approaches to PEDOT:PSS microparticles can be found in the patent literature.

[0005] For example, EP 28 311 83 B1 describes a composite particle comprising: a single spherical core comprising at least one inorganic oxide; and a polymer layer disposed on and delimiting the spherical core, the polymer layer comprising a cationic polymer and an anionic polymer.

[0006] Furthermore, EP 01 953 81 B1 discloses a composite material made of porous materials and electrically conductive polymers, wherein the surfaces of the pores are first coated with a layer of an electrically conductive polymer obtained by treating the monomers with an oxidizing agent, and a layer of an electrically conductive polymer obtained by anodic oxidation of the monomers is applied thereon.

[0007] Another patent document, CN 110 233 061 A, discloses a manufacturing method for a porous, flexible PEDOT:PSS film with high conductivity. According to the method, polystyrene nanospheres are used as matrices; PEDOT:PSS dispersion liquid and the polystyrene nanospheres are mixed in situ; a porous PEDOT:PSS film is obtained by vacuum suction filtration. The conductivity of the film is optimized by solvent post-treatment. The produced PEDOT:PSS film has a porous structure, exhibits excellent electrochemical properties such as relatively high conductivity, high charge-discharge stability, high rate performance, and the like, and can be used for a high-performance film electrode or high-performance film capacitor.

[0008] Further processes for producing particles are described, for example, in CN 108 381 571 A, US 2018 / 094119 A1, CN 106 914197 A, WO 2018 / 148807 A1 and US 2016 / 064672 A1.

[0009] Such solutions known from the prior art may offer further potential for improvement, in particular with regard to the simplicity of the manufacturing process, the reproducibility and the uniformity of the particles that can be produced using the process.

[0010] It is therefore the object of the present invention to at least partially overcome the disadvantages known from the prior art. In particular, it is the object of the present invention to disclose a simple and reproducible manufacturing process that is easily upscalable and delivers highly precisely defined PEDOT-PSS particles within short processing times. Furthermore, the object of the present invention is to provide PEDOT:PSS particles that exhibit a very uniform shape and size distribution without further polymer stabilization.

[0011] The object is achieved by the features of the respective independent claims, directed to the method according to the invention, the particles according to the invention, and the use of the particles according to the invention. Preferred embodiments of the invention are described in the subclaims, in the description, or in the figures. Further features described or shown in the subclaims or in the description or in the figures may, individually or in any combination, constitute a subject matter of the invention, unless the context clearly indicates otherwise.

[0012] The object is achieved according to the invention by a process for the production of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) particles comprising at least the steps: a) Providing a mixture comprising poly(3,4-ethylenedioxythiophene) and polystyrenesulfonate in a solvent at least comprising water; b) Forming one or more PEDOT:PSS droplets by introducing the mixture from process step a) into an organic solvent A, wherein the aqueous PEDOT:PSS mixture forms the droplet interior and the organic solvent A forms the droplet exterior; c) Contacting the PEDOT:PSS droplets obtained from process step b) with a coagulating solution comprising a curing agent and at least one further solvent B, wherein the density of the coagulating solution is greater than the density of the organic solvent A and less than the density of the aqueous poly(3,4-ethylenedioxythiophene) and polystyrenesulfonate mixture; with curing of the PEDOT:PSS droplets to PEDOT:PSS particles.

[0013] Surprisingly, it was found that the above-described process allows the flexible production of solid and porous PEDOT:PSS particles, whereby the particles are mechanically stable even without additional composite or support substances. Due to the absence of further mechanically stabilizing substances, the native properties of the polymer system are retained in their entirety and unwanted incompatibilities in application are avoided. The two-step process according to the invention allows cost-effective production and offers simple upscaling options. Different particle sizes and densities can be flexibly produced, with highly reproducible, preferably round, geometries being obtainable via the process. Another advantage is that a very homogeneous and narrow particle size distribution can be obtained.After reaction, the PEDOT:PSS polymer complex forms a biocompatible, porous hydrogel with steric and mechanical properties comparable to an extracellular matrix, thus providing a good basis for use in cell culture applications. The lack of additional stabilizing polymers can also have a positive effect on the electrical properties of the particles.

[0014] The process according to the invention is a process for producing poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) particles. The process according to the invention yields PEDOT:PSS particles which consist of or comprise a PEDOT:PSS matrix. The particles can therefore consist of or comprise only these two monomers. The matrix can preferably consist only of PEDOT and PSS. The particles have either a closed, dense surface or a porous structure, with pores being present in the particle interior and / or on the particle surface. The pores can also provide a continuous diffusion path through individual particles. The particle density can be adjusted, for example, via the solids content of the PEDOT:PSS solution used, whereby a broad concentration range can be processed using the process. The solids content of the aqueous PEDOT:PSS solution can preferably be greater than or equal to 0.5 wt.-% and less than or equal to 10 wt.%, further preferably greater than or equal to 1.0 wt.% and less than or equal to 5.0 wt.%. Even with relatively low solids contents, sufficiently mechanically dimensionally stable particles can be produced using the process presented. The degree of porosity of the particles can be varied within a wide range by changing the proportion of other solvents in the aqueous solution and can preferably be greater than or equal to 0% by volume and less than or equal to 95% by volume, further preferably greater than or equal to 15% by volume and less than or equal to 60% by volume.

[0015] In process step a), a mixture comprising poly(3,4-ethylenedioxythiophene) and polystyrenesulfonate is prepared in a solvent containing at least water. The starting material for the production is an aqueous PEDOT and PSS mixture in which the polymer complexes of positively charged PEDOT and negatively charged PSS are dispersed. This aqueous starting solution can contain other solvents or dispersants in addition to water, whereby the porosity of the particles, for example, can be adjusted by the proportion and type of solvent. The term "solvent" is not used here in the physical sense of producing a true "solution," but rather in the sense that these substances normally fall under the category of a liquid solvent. If "only" water is used as the solvent or dispersant, nonporous particles result.For example, PEDOT:PSS can be present in a molar ratio of greater than or equal to 1:6 and less than or equal to 6:1. The weight concentration of PEDOT:PSS in the aqueous mixture can be, for example, greater than or equal to 1 wt% and less than or equal to 10 wt%.

[0016] In process step b), one or more PEDOT:PSS droplets are formed by introducing the mixture from process step a) into an organic solvent A, with the aqueous PEDOT:PSS mixture forming the interior of the droplet and the organic solvent A forming the exterior. The aqueous PEDOT:PSS dispersion is emulsified in an organic solvent and forms a water (PEDOT:PSS)-in-solvent A emulsion. The aqueous PEDOT:PSS thus forms the inner phase and the organic solvent the outer phase. The organic solvent A must therefore not be completely miscible with water. Preferably, the organic solvent A can have a miscibility with water of less than or equal to 10 g / l, further preferably less than or equal to 5 g / l at 20°C. Emulsification can take place purely mechanically without the further use of emulsifiers.For example, the use of a mechanical stirrer, a Turrax, or a microfluidic setup with a T-junction geometry can be useful to obtain an emulsion with the most uniform droplet size possible. The emulsion can also be maintained using ultrasonic treatment. The emulsion does not have to be stable for extended periods. Suitable organic solvents A are organic solvents that are stable under the chemical conditions during the further course of the process. These can be, for example, medium-chain hydrocarbons without other reactive groups. For example, C4-C10 hydrocarbons or alkanes can be used. Furthermore, it is also possible to use organic solvents that consist of hydrocarbons and one or more other functional groups. For example, medium-chain alcohols, such as C5-C10 alcohols, can also be used as solvent A.

[0017] Process step b) can, for example, take place within a coaxial droplet break-off process in which the emulsion droplets are separated from the nozzle by a continuous phase. The PEDOT:PSS is thereby transformed into a spherical shape. The continuous phase from solvent A completely envelops the PEDOT:PSS emulsion and serves as a shell to delay the curing process. The generation of monodisperse PEDOT:PSS emulsion droplets in the continuous phase can, for example, be carried out using one or more cannulas which are concentrically inserted into a slightly kinked tube. The continuous phase from solvent A is fed through the tube and the PEDOT:PSS emulsion is fed via the cannula. The protective shell consisting of the continuous phase of solvent A prevents the PEDOT:PSS emulsion from curing within the nozzle and the apparatus from clogging.The process cannot be carried out as a continuous phase without the retarding effect of the droplet exterior, consisting of solvent A. Slots or nozzles of other designs can also be used to create other shaped body geometries. By selecting the extrusion rate and speed, more or less elongated shaped bodies, such as fibers, can also be produced.

[0018] In process step c), the PEDOT:PSS droplets obtained from process step b) are contacted with a coagulating solution comprising a curing agent and at least one further solvent B. The mechanical energy input resulted in an emulsion containing PEDOT:PSS droplets, at least temporarily, from the organic solvent A and the aqueous PEDOT:PSS solution, with the droplets protected by an outer solvent A phase. These encapsulated droplets are then transferred into a coagulating solution. The encapsulated droplets can be transferred into the coagulating solution directly from the tube used, for example, to supply the continuous phase in process step b).The protective shell consisting of the continuous phase is then rapidly separated from the PEDOT:PSS emulsion droplet via the density difference between the coagulation bath and the continuous phase, whereby the emulsion of aqueous PEDOT:PSS solution meets the coagulating solution, which comprises at least one further solvent B and a curing agent. The curing agent can preferably be homogeneously dissolved or dispersed in the organic solvent B. Any substances capable of dissolving PSS from the PEDOT-PSS polymer complex and causing crystallization of the PEDOT can be used as the curing agent. The curing agent can preferably be dissolved in the organic solvent B. Possible curing agents can be selected, for example, from the group consisting of sulfuric acid, ionic liquids, highly concentrated salt solutions, or mixtures of at least two curing agents from this list.Suitable organic solvents B can, for example, be selected from the group consisting of branched or unbranched C1-C10 alcohols or water, or mixtures of at least two of these solvents. Suitable organic solvents must have a density less than PEDOT:PSS to enable separation of the protective solvent A shell and should ideally have high solubility with respect to solvent A.

[0019] The density of the coagulating solution is greater than the density of organic solvent A and less than the density of the aqueous PEDOT:PSS mixture. According to the invention, the density of the coagulating solution consisting of organic solvent B and curing agent must therefore be greater than the density of organic solvent A, as well as greater than the density of other solvents in cases where the aqueous PEDOT:PSS mixture also contains other solvents. This relationship between the different solvents can be controlled, for example, via the density of the coagulating solution. The density of the coagulating solution can, in principle, be influenced via two different parameters. Firstly, the density of the coagulating solution can, of course, be determined by the choice of solvent B itself. Secondly, the density of solvent B itself can be further adjusted by selecting the concentration of the curing agent in solvent B.To obtain the above-mentioned relationship, the densities of organic solvent A and organic solvent B, including the curing agent, are naturally compared under identical temperature conditions. If the coagulating solution contains other density-relevant additives or substances in addition to the curing agent and solvent B, these are included in the density of the coagulating solution. Changes in the density of the coagulating solution due to the dropwise addition of the emulsion are not taken into account, as the volume of the coagulating solution is considered to be very large compared to the volume of the added solution. Furthermore, the density of the coagulating solution consisting of solvent B and curing agent must be lower than that of the aqueous PEDOT:PSS mixture.Preferably, the density differences between the aqueous PEDOT:PSS mixture, organic solvent A, and coagulation bath comprising organic solvent B + curing agent can be greater than or equal to 5%, further preferably greater than or equal to 10%. Within these density differences, the protective layer of the PEDOT:PSS droplets consisting of organic solvent A can be removed very quickly, and very uniform particles can be produced. The absolute density difference counts; depending on the sign of the density difference, the solution can be introduced into the coagulation bath once from above or once from below. The separation of the protective shell consisting of solvent A is further assisted by the solubility of solvent A in solvent B.

[0020] By introducing the PEDOT:PSS emulsion coated in solvent A into the coagulating solution, the PEDOT:PSS droplets are cured into PEDOT:PSS particles. The density relationships specified above allow the shell surrounding the PEDOT:PSS droplets to slowly separate from the aqueous PEDOT:PSS mixture due to the density difference and the solubility in solvent B. The protection of the inner aqueous PEDOT:PSS droplets by organic solvent A is removed, and curing of the PEDOT:PSS complex in the coagulating bath begins due to the curing agent. The curing agent leads to partial crystallization of the PEDOT:PSS droplets, while solvent B simultaneously leads to non-solvent-induced phase separation. Thus, the PEDOT:PSS droplet completely hardens into a particle within a short time through interaction with the coagulation bath.In the case of porous particles, additional emulsion droplets measuring 1 to 40 µm, consisting of a solvent, for example solvent A, can form within the PEDOT:PSS particle, which create the porosity of the particle during the curing process in the coagulation bath. These remaining droplets of organic solvent A, which are still present in the particles, can not only create particle porosity but also serve as a framework for the formation of a spherical shape. If additional solvents are present in the aqueous PEDOT:PSS mixture that can be dissolved out due to density differences, these ensure the formation of cured porosity. Since organic solvent B can also partially act as a solvent for organic solvent A, this structure not only guarantees sufficient particle consolidation but also the liberation of the particle pores from the additional solvent.

[0021] In a preferred embodiment of the process, the organic solvent A can be selected from the group consisting of branched or unbranched C5-C10 alkanes, branched or unbranched C5-C10 alcohols, or mixtures of at least two solvents thereof. The solvent group specified above has proven particularly suitable for obtaining a sufficiently stable emulsion of the aqueous PEDOT:PSS mixture in the organic solvent A. Sufficiently homogeneous and small droplets can be produced with very low shear forces, which are not too soluble in water. Without being bound by theory, this solvent selection can also advantageously have a particularly positive effect on the surface porosity of the particles.A further advantage may be that, if the aqueous PEDOT:PSS mixture contains additional solvents to form porosity, the removal of the solvent from the pores is particularly rapid due to a possible good solubility in solvent B.

[0022] Within a preferred aspect of the process, solvent B can further be selected from the group consisting of branched or unbranched C1-C5 alcohols or mixtures of at least two substances thereof. This group of solvents B in the coagulation bath has proven to be sufficiently stable for a number of different curing agents. Furthermore, these solvents have a sufficiently high solubility for the most important curing agents, resulting in a homogeneous coagulation bath. A further advantage of this group is that it results in preferential interaction with any solvent A emulsified in the droplet. The dissolution of solvent A occurs within an optimal time window, allowing sufficient time to stabilize the droplet shape during curing and to completely separate the surrounding organic phase from the particle interior within the same process step.

[0023] In a further preferred embodiment of the process, solvent A can comprise octanol, and the coagulating solution in process step b) can comprise isopropanol as solvent B and sulfuric acid as curing agent. This combination of solvents and curing agents in the various process steps has proven particularly advantageous. It results in particularly stable and homogeneously cross-linked PEDOT:PSS particles, which can also be characterized by particularly uniform porosity. Without being bound by theory, the synergistic advantages arise from a particularly advantageous solubility of solvents A and B in and with each other. The droplet freed from the octanol shell comes into contact with the coagulation mixture and cures completely through interaction with the sulfuric acid as curing agent.The octanol droplets, which are still present in emulsified form in the aqueous PEDOT:PSS solution or dispersion, can act as a framework for the formation of a spherical shape and ensure the development of controlled porosity. Since isopropanol is a partial solvent for octanol and, if present, the other emulsified solvent, the coagulation mixture not only ensures particle curing by removing the droplet shell, but also a controlled release of the pores from the remaining solvent. 1-octanol is preferably used as the octanol. The latter can contribute to the formation of particularly uniform droplets.

[0024] Within the scope of a preferred aspect of the process, the weight ratio of curing agent and solvent B in the coagulating solution, expressed as weight of curing agent divided by weight of solvent B, can be greater than or equal to 0.005 and less than or equal to 0.2. The above-specified ratio has proven particularly suitable for efficient and controlled curing while obtaining particularly uniform, spherical PEDOT:PSS particles. Firstly, the detachment rate of the enveloping solvent A, optionally the removal of further solvent from the aqueous PEDOT:PSS mixture, and the subsequent contact time with the curing agent are subjected to a dynamic equilibrium, which, based on kinetic considerations, can be used in particular to form more spherical particles. Thus, higher amounts of curing agent can contribute to the formation of more non-spherical particles.Lower curing agent contents may result in insufficient solidification of the PEDOT:PSS droplets or excessively long contact times in the coagulation bath. In a preferred embodiment, the lower limit of the range may be 0.01.

[0025] In a further preferred characteristic of the process, the PEDOT:PSS mixture in process step a) may not contain any further mechanically strengthening substances. Surprisingly, it has been found that the process according to the invention can produce mechanically very stable particles which, in addition to PEDOT and PSS, are free of further mechanically strengthening substances in the sense of mechanical stabilizers. Commonly strengthening substances are selected from the group of polymeric admixtures or purely supporting or shaping solids. These substances are also known to those skilled in the art under the term "template particles." In the area of ​​polymeric admixtures, this means that the PEDOT:PSS solution used can, for example, be free of further monomers or polymers. Polymeric constituents can, for example, be substances with a molecular weight of greater than or equal to 2.000 g / mol, whereby these substances can be present in the aqueous PEDOT:PSS solution or form during production. Furthermore, the PEDOT:PSS particles can be free of other mechanically strengthening substances such as plastic microparticles, e.g. polystyrene microparticles, silicon dioxide microparticles or salt crystals such as calcium carbonate. The group of strengthening substances with a non-polymeric character therefore includes at least salt crystals, plastic microparticles, quartz microparticles or mixtures thereof. In addition, the PEDOT:PSS solution used can still contain other low molecular weight substances which can, for example, influence or adapt the electrical properties of the PEDOT:PSS network.

[0026] Within a further preferred aspect of the process, the aqueous PEDOT:PSS mixture in process step a) can comprise, in addition to water, an organic solvent A as a further solvent component. To achieve controlled porosity and to form mechanically stable particles, the use of a solvent A to generate an emulsion of solvent A in an aqueous PEDOT:PSS solution has proven to be simple and efficient. The number of substances involved is kept low, and separation from the emulsion is rapid and largely complete. Furthermore, the volume fraction of solvent A in the total volume of the aqueous PEDOT:PSS mixture can be greater than or equal to 15% and less than or equal to 60%.Within these volume fractions of organic solvent A in the aqueous mixture, mechanically very stable particles can be obtained within very short processing times, which also exhibit a very uniform pore size distribution. Smaller fractions can be disadvantageous, since the presence of only isolated drops of solvent A prevents cross-linked porosity, but rather only isolated defects in the particles. Higher fractions can contribute to insufficient mechanical stability of the particles.

[0027] Furthermore, the invention relates to poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate particles, wherein the particles are spherical and contain no other mechanically strengthening substances besides PEDOT:PSS. Even without further mechanically strengthening admixtures in the starting material or in the formed particle, extremely mechanically stable PEDOT:PSS particles can be obtained, which are also characterized by a particularly uniform, spherical shape. The strengthening substances are defined above in connection with the process according to the invention. Polymeric constituents can, for example, be substances having a molecular weight of greater than or equal to 2,000 g / mol, whereby these substances can be present in the aqueous PEDOT:PSS solution or form during production. In addition to the special configuration in the form of spheres, the particles can also have a particularly narrow sphere size distribution.

[0028] The spherical configuration can be mathematically captured, for example, by the sphericity of the particles, which, according to the invention, can be greater than or equal to 0.91. This sphericity range can be determined microscopically and generally describes the ratio of the surface area of ​​a sphere of the same volume to the surface area of ​​the body in question. An average of at least 20 individual particles can be used for the determination. Furthermore, the sphericity of the particles can be greater than or equal to 0.95 and less than or equal to 1. Furthermore, the particles can be free of emulsifiers, wetting agents, or other surface-active substances that are commonly used to produce emulsions.

[0029] Furthermore, according to the invention, PEDOT:PSS particles are produced by the process according to the invention. In addition to the size distribution, mechanical stability, and porosity, further properties can be determined by the process according to the invention that differ from the properties of processes produced by the prior art. For further advantages of these particles obtainable by the process according to the invention, explicit reference is made to the advantages mentioned in connection with the process according to the invention.

[0030] Within a further preferred aspect of the particles, the particles can have a modulus of elasticity of greater than or equal to 0.05 MPa and less than or equal to 15 MPa. The mechanical properties of the particles according to the invention can be adjusted over a wide range even without the addition of further mechanically active substances. In addition to the porosity of the particles, the crystallinity in particular can have a significant influence on the modulus of elasticity. The degree of crystallization of the individual chain segments can be influenced, for example, via the acid catalyst concentration, whereby the acid concentration influences the molecular arrangement of the individual chain segments. The modulus of elasticity (Young's modulus) of the particles can be determined via tensile tests on strip-shaped particles. The modulus of elasticity is determined on particles in fiber form in the wet state, as described, for example, in the examples.

[0031] According to a preferred characteristic of the particles, the particle can be at least partially crystalline with Bragg reflections in an XRD spectrum at 4.3 (+- 0.2) nm -1< and 18.4 (+- 0.2) nm -1<. The process according to the invention makes it possible to obtain mechanically very stable particles, which are characterized in particular by a high degree of crystallization. The degree of crystallization can in particular lead to particles with a high elastic modulus. The crystalline particles are characterized by a solid-state powder X-ray diffractogram, which shows visible reflections at the positions specified above. Furthermore, the diffractogram can show a further peak at 8.6 nm -1<. The ratio of the peak heights at 4.3 and 8.6 nm -1< can be, for example, 1:2. These reflections can be assigned to the lamellar arrangement of the individual chains with a periodicity of 1.5 nm in the particle. The reflection at approx.The 18 nm -1< most likely results from regularly arranged π-π stacks of adjacent PEDOT chains. In contrast, less crystalline particles, for example, produced with low acid concentrations in the coagulation bath, exhibit a small crystalline region size of only 1.8 nm. In these low-crystallinity particles, no distinct lamellar structure can be detected via defined Bragg reflections.

[0032] In a further preferred embodiment of the particles, the surface of the particle can have a zeta potential of less than or equal to 0 mV. Using the process according to the invention, particularly suitable, mechanically stable particles can be obtained without the addition of further polymeric framework substances or mechanically active fillers, which particles are also characterized by a favorable, negative zeta potential. This negative surface charge can contribute to improved functionalization of the particle surfaces, particularly in the field of cell cultures. The electrically negative functionalization of the surface can be used in several steps, for example to apply a positive charge and thus subsequently achieve improved cell adhesion. This can therefore result in more biocompatible particles which show faster adhesion and improved proliferation of the cells on and within the particle.The zeta potential can be determined, for example, using a combined optical / electrical measurement that measures the migration velocity of the particles as a function of an applied voltage. The influence of individual particle geometries on the measurement result is known to those skilled in the art, and these effects can be eliminated. Preferably, the surface charge can be less than or equal to -10 mV, and more preferably less than or equal to -15 mV. The lower limit of the potential can be, for example, -75 mV, and more preferably -50 mV.

[0033] In a preferred embodiment of the particles, the particles can have a size distribution with a D50 quantile in a range of greater than or equal to 10 µm and less than or equal to 1,000 µm. The particles obtainable by the process according to the invention can be produced over a wide size range by selecting the nozzle size and the flow rate ratio between the continuous phase and the aqueous PEDOT:PSS dispersion. This results in very homogeneous size distributions, which can have a polydispersity index of less than or equal to 1.2, more preferably less than or equal to 1.1. The polydispersity index can be determined by microscopic measurements.

[0034] Within the scope of a preferred embodiment of the particles, they can be porous and have a porosity of greater than 0 volume % and less than or equal to 95 volume %. It has been shown that a wide range of particle porosities is accessible by means of the method according to the invention, wherein it is particularly surprising that even at high porosities the particles display sufficient mechanical strength, even in the absence of further stabilizing substances. Thus, particles can be provided which display very high specific surface areas and which do not contain, for example, electrically interfering or inactive substances. The particle porosity can be determined, for example, by microscopy on freeze-dried particles.

[0035] Furthermore, according to the invention, the use of the particles according to the invention can be selected from the group consisting of cell culture microcarriers, suspension electrodes, switchable redox absorber material, catalyst supports, or combinations thereof. Due to the uniformity of the size distribution, the controllable porosity, and the fact that, apart from PEDOT:PSS, no other mechanically strengthening and / or surface-active substances need to be present on or in the particles, the particles are suitable for a number of different applications. When used as a suspension electrode, the use of the particles results in a multiphase material system that has the particles as the active charge-storing component. These can be suspended in an ionic solution or an electrolyte. From a gravimetric perspective, the electrolyte is the main component and contributes to the physical transport of the active material.The internal and surface porosity of the particles according to the invention leads to an improvement in the electrochemical properties, including improved utilization of the electrical capacity and faster charging and discharging kinetics, which gives the particles according to the invention great potential for electrochemical energy storage in the form of supercapacitors or batteries. The PEDOT:PSS particles, which can be flexibly produced using the process according to the invention, are non-toxic and thus cell-compatible. In addition to high mechanical stability in aqueous systems, they also exhibit excellent redox reversibility. The achievable conductivities are higher than those of state-of-the-art polymer particles.Furthermore, the PEDOT:PSS particles according to the invention exhibit very fast charge-discharge kinetics as a material system, whereby the charge can be stored not only in a superficial electrical double layer but also within the polymer matrix. The latter results in particular in a high energy and power density of the particles.

[0036] Within a preferred aspect of the use, the particles can be used as cell culture microcarriers, wherein the surface of the particles is coated prior to cultivation with one or more molecules selected from the group consisting, among others, of poly-L-lysine, laminin, collagen, fibronectin, vitronectin, or mixtures thereof. By excluding other carrier substances in the basic particle structure, highly biocompatible carriers can be obtained which, due to their surface charge, also offer the possibility of subsequent electrostatic functionalization. All extracellular matrix proteins that have an isoelectric point < 7 in aqueous solutions can be coated onto the particles. These compounds therefore have a negative charge and can therefore adhere, for example, to poly-L-lysine.For example, additional charged components of the extracellular matrix or synthetic polyelectrolytes can be bound to the surface. These components can promote faster and better adhesion, as well as a higher cell division rate.

[0037] In a further embodiment of the use, the surface of the particles can be coated first with poly-L-lysine and then with laminin. Successive and double coating can contribute to improved biocompatibility of the carriers. Even difficult-to-cultivate cell lines can be processed with high yields. For coating, the surface of the particles can first be treated with poly-L-lysine. After sufficient absorption of the poly-L-lysine, laminin can then be absorbed onto the applied poly-L-lysine layer in a second step. Examples I Structure

[0038] The microfluidic co-flow device for producing spherical PEDOT:PSS particles according to the invention is manufactured from a polyethylene tube with an inner diameter of 0.86 mm, a 30G disposable cannula, and epoxy glue. The tube is bent at a 45° angle and fixed to a microscope slide with the epoxy glue. The cannula is then inserted into the tube at the bend. The cannula is finally positioned concentrically in the tube and attached to the microscope slide with epoxy glue. The end of the polyethylene tube facing towards the cannula tip represents the future device outlet, while the end facing away from the cannula tip is the inlet for the continuous phase. The male screw cap of the inserted 30G disposable cannula is then connected to a female-female connector, which is connected to another polyethylene tube via a second 30G disposable cannula.This polyethylene tube is used in the manufacturing process for feeding the pure PEDOT:PSS dispersion (solid particles) or the 1-octanol PEDOT:PSS emulsion (porous PEDOT:PSS particles). II Particle production

[0039] To produce the full PEDOT:PSS particles, a 10 mL disposable syringe is filled with a 1.3 wt.% aqueous PEDOT:PSS mixture (Haereus). The filled syringe is then connected to the corresponding tubing end of the co-flow apparatus via a 30G cannula. Using another 10 mL disposable syringe, 1-octanol is drawn up as solvent A. This syringe is connected to the tubing end via a 30G cannula. The two filled syringes are finally attached to the holders of two separate syringe pumps, which are used to pump the respective phase. Ideally, the flow rate of the aqueous PEDOT:PSS base solution can be set to 0.01 mL / min and the flow rate of the 1-octanol to 0.5 mL / min. These values ​​have proven particularly favorable for droplet formation, as they guarantee a sufficiently large droplet spacing in the tubing and result in the desired droplet size.For curing, the still liquid PEDOT:PSS droplets, together with the surrounding continuous 1-octanol phase, are passed through the end of the tube into a coagulation bath consisting of 5 vol.% sulfuric acid and 95 vol.% isopropanol. The 1-octanol shell surrounding the PEDOT:PSS droplet prevents the PEDOT:PSS from curing in the cannula and is later gently removed in the coagulation bath via the density difference. With the removal of the 1-octanol shell by detachment in the coagulation bath, the curing process of the PEDOT:PSS droplet begins, which sediments in the coagulation bath due to its higher density. During the curing process, PSS is removed from the PEDOT:PSS polyelectrolyte complex due to complex formation with H +< ions, causing the hydrophobic PEDOT to aggregate and crystallize via π-π interactions. Completely cured, pure PEDOT:PSS particles can finally be collected at the bottom of the coagulation bath.

[0040] For the production of porous PEDOT:PSS particles, the experimental setup remains unchanged. However, instead of a pure aqueous 1.3 wt.% PEDOT:PSS solution, a 1-octanol (solvent A) in PEDOT:PSS emulsion is filled into a syringe. The emulsion is emulsified using a UP200S from Hielscher Ultrasound Technology with 0.5 cycles and an amplitude of 50% for 1 minute. Depending on the desired porosity, the volume ratio of 1.3 wt.% PEDOT:PSS solution and the other solvent from group A, for example, 1-octanol, in the emulsion can be varied. For cell culture experiments, particles with a 30 vol.% 1-octanol content in the 1.3 wt.% aqueous PEDOT:PSS solution may be suitable. III Measurement methodology III.1 XRD measurements

[0041] Powder X-ray diffraction spectroscopy (WAXS) was performed using an Empyrean setup from PANalytical. A Cu X-ray tube (line source of 12 × 0.04 mm²) delivered CuK α radiation with λ = 0.1542 nm. The source and detector moved vertically around a fixed horizontal sample. After passing through a 1 / 8° divergence slit and a 1 / 4° antiscattering slit, the beam reached the sample at the center of a phi-chi-z stage. In the Bragg-Bretano geometry used, the beam was refocused at a secondary 1 / 4° divergence slit. Finally, the signal was recorded with a pixel detector (256 × 256 pixels of 55 µm) as a function of the scattering angle 2θ. The peak positions were then calculated from q = 2π / d = (4π / λ)sinθ, where q is the scattering vector. The detector was used in a scanning geometry that allowed all rows to be used simultaneously.To reduce the background, the divergent beam perpendicular to the scattering plane was controlled by a 4 mm mask, which limited the beam width at the sample position to approximately 10 mm. In addition, the vertical divergence was limited to angles ≤ 2.3 ° by Soller slits. The height of the (powder) sample was optimized for each new measurement. The scans were performed with 2θ of the detector axis, which moves at twice the speed of the θ axis of the incident beam. The calibration was verified with a Si reference sample. The resolution of the entire setup was determined by measuring a high-quality Si wafer, which yielded a resolution-limited peak with a half-width of 0.026 degrees. III.2 Mechanical measurements

[0042] The tensile tests were conducted on a custom-built laboratory setup consisting of a micromanipulator linear arm (MM33, Märzhäuser Wetzlar GmbH & Co. KG, Germany), a stepper motor (NEMA 17, Stepperonline), and a high-precision balance (Mettler Toledo, Switzerland). The PEDOT:PSS fibers were fixed on C-shaped cardboard holders with an inner leg spacing of 10 mm. The cardboard holders guaranteed a defined initial fiber length and prevented elongation prior to the tensile tests. The immobilized PEDOT:PSS fibers were then soaked in DI water for 10 seconds before the cardboard holder was attached to the linear arm and the balance via clamps. Finally, the cardboard legs were separated by a cut, and the PEDOT:PSS fibers were stretched to failure at a pulling speed of 0.2 mm / s. Strain and mass were recorded using a custom Python script. III.3 Coating with ECM molecules

[0043] The adsorption behavior of differently charged polyelectrolytes (PE) on the surface of PEDOT:PSS particles was investigated using fluorescein isothiocyanate (FITC)-labeled PEs. Positively charged poly-L-lysine (PLL) (15,000–30,000 Da, Sigma Aldrich) and negatively charged polystyrene sulfonate (PSS) (Surflay Nanotec GmbH) with a labeling degree of 10% were dissolved in 0.1 M sodium chloride (NaOH) aqueous solutions at a concentration of 1 mg / ml under constant stirring at room temperature overnight. The PEDOT:PSS particles were then incubated in the respective PE solutions for 5 days under light-protected conditions. Finally, the samples were rinsed twice in a 0.1 M NaOH aqueous solution and imaged with a TCS SP8 Falcon confocal microscope (Leica, Germany). For the cultivation of MRC-5 cells, PEDOT:PSS particles were coated layer by layer with PLL and laminin (from human placenta, Sigma Aldrich).The microcarriers were incubated in 0.1 mg / ml PLL solution on a roller device at room temperature for 24 h. Subsequently, the samples were rinsed in Milliq water and incubated in a 40 µg / ml laminin solution on a roller device at 37 °C for another 24 h. III.4 Cell culture

[0044] Cell maintenance: L929 mouse fibroblast cells were cultured in Roswell Park Memorial Institute (RPMI) 1640 medium (4500 mg / L glucose, L-glutamine, sodium pyruvate, sodium bicarbonate) (Thermo Fisher Scientific), while MRC-5 human embryonic fibroblast cells were cultured in Minimal Essential Medium (MEM) (1000 mg / L glucose, 1X non-essential amino acids, L-glutamine, sodium bicarbonate) (Sigma Aldrich). Both cell culture media were additionally supplemented with 10% (v / v) fetal bovine serum (FBS) and 1% (v / v) penicillin / streptomycin. The cell lines were maintained at 37°C in an atmosphere of 5% CO2 and 95% humidity. The passage number was limited to 30 subcultures regardless of the cell line.

[0045] The cytotoxicity of the particles was assessed by comparing cell proliferation in fresh medium with cell proliferation in leached medium using a tetrazolium salt-based Cell Proliferation Kit II (XTT) (Roche Diagnostics GmbH) on the fifth and ninth day of culture. The leached medium was prepared by incubating low- or high-crystalline PEDOT:PSS microcarriers in RPMI and MEM media for 5 days at 37°C at a ratio of 10 particles per 100 µl of medium. The leached medium was collected and stored at 4°C until use. Cells were seeded into TC-treated microtiter plates (96-well, Corning Life Sciences) at an L929 seeding concentration of 1,500 cells per well and an MRC-5 seeding concentration of 10,000 cells per well.The cells were then maintained in fresh or depleted medium for 9 days, with medium changes every 48 h to ensure adequate nutrient supply. For cell viability analysis, the cell-containing microtiter plates were washed with PBS (1x) (Lonza, Switzerland) before being exposed to 150 µl of XTT solution for 4 h at 37°C. Subsequently, 100 µl of each sample was transferred to a fresh TC-treated microtiter plate (96 wells), and the absorbance was measured at 450 and 630 nm using a microplate reader (Synergy HT, BioTek). Cell viability was determined from the ratio of the absorbance values ​​of cells cultured in depleted medium to cells cultured in fresh medium (control).

[0046] Immunostaining: For morphological assessment, cells were stained for nuclei and F-actin by treating the samples with DAPI solution (abcam, UK) for 5 min and with Phalloidin-iFluor 488 reagent (abcam, UK) for 60 min. Prior to staining, all samples were fixed in 4% (v / v) paraformaldehyde (PFA) solution for 15 min, permeabilized in a 0.1% (v / v) Triton X-100 solution for 5 min, and thoroughly rinsed in PBS (1x). Visual analysis of cell viability was performed using a Live / Dead Cell Double Staining Kit (Sigma Aldrich). Cell samples were exposed to a sterile PBS (1x) solution containing 0.1% (v / v) calcein-AM and 0.2% (v / v) propidium iodide for 30 min at 37°C.

[0047] Further advantages and advantageous embodiments of the inventive objects are illustrated by the figures and explained in the following examples. It should be noted that the figures are for descriptive purposes only and are not intended to limit the invention in any form.

[0048] The figures show: Figure 1 shows an FeSEM image of a porous PEDOT:PSS particle produced according to the invention; Figure 2 shows an FeSEM image of a porous PEDOT:PSS particle produced according to the invention with fibroblast colonization; Figure 3 shows the gravimetric capacity of PEDOT:PSS particles according to the invention as a function of porosity; Figure 4 shows the dependence of the redox kinetics of PEDOT:PSS particles according to the invention as a function of porosity; Figure 5 shows the dependence of the particle diameters of PEDOT:PSS particles according to the invention as a function of porosity; Figure 6 shows the size distribution of PEDOT:PSS particles according to the invention produced with a volume fraction of 30% of 1-octanol in the aqueous PEDOT:PSS mixture; Figure 7 shows the pore size distribution of inventive PEDOT:PSS particles prepared with a volume fraction of 30% 1-octanol in the aqueous PEDOT:PSS mixture.Figure 8 shows the proliferation of L929 cells on particles according to the invention as a function of time and as a function of the crystallinity of the carrier material; Figure 9 shows the influence of crystallinity on the aspect ratio of L929 cells proliferating on particles according to the invention; Figure 10 shows the influence of the crystallinity of particles according to the invention on the spreading area of ​​L929 cells.

[0049] The Figure 1 shows a FeSEM image of a porous PEDOT:PSS particle prepared according to the invention. The PEDOT:PSS particle was prepared with a 1-octanol volume fraction of 30% in the aqueous PEDOT:PSS mixture. Since PEDOT:PSS particles are hydrogels and thus collapse in anhydrous environments, the particle was freeze-dried prior to optical analysis.

[0050] The Figure 2shows a FeSEM image of a porous PEDOT:PSS particle seeded with L929 mouse fibroblasts. Colonization of the microcarrier is demonstrated after 4 days of cultivation at 37°C, 95% humidity, and 5% CO 2 . RPMI supplemented with 10% fetal calf serum and 1% penicillin-streptomycin served as culture medium. The inoculation concentration was 10,000 cells / cm 2 . Since PEDOT:PSS particles are hydrogels and thus collapse in anhydrous environments, the particles were dried with an ethanol series (35, 50, 70, 100%) and subsequently treated with hexamethyldisilazane (HMDS) prior to optical analysis.

[0051] The Figure 3shows the gravimetric electrical capacitance of the PEDOT:PSS particles as a function of the 1-octanol volume fraction in the 1-octanol PEDOT:PSS emulsion and as a function of the scan rate. Higher 1-octanol fractions indicate a larger proportion of pore volume to the particle volume (porosity) and thus a higher specific surface area. The electrical capacitances were determined from cyclic voltammetry measurements in a 3-electrode setup as a function of the scan rate. Since the specific surface area of ​​the particles is directly proportional to the particle capacitance, more porous particles exhibit a higher gravimetric capacitance. Higher scan rates lead to smaller capacitances, since the faster voltage sweeps mean that not all of the particle's surface area, which contributes to the capacitance, is utilized.

[0052] The Figure 4shows the current curve as a function of time. The redox kinetics of the PEDOT:PSS particles were recorded using chronoamperometry measurements as a function of the volume fraction of 1-octanol and thus the porosity in a 3-electrode setup. The reaction time of the particles shortens with increasing porosity, although the charge density increases with increasing porosity. The shortened reaction time is attributed to the high specific surface area and the good accessibility of the pore system, which enables fast redox kinetics. The measurements were carried out over 9 cycles, although only one cycle is shown in the diagram.

[0053] The Figure 5shows the average particle diameter as a function of the 1-octanol volume fraction in the 1-octanol PEDOT:PSS emulsion as a measure of particle porosity. All particles shown in the diagram were produced with a 1-octanol flow rate (continuous phase) of 0.5 mL / min and a PEDOT:PSS dispersion / emulsion flow rate of 0.05 mL / min. Regardless of particle porosity, the particles have a particle diameter of approximately 540 µm. The small standard deviation of the particle diameter is likely due to the fact that the droplets are generated monodispersely in the co-flow device. Smaller variations in particle diameter are caused by very slight differences in the separation kinetics of the protective 1-octanol shell in the coagulation bath.

[0054] The Figure 6shows the size distribution of highly (left) and low (right) crystalline PEDOT:PSS particles prepared with a volume fraction of 1-octanol of 30% in the aqueous PEDOT:PSS mixture. A rather narrow particle size distribution is observed for both cases.

[0055] The Figure 7 shows the porogen and pore size distributions for highly and low-crystalline, porous PEDOT:PSS particles prepared with a volume fraction of 1-octanol of 30%. Most pores have a size between 15 and 20 µm. Over 90% of the pores have a pore size between 10 and 30 µm.

[0056] The Figures 8-10show the results of cell colonization of the particles in the invention. For the culture experiments, spherical PEDOT:PSS particles were prepared from a 30 vol.% 1-octanol in PEDOT:PSS (1.1-1.3 wt.%) emulsion, which was brought to droplet detachment in a continuous 1-octanol phase. The emulsion was obtained using an ultrasonic homogenizer (Hierschler UP100H). Both phases were combined using a syringe pump (Chemyx, Nexus Fusion 4000) at a flow rate of 0.05 and 0.5 ml / min, respectively. Unless otherwise stated, the coagulation bath consisted of 5 vol.% sulfuric acid in isopropanol.

[0057] The Figure 8shows the results of the proliferation of L929 cells on particles according to the invention as a function of time and as a function of the crystallinity of the support material. By coagulation with different amounts of acid, porous particles with different degrees of crystallinity were produced. The low-crystalline particles were coagulated with 5 vol.% sulfuric acid, and the highly crystalline particles were coagulated with 95 vol.% sulfuric acid. This resulted in particles with different mechanical properties. The properties are as follows: Crystallinity Young's modulus in MPa Breaking load in kPa Elongation at break % High 0,07 28 (+ / - 13) 36 (+ / - 6) Low 9,85 626 (+ / - 32) 13 (+ / - 6)

[0058] The different mechanical properties are a strong indication that the structure of the two samples is different, despite their identical composition. These different properties of the spherical particles also lead to changes in the biological properties. Figure 8shows the results of cell proliferation of L929 mouse fibroblasts at a seeding density of 2,600 cells / cm 2 , N = 5, on pure PEDOT:PSS microcarriers. The viability was quantified using an XTT proliferation assay. It is clearly evident that the crystallinity of the carrier material influences cell proliferation. Proliferation from day 5 onwards is significantly higher on highly crystalline samples (triangles) than on low-crystalline samples (circles).

[0059] The Figure 9shows the influence of crystallinity on the aspect ratio of proliferating L929 cells on particles according to the invention. The degree of crystallinity of the particles also appears to influence the achievable morphology of the cell lines used. L929 cells stained with DAPI / phalloidin can be morphologically assessed using confocal microscopy. One way to demonstrate cell symmetry is to determine the aspect ratio of the L929 cells. Different cell morphologies are found on low- and high-crystalline particles, with low crystallinity resulting in more rounded cell morphologies and high-crystalline particles resulting in more elongated cell morphologies. The seeding density was 2,600 cells / cm², and the measurement was carried out on the second day on 250 cells.

[0060] The Figure 10shows the influence of the crystallinity of inventive particles on the spreading area of ​​L929 cells. The different degrees of crystallinity of the particles were obtained by a different coagulation treatment of spherical particles. It can be seen that a single L929 cell colonizes a significantly larger area on crystalline particles. In contrast, the spread of the cells on particles with low crystallinity is significantly more restricted. Furthermore, it can be seen that the cells on particles with low crystallinity likely proliferate deeper into the particle interior. The colonization density inside the particles, in contrast, appears to be reduced in highly crystalline particles.

Claims

1. A method for producing poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) particles comprising at least the steps of: a) providing a mixture comprising poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate in a solvent comprising at least water; b) forming one or more PEDOT:PSS drops by introducing the mixture from method step a) into an organic solvent A, the aqueous PEDOT:PSS mixture forming the interior of the drop and the organic solvent A forming the exterior of the drop; c) contacting the PEDOT:PSS drops obtained from step b) with a coagulation solution comprising a curing agent and at least one further solvent B, wherein the density of the coagulating solution is greater than the density of the organic solvent A and less than the density of the aqueous poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate mixture; thereby curing the PEDOT:PSS drops into PEDOT:PSS particles.

2. The method according to claim 1, wherein the organic solvent A is selected from the group consisting of branched or unbranched C5-C10 alkanes, branched or unbranched C5-C10 alcohols or mixtures of at least two solvents therefrom.

3. The method according to any one of the preceding claims, wherein the further solvent B is selected from the group consisting of branched or unbranched C1-C5 alcohols or mixtures of at least two solvents therefrom.

4. The method according to any one of the preceding claims, wherein the solvent A comprises octanol and the coagulating solution in process step c) comprises isopropanol as the solvent B and sulfuric acid as curing agent.

5. The method according to any one of the preceding claims, wherein the weight ratio of the curing agent and solvent B in the coagulating solution, expressed as the weight of the curing agent divided by the weight of solvent B, is greater than or equal to 0.005 and less than or equal to 0.2.

6. The method according to any one of the preceding claims, wherein the PEDOT:PSS mixture in method step a) has no further mechanically strengthening substances.

7. The method according to any one of the preceding claims, wherein the PEDOT:PSS mixture in method step a) has an organic solvent A, in addition to water as a further solvent component.

8. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate particles, characterised in that the particles are produced by a method according to any one of claims 1-7.

9. Particles according to claim 8, wherein the particles are spherical and do not contain any further mechanically strengthening substances besides PEDOT:PSS.

10. Particles according to any one of claims 8 or 9, wherein the particle has a modulus of elasticity greater than or equal to 0.05 MPa and less than or equal to 15 MPa.

11. Particle according to any one of claims 8-10, wherein the particle is at least partially crystalline with Bragg reflections in an XRD spectrum at 4.3 (+- 0.2) nm-1 and 18.4 (+- 0.2) nm-1.

12. Particles according to any one of claims 8-11, wherein the surface of the particle has a zeta potential of less than or equal to 0 mV.

13. Use of the particles according to any one of claims 8-12 selected from the group consisting of cell culture microcarriers, suspension electrodes, switchable redox absorber material, catalyst carriers or combinations thereof.

14. Use according to claim 13, wherein the particles are used as cell culture microcarriers, wherein the surface of the particles being coated prior to culturing with one or more molecules selected from the group consisting of poly-L-lysine, laminin, collagen, fibronectin, vitronectin or mixtures thereof.

15. Use according to claim 14, wherein the surface of the particles is first coated with poly-L-lysine and then with laminin.