EP4087911A1

EP4087911A1 - Microcarriers for cell culture, and method for producing microcarriers

Info

Publication number: EP4087911A1
Application number: EP21700373.0A
Authority: EP
Inventors: Tarek Fathallah
Original assignee: Carroucell
Current assignee: Carroucell
Priority date: 2020-01-09
Filing date: 2021-01-06
Publication date: 2022-11-16
Also published as: US20230033382A1; FR3106141A1; WO2021140129A1

Abstract

Disclosed is a method for forming microcarriers (1), comprising: a) forming liquid drops (12) from a sol-gel solution (2); b) depositing the drops in the form of a liquid on a first preferably hydrophobic support (10); c) deforming the drops deposited on the first support (10); d) solidifying the drops by gelling and drying same so as to form solid microcarriers; e) extracting the solidified microcarriers from the first support (10).

Description

MICROPORTEURS FOR CELL CULTURE AND PROCESS FOR MANUFACTURING MICROPORTEURS

TECHNICAL AREA

The technical field of the invention is the production of microcarriers of micrometric or millimeter size, conducive to the adhesion and development of cells.

PRIOR ART

Certain biological culture methods use culture supports carrying cells. The supports are usually designated by the term microcarrier. The microcarriers are placed in suspension in a culture medium, the objective being to grow the cells outside their original medium. The culture medium is usually subjected to moderate agitation. This allows regular renewal of the culture medium to which the cells are exposed.

Microcarriers intended to be suspended in a culture medium often take the form of microbeads, made of glass, or of plastic or an organic compound, for example a polymer (for example polystyrene or a polysaccharide). Generally, the microbeads have previously undergone a surface treatment, called surface functionalization, so as to promote cell grafting. This is to promote cell hooking or adhesion. Microcarriers are frequently used for the cultivation of adherent cells. They then act as supports, on which cells can develop and multiply. Functionalization makes it possible to apply a compound suitable for grafting cells. It can be a biological compound (eg collagen, gelatin, elastin, Poly D-Lysine, fibronectrin), or a molecule allowing positive or negative surface charge (eg cationic trimethyl ammonium or diethylaminoethyl). .

When the cells are suspended in the culture medium, they develop on the surface of the microcarriers. They frequently form, on the surface of the latter, three-dimensional edifices, usually referred to as “agglomerates” formed by a superposition of several layers of cells. It then appears conglomerates, under the effect of a

30 grouping of agglomerates. This results in some disadvantages: Cell lysis: the cells which are at the center of the agglomerates have reduced access to the culture medium, and in particular to the oxygen or to the nutrients present in the latter. Some may undergo lysis, which decreases the yield of cell differentiation culture: in the case of pluripotent stem cell culture, the formation of agglomerates can promote uncontrolled cell differentiation. Now, it is generally desirable to keep cells in the stem cell state, or to obtain differentiation, into a predetermined cell type, in a controlled manner, contact inhibition: when seeking synthesis of molecules by cell culture eg proteins, growth factors, antibodies, formation of agglomerates reduces production. unhooking difficulty: in certain applications, for example applications related to cell therapy, cell recovery is essential. This involves removing the cells from the microcarriers, so as to obtain unitary cells (cells isolated from each other), and viable. The formation of agglomerates makes detachment difficult, the cells recovered not being unitary.

In addition, the use of such microcarriers can generate other drawbacks. surface functionalization uses chemical compounds that can have an effect on cell development; the need to resort to relatively high stirring in the culture medium, so as to keep the microcarriers in suspension, which can lead to cellular stress.

The inventor has developed a new type of microcarriers, which does not have the disadvantages of ball-shaped microcarriers. The microcarriers designed by the inventor also have significant advantages as described below. DISCLOSURE OF THE INVENTION

A first object of the invention is a process for forming microcarriers, comprising: a) forming liquid drops from a sol-gel solution; b) depositing the liquid drops on a first support, preferably flat, preferably hydrophobic; c) deformation of the drops deposited on the first support; d) solidification of the drops by gelation and drying, so as to form solid microcarriers; e) extraction of the solidified microcarriers from the first support.

According to one embodiment, the first support is hydrophobic. The first support is preferably flat. The first support is preferably rigid.

During step b), the liquid drops are preferably spaced apart from each other.

According to one embodiment, during step c), the deformation of the drops is a flattening. The process can be such that step c) comprises a flattening of the drops on the first support, the flattening being obtained spontaneously, during drying, during step d).

According to one embodiment, step c) comprises an application of a second support, preferably hydrophobic, on the drops, at a distance from the first support, such that the drops are interposed between the first support and the second support. , the application of the second support resulting in a flattening of the drops between the two supports, the spacing between the first support and the second support conditioning the thickness of the microcarriers formed during step d). Preferably, the diameter of the drops formed during step a) and the spacing between the first support and the second support taken into account during step c) are adjusted as a function of a diameter or more large diagonal, parallel to the first support, of the microcarriers resulting from step e). Step d) may include an arrangement of an assembly, formed at least by the first support, the drops during gelation and the second support, in an oven, so as to promote drying. The temperature of the oven can be between 30 ° C and 70 ° C. The oven can be placed under partial vacuum. Preferably, during step c), the spacing between the first support and the second support is between 30 μm and 5 mm.

Preferably, the second support is a flat support. Preferably, the second support is hydrophobic. The second support is preferably rigid.

During step a), the drops can be formed at a distance from the first support, the distance preferably being less than 10 mm. During step a), the drops can be formed in contact with the first support.

During step a), the drops formed may have a diameter of between 100 nm and 2 mm.

According to one embodiment, the first support comprises first parts and at least a second part, the first parts being less hydrophobic than each second part, each first part being bypassed by a second part, the second part forming a closed contour around it. said first part, so that during step a), the drops are deposited on each first part, and extend, along each first part, to the contour of said first part. According to one possibility, each second part is hydrophobic and each first part is less hydrophobic than each second part which goes around it. According to one possibility, each second part is hydrophobic and each first part is hydrophilic.

According to one embodiment, the first support comprises first parts and at least a second part, the first parts being hollow with respect to each second part, each first part being bypassed by a second part, said second part forming an outline, taking the shape of an edge, closed around said first part, so that during step a), the drops are deposited on each first part, and extend, along each first part, up to outline of said first part.

The sol-gel solution can comprise a functionalization compound, suitable for the formation of a grafting agent on the surface of the microcarriers, the grafting agent promoting grafting with a predetermined biological species or a predetermined chemical species. The predetermined chemical species can be a molecule. The predetermined biological species can be a cell, or a protein, or an antibody. The functionalization compound can be inorganic or organic. The sol-gel solution can contain different functionalization compounds.

A second object of the invention is a microcarrier, in particular obtained by implementing a method according to the first object of the invention. The microcarrier may include a first planar surface and a second surface, the first planar surface and the second surface being connected to each other by a lateral surface forming a border of the microcarrier. The second surface can be planar, and parallel to the first surface. The second surface may be convex, and extend facing the first surface. The diameter, or the greater diagonal, of the first planar surface and / or the second surface is preferably less than 5 mm or less than 1 mm, and preferably greater than 5 µm. Preferably, the thickness of the microcarrier, corresponding to the distance between the first flat surface and the second surface, is less than 1 mm.

A third object of the invention is a use of a microcarrier according to the second object of the invention for the culture of cells, excluding embryonic stem cells of human origin, the microcarrier being intended to be placed in suspension. in a biological medium, for example a culture medium. The invention will be better understood on reading the description of the exemplary embodiments presented, in the remainder of the description, in connection with the figures listed below.

FIGURES

FIG. 1A represents an example of a microcarrier according to the invention.

FIG. 1B shows another example of a microcarrier according to the invention.

FIG. 1C shows another example of a microcarrier according to the invention.

FIG. 2A illustrates a step of forming drops on a first support, preferably hydrophobic.

FIG. 2B shows schematically an affixing of a second support, preferably hydrophobic, facing the first support.

Figure 2C is a diagram illustrating the definition of a contact angle.

FIG. 2D schematically shows a flattening of a drop during drying.

FIG. 3 shows schematically the main steps of a process for forming microcarriers.

FIGS. 4A to 4C show a deformation of a drop according to a particular embodiment.

FIG. 4D shows examples of microcarriers obtained by the embodiment shown schematically in FIGS. 4A to 4C.

FIG. 4E shows schematically a first substrate structured between hydrophobic parts delimited by strongly hydrophobic zones.

Figure 5 shows an example of cells that have grown on microcarriers.

EXPOSURE OF PARTICULAR EMBODIMENTS

An example of a microcarrier according to the invention has been shown in FIG. 1A. The microcarrier has two flat surfaces, or considered as such, opposite to each other. Thus, the microcarrier has a first plane surface, or substantially plane Si, and a second plane surface, or substantially plane, S2. The first planar surface and the second planar surface are parallel to each other, or substantially parallel to each other.

By substantially parallel is meant parallel, taking into account an angular tolerance, for example less than or equal to ± 20 °, and preferably less than or equal to ± 10 °.

By substantially planar surface is meant planar, admitting surface elements exhibiting a local flatness defect, within a limit of ± 10 ° with respect to the rest of the surface. The first surface Si has a diameter F, or a greater diagonal, less than or equal to 20 mm, and preferably less than or equal to 10 mm, and preferably less than or equal to 1 mm. The same is true of the second surface S. The diameter F is preferably greater than 5 µm or 10 µm. The diameter F is preferably between 50 μm and 1 mm, and more preferably between 100 μm and 1 mm. The first surface Si and the second surface S extend parallel to a main plane Rcg. The microcarrier 1 comprises a lateral surface S3, extending between the first surface Si and the second surface S2. The lateral surface S3 extends along a thickness e around a transverse axis Z perpendicular to the main plane Rcg.

FIG. 1A corresponds to a preferred embodiment, according to which the microcarrier 1 has a cylindrical geometry of revolution. The first surface Si and the second surface S ₂ have a circular shape, of revolution, the lateral surface S3 being an annular surface. Other cylindrical configurations are possible, for example a cylinder with a polygonal base, for example in the shape of a quadrilateral, as shown in FIG. 1B.

Whatever the configuration, the thickness e of the microcarrier 1 is preferably: less than a fifth of the diameter (or of the largest diagonal)

- and preferably greater than one tenth, and preferably one twentieth of the diameter (or of the largest diagonal) F.

When the microcarrier is cylindrical of revolution, due to this small thickness, such a microcarrier takes the form of a thin disc. The thickness and the diameter are adjusted so as to avoid breakage of the microcarriers.

Thus, whatever the configuration, the microcarrier is essentially in the form of two surfaces Si and S2, extending one facing the other, the area of the lateral surface S3 being negligible. The two surfaces Si and S can in particular be plane or substantially plane.

Preferably, the microcarrier is transparent.

The inventor chose such a geometry because of the advantages that it confers: an increased specific surface area, compared with the ball microcarriers usually used in the prior art. The specific surface corresponds to the surface available per unit of mass:

• For a spherical microcarrier, made of glass, the diameter of which is between 160 μm and 180 μm, the specific surface varies between 340 cm ² / g and 360 cm ² / g. • For a cylindrical microcarrier of revolution, made of glass, the specific surface depends on the thickness e. For thicknesses of 5 μm, 10 μm and 20 μm, the specific surface area reaches 3338 cm ² / g, 1722 cm ² / g and 888 cm ² / g, respectively. On this type of microcarrier, the available surface corresponds to the cumulated area of the plane surfaces Si and S2. The higher the specific surface area, the greater the quantity of cells which can be cultured, per unit mass of microcarrier, is also high.

- better flotation ability, due to the high specific surface area, giving high lift. One consequence is that with microcarriers according to the invention, obtaining a suspension in the culture medium does not require as much agitation as using bead microcarriers. This significantly reduces the stress of cells developing on the surface of the microcarriers, due to increased lift. Indeed, the impact of agitation on cell development has already been described, for example in the publication Wang. Y "Cell adhesion and mechanical stimulation in the regulation of mesenchymal stem cell differentiation, J. Cell. Mol. Med 17 (7), pp 823-832 or in the publication Yeats, A." Bioreactors to influence stem cell fate: augmentation of mesenchymal stem cell signaling pathways via dynamic culture Systems ", Biochim Biophys Acta, 1830 (2), pp 2470-2480. The inventor considered that slower stirring allows better stability of the cellular environment. Agitation also limits the risk of shock between several microcarriers in suspension in the same culture medium This also limits the hydrodynamic stress to which the cells are subjected.

Other advantages will be described in connection with the experimental tests carried out and described below.

The microcarriers according to the invention can be obtained by implementing a method of sol-gel type, short for solution-gelation. This is a chemical process known to those skilled in the art, making it possible to manufacture, at low temperature, glasses or ceramics. Such a method comprises the use of a sol-gel solution, formed: of a molecular precursor of a metal or of a metalloid, for example an organometallic compound or a metal salt; an organic solvent; water; an acidic or basic catalyst.

In the presence of water, a network of oxides is formed, through hydrolysis-condensation reactions, trapping the organic solvent, so as to form a gel. The latter then undergoes drying, to remove the organic solvent present in the gel. The drying can be of the evaporative type, at a pressure less than or equal to atmospheric pressure, so as to form a dry gel, usually designated by the term xerogel, in the form of a monolithic solid.

The molecular precursor can for example be an organometallic compound of metal or metalloid, for example a metal alkoxide of formula M (OR) n, where M is a metal or a metalloid, and R is an organic group.

The metal M can be for example a transition metal, a lanthanide: it can be Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh , Pd, Ag, Cd, Hf, Ra, W, Re, Os, Ir, Pt, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, Al, Ga, In, Ge , Sn, Pb.

The metalloid element can be chosen from Si, Se, Te. - R can be an alkyl group, comprising for example between 1 and 10 carbon atoms, or a phenyl group. n is a natural integer corresponding to the number of ligands bound to M, which corresponds to the valence of M.

The molecular precursor is placed in an organic solution, for example an alcoholic solution. The organic solvent can be an aliphatic or aromatic monoalcohol, or a diol.

The sol-gel solution can also comprise a catalyst, and / or water, or compounds making it possible to act on the porosity, for example a surfactant.

According to one embodiment, the sol-gel solution comprises a functionalization compound, in particular an organic compound, the function of which is to form a grafting agent. By grafting agent is meant a molecule or a functional group capable of promoting attachment, by grafting, of a chemical or biological element to the surface of the xerogel resulting from the implementation of the sol-gel process. The chemical or biological element is predetermined. It can be a molecule, a cell, or a protein or another organic compound, for example a growth factor or an antibody. For applications related to cell culture, the grafting agent promotes grafting of a cell, of predetermined type. The grafting agent can then be collagen, or polylysine, or a milk protein. However, due to regulatory or quality control constraints, it is sometimes preferable to avoid molecules of animal origin. It is then possible to use a functionalization compound comprising an epoxy function, the latter being conducive to the formation of chemical bonds with amine functions, the latter being present in most cell membranes. The incorporation of an epoxy function can be carried out by a compound of glycidoxypropyltrimethoxysilane type, usually designated by the acronym GPTM. An amine function can also be integrated into the sol-gel, by means of a compound of APTES (3-aminopropyl-triethoxysilane) type. Such a compound allows the formation of positive charges on the surface of the microcarriers, which promotes adhesion of cells exhibiting negative surface charges. An amine function is conducive to the formation of peptide bonds with amino acids in the cell wall.

The possibility of adding a functionalization compound in the sol-gel solution constitutes an advantageous advantage, since this avoids carrying out a post-manufacturing functionalization, as in the beads of the prior art. This makes it possible to manufacture specific microcarriers for a predefined application, taking into account the chemical or biological element intended to be fixed on the microcarriers, and / or the medium in which the microcarrier is intended to be placed.

The sol-gel microcarriers obtained have a density generally less than 2, and preferably less than 1.8. The density is preferably strictly greater than 1 and advantageously between 1 and 1.4 and even more advantageously between 1.02 and 1.04. Such a density confers good flotation of the microcarriers in aqueous culture media.

A first example of a process for manufacturing a microcarrier, by the sol-gel process, is now described, in connection with FIGS. 2A to 2B. The main steps are shown in Figure 3.

Step 100: formation of the drops

A sol-gel solution 2, as described above, is introduced into a distributor 3, making it possible to form drops 12, and preferably calibrated drops. The drops are preferably microdrops, the volume of which is between 5.10 ¹⁰ μl and 15 μl.

The diameter of the drops formed is preferably between 100 nm and 5 mm, or between 100 nm and 1 mm.

The distributor 3 is placed at a distance from or in contact with a first support 10. The first support 10 is preferably planar and preferably hydrophobic. In this example, the first support is a flat support, which corresponds to a preferred embodiment: it is a rigid plate. The hydrophobic character of a material can be characterized by an angle of contact Q, as shown in Figure 2C. The contact angle Q is measured in the presence of a drop of the sol-gel solution used. Preferably, the contact angle Q is between 70 ° and 150 °. This makes it possible to avoid excessive spreading of the drops on the first support. The material forming the first support 10 can for example be glass, or polypropylene, or Teflon, or silicon. Preferably, the first support 10 is hydrophobic or has previously undergone a hydrophobic treatment.

The distance d between the dispenser and the first support 10 is preferably less than 10 cm. The drops can be formed in contact with the first support 10. The closer the distance, the better the precision with regard to the localization of the drops.

During step 100, the drops formed on the first support 10 are spaced apart from each other. The spacing between two adjacent drops is dimensioned such that during the flattening of the drops, resulting from the implementation of step 110, the latter remain spaced from one another.

The fact that the first support 10 is hydrophobic makes it possible to avoid excessive spreading of the drops 12.

Step 110: flattening of the drops

Following the formation of the drops, a second support 20, preferably hydrophobic, is applied parallel to the first support 10. The second support 20 is preferably flat and preferably rigid. The second support 20 is applied facing the first support 10, being spaced from the latter by a spacing s depending on the thickness e of the microcarriers that it is desired to form. Taking into account a shrinkage occurring during drying (see step 120), the spacing s between the first support 10 and the second support 20 is greater than the thickness e of the microcarriers 1 resulting from the use of process. The spacing s between the first support 10 and the second support 20 can be ensured by arranging the spacers 30 between the first support 10 and the second support 20. The spacing s between the first support 10 and the second support 20 can be included between a few μm, for example 5 μm, and 5 mm or, preferably, between 50 μm and 2 mm or 1 mm.

The application of the second support 20 leads to a flattening of the drops 12. After their application to the first support 10, the drops 12 rapidly form a gel. It is therefore preferable that the flattening is carried out before the gelation is not too advanced, as soon as all of the drops 12 have been formed. Also, step 110 is carried out as quickly as possible after step 100. The solvent used in the sol-gel composition can be chosen with low volatility, so as to be able to postpone the application of the second support 20. This prevents drying and premature gelation of the drops which would occur before the application of the second support 20. It is also possible to lower the temperature or increase the temperature. the pressure in order to be able to delay the gelation of the drops deposited on the first support 10.

Step 120: gelation and drying

During gelation and drying, the assembly 40 formed by the first support 10 and the second support 20 is preferably placed in an oven, so as to finalize the gelation and facilitate drying of the gel. The temperature of the oven may for example be between 30 ° C and 80 ° C. The oven can be placed at a pressure below atmospheric pressure, for example at a pressure between -200 mbar and -970 mbar with respect to atmospheric pressure. This significantly speeds up drying. The duration of the passage in the oven can be between 10 minutes and 24 hours.

During drying, the gel resulting from each drop solidifies, so as to form a solid monolithic microcarrier 1. Thus, each drop 12 deposited during step 100 results in the formation of a solid monolithic microcarrier 1.

During drying, the microcarriers undergo shrinkage, which is a known phenomenon in the field of sol-gel. Thus, during drying, the thickness e of each microcarrier 1 decreases, the reduction being for example 50% when the thickness is 100 μm or 50 μm. Also, following drying, the microcarriers 1 are only in contact with a single support, for example the first support 10 on which they rest by gravity. Certain microcarriers can remain attached to the second support 20. When the second support 20 is hydrophobic, the latter are easily removed.

The fact that each support is hydrophobic facilitates loss of contact between each microcarrier and the support facing it, during shrinking. The support facing is the support opposite to the support supporting, by gravity, the microcarriers in formation. In fact, in the absence of hydrophobic treatment, bonds, for example OH bonds, can form between the gel and the supports. This leads to a risk of breakage when contact is lost, when the microcarrier retracts under the effect of drying. The hydrophobic treatment of each support limits the risk of breakage.

Step 130: recovery of the microcarriers

Following drying, the microcarriers 1 can easily be separated from the first support 10 or from the second support 20, due to the hydrophobic nature of the latter. During the recovery, the microcarriers 1 can be collected on a recovery support, preferably flexible, for example a canvas. It can be a porous nylon filter. The porosity is optimized to retain the microcarriers 1 while allowing the removal of debris, for example residues of microcarriers which have broken during the implementation of the process, the latter passing through the recovery support. For example, when the diameter (or the largest diagonal) of the microcarriers is equal to 600 µm, the particle size of the recovery medium can be 400 µm. When the diameter of the microcarriers is 200 µm, the particle size can be 150 µm.

The fact that the first support 10 is hydrophobic makes it possible to avoid formation of OH bonds between the microcarriers, resulting from the implementation of the process, and the first support 10. This facilitates the recovery of the microcarriers.

Step 140: washing

The microcarriers recovered during step 130, placed on the recovery support, are washed, for example by a bath in a washing solution making it possible to remove residual acids present in the sol-gel solution or any precursors n 'having not reacted. The washing solution can be an aqueous solution, for example an aqueous solution comprising 50% by mass of isopropanol. The method can successively comprise several baths, for example two or three successive baths.

Step 150: post-wash drying

Following step 140, the microcarriers are subjected to drying. Drying can be carried out at room temperature or at a higher temperature, for example up to 100 ° C or above. The drying temperature can be lowered if a partial vacuum is formed around the microcarriers. During drying, the microcarriers can be placed on the recovery support and the whole is placed in an oven.

According to one possibility, the drying can be carried out by applying different successive pressure levels in the oven, for example by gradually lowering the pressure. This reduces the drying time. The temperature is for example 50 °. The drying time depends on the temperature and pressure conditions. It can be between 10 minutes and 5 hours, or even more.

According to a variant of the first embodiment, the spacers 30 arranged between the two supports during step 110 are compressible. The spacers are dimensioned such that when affixing the second support 20 facing the first support 10, each drop 12 is not in contact with the second support 20. See FIG. 4A. During step 110, pressure is exerted on the second support 20, so as to temporarily bring it closer to the first support 10. The second support 20 then comes into contact with each drop 12. See FIG. 4B. When the pressure is released, the second support 20 moves away from the first support 10. See FIG. 4C. According to this variant, step 110 corresponds to a deformation of the drop 12. When the pressure is released, the drop 12 remains in contact with the second support 20, by surface tension of the liquid. Thus, when the pressure is released, the drop 12 stretches along the transverse axis Z. This results in a particular form of microcarrier, comprising a thinning h extending between two ends I2. When the microcarriers are cylindrical of revolution, the shape resembles that of an hourglass.

FIG. 4D is a photograph of microcarriers 1 in the shape of an hourglass obtained by implementing such a variant.

According to a second embodiment, the drops 12 are deposited on the first support 10, as described in connection with step 100 of the first embodiment. See figure 2A.

Unlike the first embodiment, during step 110, the flattening of the drops 12 does not result from the affixing of a second support 20. The flattening of the drops is spontaneous. It is carried out in particular gradually, during drying. See figure 2D. This makes it possible to obtain microcarriers 1 whose thickness is between a few μm, for example 2 μm or 3 μm, up to several μm, or even hundreds of μm. This embodiment is particularly suitable for obtaining microcarriers 1 whose thickness is fine, typically less than 30 μm, or even less than 10 μm. This makes it possible to have microcarriers 1 having good buoyancy.

The geometry of the microcarriers 1 obtained according to the second embodiment is not as cylindrical as that of the microcarriers obtained according to the first embodiment. In particular, the face opposite to the face resting on the support 10 may be slightly convex.

According to this embodiment, the drying and gelation step 120 can be carried out in the open air, without passing through an oven.

The second embodiment is particularly suitable for obtaining microcarriers of low thickness, for example less than 10 μm. In general, the second embodiment makes it possible to obtain a very high diameter / thickness ratio, which is favorable to good flotation. The first embodiment allows better control of the flatness microcarriers. It is particularly suitable for microcarriers of large diameters, typically greater than 100 μm.

Steps 130 to 150 of the second embodiment are identical to those described in connection with the first embodiment.

The second embodiment is preferably implemented by lowering the concentration of precursors in the sol-gel solution compared to the first embodiment. Preferably, in the second embodiment, the contact angle Q of each drop is smaller than in the first embodiment, this to promote spreading of the drop on the first support 10. To lower the angle of contact Q, it is possible to use a solvent having a specific tension lower than that of water, for example an alcohol of the ethanol or isopropanol type. A surfactant can also be added to the sol-gel composition.

Whatever the embodiment, the first support 10 can be structured so that under the effect of the flattening, each drop 12 spreads out, on the first support 10, in a predetermined shape, according to the structuring of the first support. An example of such a support is shown in FIG. 4E. The structuring of the support 10 makes it possible to form first parts 10i, intended to receive the drops, and second parts IO2. Each first part is bounded by a second part, such that a second part forms a closed contour around each first part.

According to one possibility, the first support 10 can be microstructured, so as to comprise first hollow parts 10i of predetermined shapes, for example polygons of the quadrilateral type or hexagons, and delimited by an edge, formed by a second part 10 ₂ . The drops are deposited on each first part 10i, and extend as far as the edge delimiting said first part. Microcarriers are thus obtained as shown in FIGS. IB or IC, the shape of which corresponds to the shape of each first part 10i.

According to another possibility, the structuring of the first support 10 forms first parts 10i which are less hydrophobic than each second part IO2. The water repellency of a material is a concept known to those skilled in the art and can be determined by measuring the contact angle. The higher the latter, the more hydrophobic the material with respect to the solution forming the drop. The first parts 10i can be poorly hydrophobic or hydrophilic. Each second part 10 ₂ is preferably hydrophobic. By slightly hydrophobic is meant a part in which the contact angle Q is at least 5 ° or 10 ° smaller than the contact angle on the more hydrophobic part. According to this embodiment, each first part 10i is delimited by a second part 10 ₂ , so that during step 110, the drop spreads out along the first part on which it has been deposited. This variant allows better control of the shape of the microcarrier. It also makes it possible to obtain microcarriers whose shape is controlled by the structuring of the first support 10.

Experimental tests.

A first series of tests was carried out, the experimental conditions being described below: Distributor: Vermes MDV 3200 A metering valve equipped with a Vermes Nll-150 nozzle to form sol-gel microdrops. The dispenser was mounted on a Janome 200mm / 200mm triaxial robot, allowing the dispenser to move parallel to a first support 10.

First support 10: glass plate 200 mm × 170 mm, thickness 6 mm, hydrophobic treated beforehand by exposure to dichlorodimethylsilane.

Second support 20: identical to the first support.

Spacing s between the first support 10 and the second support: 140 µm. the spacing is obtained by arranging spacers 30 of the adhesive tape type. Precursor: Tetramethoxysilane 98% (Alfa Aesar).

Solvent: Isopropanol Technical (Alfa Aesar).

Catalyst: 6M HCl (Sigma Aldrich).

Compound of mineral functionalization: Hydroxyapatite Ca5 (OH) (PC> ₄ ) ₃ (Sigma Aldrich). Compound of organic functionalization: Bovine collagen type 1: 10mg / ml (Vornia

Ltd).

Was poured into a 50 ml beaker, 10 ml of tetramethoxysilane, kept under stirring at room temperature. A solution of 5 ml of deionized water was prepared in which 0.1 ml of HCl was added. The solution was poured slowly into the beaker containing the tetramethoxysilane (10 ml). The hydrolysis of tetramethoxysilane being exothermic, the water + HCl mixture is poured in at a rate of 2.5 ml / min. 20 ml of water were then added to the beaker. 3ml of hydroxyapatite solution was added, as well as 4ml of collagen solution. The hydroxyapatite solution was obtained by dissolving 200 mg of hydroxyapatite powder in 2.5 ml of deionized water and 0.5 ml of HCl, HCl facilitating dissolution of the hydroxyapatite powder.

The sol-gel solution, the preparation of which is described in the previous paragraph, was introduced into a syringe of the metering valve, the adjustment parameters of which are as follows: rising: 0.25 ms; falling: 0.35 ms; open time: 2 ms; needle lift: 30; delay: 7 ms; air pressure: 0.5 bar. These parameters are adjusted on a case-by-case basis by those skilled in the art.

A first hydrophobic glass plate, acting as the first support 10, was placed on the aforementioned robot, the latter being programmed to move parallel to the first glass plate, describing lines spaced apart from each other at a distance. distance of 3 mm. The drops are formed at a distance of 2 mm from the hydrophobic plate. The spacing between two adjacent drops, arranged on the same line, was 2 mm. The volume of each drop was 500 µl.

An adhesive film, acting as a spacer 30, was placed at the four corners of the first glass plate. The thickness of the adhesive wire was 0.14 mm.

The number of drops formed was 5000. After all the drops had been formed, a second hydrophobic glass plate, acting as a second support 20, was gently placed above the first glass plate, in contact with the film. adhesive, so as to flatten the drops, as described in connection with step 110.

The two glass plates, confining the drops in gelation / drying, were then placed in an oven at 50 ° C. The temperature was then maintained at 50 ° C and the pressure gradually lowered in 8 pressure stages, respectively -200 mBar, -400 mBar, - 500 mBar, - 600 mBar, - 700 mBar, - 800 mBar, - 900 mBar and - 970 mBar relative to atmospheric pressure. The duration of each stage was 15 minutes. Solid microcarriers were thus formed between the two glass plates, resulting from the gelation and the drying of the beads.

After drying, the plates were separated and the microcarriers were collected on a porous nylon filter, the pores measuring 400 µm in diameter. The filter, retaining the microcarriers was placed in a crystallizer, comprising isopropanol diluted to 50% (mass fraction) in deionized water, so as to carry out washing. The washing time was 2 hours. The washing was repeated three times. Following the washings, the filter retaining the microcarriers was dried in a study at 100 ° C. for 1 h 30 min.

The microcarriers resulting from the implementation of the process had a thickness of 70 μm and a diameter of 700 μm.

The microcarriers have been used for cell culture applications. For example, stem cells from human adipose tissue were cultured (ASC: Adipose-derived Stem Cells). FIG. 5 shows a photograph of culture microcarriers after 72 hours of static culture in a culture medium of the “mesenchymal stem cell growth medium 2” type (Promocell). The development of cells, on the microcarriers, in a monolayer was confirmed by microscopy.

During these tests, other advantages conferred by the microcarriers according to the invention were observed: a flat culture surface, suitable for the development of cells under the same conditions as in culture supports of the culture flask or dish type. usually used Petri dishes. These are different culture conditions from those resulting from ball-shaped microcarriers. Indeed, on the latter, the cultivation surface is strongly curved. On the ball-shaped microcarriers, cells develop forming aggregates. It is believed that cells tend to favor cell-to-cell bonding to the detriment of bonding with the bead surface. On microcarriers with flat surfaces, the cells develop forming a monolayer, because they favor bonds with the flat surface of the microcarrier. easy recovery of cells cultured on each microcarrier. The cells develop by forming a monolayer, which facilitates their detachment from the microcarriers. Separation of cells from each microcarrier can be facilitated by an enzyme, for example TrypLE (Microfischer). a recovery of individual (or unit) cells, which can be used to be reseeded for a new culture. a behavior, after culture, close to cells cultivated in culture flasks or in a Petri dish. Tests have shown that after recovery of the cells and their reseeding in a culture flask, the cells extend in a fibroblastic form, characteristic of mesenchymal stem cells. Their capacity for osteogenic, chondrogenic and adipogenic differentiation remains intact. The cells remain pluripotent stem cells, unlike what can be observed when the cells form clumps. In addition, a rate of sensescent cells similar to that obtained during 2D culture on conventional flasks was observed; a higher rate of viable cells than that obtained by using ball-shaped microcarriers, in particular due to better access to nutrients and oxygen in the culture medium; better productivity of the cells, because the latter are cultivated in the form of monolayers, without formation of agglomerate. This avoids the drawback of the contact inhibition described in connection with the prior art.

The invention may, without limitation, be implemented for applications related to cell culture.

Claims

1. A method of forming microcarriers (1), comprising: a) forming liquid drops (12) from a sol-gel solution (2); b) depositing the liquid drops on a first support (10); c) deformation of the drops deposited on the first support (10); d) solidification of the drops by gelation and drying, so as to form solid microcarriers; e) extracting the solidified microcarriers from the first support (10).

2. The method of claim 1, wherein the first support (10) is hydrophobic.

3. The method of claim 1 or claim 2, wherein during step c), the deformation of the drops is a flattening.

4. The method of claim 3, wherein step c) comprises a flattening of the drops (12) on the first support (10), the flattening being obtained spontaneously, during drying, during step d). .

5. Method according to any one of claims 1 to 3, wherein step c) comprises an application of a second support (20), preferably hydrophobic, on the drops (12), at a distance from the first support, such that the drops are interposed between the first support and the second support, the application of the second support resulting in a flattening of the drops between the two supports, the spacing (s) between the first support and the second support conditioning the thickness of the microcarriers formed during step d).

6. The method of claim 5, wherein the diameter of the drops formed during step a) and the spacing between the first support (10) and the second support (20) taken into account during step c). microcarriers resulting from step e) are adjusted as a function of a diameter or of a larger diagonal, parallel to the first support.

7. The method of claim 5 or claim 6, wherein step d) comprises an arrangement of an assembly (40), formed at least by the first support (10), the drops (12) during gelation. and the second support (20), in an oven, so as to promote drying.

8. The method of claim 7, wherein the temperature of the oven is between 30 ° C and 70 ° C.

9. The method of claim 7 or claim 8, wherein the oven is placed under partial vacuum.

10. Method according to any one of claims 5 to 9, wherein during step c), the spacing between the first support (10) and the second support (20) is between 30 μm and 5 mm.

11. Method according to any one of the preceding claims, wherein during step a), the drops (12) are formed at a distance (d) from the first support (10), the distance being less than 10 mm.

12. A method according to any one of claims 1 to 10 wherein during step a), the drops are formed in contact with the first support (10).

13. Method according to any one of the preceding claims, in which during step a), the drops (12) formed have a diameter of between 100 nm and 2 mm.

14. Method according to any one of the preceding claims, wherein the first support (10) comprises first parts (10i) and at least a second part (IO2), the first parts being less hydrophobic than each second part, each first part. part being bypassed by a second part, the second part forming a closed contour around said first part, so that during step a), the drops are deposited on each first part (10i), and extend, along each first part, up to the contour of said first part.

15. The method of claim 14, wherein:

- each second part (IO2) is hydrophobic and each first part (10i) is less hydrophobic than the second part which goes around it;

- or each second part is hydrophobic (IO2) and each first part (10i) is hydrophilic.

16. A method according to any one of claims 1 to 13, wherein the first support (10) comprises first parts (10i) and at least a second part (IO2), the first parts being hollow with respect to each second part, each first part being bypassed by a second part, said second part forming an outline, taking the form of a ridge, closed around said first part, so that when l 'step a), the drops are deposited on each first part (10i), and extend, along each first part, to the contour of said first part.

17. Process according to any one of the preceding claims, in which the sol-gel solution comprises a functionalization compound, conducive to the formation of a grafting agent on the surface of the microcarriers, the grafting agent promoting grafting with a predetermined biological species or a predetermined chemical species.

18. The method of claim 17, wherein the functionalizing compound is inorganic or organic.

19. The method of claim 17 or claim 18, wherein the sol-gel solution comprises different functionalization compounds.

20. Microcarrier (1), obtained by implementing a method according to any one of claims 1 to 19.

21. Microcarrier (1), according to claim 20, comprising a first flat surface (Si) and a second surface (S ₂ ), the first flat surface and the second surface being connected to each other by a lateral surface. (S ₃ ) forming a border of the microcarrier.

22. Microcarrier (1) according to claim 20, comprising a first flat surface (Si) and a second surface (S ₂ ) curved with respect to the first flat surface, the first flat surface and the second surface being connected to one another. the other by a lateral surface (S ₃ ) forming a border of the microcarrier.

23. Microcarrier according to any one of claims 20 to 22, in which:

- the diameter, or the largest diagonal, of the first flat surface is less than 5 mm or less than 1 mm, and greater than 5 pm,

- And / or the diameter, or the largest diagonal of the second flat surface is less than 5 mm or less than 1 mm, and greater than 5 μm.

24. Microcarrier according to claim 23, wherein the thickness of the microcarrier, corresponding to the distance between the first flat surface and the second surface, is less than 1 mm.

25. Use of a microcarrier according to any one of claims 19 to 24 for the culture of cells, excluding embryonic stem cells of human origin, the microcarrier being intended to be placed in suspension in a culture medium. .