Cellulose-based microfluidic device

Abstract

Cellulose-Based Microfluidic Device. The present invention relates to a method for preparing a microfluidic device essentially based on cellulose. More particularly, said method is an additive process consisting notably of encapsulating a microfluidic strip in a hydrophobic mixture comprising microfibrillated cellulose and at least one hydrophobic agent, preferably selected from alkyl ketene dimers (AKD), alkenyl succinic acid anhydrides, rosin resins, silicones and mixtures thereof, preferably alkyl ketene dimers. The invention also relates to a microfluidic device essentially based on cellulose. Figure for the abstract: none

Description

Title of the invention: Cellulose-based microfluidic device

[0001] The present invention relates to a method for preparing a microfluidic device essentially based on cellulose and an associated microfluidic device.

[0002] Point-of-care (POC) devices, particularly microfluidic strip devices, enable rapid and reliable testing close to the patient. They have proven especially effective in containing epidemics. To regulate these devices, the World Health Organization (WHO) established the ASSURED criteria, which can be broken down into eight criteria: Affordable, Sensitive, Specific, User-Friendly, Rapid and Robust, Equipment-Free, and Deliverable to End Users. Microfluidic strip devices (pPADs) meet this challenge well, particularly because they operate without an external system or pump, relying solely on capillary action.

[0003] However, current POC devices are mainly based on non-biodegradable and non-recyclable materials, such as the plastic cartridge that encapsulates the test. More generally, pollution from plastics and petroleum resources is a major problem we must address. The packaging sector contributes significantly to this pollution because plastic is an excellent material due to its good mechanical, barrier, and protective properties. To address this issue, the European Union has adopted legislation that aims to phase out single-use plastics by January 1, 2030, and to promote recycled plastics. Another alternative to address this problem is to replace the plastics used with other materials.

[0004] Cellulose is a biodegradable, non-toxic and abundant material derived from trees, plants such as cotton, algae or even agricultural waste. It is currently being studied as a promising base material to replace plastics, particularly in the field of packaging.

[0005] Cellulose films, particularly microfibrillated cellulose (MFC) films, can be produced by various processes such as sheet-fed printing or bar coating. Lavoine and colleagues published a very detailed review of the impact of these two processes on the mechanical and barrier properties of the film (Lavoine N, Desloges I, Khelifi B, Bras J (2014) Impact of different coating processes of microfibrillated cellulose on the mechanical and barrier properties of paper. J Mater Sci 49:2879-2893). However, these processes are limited to 2D deposition and are not compatible with 3D surfaces and objects.

[0006] MFC films are known to have very low permeability to air and, more specifically, to oxygen, which decreases with increasing film weight. This is mainly due to the film's inhomogeneity and the presence of pores in its structure. Regarding their properties with water, cellulosic materials are completely hydrophilic. Therefore, the cellulose must be modified to become hydrophobic.

[0007] The object of the invention is to provide a microfluidic device and, optionally, an associated microfluidic strip, essentially based on cellulose, while addressing all the aforementioned problems. The microfluidic device is a 3D object and must constitute a protective envelope for the microfluidic strip, having very low permeability to air and fluids, particularly water. The device must also exhibit good mechanical properties, particularly to ensure ease of handling by the user.

[0008] The Applicant has discovered, surprisingly, that this objective can be achieved by proposing a method for preparing a microfluidic device comprising the steps of: a. supply of a microfluidic strip or an ink suitable for the preparation of a microfluidic strip; b. supply of a hydrophobic mixture comprising microfibrillated cellulose and at least one hydrophobic agent, preferably chosen from alkyl ketene dimers (AKD), alkenylsuccinic acid anhydrides (ASA), rosin resins (Colophane), silicones and mixtures thereof, more preferably alkyl ketene dimers (AKD); c. supply of at least one fibrous support, preferably made of vegetable fibers, more preferably of cellulose fibers, animal fibers, synthetic fibers or a mixture thereof, more preferably of cellulose fibers; d. application, preferably by spraying, of the hydrophobic mixture previously suspended, preferably in water, onto a first fibrous support to obtain a first impregnated fibrous support; then e. deposition of the microfluidic strip onto at least part of a surface of the first impregnated fibrous support, or extrusion of the ink onto at least part of a surface of the first impregnated fibrous support to obtain an ink track preferably of 0.2 to 0.6 g dry mass per cm3, more preferably of 0.3 to 0.5 g dry mass per cm3; then f. Optionally, deposition of a second fibrous support so as to cover the ink strip or track and, optionally, at least part of a surface of the first impregnated fibrous support; then g. deposition, preferably by spraying, of the hydrophobic mixture previously suspended, preferably suspended in water, onto the ink track or the strip or the second fibrous support, and optionally at least a part of the first impregnated fibrous support to obtain an encapsulated ink track or a strip encapsulated in the hydrophobic mixture impregnated or not in a fibrous support; h. heat treatment of the encapsulated track or encapsulated strip, preferably under a compression of 5000 to 100000 Pa, at a temperature greater than or equal to the activation temperature of the hydrophobic agent, preferably at a temperature of 90 to 150°C, whereby the hydrophobic mixture forms a film, impregnated or not in a fibrous support, to obtain a strip encapsulated in a film of hydrophobic mixture; i. Optionally, ablation, preferably laser ablation, of at least two portions of the hydrophobic blend film, impregnated or not in a fibrous support, so as to obtain at least two through-holes configured to allow the deposition of a fluid directly onto the strip and / or the circulation of gas from the strip to the outside of the device.

[0009] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0010] [Fig-1] The [Fig. 1] represents the angle of contact of water on the substrate coated with MFC + AKD (12.4 ± 1.8 gm-2) as a function of the concentration of AKD 5%m (square), 1%m (triangle), 0.5%m (diamond), 0.1%m (circle) and 0.05%m (cross).

[0011] The term "microfluidic device" herein refers to any device described as a "rapid test," preferably a "rapid lateral flow test," for performing immunochromatographic tests. Such devices are described in particular in the article by Yager et al. (Yager P., Edwards T., Fu E., Helton K., Nelson K., R Tarn M., H Weigl B., (2006) Microfluidic diagnostic technologies for global public health. Nature 442412-418). These devices belong to the class of point-of-care (POC) devices. Such devices allow for the rapid detection of numerous biological parameters as well as pathogens. They enable the provision of a diagnostic test in a practical and immediate manner to the patient, at the time and place of care and / or according to the patient's needs. Such devices are well known to those skilled in the art and widely used: pregnancy tests, COVID tests, urine tests, etc.

[0012] These tests classically use dipsticks, generally nitrocellulose strips, as a support for the migration of the biological fluids to be tested, on which reagents for the substances of interest are immobilized.

[0013] This can be a one-dimensional test (“1D lateral-flow device” in English) or a three-dimensional test (“3D microfluidic devices” in English).

[0014] The term "microfluidic strip" herein refers to any so-called "rapid test strip," in particular any so-called "lateral flow" strip, suitable for performing immunochromatographic tests. Such a microfluidic strip is therefore suitable for the capillary diffusion of liquid within it. It is also suitable for immobilizing reagents for the substances of interest to be tested.

[0015] Method for preparing a microfluidic device

[0016] The process for preparing a microfluidic device as described above covers several embodiments.

[0017] A first embodiment of the process for preparing a microfluidic device is such that it comprises the successive steps of: a. provision of a microfluidic strip; b. supply of a hydrophobic mixture comprising microfibrillated cellulose and at least one hydrophobic agent; c. provision of at least one fibrous support; d. deposition, preferably by spraying, of the hydrophobic mixture previously suspended on a first fibrous support to obtain a first impregnated fibrous support; e. deposition of the microfluidic strip on at least part of a surface of the first impregnated fibrous support; f. Optionally, deposition of a second fibrous support so as to cover the strip and, optionally, at least part of a surface of the first impregnated fibrous support; then g. deposition, preferably by spraying, of the hydrophobic mixture previously suspended, preferably suspended in water, onto the strip or the second fibrous support, and optionally at least a part of the first impregnated fibrous support to obtain a strip encapsulated in the hydrophobic mixture impregnated or not in a fibrous support; h. heat treatment of the encapsulated strip at a temperature greater than or equal to the activation temperature of the hydrophobic agent, by which the hydrophobic mixture forms a film, impregnated or not in a fibrous support, to obtain a strip encapsulated in a film of hydrophobic mixture; i. Optionally, ablation, preferably laser ablation, of at least two parts of the hydrophobic mixing film, impregnated or not in a fibrous support, so as to obtain at least two through openings configured to allow the deposition of a fluid directly onto the strip and / or the circulation of gas from the strip to the outside of the device.

[0018] A second embodiment of the process for preparing a microfluidic device is such that it comprises the successive steps of: a. supply of an ink suitable for the preparation of microfluidic strips; b. supply of a hydrophobic mixture comprising microfibrillated cellulose and at least one hydrophobic agent, preferably chosen from alkyl ketene dimers (AKD), alkenylsuccinic acid anhydrides (ASA), rosin resins (Colophane), silicones and mixtures thereof, more preferably alkyl ketene dimers (AKD); c. supply of at least one fibrous support, preferably made of vegetable fibers, more preferably of cellulose fibers, animal fibers, synthetic fibers or a mixture thereof, more preferably of cellulose fibers; d. application, preferably by spraying, of the hydrophobic mixture previously suspended, preferably in water, onto a first fibrous support to obtain a first impregnated fibrous support; then e. extrusion of ink onto at least part of a surface of the first impregnated fibrous support to obtain an ink track preferably of 0.2 to 0.6 g dry mass per cm3, more preferably of 0.3 to 0.5 g dry mass per cm3; f. Optionally, deposition of a second fibrous support so as to cover the ink track and, optionally, at least part of a surface of the first impregnated fibrous support; then g. deposition, preferably by spraying, of the hydrophobic mixture previously suspended, preferably suspended in water, onto the ink track or the second fibrous support, and optionally at least a part of the first impregnated fibrous support to obtain an ink track encapsulated in the hydrophobic mixture impregnated or not in a fibrous support; h. heat treatment of the encapsulated track, preferably under a compression of 5000 to 100000 Pa, at a temperature greater than or equal to the activation temperature of the hydrophobic agent, preferably at a temperature of 90 to 150°C, whereby the hydrophobic mixture forms a film, impregnated or not in a fibrous support, to obtain a strip encapsulated in a film of hydrophobic mixture; i. Optionally, ablation, preferably laser ablation, of at least two parts of the hydrophobic mixing film, impregnated or not in a fibrous support, so as to obtain at least two through openings configured to allow the deposition of a fluid directly onto the strip and / or the circulation of gas from the strip to the outside of the device.

[0019] Another embodiment of the process for preparing a microfluidic device, compatible with the first or second preceding embodiment, is such that it comprises the successive steps of: a. supply of a microfluidic strip or an ink suitable for the preparation of a microfluidic strip; b. supply of a hydrophobic mixture comprising microfibrillated cellulose and at least one hydrophobic agent, preferably chosen from alkyl ketene dimers (AKD), alkenyl succinic acid anhydrides (ASA), rosin resins (Colophane), silicones and mixtures thereof, more preferably alkyl ketene dimers (AKD); c. supply of a fibrous support, preferably made of vegetable fibers, more preferably of cellulose fibers, animal fibers, synthetic fibers or a mixture thereof, more preferably of cellulose fibers; d. application, preferably by spraying, of the hydrophobic mixture previously suspended, preferably in water, onto a first fibrous support to obtain a first impregnated fibrous support; then e. deposition of the microfluidic strip onto at least part of a surface of the first impregnated fibrous support, or extrusion of the ink onto at least part of a surface of the first impregnated fibrous support to obtain an ink track preferably of 0.2 to 0.6 g dry mass per cm3, more preferably of 0.3 to 0.5 g dry mass per cm3; then f. application, preferably by spraying, of the hydrophobic mixture previously suspended, preferably suspended in water, on the ink track or strip, and optionally at least a portion of the first impregnated fibrous support to obtain an encapsulated ink track or a strip encapsulated in the hydrophobic mixture impregnated or not in a fibrous support; g. heat treatment of the encapsulated track or encapsulated strip, preferably under a compression of 5000 to 100000 Pa, at a temperature greater than or equal to the activation temperature of the hydrophobic agent, preferably at a temperature of 90 to 150°C, whereby the hydrophobic mixture forms a film, impregnated or not in a fibrous support, to obtain a strip encapsulated in a film of hydrophobic mixture; h. Optionally, ablation, preferably laser ablation, of at least two portions of the hydrophobic mixing film, impregnated or not in a fibrous support, so as to obtain at least two through-holes configured to allow the deposition of a fluid directly onto the strip and / or the circulation of gas from the strip to the outside of the device.

[0020] An embodiment of the method for preparing a microfluidic device, compatible with the first or second preceding embodiment, comprises the successive steps of: a. supply of a microfluidic strip or an ink suitable for the preparation of a microfluidic strip; b. supply of a hydrophobic mixture comprising microfibrillated cellulose and at least one hydrophobic agent, preferably chosen from alkyl ketene dimers (AKD), alkenyl succinic acid anhydrides (ASA), rosin resins (Colophane), silicones and mixtures thereof, more preferably alkyl ketene dimers (AKD); c. supply of at least two fibrous supports, preferably made of vegetable fibers, more preferably of cellulose fibers, animal fibers, synthetic fibers or a mixture thereof, more preferably of cellulose fibers; d. application, preferably by spraying, of the hydrophobic mixture previously suspended, preferably in water, onto a first fibrous support to obtain a first impregnated fibrous support; then e. deposition of the microfluidic strip onto at least part of a surface of the first impregnated fibrous support, or extrusion of ink onto at least part of a surface of the first impregnated fibrous support to obtain an ink track preferably of 0.2 to 0.6 g dry mass per cm3, more preferably 0.3 to 0.5 g dry mass per cm3; then f. deposition of a second fibrous support so as to cover the ink strip or track and, optionally, at least part of a surface of the first impregnated fibrous support; then g. deposition, preferably by spraying, of the hydrophobic mixture previously suspended, preferably suspended in water, onto the ink track or strip, the second fibrous support, and optionally at least a part of the first impregnated fibrous support to obtain an encapsulated ink track or a strip encapsulated in the hydrophobic mixture impregnated in a fibrous support; h. heat treatment of the encapsulated track or encapsulated strip, preferably under a compression of 5000 to 100000 Pa, at a temperature greater than or equal to the activation temperature of the hydrophobic agent, preferably at a temperature of 90 to 150°C, whereby the hydrophobic mixture forms a film, in a fibrous support, to obtain a strip encapsulated in a film of hydrophobic mixture; i. Optionally, ablation, preferably laser ablation, of at least two parts of the hydrophobic mixing film impregnated in a fibrous support so as to obtain at least two through openings configured to allow the deposition of a fluid directly onto the strip and / or the circulation of gas from the strip to the outside of the device.

[0021] Supply of a microfluidic strip or an ink suitable for the preparation of a microfluidic strip 1) First method of implementation

[0022] According to a first embodiment, any microfluidic strip can be used in the process according to the invention. This may include, in particular, conventional nitrocellulose-based strips, especially strips marketed under the names High Flow 120 and 135 (HF120 and HF135) by Merck Millipore (MA, USA). It may also include any other microfluidic strip, for example, composite-based strips.

[0023] Cellulose as described by Liu et al. (Liu W, Du H, Zhang M, et al (2020) Bacterial Cellulose-Based Composite Scaffolds for Biomedical Applications: A Review. ACS Sustainable Chem Eng 8:7536-7562) or Hilber and Jakoby (Hilber W, Jakoby B (2023) Solid State fluid transport and sensing based on printed and embedded cellulose-polymer composites: An alternative pathway to paper-based microfluidic devices. Micro and Nano Engineering 19:100183). 2) Second embodiment

[0024] According to a second embodiment, these may be strips prepared from an ink essentially based on cellulose. More particularly, said ink comprises, preferably, of: • microfibrillated cellulose; • microcrystalline cellulose; • silicon oxide particles; and • an aqueous phase. Microfibrillated Cellulose (MFC)

[0025] Microfibrillated cellulose (MFC) is a compound generally obtained from lignocellulosic fibers, for example, lignocellulosic fibers from wood or annual plants, or recycled pulp. MFC production is based on the release of the constituent elements of the secondary cell wall of lignocellulosic fibers by mechanical means coupled with enzymatic or chemical pretreatments. For example, this could involve a mechano-enzymatic pretreatment or TEMPO oxidation followed by a high-pressure homogenization treatment. MFC is therefore an abundant, bio-based, and easily recyclable compound.

[0026] According to one embodiment, the ink comprises, as a percentage of dry mass relative to the total dry mass of the ink, from 10% to 30%, preferably 15% to 25%, of microfibrillated cellulose.

[0027] According to one embodiment, the MFC is composed of particles with an average length of 0.5 pm to 50 pm, preferably from 1 pm to 20 pm, more preferably from 4 pm to 10 pm. Microcrystalline cellulose (MCC)

[0028] Microcrystalline cellulose (MCC) is a polysaccharide consisting of a chain of glucose molecules derived from cellulose. Microcrystalline cellulose is purified, partially depolymerized cellulose obtained, for example, by processing alpha cellulose derived from plant pulp, particularly wood pulp. MCC, like MFC, is therefore an abundant, bio-based, and biodegradable compound.

[0029] The MCC is in the form of particles or microparticles. According to a preferred mode, the MCC is in the form of particles having a length in their greatest dimension of 50 pm to 200 pm, preferably of 70 pm to 150 pm, more preferably of 80 pm to 110 pm. Silicon dioxide (SiO2) particles

[0030] Silicon dioxide, or silica, is a chemical compound with the formula SiO2. It consists of colorless solid particles. This compound is present in abundance in silicon dioxide is found in the natural environment and in various living organisms. It exists in its free state in different crystalline or amorphous forms, and chemically combined with other oxides in silicates, which are the main constituents of the Earth's crust and mantle. Whether free or combined, it represents 60.6% of the mass of the continental crust. It is particularly abundant in the form of quartz, notably in granites. As such, silicon dioxide is also an abundant, bio-based, and biodegradable compound.

[0031] According to one embodiment, the ink comprises silicon oxide particles having a median diameter D50 of 1 pm to 70 pm, preferably from 1 pm to 20 pm, and more preferably from 1 pm to 10 pm. The median diameter D50 is evaluated according to the laser diffraction method ISO 13320:2020.

[0032] According to an advantageous embodiment, the ink comprises, in percentages of dry mass relative to the total dry mass of the ink, from 70% to 90%, preferably 75% to 85%, of a mixture of microcrystalline cellulose and silicon oxide particles.

[0033] According to another embodiment compatible with the preceding embodiments, the ink is such that the ratio between the dry masses of microcrystalline cellulose and silicon oxide particles is 1 and 5, preferably 2 to 4, more preferably 2.5 to 3.5. Aqueous phase

[0034] The ink is an aqueous ink. As such, it comprises an aqueous phase containing water and, optionally, other solvents soluble or miscible in water. Preferably, the aqueous phase is chosen from water, distilled water, and deionized water.

[0035] Advantageously, the ink comprises, as a percentage by mass relative to the total mass of ink, from 75% to 95%, preferably 80% to 90% of aqueous phase.

[0036] According to one embodiment, the MFC is introduced in the form of a suspension into said aqueous phase. The MCC and SiO2 particles are then added, under stirring, to the aqueous suspension of MFC.

[0037] The ink thus has the advantages of being essentially, or even exclusively, composed of abundant, bio-based, and biodegradable compounds. Furthermore, it is easy to obtain and requires no special equipment for its application. The ink also has the advantage of exhibiting low shrinkage upon drying.

[0038] Method for preparing the microfluidic strip

[0039] The microfluidic strip preparation process comprises the steps of: • supply of ink as described above; • optionally, dilution of said ink by adding, as a percentage by mass relative to the total mass of ink, from 5% to 35%, preferably from 10% to 30%, more preferably from 15% to 25% of an aqueous and / or alcoholic solvent, preferably chosen from water, distilled water, deionized water, ethanol and mixtures thereof, to obtain a diluted ink; • molding or extrusion of said ink or of said ink diluted to obtain an ink track of 0.2 to 0.6 g dry mass per cm3, preferably of 0.3 to 0.5 g dry mass per cm3; • drying of the ink track to obtain a microfluidic strip.

[0040] The microfluidic strip preparation process is an additive manufacturing process. Thus, unlike the conventional microfluidic strip manufacturing process, it has the advantage of not inducing material loss, being easily automated, and producing strips of various geometries without a subtractive material step.

[0041] For the purposes of this description, "molding" means any process of depositing material into a mold that has the impression of the part to be obtained. The part, as defined in this description, is a strip. The deposition can, in particular, be carried out by pouring ink as described above into the impression or impressions of a suitable mold.

[0042] According to one embodiment, the mold is an acrylonitrile butadiene styrene (ABS) mold. ABS has the advantage of being stable at the temperatures and pressures of the drying stage(s).

[0043] Advantageously, the mold has several impressions. Preferably, each impression has a volume between 250 and 300 mm3, preferably on the order of 275 mm3.

[0044] According to such an embodiment, the strip is detached from the mold at the end of the drying step(s).

[0045] For the purposes of this invention, "extrusion" means any mechanical, or possibly thermomechanical, deposition process in which ink is forced through a die having a cross-section adapted to produce an ink track, said track having substantially the shape and dimensions of a microfluidic strip according to the invention. The ink extrudate is formed continuously or discontinuously. This process offers the advantage of a high production rate and good reproducibility.

[0046] Advantageously, the ink is extruded using a pneumatic needle valve, the needle constituting the die of the extrusion device. Preferably, this is a robotic extrusion device capable of controlling the opening and the The valve is closed to obtain a series of ink tracks of a specific volume. Preferably, extrusion is carried out under a pressure ranging from 2 to 7 bars, preferably from 3 to 6 bars.

[0047] According to one embodiment of the extrusion, the die is an ellipsoidal needle, advantageously said needle having a major and minor axis of 4.2 and 0.5 mm, respectively.

[0048] According to this embodiment, it is possible to vary the width and thickness of the ink tracks according to the speed of the robotic arm on which the die is mounted. Advantageously, the speed of the robotic arm varies between 150 and 350 mm / s and the extrusion flow rate is on the order of 1.6 g / s. Depending on the extrusion parameters, the width and thickness vary from 5 to 3 mm and from 0.8 to 0.4 mm, respectively.

[0049] For the purposes of the invention, "ink track" means the deposition of ink by extrusion prior to any drying stage capable of evaporating the aqueous phase and / or any solvent constituting the ink.

[0050] For the purposes of this invention, "drying" means any step capable of evaporating the aqueous phase and / or any solvent constituting the ink. This may involve a heat treatment carried out at atmospheric pressure or a heat treatment under pressure, for example under a pressure of 5000 to 100000 Pa, preferably 10000 to 50000 Pa.

[0051] The ink drying step can be carried out in one or more successive steps. Advantageously, the drying step is carried out in at least two successive steps: • a first drying stage being carried out at a temperature above 70°C, preferably from 70°C to 120°C, more preferably from 80°C to 100°C; and • at least one additional drying step being carried out under a pressure of 5000 to 100000 Pa, preferably 10000 to 50000 Pa, preferably at a temperature above 50°C, preferably 60°C to 120°C, more preferably 70°C to 90°C.

[0052] The additional step of drying under pressure has the advantage of directly obtaining a flat strip, that is to say substantially free from any curvature. 3) Third embodiment

[0053] According to a third embodiment, it may be a strip obtained from an ink such as described above in the second embodiment, said strip being prepared simultaneously with the microfluidic device according to the invention.

[0054] Thus, according to this embodiment, the process according to the invention further comprises a step of extruding the ink onto at least a part of a surface of a first impregnated fibrous support to obtain an ink track preferably of 0.2 to 0.6 g of dry mass per cm3, more preferably of 0.3 to 0.5 g of dry mass per cm3. Supply of a hydrophobic mixture

[0055] For the purposes of the invention, "hydrophobic mixture" means any mixture comprising microfibrillated cellulose and at least one hydrophobic agent, said mixture preferably being in the form of a suspension and / or a solution, more preferably an aqueous suspension and / or an aqueous solution.

[0056] For the purposes of the invention, the term "hydrophobic mixture film" means a hydrophobic mixture that has undergone heat treatment at a temperature greater than or equal to the activation temperature of the hydrophobic agent and such that the hydrophobic agent and the microfibrillated cellulose form, after heat treatment, a bonded hydrophobic mixture, i.e., a film exhibiting very low permeability to water, and possibly also to air. Advantageously, a bonded hydrophobic mixture film as defined in the invention has an air permeability, evaluated according to the method described in Example 2, of less than 0.5 pm / Pa.s, preferably less than 0.4 pm / Pa.s, and more preferably less than pm / Pa.s.Also advantageously, a hydrophobic mixture film related to the meaning of the invention has a contact angle with water, evaluated according to the method described in Example 2, greater than 90°, preferably greater than 100° and more preferably greater than 105° for a period of at least 1 minute, preferably at least 2 minutes.

[0057] The hydrophobic mixture comprises microfibrillated cellulose, preferably microfibrillated cellulose having an average length of 0.5 pm to 50 pm, preferably 1 pm to 20 pm, more preferably 4 pm to 10 pm.

[0058] The hydrophobic agent may be selected from among the conventional hydrophobic agents used in the paper industry. In particular, it may be selected from alkyl ketene dimers (AKD), alkenyl succinic acid anhydrides (ASA), rosin resins (Colophane), silicones, and mixtures thereof. Preferably, the hydrophobic agent comprises at least one alkyl ketene dimer (AKD), and preferably said hydrophobic agent is an alkyl ketene dimer (AKD).

[0059] Alkyl ketene dimers (AKDs) are conventionally used for sizing paper and cardboard, as well as for hydrophobicizing cellulose fibers. Products thus modified are distinguished in particular by greater mechanical strength and reduced penetration of water, inks, or any other fluid.

[0060] AKDs are characterized by hydrophobic alkyl groups extending from a beta-propiolactone ring. A specific example is derived from the dimerization of the ketene of stearic acid. This ketene can be generated by the pyrolysis of stearoyl chloride. AKDs react with the hydroxyl groups of cellulose via an esterification reaction. Esterification is competitive with the hydrolysis of AKD.

[0061] Alkenylsuccinic anhydride (ASA) is related to AKD. As with AKD, ASA reacts with the hydroxyl groups of cellulose to form an ester, anchoring the hydrophobic group to the surface. ASA can be prepared by the reaction of unsaturated hydrocarbons with maleic anhydride.

[0062] According to one embodiment, the hydrophobic mixture comprising more than 0.5% by mass, preferably from 0.7 to 2% by mass, more preferably from 0.9 to 1.1% by mass of hydrophobic agent relative to the dry mass of microfibrillated cellulose.

[0063] Advantageously, the hydrophobic mixture is deposited on the surface to be made non-permeable to water and / or air in the sense of the invention, at a rate of 10 to 40 g of dry mass of microfibrillated microcellulose per m2, preferably 12 to 30 g of dry mass of microfibrillated microcellulose per m2, more preferably 14 to 30 g of dry mass of microfibrillated microcellulose per m2.

[0064] The hydrophobic mixture, previously suspended, can be deposited by any means, preferably it is deposited by spraying.

[0065] The hydrophobic mixture can be deposited onto a fibrous support to obtain an impregnated fibrous support as described below. It can also be deposited onto any other compound or surface, for example, onto the ink track or the strip and / or a fibrous support. The hydrophobic mixture is therefore capable of forming, after heat treatment and subsequent cooling, a hydrophobic mixture film on its own, in the form of a bonded hydrophobic mixture, or a hydrophobic mixture film impregnated within a fibrous support. Provision of a fibrous support

[0066] The process for preparing a microfluidic device includes a step of supplying at least one fibrous support. The fibrous support may be woven or non-woven. Preferably, it is a non-woven support. The fibrous support is because it is porous, thus allowing its impregnation by the hydrophobic mixture, that is to say the penetration of the hydrophobic mixture into it.

[0067] For the purposes of the invention, "impregnated fibrous support" means a fibrous support comprising within it, that is to say inside the pores which constitute it, and possibly, or even advantageously on its surface, a hydrophobic mixture, that is to say a mixture of MFC and hydrophobic agent.

[0068] Advantageously, the fibrous support comprises, or is made up of, plant fibers, preferably cellulose fibers, animal fibers, synthetic fibers, or a mixture thereof. Preferably, the fibrous support is made up of cellulose fibers.

[0069] According to an advantageous embodiment, the basis weight of the fibrous support is from 5 to 20 g / m2, more preferably from 8 to 18 g / m2 and more preferably from 10 to 15 g / m2. Application of a hydrophobic mixture

[0070] Encapsulation of the ink track or strip

[0071] The steps for deposition of the hydrophobic mixture result in an ink track or a strip encapsulated within the hydrophobic mixture, whether or not it is impregnated with a fibrous support. In other words, the hydrophobic mixture is deposited so as to cover, alone or in combination with a fibrous support that it impregnates, all the external surfaces of the ink track or the strip. The ink track or the strip is thus encapsulated within said hydrophobic mixture, which, after being subjected to heat treatment, constitutes a water- and / or air-impermeable film as described above.

[0072] In addition to providing a barrier against water and / or air, the hydrophobic mixing film also imparts rigidity to the microfluidic device according to the invention. The presence of at least one fibrous support within at least a portion of the hydrophobic mixing film increases the rigidity of said microfluidic device.

[0073] Spray deposition is a non-contact technique that allows a composition, in this case a hydrophobic mixture, to be deposited onto any surface, whether flat (1D) or three-dimensional. Spray deposition is also a process that is easy to implement on an industrial-scale production line. First application of a hydrophobic mixture

[0074] Thus, the process of preparing a microfluidic device according to the invention includes a step of depositing, preferably by spraying, the hydrophobic mixture previously suspended, preferably suspended in water, onto a first fibrous support to obtain a first impregnated fibrous support. Second application of a hydrophobic mixture

[0075] The method for preparing a microfluidic device according to the invention further comprises a second deposition step as described below: deposition, preferably by spraying, of the hydrophobic mixture previously suspended, preferably suspended in water, onto the ink track, the strip, the first impregnated fibrous support and / or the second fibrous support to obtain an ink track or a strip encapsulated in the hydrophobic mixture impregnated or not in a fibrous support.

[0076] According to one embodiment, this second deposition step is preceded by a step of deposition of a second fibrous support so as to cover the ink strip or track and, optionally, at least part of a surface of the first impregnated fibrous support. This embodiment makes it possible to increase the rigidity of the microfluidic device obtained at the end of the process according to the invention. Thermal treatment

[0077] According to the process of the invention, the encapsulated track or strip is subjected to a treatment. This heat treatment not only removes the aqueous phase and / or solvents from the ink track and the hydrophobic mixture in suspension / solution, but also produces a hydrophobic mixture film with a barrier function against water and / or air. The heat treatment is therefore carried out at a temperature higher than the activation temperature of the hydrophobic binder. Depending on the hydrophobic agent, the activation mechanism of said hydrophobic agent, to form a bound hydrophobic mixture, can be a melting mechanism, a spreading-crosslinking mechanism, chemical modifications such as an esterification reaction, etc.

[0078] In a preferred embodiment, the heat treatment is carried out at a temperature of 90 to 150°C. This temperature range is particularly suitable when the hydrophobic agent is AKD. The temperature range can therefore be more specifically adapted depending on the hydrophobic agent selected.

[0079] Preferably the heat treatment is carried out under very slight compression, for example on the order of 5000 to 100000 Pa. The compression has the effect of allowing the melting of the hydrophobic mixture and the evaporation of the fluids without inducing substantial changes in the conformation of the device, in particular without inducing substantial changes in its flatness.

[0080] At the end of the manufacturing process of a microfluidic device according to the invention, the microfluidic strip is fully encapsulated by a hydrophobic mixture film, impregnated or not in a fibrous support, having in particular a barrier function to water and / or air.

[0081] Removal of at least two parts of the bound hydrophobic mixture

[0082] In order to allow the deposition of fluid on or within the microfluidic strip, in particular biological fluid to be analyzed, and / or the evacuation of the air encapsulated inside the device, at least two through openings may be provided in the hydrophobic mixing film, impregnated or not in a fibrous support.

[0083] The process therefore includes an optional ablation step, preferably laser ablation, of at least two portions of the hydrophobic mixture film, whether or not impregnated in a fibrous support, so as to obtain at least two through-holes configured to allow the deposition of a fluid directly onto the strip and / or the circulation of gas from the strip to the outside of the device. This optional ablation step is, of course, carried out on a dry device that has been stiffened by returning it to approximately ambient temperature.

[0084] Thus, the method for preparing a microfluidic device according to the invention has the particular advantage of simplifying the conventional manufacturing process for such devices and of combining all its steps on a single production line. Conventional manufacturing processes involve one production line for obtaining a strip, other lines for obtaining the components of the plastic cassette that make up the microfluidic device, and for assembling them with the strip. Microfluidic device

[0085] The invention finally relates to a microfluidic device obtained according to the process described above.

[0086] The microfluidic device according to the invention is essentially cellulose-based, readily available, and has little environmental impact because it is primarily composed of bio-based and biodegradable compounds. Furthermore, the device has a microfluidic strip encapsulation weight that is 10 times lower than that of a conventional plastic cartridge device, with the weight being approximately 5 g for a conventional plastic cartridge versus 0.5 g for a device according to the invention.

[0087] Throughout the description, including the claims, the expression "comprising one" shall be understood as synonymous with "comprising at least one", unless otherwise specified.

[0088] The expressions "between ... and ..." and "ranging from ... to ..." should be understood inclusive of bounds, unless otherwise specified.

[0089] In the description and examples, unless otherwise stated, percentages are percentages by mass. Temperature is expressed in degrees Celsius unless otherwise stated, and pressure is atmospheric pressure unless otherwise stated.

[0090] The invention is illustrated in more detail by the non-limiting examples presented below. Examples

[0091] Example 1: Preparation of a microfluidic device according to the invention

[0092] The objective is to manufacture a barrier coating by spraying a mixture of MFC and a hydrophobic agent, and to study the surface, air permeability, and mechanical properties. The MFC will be made hydrophobic by the use of AKD (hydrophobic agent), and the surface contact angle will be measured. 1 / Materials and methods Chemicals

[0093] Microfibrillated cellulose (MFC) was supplied by Weidmann in the form of an aqueous suspension at a mass concentration of 3%. This MFC is obtained by mechanical processing. The average length of the microfibrils is 9.4 pm.

[0094] The alkyl ketene dimer (AKD) is Aquapel J220 Alkaline Size supplied by Solenis. It is presented as an emulsion at a concentration of 20% which must be dried at 105°C for 10 minutes to indicate the final gluing.

[0095] The porous support onto which the MFC / AKD mixture is sprayed is a gauze made of plant fibers. It is a wet-resistant paper of the tea filter type (PDM Industries, FILTEA).

[0096] Formulation of the aqueous encapsulation composition

[0097] MFC is diluted to a concentration of 2% by mass by adding deionized water and then the suspension is homogenized with an ultra turrax at 7000 rotations per minute for 10 minutes.

[0098] The aqueous encapsulation composition is obtained by adding the AKD emulsion to the MFC suspension during the homogenization step. The amount added is calculated as a mass of active material based on the mass of dried cellulose. This concentration varies between 0.05% and 5%. Sample production

[0099] Before the spraying step, the Filtea paper (non-woven fibrous support) is loaded into a sheet former and then moistened. The aqueous encapsulation composition is placed in a 1-liter pressurized tank, supplied by Polydispensing (France), connected to an SV1000SS Adjustable Stainless-Steel Spray Dispensing Valve supplied by Fisnar (WI, USA) and installed on the robot's axis arm. The quantity of the aqueous encapsulation composition to be sprayed onto the Filtea paper is determined by taking into account the manufacturing parameters and the 2% concentration of the MFC. This is the mass of MFC per unit area.

[0100] Once the aqueous encapsulation composition has been sprayed, excess water is removed by vacuum suction for 5 minutes. The Filtea paper impregnated with the aqueous encapsulation composition is then placed inside a manual high-speed kothen sheet former (supplied by Savoie Maintenance Service, France) at 85°C for 2 minutes and then for an additional 10 minutes. Characterization of impregnated substrates

[0101] To qualify and quantify the impact of the MFC spray coating on the substrate sheets, several physical characterizations are performed. The base weight of the MFC is determined by a thickness measurement using a mechanical micrometer (MI20, Adamel Lhomargy, France) and the weight using a precision balance. To qualify the homogeneity of the coating, the theoretical thickness for a specific base weight can be determined using the following equation:

[0102] [Math.l] bwMFC

[0103] where es is the substrate thickness (m), bw^rc is the base weight of the MFC coating (g.m2) and pFMC is the MFC density equal to 1.5 g.cm3. Air permeability is measured as an airflow through a 10 cm2 surface under 10.0 kPa with a Bendsten tester, Noviprofibre, France. It is expressed in cm3 / (m2.Pa.s). It is expressed using the AFNOR permeability index:

[0104] [Math.2] *AF~ S*AP

[0105] where Q is the air flow through the sample (cm3 / s), S is the sample surface area (m2) and AP is the applied pressure drop (Pa).

[0106] Surface characterization is performed by SEM observation, 1x00 magnification (Quanta 200, FEI, USA) and surface roughness is measured with an optical profilometer (Infinity Focus, Alicona, Austria) on a 1.4 x 1.1 mm square. Roughness values ​​are determined as the average height of the selected area on 1.42 x 1.08 mm sample surfaces.

[0107] The contact angle of water on the AKD-treated MFC-coated substrate is measured using the OCA contact angle system, provided by the APOLLO instrument (France). The measurement is performed for 120 seconds at a frequency of 6 frames per second. Mechanical characterization

[0108] Mechanical characterizations are performed with an Instron 3365 dynamometer (supplied by Instron, ILL, USA) on a 100x15 mm strain gauge. The samples are stretched at a speed of 10 mm / min. II / Results Surface characterization

[0109] Table 2 presents the results obtained in terms of theoretical thickness and measured thickness of the substrate + MFC / AKD coating as a function of the base weight of the sprayed MFC coating (G in g / m2).

[0110] [Tableaux2] G (g / m²) Theoretical thickness (mm) Measured thickness (mm) 4.3 0.052 0.051 +0.001 5.2 0.053 0.052 +0.001 11 0.053 0.057 +0.001 12.4 0.058 0.059 +0.001 24.1 0.063 0.066 +0.001 30 0.068 0.070 +0.001 36.8 0.073 0.076 +0.011

[0111] The results show that the spray coating of MFC / AKD allows to obtain a homogeneous sheet of MFC-Filtea with an MFC base weight between 5 and 35 g / m². First, the theoretical thickness is greater than the measured thickness due to the topography of the Filtea substrate. The coating needs to fill the pores of the substrate, which prevents the creation of a homogeneous MFC / AKD layer. Second, the observation is reversed because the coating is not perfectly flat, even though the surface roughness decreases. Nevertheless, there is good agreement between the theoretical and measured thicknesses. The measured results demonstrate that spray coating MFC / AKD onto a porous substrate like Filtea is a reliable and reproducible process.

[0112] Table 3 presents the results of the roughness analyses as a function of the base weight of the sprayed MFC coating (G in g / m2).

[0113] [Tables3] Measured Gmfc (g / m2) Roughness (pm) 4.3 7.23 +1.78 5.2 5.99 +1.28 11 4.11 +1.19 12.4 4.40 +1.05 24.1 3.22 + 0.34 36.8 3.79 + 0.35

[0114] Roughness measurement confirms the homogenization of the MFC / AKD coating with increasing base weight. Thus, between 5 and 15 g / m² of sprayed coating, the roughness decreases from 7 to 4 pm. Subsequently, the roughness stabilizes around 3.5 pm but with a significant decrease in the standard deviation.

[0115] These results were confirmed by SEM observations. Permeability characterization

[0116] The results of the permeability test are presented in Table 4.

[0117] [Tables4] GMfc measured (g / m2) Permeability (pm / P as) 5.3 6.72 + 2.09 6.9 4.87 + 0.54 8.5 3.31 + 0.77 11.0 2.35 + 0.61 12.4 0.29 + 0.19 14.0 0.18 + 0.11 24.1 0.08 + 0.03 30.0 0.04 + 0.02 36.8 0.01 + 0.01

[0118] The air permeability of MFC / AKD-impregnated sheets is strongly affected by the homogeneity and thickness of the MFC / AKD layer. Indeed, a significant decrease in permeability can be observed between a porous medium, 6.72 ± 2.08 pm / Pa·s, and 0.29 ± 0.19 pm / Pa·s, corresponding respectively to 0.5 and 12 g / m² of MFC coated on the surface. The formed MFC / AKD layer fills the pores of the substrate, which induces a decrease in permeability until a homogeneous closed surface is obtained. This is also observed with the decrease in the value of the coefficient associated with the air permeability measurement, as the better the homogeneity, the better the repeatability of the measurement. Beyond 12 g.m2, air permeability continues to decrease slightly, going from 0.18 ± 0.11 pm / Pa.s to 0.01 ± 0.07 pm / Pa.s, which corresponds to 14 and 37 g.m2 of MFC / AKD.Since the surface is already sealed, increasing the layer thickness does not significantly affect air permeability.

[0119] Based on the above observations, tests modifying MFCs with AKD were carried out for a breaking strength between 12 and 14 g.m² and 12.4 ± 1.8 g.m², respectively. The results are shown in [Fig. 1] with the variation of the contact angle as a function of time for different added quantities of active ingredient as a function of the dried mass of MFC. A significant difference can be observed between 0.1%m or less and 0.5%m or more. In the first case, the measured contact angle is between 70 and 75° and decreases over 2 minutes. The smaller the quantity of AKD added, the faster the decrease over 2 minutes. There is slow impregnation of the water droplet inside the impregnated paper. This means that all the MFCs are treated with AKD. However, without AKD treatment of the MFC, impregnation is instantaneous.No measurement can be taken because the droplet is absorbed by the paper while still connected to the syringe nozzle. In comparison, with an AKD concentration of 0.5% w / w or higher, the contact angle is measured between 110 and 120°. Furthermore, the measurement remains stable for 2 minutes. Mechanical characterization

[0120] MFCs can also be used to improve the mechanical properties of a sheet. As shown in Table 5, the Young's modulus increases with increasing MFC coating thickness from 0.5 to 4 GPa, corresponding respectively to the substrate alone and to 36 g / m² coated with MFC.

[0121] [Tables5] Measured GMfc (g / m2) Young's modulus (G Pa) 0 0.42 + 0.05 5.3 0.7 + 0.31 11 1.29 + 0.17 14 2.26 + 0.20 24.1 2.93 + 0.33 36.8 3.87 + 0.33

[0122] A discrepancy can be observed in the measurement between 0 to 10 g / m² and 15 to 36 g / m². This observation is consistent with the previous one concerning the homogeneity of the surface. Indeed, the substrate must be filled, which induces weaknesses in the structure and then points of failure.

[0123] As with Young's modulus, the stress at break increases with increasing basic weight of the MFCs as shown in the results in Table 6.

[0124] [Tableauxô] Measured Gmfc (g / m²) Tensile strength (MPa) 0 7.1 + 0.1 5.3 14.6 + 5.9 11 19.5 + 3.1 14 29.3 + 5.2 24.1 45.0 + 6.4 36.8 50.0 + 4.5

[0125] The evolution tends to be linear between 5 and 30 g / m2. Then, the evolution tends to stabilize around 50 MPa. Conclusion

[0126] The feasibility of encapsulating air and water by a spray-applied coating of an MFC / AKD mixture has been demonstrated. The ideal configuration is a coating of 15 g / m² by surface mass of MFC and 1% AKD by dry mass of MFC.

[0127] It has also been demonstrated that it was possible to obtain a microfluidic device essentially based on cellulose according to the above-described process by reducing the mass of the encapsulation of a microfluidic strip by a factor of 10, going from 5 g for a conventional plastic cartridge to 0.5 g by means of a device according to the invention.

[0128] Example 2: Microfluidic test using the device according to the invention Materials and methods

[0129] The following compounds were used in the preparation of the ink:

[0130] _ microfibrillated cellulose (MFC) supplied by Weidmann (CH) in the form of Aqueous suspension at 3% weight concentration. These MFCs are obtained by mechanical processing. The average microfibril length is 9.4 pm.

[0131] _ microcrystalline cellulose (MCC) in the form of ground cellulose powder of which The largest particle size varies from +60 mesh (250 pm) to +200 mesh (74 pm)

[0132] _ SiO2 microparticles in the form of spheres with a diameter D50 4 pm evaluated according to the ISO 13320:2020 laser diffraction method, provided by Sigma-Aldrich (Saint Louis, Missouri, USA).

[0133] Strips obtained from an ink comprising, as percentages by dry mass relative to the total dry mass of the ink, 20% MFC, 60% MCC and 20% SiO2, then diluted in water by adding 20% ​​water by mass relative to the total mass of ink were integrated into microfluidic devices according to the invention.

[0134] To achieve this, the strip is encapsulated using a spray coating of MFC treated with an alkyl ketene dimer (AKD). The MFCs are the same as those supplied by Weidmann (Switzerland) and used to manufacture the strips. The AKD is Aquapel J220 Alkaline Size supplied by Solenis. It is in the form of an emulsion at a concentration of 20%.

[0135] AKD is added to the MFC suspension at a rate of 1% by mass of dry MFC and sprayed at 2% concentration to reach 15 g / m2 on each face.

[0136] The porous support onto which the MFC / AKD mixture is sprayed is a gauze made of plant fibers. It is a wet-resistant paper of the tea filter type (PDM Industries, FILTEA).

[0137] Two openings are then made by laser engraving in one of the coating faces (laser supplied by Keyence, France). The selected laser power is 45% and the speed is between 600 and 900 mm / s. Such laser parameters make it possible to ablate only the MFC / AKD coating without damaging the strip.

[0138] For better visual observation, the liquid test is a deposit of water and bromonaphthalene using a Pasteur pipette in one of the two openings. Results

[0139] The feasibility of manufacturing microfluidic devices from the strips according to the invention used in previous sections B and C (part "results") and encapsulated according to section E of the part "Materials and method" has been confirmed. It is thus possible to encapsulate the strip in order to avoid any contact between external contamination and the fluid.

[0140] The test liquid combined with bromonaphthalene was deposited in a first opening of the coating layer located above one end of the test strip. The mixture migrated towards the second opening of the coating layer, which allows air to escape, as it progressed by capillary action within the strip. The deposit spread only onto the strip and not onto the encapsulation. Furthermore, colored droplets were deposited on the top of the encapsulation; these droplets did not penetrate the encapsulation, indicating that the strip was properly sealed because the hydrophobic barrier was effective.

Claims

1. Demands A method for preparing a microfluidic device comprising the steps of: a) supply of a microfluidic strip or an ink suitable for the preparation of a microfluidic strip; b) supply of a hydrophobic mixture comprising microfibrillated cellulose and at least one hydrophobic agent, preferably selected from alkyl ketene dimers (AKD), alkenyl succinic acid anhydrides (ASA), rosin resins (Colophane), silicones and mixtures thereof, more preferably alkyl ketene dimers (AKD); (c) supply of at least one fibrous support, preferably made of vegetable fibers, more preferably of cellulose fibers, animal fibers, synthetic fibers or a mixture thereof, more preferably of cellulose fibers; d) application, preferably by spraying, of the hydrophobic mixture previously suspended, preferably in water, onto a first fibrous support to obtain a first impregnated fibrous support; then e) deposition of the microfluidic strip onto at least part of a surface of the first impregnated fibrous support, or extrusion of the ink onto at least part of a surface of the first impregnated fibrous support to obtain an ink track preferably of 0.2 to 0.6 g dry mass per cm3, more preferably of 0.3 to 0.5 g dry mass per cm3; then f) optionally, deposition of a second fibrous support so as to cover the strip or the ink track and, optionally, at least part of a surface of the first impregnated fibrous support; then (g) deposition, preferably by spraying, of the hydrophobic mixture previously suspended, preferably suspended in water, onto the ink track or the strip or the second fibrous support, and optionally at least a part of the first impregnated fibrous support to obtain an encapsulated ink track or a strip encapsulated in the hydrophobic mixture impregnated or not in a fibrous support; (h) heat treatment of the encapsulated track or encapsulated strip, preferably under a compression of 5000 to 100000 Pa, at a temperature greater than or equal to the activation temperature of the hydrophobic agent, preferably at a temperature of 90 to 150°C, whereby the hydrophobic mixture forms a film, impregnated or not in a fibrous support, to obtain a strip encapsulated in a film of hydrophobic mixture; (i) optionally, ablation, preferably laser ablation, of at least two parts of the hydrophobic mixture film, impregnated or not in a fibrous support, so as to obtain at least two through openings configured to permit the deposition of a fluid directly onto the strip and / or the circulation of gas from the strip to the outside of the device.

2. A method for preparing a microfluidic device according to claim 1, wherein the hydrophobic mixture is deposited at a rate of 10 to 40 g of dry mass of microfibrillated microcellulose per m2, preferably 12 to 30 g of dry mass of microfibrillated microcellulose per m2, more preferably 14 to 30 g of dry mass of microfibrillated microcellulose per m2.

3. A method for preparing a microfluidic device according to claim 1 or 2, wherein the hydrophobic mixture comprises more than 0.5% by mass, preferably from 0.7 to 2% by mass, more preferably from 0.9 to 1.1% by mass of hydrophobic agent relative to the dry mass of microfibrillated cellulose.

4. A method for preparing a microfluidic device according to any one of the preceding claims, wherein the microfibrillated cellulose has an average length of 0.5 pm to 50 pm, preferably 1 pm to 20 pm, more preferably 4 pm to 10 pm.

5. A method for preparing a microfluidic device according to any one of the preceding claims, wherein the fibrous support has a basis weight of 5 to 20 g / m2, preferably 8 to 18 g / m2 and, more preferably, 10 to 15 g / m2.

6. A method for preparing a microfluidic device according to any one of the preceding claims, wherein the ink comprises: - microfibrillated cellulose, preferably microfibrillated cellulose having an average length of 0.5 pm to 50 pm, preferably 1 pm to 20 pm, more preferably 4 pm to 10 pm; - microcrystalline cellulose, preferably microcrystalline cellulose in the form of particles having a length in their greatest dimension of 50 pm to 200 pm, preferably 70 pm to 150 pm, more preferably 80 pm to 110 pm; _ silicon oxide particles, preferably silicon oxide particles having a median diameter D50 of 1 pm to 70 pm, preferably from 1 pm to 20 pm, and more preferably from 1 pm to 10 pm; and _ an aqueous phase, preferably chosen from water, distilled water and deionized water.

7. A method for preparing a microfluidic device according to claim 6, wherein the ink comprises, in percentages of dry mass relative to the total dry mass of the ink, - from 10% to 30%, preferably 15% to 25%, of microfibrillated cellulose; - from 70% to 90%, preferably 75% to 85%, of a mixture of microcrystalline cellulose and silicon oxide particles.

8. A method for preparing a microfluidic device according to any one of claims 6 or 7, wherein the ink comprises, as a percentage by mass relative to the total mass of ink, from 75% to 95%, preferably 80% to 90% of aqueous phase.

9. A method for preparing a microfluidic device according to any one of claims 6 to 8, wherein the ink has a ratio between the dry masses of microcrystalline cellulose and silicon oxide particles of 1 and 5, preferably of 2 to 4, more preferably of 2.5 to 3.

5.

10. Microfluidic device obtained according to the method of any one of the preceding claims

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