Cellulose-based strip for microfluidic devices

Abstract

Cellulose-based strip for microfluidic devices. The present invention relates to an ink for the additive manufacturing of microfluidic strips comprising microfibrillated cellulose, microcrystalline cellulose, silicon oxide particles, and an aqueous phase. It also relates to a method for preparing a microfluidic strip and an associated microfluidic strip. Finally, it relates to a method for preparing a microfluidic device and an associated microfluidic device. Figure for abstract: none

Description

Title of the invention: Cellulose-based strip for microfluidic devices

[0001] The present invention relates to an ink essentially based on cellulose for the additive manufacturing of microfluidic strips. It also relates to a process for preparing microfluidic strips 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 forces within the strip itself.

[0003] However, current devices generally use nitrocellulose (NC) strips. Nitrocellulose is produced by the esterification of cellulose, such as cotton linters, with a mixture of sulfuric and nitric acids. Nitrocellulose is manufactured in roll form, which then requires cutting, processing, and modification to fit the design of the pPAD. Several unit operations are used, such as cutting and thermoforming, to modify the structure of the nitrocellulose sheet or to make it hydrophobic to manage fluid passage.The major drawbacks of nitrocellulose are therefore due to a complex and polluting manufacturing process, the need to use a surfactant to increase its wettability, and the use of a subtractive process to produce pPAD (cutting and removing material from a sheet produced in roll form to obtain microfluidic strips of the desired size and shape).

[0004] In this context, new microfluidic strip design strategies have been proposed to overcome the aforementioned drawbacks. In particular, 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) and 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) have proposed the development of composites from cellulose suitable for the manufacture of microfluidic strips by an additive process such as 3D printing.

[0005] This manufacturing method makes it possible to produce a pPAD with a chosen design without consuming additional raw materials. Furthermore, the composites comprise a cellulosic matrix, cellulose being a natural and abundant polymer. Such a matrix, however, needs to be combined with other compounds such as micro- and / or nanoparticles to enhance its structural and mechanical properties for the intended use. The micro- and / or nanoparticles also allow for the management of fluid flow within the microfluidic strip by influencing, in particular, the porosity and density variation within the matrix.

[0006] These approaches, while promising, nevertheless require improvement by proposing an optimized composite, in the form of an ink composition, that addresses all the issues mentioned above. In particular, the ink must be easy to obtain and composed of environmentally friendly, ideally biodegradable, elements. The ink must also allow for the additive manufacturing of microfluidic strips with properties equivalent to those of conventional nitrocellulose strips, so that they can be easily adapted to any pPAD-type device. Finally, there is a need for pPAD-type devices themselves, in their entirety, that are more environmentally friendly and easy to manufacture.

[0007] The aim of the invention is then to propose an ink composition, a microfluidic strip and a microfluidic device that addresses all of the aforementioned problems.

[0008] The Applicant has discovered in a surprising way that this objective can be achieved with an ink composition essentially based on cellulose and silica (SiO2).

[0009] The present invention therefore relates to an ink for the additive manufacturing of microfluidic strips comprising microfibrillated cellulose, microcrystalline cellulose, and silicon dioxide particles. Such an ink, composed of environmentally friendly compounds, readily available and requiring no complex and / or polluting processes for its preparation, is easy to formulate and then to use in an additive process for manufacturing, in particular, microfluidic strips. The microfluidic strips thus obtained also exhibit excellent structural, mechanical, and fluidic properties.

[0010] The invention further relates to a method for preparing a microfluidic strip comprising the steps: • supply of an ink according to the invention; • 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 to obtain a diluted ink; • molding or extrusion of said ink or of said diluted ink to obtain an ink track; • drying the ink track to obtain a microfluidic strip.

[0011] The invention also relates to a method for preparing a microfluidic device comprising the steps of: a. supply of an ink or a strip according to the invention; b. supply of a hydrophobic mixture comprising microfibrillated cellulose and at least one hydrophobic agent, selected from alkyl ketene dimers (AKD), alkenyl succinic acid anhydrides (ASA), rosin resins (Colophane), silicones and mixtures thereof, preferably alkyl ketene dimers (AKD); c. provision of at least one fibrous support; d. application, preferably by spraying, of the hydrophobic mixture previously suspended 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, or deposition of the microfluidic strip onto at least part of a surface of the first impregnated fibrous support; 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 on the ink track or strip or second fibrous support, and optionally on at least 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 compression of 5,000 to 100,000 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 hydrophobic mixture film; 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 thus obtained.

[0012] The invention finally relates to a microfluidic strip obtained from an ink according to the invention and an associated microfluidic device.

[0013] 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:

[0014] [Fig-1] Fig. 1 presents the results of the capillary rise test for the MFC / MCC or MFC / SiO2 strips and the HF135 reference (square) at 30 seconds.

[0015] [Fig.2] Fig.2 presents the results of the capillary rise test for the MFC / MCC or MFC / SiO2 or MFC / MCC / SiO2 strips with 20% MFC and the HF135 reference (square) at 30 seconds.

[0016] [Fig.3] Fig.3 presents the results of the capillary rise test for the strips obtained from an MFC / MCC / SiO2 ink containing 20% ​​MFC and diluted with 20% water or ethanol

[0017] [Fig.4] Fig.4 presents the results of the capillary rise test for the strips obtained from diluted ink according to the invention and obtained by molding or extrusion.

[0018] [Fig.5] Fig.5 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).

[0019] The term "microfluidic device" herein refers to any device described as a "rapid test," preferably a "lateral flow rapid 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.

[0020] These tests classically use, as a support for the migration of the biological fluids to be tested, strips (“dipsticks” in English), generally nitrocellulose strips, on which reagents for the substances of interest are immobilized.

[0021] This can be a one-dimensional test (“1D lateral-flow device” in English) or a three-dimensional test (“3D microfluidic devices” in English).

[0022] 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.

[0023] The microfluidic strip according to the invention can be used in any type of device as described above, as well as in a device according to the invention. Ink composition

[0024] The ink for the additive manufacturing of microfluidic strips according to the invention is essentially cellulose-based. It preferably comprises: • microfibrillated cellulose; and • microcrystalline cellulose; and • 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, readily available, and biodegradable compound.

[0026] According to one embodiment, the ink according to the invention 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 of the invention, 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, which is obtained from plant pulp, particularly wood pulp. MCC, like MFC, is therefore an abundant, bio-based, readily available, and biodegradable compound.

[0029] The MCC is in the form of particles or microparticles. According to a preferred embodiment of the present invention, the MCC is in the form of particles having a length in their longest dimension of 50 pm to 200 pm, preferably from 70 pm to 150 pm, more preferably from 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 abundant 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. 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 of the present invention, 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 to 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] According to one embodiment, the ink is used in a microfluidic strip preparation process. Preferably, it is used in this process in a diluted state in any suitable solvent. Thus, advantageously, for the manufacture of strips according to the invention, said ink is diluted by adding, as a percentage by mass relative to the total mass of ink, from 5% to 35%, preferably from 10% to 30%, and more preferably from 15% to 25% of a solvent. Preferably, the solvent is an aqueous and / or alcoholic solvent, preferably chosen from water, distilled water, deionized water, ethanol, and mixtures thereof.

[0038] The ink according to the invention 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 specific equipment for its application. The ink according to the invention also has the advantage of exhibiting low shrinkage upon drying.

[0039] Method for preparing a microfluidic strip

[0040] The ink according to the invention is particularly suitable for the manufacture of microfluidic strips.

[0041] The microfluidic strip preparation process according to the invention 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 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; • Drying the ink track to obtain a microfluidic strip.

[0042] The microfluidic strip preparation process according to the invention is an additive manufacturing process. Thus, unlike the conventional microfluidic strip manufacturing process, it has the advantage of not inducing any loss of material, to be easily automated, to allow the production of strips of various geometries without a subtractive step of material.

[0043] For the purposes of this invention, "molding" means any process of depositing ink into a mold that has the impression of the part to be obtained. The part in this invention is a strip. The deposition can, in particular, be carried out by pouring ink according to the invention into the impression or impressions of a suitable mold.

[0044] 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).

[0045] Advantageously, the mold has several impressions which may be identical or different. Preferably, each impression has a volume between 250 and 300 mm3, preferably on the order of 275 mm3.

[0046] According to such an embodiment, the strip according to the invention is detached from the mold at the end of the drying step(s).

[0047] 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 the desired microfluidic strip. The ink extrudate is formed continuously or discontinuously. This process offers the advantage of a high production rate and good reproducibility.

[0048] Advantageously, the ink is extruded using a pneumatic needle valve, the needle forming the die of the extrusion device. Preferably, this is a robotic extrusion device capable of controlling the opening and closing of the valve to obtain a series of ink tracks of a determined volume. Preferably, the extrusion is carried out under a pressure ranging from 2 to 7 bar, preferably from 3 to 6 bar.

[0049] According to one embodiment of the extrusion, the die is an ellipsoidal needle, advantageously said needle has a major and minor axis of 4.2 and 0.5 mm, respectively.

[0050] 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.

[0051] 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.

[0052] 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 5,000 to 100,000 Pa, preferably 10,000 to 50,000 Pa.

[0053] 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.

[0054] 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. Microfluidic strip

[0055] The invention also relates to a microfluidic strip obtained according to the above-described process.

[0056] The microfluidic strip is particularly suitable for the capillary diffusion of any fluid within it, in particular of a fluid such as water, migration buffers classically used with microfluidic devices, in particular buffers chosen from sodium saline citrate (SSC) buffers, sodium dodecyl sulfate (SDS) buffers, urea and their mixtures, biological fluids.

[0057] The strip according to the invention comprises, as a percentage of dry mass relative to the total dry mass of the ink, 10% to 30%, preferably 15% to 25%, of microfibrillated cellulose; and 70% to 90%, preferably 75% to 85%, of a mixture of microcrystalline cellulose and silicon dioxide particles. Advantageously, said strip has a ratio between the dry masses of microcrystalline cellulose and silicon dioxide particles of 1 to 5, preferably 2 to 4, and more preferably 2.5 to 3.5.

[0058] According to one embodiment, the strip according to the invention has a density of 0.2 to 0.6 g of dry mass per cm3, preferably of 0.3 to 0.5 g of dry mass per cm3.

[0059] The strip according to the invention presents an excellent compromise of properties, particularly in terms of flexibility, apparent or open porosity and capillary rise.

[0060] The strip according to the invention advantageously has an apparent porosity, evaluated according to the method described in Example 1 below, of 0.60 to 0.85, preferably of 0.75 to 0.85.

[0061] The strip according to the invention advantageously has an open porosity, evaluated according to the method described in Example 1 below, of 0.35 to 0.70, preferably of 0.55 to 0.65.

[0062] The strip according to the invention advantageously exhibits a capillary rise, evaluated according to the method described in Example 1 below, of 20 to 45 mm, preferably of 35 to 45 mm.

[0063] Method for preparing a microfluidic device

[0064] The invention also relates to a method for preparing a microfluidic device comprising the steps of: a. supply of an ink as described above or of a microfluidic strip as described above; b. supply of a hydrophobic mixture comprising 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, and at least one hydrophobic agent, selected from alkyl ketene dimers (AKD), alkenyl succinic acid anhydrides (ASA), rosin resins (Colophane), silicones and mixtures thereof, preferably alkyl ketene dimers (AKD), preferably said hydrophobic mixture comprising more than 0.5% by mass, preferably 0.7 to 2% by mass, more preferably 0.9 to 1.1% by mass of hydrophobic agent relative to the dry mass of microfibrillated cellulose; c. supply of at least one fibrous support, preferably with a basis weight of 5 to 20 g / m2, more preferably of 8 to 18 g / m2 and more preferably of 10 to 15 g / m2 and, preferably made up of vegetable fibers, preferably of cellulose fibers, animal fibers, synthetic fibers or a mixture thereof; 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 the ink onto at least part of a surface of the first impregnated fibrous support to obtain an ink track, preferably an ink track of 0.2 to 0.6 g dry mass per cm3, more preferably of 0.3 to 0.5 g dry mass per cm3, or deposition of the microfluidic strip onto at least part of a surface of the first impregnated fibrous support; 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 onto at least part of the first impregnated fibrous support, to obtain an ink track encapsulated 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 the 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. Hydrophobic mixture

[0065] 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 an emulsion, more preferably an aqueous suspension and / or an aqueous emulsion.

[0066] For the purposes of this 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, after heat treatment, the hydrophobic agent and the microfibrillated cellulose form 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 this 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 0.1 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.

[0067] 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.

[0068] The hydrophobic agent can be selected from among the conventional hydrophobic agents used in the paper industry. In particular, it can 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).

[0069] 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.

[0070] 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.

[0071] 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.

[0072] According to one embodiment, 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.

[0073] Advantageously, the hydrophobic mixture is deposited on the surface to be made impermeable 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.

[0074] The hydrophobic mixture, previously suspended, can be deposited by any means, preferably it is deposited by spraying.

[0075] 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 film of the hydrophobic mixture on its own, in the form of a bonded hydrophobic mixture, or a film of the hydrophobic mixture impregnated within a fibrous support. fibrous support

[0076] 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 porous, thus allowing its impregnation by the hydrophobic mixture, i.e., the penetration of the hydrophobic mixture into its structure.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] Encapsulation of the ink track or strip

[0081] The steps for deposition of the hydrophobic mixture result in an ink track or strip encapsulated within the hydrophobic mixture, whether or not it is impregnated with a fibrous support. In other words, the hydrophobic mixture is deposited in such a way as to cover, alone or in combination with a fibrous support that it impregnates, all the external surfaces of the ink track or strip. The ink track or strip is thus encapsulated within said hydrophobic mixture, which, after undergoing heat treatment, forms a water- and / or air-impermeable film as described above.

[0082] In addition to acting as a water and / or air barrier, the hydrophobic blending film also provides 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 blending yarn increases the rigidity of said microfluidic device. Heat treatment

[0083] 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 forms a film of the hydrophobic mixture, i.e., a bound hydrophobic mixture, exhibiting a barrier function against water and / or air. The heat treatment is therefore carried out at a temperature greater than or equal to 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.

[0084] 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.

[0085] 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 enabling the activation 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. Removal of the support

[0086] 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, constituting a barrier to water and / or air.

[0087] 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.

[0088] 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 thus obtained. This optional ablation step is, of course, carried out on a dry device that has been stiffened by returning it to approximately ambient temperature. Microfluidic device

[0089] The invention finally relates to a microfluidic device, comprising a strip according to the invention, or a strip obtained from an ink according to the invention, or obtained according to the process described above.

[0090] 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.

[0091] Throughout the description, including the claims, the expression "comprising one" shall be understood as synonymous with "comprising at least one", unless otherwise specified.

[0092] The expressions "between ... and ..." and "ranging from ... to ..." should be understood inclusive of bounds, unless otherwise specified.

[0093] 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.

[0094] The invention is illustrated in more detail by the non-limiting examples presented below. Examples

[0095] Example 1: Preparation of an ink and additive manufacturing of microfluidic strips according to the invention Materials and methods A / Chemicals and equipment

[0096] The following compounds were used in the preparation of the ink:

[0097] _ 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.

[0098] _ 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)

[0099] _ 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).

[0100] The High Flow 135 (HF135) nitrocellulose microfluidic strip, immersion pads, conjugated fiberglass pads, and absorbent pads were supplied by Merck Millipore (Darmstadt, Germany). The High Flow strip has a water absorption rate of 4 cm in 135 s.

[0101] Sodium chloride-sodium citrate (SSC) 20x concentrated buffer (pH 7.0) and biotinylated bovine serum albumin (BSA) were purchased from Thermo Fisher Scientific (Waltham, MA, USA).

[0102] Sodium dodecyl sulfate (SDS), Tween 20 and urea were purchased from Sigma-Aldrich (St. Louis, Missouri, USA).

[0103] Antibiotin antibodies conjugated to gold nanoparticles (40 nm, 9 x 1010 particles / mL) were supplied by BBI Solutions. B / Water-based inks

[0104] In order to produce microfluidic tracks or strips, two ink formulations were tested. Each formulation consists of a matrix and one or more secondary components:

[0105] - The matrix is ​​a suspension of MFC

[0106] - The secondary components studied are the MCC and the SiO2 particles.

[0107] For each formulation, different ratios between the MFC matrix and the secondary components were tested.

[0108] The resulting suspension consists of 10% to 30% MFC by mass and 70% to 90% secondary components by mass of the final formulation. The mass of the 3% MFC suspension introduced for each formulation was fixed at 5 g. The 5 g MFC suspension was added to a beaker. The secondary components were then added and stirred for 2 minutes using a spatula.

[0109] Composition of the inks tested (% by mass of dry matter, relative to the total mass of the ink):

[0110] _ MFC + SiO2 (comparative inks):

[0111] MFC 10 / SiO2 90; MFC 20 / SiO2 80; MFC 30 / SiO2 70

[0112] _ MFC + MCC (comparative inks):

[0113] MFC 10 / MCC 90; MFC 20 / MCC 80; MFC 30 / MCC 70

[0114] _ MFC + MCC + SiO2 (inks according to the invention) C / Manufacturing the strips

[0115] Two different processes were used to manufacture strip samples. i / Molding of the strips

[0116] The first samples studied were molded samples. The mold used was printed in ABS (acrylonitrile butadiene styrene) due to its stability during the drying stage. It consisted of six channels, each 56 mm long, 7 mm wide, and 0.7 mm thick, for a total volume of 275 mm³ per strip. The formulations were spread into each mold using a spatula.

[0117] ii / Printing / extrusion of strips using a dispenser

[0118] The printed samples, also called extruded samples, were manufactured using a Vieweg “DV-5425” pneumatic needle valve, coupled to a mounted needle connected to a 6-axis robotic arm (Staublï, Switzerland). The robotic arm controls the opening and closing of the valve. The formulations were placed in a pressurized plastic syringe connected to the valve. The pressure applied inside the syringe was 4.6 bar, and the needle lift was 2 mm. An ellipsoidal needle with a major and minor axis of 4.2 mm and 0.5 mm, respectively, was connected to the dispenser and used to print 80 mm long tracks or strips. The width and thickness of the tracks depend on the speed of the robotic arm, which varies between 150 and 350 mm.s*, and the extrusion flow rate, which has been set at 1.6 g.s1.Depending on the printing settings, the width and thickness vary between 5 and 3 mm and 0.8 and 0.4 mm, respectively.

[0119] iii / Drying of molded or printed / extruded strips

[0120] Each sample was dried in two stages.

[0121] The first step consisted of drying in an oven at 90°C for 5 to 10 minutes in order to evaporate most of the water present in the aqueous ink.

[0122] The second step consisted of drying under very light pressure, between 5,000 and 100,000 Pa, in a Rapid Kôthen manual sheet former supplied by Savoie Maintenance Service (France) at 85°C for 30 minutes in order to evaporate the residual water. The absence of this second drying step under compression prevents obtaining a substantially flat strip.

[0123] This manufacturing method makes it possible to produce reproducible samples without having to optimize the process. D / Experimental characterizations

[0124] All initial characterizations are performed with molded samples. i / Structural characterization

[0125] Two types of porosity were studied:

[0126] _ apparent porosity, which takes into account all porosity such as the closed and open porosity, but also surface porosity;

[0127] _ open porosity, which is porosity accessible to liquid absorption. The more the The higher the open porosity, the greater the flow rate of liquid through the belt.

[0128] The apparent porosity was calculated taking into account the size of the strip measured using an electronic caliper and the mass measured using a precision balance.

[0129] The open porosity was obtained by calculating the difference between the geometric and gravimetric (underwater) air fractions. The air fraction was calculated using mathematical formula 1:

[0130] [Math.l] *1 1 1 . i PaPP \ P^air - i - Pa ; + i-pcelMise)

[0131] where papp is the apparent density of the sample (g.m3), pceiiuioSe is the density of the cellulose MFC (g.m3) and pcs is the density of the secondary components (g.m3).

[0132] The gravimetric density is obtained by measuring the mass of the sample underwater using a tensiometer (Biolin add model) and is expressed by the following mathematical formula:

[0133] [Math.2] P gravimetry \Pwater P(âr)+Pair

[0134] where mair is the mass of the sample in air (g), mwater is the mass of the sample in water (g), pair is the density of air (g.m3) and pwater is the density of water (g.m3).

[0135] The internal structure is observed by SEM observation (Quanta 200, FEI, USA) at 40x-200x magnification on a transverse section of the lamellae, ii / Liquid absorption

[0136] To evaluate the microfluidic properties of ink-based strips, water absorption is measured in the vertical state. Commercial nitrocellulose strips are characterized by the time required to reach 4 cm of water absorption as a high-flow membrane (as described in the article Yahaya ML, Zakaria ND, Noordin R, Razak KA (2019) “The Effect of Nitrocellulose Membrane Pore Size of Lateral Flow Immunoassay on Sensitivity for Detection of Shigella sp. in Milk Sample. Materials Today: Proceedings » 17:878-883. https: / / doi.org / 10.1016 / j.matpr.2019.06.384). The measurement of liquid absorption is well defined by the Lucas-Washburn law, which expresses the advance of the fluid front as a function of time:

[0137] [Math.3]

[0138] with r (m) the radius of the pores, y (N.m1) the surface tension of the fluid, q (Pa.s) the dynamic viscosity of the fluid and 0 (°) the contact angle between the liquid and the solid phase.

[0139] In this case, the assumption of cylindrical pores / constant cross-section, a rigid and incompressible solid phase, and a negligible effect of gravity is maintained. The case of porous materials introduces notions of porosity, tortuosity, and pore shape other than a perfect circle. This law is then modified by taking into account the pore size, the pore shape factor, and the tortuosity.

[0140] Experimentally, capillary absorption was measured by recording the mass change of strips immersed vertically 2 mm in a liquid at 25°C using a force tensiometer (Biolin Scientific, model Sigma 700, Finland). Liquid absorption was measured for 5 minutes with a sampling frequency of 2 Hz. The height of capillary absorption was calculated as follows:

[0141] [Math.4] “pI

[0142] where h(t) is the height of the capillary rise, m(t) the measured mass, e the open porosity, S the surface area of ​​the cross-section of the strip and pi the density of the liquid.

[0143] All experiments are carried out with deionized water. One test is nevertheless carried out with a buffer used in lateral flow tests. It is composed of 1x SSC, 0.5% SDS, 10% Tween 20.

[0144] iii / Characterization of density and surface tension

[0145] The density and surface tension of the liquid are measured using the tensiometer used for liquid absorption. The density modulus is measured with a spherical density probe with a volume of 0.918 cm³ calibrated with water, while the surface tension is measured using the De Nouy ring. The surface tension is the average of ten measurements.

[0146] E / Integration of strips into microfluidic devices

[0147] The strips optimized according to the invention (MFC 20 / MCC 60 / SiO220 + water or ethanol) are then integrated into microfluidic devices.

[0148] In the first case, 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%.

[0149] 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.

[0150] 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).

[0151] 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.

[0152] For better visual observation, the liquid test is a deposit of water and bromonaphthalene using a Pasteur pipette in one of the two openings.

[0153] In the second case, a conventional fluidic device configuration is used such as that described by Gomez-Martinez et al. 2018 (Gomez-Martinez J, Silvy M, Chiaroni J, et al (2018) Multiplex Lateral Flow Assay for Rapid Visual Blood Group Genotyping. Anal Chem 90:7502-7509), the nitrocellulose strip being simply replaced by a strip as described above.

[0154] Antibiotin antibodies conjugated to gold nanoparticles are transported by the migration buffer. According to the results of a parallel project, the buffer is composed of Ix SSC, 0.5% SDS and urea (IM) (Tween 20-free migration buffer). Results

[0155] A / Structural characterization of molded strips

[0156] A structural characterization of molded strips from comparative inks MFC + SiO2 (MFC 10 / SiO2 90; MFC 20 / SiO2 80; MFC 30 / SiO2 70) and MFC + MCC (MFC 10 / MCC 90; MFC 20 / MCC 80; MFC 30 / MCC 70) was carried out.

[0157] A significant impact of the particle weight fraction on the sample handling properties is observed. Indeed, the MFC matrix is ​​used to maintain cohesion between the particles, making them less brittle and more flexible. However, more MFC in the ink formulation implies more water to evaporate and therefore greater shrinkage upon drying, and a lower weight fraction of amorphous components with little or no dimensional change. This implies A lower geometric density can lead to lower open porosity. Thus, samples containing 30% MFC are thicker, less brittle, more flexible, and have a lower geometric density than samples containing 10% MFC.

[0158] Samples composed of 20% MFC and 80% secondary components offer a good compromise between these two parameters.

[0159] From these strips, porosity characterizations were carried out, the results of which are presented in Table 1.

[0160] [Tables 1] MFC / SiO 2 MFC / MCC SiO270 % SiO280 % SiO2 90% MCC 70% MCC 80% MCC 90% Open porosity (%) 0.41 + 0.01 0.43 + 0.01 0.48 + 0.03 0.43 + 0 .01 0.41 + 0 .04 0.39 + 0.02 Apparent porosity (%) 0.82 + 0.01 0.82 + 0.01 0.80 + 0.001 0.73 + 0.01 0.70 + 0.02 0.62 + 0.02

[0161] It is observed that the apparent porosity is consistently greater than the open porosity due to the presence of water-accessible and water-inaccessible pores. Strips made from SiO2 particles have a higher test-liquid-accessible porosity than strips made from MFC and microcrystalline cellulose. This may indicate better structural homogeneity with small, homogeneous particles within the structure compared to larger, heterogeneous particles such as MCC. It can also be observed that with increasing particle weight fraction, the two ink formulations, MFC / SiO2 and MFC / MCC, exhibit different behavior. In fact, the formulation containing MCC particles shows a decrease in porosity, which may be due to structural stratification and pore closure.At the same time, the SiO2-containing one sees its open porosity increase and approach its apparent porosity, which can be explained by a better organization and better meshing of the pores, and therefore a lower tortuosity.

[0162] The strips were observed by scanning electron microscopy (SEM). SEM analyses of the strips obtained with the two formulations at 80% of the particle weight fraction (MFC 20 / SiO2 80 and MFC 20 / MCC 80) confirmed the previous analysis. The MFC 20 / MCC 80 strips exhibit a closed, stratified structure with the presence of large pores. In comparison, the MFC 20 / SiO2 80 strips exhibit a more homogeneous structure with many of smaller pores. Depending on the size and shape factor of the particles, the final structure of the strip shows a clear difference in terms of apparent and open porosity and in terms of the size and homogeneity of these pores. B / Water absorption by the molded strips

[0163] The capillary rise of the strips was characterized in comparison with that of the high-flow nitrocellulose reference strips. Figure 1 shows the results obtained from this characterization.

[0164] It is observed that the size of the introduced particles (MCC or SiO2) plays a role in capillary rise phenomena. Indeed, the best result was obtained for the formulation composed of 30% MFC and 70% MCC. Furthermore, all the ink formulations tested with MCC particles showed greater capillary rise than those composed of smaller SiO2 particles.

[0165] The results obtained are nevertheless inferior to those obtained with the nitrocellulosic reference HF135. Only the formulation composed of 30% MFC and 70% MCC is comparable after 30 s. Subsequently, the capillary rise of the references saturated a 5 cm long band in 200 s.

[0166] It is also observed that in the case of MCC, increasing the mass fraction of the particles reduces the velocity and height of capillary rise. For SiO2 particles, increasing the mass fraction of the secondary component significantly improves capillary rise. This observation is supported by observations of apparent and open porosity and by SEM observations. Furthermore, it is observed that capillary rise in the first few seconds is faster than for MCC particles.

[0167] Based on these observations, three new formulations were prepared with 20% MFC by mass and 20, 40, and 60% by mass of the two secondary components (MFC 20 / MCC 60 / SiO220; MFC 20 / MCC 40 / SiO240; and MFC 20 / MCC 20 / SiO260). The objective was to use the MCC particles to increase capillary rise and the SiO2 to prevent the breakdown of the composite structure. The capillary rise results are shown in [Fig. 2].

[0168] The formula with the highest MCC content has the highest water absorption, and the formula with the highest SiO2 content has the lowest water absorption. The formulas with 60% MCC and 20% SiO2 and with 40% MCC and 40% SiO2 have the same water absorption as the formula with 80% MCC. However, the formulations are more homogeneous and easier to print.

[0169] In order to obtain an ink formula with the highest possible cellulose content and resulting in a strip with an interesting compromise of properties, the ink of The formulation 20% MFC 60% MCC 20%SiO2 was selected for further optimizations.

[0170] To manage pore connectivity, and therefore liquid absorption, diluted, solvent-based precipitations are used to manufacture new strips. Two new ink formulations have been developed. These are diluted inks containing 20% ​​by weight of deionized water or ethanol relative to the total weight of the previous ink formulations:

[0171] _ MFC 20 / MCC 60 / SiO220 + water

[0172] _ MFC 20 / MCC 60 / SiO220 + ethanol

[0173] The results of capillary rise of the strips obtained with these two new formulations are presented in [Fig.3] in comparison with strips obtained with the same ink composition but undiluted.

[0174] Diluted ink formulations allow for strips with better performance than those obtained with undiluted ink formulations, probably by improving pore connectivity. The measured open porosities are all higher with undiluted ink formulations: 0.42 without dilution, 0.54 for dilution with 20 wt% water, and 0.66 for dilution with 20 wt% ethanol. C / Water absorption by the extradosed strips

[0175] 3D additive manufacturing tests of strips with the following ink formulations i) still undiluted: 20 MFC / 60 MCC / 20 SiO2 and ii) diluted ink: 20 MFC / 60 MCC / 60 SiO2 + 20 of distilled water were carried out.

[0176] The capillary rise of the strips was characterized in comparison with that of the high-flow nitrocellulose reference strips.

[0177] The results of the capillary rise tests obtained are presented in [Fig.4].

[0178] D / Implementation of the strips and devices according to the invention

[0179] The feasibility of manufacturing microfluidic devices from the strips according to the invention used in previous sections B and C (the "Results" section) has been confirmed. Two tests were carried out according to the configurations in section E of the "Materials and Methods" section: one with an encapsulated track to prevent any contact between external contamination and the fluid, and the other with a track used in an assembly according to the lateral flow test configuration of Gomez-Martinez et al. (Gomez-Martinez J, Silvy M, Chiaroni J, et al (2018) Multiplex Lateral Flow Assay for Rapid Visual Blood Group Genotyping. Anal Chem 90:7502-7509) to reveal BSA deposits.

[0180] During the first test, the test liquid coupled with bromonaphthalene was deposited in a first opening of the coating layer located above a The first end of the strip was exposed. The entire assembly migrated towards the second opening in the coating layer, allowing 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 surface of the encapsulation; these droplets did not penetrate the encapsulation, indicating that the strip was well sealed because the hydrophobic barrier was effective.

[0181] During the second test, BSA deposits were successfully detected using gold nanoparticles. The BSA deposits were applied to a first area in the middle of the strip. The gold nanoparticles were immobilized on a conjugated pad before the device was assembled. Once assembled, the device was then immersed vertically in the migration buffer (without Tween 20), and the buffer migrated by capillary action within the strip towards the conjugated pad, revealing the immobilized BSA and confirming the successful completion of the test.

[0182] Example 2: Preparation of a microfluidic device according to the invention

[0183] 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

[0184] 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.

[0185] 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 final sizing.

[0186] 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).

[0187] Formulation of the aqueous encapsulation composition

[0188] 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.

[0189] 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 ingredient based on the mass of dried cellulose. This concentration varies between 0.05% and 5%. Sample production

[0190] 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.

[0191] 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 a further 10 minutes. Characterization of impregnated substrates

[0192] 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:

[0193] [Math.5]

[0194] where es is the substrate thickness (m), bwMFc is the base weight of the coating MFC (g.m²) and pFMC is the MFC density equal to 1.5 g.cm³. Air permeability is measured as the airflow through a 10 cm² surface under 10.0 kPa using a Bendsten tester, Noviprofibre, France. It is expressed in cm³ / (m².Pa.s). It is expressed using the AFNOR permeability index:

[0195] [Math.6] 1AF~ S^AP

[0196] 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).

[0197] Surface characterization is performed by SEM observation, magnification 1x00 (quanta 200, FEI, USA) and their surface roughness is measured with a profilometer optical (Infinity focus, Alicona, Austria) on a 1.4x1.1 mm square. Roughness values ​​are determined as the average height of the selected area on 1.42 x 1.08 sample surfaces.

[0198] 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

[0199] 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

[0200] 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).

[0201] [Tables2] 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

[0202] The results show that spray coating with MFC / AKD produces 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 layer of MFC / AKD. Second, the observation is reversed because the coating is not completely flat, even though the surface roughness decreases. Nevertheless, there is good agreement between the theoretical and measured thicknesses. The results Measures allow us to establish that spray coating of MFC / AKD on a porous substrate of the Filtea type is a reliable and reproducible process.

[0203] 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).

[0204] [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

[0205] 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.

[0206] These results were confirmed by SEM observations. Permeability characterization

[0207] The results of the permeability test are presented in Table 4.

[0208] [Tables4] Measured Gmfc (g / m²) Permeability (pm / Pas) 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

[0209] 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 gm2, air permeability continues to decrease slightly, 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.

[0210] Based on the above observations, tests modifying MFCs with AKD were carried out for a breaking strength between 12 and 14 gm² and 12.4 ± 1.8 gm², respectively. The results are shown in [Fig. 5], 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 former 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

[0211] 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 from 0.5 to 4 GPa, corresponding respectively to the substrate alone and to 36 g / m² coated with MFC.

[0212] [Tables5] Gmfc nie sur re (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

[0213] 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.

[0214] 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.

[0215] [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

[0216] The evolution tends to be linear between 5 and 30 g / m2. Then, the evolution tends to stabilize around 50 MPa. Conclusion

[0217] 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.

[0218] 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.

Claims

Demands

1. Ink for the additive manufacturing of microfluidic strips comprising: _ 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; and _ 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; and _ silicon oxide particles, preferably silicon oxide particles having a median diameter D50 of 1 pm to 70 pm, preferably 1 pm to 20 pm, and more preferably 1 pm to 10 pm; and an aqueous phase, preferably chosen from water, distilled water and deionized water.

2. Ink according to claim 1 comprising, 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; and - from 70% to 90%, preferably 75% to 85%, of a mixture of microcrystalline cellulose and silicon oxide particles.

3. Ink according to claim 1 or 2 comprising, as a percentage by mass relative to the total mass of ink, from 75% to 95%, preferably 80% to 90% aqueous phase.

4. Ink according to any one of the preceding claims, wherein the ratio of the dry masses of microcrystalline cellulose to silicon oxide particles is 1 to 5, preferably 2 to 4, more preferably 2.5 to

5. J • Method for preparing a microfluidic strip comprising the steps: _ supplying an ink according to any one of claims 1 to 4; _ optionally, diluting said ink by adding, as a percentage by mass relative to the total mass of ink, from 5% to 35%, preferably 10% to 30%, more preferably 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 diluted ink to obtain an ink track, preferably 0.2 to 0.6 g dry mass per cm3, more preferably 0.3 to 0.5 g dry mass per cm3; - drying of the ink track to obtain a microfluidic strip.

6. A method for preparing a microfluidic strip according to claim 5, wherein the drying step is carried out in at least two successive steps: - a first drying step carried out at a temperature above 70°C, preferably from 70°C to 120°C, more preferably from 80°C to 100°C; - at least one additional drying step carried out under a pressure of 5000 to 100000 Pa, preferably from 10000 to 50000 Pa, preferably at a temperature above 50°C, preferably from 60°C to 120°C, more preferably from 70°C to 90°C.

7. Microfluidic strip obtained according to the process of any one of claims 5 to 6.

8. A method for preparing a microfluidic device comprising the steps of: a) providing an ink according to any one of claims 1 to 4 or a microfluidic strip according to claim 7; b) providing a hydrophobic mixture comprising 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, and at least one hydrophobic agent, selected from alkyl ketene dimers (AKD), alkenyl succinic acid anhydrides (ASA), rosin resins (Colophane), silicones and mixtures thereof, preferably alkyl ketene dimers (AKD), preferably said 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; c) supply of at least one fibrous support, preferably with a basis weight of 5 to 20 g / m2, more preferably of 8 to 18 g / m2 and more preferably of 10 to 15 g / m2 and, preferably made up of vegetable fibres, preferably of cellulose fibres, animal fibres, synthetic fibres or a mixture thereof; 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 an ink track of 0.2 to 0.6 g dry mass per cm3, more preferably of 0.3 to 0.5 g dry mass per cm3, or deposition of the microfluidic strip onto at least part of a surface of the first impregnated fibrous support; 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 onto at least part of the first impregnated fibrous support, to obtain an ink track encapsulated 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 compression of 5,000 to 100,000 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, thereby causing the hydrophobic mixture forms a film, impregnated or not in a fibrous support, to obtain a strip encapsulated in a film of the 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 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.

9. A method for preparing a microfluidic device according to claim 8, wherein the hydrophobic mixture is deposited at a rate of 10 to 40 gg of dry mass of microfibrillated microcellulose per m2, preferably 12 to 30 gg of dry mass of microfibrillated microcellulose per m2, more preferably 14 to 30 g of dry mass of microfibrillated microcellulose per m2.

10. Microfluidic device, comprising a strip according to claim 7, or a strip obtained from an ink according to any one of claims 1 to 4, or obtained according to the process of claim 8 or 9.

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