WO2021062487A1

WO2021062487A1 - 3d printed device

Info

Publication number: WO2021062487A1
Application number: PCT/AU2020/051064
Authority: WO
Inventors: Michael C. Breadmore; Fernando Maya ALEJANDRO; Sepideh Keshan BALAVANDY; Kimberley A. FREDERICK
Original assignee: University Of Tasmania
Priority date: 2019-10-04
Filing date: 2020-10-02
Publication date: 2021-04-08

Abstract

A 3D printed porous membrane and a method of producing same. The method including depositing an array of droplets of a first curable material and droplets of a second curable material across a build plane, wherein the first material is insoluble in a solvent and the second material is soluble in the solvent; flattening the droplets of the first and second material so that a plurality of droplets of the first material are intermixed with a plurality of droplets of the second material; curing the first and second material to form a layer of rigid material; depositing, flattening and curing further arrays of droplets on top of the layer of rigid material to form a 3D structure; soaking the 3D structure in the solvent to at least partially dissolve the second material and producing a 3D printed porous membrane made of the first material.

Description

3D PRINTED DEVICE

Technical Field

[0001] The present disclosure relates to a 3D printed microfluidic device, in particular for tests involving the use of a membrane such as for sensing soil chemistry.

Background of the Disclosure

[0002] Much research has been carried out in developing microfluidic systems and devices for applications in a range of fields such as chemistry, biology and engineering. These systems and devices are predicated on performing at least one specified test or task on a small volume of fluid. The prototypes of these devices are made most commonly of polydimethylsiloxane (PDMS) or similar polymers or from glass. Despite the strong research effort, microfluidic technology has not found widespread commercial uptake, due partially to the difficulties in translating the devices from an academic setting to more commercially viable production methods, both in terms of cost and time required to manufacture each device.

[0003] Commonly, such devices require some form of membrane, for example in sample pretreatment, separation, purification or dialysis among others. A great difficulty in developing membrane-containing devices is that these membranes must be incorporated into the device without creating or allowing any leaks within the chambers of the device. Attempts to prepare membranes in situ after the fabrication of the device have also been limited by the difficulties in selecting suitable materials as well as the difficulties in tailoring the membrane towards the retention of certain analytes. Thus, there exists a need for an improved method of creating membranes for use with or incorporation into microfluidic devices.

[0004] 3D printing, also known as additive manufacturing or rapid prototyping, has seen a recent boom in use and the development of techniques for producing complex objects in a relatively short time frame. Some of the common techniques for 3D printing include fused deposition modelling (FDM), stereolithography (SLA), two photon lithography, and inkjet printing (also referred to as material jetting). These methods typically involve adding material layer by layer to form a 3D structure in accordance with a computer-aided design (CAD) or 3D model. In some methods (such as FDM), the material is a thermoplastic material and each layer cools to form a rigid structure after being deposited from a hot extruder. In other methods (such as SLA or material jetting), the material is typically a curable resin, most commonly photocurable with UV radiation. In order to create more complex or delicate structures, some 3D printing processes use a build material and a support material, the latter of which is often water-soluble or has low melting point so that it can be easily removed post printing. While there has been some interest in the use of 3D printing techniques for the fabrication of microfluidic devices, the difficulties in integrating or attaching a membrane into a device printed using these techniques remain prevalent.

[0005] One possible application in which microfluidic devices could be used is in the determination of soil conditions. Agricultural decisions such as the nature and amount of crops to be grown are commonly made on the chemical properties of the available soil. Examples of such properties include pH as well as (but not limited to) nitrite, phosphate, potassium, iron, zinc, magnesium and copper content. Soil testing may also be carried out to measure or avoid environmental contamination. Additionally, the chemical properties of the soil change over time or with use, so testing must be carried out periodically.

[0006] Presently, there are two main approaches to soil testing. The first is to collect soil samples and send them to a laboratory for analysis, where the sample can be filtered, prepared, and techniques such as atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (ICP-AES), or inductively coupled plasma mass spectroscopy (ICP-MS) used to provide accurate quantitative measurements but which require relatively high costs and time to provide their measurements. Further, this approach requires training and expertise to use correctly, and the equipment is too large to use in the field. The second approach is to use paper strips or similar field applicable tests, which typically give a colorimetric response. While this provides easy use by a user, the ability to 'field-test' the soil, and a general indication of the content of the soil, it does not provide quantitative results and is far less accurate than the laboratory testing methods. Accordingly, there exists a need for a method which can combine the easy usability and portability of the paper strip methods with the accurate, quantitative results achieved by laboratory testing.

[0007] The present invention seeks to provide a 3D printable microfluidic device with an integrated membrane and associated method which is inexpensive, and fast and easy to mass produce. Such a device may be suitable for a range of applications, including but not limited to soil testing, where the portability of the microfluidic device may achieve accurate, quantitative results in the field. Summary of the Invention

[0008] According to a first aspect, there is a method for creating a 3D printed porous membrane, comprising: depositing an array of droplets of a first curable material and droplets of a second curable material across a build plane, wherein the first material is insoluble in a solvent and the second material is soluble in the solvent; flattening the droplets of the first and second material so that a plurality of droplets of the first material are intermixed with a plurality of droplets of the second material; curing the first and second material to form a layer of rigid material; depositing, flattening and curing further arrays of droplets on top of the layer of rigid material to form a 3D structure; soaking the 3D structure in the solvent to at least partially dissolve the second material and producing a 3D printed porous membrane made of the first material.

[0009] In certain embodiments, the droplets of the first material are arranged at least partially linearly, and the flattening occurs in a non-parallel direction to the lengthwise direction of the droplets of the first material.

[0010] In certain embodiments, the flattening occurs at between about 10° to about 90° to the lengthwise direction of the droplets of the first material. In one form, the flattening occurs at between about 40° to about 90°. In a further form, the flattening occurs at between about 60° to about 90°.

[0011] In certain embodiments, the first and second material are UV-curable and the curing is carried out using UV radiation.

[0012] In certain embodiments, the solvent is water.

[0013] In certain embodiments, the 3D structure is soaked in water for up to 2 hours.

[0014] In certain embodiments, the 3D structure is additionally soaked in a 2% NaOH solution for up to 1 day following soaking the 3D structure in water.

[0015] In certain embodiments, the first material is transparent or semi-transparent.

[0016] In certain embodiments, at least one of the first material and the second material are acrylic or methacrylic based materials. [0017] In certain embodiments, the acrylic or methacrylic based materials include at least one acrylic monomer and/or oligomer and optionally at least one crosslinking agent, curable diluent and/or a cyclic ketone.

[0018] In certain embodiments, the acrylic or methacrylic based materials further include a photoinitiator.

[0019] In certain embodiments, the acrylic or methacrylic based materials include isobornyl acrylate, 4-acryloylmorpholine, tricyclodecane dimethanoldiacrylate as acrylic monomers; glycerol propoxylate (1PO/OH) triacrylate as a cross linker; a photoinitator; and a cyclic ketone.

[0020] In certain embodiments, a filtration ability of the porous membrane is controlled by increasing or decreasing a thickness of the membrane.

[0021] According to a second aspect, there is provided a porous membrane created by a method according to the first aspect.

[0022] In certain embodiments, the thickness of the porous membrane is between 80 to 300 pm. In one form the thickness of the porous membrane is between 80 to 200 pm.

[0023] According to a third aspect, there is provided a microfluidic device for performing chemistry tests, the microfluidic device comprising: a body including a sample chamber, a reagent chamber, and a porous membrane located between the sample and reagent chambers; and wherein the porous membrane is produced by a 3D printing process.

[0024] In certain embodiments, the body is produced concurrently to the membrane by the 3D printing process.

[0025] In some embodiments, the porous membrane is negatively charged.

[0026] In certain embodiments, the thickness of the porous membrane is between 80 to 300 pm. In one form the thickness of the porous member is between 80 and 200 pm.

[0027] In certain embodiments, the 3D printing process is material jetting or inkjet printing. [0028] In certain embodiments, the body and porous membrane are made of a single material.

[0029] In certain embodiments, the single material is at least partially transparent.

[0030] In certain embodiments, the single material is an acrylic or methacrylic based material.

[0031] In certain embodiments, the acrylic or methacrylic based materials further include a photoinitiator.

[0032] In certain embodiments, the acrylic or methacrylic based materials include at least one acrylic monomer and/or oligomer and optionally at least one crosslinking agent, curable diluent and/or a cyclic ketone.

[0033] In certain embodiments, the acrylic or methacrylic based materials include isobornyl acrylate, 4-acryloylmorpholine, tricyclodecane dimethanol diacrylate as acrylic monomers; glycerol propoxylate (1PO/OH) triacrylate as a cross linker; a photoinitator; and a cyclic ketone.

[0034] In certain embodiments, the body is a solid body and the sample and reagent chambers are channels within the solid structure.

[0035] In certain embodiments, the channels have a U or square U shape including two outer portions and a central portion between them; wherein at least part of an outer surface of the central portion of the channel is formed by the integrated membrane.

[0036] In certain embodiments, at least one of the sample chamber and reagent chamber include an inlet through which fluid may be conveyed into said chamber.

[0037] In certain embodiments, the porous membrane is created by a method according to the first aspect.

[0038] In certain embodiments, the device is adapted for performing colorimetric assays.

[0039] In certain embodiments, the device is adapted for measuring soil chemistry.

[0040] In certain embodiments, the device is adapted to measure at least one of an iron, nitrogen, phosphorous and/or potassium content and/or the pH of a soil sample. [0041] According to a fourth aspect, there is provided a soil condition test when carried out using a device according to the third aspect.

[0042] The soil condition test according to claim 32, wherein the pixel intensity of at least one of the porous membrane and the reagent chamber is used to determine at least one soil condition.

[0043] In certain embodiments, the at least one soil condition is the iron concentration.

[0044] In certain embodiments, a sample mixed with hydroxylammonium is added to the sample chamber, and orthophenanthroline is added to the reagent chamber.

[0045] In certain embodiments, the orthophenantholine is a solution containing 0.2% orthophenantholine .

[0046] In certain embodiments, the pixel intensity of the porous membrane is used to determine iron concentration below a predetermined intensity of the reagent chamber, and the pixel intensity of the reagent chamber is used to determine iron concentration above the predetermined intensity.

[0047] In certain embodiments the predetermined intensity is 40 (arbitrary units).

[0048] Other aspects, features, and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of the inventions disclosed.

Brief Description of the Figures

[0049] The present disclosure will become better understood from the following detailed description of various non-limiting embodiments thereof, described in connection with the accompanying figures, wherein:

[0050] FIGURE 1A shows a schematic view of a microfluidic device according to the present invention.

[0051] FIGURE IB shows a diagrammatic view of droplets of the build and support materials prior to and post flattening when printed at 0°. [0052] FIGURE 1C shows a photograph of a device printed at 0° used to investigate the movement of ions across the membrane.

[0053] FIGURE ID shows a photograph of a device printed at 0° used to investigate the movement of fluid across the membrane.

[0054] FIGURE IE shows an optical photograph of the membrane surface of a device printed at 0°.

[0055] FIGURE IF shows an SEM photograph of the membrane surface of a device printed at 0°.

[0056] FIGURE 2A shows a schematic view of a microfluidic device according to the present invention.

[0057] FIGURE 2B shows a diagrammatic view of droplets of the build and support materials prior to and post flattening when printed at 90°.

[0058] FIGURE 2C shows a photograph of a device printed at 90° used to investigate the movement of ions across the membrane.

[0059] FIGURE 2D shows a photograph of a device printed at 90° used to investigate the movement of fluid across the membrane.

[0060] FIGURE 2E shows an optical photograph of the membrane surface of a device printed at 90°.

[0061] FIGURE 2F shows an SEM photograph of the membrane surface of a device printed at 90°.

[0062] FIGURE 3A shows a schematic view of a microfluidic device according to the present invention.

[0063] FIGURE 3B shows a diagrammatic view of droplets of the build and support materials prior to and post flattening when printed at 45°.

[0064] FIGURE 3C shows a photograph of a device printed at 45° used to investigate the movement of ions across the membrane. [0065] FIGURE 3D shows a photograph of a device printed at 45° used to investigate the movement of fluid across the membrane.

[0066] FIGURE 3E shows an optical photograph of the membrane surface of a device printed at 45°.

[0067] FIGURE 3F shows an SEM photograph of the membrane surface of a device printed at 45°.

[0068] FIGURE 4 shows photographs of devices according to the invention with differing membrane thicknesses at different time points.

[0069] FIGURE 5 shows a graph of the pixel intensity vs time for differing membrane thicknesses.

[0070] FIGURE 6 shows a graph of the time to equilibrium vs membrane thickness for a series of devices according to the present invention.

[0071] FIGURE 7A shows a fluorescence microscopy image of a membrane with a thickness of 80 pm and fluorescent particles.

[0072] FIGURE 7B shows a fluorescence microscopy image of a membrane with a thickness of 100 pm and fluorescent particles.

[0073] FIGURE 7C shows a fluorescence microscopy image of a membrane with a thickness of 130 pm and fluorescent particles.

[0074] FIGURE 8 shows a series of devices with a thickness of 100 pm for differing concentrations of FcCh mixed with hydroxyammonium in the sample chamber and orthophenanthroline in the reagent chamber.

[0075] FIGURE 9 shows a graph of the measured intensity at the membrane after 15 minutes for differing iron concentrations.

[0076] FIGURE 10 shows a graph of the measured intensity in the reagent chamber after 15 minutes for differing iron concentrations. [0077] FIGURE 11A shows a device containing a soil sample mixed with hydroxyammonium in the sample chamber and orthophenantholine (0.2%) immediately after being placed in the device.

[0078] FIGURE 11B shows a device containing a soil sample mixed with hydroxyammonium in the sample chamber and orthophenantholine (0.2%) 15 minutes after being placed in the device.

[0079] FIGURE 12A shows a device containing a river water sample mixed with hydroxyammonium in the sample chamber and orthophenantholine (0.2%) immediately after being placed in the device.

[0080] FIGURE 12B shows a device containing a river water sample mixed with hydroxyammonium in the sample chamber and orthophenantholine (0.2%) 15 minutes after being placed in the device.

[0081] FIGURE 13 shows a schematic view of a microfluidic device according to another embodiment of the present invention.

[0082] FIGURE 14 shows a schematic diagram depicting the different printing orientationsrelative to the lengthwise direction of the membrane.

[0083] FIGURE 15 provides illustrative and microscopic images of various membranes prepared from differing printer orientations relative to the lengthwise direction of the membrane.

Detailed Description

[0084] The inventors have found a microfluidic device incorporating an integrated membrane can be created based on existing 3D printing methods. This device utilizes the formation of a highly porous micro structure at the interface between build and support materials. The inventors found that by creating these microstmctures on either side of a thin section of the build material, a membrane could be created. Further, by altering the printing direction of the materials, the microscale mixing of the build and support material may be altered, tuning the properties of the membrane. [0085] Material jetting 3D printers include one or more inkjet heads capable of depositing an array of droplets of one or more curable materials (by use of multiple heads) across a 2D plane on a build tray or platform according to a CAD or 3D model file. A levelling roller or blade flattens the droplets to provide an even and flat layer of the materials. A curing method, most commonly a UV light is provided to cure the layer of materials. The build tray then moves down so that a further layer of droplets can be deposited over this layer, forming a 3D structure through the deposition of successive layers.

[0086] To verify the suitability of the present method for creating an integrated membrane, a number of colorimetric sensors, each containing an integrated membrane were produced. A number of experiments were also performed in order to assess the produced membranes' properties. Each device was created using a material jetting (also referred to as inkjet or under the trade name PolyJet) 3D printer (Objet Eden 260VS) utilizing an acrylic based material (Veroclear-RGD810) and a water soluble support material (SUP707). Veroclear-RGD810 is a photocurable acrylic resin which forms a transparent rigid material when cured, including the following: a photo curable diluent (isobomyl acrylate), an acrylic monomer (4- acrylolmorpholine), a monomer of low shrinkage and high refractive index (tricyclodecane dimethanoldiacrylate), a photoinitiator (Irgacure 184), a cross-linker (glycerol propoxylate (1PO/OH) triacrylate) and a cyclic ketone (cyclo-hexanone). SUP707 is a water-soluble photocurable acrylic resin including alkoxylated trimethylolpropane, an acrylic monomer, water, photo initiators, a silicone surfactant and aluminium, tris(N-hydroxy-N- nitrosobenzenaminato-0,0'). It will be understood that other curable materials, preferably polymerizable formulations and resins may also be used as the build and support material without deviating from the scope of the invention.

[0087] Following the printing process, the support material was removed by soaking the devices in water for between 1-2 hours, then soaking them in 2% NaOH for up to 24 hours. These processes were carried out without ultrasound, air or water jet methods to prevent damage to any produced membrane structure.

[0088] The inventors found that when printed in the conventional manner, that is to say that when the print direction, i.e. the direction in which the flattening roller or blade moves, is oriented in a direction substantially parallel to the lengthways direction of the thin section of the build material, the thin section of the resultant device is non-porous and thus does not allow ionic or fluid transport through the section. When the process was altered so that the print direction (and roller direction) was in a non-parallel direction to the lengthways direction of the thin section, the porosity of the thin section increased to form a porous membrane. Without wishing to be bound by theory, it is thought that the non-parallel direction results in increased intermixing of the build and support material during printing, increasing the porosity of the material to a sufficient extent to permit ionic or fluid transport.

[0089] An embodiment of a device and the different mixing behavior of the support and build materials at the membrane caused by printing direction are shown in FIGURES 1A-3A and FIGURES 1B-3B respectively. Each of these figures includes a device consisting of a body 1, sample chamber 2, reagent chamber 3 and membrane 4 separating the two chambers. Both the sample chamber 2 and reagent chamber 3 are in the form of channels, each of which include two 90° turns in the same direction, that is to say that when the channels are viewed from above, have a 'square U' shape consisting of two outer portions or 'arms' and a central portion between them. The channels both meet at and are separated by a membrane 4 at the central portion of said channels. At a distal end of each arm of the sample and reagent chambers is an inlet 5 which is open to the environment such that fluids may be conveyed into the respective chambers. For example, a soil slurry or water sample can be added to the sample chamber, for example by injecting the fluid into the chamber with a syringe, and a colorimetric reagent such as potassium thiocyanate or orthophenanthroline similarly added to the reagent chamber. These particular devices were fabricated to measure 16 x 11 x 1.4 mm in the XYZ plane with channels measuring 2 x 1 mm, though it will be understood that other devices have other dimensions while still incorporating some or all of the same features.

[0090] Further, it will be understood that the terms 'sample chamber' and 'reagent chamber' are used merely for clarity, that is to say that a sample could be added to the reagent chamber and the reagent to the sample chamber and still perform as intended. Alternative names for these chambers could include 'upper' and 'lower' chambers, or 'a first' and 'a second' chamber without deviating from the scope of the invention. In some embodiments, there may be no structural differences between the sample and reagent chambers.

[0091] Throughout the following descriptions of the figures, the same numbering will be used to denote like components.

[0092] FIGURE 1A shows a microfluidic device when the device is printed in the conventional orientation, that is to say that the printing direction (as indicated by the direction of the arrow below the device body 1) is substantially parallel or at an angle close to 0° relative to the lengthways direction of the membrane 4. FIGURE IB shows droplets of the support material 6 and build material 7 prior to the flattening by a levelling roller, blade, or other method proceeding in a direction as highlighted by the arrow in FIGURE 1A. A thin section of build material 7 is created by depositing a single line of droplets between droplets of the support material. On curing, this thin section will form a layer of the porous membrane. While in this embodiment there is only a single line of droplets, it will be understood that the thin section may be composed of multiple lines of droplets, for example, devices were fabricated by the inventors with up to four droplets, which on the specific 3D printer being used (Objet Eden, Stratasys Inc) meant that the thin section (and thus the resultant membrane) had a thickness of between 80-200 pm.

[0093] As the droplets are flattened, droplets of the support material 8 are dragged into adjacent droplets of the support material, and droplets of the build material 9 are dragged onto adjacent droplets of the build material. This results in the formation of a non-porous thin section wherein the pores formed at the interface of the build and support material do not penetrate the depth of the build material. This was verified by testing the fabricated devices as shown in FIGURES 1C and ID.

[0094] FIGURE 1C shows a device wherein 30 mM ferric chloride (FcCh) was placed in the sample chamber 2 and 1 mol/L potassium thiocyanate (KSCN) was placed in the reagent chamber 3. If SCN ions are able to pass through the thin section 4, the solution in the sample chamber will undergo a colour change as a result of the formation of red iron (III) thiocyanate (FeSCN²⁺) complex ions. No colour change was observed after 12 hours, indicating that the structure is non-porous. FIGURE ID shows a device where a coloured solution (food dye) was placed in the sample chamber 2 and Milli-Q water was placed in the reagent chamber 3 to determine whether fluid was transported between the chambers. Similarly, no transport was observed, with the reagent chamber remaining colourless. FIGURES IE and IF show optical and SEM images respectively of the thin structure produced when the droplets are flattened in a direction parallel to the lengthways direction of the thin section. A substantially uniform, ordered structure is produced, in accordance with standard 3D printed sections.

[0095] FIGURE 2A shows a device with the same features as FIGURE 1A printed in an orientation 90° to the lengthwise direction of the membrane 4, as illustrated by the arrow. Similar to FIGURE IB, a single line of droplets of the build material 7 is deposited to form a layer of a thin section, however in this embodiment, the orientation means that upon flattening, support material 8 is intermixed with build material 9 and vice versa for droplets adjacent to a different material.

[0096] As shown by FIGURES 2C to 2F, the multiple layers of the thin section form a porous structure, i.e. a membrane 4 through which ionic transport is possible. FIGURE 2C shows a device in which ferric chloride (FeCb₎ has been added to the sample chamber 2 and potassium thiocyanate (KSCN) added to the reagent chamber 3. SCN ions have been able to pass through the membrane 4 and have reacted to form red iron (III) thiocyanate ions in the sample chamber 2. FIGURE 2D shows a device wherein a coloured solution (food dye) has been added to the sample chamber 2 and Milli-Q water placed in the reagent chamber 3. The limited colour formed in the reagent chamber 3 shows that the membrane restricts the flow of fluid between the chambers. FIGURE 2E and 2F show optical and SEM images respectively of the membrane produced when the droplets are flattened in a direction perpendicular (90°) to the lengthwise direction of the section. The resultant structure is rougher and more chaotic compared with the images in FIGURE IE and IF.

[0097] FIGURE 3A shows a further device printed at an orientation of 45° to the lengthways direction of the membrane (illustrated by the arrow). FIGURE 3B shows that the build material 7 is angled at a 45° direction. Similar to FIGURE 2B, droplets of build material adjacent to droplets of support material 8 are intermixed when flattened prior to curing.

[0098] FIGURE 3C shows a device where ferric chloride and potassium thiocyanate have been added to the sample and reagent chamber respectively. The presence of red colouring in both chambers suggest either an unstable membrane was formed or that there were cracks or defects within the membrane. FIGURE 3D, wherein a coloured solution was added to one chamber of the device show a physical break in the membrane. FIGURES 3E and 3F show optical and SEM images respectively show a rougher and more chaotic structure compared to both devices printed at 0° and 90° (FIGURES IF and 2F respectively).

[0099] The inventors created a number of devices, varying the thickness of the membrane between 80 pm and 200 pm when printed at an orientation of 90° to the lengthwise direction of the membrane. These devices were evaluated both in terms of the diffusion rates through the membrane as well as the filtering capabilities. [00100] Throughout these experiments, the term 'intensity' is intended to refer to pixel intensity, as measurable by commonly available software such as ImageJ and are based on the number of pixels within a contained area. The pixel values are summed and divided by the number of pixels within the specified area.

[00101] To assess the diffusion through the membrane, 29 mmol/L FcC and 2.5 mol/L KSCN were added to the sample and reagent chamber respectively and the intensity of the red colour that developed in the sample chamber. Photographs of devices with 80, 100, 130, 150 and 200 pm and the resultant colour that developed at 1, 5 and 10 minutes post addition of the FcCl i and KSCN are shown in FIGURE 4. The development of colour in both chambers after 1 minute for a device 10 with a membrane thickness of 80 pm suggested an unstable membrane, a fact confirmed by subsequent testing with coloured food dye and Milli-Q water. A device 11 with a thickness of 100 pm showed colour in the sample chamber after 1 minute, suggesting a stable membrane allowing flow of SCN ions. For device 12 with a membrane thickness of 130 pm, colour developed at the membrane only after 1 minute. Devices 13 and 14 with membrane thicknesses of 150 and 200 pm respectively showed little to no colour development after 1 minute, and showed increasing colour developing at the membrane after 5 and 10 minutes. The preferential development of colour at the membrane is regarded as indicative of a negative charge forming on the surface of the membrane which attracts iron ions to the membrane.

[00102] To quantify the developed colour in each device, images were taken and standardized by converting the images to grayscale before determining the average grey value after background subtraction. The average grey value will henceforth be referred to as colour intensity. A graph showing the developed intensity for each membrane thickness over 120 minutes is shown in FIGURE 5. As the graph shows, the colour intensity (indicative of the speed of ion transport) develops slower with increasing membrane thickness. FIGURE 6 is graph showing the reaction time to establish equilibrium with varying membrane thickness. For membranes between 100 and 200 pm, an exponential relationship can be seen.

[00103] Devices with membranes of differing thicknesses were also used to evaluate the ability of the membrane to serve as a filter. Fluorescent particles with diameters ranging from 1 pm to 15 pm were added to a coloured food dye which was then injected into the sample chamber of devices with membrane thicknesses of 80, 100 and 130 pm. Milli-Q water was added to the reagent chamber and the devices left for 15 minutes. Fluorescence microscopy was then used to determine how many particles were able to pass through the device. These images can be seen in FIGURES 7A-7C. For the device with a membrane thickness of 80 mhi (FIGURE 7A), 30% of fluorescent particles were able to pass through the membrane. For the device with a membrane thickness of 100 pm (FIGURE 7B), only 3% of the particles were able to pass through the membrane. For the device with a membrane thickness of 130 pm (FIGURE 7C), no fluorescent particles were observed in the reagent chamber. This is particularly useful for the measurement of slurries or other solutions featuring relatively large particles which would otherwise have to be filtered or otherwise removed before testing through conventional methods (such as ICP-MS) can be used.

[00104] Different values of separator thickness and printing orientations were also evaluated to determine their impact on the membranes obtained. An alternative embodiment of a microfluidic device as herein described is depicted in FIGURE 13. The device consists of a body 1, sample chamber 2, reagent chamber 3 and membrane 4 separating the two chambers. Thickness of the membrane 4 can be selected from minimum values of 100 pm up to 1000 pm At a thickness of 1000 pm it was found the resultant membrane contains significantly reduced porosity. Printing orientation may be altered to any possible degree relative to the lengthwise direction of the membrane on the printer-build platform.

[00105] As depicted in FIGURE 14, ten printing orientations were evaluated including a structure which is parallel to the print head movement (i.e. 0°) and then at 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80° and 90°. A detailed experiment investigating the relation of process parameters namely orientation and thickness was documented in order to investigate the filtration ability/porosity of the structure.

[00106] It was found that penetration of support droplets into the build droplets during the printing process at the 0° orientation was substantially negligible. This resulted in in a membrane 4 that was non porous. Moving to the 10° orientation, a degree of support droplets was found to penetrate the build droplets due to the 10° angle to the nozzles array and possibly cause an increase in porosity of the resultant membrane following the support removal step. Following this pattern, from 10° to 90° the interaction of support and build material droplets gradually increase and reach a maximum interpenetration and with a resultant membrane with significant porosity at a printer orientation of 90° relative to the lengthwise direction of the membrane. Figure 15 shows both an illustrative and microscopic image of how increasing the degree of printer orientation relative to the lengthwise direction of the membrane increases mixing and also generates more pores in the resulting membrane 4. [00107] These devices may have a variety of uses and applications in a number of fields. The inventors investigated one such application and developed a test for determining the iron content of soil as a model for the suitability of the device's use in colorimetric assays in general as well as the ability of the device to filter solid particles from slurries (such as soil). It will be understood that the following experimental embodiments are intended to be non-limiting, that is to say that the membranes and associated devices according to the present invention may be suitable or adapted for further applications beyond soil testing. Otherwise stated, the devices and method described below may be used or adapted for almost any colorimetric analytic measurement where the product can be determined in the visible light range. This includes metals which may be used to obtain a coloured complex, or other anions or cations which can be determined with a colorimetric method. It may also have applications in other colorimetric based measurements such as pH or total indexes (total phenols).

[00108] The sensitivity of the devices for determining iron was assessed by mixing differing concentrations of FeC13 solutions with hydroxylammonium chloride (to reduce Fe(III) to Fe(II)) and injecting the mixture into the sample chamber of devices with a membrane thickness of 100 pm. Orthophenanthroline (0.2%) was injected into the reagent chamber. Orthophenanthroline was chosen as it is known to form a highly stable orange coloured complex on reaction with ferrous ions. As with the previous experiments, colour appeared first at the membrane before appearing in the reagent chamber. This is again thought to be the result of the membrane being negatively charged. The tendency for iron to be attracted to the membrane is in fact beneficial to colorimetric analysis of iron as it may provide increased sensitivity at lower concentrations. For higher iron concentrations, colour appeared in both chambers, however measurements were taken on the colour intensity of the reagent chamber. Photographs of the devices with 2, 4, 6, 8, 10, 25, 50, 75 and 100 mg/L of Fe(III) and the resultant colour in the membrane and chambers after 15 minutes is shown in FIGURE 8.

[00109] The colour intensity was again measured by converting each image to greyscale and measuring the intensity of the membrane and reagent chamber after subtracting the background intensity. It was found that the colour intensity of the membrane was well suited for determining concentrations between 0 and 10 mg/L owing to the linear relationship between concentration and intensity at the membrane, as seen in FIGURE 9. Above these concentrations, the concentration at the membrane levels off due to reaching colour saturation. The colour intensity of the reagent chamber, however, increases linearly for concentrations between 8 and 100 mg/L before reaching colour saturation. The device can thus be used to measure samples containing iron concentrations between 0-100 mg/L.

[00110] As previously stated, iron is attracted to the negatively charged resin and thus colour develops at the membrane prior to the chamber. It will be understood that in other embodiments which measure other ions, the surface of the membrane may be positively charged or neutral depending on the type of ion or colorimetric test. For example, in embodiments of the device and method adapted for measuring the concentration of a negatively charged ion, the membrane may be positively charged to provide analogous behaviour, i.e colour developing first at the membrane to allow measurement of lower concentrations of the ion. The charge on the surface of the membrane may be altered by fabricating the membrane out of other commercial or homemade resins or other curable materials.

[00111] The reliability of this testing method was tested by measuring iron concentrations with 6 and 50 mg/L five times with devices printed in different batches. Similar colour intensities were measured after 15 minutes in both cases, with a relative standard deviation of 2.2% and 6.7% for the membrane intensity and reagent chamber intensity respectively.

[00112] From this, a process for determining the iron concentration of an unknown sample may be established. The unknown sample is mixed with hydroxylammonium and injected into the sample chamber of the device which has orthophenanthroline in the reagent chamber (either by injecting into the reagent chamber or by any other method). A picture of the reagent chamber and membrane is then taken, preferably after 15 minutes. The intensity of the reagent chamber is then measured. If the measured intensity is less than 40, then the intensity of the membrane is taken and the linear relationship between the membrane intensity and concentration used to find the iron concentration of the sample. If the measured intensity is between 40 and 105, then the linear relationship between the reagent chamber and concentration used to find the iron concentration of the sample. If the measured intensity is greater than 105, then the sample can be diluted two-fold and the measurement repeated to find a concentration if the intensity is now lower than 105, and multiplying the value by two to find the iron concentration of the sample.

[00113] Such a process may be in some embodiments integrated into the device or into a phone app which could in some circumstances use the existing phone camera infrastructure to take a photo and perform the necessary processing, providing a result with minimal user input. [00114] This process was tested on two real-world samples: a soil slurry and river water below a local mine. The soil slurry in the sample chamber of the device is shown at 0 minutes in FIGURE 11A and at 15 minutes in FIGURE 1 IB, and the river water in the sample chamber of the device is shown at 0 minutes in FIGURE 12A and at 15 minutes in FIGURE 12B. For both samples, the reagent chamber was filled with orthophenanthroline (0.2%). Using the method detailed above, the soil sample was found to have 50 mg/L, which is in accordance with ICP-MS results which showed 48 mg/L. The river water sample was found to have 96 mg/L using the above method, also in accordance with ICP-MS results which showed 100 mg/L.

[00115] Similar devices and methods could be used to test other soil conditions, such as for "NPK" tests which measure the nitrogen, phosphorous and potassium in a soil sample using colorimetric analysis. Further, devices and methods could be adapted for applications outside of soil sensing without major alteration to the design or function of the aforementioned device and method.

[00116] In accordance with another embodiment, the device as herein described may be used to perform a pH test of a sample material, such as for example a soil sample. In this embodiment, pH indicator may be injected into the reagent chamber and optionally mixed together with glycerol. The sample, such as a soil sample is then injected into the sample chamber of the device and a colour change is then observed.

[00117] The pH indicator may be prepared from a mixture including phenolphthalein, methyl red, bromothymol blue, methyl orange and sodium hydroxide. In a preferred form, the pH indicator may be produced by separately dissolving phenolphthalein in ethanol, methyl red in ethanol, bromothymol blue in water, methyl orange in water and sodium hydroxide in water. Each of these components is then mixed and the resultant mixture diluted to about four parts water to one part of the mixture.

[00118] In an example embodiment a pH indicator may be produced by the following steps: (1) 0.08 g phenolphthalein is dissolved in 5 ml of ethanol, 0.04 g of methyl red is dissolved in 2 ml of ethanol; 0.08 g bromothymol blue is dissolved in 5 ml of Milli-Q water; 0.01 g methyl orange is dissolved in 5 ml of hot Milli-Q water; and, 0.007 g of sodium hydroxide is dissolved in 5 ml of Milli-Q water; (2) each of these components is then mixed and is then added to 78 ml of Milli-Q water to make 100 ml of pH indicator. [00119] In accordance with a further embodiment, the device as herein described may be used as a frit for column chromatography, and in particular for high performance liquid chromatography (HPLC). In this embodiment, the device such as for example shown in FIGURE 13 may be filled with a packing particle such as for example styrene-divinylbenzene (SDVB), a silica gel coated with C18, or a PS-DVB polymeric SPE phase. The packing particle is filled via the reagent chamber 3 which in this embodiment is in the form of an inlet for the frit. In a preferred form of the embodiment, the device when used as a frit for column chromatography includes a membrane with a thickness of about 100 pm to about 200 pm and preferably about 150 pm. In a preferred for of the embodiment the device when used as a frit for column chromatography includes a membrane that has been printed at between about 20° and about 50° and preferably about 30° relative to the lengthwise direction of the membrane.

[00120] In summary, the inventors have found a porous structure suitable as a membrane and/or filter can be created by altering the orientation of the printing direction (and accordingly the direction in which the droplets are flattened) of a thin section of material. The properties of the filter, such as surface roughness and filtering ability may be further tuned by adjusting the printing orientation and membrane thickness. Beneficially, this structure can be cheaply made and mass produced by conventional 3D printing techniques. Additionally, it is possible to 3D print a device of the same material at the same time as the membrane so that the membrane is integral to the device, reducing the chance of leaks to form between the membrane and the rest of the device as well as reducing the manufacturing time and cost. For example, on the Objet Eden printer used to fabricate the example embodiments described above, 221 devices could be made in 90 minutes with a material cost of AUD$2.50 per device.

[00121] These easily mass-produced and inexpensive devices may be applicable to a range of uses, such as performing colorimetric tests on for example soil samples. Such a device would be easy to use by a single operator without any substantial prior training and would be able to produce a quantitative measurement of at least one condition in a far shorter span of time compared to existing laboratory methods.

[00122] In the foregoing description of certain embodiments, specific terminology has been resorted to for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes other technical equivalents which operate in a similar manner to accomplish a similar technical purpose. [00123] In this specification, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of’. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear.

[00124] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavor to which this specification relates.

[00125] In addition, the foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

[00126] Furthermore, invention(s) have described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention(s). Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment.

Claims

The claims

1. A method for creating a 3D printed porous membrane, comprising: depositing an array of droplets of a first curable material and droplets of a second curable material across a build plane, wherein the first material is insoluble in a solvent and the second material is soluble in the solvent; flattening the droplets of the first and second material so that a plurality of droplets of the first material are intermixed with a plurality of droplets of the second material; curing the first and second material to form a layer of rigid material; depositing, flattening and curing further arrays of droplets on top of the layer of rigid material to form a 3D structure; soaking the 3D structure in the solvent to at least partially dissolve the second material and producing a 3D printed porous membrane made of the first material.

2. The method according to claim 1, wherein the droplets of the first material are arranged at least partially linearly, and the flattening occurs in a non-parallel direction to the lengthwise direction of the droplets of the first material.

3. The method according to claim 2, wherein the flattening occurs at between about 10° to about 90° to the lengthwise direction of the droplets of the first material.

4. The method according to any one of the preceding claims, wherein the first and second material are UV-curable and the curing is carried out using UV radiation.

5. The method according to any one of the preceding claims, wherein the solvent is water.

6. The method according to claim 5, wherein the 3D structure is soaked in water for up to 2 hours.

7. The method according to claim 6, wherein the 3D structure is additionally soaked in a 2% NaOH solution for up to 1 day following soaking the 3D structure in water.

8. The method according to any one of the preceding claims, wherein the first material is transparent or semi-transparent.

9. The method according to any one of the preceding claims, wherein at least one of the first material and the second material are acrylic or methacrylic based materials.

10. The method according to claim 9 wherein the acrylic or methacrylic based materials include at least one acrylic monomer and/or oligomer and optionally at least one crosslinking agent, curable diluent and/or a cyclic ketone.

11. The method according to claim 10, wherein the acrylic or methacrylic based materials further include a photoinitiator.

12. The method according to claim 11, wherein the acrylic or methacrylic based materials include isobomyl acrylate, 4-acryloylmorpholine, tricyclodecane dimethanoldiacrylate as acrylic monomers; glycerol propoxylate (1PO/OH) triacrylate as a cross linker; a photoinitator; and a cyclic ketone.

13. The method according to any of the preceding claims, wherein a filtration ability of the porous membrane is controlled by increasing or decreasing a thickness of the membrane.

14. A porous membrane created by a method according to any one of claims 1 to 13.

15. The porous membrane according to claim 14, wherein the thickness of the porous membrane is between 80 to 300 pm.

16. A microfluidic device for performing chemistry tests, the microfluidic device comprising: a body including a sample chamber, a reagent chamber, and a porous membrane located between the sample and reagent chambers; and wherein the porous membrane is produced by a 3D printing process.

17. The microfluidic device according to claim 16, wherein the body is produced concurrently to the membrane by the 3D printing process.

18. The microfluidic device according to claim 16 or 17, wherein the 3D printing process is material jetting or inkjet printing.

19. The microfluidic device according to any one of claims 16 to 18, wherein the porous membrane is negatively charged.

20. The microfluidic device according to any one of claims 16 to 19, wherein the thickness of the porous membrane is between 80 to 300 pm.

21. The microfluidic device according to any one of claims 16 to 20, wherein the body and porous membrane are made of a single material.

22. The microfluidic device according to claim 21, wherein the single material is at least partially transparent.

23. The microfluidic device according to either claim 2 lor 22, wherein the single material is an acrylic or methacrylic based material.

24. The microfluidic device according to claim 23, wherein the acrylic or methacrylic based materials further include a photoinitiator.

25. The microfluidic device according to claim 24, wherein the acrylic or methacrylic based materials include at least one acrylic monomer and/or oligomer and optionally at least one crosslinking agent, curable diluent and/or a cyclic ketone.

26. The microfluidic device according to claim 25, wherein the acrylic or methacrylic based materials include isobornyl acrylate, 4-acryloylmorpholine, tricyclodecane dimethanol diacrylate as acrylic monomers; glycerol propoxylate (1PO/OH) triacrylate as a cross linker; a photoinitator; and a cyclic ketone.

27. The microfluidic device according to any one of claims 16 to 26, wherein the body is a solid body and the sample and reagent chambers are channels within the solid structure.

28. The microfluidic device according to claim 27, wherein the channels have a U or square U shape including two outer portions and a central portion between them; wherein at least part of an outer surface of the central portion of the channel is formed by the integrated membrane.

29. The microfluidic device according to any one of the claims 16 to 28, wherein at least one of the sample chamber and reagent chamber include an inlet through which fluid may be conveyed into said chamber.

30. The microfluidic device according to any one of claims 16 to 29, wherein the porous membrane is created by a method according to any one of claims 1 to 13.

31. The device according to any one of claims 16 to 30, adapted for performing colorimetric assays.

32. The device according to any one of claims 16 to 31, adapted for measuring soil chemistry.

33. The device according to claim 32, wherein the device is adapted to measure at least one of an iron, nitrogen, phosphorous and/or potassium content and/or the pH of a soil sample.

34. A soil condition test when carried out using a device according to any one of claims 16- 32.

35. The soil condition test according to claim 34, wherein the pixel intensity of at least one of the porous membrane and the reagent chamber is used to determine at least one soil condition.

36. The soil condition test according to claim 35, wherein the at least one soil condition is the iron concentration.

37. The soil condition test according to claim 36, wherein a sample mixed with hydroxylammonium is added to the sample chamber, and orthophenanthroline is added to the reagent chamber.

38. The soil condition test according to claim 37, wherein the orthophenantholine is a solution containing 0.2% orthophenantholine.

39. The soil condition test according to claim 38, wherein the pixel intensity of the porous membrane is used to determine iron concentration below a predetermined intensity of the reagent chamber, and the pixel intensity of the reagent chamber is used to determine iron concentration above the predetermined intensity.

40. The soil condition test according to claim 39, wherein the predetermined intensity is 40 (arbitrary units).