WO2022005467A1

WO2022005467A1 - Hydrophobic flow barriers

Info

Publication number: WO2022005467A1
Application number: PCT/US2020/040427
Authority: WO
Inventors: Beverly CHOU; Anita Rogacs; Klara KUKOWSKI
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2020-07-01
Filing date: 2020-07-01
Publication date: 2022-01-06
Anticipated expiration: 2023-01-01

Abstract

The present disclosure describes methods of forming flow barriers in porous substrates. In one example, a method of forming a flow barrier in a porous substrate can include applying a pre-treatment composition to an area of a surface of a porous substrate. The pre-treatment composition can include a solvent, a cationic salt, a cationic polymer, or a combination thereof. The method can also include applying a flow modifier composition onto an area of a surface of the porous substrate. The flow modifier composition can include an aqueous solvent, dispersed hydrophobic material particles, and a dispersant. The flow modifier composition can wick through pores of the porous substrate. The pre-treatment composition can reduce a penetration rate of the dispersed hydrophobic material particles in the area where the pre-treatment composition is applied.

Description

HYDROPHOBIC FLOW BARRIERS

BACKGROUND

[0001] Certain types of chemical testing utilize a porous material through which a sample fluid flows by capillary action. As an example, lateral flow immunoassays are a type of test in which a sample fluid flows along a porous material such as a porous nitrocellulose pad. Lateral flow immunoassays often include a test line and a control line. The test line can include a suitable test reactant that is reactive with a target molecule in the sample fluid. In some cases, the test line can indicate the presence of the target molecule with a visible color change of the test line. In some types of lateral flow immunoassays, the target molecules in the sample fluid can be antigens. The antigens can pick up a tag molecule on a conjugate pad before flowing to the test line. In these particular examples, the test line can include an antibody as the test reactant. The antibodies can bind to the tagged antigens, which in some cases can cause a visible color to form along the test line. A control line is often located beyond the test line so that the sample fluid reaches the control line after the sample fluid has already flowed past the test line. The control line can indicate that the sample fluid has flowed sufficiently past the test line so that the test can be considered valid.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 is a flowchart illustration of an example method of forming a flow barrier in a porous substrate in accordance with examples of the present disclosure;

[0003] FIG. 2 shows an example lateral flow device in accordance with the present disclosure; [0004] FIG. 3 shows another example lateral flow device in accordance with the present disclosure;

[0005] FIG. 4 shows yet another example lateral flow device in accordance with the present disclosure;

[0006] FIGs. 5A-5B are schematic illustrations of an example process for forming a flow barrier in a porous substrate in accordance with the present disclosure;

[0007] FIGs. 6A-6B are schematic illustrations of another example process for forming a flow barrier in a porous substrate in accordance with the present disclosure;

[0008] FIGs. 7A-7C are schematic illustrations of yet another example process for forming a flow barrier in a porous substrate in accordance with the present disclosure;

[0009] FIGs. 8A-8B are schematic illustrations of another example process for forming a flow barrier in a porous substrate in accordance with the present disclosure;

[0010] FIG. 9 is a schematic illustration of an example lateral flow assay in accordance with the present disclosure;

[0011] FIG. 10 is a schematic illustration of an example fluid ejection device in accordance with the present disclosure; and

[0012] FIG. 11 is a graph showing concentration of latex at multiple depths in a nitrocellulose membrane for a pre-treated sample membrane and a non-pre-treated sample membrane.

DETAILED DESCRIPTION

[0013] The present disclosure describes methods of forming hydrophobic flow barriers, such as in a porous substrate. In certain examples, the hydrophobic flow barriers can form fluid flow channels that direct fluids to flow in particular ways through the porous substrates. In one example, a method of forming a hydrophobic flow barrier in a porous substrate includes applying a pre-treatment composition to an area of a surface of a porous substrate. The pre-treatment composition includes a solvent, a cationic salt, a cationic polymer, or a combination thereof. The method also includes applying a flow modifier composition onto an area of a surface of the porous substrate. The flow modifier composition includes an aqueous solvent, dispersed hydrophobic material particles, and a dispersant. The flow modifier composition wicks through pores of the porous substrate, and the pre-treatment composition reduces a penetration rate of the dispersed hydrophobic material particles in the area where the pre-treatment composition is applied. In some examples, the pre-treatment composition, the flow modifier composition, or both, can be applied by a digital fluidic actuator. In further examples, the pre-treatment composition can include a calcium salt, a magnesium salt, a sodium salt, a polyvinyl alcohol modified with ammonium salt, a polyethyleneimine, a polyamine, a polydiallyldimethylarnmonium chloride, or a combination thereof. In certain examples, the pre-treatment composition can be applied to the same area where the flow modifier composition is applied, and the pre-treatment composition can reduce a penetration depth of the hydrophobic material particles so that the hydrophobic flow barrier extends partially through the thickness of the porous substrate. In still further examples, a test reactant can be applied to the area of the porous substrate on an opposite surface from the surface on which the flow modifier composition is applied. In some examples, the porous substrate can have a thickness from about 50 micrometers to about 200 micrometers and the hydrophobic flow barrier can extend through the porous substrate to a depth of from about 1 micrometer to about 199 micrometers. In other examples, the pre-treatment composition can be applied to a different area than the area where the flow modifier composition is applied, and the flow modifier composition can wick laterally through the porous substrate toward the area where the pre-treatment composition is applied. The pre-treatment composition can stop the penetration of the hydrophobic material particles such that the hydrophobic flow barrier has an edge at the area where the pre-treatment composition is applied.

[0014] The present disclosure also describes lateral flow devices. In one example, a lateral flow device includes a porous substrate having a flow path through the porous substrate for wicking an aqueous fluid along the flow path through the porous substrate. The lateral flow device also includes a hydrophobic flow barrier including a hydrophobic material. The hydrophobic flow barrier is formed in an area of the porous substrate such that the flow path is redirected around the hydrophobic flow barrier. The lateral flow device also includes a pre-treatment material including a cationic salt, a cationic polymer, or a combination thereof, in an area of the porous substrate. In some examples, the pre-treatment material can be in the same area of the porous substrate as the hydrophobic flow barrier, and the hydrophobic barrier can penetrate partially through the thickness of the porous substrate, leaving a portion of the thickness of the porous substrate without the hydrophobic material, such that the flow path is redirected through the portion of the thickness of the porous substrate without the hydrophobic material. In further examples, the lateral flow device can also include a test reactant penetrating the portion of the thickness of the porous substrate without the hydrophobic material. In other examples, the pre-treatment material can be in an area laterally adjacent to an edge of the hydrophobic flow barrier. In still further examples, the lateral flow device can also include a lateral flow assay housing around the porous substrate, and the housing can include a sample fluid inlet.

[0015] The present disclosure also describes fluid ejection devices that can be used to make the hydrophobic flow barriers described above. In one example, a fluid ejection device includes a substrate support to receive a porous substrate. The fluid ejection device also includes a first fluidic actuator to receive a pre-treatment composition. The first fluidic actuator is positioned to jet the pre-treatment composition onto an area of a surface of the porous substrate. The pre-treatment composition includes a solvent, a cationic salt, a cationic polymer, or a combination thereof. The fluid ejection device also includes a second fluidic actuator to receive a flow modifier composition. The second fluidic actuator is positioned to jet the flow modifier composition onto an area of a surface of the porous substrate. The flow modifier composition includes an aqueous solvent, dispersed hydrophobic material particles, and a dispersant. The flow modifier composition wicks through the porous substrate. The fluid ejection device also includes a controller to control the lateral spread, penetration depth, or both, of the flow modifier composition through the porous substrate to form a hydrophobic flow barrier. In some examples, the controller can control the lateral spread of the flow modifier composition through the porous substrate by causing the first fluidic actuator to jet the pre-treatment composition on an area laterally adjacent to the flow modifier composition. In other examples, the controller can control the penetration depth of the flow modifier composition by causing the first fluidic actuator to jet the pre-treatment composition in the same area as the flow modifier composition.

[0016] In addition to the examples described above, the methods and devices will be described in greater detail below. It is also noted that when discussing the methods of forming hydrophobic flow barriers in porous substrates, the lateral flow devices, and the fluid ejection devices described herein, these relative discussions can be considered applicable to the other examples, whether or not they are explicitly discussed in the context of that example. Thus, for example, in discussing a flow modifier composition in the context of a method of forming a hydrophobic flow barrier, this description can also apply to flow modifier compositions used with the fluid ejection devices and the flow modifier composition used to make the hydrophobic barriers in the lateral flow devices, and vice versa.

Methods of Forming Hydrophobic Flow Barriers

[0017] As mentioned above, the present disclosure describes methods of forming flow barriers, such as in porous substrates. The porous substrates with hydrophobic flow barriers can be used in a variety of applications, such as lateral flow assays, dot blot assays, western blots, catalytic substrates, enzymatic substrates, filtration, separation, and others. In some examples, the methods described herein can be used to form hydrophobic flow barriers within porous substrates, such as porous paper, nitrocellulose membranes, or other capillary flow membranes. In certain examples, the methods described herein can allow the shape of the hydrophobic flow barriers to be controlled in all directions (i.e. , x-, y-, and z-dimensional control) to form the hydrophobic flow barriers with a variety of three-dimensional shapes. In many examples, the hydrophobic barriers can be designed to block or channel the flow of fluids through the porous substrates. In some examples, the hydrophobic barriers can be used to form fluid flow paths that can be designed for various microfluidic purposes.

[0018] In certain examples, the methods described herein can be used to make a lateral flow device such as a membrane for a lateral flow immunoassay. In many cases, the reliability of this type of test can depend on tight control over the properties of the materials and the conditions involved in performing the test. However, controlling properties of the materials in the tests can be difficult due to an insufficient level of quality control in the raw materials used to manufacture the tests, such as the porous substrate material, reactants, and so on. The methods described herein can provide a way to form hydrophobic flow barriers in the porous substrates with a high level of precision. These hydrophobic flow barriers can allow for customized control of the flow of fluids through the porous substrate material. Controlling the flow of sample fluids through the porous membrane in this type of test can be helpful to make the test results more reliable and reproducible.

[0019] The methods of forming hydrophobic flow barriers describes herein can also help to conserve sample fluids and reactants or other materials used in manufacturing lateral flow assays or other chemical test devices. The hydrophobic flow barriers can be designed to form microfluidic channels with small sizes (for example 1 -100 micrometers in width). Miniaturizing the flow channels in this way can allow for very small volumes of sample fluid to be used in a variety of chemical test devices. Any additional reactants that are used can also be conserved because a relatively small amount of the reactants can be precisely placed in the narrow flow path of the sample fluid, in some examples. Some reactants used in these tests can be expensive, and therefore conserving the reactants can result in significant cost savings.

[0020] In the specific examples of lateral flow immunoassays, a test line is often formed by applying antibodies to the porous substrate. A fluid including the antibodies can be applied in a line to the porous substrate. If unrestricted, the fluid can penetrate through the entire thickness of the porous substrate. Therefore, the antibodies can be located throughout the whole thickness of the porous substrate. As mentioned above, in some examples the test line can indicate the presence of a target antigen with a visible color change due to the binding of tagged antigens. However, in practice, many of the antibodies in the test line are located too deep beneath the surface of the porous substrate for the color to be visible. In some cases, tagged antigens in the top 40 micrometers or less can be visible to an observer. The porous membranes used in lateral flow immunoassays are often 100 micrometers to 200 micrometers or more in thickness. Therefore, a significant portion of the antibodies are located deep within the porous substrate where the antibodies can bind to tagged antigens, but without contributing to the visible color change that indicates a positive test result. Accordingly, the antibodies and antigens bound in the deeper portions of the porous substrate are effectively wasted.

[0021] In certain examples, the methods described herein can be used to form hydrophobic flow barriers that occupy the deeper portions of the thickness of the porous substrate. The hydrophobic flow barrier can penetrate partially through the porous substrate, from the underside of the substrate. An upper portion of the porous substrate can remain free of the hydrophobic flow barrier material, so that sample fluid can flow through the top portion. In further examples, the hydrophobic flow barrier can be formed before the antibodies are applied to the substrate to form the test line. The antibodies can be applied in the top portion of the substrate, and the hydrophobic flow barrier can prevent the antibodies from penetrating into the deeper portions of the substrate. Therefore, the test line can be formed using a smaller amount of antibodies and the antibodies can be concentrated in the top portion of the substrate where the color change indicating a positive test will be visible. This can also increase the sensitivity of the assay because all of the target antigens present in the sample fluid are forced to flow through the upper portion of the substrate where the antibodies are concentrated.

[0022] In other examples, the accuracy of a lateral flow immunoassay can be increased even further by using hydrophobic flow barriers to direct the sample fluid to an area with concentration conjugate reactants, such as tagging molecules. This can increase the number of target antigens that interact with the conjugate reactants before reaching the test line. [0023] With this description in mind, FIG. 1 is a flowchart illustrating an example method 100 of forming a hydrophobic flow barrier in a porous substrate. The method includes: applying a pre-treatment composition to an area of a surface of a porous substrate, wherein the pre-treatment composition includes a solvent, a cationic salt, a cationic polymer, or a combination thereof 110; and applying a flow modifier composition onto an area of a surface of the porous substrate, wherein the flow modifier composition includes an aqueous solvent, dispersed hydrophobic material particles, and a dispersant, wherein the flow modifier composition wicks through pores of the porous substrate, and wherein the pre-treatment composition reduces a penetration rate of the dispersed hydrophobic material particles in the area where the pre-treatment composition is applied 120.

[0024] An example of a hydrophobic flow barrier formed in a porous substrate is shown in FIG. 2. This figure shows a cross-section of an example lateral flow device 200 that includes a porous substrate 210 and a hydrophobic flow barrier 220 formed within the porous substrate. The hydrophobic flow barrier in this example extends partially through the thickness of the porous substrate. Therefore, the hydrophobic flow barrier blocks fluid flow through a portion of the thickness of the porous substrate while fluid can flow through the remaining portion of the thickness of the porous substrate. The figure shows flow pathway lines 230 to indicate how fluid flows around the hydrophobic flow barrier.

[0025] FIG. 3 shows another example lateral flow device 200. In this example, the device includes a test line 240 and a control line 250 formed in the porous substrate in the portion that is not blocked by the hydrophobic flow barrier 220. The flow pathway lines 230 shows how fluid is directed to the test line and control line by the hydrophobic flow barrier. The test line can include a test reactant that can react with a target molecule to detect the presence of the target molecule. As explained above, in some examples the lateral flow device can be an immunoassay and the test line can include antibodies that can react with a target antigen.

[0026] Although the methods described herein can be used to make chemical tests, such as lateral flow assays in some examples, the methods can also be used for a variety of microfluidic applications unrelated to chemical testing. The methods described herein can allow for three-dimensional control of the shape of hydrophobic flow barriers formed in porous substrates. Three-dimensional hydrophobic flow barriers can be useful in a variety of microfluidic devices. In some examples, the hydrophobic flow barriers can be used to form microfluidic channels through a porous substrate. In certain examples, hydrophobic flow barriers can be used to slow flow of a fluid through a porous substrate by making a longer and more tortuous flow pathway. FIG. 4 shows an example lateral flow device 200 in which the fluid flow pathway is lengthened by placing multiple hydrophobic flow barriers 220 in the porous substrate 210. The flow pathway line 230 shows that fluid flows around the hydrophobic flow barriers, making the flow pathway longer compared to the porous substrate without the hydrophobic flow barriers.

[0027] The methods of forming flow barriers described herein can utilize a combination of a pretreatment composition and a flow modifier composition that can be applied to a porous substrate. The flow modifier composition can include dispersed hydrophobic material particles. When the flow modifier composition is applied to the porous substrate, the flow modifier composition can wick through pores of the porous substrate. After the flow modifier composition dries, the hydrophobic material particles can form a hydrophobic flow barrier. The pre-treatment composition can include a pre-treatment material that can reduce the penetration rate or stop the flow of the hydrophobic material particles in the flow modifier composition. Therefore, the pre-treatment composition can be applied to the porous substrate in selected areas where it is desired to prevent the flow of the hydrophobic material particles or to reduce the penetration of the hydrophobic material particles.

[0028] In some examples, applying the pre-treatment composition to an area of the porous substrate and then applying the flow modifier composition over the pre-treatment composition can result in partial penetration of the flow modifier composition into the porous substrate due to the presence of the pre-treatment material. In certain examples, the amount or concentration of the pre-treatment material can be adjusted to control the penetration depth of the hydrophobic material particles in the flow modifier composition. In other examples, the pre-treatment composition can be applied to one area of the porous substrate, and the flow modifier composition can be applied to a laterally adjacent area of the porous substrate. When the flow modifier composition wicks to the interface between the two areas, the pre-treatment composition can slow or stop the spread of the hydrophobic material particles. Thus, the pre-treatment composition can be used to control the lateral spread and the penetration depth of the hydrophobic material particles. This can allow for precise control over the three-dimensional shape of the hydrophobic flow barriers that form from the hydrophobic material.

[0029] The pre-treatment composition and flow modifier composition can be applied by a variety of application processes. In some examples, the pre-treatment composition can be applied by an analog method, such as spraying, or another coating method. However, in other examples, the pre-treatment composition can be applied by a digital method, such as a digital fluid actuator. In further examples, the flow modifier composition can also be applied by a digital fluid actuator. The digital fluid actuator can allow for targeted application of the pre-treatment composition and flow modifier composition at particular locations or x/y coordinates on the surface of the porous substrate. In certain examples, the digital fluid actuator can include a thermal jet that can jet droplets of the fluid compositions. Thermal jet actuators can use a thermal resistor to heat a small quantity of fluid until an evaporation bubble forms. This bubble can displace a sufficient amount of surrounding fluid to force a droplet of fluid out a nozzle. This droplet can be directed onto the porous substrate. In other examples, the digital fluid actuator can include a piezoelectric jet. Piezoelectric jets can include a piezoelectric element that physically first a droplet of fluid in response to an electric current supplied to the piezoelectric element. In some examples, the digital fluid actuator can be an inkjet printhead, or can be similar or identical to an inkjet printhead. It should be noted that although the pre-treatment composition and flow modifier composition can be applied using an inkjet printhead, this does not imply that the compositions are inks or marking fluids. However, in some examples, the compositions can be applied by a system similar to an inkjet printer. The fluid actuator can be moveable to allow the fluid compositions to be jetted onto specific locations in the x/y plane on the surface of the porous substrate.

[0030] Using a digital fluid actuator to apply the pre-treatment composition and the flow modifier composition onto the porous substrate can provide a high level of control over the x/y size and shape of the hydrophobic flow barriers. Although the digital fluid actuator can be quite precise, the porous nature of the porous substrate can tend to make the flow modifier composition spread through the thickness of the substrate (i.e. , the “z” direction) and laterally (i.e., the “x” and “y” directions). Therefore, applying the flow modifier composition alone can be somewhat imprecise, based on the lateral spread and penetration that occur through the porous substrate. It can therefore be useful to control the lateral spread and penetration depth of the flow modifier composition by using the pre-treatment composition. In some examples, the pre-treatment composition can include a pre-treatment material that can interact with dispersed hydrophobic material particles by causing the particles to come out of dispersion and to become fixed in the porous substrate. In certain examples, this pre-treatment material can be a cationic material, such as a cationic metal salt or a cationic polymer. In other examples, the pre-treatment composition can include an appropriate amount of a solvent that can occupy the pore volume in a particular area of the porous substrate. By occupying the pore volume, the pre-treatment composition can reduce the tendency of the flow modifier composition to spread into that area of the porous substrate. Example formulations of the pre-treatment composition area are described in more detail below.

[0031] The methods described herein can include several ways that the pre-treatment composition can be used in combination with the flow modifier composition to control the size and shape of hydrophobic flow barriers. FIGs. 5A-5B show an example process for forming a hydrophobic flow barrier in a porous substrate 210 while controlling the penetration depth and lateral spread of flow modifier composition 260. In this example, the pre-treatment composition 270 is applied to an area of the surface of the porous substrate using a first fluidic actuator 272. Then, as shown in FIG. 5B, the flow modifier composition is applied by a second fluidic actuator 262. The flow modifier composition is applied to the same area where the pre-treatment composition was applied. The pre-treatment composition reduces the penetration depth of the flow modifier composition so that the flow modifier composition penetrates partially into the porous substrate. Without the pre-treatment composition, the flow modifier composition can penetrate all the way through the thickness of the porous substrate. When the flow modifier composition dries, the hydrophobic material particles in the flow modifier composition can form a hydrophobic flow barrier that penetrates partially through the thickness of the porous substrate.

[0032] In some examples, the penetration depth of the flow modifier composition can depend on the concentration of the pre-treatment composition that is present in the porous substrate. If the pre-treatment composition includes a cationic pre-treatment material such as a cationic salt or a cationic polymer, then the concentration of this agent in the porous substrate can affect the penetration depth of the flow modifier composition. As used herein, “penetration depth of the flow modifier composition” can refer to the penetration of the flow modifier composition as a whole, i.e. , including the aqueous solvent and other ingredients, or this phrase can refer to the penetration of the hydrophobic material particles specifically. The hydrophobic material particles can be the ingredient in the flow modifier composition that forms the hydrophobic flow barriers. Therefore, controlling the penetration depth of these hydrophobic material particles in particular can have the effect of controlling the shape of the hydrophobic flow barriers.

[0033] Regarding the concentration of the pre-treatment material in the porous substrate, in some examples this can be controlled by adjusting the volume of the pre-treatment composition that is applied to the porous substrate. In certain examples, the pre-treatment composition can be applied with a higher density, in terms of volume per area of porous substrate, in areas where a smaller penetration depth of the hydrophobic material particles is desired. In some examples, the pre-treatment composition can be applied in multiple passes, where a higher number of passes applies a larger volume of the pre-treatment composition. In other examples, the concentration of a cationic pre-treatment material in the pre-treatment composition can be adjusted to change the amount of pre-treatment material that is applied to the porous substrate. If a high concentration of the pre-treatment material in the porous substrate is desired, then the methods can utilize a pre-treatment composition that has a high concentration of the cationic pre-treatment material. In certain examples, the pre-treatment composition can be applied to the porous substrate in an amount from about 0.05 drops per pixel (dpp) to about 4 dpp, based on a square pixel size of 1 /300^th inch by 1 /300^th inch. In further examples, the pre-treatment composition can be applied in an amount from about 0.1 dpp to about 2 dpp. A drop per pixel (dpp) can be about 36 nanograms per pixel area of 1 /300^th inch squared (ng/(300^th in.)²), in some examples. In further examples, the pre-treatment composition can include a cationic material such as a cationic salt or cationic polymer in an amount from about 0.5 wt% to about 20 wt%. Accordingly, in some examples the amount of the cationic material that is deposited onto the porous substrate can be from about 0.25 grams per square meter (gsm) to about 20 gsm, or from about 0.5 gsm to about 10 gsm, in some examples. In further examples, the pre-treatment composition and the flow modifier composition can be applied to amounts selected such that the hydrophobic flow barrier formed penetrates from about 1 % to about 100% of the way through the thickness of the porous substrate. In still further examples, the amounts can be selected so that the hydrophobic flow barrier penetrates from about 50% to about 100% of the way through the porous substrate.

[0034] In further examples, the flow modifier composition can be applied by a fluidic actuator and the amount of flow modifier composition applied per pass can be measured in drops per pixel (dpp). In certain examples, the amount of flow modifier composition applied in a single pass can be from about 1 dpp to about 16 dpp, or from about 1 dpp to about 8 dpp, or from about 2 dpp to about 8 dpp. The number of passes can be from about 1 to about 32, or from about 1 to about 16, or from about 2 to about 8. In certain other examples, the total amount of flow modifier composition applied in all the passes cumulatively can be from about 1 dpp to about 32 dpp, or from about 1 dpp to about 16 dpp, or from about 2 dpp to about 16 dpp. In other examples, the amount of flow modifier composition applied can be measured in units of nanograms per 300^th inch (ng/300^th in.). A drop per pixel (dpp) can be about 36 ng/300^th in.

[0035] In further examples, three-dimensional hydrophobic flow barriers can be formed by applying the pre-treatment composition in certain areas where partial penetration of the hydrophobic flow barrier is desired, and then applying the flow modifier composition over the pre-treatment composition and additional areas where no pre-treatment composition has been applied. In certain examples, the hydrophobic flow barrier composition can penetrate all the way through the porous substrate in the areas where the pre-treatment composition was not applied. FIGs. 6A-6B show one such example in which a pre-treatment composition 270 is applied to one area of the porous substrate 210. A flow modifier composition 260 is then applied to a larger area that overlaps the pre-treatment composition. In the area where the flow modifier composition overlaps the pre-treatment composition, the penetration depth of the hydrophobic material particles is reduced. In the area where flow modifier composition is applied without any pre-treatment composition, the hydrophobic material particles penetrate all the way through the porous substrate. The hydrophobic material particles can become a hydrophobic low barrier when the flow modifier composition dries. In this way, a three-dimensional hydrophobic barrier having two different penetration depths can be formed. In further examples, hydrophobic flow barriers can be formed with other profiles in the “z” depth direction, such as hydrophobic flow barriers having multiple steps at different depths, or hydrophobic flow barriers having sloping surfaces that slope over a range of depths. In some examples, these shapes can be controlled by varying the amount of pre-treatment composition or the concentration of a cationic pre-treatment material that is present in the porous substrate.

[0036] FIGs. 7A-7C show yet another example. In this example, the pre-treatment composition 270 is applied to an area of the porous substrate 210. Then, the flow modifier composition 260 is applied in the same area where the pre-treatment composition was applied. The pre-treatment composition reduces the penetration depth of the flow modifier composition. The hydrophobic material particles in the flow modifier composition form a hydrophobic flow barrier 220 that penetrates partially through the porous substrate. FIG. 7C shows that the porous substrate is flipped over so that the hydrophobic flow barrier is on the bottom of the porous substrate. Then, a test line 240 and a control line 250 are formed over the hydrophobic flow barrier. The test line and control line can be formed by applying appropriate reactants. The reactants can be applied by a variety of application methods. In some examples, the reactants can be applied by a striping device. In other examples, the reactants can be applied by a fluidic actuator such as an inkjet printhead.

[0037] The above examples illustrate how the pre-treatment composition can be used to control the penetration depth of the hydrophobic flow barriers. In other examples, the pre-treatment composition can be used to control lateral spread of the hydrophobic material particles. For example, the pre-treatment composition and the flow modifier composition can be applied on laterally adjacent areas, and the pre-treatment composition can reduce the rate flow of the hydrophobic material particles into the area where the pre-treatment composition is applied. If a sufficient amount of pre-treatment composition is applied, then the flow of the hydrophobic material particles can effectively be stopped at the interface of the area where the pre-treatment composition was applied. In this way, the shape of the hydrophobic flow barrier can be precisely controlled in the lateral, or x/y directions.

[0038] FIGs. 8A-8B show an example in which the lateral spread of the hydrophobic material particles is stopped in this way. In this example, the pre-treatment composition 270 is jetted onto areas of the porous substrate along edges of the area where a hydrophobic flow barrier is desired. The flow modifier composition 260 is then jetted onto the area between the edges. The flow modifier composition wicks through the thickness of the porous substrate, but the pre-treatment composition prevents the flow of hydrophobic material particles into the areas where the pre-treatment composition was applied. In this way, a hydrophobic barrier with well-defined edges can be formed. In certain examples, this method can produce hydrophobic flow barriers that are narrower than would be possible by jetting the flow modifier alone because the flow modifier composition would tend to spread laterally through the porous substrate.

[0039] In further examples, any of the methods described above can be used in combination. For example, the penetration depth of the flow modifier composition can be controlled by applying the pre-treatment composition to the same area where the flow modifier composition is applied, and the lateral spread of the flow modifier composition can also be controlled using the pre-treatment composition. In one example, a higher concentration or amount of the pre-treatment composition can be applied around the lateral edges to prevent the hydrophobic material particles from flowing across the edges and a lower concentration of the pre-treatment composition can be applied in the area where the penetration depth is to be controlled. This can result in a hydrophobic flow barrier that has a controlled penetration depth and controlled lateral edges.

[0040] Additionally, in some examples, the hydrophobic material from the flow modifier composition can be cured after the flow modifier composition is applied to the porous substrate. Curing can include heating the hydrophobic material to a curing temperature. In some examples, the curing temperature can be from about 50 °C to about 150 °C. However, in other examples, the hydrophobic flow barriers can be formed without any additional curing operation. In certain examples, the hydrophobic material can be capable of forming a hydrophobic flow barrier at room temperature.

Pre-treatment Compositions

[0041] The pre-treatment compositions used in the methods described above can include a solvent, a cationic salt, a cationic polymer, or a combination thereof. The solvent in the pre-treatment composition can include water, an organic solvent, or a combination thereof. In some examples, the pre-treatment composition can include water and an organic co-solvent. In certain examples, the solvent can be sufficient for use as a pre-treatment composition without any cationic salt or cationic polymer. For example, a pre-treatment composition consisting of a solvent can be applied to a porous substrate, and occupy the volume of the pores in the porous substrate. If a flow modifier composition is then applied to the porous substrate, the pre-treatment composition occupying the pores can reduce or stop the spread of the flow modifier composition in the area where the pre-treatment composition was applied.

[0042] In further examples, the pre-treatment composition can include a cationic salt. The cationic salt can include a metal cation and an anion. In some examples, the cationic salt can be a polyvalent metal salt. In other examples, the cationic salt can be a monovalent metal salt. In certain examples, the cationic salt can include a cation such as calcium, magnesium, or sodium. The cationic salt can also include an anion such as chloride, bromide, iodide, or others. In certain examples, the cationic salt can include calcium chloride, magnesium chloride, sodium chloride, or a combination thereof. In other examples, the pre-treatment composition can include a cationic polymer. Non-limiting examples of cationic polymers that can be used can include polyvinyl alcohol modified with ammonium salt, polyethyleneimine, polyamine, polydiallyldimethylammonium chloride, and combinations thereof. In still further examples, the pre-treatment composition can include a combination of a cationic salt and a cationic polymer.

[0043] In some examples, the cationic salt, cationic polymer, or combination thereof can be present in an amount from about 0.5 wt% to about 20 wt% with respect to the total weight of the pre-treatment composition. In further examples, the amount of the cationic material can be from about 1 wt% to about 15 wt% or from about 5 wt% to about 10 wt%.

[0044] As mentioned above, in some examples the pre-treatment composition can include water and an organic co-solvent. In certain examples, a co-solvent can be included in the pre-treatment composition in an amount of from about 1 wt% to about 20 wt%, based on the total weight of the pre-treatment composition. In further examples, the co-solvent can be present in an amount of from about 3 wt% to about 12 wt%, or from about 5 wt% to about 10 wt%, or from about 5 wt% to about 7 wt%. Including an organic co-solvent can help to make the pre-treatment composition jettable from a fluid actuator such as a thermal inkjet printhead. Non-limiting examples of suitable co-solvents can include aliphatic alcohols, aromatic alcohols, diols, triols, glycol ethers, poly(glycol) ethers, lactams, formamides, acetamides, long chain alcohols, ethylene glycol, propylene glycol, diethylene glycols, triethylene glycols, glycerine, dipropylene glycols, glycol butyl ethers, polyethylene glycols, polypropylene glycols, amides, ethers, carboxylic acids, esters, organosulfides, organosulfoxides, sulfones, alcohol derivatives, carbitol, butyl carbitol, cellosolve, ether derivatives, amino alcohols, and ketones. For example, co-solvents can include primary aliphatic alcohols of 30 carbons or less, primary aromatic alcohols of 30 carbons or less, secondary aliphatic alcohols of 30 carbons or less, secondary aromatic alcohols of 30 carbons or less, 1 ,2-diols of 30 carbons or less, 1 ,3-diols of 30 carbons or less, 1 ,5-diols of 30 carbons or less, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, poly(ethylene glycol) alkyl ethers, higher homologs of poly(ethylene glycol) alkyl ethers, polypropylene glycol) alkyl ethers, higher homologs of polypropylene glycol) alkyl ethers, lactams, substituted formamides, unsubstituted formamides, substituted acetamides, and unsubstituted acetamides.

[0045] Certain specific examples of co-solvents can include hydantoin glycol (such as, e.g., 1 ,3-bis-(2-hydroxyethyl)-5,5-dimethylhydantoin),

1-(2-hydroxyethyl)-2-pyrrolidinone, 1-(2-hydroxyethyl)-2-imidazolidinone, tetratethylene glycol, 1 ,2,6-hexanetriol, glycerol, glycerol propoxylate, 1 ,5-pentanediol, LIPONIC® ethoxylated glycerol 1 (LEG-1) or LIPONIC® ethoxylated glycerol 7 (LEG-7) from Vantage Specialty Chemicals (USA),, 2-methyl-2,4-pentanediol,

2-methyl-1 ,3-propanediol, 2-ethyl-2-hydroxymethyl-1 ,3-propanediol, diethylene glycol,

3-methoxybutanol, propylene glycol monobutyl ether, 1 ,3-dimethyl-2-imidazolidinone, or combinations thereof.

[0046] In further examples, the pre-treatment composition can include other additives. Some additives can be included to increase the jettability of the pre-treatment composition. These additives can include surfactants, anti-kogation agents, pH adjusters, antimicrobial agents, sequestering agents, viscosity modifiers, humectants, penetrants, wetting agents, preservatives, jettability additives, and mixtures thereof. In various examples, these additives can include specific materials and amounts as described below in the fluid modifier compositions. In certain examples, the additives can be present collectively in an amount from about 0.1 wt% to about 10 wt% with respect to the total weight of the pre-treatment composition.

Flow Modifier Compositions

[0047] The flow modifier compositions used in the methods described above can include an aqueous solvent, dispersed hydrophobic material particles, and a dispersant. The properties of the flow modifier composition and the porous substrate can be such that the flow modifier composition wicks through the pores in the porous substrate when applied.

[0048] As used herein, “aqueous solvent” refers to a solvent system that includes water and which may include additional solvents, such as organic solvents. In some examples, the aqueous solvent can be water. In other examples, the aqueous solvent can include water and an organic solvent. Water used in the aqueous solvent can include deionized water, distilled water, purified water, filtered water, or other water. In certain examples, the flow modifier composition can include the aqueous solvent in an amount from about 1 wt% to about 99 wt% based on the total weight of the flow modifier composition. In further examples, the flow modifier composition can include dispersed hydrophobic material particles in an amount from about 0.1 wt% to about 20 wt% and a dispersant in an amount from about 0.05 wt% to about 5 wt%. In certain examples, the flow modifier composition can consist of the aqueous solvent, dispersed hydrophobic material particles, and dispersant. In a particular example, the flow modifier composition can consist of water, dispersed hydrophobic material particles, and dispersant. In other examples, the flow modifier composition can include other ingredients such as surfactants, biocides, anti-kogation agents, and other additives.

[0049] In further examples, the flow modifier composition can include the aqueous solvent in an amount of from about 1 wt% to about 99 wt%, dispersed hydrophobic material particles in an amount of from about 1 wt% to about 20 wt%, and a dispersant in an amount of from about 0.05 wt% to about 5 wt%. In certain examples, these flow modifier compositions can also include a surfactant in an amount from about 0.1 wt% to about 10 wt%. In some further examples, the flow modifier composition can include water in an amount of from about 1 wt% to about 90 wt%, an organic co-solvent in an amount of from about 1 wt% to about 20 wt%, dispersed hydrophobic material particles in an amount of from about 1 wt% to about 20 wt%, a dispersant in an amount of from about 0.05 wt% to about 5 wt%, and a surfactant in an amount of from about 0.1 wt% to about 10 wt%. In some examples, the flow modifier composition can consist of the water, co-solvent, dispersed hydrophobic material particles, dispersant, and surfactant as described above.

[0050] In some examples, the aqueous solvent can be included in the flow modifier composition in an amount greater than about 50 wt%. In further examples, the aqueous solvent can be included in an amount of from about 50 wt% to about 99 wt%, or from about 60 wt% to about 97.4 wt%, or from about 70 wt% to about 90.4 wt%, or from about 70 wt% to about 87.6 wt%, or from about 70 wt% to about 97.4 wt%.

[0051] As mentioned above, the aqueous solvent can include an organic co-solvent in some examples. In certain examples, a co-solvent can be included in the flow modifier composition in an amount of from about 1 wt% to about 20 wt%, based on the total weight of the flow modifier composition. In further examples, the co-solvent can be present in an amount of from about 3 wt% to about 12 wt%, or from about 5 wt% to about 10 wt%, or from about 5 wt% to about 7 wt%. Including an organic co-solvent can help to make the flow modifier composition jettable from a fluid actuator such as a thermal inkjet printhead. In various examples, the co-solvent can include any of the co-solvents described above in the pre-treatment composition.

[0052] The dispersed hydrophobic material particles in the flow modifier composition can include a variety of hydrophobic materials capable of forming a hydrophobic barrier in the porous substrate. In some examples, the hydrophobic material can be a polymer, such as a wax or a latex polymer. In certain examples, the hydrophobic material can be a wax. In some examples the wax can be selected from a group consisting of a paraffin wax, a polyethylene wax, a fluorothermoplastic, and combinations thereof. The wax can be a wax emulsion. Wax emulsions are commercially available from a number of vendors, for example Keim-Additec (Germany), Lubrizol (USA), Michelman (USA), and BYK Chemie (Germany). Specific examples of wax emulsions include: Lubrizol: LIQUILUBE™ 488 (melting point (mp) 85°C), LIQUILUBE™ 443 (mp 80°C), LIQUILUBE™ 405; Michelman: ME48040 (mp 85°C), ME98040M1 (mp 98°C), ML160 (mp 85°C); Keim-Additec: ULTRALUBE® E-7093 (mp 84°C), ULTRALUBE® 7095/1 (mp 80°C), BYK:

AQUACER® 2650 (mp 85°C), AQUACER® 533 (mp 95°C), and AQUASLIP™ 942 (mp 83°C).

[0053] In some examples, the wax can include a paraffin wax or modified paraffin wax with a relatively low melting point. Specific examples of a paraffin wax or modified paraffin wax with a relatively low melting point include BYK AQUACER® A494 with a melting point of about 60 °C, BYK AQUACER® A497 with a melting point of about 60 °C, BYK AQUACER® 8330 with a melting point of about 60 °C, BYK AQUACER® 8333 with a melting point of about 60 °C, and BYK AQUACER® 8335 with a melting point of about 58 °C. Other examples of paraffin wax can include BYK AQUACER® 494, BYK AQUACER® 533, BYK AQUACER® 539, BYK AQUACER® 1039, BYK AQUACER® 565, BYK AQUACER® 581 , BYK AQUACER® 2650, BYK AQUACER® 8603, and BYK AQUACER® 8669 (available from BYK, Germany).

[0054] In other examples, the flow modifier composition can include a polymer emulsion such as a latex polymer. In certain examples, the latex polymer can include styrene, styrene-butadiene, acrylic, acrylate, methyl methacrylate, butyl acrylate, methacrylic acid, or copolymers thereof. In one example, the flow modifier composition can include ROVENE® 4100, which is a carboxylated styrene-butadiene emulsion available from Mallard Creek Polymers (USA). [0055] In various examples, the dispersed hydrophobic particles can be included in the flow modifier composition in an amount of from about 0.1 wt% to about 20 wt%. In other examples, the amount can be from about 0.1 wt% to about 10 wt%, or from about 0.1 wt% to about 5 wt%, or from about 0.1 wt% to about 3 wt%, or from about 1 wt% to about 5 wt%, or from about 2 wt% to about 5 wt%.

[0056] The hydrophobic particles can have an average particle size that can allow the particles to flow through the pores in the porous substrate. In some examples, the hydrophobic particles can have an average particle size of from about 0.01 micrometers to about 2.0 micrometers. In further examples, the average particle size can be from about 0.1 micrometers to about 1 micrometer or from about 0.1 micrometers to about 0.3 micrometers.

[0057] The hydrophobic material particles can be dispersed in the aqueous solvent by a dispersant. In certain examples, the dispersant can include an alcohol ethoxylate dispersant. In a particular example, the residual dispersant can include UNITHOX™ 750 (Baker Hughes, USA), which is an alcohol ethoxylate dispersant with a molecular weight of 1400 g/mol, with a 50% ethylene oxide content by weight.

[0058] As mentioned above, in some examples, the flow modifier composition can also include a surfactant. The surfactant can include non-ionic, cationic, or anionic surfactants. In some examples, the surfactant can be present in an amount of from about 0.1 wt% to about 10 wt% with respect to the total weight of the flow modifier composition. In further examples, the surfactant can be included in an amount of from about 0.1 wt% to about 5 wt% or from about 0.1 wt% to about 2 wt%.

[0059] In certain examples, the surfactant can include an ethoxylated alcohol such as those from the TERGITOL® series (e.g., TERGITOL® 15S30, or TERGITOL® 15S9), manufactured by The Dow Chemical Company (USA); surfactants from the SURFYNOL® series (e.g., SURFYNOL® 104, SURFYNOL® 440 and SURFYNOL® 465), and DYNOL™ series (e.g., DYNOL™ 360, DYNOL™ 604, and DYNOL™ 607) manufactured by Air Products and Chemicals, Inc. (USA). In other examples, the surfactant can include a polysorbate surfactant. Examples of polysorbate surfactants can include Polysorbate 20 (or polyoxyethylene 20 sorbitan monolaurate), Polysorbate 40 (or polyoxyethylene 20 sorbitan monopalmitate), Polysorbate 60 (or polyoxyethylene 20 sorbitan monostearate), Polysorbate 80 (or polyoxyethylene 20 sorbitan monooleate), or the like. Other polysorbates can likewise be used, including Polysorbate 85, or TWEEN® 85, which is polyethylene glycol sorbitan trioleate; or Polysorbate 81 , TWEEN® 81 , which is a polyoxyethylene (5) sorbitan monooleate, or TWEEN® 20 which is a polyoxyethylenesorbitan monolaurate (available from Croda, United Kingdom). Polyoxyethylene sorbitan dioleate can also be used. In other examples, the surfactant can include a polyoxyethylene glycol ether. Examples of such surfactants that can be used include BRIJ® S, BRIJ® O, BRIJ® C, and BRIJ® L type surfactants (available from Croda, United Kingdom). SYNPERONIC® surfactants can also be used (available from Croda, United Kingdom). Specific examples include BRIJ® S10, BRIJ® S5, BRIJ®, S15, BRIJ® S20, BRIJ® S2/93, BRIJ® S7, BRIJ® 98/020, BRIJ® O10, BRIJ® 35, BRIJ® 02, BRIJ®, 03, BRIJ® 05, BRIJ® C2, BRIJ® C7, BRIJ® C10, BRIJ®, C20, BRIJ® L4/30 , BRIJ® L9, BRIJ® L15, SYNPERONIC® 91-2.5, SYNPERONIC® 91-2.5, SYNPERONIC® 91-10, or mixtures thereof (available from Croda, United Kingdom). In some examples, the surfactant can be TRITON™ X100, which is a polyethylene glycol tert-octylphenyl ether surfactant manufactured by Air Products and Chemicals, Inc. (USA).

[0060] In certain examples, the flow modifier composition can be free of certain ingredients. In one example, the flow modifier composition can be acid-free. For example, the flow modifier composition can be free of hydrochloric acid, sulphuric acid, sulphurous acid, phosphoric acid, citric acid, oxalic acid, acetic acid, formic acid, sulphamic acid, tartaric acid, phytic acid, boric acid, succinic acid, suberic acid, and/or benzoic acid. In further examples, the flow modifier composition can be colorant-free. The flow modifier composition can be free of colorants such as pigments and dyes, which are often used in marking agents such as inks. However, the flow modifier compositions described herein can, in some examples, be applied using similar devices to those used in inkjet printers. In particular, a thermal fluid jet similar to a thermal inkjet printhead can be used to jet the flow modifier composition. However, the flow modifier composition is not an ink and therefore, in some examples, the flow modifier composition can be free of colorants. In further examples, the flow modifier composition can be free of binders. Binders can include additional polymers besides the dispersed hydrophobic particles. In certain examples, binders can include polyurethane polymers. Accordingly, in some examples, the flow modifier composition can be free of these binders.

[0061] In other examples, the flow modifier composition can include an acid, or a colorant, or a binder, but in a relatively small amount. In certain examples, the flow modifier composition can include an acid, a colorant, or a binder in an amount of less than about 5 wt%, or less than about 3 wt%, or less than about 1 wt%, or less than about 0.1 wt%.

[0062] In still further examples, the flow modifier composition can be free of photocurable or ultraviolet (UV) curable materials. These materials can include monomers or polymers that can be polymerized and/or cross-linked upon exposure to ultra-violet radiation. In some examples, the flow modifier compositions can be used without application of UV light. The hydrophobic material particles in the flow modifier composition can form hydrophobic barriers without the use of UV light for curing. In certain examples, the flow modifier composition can be free of UV curable monomers. In further examples, the flow modifier composition can be free of photoinitiators.

[0063]The flow modifier compositions can also include additional additives. Additives can include anti-kogation agents, pH adjusters, antimicrobial agents, sequestering agents, viscosity modifiers, humectants, penetrants, wetting agents, preservatives, jettability additives, and mixtures thereof.

[0064] Kogation refers to the deposit of residue on a heating element of a thermal inkjet printhead. An anti-kogation agent can be included to assist in preventing the buildup of kogation. Anti-kogation agents can include an anionic surfactant, a nonionic surfactant, a zwitterionic surfactant, an amphoteric surfactant, or mixtures thereof. A list of surfactants is given above. In some examples, the anti-kogation agents can include oleth-3-phosphate (commercially available as CRODAFOS® 03A or CRODAFOS® N-3 acid, from Croda, United Kingdom) or dextran 500k. The anti-kogation agent can be present in the flow modifier composition in an amount ranging from about 0.1 wt% to about 3.0 wt% of the total weight of the flow modifier composition.

[0065]A pH adjuster can also be added to the flow modifier compositions in some examples. A pH adjuster can include sodium hydroxide, potassium hydroxide, ammonia, hydrochloric acid, nitric acid, sulfuric acid, and (poly)alkanolamines such as triethanolamine and 2-amino-2-methyl-1-propaniol, phosphate, Tris, HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid), MOPS

(3-(N-morpholino)propanesulfonic acid), or mixtures thereof. In some examples, the pH adjuster can provide a buffered solution to control the pH of the flow modifier composition within a range based on the biomolecules that may be used on the porous substrate.

[0066] In some examples, the flow modifier composition can also include an antimicrobial agent. Suitable antimicrobial agents include biocides and fungicides. Examples of antimicrobial agents include ACTICIDE® M20 (/.e., active ingredient is 2-methyl-4-isothiazolin-3-one), ACTICIDE® B20 (/.e., active ingredient is 1 ,2-benzisothiazolin-3-one) (available from Thor, United Kingdom), AMP (/.e., amino-tris-(methylene phosphonate), TRIS (/.e., tris(hydroxymethyl)nitromethane), and mixtures thereof. Other examples of antimicrobial agent include NUOSEPT® (Ashland Inc., USA), UCARCIDE™ or KORDEK™ (The Dow Chemical Co., USA), and PROXEL® (Arch Chemicals, USA) series, and combinations thereof.

[0067] In some examples, sequestering agents can be added to the flow modifier compositions. These sequestering agents can be useful to impart increased stability characteristics to the flow modifier composition and can include an alkali metal, an alkaline earth metal, and an ammonium salt of a linear aliphatic substituted glycine compound. The term linear aliphatic substituted glycine designates glycine compounds in which the amino group of glycine has been substituted with linear aliphatic groups. In some examples, the sequestering agents can include the alkali metal (e.g., sodium), alkaline earth metal (e.g., calcium) and ammonium salts of ethylene diamine tetraacetic acid, nitrilo triacetic acid, diethylene triamine pentaacetic acid, hydroxyethylene diamine triacetic acid, di hydroxy ethyl glycine, iminodiacetic acid and ethanol diglycine. Similar salts of other linear aliphatic substituted glycine compounds can also be used.

[0068] In some examples, viscosity modifiers can be added to the flow modifier compositions. Examples of viscosity modifiers include aliphatic ketones, stearone, 2-hydroxy benzyl alcohol, 4- hydroxy benzyl alcohol, 4-nitrobenzyl alcohol, 4-hydroxy-3-methoxy benzyl alcohol, 3-methoxy-4-nitrobenzyl alcohol,

2-amino-5-chlorobenzyl alcohol, 2-amino-5-methylbenzyl alcohol,

3-amino-2-methylbenzyl alcohol, 3-amino-4-methyl benzyl alcohol, 2(2-(aminomethyl)phenylthio)benzyl alcohol, 2,4,6-trimethylbenzyl alcohol,

2-amino-2-methyl-1 ,3-propanediol, 2-amino-1 -phenyl-1 ,3-propanediol,

2.2-dimethyl-1 -phenyl- 1 ,3-propanediol, 2-bromo-2-nitro-1 ,3-propanediol,

3-tert-butylamino-1 ,2-propanediol, 1 , 1 -diphenyl-1 ,2-propanediol,

1 ,4-dibromo-2,3-butanediol, 2,3-dibromo-1 ,4-butanediol,

2.3-dibromo-2-butene-1 ,4-diol, 1 ,1 ,2-triphenyl-1 ,2-ethanediol, 2-naphthalenemethanol, 2-methoxy-1 -naphthalenemethanol, decafluoro benzhydrol, 2-methylbenzhydrol, 1-benzeneethanol, 4,4'-isopropylidene bis(2-(2,6-dibromo phenoxy)ethanol), 2,2'-(1 ,4-phenylenedioxy)diethanol, 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol, di(trimethylolpropane), 2-amino-3-phenyl-1 -propanol, tricyclohexyl methanol, tris(hydroxymethyl)aminomethane succinate, 4,4'-trimethylene bis(1 -piperidine ethanol), N-methyl glucamine, or mixtures thereof.

[0069] In some examples, the flow modifier compositions can also contain penetrants for accelerating penetration of the flow modifier composition into the substrate. Suitable penetrants include polyhydric alcohol alkyl ethers (glycol ethers) and/or 1 ,2-alkyldiols. Examples of suitable polyhydric alcohol alkyl ethers are ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether, ethylene glycol mono-isopropyl ether, diethylene glycol mono-isopropyl ether, ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1 -methyl-1 -methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-isopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-isopropyl ether, propylene glycol mono-n-butyl ether, dipropylene glycol mono-n-butyl ether, or combinations thereof. Examples of 1 ,2-alkyldiols can include 1 ,2-pentanediol, 1 ,2-hexanediol, or combinations thereof. The penetrant can also be selected from straight-chain hydrocarbon diols, such as 1 ,3-propanediol, 1 ,4-butanediol, 1 ,5-pentanediol,

1 ,6-hexanediol, 1 ,7-heptanediol, 1 ,8-octanediol, and combinations thereof.

[0070] In some examples, the flow modifier compositions can include preservatives. Specific examples of preservatives can include dichlorophene, hexachlorophene, 1 , 2-benzothiazolin-3-one, 3,4-isothiazolin-3-one, or 4,4-dimethyl oxazolidine, alkyl isothiazolone, chloroalkyl isothiazolone, benzoisothiazolone, bromonitroalcohol, chloroxylenol, or mixtures thereof.

[0071] In various examples, the flow modifier composition can include a single additive from the additives described above, or a combination of multiple additives.

In some examples, the additives can be included in a total amount from about 0.1 wt% to about 10 wt% based on the total weight of the fluid modifier composition.

Porous Substrates

[0072] The porous substrates used with the present methods can include a variety of porous materials that can allow fluid flow within the pores of the material. In some examples, the porous substrate can wick fluids through the substrate material by capillary action. This can allow the flow modifier composition to spread throughout the porous substrate by capillary action. The spreading of the flow modifier composition can be controlled by any of the methods described above. The ability to wick fluids by capillary action can also be utilized to allow sample fluids to flow through the porous substrate when the porous substrate is incorporated into a device such as a lateral flow assay.

[0073] In some examples, the porous substrate can be hydrophilic. Aqueous fluids can flow through hydrophilic substrates by capillary at a high flow rate. In other examples, the porous substrate can include a hydrophobic material. In certain examples, hydrophobic porous substrates can be treated with a detergent or other material to help aqueous fluids flow through the substrate. In further examples, the porous substrate can include fibers. In various examples, the fibers can include hydrophilic fibers, hydrophobic fibers, or both. In further examples, the fibers can include natural fibers, synthetic fibers, or both. In other examples, the porous substrate can be a sintered material having a porous network through which fluid can flow. In still other examples, the porous substrate can be a microstructured material that includes a porous network formed by another suitable method. Non-limiting examples of porous substrate materials that can be used include porous paper, filter paper, cellulose membranes, nitrocellulose membranes, polyvinylidene difluoride membranes, microstructured polymers, sintered polymers, fiberglass, and combinations thereof.

[0074] In many examples, the porous substrate can be in the form of a sheet, pad, or membrane. In certain examples, the porous substrate can have a thickness from about 50 micrometers to about 200 micrometers. In some examples, the thickness of the porous substrate can be referred to as the “z-dimension” of the porous substrate. The other dimensions (i.e. , length and width, or “x-dimension” and “y-dimension”) can have a size suitable for the particular application that the porous substrate is to be used for. In certain examples, a porous substrate used in a chemical test such as a lateral flow assay can have a length and width from about 1 mm to about 10 cm, or from about 2 mm to about 5 cm, or from about 5 mm to about 2 cm. In further examples, hydrophobic flow barriers for several devices can be formed on a single sheet, and then the sheet can be cut into smaller substrates to be used in multiple test devices.

[0075] In further examples, the porous substrate can include pores that can allow fluids to flow through the porous substrate. In particular, the flow modifier composition can flow through the pores when the flow modifier composition is applied to form the hydrophobic flow barriers. The dispersed hydrophobic particles in the flow modifier composition can be left in the pores of the porous substrate to form the hydrophobic flow barriers. Additionally, other fluids such as sample fluids can flow through the pores of the porous substrate. In some examples, the porous substrate can have an average pore size from about 0.1 micrometer to about 30 micrometers. In further examples, the porous substrate can have an average pore size from about 0.2 micrometers to about 20 micrometers, or from about 1 micrometer to about 15 micrometers. In some examples, the average pore size can be measured using a standard measurement technique, such as mercury intrusion porosimetry, gas adsorption porosimetry, capillary flow porometry, and so on.

Hydrophobic Flow Barriers

[0076] The hydrophobic flow barriers described herein can be located within the porous substrate and/or on a surface of the porous substrate. As explained above, the lateral spread and penetration depth of the flow modifier composition can be controlled when the flow modifier composition is applied onto the porous substrate. Then, the flow modifier composition can dry or partially dry to leave behind the hydrophobic material. The hydrophobic material can initially be in the form of dispersed particles when the hydrophobic material is in the flow modifier composition. In some examples, the hydrophobic material can remain in the form of discrete particles in the hydrophobic flow barrier, or the hydrophobic material can soften or melt to form a consolidated hydrophobic material. In certain examples, hydrophobic materials with a lower melting point can be more likely to melt and consolidate when forming the hydrophobic flow barrier. In further examples, a curing operation can be performed after applying the flow modifier composition. Curing can include heating the porous substrate to a temperature at which the hydrophobic material particles consolidate or partially consolidate.

[0077] Whether the hydrophobic material particles remain as discrete particles, or consolidate to form a consolidated material, or partially consolidate, the hydrophobic material can be present in the porous substrate in a sufficient amount to reduce or prevent the flow of an aqueous fluid through the hydrophobic flow barriers. Accordingly, in some examples, the hydrophobic flow barrier may not be a completely solid wall of hydrophobic material. Rather, in some examples the hydrophobic flow barrier can be somewhat porous. In certain examples, the porous substrate can include fibers and the hydrophobic flow barrier can include the hydrophobic material coating the fibers.

[0078] The hydrophobic flow barriers can be formed with any desired shape and size. The methods described above can allow for precise control of the lateral spread and penetration depth of the flow modifier composition. Therefore, the dimensions of the hydrophobic flow barriers can be precisely controlled in the x, y, and z directions. In some examples, the hydrophobic flow barrier can penetrate partially through the porous thickness of the porous substrate. In other examples, the hydrophobic flow barrier can penetrate fully through the thickness of the porous substrate. In certain examples, the hydrophobic flow barrier can penetrate from about 1 % to about 100% of the thickness of the porous substrate. In other examples, the size of the hydrophobic flow barriers can be controlled with a resolution of the size of the pores in the porous material. Therefore, in some examples the hydrophobic flow barrier can penetrate to any depth in the porous substrate with the precision of about the average pore size of the porous material. In some examples, the resolution can be from about 0.1 micrometer to about 10 micrometers, or from about 0.2 micrometer to about 5 micrometers, or from about 0.2 micrometer to about 1 micrometer. In certain examples, the porous substrate can have a thickness from about 50 micrometers to about 200 micrometers, and the hydrophobic flow barrier can have a penetration depth from about 1 micrometer to about 199 micrometers. [0079] The size of the hydrophobic barriers in the lateral (x/y) directions can be any desired size. The lateral size can be controlled by using a digital fluidic actuator to apply the flow modifier composition in any desired location on the surface of the porous substrate, in addition to using the methods described above to control the lateral spread of the flow modifier composition. The methods described herein can be used to form hydrophobic flow barriers having very small lateral dimensions. The methods can also be used to form microfluidic features, such as flow channels between two hydrophobic flow barriers, with very small dimensions. In some examples, these features may not be possible using less precise methods. In certain examples, the hydrophobic flow barrier can have a length or width (i.e. , x or y dimension) from about 1 micrometer to about 100 micrometers, or from about 1 micrometer to about 50 micrometers, or from about 1 micrometer to about 10 micrometers, or from about 1 micrometer to about 5 micrometers. In further examples, two hydrophobic flow barriers can be formed with a microfluidic flow channel between the hydrophobic flow barriers. The microfluidic flow channel can have a width from about 1 micrometer to about 100 micrometers, or from about 1 micrometer to about 50 micrometers, or from about 1 micrometer to about 10 micrometers, or from about 1 micrometer to about 5 micrometers, or from about 10 micrometers to about 100 micrometers, or from about 10 micrometers to about 50 micrometers.

[0080] The hydrophobic material can be the main compositional component of the hydrophobic flow barriers. However, in some examples, the hydrophobic flow barriers can also include other materials, such as residual materials from the flow modifier composition. In some examples, the hydrophobic flow barriers can include residual dispersant, which is used to disperse the hydrophobic material particles in the flow modifier composition. In certain examples, the residual dispersant can include an alcohol ethoxylate dispersant. In a particular example, the residual dispersant can include UNITHOX™ 750 (Baker Hughes, USA), which is an alcohol ethoxylate dispersant with a molecular weight of 1400 g/mol, with a 50% ethylene oxide content by weight. In certain examples, the hydrophobic flow barriers can include residual dispersants in an amount from about 1 wt% to about 20 wt%. In other examples, the hydrophobic flow barriers can include other residual ingredients that were present in the flow modifier composition. These residual ingredients can include components that were included in the flow modifier composition to increase the jettability of the flow modifier composition. In some examples, the hydrophobic flow barriers can include residual ingredients such as a co-solvent, a surfactant, an anti-kogation agent, a biocide, or others.

[0081] In certain examples, the hydrophobic flow barrier can overlap or partially overlap with areas where the pre-treatment composition was applied. Accordingly, the hydrophobic flow barriers can also include residual ingredients of the pre-treatment composition. In some examples, the hydrophobic flow barriers can include a cationic salt or cationic polymer from the pre-treatment composition. Depending on whether the entire hydrophobic flow barrier overlaps with the pre-treatment composition, or whether the hydrophobic flow barrier partially overlaps with the pre-treatment composition, the cationic agent can be found throughout the entire flow barrier or in portions of the flow barrier.

Lateral Flow Devices

[0082] The present disclosure also describes lateral flow devices. Lateral flow devices can include any device having a porous substrate and a hydrophobic flow barrier formed therein. In various examples, the lateral flow devices can have any of the features described above.

[0083] In some examples, a lateral flow device can include a porous substrate having a flow path through the porous substrate for wicking an aqueous fluid along the flow path through the porous substrate. Depending on the type of lateral flow device, the aqueous fluid can be a variety of different fluids, such as sample fluids, bodily fluids, fluids containing reactants, fluids that are to be mixed, fluids that are to be separated, fluids that are to be filtered, and so on. The lateral flow device can also include a hydrophobic flow barrier. The hydrophobic flow barrier can include a hydrophobic material. In some examples, the hydrophobic flow barrier can also include a residual dispersant suitable for dispersing the hydrophobic material in an aqueous solvent. The residual dispersant can be left behind from the flow modifier composition, in which the dispersant was used to disperse the hydrophobic material. The hydrophobic flow barrier can be formed in an area of the porous substrate such that the flow path is redirected around the hydrophobic flow barrier.

[0084] In further examples, the lateral flow device can also include a residual material from the pre-treatment composition. In certain examples, the residual material from the pre-treatment composition can include a cationic salt or a cationic polymer. The cationic salt can be a calcium salt, a magnesium salt, a sodium salt, or a combination thereof. The cationic polymer can be a polyvinyl alcohol modified with ammonium salt, a polyethyleneimine, a polyamine, a polydiallyldimethylarnmonium chloride, or a combination thereof. Other residual materials from the pre-treatment composition can also be present, such as any of the additives described above.

[0085] As explained above, the pre-treatment composition can be applied to the porous substrate in various patterns, depending on the desired effect on the penetration depth and lateral spread of the flow modifier composition. Accordingly, the residual materials from the pre-treatment composition can be found in the porous substrate in any of the same patterns. FIG. 8 shows one example of a lateral flow device 200 that includes a porous substrate 210, a narrow hydrophobic flow barrier 220 that penetrates all the way through the thickness of the porous substrate, and a cationic salt 274 that is present in areas of the porous substrate adjacent to the hydrophobic flow barrier. In this example, the pre-treatment composition was applied to areas adjacent to where the flow barrier was to be formed. The flow modifier composition was then applied in the area between the pre-treatment compositions. The cationic salt in the pre-treatment composition caused the hydrophobic material particles in the flow modifier composition to come out of dispersion, which prevented the hydrophobic material particles from spreading laterally.

[0086] In certain examples, a lateral flow device can be a lateral flow assay, such as a lateral flow immunoassay. FIG. 9 shows one example of a lateral flow assay 300. The lateral flow assay includes a porous substrate 210 with a hydrophobic flow barrier 220 as described above. In this example, a cationic salt 274 is also present in the same area where the hydrophobic flow barrier was formed. The cationic salt is a residue of the pre-treatment composition, which was applied in the same area as the flow modifier composition to reduce the penetration depth of the flow modifier composition. A test line 240 and a control line 250 are formed over the hydrophobic flow barrier. The lateral flow assay also includes a housing 390 around the porous substrate with a sample inlet 392 in the housing.

[0087] In further examples, lateral flow assays can include a variety of additional components, such as a sample pad, a conjugate pad, an absorbent pad, conjugate molecules, additional test lines, backing materials, test line viewing windows, and others.

Fluid Ejection Devices

[0088] In some examples, the flow modifier compositions can be applied to porous substrates using a fluid ejection device. FIG. 10 shows one example fluid ejection device 400 that can be used. This fluid ejection device includes a substrate support 412 to receive a porous substrate. The fluid ejection device also includes two fluidic actuators. A first fluidic actuator 272 receives a pre-treatment composition and a second fluidic actuator 262 receives a flow modifier composition. The fluidic actuators are positioned to jet the pre-treatment composition and the flow modifier composition onto an area of a surface of the porous substrate. As described above, the pre-treatment composition can include a solvent, a cationic salt, a cationic polymer, or a combination thereof. The flow modifier composition can include an aqueous solvent, dispersed hydrophobic material particles, and a dispersant. The flow modifier composition can wick through the porous substrate. The fluid ejection device also includes a controller 410 to control the lateral spread, penetration depth, or both, of the flow modifier composition through the porous substrate. In this way, the controller can control the formation of a hydrophobic flow barrier in the porous substrate.

[0089] In various examples, the controller can control the lateral spread and penetration depth of the flow modifier composition using any of the methods described above. In a certain example, the controller can control the lateral spread of the flow modifier composition by using the first fluidic actuator to jet the pre-treatment composition on an area laterally adjacent to the flow modifier composition. In particular, the controller can cause the first fluid actuator to jet the pre-treatment composition first, and then the controller can use the second fluid actuator to jet the flow modifier composition next to the pre-treatment composition.

[0090] In another example, the controller can control the penetration depth of the flow modifier composition by causing the first fluidic actuator to jet the pre-treatment composition in the same area as the flow modifier composition. In some examples, the controller can use the first fluidic actuator to jet the pre-treatment composition onto the porous substrate first. Then the controller can use the second fluidic actuator to jet the flow modifier composition onto the same area over the pre-treatment composition. As explained above, the pre-treatment composition can reduce the penetration depth of the flow modifier composition. In further examples, the controller can adjust the penetration depth by changing the amount of pre-treatment composition and/or the amount of flow modifier composition that is applied to the porous substrate. In certain examples, the controller can select a number of passes for jetting the pre-treatment composition and the flow modifier composition. The number of passes can be selected to provide a penetration depth that is from about 1 % to about 100% of the thickness of the porous substrate.

[0091] The controller can be or can include a special purpose processor, or a general purpose processor, or both. In certain examples, the controller can include modules for performing operations in the methods described above. For example, the controller can include a jetting module for positioning the fluidic actuators in a desired position over the porous substrate and jetting a desired volume of pre-treatment composition and flow modifier composition onto the porous substrate. In examples that utilize a curing operation, the controller can include a curing module to cure the hydrophobic material to form hydrophobic flow barriers. The controller can include a processor that can utilize these modules to perform the various functions of the controller. [0092] In some examples, the fluid ejection device can include a substrate support to receive a porous substrate. The porous substrate can be any of the types of porous substrate described above. The substrate support can be any size and shape designed to be compatible with the porous substrate. In some examples, the substrate support can be a platform or platen for holding a porous substrate while the fluid compositions are jetted onto the porous substrate. In certain examples, the substrate support can include heaters for controlling the temperature of the porous substrate. In other examples, the substrate support can include rollers or other mechanical features for moving the porous substrate through the device as the fluid compositions are jetted onto the porous substrate.

[0093] In some examples, the fluid ejection device can include a reservoir of the pre-treatment composition and a reservoir of the flow modifier composition. In other examples, the fluid ejection device can include connections for connecting to such reservoirs, and the reservoirs may be provided separately. The fluidic actuators can be connectable to the reservoirs of pre-treatment composition and flow modifier composition so that the fluidic actuators can jet these compositions onto the porous substrate.

[0094] Some of the functional units described in the fluid ejection device have been labeled as modules, in order to more particularly emphasize their implementation independence. For example, a module can be implemented as a hardware circuit including custom very-large-scale integration (VLSI) circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A module can also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like.

[0095] Modules can also be implemented in machine-readable software for execution by various types of processors. An identified module of executable code can, for instance, include block(s) of computer instructions, which can be organized as an object, procedure, or function. Nevertheless, the executables of an identified module need not be physically located together, but can include disparate instructions stored in different locations which include the module and achieve the stated purpose for the module when joined logically together. [0096] Indeed, a module of executable code can be a single instruction, or many instructions, and can even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data can be identified and illustrated herein within modules, and can be embodied in a suitable form and organized within a suitable type of data structure. The operational data can be collected as a single data set, or can be distributed over different locations including over different storage devices. The modules can be passive or active, including agents operable to perform desired functions.

[0097] The modules described here can also be stored on a computer readable storage medium that includes volatile and non-volatile, removable and non-removable media implemented with a disclosure for the storage of information such as computer readable instructions, data structures, program modules, or other data. Computer readable storage media can include, but are not limited to, RAM, ROM, electrically erasable programmable read-only memory (EEPROM), flash memory or other memory disclosure, compact disc read-only memory (CD-ROM), digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tapes, magnetic disk storage or other magnetic storage devices, or other computer storage medium which can be used to store the desired information.

[0098] As described above, in some examples the controller can include a special purpose processor. In certain examples, the special purpose processor can include some or all of the modules described above as hardware components. In other examples, the controller can include a general purpose processor. The general purpose processor can be capable of executing the modules described above as software modules. In some examples, a combination of hardware and software modules can be used.

[0099] It is noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise.

[00100] As used herein, particle size with respect to the dispersed hydrophobic material particles, or any other particles, can be based on volume of the particle size normalized to a spherical shape for diameter measurement, for example. Particle size can be collected using a Malvern ZETASIZER™ system (Malvern Panalytical, United Kingdom), for example. Particle size information can also be determined and/or verified using a scanning electron microscope (SEM).

[00101] As used herein, the term “about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be “a little above” or “a little below” the endpoint. The degree of flexibility of this term can be dictated by the particular variable based on experience and the associated description herein.

[00102] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though individual members of the list are individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

[00103] Concentrations, dimensions, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include the numerical values explicitly recited as the limits of the range, but also all the individual numerical values or sub-ranges encompassed within that range as if individual numerical values and sub-ranges are explicitly recited. For example, a weight ratio range of about 1 wt% to about 20 wt% should be interpreted to include the explicitly recited limits of about 1 wt% and about 20 wt%, but also to include individual weights such as 2 wt%, 11 wt%, 14 wt%, and sub-ranges such as 10 wt% to 20 wt%, 5 wt% to 15 wt%, etc. EXAMPLES

[00104] The following example illustrates the technology of the present disclosure. However, it is to be understood that the following are illustrative of the application of the principles of the presented fabric print media and associated methods. Numerous modifications and alternatives may be devised without departing from the present disclosure. The appended claims are intended to cover such modifications and arrangements. Thus, while the disclosure has been provided with particularity, the following describes further detail in connection with what are presently deemed to be the acceptable examples.

Example 1 - Controlling Penetration Depth

[00105] A sample porous substrate (nitrocellulose membrane) was treated with a pre-treatment composition. The pre-treatment composition in this example was a solution of calcium chloride in water. The membrane was dried on a hot plate after the pre-treatment composition was applied. A drop of a flow modifier composition was then placed on the membrane. The flow modifier composition included ROVENE® 4100 (Mallard Creek Polymers, USA) in water. For comparison, a drop of the flow modifier composition was also placed on a sample of the nitrocellulose membrane that was not treated with the pre-treatment composition.

[00106] The flow modifier composition absorbed almost immediately into the nitrocellulose membrane that was not treated with the pre-treatment composition. However, on the nitrocellulose membrane that was treated with the pre-treatment composition, the flow modifier composition formed a bead and did not visibly absorb into the membrane. The flow modifier composition dried to form a thin film of latex on the surface of the membrane.

[00107] The relative concentrations of the hydrophobic latex material was measured at depth intervals through the cross section of the nitrocellulose membranes. FIG. 11 shows a graph of the normalized amounts of latex present at multiple depths throughout the membrane thickness. On the membrane that was treated with the pre-treatment composition, the latex was concentrated in the upper 15 micrometers of the membrane. In the membrane that was not treated with the pre-treatment composition, the latex was relatively evenly distributed throughout the whole thickness of the membrane.

[00108] While the present technology has been described with reference to certain examples, various modifications, changes, omissions, and substitutions can be made without departing from the technology of this disclosure. It is intended, therefore, that the disclosure be limited by the scope of the following claims.

Claims

CLAIMS What is Claimed Is:

1 . A method of forming a hydrophobic flow barrier comprising: applying a pre-treatment composition to an area of a surface of a porous substrate, wherein the pre-treatment composition comprises a solvent, a cationic salt, a cationic polymer, or a combination thereof; applying a flow modifier composition onto an area of a surface of the porous substrate, wherein the flow modifier composition comprises an aqueous solvent, dispersed hydrophobic material particles, and a dispersant, wherein the flow modifier composition wicks through pores of the porous substrate, and wherein the pre-treatment composition reduces a penetration rate of the dispersed hydrophobic material particles in the area where the pre-treatment composition is applied.

2. The method of claim 1 , wherein the pre-treatment composition, the flow modifier composition, or both, are applied by a digital fluidic actuator.

3. The method of claim 1 , wherein the pre-treatment composition comprises a calcium salt, a magnesium salt, a sodium salt, a polyvinyl alcohol modified with ammonium salt, a polyethyleneimine, a polyamine, a polydiallyldimethylammonium chloride, or a combination thereof.

4. The method of claim 1 , wherein the pre-treatment composition is applied to the same area where the flow modifier composition is applied, and the pre-treatment composition reduces a penetration depth of the hydrophobic material particles so that the hydrophobic flow barrier extends partially through the thickness of the porous substrate.

5. The method of claim 4, further comprising applying a test reactant to the area of the porous substrate on an opposite surface from the surface on which the flow modifier composition is applied.

6. The method of claim 4, wherein the porous substrate has a thickness from about 50 micrometers to about 200 micrometers and wherein the hydrophobic flow barrier extends through the porous substrate to a depth of from about 1 micrometer to about 199 micrometers.

7. The method of claim 1 , wherein the pre-treatment composition is applied to a different area than the area where the flow modifier composition is applied, wherein the flow modifier composition wicks laterally through the porous substrate toward the area where the pre-treatment composition is applied, and wherein the pre-treatment composition stops the penetration of the hydrophobic material particles such that the hydrophobic flow barrier has an edge at the area where the pre-treatment composition is applied.

8. A lateral flow device comprising: a porous substrate having a flow path through the porous substrate for wicking an aqueous fluid along the flow path through the porous substrate; a hydrophobic flow barrier comprising a hydrophobic material, the hydrophobic flow barrier being formed in an area of the porous substrate such that the flow path is redirected around the hydrophobic flow barrier; and a pre-treatment material comprising a cationic salt, a cationic polymer, or a combination thereof, in an area of the porous substrate.

9. The lateral flow device of claim 8, wherein the pre-treatment material is in the same area of the porous substrate as the hydrophobic flow barrier, and wherein the hydrophobic barrier penetrates partially through the thickness of the porous substrate, leaving a portion of the thickness of the porous substrate without the hydrophobic material, such that the flow path is redirected through the portion of the thickness of the porous substrate without the hydrophobic material.

10. The lateral flow device of claim 9, further comprising a test reactant penetrating the portion of the thickness of the porous substrate without the hydrophobic material.

11 . The lateral flow device of claim 8, wherein the pre-treatment material is in an area laterally adjacent to an edge of the hydrophobic flow barrier.

12. The lateral flow device of claim 8, further comprising a lateral flow assay housing around the porous substrate, wherein the housing comprises a sample fluid inlet.

13. A fluid ejection device comprising: a substrate support to receive a porous substrate; a first fluidic actuator to receive a pre-treatment composition and positioned to jet the pre-treatment composition onto an area of a surface of the porous substrate, wherein the pre-treatment composition comprises a solvent, a cationic salt, a cationic polymer, or a combination thereof; a second fluidic actuator to receive a flow modifier composition and positioned to jet the flow modifier composition onto an area of a surface of the porous substrate, wherein the flow modifier composition comprises an aqueous solvent, dispersed hydrophobic material particles, and a dispersant, wherein the flow modifier composition wicks through the porous substrate; and a controller to control the lateral spread, penetration depth, or both, of the flow modifier composition through the porous substrate to form a hydrophobic flow barrier.

14. The system of claim 13, wherein the controller controls the lateral spread of the flow modifier composition through the porous substrate by causing the first fluidic actuator to jet the pre-treatment composition on an area laterally adjacent to the flow modifier composition.

15. The system of claim 13, wherein the controller controls the penetration depth of the flow modifier composition by causing the first fluidic actuator to jet the pre-treatment composition in the same area as the flow modifier composition.