A preparation method of a microfluidic chip mold

Abstract

The present invention belongs to the technical field of microfluidic chip mold manufacturing, and particularly relates to a preparation method of a microfluidic chip mold and a microfluidic chip mold. The preparation method of the microfluidic chip mold comprises the following steps: mold making, preparing a first template, and processing a flow channel groove on one side surface of the first template to prepare the first template into a master mold; mold casting, preparing a second template and fixing the master mold, laminating the second template on the master mold through the flow channel groove and covering the flow channel groove, and heating to soften the second template; pressing the second template towards the master mold so that a part of the second template is extruded into the flow channel groove to form micro-protrusions, and processing the second template into a microfluidic chip mold; demolding, separating the microfluidic chip mold from the master mold. By processing a flow channel groove on the first template and then processing micro-protrusions on the second template, the whole process is simple and efficient, and the preparation cost of the microfluidic chip mold is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of microfluidic chip mold manufacturing, and particularly relates to a method for preparing a microfluidic chip mold. Background Art

[0002] A microfluidic chip is a programmable and controllable micro multi-functional device composed of a microchannel network. Glass microfluidic chips play an important role in many fields such as life science, environmental monitoring, chemical synthesis, and advanced research due to their excellent material properties and versatility.

[0003] With the increasing demand for miniaturization, precision, and efficiency, the application scope of glass microfluidic chips is also constantly expanding. Glass has good chemical inertness and can resist the erosion of various chemicals, making it an ideal material for microfluidic devices for handling reactive or corrosive substances and is widely used in applications with high-purity reagents or corrosive solvents. Among them, the preparation of the channel structure is the most critical step in glass microfluidic chips. Generally, the channel structure is prepared on a glass blank through a microfluidic chip mold. Therefore, it is particularly important to prepare a microfluidic chip mold for processing the glass blank.

[0004] The current microfluidic chip mold processing technologies include electrical discharge machining and ultra-precision cutting. Electrical discharge machining gradually removes tungsten carbide material by generating high-frequency discharges between the workpiece and the electrode, but the wear of the electrode will lead to a decrease in accuracy and low processing efficiency; ultra-precision cutting can achieve high surface finish and high dimensional accuracy, but the tool wears quickly, and the processing cost is relatively high during batch preparation. Summary of the Invention

[0005] The purpose of the embodiments of the present application is to provide a method for preparing a microfluidic chip mold, aiming to solve the problem of how to improve the preparation accuracy of the microfluidic chip mold and reduce the preparation cost.

[0006] To achieve the above purpose, the technical solution adopted by the present application is as follows:

[0007] In the first aspect, a method for preparing a microfluidic chip mold is provided, which includes the following steps:

[0008] Mold making: Prepare a first template, and process a channel groove on one side surface of the first template to prepare the first template into a master mold.

[0009] Mold casting: Prepare a second template and fix the master mold. Stack the second template on the master mold through the channel groove to cover the channel groove, and heat to soften the second template; press the second template against the master mold so that a part of the second template is squeezed into the channel groove and forms a micro-protrusion, and process the second template into a microfluidic chip mold.

[0010] Demold and separate the microfluidic chip mold from the master mold.

[0011] In some embodiments, a plurality of the second templates are prepared, and each of the second templates sequentially repeats the mold pouring step and the demolding step to prepare a plurality of the microfluidic chip molds, and the heights of the micro-protrusions are different.

[0012] In some embodiments, the flow channel groove penetrates through both side plates of the first template, and the demolding step includes:

[0013] S31: Fill the flow channel groove with a flexible medium;

[0014] S32: Drive the flexible medium towards the microfluidic chip mold so that the flexible medium pushes the microfluidic chip mold to separate from the master mold.

[0015] In some embodiments, the first template is provided with a plurality of material passing through holes arranged at intervals, both ends of the material passing through holes penetrate through both side plates of the first template respectively, and at least one of the material passing through holes communicates with the flow channel groove.

[0016] In some embodiments, the flexible medium is a gas or a liquid.

[0017] In some embodiments, in the step S31, a positioning seat having a receiving cavity is further prepared, the receiving cavity contains the flexible medium and has an opening, the opening is arranged upwards, the master mold is hermetically fixed at the opening, and the flow channel groove communicates with the receiving cavity.

[0018] In some embodiments, a rotating mechanism is prepared, and the rotating mechanism is connected to the positioning seat; in the demolding step, the rotating mechanism drives the positioning seat to rotate 180 degrees so that the microfluidic chip mold is arranged downwards, and then the microfluidic chip mold is separated from the master mold.

[0019] In some embodiments, the shrinkage rate of the master mold is less than the shrinkage rate of the microfluidic chip mold. In the step S32, first, a cooling gas is filled into the upper surface of the microfluidic chip mold, and then the microfluidic chip mold is driven to separate from the master mold.

[0020] In some embodiments, the flow channel groove is machined on the first template by using a wire electrical discharge machining process.

[0021] In a second aspect, a microfluidic chip mold is provided, which is prepared by the method for preparing the microfluidic chip mold.

[0022] The beneficial effects of the present application are as follows: By preparing a master mold with a flow channel groove, and then replicating the flow channel groove on the master mold through a first template, micro-protrusions are formed on the second template. The replicated micro-protrusions can ensure dimensional accuracy and surface accuracy, ensuring the precise replication of the flow channel groove. The master mold can be reused multiple times, improving the preparation efficiency and reducing the preparation cost. The preparation process is simple and efficient. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or exemplary technical descriptions. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0024] Figure 1 is a schematic flowchart of a method for preparing a microfluidic chip mold provided by an embodiment of the present application;

[0025] Figure 2 is an assembly schematic diagram of a positioning seat and a microfluidic chip mold in a demolding step provided by another embodiment of the present application;

[0026] Figure 3 is Figure 2 a cross-sectional schematic diagram of the separation of the positioning seat and the microfluidic chip mold in the demolding step of;

[0027] Figure 4 is a three-dimensional structural schematic diagram of a master mold provided by still another embodiment of the present application;

[0028] Figure 5 is a three-dimensional structural schematic diagram of a microfluidic chip mold provided by still another embodiment of the present application;

[0029] Figure 6 is an assembly schematic diagram of a microfluidic chip and a glass blank provided by yet another embodiment of the present application;

[0030] Figure 7 is a structural schematic diagram of a microfluidic chip provided by yet another embodiment of the present application.

[0031] Among them, the reference numerals in the drawings:

[0032] 101, master mold; 102, microfluidic chip mold; 103, positioning seat; 104, micro-protrusion; 105, flow channel groove; 1031, accommodation cavity; 106, air inlet hole; 107, material passing through hole; 108, glass blank; Detailed Embodiments

[0033] To make the objectives, technical solutions and advantages of this application more clear and understandable, the following further elaborates on this application in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit this application.

[0034] It should be noted that when a component is referred to as "fixed to" or "disposed on" another component, it can be directly on the other component or indirectly on the other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to the other component. The orientation or positional relationship indicated by terms such as "upper", "lower", "left", and "right" is based on the orientation or positional relationship shown in the accompanying drawings, and is only for convenience of description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation to this application. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances. The terms "first" and "second" are only used for the purpose of convenient description, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of technical features. The meaning of "a plurality" is two or more, unless otherwise specifically defined.

[0035] Please refer to Figures 1 to 3 , the embodiment of this application provides a preparation method for a microfluidic chip mold, which can prepare a microfluidic chip mold 102, and a glass blank 108 can be prepared into a microfluidic chip through the microfluidic chip mold 102.

[0036] Please refer to Figures 1 to 3 , the preparation method for the microfluidic chip mold includes the following steps:

[0037] S1: Mold making. Prepare a first template, and process a flow channel groove 105 on one side surface of the first template to prepare the first template into a master mold 101; the flow channel groove 105 is a groove structure, and the shape of its length extension can be set according to actual needs, such as linear extension, arc extension or serpentine detour extension. The size range of the flow channel groove is 0.1~2mm. For example, the groove width of the flow channel groove 105 can be 0.1mm, 0.2mm, 0.8mm, 1mm or 2mm.

[0038] It can be understood that the material of the first template can be materials such as tungsten carbide, silicon carbide or glassy carbon, and these materials have the characteristics of high hardness and high temperature resistance. In the embodiment of this application, the material of the first template is tungsten carbide. In other embodiments, it can be selected according to actual circumstances, and no limitation is made here.

[0039] Please refer to Figures 2 to 5, S2: Reverse molding. Prepare the second template and fix the master mold 101 with the surface having the runner groove 105 facing upward. Stack the second template on the master mold 101 and cover the runner groove 105. Heat to soften the second template to make it have a certain plasticity. Press the second template against the master mold 101 so that part of the second template is extruded into the runner groove 105, and micro-protrusions 104 are formed by hot pressing. That is, at the position of the second template corresponding to the runner groove 105, due to the extrusion of pressure, part of the material enters the runner groove and forms micro-protrusions 104, and the second template is processed into a microfluidic chip mold 102.

[0040] It can be understood that the material of the second template can be an amorphous alloy, such as zirconium-based metallic glass. The second template has a glass transition temperature Tg. By heating the second template above its glass transition temperature, slightly higher than 10 degrees Celsius, it is softened and its plasticity is improved. Then, a downward pressure is applied to extrude part of the material of the second template into the runner groove 105, so that the second template replicates the shape of the runner groove 105. After cooling, micro-protrusions 104 are formed on the second template, and thus a microfluidic chip mold 102 with micro-protrusions 104 is processed. The micro-protrusions 104 directly replicate the shape of the runner groove 105, so they have high processing accuracy, a simple process, high efficiency, and the master mold 101 can be reused multiple times to batch prepare microfluidic chip molds 102, thereby effectively reducing the preparation cost of the microfluidic chip mold 102.

[0041] S3: Demolding. Separate the microfluidic chip mold 102 from the master mold 101.

[0042] Please refer to Figures 2 to 5 , in the embodiment of the present application, by preparing a master mold 101 with a runner groove 105, and then replicating the runner groove 105 on the master mold 101 through the first template, micro-protrusions 104 are formed on the second template. The replicated micro-protrusions 104 can ensure dimensional accuracy and surface accuracy, ensuring the precise replication of the runner groove 105. The master mold 101 can be reused multiple times, improving the preparation efficiency and reducing the preparation cost. The preparation process is simple and efficient.

[0043] Optionally, the obtained microfluidic chip mold 102 is subjected to crystallization treatment to improve its hardness and strength.

[0044] Please refer to Figures 2 to 5 , it can be understood that through the microfluidic chip mold 102, a glass blank 108 can be processed to transfer the runner groove 105 on the master mold 101 to the glass blank 108, and the glass blank 108 is processed into a microfluidic chip, which can reduce the processing cost of the microfluidic chip. Among them, the depth of the runner groove on the microfluidic chip is controlled by the height of the micro-protrusions 104 on the microfluidic chip mold 102.

[0045] It is understandable that a pressing head is provided on the second template, and the pressing head is connected to a force-applying mechanism. Pressure can be applied to the second template through the pressing head, and the range of the pressure applied to the second template can be 5 MPa to 40 MPa, such as 5 MPa, 10 MPa, 20 MPa, 35 MPa or 40 MPa. There is no limitation here and it can be selected according to the actual situation.

[0046] In some embodiments, multiple second templates are prepared, and each second template repeats the mold pouring step and the demolding step in sequence to prepare multiple microfluidic chip molds 102. The heights of the micro-protrusions 104 of each microfluidic chip mold 102 are different.

[0047] Please refer to Figures 2 to 5 , by controlling the magnitude of the pressure applied to the second template, the amount of the material of the second template entering the flow channel groove 105 can be controlled, so as to form micro-protrusions 104 with different heights. During the replication process, the pressure is evenly distributed on the force-bearing surface of the second template, so that the heights of all positions of the same micro-protrusion 104 are the same. Multiple different microfluidic chip molds 102 can be batch-prepared through one master mold 101, and then different microfluidic chips can be manufactured, reducing the preparation cost of the microfluidic chips.

[0048] Please refer to Figures 2 to 5 , in some embodiments, the flow channel groove 105 penetrates through both side plates of the first template, that is, the flow channel groove 105 has a through-groove structure. The demolding step includes:

[0049] S31: Filling a flexible medium into the flow channel groove 105;

[0050] S32: Driving the flexible medium towards the microfluidic chip mold 102, so that the flexible medium pushes the microfluidic chip mold 102 to separate from the master mold 101.

[0051] In some embodiments, the flexible medium can be a gas or a liquid.

[0052] For example, when the flexible medium is pure water, by connecting the hydraulic source to the flow channel groove 105 and then filling the flow channel groove 105 with high-pressure liquid, the flexible medium can uniformly apply pressure to the micro-protrusions 104 in the flow channel groove 105, and the forces at various positions of the micro-protrusions 104 are uniform. As a result, the microfluidic chip mold 102 becomes loose as a whole relative to the master mold 101, and then the microfluidic chip mold 102 can be manually or automatically removed. The pressure range of the high-pressure liquid can be 0.5 MPa to 4 MPa to ensure the separation effect and the safety of the micro-protrusions 104. For example, the pressure of the high-pressure liquid can be 0.5 MPa, 0.8 MPa, 1 MPa, 1.8 MPa, 2.1 MPa, 2.3 MPa, 3.3 MPa, 3.6 MPa, or 4 MPa, which can be selected according to the actual situation and is not limited here.

[0053] Please refer to Figures 2 to 5 , in some embodiments, the flexible medium can also be a gas. By connecting the air pressure source to the lower surface of the master mold 101 to the flow channel groove 105 and then filling the flow channel groove 105 with high-pressure gas, the forces at various positions of the micro-protrusions 104 are uniform. As a result, the microfluidic chip mold 102 becomes loose as a whole relative to the master mold 101, and then the microfluidic chip mold 102 can be manually or automatically removed. The pressure range of the high-pressure gas can be 1 MPa to 5 MPa to ensure the separation effect and the safety of the micro-protrusions 104. For example, the pressure of the high-pressure gas can be 1 MPa, 1.5 MPa, 2 MPa, 2.3 MPa, 3 MPa, 3.6 MPa, 4 MPa, 4.8 MPa, or 5 MPa, which can be selected according to the actual situation and is not limited here.

[0054] Since the flexible medium is in flexible contact with the micro-protrusions 104, it can not only separate the microfluidic chip mold 102 from the master mold 101, but also cause no physical damage to the micro-protrusions 104 during the separation process, improving the reliability of the separation of the microfluidic chip mold 102 from the master mold 101.

[0055] In some embodiments, the positioning seat 103 is fixed on the ultrasonic vibration device. While filling the flexible medium, a micro-vibration is applied to the positioning seat 103 through the ultrasonic vibration device. The range of the vibration frequency can be 20 kHz to 40 kHz, and the amplitude can be 1 μm to 5 μm, so as to weaken the static friction and adhesion between the micro-protrusions 104 and the flow channel groove 105 through vibration. The vibration direction can be perpendicular to the demolding direction. For example, when the demolding direction is vertically upward, the vibration direction is horizontal to avoid directly impacting and compressing the micro-protrusions 104, improving the reliability and convenience of demolding. Please refer to Figures 2 to 5, in some embodiments, the first template is provided with a plurality of material passing through holes 107 arranged at intervals, and both ends of the material passing through holes 107 penetrate through the two side plates of the first template; at least one material passing through hole 107 communicates with the flow channel groove 105.

[0056] Optionally, each material passing through hole 107 communicates with the flow channel groove 105. Through the material passing through holes 107, the flexible medium can smoothly enter the flow channel groove 105. The size of the material passing through holes 107 is larger than the size of the flow channel groove 105. For example, the size of the material passing through holes is three times the size of the flow channel groove 105, ensuring that the flexible medium can act on the micro-protrusions 104 uniformly and guaranteeing the uniformity and stability of the demolding process.

[0057] Please refer to Figures 2 to 5 , in some embodiments, in step S31, it further includes preparing a positioning seat 103 having a receiving cavity 1031. The receiving cavity 1031 contains a flexible medium and has an opening which is arranged upward. The four peripheral edges of the female mold 101 are hermetically fixed at the opening, and the flow channel groove 105 communicates with the receiving cavity 1031, enabling the flexible medium located in the receiving cavity 1031 to enter the flow channel groove 105, ensuring that the flexible medium uniformly applies a thrust force to the micro-protrusions 104 during the demolding process and improving the demolding efficiency.

[0058] Optionally, an air inlet hole 106 communicating with the receiving cavity 1031 is opened at the bottom of the positioning seat 103, and a pneumatic source or a hydraulic source is connected to the positioning seat 103 at the air inlet hole 106.

[0059] Please refer to Figures 2 to 5 , in some embodiments, prepare a rotating mechanism which is connected to the positioning seat 103; in the demolding step, the rotating mechanism drives the positioning seat 103 to rotate 180 degrees so that the microfluidic chip mold 102 is arranged downward, and then the microfluidic chip mold 102 and the female mold 101 are separated downward.

[0060] Optionally, when the flexible medium is a liquid, by flipping the positioning seat 103 by 180 degrees, the microfluidic chip mold 102 is also flipped by 180 degrees, and the female mold 101 is located above the microfluidic chip mold 102. Demolding is carried out by using the gravity of the microfluidic chip mold 102 itself, the gravity of the flexible medium itself, and the pressure applied to the flexible medium. Under the action of gravity and pressure, the microfluidic chip mold 102 becomes loose relative to the female mold 101 or falls onto the flexible receiving platform below. The flexible receiving platform can be a container filled with liquid, and the microfluidic chip mold 102 falls into the liquid in the container. The liquid can be an aqueous solution. This avoids the situation that when demolding upward, the microfluidic chip mold 102 first detaches from the female mold 101 upward under the action of pressure and then falls downward onto the female mold 101 due to its own gravity, resulting in irreversible physical damage to the micro-protrusions 104.

[0061] Please refer toFigures 2 to 5 , in some embodiments, the shrinkage rate of the master mold 101 is less than that of the microfluidic chip mold 102. In step S32, cooling gas is first filled onto the upper surface of the microfluidic chip mold 102, and then the microfluidic chip mold 102 is driven to separate from the master mold 101.

[0062] Optionally, the cooling gas can be nitrogen, and the temperature range of the nitrogen can be -100°C to 0°C. By blowing low-temperature nitrogen onto the upper surface of the microfluidic chip mold 102, the microfluidic chip mold 102 is cooled. Since the materials of the microfluidic chip mold 102 and the master mold 101 are different and have different shrinkage rates, under the action of the cooling gas, the micro-protrusions 104 shrink relative to the inner wall of the flow channel groove 105, causing the micro-protrusions 104 to form pre-demolding within the flow channel groove 105. Then, the separation of the microfluidic chip mold 102 and the master mold 101 is promoted by a flexible medium, improving the efficiency and convenience of demolding.

[0063] Please refer to Figures 2 to 5 , in some embodiments, the flow channel groove 105 is machined on the first template using the wire electrical discharge machining process.

[0064] Optionally, a slow wire electrical discharge machine tool can be used to machine the flow channel groove 105 on the first template, with a discharge pulse interval of 10 μs and a flow rate of the spark oil of 7 L / min. During the pulsed discharge machining process, the first template is immersed in the oil to prevent the machining interface from being oxidized by air and to accelerate the discharge of debris. To improve the surface quality of the master mold 101, the flow channel groove 105 is subjected to at least 3 times of precision finishing cutting.

[0065] Optionally, after the discharge machining of the first template is completed, surface polishing treatment and ultrasonic vibration cleaning with alcohol are required.

[0066] Please refer to Figures 2 to 5 , the present application also proposes a microfluidic chip mold 102, which is prepared by the above-mentioned preparation method of the microfluidic chip mold.

[0067] The microfluidic chip mold 102 prepared by the above-mentioned preparation method has the characteristics of high precision, high stability, and low cost, thus promoting the further development of microfluidic chip technology.

[0068] Please refer to Figures 6 to 7 , the present application also proposes a hot pressing method, which uses the above-mentioned microfluidic chip mold 102 to prepare a microfluidic chip 200. The hot pressing method includes the following steps;

[0069] T1: Place the glass blank 108 on the microfluidic chip mold 102. The glass transition temperature of the glass blank 108 is lower than that of the microfluidic chip mold 102. The material of the glass blank 108 can be D-K9, and its glass transition point temperature is about 550 °C.

[0070] T2: Heat the microfluidic chip mold 102 and the glass blank 108 to the glass transition temperature of the glass blank 108 to soften the glass blank 108.

[0071] T3: Apply a downward pressure to the glass blank 108 through the lower pressing head, and process a microchannel 201 on the glass blank 108 through the microprotrusions 104 on the microfluidic chip mold 102 to process the glass blank 108 into a microfluidic chip 200. The microchannel 201 on the glass blank 108 is a blind groove structure.

[0072] T4: Cool and separate the microfluidic chip 200 from the microfluidic chip mold 102.

[0073] The hot pressing method provided by this application can improve the processing efficiency of the microfluidic chip 200 and reduce its manufacturing cost, promoting the wide application and rapid development of microfluidic technology in the fields of life science, environmental monitoring, chemical analysis, etc.

[0074] The above are only optional embodiments of this application and are not used to limit this application. For those skilled in the art, this application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the scope of the claims of this application.

Claims

1. A method for preparing a microfluidic chip mold, characterized in that: The steps include: Molding, preparing a first template, processing a flow channel groove on a side plate surface of the first template to prepare the first template into a master mold, wherein the shape of the length extension of the flow channel groove is a serpentine extension; Inverting the mold, preparing a second template and fixing the master mold, the flow channel groove is stacked on the master mold and covers the flow channel groove, heating to soften the second template; pressing the second template toward the master mold so that the second template is partially squeezed into the flow channel groove and forms micro protrusions, and processing the second template into a microfluidic chip mold; Demolding, separating the microfluidic chip mold from the master mold; A plurality of the second templates are prepared, and the inverting step and the demoulding step are repeated in sequence for each of the second templates to prepare a plurality of the microfluidic chip molds, and the height of each micro-protrusion is different; The runner groove passes through the two side surfaces of the first template, and the demoulding step includes: S31: Filling the flow channel groove with a flexible medium; S32: driving the flexible medium toward the microfluidic chip mold, the flexible medium uniformly applies pressure to the micro-protrusions in the flow channel, and the micro-protrusions are uniformly stressed at all positions, so that the microfluidic chip mold is loosened relative to the mother mold as a whole, so that the flexible medium pushes the microfluidic chip mold to separate from the mother mold; the flexible medium is gas or liquid.

2. The method for preparing a microfluidic chip mold according to claim 1, characterized in that: The first template is provided with a plurality of material passing through holes arranged at intervals, the two ends of the material passing through holes respectively pass through the two side plate surfaces of the first template, and at least one of the material passing through holes is connected to the flow channel groove.

3. The method for preparing a microfluidic chip mold according to claim 1, characterized in that: The step S31 further includes preparing a positioning seat having a receiving cavity, wherein the receiving cavity receives the flexible medium and has an opening, the opening is arranged upward, the mother mold is sealed and fixed at the opening, and the flow channel groove is connected to the receiving cavity.

4. The method for preparing a microfluidic chip mold according to claim 3, characterized in that: Prepare a rotating mechanism, which is connected to the positioning seat; in the demolding step, the rotating mechanism drives the positioning seat to rotate 180 degrees so that the microfluidic chip mold is set downward, and then the microfluidic chip mold is separated from the mother mold. Under the action of gravity and pressure, the microfluidic chip mold loosens relative to the mother mold and falls onto the flexible receiving platform below.

5. The method for preparing a microfluidic chip mold according to claim 1, characterized in that: The shrinkage rate of the master mold is smaller than the shrinkage rate of the microfluidic chip mold. In the step S32, cooling gas is firstly filled into the upper surface of the microfluidic chip mold, and then the microfluidic chip mold is driven to separate from the master mold.

6. The method for preparing a microfluidic chip mold according to any one of claims 1 to 5, characterized in that: The flow channel groove is processed on the first template by using an electric spark wire cutting process.

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