Micro pump and manufacturing method thereof

Abstract

The present invention discloses a micropump and its manufacturing method. The micropump comprises a pump body and a peripheral power supply system. The pump body comprises an upper cover and a lower cover. The upper cover includes internal structures such as a chip encapsulation layer, an elastic membrane, an elastic membrane drive plug, and a magnetic field generating coil, all of which are integrated onto the upper cover via an integrated processing method. The lower cover is a fully PDMS integrated module with an inwardly recessed microchannel structure. The upper and lower covers are secured by bonding. The power supply system generates electrical signals to drive the micropump actuator. This micropump has few components, a simple structure, and is entirely covered with PDMS. It can address the problems of current on-chip micropumps, such as complex structures, difficult assembly, poor airtightness, poor durability, and difficulty integrating with other chips.

Description

Technical Field

[0001] The invention belongs to the technical field of microfluidics and micromanufacturing, and in particular relates to a micropump and a manufacturing method thereof. Background Art

[0002] Microfluidic systems, characterized by miniaturized structures, sample miniaturization, and refined fluid manipulation, are ideal platforms for research in biology, chemistry, medicine, and other fields. The microfluidic actuator is the core module of a microfluidic system, capable of driving and transporting fluids from a storage location to a target location. On-chip micropumps, as microfluidic actuators, offer advantages such as small size, simple structure, ease of manufacture, and flexible integration with microfluidic systems. They are widely used in fluid transport, cell culture, and particle manipulation.

[0003] Current on-chip micropumps have numerous functional components, numerous chip layers, and a wide variety of materials. Firstly, micropumps are composed of multiple functional components, such as drivers and actuators, which are often connected to the chip through splicing or gluing. This complex assembly process increases the processing cost and assembly difficulty of the micropump, reducing its durability. Secondly, the microfluidic chip, the main body of the micropump, is composed of a multi-layered structure, including the upper cover, driver membrane, middle plate, and substrate. This multi-layer structure makes the micropump susceptible to poor airtightness, increases assembly difficulty, and reduces its durability. Furthermore, the various micropump components are composed of a variety of materials, such as metal, ceramic, glass, and PMMA (polymethyl methacrylate), which hinders their integration with other chips. Currently, microfluidic chips are primarily made of PDMS (polydimethylsiloxane). While different PDMS chips are easily integrated, PDMS is difficult to integrate with other materials.

[0004] Therefore, there is an urgent need to propose an on-chip micropump with few components, simple structure, and easy integration with other microfluidic chips in terms of materials. Summary of the Invention

[0005] The main purpose of the present invention is to improve the defects of the existing technology and propose a micropump and its manufacturing method to solve the problems of the existing micropump such as complex structure, cumbersome manufacturing, poor durability, poor airtightness, and difficulty in integration with other chips.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions:

[0007] A micro pump is composed of a pump body and a peripheral power supply system. The pump body is composed of a pump body upper cover and a pump body lower cover.

[0008] The pump body cover is an integrated component whose entire surface is covered with PDMS material, including a chip packaging layer, an elastic membrane, an elastic membrane driving plug, a driving plug movement cavity and a magnetic field generating coil; wherein, a vertical cylindrical through hole is provided in the center of the chip packaging layer as the driving plug movement cavity, the elastic membrane covers the lower surface of the through hole, the lower surface of the elastic membrane is flush with the lower surface of the chip packaging layer, and there is no gap between the two, and the lower surface of the pump body cover is an integrated plane; the magnetic field generating coil is composed of a cylindrical iron core with a through hole in the center and a coil, the coil is wound on the cylindrical iron core, the magnetic field generating coil is embedded in the chip packaging layer as a whole, and the through hole of the cylindrical iron core coincides with the driving plug movement cavity; the elastic membrane driving plug is a cylindrical structure, located in the driving plug movement cavity, placed on the upper surface of the elastic membrane, and the elastic membrane and the elastic membrane driving plug are fixed as a whole by ionic bonds between the PDMS materials; two vertical microfluidic holes are symmetrically provided on the chip packaging layer, located on both sides of the cylindrical through hole in the center, and the top of the microfluidic hole is connected to a guide tube, which is used for the entry and exit of liquid respectively.

[0009] The peripheral power supply system is connected to the coil of the magnetic field generating coil and supplies power to the magnetic field generating coil to generate a changing magnetic field.

[0010] The pump body lower cover is a full PDMS integrated module with a concave microchannel structure, wherein the concave microchannel structure includes a microchamber, a liquid inlet cavity, a liquid outlet cavity, an inlet channel and an outlet channel; the microchamber, the liquid inlet cavity and the liquid outlet cavity are top-opening structures; when the pump body lower cover and the pump body upper cover are combined into one, the upper surface of the pump body lower cover and the lower surface of the pump body upper cover are fixed together through ionic bonds between the PDMS materials, the top opening of the microchamber corresponds to the lower surface of the elastic membrane, forming a complete chamber, the liquid inlet cavity and the liquid outlet cavity respectively correspond to the bottom ends of the two microfluidic holes and are connected; the liquid inlet cavity and the liquid outlet cavity are connected to the microchamber through the inlet channel and the outlet channel respectively.

[0011] The elastic film and the chip packaging layer are made of PDMS material.

[0012] The elastic membrane driving plug has a neodymium iron boron permanent magnet inside and its outer surface is completely wrapped with PDMS material.

[0013] A method for manufacturing a micro pump, the specific steps are as follows:

[0014] Step 1: Integrate the elastic membrane on the pump body cover with the chip packaging layer. By coordinating the processing mold and auxiliary parts, the elastic membrane and the chip packaging layer are solidified into one during the curing process of the PDMS solution.

[0015] Step 2: Embed the magnetic field generating coil. By coordinating the mold and auxiliary parts, the magnetic field generating coil is embedded into the chip packaging layer during the curing process of the PDMS solution.

[0016] Step 3: Preparation of the elastic membrane drive plug: By processing the mold and auxiliary parts, the PDMS is wrapped on the surface of the NdFeB permanent magnet during the PDMS solution curing process, and then the elastic membrane drive piston is placed on the upper surface of the elastic membrane.

[0017] Step 4: Processing of microfluidic holes: Two microfluidic holes are symmetrically processed on the chip packaging layer.

[0018] Step 5: Processing the concave microchannel structure of the lower cover of the pump body: By coordinating the processing mold and auxiliary parts and solidifying the PDMS solution, a full PDMS integrated module with a concave microchannel structure is formed.

[0019] Step 6: Bond the pump cover to the lower cover using a bonding machine. Then insert the flow guide tube into the micro-flow hole in the pump cover to complete the assembly.

[0020] Furthermore, the specific method of step 1 is as follows:

[0021] The elastic film is attached to a glass sheet, and then plastic tin foil tape is used to stick to the edge of the glass sheet to form the side wall of the glass sheet. The glass sheet and the elastic film are then clamped between the magnetic force between the NdFeB permanent magnet and the T-shaped polished steel mold. The mold is placed at the corresponding position of the drive plug movement cavity of the chip packaging layer mold, and the elastic film is flush with the bottom surface. The PDMS solution is poured into half the height of the mold, and after removing bubbles, it is placed in a drying oven for curing. After being taken out and allowed to stand, an integrated elastic film and chip packaging layer are obtained.

[0022] Furthermore, the specific method of step 2 is as follows:

[0023] Place a cylindrical iron core with a through hole and a coil on the upper surface of an integrated elastic membrane and chip packaging layer, with the center of the circle coinciding with the center of the driving plug movement cavity; insert a T-shaped polished steel mold into the through hole of the cylindrical iron core and the driving plug movement cavity until the bottom of the chip packaging layer, and place a NdFeB permanent magnet under the elastic membrane and fix it by the magnetic force between the NdFeB permanent magnet and the T-shaped polished steel mold; continue to pour the PDMS solution into the mold until the magnetic field generating coil is completely submerged, and after removing bubbles again, put it into a drying oven for curing, take it out and let it stand, and separate the mold to achieve the embedding of the magnetic field generating coil.

[0024] Furthermore, the specific method of step 3 is as follows:

[0025] First, assemble the mold, use a polished steel sheet as the substrate, and use tin foil tape to make the side walls of the substrate; then pour in the PDMS solution, remove bubbles and dry it, then place one or more NdFeB permanent magnets on the solidified PDMS surface, and then pour in the PDMS solution; finally, after removing bubbles, drying, and cooling, separate and cut to obtain the elastic membrane drive plug wrapped in PDMS.

[0026] The micropump provided by this invention features a simple, highly integrated structure, making it easy to integrate with other microfluidic chips. Firstly, the micropump primarily consists of two components: an upper cover and a lower cover, resulting in a minimal number of components and simplified assembly. Secondly, the micropump's elastic membrane is integrated with the chip, and the upper and lower covers are bonded together, ensuring excellent airtightness, stability, and durability. Furthermore, the micropump is entirely covered in PDMS, making it easy to integrate with other chips.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. The micropump proposed in this invention offers lower manufacturing costs. First, the micropump is primarily made of PDMS, making both the processing material and components inexpensive and readily available. Furthermore, the micropump is structurally simple, consisting of only two integrated components: an upper pump cover and a lower pump cover. Furthermore, the micropump is easily manufactured, with the two components assembled by bonding, eliminating the need for bolts or glue. Therefore, the micropump can be manufactured and assembled using only inexpensive materials and simple processes.

[0029] 2. The micropump proposed in this invention has improved durability. The micropump proposed in this invention consists of only two integrated components: the upper pump cover and the lower pump cover, which are bonded together. The interiors of the two components are formed as one piece during the PDMS curing process. This highly integrated structure effectively avoids problems that are common during use, such as increased gaps between components, bolt slippage, and loose joints.

[0030] 3. The micropump proposed in the present invention has better airtightness. The microchamber and the elastic membrane are fixed by bonding. Compared with the existing "sandwich" multi-layer assembly structure, the elastic membrane covers the microchamber more tightly, eliminating air gaps and thus achieving better airtightness.

[0031] 4. The micropump proposed in this invention is more easily integrated with other microfluidic chips. The micropump proposed in this invention is entirely covered in PDMS, a material also commonly used in other microfluidic chips. By integrating the microchannel structure proposed in this invention with the microchannels of other chips on a single chip, the micropump can be integrated with other chips on-chip. Therefore, compared with micropumps constructed from materials such as glass, metal, and PMMA, the micropump proposed in this invention is easier to integrate with other chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a complete structural diagram of the micropump.

[0033] Figure 2 This is a schematic diagram of the integrated production of the elastic film and chip packaging layer.

[0034] Figure 3 This is a schematic diagram of the embedded production of the magnetic field generating coil.

[0035] Figure 4 This is a schematic diagram of the production of an elastic membrane drive plug.

[0036] Figure 5 It is a schematic diagram of the pump body lower cover structure.

[0037] In the figure: S1 pump body upper cover; S2 pump body lower cover; 1 chip packaging layer; 2 elastic membrane; 3 elastic membrane driving plug; 4 driving plug movement cavity; 5 magnetic field generating coil; 6 micro chamber; 7 inlet channel; 8 outlet channel; 9 liquid inlet cavity; 10 liquid outlet cavity; 11 T-shaped polished steel mold; 12 NdFeB permanent magnet; 13 micro flow hole; 14 flow guide tube. DETAILED DESCRIPTION

[0038] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0039] like Figure 1 As shown, a micropump according to the present invention comprises a pump body and a peripheral power supply system. The pump body comprises an upper cover S1 and a lower cover S2, and the peripheral power supply system is used to generate a high-frequency alternating current signal. The upper cover S1 is an integrated component entirely covered in PDMS material, enabling the micropump to receive drive signals, execute drive commands, and drive fluid. The upper cover S1 comprises an internal structure including a chip encapsulation layer 1, an elastic membrane 2, an elastic membrane drive plug 3, a drive plug motion cavity 4, and a magnetic field generating coil 5. Two vertical microfluidic holes 13 are also provided on the upper cover S1, connected to a flow guide tube 14 for fluid entry and exit. The elastic membrane 2 and chip encapsulation layer 1 are seamlessly bonded during the PDMS curing process, forming a single, flat surface. The magnetic field generating coil 5, elastic membrane 2, and chip encapsulation layer 1 are also bonded together during the PDMS curing process. The elastic membrane drive plug 3 is a cylindrical structure entirely made of PDMS, with its lower surface secured to the elastic membrane surface via ionic bonds between the PDMS materials. The pump body lower cover S2 is a fully integrated PDMS module with a concave microchannel structure. The concave microchannel structure includes a microchamber 6, an inlet channel 7, an outlet channel 8, and a liquid inlet cavity 9 and a liquid outlet cavity 10. The liquid inlet cavity 9 and the liquid outlet cavity 10 are respectively connected to the bottom of two microfluidic holes 13. The elastic membrane 2 is located above the microchamber 6 to form a complete chamber.

[0040] The working process of micropump of the present invention is as follows:

[0041] The peripheral power supply system supplies power to the magnetic field generating coil 5, generating a changing magnetic field. The interaction between the changing magnetic field and the elastic membrane driver plug 3 causes the elastic membrane driver plug 3 to drive the elastic membrane 2, fixed at its base, to oscillate back and forth. In the supply mode, the upward oscillation of the elastic membrane 2 increases the volume of the microchamber 6, which in turn decreases the pressure within the microchamber 6. This pressure drop causes fluid to enter the liquid inlet chamber 9 through the micropores 13 at the inlet end, and then flow through the inlet channel 7 to the microchamber 6. In the pumping mode, the elastic membrane 2 bends in the opposite direction, causing the volume of the microchamber 6 to decrease, thereby increasing the pressure within the microchamber 6. This causes the fluid to flow from the microchamber 6 through the outlet channel 8 to the liquid outlet chamber 10, and then out through the micropores 13 at the outlet end.

[0042] The production process of the micropump of this embodiment includes the following steps:

[0043] (1) First, make the pump body cover S1, the steps are as follows:

[0044] Step 1.1: Preparation of PDMS solution. Mix the PDMS liquid and curing agent in a mass ratio of 10:1, stir well, and let stand under vacuum for 30 minutes to remove bubbles in the solution to obtain a uniformly mixed PDMS solution.

[0045] Step 1.2: Integration of the elastic membrane 2 and the chip packaging layer 1. Cut a PDMS membrane with a side length of 14mm and a thickness of 0.1mm as the elastic membrane 2, and then stick the elastic membrane 2 on the glass sheet. Then use plastic tin foil tape to stick it on the edge of the glass sheet to form the side wall of the glass sheet. Then use the magnetic force between the NdFeB permanent magnet 12 and the T-shaped polished steel mold 11 to clamp the glass sheet and the elastic membrane 2 between them. Place it in the corresponding position of the drive plug movement cavity 4 of the chip packaging layer 1 mold, and make the elastic membrane 2 flush with the bottom surface. Figure 2 As shown, the mixed PDMS solution is poured into half the height of the mold, i.e. h1, and after removing bubbles again, it is placed in a drying oven for curing. After being taken out and allowed to stand, an integrated elastic film and chip packaging layer is obtained.

[0046] Step 1.3: Embedding of the magnetic field generating coil 5. Place the cylindrical iron core with through holes and the coil on the upper surface of the integrated elastic membrane and chip packaging layer obtained in step 1.2, with the center of the circle coinciding with the center of the driving plug movement cavity 4. Insert the T-shaped polished steel mold 11 into the through hole of the cylindrical iron core and the driving plug movement cavity 4 until it reaches the bottom of the chip packaging layer 1. Place the NdFeB permanent magnet 12 under the elastic membrane 2 and fix it with the magnetic force between the NdFeB permanent magnet 12 and the T-shaped polished steel mold 11. Figure 3 As shown, the mixed PDMS solution is poured into the mold until the magnetic field generating coil is completely submerged, and after removing bubbles again, it is placed in a drying oven for curing. After being taken out and allowed to stand, the mold is separated to achieve the embedding of the magnetic field generating coil 5.

[0047] Step 1.4: Preparation of elastic membrane drive plug 3. First assemble the mold, use the polished steel sheet as the substrate, and use the aforementioned tin foil tape to make the side walls of the substrate. Then pour the mixed PDMS solution in, remove bubbles and dry for 30 minutes, then place one or more NdFeB permanent magnets 12 (height 1mm, radius 2mm) on the solidified PDMS surface. At this time, due to the magnetic field force between the NdFeB permanent magnet 12 and the steel substrate, the NdFeB permanent magnet 12 is magnetically fixed in the placement position, and there is no gap between the NdFeB permanent magnet 12 and the solidified PDMS surface. At this time, pour in the PDMS solution, as shown in the following figure: Figure 4 As shown. Finally, after degassing, drying, and cooling, the PDMS-wrapped elastic membrane drive plug 3 is separated and cut, completing the solid PDMS wrapping of the NdFeB permanent magnet 12. The lower surface of the elastic membrane drive plug 3 is fixed to the upper surface of the elastic membrane 2 via ionic bonds between the PDMS materials.

[0048] Step 1.5: Processing the Microfluidic Holes 13. Mark the positions on both sides of the drive plug movement cavity 4 on the pump body cover S1, ensuring that both positions are the same distance from the drive plug movement cavity 4. Quickly advance the small syringe at the marked position until it penetrates the bottom of the pump body cover S1. This creates microfluidic holes 13 on both sides of the drive plug movement cavity 4 for inserting the flow guide tube 14.

[0049] (2) Make the pump body lower cover S2, the steps are as follows:

[0050] Step 2.1: Fabrication of the Concave Microchannel Mold. A two-dimensional plan view of the microchannel structure was drawn using CAD 2017 software. Next, a raised PDMS channel structure with a height of 200 μm was fabricated on a single-side polished chromium plate using soft lithography. This yielded the mold for the concave microchannel structure.

[0051] Step 2.2: Preparation of a PDMS body with a concave microchannel structure, i.e., the pump body lower cover S2. Place the mold in a glass dish, then pour in the mixed PDMS solution. After standing under vacuum for 20 minutes to remove bubbles, place it in a drying oven and bake it at 75°C for 60 minutes to solidify the PDMS solution. Then, remove the glass dish from the drying oven, leave it at room temperature for 20 minutes, and then separate the solidified PDMS from the mold to obtain a fully integrated PDMS module with a concave microchannel structure, i.e., the pump body lower cover S2. Figure 5 shown.

[0052] (3) Assemble all components as follows:

[0053] Step 3.1: Bond the pump cover S1 and the pump cover S2. Place the pump cover S1 and the pump cover S2 in the bonding machine with the surfaces to be bonded facing up. Once the bonding is complete, immediately butt the two surfaces together. After ensuring there are no gaps, place them in a drying oven and dry for 40 minutes. This completes the bonding process.

[0054] Step 3.2: Assemble peripheral components. Insert the flow guide tube 14 into the micro-flow hole 13 in the pump cover S1 to complete the assembly. The complete structure is as follows: Figure 1 shown.

Claims

1. A micro pump, characterized in that: The micro pump is composed of a pump body and a peripheral power supply system, and the pump body is composed of a pump body upper cover and a pump body lower cover; The pump body cover is an integrated component whose entire surface is covered with PDMS material, including a chip packaging layer, an elastic membrane, an elastic membrane driving plug, a driving plug movement cavity and a magnetic field generating coil; wherein, a vertical cylindrical through hole is provided in the center of the chip packaging layer as the driving plug movement cavity, the elastic membrane covers the lower surface of the through hole, the lower surface of the elastic membrane is flush with the lower surface of the chip packaging layer, and there is no gap between the two, and the lower surface of the pump body cover is an integrated plane; the magnetic field generating coil is composed of a cylindrical iron core with a through hole in the center and a coil, the coil is wound on the cylindrical iron core, the magnetic field generating coil is embedded in the chip packaging layer as a whole, and the through hole of the cylindrical iron core coincides with the driving plug movement cavity; the elastic membrane driving plug is a cylindrical structure, located in the driving plug movement cavity, placed on the upper surface of the elastic membrane, and the elastic membrane and the elastic membrane driving plug are fixed as a whole by ionic bonds between the PDMS materials; two vertical microfluidic holes are symmetrically provided on the chip packaging layer, located on both sides of the cylindrical through hole in the center, and the top of the microfluidic hole is connected to a guide tube, which is used for the entry and exit of liquid respectively; The peripheral power supply system is connected to the coil of the magnetic field generating coil to supply power to the magnetic field generating coil to generate a changing magnetic field; The pump body lower cover is a full PDMS integrated module with a concave microchannel structure, wherein the concave microchannel structure includes a microchamber, a liquid inlet cavity, a liquid outlet cavity, an inlet channel and an outlet channel; the microchamber, the liquid inlet cavity and the liquid outlet cavity are top-opening structures; when the pump body lower cover and the pump body upper cover are combined into one, the upper surface of the pump body lower cover and the lower surface of the pump body upper cover are fixed together through ionic bonds between the PDMS materials, the top opening of the microchamber corresponds to the lower surface of the elastic membrane, forming a complete chamber, the liquid inlet cavity and the liquid outlet cavity respectively correspond to the bottom ends of the two microfluidic holes and are connected; the liquid inlet cavity and the liquid outlet cavity are connected to the microchamber through the inlet channel and the outlet channel respectively.

2. A micro pump according to claim 1, characterized in that: The elastic film and the chip packaging layer are made of PDMS material.

3. A micro pump according to claim 1 or 2, characterized in that: The elastic membrane driving plug has a neodymium iron boron permanent magnet inside and its outer surface is completely wrapped with PDMS material.

4. A method for manufacturing a micropump according to any one of claims 1 to 3, characterized in that: The specific steps are as follows: Step 1: Integration of the elastic membrane on the pump body cover and the chip packaging layer: By coordinating the processing mold and auxiliary parts, the elastic membrane and the chip packaging layer are solidified into one during the curing process of the PDMS solution; Step 2: Embedding the magnetic field generating coil: By coordinating the mold and auxiliary parts, the magnetic field generating coil is embedded in the chip packaging layer during the curing process of the PDMS solution; Step 3, preparation of the elastic membrane driving plug: by processing the mold and the auxiliary parts, the PDMS is wrapped on the surface of the NdFeB permanent magnet during the curing process of the PDMS solution, and then the elastic membrane driving plug is placed on the upper surface of the elastic membrane; Step 4: Processing of microfluidic holes: symmetrically process two microfluidic holes on the chip packaging layer; Step 5: Processing the concave microchannel structure of the lower cover of the pump body: by coordinating the processing mold with auxiliary parts and curing the PDMS solution, a full PDMS integrated module with a concave microchannel structure is formed; Step 6: Bond the upper cover of the pump body to the lower cover of the pump body: Bond them using a bonding machine, then insert the guide tube into the microflow hole in the upper cover of the pump body to complete the assembly.

5. The method for manufacturing a micro pump according to claim 4, characterized in that: The specific method of step 1 is as follows: The elastic film is attached to a glass sheet, and then plastic tin foil tape is used to stick to the edge of the glass sheet to form the side wall of the glass sheet. The glass sheet and the elastic film are then clamped between the magnetic force between the NdFeB permanent magnet and the T-shaped polished steel mold. The mold is placed at the corresponding position of the drive plug movement cavity of the chip packaging layer mold, and the elastic film is flush with the bottom surface. The PDMS solution is poured into half the height of the mold, and after removing bubbles, it is placed in a drying oven for curing. After being taken out and allowed to stand, an integrated elastic film and chip packaging layer are obtained.

6. The method for manufacturing a micro pump according to claim 4, characterized in that: The specific method of step 2 is as follows: Place a cylindrical iron core with a through hole and a coil on the upper surface of an integrated elastic membrane and chip packaging layer, with the center of the circle coinciding with the center of the driving plug movement cavity; insert a T-shaped polished steel mold into the through hole of the cylindrical iron core and the driving plug movement cavity until the bottom of the chip packaging layer, and place a NdFeB permanent magnet under the elastic membrane and fix it by the magnetic force between the NdFeB permanent magnet and the T-shaped polished steel mold; continue to pour the PDMS solution into the mold until the magnetic field generating coil is completely submerged, and after removing bubbles again, put it into a drying oven for curing, take it out and let it stand, and separate the mold to achieve the embedding of the magnetic field generating coil.

7. The method for manufacturing a micro pump according to claim 4, characterized in that: The specific method of step 3 is as follows: First, assemble the mold, use a polished steel sheet as the substrate, and use tin foil tape to make the side walls of the substrate; then pour in the PDMS solution, remove bubbles and dry it, then place one or more NdFeB permanent magnets on the solidified PDMS surface, and then pour in the PDMS solution; finally, after removing bubbles, drying, and cooling, separate and cut to obtain the elastic membrane drive plug wrapped in PDMS.

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