FEDSM 2022

Carson Emeigh Author

06/16/2022 Added

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[00:00:00.994]Hi my name is Carson Emeigh,
[00:00:02.119]and I am an undergraduate researcher at
[00:00:03.506]the University of Nebraska-Lincoln in the
[00:00:05.376]United States of America.
[00:00:06.917]Today, I will be giving a presentation for
[00:00:08.896]ASME's FEDSM 2022 meeting in Toronto, Canada.
[00:00:12.581]The title of my presentation today is
[00:00:14.830]Fabrication of a Microfluidic
[00:00:15.990]Cell Compressor Using a 3D-Printed Mold.
[00:00:20.223]Microfluidics are devices that can control
[00:00:22.163]fluids at the microscopic level.
[00:00:23.768]They are especially important for
[00:00:25.838]cellular studies as microfluidics and
[00:00:27.675]cells are on a similar length scale.
[00:00:29.629]In particular, microfluidics can be used
[00:00:32.262]to study the mechanobiology of cells,
[00:00:34.285]or the way mechanics affect the cells biology.
[00:00:37.009]Some common mechanobiological properties
[00:00:40.024]of cells that are studied using
[00:00:41.294]microfluidics include cancer development
[00:00:43.024]and the maintenance of articular cartilage.
[00:00:44.854]Below, are a few microfluidic devices
[00:00:47.621]that are used to study the
[00:00:48.594]mechanobiological properties of cells.
[00:00:53.629]In this top figure there is a
[00:00:54.868]cell stretcher that is shown.
[00:00:56.646]There is a thin film which cells are
[00:00:58.592]attached to. Beneath this film,
[00:01:00.630]there is an actuator attached to
[00:01:02.380]a secondary thin film.
[00:01:04.190]When a pressure is applied with
[00:01:05.633]an air pump to the secondary film,
[00:01:08.114]the actuator is inflated pushing
[00:01:09.620]the thin film that the cells are
[00:01:11.000]attached to upwards.
[00:01:12.687]As the thin film that the cells are on
[00:01:14.543]stretches, so do the cells.
[00:01:18.427]In the secondary figure, there
[00:01:20.332]is another device used to study
[00:01:21.846]cancer development in a different way.
[00:01:23.705]Cells are loaded into a cell channel
[00:01:26.094]which is below another channel
[00:01:27.504]called the control channel.
[00:01:28.883]Once the cells are loaded,
[00:01:30.527]the control channel can be pressurized
[00:01:32.227]using an air pump and little pistons
[00:01:34.576]in the control channel press down
[00:01:36.196]onto the cells in the cell channel.
[00:01:38.977]By looking at the places where the cells
[00:01:40.701]were compressed verses the control
[00:01:42.344]cells, you can see how they differ
[00:01:44.266]because of the mechanical stimulation
[00:01:45.984]applied. Both these devices are used to
[00:01:49.324]study the way certain mechanics affect the
[00:01:51.087]development and movement of cancer cells.
[00:01:54.780]The 3rd figure shows a microfluidic device
[00:01:57.196]that can be used to study the maintenance
[00:01:58.856]of articular cartilage. There are 3
[00:02:01.061]sections to this microfluidic device.
[00:02:03.189]The 1st section can be pressurized similar
[00:02:06.037]to what we talked about in the
[00:02:07.334]previous devices. When this is pressurized,
[00:02:09.834]it will apply a compressive force to a
[00:02:12.134]sample area to which cells or hydrogels
[00:02:14.215]can be loaded.
[00:02:17.233]Below that, there is a perfusion chamber
[00:02:19.604]that will further simulate bodily
[00:02:21.255]conditions for articular cartilage.
[00:02:23.386]Articular cartilage samples are loaded into
[00:02:26.369]this area, a compressive force is applied
[00:02:28.738]to them, and the movement of cells and
[00:02:31.460]their nutrients is allowed.
[00:02:32.848]Using this device, you can study how the
[00:02:34.792]maintenance of articular cartilage is
[00:02:36.565]affected by mechanical force.
[00:02:40.094]When making microfluidic devices molds
[00:02:42.685]are required. The most common method
[00:02:44.700]for making molds is photolithography.
[00:02:46.791]In this paper, we look to find a way
[00:02:48.955]to make microfluidic molds without
[00:02:50.936]photolithography as photolithography
[00:02:52.973]can be very tedious and costly.
[00:02:56.956]In this study, we made a cell compression
[00:02:59.216]device that was previously made with
[00:03:00.710]photolithography using 3D printing.
[00:03:02.701]Below is a schematic of the device
[00:03:05.262]developed. Here is the overall device
[00:03:07.505]with its multiple layers, here is a
[00:03:09.677]cross-section of the layers of the device,
[00:03:11.962]where we have a glass plate and an air
[00:03:14.503]chamber that can be pressurized using
[00:03:16.497]an air pump that has a thin film above it.
[00:03:18.467]When a pressure is applied, this thin film
[00:03:21.467]is deformed and cell cultures above are
[00:03:25.467]compressed between the film and a
[00:03:26.807]glass plate shown here. A picture of the
[00:03:30.807]device is shown below. The previous
[00:03:33.899]fabrication steps of this device involve
[00:03:35.833]making a mold with photolithography.
[00:03:38.096]Photolithography consists of taking a
[00:03:40.096]silicone wafer and coating it with a
[00:03:41.786]photoresist, using a photomask and UV
[00:03:44.587]light to solidify certain portions of
[00:03:46.365]the photoresist, baking and developing
[00:03:48.880]of the mold, and using a complex clamping
[00:03:51.215]and laying system to develop just the
[00:03:53.155]channel layer. Then, the thin layer that
[00:03:57.155]is deformed when pressurized air is
[00:03:59.143]applied must be made by spin-coating PDMS
[00:04:01.572]onto a glass slide with transparency film,
[00:04:04.056]and aligning this film onto the channel
[00:04:06.365]layer. Overall, photolithography is
[00:04:09.262]lengthy, expensive, and sensitive to
[00:04:12.012]defects. Therefore, a better way of making
[00:04:14.958]a mold is developed that allows for
[00:04:16.550]quicker development, less money and
[00:04:18.980]manpower, and less steps to create.
[00:04:22.618]In our study, we used 3D printing to
[00:04:24.769]develop the molds instead of
[00:04:25.935]photolithography. 3D printing compared to
[00:04:28.572]photolithography is much cheaper, quicker,
[00:04:31.495]has more design flexibility as designs can
[00:04:34.265]be changed quicker and easier, it has less
[00:04:36.855]fabrication steps, and it allows for the
[00:04:39.306]molds to have different heights in
[00:04:40.839]different sections. Below, a picture of
[00:04:43.148]the mold is shown. There are microchannels
[00:04:45.851]with a portion to place an inlet that
[00:04:48.467]leads to balloon pegs which act as the
[00:04:50.750]pressurization chamber with spacers that
[00:04:53.426]will help us control the overall device
[00:04:55.233]thickness as well as the thickness of the
[00:04:57.382]thin film that will be above the balloon
[00:04:59.331]pegs. When making molds using 3D printing,
[00:05:04.501]there are a few steps that must be taken.
[00:05:06.352]First, the mold must be printed. Second,
[00:05:09.442]it must be washed in 99% isopropyl
[00:05:12.020]alcohol for 50 minutes. Third, it must be
[00:05:14.978]baked in a UV oven for 40 minutes flipping
[00:05:17.362]after each cycle. Finally, it is baked in
[00:05:20.054]a convection oven at 130 C overnight.
[00:05:25.198]Once the mold is made, PDMS, or a clear
[00:05:28.760]rubber, is poured into the mold and
[00:05:30.225]it is allowed to solidify. Then, it is
[00:05:32.721]peeled off the mold and bonded onto a
[00:05:34.578]glass plate using plasma bonding. Once it
[00:05:37.390]is bonded onto a glass plate, an inlet
[00:05:39.357]port is plasma bonded onto the device.
[00:05:41.599]As you can see, the device also has an air
[00:05:44.269]chamber that inflates when pressurized air
[00:05:46.285]is applied, but now it is a single layer
[00:05:48.292]of PDMS rather than multiple layers.
[00:05:51.802]When developing these molds we found
[00:05:53.942]PDMS had a hard time solidifying at the
[00:05:56.462]interface between the mold and PDMS unless
[00:05:58.887]critical maintenance steps were taken when
[00:06:00.635]using the 3D printer. The printer is shown
[00:06:02.956]below in this figure, and the inside of
[00:06:05.227]the printer is shown in the secondary
[00:06:06.685]figure. Maintenance steps that allowed
[00:06:08.965]PDMS to solidify on the mold were to
[00:06:10.946]remove debris from the material vat so
[00:06:12.828]that there was no particulate and it was
[00:06:14.446]clean resin. You must stir the resin
[00:06:16.597]between each use to homogenize the resin.
[00:06:18.795]You must also make sure that the Teflon
[00:06:21.287]film at the bottom of the material vat
[00:06:23.050]is completely clear such that UV light can
[00:06:25.310]pass through the filter properly.
[00:06:26.822]You also want to make sure that the UV
[00:06:29.000]filter is clean and oil free
[00:06:31.780]so the UV light can pass through the
[00:06:33.819]filter properly, and it is also important
[00:06:36.145]to wash the build plate with isopropyl
[00:06:38.115]alcohol so you are not introducing
[00:06:40.102]particulate or debris into the material
[00:06:42.172]when printing. Once the microfluidic device
[00:06:46.172]was developed, the device was characterized.
[00:06:48.862]To operate the device, a silicone tube
[00:06:51.719]was connected to the inlet port of the
[00:06:53.669]device, and the other end of the silicone
[00:06:55.026]tube was connected to an air pump which
[00:06:57.121]is then connected to a DC power supply.
[00:06:59.156]Depending on the voltage supplied by the
[00:07:01.676]DC power supply, the pump will create
[00:07:03.982]different levels of pressure. In our study,
[00:07:06.565]we ran the DC power supply at 4.3 Volts,
[00:07:09.673]which applied a pressure of 70 kPa to the
[00:07:12.873]device. Once the pressure was supplied
[00:07:16.873]by the air pump, the balloons of the
[00:07:18.940]device were inflated. To characterize
[00:07:21.395]the device the surface profile of
[00:07:23.263]inflated balloons were imaged using a
[00:07:24.979]Keyence Laser Scanning Microscope shown in
[00:07:27.187]the figure below. The microscope works by
[00:07:30.115]shooting a laser at the device and collecting
[00:07:32.007]the reflected light. Because the microscope
[00:07:34.385]works off reflected light, and the device
[00:07:36.979]is transparent, the device was coated with
[00:07:39.199]powdered chalk to make it opaque. Balloons
[00:07:43.199]of each diameter ranging from 0.6 mm to
[00:07:47.199]1.44 mm with a step size of 0.2 mm were
[00:07:52.162]imaged. Below is an image generated from
[00:07:54.946]the largest balloon diameter of 1.4 mm.
[00:07:58.284]Once the data was obtained, it was analyzed
[00:08:01.415]using Keyence's VK Analyzer software.
[00:08:04.485]From our study, we found we were able to
[00:08:08.241]develop molds that were effective.
[00:08:10.195]Fabricating the device with 3D printing
[00:08:12.576]took approximately 1 day, while developing
[00:08:14.703]the device with photolithography took at
[00:08:16.457]least 2. To the right, we can see the data
[00:08:19.032]that was obtained. From bottom to top,
[00:08:22.157]the balloon with a diameter of 0.6 mm
[00:08:25.857]had a height of 50 um, the balloon with a
[00:08:28.679]diameter of 0.8 mm had a height of 113 um,
[00:08:32.679]the balloon with a diameter of 1.0 mm had
[00:08:36.238]a height of 208 um, the balloon with a
[00:08:39.517]diameter of 1.2 mm had a height of 328 um,
[00:08:43.831]and the balloon with a diameter of 1.4 mm
[00:08:47.060]had a height of 450 um. The graph below
[00:08:51.060]visualizes the data. What we can see is
[00:08:54.282]that as the balloon's diameter increased,
[00:08:57.697]so did the height of the balloon. Compared
[00:09:00.134]to our previous study, our balloons had a
[00:09:02.264]different diameter, thickness, and applied
[00:09:05.010]pressure to make the fabrication of the
[00:09:06.540]device easier as well as allow for higher
[00:09:09.710]inflation of the device. Our points are
[00:09:13.710]shown by the red circles, and the previous
[00:09:15.911]device's data is shown by the blue squares.
[00:09:18.436]What we can see is that 2 of the diameters
[00:09:21.514]are the same, but the device developed in
[00:09:24.599]this study had a much higher level of
[00:09:26.674]inflation. In the previous study, a model
[00:09:30.674]for the height of the balloons was
[00:09:32.312]developed based on a clamped thin film
[00:09:34.589]deformation equation. H is the balloon
[00:09:37.696]height, P is the applied pressure, D is the
[00:09:41.568]balloon diameter, Nu is the Poisson's
[00:09:43.949]ratio of PDMS, E is the Young's modulus
[00:09:47.418]of PDMS, and t is the thickness of the
[00:09:50.116]balloon film. Young's modulus and Poisson's
[00:09:53.442]ratio were constant between the device
[00:09:55.427]developed in this study and the device
[00:09:57.507]developed in the previous study. As such,
[00:10:00.337]the devices were compared using a height
[00:10:02.248]ratio. The height ratio of a specific
[00:10:04.737]diameter depended on the applied pressure
[00:10:06.971]and the balloon film thickness as the
[00:10:08.897]other variables were held constant. Based
[00:10:12.897]on the pressure and thickness, the height
[00:10:15.126]ratio was expected to be 2.15 for each
[00:10:18.127]diameter. What we found was that the
[00:10:21.299]height ratio for the diameter of 1.2 mm
[00:10:24.091]was 2.12, and the height ratio for the
[00:10:27.589]diameter of 1.4 mm was 2.22. These values
[00:10:32.081]are relatively close to what was expected.
[00:10:34.576]Therefore, the new device's operation was
[00:10:37.226]validated. In summary, 3D printing
[00:10:41.835]microfluidic molds is cheap, quick, and
[00:10:44.395]highly flexible. A protocol to fabricate
[00:10:47.026]microfluidics using 3D printing was
[00:10:49.094]developed that required less steps.
[00:10:50.743]The maintenance of the 3D printer and
[00:10:53.190]post-processing of the mold is critical
[00:10:55.371]for PDMS solidification. Finally, complex
[00:10:59.371]microfluidic devices can be fabricated
[00:11:01.759]with 3D printing. In the future,
[00:11:03.995]devices with different balloon diameters
[00:11:06.118]and thicknesses will be developed, as well
[00:11:08.139]as microfluidic device motherboards will
[00:11:10.552]be developed to connect multiple devcies
[00:11:12.522]together for simultaneous operation.
[00:11:14.690]Multiple flow components will also be added
[00:11:17.523]to the device so multiple types of stimuli
[00:11:19.718]can be applied at the same time. We will
[00:11:22.079]also investigate other applications for
[00:11:24.203]inflatable microfluidics. Thank you for
[00:11:28.462]your attention, and here are our
[00:11:30.337]acknowledgements.

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