3D Printed Microfluidic Cell Stimulating Device for Studying Bone Cell Mechanobiology

Carson Emeigh Author

07/28/2021 Added

18 Plays

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A procedure was developed that fabricated master molds for microfluidic device using 3D printing that can stimulate cells for cellular studies.

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[00:00:00.810]Hi, my name is Carson Emeigh,
[00:00:02.100]and I'm a student here at the University of Nebraska Lincoln,
[00:00:04.260]studying mechanical engineering, and I'll be entering my senior year, this fall.
[00:00:07.800]And today I would like to give a presentation on 3d printed microfluidic cell
[00:00:11.040]stimulating device for studying bone cell mechanobiology.
[00:00:15.570]The motivation for this project was to prove that we could use 3d printing to
[00:00:18.630]create microfluidic device master molds.
[00:00:20.910]We wanted to use 3d printing because it is cheaper, quicker,
[00:00:23.730]has higher design flexibility and can,
[00:00:26.390]produce variable height molds compared to traditional methods.
[00:00:30.270]One of the biggest challenges that we experienced while working on this project
[00:00:33.570]was the way that PDMS interacts with the master mold material.
[00:00:37.290]So PDMS needs to cure in order to create microfluidic devices.
[00:00:40.920]And sometimes we found that the master mold material would inhibit the PDMS curing.
[00:00:45.357]And another challenge that we faced was increasing the mold reusability.
[00:00:48.990]So we want to be able to reuse the mold many times to create many microfluidic
[00:00:52.200]devices, and that will increase the efficacy of using 3d printing.
[00:00:56.760]Previous work developed a PDMS based microfluidic device using more traditional
[00:01:00.480]methods, such as photolithography.
[00:01:02.550]Photolithography involves taking a Silicon wafer and covering it in a photoresist
[00:01:06.065]using a photo mask to solidify the channel design onto the photoresist
[00:01:10.170]and then washing away the excess photoresist with some baking and curing steps
[00:01:13.740]thrown in between. The device, again, is a PDMS based microfluidic device.
[00:01:18.450]And the device overview is there is an inlet
[00:01:21.090]for an air pump to connect up to that leads to a channel portion that leads to a
[00:01:25.200]thin PDMS layer. So the thin PDMS layer,
[00:01:28.740]when you apply pressurized air to it, will inflate like balloons.
[00:01:32.490]So if you put cells on top of that thin PDMS layer and then inflate it,
[00:01:36.420]the cells will experience stresses similar to us walking and moving in our
[00:01:40.110]day-to-day lives.
[00:01:41.723]To fabricate this device, the mold is first printed using the 3d printer.
[00:01:45.120]Then it is removed from the build plate and placed into a 99% isopropyl wash for
[00:01:49.410]around 50 minutes. Once the excess material has been washed off,
[00:01:52.980]it is then placed into a UV oven to fully solidify the device.
[00:01:56.790]And it is flipped halfway through to ensure both sides get fully solidified.
[00:02:00.360]Then it is removed from the UV oven and placed into a conventional oven at 130
[00:02:04.080]degrees Celsius to bake out any toxins and impurities that would inhibit the
[00:02:07.350]PDMS from curing. Then PDMS is poured into the mold.
[00:02:10.740]Then a glass plate is placed on top of the mold to control the thickness so we
[00:02:13.620]can control the thickness of the balloon layer.
[00:02:15.930]Then the PDMS is cured and peeled off of the mold. And finally,
[00:02:19.230]the PDMS is bonded onto a glass plate,
[00:02:21.750]as well as the connection piece is bonded onto the PDMS to create a fully
[00:02:25.200]functioning microfluidic cell stimulating device.
[00:02:29.580]Now for results & discussion.
[00:02:31.140]First, I would like to compare more traditional methods,
[00:02:32.580]such as photolithography with 3d printing.
[00:02:34.590]The first consideration is going to be time photolithography takes around a week
[00:02:38.040]to produce a mold because of the amount of steps that it takes to create the
[00:02:41.640]molds, as well as the processing
[00:02:43.020]and post-processing all of which need time before you can move on to the next step.
[00:02:46.536]3d printing on the other hand only takes about three hours.
[00:02:49.170]So it takes about an hour to print the mold an hour to wash the mold,
[00:02:52.440]and then an hour to bake the mold.
[00:02:53.880]Before you're able to pour PDMS onto the mold to create a microfluidic device.
[00:02:57.590]The second consideration is going to be cost. The cost of photolithography is going to
[00:03:01.209]be much higher because it requires much more manpower, as well as time,
[00:03:04.360]and just more resources. And 3d printing is relatively low, seeing as the
[00:03:09.400]biggest recurring cost is just the material in the printer.
[00:03:11.680]And you can print a piece for about $5.
[00:03:14.350]Photolithography also does not allow for variable height.
[00:03:16.720]So the height across the entire mold is the exact same.
[00:03:20.230]Whereas with 3d printing, using additive manufacturing,
[00:03:22.390]we're able to choose which parts of the mold have different heights.
[00:03:24.910]So for example,
[00:03:25.960]the channel height is a different height compared to the balloon peg height on
[00:03:29.080]my mold. Next, the thing we want to consider is design flexibility.
[00:03:33.400]So photo photography has very,
[00:03:34.750]very little design flexibility because you use photomasks, and sometimes they
[00:03:37.880]can take time to receive new photo masks if we want to change the design.
[00:03:42.220]And so that can make it very,
[00:03:42.970]very hard to change the mold once it's been created. Whereas with 3d printing,
[00:03:46.360]if I want to change the design,
[00:03:47.900]I need about 10 minutes in SolidWorks to create the new design and then simply
[00:03:52.300]print it. And with photolithography, the probability of defects is very high.
[00:03:56.560]Um, usually you need a clean room in order to use photography,
[00:03:59.530]whereas the 3d printing, you can be a little less careful.
[00:04:02.816]Next, what I found is that during my project PDMS curing inhibition occurred,
[00:04:06.160]and I took some steps to solve that.
[00:04:08.440]So first I realized that only a small area of the PDMS was,
[00:04:11.590]cured and the rest was uncured.
[00:04:12.940]So what I did is I decreased the area of the mold,
[00:04:15.070]but I was not able to clear PDMS once or twice on this mold. Next,
[00:04:18.910]I realized that the mold had a sticky residue after post-processing.
[00:04:21.190]So I increased the layer, curing time on the printer. And again,
[00:04:24.220]I found that I was not able to cure PDMS once or twice,
[00:04:27.040]and it also degraded the quality of the print. Next.
[00:04:29.920]I realized that the mold was still sticky.
[00:04:32.200]So I increased the IPA concentration to 99%,
[00:04:35.050]and that allowed me to cure PDMs on the mold once, but not twice,
[00:04:37.900]meaning that it could not be reused.
[00:04:40.464]Next, I saw master mold material spots on the device.
[00:04:44.230]So I increased the IPA wash time to 55 minutes. And again,
[00:04:47.380]I was only able to him PDMS once. Then I realized that there were surface defects
[00:04:50.650]in the mold. So I cleaned and repaired the printer and replaced parts.
[00:04:53.140]And I found that again, I was only able to cure PDMS once.
[00:04:56.670]Next, I figured that there must be a chemical reaction occurring with the material of
[00:05:00.100]the mold and PDMS at high temperatures.
[00:05:02.310]So I tested curing the PDMS at room temperature and found that I was able to
[00:05:06.220]cure PDMS twice, and this is good for the reusability mold,
[00:05:10.300]but I need to be able to cure the mold at high temperatures in order to get the
[00:05:12.940]proper PDMS qualities to make the balloons inflate properly.
[00:05:15.700]So I baked the mold at 130 degrees Celsius for one day before use,
[00:05:19.930]and I was able to cure PDMs twice on that mold,
[00:05:22.840]meaning that it could be reused. In summary,
[00:05:25.870]I was able to create a mold that could produce high quality microfluidic devices
[00:05:29.770]with low cost, high reusability, high strength, and minimal surface defects.
[00:05:33.790]And I also had to debug PDMS curing to ensure that I was able to get high
[00:05:38.110]quality parts.
[00:05:40.090]3d printing allows for ease of fabrication because it reduces the number of
[00:05:43.150]steps, the costs and the manpower.
[00:05:45.040]And it also increases design flexibility with additive manufacturing.
[00:05:48.880]And I was able to get a proper operation set up working for the device.
[00:05:52.180]So here's the device, here's the air pump.
[00:05:54.550]And then the air pump is connected to a power supply at that powers it.
[00:05:59.620]Next, for my project,
[00:06:00.370]I will validate the devices work just as good as the previous ones did.
[00:06:04.060]And I will do that with 3d laser scanning microscopy to ensure that the balloons
[00:06:07.570]inflate to a proper height and in a proper way so that the cells will be
[00:06:11.080]properly deformed. Once the device has been validated,
[00:06:13.750]I will send it to UNMC to Dr. Dudley for cell experimentation.
[00:06:17.930]And then after that,
[00:06:18.850]I will work to create a modular motherboard that allows for multiple of these
[00:06:22.450]devices to be connected and operate simultaneously.
[00:06:25.600]The motherboard needs to allow for quick, reversible, leak-free seals between the
[00:06:28.960]devices. So down here, I have a prototype of one that I made.
[00:06:31.810]So here's the motherboard and here's a PDMs device and the PDMS device can plug
[00:06:35.230]into this motherboard, and you can see that it's able to create quick, reversible,
[00:06:39.670]leak-free seals for this device.
[00:06:41.890]And the motherboard that I'll be creating will be able to connect multiple of
[00:06:44.700]the devices together.
[00:06:46.900]I would also like to thank John Woollam and UCARE for the funding on this and
[00:06:50.140]allowing me to further my research.
[00:06:52.240]Thank you.

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3D Printed Microfluidic Cell Stimulating Device for Studying Bone Cell Mechanobiology

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