The overall goal of the following experiment is to demonstrate complex fluid shaping as observed by the production of microfibers. This is achieved by assembling a microfluidic channel with specific grooves to produce a polymer realizable core with a predetermined cross-sectional shape. As a second step, a pre polymer solution is prepared, which will be shaped and polymerized once it passes through the channel.
Next UV light is turned on at the bottom of the channel in order to polymerize the polymer material. These scanning electron micrographs show several microfiber shapes that were fabricated. Similarly, Advantages of this technique in comparison with other existing methods like electro spinning and melt spinning, include the fact that this technique can be performed at room temperature, and this technique can be used with a variety of polymer reasonable materials.
In addition, this technique does not require high voltages. It does not require high temperature followed by rapid cooling times, and it also does not require control of environmental factors like humidity. Visual demonstration of this technique is critical because microfluidic fiber fabrication is not as common as some other methods, and therefore it may be difficult to conceptualize without having seen it.
Visually, Though, this method has been used for the production of polymer microfibers. The same principles are in use in our lab for the development of other systems like micro blood vessels. We initially had this idea while observing micro mixers and microchip flow cytometry systems confocal.
As we saw sustained ornate cross-sections develop. We posited that by introducing a polymer solution, the shapes could be locked in via photo polymerization continuously and with relative ease. Demonstrating the procedure will be Michael Danielle and Darrell Boyd, who are postdocs from my laboratory.
First assemble a previously designed sheath flow device from the bottom up by placing one fastening plate at the bottom, followed by A COC cyclic olefin copolymer layer, and the remaining fastening plate. Ensure that the shaping grooves align with each other along the edges of the channel, and that the fluid shaping geometries in the COC layers perfectly overlap. Insert bolts across the center of the device and using a power screwdriver, tighten the nuts and bolts to clamp the device together, alternating from left to right of center.
Repeat the previous step from the center out to lock in the alignment and to prevent leaks. Add on the inlet chuck when its mounting holes are reached and continue mounting the screws in an alternating fashion. Next, connect the sheath flow device to tigon tubing.
Using standard HPLC fittings, manually tighten all the connections, mount the device vertically using a ring stand and clamp, ensure that the device is vertical using a level on the topmost portion. Then position the UV source perpendicularly about one centimeter from the COC face of the sheath flow device such that the last three to five centimeters of the micro channel is irradiated. Fill a one milliliter lure tip syringe with PEG 400 to serve as a non polymer core fluid and fill a 30 milliliter lure tip syringe with PEG 400 to serve as the sheath fluid.
Next, supplement a freshly prepared thiol line solution with four times 10 to the minus fourth moles of DMPA photo initiator in a small vial. After approximately two minutes of stirring, load a five milliliter aluminum foil wrapped lower tip syringe with a pre polymer solution. Following this place, the outlet of the microfluidic channel in a collection bath containing water.
Set the core cladding and sheath fluid syringe pumps to infuse at one 30 and 120 microliters per minute respectively. Then enter the respective syringe diameters into the syringe pumps. Then mount the syringes into their corresponding syringe pumps and connect them to the sheath flow device.
With UV protective tigon tubing, start the sheath fluid to prime the sheath flow device and eliminate air from the system. Visually inspect the microchannel and pay particular attention to the shaping grooves to ensure that no air bubbles remain in the microchannel before going on to the next step. If air bubbles are present, agitate the device by rotating and or tapping gently while under flow to flush them out of the device.
Start the cladding fluid, also allowing the flow to stabilize. After inspecting the microchannel and flushing out air bubbles, start the core fluid and ensure that bubbles aren't present in the system in the same manner as before. Finally, turn on the UV source and observe the collection bath for continuous production of the hollow microfiber as it is ejected with the sheath fluid.
Retrieve the fiber from the collection bath, a simple two stage design using shaping grooves and three solution inputs was used to create hollow fibers. Comsol simulations were used to determine the appropriate flow rate ratios to obtain the desired cross-sectional size. A combination of milling and molding produced the components for the sheath flow assembly to fabricate the fibers.
Polymerization of the cladding material was initiated by the UV light source, and hollow fibers were extruded from the microchannel into the collection bath. The production of fibers continued for minutes and generated a single fiber over a meter in length. Fibers made under these conditions were approximately 200 micrometers in diameter.
The structure of the fibers was visualized using optical and electron microscopy. The fibers had an oval shape with a hollow core. Capillary action was used to introduce liquid and bubbles into the interior of the fiber and confirmed that the hollow structure was continuous over the length of the fiber.
Once mastered, this process can take as little as 45 minutes. That includes the time to set up the channel, the solution preparation, the fiber fabrication, as well as the collecting of the fibers. After watching this video, you should have good understanding how to design and assemble a microfluidic channel to produce hollow microfibers.
Don't forget that when working with hazardous chemicals and UV irradiation, you should always wear your personal protective equipment.
