The overall goal of this procedure is to fabricate three dimensional microvascular structures. This is accomplished by first creating sacrificial fibers by incorporating tin two oxalate into polylactic acid fibers. The second step is to pattern the fibers three dimensionally using patterning plates.
Next, the fibers are cast in an embedding resin. The final step is to evacuate the fibers from the resin under heat and vacuum. Ultimately, the microvascular system can be used for many purposes, including heat exchange, mass transport, and self-healing systems.
Generally, individuals new to this method will struggle because of the degree of manual dexterity and visual awareness needed to work with the fibers is high. Visual demonstration of this method is critical as the chemical treatment of fibers and the stringing of pattern plates are hard to learn because they require hand-eye coordination and specialized equipment. Start the fiber catalyst infusion process with a customized spindle and a source of polylactic acid fibers of known diameter.
Here, 200 microns. Wrap the desired amount of the fibers around the lower three quarters of the spindle. Reduce fiber overlap to provide maximum surface area exposure in a bottle that can be sealed.
Mix 400 milliliters of deionized water with 40 milliliters of dysbaric. One 30. Close the bottle and shake it until a homogenous solution is obtained.
Next place a 1000 milliliter beaker in a water bath at 37 degrees Celsius. Pour 400 milliliters of tri fluoro ethanol into the beaker. Add the water disper solution to the beaker and stir until uniform.
Add one gram of malachite green or other dye to the mixture and stir until dissolved. Now, attach the spindle to the digital mixer and adjust the height so the spindle is half an inch from the bottom. Set the mixer to 400 RPM and begin mixing slowly.
Add 1.3 grams of tin oxalate catalyst to the mixture. Adjust the pH in the mixture using sodium hydroxide until the pH is approximately 6.8 to 7.2. Next, secure a lid to the beaker and increase the spindle rotation to 500 RPM.
Maintain this for 24 hours within the first two hours. Manually break up any agglomeration of tin oxalate that develops. At the end of 24 hours, have an oven preheated to 35 degrees Celsius.
Remove the spindle from the mixer and place it in the oven. Leave it to dry overnight. After at least eight hours of drying, remove the spindle from the oven, unwrap the fibers from the spindle.
Remove the excess catalyst from the fibers. Fabrication of the microvascular gas exchange unit begins with obtaining a pair of laser cut brass patterning plates with the desired microvascular pattern. Affix the plates on clip holders.
Cut a 10 inch length of catalyzed fiber per micro channel. Use a plate cut to the fiber diameter to remove any remaining catalyst from the fibers. Use the tip of a hot glue gun to taper the edges of the fiber.
Do this by slowly extruding the fiber tips. Once done, thread the fibers through matching holes in the brass patterning plate pairs. Next, screw the plates onto a molding box.
Make sure the fibers are not twisted when attaching the plates. Then string the fiber tips through the tuning pegs of the custom tensioning board tension the PLA fibers until taut. Be careful not to over tension and snap the fibers.
Remove excess particulates from the fiber pattern using compressed air. Now mix poly dimethyl xin base with its curing agent in a 10 to one volume ratio, place the mixture in a desiccate jar. Degas the mixture for 10 minutes under a vacuum.
Pour the PDMS mixture into the molding box, but not directly over the fibers. Use a 26 gauge needle to remove any bubbles in the molding box or between the fibers. Once done, cure the assembly at 85 degrees Celsius for 30 minutes.
When the box is cooled, unfastened the brass plates from the molding box, making sure not to bend the plates or pull too hard. Remove the cured first stage from the molding box. Use a hypodermic needle with a gauge that is at least twice the outer diameter of the fibers to puncture holes in an RTV end cap with needle in place thread of fiber through the hole.
Then remove the needle. The hole pattern should be similar to the brass patterning plate, but more widely spread out. Next, fasten the end caps to a larger molding box.
Pour a second stage of PDMS and remove any remaining gas bubbles. Again, cured 85 degrees Celsius for 30 minutes. After the second curing, cut any excess PLA fibers from the sample.
Place it in a vacuum oven at 210 degrees Celsius for 24 hours or until most of the PLA fibers have been evacuated. If any PLA cannot be removed, inject one milliliter of chloroform to dissolve what remains in the micro channels. This completes the unit fabrication.
This procedure provides a method for fabricating microvascular structures in resin as seen in the gas exchange unit. Shown at the top. On the bottom left is a detail of a segment of the structure.
Dyes have been used for visual clarity. On the right is the hexagonal pattern of 200 micron and 300 micron holes used to create the micro channels. The micro channels are completely hollow and can be separated by less than 50 microns.
The structure of the microvascular network is only limited by the structures that can be formed by the sacrificial fibers. It is possible for both leaks and plugs to appear within the micro channels. On the left side of this gas exchange unit is a plug.
These can often be removed with a solvent. On the right side is an example of a leak. These form when the sacrificial fibers are not thoroughly cleaned or well tensioned Once mastered, this technique can be done in 45 minutes for creating fibers and 60 minutes for fabricating microvascular units.
After watching this video, you should have a good understanding of how to make sacrificial fibers create a three-dimensional pattern, and troubleshoot the vast process.
