The overall goal of this procedure is to describe and demonstrate the fabrication of a multi-layered synthetic self oscillating vocal fold model. First rapid prototype positives from three-dimensional computer models are created. Then mold negatives are built from the rapid prototypes.
Finally, each layer of the vocal fold model is cast, including the body, the ligament, with the fiber in the center, the superficial lamin propria and the epithelium. Ultimately by comparing sub glottal pressure, vibration frequency, glottal flow rate, and medial surface motion, the results show that the multilayered synthetic vocal fold models exhibit similar flow induced response characteristics with those of human vocal fold vibration. The main advantage of of these models over existing multilayered models, such as a two layered model, is that the structure of these multi-layered models is more similar to that of the human VCA folds, making them more applicable for voice production research.
First, create solid models of three vocal fold layers, the superficial Lamin propria ligament and body layers. This is typically done by creating 3D computer-aided design or CAD models with the desired geometries exporting the CAD models as stereolithography or STL files and sending the STL files to a custom machine. Shop for rapid prototyping.
Construct a box shaped mold form using thin pieces of acrylic material. Cut to the desired dimensions. Make the bottom of the form by adhering it to a flat acrylic plate with vacuum grease.
Place a small amount of vacuum grease on the lateral side of the solid model of the desired geometry. Press the model into the bottom of the mold form cavity, vacuum grease side down so that the vacuum grease holds the part in place. Liberally coat the mold form and solid model with release agent using a paintbrush, ensure that release agent reaches into all corners of the mold form cavity.
Mix together 10 parts A and one part B of smooth cell, nine 50 platinum silicone rubber in a container that will allow for product volume expansion during vacuuming. To remove any air bubbles, place the container in a vacuum chamber and reduce the pressure to around 26 inches of mercury below atmospheric pressure for approximately three minutes. Remove the DGAs silicone from the chamber and pour it into a mold form cavity.
Place this into the vacuum chamber and DGAs again. Remove the mold from the vacuum chamber and place it on a level surface. Allow it to cure for 24 hours After the rubber is cured, remove the mold from the mold form.
Repeat this process to create molds for each of the other solid model geometries. Once all the molds have been created, cut the ligament layer mold at the center of the medial surface in the anterior posterior direction with a straight razor to allow for fiber insertion to cast the body layer. First, apply a thin layer of release agent to the body mold cavity with a paintbrush.
Mix together one part B and one part A of eFlex 0 0 30 super soft platinum silicone. And then add one part silicone thinner to reduce the eventual cured stiffness of the material. Mix for 30 seconds and then place it in the vacuum chamber for one minute.
To remove entrapped air, remove the mixture from the vacuum and pour it into the body mold cavity, but do not fill to the top. Place the mold in an oven preheated to 200 degrees Fahrenheit for 30 minutes. After baking, remove the mold from the oven and cool.
Next, create the body backing model by mixing one part B and one part A of dragon skin. Add one part silicone thinner and mix vigorously for 30 seconds. After removing any bubbles using the vacuum, pour the mixture into the body mold cavity until completely full.
Place the mold in an oven at 200 degrees Fahrenheit for 30 minutes. Once cooled, remove the model from the mold. Then remove any release agent on the surface of the body layer with a paper towel.
To cast the ligament layer, apply a thin layer of release agent to the ligament mold cavity surface with a paint brush. Place a 30 centimeter long thread in the mold by pushing it into the cut from the straight razor thoroughly. Mix one part B and one part A of eco Lex 0, 0 30, and four parts of silicone thinner.
Place the mixture in the vacuum chamber to remove air bubbles and then pour the mixture into the ligament mold cavity. Press the body backing model into the ligament mold cavity. Begin insertion at one side and gently move to the other so that the model pushes the excess uncured, silicone and air bubbles out of the mold cavity.
After baking for 30 minutes, cool the mold and remove the model. Wipe off any release agent with paper towels. To cast the superficial Lamin propria or SLP layer, apply a thin layer of release agent on the SLP mold cavity surface with a paint brush.
Mix one part B, one part A of eco flex, 0 0 30 and eight part silicone thinner by weight vacuum, and pour the mixture into the mold cavity. Insert the ligament body backing model into the SLP mold cavity After baking at 200 degrees Fahrenheit for one hour and cooling, remove the model slowly and with extreme care so that the superficial Lamin propria remains intact. Finally, for the epithelium layer, place the vocal fold model on a flat surface with the backing down and remove the support material with a straight razor.
Suspend the threads in the air by attaching them to an object of greater height than the model. After mixing one part B and one part A of dragon skin with one part of silicone thinner and vacuuming, pour over the model and allow to cure for one hour. Repeat the process to create a thicker layer, and after the model is fully cured, remove excess material with a straight razor mount each completed vocal fold model into an acrylic mounting plate by first applying a thin layer of silicone glue on the lateral and anterior posterior model surfaces.
Insert the model into the recessed cut of the mounting plate and align the model medial surface with the top of the acrylic plate. Wipe away excess glue and allow the glue to cure. For one hour, apply talc powder to the model surface to reduce surface tackiness for medial surface tracking.
Use a fine point sharpie pen to mark dots on the model. After the talc has been applied, insert long bolts through the holes of the mounting plate with the threaded ends pointed toward the model to which the existing model will be paired. Lay the threads over the bolts and put closed cell foam over the bolts to close any air gaps.
Pair this prepared model with another vocal fold model that has been similarly mounted to an acrylic holder. Tighten the screws to compress the foam and bring the medial surfaces together until the desired pre vibratory gap is reached. Ensure both sets of threads are placed over the bolts and extend outward from the acrylic plates in the anterior posterior direction, and then mount the vocal fold pair onto an air supply tube.
Tie the anterior threads together to form a loop followed by the posterior threads, hang desired weight on the loop simultaneously and proceed to testing and data collection. Using the fabricated model with tension of approximately 31 grams applied to the fibers, the onset pressure was 400 pascals at a sub glottal pressure of 10%above onset pressure. The model vibrated at 115 hertz with a glottal flow rate of 210 milliliters per second.
These values are in good agreement with values reported for those of humans. High speed video recordings of the vibrating model showed that it moves with more lifelike motion than previous two layer models. For comparison.
In this video of the superior surface of a two layer model, there is no mucosal wave and the glottis profile appears to be mostly divergent throughout the cycle. This limitation of two layer models can be better seen in high-speed video recordings of the two layer model in a Hemi larynx configuration. Looking at high-speed recordings of the superior view of the new multi-layer model.
Evidence of a mucosal wave can be seen and the glottis profile now no longer appears to be divergent throughout the cycle. A video gram from the high speed recording of the superior view of the new multilayer model reveals evidence of a phase difference between the superior and margins. The superior margin conceals the inferior margin during the open phase of the vibration period.
High-speed video of the new multilayer model in a Hemi larynx configuration provides stronger evidence of the mucosal wave and alternating convergent divergent motion that is characteristic of human vocal fold. Vibration trajectories extracted from stereo images of the dots applied to the medial and inferior surfaces of the vocal fold.Model. Show that the model exhibits an alternating convergent divergent profile that is typical of human phonation.
The points are labeled A through F starting at the lowest point. The left plot shows a convergent glottis during the opening phase, and the right plot shows a divergent glottis during the closing phase. This method of fabricating synthetic vocal fold models yields models that exhibit vibratory behavior similar to that of human vocal folds.
The multilayer concept results in significant advantages over previous one and two layer model designs in terms of reduced onset and improved model motion. While attempting this procedure, it's important to only use the necessary amount of release agents so the layers properly adhere to each other.There.
