1 Preliminary Design Report - Bioreactor for Vocal Fold Tissue Engineering Rachel Mosher, Kara Barnhart, Joel Gaston University of Wisconsin – Madison BME design 200/300 Dr. Brenda Ogle October 10, 20072 Table of Contents Abstract………………………………………………………………………………. 3 Problem Summary…………………………………………………………….………. 4 Background Bioreactor…………………………………....………………..………………. 4 Vocal Folds………………………………………………………...………….. 4 Problem Motivation……………………………………………………………. 8 Team Goals…………………………………………………………………….. 8 Design Constraints…………………………………………………………… 8 Current Device………………………………………………………………… 9 Competition……………………………………………………………………. 10 Alternative Design Descriptions Pneumatic System…………………………………………………………….. 11 Bearing Design………………………………………………………………... 11 Magnetic Repulsion…………………………………………………………… 12 Suspension System…………………………………………………………….. 13 Design Matrix 14 Final Design………………………………………………………………………...… 15 Future Work.…………………………………………………………………...……… 16 Conclusion…………………………………………………………………………….. 17 Appendices A: Product Design Specifications ……………………………………...….. 18 B: References………………………………………………………………….. 23 C: Parts Inventory……………………………………………………………... 243 Abstract In order to effectively study vocal fold tissue outside of the human body, a bioreactor needs to be constructed that appropriately stimulates vocal fold tissue to behave as naturally as possible. Such stimuli include, but are not limited to, vibration, tensile stress, changing angles between the cell-seeded strips, and pressure variation. Previous bioreactors have been made, both by researchers and a previous biomedical engineering student team, but did not sufficiently mimic the stimuli provided by the human body. Our objective for this semester is to improve upon the pre-existing bioreactor designs by completing the design and construction of a new bioreactor which has one or more improved cellular substrates, vibratory stimuli, tensile stress, and changing angles between each pair of cell-seeded strips.4 Problem Summary The aim of this project is to re-design and improve upon a previous version of a bioreactor that will be used for the culturing of human vocal fold fibroblasts. The bioreactor needs to provide appropriate stimulation to fibroblasts in order to elicit behavior typical of in vivo human vocal fold tissue. The bioreactor will be used for studying healthy and diseased states of vocal fold fibroblasts, as well as researching possible therapies that may be applied to humans with injured vocal folds. The previous bioreactor design was able to vibrate two pairs of cell-seeded strips under tensile stress, but had design flaws that needed improvement, including keeping the bioreactor leak-proof, subjecting the cells to more stimuli, and allowing the equipment providing the stimuli to be controlled by a computer. Our goals for this semester include finishing the design and fabrication of this new model, to obtain a substitute for the cellular substrate, Tecoflex, and to test the bioreactor and cellular substrate for optimal design and operating conditions. The bioreactor will be made from two T-flasks, two moving magnet linear voice coil actuators, two rotary stepper motors, and two linear stepper motors. A total of four pairs of cell strips will be immersed in a buffer in two T-flasks, and subjected to vibration, tensile stress, and angular changes between each pair of strips. This device needs to be easily replaced with disposable and/or sterilizable parts, fit inside a standard incubator, and have a capacity to generate vibrations within the frequency range of 50-400 Hz.5 Background Information Bioreactor A bioreactor is a system or device that supports a biological environment (Wikipedia). In this project, a bioreactor will be used for growing and maintaining fibroblasts in conditions that closely resemble the in vivo environment. To grow as fibroblasts, the cultured cells require a sterile environment with a constant temperature of 37° Celsius, a high level of humidity, and a 5% CO2 level. To sustain or obtain properties of vocal fold fibroblasts, the cells require stimuli that occur in the larynx, such as tensile stress and vibration (Titze). Vocal Folds The vocal folds are a pair of elastic tissue found horizontally inside the larynx (Figure 1). When air is exhaled through the lungs and reaches the closed vocal folds, the folds open and close many times per second, causing a “mucosal wave”, with vibrations that can be manipulated by the throat, mouth, and lips into speech (Altman)(Figure 2). The vibration of human vocals folds could naturally occur at the frequency ranging from 100-1000Hz, at and amplitude of 1mm (Titze). However, the frequency that they mostly vibrate at is a range from 50-400Hz. The length of male vocal folds ranges from 17 and 25 mm, whereas the length of female vocal folds is between 12.5 and 17.5 mm (Wikipedia). The vocal folds mainly consist of mucous membranes, however there is also a layer of extra-cellular matrix (ECM), which is attached to the cell surface and provides traction and positional recognition to the cell (Titze). Fibroblasts are critical for creating and maintaining the ECM in the vocal folds (Wikipedia). When the ECM is not in the6 proper condition, pathologies often result because of changes in viscoelasticity (Engineering). A literature search was performed to see if other similar bioreactors have been built, and it seems that the only previous bioreactor for vocal fold tissue was
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