Date of Award

January 2021

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Jennifer L. Long

Abstract

The voice is an important source of communication. Voice disorders, dysphonia, has an estimated 30 percent lifetime prevalence in the United States with a significant economic and social cost. Severe vocal fold scarring can lead to persistent dysphonia, has no optimal treatment and negatively impacts those affected by impairing their quality of life and general health. We propose a novel approach to treating sever vocal fold scarring by replacing the entirety of the vocal fold mucosa with a tissue engineered implant, the cell-based outer vocal fold replacement (COVR). We hypothesized that intermediate and long-term implantation of human stem-cell derived COVR implants would lead to regeneration of vocal fold epithelium and lamina propria and establish an extracellular matrix (ECM) approximating normal parameters. We aimed to assess the development of these structures by assessing active factors in wound healing including white blood cell presence, collagen and fibrin deposition, and glycosaminoglycan incidence. We resected the vocal fold mucosa and implanted COVR gels, COVR gel components including a decellularized gel scaffold (DECELL) and human-derived adipose stem-cell injection (hASC Injection), or performed no treatment following intervention (SCAR) in 49 New Zealand white rabbits with intermediate, 6-weeks, postoperative recovery and three Yucatan Mini Pigs with long-term, 6 months, post-operative recovery prior to laryngeal harvest. Vocal folds were sectioned and assessed through light microscopy, fluorescent microscopy, and/or nonlinear scanning laser microscopy (NLSM) to assess outcomes of the intervention. Analysis of light microscopy of the intermediate implantation groups showed that the COVR implantation had the lowest levels of collagen deposition (50% in COVR, 67% in DECELL, 82% in hASC Injection, and 83% in SCAR), greatest glycosaminoglycan incidence (50% in COVR, 8% in DECELL, 9% in HASC injection, and 25% in SCAR), equivalent white cell presence (50% in COVR, 83% in DECELL, 45% in hASC Injection, and 42% in SCAR) at laryngeal harvest. Additionally, fluorescent microscopy showed persistence of HLA-staining cells in the COVR and hASC Injection groups and none in the DECELL or SCAR treatment groups. NLSM imaging of the long-term implantation of COVR showed increased collagen deposition in the superficial lamina propria in the hASC Injection group, while the SCAR had no change in collagen levels, and the COVR implant animal had decreased collagen levels compared to untreated control folds. The superficial lamina propria also had increased elastin deposition in the COVR group, decreased levels in the SCAR animal, and no change in the hASC Injection animal. In the rabbits, COVR implantation promotes improved healing and decreased scarring at six weeks, as evidenced by increased glycosaminoglycan deposition and decreased collagen development. Additionally, there is evidence of xenograph ASC grafts persist for several weeks with continued immunomodulatory effects. Our data suggest decreases of overall elastin levels are a more sensitive marker of fibrosis in NLSM imaging than increases in collagen levels.

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This is an Open Access Thesis.

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