Optical Characterization of the Vocal Fold Microenvironment in New Zealand White Rabbits

Glottic insufficiency is a laryngeal disorder characterized by the inability of the throat to fully close. One common cause of this condition is vocal fold atrophy, in which the vocalis muscle loses both volume and function. In recent years, a new microporous annealed particle (MAP) gel has been developed, which can be injected directly into the vocalis muscle. The MAP gel provides immediate volume restoration, thus reducing one of the main side effects of muscle atrophy. Another benefit of the MAP gel is that its spherical nature acts as a scaffold for collagen regrowth, which promotes muscle regeneration over time.
One of the variables that can induce an immune response in the body is for a foreign object, such as the MAP gel, to have a different modulus than the surrounding tissue. This immune response can cause inflammation and possible rejection of the foreign body. One way to get around this immune response is to match the modulus of the MAP gel to that of the laryngeal tissue. Since injured tissue has a large buildup of scar tissue, primarily made of collagen, the MAP gel should match the mechanical properties of the collagen present during the wound healing process. The mechanical properties of bulk collagen, as well as single fibers of collagen, are well published in the literature, but there is a lack of information of the mechanical properties of collagen within tissue.
In these experiments, we use two-dimensional (2D) Raman spectroscopy mapping and Time-Domain Brillouin Scattering (TDBS) to characterize the collagen microenvironment of sectioned rabbit vocal folds. Raman spectroscopy is used to map the presence of select biomolecules, mainly focusing on collagen, at twelve different points throughout each sample. Once the chemical environment has been analyzed, we then use TDBS to characterize the mechanical properties of the chosen regions within the samples. We show that there is a correlation between collagen composition and the mechanical properties of rabbit vocal folds.