The importance of hyaluronic acid in vocal fold biomechanics

Objective: This study examined the influence of hyaluronic acid (HA) on the biomechanical properties of the human vocal fold cover (the superficial layer of the lamina propria). Study Design: Vocal fold tissues were freshly excised from 5 adult male cadavers and were treated with bovine testicular hyaluronidase to selectively remove HA from the lamina propria extracellular matrix (ECM). Linear viscoelastic shear properties (elastic shear modulus and dynamic viscosity) of the tissue samples before and after enzymatic treatment were quantified as a function of frequency (0.01 to 15 Hz) by a parallel-plate rotational rheometer at 37°C. Results: On removing HA from the vocal fold ECM, the elastic shear modulus (G′) or stiffness of the vocal fold cover decreased by an average of around 35%, while the dynamic viscosity (η′) increased by 70% at higher frequencies (>1 Hz). Conclusion: The results suggested that HA plays an important role in determining the biomechanical properties of the vocal fold cover. As a highly hydrated glycosaminoglycan in the vocal fold ECM, it likely contributes to the maintenance of an optimal tissue viscosity that may facilitate phonation, and an optimal tissue stiffness that may be important for vocal fundamental frequency control. Significance: HA has been proposed as a potential bioimplant for the surgical repair of vocal fold ECM defects (eg, vocal fold scarring and sulcus vocalis). Our results suggested that such clinical use may be potentially optimal for voice production from a biomechanical perspective.