A synthetic anisotropic vocal fold model with tunable longitudinal stiffness

This study introduces a synthetic vocal fold model that captures the biomechanical properties of human vocal folds, specifically their anisotropic mechanical behavior characterized by a pronounced longitudinal-transverse stiffness contrast, while also enabling post-fabrication tunability. Conventional models are often isotropic or necessitate complex multilayer construction, limiting reproducibility. To address this, we developed a room temperature vulcanized silicone model with an embedded latex tube. This model employs the internal air-water volumetric ratio as a mechanism to modulate stiffness. Increasing the water ratio increases longitudinal stiffness while leaving transverse properties unchanged without macroscopically altering geometry. Finite element simulations and uniaxial compression tests confirmed this behavior, demonstrating a remarkable 12.5-fold increase in longitudinal Young's modulus (rising from 15.7  to 196 kPa), whereas transverse stiffness remained close to that of the silicone. Dynamic testing with modulated and constant airflow demonstrated vibrational patterns consistent with physiological phonation. Fundamental frequencies increased with stiffness, reaching 2% and 8% above the original fundamental resonance at 50%, and 100% water ratios, relative to the empty-tube (0% water) baseline. Compared to its counterpart constructs, this model offers simplicity and most importantly post-manufacture tunability. These advantages make it a promising tool for research in phonation, pathological modeling, and device testing.