Reproducibility and Aging of Different Silicone Vocal Folds Models

In this study, silicone vocal fold models with different geometries were manufactured using the common silicone brand EcoFlex 00-30 with typical oil mixing ratios. However, the proportions of oil typically used are higher than the manufacturer's recommended limit, in order to attain the softness of human vocal folds. This additional oil causes direct effects on the silicone, such as shrinkage, stickiness, evaporation, embrittlement, and uneven vulcanization. This study investigated the impact of these effects on the oscillation characteristics of the silicone vocal fold models and how they change over time. The goal was to examine the comparability of produced silicone vocal fold models and the results obtained from experiments performed with these models. For the manufactured models, the phonation onset pressure, offset pressure, mean volume velocity, pulmonary power, fundamental frequency, and measures of the glottal area waveform were collected over a period of up to 8 weeks. The results showed that the data for the models were highly scattered. Furthermore, over time, the phonation onset/offset pressures increased, leading to failure to oscillate for some models, and the glottal area waveform also changed. In conclusion, when working with over-thinned silicone vocal fold models, their characteristics depend strongly on the time of measurement. Therefore, it is recommended to carefully consider the effects of oil-oversaturation and timing of measurements when using silicone vocal fold models in experiments.