fabrication of multi-layered silicone vocal fold models

多層シリコーン声帯モデルの3Dプリンティング

Vocal fold models are used to simulate and investigate human voice production under normal and pathological conditions1,2. One of the biggest challenges in creating vocal fold models is to achieve a realistic softness and flexibility that closely approximates those of humans. To achieve these properties, silicone elastomers are often used, which are diluted with high amounts of silicone oil to achieve the corresponding elasticity moduli3,4. Another crucial factor in creating realistic vocal fold models is layering, as vocal folds consist of multiple layers of varying softness, which determine the pattern of flow-induced vibration and the frequency at which vibration is possible.
In this study, we created a typical vocal fold model. We used the common geometry provided by Scherer5, which represents typical dimensions for male vocal folds with 17 mm length according to Zhang6 and consists of three layers: one layer for the vocalis muscle (body layer), one for the entire mucosal layer (cover layer), and one for the epithelium. This structure can be seen in the coronal cross-section view in Figure 1.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/66222/66222fig01v2.jpg" /> 
Figure 1: Coronal cross-section of the larynx modules. Coronal cross-section of the larynx modules illustrating the widest width of the vocal folds (8.5 mm). Each vocal fold comprises a body layer, a cover layer, and an epithelium layer. This figure has been modified from13. Reproduced from H&#228;sner, P., Prescher, A., Birkholz, P. Effect of wavy trachea walls on the oscillation onset pressure of silicone vocal folds. J Acoust Soc Am.149 (1), 466-475 (2021) with the permission of the Acoustical Society of America. <a href="https://www.jove.com/files/ftp_upload/66222/66222fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Other publications use partially only one layer7, two layers without epithelium layer2 or model the mucosa with multiple layers3. Usually, the layers are cast from the inside out, i.e., starting with the deepest layer. The epithelium, which is very thin with 30 &#181;m thickness, is cast at the end over the entire body to envelop it with a sturdy skin8.
The cover layer in the model is the softest part, with Young&#39;s modulus of about 1.1 kPa9. For the body layer, the approximate Young&#39;s modulus in the transverse direction using in vitro measurements10 is 2 kPa. In vivo, the Young&#39;s modulus of the thyroarytenoid muscle may be higher due to the presence of fibers in the longitudinal direction as well as the possible tensing of the muscle. To achieve this extremely low Young&#39;s modulus, it is necessary to add a high amount of silicone oil to the silicone mixture (approximately 72%). However, the manufacturer strongly advises against using an oil proportion greater than 5%. In general, the addition of silicone oil to the elastomer is intended to increase flow and drip time, as well as reduce the shrinkage of the cured silicone polymer. It helps the silicone to cure more uniformly, thereby reducing stress in the material. Its purpose is to optimize the moldability and properties of the cured material, rather than to increase its softness, although this is also a consequence. This is because silicone oil is chemically inert, meaning that it cannot polymerize itself and is not integrated into the network of the silicone polymer11. Instead, it remains as a liquid phase in the polymer matrix, weakening the polymer structure at higher levels and potentially causing it to dissolve out of the cured material and adhere to the surface. As a result, other negative properties such as curing disorders, uneven vulcanization, chemical shrinkage, and brittleness are possible. Vocal fold models with high silicone oil contents were investigated with regard to aging and reproducibility, and it was found that there is a high variability in the properties of different models and a change in their properties over time11.
When producing vocal fold models in the conventional way7,12, the stickiness of the epithelial layer can be a problem as it can affect the homogeneity of vibration and lead to rupture of the epithelium. Although the silicone used to make the epithelium is undiluted, it can be assumed that the oil that leaks from the neighboring mucosa layer has similar effects on the silicone as if it had been diluted. The problem of stickiness was addressed by adding various powders such as talcum or carbon powder as an intermediate layer between the mucosa and the epithelial layer12. This approach may have been successful because the oil was partially absorbed by the powder and, as a result, the stickiness of the epithelial surface could be reduced.
In this publication, we show that the problem of stickiness can be circumvented by a slight modification of the process of vocal fold manufacturing. By changing the order of layering and starting with the undiluted epithelial silicone (so-called closed silicone), non-sticky super-soft vocal fold models can be produced. This change involves unusual types of molds and methods that are best presented and explained in the form of a video. In this paper, we describe our manufacturing process in detail and demonstrate how the properties of the vocal fold models can be characterized in an application.

著者スポットライト:音声およびロボットアプリケーションのための合成声帯モデルの製造における進歩

非粘着性超軟質ボーカルフォールドモデルの製造工程

Our research aims at improving the manufacturing process of synthetic vocal folds. Such models can be used in basic phonetic and voice research, in medical research, and to create models of the human vocal tract that produce speech like human beings. Synthetic vocal fold models are usually made of multiple layers of soft silicone with different degrees of softness.They correspond to the properties of human vocal fold tissue. The technologies used to make these models include computer-aided design, 3D printing, and silicone casting. Highly diluted silicone vocal fold models have reduced quality due to stickiness and rapid aging.This decreases the reproducibility of research using these models. This protocol addresses the issue of vocal fold stickiness. We have reversed the order of producing the silicone layers in our fabrication process.We started with the epithelium layer. This allowed us to create a very soft mucosal layer from diluted silicone without causing the epithelium layer to become sticky.

多層シリコン声帯モデルの作製 

声帯層を作るには、声帯ポジ、声帯モールドキャップ、ボーカルスモールド本体、ボーカルスモールドホール、一次シリコーン、離型剤、シンナーを集めます。離型剤をすべての金型部品の内面に塗布します。金型の主要部品とキャップをポジの上に組み立てます。次に、型パッケージを指定されたポットに入れます。シリコーンを注ぐためのプラスの穴が上を向いており、金型が平らな面に安定した足場を持っていることを確認してください。6グラムの一次シリコーン混合物と3部のシンナーを準備します。気泡の形成を防ぐために、真空チャンバー内で混合物を最低1バールの副圧で真空にします。真空にしたシリコーン混合物を金型キャビティに慎重に注ぎ、金型ポットの周囲を埋めて、薄いシリコン混合物が金型の接合部を通って沈むのを防ぎます。1日硬化させた後、ポジを含む型を鍋から取り出します。型と鍋の間のシリコンを取り除きます。次に、プラスの裏側から蓋を慎重に取り外します。次に、金型本体を取り外します。メスまたはサイドカッターを使用して、金型から余分なシリコンを慎重に取り除きます。2つの金型部品を組み立て、船体に配置します。金型の内壁を離型剤でコーティングし、風乾させます。シンナーなしで二次シリコーン混合物を調製し、気泡の形成を防ぐために1バールのサブ圧力で真空チャンバー内で混合物を真空にします。シリコーン混合物を型に流し込み、すべての内面がシリコーンでコーティングされるまで渦を巻きます。型を火格子の上に固定し、シリコンを硬化させます。型をひっくり返し、余分なシリコンを排出させます。4グラムの一次シリコーン混合物と5部のシンナーを準備します。気泡の発生を防ぐには、真空チャンバー内でシリコーン混合物を真空にします。シリコーン混合物を上皮シリコーンで調製した粘膜型に注ぎます。金型を傾けて、上皮シリコーンの内面を油の薄い層で覆います。ボーカルボディ付きのポジを慎重に型に挿入します。必要に応じて、クランプでプラスを固定します。ボイカリス層を鋳造するためのシリコーン混合物を金型に充填します。24時間硬化した後、シェルから型を取り除きます。次に、後部から始めて、金型を開き、金型の主要部分を取り外します。声帯モデルを型から取り出します。ボーカルボディから余分なシリコンを慎重に取り除きます。最後に、ボーカルボディの表面を洗い、乾かします。

Research

JoVE Journal

Engineering

Fabrication of Multi-Layered Silicone Vocal Fold Models

Manufacturing Process for Non-Adhesive Super-Soft Vocal Fold Models

This study aims to develop super-soft, non-sticky vocal fold models for voice research. The conventional manufacturing process of silicone-based vocal ...

工学

3D Printing and Design of Multi-Layered Silicone Vocal Fold Models

3Dプリンティングと多層シリコンボーカルフォールドモデルの設計