fabrication of multi-layered silicone vocal fold models

다층 실리콘 보컬 폴드 모델의 3D 프린팅

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.

저자 스포트라이트: Advancements in the Fabrication of Synthetic Vocal Fold Models for Phonetic and Robotic Applications (음성 및 로봇 응용 프로그램을 위한 합성 성대 모델 제작의 발전)

비접착식 Super-Soft 보컬 폴드 모델의 제조 공정

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.

다층 실리콘 보컬 폴드 모델 제작 

성대체를 만들기 위해서는 성대 포지티브, 성대 몰드 캡, 보이스 몰드 주요 부분, 보이스 몰드 홀, 1차 실리콘, 이형제, 시너를 수집합니다. 모든 금형 부품의 내부 표면에 이형제를 도포합니다. 금형의 주요 부분과 캡을 포지티브 위에 조립합니다.그런 다음 지정된 냄비에 금형 패키지를 놓습니다. 실리콘을 위쪽으로 붓기 위한 포지티브의 구멍과 금형이 평평한 표면에 안정적인 발판을 가지고 있는지 확인하십시오. 시너 3부와 함께 1차 실리콘 혼합물 6g을 준비합니다.기포 형성을 방지하려면 최소 1bar 하위 압력의 진공 챔버에서 혼합물을 진공 청소기로 청소하십시오. 진공 청소기로 청소한 실리콘 혼합물을 몰드 캐비티에 조심스럽게 붓고 얇은 실리콘 혼합물이 몰드 조인트를 통해 가라앉는 것을 방지하기 위해 몰드 포트의 주변 영역을 채웁니다. 하루 동안 경화 한 후 냄비에서 양극을 포함한 곰팡이를 제거하십시오.금형과 냄비 사이의 실리콘을 제거합니다. 이제 포지티브 뒷면부터 뚜껑을 조심스럽게 제거합니다. 그런 다음 금형의 본체를 제거합니다.메스나 사이드 커터를 사용하여 금형에서 여분의 실리콘을 조심스럽게 제거합니다. 두 개의 금형 부품을 조립하여 선체에 놓습니다. 금형의 내벽을 이형제로 코팅하고 공기 중에서 건조시킵니다.희석제가 없는 2차 실리콘 혼합물을 준비하고 기포 형성을 방지하기 위해 1bar 하위 압력의 진공 챔버에서 혼합물을 진공 청소기로 청소합니다. 실리콘 혼합물을 몰드에 붓고 모든 내부 표면이 실리콘으로 코팅될 때까지 휘젓습니다. 화격자 위에 몰드를 고정하고 실리콘이 경화되도록 합니다.금형을 뒤집고 여분의 실리콘을 빼냅니다. 시너 5 부와 함께 1 차 실리콘 혼합물 4g을 준비합니다. 기포 형성을 방지하려면 진공 챔버에서 실리콘 혼합물을 진공 청소기로 청소하십시오.실리콘 혼합물을 상피 실리콘으로 준비된 점막 주형에 붓습니다. 몰드를 기울여 상피 실리콘의 내부 표면을 얇은 오일 층으로 덮습니다. 성대와 함께 포지티브를 금형에 조심스럽게 삽입하십시오.필요한 경우 cl로 양극을 고정하십시오.amp. 성대 층의 주조를 위해 실리콘 혼합물로 금형을 채웁니다. 경화 24시간 후 껍질에서 곰팡이를 제거합니다.그런 다음 후면부부터 시작하여 금형을 열고 금형의 주요 부분을 제거합니다. 금형에서 성대 모델을 제거합니다. 보컬 바디에서 여분의 실리콘을 조심스럽게 제거합니다.마지막으로 성대 표면을 씻고 말리십시오.

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 ...

연구

공학

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

3D 프린팅 및 다층 실리콘 보컬 폴드 모델의 설계