Bioreactors for Vocal Fold Tissue Engineering

It is estimated that almost one-third of the United States population will be affected by a vocal fold (VF) disorder during their lifespan. Promising therapies to treat VF injury and scarring are mostly centered on VF tissue engineering strategies such as the injection of engineered biomaterials and cell therapy. VF tissue engineering, however, is a challenging field as the biomechanical properties, structure, and composition of the VF tissue change upon exposure to mechanical stimulation. As a result, the development of long-term VF treatment strategies relies on the characterization of engineered tissues under a controlled mechanical environment. In this review, we highlight the importance of bioreactors as a powerful tool for VF tissue engineering with a focus on the current state of the art of bioreactors designed to mimic phonation in vitro. We discuss the influence of the phonatory environment on the development, function, injury, and healing of the VF tissue and its importance for the development of efficient therapeutic strategies. A concise and comprehensive overview of bioreactor designs, principles, operating parameters, and scalability are presented. An in-depth analysis of VF bioreactor data to date reveals that mechanical stimulation significantly influences cell viability and the expression of proinflammatory and profibrotic genes in vitro. Although the precision and accuracy of bioreactors contribute to generating reliable results, diverse gene expression profiles across the literature suggest that future efforts should focus on the standardization of bioreactor parameters to enable direct comparisons between studies. Impact statement We present a comprehensive review of bioreactors for vocal fold (VF) tissue engineering with a focus on the influence of the phonatory environment on the development, function, injury, and healing of the VFs and the importance of mimicking phonation on engineered VF tissues in vitro. Furthermore, we put forward a strong argument for the continued development of bioreactors in this area with an emphasis on the standardization of bioreactor designs, principles, operating parameters, and oscillatory regimes to enable comparisons between studies.

Dimensions and morphological characteristics of human newborn glottis

OBJECTIVES

The anterior glottis has the most important role in phonation. However, the posterior glottis appears to have an equally important role in respiration. Dimensions and morphological characteristics of the newborn glottis were investigated.

STUDY DESIGN

Histologic analysis of the human newborn glottis.

METHODS

A total of 16 larynges were used. The whole organ section technique was employed.

RESULTS

There was no statistically significant difference between the genders. The average length of the glottis was 5.4 ± 0.6 mm in males and 5.7 ± 0.4 mm in females. The average length of the posterior glottis was 3.1 ± 0.5 mm in males and 3.2 ± 0.4 mm in females. It accounted for 57.5 ± 3.2% of the entire glottic length in males and 55.5 ± 5.3% in females and also accounted for 56.3 ± 4.6% of the entire glottic area in both sexes. The average area of the glottis was 7.5 ± 2.5 mm(2) in males and 8.2 ± 1.7 mm(2) in females. The average area of the posterior glottis was 5.3 ± 2.0 mm(2) in males and 5.5 ± 1.4 mm(2) in females. It accounted for 69.2% ± 4.6% of the entire glottic area in males and 67.3% ± 5.8% in females. It also accounted for 68.0% ± 5.3% of the entire glottic area in both sexes. The epithelium in the newborn posterior glottis was a ciliated epithelium, whereas it was stratified squamous epithelium in the anterior glottis.

CONCLUSIONS

The newborn posterior glottis occupied approximately 70% of the entire glottic area and was covered with respiratory epithelium. Due to size and configuration, the newborn glottis appears to be favored for respiration over phonation.

LEVEL OF EVIDENCE

NA. Laryngoscope, 125:E186-E189, 2015.

Mechanical Regulation of Human Vocal Fold Stellate Cells

Objective:

It is generally accepted that tensile and compressive strains have direct effects on cell morphology and structure, including changes in cytoskeletal structure and organization. Cytoskeletons play the role of mechanoreceptor of the cells. Vocal fold stellate cells (VFSCs) in the human maculae flavae (MFe) are inferred to be involved in the metabolism of extracellular matrices essential for the viscoelasticity of the vocal fold mucosa. Our previous studies have supported the hypothesis that the tension caused by phonation (vocal fold vibration) regulates the behavior of the VFSCs. The microstructure of the intermediate filaments and the expression of their proteins were investigated in VFSCs in the MFe, which had remained unphonated since birth.

Methods:

Three adult vocal fold mucosae that had remained unphonated since birth were investigated by immunohistochemistry and electron microscopy.

Results:

The intermediate filaments of the VFSCs were fewer in number. The expression of their characteristic proteins (vimentin, desmin, and glial fibrillary acidic protein) was also reduced.

Conclusion:

Vocal fold vibration seems to affect VFSC morphology and structure, such as cytoskeletal structure and organization. This supports the hypothesis that vocal fold vibration regulates VFSC behavior in the human MFe. In addition to chemical factors, mechanical factors also appear to modulate VFSC behavior.

Cytoskeleton of newborn vocal fold stellate cells

OBJECTIVES/HYPOTHESIS

Vocal fold stellate cells (VFSCs) in the human maculae flavae located at both ends of the vocal fold mucosa are inferred to be involved in the metabolism of extracellular matrices of the vocal fold mucosa. Tension caused by phonation (vocal fold vibration) likely regulates the behavior of the VFSCs in the human maculae flava. Tensile and compressive strains have direct effects on cell morphology and structure, including changes in cytoskeletal structure and organization. Cytoskeletons play a role as mechanoreceptors for the cells. The microstructure of the intermediate filaments and the expression of their characteristic proteins were investigated regarding the human newborn VFSCs.

STUDY DESIGN

Histopathologic analysis of the human newborn vocal fold.

METHODS

Three newborn vocal fold mucosae were investigated by immunohistochemistry and electron microscopy.

RESULTS

The intermediate filaments in the cytoplasm of the newborn VFSCs were few in number. However, their characteristic proteins (vimentin, desmin, GFAP [Glial fibrillary acidic protein], cytokeratin) had already expressed.

CONCLUSION

The function and fate of VFSCs are regulated by various microenvironmental factors. Not only chemical factors but also mechanical factors could also modulate VFSC behaviors. The cytoskeletal structure of the newborn VFSCs is under development. And the newborn VFSCs have not acquired mechanical regulation.

LEVEL OF EVIDENCE

N/A.

Hyaluronic acid for the treatment of vocal fold scars

PURPOSE OF REVIEW

In vocal fold scars the lamina propria layer is lost or deficient. Lamina propria replacement therapy remains a clinical challenge because this layer has a highly specialized three-dimensional organization of extracellular matrix molecules and unique viscoelastic properties. Use of a polymer such as hyaluronic acid appears most promising for replacement therapy because it has the optimal viscoelasticity and also plays a role in the maturation and maintenance of vocal fold lamina propria.

RECENT FINDINGS

A variety of cross-linked hyaluronic acid formulations and growth factor therapies targeted to increase hyaluronic acid production have been used in the treatment of both acute and established vocal fold scars. Therapeutic strategies have focused on prevention of scar at the time of initial injury, and rejuvenation of lamina propria layer in established scars. Both strategies show improved histologic, viscoelastic, acoustic, and aerodynamic measures.

SUMMARY

Cross-linked hyaluronic acid formulations appear useful in the treatment of vocal fold scarring. Their use at the time of acute injury especially appears to lessen the degree of long-term scar formation and appears promising. While animal studies have demonstrated the safety profile of many hyaluronic acid formulations, further improvement in these materials and well designed and controlled human trials are needed to further establish the safety and efficacy of these materials and therapeutic approaches.