Assessment of canine vocal fold function after injection of a new biomaterial designed to treat phonatory mucosal scarring

Versatile fiber-reinforced hydrogels to mimic the microstructure and mechanics of human vocal-fold upper layers

Human vocal folds are remarkable soft laryngeal structures that enable phonation due to their unique vibro-mechanical performances. These properties are tied to their specific fibrous architecture, especially in the upper layers, which comprise a gel-like composite called lamina propria. The lamina propria can withstand large and reversible deformations under various multiaxial loadings. Despite their importance, the relationships between the microstructure of vocal folds and their resulting macroscopic properties remain poorly understood. There is a need for versatile models that encompass their structural complexity while mimicking their mechanical features. In this study, we present a candidate model inspired by histological measurements of the upper layers of human vocal folds. Bi-photonic observations were used to quantify the distribution, orientation, width, and volume fraction of collagen and elastin fibers between histological layers. Using established biomaterials, polymer fiber-reinforced hydrogels were developed to replicate the fibrillar network and ground substance of native vocal fold tissue. To achieve this, jet-sprayed poly(ε-caprolactone) fibrillar mats were successfully impregnated with poly(L-lysine) dendrimers/polyethylene glycol hydrogels. The resulting composites exhibited versatile structural, physical and mechanical properties that could be customized through variations in the chemical formulation of their hydrogel matrix, the microstructural architecture of their fibrous networks (i.e., fiber diameter, orientation and volume fraction) and their assembly process. By mimicking the collagen network of the lamina propria with polymer fibers and the elastin/ground substance with the hydrogel composition, we successfully replicated the non-linear, anisotropic, and viscoelastic mechanical behavior of the vocal-fold upper layers, accounting for inter/intra-individual variations. The development of this mimetic model offers promising avenues for a better understanding of the complex mechanisms involved in voice production. STATEMENT OF SIGNIFICANCE: Human vocal folds are outstanding vibrating soft living tissues allowing phonation. Simple physical models that take into account the histological structure of the vocal fold and recapitulate its mechanical features are scarce. As a result, the relations between tissue components, organisation and vibro-mechanical performances still remain an open question. We describe here the development and the characterization of fiber-reinforced hydrogels inspired from the vocal-fold microstructure. These systems are able to reproduce the mechanics of vocal-fold tissues upon realistic cyclic and large strains under various multi-axial loadings, thus providing a mimetic model to further understand the impact of the fibrous network microstructure in phonation.

Ultrafast Laser Microlaryngeal Surgery for In Vivo Subepithelial Void Creation in Canine Vocal Folds

BACKGROUND/OBJECTIVES

Tightly-focused ultrafast laser pulses (pulse widths of 100 fs-10 ps) provide high peak intensities to produce a spatially confined tissue ablation effect. The creation of sub-epithelial voids within scarred vocal folds (VFs) via ultrafast laser ablation may help to localize injectable biomaterials to treat VF scarring. Here, we demonstrate the feasibility of this technique in an animal model using a custom-designed endolaryngeal laser surgery probe.

METHODS

Unilateral VF mucosal injuries were created in two canines. Four months later, ultrashort laser pulses (5 ps pulses at 500 kHz) were delivered via the custom laser probe to create sub-epithelial voids of ~3 × 3-mm2 in both healthy and scarred VFs. PEG-rhodamine was injected into these voids. Ex vivo optical imaging and histology were used to assess void morphology and biomaterial localization.

RESULTS

Large sub-epithelial voids were observed in both healthy and scarred VFs immediately following in vivo laser treatment. Two-photon imaging and histology confirmed ~3-mm wide subsurface voids in healthy and scarred VFs of canine #2. Biomaterial localization within a void created in the scarred VF of canine #2 was confirmed with fluorescence imaging but was not visualized during follow-up two-photon imaging. As an alternative, the biomaterial was injected into the excised VF and could be observed to localize within the void.

CONCLUSIONS

We demonstrated sub-epithelial void formation and the ability to inject biomaterials into voids in a chronic VF scarring model. This proof-of-concept study provides preliminary evidence towards the clinical feasibility of such an approach to treating VF scarring using injectable biomaterials.

LEVEL OF EVIDENCES

N/A Laryngoscope, 133:3042-3048, 2023.

Ultrafast laser surgery probe for sub-surface ablation to enable biomaterial injection in vocal folds

Creation of sub-epithelial voids within scarred vocal folds via ultrafast laser ablation may help in localization of injectable therapeutic biomaterials towards an improved treatment for vocal fold scarring. Several ultrafast laser surgery probes have been developed for precise ablation of surface tissues; however, these probes lack the tight beam focusing required for sub-surface ablation in highly scattering tissues such as vocal folds. Here, we present a miniaturized ultrafast laser surgery probe designed to perform sub-epithelial ablation in vocal folds. The requirement of high numerical aperture for sub-surface ablation, in addition to the small form factor and side-firing architecture required for clinical use, made for a challenging optical design. An Inhibited Coupling guiding Kagome hollow core photonic crystal fiber delivered micro-Joule level ultrashort pulses from a high repetition rate fiber laser towards a custom-built miniaturized objective, producing a 1/e2 focal beam radius of 1.12 ± 0.10 μm and covering a 46 × 46 μm2 scan area. The probe could deliver up to 3.8 μJ pulses to the tissue surface at 40% transmission efficiency through the entire system, providing significantly higher fluences at the focal plane than were required for sub-epithelial ablation. To assess surgical performance, we performed ablation studies on freshly excised porcine hemi-larynges and found that large area sub-epithelial voids could be created within vocal folds by mechanically translating the probe tip across the tissue surface using external stages. Finally, injection of a model biomaterial into a 1 × 2 mm2 void created 114 ± 30 μm beneath the vocal fold epithelium surface indicated improved localization when compared to direct injection into the tissue without a void, suggesting that our probe may be useful for pre-clinical evaluation of injectable therapeutic biomaterials for vocal fold scarring therapy. With future developments, the surgical system presented here may enable treatment of vocal fold scarring in a clinical setting.

In vivo hamster cheek pouch subepithelial ablation, biomaterial injection, and localization: pilot study

SIGNIFICANCE

The creation of subepithelial voids within scarred vocal folds via ultrafast laser ablation may help in localization of injectable biomaterials toward a clinically viable therapy for vocal fold scarring.

AIM

We aim to prove that subepithelial voids can be created in a live animal model and that the ablation process does not engender additional scar formation. We demonstrate localization and long-term retention of an injectable biomaterial within subepithelial voids.

APPROACH

A benchtop nonlinear microscope was used to create subepithelial voids within healthy and scarred cheek pouches of four Syrian hamsters. A model biomaterial, polyethylene glycol tagged with rhodamine dye, was then injected into these voids using a custom injection setup. Follow-up imaging studies at 1- and 2-week time points were performed using the same benchtop nonlinear microscope. Subsequent histology assessed void morphology and biomaterial retention.

RESULTS

Focused ultrashort pulses can be used to create large subepithelial voids in vivo. Our analysis suggests that the ablation process does not introduce any scar formation. Moreover, these studies indicate localization, and, more importantly, long-term retention of the model biomaterial injected into these voids. Both nonlinear microscopy and histological examination indicate the presence of biomaterial-filled voids in healthy and scarred cheek pouches 2 weeks postoperation.

CONCLUSIONS

We successfully demonstrated subepithelial void formation, biomaterial injection, and biomaterial retention in a live animal model. This pilot study is an important step toward clinical acceptance of a new type of therapy for vocal fold scarring. Future long-term studies on large animals will utilize a miniaturized surgical probe to further assess the clinical viability of such a therapy.

MRI imaging versus histologic volumetric estimation of residual injection laryngoplasty material

Objectives

To examine the degree of agreement between MRI and histologically generated volumetric measurements of residual injection laryngoplasty material.

Methods

Following left recurrent laryngeal nerve transection, rabbit vocal cords were injected with jellyfish collagen, Cymetra®, or Restylane®. Laryngeal tissue was harvested 4 or 12 weeks post injection followed by MRI imaging and histologic cross‐sectioning. Two raters estimated the volume of remaining injection material in specimens within MRI and histologic axial cross sections. Wilcoxon signed rank tests were employed to detect gross differences between inter‐rater measurements and between imaging modalities across time. Agreement between rater measurements and imaging (histology and MRI) was assessed using intra‐class correlation coefficients.

Results

Data was available from 16 rabbits sacrificed at 4 weeks (n = 8) and 12 weeks (n = 8). Inter‐rater testing of MRI imaging revealed no significant differences (p > .05) between rater measurements across time points, and excellent agreement (0.93; 95% confidence interval 0.80–0.98) while histologically estimated volumes demonstrated a significant difference at 4 weeks (p < .05) and overall good agreement (0.89; 95% confidence interval 0.59–0.97). Comparison of MRI and histologically estimated volume measurements revealed significant differences at the 4‐week time point (p < .05) but not at 12 weeks (p > .05). Overall, there is only moderate agreement between MRI and histology estimates (0.72; 95% confidence interval 0.22–0.90).

Conclusions

MRI imaging demonstrates good reliability and similar estimates of volume to histologically estimated measurements of residual injection laryngoplasty material at time points clinically relevant for future injection laryngoplasty experiments.

Level of Evidence

NA.

Progress in Vocal Fold Regenerative Biomaterials: An Immunological Perspective

Vocal folds, housed in the upper respiratory tract, are important to daily breathing, speech and swallowing functions. Irreversible changes to the vocal fold mucosae, such as scarring and atrophy, require a regenerative medicine approach to promote a controlled regrowth of the extracellular matrix (ECM)-rich mucosa. Various biomaterial systems have been engineered with an emphasis on stimulating local vocal fold fibroblasts to produce new ECM. At the same time, it is imperative to limit the foreign body reaction and associated immune components that can hinder the integration of the biomaterial into the host tissue. Modern biomaterial designs have become increasingly focused on actively harnessing the immune system to accelerate and optimize the process of tissue regeneration. An array of physical and chemical biomaterial parameters have been reported to effectively modulate local immune cells, such as macrophages, to initiate tissue repair, stimulate ECM production, promote biomaterial-tissue integration, and restore the function of the vocal folds. In this perspective paper, the unique immunological profile of the vocal folds will first be reviewed. Key physical and chemical biomaterial properties relevant to immunomodulation will then be highlighted and discussed. A further examination of the physicochemical properties of recent vocal fold biomaterials will follow to generate deeper insights into corresponding immune-related outcomes. Lastly, a perspective will be offered on the opportunity of integrating material-led immunomodulatory strategies into future vocal fold tissue engineering therapies.

In Vitro Evaluation of Biomaterials for Vocal Fold Injection: A Systematic Review

Vocal fold injection is a preferred treatment in glottic insufficiency because it is relatively quick and cost-saving. However, researchers have yet to discover the ideal biomaterial with properties suitable for human vocal fold application. The current systematic review employing PRISMA guidelines summarizes and discusses the available evidence related to outcome measures used to characterize novel biomaterials in the development phase. The literature search of related articles published within January 2010 to March 2021 was conducted using Scopus, Web of Science (WoS), Google Scholar and PubMed databases. The search identified 6240 potentially relevant records, which were screened and appraised to include 15 relevant articles based on the inclusion and exclusion criteria. The current study highlights that the characterization methods were inconsistent throughout the different studies. While rheologic outcome measures (viscosity, elasticity and shear) were most widely utilized, there appear to be no target or reference values. Outcome measures such as cellular response and biodegradation should be prioritized as they could mitigate the clinical drawbacks of currently available biomaterials. The review suggests future studies to prioritize characterization of the viscoelasticity (to improve voice outcomes), inflammatory response (to reduce side effects) and biodegradation (to improve longevity) profiles of newly developed biomaterials.

Multifaceted Design and Emerging Applications of Tissue Adhesives

Tissue adhesives can form appreciable adhesion with tissues and have found clinical use in a variety of medical settings such as wound closure, surgical sealants, regenerative medicine, and device attachment. The advantages of tissue adhesives include ease of implementation, rapid application, mitigation of tissue damage, and compatibility with minimally invasive procedures. The field of tissue adhesives is rapidly evolving, leading to tissue adhesives with superior mechanical properties and advanced functionality. Such adhesives enable new applications ranging from mobile health to cancer treatment. To provide guidelines for the rational design of tissue adhesives, here, existing strategies for tissue adhesives are synthesized into a multifaceted design, which comprises three design elements: the tissue, the adhesive surface, and the adhesive matrix. The mechanical, chemical, and biological considerations associated with each design element are reviewed. Throughout the report, the limitations of existing tissue adhesives and immediate opportunities for improvement are discussed. The recent progress of tissue adhesives in topical and implantable applications is highlighted, and then future directions toward next-generation tissue adhesives are outlined. The development of tissue adhesives will fuse disciplines and make broad impacts in engineering and medicine.

Porcine Vocal Fold Lamina Propria-Derived Biomaterials Modulate TGF-β1-Mediated Fibroblast Activation in Vitro

The vocal fold lamina propria (VFLP), one of the outermost layers of the vocal fold (VF), is composed of tissue-specific extracellular matrix (ECM) proteins and is highly susceptible to injury. Various biomaterials have been clinically tested to treat voice disorders (e.g., hydrogels, fat, and hyaluronic acid), but satisfactory recovery of the VF functionality remains elusive. Fibrosis or scar formation in the VF is a major challenge, and the development and refinement of novel therapeutics that promote the healing and normal function of the VF are needed. Injectable hydrogels derived from native tissues have been previously reported with major advantages over synthetic hydrogels, including constructive tissue remodeling and reduced scar tissue formation. This study aims to characterize the composition of a decellularized porcine VFLP-ECM scaffold and the cytocompatibility and potential antifibrotic properties of a hydrogel derived from VFLP-ECM. In addition, we isolated potential matrix-bound vesicles (MBVs) and macromolecules from the VFLP-ECM that also downregulated smooth muscle actin ACTA2 under transforming growth factor-beta 1 (TGF-β1) stimulation. The results provide evidence of the unique protein composition of the VFLP-ECM and the potential link between the components of the VFLP-ECM and the inhibition of TGF-β1 signaling observed in vitro when transformed into injectable forms.

Scattering properties and femtosecond laser ablation thresholds of human and canine vocal folds at 776-nm wavelength

Ultrafast laser ablation may provide a treatment for vocal fold (VF) scarring. Optical properties of VFs must be known prior to clinical implementation to select appropriate laser surgery conditions. We present scattering lengths of epithelium ℓs  ,  ep, superficial lamina propria ℓs  ,  SLP, and ablation thresholds Fth of human and canine VF tissues. Our experimental approach involves an image-guided, laser-ablation-based method that allows for simultaneous determination of ℓs and Fth in these multilayered tissues. Studying eight canine samples, we found ℓs  ,  ep  =  75.3  ±  5.7  μm, ℓs  ,  SLP  =  26.1  ±  1.2  μm, Fth  ,  ep  =  1.58  ±  0.06  J  /  cm2, and Fth  ,  SLP  =  1.55  ±  0.17  J  /  cm2. Studying five human samples, we found ℓs  ,  ep  =  42.8  ±  3.3  μm and Fth  ,  ep  =  1.66  ±  0.10  J  /  cm2. We studied the effects of cumulative pulse overlap on ablation threshold and found no significant variations beyond 12 overlapping pulses. Interestingly, our studies about the effect of sample storage on the scattering properties of porcine VF show a 60% increase in ℓs  ,  ep for fresh porcine VF when compared to the same sample stored in isotonic solution. These results provide guidelines for clinical implementation by enabling selection of optimal laser surgery parameters for subsurface ablation of VF tissues.

Pathophysiology of Fibrosis in the Vocal Fold: Current Research, Future Treatment Strategies, and Obstacles to Restoring Vocal Fold Pliability

Communication by voice depends on symmetrical vibrations within the vocal folds (VFs) and is indispensable for various occupations. VF scarring is one of the main reasons for permanent dysphonia and results from injury to the unique layered structure of the VFs. The increased collagen and decreased hyaluronic acid within VF scars lead to a loss of pliability of the VFs and significantly decreases their capacity to vibrate. As there is currently no definitive treatment for VF scarring, regenerative medicine and tissue engineering have become increasingly important research areas within otolaryngology. Several recent reviews have described the problem of VF scarring and various possible solutions, including tissue engineered cells and tissues, biomaterial implants, stem cells, growth factors, anti-inflammatory cytokines antifibrotic agents. Despite considerable research progress, these technical advances have not been established as routine clinical procedures. This review focuses on emerging techniques for restoring VF pliability using various approaches. We discuss our studies on interactions among adipose-derived stem/stromal cells, antifibrotic agents, and VF fibroblasts using an in vitro model. We also identify some obstacles to advances in research.

In vitro evaluation of anti-fibrotic effects of select cytokines for vocal fold scar treatment

Scarring of the vocal fold lamina propria (LP) can cause considerable voice disorders due to reduced pliability in scar tissue, attributed in part to abnormal extracellular matrix (ECM) deposition produced by the fibrotic vocal fold fibroblast (fVFF). Cytokines with anti-fibrotic potential have been investigated to limit abnormal LP ECM, but are limited by the need for repeat injections. Moreover, the potentially significant role played by activated macrophages (AMOs) is usually not considered even though the interaction between AMO and fibrotic fibroblasts is known to regulate scar formation across different tissues. AMO are also regulated by cytokines that are used for LP scar removal, but little is known about AMO behaviors in response to these cytokines within the context of LP scar. In the present study, we evaluated anti-fibrotic effects of hepatocyte growth factor (HGF), interleukin-10 (IL-10) and interleukin-6 (IL-6) in a 3D, in vitro fVFF-AMO co-culture system using poly(ethylene glycol) diacrylate (PEGDA) hydrogels. Data from all cytokines was synthesized into a heat-map that enabled assessment of specific associations between AMO and fVFF phenotypes. Cumulatively, our results indicated that both HGF and IL-10 are potentially anti-fibrotic (reduction in fibrotic markers and enhancement in normal, anti-fibrotic VFF markers), while IL-6 displays more complex, marker specific effects. Possible associations between AMO and fVFF phenotypes were found and may highlight a potential desirable macrophage phenotype. These data support the therapeutic potential of HGF and IL-10 for LP scar treatment, and shed light on future strategies aimed at targeting specific AMO phenotypes. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1056-1067, 2019.

Incorporation of types I and III collagen in tunable hyaluronan hydrogels for vocal fold tissue engineering

Vocal fold scarring is the fibrotic manifestation of a variety of voice disorders, and is difficult to treat. Tissue engineering therapies provide a potential strategy to regenerate the native tissue microenvironment in order to restore vocal fold functionality. However, major challenges remain in capturing the complexity of the native tissue and sustaining regeneration. We hypothesized that hydrogels with tunable viscoelastic properties that present relevant biological cues to cells might be better suited as therapeutics. Herein, we characterized the response of human vocal fold fibroblasts to four different biomimetic hydrogels: thiolated hyaluronan (HA) crosslinked with poly(ethylene glycol) diacrylate (PEGDA), HA-PEGDA with type I collagen (HA-Col I), HA-PEGDA with type III collagen (HA-Col III) and HA-PEGDA with type I and III collagen (HA-Col I-Col III). Collagen incorporation allowed for interpenetrating fibrils of collagen within the non-fibrillar HA network, which increased the mechanical properties of the hydrogels. The addition of collagen fibrils also reduced hyaluronidase degradation of HA and hydrogel swelling ratio. Fibroblasts encapsulated in the HA-Col gels adopted a spindle shaped fibroblastic morphology by day 7 and exhibited extensive cytoskeletal networks by day 21, suggesting that the incorporation of collagen was essential for cell adhesion and spreading. Cells remained viable and synthesized new DNA throughout 21 days of culture. Gene expression levels significantly differed between the cells encapsulated in the different hydrogels. Relative fold changes in gene expression of MMP1, COL1A1, fibronectin and decorin suggest higher degrees of remodeling in HA-Col I-Col III gels in comparison to HA-Col I or HA-Col III hydrogels, suggesting that the former may better serve as a natural biomimetic hydrogel for tissue engineering applications. STATEMENT OF SIGNIFICANCE: Voice disorders affect about 1/3rd of the US population and significantly reduce quality of life. Patients with vocal fold fibrosis have few treatment options. Tissue engineering therapies provide a potential strategy to regenerate the native tissue microenvironment in order to restore vocal fold functionality. Various studies have used collagen or thiolated hyaluronan (HA) with gelatin as potential tissue engineering therapies. However, there is room for improvement in providing cells with more relevant biological cues that mimic the native tissue microenvironment and sustain regeneration. The present study introduces the use of type I collagen and type III collagen along with thiolated HA as a natural biomimetic hydrogel for vocal fold tissue engineering applications.

A Method for Reconstruction of Anterior Commissure Glottal Webs With Endoscopic Fibro-Mucosal Flaps

Background:

Anterior-commissure (AC) cicatrization and web formation is a difficult problem that can result from a variety of clinical scenarios. An advancement-rotation flap utilizing papillomatous epithelium and subepithelial fibrous tissue has been previously described. For patients in whom there was not excessive redundant papillomatosis covering the AC web, including other clinical scenarios, a microlaryngoscopic procedure was designed to lengthen the glottal/subglottal aperture using substantial local fibro-mucosal tissue. Although it has been done for over a decade, this approach is not widely known and to our knowledge not photo-documented.

Study Design:

Retrospective.

Material and Methods:

An analysis was done with Institutional Review Board approval that identified 42 patients who underwent 53 procedures to treat AC webs, which were reconstructed with local soft-tissue flaps and without any device/stent to maintain the glottal aperture. The microlaryngoscopic method and technical nuances for this approach with and without diseased epithelium are described and photo-documented. Tactical mucosal incisions were made to facilitate advancement and/or rotation of fibro-mucosal flaps with enough length to resurface the medial aspect of 1 vocal fold. The scarred submucosal soft tissue in the AC region was separated with cold instruments, and the flaps were sutured in position. Variations of this method are demonstrated mobilizing fibro-mucosal soft tissue from different locations, including the web itself, contralateral vocal fold, infrapetiole region, and/or the inner aspect of the thyroid lamina below the anterior-commissure tendon.

Results:

Of the 53 cases in which anterior commissure glottal webs were reconstructed with endoscopic fibro-mucosal flaps, 31 of 53 had recurrent respiratory papillomatosis (RRP). Redundant RRP comprised the majority of the flap in 14 of 31 RRP cases. Fibro-mucosal tissue without a substantial amount of disease occurred in 17 of 31 RRP cases. Of the remaining 22 AC web cases, the primary diagnoses observed were: glottic cancer = 7 of 22, intraepithelial dysplasia = 10 of 22, glottic trauma = 3 of 22, congenital = 1 of 22, and radiotherapy = 1 of 22.

Conclusion:

Endolaryngeal utilization of local fibro-mucosal tissue to lengthen the glottal/subglottal aperture for AC webs is an effective strategy. It can be done without using devices or keels for webs that are congenital or from nonsurgical trauma, idiopathic disease, or postsurgical traumatic cicatrization of the anterior commissure subsequent to treatment of epithelial disease (eg, cancer, dysplasia, and RRP). Normalizing the architecture of the anterior commissure was a valuable asset in patients who require future treatment of epithelial diseases, especially in an office-based setting.

The Art and Craft of Phonomicrosurgery in Grammy Award–Winning Elite Performers

Background:

Since the renowned opera maestro Manuel Garcia presented “Observations on the Human Voice” using mirror laryngoscopy in 1855, there has been an inextricable link between performing vocalists and laryngologists. Today, specialized laryngeal surgeons continue the tradition of integrating medical and surgical management of performers with those skilled in vocal arts, voice science, and voice therapy. With advances in surgical instrumentation and techniques, increasing opportunities have evolved to surgically restore lost performing voices. However, it is especially challenging because of a range of factors, including the need for optimal technical precision, management of expectations, complexity of informed consent, public visibility of these patients, and the economics related to the success and failure of surgery. A number of these key issues apply to phonomicrosurgical procedures in nonsingers as well. Consequently, reviewing the art and craft of phonomicrosurgery in elite performers provides valuable insights into the optimal management of any patient.

Methods:

A retrospective review was done of microlaryngeal procedures for the past 20 years, and 18 elite performers were identified who were Grammy Award winners. Microsurgical methods for different lesions are illustrated. Composite analyses of the group along with their associated pathology was done to provide insights into key issues.

Results:

The 18 patients in this cohort have won 80 Grammy Awards, which were garnered from 242 nominations. All 18 had substantial deterioration in voice quality and could retain more than 1 pathology. Significant loss of superficial lamina propria (SLP) pliability was present in 15 of 18, varices and/or ectasias leading to vocal hemorrhage in 6, vocal polyps in 9, fibrovascular nodules in 6, arytenoid granuloma in 1, sulcus from prior microlaryngeal surgery leading to vocal fold SLP scarring in 4, sulcus from long-term phonotrauma leading to vocal fold SLP scarring in 4, benign cyst in 1, precancerous dysplasia in 2, and invasive carcinoma in 2. Subsequent to phonomicrosurgery, all reported improvement in their performance.

Conclusions:

Laryngologists and laryngeal surgeons have shouldered a burden of responsibility for elite performing vocalists since the origin of our specialty. Most lesions and diagnoses that are encountered result from phonotrauma. Optimizing singers’ care provides surgeons with extremely complex technical, emotional, social, and financial challenges. Focused analysis of managing elite performing vocalists effectively integrates a range of essential issues, which provide key insights to assist clinicians treating nonperforming patients requiring phonomicrosurgery.

A mixed-effects model approach for the statistical analysis of vocal fold viscoelastic shear properties

A mixed-effects model approach was introduced in this study for the statistical analysis of rheological data of vocal fold tissues, in order to account for the data correlation caused by multiple measurements of each tissue sample across the test frequency range. Such data correlation had often been overlooked in previous studies in the past decades. The viscoelastic shear properties of the vocal fold lamina propria of two commonly used laryngeal research animal species (i.e. rabbit, porcine) were measured by a linear, controlled-strain simple-shear rheometer. Along with published canine and human rheological data, the vocal fold viscoelastic shear moduli of these animal species were compared to those of human over a frequency range of 1-250Hz using the mixed-effects models. Our results indicated that tissues of the rabbit, canine and porcine vocal fold lamina propria were significantly stiffer and more viscous than those of human. Mixed-effects models were shown to be able to more accurately analyze rheological data generated from repeated measurements.

In vitro evaluation of a basic fibroblast growth factor-containing hydrogel toward vocal fold lamina propria scar treatment

Scarring of the vocal fold lamina propria can lead to debilitating voice disorders that can significantly impair quality of life. The reduced pliability of the scar tissue-which diminishes proper vocal fold vibratory efficiency-results in part from abnormal extracellular matrix (ECM) deposition by vocal fold fibroblasts (VFF) that have taken on a fibrotic phenotype. To address this issue, bioactive materials containing cytokines and/or growth factors may provide a platform to transition fibrotic VFF within the scarred tissue toward an anti-fibrotic phenotype, thereby improving the quality of ECM within the scar tissue. However, for such an approach to be most effective, the acute host response resulting from biomaterial insertion/injection likely also needs to be considered. The goal of the present work was to evaluate the anti-fibrotic and anti-inflammatory capacity of an injectable hydrogel containing tethered basic fibroblast growth factor (bFGF) in the dual context of scar and biomaterial-induced acute inflammation. An in vitro co-culture system was utilized containing both activated, fibrotic VFF and activated, pro-inflammatory macrophages (MΦ) within a 3D poly(ethylene glycol) diacrylate (PEGDA) hydrogel containing tethered bFGF. Following 72 h of culture, alterations in VFF and macrophage phenotype were evaluated relative to mono-culture and co-culture controls. In our co-culture system, bFGF reduced the production of fibrotic markers collagen type I, α smooth muscle actin, and biglycan by activated VFF and promoted wound-healing/anti-inflammatory marker expression in activated MΦ. Cumulatively, these data indicate that bFGF-containing hydrogels warrant further investigation for the treatment of vocal fold lamina propria scar. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1258-1267, 2018.

Tissue engineering-based therapeutic strategies for vocal fold repair and regeneration

Vocal folds are soft laryngeal connective tissues with distinct layered structures and complex multicomponent matrix compositions that endow phonatory and respiratory functions. This delicate tissue is easily damaged by various environmental factors and pathological conditions, altering vocal biomechanics and causing debilitating vocal disorders that detrimentally affect the daily lives of suffering individuals. Modern techniques and advanced knowledge of regenerative medicine have led to a deeper understanding of the microstructure, microphysiology, and micropathophysiology of vocal fold tissues. State-of-the-art materials ranging from extracecullar-matrix (ECM)-derived biomaterials to synthetic polymer scaffolds have been proposed for the prevention and treatment of voice disorders including vocal fold scarring and fibrosis. This review intends to provide a thorough overview of current achievements in the field of vocal fold tissue engineering, including the fabrication of injectable biomaterials to mimic in vitro cell microenvironments, novel designs of bioreactors that capture in vivo tissue biomechanics, and establishment of various animal models to characterize the in vivo biocompatibility of these materials. The combination of polymeric scaffolds, cell transplantation, biomechanical stimulation, and delivery of antifibrotic growth factors will lead to successful restoration of functional vocal folds and improved vocal recovery in animal models, facilitating the application of these materials and related methodologies in clinical practice.

Formulation and characterization of a porous, elastomeric biomaterial for vocal fold tissue engineering research

OBJECTIVE

Biomaterials able to mimic the mechanical properties of vocal fold tissue may be particularly useful for furnishing a 3-dimensional microenvironment allowing for in vitro investigation of cell and molecular responses to vibration. Motivated by the dearth of biomaterials available for use in an in vitro model for vocal fold tissue, we investigated polyether polyurethane (PEU) matrices, which are porous, mechanically tunable biomaterials that are inexpensive and require only standard laboratory equipment for fabrication.

METHODS

Rheology, dynamic mechanical analysis, and scanning electron microscopy were performed on PEU matrices at 5%, 10%, and 20% w/v mass concentrations.

RESULTS

For 5%, 10%, and 20% w/v concentrations, shear storage moduli were 2 kPa, 3.4 kPa, and 6 kPa, respectively, with shear loss moduli being 0.2 kPa, 0.38 kPa, and 0.62 kPa, respectively. Storage moduli responded to applied frequency as a linear function. Mercury intrusion porosimetry revealed that all 3 mass concentrations of PEU have a similar overall percentage porosity but differ in pore architecture.

CONCLUSION

Twenty-µm diameter pores are ideal for cell seeding, and a range of mechanical properties indicates that the lower [corrected] mass concentration PEU formulations are best suited for mimicking the viscoelastic properties of vocal fold tissue for in vitro research.

Voice Outcome of Modified Frontolateral Partial Laryngectomy in Excised Canine Larynges and Finite Element Model

OBJECTIVE

To evaluate vocal parameters after modified frontolateral partial laryngectomy (MFLPL) and frontolateral partial laryngectomy (FLPL) in both excised canine and finite element models.

STUDY DESIGN

FLPL and MFLPL were compared, using a prospective paired case control laboratory study with excised canine larynx and computational modeling.

SETTING

Basic science study conducted in university laboratory.

METHODS

FLPL and MFLPL were performed serially on 9 excised canine larynges. The excised larynx bench apparatus was used to collect phonation threshold pressure (PTP) and high-speed video data. A finite element model was built to compare a normal vocal fold with applied tension, a cut fold with no applied tension (simulating FLPL), and a cut fold with applied tension (simulating MFLPL). Stress values and distributions across the 3 conditions were computed.

RESULTS

The mean PTP increase after MFLPL (15.45-17.46 cmH2O) was not statistically significant. In the excised canine model, fundamental frequency (F0) showed a significant increase for the MFLPL (P = .039). Differences in vibration amplitudes were not statistically significant. Von Mises stress distribution was most similar between the MFLPL model and the normal fold. Maximum von Mises stresses at the midline were 17.56, 21.63, and 5.10 kPa for the normal, MFLPL, and FLPL, respectively, and 47.57, 63.98, and 101.97 kPa at the peripheries.

CONCLUSIONS

From these results, we conclude that MFLPL has the potential to give a better voice outcome while avoiding tracheotomy in partial laryngectomy patients. In vivo study in canines to examine the healing process would lend further evidence-based support for this surgical method.

Voice disorders in children

This article reviews the management of voice disorders in children. We describe the relevant anatomy and development of the larynx throughout childhood, which affects voice. We consider the epidemiologic data to establish the size of the problem. The assessment of the patient in the clinic is described stepwise through the history, examination, laryngoscopy, and extra tests. We then review the common voice disorders encountered and their management, concluding with discussion of future directions, which may herald advances in this field.

Voice Outcomes from Subligamentous Cordectomy for Early Glottic Cancer

Objectives:

We evaluated the voice and vocal fold pliability outcomes of European Laryngological Society (ELS) deep type I (subepithelial) and type II (subligamentous) cordectomies for early glottic cancer.

Methods:

We reviewed the medical records of patients with glottic carcinoma at a tertiary care medical center between 2005 and 2011. Their procedures were stratified into ELS type I and ELS type II cordectomies. The data recorded included age, gender, tumor stage, recurrence, patient-assessed voice-related quality of life, perceptual voice evaluation, and stroboscopy.

Results:

Four patients were identified as having subepithelial cordectomy, and 13 as having subligamentous cordectomy. The average preoperative and postoperative voice-related quality of life scores were 65 and 74 for the ELS I cohort and 64 and 95 for the ELS II group. The preoperative and postoperative perceptual voice evaluation scores were 56 and 35 for the ELS I cohort and 45 and 21 for the ELS II cohort. The ELS I cohort had a moderately to severely reduced mucosal wave, with 75% of patients demonstrating glottic insufficiency, whereas the ELS II cohort had a mildly to moderately reduced mucosal wave, with 8% of patients demonstrating glottic insufficiency. The survival outcomes were the same.

Conclusions:

Patients who underwent subligamentous excision of early glottic cancer had significantly improved postoperative voice and stroboscopy scores. This finding suggests that if tumor resection reaches the vocal ligament, and minimal superficial lamina propria can be preserved, subligamentous cordectomy should be performed.

High-speed digital imaging of the larynx: recent advances

PURPOSE OF REVIEW

This review presents recent advances in high-speed digital imaging (HSDI) of the larynx including data acquisition, data analysis, and clinical applicability.

RECENT FINDINGS

Software designed to summarize the large amounts of data captured with HSDI makes it possible to quantitatively analyze recordings from patients, improving the accuracy of the methodology. The new software has been used in studies of normal individuals, increasing our knowledge of normal vocal fold vibratory behavior. HSDI has also been used in patient populations and shows promise in distinguishing various laryngeal conditions that are difficult to distinguish with other imaging modalities. Studies of postoperative patients with HSDI demonstrate the return of some vibratory characteristics but not others, potentially leading the way to improvements in surgical technique.

SUMMARY

Recent advances in HSDI technology have increased the clinical usefulness of the imaging technology and recent studies demonstrate the clinical applicability of HSDI. However, challenges to widespread clinical use of HSDI remain.

Modification and testing of a pneumatic dispensing device for controlled delivery of injectable materials

OBJECTIVES/HYPOTHESIS

Vocal fold (VF) injections of viscous materials are typically performed using hand-operated syringes or injection guns; however, these methods can be imprecise due to accumulation of pressure, effort-related tremor, and poor feedback regarding injection volume and rate.

STUDY DESIGN

Apparatus development with laboratory bench-top and animal model testing.

METHODS

A foot pedal-triggered device for dispensing viscous materials was modified by adding a linear transducer and display for monitoring dispensed volume. In bench tests, bovine VFs were injected with fluids/materials of different viscosities (saline, glycerol, hydrogel, and liposuctioned fat) through narrow-bore needles using a range of driving pressures and air pulse durations. The device was further evaluated in >50 in vivo VF injection experiments.

RESULTS

Device function was repeatable, with high correlations (typically R(2) > 0.98) between the readout and direct measures of volume, even for small volumes (<5 μL/pulse). Foot pedal control enabled surgeons to make steady, accurate injections into ferret and dog VFs during phonosurgery, and, because the dispenser released all driving pressure between pulses, there were no instances of clog-related overinjection when the obstruction cleared.

CONCLUSIONS

This VF injection system shows promise for development to enhance human phonosurgery by increasing injection control and precision.

Therapeutic potential of gel-based injectables for vocal fold regeneration

Vocal folds are anatomically and biomechanically unique, thus complicating the design and implementation of tissue engineering strategies for repair and regeneration. Integration of an enhanced understanding of tissue biomechanics, wound healing dynamics and innovative gel-based therapeutics has generated enthusiasm for the notion that an efficacious treatment for vocal fold scarring could be clinically attainable within several years. Fibroblast phenotype and gene expression are mediated by the three-dimensional mechanical and chemical microenvironment at an injury site. Thus, therapeutic approaches need to coordinate spatial and temporal aspects of the wound healing response in an injured vocal tissue to achieve an optimal clinical outcome. Successful gel-based injectables for vocal fold scarring will require a keen understanding of how the native inflammatory response sets into motion the later extracellular matrix remodeling, which in turn will determine the ultimate biomechanical properties of the tissue. We present an overview of the challenges associated with this translation as well as the proposed gel-based injectable solutions.

Experiments on Analysing Voice Production: Excised (Human, Animal) and In Vivo (Animal) Approaches

Experiments on human and on animal excised specimens as well as in vivo animal preparations are so far the most realistic approaches to simulate the in vivo process of human phonation. These experiments do not have the disadvantage of limited space within the neck and enable studies of the actual organ necessary for phonation, i.e., the larynx. The studies additionally allow the analysis of flow, vocal fold dynamics, and resulting acoustics in relation to well-defined laryngeal alterations.

PURPOSE OF REVIEW

This paper provides an overview of the applications and usefulness of excised (human/animal) specimen and in vivo animal experiments in voice research. These experiments have enabled visualization and analysis of dehydration effects, vocal fold scarring, bifurcation and chaotic vibrations, three-dimensional vibrations, aerodynamic effects, and mucosal wave propagation along the medial surface. Quantitative data will be shown to give an overview of measured laryngeal parameter values. As yet, a full understanding of all existing interactions in voice production has not been achieved, and thus, where possible, we try to indicate areas needing further study.

RECENT FINDINGS

A further motivation behind this review is to highlight recent findings and technologies related to the study of vocal fold dynamics and its applications. For example, studies of interactions between vocal tract airflow and generation of acoustics have recently shown that airflow superior to the glottis is governed by not only vocal fold dynamics but also by subglottal and supraglottal structures. In addition, promising new methods to investigate kinematics and dynamics have been reported recently, including dynamic optical coherence tomography, X-ray stroboscopy and three-dimensional reconstruction with laser projection systems. Finally, we touch on the relevance of vocal fold dynamics to clinical laryngology and to clinically-oriented research.

Triggered optical coherence tomography for capturing rapid periodic motion

Quantitative cross-sectional imaging of vocal folds during phonation is potentially useful for diagnosis and treatments of laryngeal disorders. Optical coherence tomography (OCT) is a powerful technique, but its relatively low frame rates makes it challenging to visualize rapidly vibrating tissues. Here, we demonstrate a novel method based on triggered laser scanning to capture 4-dimensional (4D) images of samples in motu at audio frequencies over 100 Hz. As proof-of-concept experiments, we applied this technique to imaging the oscillations of biopolymer gels on acoustic vibrators and aerodynamically driven vibrations of the vocal fold in an ex vivo calf larynx model. Our results suggest that triggered 4D OCT may be useful in understanding and assessing the function of vocal folds and developing novel treatments in research and clinical settings.