Effect of a synthetic extracellular matrix on vocal fold lamina propria gene expression in early wound healing

Exploring the anti-inflammatory potential of topical hyaluronic acid for vocal fold injury in a rat model

PURPOSE

Vocal fold injuries are associated with fibrosis and dysphonia, which is a major obstacle to surgical treatment. The aim of this study is to evaluate the effect of topical hyaluronic acid with or without diclofenac on the inflammatory phase of vocal fold wound healing.

METHODS

Forty-one male Sprague-Dawley rats were randomly assigned to four groups: an uninjured control group, an injured control group without any treatment, and two intervention groups in which hyaluronic acid with or without diclofenac was applied to the injured vocal fold. Gene expression of inflammatory markers and ECM-related molecules were examined.

RESULTS

Vocal fold injury resulted in a significant upregulation of inflammatory parameters [Ptgs2, Il1b and Il10] and Has1. Tgfb1, Has3 and Eln gene expression were significantly downregulated by the topical application of hyaluronic acid. The combination of hyaluronic acid and diclofenac did not result in any significant changes.

CONCLUSIONS

Vocal fold wound healing was significantly improved by a single post-operative topical application of hyaluronic acid. The addition of diclofenac may provide no additional benefit.

Construction and Properties of High-Toughness Soft-Soft Interfaces Based on the Adhesion of Natural Polyphenols

Artificial joint replacement is the most effective way to treat osteoarthritis. However, these artificial joints are too stiff with high interfacial contact stress and poor surface lubrication, resulting in stress shielding and severe wear and tear lead to an extremely high failure rate. At present, hydrogels are considered the most promising substitute for artificial joint prostheses owing to their good biocompatibility, adjustable mechanical properties, and excellent flexibility. Nevertheless, a traditional single-layer hydrogel has poor bearing capacity and lubrication, which are far from the properties of natural articular cartilage. The high strength and low friction properties of natural articular cartilage are based on its own multilayer fibrous structure. Therefore, by simulating the multilayer structure of natural cartilage, a bilayer bionic cartilage hydrogel was prepared; that is, the upper hydrogel realized excellent lubrication and the lower hydrogel realized high load-bearing capacity. However, the interface binding of bilayer hydrogels is a challenge at present. Therefore, the interfacial adhesion of the bilayer hydrogel is improved by adding tannic acid (TA) based on the adhesion of the natural polyphenol structure. The average interfacial toughness reaches 3650 J/m2, and the average interfacial shear force reaches 800 kPa. In the preparation of the bilayer hydrogel, taking advantage of the coordination reaction between TA and metal cations, Fe3+ is further added to endow the bilayer hydrogel with excellent mechanical properties and good sliding friction performance. Therefore, this work opens up a new way to construct cartilage-like materials with high toughness and a soft-soft interface.

Culture of Mesenchymal Stem Cells in a Hydrogel Model of Vocal Fold Lamina Propria

Stem cell injection has been proposed as an alternative approach for the restoration of vocal fold (VF) function in patients with VF scarring. To assess the therapeutic efficacy of this treatment strategy, we evaluated the behaviors of human mesenchymal stem cells (hMSCs) in hydrogels derived from thiolated hyaluronic acid (HA-SH) and poly(ethylene glycol) diacrylate (PEG-DA) entrapping assembled collagen fibrils (abbreviated as HPC gels). Three hydrogel formulations with varying amounts of collagen (0, 1 and 2 mg/mL) but a fixed HA-SH (5 mg/mL) and PEG-DA (2 mg/mL) concentration, designated as HPC0, HPC1 and HPC2, were investigated. The HPC gels exhibit similar pore sizes (35-50 nm) and AFM indentation moduli (~175 Pa), although the elastic shear modulus for HPC1 (~32 Pa) is lower than HPC0 and HPC2 (~55 Pa). Although HPC1 and HPC2 gels both promoted the development of an elongated cell morphology, greater cell spreading was observed in HPC2 than in HPC1 by day 7. At the transcript level, cells cultured in HPC1 and HPC2 gels had an increased expression of fibronectin and integrin β1, but a decreased expression of tissue inhibitor of metalloproteinase-1, collagen types I/III and HA synthase-1 when compared to cells cultured in HPC0 gels. Cellular expression of connective tissue growth factor was also elevated in HPC1 and HPC2 cultures. Importantly, the HPC2 hydrogels promoted a signficant up-regulation of matrix metalloproteinase 1, transforming growth factor β1, and epithelial growth factor receptor, indicating an increased tissue turnover. Overall, hMSCs cultured in HPC2 gels adopt a phenotype reminiscent of cells involved in the wound healing process, providing a platform to study the effectiveness of therapeutic stem cell treatments for VF scarring.

Characterizing Vocal Fold Injury Recovery in a Rabbit Model With Three-Dimensional Virtual Histology

OBJECTIVES/HYPOTHESIS

In animal studies of vocal fold scarring and treatment, imaging-based evaluation is most often conducted by tissue slicing and histological staining. Given variation in anatomy, injury type, severity, and sacrifice timepoints, planar histological sections provide limited spatiotemporal details of tissue repair. Three-dimensional (3D) virtual histology may provide additional contextual spatial information, enhancing objective interpretation. The study's aim was to evaluate the suitability of magnetic resonance imaging (MRI), microscale computed tomography (CT), and nonlinear laser-scanning microscopy (NM) as virtual histology approaches for rabbit studies of vocal fold scarring.

METHODS

A unilateral injury was created using microcup forceps in the left vocal fold of three New Zealand White rabbits. Animals were sacrificed at 3, 10, and 39 days postinjury. ex vivo imaging of excised larynges was performed with MRI, CT, and NM modalities.

RESULTS

The MRI modality allowed visualization of injury location and morphological internal features with 100-μm spatial resolution. The CT modality provided a view of the injury defect surface with 12-μm spatial resolution. The NM modality with optical clearing resolved second-harmonic generation signal of collagen fibers and two-photon autofluorescence in vocal fold lamina propria, muscle, and surrounding cartilage structures at submicrometer spatial scales.

CONCLUSIONS

Features of vocal fold injury and wound healing were observed with MRI, CT, and NM. The MRI and CT modalities provided contextual spatial information and dissection guidance, whereas NM resolved extracellular matrix structure. The results serve as a proof of concept to motivate incorporation of 3D virtual histology techniques in future vocal fold injury animal studies.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:1578-1587, 2021.

A tissue-specific, injectable acellular gel for the treatment of chronic vocal fold scarring

Gel-based injectable biomaterials have significant potential for treating vocal fold defects such as scarring. An ideal injectable for vocal fold lamina propria restoration should mimic the microenvironment of the lamina propria to induce scarless wound healing and functional tissue regeneration. Most current synthetic or natural injectable biomaterials do not possess the same level of complex, tissue-specific constituents as the natural vocal fold lamina propria. In this study we present a newly-developed injectable gel fabricated from decellularized bovine vocal fold lamina propria. Blyscan assay and mass spectrometry indicated that the vocal fold-specific gel contained a large amount of sulfated glycosaminoglycans and over 250 proteins. Gene Ontology overrepresentation analysis revealed that the proteins in the gel dominantly promote antifibrotic biological process. In vivo study using a rabbit vocal fold injury model showed that the injectable gel significantly reduced collagen density and decreased tissue contraction of the lamina propria in vocal folds with chronic scarring. Furthermore, this acellular gel only elicited minimal humoral immune response after injection. Our findings suggested that the tissue-specific, injectable extracellular matrix gel could be a promising biomaterial for treating vocal fold scarring, even after the formation of mature scar. STATEMENT OF SIGNIFICANCE: Vocal fold lamina propria scarring remains among the foremost therapeutic challenges in the management of patients with voice disorders. Surgical excision of scar may cause secondary scarring and yield inconsistent results. The present study reports an extracellular matrix-derived biomaterial that demonstrated antifibrotic effect on chronic scarring in vocal fold lamina propria. Its injectability minimizes the invasiveness of the delivery procedure and the degree of mucosal violation. In this work we also describe a new methodology which can more accurately identify proteins from the complex mixture of an acellular extracellular matrix gel by excluding interfering peptides produced during the enzymatic digestion in gel fabrication.

Regenerative potential of basic fibroblast growth factor contained in biodegradable gelatin hydrogel microspheres applied following vocal fold injury: Early effect on tissue repair in a rabbit model

Introduction

Postoperative dysphonia is mostly caused by vocal fold scarring, and careful management of vocal fold surgery has been reported to reduce the risk of scar formation. However, depending on the vocal fold injury, treatment of postoperative dysphonia can be challenging.

Objective

The goal of the current study was to develop a novel prophylactic regenerative approach for the treatment of injured vocal folds after surgery, using biodegradable gelatin hydrogel microspheres as a drug delivery system for basic fibroblast growth factor.

Methods

Videoendoscopic laryngeal surgery was performed to create vocal fold injury in 14 rabbits. Immediately following this procedure, biodegradable gelatin hydrogel microspheres with basic fibroblast growth factor were injected in the vocal fold. Two weeks after injection, larynges were excised for evaluation of vocal fold histology and mucosal movement.

Results

The presence of poor vibratory function was confirmed in the injured vocal folds. Histology and digital image analysis demonstrated that the injured vocal folds injected with gelatin hydrogel microspheres with basic fibroblast growth factor showed less scar formation, compared to the injured vocal folds injected with gelatin hydrogel microspheres only, or those without any injection.

Conclusion

A prophylactic injection of basic fibroblast growth factor -containing biodegradable gelatin hydrogel microspheres demonstrates a regenerative potential for injured vocal folds in a rabbit model.

An investigation of left-right vocal fold symmetry in rheological and histological properties

OBJECTIVES

The primary objective was to investigate the left-right vocal fold symmetry in rheological and histological properties using a rabbit model. The other objective was to develop statistical models for the comparison of rheological properties between paired vocal folds.

METHODS

Viscoelastic shear properties of six pairs of vocal fold lamina propria specimens were measured over a frequency range of 1 to 250 Hz by a linear, controlled-strain, simple-shear rheometer. The rheological data of the left and right vocal folds was statistically compared using the mixed-effects model approach. Six additional rabbit larynges were histologically analyzed for left-right symmetry in distribution patterns and relative densities of major extracellular matrix constituents.

RESULTS

There were no significant differences in elastic shear modulus (P = 0.1069) and dynamic viscosity (P = 0.944) of the lamina propria between the two vocal folds of the same larynx. Left-right vocal fold symmetry in densities and distribution patterns of the key molecular constituents was also demonstrated in histological results.

CONCLUSION

By showing that the left and right vocal folds were rheologically and histologically symmetrical in rabbit, this study validated an underlying assumption made in many previous reports. Statistical models for the analysis of hierarchically correlated left-right vocal fold rheological data were also presented.

LEVEL OF EVIDENCE

NA. Laryngoscope, 128:E359-E364, 2018.

The Ability of Human Nasal Inferior Turbinate-Derived Mesenchymal Stem Cells to Repair Vocal Fold Injuries

Objective This study investigated the ability of implanted human nasal inferior turbinate-derived mesenchymal stem cells (hTMSCs) to repair injured vocal folds. To this end, we used quantitative real-time polymerase chain reaction (PCR) to analyze the early phase of wound healing and histopathological analysis to explore the late phase of wound healing in xenograft animal models. Study Design Prospective animal study. Setting Research laboratory. Subjects and Methods The right-side lamina propria of the vocal fold was injured in 20 rabbits and 30 rats. Next, hTMSCs were implanted into half of the injured vocal folds (hTMSC groups). As a control, phosphate-buffered saline (PBS) was injected into the other half of the injured vocal folds (PBS groups). Rat vocal folds were harvested for polymerase chain reaction (PCR) at 1 week after injury. Rabbit vocal folds were evaluated endoscopically and the larynges harvested for histological and immunohistochemical examination at 2 and 8 weeks after injury. Results In the hTMSC group, PCR showed that hyaluronan synthase ( HAS) 1, HAS 2, and transforming growth factor ( TGF)-β1 were significantly upregulated compared with the PBS group. Procollagen type III ( COL III) messenger RNA expression was significantly upregulated in the PBS group compared with the normal group. Histological analyses showed that hTMSC administration afforded more favorable collagen and hyaluronic acid deposition than was evident in the controls. Implanted hTMSCs were observed in injured vocal folds 2 weeks after implantation. Conclusions Our results show that hTMSCs implantation into injured vocal folds facilitated vocal fold regeneration, with presenting antifibrotic effects.

The Ferret as a Surgical Model for Vocal Fold Scar Creation and Treatment

Objectives:

To develop a vocal fold (VF) scarring procedure in the ferret, characterize the scars histologically, and test the injectability of the lamina propria (LP). Secondarily, to compare laryngeal anatomy of the ferret with rat and rabbit.

Materials and Methods:

The larynges of 18 male ferrets were prepared by unilateral scarring, and normal larynges from 6 female Wistar rats and 5 male albino rabbits were used for comparative purposes. For scarring, the right VF were electrocauterized, ablating the entire LP. Prior to harvesting the larynges at 4 and 16 weeks, each ferret was re-anesthetized, and in 3 animals, India ink was injected into the LPs of both normal and scarred VFs.

Results:

Laryngoscopic methods and instrumentation for precise visualization, scarring, and injection were developed. The scarred VFs had reduced hyaluronic acid and increased collagen type I, III, and fibronectin compared with normal VFs. The 2 timepoints (4 and 16 weeks) differed significantly only in collagen type III level (levels were higher at 4 weeks). Injected ink migrated from scarred LP to muscle layer just beneath the scarred tissue 3 hours after injection.

Conclusion:

The ferret is a promising species for creation and experimental treatment of vocal fold scar.

Mesenchymal stromal cell injection promotes vocal fold scar repair without long-term engraftment

BACKGROUND

Regenerative medicine holds promise for restoring voice in patients with vocal fold scarring. As experimental treatments approach clinical translation, several considerations remain. Our objective was to evaluate efficacy and biocompatibility of four bone marrow mesenchymal stromal cell (BM-MSC) and tunable hyaluronic acid based hydrogel (HyStem-VF) treatments for vocal fold scar using clinically acceptable materials, a preclinical sample size and a dosing comparison.

METHODS

Vocal folds of 84 rabbits were injured and injected with four treatment variations (BM-MSC, HyStem-VF, and BM-MSC in HyStem-VF at two concentrations) 6 weeks later. Efficacy was assessed with rheometry, real-time polymerase chain reaction (RT-PCR) and histology at 2, 4 and 10 weeks following treatment. Lung, liver, kidney, spleen and vocal folds were screened for biocompatibility by a pathologist.

RESULTS AND DISCUSSION

Persistent inflammation was identified in all hydrogel-injected groups. The BM-MSC alone treatment appeared to be the most efficacious and safe, providing an early resolution of viscoelasticity, gene expression consistent with desirable extracellular matrix remodeling (less fibronectin, collagen 1α2, collagen 3, procollagen, transforming growth factor [TGF]β1, alpha smooth muscle actin, interleukin-1β, interleukin-17β and tumor necrosis factor [TNF] than injured controls) and minimal inflammation. Human beta actin expression in BM-MSC-treated vocal folds was minimal after 2 weeks, suggesting that paracrine signaling from the BM-MSCs may have facilitated tissue repair.

Macrophage Response to Allogeneic Adipose Tissue-Derived Stromal Cells in Hyaluronan-Based Hydrogel in a Porcine Vocal Fold Injury Model

OBJECTIVE

Adipose tissue-derived stromal cells (ASC) embedded in hyaluronan scaffold is a beneficial prophylactic treatment for vocal fold (VF) surgical scar. Here, we investigated the macrophage inflammatory response to allogeneic ASC-constructs and identified changes in lamina propria extracellular matrix.

METHOD

Pig ASC were characterized and transfected with GFP+ lentivirus. Thirty-three pigs underwent VF biopsies, and after 3 days, gel alone, gel+pASC, placebo, or pASC alone was injected into wound bed. Animals were sacrificed 3, 7, or 26 days post-injection. Flow cytometry; qPCR for NF-α, TGFβ, IL-10, IL-4, IFNγ, IL-12, FGF2, Col1A1, and HGF; and immunohistochemistry for collagen, elastin, HA, and fibronectin were performed to characterize macrophage phenotype, quantify cytokine transcription, analyze extracellular matrix remodeling, and track GFP+ cells.

RESULTS

No significant differences were found in SWC3+/SWC9+ phenotype or mRNA expression between cells+gel, gel, or placebo. The ASC alone exhibited significantly greater collagen, gel alone resulted in significantly less hyaluronan, and gel+pASC significantly more fibronectin (all P < .05). The pASC-GFP+ were detected 26 days post-injection.

CONCLUSIONS

The ASC-constructs were biocompatible; they did not influence the macrophage inflammatory response or provoke increases in collagen expression. Long-term engraftment was confirmed.

A Review of Hyaluronic Acid and Hyaluronic Acid-based Hydrogels for Vocal Fold Tissue Engineering

Vocal fold scarring is a common cause of dysphonia. Current treatments involving vocal fold augmentation do not yield satisfactory outcomes in the long term. Tissue engineering and regenerative medicine offer an attractive treatment option for vocal fold scarring, with the aim to restore the native extracellular matrix microenvironment and biomechanical properties of the vocal folds by inhibiting progression of scarring and thus leading to restoration of normal vocal function. Hyaluronic acid is a bioactive glycosaminoglycan responsible for maintaining optimum viscoelastic properties of the vocal folds and hence is widely targeted in tissue engineering applications. This review covers advances in hyaluronic acid-based vocal fold tissue engineering and regeneration strategies.

Retention of Human-Induced Pluripotent Stem Cells (hiPS) With Injectable HA Hydrogels for Vocal Fold Engineering

Objective:

One prospective treatment option for vocal fold scarring is regeneration with an engineered scaffold containing induced pluripotent stem cells (iPS). In the present study, we investigated the feasibility of utilizing an injectable hyaluronic acid (HA) scaffold encapsulated with human-iPS cell (hiPS) for regeneration of vocal folds.

Methods:

Thirty athymic nude rats underwent unilateral vocal fold injury. Contralateral vocal folds served as uninjured controls. Hyaluronic acid hydrogel scaffold, HA hydrogel scaffold containing hiPS, and HA hydrogel scaffold containing hiPS with epidermal growth factor (EGF) were injected in both vocal folds immediately after surgery. One and 2 weeks after injection, larynges were excised for histology, immunohistochemistry, and fluorescence in situ hybridization (FISH).

Results:

Presence of HA hydrogel was confirmed in vocal folds 1 and 2 weeks post injection. The FISH analysis confirmed the presence and viability of hiPS in the injected vocal folds. Histological results demonstrated that vocal folds injected with HA hydrogel scaffold containing EGF demonstrated less fibrosis than those with HA hydrogel only.

Conclusions:

Human-iPS survived in injured rat vocal folds. The HA hydrogel with hiPS and EGF ameliorated the fibrotic response. Additional work is necessary to optimize hiPS differentiation and further confirm the safety of hiPS for clinical applications.

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.

Bioprinting Cellularized Constructs Using a Tissue-specific Hydrogel Bioink

Bioprinting has emerged as a versatile biofabrication approach for creating tissue engineered organ constructs. These constructs have potential use as organ replacements for implantation in patients, and also, when created on a smaller size scale as model "organoids" that can be used in in vitro systems for drug and toxicology screening. Despite development of a wide variety of bioprinting devices, application of bioprinting technology can be limited by the availability of materials that both expedite bioprinting procedures and support cell viability and function by providing tissue-specific cues. Here we describe a versatile hyaluronic acid (HA) and gelatin-based hydrogel system comprised of a multi-crosslinker, 2-stage crosslinking protocol, which can provide tissue specific biochemical signals and mimic the mechanical properties of in vivo tissues. Biochemical factors are provided by incorporating tissue-derived extracellular matrix materials, which include potent growth factors. Tissue mechanical properties are controlled combinations of PEG-based crosslinkers with varying molecular weights, geometries (linear or multi-arm), and functional groups to yield extrudable bioinks and final construct shear stiffness values over a wide range (100 Pa to 20 kPa). Using these parameters, hydrogel bioinks were used to bioprint primary liver spheroids in a liver-specific bioink to create in vitro liver constructs with high cell viability and measurable functional albumin and urea output. This methodology provides a general framework that can be adapted for future customization of hydrogels for biofabrication of a wide range of tissue construct types.

A hydrogel bioink toolkit for mimicking native tissue biochemical and mechanical properties in bioprinted tissue constructs

Advancement of bioprinting technology is limited by the availability of materials that both facilitate bioprinting logistics as well as support cell viability and function by providing tissue-specific cues. Herein we describe a modular hyaluronic acid (HA) and gelatin-based hydrogel toolbox comprised of a 2-crosslinker, 2-stage polymerization technique, and the capability to provide tissue specific biochemically and mechanically accurate signals to cells within biofabricated tissue constructs. First, we prepared and characterized several tissue-derived decellularized extracellular matrix-based solutions, which contain complex combinations of growth factors, collagens, glycosaminoglycans, and elastin. These solutions can be incorporated into bioinks to provide the important biochemical cues of different tissue types. Second, we employed combinations of PEG-based crosslinkers with varying molecular weights, geometries (linear, 4-arm, and 8-arm), and functional groups to yield hydrogel bioinks that supported extrusion bioprinting and the capability to achieve final construct shear stiffness values ranging from approximately 100 Pa to 20 kPa. Lastly, we integrated these hydrogel bioinks with a 3-D bioprinting platform, and validated their use by bioprinting primary liver spheroids in a liver-specific bioink to create in vitro liver constructs with high cell viability and measurable functional albumin and urea output. This hydrogel bioink system has the potential to be a versatile tool for biofabrication of a wide range of tissue construct types.

STATEMENT OF SIGNIFICANCE

Biochemical and mechanical factors both have important implications in guiding the behavior of cells in vivo, yet both realms are rarely considered together in the context of biofabrication in vitro tissue construct models. We describe a modular hydrogel system that (1) facilitates extrusion bioprinting of cell-laden hydrogels, (2) incorporates tissue-specific factors derived from decellularized tissue extracellular matrix, thus mimicking biochemical tissue profile, and (3) allows control over mechanical properties to mimic the tissue stiffness. We believe that employing this technology to attend to both the biochemical and mechanical profiles of tissues, will allow us to more accurately recapitulate the in vivo environment of tissues while creating functional 3-D in vitro tissue constructs that can be used as disease models, personalized medicine, and in vitro drug and toxicology screening systems.

Effect of DMSO concentration, cell density and needle gauge on the viability of cryopreserved cells in three dimensional hyaluronan hydrogel

For cells seeded in scaffolds, transplanted cell survival rate plays an important role for cell transplantation efficiency, and is essential for successful cell transplantation. Fibroblast viability in HyStem-C was examined by a double staining Live/Dead Viability/Cytotoxicity assay, and cell images were analyzed using MetaMorph software for calculating live cell percentage for fresh and cryopreserved cells at different incubation time points, delivery methods, differing DMSO and cell concentrations. The results of this research demonstrated that in HyStem-C, the viability of cryopreserved cells (85%) was significantly lower than fresh collected cells (96.7%). In addition, the physical force from a 27 gauge needle significantly decreased frozen cell survival rates to 83-85% compared to pipette delivered cells. Higher DMSO concentration (1.0%) and higher cell density (2 × 10(7) per milliliter) also significantly decreased cell survival to 73%. Cryopreserved cell viability in three dimensional scaffolding can be maintained over 80% with cell density of 1 × 10(7) per milliliter, total DMSO concentration of 0.5%, and passed through a 27-gauge needle. These results demonstrate the viability of cells seeded in hyaluronan hydrogel with commonly used storage and delivery methods can bring rather satisfactory cell transplantation efficiency.

Viscoelasticity of hyaluronic acid-gelatin hydrogels for vocal fold tissue engineering

Crosslinked injectable hyaluronic acid (HA)-gelatin (Ge) hydrogels have remarkable viscoelastic and biological properties for vocal fold tissue engineering. Patient-specific tuning of the viscoelastic properties of this injectable biomaterial could improve tissue regeneration. The frequency-dependent viscoelasticity of crosslinked HA-Ge hydrogels was measured as a function of the concentration of HA, Ge, and crosslinker. Synthetic extracellular matrix hydrogels were fabricated using thiol-modified HA and Ge, and crosslinked by poly(ethylene glycol) diacrylate. A recently developed characterization method based on Rayleigh wave propagation was used to quantify the frequency-dependent viscoelastic properties of these hydrogels, including shear storage and loss moduli, over a broad frequency range; that is, from 40 to 4000 Hz. The viscoelastic properties of the hydrogels increased with frequency. The storage and loss moduli values and the rate of increase with frequency varied with the concentrations of the constituents. The range of the viscoelastic properties of the hydrogels was within that of human vocal fold tissue obtained from in vivo and ex vivo measurements. Frequency-dependent parametric relations were obtained using a linear least-squares regression. The results are useful to better fine-tune the storage and loss moduli of HA-Ge hydrogels by varying the concentrations of the constituents for use in patient-specific treatments.

Tissue engineering for otorhinolaryngology-head and neck surgery

Tissue regeneration in otorhinolaryngology-head and neck surgery is a diverse area filled with specialized tissues and functions. Head and neck structures govern many of the 5 senses, swallowing, breathing, communication, facial animation, and aesthetics. Loss of these functions can have a severe negative effect on patient quality of life. Regenerative medicine techniques have the potential to restore these functions while minimizing the risks associated with traditional reconstruction techniques. This article serves as a review and update on some of the regenerative medicine research in this field. A description of the predominant clinical problems is presented, followed by a discussion of some of the most promising research working toward a solution. There are many noteworthy findings appropriate for inclusion, but limitations preclude mention of them all. This article focuses on laryngeal surgery, craniofacial reconstruction and plastic surgery, and otology and hearing.

In vitro epithelial differentiation of human induced pluripotent stem cells for vocal fold tissue engineering

OBJECTIVES

We determined the feasibility and optimization of differentiating human induced pluripotent stem cells (hiPS) into nonkeratinized stratified squamous epithelial cells for vocal fold engineering.

METHODS

hiPS were cultured and assessed for differentiation in 3 conditions: a 3-dimensional (3D) hyaluronic acid (HA) hydrogel scaffold, a 3D HA hydrogel scaffold with epidermal growth factor (EGF), and a 3D HA hydrogel scaffold cocultured with human vocal fold fibroblasts (hVFF). After 1, 2, and 4 weeks of cultivation, hiPS were selected for histology, immunohistochemistry, and/or transcript expression analysis.

RESULTS

At 4 weeks, hiPS cultivated with hVFF or with EGF had significantly decreased levels of Oct 3/4, indicating loss of pluripotency. Immunofluorescence revealed the presence of pancytokeratin and of cytokeratin (CK) 13 and 14 epithelial-associated proteins at 4 weeks after cultivation in hiPS EGF and hiPS hVFF cultures. The transcript expression level of CK14 was significantly increased for hiPS hVFF cultures only and was measured concomitantly with cell morphology that was clearly cohesive and displayed a degree of nuclear polarity suggestive of epithelial differentiation.

CONCLUSIONS

We found that hiPS cultivated in 3D HA hydrogel with hVFF demonstrated the most robust conversion evidence to date of epithelial differentiation. Further work is necessary to focus on amplification of these progenitors for application in vocal fold regenerative biology.

Restructuring the vocal fold lamina propria with endoscopic microdissection

OBJECTIVES/HYPOTHESIS

The purposes of this preclinical study were to investigate histologic and rheologic outcomes of Microendoscopy of Reinke's space (MERS)-guided minithyrotomy and to assess its instrumentation.

STUDY DESIGN

Human cadaveric and in vivo animal study.

METHODS

Three human cadaveric larynges were treated with MERS-guided placement of Radiesse VoiceGel and immediately evaluated histologically for biomaterial location. In the second part of this investigation, two scarred porcine larynges were treated with MERS-guided placement of HyStem-VF and rheologically evaluated 6 weeks later. Student t tests determined differences in viscoelastic properties of treated/untreated vocal folds. Sialendoscopes and microendoscopes were subjectively compared for their visualization capacity.

RESULTS

MERS imaged the subepithelial area and vocal ligament, guiding both tissue dissection and biomaterial positioning. Sialendoscopes provided adequate visualization and feature incorporated working channels. Enhanced image clarity was created in a gas-filled rather than saline-filled environment, per rater judgment. Histological analysis revealed desirable biomaterial positioning with MERS. Per rheological analysis, viscoelastic properties of the MERS-treated porcine vocal folds compared to uninjured vocal folds 6 weeks following treatment did not statistically differ.

CONCLUSIONS

MERS-guided laryngoplasty using sialendoscopes yielded satisfactory biomaterial positioning in the short-term and normalized rheologic tissue properties in the long-term, contributing to proof of concept for MERS in the treatment of scarring. Strengths of MERS include direct, real-time visualization of Reinke's space and an ability to manipulate surgical instruments parallel to the vocal fold edge while maintaining an intact epithelium. Future work will explore the clinical utility of MERS for addressing scarring, sulcus vocalis, and other intracordal processes.

In vitro characterization of macrophage interaction with mesenchymal stromal cell-hyaluronan hydrogel constructs

Macrophages play a critical role in mediating not only normal tissue healing, but also the host reaction against biomaterial scaffolds. There is increasing interest in regenerative medicine to combine mesenchymal stromal/stem cells (MSCs) with biomaterial scaffolds to modulate inflammatory response while restoring tissue architecture. The objective of the current study was to investigate the interaction between MSCs (derived from bone marrow, adipose or vocal fold tissue) encapsulated in hyaluronan-based hydrogel and differentiating macrophages as measured by extracellular matrix (ECM) gene expression and cytokine, chemokine, and growth factor concentrations. Gene expression was analyzed using real-time polymerase chain reaction from MSCs embedded in Carbylan-GSX after 7 days of coculture with or without CD14+ cells. Protein concentrations were measured using a Bio-plex assay from cell culture supernatants on days 3 and 7 for all conditions. Following 7 days, we identified upregulation of collagen-I, collagen-III, procollagen, and matrix metalloproteinase-9 genes compared to control conditions. We demonstrate increased concentrations of immunoregulatory cytokines [interleukin (IL)-1β, tumor necrosis factor-α, macrophage inflammatory protein-1α, IFN-γ, IL-12, and IL-10] and remodeling growth factors (vascular endothelial growth factor, hepatocyte growth factor) in MSC-3D constructs cocultured with macrophages compared to control conditions, with some temporal variation. Our results indicate an alteration of expression of ECM proteins important to tissue regeneration and cytokines critical to the inflammatory cascade when 3D constructs were cultured with differentiating macrophages.

Cell-cell interaction between vocal fold fibroblasts and bone marrow mesenchymal stromal cells in three-dimensional hyaluronan hydrogel

Mesenchymal stromal cells (MSCs) are multipotential adult cells present in all tissues. Paracrine effects and differentiating ability make MSCs an ideal cell source for tissue regeneration. However, little is known about how interactions between implanted MSCs and native cells influence cellular growth, proliferation, and behaviour. By using an in vitro three-dimensional (3D) co-culture assay of normal or scarred human vocal fold fibroblasts (VFFs) and bone marrow-derived MSCs (BM-MSCs) in a uniquely suited hyaluronan hydrogel (HyStem-VF), we investigated cell morphology, survival rate, proliferation and protein and gene expression of VFFs and BM-MSCs. BM-MSCs inhibited cell proliferation of both normal and scarred VFFs without changes in VFF morphology or viability. BM-MSCs demonstrated decreased proliferation and survival rate after 7 days of co-culture with VFFs. Interactions between BM-MSCs and VFFs led to a significant increase in protein secretion of collagen I and hepatocyte growth factor (HGF) and a decrease of vascular endothelial growth factor (VEGF), monocyte chemotactic protein-1 (MCP-1) and interleukin-6 (IL-6). In particular, BM-MSCs significantly upregulated matrix metalloproteinase 1 (MMP1) and HGF gene expression for scarred VFFs compared to normal VFFs, indicating the potential for increases in extracellular matrix remodelling and tissue regeneration. Application of BM-MSCs-hydrogels may play a significant role in tissue regeneration, providing a therapeutic approach for vocal fold scarring. Copyright © 2013 John Wiley & Sons, Ltd.

Vocal fold scars: current concepts and future directions. Consensus report of the Phonosurgery Committee of the European Laryngological Society

Scarring of the vocal folds leads to a deterioration of the highly complex micro-structure with consecutively impaired vibratory pattern and glottic insufficiency. The resulting dysphonia is predominantly characterized by a reduced vocal capacity. Despite the considerable progress in understanding of the underlying pathophysiology, the treatment of scarred vocal folds is still an unresolved chapter in laryngology and phonosurgery. Essential for a successful treatment is an individual, multi-dimensional concept that comprises the whole armamentarium of surgical and non-surgical (i.p. voice therapy) modalities. An ideal approach would be to soften the scar, because the reduced pliability and consequently the increased vibratory rigidity impede the easiness of vibration. The chosen phonosurgical method is determined by the main clinical feature: Medialization techniques for the treatment of glottic gap, or epithelium freeing techniques for improvement of vibration characteristics often combined with injection augmentation or implantation. In severe cases, buccal mucosa grafting can be an option. New developments, include treatment with anxiolytic lasers, laser technology with ultrafine excision/ablation properties avoiding coagulation (Picosecond infrared laser, PIRL), or techniques of tissue engineering. However, despite the promising results by in vitro experiments, animal studies and first clinical trials, the step into clinical routine application has yet to be taken.

The anisotropic nature of the human vocal fold: an ex vivo study

The purpose of this study was to measure the relationship between the shear elastic properties of vocal fold with respect to the direction of applied stress. There is extensive published material that quantifies the shear viscoelastic properties of the vocal fold, but as much of these data were obtained using rotating parallel plate rheometers, which are unable to resolve out difference of the shear elastic behaviour with respect to direction, there is very little data that indicates anisotropic behaviour. To overcome this gap in knowledge, the team devised an apparatus that is capable of applying a shear stress in a known direction. A series of measurements were taken at the mid-membranous position, in the transverse and longitudinal directions. Point-specific measurements were performed using fourteen human cadaver excised larynges, which were hemi-sectioned to expose the vocal fold. An extremely low sinusoidal shear force of 1 g was applied tangentially to the membrane surface in both the longitudinal and transverse direction, and the resultant shear strain was measured. With the probe applied to the intact vocal fold, the average ratio of the elasticity in the transverse with respect to the longitudinal direction was 0.55. Further investigation using histological staining of collagens in the lamina propria indicates that there is a visible difference in the general alignment of collagen fibres when comparing the coronal and the sagittal sections. Our conclusion is that there is a quantifiable difference between the shear elastic response of the lamina propria in the longitudinal and transverse directions, and that this could be explained by the difference in alignment of collagen fibres within the lamina propria.

Hyaluronic acid hydrogels for vocal fold wound healing

The unique vibrational properties inherent to the human vocal fold have a significant detrimental impact on wound healing and scar formation. Hydrogels have taken prominence as a tissue engineered strategy to restore normal vocal structure and function as cellularity is low. The frequent vibrational and shear forces applied to, and present in this connective tissue make mechanical properties of such hydrogels a priority in this active area of research. Hyaluronic acid has been chemically modified in a variety of ways to address cell function while maintaining desirable tissue mechanical properties. These various modifications have had mixed results when injected in vivo typically resulting in better biomechanical function but not necessarily with a concomitant decrease in tissue fibrosis. Recent work has focused on seeding mesenchymal progenitor cells within 3D architecture of crosslinked hydrogels. The data from these studies demonstrate that this approach has a positive effect on cells in both early and late wound healing, but little work has been done regarding the biomechanical effects of these treatments. This paper provides an overview of the various hyaluronic acid derivatives, their crosslinking agents, and their effect when implanted into the vocal folds of various animal models.

[Vocal fold scars: pathogenesis, diagnosis, therapy]

Scarring of the vocal folds leads to a deterioration of the highly complex microstructure with consecutively impaired vibratory pattern and glottic insufficiency. The resulting dysphonia is predominantly characterized by a reduced vocal capacity. Despite considerable progress in the understanding of the underlying pathophysiology, treatment of scarred vocal folds is still an unresolved chapter in laryngology and phonosurgery. Decisive for successful treatment is an individual, multidimensional concept that comprises the whole armamentarium of surgical and nonsurgical (e.g. voice therapy) modalities. The chosen phonosurgical method is determined by the main clinical feature: medialization techniques for treatment of glottic insufficiency, or epithelium-freeing techniques for improvement of vibration characteristics often combined with injection augmentation or implantation. In severe cases, buccal mucosa grafting can be an option. New developments include treatment with angiolytic lasers [pulse dye laser, PDL; potassium titanyl phosphate (KTP) laser], or techniques of tissue engineering. However, despite promising results with in vitro experiments, animal studies and first clinical trials, application in clinical routine has not yet been achieved.

Response of fibroblasts to transforming growth factor-β1 on two-dimensional and in three-dimensional hyaluronan hydrogels

Transforming growth factor-β1 (TGF-β1), an important cytokine with multiple functions, is secreted during wound healing. Previous studies have utilized two-dimensional (2D) cell culture to elucidate the functions of TGF-β1; however, 2D culture does not represent the complex three-dimensional (3D) in vivo environment. Using a synthetic hyaluronan (HA) extracellular matrix (ECM) hydrogel, we investigated the effect of TGF-β1 on fibroblasts cultured in three conditions--on tissue culture polystyrene (TCP), on HA (2D), and in HA (3D). After TGF-β1 treatment (0.1 to 20 ng/mL), morphological features and ECM regulation were analyzed by immunocytochemistry, Western blot, quantitative polymerase chain reaction, and zymogram assays. On TCP, cells showed the typical spindle shape with strong alpha smooth muscle actin (α-SMA) staining of cytoplasmic myofilaments along the cell axes after TGF-β1 treatment; on HA (2D), spindle-shape cells showed little α-SMA staining; in HA (3D), cells were smaller and rounded with less α-SMA deposition. The α-SMA gene and protein expression on TCP were significantly upregulated by TGF-β1, but TGF-β1 did not induce α-SMA expression in the presence of HA (both 2D and 3D). 3D HA culture significantly downregulated collagen I, III, and fibronectin expression, increased matrix metalloproteinase 1 and 2 (MMP1/MMP2) activity, upregulated MMP1 mRNA and downregulated TIMP3 mRNA expression. This study suggested that exogenous HA, particularly in 3D culture, appears to suppress ECM production, enhances ECM degradation and remodeling, and inhibits myofibroblast differentiation without decreasing TGF-β receptor expression.

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.

Effect of Fibrin Glue on Collagen Deposition after Autologous Fascia Grafting in Rabbit Vocal Folds

Objectives:

Fibrin glue (FG) is a reaction product of fibrinogen and thrombin that forms a fibrin clot responsible for tissue adhesion. However, FG and its components may interfere with wound healing by interacting with cytokines such as transforming growth factor–β (TGF-β). The objective of this study was to investigate the effect of FG on collagen deposition after fascia grafting in the vocal folds of rabbits.

Methods:

Eighteen rabbits underwent autologous fascia grafting in both vocal folds, and the left side was fixed with FG. Each animal was painlessly sacrificed after 7, 30, or 90 days. The larynx was removed, and the vocal folds were prepared for histomorphometric analysis by picrosirius red staining to evaluate collagen deposition around the graft.

Results:

There was a significant increase in collagen density around the grafts at 90 days in the vocal folds that were fixed with FG (p = 0.0102) compared with the control vocal folds.

Conclusions:

Application of FG altered collagen deposition around the fascia grafts, leading to significantly increased collagen density after 90 days. Differences found in the composition of the extracellular matrix in later stages of the healing process are a result of changes that occur in the beginning of this process. Therapeutic interventions, such as the use of FG and/or its components, performed in the early stages of wound healing may interfere with the complex interactions of fibroblasts, inflammatory cells, and cytokines (especially TGF-β), thereby modulating the healing process.

Tissue engineering for treatment of vocal fold scar

PURPOSE OF REVIEW

Creating a neovocal fold or lamina propria by tissue engineering is a potential scheme for treating severe vocal fold scar. Although still investigational, multiple approaches have recently been described in tissue culture or animal models.

RECENT FINDINGS

Proposed cell types for vocal fold application have been native vocal fold fibroblasts, autologous fibroblasts from nonlaryngeal tissues, and adult-derived stem cells. Scaffolds of interest include decellularized matrix, biological polymers, and synthetic or chemically modified biopolymers. Chemical, mechanical, and spatial signals have been applied, such as hepatocyte growth factor, cyclic stretch, and air interface. Cells, matrix, and signals are combined in an effort to replicate normal vocal fold tissue as closely as possible. Each of these components of vocal fold tissue engineering is discussed here.

SUMMARY

Multiple tissue engineering approaches hold promise for reproducing functional vocal fold tissue. Scar prevention techniques have been the most successful. Modifying existing scar is more difficult and may necessitate complete scar excision and replacement with a three-dimensional neotissue. Functional assessment in vivo is essential to the ongoing evaluation of techniques.

Implantation of atelocollagen sheet for vocal fold scar

PURPOSE OF REVIEW

This article reviews recent advances in scaffold-based interventions for the treatment of vocal fold scarring, with a particular emphasis on atelocollagen sheet implantation in the vocal fold lamina propria.

RECENT FINDINGS

Scaffold-based therapies have demonstrated therapeutic promise in both preclinical and early clinical studies. Recent research has begun to shed light on the interactions between scaffold material properties, encapsulated and infiltrating cells, stimulatory molecules such as growth factors, and external regulatory variables such as stress, strain, and vibration. The atelocollagen sheet, a cross-linked collagen material with abundant micropores, has an established clinical track record as a scaffold for dermal and epidermal repair and exhibited potential therapeutic benefit in a recent study of patients with vocal fold scarring and sulcus vocalis.

SUMMARY

Scaffolding is one of the useful tools in tissue engineering and atelocollagen sheet implantation has been shown to be effective in vocal fold regeneration. However, many of the scaffold materials under investigation still await clinical translation and those that have been investigated in human patients (such as the atelocollagen sheet) require additional research in appropriately powered placebo-controlled studies.

The effect of mesenchymal stromal cell-hyaluronic acid hydrogel constructs on immunophenotype of macrophages

During the past several years, multipotent mesenchymal stromal cells (MSCs) have rapidly moved from in vitro and animal studies into clinical trials as a therapeutic modality potentially applicable to a wide range of disorders. It has been proposed that ex vivo culture-expanded MSCs exert their tissue regeneration potential through their immunomodulatory and anti-inflammatory properties, and paracrine effects more than their ability to differentiate into multiple tissue lineages. Since extracellular matrix (ECM) deposition and tissue support is also one of many physiological roles of MSCs, there is increasing interest in their potential use for tissue engineering, particularly in combination with ECM-based scaffolds such as hyaluronic acid (HA). We investigated the effect of MSCs on immunophenotype of macrophages in the presence of an HA-hydrogel scaffold using a unique 3D coculture system. MSCs were encapsulated in the hydrogel and peripheral blood CD14+ monocyte-derived macrophages plated in direct contact with the MSC-gel construct. To determine the immunophenotype of macrophages, we looked at the expression of cell surface markers CD14, CD16, CD206, and human leukocyte antigen (HLA)-DR by flow cytometry. MSCs and macrophages cultured on the HA-hydrogel remained viable and were able to be recovered from the construct. There was a significant difference in the immunophenotype observed between monocyte-derived macrophages cultured on the HA scaffold compared to tissue culture polystyrene. Macrophages cultured on gels with MSCs expressed lower CD16 and HLA-DR with higher expression of CD206, indicating the least inflammatory profile overall, compatible with the immunophenotype of alternatively activated macrophages. Development of macrophages, with this immunophenotype, upon interaction with the MSC-hydrogel constructs may play a potentially significant role in tissue repair when using a cellular-biomaterial therapeutic approach.

Biocompatibility of a synthetic extracellular matrix on immortalized vocal fold fibroblasts in 3-D culture

In order to promote wound repair and induce tissue regeneration, an engineered hyaluronan (HA) hydrogel - Carbylan GSX, which contains di(thiopropionyl) bishydrazide-modified hyaluronic acid, di(thiopropionyl) bishydrazide-modified gelatin and polyethylene glycol diacrylate - has been developed for extracellular matrix (ECM) defects of the superficial and middle layers of the lamina propria. The purpose of this study was to evaluate the biocompatibility of Carbylan GSX in a previously established immortalized human vocal fold fibroblast (hVFF) cell line prior to human clinical trials. Immortalized hVFF proliferation, viability, apoptosis and transcript analysis for both ECM constituents and inflammatory markers were measured for two-dimensional and three-dimensional (3-D) culture conditions. There were no significant differences in morphology, cell marker protein expression, proliferation, viability and apoptosis of hVFF cultured with Carbylan GSX compared to Matrigel, a commercial 3-D control, after 1 week. Gene expression levels for fibromodulin, transforming growth factor-beta1 and tumor necrosis factor-alpha were similar between Carbylan GSX and Matrigel. Fibronectin, hyaluronidase 1 and cyclooxygenase II expression levels were induced by Carbylan GSX, whereas interleukins 6 and 8, Col I and hyaluronic acid synthase 3 expression levels were decreased by Carbylan GSX. This investigation demonstrates that Carbylan GSX may serve as a natural biomaterial for tissue-engineering of human vocal folds.

Inhibitory effects of hepatocyte growth factor and interleukin-6 on transforming growth factor-beta1 mediated vocal fold fibroblast-myofibroblast differentiation

OBJECTIVES

The role of myofibroblasts in vocal fold scarring has not been extensively studied, partly because of the lack of a robust in vitro model. The objective of this investigation was to develop and characterize a myofibroblast in vitro model that could be utilized to investigate the molecular mechanism of myofibroblast differentiation and function in injured vocal fold tissue.

METHODS

Differentiation of human primary vocal fold fibroblasts (hVFFs) to myofibroblasts was stimulated with 5, 10, or 20 ng/mL of recombinant transforming growth factor-beta1 (TGF-beta1). Cultures were analyzed by immunofluorescence and Western blotting, with an alpha-smooth muscle actin (alpha-SMA) antibody used as a myofibroblast marker. Normal rabbit vocal folds were treated with 10 ng/mL of TGF-beta1 for 7 days for in vivo corroboration. The effects of interleukin-6 (IL-6) and hepatocyte growth factor (HGF) on myofibroblast differentiation were studied with Western blots.

RESULTS

The hVFFs demonstrated positive alpha-SMA labeling in cells stimulated by 10 and 20 ng/mL TGF-beta1, indicating that hVFFs were capable of differentiation to myofibroblasts. Transforming growth factor-beta1 induced the largest increase in alpha-SMA at 10 ng/mL on day 5 of treatment. Both HGF and IL-6 suppressed the expression of TGF-beta1-induced alpha-SMA.

CONCLUSIONS

Our work characterizes a useful in vitro model of TGF-beta1-mediated vocal fold fibroblast-myofibroblast differentiation. The extent of differentiation appears to be attenuated by HGF, suggesting a potential mechanism to support prior work indicating that HGF plays a protective role in reducing scar formation in vocal fold injuries. Paradoxically, IL-6, which has been shown to play a profibrotic role in dermal studies, also attenuated the TGF-beta1 response.

Injectable hyaluronic acid-dextran hydrogels and effects of implantation in ferret vocal fold

Injectable hydrogels may potentially be used for augmentation/regeneration of the lamina propria of vocal fold tissue. In this study, hyaluronic acid (HA) and dextran were chemically modified and subsequently crosslinked via formation of hydrazone bonds in phosphate buffer. Swelling ratios, degradation, and compressive moduli of the resulting hydrogels were investigated. It was found that the properties of HA-dextran hydrogels were variable and the trend of variation could be correlated with the hydrogel composition. The biocompatibility of three injectable HA-dextran hydrogels with different crosslinking density was assessed in the vocal fold region using a ferret model. It was found that HA-dextran hydrogels implanted for three weeks stimulated mild foreign-body reactions. Distinct tissue-material interactions were also observed for hydrogels made from different formulations: the hydrogel with the lowest crosslinking density was completely degraded in vivo; while material residues were visible for other types of hydrogel injections, with or without cell penetration into the implantation depending on the hydrogel composition. The in vivo results suggest that the HA-dextran hydrogel matrices can be further developed for applications of vocal fold tissue restoration.

In Vivo engineering of the vocal fold ECM with injectable HA hydrogels-late effects on tissue repair and biomechanics in a rabbit model

OBJECTIVES

To determine if the utilization of injectable chemically modified hyaluronan (HA) derivative at the time of intentional vocal fold resection may facilitate wound repair and preserve the unique viscoelastic properties of the extracellular matrix (ECM) and lamina propria 6 months after treatment.

STUDY DESIGN

Prospective, controlled animal study.

METHODS

Twelve rabbit vocal folds were biopsied bilaterally, and the left side of vocal fold was treated with Extracel, an injectable, chemically modified HA derivative, and the right side of vocal fold was injected with saline as control at the time of resection. Animals were sacrificed 6 months after biopsy and injection. Outcomes measured include transcription levels for procollagen, fibronectin, fibromodulin, transforming growth factor beta one (TGF-β1), HA synthase, and hyaluronidase, and tissue biomechanics-viscosity and elasticity.

RESULTS

Extracel-treated vocal folds were found to have significantly less fibrosis than saline-treated controls. Extracel-treated vocal folds had significantly improved biomechanical properties of elasticity and viscosity. Significantly decreased levels of fibronectin, fibromodulin, TGF-β1, procollagen I, and HA synthase were measured.

CONCLUSIONS

Prophylactic in vivo manipulation of the ECM with an injectable HA hydrogel appears to induce vocal fold tissue regeneration to yield improved tissue composition and biomechanical properties at 6 months.

Tissue regeneration of the vocal fold using bone marrow mesenchymal stem cells and synthetic extracellular matrix injections in rats

OBJECTIVES/HYPOTHESIS

To determine the effectiveness of bone marrow mesenchymal stem cell (BM-MSC) transplantation in isolation or within a synthetic extracellular matrix (sECM) for tissue regeneration of the scarred vocal fold lamina propria.

METHODS

In vitro stability and compatibility of mouse BM-MSC embedded in sECM was assessed by flow cytometry detection of BM-MSC marker expression and proliferation. Eighteen rats were subjected to vocal fold injury bilaterally, followed by 1 month post-treatment with unilateral injections of saline or sECM hydrogel (Extracel; Glycosan BioSystems, Inc., Salt Lake City, UT), green fluorescence protein (GFP)-mouse BM-MSC, or BM-MSC suspended in sECM. Outcomes measured 1 month after treatment included procollagen-III, fibronectin, hyaluronan synthase-III (HAS3), hyaluronidase (HYAL3), smooth muscle actin (SMA), and transforming growth factor-beta 1(TGF-beta1) mRNA expression. The persistence of GFP BM-MSC, proliferation, apoptosis, and myofibroblast differentiation was assessed by immunofluorescence.

RESULTS

BM-MSC grown in vitro within sECM express Sca-1, are positive for hyaluronan receptor CD44, and continue to proliferate. In the in vivo study, groups injected with BM-MSC had detectable GFP-labeled BM-MSC remaining and showed proliferation and low apoptotic or myofibroblast markers compared to the contralateral side. Embedded BM-MSC in the sECM group exhibited increased levels of procollagen III, fibronectin, and TGF-beta1. BM-MSC within sECM downregulated the expression of SMA compared to BM-MSC alone and exhibited upregulation of HYAL3 and no change in HAS3 compared to saline.

CONCLUSIONS

Treatment of vocal fold scarring with BM-MSC injected in a sECM displayed the most favorable outcomes in ECM production, hyaluronan metabolism, myofibroblast differentiation, and production of TGF-beta1. Furthermore, the combined treatment had no detectable cytotoxicity and preserved local cell proliferation.

Characterization of mesenchymal stem cells from human vocal fold fibroblasts

OBJECTIVES/HYPOTHESIS

Mesenchymal stem cells (MSCs) originally isolated from bone marrow (BM), are fibroblast-looking cells that are now assumed to be present in the stromal component of many tissues. MSCs are characterized by a certain set of criteria, including their growth culture characteristics, a combination of cell surface markers, and the ability to differentiate along multiple mesenchymal tissue lineages. We hypothesized that human vocal fold fibroblasts (hVFF) isolated from the lamina propria meet the criteria established to define MSCs and are functionally similar to MSCs derived from BM and adipose tissue.

STUDY DESIGN

In vitro study.

METHODS

hVFF were previously derived from human vocal fold tissues. MSCs were derived from adipose tissue (AT), and BM of healthy donors based on their attachment to culture dishes and their morphology and expanded in culture. Cells were analyzed for standard cell surface markers identified on BM-derived MSCs and the ability to differentiate into cells of mesenchymal lineage (i.e., fat, bone, and cartilage). We investigated the immunophenotype of these cells before and after interferon-gamma (INF-gamma) stimulation.

RESULTS

hVFF displayed cell surface markers and multipotent differentiation capacity characteristic of MSCs. Furthermore, these cells exhibited similar patterns of expression of human leukocyte antigen and costimulatory molecules, after stimulation with INF-gamma compared to MSCs derived from BM and AT.

CONCLUSIONS

Based on our findings, hVFF derived from lamina propria have the same cell surface markers, immunophenotypic characteristics, and differentiation potential as BM- and AT-derived MSCs. We propose that vocal fold fibroblasts are MSCs resident in the vocal fold lamina propria.

Novel isolation and biochemical characterization of immortalized fibroblasts for tissue engineering vocal fold lamina propria

Tissue regeneration of the vocal fold lamina propria extracellular matrix (ECM) will be facilitated by the use of suitable vocal fold fibroblast (VFF) cell lines in appropriate model systems. Primary human VFFs (hVFFs) were steadily transduced by a retroviral vector containing human telomerase reverse transcriptase (hTERT) gene; immortalized cells grew and divided vigorously for more than 120 days. Biochemical characterization of the six transduced lines included, at different time points, expression of hTERT, telomerase activity, telomere lengths, and transcript levels of ECM constituents. Telomere lengths of the transfected lines were elongated and stable. Gene expression levels of collagen Ialpha1, collagen Ialpha2, collagen VIalpha3, elastin, and fibronectin were measured between the transduced cell clones and the primary hVFFs to verify transcription. Absence of inter- and intraspecies contamination was confirmed with DNA fingerprinting and karyotype analysis. Cell morphology, growth, and transcription expression were examined on 2D scaffolds-collagen, fibronectin, and hyaluronic acid. Immortalized hVFFs demonstrated normal attachment and spread on 2D scaffolds. Collagen Ialpha1, collagen Ialpha2, collagen VIalpha3, elastin, and fibronectin transcript expression was measured from immortalized hVFFs, for all surfaces. This is the first report of immortalization and biochemical characterization of hVFFs, providing a novel and invaluable tool for tissue regeneration applications in the larynx.

In vivo comparison of biomimetic approaches for tissue regeneration of the scarred vocal fold

The objective of this study was to determine if three different biomimetic approaches could facilitate tissue regeneration and improve viscoelastic properties in the scarred vocal fold lamina propria extracellular matrix (ECM). Twenty rabbit vocal folds were biopsied bilaterally; 2 months postinjury rabbits were unilaterally treated with (i) autologous fibroblasts, (ii) a semisynthetic ECM (sECM), or (iii) autologous fibroblasts encapsulated in sECM. Saline was injected as a control into the contralateral fold. Animals were sacrificed 2 months after treatment. Outcomes measured were procollagen, collagen, and fibronectin levels in the lamina propria, and tissue viscosity and elasticity across three frequency decades. All treatment groups demonstrated accelerated proliferation of the ECM. Vocal fold lamina propria treated with autologous fibroblasts were found to have significantly improved viscosity (p = 0.0077) and elasticity (p = 0.0081) compared to saline. This treatment group had significantly elevated fibronectin levels. sECM and autologous fibroblasts/sECM groups had significantly elevated levels of procollagen, collagen, and fibronectin, indicating abundant matrix production as compared to saline with viscoelastic measures that did not differ statistically from controls. The use of autologous fibroblasts led to better restoration of the vocal fold lamina propria biomechanical properties. Optimization of cell-scaffold interactions and subsequent cell behavior is necessary for utilization of scaffold and scaffold-cell approaches.

Extracellular matrix gene expression during wound healing of the injured rat vocal fold

OBJECTIVES

To measure the expression of procollagen-I and -III, decorin, and hyaluronan synthase (HAS)-1, -2, and -3 during the inflammatory, proliferative, and remodeling phases of rat vocal fold injury.

STUDY DESIGN

Prospective, animal model.

SUBJECTS AND METHODS

Vocal folds were injured in 30 rats. Injured specimens were harvested on postinjury days 1, 3, 7, 14, 28, and 56. Five uninjured rats were used for polymerase chain reaction (PCR) control. Real-time PCR was used to measure the expression of procollagen-I and -III, decorin, and hyaluronan synthase (HAS)-1, -2, and -3.

RESULTS

Compared with control, expression of procollagen-I and -III were significantly decreased on postinjury days 1 and 56; decorin expression was significantly decreased on postinjury days 1, 3, 7, and 56; HAS-1 expression was significantly decreased on postinjury days 3, 7, 14, 28, and 56; HAS-2 expression was significantly decreased on postinjury days 28 and 56; HAS-3 expression was significantly decreased on postinjury day 56.

CONCLUSIONS

Results revealed time-dependent alterations in the expression of genes coding procollagen-I and -III, decorin, and HAS-1, -2, and -3. Knowledge of the temporal regulation of these genes and underlying histology will be used in future studies to investigate molecular approaches for manipulation of vocal fold injury.

Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.

Inflammatory cytokine responses to synthetic extracellular matrix injection to the vocal fold lamina propria

OBJECTIVES

We determined cytokine profiles for tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-6, IL-1alpha, and IL-1beta after injection of a synthetic extracellular matrix into the vocal fold lamina propria.

METHODS

Transcript expression of inflammatory cytokines was measured with real-time polymerase chain reaction on postoperative days 1, 3, 5, 10, and 21 in 25 rabbits that underwent bilateral vocal fold biopsy with Extracel-LG (Carbylan-GSX 5%) immediately injected into the wound in the left vocal fold and saline solution injected into the wound in the right vocal fold. Two unwounded normal rabbit larynges were also harvested for controls.

RESULTS

Significantly elevated levels of TNF-alpha, IL-1beta, and IL-6 were measured on day 3 in a comparison between Extracel-LG-injected vocal folds and saline solution-injected control vocal folds and between Extracel-LG-injected vocal folds and normal vocal folds. All cytokine levels returned to baseline by day 21.

CONCLUSIONS

A mild short-term inflammatory response was measured early after injection of a synthetic extracellular matrix into the vocal fold lamina propria.

Modular extracellular matrices: solutions for the puzzle

The common technique of growing cells in two-dimensions (2-D) is gradually being replaced by culturing cells on matrices with more appropriate composition and stiffness, or by encapsulation of cells in three-dimensions (3-D). The universal acceptance of the new 3-D paradigm has been constrained by the absence of a commercially available, biocompatible material that offers ease of use, experimental flexibility, and a seamless transition from in vitro to in vivo applications. The challenge-the puzzle that needs a solution-is to replicate the complexity of the native extracellular matrix (ECM) environment with the minimum number of components necessary to allow cells to rebuild and replicate a given tissue. For use in drug discovery, toxicology, cell banking, and ultimately in reparative medicine, the ideal matrix would therefore need to be highly reproducible, manufacturable, approvable, and affordable. Herein we describe the development of a set of modular components that can be assembled into biomimetic materials that meet these requirements. These semi-synthetic ECMs, or sECMs, are based on hyaluronan derivatives that form covalently crosslinked, biodegradable hydrogels suitable for 3-D culture of primary and stem cells in vitro, and for tissue formation in vivo. The sECMs can be engineered to provide appropriate biological cues needed to recapitulate the complexity of a given ECM environment. Specific applications for different sECM compositions include stem cell expansion with control of differentiation, scar-free wound healing, growth factor delivery, cell delivery for osteochondral defect and liver repair, and development of vascularized tumor xenografts for personalized chemotherapy.