Effects of Growth Factors on Extracellular Matrix Production by Vocal Fold Fibroblasts in 3-Dimensional Culture

Elastogenesis in Focus: Navigating Elastic Fibers Synthesis for Advanced Dermal Biomaterial Formulation

Elastin, a fibrous extracellular matrix (ECM) protein, is the main component of elastic fibers that are involved in tissues' elasticity and resilience, enabling them to undergo reversible extensibility and to endure repetitive mechanical stress. After wounding, it is challenging to regenerate elastic fibers and biomaterials developed thus far have struggled to induce its biosynthesis. This review provides a comprehensive summary of elastic fibers synthesis at the cellular level and its implications for biomaterial formulation, with a particular focus on dermal substitutes. The review delves into the intricate process of elastogenesis by cells and investigates potential triggers for elastogenesis encompassing elastin-related compounds, ECM components, and other molecules for their potential role in inducing elastin formation. Understanding of the elastogenic processes is essential for developing biomaterials that trigger not only the synthesis of the elastin protein, but also the formation of a functional and branched elastic fiber network.

Drug delivery systems for wound healing treatment of upper airway injury

INTRODUCTION

Endotracheal intubation is a common procedure to maintain an open airway with risks for traumatic injury. Pathological changes resulting from intubation can cause upper airway complications, including vocal fold scarring, laryngotracheal stenosis, and granulomas and present with symptoms such as dysphonia, dysphagia, and dyspnea. Current intubation-related laryngotracheal injury treatment approaches lack standardized guidelines, relying on individual clinician experience, and surgical and medical interventions have limitations and carry risks.

AREAS COVERED

The clinical and preclinical therapeutics for wound healing in the upper airway are described. This review discusses the current developments on local drug delivery systems in the upper airway utilizing particle-based delivery systems, including nanoparticles and microparticles, and bulk-based delivery systems, encompassing hydrogels and polymer-based approaches.

EXPERT OPINION

Complex laryngotracheal diseases pose challenges for effective treatment, struggling due to the intricate anatomy, limited access, and recurrence. Symptomatic management often requires invasive surgical procedures or medications that are unable to achieve lasting effects. Recent advances in nanotechnology and biocompatible materials provide potential solutions, enabling precise drug delivery, personalization, and extended treatment efficacy. Combining these technologies could lead to groundbreaking treatments for upper airways diseases, significantly improving patients' quality of life. Research and innovation in this field are crucial for further advancements.

Hyaluronic Acid/Alginate Hydrogel Containing Hepatocyte Growth Factor and Promotion of Vocal Fold Wound Healing

BACKGROUND

Hepatocyte growth factor (HGF) has been shown to facilitate vocal fold (VF) wound healing. This study was undertaken to determine whether the therapeutic efficacy of HGF could be enhanced by applying it in hyaluronic acid and alginate (HA/ALG) composite hydrogels into VFs after injury in a rabbit model.

METHODS

HGF was loaded into HA/ALG composite hydrogel (HGF-HA/ALG) and its in vitro release profile was evaluated. In addition, HGF-HA/ALG was injected into the VFs of rabbits immediately after direct injury and HGF or PBS was injected in the same manner into control groups. Macroscopic features were observed by endoscopy at 3 months post-injury. Functional analyses including mucosal waves of VFs and viscoelastic properties were performed by kymography following high-speed digital imaging and rheometer. Histopathological and immunohistochemical evaluations were also conducted on VFs.

RESULTS

HGF release from HGF-HA/ALG was sustained for up to 3 weeks. Rabbits treated with HGF-HA/ALG showed improved mucosal vibrations and VF viscoelastic properties as compared with the PBS and HGF controls. Histopathological staining revealed HGF-HA/ALG treated VFs showed less fibrosis than PBS and HGF controls, and immunohistochemical analysis demonstrated amounts of type I collagen and fibronectin were lower in HGF-HA/ALG treated animals than in PBS and HGF controls at 3 months post-injury.

CONCLUSION

HGF containing HA/ALG hydrogel enhanced healing in our rabbit model of VF injury.

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.

Methodology for the establishment of primary porcine vocal fold epithelial cell cultures

OBJECTIVE

A current lack of methods for epithelial cell culture significantly hinders our understanding of the role of the epithelial and mucus barriers in vocal fold health and disease. Our first objective was to establish reproducible techniques for the isolation and culture of primary porcine vocal fold epithelial cells. Our second objective was to evaluate the functional significance of cell cultures using an in vitro exposure to an inflammatory cytokine.

METHODS

Epithelial cells were isolated from porcine vocal folds and expanded in culture. Characterization of cultures was completed by immunostaining with markers for pan-cytokeratin (epithelial cells), vimentin (stromal cells), von Willebrand factor (endothelial cell), and MUC1 and MUC4 (mucin) glycoproteins. Established epithelial cell cultures were then exposed to the inflammatory cytokine tumor necrosis factor alpha (TNF-α) for 24-hours, and transcript expression of MUC1 and MUC4 was evaluated.

RESULTS

Reproducible, porcine vocal fold epithelial cell cultures, demonstrating cobblestone appearance characteristic of the typical morphology of epithelial cell cultures were created. Cells showed positive staining for pan-cytokeratin with limited expression of vimentin and von Willebrand factor. Epithelial cells also expressed MUC1 and MUC4. TNF-α significantly increased transcript expression of MUC4.

CONCLUSION

Here, we present the first report of successful culture of primary porcine vocal fold epithelial cells. Cultures will provide researchers with a valuable new in vitro tool to investigate vocal fold epithelium and mucus as well as the effects of common challenges, including inflammatory cytokines, on these barriers.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:E355-E364, 2019.

Dual growth factor-immobilized bioactive injection material for enhanced treatment of glottal insufficiency

With increasing demand for treatment of glottal insufficiency, several injection materials have been examined. However, biological resorption, degradation of injected materials, and the subsequent need to perform multiple injections still remain major clinical problems. In this study, we fabricated two different growth factor (GF) [single basic fibroblast growth factor (bFGF), single hepatocyte growth factor (HGF), or dual bFGF/HGF]-immobilized polycaprolactone (PCL)/Pluronic F127 microspheres. These materials were investigated for their potential use as bioactive injection laryngoplasty agents. HGF was found to be continuously released over 20 days and the bFGF was found to be continuously released over 25 days, as demonstrated by ELISA assay. Human vocal fold fibroblasts (hVFFs) showed significantly higher proliferative ability on dual GF-immobilized microspheres. GF-immobilized microspheres (bFGF, HGF, and dual GF) were injected into paralyzed vocal folds of New Zealand white rabbits. Through endoscopic observation and H&E staining, we identified that the microspheres remained localized at the injection site, resulting in constant volume augmentation of the paralyzed vocal fold without significant loss of the initial volume after 4 weeks. The expression of genes related to the extracellular matrix (ECM) in the vocal fold was upregulated by dual GF-immobilized microspheres. Furthermore, dual GF-immobilized microspheres inhibited muscle degeneration and upregulation of myogenic-related genes. In conclusion, dual GF-immobilized microspheres passively augmented the volume of the paralyzed vocal fold while actively inducing ECM synthesis at the injected vocal fold and preserving muscle tissue. Dual GF-immobilized microspheres could be a new and promising injection material for paralyzed vocal folds. STATEMENT OF SIGNIFICANCE: Limitation of prolonged augmentation of vocal fold and degeneration of vocal fold tissue still remain as major clinical problems in the treatment of vocal fold paralysis. Herein, we fabricated the polycaprolactone (PCL)/Pluronic F127 microspheres to augment volume of paralyzed vocal folds. On top of that, we additionally immobilized the growth factors (bFGF, HGF, or dual bFGF/HGF) on the surface of these microspheres. We highlight the efficacy of the dual GF-immobilized microspheres which augmented the volume of the paralyzed vocal fold passively, induced ECM synthesis actively at the injected vocal fold and preserved laryngeal muscle tissue. Our results suggest that the dual GF-immobilized microsphere could be a new promising injection material for injection laryngoplasty to treat paralyzed vocal fold.

The Effect of Fibroblast Growth Factors in Grafted Fascia into the Vocal Fold of Rabbits

Introduction  The human larynx is a very important organ for communication. Many conditions lead to scarring of the vocal folds, decreasing voice quality. Objective  We aimed to determine whether fibroblast growth factors (FGFs) may influence tissue integration of grafted fascia into the vocal folds of an animal model. Methods  This is an experimental animal study with 12 adult rabbits that were submitted to a grafting fragment obtained from superficial cervical fascia into the vocal fold lamina propria, bilaterally. The right vocal fold was injected with FGFs. The animals were sacrificed after 1 month or 12 months, depending on the group they were assigned to, and a histological analysis of their vocal folds was performed. We analyzed the histological changes (such as the presence of fibrosis and neovascularization) induced by the acute or chronic inflammatory reactions. Results  The FGFs induced acute inflammatory changes in all animals after 1 month of the initial experiment. The presence of FGFs triggered more fibrosis than the expected due to the surgical procedure itself when compared with the control side of all animals after 12 months of the initial experiment. Conclusions  Fibroblast growth factors alone do not represent a good therapeutic option in phonosurgery, since we observed higher levels of fibrosis in the vocal fold lamina propria. Further studies combining more substances may be necessary to elucidate the best option to be used in this kind of surgery.

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.

Evaluation of the Grafted Fascia in the Vocal Fold of Dogs: A Histologic Study

INTRODUCTION

There is no consensus on the ideal graft for medialization surgery of the vocal folds in the literature. One of the most favorable proposals is the use of autologous fascia, which seems limited by the lack of information regarding the integration of grafted tissue. Our study aims to evaluate the degree of fully engrafted fascia integration in the vocal fold lamina propria of dogs.

MATERIALS AND METHODS

Fourteen adult mongrel dogs that underwent intravenous general anesthesia were selected and kept under spontaneous ventilation. A fascia lata fragment of 4 cm² was obtained from the right leg of each dog. The dogs underwent laryngoscopy; a 3 mm incision was made in the vocal process, next to the vestibular process, and the fascia was grafted into the right vocal fold. The left vocal fold was used as a control. The animals were divided into two groups: group A, evaluated after 2 months of the procedure, and group B, evaluated after 6 months of the procedure. Histologic analysis was made semiquantitatively regarding the presence of inflammatory reaction, fibrosis, and neovascularization.

RESULTS

Our final studied group comprised 12 dogs. Microscopic examination of the larynx revealed the absence of any detectable inflammation in the incision site. The lamina propria of the grafted vocal fold showed identifiable compact, thick, and eosinophilic collagen bands. The surrounding tissue showed thin collagen bands with some organization, similar to the contralateral vocal fold.

CONCLUSION

The grafted fascia integrates into the vocal fold lamina propria and seems not to cause inflammatory reaction response.

Cogels of Hyaluronic Acid and Acellular Matrix for Cultivation of Adipose-Derived Stem Cells: Potential Application for Vocal Fold Tissue Engineering

Stem cells based tissue engineering has been one of the potential promising therapies in the research on the repair of tissue diseases including the vocal fold. Decellularized extracellular matrix (DCM) as a promising scaffold has be used widely in tissue engineering; however, it remained to be an important issue in vocal fold regeneration. Here, we applied the hydrogels (hyaluronic acid [HA], HA-collagen [HA-Col], and HA-DCM) to determine the effects of hydrogel on the growth and differentiation of human adipose-derived stem cells (hADSCs) into superficial lamina propria fibroblasts. hADSCs were isolated and characterized by fluorescence-activated cell sorting. The results indicated that HA-DCM hydrogel enhanced cell proliferation and prolonged cell morphology significantly compared to HA and HA-Col hydrogel. Importantly, the differentiation of hADSCs into fibroblasts was also promoted by cogels of HA-Col and HA-DCM significantly. The differentiation of hADSCs towards superficial lamina propria fibroblasts was accelerated by the secretion of HGF, IL-8, and VEGF, the decorin and elastin expression, and the synthesis of chondroitin sulfate significantly. Therefore, the cogel of HA-DCM hydrogel was shown to be outstanding in apparent stimulation of hADSCs proliferation and differentiation to vocal fold fibroblasts through secretion of important growth factors and synthesis of extracellular matrix.

Functional remodeling after vocal fold injury by small intestinal submucosa gel containing hepatocyte growth factor

A biomaterial derived from porcine small intestinal submucosa (SIS) was used in smart drug delivery and tissue remodeling. SIS suspensions were easily formulated by simple mixing with the drug of choice and formed an in situ gel upon injection into tissues, enabling them to act as protein drug depots. This study was conducted to determine whether functional remodeling of an injured vocal fold (VF) could be achieved by hepatocyte growth factor (HGF)-containing SIS in situ-forming gel after VF injury in a rabbit model. To accomplish this, we loaded HGF in SIS suspensions and observed a gradual, sustained release of HGF for at least 21 days in vitro. Evaluation of the in vivo efficacy demonstrated that the HGF and HGF-loaded SIS treated VFs showed improved mucosal healing when compared with the PBS-injected VFs. Histopathological evaluations revealed that treatment with the HGF/SIS group alone successfully ameliorated the deposition of type I collagen and increased synthesis of hyaluronic acids relative to the PBS group at three months post-injury. Functional analyses showed that the HGF/SIS group prevented deterioration of mucosal vibration and induced significant improvement in the mean viscoelastic modulus, but that other groups failed to achieve functional rescue of VF biomechanics. Additionally, the VF oscillation in the HGF/SIS group was superior to that in the HGF group. The results of this study suggest that SIS in situ gel has the potential for use as an HGF delivery carrier for enhancement of wound healing and improvement of functional remodeling following VF injury.

Microbead-based biomimetic synthetic neighbors enhance survival and function of rat pancreatic β-cells

Diabetes is caused by the loss or dysfunction of insulin-secreting β-cells in the pancreas. β-cells reduce their mass and lose insulin-producing ability in vitro, likely due to insufficient cell-cell and cell-extracellular matrix (ECM) interactions as β-cells lose their native microenvironment. Herein, we built an ex-vivo cell microenvironment by culturing primary β-cells in direct contact with ‘synthetic neighbors', cell-sized soft polymer microbeads that were modified with cell-cell signaling factors as well as components from pancreatic-tissue-specific ECMs. This biomimetic 3D microenvironment was able to promote native cell-cell and cell-ECM interactions. We obtained sustained maintenance of β-cell function in vitro enhanced cell viability from the few days usually observed in 2D culture to periods exceeding three weeks, with enhanced β-cell stability and insulin production. Our approach can be extended to create a general 3D culture platform for other cell types.

A cytokine axis regulates elastin formation and degradation

Underlying the dynamic regulation of tropoelastin expression and elastin formation in development and disease are transcriptional and post-transcriptional mechanisms that have been the focus of much research. Of particular importance is the cytokine-governed elastin regulatory axis in which the pro-elastogenic activities of transforming growth factor β-1 (TGFβ1) and insulin-like growth factor-I (IGF-I) are opposed by anti-elastogenic activities of basic fibroblast growth factor (bFGF/FGF-2), heparin-binding epidermal growth factor-like growth factor (HB-EGF), EGF, PDGF-BB, TGFα, tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β and noncanonical TGFβ1 signaling. A key mechanistic feature of the regulatory axis is that cytokines influence elastin formation through effects on the cell cycle involving control of cyclin-cyclin dependent kinase complexes and activation of the Ras/MEK/ERK signaling pathway. In this article we provide an overview of the major cytokines/growth factors that modulate elastogenesis and describe the underlying molecular mechanisms for their action on elastin production.

Regulation of wound healing by granulocyte-macrophage colony-stimulating factor after vocal fold injury

Objectives

Vocal fold (VF) scarring remains a therapeutic challenge. Granulocyte-macrophage colony-stimulating factor (GM-CSF) facilitates epithelial wound healing, and recently, growth factor therapy has been applied to promote tissue repair. This study was undertaken to investigate the effect of GM-CSF on VF wound healing in vivo and in vitro.

Methods

VF scarring was induced in New Zealand white rabbits by direct injury. Immediately thereafter, either GM-CSF or PBS was injected into the VFs of rabbits. Endoscopic, histopathological, immunohistochemical, and biomechanical evaluations of VFs were performed at 3 months post-injury. Human vocal fold fibroblasts (hVFFs) were cultured with GM-CSF. Production of type I and III collagen was examined immunocytochemically, and the synthesis of elastin and hyaluronic acids was evaluated by ELISA. The mRNA levels of genes related to ECM components and ECM production-related growth factors, such as HGF and TGF-ß1, were examined by real time RT-PCR.

Results

The GM-CSF-treated VFs showed reduced collagen deposition in comparison to the PBS-injected controls (P<0.05). Immunohistochemical staining revealed lower amounts of type I collagen and fibronectin in the GM-CSF-treated VFs (P<0.05 and P<0.01, respectively). Viscous and elastic shear moduli of VF samples were significantly lower in the GM-CSF group than in the PBS-injected group (P<0.001 and P<0.01, respectively). Mucosal waves in the GM-CSF group showed significant improvement when compared to the PBS group (P = 0.0446). GM-CSF inhibited TGF-β1-induced collagen synthesis by hVFFs (P<0.05) and the production of hyaluronic acids increased at 72 hours post-treatment (P<0.05). The expressions of HAS-2, tropoelastin, MMP-1, HGF, and c-Met mRNA were significantly increased by GM-CSF, although at different time points (P<0.05).

Conclusion

The present study shows that GM-CSF offers therapeutic potential for the remodeling of VF wounds and the promotion of VF regeneration.

Advances in biomimetic regeneration of elastic matrix structures

Elastin is a vital component of the extracellular matrix, providing soft connective tissues with the property of elastic recoil following deformation and regulating the cellular response via biomechanical transduction to maintain tissue homeostasis. The limited ability of most adult cells to synthesize elastin precursors and assemble them into mature crosslinked structures has hindered the development of functional tissue-engineered constructs that exhibit the structure and biomechanics of normal native elastic tissues in the body. In diseased tissues, the chronic overexpression of proteolytic enzymes can cause significant matrix degradation, to further limit the accumulation and quality (e.g., fiber formation) of newly deposited elastic matrix. This review provides an overview of the role and importance of elastin and elastic matrix in soft tissues, the challenges to elastic matrix generation in vitro and to regenerative elastic matrix repair in vivo, current biomolecular strategies to enhance elastin deposition and matrix assembly, and the need to concurrently inhibit proteolytic matrix disruption for improving the quantity and quality of elastogenesis. The review further presents biomaterial-based options using scaffolds and nanocarriers for spatio-temporal control over the presentation and release of these biomolecules, to enable biomimetic assembly of clinically relevant native elastic matrix-like superstructures. Finally, this review provides an overview of recent advances and prospects for the application of these strategies to regenerating tissue-type specific elastic matrix structures and superstructures.

Using growth factor conditioning to modify the properties of human cell derived extracellular matrix

We have recently reported on a bench-top approach for isolating extracellular matrix (ECM) from pure populations of cells grown in culture using sacrificial, open-celled foams to concentrate and capture the ECM. To increase both the accumulation and the strength of the ECM harvested, cell-seeded polyurethane (PU) foams were cultured in media supplemented with either transforming growth factor β-1 (TGFβ1) or hepatocyte growth factor (HGF). At the end of a 3-week culture period, ECM yield was significantly increased for samples conditioned in supplemented media. Control foams yielded 48 ± 12 mg of material for every gram of PU foam seeded. Yield values increased to 102 ± 21 and 243 ± 25 mg for HGF and TGFβ1-treated samples, respectively. HGF supplementation increased the modulus by 59%, while TGFβ1 treatment increased the elastic modulus by 204%. TGFβ1-stimulated material was organized into a network that was markedly denser than control material, with HGF-stimulated network density intermediate to TGFβ1 and controls. Our study showed that TGFβ1-treated samples were collagen enriched while HGF samples had an increased gylcosaminoglycan concentration. The results demonstrate that growth factor supplementation, particularly with TGFβ1, can significantly alter the biomechanical properties of cell-derived ECM that may be used for therapeutic applications.

Regenerative medicine of the larynx. Where are we today? A review

Tissue engineering is a multidimensional process combining cells, scaffold matrices, and chemical signals to produce a structure similar to a target tissue. These techniques have opened a completely new field in diagnosis and therapy in numerous fields, including that of laryngology. Laryngeal tissue engineering has emerged in the last decade, although clinical applications are rare. The reasons therefore are numerous including ethical reasons, as well as the extremely complex anatomical structure of the vocal fold. The search for new treatment options has also enlarged our knowledge about the microphysiology and micropathophysiology of the vocal fold. To date, only specific growth factors are in clinical use for treatment of vocal fold atrophy. Big advances have been made in creating state-of-the-art scaffolds with various techniques including biomaterials as well as fully synthetic polymers. These scaffolds are supposed to provide an optimal environment for residual or implanted cells. Several in vitro settings showed practicability of these scaffolds, also in studying effects of growth factors. Cell therapy is a powerful tool in regenerative medicine but bears the uncertainty of possible malignant transformation. The aim of this review was to give a comprehensive overview about current knowledge in the field of laryngeal tissue engineering and regenerative medicine, including restoration of both vocal folds and laryngeal cartilage, and furthermore to elucidate further trends in this fascinating field.

Engineering airway epithelium

Airway epithelium is constantly presented with injurious signals, yet under healthy circumstances, the epithelium maintains its innate immune barrier and mucociliary elevator function. This suggests that airway epithelium has regenerative potential (I. R. Telford and C. F. Bridgman, 1990). In practice, however, airway regeneration is problematic because of slow turnover and dedifferentiation of epithelium thereby hindering regeneration and increasing time necessary for full maturation and function. Based on the anatomy and biology of the airway epithelium, a variety of tissue engineering tools available could be utilized to overcome the barriers currently seen in airway epithelial generation. This paper describes the structure, function, and repair mechanisms in native epithelium and highlights specific and manipulatable tissue engineering signals that could be of great use in the creation of artificial airway epithelium.

Biosimulation of acute phonotrauma: an extended model

OBJECTIVES/HYPOTHESIS

Personalized, preemptive, and predictive medicine is a central goal of contemporary medical care. The central aim of the present study was to investigate the utility of mechanistic computational modeling of inflammation and healing to address personalized therapy for patients with acute phonotrauma.

STUDY DESIGN

Computer simulation.

METHODS

Previously reported agent-based models (ABMs) of acute phonotrauma were extended with additional inflammatory mediators as well as extracellular matrix components. The models were calibrated with empirical data for a panel of biomarkers--interleukin (IL)-1β, IL-6, IL-8, IL-10, tumor necrosis factor-α and matrix metalloproteinase-8--from individual subjects following experimentally induced phonotrauma and a randomly assigned voice treatment namely voice rest, resonant voice exercise, and spontaneous speech. The models' prediction accuracy for biomarker levels was tested for a 24-hour follow-up time point.

RESULTS

The extended ABMs reproduced and predicted trajectories of biomarkers seen in experimental data. The simulation results also agreed qualitatively with various known aspects of inflammation and healing. Model prediction accuracy was generally better following individual-based calibration as compared to population-based calibration. Simulation results also suggested that the special form of vocal fold oscillation in resonant voice may accelerate acute vocal fold healing.

CONCLUSIONS

The calibration of inflammation/healing ABMs with subject-specific data appears to optimize the models' prediction accuracy for individual subjects. This translational application of biosimulation might be used to predict individual healing trajectories, the potential effects of different treatment options, and most importantly, provide new understanding of health and healing in the larynx and possibly in other organs and tissues as well.

Influence of glycosaminoglycan identity on vocal fold fibroblast behavior

Poly(ethylene glycol) (PEG) hydrogels have recently begun to be studied for the treatment of scarred vocal fold lamina propria due, in part, to their tunable mechanical properties, resistance to fibroblast-mediated contraction, and ability to be polymerized in situ. However, pure PEG gels lack intrinsic biochemical signals to guide cell behavior and generally fail to mimic the frequency-dependent viscoelastic response critical to normal superficial lamina propria function. Recent results suggest that incorporation of viscoelastic bioactive substances, such as glycosaminoglycans (GAGs), into PEG networks may allow these gels to more closely approach the mechanical responses of normal vocal fold lamina propria while also stimulating desired vocal fold fibroblast behaviors. Although a number of vocal fold studies have examined the influence of hyaluronan (HA) on implant mechanics and vocal fold fibroblast responses, the effects of other GAG types have been relatively unexplored. This is significant, since recent studies have suggested that chondroitin sulfate C (CSC) and heparan sulfate (HS) are substantially altered in scarred lamina propria. The present study was therefore designed to evaluate the effects of CSC and HS incorporation on the mechanical response of PEG gels and vocal fold fibroblast behavior relative to HA. As with PEG-HA, the viscoelasticity of PEG-CSC and PEG-HS gels more closely approached that of the normal vocal fold lamina propria than pure PEG hydrogels. In addition, collagen I deposition and fibronectin production were significantly higher in CSC than in HA gels, and levels of the myofibroblast marker smooth muscle α-actin (SM α-actin) were greater in CSC and HS gels than in HA gels. Since collagen I, fibronectin, and SM α-actin are generally elevated in scarred lamina propria these results suggest that CSC and HS may be undesirable for vocal fold implants relative to HA. Investigation of various signaling intermediates indicated that alterations in NFκB-p50, NFκB-p65, or pERK1/2 levels may underlie the observed differences among the PEG-GAG gels.

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.

Prospective multi-arm evaluation of surgical treatments for vocal fold scar and pathologic sulcus vocalis

OBJECTIVES/HYPOTHESIS

The purpose of this study was to compare the clinical effectiveness of type I thyroplasty, injection laryngoplasty, and graft implantation for the treatment of vocal fold scar and pathologic sulcus vocalis.

STUDY DESIGN

Prospective, multi-arm, quasi-experimental research design.

METHODS

Twenty-eight patients with newly diagnosed vocal fold scar and/or pathologic sulcus vocalis were assigned to one of three treatment modalities: type I thyroplasty (n = 9), injection laryngoplasty (n = 9), and graft implantation (n = 10). Psychosocial, auditory-perceptual, acoustic, aerodynamic, and videostroboscopic data were collected pretreatment and at 1, 6, 12, and 18 months posttreatment.

RESULTS

Type I thyroplasty and graft implantation both resulted in reduced voice handicap with no concomitant improvement in auditory-perceptual, acoustic, aerodynamic, or vocal fold physiologic performance. Injection laryngoplasty resulted in no improvement on any vocal function index. Patients who underwent graft implantation exhibited the slowest improvement trajectory across the 18-month follow-up period.

CONCLUSIONS

A persistent challenge in this area is that no single treatment modality is successful for the majority of patients, and there is no evidence-based decision algorithm for matching a given treatment to a given patient. Progress therefore requires the identification and categorization of predictive clinical features that can drive evidence-based treatment assignment.

Regulation of smooth muscle cell phenotype by glycosaminoglycan identity

The retention of lipoproteins in the arterial intima is an initial event in early atherosclerosis and occurs, in part, through interactions between negatively charged glycosaminoglycans (GAGs) and the positively charged residues of apolipoproteins. Smooth muscle cells (SMCs) which infiltrate into the lipoprotein-enriched intima have been observed to transform into lipid-laden foam cells. This phenotypic switch is associated with SMC acquisition of a macrophage-like capacity to phagocytose lipoproteins and/or of an adipocyte-like capacity to synthesize fatty acids de novo. The aim of the present work was to explore the impact of GAG identity on SMC foam cell formation using a scaffold environment intended to be mimetic of early atherosclerosis. In these studies, we focused on chondroitin sulfate C (CSC), dermatan sulfate (DS), and an intermediate molecular weight hyaluronan (HAIMW, ∼400 kDa), the levels and/or distribution of each of which are significantly altered in atherosclerosis. DS hydrogels were associated with greater SMC phagocytosis of apolipoprotein B than HAIMW gels. Similarly, only SMCs in DS constructs maintained increased expression of the adipocyte marker A-FABP relative to HAIMW gels over 35 days of culture. The increased SMC foam cell phenotype in DS hydrogels was reflected in a corresponding decrease in SMC myosin heavy chain expression in these constructs relative to HAIMW gels at day 35. In addition, this DS-associated increase in foam cell formation was mirrored in an increased SMC synthetic phenotype, as evidenced by greater levels of collagen type I and glucose 6-phosphate dehydrogenase in DS gels than in HAIMW gels. Combined, these results support the increasing body of literature that suggests a critical role for DS-bearing proteoglycans in early atherosclerosis.

The isolation of cell derived extracellular matrix constructs using sacrificial open-cell foams

Extracellular matrix derived from human and animal tissues is being used to repair and reconstruct a variety of tissues clinically. The utility of such constructs is limited by the geometry, composition and constitutive properties of the tissue or organ from which the ECM is harvested. To address this limitation, we have developed an approach to isolate extracellular matrix in bulk from populations of living cells grown in culture on three-dimensional substrates. Human biopsy derived fibroblasts were seeded within open-cell foams and cultured in-vitro for periods up to three weeks, after which the synthetic component was removed by incubation in a water miscible solvent. After several wash steps and lyophilization, a white, lacy, multi-molecular construct was isolated. Tandem mass spectroscopy showed that it contained 22 extracellular matrix constituents, including such proteins and proteoglycans as collagen type I and type III, fibronectin, transforming growth factor beta, decorin and biglycan among others. On average 47 mg of construct was isolated for each gram of synthetic substrate initially seeded with cells. The biomaterial harvested from human tracheal fibroblasts had an elastic modulus (250 kPa) and a composition similar to that of human vocal fold tissue, and supported reseeding with human tracheal derived fibroblasts. An important finding was that the approach was useful in isolating ECM from a variety of cell lineages and developmental stages including skin fibroblasts, brain derived astrocytes and mesenchymal stem cells. The results, together with the archival literature, suggest that the approach can be used to produce a range of cell derived constructs with unique physical and chemical attributes for a variety of research and medical applications.

Simple and high yielding method for preparing tissue specific extracellular matrix coatings for cell culture

BACKGROUND

The native extracellular matrix (ECM) consists of a highly complex, tissue-specific network of proteins and polysaccharides, which help regulate many cellular functions. Despite the complex nature of the ECM, in vitro cell-based studies traditionally assess cell behavior on single ECM component substrates, which do not adequately mimic the in vivo extracellular milieu.

METHODOLOGY/PRINCIPAL FINDINGS

We present a simple approach for developing naturally derived ECM coatings for cell culture that provide important tissue-specific cues unlike traditional cell culture coatings, thereby enabling the maturation of committed C2C12 skeletal myoblast progenitors and human embryonic stem cells differentiated into cardiomyocytes. Here we show that natural muscle-specific coatings can (i) be derived from decellularized, solubilized adult porcine muscle, (ii) contain a complex mixture of ECM components including polysaccharides, (iii) adsorb onto tissue culture plastic and (iv) promote cell maturation of committed muscle progenitor and stem cells.

CONCLUSIONS

This versatile method can create tissue-specific ECM coatings, which offer a promising platform for cell culture to more closely mimic the mature in vivo ECM microenvironment.

Biosimulation of inflammation and healing in surgically injured vocal folds

OBJECTIVES

The pathogenesis of vocal fold scarring is complex and remains to be deciphered. The current study is part of research endeavors aimed at applying systems biology approaches to address the complex biological processes involved in the pathogenesis of vocal fold scarring and other lesions affecting the larynx.

METHODS

We developed a computational agent-based model (ABM) to quantitatively characterize multiple cellular and molecular interactions involved in inflammation and healing in vocal fold mucosa after surgical trauma. The ABM was calibrated with empirical data on inflammatory mediators (eg, tumor necrosis factor) and extracellular matrix components (eg, hyaluronan) from published studies on surgical vocal fold injury in the rat population.

RESULTS

The simulation results reproduced and predicted trajectories seen in the empirical data from the animals. Moreover, the ABM studies suggested that hyaluronan fragments might be the clinical surrogate of tissue damage, a key variable that in these simulations both is enhanced by and further induces inflammation.

CONCLUSIONS

A relatively simple ABM such as the one reported in this study can provide new understanding of laryngeal wound healing and generate working hypotheses for further wet-lab studies.

Effects of matrix composition, microstructure, and viscoelasticity on the behaviors of vocal fold fibroblasts cultured in three-dimensional hydrogel networks

Vocal fold diseases and disorders are difficult to treat surgically or therapeutically. Tissue engineering offers an alternative strategy for the restoration of functional vocal folds. As a first step toward vocal fold tissue engineering, we investigated the responses of primary vocal fold fibroblasts (PVFFs) to two types of collagen and hyaluronic acid (HA)-based hydrogels that are compositionally similar, but structurally variable and mechanically different. Type A hydrogels were composed of mature collagen fibers reinforced by oxidized HA, whereas type B hydrogels contained immature collagen fibrils interpenetrated in an amorphous, covalently cross-linked HA matrix. PVFFs encapsulated in either matrix adopted a fibroblastic morphology and expressed genes related to important extracellular matrix proteins. DNA analysis indicated a linear growth profile for cells encapsulated in type B gels from day 0 to 21, in contrast to an initial dormant, nonproliferative period from day 0 to 3 experienced by cells in type A gels. At the end of the culture, similar DNA content was detected in both types of constructs. A reduction in collagen content was observed for both types of constructs after 28 days of culture, with type A constructs generally retaining higher amounts of collagen than type B constructs. The HA content in the constructs decreased steadily throughout the culture, with type A constructs consistently exhibiting less HA than type B constructs. Using the torsional wave analysis, we found that the elastic moduli for type A constructs decreased sharply during the first week of culture, followed by 2 weeks of matrix stabilization without significant changes in matrix stiffness. Conversely, the elastic modulus for type B constructs increased moderately over time. It is postulated that PVFFs residing in gels alter the matrix organization, chemical compositions, and viscoelasticity through cell-mediated remodeling processes.

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.

Epithelial differentiation of adipose-derived stem cells for laryngeal tissue engineering

OBJECTIVES/HYPOTHESIS

One potential treatment option for severe vocal fold scarring is to replace the vocal fold cover layer with a tissue-engineered structure containing autologous cells. As a first step toward that goal, we sought to develop a three-dimensional cell-populated matrix resembling the vocal fold layers of lamina propria and epithelium.

STUDY DESIGN

Basic science investigation.

METHODS

Adipose-derived stem cells were cultured in fibrin hydrogels with various growth factors. At the end of the culture period, matrices were sectioned and labeled with immunomarkers to identify cell phenotype.

RESULTS

Adipose-derived stem cells survived, attached, and populated three-dimensional fibrin matrices. Under select conditions, a superficial layer of cells expressing epithelial marker proteins overlay a deeper mesenchymal cell layer.

CONCLUSIONS

A three-dimensional structure of fibrin and adipose-derived stem cells was created as a prototype vocal fold replacement. Two segregated cell phenotypes occurred, producing a bilayered structure resembling epithelium over lamina propria. This preliminary work demonstrates the feasibility of tissue engineering to produce structures for vocal fold replacement.

Probing vocal fold fibroblast response to hyaluronan in 3D contexts

A number of treatments are being investigated for vocal fold (VF) scar, including designer implants. The aim of the present study was to validate a 3D model system for probing the effects of various bioactive moieties on VF fibroblast (VFF) behavior toward rational implant design. We selected poly(ethylene glycol) diacrylate (PEGDA) hydrogels as our base-scaffold due to their broadly tunable material properties. However, since cells encapsulated in PEGDA hydrogels are generally forced to take on rounded/stellate morphologies, validation of PEGDA gels as a 3D VFF model system required that the present work directly parallel previous studies involving more permissive scaffolds. We therefore chose to focus on hyaluronan (HA), a polysaccharide that has been a particular focus of the VF community. Toward this end, porcine VFFs were encapsulated in PEGDA hydrogels containing consistent levels of high Mw HA (HA(HMW)), intermediate Mw HA (HA(IMW)), or the control polysaccharide, alginate, and cultured for 7 and 21 days. HA(HMW) promoted sustained increases in active ERK1/2 relative to HA(IMW). Furthermore, VFFs in HA(IMW) gels displayed a more myofibroblast-like phenotype, higher elastin production, and greater protein kinase C (PkC) levels at day 21 than VFFs in HA(HMW) and alginate gels. The present results are in agreement with a previous 3D study of VFF responses to HA(IMW) relative to alginate in collagen-based scaffolds permissive of cell elongation, indicating that PEGDA hydrogels may serve as an effective 3D model system for probing at least certain aspects of VFF behavior.

A rat excised larynx model of vocal fold scar

PURPOSE

To develop and evaluate a rat excised larynx model for the measurement of acoustic, aerodynamic, and vocal fold vibratory changes resulting from vocal fold scar.

METHOD

Twenty-four 4-month-old male Sprague-Dawley rats were assigned to 1 of 4 experimental groups: chronic vocal fold scar, chronic vocal fold scar treated with 100-ng basic fibroblast growth factor (bFGF), chronic vocal fold scar treated with saline (sham treatment), and unscarred untreated control. Following tissue harvest, histological and immunohistochemical data were collected to confirm extracellular matrix alteration in the chronic scar group; acoustic, aerodynamic, and high-speed digital imaging data were collected using an excised larynx setup in all groups. Phonation threshold pressure (P(th)), glottal resistance (R(g)), glottal efficiency (E(g)), vibratory amplitude, and vibratory area were used as dependent variables.

RESULTS

Chronically scarred vocal folds were characterized by elevated collagen Types I and III and reduced hyaluronic acid abundance. Phonation was achieved, and data were collected from all control and bFGF-treated larynges; however, phonation was not achieved with 3 of 6 chronically scarred and 1 of 6 saline-treated larynges. Compared with control, the chronic scar group was characterized by elevated P(th), reduced E(g), and intralarynx vibratory amplitude and area asymmetry. The bFGF group was characterized by P(th) below control-group levels, E(g) comparable with control, and vocal fold vibratory amplitude and area symmetry comparable with control. The sham group was characterized by P(th) comparable with control, E(g) superior to control, and vocal fold vibratory amplitude and area symmetry comparable with control.

CONCLUSIONS

The excised larynx model reported here demonstrated robust deterioration across phonatory indices under the scar condition and sensitivity to treatment-induced change under the bFGF condition. The improvement observed under the sham condition may reflect unanticipated therapeutic benefit or artifact. This model holds promise as a tool for the functional characterization of biomechanical tissue changes resulting from vocal fold scar and the evaluation of experimental therapies.

Fibroblast elongation and dendritic extensions in constrained versus unconstrained microtissues

Cytoskeletal tension is fundamental to many biological processes, including germ layer sorting during embryogenesis [Krieg et al., 2008]. In vitro, such tension influences cell sorting in self-assembled, 3D microtissues and can be of sufficient magnitude to cause complex-shaped microtissue failure [Dean et al., 2007]. To examine the process of failure under cell-derived tension, we subjected normal human fibroblasts (NHFs) to directed self-assembly [Dean et al., 2007] in micro-molds designed to yield self-constraining microtissues. As cells contracted in this assay, the constrained microtissues narrowed, thinned and ultimately failed at their midpoints. By adding small numbers of GFP+ cells, changes in cell movement and morphology were assessed and compared to those of unconstrained microtissues. We found that cells formed numerous dendritic extensions within an hour of self-assembly and retracted these extensions as they elongated up to 30 times their initial diameter ( approximately 600 microm) just prior to failure. Surprisingly, significant coordination in cell motility was observed over large distances within microtissues. Pharmacologic interventions showed that failure was myosin II and Rho kinase dependent and inhibition of failure resulted in shorter cells with greater numbers of extensions. These findings further our understanding of cellular self-assembly and introduce the use of GFP+ cells with directed self-assembly as a scaffold-free analogue to fibroblast-populated collagen gels (FPCGs).

Influence of hydrogel mechanical properties and mesh size on vocal fold fibroblast extracellular matrix production and phenotype

Current clinical management of vocal fold (VF) scarring produces inconsistent and often suboptimal results. Researchers are investigating a number of alternative treatments for VF lamina propria (LP) scarring, including designer implant materials for functional LP regeneration. In the present study, we investigate the effects of the initial scaffold elastic modulus and mesh size on encapsulated VF fibroblast (VFF) extracellular matrix (ECM) production toward rational scaffold design. Poly(ethylene glycol) diacrylate (PEGDA) hydrogels were selected for this study since their material properties, including mechanical properties, mesh size, degradation rate and bioactivity, can be tightly controlled and systematically modified. Porcine VFF were encapsulated in four PEGDA hydrogels with degradation half lives of approximately 25 days, but with initial elastic compressive moduli and mesh sizes ranging from approximately 30 to 100kPa and from approximately 9 to 27nm, respectively. After 30 days of static culture, VFF ECM production and phenotype in each formulation was assessed biochemically and histologically. Sulfated glycosaminoglycan synthesis increased in similar degree with both increasing initial modulus and decreasing initial mesh size. In contrast, elastin production decreased with increasing initial modulus but increased with decreasing initial mesh size. Both collagen deposition and the induction of a myofibroblastic phenotype depended strongly on initial mesh size but appeared largely unaffected by variations in initial modulus. The present results indicate that scaffold mesh size warrants further investigation as a critical regulator of VFF ECM synthesis. Furthermore, this study validates a systematic and controlled approach for analyzing VFF response to scaffold properties, which should aid in rational scaffold selection/design.

Changes in cytokine signaling and extracellular matrix production induced by inflammatory factors in cultured vocal fold fibroblasts

OBJECTIVES

Modulating cytokine signaling in vocal fold fibroblasts after injury may influence extracellular matrix (ECM) production and eventual fibrotic outcome. To evaluate previously established in vivo cytokine and ECM gene expression hypotheses, we examined in vitro vocal fold fibroblast responses to exogenous inflammatory factor stimulation.

METHODS

Rat vocal fold fibroblast lines derived from explants were separately treated with interleukin-13 (IL-13), interferon gamma (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), transforming growth factor beta subtype 1 (TGF-beta1), or prostaglandin E2 (PGE2). We examined the in vitro messenger RNA expression profiles of IL-1beta, IFN-gamma, TNF-alpha, TGF-beta1, and cyclooxygenase 2 (COX-2), as well as those of hyaluronic acid synthase (HAS) 1, HAS-2, procollagen subtype 1, and procollagen subtype 3, at 1,4, 8, 16, 24, and 72 hours after treatment, and compared them to those of untreated fibroblasts and in vivo data, using real-time reverse transcription-polymerase chain reaction.

RESULTS

IL-1beta and TNF-alpha induced each other and synergistically increased HAS-1 and HAS-2 expression. PGE2 also up-regulated HAS-1 and HAS-2 expression. IFN-gamma, IL-1beta, TNF-alpha, and TGF-beta1 up-regulated HAS expression alongside either transient up-regulation of, or no change in, procollagen 1 and 3 expression. Most treatments appeared to suppress procollagen expression, possibly through HAS up-regulation. All inflammatory factors attenuated TGF-beta1 expression.

CONCLUSIONS

These results confirm several in vivo trends, identify potential cytokine pathways and therapeutic candidates, and suggest the utility of this in vitro setup for future studies.

The effect of bioactive hydrogels on the secretion of extracellular matrix molecules by valvular interstitial cells

Valvular interstitial cells (VICs) were encapsulated in enzymatically degradable, crosslinked hydrogels formed from hyaluronic acid (HA) and poly(ethylene glycol) (PEG) macromolecular monomers. Titration of PEG with HA allowed for the synthesis of gels with a broad compositional spectrum, leading to a range of degradation behavior upon exposure to bovine testes hyaluronidase. The rate of mass loss and release of HA fragments from the copolymer gels depended on the PEG content of the network. These hydrogels were shown to have the dual function of permitting the diffusion of ECM elaborated by 3D cultured VICs and promoting the development of a specific matrix composition. Initial cleavage of hydrogel crosslinks, prior to network mass loss, permit the diffusion of collagen, while later stages of degradation promote elastin elaboration and suppress collagen production due to HA fragment release. Exogenous HA delivery through the cell culture media further demonstrated the utility of delivered HA on manipulating the secretory properties of encapsulated VICs.

Hydrogels for tissue engineering and delivery of tissue-inducing substances

This manuscript presents hydrogels (HGs) from a tissue engineering perspective being especially written for those who are approaching this field by offering a concise but inclusive review of hydrogel synthesis, properties, characterization methods, and applications.