Using vocally inspired mechanical conditioning to enhance the synthesis of a cell-derived biomaterial

Cell-Derived Extracellular Matrix Fiber Scaffolds Improve Recovery from Volumetric Muscle Loss

There are currently no surgical procedures that effectively address the treatment of volumetric muscle loss (VML) injuries that has motivated the development of implantable scaffolding. In this study, the effectiveness of an allogenic scaffold fabricated using fibers built from the extracellular matrix (ECM) collected from muscle fibroblast cells during growth in culture was explored using a hindlimb VML injury (tibialis anterior muscle) in a rat model. Recovery outcomes (8 weeks) were explored in comparison with unrepaired controls as well previously examined allogenic scaffolds prepared from decellularized skeletal muscle (DSM) tissue (n = 9/sample group). At 8-week follow-up, we found that the repair of VML injuries using ECM fiber scaffolds in combination with an autogenic mince muscle (MM) paste significantly improved the recovery of peak contractile torque (79% ± 13% of uninjured contralateral muscle) when compared with unrepaired VML controls (57% ± 13%). Similar significant improvements were measured for muscle mass restoration (93% ± 10%) in response to ECM fiber+MM repair when compared with unrepaired VML controls (73% ± 13%). Of note, mass and contractile strength recovery outcomes for ECM fiber scaffolds were not significantly different from DSM+MM repair controls. These in vivo findings support the further exploration of cell-derived ECM fiber scaffolds as a promising strategy for the repair of VML injury with recovery outcomes that compare favorably with current tissue-sourced ECM scaffolds. Furthermore, although the therapeutic potential of ECM fibers as a treatment strategy for muscle injury was explored in this study, they could be adapted for high-throughput fabrication methods developed and routinely used by the textile industry to create a broad range of woven implants (e.g., hernia meshes) for even greater clinical impact.

Repeated In Vitro Impact Conditioning of Astrocytes Decreases the Expression and Accumulation of Extracellular Matrix

Pathological changes to the physical and chemical properties of brain extracellular matrix (ECM) occur following injury. It is generally assumed that astrocytes play an important role in these changes. What remain unclear are the triggers that lead to changes in the regulation of ECM by astrocytes following injury. We hypothesize that mechanical stimulation triggers genotypic and phenotypic changes to astrocytes that could ultimately reshape the ECM composition of the central nervous system following injury. To explore astrocyte mechanobiology, an in vitro drop test bioreactor was employed to condition primary rat astrocytes using short duration (10 ms), high deceleration (150G) and strain (20%) impact stimuli. Experiments were designed to explore the effect of single and repeated impact (single vs. double) on mechano-sensitive behavior including cell viability; ECM gene (collagens I and IV, fibronectin, neurocan, versican) and reactivity gene [glial fibrillary acidic protein (GFAP), S100B, vimentin] expression; matrix regulatory cytokine secretion [matrix metalloproteinase 2 (MMP-2), tissue inhibitor of metalloproteinases 1 (TIMP1), transforming growth factor beta 1 (TGFβ1)]; and matrix accumulation [collagen and glycosaminoglycan (GAG)]. Experiments revealed that both ECM and reactive gliosis gene expression was significantly decreased in response to impact conditioning. The decreases for several genes, including collagen, versican, and GFAP were sensitive to impact number, suggesting mechano-sensitivity to repeated impact conditioning. The measured decreases in ECM gene expression were supported by longer-term in vitro experiments that demonstrated significant decreases in chondroitin sulfate proteoglycan (CSPG) and collagen accumulation within impact conditioned 3-D scaffolds accompanied by a 25% decrease in elastic modulus. Overall, the general trend across all samples was towards altered ECM and reactive gliosis gene expression in response to impact. These results suggest that the regulation of ECM production by astrocytes is sensitive to mechanical stimuli, and that repeated impact conditioning may increase this sensitivity.

Mechanotransduction of vocal fold fibroblasts and mesenchymal stromal cells in the context of the vocal fold mechanome

The design of cell-based therapies for vocal fold tissue engineering requires an understanding of how cells adapt to the dynamic mechanical forces found in the larynx. Our objective was to compare mechanotransductive processes in therapeutic cell candidates (mesenchymal stromal cells from adipose tissue and bone marrow, AT-MSC and BM-MSC) to native cells (vocal fold fibroblasts-VFF) in the context of vibratory strain. A bioreactor was used to expose VFF, AT-MSC, and BM-MSC to axial tensile strain and vibration at human physiological levels. Microarray, an empirical Bayes statistical approach, and geneset enrichment analysis were used to identify significant mechanotransductive pathways associated with the three cell types and three mechanical conditions. Two databases (Gene Ontology, Kyoto Encyclopedia of Genes and Genomes) were used for enrichment analyses. VFF shared more mechanotransductive pathways with BM-MSC than with AT-MSC. Gene expression that appeared to distinguish the vibratory strain condition from polystyrene condition for these two cells types related to integrin activation, focal adhesions, and lamellipodia activity, suggesting that vibratory strain may be associated with cytoarchitectural rearrangement, cell reorientation, and extracellular matrix remodeling. In response to vibration and tensile stress, BM-MSC better mimicked VFF mechanotransduction than AT-MSC, providing support for the consideration of BM-MSC as a cell therapy for vocal fold tissue engineering. Future research is needed to better understand the sorts of physical adaptations that are afforded to vocal fold tissue as a result of focal adhesions, integrins, and lamellipodia, and how these adaptations could be exploited for tissue engineering.

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.

Development of Vibrational Culture Model Mimicking Vocal Fold Tissues

The vocal folds (VFs) are connective tissues with complex matrix structures that provide the required mechanical properties for voice generation. VF injury leads to changes in tissue structure and properties, resulting in reduced voice quality. However, injury-induced biochemical changes and repair in scarred VF tissues have not been well characterized to date. To treat scarred VFs, it is essential to understand how physiological characteristics of VFs tissue change in response to external perturbation. In this study, we designed a simple vibrational culture model to mimic vibratory microenvironments observed in vivo. This model consists of a flexible culture plate, three linear actuators, a stereo splitter, and a function generator. Human vocal fold fibroblast (hVFF) monolayers were established on the flexible membrane, to which normal phonatory vibrations were delivered from linear actuators and a function generator. The hVFF monolayers were exposed to the vibrational stresses at a frequency of 205 Hz for 2, 6, and 10 h with maximum displacement of 47.1 μm, followed by a 6 h rest. We then observed the changes in cell morphology, cell viability, and gene expression related to extracellular matrix components. In our dynamic culture device mimicking normal phonatory frequencies, cell proliferation increased and expression of hyaluronic acid synthase 2 was downregulated in response to vibrational stresses. The results presented herein will be useful for evaluating cellular responses following VF injuries in the presence or absence of vibrational stresses.

Biomechanical Screening of Cell Therapies for Vocal Fold Scar

Candidate cell sources for vocal fold scar treatment include mesenchymal stromal cells from bone marrow (BM-MSC) and adipose tissue (AT-MSC). Mechanosensitivity of MSC can alter highly relevant aspects of their behavior, yet virtually nothing is known about how MSC might respond to the dynamic mechanical environment of the larynx. Our objective was to evaluate MSC as a potential cell source for vocal fold tissue engineering in a mechanically relevant context. A vibratory strain bioreactor and cDNA microarray were used to evaluate the similarity of AT-MSC and BM-MSC to the native cell source, vocal fold fibroblasts (VFF). Posterior probabilities for each of the microarray transcripts fitting into specific expression patterns were calculated, and the data were analyzed for Gene Ontology (GO) enrichment. Significant wound healing and cell differentiation GO terms are reported. In addition, proliferation and apoptosis were evaluated with immunohistochemistry. Results revealed that VFF shared more GO terms related to epithelial development, extracellular matrix (ECM) remodeling, growth factor activity, and immune response with BM-MSC than with AT-MSC. Similarity in glycosaminoglycan and proteoglycan activity dominated the ECM analysis. Analysis of GO terms relating to MSC differentiation toward osteogenic, adipogenic, and chondrogenic lineages revealed that BM-MSC expressed fewer osteogenesis GO terms in the vibrated and scaffold-only conditions compared to polystyrene. We did not evaluate if vibrated BM-MSC recover osteogenic expression markers when returned to polystyrene culture. Immunostaining for Ki67 and cleaved caspase 3 did not vary with cell type or mechanical condition. We conclude that VFF may have a more similar wound healing capacity to BM-MSC than to AT-MSC in response to short-term vibratory strain. Furthermore, BM-MSC appear to lose osteogenic potential in the vibrated and scaffold-only conditions compared to polystyrene, potentially attenuating the risk of osteogenesis for in vivo applications.

Development of a biological scaffold engineered using the extracellular matrix secreted by skeletal muscle cells

The performance of implantable biomaterials derived from decellularized tissue, including encouraging results with skeletal muscle, suggests that the extracellular matrix (ECM) derived from native tissue has promising regenerative potential. Yet, the supply of biomaterials derived from donated tissue will always be limited, which is why the in-vitro fabrication of ECM biomaterials that mimic the properties of tissue is an attractive alternative. Towards this end, our group has utilized a novel method to collect the ECM that skeletal muscle myoblasts secrete and form it into implantable scaffolds. The cell derived ECM contained several matrix constituents, including collagen and fibronectin that were also identified within skeletal muscle samples. The ECM was organized into a porous network that could be formed with the elongated and aligned architecture observed within muscle samples. The ECM material supported the attachment and in-vitro proliferation of cells, suggesting effectiveness for cell transplantation, and was well tolerated by the host when examined in-vivo. The results suggest that the ECM collection approach can be used to produce biomaterials with compositions and structures that are similar to muscle samples, and while the physical properties may not yet match muscle values, the in-vitro and in-vivo results indicate it may be a suitable first generation alternative to tissue derived biomaterials.