Matrix scaffolding for stem cell guidance toward skeletal muscle tissue engineering

Biomaterials-mediated CRISPR/Cas9 delivery: recent challenges and opportunities in gene therapy

The use of biomaterials in delivering CRISPR/Cas9 for gene therapy in infectious diseases holds tremendous potential. This innovative approach combines the advantages of CRISPR/Cas9 with the protective properties of biomaterials, enabling accurate and efficient gene editing while enhancing safety. Biomaterials play a vital role in shielding CRISPR/Cas9 components, such as lipid nanoparticles or viral vectors, from immunological processes and degradation, extending their effectiveness. By utilizing the flexibility of biomaterials, tailored systems can be designed to address specific genetic diseases, paving the way for personalized therapeutics. Furthermore, this delivery method offers promising avenues in combating viral illnesses by precisely modifying pathogen genomes, and reducing their pathogenicity. Biomaterials facilitate site-specific gene modifications, ensuring effective delivery to infected cells while minimizing off-target effects. However, challenges remain, including optimizing delivery efficiency, reducing off-target effects, ensuring long-term safety, and establishing scalable production techniques. Thorough research, pre-clinical investigations, and rigorous safety evaluations are imperative for successful translation from the laboratory to clinical applications. In this review, we discussed how CRISPR/Cas9 delivery using biomaterials revolutionizes gene therapy and infectious disease treatment, offering precise and safe editing capabilities with the potential to significantly improve human health and quality of life.

Application of stem cells in regeneration medicine

Regeneration is a complex process affected by many elements independent or combined, including inflammation, proliferation, and tissue remodeling. Stem cells is a class of primitive cells with the potentiality of differentiation, regenerate with self-replication, multidirectional differentiation, and immunomodulatory functions. Stem cells and their cytokines not only inextricably linked to the regeneration of ectodermal and skin tissues, but also can be used for the treatment of a variety of chronic wounds. Stem cells can produce exosomes in a paracrine manner. Stem cell exosomes play an important role in tissue regeneration, repair, and accelerated wound healing, the biological properties of which are similar with stem cells, while stem cell exosomes are safer and more effective. Skin and bone tissues are critical organs in the body, which are essential for sustaining life activities. The weak repairing ability leads a pronounced impact on the quality of life of patients, which could be alleviated by stem cell exosomes treatment. However, there are obstacles that stem cells and stem cells exosomes trough skin for improved bioavailability. This paper summarizes the applications and mechanisms of stem cells and stem cells exosomes for skin and bone healing. We also propose new ways of utilizing stem cells and their exosomes through different nanoformulations, liposomes and nanoliposomes, polymer micelles, microspheres, hydrogels, and scaffold microneedles, to improve their use in tissue healing and regeneration.

Engineering Cell-ECM-Material Interactions for Musculoskeletal Regeneration

The extracellular microenvironment regulates many of the mechanical and biochemical cues that direct musculoskeletal development and are involved in musculoskeletal disease. The extracellular matrix (ECM) is a main component of this microenvironment. Tissue engineered approaches towards regenerating muscle, cartilage, tendon, and bone target the ECM because it supplies critical signals for regenerating musculoskeletal tissues. Engineered ECM-material scaffolds that mimic key mechanical and biochemical components of the ECM are of particular interest in musculoskeletal tissue engineering. Such materials are biocompatible, can be fabricated to have desirable mechanical and biochemical properties, and can be further chemically or genetically modified to support cell differentiation or halt degenerative disease progression. In this review, we survey how engineered approaches using natural and ECM-derived materials and scaffold systems can harness the unique characteristics of the ECM to support musculoskeletal tissue regeneration, with a focus on skeletal muscle, cartilage, tendon, and bone. We summarize the strengths of current approaches and look towards a future of materials and culture systems with engineered and highly tailored cell-ECM-material interactions to drive musculoskeletal tissue restoration. The works highlighted in this review strongly support the continued exploration of ECM and other engineered materials as tools to control cell fate and make large-scale musculoskeletal regeneration a reality.

Triphasic 3D In Vitro Model of Bone-Tendon-Muscle Interfaces to Study Their Regeneration

The transition areas between different tissues, known as tissue interfaces, have limited ability to regenerate after damage, which can lead to incomplete healing. Previous studies focussed on single interfaces, most commonly bone-tendon and bone-cartilage interfaces. Herein, we develop a 3D in vitro model to study the regeneration of the bone-tendon-muscle interface. The 3D model was prepared from collagen and agarose, with different concentrations of hydroxyapatite to graduate the tissues from bones to muscles, resulting in a stiffness gradient. This graduated structure was fabricated using indirect 3D printing to provide biologically relevant surface topographies. MG-63, human dermal fibroblasts, and Sket.4U cells were found suitable cell models for bones, tendons, and muscles, respectively. The biphasic and triphasic hydrogels composing the 3D model were shown to be suitable for cell growth. Cells were co-cultured on the 3D model for over 21 days before assessing cell proliferation, metabolic activity, viability, cytotoxicity, tissue-specific markers, and matrix deposition to determine interface formations. The studies were conducted in a newly developed growth chamber that allowed cell communication while the cell culture media was compartmentalised. The 3D model promoted cell viability, tissue-specific marker expression, and new matrix deposition over 21 days, thereby showing promise for the development of new interfaces.

Tissue Engineering Applied to Skeletal Muscle: Strategies and Perspectives

Muscle tissue is formed by elongated and contractile cells with specific morphofunctional characteristics. Thus, it is divided into three basic types: smooth muscle tissue, cardiac striated muscle tissue and skeletal striated muscle tissue. The striated skeletal muscle tissue presents high plasticity, regeneration and growth capacity due to the presence of satellite cells, quiescent myoblasts that are activated in case of injury to the tissue and originate new muscle fibers when they differentiate. In more severe deficiencies or injuries there is a loss of their regenerative capacity, thus compromising the body's functionality at different levels. Tissue engineering studies the development of biomaterials capable of stimulating the recovery of cellular activity in injured body tissues, as well as the activity of cells with muscle differentiation potential in injury repair. However, the need for three-dimensional re-assembly in a complex organization makes it difficult to mimic this tissue and fully regenerate it for the sake of precise and effective movements. Thus, this article aims to provide a narrative review of tissue engineering strategies applied to the regeneration of skeletal muscle, in a critical evaluation of research, whether aimed at injury or atrophies such as spinal muscular atrophy.

Synthetic materials in craniofacial regenerative medicine: A comprehensive overview

The state-of-the-art approach to regenerating different tissues and organs is tissue engineering which includes the three parts of stem cells (SCs), scaffolds, and growth factors. Cellular behaviors such as propagation, differentiation, and assembling the extracellular matrix (ECM) are influenced by the cell's microenvironment. Imitating the cell's natural environment, such as scaffolds, is vital to create appropriate tissue. Craniofacial tissue engineering refers to regenerating tissues found in the brain and the face parts such as bone, muscle, and artery. More biocompatible and biodegradable scaffolds are more commensurate with tissue remodeling and more appropriate for cell culture, signaling, and adhesion. Synthetic materials play significant roles and have become more prevalent in medical applications. They have also been used in different forms for producing a microenvironment as ECM for cells. Synthetic scaffolds may be comprised of polymers, bioceramics, or hybrids of natural/synthetic materials. Synthetic scaffolds have produced ECM-like materials that can properly mimic and regulate the tissue microenvironment's physical, mechanical, chemical, and biological properties, manage adherence of biomolecules and adjust the material's degradability. The present review article is focused on synthetic materials used in craniofacial tissue engineering in recent decades.

Unraveling Muscle Impairment Associated With COVID-19 and the Role of 3D Culture in Its Investigation

COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been considered a public health emergency, extensively investigated by researchers. Accordingly, the respiratory tract has been the main research focus, with some other studies outlining the effects on the neurological, cardiovascular, and renal systems. However, concerning SARS-CoV-2 outcomes on skeletal muscle, scientific evidence is still not sufficiently strong to trace, treat and prevent possible muscle impairment due to the COVID-19. Simultaneously, there has been a considerable amount of studies reporting skeletal muscle damage in the context of COVID-19. Among the detrimental musculoskeletal conditions associated with the viral infection, the most commonly described are sarcopenia, cachexia, myalgia, myositis, rhabdomyolysis, atrophy, peripheral neuropathy, and Guillain-Barré Syndrome. Of note, the risk of developing sarcopenia during or after COVID-19 is relatively high, which poses special importance to the condition amid the SARS-CoV-2 infection. The yet uncovered mechanisms by which musculoskeletal injury takes place in COVID-19 and the lack of published methods tailored to study the correlation between COVID-19 and skeletal muscle hinder the ability of healthcare professionals to provide SARS-CoV-2 infected patients with an adequate treatment plan. The present review aims to minimize this burden by both thoroughly exploring the interaction between COVID-19 and the musculoskeletal system and examining the cutting-edge 3D cell culture techniques capable of revolutionizing the study of muscle dynamics.

Assembled Cell-Decorated Collagen (AC-DC) Fiber Bioprinted Implants with Musculoskeletal Tissue Properties Promote Functional Recovery in Volumetric Muscle Loss

Musculoskeletal tissue injuries, including volumetric muscle loss (VML), are commonplace and often lead to permanent disability and deformation. Addressing this healthcare need, an advanced biomanufacturing platform, assembled cell-decorated collagen (AC-DC) bioprinting, is invented to rapidly and reproducibly create living biomaterial implants, using clinically relevant cells and strong, microfluidic wet-extruded collagen microfibers. Quantitative analysis shows that the directionality and distribution of cells throughout AC-DC implants mimic native musculoskeletal tissue. AC-DC bioprinted implants further approximate or exceed the strength and stiffness of human musculoskeletal tissue and exceed collagen hydrogel tensile properties by orders of magnitude. In vivo, AC-DC implants are assessed in a critically sized muscle injury in the hindlimb, with limb torque generation potential measured over 12 weeks. Both acellular and cellular implants promote functional recovery compared to the unrepaired group, with AC-DC implants containing therapeutic muscle progenitor cells promoting the highest degree of recovery. Histological analysis and automated image processing of explanted muscle cross-sections reveal increased total muscle fiber count, median muscle fiber size, and increased cellularization for injuries repaired with cellularized implants. These studies introduce an advanced bioprinting method for generating musculoskeletal tissue analogs with near-native biological and biomechanical properties with the potential to repair myriad challenging musculoskeletal injuries.

Biofabricating murine and human myo-substitutes for rapid volumetric muscle loss restoration

The importance of skeletal muscle tissue is undoubted being the controller of several vital functions including respiration and all voluntary locomotion activities. However, its regenerative capability is limited and significant tissue loss often leads to a chronic pathologic condition known as volumetric muscle loss. Here, we propose a biofabrication approach to rapidly restore skeletal muscle mass, 3D histoarchitecture, and functionality. By recapitulating muscle anisotropic organization at the microscale level, we demonstrate to efficiently guide cell differentiation and myobundle formation both in vitro and in vivo. Of note, upon implantation, the biofabricated myo-substitutes support the formation of new blood vessels and neuromuscular junctions-pivotal aspects for cell survival and muscle contractile functionalities-together with an advanced muscle mass and force recovery. Altogether, these data represent a solid base for further testing the myo-substitutes in large animal size and a promising platform to be eventually translated into clinical scenarios.

Muscle functional recovery is driven by extracellular vesicles combined with muscle extracellular matrix in a volumetric muscle loss murine model

Biological scaffolds derived from decellularized tissues are being investigated as a promising approach to repair volumetric muscle losses (VML). Indeed, extracellular matrix (ECM) from decellularized tissues is highly biocompatible and mimics the original tissue. However, the development of fibrosis and the muscle stiffness still represents a major problem. Intercellular signals mediating tissue repair are conveyed via extracellular vesicles (EVs), biologically active nanoparticles secreted by the cells. This work aimed at using muscle ECM and human EVs derived from Wharton Jelly mesenchymal stromal cells (MSC EVs) to boost tissue regeneration in a VML murine model. Mice transplanted with muscle ECM and treated with PBS or MSC EVs were analyzed after 7 and 30 days. Flow cytometry, tissue analysis, qRT-PCR and physiology test were performed. We demonstrated that angiogenesis and myogenesis were enhanced while fibrosis was reduced after EV treatment. Moreover, the inflammation was directed toward tissue repair. M2-like, pro-regenerative macrophages were significantly increased in the MSC EVs treated group compared to control. Strikingly, the histological improvements were associated with enhanced functional recovery. These results suggest that human MSC EVs can be a naturally-derived boost able to ameliorate the efficacy of tissue-specific ECM in muscle regeneration up to the restored tissue function.

Full wave 3D inverse scattering transmission ultrasound tomography in the presence of high contrast

We present here a quantitative ultrasound tomographic method yielding a sub-mm resolution, quantitative 3D representation of tissue characteristics in the presence of high contrast media. This result is a generalization of previous work where high impedance contrast was not present and may provide a clinically and laboratory relevant, relatively inexpensive, high resolution imaging method for imaging in the presence of bone. This allows tumor, muscle, tendon, ligament or cartilage disease monitoring for therapy and general laboratory or clinical settings. The method has proven useful in breast imaging and is generalized here to high-resolution quantitative imaging in the presence of bone. The laboratory data are acquired in ~ 12 min and the reconstruction in ~ 24 min-approximately 200 times faster than previously reported simulations in the literature. Such fast reconstructions with real data require careful calibration, adequate data redundancy from a 2D array of 2048 elements and a paraxial approximation. The imaging results show that tissue surrounding the high impedance region is artifact free and has correct speed of sound at sub-mm resolution.

Biomimetic glycosaminoglycan-based scaffolds improve skeletal muscle regeneration in a Murine volumetric muscle loss model

Volumetric muscle loss (VML) injuries characterized by critical loss of skeletal muscle tissues result in severe functional impairment. Current treatments involving use of muscle grafts are limited by tissue availability and donor site morbidity. In this study, we designed and synthesized an implantable glycosaminoglycan-based hydrogel system consisting of thiolated hyaluronic acid (HA) and thiolated chondroitin sulfate (CS) cross-linked with poly(ethylene glycol) diacrylate to promote skeletal muscle regeneration of VML injuries in mice. The HA-CS hydrogels were optimized with suitable biophysical properties by fine-tuning degree of thiol group substitution to support C2C12 myoblast proliferation, myogenic differentiation and expression of myogenic markers MyoD, MyoG and MYH8. Furthermore, in vivo studies using a murine quadriceps VML model demonstrated that the HA-CS hydrogels supported integration of implants with the surrounding host tissue and facilitated migration of Pax7⁺ satellite cells, de novo myofiber formation, angiogenesis, and innervation with minimized scar tissue formation during 4-week implantation. The hydrogel-treated and autograft-treated mice showed similar functional improvements in treadmill performance as early as 1-week post-implantation compared to the untreated groups. Taken together, our results demonstrate the promise of HA-CS hydrogels as regenerative engineering matrices to accelerate healing of skeletal muscle injuries.

Skeletal Muscle-Derived Human Mesenchymal Stem Cells: Influence of Different Culture Conditions on Proliferative and Myogenic Capabilities

Skeletal muscle tissue is characterized by restrained self-regenerative capabilities, being ineffective in relation to trauma extension both in time span (e.g., chronic diseases) and in size (e.g., large trauma). For these reasons, tissue engineering and/or cellular therapies represent a valuable solution in the cases where the physiological healing process failed. Satellite cells, the putative skeletal muscle stem cells, have been the first solution explored to remedy the insufficient self-regeneration capacity. Nevertheless, some limitation related to donor age, muscle condition, expansion hitch, and myogenic potentiality maintenance have limited their use as therapeutic tool. To overcome this hindrance, different stem cells population with myogenic capabilities have been investigated to evaluate their real potentiality for therapeutic approaches, but, as of today, the perfect cell candidate has not been identified yet. In this work, we analyze the characteristics of skeletal muscle-derived human Mesenchymal Stem Cells (hMSCs), showing the maintenance/increment of myogenic activity upon differential culture conditions. In particular, we investigate the influence of a commercial enriched growth medium (Cyto-Grow), and of a medium enriched with either human-derived serum (H.S.) or human Platelet-rich Plasma (PrP), in order to set up a culture protocol useful for employing this cell population in clinical therapeutic strategies. The presented results reveal that both the enriched medium (Cyto-Grow) and the human-derived supplements (H.S. and PrP) have remarkable effects on hMSCs proliferation and myogenic differentiation compared to standard condition, uncovering the real possibility to exploit these human derivatives to ameliorate stem cells yield and efficacy.

Evaluation of the Therapeutic Potential of Human iPSCs in a Murine Model of VML

Volumetric muscle loss injury is a common health problem with long-term disabilities. One common treatment is using muscle flaps from donor site, which has limited potentials due to donor site availability and morbidity. Although several stem cell therapies have been evaluated so far, most suffer from limited availability, immune incompatibility, or differentiation potential. Therefore, induced pluripotent stem cells (iPSCs) have a great promise for this purpose due to their unique differentiation, self-renewal, and immunocompatibility. Current study was designed to determine therapeutic potential of human iPSCs (hiPSCs) in a mouse model of volumetric muscle loss. Muscles were subjected to excision to generate 30%-40% muscle loss. Next, hiPSCs were differentiated toward skeletal myogenic progenitors and used with fibrin hydrogel to reconstruct the lost muscle. Histologic evaluation of the treated muscles indicated abundant engraftment of donor-derived mature fibers expressing human markers. Donor-derived fibers were also positive for the presence of neuromuscular junction (NMJ), indicating their proper innervation. Evaluation of the engrafted region indicated the presence of donor-derived satellite cells expressing human markers and Pax7. Finally, in situ muscle function analysis demonstrated significant improvement of the muscle contractility in muscles treated with hiPSCs. These results therefore provide key evidence for the therapeutic potential of human iPSCs in volumetric muscle loss injuries.

The Diversity of Muscles and Their Regenerative Potential across Animals

Cells with contractile functions are present in almost all metazoans, and so are the related processes of muscle homeostasis and regeneration. Regeneration itself is a complex process unevenly spread across metazoans that ranges from full-body regeneration to partial reconstruction of damaged organs or body tissues, including muscles. The cellular and molecular mechanisms involved in regenerative processes can be homologous, co-opted, and/or evolved independently. By comparing the mechanisms of muscle homeostasis and regeneration throughout the diversity of animal body-plans and life cycles, it is possible to identify conserved and divergent cellular and molecular mechanisms underlying muscle plasticity. In this review we aim at providing an overview of muscle regeneration studies in metazoans, highlighting the major regenerative strategies and molecular pathways involved. By gathering these findings, we wish to advocate a comparative and evolutionary approach to prompt a wider use of “non-canonical” animal models for molecular and even pharmacological studies in the field of muscle regeneration.

Using Acoustic Fields to Fabricate ECM-Based Biomaterials for Regenerative Medicine Applications

Ultrasound is emerging as a promising tool for both characterizing and fabricating engineered biomaterials. Ultrasound-based technologies offer a diverse toolbox with outstanding capacity for optimization and customization within a variety of therapeutic contexts, including improved extracellular matrix-based materials for regenerative medicine applications. Non-invasive ultrasound fabrication tools include the use of thermal and mechanical effects of acoustic waves to modify the structure and function of extracellular matrix scaffolds both directly, and indirectly via biochemical and cellular mediators. Materials derived from components of native extracellular matrix are an essential component of engineered biomaterials designed to stimulate cell and tissue functions and repair or replace injured tissues. Thus, continued investigations into biological and acoustic mechanisms by which ultrasound can be used to manipulate extracellular matrix components within three-dimensional hydrogels hold much potential to enable the production of improved biomaterials for clinical and research applications.

Structural and Functional Changes in the Coupling of Fascial Tissue, Skeletal Muscle, and Nerves During Aging

Aging is a one-way process associated with profound structural and functional changes in the organism. Indeed, the neuromuscular system undergoes a wide remodeling, which involves muscles, fascia, and the central and peripheral nervous systems. As a result, intrinsic features of tissues, as well as their functional and structural coupling, are affected and a decline in overall physical performance occurs. Evidence from the scientific literature demonstrates that senescence is associated with increased stiffness and reduced elasticity of fascia, as well as loss of skeletal muscle mass, strength, and regenerative potential. The interaction between muscular and fascial structures is also weakened. As for the nervous system, aging leads to motor cortex atrophy, reduced motor cortical excitability, and plasticity, thus leading to accumulation of denervated muscle fibers. As a result, the magnitude of force generated by the neuromuscular apparatus, its transmission along the myofascial chain, joint mobility, and movement coordination are impaired. In this review, we summarize the evidence about the deleterious effect of aging on skeletal muscle, fascial tissue, and the nervous system. In particular, we address the structural and functional changes occurring within and between these tissues and discuss the effect of inflammation in aging. From the clinical perspective, this article outlines promising approaches for analyzing the composition and the viscoelastic properties of skeletal muscle, such as ultrasonography and elastography, which could be applied for a better understanding of musculoskeletal modifications occurring with aging. Moreover, we describe the use of tissue manipulation techniques, such as massage, traction, mobilization as well as acupuncture, dry needling, and nerve block, to enhance fascial repair.

On the Interaction between 1D Materials and Living Cells

One-dimensional (1D) materials allow for cutting-edge applications in biology, such as single-cell bioelectronics investigations, stimulation of the cellular membrane or the cytosol, cellular capture, tissue regeneration, antibacterial action, traction force investigation, and cellular lysis among others. The extraordinary development of this research field in the last ten years has been promoted by the possibility to engineer new classes of biointerfaces that integrate 1D materials as tools to trigger reconfigurable stimuli/probes at the sub-cellular resolution, mimicking the in vivo protein fibres organization of the extracellular matrix. After a brief overview of the theoretical models relevant for a quantitative description of the 1D material/cell interface, this work offers an unprecedented review of 1D nano- and microscale materials (inorganic, organic, biomolecular) explored so far in this vibrant research field, highlighting their emerging biological applications. The correlation between each 1D material chemistry and the resulting biological response is investigated, allowing to emphasize the advantages and the issues that each class presents. Finally, current challenges and future perspectives are discussed.

Deciphering skin re-pigmentation patterns in vitiligo: an update on the cellular and molecular events involved

Current treatment of vitiligo is still a great challenge, since most cases of vitiligo have variable re-pigmentation outcomes due to their unpredictable responses to existing therapeutic regimens. There is an urgent need to identify this re-pigmentation process and to develop novel therapies. This review illustrates the most current research and latest understanding of vitiligo skin re-pigmentation and related regulatory mechanisms. Literature was collected from PubMed until January 2020, using the search terms including "vitiligo," "re-pigmentation," "phototherapy," "narrow-band ultraviolet B, " "excimer," "fractional carbon dioxide laser," and "melanocyte stem cells." Literature was mainly derived from English articles. Article type was not limited. Emerging evidence suggests that patients with vitiligo present various re-pigmentation patterns following ultraviolet B phototherapy, which relies on different cell reservoirs from the perilesional margins and/or from uninvolved hair follicles to replenish functional melanocytes that are lost in vitiliginous skin. The following events are likely to be involved in this re-pigmentation process, including: 1) changes in the paracrine secretion and distribution of transforming growth factor-β1 in the bulge area and in the epidermis; 2) the enhanced transfer of dermal pro-melanogenic growth factors to the epidermis; and 3) the induction of a C-X-C motif chemokine ligand (CXCL) 12-enriched micro-environment that efficiently recruits CXCR4- or CXCR7-positive melanocytes. Ongoing studies on the cellular and molecular events underlying vitiligo re-pigmentation will help design new therapeutic strategies to improve treatment outcomes.

Novel Insights into the Pathogenesis of Spinal Sarcopenia and Related Therapeutic Approaches: A Narrative Review

Spinal sarcopenia is a complex and multifactorial disorder associated with a loss of strength, increased frailty, and increased risks of fractures and falls. In addition, spinal sarcopenia has been associated with lumbar spine disorders and osteoporosis, which renders making decisions on treatment modalities difficult. Patients with spinal sarcopenia typically exhibit lower cumulative survival, a higher risk of in-hospital complications, prolonged hospital stays, higher postoperative costs, and higher rates of blood transfusion after thoracolumbar spine surgery. Several studies have focused on the relationships between spinal sarcopenia, appendicular muscle mass, and bone-related problems-such as osteoporotic fractures and low bone mineral density-and malnutrition and vitamin D deficiency. Although several techniques are available for measuring sarcopenia, each of them has its advantages and shortcomings. For treating spinal sarcopenia, nutrition, physical therapy, and medication have been proven to be effective; regenerative therapeutic options seem to be promising owing to their repair and regeneration potential. Therefore, in this narrative review, we summarize the characteristics, detection methodologies, and treatment options for spinal sarcopenia, as well as its role in spinal disorders.

Graft alignment impacts the regenerative response of skeletal muscle after volumetric muscle loss in a rat model

A key event in the etiology of volumetric muscle loss (VML) injury is the bulk loss of structural cues provided by the underlying extracellular matrix (ECM). To re-establish the lost cues, there is broad consensus within the literature supporting the utilization of implantable scaffolding. However, while scaffold based regenerative medicine strategies have shown potential, there remains a significant amount of outcome variability observed across the field. We suggest that an overlooked source of outcome variability is differences in scaffolding architecture. The goal of this study was to test the hypothesis that implant alignment has a significant impact on genotypic and phenotypic outcomes following the repair of VML injuries. Using a rat VML model, outcomes across three autograft implant treatment groups (aligned implants, 45° misaligned, and 90° misaligned) and two recovery time points (2 weeks and 12 weeks) were examined (n = 6-8/group). At 2 weeks post-repair there were no significant differences in muscle mass and torque recovery between the treatment groups, however we did observe a significant upregulation of MyoD (2.5 fold increase) and Pax7 (2 fold increase) gene expression as well as the presence of immature myofibers at the implant site for those animals repaired with aligned autografts. By 12 weeks post-repair, functional and structural differences between the treatment groups could be detected. Aligned autografts had significantly greater mass and torque recovery (77 ± 10% of normal) when compared to 45° and 90° misaligned autografts (64 ± 10% and 61 ± 11%, respectively). Examination of tissue structure revealed extensive fibrosis and a significant increase in non-contractile tissue area fraction for only those animals treated using misaligned autografts. When taken together, the results suggest that implant graft orientation has a significant impact on in-vivo outcomes and indicate that the effect of graft alignment on muscle phenotype may be mediated through genotypic changes to myogenesis and fibrosis at the site of injury and repair. STATEMENT OF SIGNIFICANCE: A key event in the etiology of volumetric muscle loss injury is the bulk loss of architectural cues provided by the underlying extracellular matrix. To re-establish the lost cues, there is broad consensus within the literature supporting the utilization of implantable scaffolding. Yet, although native muscle is a highly organized tissue with network and cellular alignment in the direction of contraction, there is little evidence within the field concerning the importance of re-establishing native architectural alignment. The results of this study suggest that critical interactions exist between implant and native muscle alignment cues during healing, which influence the balance between myogenesis and fibrosis. Specifically, it appears that alignment of implant architectural cues with native muscle cues is necessary to create a pro-myogenic environment and contractile force recovery. The results also suggest that misaligned cues may be pathological, leading to fibrosis and poor contractile force recovery.

Bioprinting on sheet-based scaffolds applied to the creation of implantable tissue-engineered constructs with potentially diverse clinical applications: Tissue-Engineered Muscle Repair (TEMR) as a representative testbed

Purpose: This report explores the overlooked potential of bioprinting to automate biomanufacturing of simple tissue structures, such as the uniform deposition of (mono)layers of progenitor cells on sheetlike decellularized extracellular matrices (dECM). In this scenario, dECM serves as a biodegradable celldelivery matrix to provide enhanced regenerative microenvironments for tissue repair. The Tissue-Engineered Muscle Repair (TEMR) technology-where muscle progenitor cells are seeded onto a porcine bladder acellular matrix (BAM), serves as a representative testbed for bioprinting applications. Previous work demonstrated that TEMR implantation improved functional outcomes following VML injury in biologically relevant rodent models.Materials and Methods: In the described bioprinting system, a cell-laden hydrogel bioink is used to deposit high cell densities (1.4 × 105-3.5 × 105 cells/cm²), onto both sides of the bladder acellular matrix as proof-of-concept.Results: These bioprinting methods achieve a reproducible and homogeneous distribution of cells, on both sides of the BAM scaffold, after just 24hrs, with cell viability as high as 98%. These preliminary results suggest bioprinting allows for improved dual-sided cell coverage compared to manual-seeding.Conclusions: Bioprinting can enable automated fabrication of TEMR constructs with high fidelity and scalability, while reducing biomanufacturing costs and timelines. Such bioprinting applications are underappreciated, yet critical, to expand the overall biomanufacturing paradigm for tissue engineered medical products. In addition, biofabrication of sheet-like implantable constructs, with cells deposited on both sides, is a process that is both scaffold and cell-type agnostic, and furthermore, is amenable to many geometries, and thus, additional tissue engineering applications beyond skeletal muscle.

Vascularized and Innervated Skeletal Muscle Tissue Engineering

Volumetric muscle loss (VML) is a devastating loss of muscle tissue that overwhelms the native regenerative properties of skeletal muscle and results in lifelong functional deficits. There are currently no treatments for VML that fully recover the lost muscle tissue and function. Tissue engineering presents a promising solution for VML treatment and significant research has been performed using tissue engineered muscle constructs in preclinical models of VML with a broad range of defect locations and sizes, tissue engineered construct characteristics, and outcome measures. Due to the complex vascular and neural anatomy within skeletal muscle, regeneration of functional vasculature and nerves is vital for muscle recovery following VML injuries. This review aims to summarize the current state of the field of skeletal muscle tissue engineering using 3D constructs for VML treatment with a focus on studies that have promoted vascular and neural regeneration within the muscle tissue post-VML.

Histology of skeletal muscle reconstructed by means of the implantation of autologous adipose tissue: an experimental study

The purpose of this study was to determine the histological characteristics of a skeletal muscle reconstructed by means of the implantation of autologous adipose tissue following an experimentally-induced volumetric muscle loss. A cylindrical piece in the belly of the rat anterior tibial muscle was removed. In the hole, inguinal subcutaneous adipose tissue of the same rat was grafted. Animals were sacrificed 7, 14, 21, 28 and 60 days posttransplantation. Histological, histochemical, immunohistochemical and morphometric techniques were used. At all times analyzed, the regenerative muscle fibers formed from the edges of the muscle tissue showed histological, histochemical and immunohistochemical differences in comparison with the control group. These differences are related to delays in the maturation process and are related to problems in reinnervation and disorientation of muscle fibers. The stains for MyoD and desmin showed that some myoblasts and myotubes seem to derive from the transplanted adipose tissue. After 60 days, the transplant area was 20% occupied by fibrosis and by 80% skeletal muscle. However, the neo-muscle was chaotically organized showing muscle fiber disorientation and centronucleated fibers with irregular shape and size. Our results support the hypothesis that, at least from a morphological point of view, autologous adipose tissue transplantation favors reconstruction following a volumetric loss of skeletal muscle by combining the inherent regenerative response of the organ itself and the myogenic differentiation of the stem cells present in the adipose tissue. However, in our study, the formed neo-muscle exhibited histological differences in comparison with the normal skeletal muscle.

Biologics in the Treatment of Achilles Tendon Pathologies

Regenerative medicine is gaining more and more space for the treatment of Achilles pathologic conditions. Biologics could play a role in the management of midportion Achilles tendinopathy as a step between conservative and surgical treatment or as an augmentation. Higher-level studies are needed before determining a level of treatment recommendation for biologic strategies for insertional Achilles tendinopathy. Combining imaging with patient's functional requests could be the way to reach a protocol for the use of biologics for the treatment of midportion Achilles tendinopathy and, for this perspective, the authors describe the Foot and Ankle Reconstruction Group algorithm of treatment.

COL4A2 in the tissue-specific extracellular matrix plays important role on osteogenic differentiation of periodontal ligament stem cells

Periodontal ligament stem cells (PDLSCs) can repair alveolar bone defects in periodontitis in a microenvironment context-dependent manner. This study aimed to determine whether different extracellular matrices (ECMs) exert diverse effects on osteogenic differentiation of PDLSCs and accurately control alveolar bone defect repair. Methods: The characteristics of PDLSCs and bone marrow mesenchymal stem cells (BMSCs) with respect to surface markers and multi-differentiation ability were determined. Then, we prepared periodontal ligament cells (PDLCs)-derived and bone marrow cells (BMCs)-derived ECMs (P-ECM and B-ECM) and the related decellularized ECMs (dECMs). Transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and protein mass spectrometry were used to distinguish the ECMs. The expression of Type IV collagen A2 (COL4A2) in the ECMs was inhibited by siRNA or activated by lentiviral transduction of relevant cells. The stemness, proliferation, and differentiation of PDLSCs were determined in vitro in different dECMs. For the in vivo analysis, different dECMs under the regulation of COL4A2 mixed with PDLSCs and Bio-Oss bone powder were subcutaneously implanted into immunocompromised mice or in defects in rat alveolar bone. The repair effects were identified by histological or immunohistochemical staining and micro-CT. Results: B-dECM exhibited more compact fibers than P-dECM, as revealed by TEM, SEM, and AFM. Protein mass spectrometry showed that COL4A2 was significantly increased in B-dECM compared with P-dECM. PDLSCs displayed stronger proliferation, stemness, and osteogenic differentiation ability when cultured on B-dECM than P-dECM. Interestingly, B-dECM enhanced the osteogenic differentiation of PDLSCs to a greater extent than P-dECM both in vitro and in vivo, whereas downregulation of COL4A2 in B-dECM showed the opposite results. Furthermore, the classical Wnt/β-catenin pathway was found to play an important role in the negative regulation of osteogenesis through COL4A2, confirmed by experiments with the Wnt inhibitor DKK-1 and the Wnt activator Wnt3a. Conclusion: These findings indicate that COL4A2 in the ECM promotes osteogenic differentiation of PDLSCs through negative regulation of the Wnt/β-catenin pathway, which can be used as a potential therapeutic strategy to repair bone defects.

iPSCs: A powerful tool for skeletal muscle tissue engineering

Both volumetric muscle loss (VML) and muscle degenerative diseases lead to an important decrease in skeletal muscle mass, condition that nowadays lacks an optimal treatment. This issue has driven towards an increasing interest in new strategies in tissue engineering, an emerging field that can offer very promising approaches. In addition, the discovery of induced pluripotent stem cells (iPSCs) has completely revolutionized the actual view of personalized medicine, and their utilization in skeletal muscle tissue engineering could, undoubtedly, add myriad benefits. In this review, we want to provide a general vision of the basic aspects to consider when engineering skeletal muscle tissue using iPSCs. Specifically, we will focus on the three main pillars of tissue engineering: the scaffold designing, the selection of the ideal cell source and the addition of factors that can enhance the resemblance with the native tissue.

Functionalization of hyaluronic acid hydrogels with ECM-derived peptides to control myoblast behavior

Volumetric muscle loss (VML) occurs when skeletal muscle injury is too large for the body to fully self-repair. Typically, fibrotic tissue fills the void, which reduces muscle functionality and limb movement. Although a wide variety of natural and synthetic scaffolds have been studied with the purpose of providing the appropriate structural support, to date no scaffold has significantly restored muscle functionality after VML. Satellite cells, adult stem cells within the muscle capable of restoring smaller injuries, are sensitive to the stiffness and composition of the surrounding environment. Scaffolds that only address structural support are not sufficient to restore functionality and instead need to be designed to both promote satellite cell activation and prevent excessive fibroblast recruitment. The objective of this study was to design a scaffold that mimicked the regenerative environment and determine how the biomechanical properties differentially influence myogenic precursor and connective tissue cells. One of the main extracellular matrix (ECM) molecules upregulated during regeneration is hyaluronic acid (HA). Therefore, thiol-modified HA and poly(ethylene glycol) diacrylate hydrogels were generated and functionalized with peptides based on ECM known to influence regeneration, including fibronectin, laminin and tenascin-C. Scaffolds with different stiffness were created by varying HA content. The influence of HA stiffness and peptide functionalization on myogenic precursor and connective tissue cell proliferation, migration and gene expression was quantified. Our results indicated that HA hydrogels functionalized with the laminin peptide, IKVAV, show potential due to the enhanced promotion of myogenic cell behaviors including migration, proliferation and an increase in relevant transcription factors. STATEMENT OF SIGNIFICANCE: The goal of this study was to identify hyaluronic acid (HA) hydrogels with peptide and stiffness combinations that will direct muscle-derived cells towards regenerating phenotypes. While the interaction of skeletal muscle with RGD-functionalized HA hydrogels has been investigated, none of the other peptides described in this study had been used in the context of HA-based scaffolds and skeletal muscle-derived cells. Notably, the response of cells to variations in mechanics was dependent on ECM coating and lineage. The 3% HA functionalized with the laminin peptide, IKVAV, showed the most promise for future in vivo studies, as these hydrogels best promoted myoblast cell proliferation, attachment and spreading, enhanced migration over connective tissue cells and upregulated transcription factors associated with activated satellite cells.

Decellularized Tissue for Muscle Regeneration

Several acquired or congenital pathological conditions can affect skeletal muscle leading to volumetric muscle loss (VML), i.e., an irreversible loss of muscle mass and function. Decellularized tissues are natural scaffolds derived from tissues or organs, in which the cellular and nuclear contents are eliminated, but the tridimensional (3D) structure and composition of the extracellular matrix (ECM) are preserved. Such scaffolds retain biological activity, are biocompatible and do not show immune rejection upon allogeneic or xenogeneic transplantation. An increase number of reports suggest that decellularized tissues/organs are promising candidates for clinical application in patients affected by VML. Here we explore the different strategies used to generate decellularized matrix and their therapeutic outcome when applied to treat VML conditions, both in patients and in animal models. The wide variety of VML models, source of tissue and methods of decellularization have led to discrepant results. Our review study evaluates the biological and clinical significance of reported studies, with the final aim to clarify the main aspects that should be taken into consideration for the future application of decellularized tissues in the treatment of VML conditions.

Hierarchically aligned fibrous hydrogel films through microfluidic self-assembly of graphene and polysaccharides

Despite significant interest in developing extracellular matrix (ECM)-inspired biomaterials to recreate native cell-instructive microenvironments, the major challenge in the biomaterial field is to recapitulate the complex structural and biophysical features of native ECM. These biophysical features include multiscale hierarchy, electrical conductivity, optimum wettability, and mechanical properties. These features are critical to the design of cell-instructive biomaterials for bioengineering applications such as skeletal muscle tissue engineering. In this study, we used a custom-designed film fabrication assembly, which consists of a microfluidic chamber to allow electrostatic charge-based self-assembly of oppositely charged polymer solutions forming a hydrogel fiber and eventually, a nanocomposite fibrous hydrogel film. The film recapitulates unidirectional hierarchical fibrous structure along with the conductive properties to guide initial alignment and myotube formation from cultured myoblasts. We combined high conductivity, and charge carrier mobility of graphene with biocompatibility of polysaccharides to develop graphene-polysaccharide nanocomposite fibrous hydrogel films. The incorporation of graphene in fibrous hydrogel films enhanced their wettability, electrical conductivity, tensile strength, and toughness without significantly altering their elastic properties (Young's modulus). In a proof-of-concept study, the mouse myoblast cells (C2C12) seeded on these nanocomposite fibrous hydrogel films showed improved spreading and enhanced myogenesis as evident by the formation of multinucleated myotubes, an early indicator of myogenesis. Overall, graphene-polysaccharide nanocomposite fibrous hydrogel films provide a potential biomaterial to promote skeletal muscle tissue regeneration.

Novel ultrashort self-assembling peptide bioinks for 3D culture of muscle myoblast cells

The ability of skeletal muscle to self-repair after a traumatic injury, tumor ablation, or muscular disease is slow and limited, and the capacity of skeletal muscle to self-regenerate declines steeply with age. Tissue engineering of functional skeletal muscle using 3D bioprinting technology is promising for creating tissue constructs that repair and promote regeneration of damaged tissue. Hydrogel scaffolds used as biomaterials for skeletal muscle tissue engineering can provide chemical, physical and mechanical cues to the cells in three dimensions thus promoting regeneration. Herein, we have developed two synthetically designed novel tetramer peptide biomaterials. These peptides are self-assembling into a nanofibrous 3D network, entrapping 99.9% water and mimicking the native collagen of an extracellular matrix. Different biocompatibility assays including MTT, 3D cell viability assay, cytotoxicity assay and live-dead assay confirm the biocompatibility of these peptide hydrogels for mouse myoblast cells (C2C12). Immunofluorescence analysis of cell-laden hydrogels revealed that the proliferation of C2C12 cells was well-aligned in the peptide hydrogels compared to the alginategelatin control. These results indicate that these peptide hydrogels are suitable for skeletal muscle tissue engineering. Finally, we tested the printability of the peptide bioinks using a commercially available 3D bioprinter. The ability to print these hydrogels will enable future development of 3D bioprinted scaffolds containing skeletal muscle myoblasts for tissue engineering applications.

The overlap between regeneration and fibrosis in injured skeletal muscle is regulated by phosphatidylinositol 3-kinase/Akt signaling pathway - A bioinformatic analysis based on lncRNA microarray

Injured skeletal muscle would go through a sequence of the pathological phases of degeneration, myogenesis and fibrosis. Growing evidence indicated that fibrotic and myogenic phases might overlap within the injured skeletal muscle in the early time after injury. However, the mechanism underlying this overlapping remains unclear. Here, we performed an lncRNA microarray to identify the activated pathways in mice muscle seven days after contusion. KEGG analysis indicated that phosphatidylinositol 3-kinase/Akt (PI3K/Akt) signaling cascade was predicted to be activated by lncRNAs. The top genes targeted by lncRNAs in PI3K/Akt signaling were subunits of laminin, collagen 5, and collagen 6, which participated in either myogenic or fibrotic process. Reverse transcriptase-polymerase chain reaction analysis and immunohistochemical stain further confirmed the prediction in silico. These results suggested that the overlap might be related to an activated PI3K/Akt pathway by lncRNA regulation.

Decellularised skeletal muscles allow functional muscle regeneration by promoting host cell migration

Pathological conditions affecting skeletal muscle function may lead to irreversible volumetric muscle loss (VML). Therapeutic approaches involving acellular matrices represent an emerging and promising strategy to promote regeneration of skeletal muscle following injury. Here we investigated the ability of three different decellularised skeletal muscle scaffolds to support muscle regeneration in a xenogeneic immune-competent model of VML, in which the EDL muscle was surgically resected. All implanted acellular matrices, used to replace the resected muscles, were able to generate functional artificial muscles by promoting host myogenic cell migration and differentiation, as well as nervous fibres, vascular networks, and satellite cell (SC) homing. However, acellular tissue mainly composed of extracellular matrix (ECM) allowed better myofibre three-dimensional (3D) organization and the restoration of SC pool, when compared to scaffolds which also preserved muscular cytoskeletal structures. Finally, we showed that fibroblasts are indispensable to promote efficient migration and myogenesis by muscle stem cells across the scaffolds in vitro. This data strongly support the use of xenogeneic acellular muscles as device to treat VML conditions in absence of donor cell implementation, as well as in vitro model for studying cell interplay during myogenesis.

High-Density ZnO Nanowires as a Reversible Myogenic-Differentiation Switch

Mesoangioblasts are outstanding candidates for stem-cell therapy and are already being explored in clinical trials. However, a crucial challenge in regenerative medicine is the limited availability of undifferentiated myogenic progenitor cells because growth is typically accompanied by differentiation. Here reversible myogenic-differentiation switching during proliferation is achieved by functionalizing the glass substrate with high-density ZnO nanowires (NWs). Specifically, mesoangioblasts grown on ZnO NWs present a spherical viable undifferentiated cell state without lamellopodia formation during the entire observation time (8 days). Consistently, the myosin heavy chain, typically expressed in skeletal muscle tissue and differentiated myogenic progenitors, is completely absent. Remarkably, NWs do not induce any damage while they reversibly block differentiation, so that the differentiation capabilities are completely recovered upon cell removal from the NW-functionalized substrate and replating on standard culture glass. This is the first evidence of a reversible myogenic-differentiation switch that does not affect the viability. These results can be the first step toward for the in vitro growth of a large number of undifferentiated stem/progenitor cells and therefore can represent a breakthrough for cell-based therapy and tissue engineering.

Mesenchymal stem cells and extracellular matrix scaffold promote muscle regeneration by synergistically regulating macrophage polarization toward the M2 phenotype

Background

Skeletal muscle plays an important role in the body’s physiology but there are still no effective treatments for volumetric muscle loss (VML) resulting from severe traumatic injury or tumor excision. Recent studies show that a tissue engineering strategy using a compound containing mesenchymal stem cells (MSCs) and decellularized extracellular matrix (ECM) scaffold generates significant regenerative effects on VML injury, but the underlying mechanisms are not fully understood.

Methods

The characteristics of human umbilical cord MSCs, including multiplication capacity and multidifferentiation ability, were determined. We constructed a compound containing MSCs and decellularized ECM scaffold which was used for tissue regeneration in a VML model.

Results

We found that MSCs and decellularized ECM scaffold generated synergistic effects on promoting skeletal muscle tissue regeneration. Interestingly, both MSCs and decellularized ECM scaffold could promote macrophage polarization toward the M2 phenotype and suppress macrophage polarization toward the M1 phenotype, which is widely regarded as an important promoting factor in tissue regeneration. More importantly, MSCs and decellularized ECM scaffold generate synergistic promoting effects on macrophage polarization toward the M2 phenotype, not just an additive effect.

Conclusions

Our findings uncover a previously unknown mechanism that MSCs and decellularized ECM scaffold promote tissue regeneration via collaboratively regulating macrophage polarization.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0821-5) contains supplementary material, which is available to authorized users.

Adipose-derived stem cells in orthopaedic pathologies

INTRODUCTION

To examine the current literature regarding the clinical application of adipose-derived stem cells (ADSCs) for the management of orthopaedic pathologies.

SOURCES OF DATA

MEDLINE,SCOPUS, CINAHL and EMBASE (1950 to April 14, 2017) were searched by two independent investigators for articles published in English. Reviews, meta-analyses, expert opinions, case reports, mini case series and editorials were excluded. Furthermore, we excluded animal studies, cadaveric studies and in vitro studies.

AREAS OF AGREEMENT

ADSCs seem to produce excellent clinical results. However, the length and modalities of follow-up in the different conditions are extremely variable. Nevertheless, it appears that the use of adipose-derived stem cells is associated with subjective and objective clinical improvements and minimal complication rates.

AREAS OF CONTROVERSY

None of the studies identified is a randomized double-blinded trial, and most of the selected studies present major limitations, and different methods, confounding the results of our review.

GROWING POINTS

It is necessary to conduct more and better studies to ascertain whether ADSCs really play a role in orthopaedic surgery with particular attention to ADSCs harvesting method, type of administration and the conditions treated.

AREAS TIMELY FOR DEVELOPING RESEARCH

The current literature regarding the use of ADSCs for orthopaedic pathologies is limited. At present, long-term safety is the biggest challenge of ADSCs based regenerative medicine.

LEVEL OF EVIDENCE

Level IV-Study of Level I, II, III, IV.

Laminin mimetic peptide nanofibers regenerate acute muscle defect

Skeletal muscle cells are terminally differentiated and require the activation of muscle progenitor (satellite) cells for their regeneration. There is a clinical need for faster and more efficient treatment methods for acute muscle injuries, and the stimulation of satellite cell proliferation is promising in this context. In this study, we designed and synthesized a laminin-mimetic bioactive peptide (LM/E-PA) system that is capable of accelerating satellite cell activation by emulating the structure and function of laminin, a major protein of the basal membrane of the skeletal muscle. The LM/E-PA nanofibers enhance myogenic differentiation in vitro and the clinical relevance of the laminin-mimetic bioactive scaffold system was demonstrated further by assessing its effect on the regeneration of acute muscle injury in a rat model. Laminin mimetic peptide nanofibers significantly promoted satellite cell activation in skeletal muscle and accelerated myofibrillar regeneration following acute muscle injury. In addition, the LM/E-PA scaffold treatment significantly reduced the time required for the structural and functional repair of skeletal muscle. This study represents one of the first examples of molecular- and tissue-level regeneration of skeletal muscle facilitated by bioactive peptide nanofibers following acute muscle injury.

SIGNIFICANCE STATEMENT

Sports, heavy lifting and other strength-intensive tasks are ubiquitous in modern life and likely to cause acute skeletal muscle injury. Speeding up regeneration of skeletal muscle injuries would not only shorten the duration of recovery for the patient, but also support the general health and functionality of the repaired muscle tissue. In this work, we designed and synthesized a laminin-mimetic nanosystem to enhance muscle regeneration. We tested its activity in a rat tibialis anterior muscle by injecting the bioactive nanosystem. The evaluation of the regeneration and differentiation capacity of skeletal muscle suggested that the laminin-mimetic nanosystem enhances skeletal muscle regeneration and provides a suitable platform that is highly promising for the regeneration of acute muscle injuries. This work demonstrates for the first time that laminin-mimetic self-assembled peptide nanosystems facilitate myogenic differentiation in vivo without the need for additional treatment.

* Design of an In Vitro Model of Cell Recruitment for Skeletal Muscle Regeneration Using Hepatocyte Growth Factor-Loaded Fibrin Microthreads

Large skeletal muscle defects that result in volumetric muscle loss (VML) result in the destruction of the basal lamina, which removes key signaling molecules such as hepatocyte growth factor (HGF) from the wound site, eliminating the endogenous capacity of these injuries to regenerate. We recently showed that HGF-loaded fibrin microthreads increased the force production in muscle tissues after 60 days in a mouse VML model. In this study, we created an in vitro, three-dimensional (3D) microscale outgrowth assay system designed to mimic cell recruitment in vivo, and investigated the effect of HGF-loaded, cross-linked fibrin microthreads on myoblast recruitment to predict the results observed in vivo. This outgrowth assay discretely separated the cellular and molecular functions (migration, proliferation, and chemotaxis) that direct outgrowth from the wound margin, creating a powerful platform to model cell recruitment in axially aligned tissues, such as skeletal muscle. The degree of cross-linking was controlled by pH and microthreads cross-linked using physiologically neutral pH (EDCn) facilitated the release of active HGF; increasing the two-dimensional migration and 3D outgrowth of myoblasts twofold. While HGF adsorbed to uncross-linked microthreads, it did not enhance myoblast migration, possibly due to the low concentrations that were adsorbed. Regardless of the amount of HGF adsorbed on the microthreads, myoblast proliferation increased significantly on stiffer, cross-linked microthreads. Together, the results of these studies show that HGF loaded onto EDCn microthreads supported enhanced myoblast migration and recruitment and suggest that our novel outgrowth assay system is a robust in vitro screening tool that predicts the performance of fibrin microthreads in vivo.

Tissue-Engineered Larynx: Future Applications in Laryngeal Cancer

Purpose of Review

This article reviews the latest developments in tissue engineering for the larynx with a specific focus on the treatment of laryngeal cancer.

Recent Findings

Challenges in tissue engineering a total larynx can be divided into scaffold design, methods of re-mucosalization, and how to restore laryngeal function. The literature described a range of methods to deliver a laryngeal scaffold including examples of synthetic, biomimetic, and biological scaffolds. Methods to regenerate laryngeal mucosa can be divided into examples that use a biological dressing and those that engineer a new mucosal layer de novo. Studies aiming to restore laryngeal function have been reported, but to date, the optimum method for achieving this as part of a total laryngeal transplant is yet to be determined.

Summary

There is great potential for tissue engineering to improve the treatments available for laryngeal cancer within the next 10 years. A number of challenges exist however and advances in restoring function must keep pace with developments in scaffold design.