Functional evaluation of prevascularization in one-stage versus two-stage tissue engineering approach of human bio-artificial muscle

Engineered myovascular tissues for studies of endothelial/satellite cell interactions

In native skeletal muscle, capillaries reside in close proximity to muscle stem cells (satellite cells, SCs) and regulate SC numbers and quiescence through partially understood mechanisms that are difficult to study in vivo. This challenge could be addressed by the development of a 3-dimensional (3D) in vitro model of vascularized skeletal muscle harboring both a pool of quiescent SCs and a robust network of capillaries. Still, studying interactions between SCs and endothelial cells (ECs) within a tissue-engineered muscle environment has been hampered by the incompatibility of commercially available EC media with skeletal muscle differentiation. In this study, we first optimized co-culture media and cellular ratios to generate highly functional vascularized human skeletal muscle tissues ("myovascular bundles") with contractile properties (∼10 mN/mm2) equaling those of avascular, muscle-only tissues ("myobundles"). Within one week of muscle differentiation, ECs in these tissues formed a dense network of capillaries that co-aligned with muscle fibers and underwent initial lumenization. Incorporating vasculature within myobundles increased the total SC number by 82%, with SC density and quiescent signature being increased proximal (≤20μm) to EC networks. In vivo, at two weeks post-implantation into dorsal window chambers in nude mice, vascularized myobundles exhibited improved calcium handling compared to avascular implants. In summary, we engineered highly functional myovascular tissues that enable studies of the roles of EC-SC crosstalk in human muscle development, physiology, and disease. STATEMENT OF SIGNIFICANCE: In native skeletal muscle, intricate relationships between vascular cells and muscle stem cells ("satellite cells") play critical roles in muscle growth and regeneration. Current methods for in vitro engineering of contractile skeletal muscle do not recreate capillary networks present in vivo. Our study for the first time generates in vitro robustly vascularized, highly functional engineered human skeletal muscle tissues. Within these tissues, satellite cells are more abundant and, similar to in vivo, they are more dense and less proliferative proximal to endothelial cells. Upon implantation in mice, vascularized engineered muscles show improved calcium handling compared to muscle-only implants. We expect that this versatile in vitro system will enable studies of muscle-vasculature crosstalk in human development and disease.

Endothelial-mesenchymal transition in skeletal muscle: Opportunities and challenges from 3D microphysiological systems

Fibrosis is a pathological condition that in the muscular context is linked to primary diseases such as dystrophies, laminopathies, neuromuscular disorders, and volumetric muscle loss following traumas, accidents, and surgeries. Although some basic mechanisms regarding the role of myofibroblasts in the progression of muscle fibrosis have been discovered, our knowledge of the complex cell-cell, and cell-matrix interactions occurring in the fibrotic microenvironment is still rudimentary. Recently, vascular dysfunction has been emerging as a key hallmark of fibrosis through a process called endothelial-mesenchymal transition (EndoMT). Nevertheless, no effective therapeutic options are currently available for the treatment of muscle fibrosis. This lack is partially due to the absence of advanced in vitro models that can recapitulate the 3D architecture and functionality of a vascularized muscle microenvironment in a human context. These models could be employed for the identification of novel targets and for the screening of potential drugs blocking the progression of the disease. In this review, we explore the potential of 3D human muscle models in studying the role of endothelial cells and EndoMT in muscle fibrotic tissues and identify limitations and opportunities for optimizing the next generation of these microphysiological systems. Starting from the biology of muscle fibrosis and EndoMT, we highlight the synergistic links between different cell populations of the fibrotic microenvironment and how to recapitulate them through microphysiological systems.

Advanced PEG-tyramine biomaterial ink for precision engineering of perfusable and flexible small-diameter vascular constructs via coaxial printing

Vascularization is crucial for providing nutrients and oxygen to cells while removing waste. Despite advances in 3D-bioprinting, the fabrication of structures with void spaces and channels remains challenging. This study presents a novel approach to create robust yet flexible and permeable small (600-1300 μm) artificial vessels in a single processing step using 3D coaxial extrusion printing of a biomaterial ink, based on tyramine-modified polyethylene glycol (PEG-Tyr). We combined the gelatin biocompatibility/activity, robustness of PEG-Tyr and alginate with the shear-thinning properties of methylcellulose (MC) in a new biomaterial ink for the fabrication of bioinspired vessels. Chemical characterization using NMR and FTIR spectroscopy confirmed the successful modification of PEG with Tyr and rheological characterization indicated that the addition of PEG-Tyr decreased the viscosity of the ink. Enzyme-mediated crosslinking of PEG-Tyr allowed the formation of covalent crosslinks within the hydrogel chains, ensuring its stability. PEG-Tyr units improved the mechanical properties of the material, resulting in stretchable and elastic constructs without compromising cell viability and adhesion. The printed vessel structures displayed uniform wall thickness, shape retention, improved elasticity, permeability, and colonization by endothelial-derived - EA.hy926 cells. The chorioallantoic membrane (CAM) and in vivo assays demonstrated the hydrogel's ability to support neoangiogenesis. The hydrogel material with PEG-Tyr modification holds promise for vascular tissue engineering applications, providing a flexible, biocompatible, and functional platform for the fabrication of vascular structures.

Generating human skeletal myoblast spheroids for vascular myogenic tissue engineering

Engineered myogenic microtissues derived from human skeletal myoblasts offer unique opportunities for varying skeletal muscle tissue engineering applications, such asin vitrodrug-testing and disease modelling. However, more complex models require the incorporation of vascular structures, which remains to be challenging. In this study, myogenic spheroids were generated using a high-throughput, non-adhesive micropatterned surface. Since monoculture spheroids containing human skeletal myoblasts were unable to remain their integrity, co-culture spheroids combining human skeletal myoblasts and human adipose-derived stem cells were created. When using the optimal ratio, uniform and viable spheroids with enhanced myogenic properties were achieved. Applying a pre-vascularization strategy, through addition of endothelial cells, resulted in the formation of spheroids containing capillary-like networks, lumina and collagen in the extracellular matrix, whilst retaining myogenicity. Moreover, sprouting of endothelial cells from the spheroids when encapsulated in fibrin was allowed. The possibility of spheroids, from different maturation stages, to assemble into a more large construct was proven by doublet fusion experiments. The relevance of using three-dimensional microtissues with tissue-specific microarchitecture and increased complexity, together with the high-throughput generation approach, makes the generated spheroids a suitable tool forin vitrodrug-testing and human disease modeling.

Optimization of Culture Media and Cell Ratios for 3D In Vitro Skeletal Muscle Tissues with Endothelial Cells

A major challenge of engineering larger macroscale tissues in vitro is the limited diffusion of nutrients and oxygen to the interior. For skeletal muscle, this limitation results in millimeter scale outcomes to avoid necrosis. One method to address this constraint may be to vascularize in vitro-grown muscle tissue, to support nutrient (culture media) flow into the interior of the structure. In this exploratory study, we examine culture conditions that enable myogenic development and endothelial cell survival within tissue engineered 3D muscles. Myoblasts (C2C12s), endothelial cells (HUVECs), and endothelial support cells (C3H 10T1/2s) were seeded into Matrigel-fibrin hydrogels and cast into 3D printed frames to form 3D in vitro skeletal muscle tissues. Our preliminary results suggest that the simultaneous optimization of culture media formulation and cell concentrations is necessary for 3D cultured muscles to exhibit robust myosin heavy chain expression and GFP expression from GFP-transfected endothelial cells. The ability to form differentiated 3D muscles containing endothelial cells is a key step toward achieving vascularized 3D muscle tissues, which have potential use as tissue for implantation in a medical setting, as well as for future foods such as cultivated meats.

Upscaled Skeletal Muscle Engineered Tissue with In Vivo Vascularization and Innervation Potential

Engineering functional tissues of clinically relevant size (in mm-scale) in vitro is still a challenge in tissue engineering due to low oxygen diffusion and lack of vascularization. To address these limitations, a perfusion bioreactor was used to generate contractile engineered muscles of a 3 mm-thickness and a 8 mm-diameter. This study aimed to upscale the process to 50 mm in diameter by combining murine skeletal myoblasts (SkMbs) with human adipose-derived stromal vascular fraction (SVF) cells, providing high neuro-vascular potential in vivo. SkMbs were cultured on a type-I-collagen scaffold with (co-culture) or without (monoculture) SVF. Large-scale muscle-like tissue showed an increase in the maturation index over time (49.18 ± 1.63% and 76.63 ± 1.22%, at 9 and 11 days, respectively) and a similar force of contraction in mono- (43.4 ± 2.28 µN) or co-cultured (47.6 ± 4.7 µN) tissues. Four weeks after implantation in subcutaneous pockets of nude rats, the vessel length density within the constructs was significantly higher in SVF co-cultured tissues (5.03 ± 0.29 mm/mm²) compared to monocultured tissues (3.68 ± 0.32 mm/mm²) (p < 0.005). Although no mature neuromuscular junctions were present, nerve-like structures were predominantly observed in the engineered tissues co-cultured with SVF cells. This study demonstrates that SVF cells can support both in vivo vascularization and innervation of contractile muscle-like tissues, making significant progress towards clinical translation.

Ionically Modified Gelatin Hydrogels Maintain Murine Myogenic Cell Viability and Fusion Capacity

For tissue engineering of skeletal muscles, there is a need for biomaterials which do not only allow cell attachment, proliferation, and differentiation, but also support the physiological conditions of the tissue. Next to the chemical nature and structure of the biomaterial, its response to the application of biophysical stimuli, such as mechanical deformation or application of electrical pulses, can impact in vitro tissue culture. In this study, gelatin methacryloyl (GelMA) is modified with hydrophilic 2-acryloxyethyltrimethylammonium chloride (AETA) and 3-sulfopropyl acrylate potassium (SPA) ionic comonomers to obtain a piezoionic hydrogel. Rheology, mass swelling, gel fraction, and mechanical characteristics are determined. The piezoionic properties of the SPA and AETA-modified GelMA are confirmed by a significant increase in ionic conductivity and an electrical response as a function of mechanical stress. Murine myoblasts display a viability of >95% after 1 week on the piezoionic hydrogels, confirming their biocompatibility. The GelMA modifications do not influence the fusion capacity of the seeded myoblasts or myotube width after myotube formation. These results describe a novel functionalization providing new possibilities to exploit piezo-effects in the tissue engineering field.

Comparative analysis of hypoxic response of human microvascular and umbilical vein endothelial cells in 2D and 3D cell culture systems

In vitro cultivation conditions play a crucial role in cell physiology and the cellular response to external stimuli. Oxygen concentrations represent an essential microenvironmental factor influencing cell physiology and behaviour both in vivo and in vitro. Therefore, new approaches are urgently needed to monitor and control oxygen concentrations in 2D and 3D cultures, as well as cell reactions to these concentrations. In this work, we modified two types of human endothelial cells-human microvascular (huMECs) and umbilical vein endothelial cells (huVECs) with genetically encoded hypoxia biosensors and monitored cell reactions in 2D to different oxygen concentrations. Moreover, we fabricated 3D cell spheroids of different cell numbers and sizes to reveal the onset of hypoxia in huVECs and huMECs. We could demonstrate a quantitative sensor response of two cell types to reduced oxygen supply in 2D and reveal different thresholds for hypoxic response. In 3D cell spheroids we could estimate critical construct sizes for the appearance of a hypoxic core. This work for the first time directly demonstrates different hypoxic signatures for huVECs and huMECs in 2D and 3D cell culture systems.

Bioprinted anisotropic scaffolds with fast stress relaxation bioink for engineering 3D skeletal muscle and repairing volumetric muscle loss

Viscoelastic hydrogels can enhance 3D cell migration and proliferation due to the faster stress relaxation promoting the arrangement of the cellular microenvironment. However, most synthetic photocurable hydrogels used as bioink materials for 3D bioprinting are typically elastic. Developing a photocurable hydrogel bioink with fast stress relaxation would be beneficial for 3D bioprinting engineered 3D skeletal muscles in vitro and repairing volumetric muscle loss (VML) in vivo; however, this remains an ongoing challenge. This study aims to develop an interpenetrating network (IPN) hydrogel with tunable stress relaxation using a combination of gelatin methacryloyl (GelMA) and fibrinogen. These IPN hydrogels with faster stress relaxation showed higher 3D cellular proliferation and better differentiation. A 3D anisotropic biomimetic scaffold was further developed via a printing gel-in-gel strategy, where the extrusion printing of cell-laden viscoelastic FG hydrogel within Carbopol supported gel. The 3D engineered skeletal muscle tissue was further developed via 3D aligned myotube formation and contraction. Furthermore, the cell-free 3D printed scaffold was implanted into a rat VML model, and both the short and long-term repair results demonstrated its ability to enhance functional skeletal muscle tissue regeneration. These data suggest that such viscoelastic hydrogel provided a suitable 3D microenvironment for enhancing 3D myogenic differentiation, and the 3D bioprinted anisotropic structure provided a 3D macroenvironment for myotube organization, which indicated the potential in skeletal muscle engineering and VML regeneration. STATEMENT OF SIGNIFICANCE: The development of a viscoelastic 3D aligned biomimetic skeletal muscle scaffold has been focused on skeletal muscle regeneration. However, a credible technique combining viscoelastic hydrogel and printing gel-in-gel strategy for fabricating skeletal muscle tissue was rarely reported. Therefore, in this study, we present an interpenetrating network (IPN) hydrogel with fast stress relaxation for 3D bioprinting engineered skeletal muscle via a printing gel-in-gel strategy. Such IPN hydrogels with tunable fast stress relaxation resulted in high 3D cellular proliferation and adequate differentiation in vitro. Besides, the 3D hydrogel-based scaffolds also enhance functional skeletal muscle regeneration in situ. We believe that this study provides several notable advances in tissue engineering that can be potentially used for skeletal muscle injury treatment in clinical.

Organotypic cultures as aging associated disease models

Aging remains a primary risk factor for a host of diseases, including leading causes of death. Aging and associated diseases are inherently multifactorial, with numerous contributing factors and phenotypes at the molecular, cellular, tissue, and organismal scales. Despite the complexity of aging phenomena, models currently used in aging research possess limitations. Frequently used in vivo models often have important physiological differences, age at different rates, or are genetically engineered to match late disease phenotypes rather than early causes. Conversely, routinely used in vitro models lack the complex tissue-scale and systemic cues that are disrupted in aging. To fill in gaps between in vivo and traditional in vitro models, researchers have increasingly been turning to organotypic models, which provide increased physiological relevance with the accessibility and control of in vitro context. While powerful tools, the development of these models is a field of its own, and many aging researchers may be unaware of recent progress in organotypic models, or hesitant to include these models in their own work. In this review, we describe recent progress in tissue engineering applied to organotypic models, highlighting examples explicitly linked to aging and associated disease, as well as examples of models that are relevant to aging. We specifically highlight progress made in skin, gut, and skeletal muscle, and describe how recently demonstrated models have been used for aging studies or similar phenotypes. Throughout, this review emphasizes the accessibility of these models and aims to provide a resource for researchers seeking to leverage these powerful tools.

Enhancing Myoblast Fusion and Myotube Diameter in Human 3D Skeletal Muscle Constructs by Electromagnetic Stimulation

Skeletal muscle tissue engineering (SMTE) aims at the in vitro generation of 3D skeletal muscle engineered constructs which mimic the native muscle structure and function. Although native skeletal muscle is a highly dynamic tissue, most research approaches still focus on static cell culture methods, while research on stimulation protocols indicates a positive effect, especially on myogenesis. A more mature muscle construct may be needed especially for the potential applications for regenerative medicine purposes, disease or drug disposition models. Most efforts towards dynamic cell or tissue culture methods have been geared towards mechanical or electrical stimulation or a combination of those. In the context of dynamic methods, pulsed electromagnetic field (PEMF) stimulation has been extensively used in bone tissue engineering, but the impact of PEMF on skeletal muscle development is poorly explored. Here, we evaluated the effects of PEMF stimulation on human skeletal muscle cells both in 2D and 3D experiments. First, PEMF was applied on 2D cultures of human myoblasts during differentiation. In 2D, enhanced myogenesis was observed, as evidenced by an increased myotube diameter and fusion index. Second, 2D results were translated towards 3D bioartificial muscles (BAMs). BAMs were subjected to PEMF for varying exposure times, where a 2-h daily stimulation was found to be effective in enhancing 3D myotube formation. Third, applying this protocol for the entire 16-days culture period was compared to a stimulation starting at day 8, once the myotubes were formed. The latter was found to result in significantly higher myotube diameter, fusion index, and increased myosin heavy chain 1 expression. This work shows the potential of electromagnetic stimulation for enhancing myotube formation both in 2D and 3D, warranting its further consideration in dynamic culturing techniques.

Contractile force assessment methods for in vitro skeletal muscle tissues

Over the last few years, there has been growing interest in measuring the contractile force (CF) of engineered muscle tissues to evaluate their functionality. However, there are still no standards available for selecting the most suitable experimental platform, measuring system, culture protocol, or stimulation patterns. Consequently, the high variability of published data hinders any comparison between different studies. We have identified that cantilever deflection, post deflection, and force transducers are the most commonly used configurations for CF assessment in 2D and 3D models. Additionally, we have discussed the most relevant emerging technologies that would greatly complement CF evaluation with intracellular and localized analysis. This review provides a comprehensive analysis of the most significant advances in CF evaluation and its critical parameters. In order to compare contractile performance across experimental platforms, we have used the specific force (sF, kN/m2), CF normalized to the calculated cross-sectional area (CSA). However, this parameter presents a high variability throughout the different studies, which indicates the need to identify additional parameters and complementary analysis suitable for proper comparison. We propose that future contractility studies in skeletal muscle constructs report detailed information about construct size, contractile area, maturity level, sarcomere length, and, ideally, the tetanus-to-twitch ratio. These studies will hopefully shed light on the relative impact of these variables on muscle force performance of engineered muscle constructs. Prospective advances in muscle tissue engineering, particularly in muscle disease models, will require a joint effort to develop standardized methodologies for assessing CF of engineered muscle tissues.

The Evolution of Complex Muscle Cell In Vitro Models to Study Pathomechanisms and Drug Development of Neuromuscular Disease

Many neuromuscular disease entities possess a significant disease burden and therapeutic options remain limited. Innovative human preclinical models may help to uncover relevant disease mechanisms and enhance the translation of therapeutic findings to strengthen neuromuscular disease precision medicine. By concentrating on idiopathic inflammatory muscle disorders, we summarize the recent evolution of the novel in vitro models to study disease mechanisms and therapeutic strategies. A particular focus is laid on the integration and simulation of multicellular interactions of muscle tissue in disease phenotypes in vitro. Finally, the requirements of a neuromuscular disease drug development workflow are discussed with a particular emphasis on cell sources, co-culture systems (including organoids), functionality, and throughput.

Scaffolding Biomaterials for 3D Cultivated Meat: Prospects and Challenges

Cultivating meat from stem cells rather than by raising animals is a promising solution to concerns about the negative externalities of meat production. For cultivated meat to fully mimic conventional meat's organoleptic and nutritional properties, innovations in scaffolding technology are required. Many scaffolding technologies are already developed for use in biomedical tissue engineering. However, cultivated meat production comes with a unique set of constraints related to the scale and cost of production as well as the necessary attributes of the final product, such as texture and food safety. This review discusses the properties of vertebrate skeletal muscle that will need to be replicated in a successful product and the current state of scaffolding innovation within the cultivated meat industry, highlighting promising scaffold materials and techniques that can be applied to cultivated meat development. Recommendations are provided for future research into scaffolds capable of supporting the growth of high-quality meat while minimizing production costs. Although the development of appropriate scaffolds for cultivated meat is challenging, it is also tractable and provides novel opportunities to customize meat properties.

Recent Advances on Cell-Based Co-Culture Strategies for Prevascularization in Tissue Engineering

Currently, the fabrication of a functional vascular network to maintain the viability of engineered tissues is a major bottleneck in the way of developing a more advanced engineered construct. Inspired by vasculogenesis during the embryonic period, the in vitro prevascularization strategies have focused on optimizing communications and interactions of cells, biomaterial and culture conditions to develop a capillary-like network to tackle the aforementioned issue. Many of these studies employ a combination of endothelial lineage cells and supporting cells such as mesenchymal stem cells, fibroblasts, and perivascular cells to create a lumenized endothelial network. These supporting cells are necessary for the stabilization of the newly developed endothelial network. Moreover, to optimize endothelial network development without impairing biomechanical properties of scaffolds or differentiation of target tissue cells, several other factors, including target tissue, endothelial cell origins, the choice of supporting cell, culture condition, incorporated pro-angiogenic factors, and choice of biomaterial must be taken into account. The prevascularization method can also influence the endothelial lineage cell/supporting cell co-culture system to vascularize the bioengineered constructs. This review aims to investigate the recent advances on standard cells used in in vitro prevascularization methods, their co-culture systems, and conditions in which they form an organized and functional vascular network.

Tissue-Engineered Skeletal Muscle Models to Study Muscle Function, Plasticity, and Disease

Skeletal muscle possesses remarkable plasticity that permits functional adaptations to a wide range of signals such as motor input, exercise, and disease. Small animal models have been pivotal in elucidating the molecular mechanisms regulating skeletal muscle adaptation and plasticity. However, these small animal models fail to accurately model human muscle disease resulting in poor clinical success of therapies. Here, we review the potential of in vitro three-dimensional tissue-engineered skeletal muscle models to study muscle function, plasticity, and disease. First, we discuss the generation and function of in vitro skeletal muscle models. We then discuss the genetic, neural, and hormonal factors regulating skeletal muscle fiber-type in vivo and the ability of current in vitro models to study muscle fiber-type regulation. We also evaluate the potential of these systems to be utilized in a patient-specific manner to accurately model and gain novel insights into diseases such as Duchenne muscular dystrophy (DMD) and volumetric muscle loss. We conclude with a discussion on future developments required for tissue-engineered skeletal muscle models to become more mature, biomimetic, and widely utilized for studying muscle physiology, disease, and clinical use.

A Pound of Flesh: What Cachexia Is and What It Is Not

Body weight loss, mostly due to the wasting of skeletal muscle and adipose tissue, is the hallmark of the so-called cachexia syndrome. Cachexia is associated with several acute and chronic disease states such as cancer, chronic obstructive pulmonary disease (COPD), heart and kidney failure, and acquired and autoimmune diseases and also pharmacological treatments such as chemotherapy. The clinical relevance of cachexia and its impact on patients’ quality of life has been neglected for decades. Only recently did the international community agree upon a definition of the term cachexia, and we are still awaiting the standardization of markers and tests for the diagnosis and staging of cancer-related cachexia. In this review, we discuss cachexia, considering the evolving use of the term for diagnostic purposes and the implications it has for clinical biomarkers, to provide a comprehensive overview of its biology and clinical management. Advances and tools developed so far for the in vitro testing of cachexia and drug screening will be described. We will also evaluate the nomenclature of different forms of muscle wasting and degeneration and discuss features that distinguish cachexia from other forms of muscle wasting in the context of different conditions.

Directed self-assembly of spheroids into modular vascular beds for engineering large tissue constructs

Spheroids can be used as building-blocks for bottom-up generation of artificial vascular beds, but current biofabrication strategies are often time-consuming and complex. Also, pre-optimization of single spheroid properties is often neglected. Here, we report a simple setup for rapid biomanufacturing of spheroid-based patch-like vascular beds. Prior to patch assembly, spheroids combining mesenchymal stem/stromal cells (MSC) and outgrowth endothelial cells (OEC) at different ratios (10:1; 5:1; 1:1; 1:5) were formed in non-adhesive microwells and monitored along 7 days. Optimal OEC retention and organization was observed at 1:1 MSC/OEC ratio. Dynamic remodelling of spheroids led to changes in both cellular and extracellular matrix components (ECM) over time. Some OEC formed internal clusters, while others organized into a peripheral monolayer, stabilized by ECM and pericyte-like cells, with concomitant increase in surface stiffness. Along spheroid culture, OEC switched from an active to a quiescent state, and their endothelial sprouting potential was significantly abrogated, suggesting that immature spheroids may be more therapeutically relevant. Non-adhesive moulds were subsequently used for triggering rapid, one-step, spheroid formation/fusion into square-shaped patches, with spheroids uniformly interspaced via a thin cell layer. The high surface area, endothelial sprouting potential, and scalability of the developed spheroid-based patches make them stand out as artificial vascular beds for modular engineering of large tissue constructs.

Next Stage Approach to Tissue Engineering Skeletal Muscle

Large-scale muscle injury in humans initiates a complex regeneration process, as not only the muscular, but also the vascular and neuro-muscular compartments have to be repaired. Conventional therapeutic strategies often fall short of reaching the desired functional outcome, due to the inherent complexity of natural skeletal muscle. Tissue engineering offers a promising alternative treatment strategy, aiming to achieve an engineered tissue close to natural tissue composition and function, able to induce long-term, functional regeneration after in vivo implantation. This review aims to summarize the latest approaches of tissue engineering skeletal muscle, with specific attention toward fabrication, neuro-angiogenesis, multicellularity and the biochemical cues that adjuvate the regeneration process.