Neural cell integration into 3D bioprinted skeletal muscle constructs accelerates restoration of muscle function

3D bioprinting of a biomimetic meniscal scaffold for application in tissue engineering

Appropriate biomimetic scaffolds created via 3D bioprinting are promising methods for treating damaged menisci. However, given the unique anatomical structure and complex stress environment of the meniscus, many studies have adopted various techniques to take full advantage of different materials, such as the printing combined with infusion, or electrospining, to chase the biomimetic meniscus, which makes the process complicated to some extent. Some researchers have tried to tackle the challenges only by 3D biopringting, while its alternative materials and models have been constrained. In this study, based on a multilayer biomimetic strategy, we optimized the preparation of meniscus-derived bioink, gelatin methacrylate (GelMA)/meniscal extracellular matrix (MECM), to take printability and cytocompatibility into account together. Subsequently, a customized 3D bioprinting system featuring a dual nozzle + multitemperature printing was used to integrate the advantages of polycaprolactone (PCL) and meniscal fibrocartilage chondrocytes (MFCs)-laden GelMA/MECM bioink to complete the biomimetic meniscal scaffold, which had the best biomimetic features in terms of morphology and components. Furthermore, cell viability, mechanics, biodegradation and tissue formation in vivo were performed to ensure that the scaffold had sufficient feasibility and functionality, thereby providing a reliable basis for its application in tissue engineering.

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We have optimized the preparation of meniscus-derived bioink with good printability and cytocompatibility.

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A customized printing system for biomimetic meniscus, the dual-nozzle + multitemperature printing system was developed.

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We have achieved multilayer meniscal biomimetic strategy, especially the best biomimetics of morphology and components.

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Focusing on application prospect, we designed a few experiments to verity the feasibility and functionality of the scaffold.

A photo-crosslinkable cartilage-derived extracellular matrix bioink for auricular cartilage tissue engineering

Three-dimensional (3D) bioprinting of patient-specific auricular cartilage constructs could aid in the reconstruction process of traumatically injured or congenitally deformed ear cartilage. To achieve this, a hydrogel-based bioink is required that recapitulates the complex cartilage microenvironment. Tissue-derived decellularized extracellular matrix (dECM)-based hydrogels have been used as bioinks for cell-based 3D bioprinting because they contain tissue-specific ECM components that play a vital role in cell adhesion, growth, and differentiation. In this study, porcine auricular cartilage tissues were isolated and decellularized, and the decellularized cartilage tissues were characterized by histology, biochemical assay, and proteomics. This cartilage-derived dECM (cdECM) was subsequently processed into a photo-crosslinkable hydrogel using methacrylation (cdECMMA) and mixed with chondrocytes to create a printable bioink. The rheological properties, printability, and in vitro biological properties of the cdECMMA bioink were examined. The results showed cdECM was obtained with complete removal of cellular components while preserving major ECM proteins. After methacrylation, the cdECMMA bioinks were printed in anatomical ear shape and exhibited adequate mechanical properties and structural integrity. Specifically, auricular chondrocytes in the printed cdECMMA hydrogel constructs maintained their viability and proliferation capacity and eventually produced cartilage ECM components, including collagen and glycosaminoglycans (GAGs). The potential of cell-based bioprinting using this cartilage-specific dECMMA bioink is demonstrated as an alternative option for auricular cartilage reconstruction.

Building neuromuscular junctions in vitro

The neuromuscular junction (NMJ) has been the model of choice to understand the principles of communication at chemical synapses. Following groundbreaking experiments carried out over 60 years ago, many studies have focused on the molecular mechanisms underlying the development and physiology of these synapses. This Review summarizes the progress made to date towards obtaining faithful models of NMJs in vitro We provide a historical approach discussing initial experiments investigating NMJ development and function from Xenopus to mice, the creation of chimeric co-cultures, in vivo approaches and co-culture methods from ex vivo and in vitro derived cells, as well as the most recent developments to generate human NMJs. We discuss the benefits of these techniques and the challenges to be addressed in the future for promoting our understanding of development and human disease.

3D Bioprinted Highly Elastic Hybrid Constructs for Advanced Fibrocartilaginous Tissue Regeneration

Advanced strategies to bioengineer a fibrocartilaginous tissue to restore the function of the meniscus are necessary. Currently, 3D bioprinting technologies have been employed to fabricate clinically relevant patient-specific complex constructs to address unmet clinical needs. In this study, a highly elastic hybrid construct for fibrocartilaginous regeneration is produced by co-printing a cell-laden gellan gum/fibrinogen (GG/FB) composite bioink together with a silk fibroin methacrylate (Sil-MA) bioink in an interleaved crosshatch pattern. We characterize each bioink formulation by measuring the rheological properties, swelling ratio, and compressive mechanical behavior. For in vitro biological evaluations, porcine primary meniscus cells (pMCs) are isolated and suspended in the GG/FB bioink for the printing process. The results show that the GG/FB bioink provides a proper cellular microenvironment for maintaining the cell viability and proliferation capacity, as well as the maturation of the pMCs in the bioprinted constructs, while the Sil-MA bioink offers excellent biomechanical behavior and structural integrity. More importantly, this bioprinted hybrid system shows the fibrocartilaginous tissue formation without a dimensional change in a mouse subcutaneous implantation model during the 10-week postimplantation. Especially, the alignment of collagen fibers is achieved in the bioprinted hybrid constructs. The results demonstrate this bioprinted mechanically reinforced hybrid construct offers a versatile and promising alternative for the production of advanced fibrocartilaginous tissue.

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.

Pre-Clinical Cell Therapeutic Approaches for Repair of Volumetric Muscle Loss

Extensive damage to skeletal muscle tissue due to volumetric muscle loss (VML) is beyond the inherent regenerative capacity of the body, and results in permanent functional debilitation. Current clinical treatments fail to fully restore native muscle function. Recently, cell-based therapies have emerged as a promising approach to promote skeletal muscle regeneration following injury and/or disease. Stem cell populations, such as muscle stem cells, mesenchymal stem cells and induced pluripotent stem cells (iPSCs), have shown a promising capacity for muscle differentiation. Support cells, such as endothelial cells, nerve cells or immune cells, play a pivotal role in providing paracrine signaling cues for myogenesis, along with modulating the processes of inflammation, angiogenesis and innervation. The efficacy of cell therapies relies on the provision of instructive microenvironmental cues and appropriate intercellular interactions. This review describes the recent developments of cell-based therapies for the treatment of VML, with a focus on preclinical testing and future trends in the field.

Bioprinting stem cells: building physiological tissues one cell at a time

Bioprinting aims to direct the spatial arrangement in three dimensions of cells, biomaterials, and growth factors. The biofabrication of clinically relevant constructs for the repair or modeling of either diseased or damaged tissues is rapidly advancing, resulting in the ability to three-dimensional (3D) print biomimetic platforms which imitate a large number of tissues in the human body. Primary tissue-specific cells are typically isolated from patients and used for the fabrication of 3D models for drug screening or tissue repair purposes. However, the lack of resilience of these platforms, due to the difficulties in harnessing, processing, and implanting patient-specific cells can limit regeneration ability. The printing of stem cells obviates these hurdles, producing functional in vitro models or implantable constructs. Advancements in biomaterial science are helping the development of inks suitable for the encapsulation and the printing of stem cells, promoting their functional growth and differentiation. This review specifically aims to investigate the most recent studies exploring innovative and functional approaches for the printing of 3D constructs to model disease or repair damaged tissues. Key concepts in tissue physiology are highlighted, reporting stem cell applications in biofabrication. Bioprinting technologies and biomaterial inks are listed and analyzed, including recent advancements in biomaterial design for bioprinting applications, commenting on the influence of biomaterial inks on the encapsulated stem cells. Ultimately, most recent successful efforts and clinical potentials for the manufacturing of functional physiological tissue substitutes are reported here, with a major focus on specific tissues, such as vasculature, heart, lung and airways, liver, bone and muscle.

Pre-innervated tissue-engineered muscle promotes a pro-regenerative microenvironment following volumetric muscle loss

Volumetric muscle loss (VML) is the traumatic or surgical loss of skeletal muscle beyond the inherent regenerative capacity of the body, generally leading to severe functional deficit. Formation of appropriate somato-motor innervations remains one of the biggest challenges for both autologous grafts as well as tissue-engineered muscle constructs. We aim to address this challenge by developing pre-innervated tissue-engineered muscle comprised of long aligned networks of spinal motor neurons and skeletal myocytes on aligned nanofibrous scaffolds. Motor neurons led to enhanced differentiation and maturation of skeletal myocytes in vitro. These pre-innervated tissue-engineered muscle constructs when implanted in a rat VML model significantly increased satellite cell density, neuromuscular junction maintenance, graft revascularization, and muscle volume over three weeks as compared to myocyte-only constructs and nanofiber scaffolds alone. These pro-regenerative effects may enhance functional neuromuscular regeneration following VML, thereby improving the levels of functional recovery following these devastating injuries.

Advances in biomaterials for skeletal muscle engineering and obstacles still to overcome

Repair of injured skeletal muscle is a sophisticated process that uses immune, muscle, perivascular, and neural cells. In acute injury, the robust endogenous repair process can facilitate complete regeneration with little to no functional deficit. However, in severe injury, the damage is beyond the capacity for self-repair, often resulting in structural and functional deficits. Aside from the insufficiencies in muscle function, the aesthetic deficits can impact quality of life. Current clinical treatments are significantly limited in their capacity to structurally and functionally repair the damaged skeletal muscle. Therefore, alternative approaches are needed. Biomaterial therapies for skeletal muscle engineering have leveraged natural materials with sophisticated scaffold fabrication techniques to guide cell infiltration, alignment, and differentiation. Advances in biomaterials paired with a standardized and rigorous assessment of resulting tissue formation have greatly advanced the field of skeletal muscle engineering in the last several years. Herein, we discuss the current trends in biomaterials-based therapies for skeletal muscle regeneration and present the obstacles still to be overcome before clinical translation is possible. With millions of people affected by muscle trauma each year, the development of a therapy that can repair the structural and functional deficits after severe muscle injury is pivotal.

Extracellular Matrix-Derived Hydrogels as Biomaterial for Different Skeletal Muscle Tissue Replacements

Recently, skeletal muscle represents a complex and challenging tissue to be generated in vitro for tissue engineering purposes. Several attempts have been pursued to develop hydrogels with different formulations resembling in vitro the characteristics of skeletal muscle tissue in vivo. This review article describes how different types of cell-laden hydrogels recapitulate the multiple interactions occurring between extracellular matrix (ECM) and muscle cells. A special attention is focused on the biochemical cues that affect myocytes morphology, adhesion, proliferation, and phenotype maintenance, underlining the importance of topographical cues exerted on the hydrogels to guide cellular orientation and facilitate myogenic differentiation and maturation. Moreover, we highlight the crucial role of 3D printing and bioreactors as useful platforms to finely control spatial deposition of cells into ECM based hydrogels and provide the skeletal muscle native-like tissue microenvironment, respectively.