Biomaterials for skeletal muscle tissue engineering

Fabrication of fully aligned self-assembled cell-laden collagen filaments for tissue engineering via a hybrid bioprinting process

Cell-laden structures play a pivotal role in various tissue engineering applications, particularly in tissue restoration. Interactions between cells within bioprinted structures are crucial for successful tissue development and regulation of stem cell fate through intricate cell-to-cell signaling pathways. In this study, we developed a new technique that combines polyethylene glycol (PEG)-infused submerged bioprinting with a stretching procedure. This approach facilitated the generation of fully aligned collagen structures consisting of myoblasts and a low concentration (2 wt%) of collagen to efficiently encourage muscle tissue regeneration. By adjusting several processing parameters, we obtained biologically safe and mechanically stable cell-laden collagen filaments with uniaxial alignment. Notably, the cell filaments exhibited markedly elevated cellular activities compared to those exhibited by conventional bioprinted filaments, even at similar cell densities. Moreover, when we implanted structures containing adipose stem cells into mice, we observed a significantly increased level of myogenesis compared to that in normally bioprinted struts. Thus, this promising approach has the potential to revolutionize tissue engineering by fostering enhanced cellular interactions and promoting improved outcomes in regenerative medicine.

VEGF-delivering PEG hydrogels promote vascularization in the porcine subcutaneous space

For cell therapies, the subcutaneous space is an attractive transplant site due to its large surface area and accessibility for implantation, monitoring, biopsy, and retrieval. However, its poor vascularization has catalyzed research to induce blood vessel formation within the site to enhance cell revascularization and survival. Most studies focus on the subcutaneous space of rodents, which does not recapitulate important anatomical features and vascularization responses of humans. Herein, we evaluate biomaterial-driven vascularization in the porcine subcutaneous space. Additionally, we report the first use of cost-effective fluorescent microspheres to quantify perfusion in the porcine subcutaneous space. We investigate the vascularization-inducing efficacy of vascular endothelial growth factor (VEGF)-delivering synthetic hydrogels based on 4-arm poly(ethylene) glycol macromers with terminal maleimides (PEG-4MAL). We compare three groups: a non-degradable hydrogel with a VEGF-releasing PEG-4MAL gel coating (Core+VEGF gel); an uncoated, non-degradable hydrogel (Core-only); and naïve tissue. After 2 weeks, Core+VEGF gel has significantly higher tissue perfusion, blood vessel area, blood vessel density, and number of vessels compared to both Core-only and naïve tissue. Furthermore, healthy vital signs during surgery and post-procedure metrics demonstrate the safety of hydrogel delivery. We demonstrate that VEGF-delivering synthetic hydrogels induce robust vascularization and perfusion in the porcine subcutaneous space.

Citric Acid: A Nexus Between Cellular Mechanisms and Biomaterial Innovations

Citrate-based biodegradable polymers have emerged as a distinctive biomaterial platform with tremendous potential for diverse medical applications. By harnessing their versatile chemistry, these polymers exhibit a wide range of material and bioactive properties, enabling them to regulate cell metabolism and stem cell differentiation through energy metabolism, metabonegenesis, angiogenesis, and immunomodulation. Moreover, the recent US Food and Drug Administration (FDA) clearance of the biodegradable poly(octamethylene citrate) (POC)/hydroxyapatite-based orthopedic fixation devices represents a translational research milestone for biomaterial science. POC joins a short list of biodegradable synthetic polymers that have ever been authorized by the FDA for use in humans. The clinical success of POC has sparked enthusiasm and accelerated the development of next-generation citrate-based biomaterials. This review presents a comprehensive, forward-thinking discussion on the pivotal role of citrate chemistry and metabolism in various tissue regeneration and on the development of functional citrate-based metabotissugenic biomaterials for regenerative engineering applications.

Biomaterials-Based Technologies in Skeletal Muscle Tissue Engineering

For many clinically prevalent severe injuries, the inherent regenerative capacity of skeletal muscle remains inadequate. Skeletal muscle tissue engineering (SMTE) seeks to meet this clinical demand. With continuous progress in biomedicine and related technologies including micro/nanotechnology and 3D printing, numerous studies have uncovered various intrinsic mechanisms regulating skeletal muscle regeneration and developed tailored biomaterial systems based on these understandings. Here, the skeletal muscle structure and regeneration process are discussed and the diverse biomaterial systems derived from various technologies are explored in detail. Biomaterials serve not merely as local niches for cell growth, but also as scaffolds endowed with structural or physicochemical properties that provide tissue regenerative cues such as topographical, electrical, and mechanical signals. They can also act as delivery systems for stem cells and bioactive molecules that have been shown as key participants in endogenous repair cascades. To achieve bench-to-bedside translation, the typical effect enabled by biomaterial systems and the potential underlying molecular mechanisms are also summarized. Insights into the roles of biomaterials in SMTE from cellular and molecular perspectives are provided. Finally, perspectives on the advancement of SMTE are provided, for which gene therapy, exosomes, and hybrid biomaterials may hold promise to make important contributions.

Therapeutic applications of biological macromolecules and scaffolds for skeletal muscle regeneration: A review

Skeletal muscle (SM) mass and strength maintenance are important requirements for human well-being. SM regeneration to repair minor injuries depends upon the myogenic activities of muscle satellite (stem) cells. However, losses of regenerative properties following volumetric muscle loss or severe trauma or due to congenital muscular abnormalities are not self-restorable, and thus, these conditions have major healthcare implications and pose clinical challenges. In this context, tissue engineering based on different types of biomaterials and scaffolds provides an encouraging means of structural and functional SM reconstruction. In particular, biomimetic (able to transmit biological signals) and several porous scaffolds are rapidly evolving. Several biological macromolecules/biomaterials (collagen, gelatin, alginate, chitosan, and fibrin etc.) are being widely used for SM regeneration. However, available alternatives for SM regeneration must be redesigned to make them more user-friendly and economically feasible with longer shelf lives. This review aimed to explore the biological aspects of SM regeneration and the roles played by several biological macromolecules and scaffolds in SM regeneration in cases of volumetric muscle loss.

Glutenin-chitosan 3D porous scaffolds with tunable stiffness and systematized microstructure for cultured meat model

A glutenin (G)-chitosan (CS) complex (G-CS) was cross-linked by water annealing with aim to prepare structured 3D porous cultured meat scaffolds (CMS) here. The CMS has pore diameters ranging from 18 to 67 μm and compressive moduli from 16.09 to 60.35 kPa, along with the mixing ratio of G/CS. SEM showed the porous organized structure of CMS. FTIR and CD showed the increscent content of α-helix and β-sheet of G and strengthened hydrogen-bondings among G-CS molecules, which strengthened the stiffness of G-CS. Raman spectra exhibited an increase of G concentration resulted in higher crosslinking of disulfide-bonds in G-CS, which aggrandized the bridging effect of G-CS and maintained its three-dimensional network. Cell viability assay and immuno-fluorescence staining showed that G-CS effectively facilitated the growth and myogenic differentiation of porcine skeletal muscle satellite cells (PSCs). CLSM displayed that cells first occupied the angular space of hexagon and then ring-growth circle of PSCs were orderly formed on G-CS. The texture and color of CMS which loaded proliferated PSCs were fresh-meat like. These results showed that physical cross-linked G-CS scaffolds are the biocompatible and stable adaptable extracellular matrix with appropriate architectural cues and natural micro-environment for structured CM models.

Edible mycelium as proliferation and differentiation support for anchorage-dependent animal cells in cultivated meat production

Cultivated meat production requires bioprocess optimization to achieve cell densities that are multiple orders of magnitude higher compared to conventional cell culture techniques. These processes must maximize resource efficiency and cost-effectiveness by attaining high cell growth productivity per unit of medium. Microcarriers, or carriers, are compatible with large-scale bioreactor use, and offer a large surface-area-to-volume ratio for the adhesion and proliferation of anchorage-dependent animal cells. An ongoing challenge persists in the efficient retrieval of cells from the carriers, with conflicting reports on the effectiveness of trypsinization and the need for additional optimization measures such as carrier sieving. To surmount this issue, edible carriers have been proposed, offering the advantage of integration into the final food product while providing opportunities for texture, flavor, and nutritional incorporation. Recently, a proof of concept (POC) utilizing inactivated mycelium biomass derived from edible filamentous fungus demonstrated its potential as a support structure for myoblasts. However, this POC relied on a model mammalian cell line combination with a single mycelium species, limiting realistic applicability to cultivated meat production. This study aims to advance the POC. We found that the species of fungi composing the carriers impacts C2C12 myoblast cell attachment-with carriers derived from Aspergillus oryzae promoting the best proliferation. C2C12 myoblasts effectively differentiated on mycelium carriers when induced in myogenic differentiation media. Mycelium carriers also supported proliferation and differentiation of bovine satellite cells. These findings demonstrate the potential of edible mycelium carrier technology to be readily adapted in product development within the cultivated meat industry.

Injectable and Dynamically Crosslinked Zwitterionic Hydrogels for Anti-Fouling and Tissue Regeneration Applications

A zwitterionic injectable and degradable hydrogel based on hydrazide and aldehyde-functionalized [2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl)ammonium hydroxide (DMAPS) precursor polymers that can address practical in vivo needs is reported. Zwitterion fusion interactions between the zwitterionic precursor polymers create a secondary physically crosslinked network to enable much more rapid gelation than previously reported with other synthetic polymers, facilitating rapid gelation at much lower polymer concentrations or degrees of functionalization than previously accessible in addition to promoting zero swelling and long-term degradation responses and significantly stiffer mechanics than are typically accessed with previously reported low-viscosity precursor gelation systems. The hydrogels maintain the highly anti-fouling properties of conventional zwitterionic hydrogels against proteins, mammalian cells, and bacteria while also promoting anti-fibrotic tissue responses in vivo. Furthermore, the use of the hydrogels for effective delivery and subsequent controlled release of viable cells with tunable profiles both in vitro and in vivo is demonstrated, including the delivery of myoblasts in a mouse skeletal muscle defect model for reducing the time between injury and functional mobility recovery. The combination of the injectability, degradability, and tissue compatibility achieved offers the potential to expand the utility of zwitterionic hydrogels in minimally invasive therapeutic applications.

Emerging Therapeutic Strategies in Sarcopenia: An Updated Review on Pathogenesis and Treatment Advances

Sarcopenia is a prevalent degenerative skeletal muscle condition in the elderly population, posing a tremendous burden on diseased individuals and healthcare systems worldwide. Conventionally, sarcopenia is currently managed through nutritional interventions, physical therapy, and lifestyle modification, with no pharmaceutical agents being approved for specific use in this disease. As the pathogenesis of sarcopenia is still poorly understood and there is no treatment recognized as universally effective, recent research efforts have been directed at better comprehending this illness and diversifying treatment strategies. In this respect, this paper overviews the new advances in sarcopenia treatment in correlation with its underlying mechanisms. Specifically, this review creates an updated framework for sarcopenia, describing its etiology, pathogenesis, risk factors, and conventional treatments, further discussing emerging therapeutic approaches like new drug formulations, drug delivery systems, stem cell therapies, and tissue-engineered scaffolds in more detail.

Three-Dimensional Microfibrous Scaffold with Aligned Topography Produced via a Combination of Melt-Extrusion Additive Manufacturing and Porogen Leaching for In Vitro Skeletal Muscle Modeling

Skeletal muscle tissue (SMT) has a highly hierarchical and anisotropic morphology, featuring aligned and parallel structures at multiple levels. Various factors, including trauma and disease conditions, can compromise the functionality of skeletal muscle. The in vitro modeling of SMT represents a useful tool for testing novel drugs and therapies. The successful replication of SMT native morphology demands scaffolds with an aligned anisotropic 3D architecture. In this work, a 3D PCL fibrous scaffold with aligned morphology was developed through the synergistic combination of Melt-Extrusion Additive Manufacturing (MEAM) and porogen leaching, utilizing PCL as the bulk material and PEG as the porogen. PCL/PEG blends with different polymer ratios (60/40, 50/50, 40/60) were produced and characterized through a DSC analysis. The MEAM process parameters and porogen leaching in bi-distilled water allowed for the development of a micrometric anisotropic fibrous structure with fiber diameters ranging from 10 to 100 µm, depending on PCL/PEG blend ratios. The fibrous scaffolds were coated with Gelatin type A to achieve a biomimetic coating for an in vitro cell culture and mechanically characterized via AFM. The 40/60 PCL/PEG scaffolds yielded the most homogeneous and smallest fibers and the greatest physiological stiffness. In vitro cell culture studies were performed by seeding C2C12 cells onto a selected scaffold, enabling their attachment, alignment, and myotube formation along the PCL fibers during a 14-day culture period. The resultant anisotropic scaffold morphology promoted SMT-like cell conformation, establishing a versatile platform for developing in vitro models of tissues with anisotropic morphology.

Structural DNA nanotechnology at the nexus of next-generation bio-applications: challenges and perspectives

DNA nanotechnology has significantly progressed in the last four decades, creating nucleic acid structures widely used in various biological applications. The structural flexibility, programmability, and multiform customization of DNA-based nanostructures make them ideal for creating structures of all sizes and shapes and multivalent drug delivery systems. Since then, DNA nanotechnology has advanced significantly, and numerous DNA nanostructures have been used in biology and other scientific disciplines. Despite the progress made in DNA nanotechnology, challenges still need to be addressed before DNA nanostructures can be widely used in biological interfaces. We can open the door for upcoming uses of DNA nanoparticles by tackling these issues and looking into new avenues. The historical development of various DNA nanomaterials has been thoroughly examined in this review, along with the underlying theoretical underpinnings, a summary of their applications in various fields, and an examination of the current roadblocks and potential future directions.

Highly Aligned Ternary Nanofiber Matrices Loaded with MXene Expedite Regeneration of Volumetric Muscle Loss

Current therapeutic approaches for volumetric muscle loss (VML) face challenges due to limited graft availability and insufficient bioactivities. To overcome these limitations, tissue-engineered scaffolds have emerged as a promising alternative. In this study, we developed aligned ternary nanofibrous matrices comprised of poly(lactide-co-ε-caprolactone) integrated with collagen and Ti3C2Tx MXene nanoparticles (NPs) (PCM matrices), and explored their myogenic potential for skeletal muscle tissue regeneration. The PCM matrices demonstrated favorable physicochemical properties, including structural uniformity, alignment, microporosity, and hydrophilicity. In vitro assays revealed that the PCM matrices promoted cellular behaviors and myogenic differentiation of C2C12 myoblasts. Moreover, in vivo experiments demonstrated enhanced muscle remodeling and recovery in mice treated with PCM matrices following VML injury. Mechanistic insights from next-generation sequencing revealed that MXene NPs facilitated protein and ion availability within PCM matrices, leading to elevated intracellular Ca2+ levels in myoblasts through the activation of inducible nitric oxide synthase (iNOS) and serum/glucocorticoid regulated kinase 1 (SGK1), ultimately promoting myogenic differentiation via the mTOR-AKT pathway. Additionally, upregulated iNOS and increased NO- contributed to myoblast proliferation and fiber fusion, thereby facilitating overall myoblast maturation. These findings underscore the potential of MXene NPs loaded within highly aligned matrices as therapeutic agents to promote skeletal muscle tissue recovery.

Collagen biomaterials promote the regenerative repair of abdominal wall defects in Bama miniature pigs

Due to adhesion and rejection of recent traditional materials, it is still challenging to promote the regenerative repair of abdominal wall defects caused by different hernias or severe trauma. However, biomaterials with a high biocompatibility and low immunogenicity have exhibited great potential in the regeneration of abdominal muscle tissue. Previously, we have designed a biological collagen scaffold material combined with growth factor, which enables a fusion protein-collagen binding domain (CBD)-basic fibroblast growth factor (bFGF) to bind and release specifically. Though experiments in rodent animals have indicated the regeneration function of CBD-bFGF modified biological collagen scaffolds, its translational properties in large animals or humans are still in need of solid evidence. In this study, the abdominal wall defect model of Bama miniature pigs was established by artificial operations, and the defective abdominal wall was sealed with or without a polypropylene patch, and unmodified and CBD-bFGF modified biological collagen scaffolds. Results showed that a recurrent abdominal hernia was observed in the defect control group (without the use of mesh). Although the polypropylene patch can repair the abdominal wall defect, it also induced serious adhesion and inflammation. Meanwhile, both kinds of collagen biomaterials exhibited positive effects in repairing abdominal wall defects and reducing regional adhesion and inflammation. However, CBD-bFGF-modified collagen biomaterials failed to induce the regenerative repair reported in rat experiments. In addition, unmodified collagen biomaterials induced abdominal wall muscle regeneration rather than fibrotic repair. These results indicated that the unmodified collagen biomaterials are a better option among translational patches for the treatment of abdominal wall defects.

Extracellular matrix: the critical contributor to skeletal muscle regeneration-a comprehensive review

The regenerative ability of skeletal muscle (SM) in response to damage, injury, or disease is a highly intricate process that involves the coordinated activities of multiple cell types and biomolecular factors. Of these, extracellular matrix (ECM) is considered a fundamental component of SM regenerative ability. This review briefly discusses SM myogenesis and regeneration, the roles played by muscle satellite cells (MSCs), other cells, and ECM components, and the effects of their dysregulations on these processes. In addition, we review the various types of ECM scaffolds and biomaterials used for SM regeneration, their applications, recent advances in ECM scaffold research, and their impacts on tissue engineering and SM regeneration, especially in the context of severe muscle injury, which frequently results in substantial muscle loss and impaired regenerative capacity. This review was undertaken to provide a comprehensive overview of SM myogenesis and regeneration, the stem cells used for muscle regeneration, the significance of ECM in SM regeneration, and to enhance understanding of the essential role of the ECM scaffold during SM regeneration.

Efficient Myogenic Activities Achieved through Blade-Casting-Assisted Bioprinting of Aligned Myoblasts Laden in Collagen Bioink

This study investigated mechanical stimulation combined with three-dimensional (3D) bioprinting as a new approach for introducing biophysical and biological cues for tissue regeneration. A blade-casting method in conjunction with bioprinting was employed to fabricate bioengineered skeletal muscle constructs using a bioink composed of C2C12 myoblasts and collagen type-I. Various printing process parameters were selected and optimized to achieve a highly organized cell alignment within the constructs. The resulting cell-aligned constructs demonstrated remarkable improvement in actin filament alignment and cell proliferation compared with conventionally printed cell-laden constructs. This improvement can be attributed to the synergistic effects of mechanotransduction, facilitating the cellular response to mechanical cues and the alignment of fibrillated collagen, which plays a significant role in modulating cellular functions and promoting muscle tissue regeneration. Furthermore, we assessed the impact of blade casting combined with 3D bioprinting on gene expression. The expression levels of myogenesis-related genes were substantially upregulated, with an approximately 1.6-fold increase compared to the constructs fabricated without the blade-casting technique. The results demonstrated the effectiveness of combining mechanical stimulation through blade casting with 3D bioprinting in promoting aligned cell structures, enhancing cellular functions, and driving muscle tissue regeneration.

Electroconductivity, a regenerative engineering approach to reverse rotator cuff muscle degeneration

Muscle degeneration is one the main factors that lead to the high rate of retear after a successful repair of rotator cuff (RC) tears. The current surgical practices have failed to treat patients with chronic massive rotator cuff tears (RCTs). Therefore, regenerative engineering approaches are being studied to address the challenges. Recent studies showed the promising outcomes of electroactive materials (EAMs) on the regeneration of electrically excitable tissues such as skeletal muscle. Here, we review the most important biological mechanism of RC muscle degeneration. Further, the review covers the recent studies on EAMs for muscle regeneration including RC muscle. Finally, we will discuss the future direction toward the application of EAMs for the augmentation of RCTs.

Oral administration of a locally isolated Lactobacillus rhamnosus (NR_113332.1) improves regeneration of extensor digitorum longus muscle in mice

OBJECTIVE

The aim of this study was to examine the effects of probiotic supplementation on extensor digitorum longus (EDL) regeneration after grafting in mice.

METHODS

EDL muscles were ortho-transplanted in mice. The experimental group was given 1 ×  108 colony-forming units/g body weight of Lactobacillus rhamnosus daily after EDL muscle transplantation surgeries. EDL muscle transplants were recovered after 3, 5, 7, and 14 d post-transplantation from the control as well as the experimental animals and processed for histologic analysis.

RESULTS

At day 3 post-transplantation, the inflammatory cells had infiltrated into the grafted EDL muscles and the central section of the grafted tissue contained necrotic fibers. At day 5 post-transplantation, the concentration of inflammatory cells increased further and degenerative muscle fibers were being replaced with centrally nucleated muscle cells. The average cross-sectional area non-grafted EDL and grafted muscle in the probiotic supplemented mice at day 7 increased to 48% and 23% (P = 0.002), respectively, compared with the respective values in the control animals. Whereas in non-grafted and grafted EDL muscle it could approach 8% and 36% (P = 0.008), respectively at 14 d compared with the corresponding values of the control EDL muscle transplants. The number of muscle fibers in the non-grafted and grafted probiotic-supplemented groups increased to12% and 20% (P = 0.045) at day 7 compared with the control EDL muscle. In non-grafted and grafted EDL muscle, the number of regenerated muscle fibers increased to 73% and 64% (P = 0.110) at day 14 compared with control EDL grafted muscle.

CONCLUSION

Results of the present study regarding better regeneration of skeletal muscle fibers in the probiotic-supplemented mice than the control grafts warrant further molecular-level investigation to understand the underlying mechanism mediating the process of skeletal muscle fiber regeneration. Probiotics possibly modulate the process of muscle fiber regeneration by adjusting the composition of gut microbiota.

Nanoenzyme-Reinforced Multifunctional Scaffold Based on Ti3C2Tx MXene Nanosheets for Promoting Structure-Functional Skeletal Muscle Regeneration via Electroactivity and Microenvironment Management

The completed volumetric muscle loss (VML) regeneration remains a challenge due to the limited myogenic differentiation as well as the oxidative, inflammatory, and hypoxic microenvironment. Herein, a 2D Ti3C2Tx MXene@MnO2 nanocomposite with conductivity and microenvironment remodeling was fabricated and applied in developing a multifunctional hydrogel (FME) scaffold to simultaneously conquer these hurdles. Among them, Ti3C2Tx MXene with electroconductive ability remarkably promotes myogenic differentiation via enhancing the myotube formation and upregulating the relative expression of the myosin heavy chain (MHC) protein and myogenic genes (MyoD and MyoG) in myogenesis. The MnO2 nanoenzyme-reinforced Ti3C2Tx MXene significantly reshapes the hostile microenvironment by eliminating reactive oxygen species (ROS), regulating macrophage polarization from M1 to M2 and continuously supplying O2. Together, the FME hydrogel as a bioactive multifunctional scaffold significantly accelerates structure-functional VML regeneration in vivo and represents a multipronged strategy for the VML regeneration via electroactivity and microenvironment management.

Large Scale Zigzag Pattern Emerging from Circulating Active Shakers

We report the emergence of large zigzag bands in a population of reversibly actuated magnetic rotors that behave as active shakers, namely squirmers that shake the fluid around them without moving. The shakers collectively organize into dynamic structures displaying self-similar growth and generate topological defects in the form of cusps that connect vortices of rolling particles with alternating chirality. By combining experimental analysis with particle-based simulation, we show that the special flow field created by the shakers is the only ingredient needed to reproduce the observed spatiotemporal pattern. We unveil a self-organization scenario in a collection of driven particles in a viscoelastic medium emerging from the reduced particle degrees of freedom, as here the frozen orientational motion of the shakers.

Repurposing biomedical muscle tissue engineering for cellular agriculture: challenges and opportunities

Cellular agriculture is an emerging field rooted in engineering meat-mimicking cell-laden structures using tissue engineering practices that have been developed for biomedical applications, including regenerative medicine. Research and industrial efforts are focused on reducing the cost and improving the throughput of cultivated meat (CM) production using these conventional practices. Due to key differences in the goals of muscle tissue engineering for biomedical versus food applications, conventional strategies may not be economically and technologically viable or socially acceptable. In this review, these two fields are critically compared, and the limitations of biomedical tissue engineering practices in achieving the important requirements of food production are discussed. Additionally, the possible solutions and the most promising biomanufacturing strategies for cellular agriculture are highlighted.

Perfusable Biohybrid Designs for Bioprinted Skeletal Muscle Tissue

Engineered, centimeter-scale skeletal muscle tissue (SMT) can mimic muscle pathophysiology to study development, disease, regeneration, drug response, and motion. Macroscale SMT requires perfusable channels to guarantee cell survival, and support elements to enable mechanical cell stimulation and uniaxial myofiber formation. Here, stable biohybrid designs of centimeter-scale SMT are realized via extrusion-based bioprinting of an optimized polymeric blend based on gelatin methacryloyl and sodium alginate, which can be accurately coprinted with other inks. A perfusable microchannel network is designed to functionally integrate with perfusable anchors for insertion into a maturation culture template. The results demonstrate that i) coprinted synthetic structures display highly coherent interfaces with the living tissue, ii) perfusable designs preserve cells from hypoxia all over the scaffold volume, iii) constructs can undergo passive mechanical tension during matrix remodeling, and iv) the constructs can be used to study the distribution of drugs. Extrusion-based multimaterial bioprinting with the inks and design realizes in vitro matured biohybrid SMT for biomedical applications.

Oxidative stress: roles in skeletal muscle atrophy

Oxidative stress, inflammation, mitochondrial dysfunction, reduced protein synthesis, and increased proteolysis are all critical factors in the process of muscle atrophy. In particular, oxidative stress is the key factor that triggers skeletal muscle atrophy. It is activated in the early stages of muscle atrophy and can be regulated by various factors. The mechanisms of oxidative stress in the development of muscle atrophy have not been completely elucidated. This review provides an overview of the sources of oxidative stress in skeletal muscle and the correlation of oxidative stress with inflammation, mitochondrial dysfunction, autophagy, protein synthesis, proteolysis, and muscle regeneration in muscle atrophy. Additionally, the role of oxidative stress in skeletal muscle atrophy caused by several pathological conditions, including denervation, unloading, chronic inflammatory diseases (diabetes mellitus, chronic kidney disease, chronic heart failure, and chronic obstructive pulmonary disease), sarcopenia, hereditary neuromuscular diseases (spinal muscular atrophy, amyotrophic lateral sclerosis, and Duchenne muscular dystrophy), and cancer cachexia, have been discussed. Finally, this review proposes the alleviation oxidative stress using antioxidants, Chinese herbal extracts, stem cell and extracellular vesicles as a promising therapeutic strategy for muscle atrophy. This review will aid in the development of novel therapeutic strategies and drugs for muscle atrophy.

Polyvinyl Alcohol Nanofibers Blends as Drug Delivery System in Tissue Regeneration

Nanofibers have shown promising clinical results in the process of tissue regeneration since they provide a similar structure to the extracellular matrix of different tissues, high surface-to-volume ratio and porosity, flexibility, and gas permeation, offering topographical features that stimulate cell adhesion and proliferation. Electrospinning is one of the most used techniques for manufacturing nanomaterials due to its simplicity and low cost. In this review, we highlight the use of nanofibers produced with polyvinyl alcohol and polymeric associations (PVA/blends) as a matrix for release capable of modifying the pharmacokinetic profile of different active ingredients in the regeneration of connective, epithelial, muscular, and nervous tissues. Articles were selected by three independent reviewers by analyzing the databases, such as Web of Science, PubMed, Science Direct, and Google Scholar (last 10 years). Descriptors used were "nanofibers", "poly (vinyl alcohol)", "muscle tissue", "connective tissue", "epithelial tissue", and "neural tissue engineering". The guiding question was: How do different compositions of polyvinyl alcohol polymeric nanofibers modify the pharmacokinetics of active ingredients in different tissue regeneration processes? The results demonstrated the versatility of the production of PVA nanofibers by solution blow technique with different actives (lipo/hydrophilic) and with pore sizes varying between 60 and 450 nm depending on the polymers used in the mixture, which influences the drug release that can be controlled for hours or days. The tissue regeneration showed better cellular organization and greater cell proliferation compared to the treatment with the control group, regardless of the tissue analyzed. We highlight that, among all blends, the combinations PVA/PCL and PVA/CS showed good compatibility and slow degradation, indicating their use in prolonged times of biodegradation, thus benefiting tissue regeneration in bone and cartilage connective tissues, acting as a physical barrier that results in guided regeneration, and preventing the invasion of cells from other tissues with increased proliferation rate.

Influence of Gelatin Source and Bloom Number on Gelatin Methacryloyl Hydrogels Mechanical and Biological Properties for Muscle Regeneration

Approximately half of an adult human's body weight is made up of muscles. Thus, restoring the functionality and aesthetics of lost muscle tissue is critical. The body is usually able to repair minor muscle injuries. However, when volumetric muscle loss occurs due to tumour extraction, for instance, the body will form fibrous tissue instead. Gelatin methacryloyl (GelMA) hydrogels have been applied for drug delivery, tissue adhesive, and various tissue engineering applications due to their tuneable mechanical properties. Here, we have synthesised GelMA from different gelatin sources (i.e., porcine, bovine, and fish) with varying bloom numbers, which refers to the gel strength, and investigated for the influence of the source of gelatin and the bloom number on biological activities and mechanical properties. The results indicated that the source of the gelatin and variable bloom numbers have an impact on GelMA hydrogel properties. Furthermore, our findings established that the bovine-derived gelatin methacryloyl (B-GelMA) has better mechanical properties than the other varieties composed of porcine and fish with 60 kPa, 40 kPa, and 10 kPa in bovine, porcine, and fish, respectively. Additionally, it showed a noticeably greater swelling ratio (SR) ~1100% and a reduced rate of degradation, improving the stability of hydrogels and giving cells adequate time to divide and proliferate to compensate for muscle loss. Furthermore, the bloom number of gelatin was also proven to influence the mechanical properties of GelMA. Interestingly, although GelMA made of fish had the lowest mechanical strength and gel stability, it demonstrated excellent biological properties. Overall, the results emphasise the importance of gelatin source and bloom number, allowing GelMA hydrogels to have a wide range of mechanical and excellent biological properties and making them suitable for various muscle tissue regeneration applications.

Supplementation of GelMA with Minimally Processed Tissue Promotes the Formation of Densely Packed Skeletal-Muscle-Like Tissues

We present a simple and cost-effective strategy for developing gelatin methacryloyl (GelMA) hydrogels supplemented with minimally processed tissue (MPT) to fabricate densely packed skeletal-muscle-like tissues. MPT powder was prepared from skeletal muscle by freeze-drying, grinding, and sieving. Cell-culture experiments showed that the incorporation of 0.5-2.0% (w/v) MPT into GelMA hydrogels enhances the proliferation of murine myoblasts (C2C12 cells) compared to proliferation in pristine GelMA hydrogels and GelMA supplemented with decellularized skeletal-muscle tissues (DCTs). MPT-supplemented constructs also preserved their three-dimensional (3D) integrity for 28 days. By contrast, analogous pristine GelMA constructs only maintained their structure for 14 days or less. C2C12 cells embedded in MPT-supplemented constructs exhibited a higher degree of cell alignment and reached a significantly higher density than cells loaded in pristine GelMA constructs. Our results suggest that the addition of MPT incorporates a rich source of biochemical and topological cues, such as growth factors, glycosaminoglycans (GAGs), and structurally preserved proteins (e.g., collagen). In addition, GelMA supplemented with MPT showed suitable rheological properties for use as bioinks for extrusion bioprinting. We envision that this simple and cost-effective strategy of hydrogel supplementation will evolve into an exciting spectrum of applications for tissue engineers, primarily in the biofabrication of relevant microtissues for in vitro models and cultured meat and ultimately for the biofabrication of transplant materials using autologous MPT.

5-Azacytidine incorporated skeletal muscle-derived hydrogel promotes rat skeletal muscle regeneration

Decellularized skeletal muscle is a promising biomaterial for muscle regeneration due to the mimicking of the natural microenvironment. Previously, it has been reported that 5-Azacytidine (5-Aza), a DNA methyltransferase inhibitor, induces myogenesis in different types of stem cells. In the current study, we investigated the effect of 5-Aza incorporated muscle-derived hydrogel on the viability and proliferation of muscle-derived stem cells (MDSCs) in vitro and muscle regeneration in vivo. Wistar rat skeletal muscles were decellularized using a physico-chemical protocol. The decellularized tissue was analyzed using SEM, histological staining and evaluation of DNA content. Then, muscle-derived hydrogel was made from Pepsin-digested decellularized muscle tissues. 5-Aza was physically adsorbed in prepared hydrogels. Then, MDSCs were cultured on hydrogels with/without 5-Aza, and their proliferation and cell viability were determined using LIVE/DEAD and DAPI staining. Moreover, myectomy lesions were done in rat femoris muscles, muscle-derived hydroges with/without 5-Aza were injected to the myectomy sites, and histological evaluation was performed after three weeks. The analysis of decellularized muscle tissues showed that they maintained extracellular matrix components of native muscles, while they lacked DNA. LIVE/DEAD and DAPI staining showed that the hydrogel containing 5-Aza supported MDSCs viability. Histological analysis of myectomy sites showed an improvement in muscle regeneration after administration of 5-Aza incorporated hydrogel. These findings suggest that the combination of 5-Aza with skeletal muscle hydrogel may serve as an alternative treatment option to improve the regeneration of injured muscle tissue.

Chronic kidney disease-induced muscle atrophy: Molecular mechanisms and promising therapies

Chronic kidney disease (CKD) is a high-risk chronic catabolic disease due to its high morbidity and mortality. CKD is accompanied by many complications, leading to a poor quality of life, and serious complications may even threaten the life of CKD patients. Muscle atrophy is a common complication of CKD. Muscle atrophy and sarcopenia in CKD patients have complex pathways that are related to multiple mechanisms and related factors. This review not only discusses the mechanisms by which inflammation, oxidative stress, mitochondrial dysfunction promote CKD-induced muscle atrophy but also explores other CKD-related complications, such as metabolic acidosis, vitamin D deficiency, anorexia, and excess angiotensin II, as well as other related factors that play a role in CKD muscle atrophy, such as insulin resistance, hormones, hemodialysis, uremic toxins, intestinal flora imbalance, and miRNA. We highlight potential treatments and drugs that can effectively treat CKD-induced muscle atrophy in terms of complication treatment, nutritional supplementation, physical exercise, and drug intervention, thereby helping to improve the prognosis and quality of life of CKD patients.

Silk-Based Biomaterials for Designing Bioinspired Microarchitecture for Various Biomedical Applications

Biomaterial research has led to revolutionary healthcare advances. Natural biological macromolecules can impact high-performance, multipurpose materials. This has prompted the quest for affordable healthcare solutions, with a focus on renewable biomaterials with a wide variety of applications and ecologically friendly techniques. Imitating their chemical compositions and hierarchical structures, bioinspired based materials have elevated rapidly over the past few decades. Bio-inspired strategies entail extracting fundamental components and reassembling them into programmable biomaterials. This method may improve its processability and modifiability, allowing it to meet the biological application criteria. Silk is a desirable biosourced raw material due to its high mechanical properties, flexibility, bioactive component sequestration, controlled biodegradability, remarkable biocompatibility, and inexpensiveness. Silk regulates temporo-spatial, biochemical and biophysical reactions. Extracellular biophysical factors regulate cellular destiny dynamically. This review examines the bioinspired structural and functional properties of silk material based scaffolds. We explored silk types, chemical composition, architecture, mechanical properties, topography, and 3D geometry to unlock the body's innate regenerative potential, keeping in mind the novel biophysical properties of silk in film, fiber, and other potential forms, coupled with facile chemical changes, and its ability to match functional requirements for specific tissues.

Biomedical applications of three-dimensional bioprinted craniofacial tissue engineering

Anatomical complications of the craniofacial regions often present considerable challenges to the surgical repair or replacement of the damaged tissues. Surgical repair has its own set of limitations, including scarcity of the donor tissues, immune rejection, use of immune suppressors followed by the surgery, and restriction in restoring the natural aesthetic appeal. Rapid advancement in the field of biomaterials, cell biology, and engineering has helped scientists to create cellularized skeletal muscle-like structures. However, the existing method still has limitations in building large, highly vascular tissue with clinical application. With the advance in the three-dimensional (3D) bioprinting technique, scientists and clinicians now can produce the functional implants of skeletal muscles and bones that are more patient-specific with the perfect match to the architecture of their craniofacial defects. Craniofacial tissue regeneration using 3D bioprinting can manage and eliminate the restrictions of the surgical transplant from the donor site. The concept of creating the new functional tissue, exactly mimicking the anatomical and physiological function of the damaged tissue, looks highly attractive. This is crucial to reduce the donor site morbidity and retain the esthetics. 3D bioprinting can integrate all three essential components of tissue engineering, that is, rehabilitation, reconstruction, and regeneration of the lost craniofacial tissues. Such integration essentially helps to develop the patient-specific treatment plans and damage site-driven creation of the functional implants for the craniofacial defects. This article is the bird's eye view on the latest development and application of 3D bioprinting in the regeneration of the skeletal muscle tissues and their application in restoring the functional abilities of the damaged craniofacial tissue. We also discussed current challenges in craniofacial bone vascularization and gave our view on the future direction, including establishing the interactions between tissue-engineered skeletal muscle and the peripheral nervous system.

Skeletal muscle abnormalities in heart failure with preserved ejection fraction

Almost half of all heart failure (HF) disease burden is due to HF with preserved ejection fraction (HFpEF). The primary symptom in patients with HFpEF, even when well compensated, is severe exercise intolerance and is associated with their reduced quality of life. Recently, studies showed that HFpEF patients have multiple skeletal muscle (SM) abnormalities, and these are associated with decreased exercise intolerance. The SM abnormalities are likely intrinsic to the HFpEF syndrome, not a secondary consequence of an epiphenomenon. These abnormalities are decreased muscle mass, reduced type I (oxidative) muscle fibers, and reduced type I-to-type II fiber ratio as well as a reduced capillary-to-fiber ratio, abnormal fat infiltration into the thigh SM, increased levels of atrophy genes and proteins, reduction in mitochondrial content, and rapid depletion of high-energy phosphate during exercise with markedly delayed repletion of high-energy phosphate during recovery in mitochondria. In addition, patients with HFpEF have impaired nitric oxide bioavailability, particularly in the microvasculature. These SM abnormalities may be responsible for impaired diffusive oxygen transport and/or impaired SM oxygen extraction. To date, exercise training (ET) and caloric restriction are some of the interventions shown to improve outcomes in HFpEF patients. Improvements in exercise tolerance following aerobic ET are largely mediated through peripheral SM adaptations with minimal change in central hemodynamics and highlight the importance of targeting SM to improve exercise intolerance in HFpEF. Focusing on the abnormalities mentioned above may improve the clinical condition of patients with HFpEF.

Role of Patient-Derived Models of Cancer in Translational Oncology

Cancer is a heterogeneous disease. Each individual tumor is unique and characterized by structural, cellular, genetic and molecular features. Therefore, patient-derived cancer models are indispensable tools in cancer research and have been actively introduced into the healthcare system. For instance, patient-derived models provide a good reproducibility of susceptibility and resistance of cancer cells against drugs, allowing personalized therapy for patients. In this article, we review the advantages and disadvantages of the following patient-derived models of cancer: (1) PDC-patient-derived cell culture, (2) PDS-patient-derived spheroids and PDO-patient-derived organoids, (3) PDTSC-patient-derived tissue slice cultures, (4) PDX-patient-derived xenografts, humanized PDX, as well as PDXC-PDX-derived cell cultures and PDXO-PDX-derived organoids. We also provide an overview of current clinical investigations and new developments in the area of patient-derived cancer models. Moreover, attention is paid to databases of patient-derived cancer models, which are collected in specialized repositories. We believe that the widespread use of patient-derived cancer models will improve our knowledge in cancer cell biology and contribute to the development of more effective personalized cancer treatment strategies.

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.

Evaluation of Polysaccharide-Peptide Conjugates Containing the RGD Motif for Potential Use in Muscle Tissue Regeneration

New scaffold materials composed of biodegradable components are of great interest in regenerative medicine. These materials should be: stable, nontoxic, and biodegrade slowly and steadily, allowing the stable release of biodegradable and biologically active substances. We analyzed peptide-polysaccharide conjugates derived from peptides containing RGD motif (H-RGDS-OH (1), H-GRGDS-NH₂ (2), and cyclo(RGDfC) (3)) and polysaccharides as scaffolds to select the most appropriate biomaterials for application in regenerative medicine. Based on the results of MTT and Ki-67 assays, we can state that the conjugates containing calcium alginate and the ternary nonwoven material were the most supportive of muscle tissue regeneration. Scanning electron microscopy imaging and light microscopy studies with hematoxylin-eosin staining showed that C2C12 cells were able to interact with the tested peptide-polysaccharide conjugates. The release factor (Q) varied depending on both the peptide and the structure of the polysaccharide matrix. LDH, Alamarblue^®, Ki-67, and cell cycle assays indicated that peptides 1 and 2 were characterized by the best biological properties. Conjugates containing chitosan and the ternary polysaccharide nonwoven with peptide 1 exhibited very high antibacterial activity against Staphylococcus aureus and Klebsiella pneumoniae. Overall, the results of the study suggested that polysaccharide conjugates with peptides 1 and 2 can be potentially used in regenerative medicine.

Piezoelectric nanocomposite bioink and ultrasound stimulation modulate early skeletal myogenesis

Despite the significant progress in bioprinting for skeletal muscle tissue engineering, new stimuli-responsive bioinks to boost the myogenesis process are highly desirable. In this work, we developed a printable alginate/Pluronic-based bioink including piezoelectric barium titanate nanoparticles (nominal diameter: ∼60 nm) for the 3D bioprinting of muscle cell-laden hydrogels. The aim was to investigate the effects of the combination of piezoelectric nanoparticles with ultrasound stimulation on early myogenic differentiation of the printed structures. After the characterization of nanoparticles and bioinks, viability tests were carried out to investigate three nanoparticle concentrations (100, 250, and 500 μg mL^-1) within the printed structures. An excellent cytocompatibility was confirmed for nanoparticle concentrations up to 250 μg mL^-1. TEM imaging demonstrated the internalization of BTNPs in intracellular vesicles. The combination of piezoelectric nanoparticles and ultrasound stimulation upregulated the expression of MYOD1, MYOG, and MYH2 and enhanced cell aggregation, which is a crucial step for myoblast fusion, and the presence of MYOG in the nuclei. These results suggest that the direct piezoelectric effect induced by ultrasound on the internalized piezoelectric nanoparticles boosts myogenesis in its early phases.

Emulsion-templated microparticles with tunable stiffness and topology: Applications as edible microcarriers for cultured meat

Cultured meat has potential to diversify methods for protein production, but innovations in production efficiency will be required to make cultured meat a feasible protein alternative. Microcarriers provide a strategy to culture sufficient volumes of adherent cells in a bioreactor that are required for meat products. However, cell culture on inedible microcarriers involves extra downstream processing to dissociate cells prior to consumption. Here, we present edible microcarriers that can support the expansion and differentiation of myogenic cells in a single bioreactor system. To fabricate edible microcarriers with a scalable process, we used water-in-oil emulsions as templates for gelatin microparticles. We also developed a novel embossing technique to imprint edible microcarriers with grooved topology in order to test if microcarriers with striated surface texture can promote myoblast proliferation and differentiation in suspension culture. In this proof-of-concept demonstration, we showed that edible microcarriers with both smooth and grooved surface topologies supported the proliferation and differentiation of mouse myogenic C2C12 cells in a suspension culture. The grooved edible microcarriers showed a modest increase in the proliferation and alignment of myogenic cells compared to cells cultured on smooth, spherical microcarriers. During the expansion phase, we also observed the formation of cell-microcarrier aggregates or 'microtissues' for cells cultured on both smooth and grooved microcarriers. Myogenic microtissues cultured with smooth and grooved microcarriers showed similar characteristics in terms of myotube length, myotube volume fraction, and expression of myogenic markers. To establish feasibility of edible microcarriers for cultured meat, we showed that edible microcarriers supported the production of myogenic microtissue from C2C12 or bovine satellite muscle cells, which we harvested by centrifugation into a cookable meat patty that maintained its shape and exhibited browning during cooking. These findings demonstrate the potential of edible microcarriers for the scalable production of cultured meat in a single bioreactor.

Elastically-mediated collective organisation of magnetic microparticles

Gels are soft elastic materials made of a three-dimensional cross-linked polymer network and featuring both elastic and dissipative responses under external mechanical stimuli. Here we investigate how such gels mediate the organization of embedded magnetic microparticles when driven by an external field. By constructing a continuum theory, we demonstrate that the collective dynamics of the embedded particles result from the delicate balance between magnetic dipole-dipole interactions, thermal fluctuations and elasticity of the polymer network, verified by our experiments. The proposed model could be extended to other soft magnetic composites in order to predict how the elastic interactions mediate the aggregation of the embedded elements, fostering technological implications for multifunctional hydrogel materials.

Microfluidic Tissue Engineering and Bio-Actuation

Bio-hybrid technologies aim to replicate the unique capabilities of biological systems that could surpass advanced artificial technologies. Soft bio-hybrid robots consist of synthetic and living materials and have the potential to self-assemble, regenerate, work autonomously, and interact safely with other species and the environment. Cells require a sufficient exchange of nutrients and gases, which is guaranteed by convection and diffusive transport through liquid media. The functional development and long-term survival of biological tissues in vitro can be improved by dynamic flow culture, but only microfluidic flow control can develop tissue with fine structuring and regulation at the microscale. Full control of tissue growth at the microscale will eventually lead to functional macroscale constructs, which are needed as the biological component of soft bio-hybrid technologies. This review summarizes recent progress in microfluidic techniques to engineer biological tissues, focusing on the use of muscle cells for robotic bio-actuation. Moreover, the instances in which bio-actuation technologies greatly benefit from fusion with microfluidics are highlighted, which include: the microfabrication of matrices, biomimicry of cell microenvironments, tissue maturation, perfusion, and vascularization.

DNA-Based Daisy Chain Rotaxane Nanocomposite Hydrogels as Dual-Programmable Dynamic Scaffolds for Stem Cell Adhesion

Interlocked DNA nanostructures perform programmable movements in nanoscales such as sliding, contraction, and expansion. However, utilizing nanoscaled interlocked movements to regulate the functions of larger length scaled matrix and developing their applications has not yet been reported. Herein we describe the assembly of DNA-based daisy chain rotaxane nanostructure (DNA-DCR) composed of two hollow DNA nanostructures as macrocycles, two interlocked axles and two triangular prism-shaped DNA structures as stoppers, in which three mechanical states─fixed extended state (FES), sliding state (SS), and fixed contracted state (FCS)─are characterized by using toehold-mediated strand displacement reaction (SDR). The DNA-DCRs are further used as nanocomposites and introduced into hydrogel matrix to produce interlocked hydrogels, which shows modulable stiffness by elongating the interlocked axles to regulate the hydrogel swelling with hybridization chain reaction (HCR) treatment. Then the DCR-hydrogels are employed as dynamic biointerfaces for human mesenchymal stem cells (hMSCs) adhesion studies. First, hMSCs showed lower cell density on bare DCR-hydrogel treated with HCR-initiated swelling for stiffness decreasing. Second, the cell adhesion ligand (RGD) modified DNA-DCRs are constructed for hydrogel functionalization. DCR^(RGD) hydrogel endows the mobility of RGDs by switching the mechanical states of DNA-DCR. HMSCs showed increased cell density on DCR^SS(RGD) hydrogel than on DCR^FCS(RGD) hydrogel. Therefore, our DNA-DCR nanocomposite hydrogel exhibit dual-programmable performances including swelling adjustment and offering sliding for incorporated ligands, which can be both utilized as dynamic scaffolds for regulating the stem cell adhesion. The dual-programmable cross-scale regulation from interlocked DNA nanostructures to hydrogel matrix was achieved, demonstrating a new pathway of DNA-based materials.

Natural Polymers in Heart Valve Tissue Engineering: Strategies, Advances and Challenges

In the history of biomedicine and biomedical devices, heart valve manufacturing techniques have undergone a spectacular evolution. However, important limitations in the development and use of these devices are known and heart valve tissue engineering has proven to be the solution to the problems faced by mechanical and prosthetic valves. The new generation of heart valves developed by tissue engineering has the ability to repair, reshape and regenerate cardiac tissue. Achieving a sustainable and functional tissue-engineered heart valve (TEHV) requires deep understanding of the complex interactions that occur among valve cells, the extracellular matrix (ECM) and the mechanical environment. Starting from this idea, the review presents a comprehensive overview related not only to the structural components of the heart valve, such as cells sources, potential materials and scaffolds fabrication, but also to the advances in the development of heart valve replacements. The focus of the review is on the recent achievements concerning the utilization of natural polymers (polysaccharides and proteins) in TEHV; thus, their extensive presentation is provided. In addition, the technological progresses in heart valve tissue engineering (HVTE) are shown, with several inherent challenges and limitations. The available strategies to design, validate and remodel heart valves are discussed in depth by a comparative analysis of in vitro, in vivo (pre-clinical models) and in situ (clinical translation) tissue engineering studies.

Three-dimensional in vitro models of neuromuscular tissue

Skeletal muscle is a dynamic tissue in which homeostasis and function are guaranteed by a very defined three-dimensional organization of myofibers in respect to other non-muscular components, including the extracellular matrix and the nervous network. In particular, communication between myofibers and the nervous system is essential for the overall correct development and function of the skeletal muscle. A wide range of chronic, acute and genetic-based human pathologies that lead to the alteration of muscle function are associated with modified preservation of the fine interaction between motor neurons and myofibers at the neuromuscular junction. Recent advancements in the development of in vitro models for human skeletal muscle have shown that three-dimensionality and integration of multiple cell types are both key parameters required to unveil pathophysiological relevant phenotypes. Here, we describe recent achievement reached in skeletal muscle modeling which used biomaterials for the generation of three-dimensional constructs of myotubes integrated with motor neurons.

Progress in the Development of Graphene-Based Biomaterials for Tissue Engineering and Regeneration

Over the last few decades, tissue engineering has become an important technology for repairing and rebuilding damaged tissues and organs. The scaffold plays an important role and has become a hot pot in the field of tissue engineering. It has sufficient mechanical and biochemical properties and simulates the structure and function of natural tissue to promote the growth of cells inward. Therefore, graphene-based nanomaterials (GBNs), such as graphene and graphene oxide (GO), have attracted wide attention in the field of biomedical tissue engineering because of their unique structure, large specific surface area, good photo-thermal effect, pH response and broad-spectrum antibacterial properties. In this review, the structure and properties of typical GBNs are summarized, the progress made in the development of GBNs in soft tissue engineering (including skin, muscle, nerve and blood vessel) are highlighted, the challenges and prospects of the application of GBNs in soft tissue engineering have prospected.

Bioinks and Bioprinting Strategies for Skeletal Muscle Tissue Engineering

Skeletal muscles play important roles in critical body functions and their injury or disease can lead to limitation of mobility and loss of independence. Current treatments result in variable functional recovery, while reconstructive surgery, as the gold-standard approach, is limited due to donor shortage, donor-site morbidity, and limited functional recovery. Skeletal muscle tissue engineering (SMTE) has generated enthusiasm as an alternative solution for treatment of injured tissue and serves as a functional disease model. Recently, bioprinting has emerged as a promising tool for recapitulating the complex and highly organized architecture of skeletal muscles at clinically relevant sizes. Here, skeletal muscle physiology, muscle regeneration following injury, and current treatments following muscle loss are discussed, and then bioprinting strategies implemented for SMTE are critically reviewed. Subsequently, recent advancements that have led to improvement of bioprinting strategies to construct large muscle structures, boost myogenesis in vitro and in vivo, and enhance tissue integration are discussed. Bioinks for muscle bioprinting, as an essential part of any bioprinting strategy, are discussed, and their benefits, limitations, and areas to be improved are highlighted. Finally, the directions the field should expand to make bioprinting strategies more translational and overcome the clinical unmet needs are discussed.

Silver nanowire loaded poly(ε-caprolactone) nanocomposite fibers as electroactive scaffolds for skeletal muscle regeneration

Volumetric muscle loss (VML) due to trauma and tumor removal operations affects millions of people every year. Although skeletal muscle has a natural repair mechanism, it cannot provide self-healing above a critical level of VML. In this study, nanocomposite aligned fiber scaffolds as support materials were developed for volumetric skeletal muscle regeneration. For this purpose, silver nanowire (Ag NW) loaded poly(ε-caprolactone) (PCL) nanocomposite fiber scaffolds (PCL-Ag NW) were prepared to mimic the aligned electroactive structure of skeletal muscle and provide topographic and conductive environment to modulate cellular behavior and orientation. A computer-aided rotational wet spinning (RWS) system was designed to produce high-yield fiber scaffolds. Nanocomposite fiber bundles with lengths of 50 cm were fabricated via this computer-aided RWS system. The morphological, chemical, thermal properties and biodegradation profiles of PCL and PCL-Ag NW nanocomposite fibers were characterized in detail. The proliferation behavior and morphology of C2C12 mouse myoblasts were investigated on PCL and PCL-Ag NW nanocomposite fibrous scaffolds with and without electrical stimulation. Significantly enhanced cell proliferation was observed on PCL-Ag NW nanocomposite fibers compared to neat PCL fibers with electrical stimulations of 1.5 V, 3 V and without electrical stimulation.

Mechanomimetic 3D Scaffolds as a Humanized In Vitro Model for Ovarian Cancer

The mechanical homeostasis of tissues can be altered in response to trauma or disease, such as cancer, resulting in altered mechanotransduction pathways that have been shown to impact tumor development, progression, and the efficacy of therapeutic approaches. Specifically, ovarian cancer progression is parallel to an increase in tissue stiffness and fibrosis. With in vivo models proving difficult to study, tying tissue mechanics to altered cellular and molecular properties necessitate advanced, tunable, in vitro 3D models able to mimic normal and tumor mechanic features. First, we characterized normal human ovary and high-grade serous (HGSC) ovarian cancer tissue stiffness to precisely mimic their mechanical features on collagen I-based sponge scaffolds, soft (NS) and stiff (MS), respectively. We utilized three ovarian cancer cell lines (OVCAR-3, Caov-3, and SKOV3) to evaluate changes in viability, morphology, proliferation, and sensitivity to doxorubicin and liposomal doxorubicin treatment in response to a mechanically different microenvironment. High substrate stiffness promoted the proliferation of Caov-3 and SKOV3 cells without changing their morphology, and upregulated mechanosensors YAP/TAZ only in SKOV3 cells. After 7 days in culture, both OVCAR3 and SKOV3 decreased the MS scaffold storage modulus (stiffness), suggesting a link between cell proliferation and the softening of the matrix. Finally, high matrix stiffness resulted in higher OVCAR-3 and SKOV3 cell cytotoxicity in response to doxorubicin. This study demonstrates the promise of biomimetic porous scaffolds for effective inclusion of mechanical parameters in 3D cancer modeling. Furthermore, this work establishes the use of porous scaffolds for studying ovarian cancer cells response to mechanical changes in the microenvironment and as a meaningful platform from which to investigate chemoresistance and drug response.

Home Away From Home: Bioengineering Advancements to Mimic the Developmental and Adult Stem Cell Niche

The inherent self-organizing capacity of pluripotent and adult stem cell populations has advanced our fundamental understanding of processes that drive human development, homeostasis, regeneration, and disease progression. Translating these principles into in vitro model systems has been achieved with the advent of organoid technology, driving innovation to harness patient-specific, cell-laden regenerative constructs that can be engineered to augment or replace diseased tissue. While developmental organization and regenerative adult stem cell niches are tightly regulated in vivo, in vitro analogs lack defined architecture and presentation of physicochemical cues, leading to the unhindered arrangement of mini-tissues that lack complete physiological mimicry. This review aims to highlight the recent integrative engineering approaches that elicit spatio-temporal control of the extracellular niche to direct the structural and functional maturation of pluripotent and adult stem cell derivatives. While the advances presented here leverage multi-pronged strategies ranging from synthetic biology to microfabrication technologies, the methods converge on recreating the biochemical and biophysical milieu of the native tissue to be modeled or regenerated.

The ECM: To Scaffold, or Not to Scaffold, That Is the Question

The extracellular matrix (ECM) has pleiotropic effects, ranging from cell adhesion to cell survival. In tissue engineering, the use of ECM and ECM-like scaffolds has separated the field into two distinct areas-scaffold-based and scaffold-free. Scaffold-free techniques are used in creating reproducible cell aggregates which have massive potential for high-throughput, reproducible drug screening and disease modeling. Though, the lack of ECM prevents certain cells from surviving and proliferating. Thus, tissue engineers use scaffolds to mimic the native ECM and produce organotypic models which show more reliability in disease modeling. However, scaffold-based techniques come at a trade-off of reproducibility and throughput. To bridge the tissue engineering dichotomy, we posit that finding novel ways to incorporate the ECM in scaffold-free cultures can synergize these two disparate techniques.