Regulation of Myogenic Differentiation by Topologically Microgrooved Surfaces for Skeletal Muscle Tissue Engineering

Conductive Microgel Annealed Scaffolds Enhance Myogenic Potential of Myoblastic Cells

Conductive biomaterials may capture native or exogenous bioelectric signaling, but incorporation of conductive moieties is limited by cytotoxicity, poor injectability, or insufficient stimulation. Microgel annealed scaffolds are promising as hydrogel-based materials due to their inherent void space that facilitates cell migration and proliferation better than nanoporous bulk hydrogels. Conductive microgels are generated from poly(ethylene) glycol (PEG and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) to explore the interplay of void volume and conductivity on myogenic differentiation. PEDOT: PSS increases microgel conductivity two-fold while maintaining stiffness, annealing strength, and viability of associated myoblastic cells. C2C12 myoblasts exhibit increases in the late-stage differentiation marker myosin heavy chain as a function of both porosity and conductivity. Myogenin, an earlier marker, is influenced only by porosity. Human skeletal muscle-derived cells exhibit increased Myod1, insulin like growth factor-1, and insulin-like growth factor binding protein 2 at earlier time points on conductive microgel scaffolds compared to non-conductive scaffolds. They also secrete more vascular endothelial growth factor at early time points and express factors that led to macrophage polarization patterns observe during muscle repair. These data indicate that conductivity aids myogenic differentiation of myogenic cell lines and primary cells, motivating the need for future translational studies to promote muscle repair.

Effect of Anisotropic Structural Depth on Orientation and Differentiation Behavior of Skeletal Muscle Cells

Extensive research has been conducted to examine how substrate topological factors are involved in modulating the cell behavior. Among numerous topological factors, the vital influence of the touchable depth of substrates on cell behaviors has already been extensively characterized, but the response of cells to the topological structure at untouchable depth is still elusive. Herein, the influences of substrate depth on myoblast behaviors are systematically investigated using substrates with depths ranging from touchable depth (microgrooved) to untouchable depth (microbridges). The results show that an increase in microgroove depth is accompanied by an inhibited cell spreading, an enhanced elongation, and a more obvious orientation along microgrooves. Interestingly, myoblasts located on microbridges show a more pronounced elongation with increasing culture time but a position-dependent orientation. Myoblasts on the center and parallel boundary of microbridges orient along the bridges, while myoblasts on the vertical boundary align perpendicular to the microbridges. Moreover, the differentiation results of the myoblasts indicate that the differentiated myotubes can maintain this position-dependent orientation. The simulation of the stress field in cell monolayers suggests that the position-dependent orientation is caused by the comprehensive response of myoblasts to the substrate discontinuity and substrate depth. These findings provide valuable insights into the mechanism of cell depth sensing and could inform the design of tissue engineering scaffolds for skeletal muscle and biohybrid actuation.

Combinatorial extracellular matrix cues with mechanical strain induce differential effects on myogenesis in vitro

Skeletal muscle regeneration remains a clinical unmet need for volumetric muscle loss and atrophy where muscle function cannot be restored to prior capacity. Current experimental approaches do not account for the complex microenvironmental factors that modulate myogenesis. In this study we developed a biomimetic tissue chip platform to systematically study the combined effects of the extracellular matrix (ECM) microenvironment and mechanical strain on myogenesis of murine myoblasts. Using stretchable tissue chips composed of collagen I (C), fibronectin (F) and laminin (L), as well as their combinations thereof, we tested the addition of mechanical strain regimens on myogenesis at the transcriptomic and translational levels. Our results show that ECMs have a significant effect on myotube formation in C2C12 murine myoblasts. Under static conditions, laminin substrates induced the longest myotubes, whereas fibronectin produced the widest myotubes. Combinatorial ECMs showed non-intuitive effects on myotube formation. Genome-wide analysis revealed the upregulation in actin cytoskeletal related genes that are suggestive of myogenesis. When mechanical strain was introduced to C + F + L combinatorial ECM substrates in the form of constant or intermittent uniaxial strain at low (5%) and high (15%) levels, we observed synergistic enhancements in myotube width, along with transcriptomic upregulation in myosin heavy chain genes. Together, these studies highlight the complex role of microenvironmental factors such as ECM interactions and strain on myotube formation and the underlying signaling pathways.

Biohybrid Soft Robots Powered by Myocyte: Current Progress and Future Perspectives

Myocyte-driven robots, a type of biological actuator that combines myocytes with abiotic systems, have gained significant attention due to their high energy efficiency, sensitivity, biocompatibility, and self-healing capabilities. These robots have a unique advantage in simulating the structure and function of human tissues and organs. This review covers the research progress in this field, detailing the benefits of myocyte-driven robots over traditional methods, the materials used in their fabrication (including myocytes and extracellular materials), and their properties and manufacturing techniques. Additionally, the review explores various control methods, robot structures, and motion types. Lastly, the potential applications and key challenges faced by myocyte-driven robots are discussed and summarized.

Conductive microgel annealed scaffolds enhance myogenic potential of myoblastic cells

Bioelectricity is an understudied phenomenon to guide tissue homeostasis and regeneration. Conductive biomaterials may capture native or exogenous bioelectric signaling, but incorporation of conductive moieties is limited by cytotoxicity, poor injectability, or insufficient stimulation. Microgel annealed scaffolds are promising as hydrogel-based materials due to their inherent void space that facilitates cell migration and proliferation better than nanoporous bulk hydrogels. We generated conductive microgels from poly(ethylene) glycol and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) to explore the interplay of void volume and conductivity on myogenic differentiation. PEDOT:PSS increased microgel conductivity over 2-fold while maintaining stiffness, annealing strength, and viability of associated myoblastic cells. C2C12 myoblasts exhibited increases in the late-stage differentiation marker myosin heavy chain as a function of both porosity and conductivity. Myogenin, an earlier marker, was influenced only by porosity. Human skeletal muscle derived cells exhibited increased Myod1 , IGF-1, and IGFBP-2 at earlier timepoints on conductive microgel scaffolds compared to non-conductive scaffolds. They also secreted higher levels of VEGF at early timepoints and expressed factors that led to macrophage polarization patterns observed during muscle repair. These data indicate that conductivity aids myogenic differentiation of myogenic cell lines and primary cells, motivating the need for future translational studies to promote muscle repair.

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.

Hydrogel-Assisted Double Molding Enables Rapid Replication of Stereolithographic 3D Prints for Engineered Tissue Design

Tissue-engineered in vitro models are an essential tool in biomedical research. Tissue geometry is a key determinant of function, but controlling the geometry of microscale tissues remains challenging. Additive manufacturing approaches have emerged as a promising means for rapid and iterative changes in the geometry of microdevices. However, it has been shown that poly(dimethylsiloxane) (PDMS) cross-linking is often inhibited at the interface of materials printed with stereolithography. While approaches to replica mold stereolithographic three-dimensional (3D) prints have been described, these methods are inconsistent and often lead to print destruction when unsuccessful. Additionally, 3D-printed materials often leach toxic chemicals into directly molded PDMS. Here, we developed a double molding approach that allows precise replication of high-resolution stereolithographic prints into poly(dimethylsiloxane) (PDMS) elastomer, facilitating rapid design iterations and highly parallelized sample production. Inspired by lost wax casting, we used hydrogels as intermediary molds to transfer high-resolution features from high-resolution 3D prints into PDMS, while previously published work focused on enabling direct molding of PDMS onto 3D prints through the use of coatings and post-cross-linking treatments of the 3D print itself. Hydrogel mechanical properties, including cross-link density, predict replication fidelity. We demonstrate the ability of this approach to replicate a variety of shapes that would be impossible to create using photolithography techniques traditionally used to create engineered tissue designs. This method also enabled the replication of 3D-printed features into PDMS that would not be possible with direct molding as the stiffness of these materials leads to material fracture when unmolding, while the increased toughness in the hydrogels can elastically deform around complex features and maintain replication fidelity. Finally, we highlight the ability of this method to minimize the potential for toxic materials to transfer from the original 3D print into the PDMS replica, enhancing its use for biological applications. This minimization of the transfer of toxic materials has not been reported in other previously reported methods describing replication of 3D prints into PDMS, and we demonstrate its use through the creation of stem cell-derived microheart muscles. This method can also be used in future studies to understand the effects of geometry on engineered tissues and their constitutive cells.

Modulation of myoblast differentiation by electroactive scaffold morphology and biochemical stimuli

The physico-chemical properties of the scaffold materials used for tissue regeneration strategies have a direct impact on cell shape, adhesion, proliferation, phenotypic and differentiation. Herewith, biophysical and biochemical cues have been widely used to design and develop biomaterial systems for specific tissue engineering strategies. In this context, the patterning of piezoelectric polymers that can provide electroactive stimuli represents a suitable strategy for skeletal muscle tissue engineering applications once it has been demonstrated that mechanoelectrical stimuli promote C2C12 myoblast differentiation. In this sense, this works reports on how C2C12 myoblast cells detect and react to physical and biochemical stimuli based on micropatterned poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) electroactive scaffolds produced by soft lithography in the form of arrays of lines and hexagons (anisotropic and isotropic morphology, respectively) combined with differentiation medium. The scaffolds were evaluated for the proliferation and differentiation of C2C12 myoblast cell line and it is demonstrated that anisotropic microstructures promote muscle differentiation which is further reinforced with the introduction of biochemical stimulus. However, when the physical stimulus is not adequate to the tissue, e.g. isotropic microstructure, the biochemical stimulus has the opposite effect, hindering the differentiation process. Therefore, the proper morphological design of the scaffold combined with biochemical stimulus allows to enhance skeletal muscle differentiation and allows the development of advanced strategies for effective muscle tissue engineering.

Response of mesenchymal stem cells to surface topography of scaffolds and the underlying mechanisms

Mesenchymal stem/stromal cells (MSCs) serve as essential components of regenerative medicine. Their destiny is influenced by the interaction of the cells with the external environment. In addition to the biochemical cues in a microenvironment, physical cues of the topography of the surrounding materials such as the extracellular matrix emerge as a crucial regulator of stem cell destiny and function. With recent advances in technologies of materials production and surface modification, surfaces with micro/nanotopographical characteristics can be fabricated to mimic the micro/nanoscale mechanical stimuli of the extracellular matrix environment and regulate the biological behavior of cells. Understanding the interaction of cells with the topography of a surface is conducive to the control of stem cell fate for application in regenerative medicine. However, the mechanisms by which topography affects the biological behavior of stem cells have not been fully elucidated. This review will present the effects of surface topography at the nano/micrometer scale on stem cell adhesion, morphology, proliferation, migration, and differentiation. It also focuses on discussing current theories about the sensing and recognition of surface topology cues, the transduction of the extracellular cues into plasma, and the final activation of related signaling pathways and downstream gene expression in MSCs. These insights will provide a theoretical basis for the future design of biomaterial scaffolds for application in regenerative medicine and tissue engineering.

Mechanical and morphological responses of osteoblast-like cells to two-photon polymerized microgrooved surfaces

Microgrooved surfaces are recognized as an important strategy of tissue engineering to promote the alignment of bone cells. In this work, we have investigated the mechanical and morphological aspects of osteoblasts cells after interaction with different micro-structured polymeric surfaces. Femtosecond laser writing technique was used for the construction of circular and parallel microgrooved patterns in biocompatible polymeric surfaces based on pentaerythritol triacrylate. Additionally, we have studied the influence of the biocompatible TiO₂ nanocrystals (NCs) related to the cell behavior, when incorporated to the photoresin. The atomic force microscopy technique was used to investigate the biomechanical reaction of the human osteoblast-like MG-63 cells for the different microgroove. It was demonstrated that osteoblasts grown on circular microgrooved surfaces exhibited significantly larger Young's modulus compared to cells sown on flat films. Furthermore, we could observe that TiO₂ NCs improved the circular microgrooves effects, resulting in more populated sites, 34% more elongated cells, and increasing the cell stiffness by almost 160%. These results can guide the design and construction of effective scaffold surfaces with circular microgrooves for tissue engineering and bone regeneration.

3D printing a biocompatible elastomer for modeling muscle regeneration after volumetric muscle loss

Volumetric muscle loss (VML) injuries due to trauma, tumor ablation, or other degenerative muscle diseases are debilitating and currently have limited options for self-repair. Advancements in 3D printing allow for the rapid fabrication of biocompatible scaffolds with designer patterns. However, the materials chosen are often stiff or brittle, which is not optimal for muscle tissue engineering. This study utilized a photopolymerizable biocompatible elastomer - poly (glycerol sebacate) acrylate (PGSA) - to develop an in vitro model of muscle regeneration and proliferation into an acellular scaffold after VML injury. Mechanical properties of the scaffold were tuned by controlling light intensity during the 3D printing process to match the specific tension of skeletal muscle. The effect of both geometric (channel sizes between 300 and 600 μm) and biologic (decellularized muscle extracellular matrix (dECM)) cues on muscle progenitor cell infiltration, proliferation, organization, and maturation was evaluated in vitro using a near-infrared fluorescent protein (iRFP) transfected cell line to assess cells in the 3D scaffold. Larger channel sizes and dECM coating were found to enhance cell proliferation and maturation, while no discernable effect on cell alignment was observed. In addition, a pilot experiment was carried out to evaluate the regenerative capacity of this scaffold in vivo after a VML injury. Overall, this platform demonstrates a simple model to study muscle progenitor recruitment and differentiation into acellular scaffolds after VML repair.

Nanomedicine, a valuable tool for skeletal muscle disorders: Challenges, promises, and limitations

Muscular dystrophies are a group of rare genetic disorders characterized by progressive muscle weakness, which, in the most severe forms, leads to the patient's death due to cardiorespiratory problems. There is still no cure available for these diseases and significant effort is being placed into developing new strategies to either correct the genetic defect or to compensate muscle loss by stimulating skeletal muscle regeneration. However, the vast anatomical extension of the target tissue poses great challenges to these goals, highlighting the need for complementary strategies. Nanomedicine is an actively evolving field that merges nanotechnologies with biomedical and pharmaceutical sciences. It holds great potential in regenerative medicine, both in supporting tissue engineering and regeneration, and in optimizing drug and oligonucleotide delivery and gene therapy strategies. In this review, we will summarize the state‐of‐the‐art in the field of nanomedicine applied to skeletal muscle regeneration. We will discuss the recent work toward the development of nanopatterned scaffolds for tissue engineering, the efforts in the synthesis of organic and inorganic nanoparticles for gene therapy and drug delivery applications, as well as their use as immune modulators. Although nanomedicine holds great promise for muscle and other degenerative diseases, many challenges still need to be systematically addressed to assure a smooth transition from the bench to the bedside.

This article is categorized under:

Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement

Advances in microfabrication technologies in tissue engineering and regenerative medicine

BACKGROUND

Tissue engineering provides various strategies to fabricate an appropriate microenvironment to support the repair and regeneration of lost or damaged tissues. In this matter, several technologies have been implemented to construct close-to-native three-dimensional structures at numerous physiological scales, which are essential to confer the functional characteristics of living tissues.

METHODS

In this article, we review a variety of microfabrication technologies that are currently utilized for several tissue engineering applications, such as soft lithography, microneedles, templated and self-assembly of microstructures, microfluidics, fiber spinning, and bioprinting.

RESULTS

These technologies have considerably helped us to precisely manipulate cells or cellular constructs for the fabrication of biomimetic tissues and organs. Although currently available tissues still lack some crucial functionalities, including vascular networks, innervation, and lymphatic system, microfabrication strategies are being proposed to overcome these issues. Moreover, the microfabrication techniques that have progressed to the preclinical stage are also discussed.

CONCLUSIONS

This article aims to highlight the advantages and drawbacks of each technique and areas of further research for a more comprehensive and evolving understanding of microfabrication techniques in terms of tissue engineering and regenerative medicine applications.

The Bumpy Road to Stem Cell Therapies: Rational Design of Surface Topographies to Dictate Stem Cell Mechanotransduction and Fate

Cells sense and respond to a variety of physical cues from their surrounding microenvironment, and these are interpreted through mechanotransductive processes to inform their behavior. These mechanisms have particular relevance to stem cells, where control of stem cell proliferation, potency, and differentiation is key to their successful application in regenerative medicine. It is increasingly recognized that surface micro- and nanotopographies influence stem cell behavior and may represent a powerful tool with which to direct the morphology and fate of stem cells. Current progress toward this goal has been driven by combined advances in fabrication technologies and cell biology. Here, the capacity to generate precisely defined micro- and nanoscale topographies has facilitated the studies that provide knowledge of the mechanotransducive processes that govern the cellular response as well as knowledge of the specific features that can drive cells toward a defined differentiation outcome. However, the path forward is not fully defined, and the "bumpy road" that lays ahead must be crossed before the full potential of these approaches can be fully exploited. This review focuses on the challenges and opportunities in applying micro- and nanotopographies to dictate stem cell fate for regenerative medicine. Here, key techniques used to produce topographic features are reviewed, such as photolithography, block copolymer lithography, electron beam lithography, nanoimprint lithography, soft lithography, scanning probe lithography, colloidal lithography, electrospinning, and surface roughening, alongside their advantages and disadvantages. The biological impacts of surface topographies are then discussed, including the current understanding of the mechanotransductive mechanisms by which these cues are interpreted by the cells, as well as the specific effects of surface topographies on cell differentiation and fate. Finally, considerations in translating these technologies and their future prospects are evaluated.

Adipogenesis or osteogenesis: destiny decision made by mechanical properties of biomaterials

Regenerative medicine affords an effective approach for restoring defect-associated diseases, and biomaterials play a pivotal role as cell niches to support the cell behavior and decide the destiny of cell differentiation. Except for chemical inducers, mechanical properties such as stiffness, pore size and topography of biomaterials play a crucial role in the regulation of cell behaviors and functions. Stiffness may determine the adipogenesis or osteogenesis of mesenchymal stem cells (MSCs) via the translocation of yes-associated protein (YAP) and the transcriptional coactivator with a PDZ-binding motif (TAZ). External forces transmit through cytoskeleton reorientation to assist nuclear deformation and molecule transport, meanwhile, signal pathways including the Hippo, FAK/RhoA/ROCK, and Wnt/β-catenin have been evidenced to participate in the mechanotransduction. Different pore sizes not only tailor the scaffold stiffness but also conform to the requirements of cell migration and vessels in-growth. Topography guides cell geometry along with mobility and determines the cell fate ascribed to micro/nano-scale contact. Herein, we highlight the recent progress in exploring the regulation mechanism by the physical properties of biomaterials, which might lead to more innovative regenerative strategies for adipose or bone tissue repair.

Regenerative medicine affords an effective approach for restoring defect-associated diseases, and biomaterials play a pivotal role as cell niches to support the cell behavior and decide the destiny of cell differentiation.