Myoblast 3D bioprinting to burst in vitro skeletal muscle differentiation

Extruded alginate tubes with myogenic potential

BACKGROUND

There are currently no proven methods to reverse muscle loss in humans, which is caused by trauma (e.g., volumetric muscle loss, VML), genetic neuromuscular diseases (e.g., muscular dystrophies, MDs), and accelerated senescence (e.g., sarcopenia). Since muscle tissue is capable of regeneration through muscle satellite cells (MuSCs), the implantation of autologous (or other) donor MuSCs and MuSC-derived myoblasts into host muscles can promote donor-cell-derived myogenesis. Direct injection or implantation of MuSCs or MuSC-derived myoblasts into host muscles only promotes minimal donor-cell-derived myogenesis, whereas implantation of MuSCs/myoblasts along with associated muscle tissue (muscle fibers, extracellular matrix, neurovascular pathways, etc.) gives better results.

METHODS

We aim to leverage the benefits of constraining donor myogenic cells within a template that resembles muscle tissue. In this paper, we present a workflow for basic and translational studies aimed at promoting donor-cell-derived myogenesis to increase functional muscle mass in mice. Our workflow involves preparing a slurry of 10% sodium alginate mixed with myogenic cells in cell culture media, extruding the cell-containing slurry into 10% calcium lactate to form tubes, and implanting the cellularized alginate tubes into host muscle.

RESULTS

Our data suggest that, the extruded alginate tubes can tolerate a peak stress of 1892 ± 527 mN, that the elastic range is at ~75-125% strain beyond initial length, and that the Young's modulus (stiffness) is 14.17 ± 1.68 %/mm2. Importantly, these mechanical properties render the alginate tubes suitable for a published technique known as minimally-invasive muscle embedding (MIME) that was developed by us to implant myogenic material into host muscle. MIME involves threading donor myogenic tissue into a needle track created within a host muscle. Cellularized alginate tubes implanted into the tibialis anterior muscle of previously euthanized mice had numerous hematoxylin-stained structures similar to nuclear staining, supporting the idea that our alginate tubes can support cell seeding. Alginate tubes that were seeded with MuSCs, incubated in MuSC/myoblast growth (i.e., proliferation) media for two days, incubated in myotube differentiation media for six days, and then minced and reseeded in new dishes, were able to promote in vitro myoblast outgrowth over several days.

DISCUSSION

This pilot study is limited in its translational scope because it was performed in vitro and with previously euthanized mice. Additional studies are needed to confirm that cellularized alginate tubes can promote the de novo development of donor-cell-derived muscle fibers, which can contribute to contractile force production.

CONCLUSION

Alginate tubes with MuSC/myoblasts can be generated by a simple extrusion method. The alginate tubes have sufficient mechanical strength to tolerate insertion into a host muscle, in a minimally-invasive manner, through a needle track. The cellularized alginate tubes demonstrate myogenic potential since they are capable of being maintained in culture conditions for several days, after which they can still facilitate myoblast outgrowth in a dish.

SIRT1 activation attenuates palmitate induced apoptosis in C2C12 muscle cells

BACKGROUND

Type 2 diabetes is characterized by insulin resistance, which manifests mainly in skeletal muscles. SIRT1 has been found to play a role in the insulin signaling pathway. However, the molecular underpinnings of SIRT1's function in palmitate fatty acid-induced apoptosis still need to be better understood.

METHODS

In this research, skeletal muscle cells are treated with palmitate to be insulin resistant. It is approached that SIRT1 is downregulated in C2C12 muscle cells during palmitate-induced apoptosis and that activating SIRT1 mitigates this effect.

RESULTS

Based on these findings, palmitate-induced apoptosis suppressed mitochondrial biogenesis by lowering PGC-1 expression, while SIRT1 overexpression boosted. The SIRT1 inhibitor sirtinol, on the other hand, decreased mitochondrial biogenesis under the same conditions. This research also shows that ROS levels rise in the conditions necessary for apoptosis induction by palmitate, and ROS inhibitors can mitigate this effect. This work demonstrated that lowering ROS levels by boosting SIRT1 expression inhibited apoptotic induction in skeletal muscle cells.

CONCLUSION

This study's findings suggested that SIRT1 can improve insulin resistance in type 2 diabetes by slowing the rate of lipo-apoptosis and boosting mitochondrial biogenesis, among other benefits.

Emerging perspectives on 3D printed bioreactors for clinical translation of engineered and bioprinted tissue constructs

3D printed/bioprinted tissue constructs are utilized for the regeneration of damaged tissues and as in vitro models. Most of the fabricated 3D constructs fail to undergo functional maturation in conventional in vitro settings. There is a challenge to provide a suitable niche for the fabricated tissue constructs to undergo functional maturation. Bioreactors have emerged as a promising tool to enhance tissue maturation of the engineered constructs by providing physical/biological cues along with a controlled nutrient supply under dynamic in vitro conditions. Bioreactors provide an ambient microenvironment most appropriate for the development of functionally matured tissue constructs by promoting cell proliferation, differentiation, and maturation for transplantation and drug screening applications. Due to the huge cost and limited availability of commercial bioreactors, there is a need to develop strategies to make customized bioreactors. Additive manufacturing (AM) may be a viable tool to fabricate custom designed bioreactors with better efficiency and at low cost. In this review, we have extensively discussed the importance of bioreactors in functionalizing tissue engineered/3D bioprinted scaffolds for bone, cartilage, skeletal muscle, nerve, and vascular tissue. In addition, the importance and fabrication of customized 3D printed bioreactors for the maturation of tissue engineered constructs are discussed in detail. Finally, the current challenges and future perspectives in translating commercial and custom 3D printed bioreactors for clinical applications are outlined.

4-Axis 3D-Printed Tubular Biomaterials Imitating the Anisotropic Nanofiber Orientation of Porcine Aortae

Many of the peculiar properties of the vasculature are related to the arrangement of anisotropic proteinaceous fibers in vessel walls. Understanding and imitating these arrangements can potentially lead to new therapies for cardiovascular diseases. These can be pre-surgical planning, for which patient-specific ex vivo anatomical models for endograft testing are of interest. Alternatively, therapies can be based on tissue engineering, for which degradable in vitro cell growth substrates are used to culture replacement parts. In both cases, materials are desirable that imitate the biophysical properties of vessels, including their tubular shapes and compliance. This work contributes to these demands by offering methods for the manufacturing of anisotropic 3D-printed nanofibrous tubular structures that have similar biophysical properties as porcine aortae, that are biocompatible, and that allow for controlled nutrient diffusion. Tubes of various sizes with axial, radial, or alternating nanofiber orientation along the blood flow direction are manufactured by a customized method. Blood pressure-resistant, compliant, stable, and cell culture-compatible structures are obtained, that can be degraded in vitro on demand. It is suggested that these healthcare materials can contribute to the next generation of cardiovascular therapies of ex vivo pre-surgical planning or in vitro cell culture.

Three-Dimensional Bioprinting in Soft Tissue Engineering for Plastic and Reconstructive Surgery

Skeletal muscle tissue engineering (TE) and adipose tissue engineering have undergone significant progress in recent years. This review focuses on the key findings in these areas, particularly highlighting the integration of 3D bioprinting techniques to overcome challenges and enhance tissue regeneration. In skeletal muscle TE, 3D bioprinting enables the precise replication of muscle architecture. This addresses the need for the parallel alignment of cells and proper innervation. Satellite cells (SCs) and mesenchymal stem cells (MSCs) have been utilized, along with co-cultivation strategies for vascularization and innervation. Therefore, various printing methods and materials, including decellularized extracellular matrix (dECM), have been explored. Similarly, in adipose tissue engineering, 3D bioprinting has been employed to overcome the challenge of vascularization; addressing this challenge is vital for graft survival. Decellularized adipose tissue and biomimetic scaffolds have been used as biological inks, along with adipose-derived stem cells (ADSCs), to enhance graft survival. The integration of dECM and alginate bioinks has demonstrated improved adipocyte maturation and differentiation. These findings highlight the potential of 3D bioprinting techniques in skeletal muscle and adipose tissue engineering. By integrating specific cell types, biomaterials, and printing methods, significant progress has been made in tissue regeneration. However, challenges such as fabricating larger constructs, translating findings to human models, and obtaining regulatory approvals for cellular therapies remain to be addressed. Nonetheless, these advancements underscore the transformative impact of 3D bioprinting in tissue engineering research and its potential for future clinical applications.

Electrospun Fibers Loaded with Pirfenidone: An Innovative Approach for Scar Modulation in Complex Wounds

Hypertrophic scars (HTSs) are pathological structures resulting from chronic inflammation during the wound healing process, particularly in complex injuries like burns. The aim of this work is to propose Biofiber PF (biodegradable fiber loaded with Pirfenidone 1.5 w/w), an electrospun advanced dressing, as a solution for HTSs treatment in complex wounds. Biofiber has a 3-day antifibrotic action to modulate the fibrotic process and enhance physiological healing. Its electrospun structure consists of regular well-interconnected Poly-L-lactide-co-poly-ε-caprolactone (PLA-PCL) fibers (size 2.83 ± 0.46 µm) loaded with Pirfenidone (PF, 1.5% w/w), an antifibrotic agent. The textured matrix promotes the exudate balance through mild hydrophobic wettability behavior (109.3 ± 2.3°), and an appropriate equilibrium between the absorbency % (610.2 ± 171.54%) and the moisture vapor transmission rate (0.027 ± 0.036 g/min). Through its finer mechanical properties, Biofiber PF is conformable to the wound area, promoting movement and tissue oxygenation. These features also enhance the excellent elongation (>500%) and tenacity, both in dry and wet conditions. The ancillary antifibrotic action of PF on hypertrophic scar fibroblast (HSF) for 3 days downregulates the cell proliferation over time and modulates the gene expression of transforming growth factor β1 (TGF-β1) and α-smooth muscle actin (α-SMA) at 48-72 h. After 6 days of treatment, a decrement of α-SMA protein levels was detected, proving the potential of biofiber as a valid therapeutic treatment for HTSs in an established wound healing process.

3D Co-Printing and Substrate Geometry Influence the Differentiation of C2C12 Skeletal Myoblasts

Cells are influenced by several biomechanical aspects of their microenvironment, such as substrate geometry. According to the literature, substrate geometry influences the behavior of muscle cells; in particular, the curvature feature improves cell proliferation. However, the effect of substrate geometry on the myogenic differentiation process is not clear and needs to be further investigated. Here, we show that the 3D co-printing technique allows the realization of substrates. To test the influence of the co-printing technique on cellular behavior, we realized linear polycaprolactone substrates with channels in which a fibrinogen-based hydrogel loaded with C2C12 cells was deposited. Cell viability and differentiation were investigated up to 21 days in culture. The results suggest that this technology significantly improves the differentiation at 14 days. Therefore, we investigate the substrate geometry influence by comparing three different co-printed geometries-linear, circular, and hybrid structures (linear and circular features combined). Based on our results, all structures exhibit optimal cell viability (>94%), but the linear pattern allows to increase the in vitro cell differentiation, in particular after 14 days of culture. This study proposes an endorsed approach for creating artificial muscles for future skeletal muscle tissue engineering applications.

Modification, 3D printing process and application of sodium alginate based hydrogels in soft tissue engineering: A review

Sodium alginate (SA) is an inexpensive and biocompatible biomaterial with fast and gentle crosslinking that has been widely used in biological soft tissue repair/regeneration. Especially with the advent of 3D bioprinting technology, SA hydrogels have been applied more deeply in tissue engineering due to their excellent printability. Currently, the research on material modification, molding process and application of SA-based composite hydrogels has become a hot topic in tissue engineering, and a lot of fruitful results have been achieved. To better help readers have a comprehensive understanding of the development status of SA based hydrogels and their molding process in tissue engineering, in this review, we summarized SA modification methods, and provided a comparative analysis of the characteristics of various SA based hydrogels. Secondly, various molding methods of SA based hydrogels were introduced, the processing characteristics and the applications of different molding methods were analyzed and compared. Finally, the applications of SA based hydrogels in tissue engineering were reviewed, the challenges in their applications were also analyzed, and the future research directions were prospected. We believe this review is of great helpful for the researchers working in biomedical and tissue engineering.

Nanofibrillated cellulose/gellan gum hydrogel-based bioinks for 3D bioprinting of skin cells

The development of suitable bioinks is an important research topic in the field of three-dimensional (3D) bioprinting. Herein, novel hydrogel-based bioinks composed of nanofibrillated cellulose (NFC) and gellan gum (GG) in different NFC/GG mass proportions (90:10, 80:20, 70:30, and 60:40) were developed and characterized. The increase in the content of GG, as well as its combination with NFC, enhanced their rheological properties, increasing both storage (G') and loss (G") moduli and the G' recovery capacity of the hydrogels (from 70.05 ± 3.06 % (90:10) to 82.63 ± 1.21 % (60:40)), as well as their mechanical properties, increasing the compressive stiffness and stress from 114.02 ± 10.93 Pa (90:10) to 337.16 ± 34.03 Pa (60:40) and from 18.27 ± 1.32 kPa (90:10) to 47.17 ± 3.59 kPa (60:40), respectively. The hydrogels were non-cytotoxic against human keratinocyte cells (HaCaT), with cell viabilities above 70 % for up to 72 h. The hydrogel 60:40 was loaded with HaCaT cells (3 × 10⁶ cells mL^-1) and bioprinted. The cell viability was maintained elevated until day 7 (90 ± 3 %) after bioprinting. These results highlight that the combination of these two biopolymers was a good strategy for the development of novel hydrogel-based bioinks for extrusion 3D bioprinting applications.

Adipose-derived stem cell spheroid-laden microbial transglutaminase cross-linked gelatin hydrogel for treating diabetic periodontal wounds and craniofacial defects

BACKGROUND

Diabetes mellitus deteriorates the destruction and impairs the healing of periodontal wounds and craniofacial defects. This study is to evaluate the potential of self-assembled adipose-derived stem cell spheroids (ADsp) in microbial transglutaminase cross-linked gelatin hydrogel (mTG) for treating diabetic periodontal wounds and craniofacial defects.

METHODS

Human adipose-derived stem cells (ADSCs) were isolated by lipoaspiration, pluripotent genes and trilineage differentiation were examined, and the maintenance of ADsp properties in mTG was verified. Oral mucosal wounds and calvarial osseous defects were created in diabetic rats. Gross observation, histologic evaluation, and immunohistochemistry for proliferating cells and keratinization were conducted in the mucosal wounds within 4-28 days. Micro-CT imaging, histologic evaluation, and immunohistochemistry for proliferating cells and osteogenic differentiation were conducted in the osseous defects at 7 and 28 days.

RESULTS

ADSCs expressed pluripotent genes and were capable of trilineage differentiation. ADsp retained morphology and stemness in mTG. In diabetic mucosal wounds, wound closure, epithelization, and keratinization were accelerated in those with ADsp and ADsp-mTG. In diabetic osseous defects, osteogenic differentiation markers were evidently expressed, cell proliferation was promoted from day 7, and bone formation was significantly promoted at day 28 in those with osteogenically pretreated ADsp-mTG.

CONCLUSIONS

ADsp-mTG accelerated diabetic oral mucosal wound healing, and osteogenically pretreated ADsp-mTG promoted diabetic osseous defect regeneration, proving that ADsp-mTG facilitated diabetic periodontal wound healing and craniofacial osseous defect regeneration.

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

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

Latest developments in engineered skeletal muscle tissues for drug discovery and development

INTRODUCTION

With the advances in skeletal muscle tissue engineering, new platforms have arisen with important applications in biology studies, disease modeling, and drug testing. Current developments highlight the quest for engineering skeletal muscle tissues with higher complexity . These new human skeletal muscle tissue models will be powerful tools for drug discovery and development and disease modeling.

AREAS COVERED

The authors review the latest advances in in vitro models of engineered skeletal muscle tissues used for testing drugs with a focus on the use of four main cell culture techniques: Cell cultures in well plates, in microfluidics, in organoids, and in bioprinted constructs. Additional information is provided on the satellite cell niche.

EXPERT OPINION

In recent years, more sophisticated in vitro models of skeletal muscle tissues have been fabricated. Important developments have been made in stem cell research and in the engineering of human skeletal muscle tissue. Some platforms have already started to be used for drug testing, notably those based on the parameters of hypertrophy/atrophy and the contractibility of myotubes. More developments are expected through the use of multicellular types and multi-materials as matrices . The validation and use of these models in drug testing should now increase.

Advances in electrospinning and 3D bioprinting strategies to enhance functional regeneration of skeletal muscle tissue

Skeletal muscles are essential for body movement, and the loss of motor function due to volumetric muscle loss (VML) limits the mobility of patients. Current therapeutic approaches are insufficient to offer complete functional recovery of muscle damages. Tissue engineering provides viable ways to fabricate scaffolds to regenerate damaged tissues. Hence, tissue engineering options are explored to address existing challenges in the treatment options for muscle regeneration. Electrospinning is a widely employed fabrication technique to make muscle mimetic nanofibrous scaffolds for tissue regeneration. 3D bioprinting has also been utilized to fabricate muscle-like tissues in recent times. This review discusses the anatomy of skeletal muscle, defects, the healing process, and various treatment options for VML. Further, the advanced strategies in electrospinning of natural and synthetic polymers are discussed, along with the recent developments in the fabrication of hybrid scaffolds. Current approaches in 3D bioprinting of skeletal muscle tissues are outlined with special emphasis on the combination of electrospinning and 3D bioprinting towards the development of fully functional muscle constructs. Finally, the current challenges and future perspectives of these convergence techniques are discussed.

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.

Alginate-Lysozyme Nanofibers Hydrogels with Improved Rheological Behavior, Printability and Biological Properties for 3D Bioprinting Applications

In this study, alginate nanocomposite hydrogel bioinks reinforced with lysozyme nanofibers (LNFs) were developed. Alginate-LNF (A-LNF) suspensions with different LNF contents (1, 5 and 10 wt.%) were prepared and pre-crosslinked with 0.5% (w/v) CaCl₂ to formulate A-LNF inks. These inks exhibit proper shear-thinning behavior and good recovery properties (~90%), with the pre-crosslinking step playing a crucial role. A-LNF fully crosslinked hydrogels (with 2% (w/v) CaCl₂) that mimic 3D printing scaffolds were prepared, and it was observed that the addition of LNFs improved several properties of the hydrogels, such as the morphology, swelling and degradation profiles, and mechanical properties. All formulations are also noncytotoxic towards HaCaT cells. The printing parameters and 3D scaffold model were then optimized, with A-LNF inks showing improved printability. Selected A-LNF inks (A-LNF0 and A-LNF5) were loaded with HaCaT cells (cell density 2 × 10⁶ cells mL⁻¹), and the cell viability within the bioprinted scaffolds was evaluated for 1, 3 and 7 days, with scaffolds printed with the A-LNF5 bioink showing the highest values for 7 days (87.99 ± 1.28%). Hence, A-LNF bioinks exhibited improved rheological performance, printability and biological properties representing a good strategy to overcome the main limitations of alginate-based bioinks.

A Guide to Polysaccharide-Based Hydrogel Bioinks for 3D Bioprinting Applications

Three-dimensional (3D) bioprinting is an innovative technology in the biomedical field, allowing the fabrication of living constructs through an approach of layer-by-layer deposition of cell-laden inks, the so-called bioinks. An ideal bioink should possess proper mechanical, rheological, chemical, and biological characteristics to ensure high cell viability and the production of tissue constructs with dimensional stability and shape fidelity. Among the several types of bioinks, hydrogels are extremely appealing as they have many similarities with the extracellular matrix, providing a highly hydrated environment for cell proliferation and tunability in terms of mechanical and rheological properties. Hydrogels derived from natural polymers, and polysaccharides, in particular, are an excellent platform to mimic the extracellular matrix, given their low cytotoxicity, high hydrophilicity, and diversity of structures. In fact, polysaccharide-based hydrogels are trendy materials for 3D bioprinting since they are abundant and combine adequate physicochemical and biomimetic features for the development of novel bioinks. Thus, this review portrays the most relevant advances in polysaccharide-based hydrogel bioinks for 3D bioprinting, focusing on the last five years, with emphasis on their properties, advantages, and limitations, considering polysaccharide families classified according to their source, namely from seaweed, higher plants, microbial, and animal (particularly crustaceans) origin.