Promoting Long-Term Cultivation of Motor Neurons for 3D Neuromuscular Junction Formation of 3D In Vitro Using Central-Nervous-Tissue-Derived Bioink

In vitrothree-dimensional volumetric printing of vitreous body models using decellularized extracellular matrix bioink

Hyalocytes, which are considered to originate from the monocyte/macrophage lineage, play active roles in vitreous collagen and hyaluronic acid synthesis. Obtaining a hyalocyte-compatible bioink during the 3D bioprinting of eye models is challenging. In this study, we investigated the suitability of a cartilage-decellularized extracellular matrix (dECM)-based bioink for printing a vitreous body model. Given that achieving a 3D structure and environment identical to those of the vitreous body necessitates good printability and biocompatibility, we examined the mechanical and biological properties of the developed dECM-based bioink. Furthermore, we proposed a 3D bioprinting strategy for volumetric vitreous body fabrication that supports cell viability, transparency, and self-sustainability. The construction of a 3D structure composed of bioink microfibers resulted in improved transparency and hyalocyte-like macrophage activity in volumetric vitreous mimetics, mimicking real vitreous bodies. The results indicate that our 3D structure could serve as a platform for drug testing in disease models and demonstrate that the proposed printing technology, utilizing a dECM-based bioink and volumetric vitreous body, has the potential to facilitate the development of advanced eye models for future studies on floater formation and visual disorders.

Engineered Regenerative Isolated Peripheral Nerve Interface for Targeted Reinnervation

A regenerative peripheral nerve interface (RPNI) offers a therapeutic solution for nerve injury through reconstruction of the target muscle. However, implanting a transected peripheral nerve into an autologous skeletal muscle graft in RPNI causes donor-site morbidity, highlighting the need for tissue-engineered skeletal muscle constructs. Here, an engineered regenerative isolated peripheral nerve interface (eRIPEN) is developed using 3D skeletal cell printing combined with direct electrospinning to create a nanofiber membrane envelop for host nerve implantation. In this in vivo study, after over 8 months of RPNI surgery, the eRIPEN exhibits a minimum Feret diameter of 15-20 µm with a cross-sectional area of 100-500 µm2, representing the largest distribution of myofibers. Furthermore, neuromuscular junction formation and muscle contraction with a force of ≈28 N are observed. Notably, the decreased hypersensitivity to mechanical/thermal stimuli and an improved tibial functional index from -77 to -56 are found in the eRIPEN group. The present novel concept of eRIPEN paves the way for the utilization and application of tissue-engineered constructs in RPNI, ultimately realizing neuroprosthesis control through synaptic connections.

Advances in 3D tissue models for neural engineering: self-assembled versus engineered tissue models

Neural tissue engineering has emerged as a promising field that aims to create functional neural tissue for therapeutic applications, drug screening, and disease modelling. It is becoming evident in the literature that this goal requires development of three-dimensional (3D) constructs that can mimic the complex microenvironment of native neural tissue, including its biochemical, mechanical, physical, and electrical properties. These 3D models can be broadly classified as self-assembled models, which include spheroids, organoids, and assembloids, and engineered models, such as those based on decellularized or polymeric scaffolds. Self-assembled models offer advantages such as the ability to recapitulate neural development and disease processes in vitro, and the capacity to study the behaviour and interactions of different cell types in a more realistic environment. However, self-assembled constructs have limitations such as lack of standardised protocols, inability to control the cellular microenvironment, difficulty in controlling structural characteristics, reproducibility, scalability, and lengthy developmental timeframes. Integrating biomimetic materials and advanced manufacturing approaches to present cells with relevant biochemical, mechanical, physical, and electrical cues in a controlled tissue architecture requires alternate engineering approaches. Engineered scaffolds, and specifically 3D hydrogel-based constructs, have desirable properties, lower cost, higher reproducibility, long-term stability, and they can be rapidly tailored to mimic the native microenvironment and structure. This review explores 3D models in neural tissue engineering, with a particular focus on analysing the benefits and limitations of self-assembled organoids compared with hydrogel-based engineered 3D models. Moreover, this paper will focus on hydrogel based engineered models and probe their biomaterial components, tuneable properties, and fabrication techniques that allow them to mimic native neural tissue structures and environment. Finally, the current challenges and future research prospects of 3D neural models for both self-assembled and engineered models in neural tissue engineering will be discussed.

3D bioprinting approaches for spinal cord injury repair

Regenerative healing of spinal cord injury (SCI) poses an ongoing medical challenge by causing persistent neurological impairment and a significant socioeconomic burden. The complexity of spinal cord tissue presents hurdles to successful regeneration following injury, due to the difficulty of forming a biomimetic structure that faithfully replicates native tissue using conventional tissue engineering scaffolds. 3D bioprinting is a rapidly evolving technology with unmatched potential to create 3D biological tissues with complicated and hierarchical structure and composition. With the addition of biological additives such as cells and biomolecules, 3D bioprinting can fabricate preclinical implants, tissue or organ-like constructs, andin vitromodels through precise control over the deposition of biomaterials and other building blocks. This review highlights the characteristics and advantages of 3D bioprinting for scaffold fabrication to enable SCI repair, including bottom-up manufacturing, mechanical customization, and spatial heterogeneity. This review also critically discusses the impact of various fabrication parameters on the efficacy of spinal cord repair using 3D bioprinted scaffolds, including the choice of printing method, scaffold shape, biomaterials, and biological supplements such as cells and growth factors. High-quality preclinical studies are required to accelerate the translation of 3D bioprinting into clinical practice for spinal cord repair. Meanwhile, other technological advances will continue to improve the regenerative capability of bioprinted scaffolds, such as the incorporation of nanoscale biological particles and the development of 4D printing.

Unlocking the Complexity of Neuromuscular Diseases: Insights from Human Pluripotent Stem Cell-Derived Neuromuscular Junctions

Over the past 20 years, the use of pluripotent stem cells to mimic the complexities of the human neuromuscular junction has received much attention. Deciphering the key mechanisms underlying the establishment and maturation of this complex synapse has been driven by the dual goals of addressing developmental questions and gaining insight into neuromuscular disorders. This review aims to summarise the evolution and sophistication of in vitro neuromuscular junction models developed from the first differentiation of human embryonic stem cells into motor neurons to recent neuromuscular organoids. We also discuss the potential offered by these models to decipher different neuromuscular diseases characterised by defects in the presynaptic compartment, the neuromuscular junction, and the postsynaptic compartment. Finally, we discuss the emerging field that considers the use of these techniques in drug screening assay and the challenges they will face in the future.

3D bioprinting for organ and organoid models and disease modeling

INTRODUCTION

3D printing, a versatile additive manufacturing technique, has diverse applications ranging from transportation, rapid prototyping, clean energy, and medical devices.

AREAS COVERED

The authors focus on how 3D printing technology can enhance the drug discovery process through automating tissue production that enables high-throughput screening of potential drug candidates. They also discuss how the 3D bioprinting process works and what considerations to address when using this technology to generate cell laden constructs for drug screening as well as the outputs from such assays necessary for determining the efficacy of potential drug candidates. They focus on how bioprinting how has been used to generate cardiac, neural, and testis tissue models, focusing on bio-printed 3D organoids.

EXPERT OPINION

The next generation of 3D bioprinted organ model holds great promises for the field of medicine. In terms of drug discovery, the incorporation of smart cell culture systems and biosensors into 3D bioprinted models could provide highly detailed and functional organ models for drug screening. By addressing current challenges of vascularization, electrophysiological control, and scalability, researchers can obtain more reliable and accurate data for drug development, reducing the risk of drug failures during clinical trials.

Applications of chitosan-based biomaterials: From preparation to spinal cord injury neuroprosthetic treatment

Spinal cord injury (SCI)-related disabilities are a serious problem in the modern society. Further, the treatment of SCI is highly challenging and is urgently required in clinical practice. Research on nerve tissue engineering is an emerging approach for improving the treatment outcomes of SCI. Chitosan (CS) is a cationic polysaccharide derived from natural biomaterials. Chitosan has been found to exhibit excellent biological properties, such as nontoxicity, biocompatibility, biodegradation, and antibacterial activity. Recently, chitosan-based biomaterials have attracted significant attention for SCI repair in nerve tissue engineering applications. These studies revealed that chitosan-based biomaterials have various functions and mechanisms to promote SCI repair, such as promoting neural cell growth, guiding nerve tissue regeneration, delivering nerve growth factors, and as a vector for gene therapy. Chitosan-based biomaterials have proven to have excellent potential for the treatment of SCI. This review aims to introduce the recent advances in chitosan-based biomaterials for SCI treatment and to highlight the prospects for further application.

Induced Pluripotent Stem Cells for Modeling Physiological and Pathological Striated Muscle Complexity

Neuromuscular disorders (NMDs) are a large group of diseases associated with either alterations of skeletal muscle fibers, motor neurons or neuromuscular junctions. Most of these diseases is characterized with muscle weakness or wasting and greatly alter the life of patients. Animal models do not always recapitulate the phenotype of patients. The development of innovative and representative human preclinical models is thus strongly needed for modeling the wide diversity of NMDs, characterization of disease-associated variants, investigation of novel genes function, or the development of therapies. Over the last decade, the use of patient's derived induced pluripotent stem cells (hiPSC) has resulted in tremendous progress in biomedical research, including for NMDs. Skeletal muscle is a complex tissue with multinucleated muscle fibers supported by a dense extracellular matrix and multiple cell types including motor neurons required for the contractile activity. Major challenges need now to be tackled by the scientific community to increase maturation of muscle fibers in vitro, in particular for modeling adult-onset diseases affecting this tissue (neuromuscular disorders, cachexia, sarcopenia) and the evaluation of therapeutic strategies. In the near future, rapidly evolving bioengineering approaches applied to hiPSC will undoubtedly become highly instrumental for investigating muscle pathophysiology and the development of therapeutic strategies.

Optimization of Application-Driven Development of In Vitro Neuromuscular Junction Models

Neuromuscular junctions (NMJs) are specialized synapses responsible for signal transduction between motor neurons (MNs) and skeletal muscle tissue. Malfunction at this site can result from developmental disorders, toxic environmental exposures, and neurodegenerative diseases leading to severe neurological dysfunction. Exploring these conditions in human or animal subjects is restricted by ethical concerns and confounding environmental factors. Therefore, in vitro NMJ models provide exciting opportunities for advancements in tissue engineering. In the last two decades, multiple NMJ prototypes and platforms have been reported, and each model system design is strongly tied to a specific application: exploring developmental physiology, disease modeling, or high-throughput screening. Directing the differentiation of stem cells into mature MNs and/or skeletal muscle for NMJ modeling has provided critical cues to recapitulate early-stage development. Patient-derived inducible pluripotent stem cells provide a personalized approach to investigating NMJ disease, especially when disease etiology cannot be resolved down to a specific gene mutation. Having reproducible NMJ culture replicates is useful for high-throughput screening to evaluate drug toxicity and determine the impact of environmental threat exposures. Cutting-edge bioengineering techniques have propelled this field forward with innovative microfabrication and design approaches allowing both two-dimensional and three-dimensional NMJ culture models. Many of these NMJ systems require further validation for broader application by regulatory agencies, pharmaceutical companies, and the general research community. In this summary, we present a comprehensive review on the current state-of-art research in NMJ models and discuss their ability to provide valuable insight into cell and tissue interactions. Impact statement In vitro neuromuscular junction (NMJ) models reveal the specialized mechanisms of communication between neurons and muscle tissue. This site can be disrupted by developmental disorders, toxic environmental exposures, or neurodegenerative diseases, which often lead to fatal outcomes and is therefore of critical importance to the medical community. Many bioengineering approaches for in vitro NMJ modeling have been designed to mimic development and disease; other approaches include in vitro NMJ models for high-throughput toxicology screening, providing a platform to limit or replace animal testing. This review describes various NMJ applications and the bioengineering advancements allowing for human NMJ characteristics to be more accurately recapitulated. While the extensive range of NMJ device structures has hindered standardization attempts, there is still a need to harmonize these devices for broader application and to continue advancing the field of NMJ modeling.

Construction of a decellularized spinal cord matrix/GelMA composite scaffold and its effects on neuronal differentiation of neural stem cells

Spinal cord injury (SCI) leads to severe loss of motor and sensory functions, and the rehabilitation of SCI is a worldwide problem. Tissue-engineered scaffolds offer new hope for SCI patients, while the newly developed materials encountered a challenge in modeling the microenvironment around the lesion site. We constructed a new composite scaffold by mixing decellularized spinal cord extracellular matrix (dECM) with gelatin methacryloyl (GelMA). The dECM, as a natural biological material, retained a large number of proteins and growth factors related to neurogenesis. GelMA was a photopolymerizable material, harbored a polymer network structure, soft texture, certain shape and plenty of water. The viability, proliferation, and differentiation of neural stem cells (NSCs) on the composite scaffold were evaluated by cell count kit-8 (CCK8), Live/Dead assay, phalloidin staining, 5-Ethynyl-2'-deoxyurdine (EdU), immunofluorescence staining and western blot. The Live/Dead assay, phalloidin staining, EdU, and CCK8 assay showed that the composite scaffold had good biocompatibility and provided better support for proliferation of NSCs. Results of immunocytochemistry and western blot showed that the composite scaffolds promoted the specific differentiation of NSCs into neuron cells. Together, this dECM/GelMA composite scaffold can be used as a cell culture coating, the isolated NSCs seeded on the surface of composite scaffold expressed neuronal markers and assumed neuronal morphology. Our work provided a new method that would be widely used in tissue engineering of SCI.

Development and Application of Three-Dimensional Bioprinting Scaffold in the Repair of Spinal Cord Injury

Spinal cord injury (SCI) is a disabling and destructive central nervous system injury that has not yet been successfully treated at this stage. Three-dimensional (3D) bioprinting has become a promising method to produce more biologically complex microstructures, which fabricate living neural constructs with anatomically accurate complex geometries and spatial distributions of neural stem cells, and this is critical in the treatment of SCI. With the development of 3D printing technology and the deepening of research, neural tissue engineering research using different printing methods, bio-inks, and cells to repair SCI has achieved certain results. Although satisfactory results have not yet been achieved, they have provided novel ideas for the clinical treatment of SCI. Considering the potential impact of 3D bioprinting technology on neural studies, this review focuses on 3D bioprinting methods widely used in SCI neural tissue engineering, and the latest technological applications of bioprinting of nerve tissues for the repair of SCI are discussed. In addition to introducing the recent progress, this work also describes the existing limitations and highlights emerging possibilities and future prospects in this field.

Effect of Photobiomodulation in Suppression of Oxidative Stress on Retinal Pigment Epithelium

As the world undergoes aging, the number of age-related diseases has increased. One of them is disease related to retinal pigment epithelium (RPE) degeneration, such as age-related macular degeneration, causing vision loss without physical damage in the ocular system. It is the leading cause of blindness, with no cure. Although the exact pathogenesis is still unknown, the research shows that oxidative stress is one of the risk factors. Various molecules have been reported as anti-oxidative materials; however, the disease has not yet been conquered. Here, we would like to introduce photobiomodulation (PBM). PBM is a non-invasive treatment based on red and near-infrared light and has been used to cure various diseases by regulating cellular functions. Furthermore, recent studies showed its antioxidant effect, and due to this reason, PBM is arising as a new treatment for ocular disease. In this study, we confirm the antioxidant effect of PBM in retinal pigment epithelium via an RPE model with hypoxia. The function of RPE is protected by PBM against damage from hypoxia. Furthermore, we observed the protective mechanism of PBM by its suppression effect on reactive oxygen species generation. These results indicate that PBM shows great potential to cure RPE degeneration to help patients with blindness.

Three-Dimensional Microfilament Printing of a Decellularized Extracellular Matrix (dECM) Bioink Using a Microgel Printing Bath for Nerve Graft Fabrication and the Effectiveness of dECM Graft Combined with a Polycaprolactone Conduit

Various synthetic and decellularized materials are being used to reconstruct peripheral nerve defects and replace autologous nerve grafts. In this study, we developed a microgel printing bath to three-dimensionally (3D) print a peripheral nervous system decellularized extracellular matrix nerve graft reinforced by a polycaprolactone (PCL) conduit. The straightforward fabrication method of an alginate microgel-supplemented printing bath allows a 30 μm filament resolution of a low viscous decellularized extracellular matrix hydrogel with neutral pH. When applied to a sciatic nerve defect model of rats, the total number of regenerated axons and relative gastrocnemius muscle weight ratio were comparable to those of the autologous nerve graft group. Meanwhile, the results were superior to those of the porcine decellularized nerve graft group or the 3D printed decellularized extracellular matrix graft group. This study will be the first step demonstrating that the 3D printed decellularized extracellular matrix (dECM) graft with a PCL conduit is an effective and reliable choice to replace an autologous nerve graft in the near future.

3D bioprinting of complex tissues in vitro: state-of-the-art and future perspectives

The pharmacology and toxicology of a broad variety of therapies and chemicals have significantly improved with the aid of the increasing in vitro models of complex human tissues. Offering versatile and precise control over the cell population, extracellular matrix (ECM) deposition, dynamic microenvironment, and sophisticated microarchitecture, which is desired for the in vitro modeling of complex tissues, 3D bio-printing is a rapidly growing technology to be employed in the field. In this review, we will discuss the recent advancement of printing techniques and bio-ink sources, which have been spurred on by the increasing demand for modeling tactics and have facilitated the development of the refined tissue models as well as the modeling strategies, followed by a state-of-the-art update on the specialized work on cancer, heart, muscle and liver. In the end, the toxicological modeling strategies, substantial challenges, and future perspectives for 3D printed tissue models were explored.

Scaffold biomaterials and nano-based therapeutic strategies for skeletal muscle regeneration

Skeletal muscle is integral to the functioning of the human body. Several pathological conditions, such as trauma (primary lesion) or genetic diseases such as Duchenne muscular dystrophy (DMD), can affect and impair its functions or exceed its regeneration capacity. Tissue engineering (TE) based on natural, synthetic and hybrid biomaterials provides a robust platform for developing scaffolds that promote skeletal muscle regeneration, strength recovery, vascularization and innervation. Recent 3D-cell printing technology and the use of nanocarriers for the release of drugs, peptides and antisense oligonucleotides support unique therapeutic alternatives. Here, the authors present recent advances in scaffold biomaterials and nano-based therapeutic strategies for skeletal muscle regeneration and perspectives for future endeavors.

Recent Trends in Biofabrication Technologies for Studying Skeletal Muscle Tissue-Related Diseases

In native skeletal muscle, densely packed myofibers exist in close contact with surrounding motor neurons and blood vessels, which are embedded in the fibrous connective tissue. In comparison to conventional two-dimensional (2D) cultures, the three-dimensional (3D) engineered skeletal muscle models allow structural and mechanical resemblance with native skeletal muscle tissue by providing geometric confinement and physiological matrix stiffness to the cells. In addition, various external stimuli applied to these models enhance muscle maturation along with cell-cell and cell-extracellular matrix interaction. Therefore, 3D in vitro muscle models can adequately recapitulate the pathophysiologic events occurring in tissue-tissue interfaces inside the native skeletal muscle such as neuromuscular junction. Moreover, 3D muscle models can induce pathological phenotype of human muscle dystrophies such as Duchenne muscular dystrophy by incorporating patient-derived induced pluripotent stem cells and human primary cells. In this review, we discuss the current biofabrication technologies for modeling various skeletal muscle tissue-related diseases (i.e., muscle diseases) including muscular dystrophies and inflammatory muscle diseases. In particular, these approaches would enable the discovery of novel phenotypic markers and the mechanism study of human muscle diseases with genetic mutations.

Tissue engineering of the retina: from organoids to microfluidic chips

Despite advancements in tissue engineering, challenges remain for fabricating functional tissues that incorporate essential features including vasculature and complex cellular organisation. Monitoring of engineered tissues also raises difficulties, particularly when cell population maturity is inherent to function. Microfluidic, or lab-on-a-chip, platforms address the complexity issues of conventional 3D models regarding cell numbers and functional connectivity. Regulation of biochemical/biomechanical conditions can create dynamic structures, providing microenvironments that permit tissue formation while quantifying biological processes at a single cell level. Retinal organoids provide relevant cell numbers to mimic in vivo spatiotemporal development, where conventional culture approaches fail. Modern bio-fabrication techniques allow for retinal organoids to be combined with microfluidic devices to create anato-physiologically accurate structures or 'retina-on-a-chip' devices that could revolution ocular sciences. Here we present a focussed review of retinal tissue engineering, examining the challenges and how some of these have been overcome using organoids, microfluidics, and bioprinting technologies.