Multifunctionalized hydrogels foster hNSC maturation in 3D cultures and neural regeneration in spinal cord injuries

Association between neural stem/progenitor cells and biomaterials in spinal cord injury therapies: A systematic review and network meta-analysis

Spinal cord injury (SCI) is associated with substantial healthcare challenges, frequently resulting in enduring sensory and motor deficits alongside various chronic complications. While advanced regenerative therapies have shown promise in preclinical research, their translation into clinical application has been limited. In response, this study utilized a comprehensive network meta-analysis to evaluate the effectiveness of neural stem/progenitor cell (NSPC) transplantation across animal models of SCI. We analyzed 363 outcomes from 55 distinct studies, categorizing the treatments into NSPCs alone (cell only), NSPCs with scaffolds (cell + scaffold), NSPCs with hydrogels (cell + hydrogel), standalone scaffolds (scaffold), standalone hydrogels (hydrogel), and control groups. Our analysis demonstrated significant enhancements in motor recovery, especially in gait function, within the NSPC treatment groups. Notably, the cell only group showed considerable improvements (standardized mean difference [SMD], 2.05; 95 % credible interval [CrI]: 1.08 to 3.10, p < 0.01), as did the cell + scaffold group (SMD, 3.73; 95 % CrI: 2.26 to 5.22, p < 0.001) and the cell + hydrogel group (SMD, 3.37; 95 % CrI: 1.02 to 5.78, p < 0.05) compared to controls. These therapeutic combinations not only reduced lesion cavity size but also enhanced neuronal regeneration, outperforming the cell only treatments. By integrating NSPCs with supportive biomaterials, our findings pave the way for refining these regenerative strategies to optimize their potential in clinical SCI treatment. Although there is no overall violation of consistency, the comparison of effect sizes between individual treatments should be interpreted in light of the inconsistency. STATEMENT OF SIGNIFICANCE: This study presents a comprehensive network meta-analysis exploring the efficacy of neural stem cell (NSC) transplantation, with and without biomaterials, in animal models of spinal cord injury (SCI). We demonstrate that NSCs, particularly when combined with biomaterials like scaffolds or hydrogels, significantly enhance motor and histological recovery post-SCI. These findings underscore the potential of NSC-based therapies, augmented with biomaterials, to advance SCI treatment, offering new insights into regenerative strategies that could significantly impact clinical practices.

3D hydrogel microfibers promote the differentiation of encapsulated neural stem cells and facilitate neuron protection and axon regrowth after complete transactional spinal cord injury

Spinal cord injury (SCI) can cause permanent impairment to motor or sensory functions. Pre-cultured neural stem cell (NSC) hydrogel scaffolds have emerged as a promising approach to treat SCI by promoting anti-inflammatory effects, axon regrowth, and motor function restoration. Here, in this study, we performed a coaxial extrusion process to fabricate a core-shell hydrogel microfiber with high NSC density in the core portion. Oxidized hyaluronic acid, carboxymethyl chitosan, and matrigel blend were used as a matrix for NSC growth and to facilitate the fabrication process. During thein vitrodifferentiation culture, it was found that NSC microfibers could differentiate into neurons and astrocytes with higher efficiency compared to NSC cultured in petri dishes. Furthermore, duringin vivotransplantation, NSC microfibers were coated with polylactic acid nanosheets by electrospinning for reinforcement. The coated NSC nanofibers exhibited higher anti-inflammatory effect and lesion cavity filling rate compared with the control group. Meanwhile, more neuron- and oligodendrocyte-like cells were visualized at the lesion epicenter. Finally, axon regrowth across the whole lesion site was observed, demonstrating that the microfiber could guide renascent axon regrowth. Experiment results indicate that the NSC microfiber is a promising bioactive treatment for complete SCI treatment with superior outcomes.

The Efficacy of Different Material Scaffold-Guided Cell Transplantation in the Treatment of Spinal Cord Injury in Rats: A Systematic Review and Network Meta-analysis

Cell transplantation is a promising treatment option for spinal cord injury (SCI). However, there is no consensus on the choice of carrier scaffolds to host the cells. This study aims to evaluate the efficacy of different material scaffold-mediated cell transplantation in treating SCI in rats. According to PRISMA's principle, Embase, PubMed, Web of Science, and Cochrane databases were searched, and relevant literature was referenced. Only original research on cell transplantation plus natural or synthetic scaffolds in SCI rats was included. Direct and indirect evidence for improving hind limb motor function was pooled through meta-analysis. A subgroup analysis of some factors that may affect the therapeutic effect was conducted to understand the results fully. In total, 25 studies met the inclusion criteria, in which 293 rats received sham surgery, 78 rats received synthetic material scaffolds, and 219 rats received natural materials scaffolds. The network meta-analysis demonstrated that although synthetic scaffolds were slightly inferior to natural scaffolds in terms of restoring motor function in cell transplantation of SCI rats, no statistical differences were observed between the two (MD: -0.35; 95% CI -2.6 to 1.9). Moreover, the subgroup analysis revealed that the type and number of cells may be important factors in therapeutic efficacy (P < 0.01). Natural scaffolds and synthetic scaffolds are equally effective in cell transplantation of SCI rats without significant differences. In the future, the findings need to be validated in multicenter, large-scale, randomized controlled trials in clinical practice. Trial registration: Registration ID CRD42024459674 (PROSPERO).

Regenerative medicine strategies for chronic complete spinal cord injury

Spinal cord injury is a condition in which the parenchyma of the spinal cord is damaged by trauma or various diseases. While rapid progress has been made in regenerative medicine for spinal cord injury that was previously untreatable, most research in this field has focused on the early phase of incomplete injury. However, the majority of patients have chronic severe injuries; therefore, treatments for these situations are of fundamental importance. The reason why the treatment of complete spinal cord injury has not been studied is that, unlike in the early stage of incomplete spinal cord injury, there are various inhibitors of neural regeneration. Thus, we assumed that it is difficult to address all conditions with a single treatment in chronic complete spinal cord injury and that a combination of several treatments is essential to target severe pathologies. First, we established a combination therapy of cell transplantation and drug-releasing scaffolds, which contributes to functional recovery after chronic complete transection spinal cord injury, but we found that functional recovery was limited and still needs further investigation. Here, for the further development of the treatment of chronic complete spinal cord injury, we review the necessary approaches to the different pathologies based on our findings and the many studies that have been accumulated to date and discuss, with reference to the literature, which combination of treatments is most effective in achieving functional recovery.

In Situ Transglutaminase Cross-Linking Improves Mechanical Properties of Self-Assembling Peptides for Biomedical Applications

The development of three-dimensional (3D) biomaterials that mimic natural tissues is required for efficiently restoring physiological functions of injured tissues and organs. In the field of soft hydrogels, self-assembled peptides (SAPs) stand out as distinctive biomimetic scaffolds, offering tunable properties. They have garnered significant attention in nanomedicine due to their innate ability to self-assemble, resulting in the creation of fibrous nanostructures that closely mimic the microenvironment of the extracellular matrix (ECM). This unique feature ensures their biocompatibility and bioactivity, making them a compelling area of study over the past few decades. As they are soft hydrogels, approaches are necessary to enhance the stiffness and resilience of the SAP materials. This work shows an enzymatic strategy to selectively increase the stiffness and resiliency of functionalized SAPs using transglutaminase (TGase) type 2, an enzyme capable of triggering the formation of isopeptide bonds. To this aim, we synthesized a set of SAP sequences and characterized their cross-linking via rheological experiments, atomic force microscopy (AFM), thioflavin-T binding assay, and infrared spectroscopy (ATR-FTIR) tests. The results showed an improvement of the storage modulus of cross-linked SAPs at no cost of the maximum stress-at-failure. Further, in in vitro tests, we examined and validated the TGase capability to cross-link SAPs without hampering seeded neural stem cells (hNSCs) viability and differentiation, potentially leaving the door open for safe in situ cross-linking reactions in vivo.

Multiparametric in vitro and in vivo analysis of the safety profile of self-assembling peptides

Self-assembling peptides (SAPs) have gained significant attention in biomedicine because of their unique properties and ability to undergo molecular self-assembly driven by non-covalent interactions. By manipulating their composition and structure, SAPs can form well-ordered nanostructures with enhanced selectivity, stability and biocompatibility. SAPs offer advantages such as high chemical and biological diversity and the potential for functionalization. However, studies concerning its potentially toxic effects are very scarce, a limitation that compromises its potential translation to humans. This study investigates the potentially toxic effects of six different SAP formulations composed of natural amino acids designed for nervous tissue engineering and amenable to ready cross-linking boosting their biomechanical properties. All methods were performed in accordance with the relevant guidelines and regulations. A wound-healing assay was performed to evaluate how SAPs modify cell migration. The results in vitro demonstrated that SAPs did not induce genotoxicity neither skin sensitization. In vivo, SAPs were well-tolerated without any signs of acute systemic toxicity. Interestingly, SAPs were found to promote the migration of endothelial, macrophage, fibroblast, and neuronal-like cells in vitro, supporting a high potential for tissue regeneration. These findings contribute to the development and translation of SAP-based biomaterials for biomedical applications.

The current status and development trend of hydrogel application in spinal surgery

Spinal diseases often result in compromised mobility and diminished quality of life due to the intricate anatomy surrounding the nervous system. Medication and surgical interventions remain the primary treatment methods for spinal conditions. However, currently available medications have limited efficacy in treating spinal surgical diseases and cannot achieve a complete cure. Furthermore, surgical intervention frequently results in inevitable alterations and impairments to the initial anatomical integrity of the spinal structure, accompanied by the consequential loss of certain physiological functionalities. Changes in spine surgery treatment concepts and modalities in the last decade have led to a deepening of minimally invasive treatment, with treatment strategies focusing more on repairing and reconstructing the patient's spine and preserving physiological functions. Therefore, developing novel and more efficient treatment strategies to reduce spinal lesions and iatrogenic injuries is essential. In recent years, significant advancements in biomedical research have led to the discovery that hydrogels possess excellent biocompatibility, biodegradability, and adjustable mechanical properties. The application of hydrogel-based biotechnology in spinal surgery has demonstrated remarkable therapeutic potential. This review presents the therapeutic strategies for spinal diseases based on hydrogel tissue engineering technology.

Biomaterials and Cell Therapy Combination in Central Nervous System Treatments

Current pharmacological and surgical therapies for the central nervous system (CNS) show a limited capacity to reduce the damage progression; that together with the intrinsic limited capability of the CNS to regenerate greatly reduces the hopes of recovery. Among all the therapies proposed, the tissue engineering strategies supplemented with therapeutic stem cells remain the most promising. Neural tissue engineering strategies are based on the development of devices presenting optimal physical, chemical, and mechanical properties which, once inserted in the injured site, can support therapeutic cells, limiting the effect of a hostile environment and supporting regenerative processes. Thus, this review focuses on the employment of hydrogel and nanofibrous scaffolds supplemented with stem cells as promising therapeutic tools for the central and peripheral nervous systems in preclinical and clinical applications.

Restoring neuronal iron homeostasis revitalizes neurogenesis after spinal cord injury

Spinal cord injury (SCI) can lead to iron overloading and subsequent neuronal ferroptosis, which hinders the recovery of locomotor function. However, it is still unclear whether the maintenance of neuronal iron homeostasis enables to revitalize intrinsic neurogenesis. Herein, we report the regulation of cellular iron homeostasis after SCI via the chelation of excess iron ions and modulation of the iron transportation pathway using polyphenol-based hydrogels for the revitalization of intrinsic neurogenesis. The reversed iron overloading can promote neural stem/progenitor cell differentiation into neurons and elicit the regenerative potential of newborn neurons, which is accompanied by improved axon reinnervation and remyelination. Notably, polyphenol-based hydrogels significantly increase the neurological motor scores from ~8 to 18 (out of 21) and restore the transmission of sensory and motor electrophysiological signals after SCI. Maintenance of iron homeostasis at the site of SCI using polyphenol-based hydrogels provides a promising paradigm to revitalize neurogenesis for the treatment of iron accumulation-related nervous system diseases.

A 3D-Printed Dual Driving Forces Scaffold with Self-Promoted Cell Absorption for Spinal Cord Injury Repair

Stem cells play critical roles in cell therapies and tissue engineering for nerve repair. However, achieving effective delivery of high cell density remains a challenge. Here, a novel cell delivery platform termed the hyper expansion scaffold (HES) is developed to enable high cell loading. HES facilitated self-promoted and efficient cell absorption via a dual driving force model. In vitro tests revealed that the HES rapidly expanded 80-fold in size upon absorbing 2.6 million human amniotic epithelial stem cells (hAESCs) within 2 min, representing over a 400% increase in loading capacity versus controls. This enhanced uptake benefited from macroscopic swelling forces as well as microscale capillary action. In spinal cord injury (SCI) rats, HES-hAESCs promoted functional recovery and axonal projection by reducing neuroinflammation and improving the neurotrophic microenvironment surrounding the lesions. In summary, the dual driving forces model provides a new rationale for engineering hydrogel scaffolds to facilitate self-promoted cell absorption. The HES platform demonstrates great potential as a powerful and efficient vehicle for delivering high densities of hAESCs to promote clinical treatment and repair of SCI.

Recent Advances in the Development of Biomimetic Materials

In this review, we focused on recent efforts in the design and development of materials with biomimetic properties. Innovative methods promise to emulate cell microenvironments and tissue functions, but many aspects regarding cellular communication, motility, and responsiveness remain to be explained. We photographed the state-of-the-art advancements in biomimetics, and discussed the complexity of a "bottom-up" artificial construction of living systems, with particular highlights on hydrogels, collagen-based composites, surface modifications, and three-dimensional (3D) bioprinting applications. Fast-paced 3D printing and artificial intelligence, nevertheless, collide with reality: How difficult can it be to build reproducible biomimetic materials at a real scale in line with the complexity of living systems? Nowadays, science is in urgent need of bioengineering technologies for the practical use of bioinspired and biomimetics for medicine and clinics.

Low-power microwaves: a cell-compatible physical treatment to enhance the mechanical properties of self-assembling peptides

Biomaterials designed for tissue engineering applications should, among other requirements, mimic the native extracellular matrix (ECM) of the tissues to be regenerated, both in terms of biomimetic and mechanical properties. Ideally, the scaffold stiffness and stress resistance should be tuned for each specific implantation therapy. Self-assembling peptides (SAPs) are promising synthetic bionanomaterials prone to easy multi-functionalization, bestowing biomimetic properties. However, they usually yield soft and fragile hydrogels unsuited for the regeneration of medium-to-hard tissues. For this purpose, chemical cross-linking of SAPs is an option, but it often requires a moderately toxic and expensive chemical compound and/or the presence of specific residues/reactive sites, posing issues for its feasibility and translational potential. In this work, we introduced, characterized by rheology, atomic force microscopy (AFM), Thioflavin-T assay (ThT), and Fourier transform infrared (FT-IR) tests, and optimized (by tuning the power, temperature and treatment time) a novel fast, green and affordable methodology using mild microwave (MW) irradiation to increase the mechanical properties of diverse classes of SAPs. Low-power MWs increase stiffness, resilience, and β-structuration, while high-power MW treatments partially denature the tested SAPs. Our pure-physical methodology does not alter the SAP biomimetic properties (verified via in vitro tests of viability and differentiation of human neural stem cells), is compatible with already seeded cells, and is also synergic with genipin-based cross-linking of SAPs; therefore, it may become the next standard for SAP preparation in tissue engineering applications at hand of all research labs and in clinics.

Encapsulation of Human Spinal Cord Progenitor Cells in Hyaluronan-Gelatin Hydrogel for Spinal Cord Injury Treatment

Transplanting human induced pluripotent stem cells (iPSCs)-derived spinal cord progenitor cells (SCPCs) is a promising approach to treat spinal cord injuries. However, stem cell therapies face challenges in cell survival, cell localization to the targeted site, and the control of cell differentiation. Here, we encapsulated SCPCs in thiol-modified hyaluronan-gelatin hydrogels and optimized scaffold mechanical properties and cell encapsulation density to promote cell viability and neuronal differentiation in vitro and in vivo. Different compositions of hyaluronan-gelatin hydrogels formulated by varying concentrations of poly(ethylene glycol) diacrylate were mechanically characterized by using atomic force microscopy. In vitro SCPC encapsulation study showed higher cell viability and proliferation with lower substrate Young's modulus (200 Pa vs 580 Pa) and cell density. Moreover, the soft hydrogels facilitated a higher degree of neuronal differentiation with extended filament structures in contrast to clumped cellular morphologies obtained in stiff hydrogels (p < 0.01). When transplanted in vivo, the optimized SCPC-encapsulated hydrogels resulted in higher cell survival and localization at the transplanted region as compared to cell delivery without hydrogel encapsulation at 2 weeks postimplantation within the rat spinal cord (p < 0.01). Notably, immunostaining demonstrated that the hydrogel-encapsulated SCPCs differentiated along the neuronal and oligodendroglial lineages in vivo. The lack of pluripotency and proliferation also supported the safety of the SCPC transplantation approach. Overall, the injectable hyaluronan-gelatin hydrogel shows promise in supporting the survival and neural differentiation of human SCPCs after transplantation into the spinal cord.

Short Peptide Nanofiber Biomaterials Ameliorate Local Hemostatic Capacity of Surgical Materials and Intraoperative Hemostatic Applications in Clinics

Short designer self-assembling peptide (dSAP) biomaterials are a new addition to the hemostat group. It may provide a diverse and robust toolbox for surgeons to integrate wound microenvironment with much safer and stronger hemostatic capacity than conventional materials and hemostatic agents. Especially in noncompressible torso hemorrhage (NCTH), diffuse mucosal surface bleeding, and internal medical bleeding (IMB), with respect to the optimal hemostatic formulation, dSAP biomaterials are the ingenious nanofiber alternatives to make bioactive neural scaffold, nasal packing, large mucosal surface coverage in gastrointestinal surgery (esophagus, gastric lesion, duodenum, and lower digestive tract), epicardiac cell-delivery carrier, transparent matrix barrier, and so on. Herein, in multiple surgical specialties, dSAP-biomaterial-based nano-hemostats achieve safe, effective, and immediate hemostasis, facile wound healing, and potentially reduce the risks in delayed bleeding, rebleeding, post-operative bleeding, or related complications. The biosafety in vivo, bleeding indications, tissue-sealing quality, surgical feasibility, and local usability are addressed comprehensively and sequentially and pursued to develop useful surgical techniques with better hemostatic performance. Here, the state of the art and all-round advancements of nano-hemostatic approaches in surgery are provided. Relevant critical insights will inspire exciting investigations on peptide nanotechnology, next-generation biomaterials, and better promising prospects in clinics.

Biomimetic Electrospun Self-Assembling Peptide Scaffolds for Neural Stem Cell Transplantation in Neural Tissue Engineering

Spinal cord regeneration using stem cell transplantation is a promising strategy for regenerative therapy. Stem cells transplanted onto scaffolds that can mimic natural extracellular matrix (ECM) have the potential to significantly improve outcomes. In this study, we strived to develop a cell carrier by culturing neural stem cells (NSCs) onto electrospun 2D and 3D constructs made up of specific crosslinked functionalized self-assembling peptides (SAPs) featuring enhanced biomimetic and biomechanical properties. Morphology, architecture, and secondary structures of electrospun scaffolds in the solid-state and electrospinning solution were studied step by step. Morphological studies showed the benefit of mixed peptides and surfactants as additives to form thinner, uniform, and defect-free fibers. It has been observed that β-sheet conformation as evidence of self-assembling has been predominant throughout the process except for the electrospinning solution. In vitro NSCs seeded on electrospun SAP scaffolds in 2D and 3D conditions displayed desirable proliferation, viability, and differentiation in comparison to the gold standard. In vivo biocompatibility assay confirmed the permissibility of implanted fibrous channels by foreign body reaction. The results of this study demonstrated that fibrous 2D/3D electrospun SAP scaffolds, when shaped as micro-channels, can be suitable to support NSC transplantation for regeneration following spinal cord injury.

Synthetic extracellular matrices with function-encoding peptides

The communication of cells with their surroundings is mostly encoded in the epitopes of structural and signalling proteins present in the extracellular matrix (ECM). These peptide epitopes can be incorporated in biomaterials to serve as function-encoding molecules to modulate cell-cell and cell-ECM interactions. In this Review, we discuss natural and synthetic peptide epitopes as molecular tools to bioengineer bioactive hydrogel materials. We present a library of functional peptide sequences that selectively communicate with cells and the ECM to coordinate biological processes, including epitopes that directly signal to cells, that bind ECM components that subsequently signal to cells, and that regulate ECM turnover. We highlight how these epitopes can be incorporated in different biomaterials as individual or multiple signals, working synergistically or additively. This molecular toolbox can be applied in the design of biomaterials aimed at regulating or controlling cellular and tissue function, repair and regeneration.

Bioactive peptides for boosting stem cell culture platform: Methods and applications

Peptides, short protein fragments, can emulate the functions of their full-length native counterparts. Peptides are considered potent recombinant protein alternatives due to their specificity, high stability, low production cost, and ability to be easily tailored and immobilized. Stem cell proliferation and differentiation processes are orchestrated by an intricate interaction between numerous growth factors and proteins and their target receptors and ligands. Various growth factors, functional proteins, and cellular matrix-derived peptides efficiently enhance stem cell adhesion, proliferation, and directed differentiation. For that, peptides can be immobilized on a culture plate or conjugated to scaffolds, such as hydrogels or synthetic matrices. In this review, we assess the applications of a variety of peptides in stem cell adhesion, culture, organoid assembly, proliferation, and differentiation, describing the shortcomings of recombinant proteins and their full-length counterparts. Furthermore, we discuss the challenges of peptide applications in stem cell culture and materials design, as well as provide a brief outlook on future directions to advance peptide applications in boosting stem cell quality and scalability for clinical applications in tissue regeneration.

Generation of neural organoids for spinal-cord regeneration via the direct reprogramming of human astrocytes

Organoids with region-specific architecture could facilitate the repair of injuries of the central nervous system. Here we show that human astrocytes can be directly reprogrammed into early neuroectodermal cells via the overexpression of OCT4, the suppression of p53 and the provision of the small molecules CHIR99021, SB431542, RepSox and Y27632. We also report that the activation of signalling mediated by fibroblast growth factor, sonic hedgehog and bone morphogenetic protein 4 in the reprogrammed cells induces them to form spinal-cord organoids with functional neurons specific to the dorsal and ventral domains. In mice with complete spinal-cord injury, organoids transplanted into the lesion differentiated into spinal-cord neurons, which migrated and formed synapses with host neurons. The direct reprogramming of human astrocytes into neurons may pave the way for in vivo neural organogenesis from endogenous astrocytes for the repair of injuries to the central nervous system.

Loading neural stem cells on hydrogel scaffold improves cell retention rate and promotes functional recovery in traumatic brain injury

Neural stem cell (NSC) has gained considerable attention in traumatic brain injury (TBI) treatment because of their ability to replenish dysfunctional neurons and stimulate endogenous neurorestorative processes. However, their therapeutic effects are hindered by the low cell retention rate after transplantation into the dynamic brain. In this study, we found cerebrospinal fluid (CSF) flow after TBI is an important factor associated with cell loss following NSC transplantation. Recently, several studies have shown that hydrogels could serve as a beneficial carrier for stem cell transplantation, which provides a solution to prevent CSF flow-induced cell loss after TBI. For this purpose, we evaluated three different hydrogel scaffolds and found the gelatin methacrylate (GelMA)/sodium alginate (Alg) (GelMA/Alg) hydrogel scaffold showed the best capabilities for NSC adherence, growth, and differentiation. Additionally, we detected that pre-differentiated NSCs, which were loaded on the GelMA/Alg hydrogel and cultured for 7 days in neuronal differentiation medium (NSC [7d]), had the highest cell retention rate after CSF impact. Next, the neuroprotective effects of the NSC-loaded GelMA/Alg hydrogel scaffold were evaluated in a rat model of TBI. NSC [7d]-loaded GelMA/Alg markedly decreased microglial activation and neuronal death in the acute phase, reduced tissue loss, alleviated astrogliosis, promoted neurogenesis, and improved neurological recovery in the chronic phase. In summary, we demonstrated that the integration with the GelMA/Alg and modification of NSC differentiation could inhibit the influence of CSF flow on transplanted NSCs, leading to increased number of retained NSCs and improved neuroprotective effects, providing a promising alternative for TBI treatment.

Delivery of Induced Neural Stem Cells Through Mechano-Tuned Silk-Collagen Hydrogels for the Recovery of Contused Spinal Cord in Rats

Neural stem cells (NSC) have tremendous potential for therapeutic regeneration of diseased or traumatized neural tissues, including injured spinal cord. However, transplanted NSC suffer from low cell survival and uncontrolled differentiation, limiting in vivo efficacy. Here, this issue is tackled by delivery through silk-collagen protein hydrogels that are stiffness-matched, stress-relaxing, and shear-thinning. The mechanically-tuned hydrogels protect NSC reprogrammed from fibroblasts (iNSC) initially from injection shear-stress, and enhance long-term survival over 12 weeks. Hydrogel-iNSC treatment alleviates neural inflammation, with reduced inflammatory cells and lesions than NSC-only. The iNSC migrate from the hydrogel into surrounding tissues, secrete up-regulated neurotrophic factors, and differentiate into neural cell subtypes, forming synapses. More serotonergic axons are observed in the lesion cavity, and locomotor functions are improved in hydrogel-iNSC than in iNSC-only. This study highlights the ability of mechanically-tuned protein hydrogels to protect iNSC from the injection stress and severe inflammatory environment, allowing them to differentiate and function to recover the injured spinal cord.

Long-term cultures of human pancreatic islets in self-assembling peptides hydrogels

Human pancreatic islets transplantation is an experimental therapeutic treatment for Type I Diabetes. Limited islets lifespan in culture remains the main drawback, due to the absence of native extracellular matrix as mechanical support after their enzymatic and mechanical isolation procedure. Extending the limited islets lifespan by creating a long-term in vitro culture remains a challenge. In this study, three biomimetic self-assembling peptides were proposed as potential candidates to recreate in vitro a pancreatic extracellular matrix, with the aim to mechanically and biologically support human pancreatic islets, by creating a three-dimensional culture system. The embedded human islets were analyzed for morphology and functionality in long-term cultures (14-and 28-days), by evaluating β-cells content, endocrine component, and extracellular matrix constituents. The three-dimensional support provided by HYDROSAP scaffold, and cultured into MIAMI medium, displayed a preserved islets functionality, a maintained rounded islets morphology and an invariable islets diameter up to 4 weeks, with results analogues to freshly-isolated islets. In vivo efficacy studies of the in vitro 3D cell culture system are ongoing; however, preliminary data suggest that human pancreatic islets pre-cultured for 2 weeks in HYDROSAP hydrogels and transplanted under subrenal capsule may restore normoglycemia in diabetic mice. Therefore, engineered self-assembling peptide scaffolds may provide a useful platform for long-term maintenance and preservation of functional human pancreatic islets in vitro.

The Effect of Rosmarinic Acid on Neural Differentiation of Wartons Jelly-derived Mesenchymal Stem Cells in Two-dimensional and Three-dimensional Cultures using Chitosan-based Hydrogel

Introduction

Numerous studies have shown the positive effects of rosmarinic acid on the nervous system. Rosmarinic acid as a herbal compound with anti-inflammatory effects can prevent thedestructive effect of inflammation on the nervous system. Furthermore, various studies haveemphasized the advantages of three-dimensional (3D) culture over the two-dimensional (2D) culture of cells.

Methods

In this study, thermosensitive chitosan (CH)-based hydrogel as a 3D scaffoldwith the combination of chitosan, beta-glycerol phosphate and hydroxyl ethyl cellulose (CH-GP-HEC) loaded with rosmarinic acid was used to induce neuronal differentiation in humanWharton jelly stem cells. Also, cells were divided into eight groups to evaluate the effect of 3Dcell culture and to compare gene expression in different induction conditions.

Results

The results ofgene expression analysis showed the highest expression of neuronal markers in Whartons jelly derived mesenchymal stem cells (WJMSCs) cultured in chitosan, beta-glycerol phosphate and hydroxyl ethyl cellulose (ch-gp-hec) loaded with differentiation medium androsmarinic acid. According to the results of gene expression, rosmarinic acid alone has a positiveeffect on the induction of expression of neural markers. This positive effect is enhanced by cellculture in 3D conditions.

Conclusion

This study shows that rosmarinic acid can be considered an inexpensiveand available compound for use in neural tissue engineering. The results of this study indicatethat rosmarinic acid can be considered a cheap and available compound for use in neural tissueengineering.

Therapeutic Effect of Biomimetic Scaffold Loaded with Human Amniotic Epithelial Cell-Derived Neural-like Cells for Spinal Cord Injury

Spinal cord injury (SCI) results in devastating consequences for the motor and sensory function of patients due to neuronal loss and disrupted neural circuits, confronting poor prognosis and lack of effective therapies. A new therapeutic strategy is urgently required. Here, human amniotic epithelial cells (hAEC), featured with immunocompatibility, non-tumorgenicity and no ethical issues, were induced into neural-like cells by a compound cocktail, as evidenced with morphological change and the expression of neural cell markers. Interestingly, the hAEC-neural-like cells maintain the characteristic of low immunogenicity as hAEC. Aiming at SCI treatment in vivo, we constructed a 3D-printed GelMA hydrogel biomimetic spinal cord scaffold with micro-channels, in which hAEC-neural-like cells were well-induced and grown. In a rat full transection SCI model, hAEC-neural-like cell scaffolds that were implanted in the lesion demonstrated significant therapeutic effects; the neural circuit and hindlimb locomotion were partly recovered compared to little affection in the SCI rats receiving an empty scaffold or a sham implantation operation. Thus, the establishment of hAEC-neural-like cell biomimetic scaffolds may provide a safe and effective treatment strategy for SCI.

Biomaterials to enhance stem cell transplantation

The successful transplantation of stem cells has the potential to transform regenerative medicine approaches and open promising avenues to repair, replace, and regenerate diseased, damaged, or aged tissues. However, pre-/post-transplantation issues of poor cell survival, retention, cell fate regulation, and insufficient integration with host tissues constitute significant challenges. The success of stem cell transplantation depends upon the coordinated sequence of stem cell renewal, specific lineage differentiation, assembly, and maintenance of long-term function. Advances in biomaterials can improve pre-/post-transplantation outcomes by integrating biophysiochemical cues and emulating tissue microenvironments. This review highlights leading biomaterials-based approaches for enhancing stem cell transplantation.

Multimodal therapy strategies based on hydrogels for the repair of spinal cord injury

Spinal cord injury (SCI) is a serious traumatic disease of the central nervous system, which can give rise to the loss of motor and sensory function. Due to its complex pathological mechanism, the treatment of this disease still faces a huge challenge. Hydrogels with good biocompatibility and biodegradability can well imitate the extracellular matrix in the microenvironment of spinal cord. Hydrogels have been regarded as promising SCI repair material in recent years and continuous studies have confirmed that hydrogel-based therapy can effectively eliminate inflammation and promote spinal cord repair and regeneration to improve SCI. In this review, hydrogel-based multimodal therapeutic strategies to repair SCI are provided, and a combination of hydrogel scaffolds and other therapeutic modalities are discussed, with particular emphasis on the repair mechanism of SCI.

Regenerating the Injured Spinal Cord at the Chronic Phase by Engineered iPSCs-Derived 3D Neuronal Networks

Cell therapy using induced pluripotent stem cell-derived neurons is considered a promising approach to regenerate the injured spinal cord (SC). However, the scar formed at the chronic phase is not a permissive microenvironment for cell or biomaterial engraftment or for tissue assembly. Engineering of a functional human neuronal network is now reported by mimicking the embryonic development of the SC in a 3D dynamic biomaterial-based microenvironment. Throughout the in vitro cultivation stage, the system's components have a synergistic effect, providing appropriate cues for SC neurogenesis. While the initial biomaterial supported efficient cell differentiation in 3D, the cells remodeled it to provide an inductive microenvironment for the assembly of functional SC implants. The engineered tissues are characterized for morphology and function, and their therapeutic potential is investigated, revealing improved structural and functional outcomes after acute and chronic SC injuries. Such technology is envisioned to be translated to the clinic to rewire human injured SC.

Increased connectivity of hiPSC-derived neural networks in multiphase granular hydrogel scaffolds

To reflect human development, it is critical to create a substrate that can support long-term cell survival, differentiation, and maturation. Hydrogels are promising materials for 3D cultures. However, a bulk structure consisting of dense polymer networks often leads to suboptimal microenvironments that impedes nutrient exchange and cell-to-cell interaction. Herein, granular hydrogel-based scaffolds were used to support 3D human induced pluripotent stem cell (hiPSC)-derived neural networks. A custom designed 3D printed toolset was developed to extrude hyaluronic acid hydrogel through a porous nylon fabric to generate hydrogel granules. Cells and hydrogel granules were combined using a weaker secondary gelation step, forming self-supporting cell laden scaffolds. At three and seven days, granular scaffolds supported higher cell viability compared to bulk hydrogels, whereas granular scaffolds supported more neurite bearing cells and longer neurite extensions (65.52 ± 11.59 μm) after seven days compared to bulk hydrogels (22.90 ± 4.70 μm). Long-term (three-month) cultures of clinically relevant hiPSC-derived neural cells in granular hydrogels supported well established neuronal and astrocytic colonies and a high level of neurite extension both inside and beyond the scaffold. This approach is significant as it provides a simple, rapid and efficient way to achieve a tissue-relevant granular structure within hydrogel cultures.

Boosted Cross-Linking and Characterization of High-Performing Self-Assembling Peptides

Tissue engineering (TE) strategies require the design and characterization of novel biomaterials capable of mimicking the physiological microenvironments of the tissues to be regenerated. As such, implantable materials should be biomimetic, nanostructured and with mechanical properties approximating those of the target organ/tissue. Self-assembling peptides (SAPs) are biomimetic nanomaterials that can be readily synthesized and customized to match the requirements of some TE applications, but the weak interactions involved in the self-assembling phenomenon make them soft hydrogels unsuited for the regeneration of medium-to-hard tissues. In this work, we moved significant steps forward in the field of chemical cross-linked SAPs towards the goal of stiff peptidic materials suited for the regeneration of several tissues. Novel SAPs were designed and characterized to boost the 4-(N-Maleimidomethyl) cyclohexane-1-carboxylic acid 3-sulpho-N-hydroxysuccinimide ester (Sulfo-SMCC) mediated cross-linking reaction, where they reached G′ values of ~500 kPa. An additional orthogonal cross-linking was also effective and allowed to top remarkable G′ values of 840 kPa. We demonstrated that cross-linking fastened the pre-existing self-aggregated nanostructures, and at the same time, a strong presence of ß-structures is necessary for an effective cross-linking of (LKLK)₃-based SAPs. Combining strong SAP design and orthogonal cross-linking reactions, we brought SAP stiffness closer to the MPa threshold, and as such, we opened the door of the regeneration of skin, muscle and lung to biomimetic SAP technology.

Bioinspired photo-crosslinkable self-assembling peptides with pH-switchable "on-off" luminescence

Significant progress has been made in peptide self-assembly over the past two decades; however, the in situ cross-linking of self-assembling peptides yielding better performing nanomaterials is still in its infancy. Indeed, self-assembling peptides (SAPs), relying only on non-covalent interactions, are mechanically unstable and susceptible to solvent erosion, greatly hindering their practical application. Herein, drawing inspiration from the biological functions of tyrosine, we present a photo-cross-linking approach for the in situ cross-linking of a tyrosine-containing LDLK12 SAP. This method is based on the ruthenium-complex-catalyzed conversion of tyrosine to dityrosine upon light irradiation. We observed a stable formation of dityrosine cross-linking starting from 5 minutes, with a maximum peak after 1 hour of UV irradiation. Furthermore, the presence of a ruthenium complex among the assembled peptide bundles bestows unusual fluorescence intensity stability up to as high as 42 °C, compared to the bare ruthenium complex. Also, due to a direct deprotonation-protonation process between the ruthenium complex and SAP molecules, the fluorescence of the photo-cross-linked SAP is capable of exhibiting "off-on-off-on" luminescence switchable from acid to basic pH. Lastly, we showed that the photo-cross-linked hydrogel exhibited enhanced mechanical stability with a storage modulus of ∼26 kPa, due to the formation of a densely entangled fibrous network of SAP molecules through dityrosine linkages. As such, this ruthenium-mediated photo-cross-linked SAP hydrogel could be useful in the design of novel tyrosine containing SAP materials with intriguing potential for biomedical imaging, pH sensing, photonics, soft electronics, and bioprinting.

Efficacy of hydrogels for repair of traumatic spinal cord injuries: A systematic review and meta-analysis

Hydrogels have been used as promising biomaterials for regeneration and control of pathophysiological events after traumatic spinal cord injuries (TSCI). However, no systematic comparison was conducted to show the effect of hydrogels on pathophysiological events. This study was designed to address this issue and evaluate the regenerative potential of hydrogels after TSCI. From 2857 records found in MEDLINE and EMBASE databases (April 23, 2021), 49 articles were included based on our inclusion/exclusion criteria. All studies discussing the effect of hydrogels on at least one of the main pathophysiological events after TSCI, including inflammation, axon growth, remyelination, glial scar formation, cavity size, and locomotor functional recovery were included. For statistical analysis, we used mean difference with 95% confidence intervals for locomotor functional recovery. The results showed that both natural and synthetic hydrogels could reduce the inflammatory response, hinder glial scar formation, and promote axon growth and vascularization. Also, the meta-analysis of the BBB score showed that using the hydrogels can lead to locomotor functional recovery. It was found that hydrogels are more efficient when used in transection and hemisection injuries (SMD: 1.89; 95% CI: 1.26, 2.52; P < .00001) compared to other injury models. The pre-formed implanted hydrogels (SMD: 1.79; 95% CI: 1.24, 2.34; P < .00001) found to be more effective compared to injection (SMD: 1.58; 95% CI: 0.64, 2.52; P = 0.0009). In conclusion, based on the available evidence, it was concluded that hydrogel composition as well as implantation method are dominant factors affecting tissue regeneration after TSCI and should be chosen according to the injury model in animal studies.

Towards organoid culture without Matrigel

Organoids-cellular aggregates derived from stem or progenitor cells that recapitulate organ function in miniature-are of growing interest in developmental biology and medicine. Organoids have been developed for organs and tissues such as the liver, gut, brain, and pancreas; they are used as organ surrogates to study a wide range of questions in basic and developmental biology, genetic disorders, and therapies. However, many organoids reported to date have been cultured in Matrigel, which is prepared from the secretion of Engelbreth-Holm-Swarm mouse sarcoma cells; Matrigel is complex and poorly defined. This complexity makes it difficult to elucidate Matrigel-specific factors governing organoid development. In this review, we discuss promising Matrigel-free methods for the generation and maintenance of organoids that use decellularized extracellular matrix (ECM), synthetic hydrogels, or gel-forming recombinant proteins.

Effects of a novel self-assembling peptide scaffold on bone regeneration and controlled release of two growth factors

RADA16 is a self-assembling peptide material with good bioactivity. To improve the bioactivity of a material, some specific functional motifs can be added to its peptide sequence. Here, we report a self-assembling peptide nanogel, RADA16-RGD, that has better bioactivity than RADA16 and can simultaneously carry and control the release of two growth factors, VEGF and BMP-2, which have synergistic effects on bone formation. The peptide materials were characterized by transmission electron microscopy and scanning electron microscopy. The mechanical properties of the peptides were evaluated by the rheology test. The biocompatibility of the materials was evaluated via the use of the CCK-8 test, live/dead staining and confocal laser scanning microscopy. Osteogenesis capability in vitro was evaluated by means of ALP staining, extracellular matrix mineralization and detection of osteogenic markers. The controlled release of growth factors was examined by ELISA. The results showed that RADA16-RGD exhibited a better ability than RADA16 to promote cell proliferation, adhesion and bone formation. In addition, RADA16-RGD had good biocompatibility and exhibited effective controlled release of VEGF and BMP-2. More importantly, compared with RADA16-RGD loaded with single growth factor or without growth factors, RADA16-RGD loaded with two growth factors exhibited a stronger ability to promote cell proliferation and osteogenesis. This study provides a promising strategy for the application of self-assembling peptides to promote osteogenesis and controlled release of proteins.

Optimizing fibrin hydrogel toward effective neural progenitor cell delivery in spinal cord injury

Transplantation of neural progenitor cell (NPC) possessing the potential to differentiate into neurons may guard against spinal cord injury (SCI)- associated neuronal trauma. We propose that autologous-like NPC may reduce post-transplant immune response. The study used the rat SCI model to prove this concept. For isolation and expansion of rat NPC for cell-based SCI therapy, thein vitroprotocol standardized with human NPC seemed suitable. The primary aim of this study is to select a cell/neural tissue-compatible biomaterial for improving NPC survivalin vivo. The composition of the fibrin hydrogel is adjusted to obtain degradable, porous, and robust fibrin strands for supporting neural cell attachment, migration, and tissue regeneration. This study employed NPC culture to evaluate the cytocompatibility and suitability of the hydrogel, composed by adding graded concentrations of thrombin to a fixed fibrinogen concentration. The microstructure evaluation by scanning electron microscope guided the selection of a suitable composition for delivering the embedded cells. On adding more thrombin, fibrinogen clotted quickly but reduced porosity, pore size, and fiber strand thickness. The high activity of thrombin also affected NPC morphology and thein vitrocell survival. The selected hydrogel carried viable NPC and retained them at the injury site post-transplantation. The fibrin hydrogel played a protective role throughout the transfer process by providing cell attachment sites and survival signals. The fibrin and NPC together regulated the immune response at the SCI site reducing ED1^+ve/ED2^+vemacrophages in the early period of 8-16 d after injury. Migration ofβ-III tubulin^+veneural-like cells into the fibrin-injected control SCI is evident. The continuous use of a non-neurotoxic fibrin matrix could be a convenient strategy forin vitroNPC preparation, minimally invasive cell delivery, and better transplantation outcome.

Synthesis of an Enzyme-Mediated Reversible Cross-linked Hydrogel for Cell Culture

Detachment of fragile cell types cultured on two-dimensional (2D) surfaces has been shown to be detrimental to their viability. For example, detachment of induced pluripotent stem cell (iPSC)-derived neurons grown in vitro in 2D typically results in loss of neuronal connections and/or cell death. Avoiding cell detachment altogether by changing the properties of the substrate on which the cells are grown is a compelling strategy to maintain cell viability. Here, we present the synthesis of a reversible cross-linked hydrogel that is sufficiently stable for cell culture and differentiation and is cleaved by an external stimulus, facilitating injection. Specifically, hyaluronan (HA) and methylcellulose (MC) were modified with ketone and aldehyde groups, respectively, and a TEV protease-degradable peptide was synthesized via solid-state synthesis and modified at both termini with oxyamine groups to cross-link HA-ketone and MC-aldehyde to produce oxime-cross-linked HA × MC. The HA × MC hydrogel demonstrated good stability, enzyme-sensitive degradation, and cytocompatibility with iPSC-derived neural progenitor cells, laying the framework for broad applicability.

Stem cell-derived neuronal relay strategies and functional electrical stimulation for treatment of spinal cord injury

The inability of adult mammals to recover function lost after severe spinal cord injury (SCI) has been known for millennia and is mainly attributed to a failure of brain-derived nerve fiber regeneration across the lesion. Potential approaches to re-establishing locomotor function rely on neuronal relays to reconnect the segregated neural networks of the spinal cord. Intense research over the past 30 years has focused on endogenous and exogenous neuronal relays, but progress has been slow and the results often controversial. Treatments with stem cell-derived neuronal relays alone or together with functional electrical stimulation offer the possibility of improved repair of neuronal networks. In this review, we focus on approaches to recovery of motor function in paralyzed patients after severe SCI based on novel therapies such as implantation of stem cell-derived neuronal relays and functional electrical stimulation. Recent research progress offers hope that SCI patients will one day be able to recover motor function and sensory perception.

Perspective Insights to Bio-Nanomaterials for the Treatment of Neurological Disorders

The significance of biomaterials is well appreciated in nanotechnology, and its use has resulted in major advances in biomedical sciences. Although, currently, very little data is available on the clinical trial studies for treatment of neurological conditions, numerous promising advancements have been reported in drug delivery and regenerative therapies which can be applied in clinical practice. Among the commonly reported biomaterials in literature, the self-assembling peptides and hydrogels have been recognized as the most potential candidate for treatment of common neurological conditions such as Alzheimer's, Parkinson's, spinal cord injury, stroke and tumors. The hydrogels, specifically, offer advantages like flexibility and porosity, and mimics the properties of the extracellular matrix of the central nervous system. These factors make them an ideal scaffold for drug delivery through the blood-brain barrier and tissue regeneration (using stem cells). Thus, the use of biomaterials as suitable matrix for therapeutic purposes has emerged as a promising area of neurosciences. In this review, we describe the application of biomaterials, and the current advances, in treatment of statistically common neurological disorders.

A tuned gelatin methacryloyl (GelMA) hydrogel facilitates myelination of dorsal root ganglia neurons in vitro

Investigating axonal myelination by Schwann cells (SCs) is crucial for understanding mechanisms underlying demyelination and remyelination, which may help gain insights into incurable disorders like neurodegenerative diseases. In this study, a gelatin-based hydrogel, gelatin methacryloyl (GelMA), was optimized to achieve the biocompatibility, porosity, mechanical stability, and degradability needed to provide high cell viability for dorsal root ganglia (DRG) neurons and SCs, and to enable their long-term coculture needed for myelination studies. The results of cell viability, neurite elongation, SC function and maturation, SC-axon interaction, and myelination were compared with two other commonly used substrates, namely collagen and Poly-d Lysine (PDL). The tuned GelMA constructs (Young's modulus of 32.6 ± 1.9 kPa and the median value of pore size of 10.3 μm) enhanced single axon generation (unlike collagen) and promoted the interaction of DRG neurons and SCs (unlike PDL). While DRG cells exhibited relatively higher viability on PDL after 48 h, i.e., 83.8%, the cells had similar survival rate on GelMA and collagen substrates, 66.7% and 61.5%, respectively. Further adjusting the hydrogel properties to achieve two distinct ranges of relatively small and large pores supported SCs to extend their processes freely and enabled physical contact with and wrapping around their corresponding axons. Staining the cells with myelin basic protein (MBA) and myelin-associated glycoprotein (MAG) revealed enhanced myelination on GelMA hydrogel compared to PDL and collagen. Moreover, the engineered porosity enhanced DRGs and SCs attachments and flexibility of movement across the substrate. This engineered hydrogel structure can now be further explored to model demyelination in neurodegenerative diseases, as well as to study the effects of various compounds on myelin regeneration.

Importance of brain alterations in spinal cord injury

Spinal cord injury (SCI) destroys the sensorimotor pathway and blocks the information flow between the peripheral nerve and the brain, resulting in autonomic function loss. Numerous studies have explored the effects of obstructed information flow on brain structure and function and proved the extensive plasticity of the brain after SCI. Great progress has also been achieved in therapeutic strategies for SCI to restore the "re-innervation" of the cerebral cortex to the limbs to some extent. Although no thorough research has been conducted, the changes of brain structure and function caused by "re-domination" have been reported. This article is a review of the recent research progress on local structure, functional changes, and circuit reorganization of the cerebral cortex after SCI. Alterations of structure and electrical activity characteristics of brain neurons, features of brain functional reorganization, and regulation of brain functions by reconfigured information flow were also explored. The integration of brain function is the basis for the human body to exercise complex/fine movements and is intricately and widely regulated by information flow. Hence, its changes after SCI and treatments should be considered.

Synthetic scaffolds for 3D cell cultures and organoids: applications in regenerative medicine

Three-dimensional (3D) cell cultures offer an unparalleled platform to recreate spatial arrangements of cells in vitro. 3D cell culture systems have gained increasing interest due to their evident advantages in providing more physiologically relevant information and more predictive data compared to their two-dimensional (2D) counterpart. Design and well-established fabrication of organoids (a particular type of 3D cell culture system) are nowadays considered a pivotal achievement for their ability to replicate in vitro cytoarchitecture and the functionalities of an organ. In this condition, pluripotent stem cells self-organize into 3D structures mimicking the in vivo microenvironments, architectures and multi-lineage differentiation. Scaffolds are key supporting elements in these 3D constructs, and Matrigel is the most commonly used matrix despite its relevant translation limitations including animal-derived sources, non-defined composition, batch-to-batch variability and poorly tailorable properties. Alternatively, 3D synthetic scaffolds, including self-assembling peptides, show promising biocompatibility and biomimetic properties, and can be tailored on specific target tissue/cells. In this review, we discuss the recent advances on 3D cell culture systems and organoids, promising tools for tissue engineering and regenerative medicine applications. For this purpose, we will describe the current state-of-the-art on 3D cell culture systems and organoids based on currently available synthetic-based biomaterials (including tailored self-assembling peptides) either tested in in vivo animal models or developed in vitro with potential application in the field of tissue engineering, with the aim to inspire researchers to take on such promising platforms for clinical applications in the near future.

Progress in mimicking brain microenvironments to understand and treat neurological disorders

Neurological disorders including traumatic brain injury, stroke, primary and metastatic brain tumors, and neurodegenerative diseases affect millions of people worldwide. Disease progression is accompanied by changes in the brain microenvironment, but how these shifts in biochemical, biophysical, and cellular properties contribute to repair outcomes or continued degeneration is largely unknown. Tissue engineering approaches can be used to develop in vitro models to understand how the brain microenvironment contributes to pathophysiological processes linked to neurological disorders and may also offer constructs that promote healing and regeneration in vivo. In this Perspective, we summarize features of the brain microenvironment in normal and pathophysiological states and highlight strategies to mimic this environment to model disease, investigate neural stem cell biology, and promote regenerative healing. We discuss current limitations and resulting opportunities to develop tissue engineering tools that more faithfully recapitulate the aspects of the brain microenvironment for both in vitro and in vivo applications.

Hydrogel-Stiffening and Non-Cell Adhesive Properties of Amphiphilic Peptides with Central Alkylene Chains

Amphiphilic peptides bearing terminal alkyl tails form supramolecular nanofibers that are increasingly used as biomaterials with multiple functionalities. Insertion of alkylene chains in peptides can be designed as another type of amphiphilic peptide, yet the influence of the internal alkylene chains on self-assembly and biological properties remains poorly defined. Unlike the terminal alkyl tails, the internal alkylene chains can affect not only the hydrophobicity but also the flexibility and packing of the peptides. Herein, we demonstrate the supramolecular and biological effects of the central alkylene chain length inserted in a peptide. Insertion of the alkylene chain at the center of the peptide allowed for strengthened β-sheet hydrogen bonds and modulation of the packing order, and consequently the amphiphilic peptide bearing C2 alkylene chain formed a hydrogel with the highest stiffness. Interestingly, the amphiphilic peptides bearing internal alkylene chains longer than C2 showed a diminished cell-adhesive property. This study offers a novel molecular design to tune mechanical and biological properties of peptide materials.

Glutamatergic Neurons Differentiated from Embryonic Stem Cells: An Investigation of Differentiation and Associated Diseases

Neurons that have been derived from various types of stem cells have recently undergone significant study due to their potential for use in various aspects of biomedicine. In particular, glutamatergic neurons differentiated from embryonic stem cells (ESCs) potentially have many applications in both basic research and regenerative medicine. This review summarized the literatures published thus far and focused on two areas related to these applications. Firstly, these neurons can be used to investigate neuronal signal transduction during differentiation and this means that the genes/proteins/markers involved in this process can be identified. In this way, the dynamic spatial and temporal changes associated with neuronal morphology can be investigated relatively easily. Such an in vitro system can also be used to study how neurons during neurogenesis integrate into normal tissue. At the same time, the integration, regulation and functions of extracellular matrix secretion, various molecular interactions, various ion channels, the neuronal microenvironment, etc., can be easily traced. Secondly, the disease-related aspects of ESC-derived glutamatergic neurons can also be studied and then applied therapeutically. In the future, greater efforts are needed to explore how ESC-differentiated glutamatergic neurons can be used as a neuronal model for the study of Alzheimer’s disease (AD) mechanistically, to identify possible therapeutic strategies for treating AD, including tissue replacement, and to screen for drugs that can be used to treat AD patients. With all of the modern technology that is available, translational medicine should begin to benefit patients soon.

hiPSC-derived NSCs effectively promote the functional recovery of acute spinal cord injury in mice

Background

Spinal cord injury (SCI) is a common disease that results in motor and sensory disorders and even lifelong paralysis. The transplantation of stem cells, such as embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), mesenchymal stem cells (MSCs), or subsequently generated stem/progenitor cells, is predicted to be a promising treatment for SCI. In this study, we aimed to investigate effect of human iPSC-derived neural stem cells (hiPSC-NSCs) and umbilical cord-derived MSCs (huMSCs) in a mouse model of acute SCI.

Methods

Acute SCI mice model were established and were randomly treated as phosphate-buffered saline (PBS) (control group), repaired with 1 × 10⁵ hiPSC-NSCs (NSC group), and 1 × 10⁵ huMSCs (MSC group), respectively, in a total of 54 mice (n = 18 each). Hind limb motor function was evaluated in open-field tests using the Basso Mouse Scale (BMS) at days post-operation (dpo) 1, 3, 5, and 7 after spinal cord injury, and weekly thereafter. Spinal cord and serum samples were harvested at dpo 7, 14, and 21. Haematoxylin-eosin (H&E) staining and Masson staining were used to evaluate the morphological changes and fibrosis area. The differentiation of the transplanted cells in vivo was evaluated with immunohistochemical staining.

Results

The hiPSC-NSC-treated group presented a significantly smaller glial fibrillary acidic protein (GFAP) positive area than MSC-treated mice at all time points. Additionally, MSC-transplanted mice had a similar GFAP+ area to mice receiving PBS. At dpo 14, the immunostained hiPSC-NSCs were positive for SRY-related high-mobility-group (HMG)-box protein-2 (SOX2). Furthermore, the transplanted hiPSC-NSCs differentiated into GFAP-positive astrocytes and beta-III tubulin-positive neurons, whereas the transplanted huMSCs differentiated into GFAP-positive astrocytes. In addition, hiPSC-NSC transplantation reduced fibrosis formation and the inflammation level. Compared with the control or huMSC transplanted group, the group with transplantation of hiPSC-NSCs exhibited significantly improved behaviours, particularly limb coordination.

Conclusions

HiPSC-NSCs promote functional recovery in mice with acute SCI by replacing missing neurons and attenuating fibrosis, glial scar formation, and inflammation.

Graphical abstract

Bioengineering the neurovascular niche to study the interaction of neural stem cells and endothelial cells

The ability of mammalian neural stem cells (NSCs) to self-renew and differentiate throughout adulthood has made them ideal to study neurogenesis and attractive candidates for neurodegenerative disease therapies. In the adult mammalian brain, NSCs are maintained in the neurovascular niche (NVN) where they are found near the specialized blood vessels, suggesting that brain endothelial cells (BECs) are prominent orchestrators of NSC fate. However, most of the current knowledge of the mammalian NVN has been deduced from nonhuman studies. To circumvent the challenges of in vivo studies, in vitro models have been developed to better understand the reciprocal cellular mechanisms of human NSCs and BECs. This review will cover the current understanding of mammalian NVN biology, the effects of endothelial cell-derived signals on NSC fate, and the in vitro models developed to study the interactions between NSCs and BECs.

Self-assembling peptide scaffolds in the clinic

Well-defined scaffold hydrogels made of self-assembling peptides have found their way into clinical products. By examining the properties and applications of two self-assembling peptides-EAK16 and RADA16-we highlight the potential for translating designer biological scaffolds into commercial products.