Controlled extracellular vesicles release from aminoguanidine nanoparticle-loaded polylysine hydrogel for synergistic treatment of spinal cord injury

Biomaterial-based strategies: a new era in spinal cord injury treatment

Enhancing neurological recovery and improving the prognosis of spinal cord injury have gained research attention recently. Spinal cord injury is associated with a complex molecular and cellular microenvironment. This complexity has prompted researchers to elucidate the underlying pathophysiological mechanisms and changes and to identify effective treatment strategies. Traditional approaches for spinal cord injury repair include surgery, oral or intravenous medications, and administration of neurotrophic factors; however, the efficacy of these approaches remains inconclusive, and serious adverse reactions continue to be a concern. With advancements in tissue engineering and regenerative medicine, emerging strategies for spinal cord injury repair now involve nanoparticle-based nanodelivery systems, scaffolds, and functional recovery techniques that incorporate biomaterials, bioengineering, stem cell, and growth factors as well as three-dimensional bioprinting. Ideal biomaterial scaffolds should not only provide structural support for neuron migration, adhesion, proliferation, and differentiation but also mimic the mechanical properties of natural spinal cord tissue. Additionally, these scaffolds should facilitate axon growth and neurogenesis by offering adjustable topography and a range of physical and biochemical cues. The three-dimensionally interconnected porous structure and appropriate physicochemical properties enabled by three-dimensional biomimetic printing technology can maximize the potential of biomaterials used for treating spinal cord injury. Therefore, correct selection and application of scaffolds, coupled with successful clinical translation, represent promising clinical objectives to enhance the treatment efficacy for and prognosis of spinal cord injury. This review elucidates the key mechanisms underlying the occurrence of spinal cord injury and regeneration post-injury, including neuroinflammation, oxidative stress, axon regeneration, and angiogenesis. This review also briefly discusses the critical role of nanodelivery systems used for repair and regeneration of injured spinal cord, highlighting the influence of nanoparticles and the factors that affect delivery efficiency. Finally, this review highlights tissue engineering strategies and the application of biomaterial scaffolds for the treatment of spinal cord injury. It discusses various types of scaffolds, their integrations with stem cells or growth factors, and approaches for optimization of scaffold design.

Extracellular vesicle-derived MicroRNAs as potential therapies for spinal cord and peripheral nerve injuries

Complete nerve regeneration is limited in current therapeutic approaches for spinal cord injuries (SCIs) and peripheral nerve injuries (PNIs). Extracellular vesicles (EVs) and microRNAs (miRNAs) play a pivotal role in intercellular communication by transporting various biomolecules, including miRNAs, to the recipient cells. Thus, they are promising targets for novel neural regeneration drugs. This comprehensive study examined the roles of EV-derived miRNAs in facilitating neural rejuvenation after SCI and PNI. It also explored the mechanisms by which they augment neuroprotection and promote cell viability. It also discusses their translational potential for treating nerve injury and evaluates their potential impact on advancements in nerve resurrection and prospective research in regenerative medicine. The findings may provide effective treatments and improve outcomes, as well as contribute to addressing the direction for the next studies, for the pathologies of SCI and PNI.

Gut microbiome-derived lipopolysaccharides aggravate cognitive impairment via TLR4-mediated inflammatory signaling in neonatal rats following hypoxic-ischemic brain damage

Hypoxic-ischemic brain damage (HIBD) is a leading cause of infant mortality and neurological disabilities in children. Recent evidence indicates that gut microbiota significantly contributes to the development of inflammation and cognitive impairments following brain injury. However, the mechanisms by which gut microbiota influence inflammation and cognitive function in the neonates after HIBD are not well understood. This study established a neonatal rat model of HIBD by the classic Rice-Vannucci technique to investigate gut dysbiosis following hypoxic-ischemic (HI) insult and to elucidate the causal relationship between gut dysbiosis and cognitive impairments. Our results demonstrated that HI insult resulted in significant gut microbial dysbiosis, characterized by an expansion of Enterobacteriaceae. This dysbiosis was associated with intestinal barrier damage, lipopolysaccharides (LPS) leakage, and systemic inflammation. Conversely, administration of aminoguanidine (AG) to inhibit Enterobacteriaceae overgrowth restored intestinal barrier integrity and reduced systemic inflammation. Importantly, AG treatment effectively suppressed microglial activation, neuronal damage, and cognitive impairments in the neonatal rats subjected to HI insult. Additionally, RNA sequencing analysis revealed that differentially expressed genes in both colonic and hippocampal tissues were primarily associated with inflammation and neuronal apoptosis after HI insult. Further mechanistic exploration revealed that AG treatment mitigated intestinal LPS leakage, thereby reducing the activation of the TLR4/MyD88/NF-κB signaling pathway and production of the downstream inflammatory cytokines in both the colon and hippocampus. Notably, fecal microbiota transplantation (FMT) from the HIBD rats to the antibiotic cocktail-treated recipient rats resulted in microglial activation, neuronal damage, and cognitive impairments in the recipients. However, these adverse effects were effectively mitigated in the recipient rats that received FMT from the AG-treated donors, as well as in those undergoing hippocampal TLR4 knockdown. In conclusion, our findings indicate that LPS derived from gut Enterobacteriaceae overgrowth plays a critical role in the TLR4-mediated inflammatory signaling, providing a novel microbiota-based therapeutic approach for cognitive impairments following neonatal HIBD.

Extracellular Vesicles as Emerging Therapeutic Strategies in Spinal Cord Injury: Ready to Go

Spinal cord injury (SCI) is a prevalent central nervous system disorder that causes significant disability and mortality. Unfortunately, due to the complex pathophysiological mechanisms involved, there remains a critical paucity of effective therapeutic interventions capable of achieving neural tissue regeneration and functional recovery enhancement in SCI patients. The advancements in extracellular vesicles (EVs) as a cell-free therapy for SCI have displayed notable benefits. These include their small size, low immunogenicity, capacity to target specific areas, and ability to cross the blood‒brain barrier (BBB). EVs offer the potential to not only repair tissue damage and stimulate regeneration but also effectively deliver and release them at the site of SCI when combined with diverse biomaterials. This review explores the biological role and importance of EVs in treating SCI, highlighting the combined use of modified EVs with different biomaterials and their potential for future applications. It presents new and hopeful treatment approaches for individuals afflicted with SCI.

Biological engineering approaches for modulating the pathological microenvironment and promoting axonal regeneration after spinal cord injury

Functional recovery following spinal cord injury (SCI) presents significant challenges and imposes a substantial burden on society. Current research primarily focuses on minimizing damage and promoting regeneration to enhance functional recovery after SCI. Following SCI, secondary injuries such as mitochondrial dysfunction, vascular rupture, inflammatory responses, and glial scarring occur in the lesion area, forming the pathological microenvironment. These factors expand the extent of damage, exacerbate injury severity, and severely impede axonal regeneration after SCI. Modulating the pathological microenvironment through various interventions may facilitate axonal regeneration and promote functional recovery after SCI. This article reviews the influence and research advancements in axon regeneration concerning mitochondrial dysfunction, inflammatory response, and glial scar formation after SCI. Additionally, it integrates insights from bioengineering to improve the pathological microenvironment, summarizing the progress in axon regeneration research. The review concludes with novel strategies for enhancing axon regeneration, offering fresh perspectives for future investigations.

Review of Metal-Polyphenol Self-Assembled Nanoparticles: Synthesis, Properties, and Biological Applications in Inflammatory Diseases

Polyphenols, which are compounds characterized by the presence of phenolic hydroxyl groups, are abundantly found in natural plants and exist in highly complex forms within living organisms. As some of the most prevalent compounds in nature, polyphenols possess significant medicinal value due to their unique structural features, particularly their therapeutic efficacy in antitumor, anti-inflammatory, and antibacterial applications. In the context of inflammation therapy, polyphenolic compounds can inhibit the excessive release of inflammatory mediators from inflammatory cells, thereby mitigating inflammation. Furthermore, these compounds exhibit strong antioxidant properties, enabling them to scavenge free radicals and reactive oxygen species (ROS), reduce oxidative stress-related damage, and exert anti-inflammatory effects. Due to their multiple phenolic hydroxyl groups and their ability to chelate various metals, polyphenols are extensively utilized in the synthesis of self-assembled nanoparticles for the treatment of various diseases. Numerous studies have demonstrated that the therapeutic profile of nanoparticles formed through self-assembly with metal ions surpasses that of polyphenolic compounds alone. This Review will focus on the self-assembly of different polyphenolic compounds with various metal ions to generate nanoparticles, their characterization, and their therapeutic applications in inflammation-related diseases, providing researchers with new insights into the synthetic study of metal-polyphenol nanocomposites and their biological applications.

Extracellular vesicles as a promising tool in neuropsychiatric pharmacotherapy application and monitoring

This review deals with the application of extracellular vesicles (EVs) in the treatment of various neuropsychiatric disorders, including mood disorders, neurodegeneration, psychosis, neurological insults and injuries, epilepsy and substance use disorders. The main challenges of most neuropsychiatric pharmaceuticals nowadays are how to reach the central nervous system at therapeutic concentration and maintain it long enough and how to avoid undesirable side effects caused by unsatisfying toxicity. Extracellular vesicles, as very important mediators of intercellular communication, can have a variety of therapeutic qualities. They can act neuroprotective, regenerative and anti-inflammatory, but they also have characteristics of a good drug delivery system, including their nano- scale size, biological safety and abilities to cross BBB, to pack drugs within the lipid bilayer, and not to trigger an immunological response. Besides, due to their presence in readily accessible biofluids, they are good candidates for biomarkers of the disease, its progression and therapy response monitoring. Alternations in EVs' cargo profiles can reflect the pathogenesis of neuropsychiatric disorders, but they could also affect the disease outcomes. In the future, EVs could help physicians to tailor treatment strategies for individual patients, however, more extensive studies are needed to standardize isolation, purification and production procedures, increase efficacy of drug loading and limit unwanted effects of innate EVs' content.

A sequential stimuli-responsive hydrogel promotes structural and functional recovery of severe spinal cord injury

Utilizing drug-loaded hydrogels to restore nerve conductivity emerges as a promising strategy in the treatment of spinal cord injury (SCI). However, many of these hydrogels fail to deliver drugs on demand according to the dynamic SCI pathological features, resulting in poor functional recovery. Inspired by the post-SCI microenvironments, here we report a time-sequential and controllable drug delivery strategy using an injectable hydrogel responsive to reactive oxygen species (ROS) and matrix metalloproteinases (MMPs). This strategy includes two steps: first, the hydrogel responds to ROS and releases nanodrugs to scavenge ROS, thereby mitigating inflammation and protecting neurons from oxidative stress in the initial SCI stages; second, the accumulation of MMPs triggers the release of vascular endothelial growth factor from nanodrugs to promote angiogenesis and neural stem cell differentiation in the late stage of SCI. In two clinically relevant SCI models, a single injection of the hydrogel led to an efficient structural and functional recovery of SCI 6 weeks after the intervention. We observed less inflammation, fibrosis, and cavities but more angiogenesis and neurons in the hydrogel-treated injured spinal cord region compared with the untreated animals. The hydrogel exhibits mechanical strength and conductivity comparable to natural spinal cord, facilitating its further clinical translation.

Tβ4-exosome-loaded hemostatic and antibacterial hydrogel to improve vascular regeneration and modulate macrophage polarization for diabetic wound treatment

Diabetic wounds often exhibit delayed healing due to compromised vascular function and intensified inflammation. In this study, we overexpressed Thymosin β4 (Tβ4) in Adipose-Derived Stem Cells (ADSCs) to produce Exosomes (Exos) rich in Tβ4. We then utilized a dual photopolymerizable hydrogel composed of Hyaluronic Acid Methacryloyl (HAMA) and Poly-L-lysine Methacryloyl (PLMA) for the sustained release of Tβ4-Exos on diabetic wounds. The results showed that Tβ4-Exos could stimulate angiogenesis and collagen synthesis, and mitigate inflammation in diabetic wounds by promoting the polarization of M1-type macrophages and inhibiting that of M2-type macrophages. Furthermore, Tβ4-Exos was found to activate the PI3K/AKT/mTOR/HIF-1a signaling pathway, thereby enhancing vascular proliferation. In summary, the sustained release of Tβ4-Exos in HAMA-PLMA (HP) hydrogel and the management of inflammation through the upregulation of the HIF-1a pathway and modulation of macrophage polarization in vascular proliferation significantly accelerated the healing process of diabetic wounds.

Bioinspired conductive oriented nanofiber felt with efficient ROS clearance and anti-inflammation for inducing M2 macrophage polarization and accelerating spinal cord injury repair

Complete spinal cord injury (SCI) causes permanent locomotor, sensory and neurological dysfunctions. Targeting complex immunopathological microenvironment at SCI sites comprising inflammatory cytokines infiltration, oxidative stress and massive neuronal apoptosis, the conductive oriented nanofiber felt with efficient ROS clearance, anti-inflammatory effect and accelerating neural regeneration is constructed by step-growth addition polymerization and electrostatic spinning technique for SCI repair. The formation of innovative Fe3+-PDA-PAT chelate in nanofiber felt enhances hydrophilic, antioxidant, antibacterial, hemostatic and binding factor capacities, thereby regulating immune microenvironment of SCI. With the capabilities of up-regulating COX5A and STAT6 expressions, down-regulating the expressions of IL1β, CD36, p-ERK, NFκB2 and NFκB signaling pathway proteins, the nanofiber felt attenuates oxidative stress injury, promotes M2 macrophage polarization and down-regulates inflammatory response. After implantation into complete transection SCI rats, the nanofiber felt is revealed to recruit endogenous NSCs, induce the differentiation of NSCs into neurons while inhibit astrocytes formation and inflammation, reduces glia scar, and promotes angiogenesis, remyelination and neurological functional recovery. Overall, this innovative strategy provides a facile immune regulatory system to inhibit inflammatory response and accelerate nerve regeneration after SCI, and its targeted proteins and mechanisms are first elucidated, which holds great application promise in clinical treatment of complete SCI.

Spinal cord injury repair based on drug and cell delivery: From remodeling microenvironment to relay connection formation

Spinal cord injury (SCI) presents a formidable challenge in clinical settings, resulting in sensory and motor function loss and imposing significant personal and societal burdens. However, owning to the adverse microenvironment and limited regenerative capacity, achieving complete functional recovery after SCI remains elusive. Additionally, traditional interventions including surgery and medication have a series of limitations that restrict the effectiveness of treatment. Recently, tissue engineering (TE) has emerged as a promising approach for promoting neural regeneration and functional recovery in SCI, which can effectively delivery drugs into injury site and delivery cells and improve the survival and differential. Here, we outline the main pathophysiology events of SCI and the adverse microenvironment post injury, further discuss the materials and common assembly strategies used for scaffolds in SCI treatment, expound on the latest advancements in treatment methods based on materials and scaffolds for drug and cell delivery in detail, and propose future directions for SCI repair with TE and highlight potential clinical applications.

Advancements in Antioxidant-Based Therapeutics for Spinal Cord Injury: A Critical Review of Strategies and Combination Approaches

Spinal cord injury (SCI) initiates a cascade of secondary damage driven by oxidative stress, characterized by the excessive production of reactive oxygen species and other reactive molecules, which exacerbate cellular and tissue damage through the activation of deleterious signaling pathways. This review provides a comprehensive and critical evaluation of recent advancements in antioxidant-based therapeutic strategies for SCI, including natural compounds, RNA-based therapies, stem cell interventions, and biomaterial applications. It emphasizes the limitations of single-regimen approaches, particularly their limited efficacy and suboptimal delivery to injured spinal cord tissue, while highlighting the synergistic potential of combination therapies that integrate multiple modalities to address the multifaceted pathophysiology of SCI. By analyzing emerging trends and current limitations, this review identifies key challenges and proposes future directions, including the refinement of antioxidant delivery systems, the development of multi-targeted approaches, and strategies to overcome the structural complexities of the spinal cord. This work underscores the pressing need for innovative and integrative therapeutic approaches to advance the clinical translation of antioxidant-based interventions and improve outcomes for SCI patients.

A Functionalized Scaffold Facilitates Neurites Extension for Spinal Cord Injury Therapy

Scaffolds have garnered considerable attention for enhancing neural repairment for spinal cord injury (SCI) treatment. Both microstructural features and biochemical modifications play pivotal roles in influencing the interaction of cells with the scaffold, thereby affecting tissue regeneration. Here, a scaffold is designed with spiral structure and gradient peptide modification (GS) specifically for SCI treatment. The spiral structure provides crucial support and space, while the gradient peptide isoleucine-lysine-valine-alanine-valine (IKVAV) modification imparts directional guidance for neuronal and axonal extension. GS scaffold shows a significant nerve extension induction effect through its interlayer gap and gradient peptide density to dorsal root ganglia in vitro, while in vivo studies reveal its substantial promotion for functional recovery and neural repair. Additionally, the GS scaffold displays impressive drug-loading capacity, mesenchymal stem cell-derived exosomes can be efficiently loaded into the GS scaffold and delivered to the injury site, thereby synergistically promoting SCI repair. Overall, the GS scaffold can serve as a versatile platform and present a promising multifunctional approach for SCI treatment.

Hydrogel-based therapeutic strategies for spinal cord injury repair: Recent advances and future prospects

Spinal cord injury (SCI) is a debilitating condition that can result in significant functional impairment and loss of quality of life. There is a growing interest in developing new therapies for SCI, and hydrogel-based multimodal therapeutic strategies have emerged as a promising approach. They offer several advantages for SCI repair, including biocompatibility, tunable mechanical properties, low immunogenicity, and the ability to deliver therapeutic agents. This article provides an overview of the recent advances in hydrogel-based therapy strategies for SCI repair, particularly within the past three years. We summarize the SCI hydrogels with varied characteristics such as phase-change hydrogels, self-healing hydrogel, oriented fibers hydrogel, and self-assembled microspheres hydrogel, as well as different functional hydrogels such as conductive hydrogels, stimuli-responsive hydrogels, adhesive hydrogel, antioxidant hydrogel, sustained-release hydrogel, etc. The composition, preparation, and therapeutic effect of these hydrogels are briefly discussed and comprehensively evaluated. In the end, the future development of hydrogels in SCI repair is prospected to inspire more researchers to invest in this promising field.

Current multi-scale biomaterials for tissue regeneration following spinal cord injury

Spinal cord injury (SCI) may cause loss of motor and sensory function, autonomic dysfunction, and thus disrupt the quality of life of patients, leading to severe disability and significant psychological, social, and economic burden. At present, existing therapy for SCI have limited ability to promote neural function recovery, and there is an urgent need to develop innovative regenerative approaches to repair SCI. Biomaterials have become a promising strategy to promote the regeneration and repair of damaged nerve tissue after SCI. Biomaterials can provide support for nerve tissue by filling cavities, and improve local inflammatory responses and reshape extracellular matrix structures through unique biochemical properties to create the optimal microenvironment at the SCI site, thereby promoting neurogenesis and reconnecting damaged spinal cord tissue. Considering the importance of biomaterials in repairing SCI, this article reviews the latest progress of multi-scale biomaterials in SCI treatment and tissue regeneration, and evaluates the relevant technologies for manufacturing biomaterials.

Extracellular vesicles: Function, resilience, biomarker, bioengineering, and clinical implications

Extracellular vesicles (EVs) have emerged as key players in intercellular communication, disease pathology, and therapeutic innovation. Initially overlooked as cellular debris, EVs are now recognized as vital mediators of cell-to-cell communication, ferrying a cargo of proteins, nucleic acids, and lipids, providing cellular resilience in response to stresses. This review provides a comprehensive overview of EVs, focusing on their role as biomarkers in disease diagnosis, their functional significance in physiological and pathological processes, and the potential of bioengineering for therapeutic applications. EVs offer a promising avenue for noninvasive disease diagnosis and monitoring, reflecting the physiological state of originating cells. Their diagnostic potential spans a spectrum of diseases, including cancer, cardiovascular disorders, neurodegenerative diseases, and infectious diseases. Moreover, their presence in bodily fluids such as blood, urine, and cerebrospinal fluid enhances their diagnostic utility, presenting advantages over traditional methods. Beyond diagnostics, EVs mediate crucial roles in intercellular communication, facilitating the transfer of bioactive molecules between cells. This communication modulates various physiological processes such as tissue regeneration, immune modulation, and neuronal communication. Dysregulation of EV-mediated communication is implicated in diseases such as cancer, immune disorders, and neurodegenerative diseases, highlighting their therapeutic potential. Bioengineering techniques offer avenues for manipulating EVs for therapeutic applications, from isolation and purification to engineering cargo and targeted delivery systems. These approaches hold promise for developing novel therapeutics tailored to specific diseases, revolutionizing personalized medicine. However, challenges such as standardization, scalability, and regulatory approval need addressing for successful clinical translation. Overall, EVs represent a dynamic frontier in biomedical research with vast potential for diagnostics, therapeutics, and personalized medicine.

Metformin-grafted polycaprolactone nanoscaffold targeting sensory nerve controlled fibroblasts reprograming to alleviate epidural fibrosis

Epidural fibrosis (EF), associated with various biological factors, is still a major troublesome clinical problem after laminectomy. In the present study, we initially demonstrate that sensory nerves can attenuate fibrogenic progression in EF animal models via the secretion of calcitonin gene-related peptide (CGRP), suggesting a new potential therapeutic target. Further studies showed that CGRP could inhibit the reprograming activation of fibroblasts through PI3K/AKT signal pathway. We subsequently identified metformin (MET), the most widely prescribed medication for obesity-associated type 2 diabetes, as a potent stimulator of sensory neurons to release more CGRP via activating CREB signal way. We copolymerized MET with innovative polycaprolactone (PCL) nanofibers to develop a metformin-grafted PCL nanoscaffold (METG-PCLN), which could ensure stable long-term drug release and serve as favorable physical barriers. In vivo results demonstrated that local implantation of METG-PCLN could penetrate into dorsal root ganglion cells (DRGs) to promote the CGRP synthesis, thus continuously inhibit the fibroblast activation and EF progress for 8 weeks after laminectomy, significantly better than conventional drug loading method. In conclusion, this study reveals the unprecedented potential of sensory neurons to counteract EF through CGRP signaling and introduces a novel strategy employing METG-PCLN to obstruct EF by fine-tuning sensory nerve-regulated fibrogenesis.