Self-assembling peptide gels promote angiogenesis and functional recovery after spinal cord injury in rats

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.

Investigation on the effects and mechanisms of novel peptide nanofiber gel to promote wound healing of deep second-degree burns in mice

The self-assembled peptide RADA16-I (RADARADARADARADA) has been widely used in biomaterials. However, studies on the practical application of self-assembled peptide hydrogels loaded with bioactive peptides are still insufficient. In this study, we successfully prepared the peptide nanofiber gel RGJ by incorporating the bioactive peptides A8SGLP-1 (G) and Jagged-1 (J) into RADA16-I (R) in specific ratios. The mechanical properties, secondary structure, and microstructure of RGJ were thoroughly characterized using a rheometer, circular dichroism (CD), and transmission electron microscopy (TEM). The results showed that R and RGJ adopted stable β-folded structures at room temperature, and RGJ exhibited a nanofiber mesh structure, confirming its excellent physical properties. Cellular experiments demonstrated that RGJ significantly enhanced the proliferation and migration of HaCaT, L929, and HUVEC cells, with the most pronounced effect observed in HUVEC cells. In the 100 μg/mL RGJ-treated group, cell viability (OD value) reached 1.369, which was significantly higher than that of the control group (0.673) and the R-only group (0.848). The strongest pro-migratory effect was observed in HaCaT cells, with a scratch closure rate of 22.83 %. In vivo experiments showed that the deep second-degree burn wounds of mice in the RGJ gel-treated group healed rapidly by day 17, exhibiting 99.5 % wound closure, compared to 84.02 % in the R gel group, and 73.02 % and 70.97 % in the control and burn cream groups, respectively. Immunohistochemistry and ELISA results further confirmed that RGJ significantly reduced wound and systemic inflammatory responses while promoting the secretion of pro-angiogenic factors VEGF and CD31, revealing its potential mechanism for enhancing burn wound healing. Additionally, RGJ significantly reduced wound scar formation and increased skin collagen deposition, demonstrating a favorable biosafety profile compared to the control group, commercial burn ointment, and the R-only treatment group. In conclusion, the development of the peptide nanofiber gel RGJ holds great potential for wound management applications and lays a foundation for future related research.

The effects of self-assembling peptide on glial cell activation

Glial cells play a critical role in the healthy and diseased phases of the central nervous system (CNS). CNS diseases involve a wide range of pathological conditions characterized by poor recovery of neuronal function. Glial cell-related target therapies are progressively gaining interest in inhibiting secondary injury-related death. Modulation of the extracellular matrix by artificial scaffolds plays a critical role in the behavior of glial cells after injury. Among numerous types of scaffolds, self-assembling peptides (SAPs) notably give attention to the design of a proper biophysical and biomechanical microenvironment for cellular homeostasis and tissue regeneration. Implementing SAPs in an injured brain can induce neural differentiation in transplanted stem cells, reducing inflammation and inhibiting glial scar formation. In this review, we investigate the recent findings to elucidate the pivotal role of SAPs in orchestrating the most pivotal secondary response following CNS injury. Notably, we explore their impact on the activation of glial cells and their modulatory effects on microglial and astrocytic polarization.

lncRNA SNHG6 Knockdown Promotes Microglial M2 Polarization and Alleviates Spinal Cord Injury via Regulating the miR-182-5p/NEUROD4 Axis

Spinal cord injury (SCI) is one of the devastating neurological disorders that leads to a loss of motor and sensory functions. Long non-coding RNA small nucleolar RNA host gene 6 (lncRNA SNHG6) plays a crucial role in inflammatory regulation across various diseases. This study investigates the role of SNHG6 in SCI development and its underlying regulatory mechanisms. Two experimental models were established: an in vitro model using LPS-challenged (100 ng/mL) mouse microglia BV2 cells and an in vivo model employing controlled spinal cord impact in mice. SNHG6, miR-182-5p, and NEUROD4 expression levels were quantified through RT-qPCR and Western blot. Functional and histological assessments were performed using the Basso mouse scale (BMS) and Nissl staining, respectively. Putative binding sites between SNHG6 and miR-182-5p, as well as between miR-182-5p and NEUROD4, were predicted using the ENCORI/starBase platform. These molecular interactions were validated through dual-luciferase reporter assays and RNA pull-down experiments, with further confirmation by qRT-PCR and Western blot analyses. Both LPS-stimulated BV2 cells and spinal cord tissues from SCI mice exhibited elevated SNHG6 expression. Downregulation of SNHG6 enhanced LPS-induced polarization of BV2 cells from M1-type to M2-type, significantly modulated the expression of pro-inflammatory factors (TNF-α, IL-1β, and IL-6) and anti-inflammatory factors (TGF-β, IL-10, and IL-13), and reduced injury severity in SCI mice. Our mechanistic studies revealed that SNHG6 functions as a molecular sponge for miR-182-5p to regulate NEUROD4 expression. This study demonstrates that SNHG6 knockdown promotes microglial M2-type polarization and alleviates inflammatory responses through modulation of the miR-182-5p/NEUROD4 axis, suggesting SNHG6 as a potential therapeutic target for SCI treatment.

Bioactive Peptide Hydrogel Scaffold with High Fluidity, Thermosensitivity, and Neurotropism in 3D Spatial Structure for Promoted Repair of Spinal Cord Injury

Spinal cord injury (SCI) has been considered a clinically challenging disease that is characterized by local disturbance of the microenvironment, which inhibits post-injury neural regeneration. The simulation of a microenvironment conducive to the regeneration of spinal cord is beneficial for SCI repair. In this study, bioactive composite hydrogels are developed that mimic the regenerative microenvironment of spinal cord for enhanced SCI repair. The fabricated composite hydrogels (CRP) based on chitosan (CS), RADA16 nanofibers, and nerve-promoted peptide (PPFLMLLKGSTR) exhibit excellent injectability, superior biodegradability and biocompatibility. In addition, the CRP hydrogels can form quickly (a few minutes) by mixing three components at human body temperature, showing high potential as a biomimetic matrix for in situ repair of SCI. The in vitro studies demonstrate that the CRP hydrogels can not only promote the proliferation and migration of bone marrow mesenchymal stem cells but also induce the proliferation and differentiation of neural stem cells (NSCs) into neurons. Meanwhile, the hydrogels reveal the efficiency of protecting neurons and promoting axonal growth. Furthermore, the in vivo tests prove that the CRP hydrogels can reduce post-SCI inflammatory responses, inhibit reactive astrocyte over-proliferation, and promote the migration, proliferation, and differentiation of endogenous NSCs, which agree well with the in vitro results. The pre-clinical test demonstrates that the CRP hydrogels restore the motor function in completely transected spinal cord rats, and the SCI repair mechanism may involve the activation of the PI3K/AKT/mTOR pathway. It is believed that the strategies shown in this work will be valuable for the design and synthesis of novel hydrogels for biomedical and tissue engineering applications.

A Roadmap of Peptide-Based Materials in Neural Regeneration

Injuries to the nervous system lead to irreversible damage and limited functional recovery. The peripheral nervous system (PNS) can self-regenerate to some extent for short nerve gaps. In contrast, the central nervous system (CNS) has an intrinsic limitation to self-repair owing to its convoluted neural microenvironment and inhibitory response. The primary phase of CNS injury, happening within 48 h, results from external impacts like mechanical stress. Afterward, the secondary phase of the injury occurs, originating from neuronal excitotoxicity, mitochondrial dysfunction, and neuroinflammation. No golden standard to treat injured neurons exists, and conventional medicine serves only as a protective approach to alleviating the symptoms of chronic injury. Synthetic peptides provide a promising approach for neural repair, either as soluble drugs or by using their intrinsic self-assembly propensity to serve as an extracellular matrix (ECM) mimic for cell adhesion and to incorporate bioactive epitopes. In this review, an overview of nerve injury models, common in vitro models, and peptide-based therapeutics such as ECM mimics is provided. Due to the complexity of treating neuronal injuries, a multidisciplinary collaboration between biologists, physicians, and material scientists is paramount. Together, scientists with complementary expertise will be required to formulate future therapeutic approaches for clinical use.

Adapting to the acidic environment of the NP: RADA16-PLGA (TGF-β3) induces chondrogenic differentiation of BMSCs

Aim: RADA16-PLGA composite scaffolds constructed with simultaneous loading of BMSCs and TGF-β3 and explored their ability for chondrogenic differentiation in vitro.Methods: The performance of the composite scaffolds is assessed by rheometer assay, electron microscopic structural observation and ELISA release assay. The biosafety of the composite scaffolds is assessed by cytocompatibility assay and cell migration ability. The chondrogenic differentiation ability of composite scaffolds is evaluated by Alisin blue staining, PCR and immunofluorescence staining.Results: The composite scaffold has a good ECM-like structure, the ability to control the release of TGF-β3 and good biocompatibility. More importantly, the composite scaffolds can induce the differentiation of BMSCs to chondrocytes.Conclusion: Composite scaffolds are expected to enhance the endogenous NP repair process.

Application of Pro-angiogenic Biomaterials in Myocardial Infarction

Biomaterials have potential applications in the treatment of myocardial infarction (MI). These biomaterials have the ability to mechanically support the ventricular wall and to modulate the inflammatory, metabolic, and local electrophysiological microenvironment. In addition, they can play an equally important role in promoting angiogenesis, which is the primary prerequisite for the treatment of MI. A variety of biomaterials are known to exert pro-angiogenic effects, but the pro-angiogenic mechanisms and functions of different biomaterials are complex and diverse, and have not yet been systematically described. This review will focus on the pro-angiogenesis of biomaterials and systematically describe the mechanisms and functions of different biomaterials in promoting angiogenesis in MI.

Functional biomaterials for modulating the dysfunctional pathological microenvironment of spinal cord injury

Spinal cord injury (SCI) often results in irreversible loss of sensory and motor functions, and most SCIs are incurable with current medical practice. One of the hardest challenges in treating SCI is the development of a dysfunctional pathological microenvironment, which mainly comprises excessive inflammation, deposition of inhibitory molecules, neurotrophic factor deprivation, glial scar formation, and imbalance of vascular function. To overcome this challenge, implantation of functional biomaterials at the injury site has been regarded as a potential treatment for modulating the dysfunctional microenvironment to support axon regeneration, remyelination at injury site, and functional recovery after SCI. This review summarizes characteristics of dysfunctional pathological microenvironment and recent advances in biomaterials as well as the technologies used to modulate inflammatory microenvironment, regulate inhibitory microenvironment, and reshape revascularization microenvironment. Moreover, technological limitations, challenges, and future prospects of functional biomaterials to promote efficient repair of SCI are also discussed. This review will aid further understanding and development of functional biomaterials to regulate pathological SCI microenvironment.

Lactate promotes microglial scar formation and facilitates locomotor function recovery by enhancing histone H4 lysine 12 lactylation after spinal cord injury

Lactate-derived histone lactylation is involved in multiple pathological processes through transcriptional regulation. The role of lactate-derived histone lactylation in the repair of spinal cord injury (SCI) remains unclear. Here we report that overall lactate levels and lactylation are upregulated in the spinal cord after SCI. Notably, H4K12la was significantly elevated in the microglia of the injured spinal cord, whereas exogenous lactate treatment further elevated H4K12la in microglia after SCI. Functionally, lactate treatment promoted microglial proliferation, scar formation, axon regeneration, and locomotor function recovery after SCI. Mechanically, lactate-mediated H4K12la elevation promoted PD-1 transcription in microglia, thereby facilitating SCI repair. Furthermore, a series of rescue experiments confirmed that a PD-1 inhibitor or microglia-specific AAV-sh-PD-1 significantly reversed the therapeutic effects of lactate following SCI. This study illustrates the function and mechanism of lactate/H4K12la/PD-1 signaling in microglia-mediated tissue repair and provides a novel target for SCI therapy.

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.

Osteoporotic Bone Regeneration via Plenished Biomimetic PLGA Scaffold with Sequential Release System

Achieving satisfactory bone tissue regeneration in osteoporotic patients with ordinary biomaterials is challenging because of the decreased bone mineral density and aberrant bone microenvironment. In addressing this issue, a biomimetic scaffold (PMEH/SP), incorporating 4-hexylresorcinol (4HR), and substance P (SP) into the poly(lactic-go-glycolic acid) (PLGA) scaffold with magnesium hydroxide (M) and extracellular matrix (E) is introduced, enabling the consecutive release of bioactive agents. 4HR and SP induced the phosphorylation of p38 MAPK and ERK in human umbilical vein endothelial cells (HUVECs), thereby upregulating VEGF expression level. The migration and tube-forming ability of endothelial cells can be promoted by the scaffold, which accelerates the formation and maturation of the bone. Moreover, 4HR played a crucial role in the inhibition of osteoclastogenesis by interrupting the IκB/NF-κB signaling pathway and exhibiting SP, thereby enhancing the migration and angiogenesis of HUVECs. Based on such a synergistic effect, osteoporosis can be suppressed, and bone regeneration can be achieved by inhibiting the RANKL pathway in vitro and in vivo, which is a commonly known mechanism of bone physiology. Therefore, the study presents a promising approach for developing a multifunctional regenerative material for sophisticated osteoporotic bone regeneration.

Positive effect of microvascular proliferation on functional recovery in experimental cervical spondylotic myelopathy

Background and purpose

Cervical Spondylotic Myelopathy (CSM), the most common cause of spinal cord dysfunction globally, is a degenerative disease that results in non-violent, gradual, and long-lasting compression of the cervical spinal cord. The objective of this study was to investigate whether microvascular proliferation could positively affect neural function recovery in experimental cervical spondylotic myelopathy (CSM).

Methods

A total of 60 male adult Sprague-Dawley (SD) were randomly divided into four groups: Control (CON), Compression (COM), Angiostasis (AS), and Angiogenesis (A G),with 15 rats in each group. Rats in the AS group received SU5416 to inhibit angiogenesis, while rats in the AG group received Deferoxamine (DFO) to promote angiogenesis. Motor and sensory functions were assessed using the Basso Beattie Bresnahan (BBB) scale and somatosensory evoked potential (SEP) examination. Neuropathological degeneration was evaluated by the number of neurons, Nissl bodies (NB), and the de-myelination of white matter detected by Hematoxylin & Eosin(HE), Toluidine Blue (TB), and Luxol Fast Blue (LFB) staining. Immunohistochemical (IHC) staining was used to observe the Neurovascular Unit (NVU).

Results

Rats in the CON group exhibited normal locomotor function with full BBB score, normal SEP latency and amplitude. Among the other three groups, the AG group had the highest BBB score and the shortest SEP latency, while the AS group had the lowest BBB score and the most prolonged SEP latency. The SEP amplitude showed an opposite performance to the latency. Compared to the COM and AS groups, the AG group demonstrated significant neuronal restoration in gray matter and axonal remyelination in white matter. DFO promoted microvascular proliferation, especially in gray matter, and improved the survival of neuroglial cells. In contrast, SU-5416 inhibited the viability of neuroglial cells by reducing micro vessels.

Conclusion

The microvascular status was closely related to NVU remodeling an-d functional recovery. Therefore, proliferation of micro vessels contributed to function -al recovery in experimental CSM, which may be associated with NVU remodeling.

Recent advances in tissue repair of the blood-brain barrier after stroke

The selective permeability of the blood-brain barrier (BBB) enables the necessary exchange of substances between the brain parenchyma and circulating blood and is important for the normal functioning of the central nervous system. Ischemic stroke inflicts damage upon the BBB, triggering adverse stroke outcomes such as cerebral edema, hemorrhagic transformation, and aggravated neuroinflammation. Therefore, effective repair of the damaged BBB after stroke and neovascularization that allows for the unique selective transfer of substances from the BBB after stroke is necessary and important for the recovery of brain function. This review focuses on four important therapies that have effects of BBB tissue repair after stroke in the last seven years. Most of these new therapies show increased expression of BBB tight-junction proteins, and some show beneficial results in terms of enhanced pericyte coverage at the injured vessels. This review also briefly outlines three effective classes of approaches and their mechanisms for promoting neoangiogenesis following a stroke.

Neuro-bone tissue engineering: emerging mechanisms, potential strategies, and current challenges

The skeleton is a highly innervated organ in which nerve fibers interact with various skeletal cells. Peripheral nerve endings release neurogenic factors and sense skeletal signals, which mediate bone metabolism and skeletal pain. In recent years, bone tissue engineering has increasingly focused on the effects of the nervous system on bone regeneration. Simultaneous regeneration of bone and nerves through the use of materials or by the enhancement of endogenous neurogenic repair signals has been proven to promote functional bone regeneration. Additionally, emerging information on the mechanisms of skeletal interoception and the central nervous system regulation of bone homeostasis provide an opportunity for advancing biomaterials. However, comprehensive reviews of this topic are lacking. Therefore, this review provides an overview of the relationship between nerves and bone regeneration, focusing on tissue engineering applications. We discuss novel regulatory mechanisms and explore innovative approaches based on nerve-bone interactions for bone regeneration. Finally, the challenges and future prospects of this field are briefly discussed.

The role and mechanisms of mesenchymal stem cells regulating macrophage plasticity in spinal cord injury

Spinal Cord Injury (SCI) is a devastating neurological disorder comprising primary mechanical injury and secondary inflammatory response-mediated injury for which an effective treatment is still unavailable. It is well known that secondary inflammatory responses are a significant cause of difficulties in neurological recovery. An immune imbalance between M1/M2 macrophages at the sites of injury is involved in developing and progressing the secondary inflammatory response. Recently, Mesenchymal Stem Cells (MSCs) have shown significant therapeutic potential in tissue engineering and regenerative medicine due to their potential multidirectional differentiation and immunomodulatory properties. Accumulating evidence shows that MSCs can regulate the balance of M1/M2 macrophage polarization, suppress downstream inflammatory responses, facilitate tissue repair and regeneration, and improve the prognosis of SCI. This article briefly overviews the impact of macrophages and MSCs on SCI and repair. It discusses the mechanisms by which MSCs regulate macrophage plasticity, including paracrine action, release of exosomes and apoptotic bodies, and metabolic reprogramming. Additionally, the article summarizes the relevant signaling pathways of MSCs that regulate macrophage polarization.

Core-Shell Droplet-Based Angiogenic Patches for the Treatment of Ischemic Diseases: Ultrafast Processability, Physical Tunability, and Controlled Delivery of an Angiogenic Cocktail

The patch-based delivery system has been a promising therapeutic approach for treating various vascular diseases. However, conventional methods face several challenges, including labor-intensive and time-consuming processes associated with patch fabrication or factor incorporation, inadequate physical properties, and uncontrolled release of factors. These limitations restrict the potential applications in clinical settings. To overcome these issues, we propose a novel core-shell-shaped droplet patch system called an angiogenic patch (AP). Our system offers several distinct advantages over conventional patches. It enables a rapid and straightforward fabrication process utilizing only two biodegradable ingredients [alginate and ε-poly(l-lysine)], ensuring minimal toxicity. Moreover, the AP exhibits excellent physical integrity to match and withstand physiological mechanics and allows for customizable patch dimensions tailored to individual patients' pathological conditions. Notably, the AP enables facile loading of angiogenic cytokines during patch fabrication, allowing sustained release at a controlled rate through tunable network cross-linking. Subsequently, the AP, delivering a precisely formulated cocktail of angiogenic cytokines (VEGF, bFGF, EGF, and IGF), demonstrated significant effects on endothelial cell functions (migration and tubule formation) and survival under pathological conditions simulating ischemic injury. Likewise, in in vivo experiments using a mouse model of hindlimb ischemia, the AP encapsulating the angiogenic cocktail effectively restored blood flow following an ischemic insult, promoting muscle regeneration and preventing limb loss. With its simplicity and rapid processability, user-friendly applicability, physical tunability, and the ability to efficiently load and control the delivery of angiogenic factors, the AP holds great promise as a therapeutic means for treating patients with ischemic diseases.

Self-assembling peptide RADA16: a promising scaffold for tissue engineering and regenerative medicine

RADA16 is a peptide-based biomaterial whose acidic aqueous solution spontaneously forms an extracellular matrix-like 3D structure within seconds upon contact with physiological pH body fluids. Meanwhile, its good biocompatibility, low immunogenicity, nontoxic degradation products and ease of modification make it an ideal scaffold for tissue engineering. RADA16 is a good delivery vehicle for cells, drugs and factors. Its shear thinning and thixotropic properties allow it to fill tissue voids by injection and not to swell. However, the weaker mechanical properties and poor hydrophilicity are troubling limitations of RADA16. To compensate for this limitation, various functional groups and polymers have been designed to modify RADA16, thus contributing to its scope and progress in the field of tissue engineering.

Spinal cord injury: molecular mechanisms and therapeutic interventions

Spinal cord injury (SCI) remains a severe condition with an extremely high disability rate. The challenges of SCI repair include its complex pathological mechanisms and the difficulties of neural regeneration in the central nervous system. In the past few decades, researchers have attempted to completely elucidate the pathological mechanism of SCI and identify effective strategies to promote axon regeneration and neural circuit remodeling, but the results have not been ideal. Recently, new pathological mechanisms of SCI, especially the interactions between immune and neural cell responses, have been revealed by single-cell sequencing and spatial transcriptome analysis. With the development of bioactive materials and stem cells, more attention has been focused on forming intermediate neural networks to promote neural regeneration and neural circuit reconstruction than on promoting axonal regeneration in the corticospinal tract. Furthermore, technologies to control physical parameters such as electricity, magnetism and ultrasound have been constantly innovated and applied in neural cell fate regulation. Among these advanced novel strategies and technologies, stem cell therapy, biomaterial transplantation, and electromagnetic stimulation have entered into the stage of clinical trials, and some of them have already been applied in clinical treatment. In this review, we outline the overall epidemiology and pathophysiology of SCI, expound on the latest research progress related to neural regeneration and circuit reconstruction in detail, and propose future directions for SCI repair and clinical applications.

Engineered hydrogels for peripheral nerve repair

Peripheral nerve injury (PNI) is a complex disease that often appears in young adults. It is characterized by a high incidence, limited treatment options, and poor clinical outcomes. This disease not only causes dysfunction and psychological disorders in patients but also brings a heavy burden to the society. Currently, autologous nerve grafting is the gold standard in clinical treatment, but complications, such as the limited source of donor tissue and scar tissue formation, often further limit the therapeutic effect. Recently, a growing number of studies have used tissue-engineered materials to create a natural microenvironment similar to the nervous system and thus promote the regeneration of neural tissue and the recovery of impaired neural function with promising results. Hydrogels are often used as materials for the culture and differentiation of neurogenic cells due to their unique physical and chemical properties. Hydrogels can provide three-dimensional hydration networks that can be integrated into a variety of sizes and shapes to suit the morphology of neural tissues. In this review, we discuss the recent advances of engineered hydrogels for peripheral nerve repair and analyze the role of several different therapeutic strategies of hydrogels in PNI through the application characteristics of hydrogels in nerve tissue engineering (NTE). Furthermore, the prospects and challenges of the application of hydrogels in the treatment of PNI are also discussed.

Promoting angiogenesis and diabetic wound healing through delivery of protein transduction domain-BMP2 formulated nanoparticles with hydrogel

Decreased angiogenesis contributes to delayed wound healing in diabetic patients. Recombinant human bone morphogenetic protein-2 (rhBMP2) has also been demonstrated to promote angiogenesis. However, the short half-lives of soluble growth factors, including rhBMP2, limit their use in wound-healing applications. To address this limitation, we propose a novel delivery model using a protein transduction domain (PTD) formulated in a lipid nanoparticle (LNP). We aimed to determine whether a gelatin hydrogel dressing loaded with LNP-formulated PTD-BMP2 (LNP-PTD-BMP2) could enhance the angiogenic function of BMP2 and improve diabetic wound healing. In vitro, compared to the control and rhBMP2, LNP-PTD-BMP2 induced greater tube formation in human umbilical vein endothelial cells and increased the cell recruitment capacity of HaCaT cells. We inflicted large, full-thickness back skin wounds on streptozotocin-induced diabetic mice and applied gelatin hydrogel (GH) cross-linked by microbial transglutaminase containing rhBMP2, LNP-PTD-BMP2, or a control to these wounds. Wounds treated with LNP-PTD-BMP2-loaded GH exhibited enhanced wound closure, increased re-epithelialization rates, and higher collagen deposition than those with other treatments. Moreover, LNP-PTD-BMP2-loaded GH treatment resulted in more CD31- and α-SMA-positive cells, indicating greater neovascularization capacity than rhBMP2-loaded GH or GH treatments alone. Furthermore, in vivo near-infrared fluorescence revealed that LNP-PTD-BMP2 has a longer half-life than rhBMP2 and that BMP2 localizes around wounds. In conclusion, LNP-PTD-BMP2-loaded GH is a viable treatment option for diabetic wounds.

Implications of microglial heterogeneity in spinal cord injury progression and therapy

Microglia are widely distributed in the central nervous system (CNS), where they aid in the maintenance of neuronal function and perform key auxiliary roles in phagocytosis, neural repair, immunological control, and nutrition delivery. Microglia in the undamaged spinal cord is in a stable state and serve as immune monitors. In the event of spinal cord injury (SCI), severe changes in the microenvironment and glial scar formation lead to axonal regeneration failure. Microglia participates in a series of pathophysiological processes and behave both positive and negative consequences during this period. A deep understanding of the characteristics and functions of microglia can better identify therapeutic targets for SCI. Technological innovations such as single-cell RNA sequencing (Sc-RNAseq) have led to new advances in the study of microglia heterogeneity throughout the lifespan. Here,We review the updated studies searching for heterogeneity of microglia from the developmental and pathological state, survey the activity and function of microglia in SCI and explore the recent therapeutic strategies targeting microglia in the CNS injury.

Restoration of spinal cord injury: From endogenous repairing process to cellular therapy

Spinal cord injury (SCI) disrupts neurological pathways and impacts sensory, motor, and autonomic nerve function. There is no effective treatment for SCI currently. Numerous endogenous cells, including astrocytes, macrophages/microglia, and oligodendrocyte, are involved in the histological healing process following SCI. By interfering with cells during the SCI repair process, some advancements in the therapy of SCI have been realized. Nevertheless, the endogenous cell types engaged in SCI repair and the current difficulties these cells confront in the therapy of SCI are poorly defined, and the mechanisms underlying them are little understood. In order to better understand SCI and create new therapeutic strategies and enhance the clinical translation of SCI repair, we have comprehensively listed the endogenous cells involved in SCI repair and summarized the six most common mechanisms involved in SCI repair, including limiting the inflammatory response, protecting the spared spinal cord, enhancing myelination, facilitating neovascularization, producing neurotrophic factors, and differentiating into neural/colloidal cell lines.