Implantation of a functional TEMPO-hydrogel induces recovery from rat spinal cord transection through promoting nerve regeneration and protecting bladder tissue

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.

Hydrogels for Neural Regeneration: Exploring New Horizons

Nerve injury can significantly impair motor, sensory, and autonomic functions. Understanding nerve degeneration, particularly Wallerian degeneration, and the mechanisms of nerve regeneration is crucial for developing effective treatments. This manuscript reviews the use of advanced hydrogels that have been researched to enhance nerve regeneration. Hydrogels, due to their biocompatibility, tunable properties, and ability to create a supportive microenvironment, are being explored for their effectiveness in nerve repair. Various types of hydrogels, such as chitosan-, alginate-, collagen-, hyaluronic acid-, and peptide-based hydrogels, are discussed for their roles in promoting axonal growth, functional recovery, and myelination. Advanced formulations incorporating growth factors, bioactive molecules, and stem cells show significant promise in overcoming the limitations of traditional therapies. Despite these advancements, challenges in achieving robust and reliable nerve regeneration remain, necessitating ongoing research to optimize hydrogel-based interventions for neural regeneration.

Advancing Spinal Cord Injury Bioimaging and Repair with Multifunctional Gold Nanodots Tracking

High levels of reactive oxygen species (ROS) are known to play a critical role in the secondary cascade of spinal cord injury (SCI). The scavenging of ROS has emerged as a promising approach for alleviating acute SCI. Moreover, identifying the precise location of the SCI site remains challenging. Enhancing the visualization of the spinal cord and improving the ability to distinguish the lesion site are crucial for accurate and safe treatment. Therefore, there is an urgent clinical need to develop a biomaterial that integrates diagnosis and treatment for SCI. Herein, ultra-small-sized gold nanodots (AuNDs) were designed for dual-mode imaging-guided precision treatment of SCI. The designed AuNDs demonstrate two important functions. First, they effectively scavenge ROS, inhibit oxidative stress, reduce the infiltration of inflammatory cells, and prevent apoptosis. This leads to a significant improvement in SCI repair and promotes a functional recovery after injury. Second, leveraging their excellent dual-mode imaging capabilities, the AuNDs enable rapid and accurate identification of SCI sites. The high contrast observed between the injured and adjacent uninjured areas highlights the tremendous potential of AuNDs for SCI detection. Overall, by integrating ROS scavenging and dual-mode imaging in a single biomaterial, our work on functionalized AuNDs provides a promising strategy for the clinical diagnosis and treatment of SCI.

Design and synthesis of nano-biomaterials based on graphene and local delivery of cerebrolysin into the injured spinal cord of mice, promising neural restoration

Spinal cord injury (SCI) is an incurable and catastrophic health issue with no clinical solution. As part of cascade reactions, the inflammatory process and fibrous glial scar production aggravate the amount of lesion through a secondary damage mechanism, encouraging scientists from other disciplines to investigate new paths for solving this problem. Graphene oxide (GO) and its derivatives are among the most promising biomedical and nerve tissue regeneration materials due to their remarkable chemical, mechanical, and electrical properties. This paper designs and introduces a new GO-based nanomaterial to minimize inflammation and stimulate neurite regrowth. To improve biocompatibility, biodegradability, and cell proliferation, GO plates were modified with polyethylene glycol (PEG) and Au nanoparticles as neuroprotective and antibacterial agents, respectively. Preliminary biological investigations on bone marrow derived mesenchymal stem cells (BM-MSCs) with various concentrations of a graphenic nanocarrier indicated a lack of cell toxicity and an enhancement in BM-MSC proliferation of about 10% after 48 hours. Therapeutic nanostructures were used in the T10 segment of a mouse SCI model. The pathological and immunohistochemical data revealed that refilling tissue cavities, decreasing degeneration, and establishing neuroregeneration resulted in a considerable improvement of hind limb motor function. Furthermore, compared to the nanocomposite mixture alone, the intraspinal delivery of cerebrolysin (CRL) had a more satisfying impact on nerve regrowth, cystic cavity, hemorrhage avoidance, and motor function enhancement. This study demonstrates the potential of graphenic nanomaterials for SCI treatment and neuroregeneration applications.

Hydrogel and Nanomedicine-Based Multimodal Therapeutic Strategies for Spinal Cord Injury

Spinal cord injury (SCI) is a severe neurodegenerative disease caused by mechanical and biological factors, manifesting as a loss of motor and sensory functions. Inhibition of injury expansion and even reversal of injury in the acute damage stage of SCI are important strategies for treating this disease. Hydrogels and nanoparticle (NP)-based drugs are the most effective, widely studied, and clinically valuable therapeutic strategies in the field of repair and regeneration. Hydrogels are 3D flow structures that fill the pathological gaps in SCI and provide a microenvironment similar to that of the spinal cord extracellular matrix for nerve cell regeneration. NP-based drugs can easily penetrate the blood-spinal cord barrier, target SCI lesions, and are noninvasive. Hydrogels and NPs as drug carriers can be loaded with various drugs and biological therapeutic factors for slow release in SCI lesions. They help drugs function more efficiently by exerting anti-inflammatory, antioxidant, and nerve regeneration effects to promote the recovery of neurological function. In this review, the use of hydrogels and NPs as drug carriers and the role of both in the repair of SCI are discussed to provide a multimodal strategic reference for nerve repair and regeneration after SCI.

Research progress of hydrogels as delivery systems and scaffolds in the treatment of secondary spinal cord injury

Secondary spinal cord injury (SSCI) is the second stage of spinal cord injury (SCI) and involves vasculature derangement, immune response, inflammatory response, and glial scar formation. Bioactive additives, such as drugs and cells, have been widely used to inhibit the progression of secondary spinal cord injury. However, the delivery and long-term retention of these additives remain a problem to be solved. In recent years, hydrogels have attracted much attention as a popular delivery system for loading cells and drugs for secondary spinal cord injury therapy. After implantation into the site of spinal cord injury, hydrogels can deliver bioactive additives in situ and induce the unidirectional growth of nerve cells as scaffolds. In addition, physical and chemical methods can endow hydrogels with new functions. In this review, we summarize the current state of various hydrogel delivery systems for secondary spinal cord injury treatment. Moreover, functional modifications of these hydrogels for better therapeutic effects are also discussed to provide a comprehensive insight into the application of hydrogels in the treatment of secondary spinal cord injury.

Tissue Engineering in Neuroscience: Applications and Perspectives

Neurological disorders have always been a threat to human physical and mental health nowadays, which are closely related to the nonregeneration of neurons in the nervous system (NS). The damage to the NS is currently difficult to repair using conventional therapies, such as surgery and medication. Therefore, repairing the damaged NS has always been a vast challenge in the area of neurology. Tissue engineering (TE), which integrates the cell biology and materials science to reconstruct or repair organs and tissues, has widespread applications in bone, periodontal tissue defects, skin repairs, and corneal transplantation. Recently, tremendous advances have been made in TE regarding neuroscience. In this review, we summarize TE's recent progress in neuroscience, including pathological mechanisms of various neurological disorders, the concepts and classification of TE, and the most recent development of TE in neuroscience. Lastly, we prospect the future directions and unresolved problems of TE in neuroscience.

An antioxidative sophora exosome-encapsulated hydrogel promotes spinal cord repair by regulating oxidative stress microenvironment

Spinal cord injury (SCI) is a severe traumatic disease because of its complications and multi-organ dysfunction. After the injury, the disruption of microenvironment homeostasis in the lesion demolishes the surrounding healthy tissues via various pathways. The microenvironment regulation is beneficial for neural and functional recovery. Sustained release, cellular uptake, and long-term retention of therapeutic molecules at the impaired sites are important for continuous microenvironment improvement. In our study, a local-implantation system was constructed for SCI treatment by encapsulating exosomes derived from Flos Sophorae Immaturus (so-exos) in a polydopamine-modified hydrogel (pDA-Gel). So-exos are used as nanoscale natural vehicles of rutin, a flavonoid phytochemical that is effective in microenvironment improvement and nerve regeneration. Our study showed that the pDA-Gel-encapsulated so-exos allowed rapid improvement of the impaired motor function and alleviation of urination dysfunction by modulating the spinal inflammatory and oxidative conditions, thus illustrating a potential SCI treatment through a combinational delivery of so-exos.

A reactive oxygen species-responsive hydrogel encapsulated with bone marrow derived stem cells promotes repair and regeneration of spinal cord injury

Spinal cord injury (SCI) is an overwhelming and incurable disabling event accompanied by complicated inflammation-related pathological processes, such as excessive reactive oxygen species (ROS) produced by the infiltrated inflammatory immune cells and released to the extracellular microenvironment, leading to the widespread apoptosis of the neuron cells, glial and oligodendroctyes. In this study, a thioketal-containing and ROS-scavenging hydrogel was prepared for encapsulation of the bone marrow derived mesenchymal stem cells (BMSCs), which promoted the neurogenesis and axon regeneration by scavenging the overproduced ROS and re-building a regenerative microenvironment. The hydrogel could effectively encapsulate BMSCs, and played a remarkable neuroprotective role in vivo by reducing the production of endogenous ROS, attenuating ROS-mediated oxidative damage and downregulating the inflammatory cytokines such as interleukin-1 beta (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), resulting in a reduced cell apoptosis in the spinal cord tissue. The BMSCs-encapsulated ROS-scavenging hydrogel also reduced the scar formation, and improved the neurogenesis of the spinal cord tissue, and thus distinctly enhanced the motor functional recovery of SCI rats. Our work provides a combinational strategy against ROS-mediated oxidative stress, with potential applications not only in SCI, but also in other central nervous system diseases with similar pathological conditions.

Systematic Alignment Analysis of Neural Transplant Cells in Electrospun Nanofibre Scaffolds

Spinal cord injury is debilitating with functional loss often permanent due to a lack of neuro-regenerative or neuro-therapeutic strategies. A promising approach to enhance biological function is through implantation of tissue engineered constructs, to offer neural cell replacement and reconstruction of the functional neuro-architecture. A key goal is to achieve spatially targeted guidance of regenerating tissue across the lesion site to achieve an aligned tissue structure lost as a consequence of injury. Electrospun nanofibres mimic the nanoscale architecture of the spinal cord, can be readily aligned, functionalised with pro-regenerative molecules and incorporated into implantable matrices to provide topographical cues. Crucially, electrospun nanofibers are routinely manufactured at a scale required for clinical use. Although promising, few studies have tested whether electrospun nanofibres can guide targeted spatial growth of clinically relevant neural stem/precursor populations. The alignment fate of daughter cells (derived from the pre-aligned parent cells) has also received limited attention. Further, a standardised quantification methodology to correlate neural cell alignment with topographical cues is not available. We have adapted an image analysis technique to quantify nanofibre-induced alignment of neural cells. Using this method, we show that two key neural stem/precursor populations of clinical relevance (namely, neural stem cells (NSCs) and oligodendrocyte precursor cells), reproducibly orientate their growth to aligned, high-density electrospun nanofiber meshes, but not randomly distributed ones. Daughter populations derived from aligned NSCs (neurons and astrocytes) maintained their alignment following differentiation, but oligodendrocytes did not. Our data show that pre-aligned transplant populations can be used to generate complex, multicellular aligned-fibre constructs for neural implantation.

A tannic acid doped hydrogel with small extracellular vesicles derived from mesenchymal stem cells promotes spinal cord repair by regulating reactive oxygen species microenvironment

Spinal cord injury (SCI) is a serious disease of the central nervous system that is associated with a poor prognosis; furthermore, existing clinical treatments cannot restore nerve function in an effective manner. Inflammatory responses and the increased production of reactive oxygen species (ROS) in the microenvironment of the lesion are major obstacles that inhibit the recovery of SCI. Small extracellular vesicles (sEVs), derived from mesenchymal stem cells, are suitable options for cell-free therapy and have been shown to exert therapeutic effects in SCI, thus providing a potential strategy for microenvironment regulation. However, the effective retention, controlled release, and integration of small extracellular vesicles into injured spinal cord tissue are still a major challenge. Herein, we fabricated an N-acryloyl glycinamide/gelatin methacrylate/Laponite/Tannic acid (NAGA/GelMA/LPN/TA, NGL/T) hydrogel with sustainable sEV release (sEVs-NGL/T) to promote the recovery of motor function after SCI. The newly developed functional sEVs-NGL/T hydrogel exhibited excellent antioxidant properties in an H₂O₂-simulated peroxidative microenvironment in vitro. Implantation of the functional sEVs-NGL/T hydrogel in vivo could encapsulate sEVs, exhibiting efficient retention and the sustained release of sEVs, thereby synergistically inducing significant restoration of motor function and urinary tissue preservation. These positive effects can be attributed to the effective mitigation of the inflammatory and ROS microenvironment. Therefore, sEVs-NGL/T therapy provides a promising strategy for the sEV-based therapy in the treatment of SCI by comprehensively regulating the pathological microenvironment.

Implantation of adipose-derived mesenchymal stem cell sheets promotes axonal regeneration and restores bladder function after spinal cord injury

BACKGROUND

Cell-based therapy using adipose-derived mesenchymal stem cells (ADSCs) is a promising treatment strategy for neurogenic bladder (NB) associated with spinal cord injury (SCI). However, therapeutic efficacy is low because of inefficient cell delivery. Cell sheets improve the efficacy of cell transplantation. Therefore, this study was conducted to investigate the therapeutic efficacy of transplanting ADSC sheets into an SCI rat model and focused on the function and pathological changes of the bladder.

METHODS

ADSC sheets were prepared from adipose tissue of Sprague-Dawley (SD) rats using temperature-responsive cell culture dishes. Adult female SD rats were subjected to SCI by transection at the T10 level and administered ADSC sheets or gelatin sponge (the control group). Four and 8 weeks later, in vivo cystometrograms were obtained for voiding function assessment. Rats were sacrificed and the expression of various markers was analyzed in spinal and bladder tissues.

RESULTS

The number of β-tubulin III-positive axons in the ADSC sheet transplantation group was higher than that in the control group. Conversely, expression of glial fibrillary acidic protein in the ADSC sheet transplantation group was lower than that in the control group. Cystometry showed impairment of the voiding function after SCI, which was improved after ADSC sheet transplantation with increased high-frequency oscillation activity. Furthermore, ADSC sheet transplantation prevented disruption of the bladder urothelium in SCI rats, thereby maintaining the intact barrier. Compared with fibrosis of the bladder wall in the control group, the ADSC sheet transplantation group had normal morphology of the bladder wall and reduced tissue fibrosis as shown by downregulation of type 1 collagen. ADSC sheet transplantation also resulted in strong upregulation of contractile smooth muscle cell (SMC) markers (α-smooth muscle actin and smoothelin) and downregulation of synthetic SMC markers (MYH10 and RBP1).

CONCLUSION

ADSC sheet transplantation significantly improved voiding function recovery in rats after SCI. ADSC sheet transplantation is a promising cell delivery and treatment option for NB related to SCI.

Epigallocatechin-3-gallate selenium nanoparticles for neuroprotection by scavenging reactive oxygen species and reducing inflammation

Purpose: Spinal cord injury (SCI) is a severely crippling injury. Scavenging reactive oxygen species (ROS) and suppressing inflammation to ameliorate secondary injury using biomaterials has turned into a promising strategy for SCI recuperation. Herein, epigallocatechin-3-gallate selenium nanoparticles (EGCG-Se NP) that scavenge ROS and attenuate inflammation were used for neuroprotection in SCI.

Methods: EGCG-Se NP were arranged using a simple redox framework. The size, morphology, and chemical structure of the EGCG-Se NP were characterized. The protective effect of EGCG-Se NP for neuroprotection was examined in cell culture and in an SCI rat model.

Results: EGCG-Se NP could promptly scavenge excess ROS and safeguard PC12 cells against H₂O₂-induced oxidative harm in vitro. After intravenous delivery in SCI rats, EGCG-Se NP significantly improved locomotor capacity and diminished the injury region by safeguarding neurons and myelin sheaths. Component studies showed that the main restorative impact of EGCG-Se NP was due to their ROS-scavenging and anti-inflammatory properties.

Conclusion: This study showed the superior neuroprotective effect of EGCG-Se NP through ROS sequestration and anti-inflammatory capabilities. EGCG-Se NP could be a promising and effective treatment for SCI.

Hydrogels in Spinal Cord Injury Repair: A Review

Traffic accidents and falling objects are responsible for most spinal cord injuries (SCIs). SCI is characterized by high disability and tends to occur among the young, seriously affecting patients' lives and quality of life. The key aims of repairing SCI include preventing secondary nerve injury, inhibiting glial scarring and inflammatory response, and promoting nerve regeneration. Hydrogels have good biocompatibility and degradability, low immunogenicity, and easy-to-adjust mechanical properties. While providing structural scaffolds for tissues, hydrogels can also be used as slow-release carriers in neural tissue engineering to promote cell proliferation, migration, and differentiation, as well as accelerate the repair of damaged tissue. This review discusses the characteristics of hydrogels and their advantages as delivery vehicles, as well as expounds on the progress made in hydrogel therapy (alone or combined with cells and molecules) to repair SCI. In addition, we discuss the prospects of hydrogels in clinical research and provide new ideas for the treatment of SCI.

Photo-induced adhesive carboxymethyl chitosan-based hydrogels with antibacterial and antioxidant properties for accelerating wound healing

Designing adhesive hydrogel wound dressings with inherent antibacterial and antioxidant properties is desirable to treat cutaneous full-thickness injuries in clinical care. Herein, a series of photo-induced Schiff base crosslinking-based adhesive hydrogels with promising traits are designed and prepared through Diels-Alder (DA) reactions between functional groups-grafted carboxymethyl chitosan (CMCS) and a photo-responsive polyethylene glycol (PEG) crosslinker. The quaternary ammonium and phenol groups in modified CMCS endows hydrogels excellent antibacterial and antioxidant properties. Upon UV (365 nm) irradiation, the generated o-nitrosobenzaldehyde from the photo-isomerization of o-nitrobenzyl in PEG derivative can subsequently crosslink with amino groups on tissue interfaces via Schiff base, endowing the hydrogel with well adhesiveness. Additionally, the hydrogel exhibits good BSA adsorption capacity, cytocompatibility and hemostatic property. The in vivo full-thickness skin defect study on mice indicates that the multi-functional hydrogel with considerable collagen deposition and vascularization capacities can be an effective and promising adhesive dressing for improving wound healing.

Nerve Growth Factor-Laden Anisotropic Silk Nanofiber Hydrogels to Regulate Neuronal/Astroglial Differentiation for Scarless Spinal Cord Repair

Scarless spinal cord regeneration remains a challenge due to the complicated microenvironment at lesion sites. In this study, the nerve growth factor (NGF) was immobilized in silk protein nanofiber hydrogels with hierarchical anisotropic microstructures to fabricate bioactive systems that provide multiple physical and biological cues to address spinal cord injury (SCI). The NGF maintained bioactivity inside the hydrogels and regulated the neuronal/astroglial differentiation of neural stem cells. The aligned microstructures facilitated the migration and orientation of cells, which further stimulated angiogenesis and neuron extensions both in vitro and in vivo. In a severe rat long-span hemisection SCI model, these hydrogel matrices reduced scar formation and achieved the scarless repair of the spinal cord and effective recovery of motor functions. Histological analysis confirmed the directional regenerated neuronal tissues, with a similar morphology to that of the normal spinal cord. The in vitro and in vivo results showed promising utility for these NGF-laden silk hydrogels for spinal cord regeneration while also demonstrating the feasibility of cell-free bioactive matrices with multiple cues to regulate endogenous cell responses.

Minocycline-Loaded Poly(α-Lipoic Acid)-Methylprednisolone Prodrug Nanoparticles for the Combined Anti-Inflammatory Treatment of Spinal Cord Injury

Purpose

Traumatic spinal cord injury (TSCI) induces a powerful inflammatory response that can significantly exacerbate the extent and severity of neural damage (termed as “secondary injury”). Thus, the suppression of inflammation is crucial for reducing neurological dysfunction following TSCI. However, the conventional anti-inflammatory drugs show limited efficacy because of poor penetration and release kinetics at the injury site. This study describes the design, synthesis, release kinetics, biosafety, and preclinical efficacy of minocycline (MC)-loaded poly(α-lipoic acid)–methylprednisolone (PαLA-MP) prodrug nanoparticles (NPs) for the combined anti-inflammatory treatment of TSCI.

Methods

NPs were produced by conjugating MP to PαLA and then loading MC. The NP structure was confirmed through ¹H nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectroscopy, ultraviolet–visible absorption spectroscopy, gel permeation chromatography, dynamic light scattering, and transmission electron microscopy. Drug-loading content and efficacy were measured using high-performance liquid chromatography (HPLC) or ¹H NMR and release kinetics through HPLC. Biosafety was examined using the MTT assay, cell penetration efficiency using confocal microscopy, and flow cytometry using Cyanine5 (Cy5)-labeled MC-PαLA-MP NPs, effects on injury-induced pro-inflammatory cytokine release using enzyme-linked immunosorbent assays and immunofluorescence, and treatment efficacy by measuring motor recovery in a rat model of TSCI.

Results

The MC-PαLA-MP NPs exhibited high biocompatibility and released 81% MC and 54% MP within 24 h under TSCI-like conditions, effectively reducing 40% of pro-inflammatory cytokine release both in cultures and injured rat spinal cord tissues. Systemic injection increased the Basso, Beattie, Bresnahan score of TSCI rats from 2.33 ± 0.52 to 8.83 ± 1.83 in 8 weeks, providing effective neuroprotection and enhanced exercise recovery in the TSCI rats.

Conclusion

The MC-PαLA-MP NPs can mitigate secondary inflammation and preserve motor function following experimental TSCI, which suggests their potential for clinical application.

Supramolecular Adhesive Hydrogels for Tissue Engineering Applications

Tissue engineering is a promising and revolutionary strategy to treat patients who suffer the loss or failure of an organ or tissue, with the aim to restore the dysfunctional tissues and enhance life expectancy. Supramolecular adhesive hydrogels are emerging as appealing materials for tissue engineering applications owing to their favorable attributes such as tailorable structure, inherent flexibility, excellent biocompatibility, near-physiological environment, dynamic mechanical strength, and particularly attractive self-adhesiveness. In this review, the key design principles and various supramolecular strategies to construct adhesive hydrogels are comprehensively summarized. Thereafter, the recent research progress regarding their tissue engineering applications, including primarily dermal tissue repair, muscle tissue repair, bone tissue repair, neural tissue repair, vascular tissue repair, oral tissue repair, corneal tissue repair, cardiac tissue repair, fetal membrane repair, hepatic tissue repair, and gastric tissue repair, is systematically highlighted. Finally, the scientific challenges and the remaining opportunities are underlined to show a full picture of the supramolecular adhesive hydrogels. This review is expected to offer comparative views and critical insights to inspire more advanced studies on supramolecular adhesive hydrogels and pave the way for different fields even beyond tissue engineering applications.

Advances in Modified Hyaluronic Acid-Based Hydrogels for Skin Wound Healing

Hyaluronic acid (HA) is a natural linear anionic polysaccharide with many unique characteristics such as excellent biocompatibility and biodegradability, native biofunctionality, hydrophilicity, and non-immunoreactivity. HA plays crucial roles in numerous...

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.

Facile preparation of polysaccharides-based adhesive hydrogel with antibacterial and antioxidant properties for promoting wound healing

Infection, oxidative stress, and inflammation are the major obstacles to cutaneous wound healing. Designing adhesive wound dressings with inherent antibacterial and antioxidant properties are highly desirable. Herein, a series of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-doped multifunctional hydrogels were facilely prepared by combining quaternized carboxymethyl chitosan (QCMCS) and oxidized hyaluronate (HA-CHO). Schiff base crosslinking between amino groups in QCMCS and aldehyde groups in HA-CHO not only constructed hydrogel networks but also endowed hydrogels with good self-healing property. The hydrogel exhibited adjustable tissue adhesiveness, degradability, and rheological properties by changing the content of TEMPO groups. Moreover, the hydrogels presented excellent inherent antibacterial and antioxidant properties, along with the porous structures, swelling ability, good cytocompatibility and low hemolysis ratio, which are beneficial to promoting wound healing process. Overall, the TEMPO hydrogel showed excellent therapeutic effect in mice skin defect model, giving the hydrogel with fitness as wound dressings for treating skin wounds.

Cooperative Photocatalysis with 4-Amino-TEMPO for Selective Aerobic Oxidation of Amines over TiO2 Nanotubes

Attaching π-conjugated molecules onto TiO₂ can form surface complexes that could capture visible light. However, to make these TiO₂ surface complexes durable, integrating 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) or its analogues as a redox mediator with photocatalysis is the key to constructing selective chemical transformations. Herein, sodium 6,7-dihydroxynaphthalene-2-sulfonate (DHNS) was obtained by extending the π-conjugated system of catechol by adding a benzene ring and a substituent sodium sulfonate (-SO₃ ^- Na⁺ ). The DHNS-TiO₂ showed the best photocatalytic activity towards the blue light-induced selective aerobic oxidation of benzylamine. Compared to TEMPO, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) could rise above 70% in conversion of benzylamine over the DHNS-TiO₂ photocatalyst. Eventually, a wide range of amines could be selectively oxidized into imines with atmospheric O₂ by cooperative photocatalysis of DHNS-TiO₂ with 4-amino-TEMPO. Notably, superoxide (O₂ ^•- ) is crucial in coupling the photocatalytic cycle of DHNS-TiO₂ and the redox cycle of 4-amino-TEMPO. This work underscores the design of surface ligands for semiconductors and the selection of a redox mediator in visible light photocatalysis for selective chemical transformations.

Research advances of biomaterials-based microenvironment-regulation therapies for repair and regeneration of spinal cord injury

Traumatic spinal cord injury (SCI) usually results in restricted behaviour recovery and even life-changing paralysis, accompanied with numerous complications. Pathologically, the initial injuries trigger a series of secondary injuries, leading to an expansion of lesion site, a mass of neuron loss, and eventual failure of endogenous axon regeneration. As the advances rapidly spring up in regenerative medicine and tissue engineering biomaterials, regulation of these secondary injuries becomes possible, shedding a light on normal functional restoration. The successful tissue regeneration lies in proper regulation of the inflammatory microenvironment, including the inflammatory immune cells and inflammatory factors that lead to oxidative stress, inhibitory glial scar and neuroexcitatory toxicity. Specifically, the approaches based on microenvironment-regulating biomaterials have shown great promise in the repair and regeneration of SCI. In this review, the pathological inflammatory microenvironments of SCI are discussed, followed by the introduction of microenvironment-regulating biomaterials in terms of their impressive therapeutic effect in attenuation of secondary inflammation and promotion of axon regrowth. With the emphasis on regulating secondary events, the biomaterials for SCI treatment will become promising for clinical applications.

Preparation and Application of Quaternized Chitosan- and AgNPs-Base Synergistic Antibacterial Hydrogel for Burn Wound Healing

Infection is the major reason that people die from burns; however, traditional medical dressings such as gauze cannot restrain bacterial growth and enhance the healing process. Herein, an organic- and inorganic-base hydrogel with antibacterial activities was designed and prepared to treat burn wounds. Oxidized dextran (ODex) and adipic dihydrazide grafted hyaluronic acid (HA-ADH) were prepared, mixed with quaternized chitosan (HACC) and silver nanoparticles to fabricate Ag@ODex/HA-ADH/HACC hydrogel. The hydrogel, composed of nature biomaterials, has a good cytocompatibility and biodegradability. Moreover, the hydrogel has an excellent antibacterial ability and presents fast healing for burn wounds compared with commercial Ag dressings. The Ag@ODex/HA-ADH/HACC hydrogel will be a promising wound dressing to repair burn wounds and will significantly decrease the possibility of bacterial infection.

The design criteria and therapeutic strategy of functional scaffolds for spinal cord injury repair

Spinal cord injury (SCI) remains a therapeutic challenge in clinic. Current drug and cell therapeutics have obtained significant efficacy but are still in the early stages for complete neural and functional recovery. In the past few decades, functional scaffolds (FSs) have been rapidly developed to bridge the lesion and provide a framework for tissue regeneration in SCI repair. Moreover, a FS can act as an adjuvant for locally delivering drugs in the lesion with a designed drug release profile, and supplying a biomimetic environment for implanted cells. In this review, the design criteria of FSs for SCI treatment are summarized according to their biocompatibility, mechanical properties, morphology, architecture, and biodegradability. Subsequently, FSs designed for SCI repair in the scope of drug delivery, cell implantation and combination therapy are introduced, respectively. And how a FS promotes their therapeutic efficacy is analyzed. Finally, the challenges, perspectives, and potential of FSs for SCI treatment are discussed. Hopefully, this review may inspire the future development of potent FSs to facilitate SCI repair in clinic.

Biomaterials reinforced MSCs transplantation for spinal cord injury repair

Due to the complex pathophysiological mechanism, spinal cord injury (SCI) has become one of the most intractable central nervous system (CNS) diseases to therapy. Stem cell transplantation, mesenchymal stem cells (MSCs) particularly, appeals to more and more attention along with the encouraging therapeutic results for the functional regeneration of SCI. However, traditional cell transplantation strategies have some limitations, including the unsatisfying survival rate of MSCs and their random diffusion from the injection site to ambient tissues. The application of biomaterials in tissue engineering provides a new horizon. Biomaterials can not only confine MSCs in the injured lesions with higher cell viability, but also promote their therapeutic efficacy. This review summarizes the strategies and advantages of biomaterials reinforced MSCs transplantation to treat SCI in recent years, which are clarified in the light of various therapeutic effects in pathophysiological aspects of SCI.

Click chemistry-based biopolymeric hydrogels for regenerative medicine

Click chemistry is not a single specific reaction, but describes ways of generating products which emulate examples in nature. Click reactions occur in one pot, are not disturbed by water, generate minimal and inoffensive byproducts, and are characterized by a high thermodynamic driving force, driving the reaction quickly and irreversibly towards a high yield of a single reaction product. As a result, over the past 15 years it has become a very useful bio-orthogonal method for the preparation of chemical cross-linked biopolymer-based hydrogel, in the presence of e.g. growth factors and live cells, or in-vivo. Biopolymers are renewable and non-toxic, providing a myriad of potential backbone toolboxes for hydrogel design. The goal of this review is to summarize recent advances in the development of click chemistry-based biopolymeric hydrogels, and their applications in regenerative medicine. In particular, various click chemistry approaches, including copper-catalyzed azide-alkyne cycloaddition reactions, copper-free click reactions (e.g. the Diels-Alder reactions, the strain-promoted azide-alkyne cycloaddition reactions, the radical mediated thiol-ene reactions, and the oxime-forming reactions), and pseudo-click reactions (e.g. the thiol-Michael addition reactions and the Schiff base reactions) are highlighted in the first section. In addition, numerous biopolymers, including proteins (e.g. collagen, gelatin, silk, and mucin), polysaccharides (e.g. hyaluronic acid, alginate, dextran, and chitosan) and polynucleotides (e.g. deoxyribonucleic acid), are discussed. Finally, we discuss biopolymeric hydrogels, cross-linked by click chemistry, intended for the regeneration of skin, bone, spinal cord, cartilage, and cornea. This article provides new insights for readers in terms of the design of regenerative medicine, and the use of biopolymeric hydrogels based on click chemistry reactions.

Injectable Scaffold-Systems for the Regeneration of Spinal Cord: Advances of the Past Decade

Nowadays, whenever is possible and as an alternative to open spine surgery, minimally invasive procedures are preferred to treat spinal cord injuries (SCI), with percutaneous injections or small incisions, that are faster, less traumatic, and require less recovery time. Injectable repair systems are based on materials that can be injected in the lesion site, can eventually be loaded with drugs or even cells, and act as scaffolds for the lesion repair. The review analyzes papers written from 2010 onward on injectable materials/systems used/proposed for the regenerative and combinatorial therapies of SCI and discusses the in vivo models that have been used to validate them.

Systemic Administration of Fibroblast Growth Factor 21 Improves the Recovery of Spinal Cord Injury (SCI) in Rats and Attenuates SCI-Induced Autophagy

Protecting the death of nerve cells is an essential tactic for spinal cord injury (SCI) repair. Recent studies show that nerve growth factors can reduce the death of nerve cells and promote the healing of nerve injury. To investigate the conducive effect of fibroblast growth factor 21 (FGF21) on SCI repair. FGF21 proteins were systemically delivered into rat model of SCI via tail vein injection. We found that administration of FGF21 significantly promoted the functional recovery of SCI as assessed by BBB scale and inclined plane test, and attenuated cell death in the injured area by histopathological examination with Nissl staining. This was accompanied with increased expression of NeuN, GAP43 and NF200, and deceased expression of GFAP. Interestingly, FGF21 was found to attenuate the elevated expression level of the autophagy marker LC3-II (microtubules associated protein 1 light chain 3-II) induced by SCI in a dose-dependent manner. These data show that FGF21 promotes the functional recovery of SCI via restraining injury-induced cell autophagy, suggesting that systemic administration of FGF21 could have a therapeutic potential for SCI repair.

Selenium-Doped Carbon Quantum Dots Efficiently Ameliorate Secondary Spinal Cord Injury via Scavenging Reactive Oxygen Species

Background

The excess production of reactive oxygen species (ROS) after traumatic spinal cord injury (TSCI) has been identified as a leading cause of secondary injury, which can significantly exacerbate acute damage in the injured spinal cord. Thus, scavenging of ROS has emerged as an effective route to ameliorate secondary spinal cord injury.

Purpose

Selenium-doped carbon quantum dots (Se-CQDs) with the ability to scavenge reactive oxygen species were prepared and used for efficiently ameliorating secondary injury in TSCI.

Methods

Water-soluble Se-CQDs were easily synthesized via hydrothermal treatment of l-selenocystine. The chemical structure, size, and morphology of the Se-CQDs were characterized in detail. The biocompatibility and protective effects of the Se-CQDs against H₂O₂-induced oxidative damage were investigated in vitro. Moreover, the behavioral test, bladder function, histological observation, Western blot were used to investigate the neuroprotective effect of Se-CQDs in a rat model of contusion TSCI.

Results

The obtained Se-CQDs exhibited good biocompatibility and remarkable protective effect against H₂O₂-induced oxidative damage in astrocytes and PC12 cells. Moreover, Se-CQDs displayed marked anti-inflammatory and anti-apoptotic activities, which thereby reduced the formation of glial scars and increased the survival of neurons with unscathed myelin sheaths in vivo. As a result, Se-CQDs were capable of largely improving locomotor function of rats with TSCI.

Conclusion

This study suggests that Se-CQDs can be used as a promising therapeutic platform for ameliorating secondary injury in TSCI.

Extracellular Matrix Mimics Using Hyaluronan-Based Biomaterials

Hyaluronan (HA) is a critical element of the extracellular matrix (ECM). The regulated synthesis and degradation of HA modulates the ECM chemical and physical properties that, in turn, influence cellular behavior. HA triggers signaling pathways associated with the adhesion, proliferation, migration, and differentiation of cells, mediated by its interaction with specific cellular receptors or by tuning the mechanical properties of the ECM. This review summarizes the recent advances on strategies used to mimic the HA present in the ECM to study healthy or pathological cellular behavior. This includes the development of HA-based 2D and 3D in vitro tissue models for the seeding and encapsulation of cells, respectively, and HA particles as carriers for the targeted delivery of therapeutic agents.