Thermosensitive bFGF-Modified Hydrogel with Dental Pulp Stem Cells on Neuroinflammation of Spinal Cord Injury

Engineered exosome therapeutics for neurodegenerative diseases

An increase in life expectancy comes with a higher risk for age-related neurological and cognitive dysfunctions. Given the psycho-socioeconomic burden due to unhealthy aging in the coming decades, the United Nations has declared 2021-2030 as a decade of healthy aging. In this line, multipotent mesenchymal stromal cell-based therapeutics received special interest from the research community. Based on decades of research on cell therapy, a consensus has emerged that the therapeutic effects of cell therapy are due to the paracrine mechanisms rather than cell replacement. Exosomes, a constituent of the secretome, are nano-sized vesicles that have been a focus of intense research in recent years as a possible therapeutic agent or as a cargo to deliver drugs of interest into the central nervous system to induce neurogenesis, reduce neuroinflammation, confer neuroregeneration/neuroprotection, and improve cognitive and motor functions. In this review, we have discussed the neuroprotective properties of exosomes derived from adult mesenchymal stem cells, with a special focus on the role of exosomal miRNAs. We also reviewed various strategies to improve exosome production and their content for better therapeutic effects. Further, we discussed the utilization of ectomesenchymal stem cells like dental pulp stem cells and their exosomes in treating neurodegenerative diseases.

Dental pulp stem cells regenerate neural tissue in degenerative disorders and stroke rehabilitation: A scope systematic review

Background

Dental Pulp Stem Cells (DPSCs) possess a remarkable ability for tissue differentiation, making them highly efficient in tissue regeneration and inflammation regulation. This systematic study proposes to find an answer to the question, "Do DPSCs have the ability to regenerate and rehabilitate nerve tissue?"

Methods

This systematic review was conducted based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria, and the principle of non-bias was respected. All the articles from 2014 to 2024 were extracted from the Web of Science, PubMed, and Scopus databases. This study extracted the antigens and pro-inflammatory factors associated with DPSCs' involvement and how they affect the CNS's neural tissue regeneration.

Results

Two persons of researchers searched the database. After screening the full texts, they included 11 articles in their study. DPSCs control the following antigens: CD73, CD34, CD90, CD105, CD14, CD45, CD19Oct-4, CD73, CD31, CD34CD29CD44. Even though hematopoietic markers did not change much, OCT-4 and CD-73 were increased by DPSCs. DPSC-derived exosomes suppressed the expression of IL-6, IL-1β, TNF-α, and TGF, key mediators of nerve tissue inflammation. Additionally, DPSCs show high Vascular Endothelial Growth Factor (VEGF) expression in mice brain tissue cultures. DPSCs reduce Subarachnoid Hemorrhage (SAH), a condition in which blood collects in the subarachnoid space and causes ischemia.

Discussion

DPSCs showed the ability to regenerate nerve tissue and brain ganglia, stimulating angiogenesis by expressing cell markers and controlling growth factors in mice, and high therapeutic potential in neurodegenerative disorders. The present study invites further research in neurological disorders, specifically strokes, to prescribe these stem cells to the human population.

Combinatorial intervention with dental pulp stem cells and sulfasalazine in a rat model of ulcerative colitis

BACKGROUND

Ulcerative colitis is an inflammatory bowel disease (IBD) that involves inflammation of the colon lining and rectum. Although a definitive cure for IBD has not been identified, various therapeutic approaches have been proposed to mitigate the symptomatic presentation of this disease, primarily focusing on reducing inflammation. The aim of the present study was to evaluate the therapeutic potential of combining dental pulp stem cells (DPSCs) with sulfasalazine in an acetic acid-induced ulcerative colitis rat model and to assess the impact of this combination on the suppression of inflammatory cytokines and the regulation of oxidative stress in vivo.

METHODS

Ulcerative colitis was induced in rats through transrectal administration of 3% acetic acid. The therapeutic effect of combining DPSCs and sulfasalazine on UC was evaluated by measuring the colonic weight/length ratio and edema markers; performing histopathological investigations of colon tissue; performing immunohistochemical staining for NF-κB-P65 and IL-1β; and evaluating oxidative stress and antioxidant indices via ELISA. Moreover, the proinflammatory markers NF-κB-P65, TNF-α and TLR-4 were assessed in colon tissue via ELISA. Furthermore, qRT‒PCR was used to estimate the expression levels of the TLR-4, NF-κB-P65, and MYD88 genes in colon tissue.

RESULTS

The investigated macroscopic and microscopic signs of inflammation were markedly improved after the combined administration of sulfasalazine and DPSCs, where a noticeable improvement in histological structure, with an intact mucosal epithelium and mild inflammatory infiltration in the mucosa and submucosa, with slight hemorrhage. The administration of either DPSCs or sulfasalazine, either individually or in combination, significantly reduced ROS levels and significantly increased XOD activity. The immunohistochemical results demonstrated that the combined administration of DPSCs and sulfasalazine attenuated NFκB-p65 and IL-1β expression. Finally, the combined administration of DPSCs and sulfasalazine significantly downregulated MyD88, NF-κB and TLR4 gene expression.

CONCLUSIONS

Cotreatment with DPSCs and sulfasalazine had synergistic effects on ulcerative colitis, and these effects were relieved.

Biomaterial strategies for regulating the neuroinflammatory response

Injury and disease in the central nervous system (CNS) can result in a dysregulated inflammatory environment that inhibits the repair of functional tissue. Biomaterials present a promising approach to tackle this complex inhibitory environment and modulate the mechanisms involved in neuroinflammation to halt the progression of secondary injury and promote the repair of functional tissue. In this review, we will cover recent advances in biomaterial strategies, including nanoparticles, hydrogels, implantable scaffolds, and neural probe coatings, that have been used to modulate the innate immune response to injury and disease within the CNS. The stages of inflammation following CNS injury and the main inflammatory contributors involved in common neurodegenerative diseases will be discussed, as understanding the inflammatory response to injury and disease is critical for identifying therapeutic targets and designing effective biomaterial-based treatment strategies. Biomaterials and novel composites will then be discussed with an emphasis on strategies that deliver immunomodulatory agents or utilize cell-material interactions to modulate inflammation and promote functional tissue repair. We will explore the application of these biomaterial-based strategies in the context of nanoparticle- and hydrogel-mediated delivery of small molecule drugs and therapeutic proteins to inflamed nervous tissue, implantation of hydrogels and scaffolds to modulate immune cell behavior and guide axon elongation, and neural probe coatings to mitigate glial scarring and enhance signaling at the tissue-device interface. Finally, we will present a future outlook on the growing role of biomaterial-based strategies for immunomodulation in regenerative medicine and neuroengineering applications in the CNS.

Molars to Medicine: A Focused Review on the Pre-Clinical Investigation and Treatment of Secondary Degeneration following Spinal Cord Injury Using Dental Stem Cells

Spinal cord injury (SCI) can result in the permanent loss of mobility, sensation, and autonomic function. Secondary degeneration after SCI both initiates and propagates a hostile microenvironment that is resistant to natural repair mechanisms. Consequently, exogenous stem cells have been investigated as a potential therapy for repairing and recovering damaged cells after SCI and other CNS disorders. This focused review highlights the contributions of mesenchymal (MSCs) and dental stem cells (DSCs) in attenuating various secondary injury sequelae through paracrine and cell-to-cell communication mechanisms following SCI and other types of neurotrauma. These mechanistic events include vascular dysfunction, oxidative stress, excitotoxicity, apoptosis and cell loss, neuroinflammation, and structural deficits. The review of studies that directly compare MSC and DSC capabilities also reveals the superior capabilities of DSC in reducing the effects of secondary injury and promoting a favorable microenvironment conducive to repair and regeneration. This review concludes with a discussion of the current limitations and proposes improvements in the future assessment of stem cell therapy through the reporting of the effects of DSC viability and DSC efficacy in attenuating secondary damage after SCI.

Conditioned medium from human dental pulp stem cells treats spinal cord injury by inhibiting microglial pyroptosis

Human dental pulp stem cell transplantation has been shown to be an effective therapeutic strategy for spinal cord injury. However, whether the human dental pulp stem cell secretome can contribute to functional recovery after spinal cord injury remains unclear. In the present study, we established a rat model of spinal cord injury based on impact injury from a dropped weight and then intraperitoneally injected the rats with conditioned medium from human dental pulp stem cells. We found that the conditioned medium effectively promoted the recovery of sensory and motor functions in rats with spinal cord injury, decreased expression of the microglial pyroptosis markers NLRP3, GSDMD, caspase-1, and interleukin-1β, promoted axonal and myelin regeneration, and inhibited the formation of glial scars. In addition, in a lipopolysaccharide-induced BV2 microglia model, conditioned medium from human dental pulp stem cells protected cells from pyroptosis by inhibiting the NLRP3/caspase-1/interleukin-1β pathway. These results indicate that conditioned medium from human dental pulp stem cells can reduce microglial pyroptosis by inhibiting the NLRP3/caspase-1/interleukin-1β pathway, thereby promoting the recovery of neurological function after spinal cord injury. Therefore, conditioned medium from human dental pulp stem cells may become an alternative therapy for spinal cord injury.

Hydrogel-based immunoregulation of macrophages for tissue repair and regeneration

The rational design of hydrogel materials to modulate the immune microenvironment has emerged as a pivotal approach in expediting tissue repair and regeneration. Within the immune microenvironment, an array of immune cells exists, with macrophages gaining prominence in the field of tissue repair and regeneration due to their roles in cytokine regulation to promote regeneration, maintain tissue homeostasis, and facilitate repair. Macrophages can be categorized into two types: classically activated M1 (pro-inflammatory) and alternatively activated M2 (anti-inflammatory and pro-repair). By regulating the physical and chemical properties of hydrogels, the phenotypic transformation and cell behavior of macrophages can be effectively controlled, thereby promoting tissue regeneration and repair. A full understanding of the interaction between hydrogels and macrophages can provide new ideas and methods for future tissue engineering and clinical treatment. Therefore, this paper reviews the effects of hydrogel components, hardness, pore size, and surface morphology on cell behaviors such as macrophage proliferation, migration, and phenotypic polarization, and explores the application of hydrogels based on macrophage immune regulation in skin, bone, cartilage, and nerve tissue repair. Finally, the challenges and future prospects of macrophage-based immunomodulatory hydrogels are discussed.

The potential therapeutic roles of dental pulp stem cells in spinal cord injury

Spinal cord injury (SCI) can lead to serious functional disorders, which have serious impacts on patients and society. The current traditional treatments of SCI are not effective the injured spinal cord is difficult to repair and regenerate. In recent years, stem cell transplantation for the treatment of SCI has been a hot research topic. Dental pulp stem cells have strong abilities of self-renewal and multi-directional differentiation, and have been applied for tissue engineering and regenerative medicine. And dental pulp stem cells have certain advantages in neuro-regenetation, bringing new hope to biotherapy for SCI. This article reviews the characteristics of dental pulp stem cells and their research progress in the treatment of SCI.

Local Spinal Cord Injury Treatment Using a Dental Pulp Stem Cell Encapsulated H2S Releasing Multifunctional Injectable Hydrogel

Spinal cord injury (SCI) commonly induces nerve damage and nerve cell degeneration. In this work, a novel dental pulp stem cells (DPSCs) encapsulated thermoresponsive injectable hydrogel with sustained hydrogen sulfide (H2S) delivery is demonstrated for SCI repair. For controlled and sustained H2S gas therapy, a clinically tested H2S donor (JK) loaded octysilane functionalized mesoporous silica nanoparticles (OMSNs) are incorporated into the thermosensitive hydrogel made from Pluronic F127 (PF-127). The JK-loaded functionalized MSNs (OMSF@JK) promote preferential M2-like polarization of macrophages and neuronal differentiation of DPSCs in vitro. OMSF@JK incorporated PF-127 injectable hydrogel (PF-OMSF@JK) has a soft consistency similar to that of the human spinal cord and thus, shows a high cytocompatibility with DPSCs. The cross-sectional micromorphology of the hydrogel shows a continuous porous structure. Last, the PF-OMSF@JK composite hydrogel considerably improves the in vivo SCI regeneration in Sprague-Dawley rats through a reduction in inflammation and neuronal differentiation of the incorporated stem cells as confirmed using western blotting and immunohistochemistry. The highly encouraging in vivo results prove that this novel design on hydrogel is a promising therapy for SCI regeneration with the potential for clinical translation.

Mesenchymal Stromal Cells Derived from Dental Tissues: Immunomodulatory Properties and Clinical Potential

Mesenchymal stem/stromal cells (MSCs) are multipotent cells located in different areas of the human body. The oral cavity is considered a potential source of MSCs because they have been identified in several dental tissues (D-MSCs). Clinical trials in which cells from these sources were used have shown that they are effective and safe as treatments for tissue regeneration. Importantly, immunoregulatory capacity has been observed in all of these populations; however, this function may vary among the different types of MSCs. Since this property is of clinical interest for cell therapy protocols, it is relevant to analyze the differences in immunoregulatory capacity, as well as the mechanisms used by each type of MSC. Interestingly, D-MSCs are the most suitable source for regenerating mineralized tissues in the oral region. Furthermore, the clinical potential of D-MSCs is supported due to their adequate capacity for proliferation, migration, and differentiation. There is also evidence for their potential application in protocols against autoimmune diseases and other inflammatory conditions due to their immunosuppressive capacity. Therefore, in this review, the immunoregulatory mechanisms identified at the preclinical level in combination with the different types of MSCs found in dental tissues are described, in addition to a description of the clinical trials in which MSCs from these sources have been applied.

Hydrogel-Based Growth Factor Delivery Platforms: Strategies and Recent Advances

Growth factors play a crucial role in regulating a broad variety of biological processes and are regarded as powerful therapeutic agents in tissue engineering and regenerative medicine in the past decades. However, their application is limited by their short half-lives and potential side effects in physiological environments. Hydrogels are identified as having the promising potential to prolong the half-lives of growth factors and mitigate their adverse effects by restricting them within the matrix to reduce their rapid proteolysis, burst release, and unwanted diffusion. This review discusses recent progress in the development of growth factor-containing hydrogels for various biomedical applications, including wound healing, brain tissue repair, cartilage and bone regeneration, and spinal cord injury repair. In addition, the review introduces strategies for optimizing growth factor release including affinity-based delivery, carrier-assisted delivery, stimuli-responsive delivery, spatial structure-based delivery, and cellular system-based delivery. Finally, the review presents current limitations and future research directions for growth factor-delivering hydrogels.

Anti-inflammatory effect of dental pulp stem cells

Dental pulp stem cells (DPSCs) have received a lot of attention as a regenerative medicine tool with strong immunomodulatory capabilities. The excessive inflammatory response involves a variety of immune cells, cytokines, and has a considerable impact on tissue regeneration. The use of DPSCs for controlling inflammation for the purpose of treating inflammation-related diseases and autoimmune disorders such as supraspinal nerve inflammation, inflammation of the pulmonary airways, systemic lupus erythematosus, and diabetes mellitus is likely to be safer and more regenerative than traditional medicines. The mechanism of the anti-inflammatory and immunomodulatory effects of DPSCs is relatively complex, and it may be that they themselves or some of the substances they secrete regulate a variety of immune cells through inflammatory immune-related signaling pathways. Most of the current studies are still at the laboratory cellular level and animal model level, and it is believed that through the efforts of more researchers, DPSCs/SHED are expected to be transformed into excellent drugs for the clinical treatment of related diseases.

Application of Injectable Hydrogels as Delivery Systems in Spinal Cord Injury

Spinal cord injury (SCI) is a severe neurological injury caused by traffic accidents, trauma, or falls, which leads to significant loss of sensory, motor, and autonomous functions and seriously affects the patient's life quality. Although considerable progress has been made in mitigating secondary injury and promoting the regeneration/repair of SCI, the therapeutic effects need to be improved due to drug availability. Given their good biocompatibility, biodegradability, and low immunogenicity, injectable hydrogels can be used as delivery systems to achieve controlled release of drugs and other substances (cells and proteins, etc.), offering new hope for SCI repair. In this article, we summarized the types of injectable hydrogels, analyzed their application as delivery systems in SCI, and further discussed the mechanisms of hydrogels in the treatment of SCI, such as anti-inflammatory, antioxidant, anti-apoptosis, and pro-neurogenesis. Moreover, we highlighted the potential benefits of hydrogels in the treatment of SCI in combination with therapies, including the recent advances and achievements of these promising tools. Our review may offer new strategies for the development of SCI treatments based on injectable hydrogels as delivery systems.

Genetically engineered neural stem cells (NSCs) therapy for neurological diseases; state-of-the-art

Neural stem cells (NSCs) are multipotent stem cells with remarkable self-renewal potential and also unique competencies to differentiate into neurons, astrocytes, and oligodendrocytes (ODCs) and improve the cellular microenvironment. In addition, NSCs secret diversity of mediators, including neurotrophic factors (e.g., BDNF, NGF, GDNF, CNTF, and NT-3), pro-angiogenic mediators (e.g., FGF-2 and VEGF), and anti-inflammatory biomolecules. Thereby, NSCs transplantation has become a reasonable and effective treatment for various neurodegenerative disorders by their capacity to induce neurogenesis and vasculogenesis and dampen neuroinflammation and oxidative stress. Nonetheless, various drawbacks such as lower migration and survival and less differential capacity to a particular cell lineage concerning the disease pathogenesis hinder their application. Thus, genetic engineering of NSCs before transplantation is recently regarded as an innovative strategy to bypass these hurdles. Indeed, genetically modified NSCs could bring about more favored therapeutic influences post-transplantation in vivo, making them an excellent option for neurological disease therapy. This review for the first time offers a comprehensive review of the therapeutic capability of genetically modified NSCs rather than naïve NSCs in neurological disease beyond brain tumors and sheds light on the recent progress and prospect in this context.

Modulating neuroinflammation through molecular, cellular and biomaterial-based approaches to treat spinal cord injury

The neuroinflammatory response that is elicited after spinal cord injury contributes to both tissue damage and reparative processes. The complex and dynamic cellular and molecular changes within the spinal cord microenvironment result in a functional imbalance of immune cells and their modulatory factors. To facilitate wound healing and repair, it is necessary to manipulate the immunological pathways during neuroinflammation to achieve successful therapeutic interventions. In this review, recent advancements and fresh perspectives on the consequences of neuroinflammation after SCI and modulation of the inflammatory responses through the use of molecular-, cellular-, and biomaterial-based therapies to promote tissue regeneration and functional recovery will be discussed.

The UCMSC-bFGF/Scaffold System Accelerates the Healing of the Uterine Full-Thickness Injury

Severe uterine injury is a major cause of endometrial scar formation and female infertility. At present, the methods for accelerating injured uterine healing are still lacking. Genetic engineering modification of mesenchymal stem cells (MSCs) has been shown great promise in preclinical studies on regeneration. Here, we constructed a type of umbilical cord MSCs (UC-MSCs) with overexpressed basic fibroblast growth factor (UCMSC-bFGF) and investigated the effects of the UCMSC-bFGF/scaffold on functional regeneration of the full-thickness defect uterus of the rat model. At days 7, 14, and 30 after treatments, the rats were killed and the injured uterus was observed. The structural and functional change of uterine was assessed by hematoxylin and eosin staining, immunohistochemical staining, and fertility experiment. The UCMSC-bFGF/scaffold group exhibited anti-inflammatory effect, and the number of CD45⁺ cell in the UCMSC-bFGF/scaffold group was significantly less than that in UC-MSCs/scaffold group and scaffold group, but higher than sham-operated group at day 7 postmending. At day 14, the UCMSC-bFGF/scaffold group exhibited dramatically proangiogenesis efficacy compared with UC-MSCs/scaffold group and scaffold group. At day 30, the endometrial thickness, structure of myometrium, and blood vessels in the UCMSC-bFGF/scaffold were better than those of the UC-MSCs/scaffold group and scaffold group, even close to sham-operated group. Implantation rate at injury region postoperation 30 days in the UCMSC-bFGF/scaffold group (8/16) was significantly higher than that in UC-MSCs/scaffold group (1/16) and scaffold group (0/16). Taken together, the UCMSC-bFGF/scaffold system suppressed local inflammation, promoted angiogenesis, and accelerated regeneration of the defected uterine wall, and thereby greatly shortened the healing time of the injured uterus. Impact statement In this study, we used umbilical cord mesenchymal stem cells (UC-MSCs) with stably overexpressed basic fibroblast growth factor (UCMSC-bFGF) to repair the full-thickness defect uterine wall of the rat model and found that the UCMSC-bFGF/scaffold system suppressed early acute inflammation after uterus injury, promoted angiogenesis, and accelerated regeneration of the injured uterine wall.

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.

Application of thermosensitive-hydrogel combined with dental pulp stem cells on the injured fallopian tube mucosa in an animal model

Objectives: Fallopian tube (FT) injury is an important factor that can lead to tubal infertility. Stem-cell-based therapy shows great potential for the treatment of injured fallopian tube. However, little research has shown that mesenchymal stem cells (MSCs) can be used to treat fallopian tube damage by in situ injection. In this study, we in situ transplanted PF127 hydrogel encapsulating dental pulp stem cells (DPSCs) into the injured sites to promote the repair and regeneration of fallopian tube injury. Materials and methods: The properties of dental pulp stem cells were evaluated by flow cytometry, immunofluorescence analysis, and multi-differentiation detection. The immunomodulatory and angiogenic characteristics of dental pulp stem cells were analyzed on the basis of the detection of inflammatory factor expression and the formation of capillary-like structures, respectively. The biocompatibility of PF127 hydrogel was evaluated by using Live/Dead and CCK-8 assays. The effects of PF127 hydrogel containing dental pulp stem cells on the repair and regeneration of fallopian tube injury were evaluated by histological analysis [e.g., hematoxylin and eosin (H&E) and Masson's trichrome staining, TUNEL staining, immunofluorescence staining, and immunohistochemistry], Enzyme-linked immunosorbent assay (ELISA), and RT-PCR detections. Results: Dental pulp stem cells had MSC-like characteristics and great immunomodulatory and angiogenic properties. PF127 hydrogel had a thermosensitive feature and great cytocompatibility with dental pulp stem cells. In addition, our results indicated that PF127 hydrogel containing dental pulp stem cells could promote the repair and regeneration of fallopian tube damage by inhibiting cell apoptosis, stimulating the secretion of angiogenic factors, promoting cell proliferation, modulating the secretion of inflammatory factors, and restoring the secretion of epithelial cells. Conclusion: In this study, our results reported that in situ injection of PF127 hydrogel encapsulating dental pulp stem cells into the injured sites could provide an attractive strategy for the future treatment of fallopian tube injury in clinical settings.

Biomaterial-Based bFGF Delivery for Nerve Repair

Diseases in the nervous system are common in the human body. People have to suffer a great burden due to huge economic costs and poor prognosis of the diseases. Many treatment modalities are now available that can make recovery better. Managing nutritional factors is also helpful for such diseases. The basic fibroblast growth factor (bFGF) is one of the major nutritional factors, which plays a crucial role in organogenesis and tissue homeostasis. It plays a role in cell proliferation, migration, and differentiation, thereby regulating angiogenesis and wound healing and repair of the muscle, bone, and nerve. The study on how to improve the stability of bFGF to increase the treatment effect for different diseases has garnered tremendous attention. Biomaterials are the popular methods to improve the stability of bFGF because they are safe for the living body as they are biocompatible. Biomaterials can be loaded with bFGF and delivered locally to achieve the goal of sustained bFGF release. In the present review, we report different types of biomaterials that are used for bFGF delivery for nerve repair and briefly report how the introduced bFGF can function in the nervous system. We aim to provide summative guidance for future studies about nerve injury using bFGF.

Temperature- and pH-responsive injectable chitosan hydrogels loaded with doxorubicin and curcumin as long-lasting release platforms for the treatment of solid tumors

The efficacy of treating solid tumors with chemotherapy is primarily hindered by dose-limiting toxicity due to off-target effects and the heterogeneous drug distribution caused by the dense extracellular matrix. The enhanced permeability and retention (EPR) effect within tumors restricts the circulation and diffusion of drugs. To overcome these obstacles, hydrogels formed in situ at the tumor site have been proposed to promote drug accumulation, retention, and long-lasting release. We developed a thiolated chitosan (CSSH) hydrogel with a gelation point of 37°C. Due to the pH-sensitive characteristics of disulfides, the prepared hydrogel facilitated drug release in the acidic tumor environment. A drug release system composed of hydrophilic doxorubicin (Dox) and hydrophobic liposome-encapsulated curcumin (Cur-Lip) was designed to enhance the long-lasting therapeutic impacts and reduce adverse side effects. These composite gels possess a suitable gelation time of approximately 8-12 min under physiological conditions. The cumulative release ratio was higher at pH = 5.5 than at pH = 7.4 over the first 24 h, during which approximately 10% of the Dox was released, and Cur was released slowly over the following 24-120 h. Cell assays indicated that the Cur-Lip/Dox/CSSH gels effectively inhibited the growth of cancer cells. These in situ-formed Cur-Lip/Dox gels with long-term drug release capabilities have potential applications for tumor suppression and tissue regeneration after surgical tumor resection.

Characteristics of culture-condition stimulated exosomes or their loaded hydrogels in comparison with other extracellular vesicles or MSC lysates

Recently, it has become popular to study the use of extracellular vesicles (EVs) secreted by stem cells to repair damaged tissues or lost cells. Various cell types and physiological fluids release EVs, and they play an important role in cell-to-cell communication. Moreover, EVs have been implicated in important processes, such as immune responses, homeostasis maintenance, coagulation, inflammation, cancer progression, angiogenesis, and antigen presentation. Thus, EVs participate in both physiological and pathological progression. The main classes of EVs include exosomes, microvesicles (MVs), and apoptotic bodies (ApoBDs). Exosomes, which carry a mass of signal molecules such as RNA, DNA, proteins, and lipids, are the most important of these EVs subsets. Currently, exosomes are generating substantial interest in the scientific community. Exosomes loaded hydrogels or under different cultural environments exhibit different properties and functions. Therefore, the exosomes obtained from different sources and conditions are worth reviewing. More importantly, no review article has compared the different EVs, such as exosomes, MVs, ApoBDs, and mesenchymal stem cell (MSC) lysates, which are special soluble substances. The differentiation between EVs and MSC lysates is a logical approach. Accordingly, this review provides an update on the latest progress in studying the roles of culture-condition stimulated exosomes or their loaded hydrogels and the differentiation between exosomes, MVs, ApoBDs, and MSC lysates. Published studies were retrieved from the PubMed® database for review.

Alzheimer’s disease: Pathophysiology and dental pulp stem cells therapeutic prospects

Alzheimer’s disease (AD) is a destructive neurodegenerative disease with the progressive dysfunction, structural disorders and decreased numbers of neurons in the brain, which leads to long-term memory impairment and cognitive decline. There is a growing consensus that the development of AD has several molecular mechanisms similar to those of other neurodegenerative diseases, including excessive accumulation of misfolded proteins and neurotoxic substances produced by hyperactivated microglia. Nonetheless, there is currently a lack of effective drug candidates to delay or prevent the progression of the disease. Based on the excellent regenerative and reparative capabilities of stem cells, the application of them to repair or replace injured neurons carries enormous promise. Dental pulp stem cells (DPSCs), originated from ectomesenchyme of the cranial neural crest, hold a remarkable potential for neuronal differentiation, and additionally express a variety of neurotrophic factors that contribute to a protective effect on injured neuronal cells. Notably, DPSCs can also express immunoregulatory factors to control neuroinflammation and potentiate the regeneration and recovery of injured neurons. These extraordinary features along with accessibility make DPSCs an attractive source of postnatal stem cells for the regeneration of neurons or protection of existing neural circuitry in the neurodegenerative diseases. The present reviews the latest research advance in the pathophysiology of AD and elaborate the neurodifferentiation and neuroprotective properties of DPSCs as well as their application prospects in AD.

Graphene-collagen cryogel controls neuroinflammation and fosters accelerated axonal regeneration in spinal cord injury

Spinal cord injury (SCI) is a devastating condition resulting in loss of motor function. The pathology of SCI is multifaceted and involves a cascade of events, including neuroinflammation and neuronal degeneration at the epicenter, limiting repair process. We developed a supermacroporous, mechanically elastic, electro-conductive, graphene crosslinked collagen (Gr-Col) cryogels for the regeneration of the spinal cord post-injury. The effects of graphene in controlling astrocytes reactivity and microglia polarization are evaluated in spinal cord slice organotypic culture and rat spinal cord lateral hemisection model of SCI. In our work, the application of external electric stimulus results in the enhanced expression of neuronal markers in an organotypic culture. The implantation of Gr-Col cryogels in rat thoracic T9-T11 hemisection model demonstrates an improved functional recovery within 14 days post-injury (DPI), promoted myelination, and decreases the lesion volume at the injury site. Decrease in the expression of STAT3 in the implanted Gr-Col cryogels may be responsible for the decrease in astrocytes reactivity. Microglia cells within the implanted cryogels shows higher anti-inflammatory phenotype (M2) than inflammatory (M1) phenotype. The higher expression of mature axonal markers like β-tubulin III, GAP43, doublecortin, and neurofilament 200 in the implanted Gr-Col cryogel confirms the axonal regeneration after 28 DPI. Gr-Col cryogels also modulate the production of ECM matrix, favouring the axonal regeneration. This study shows that Gr-Col cryogels decreases neuroinflammation and accelerate axonal regeneration.

A concise review of the orofacial mesenchymal stromal cells as a novel therapy for neurological diseases and injuries

Orofacial mesenchymal stromal cells (OFMSCs) are mesenchymal stromal cells isolated from the oral and facial regions, which possess typical mesenchymal stromal cell features such as self-renewing, multilineage differentiation, and immunoregulatory properties. Recently, increasing studies have been carried out on the neurotrophic and neuroregenerative properties of OFMSCs as well as their potential to treat neurological diseases. In this review, we summarize the current evidence and discuss the prospects regarding the therapeutic potential of OFMSCs as a new approach to treat different neurological diseases and injuries.

Neuronal Cell Differentiation of Human Dental Pulp Stem Cells on Synthetic Polymeric Surfaces Coated With ECM Proteins

Stem cells serve as an ideal source of tissue regeneration therapy because of their high stemness properties and regenerative activities. Mesenchymal stem cells (MSCs) are considered an excellent source of stem cell therapy because MSCs can be easily obtained without ethical concern and can differentiate into most types of cells in the human body. We prepared cell culture materials combined with synthetic polymeric materials of poly-N-isopropylacrylamide-co-butyl acrylate (PN) and extracellular matrix proteins to investigate the effect of cell culture biomaterials on the differentiation of dental pulp stem cells (DPSCs) into neuronal cells. The DPSCs cultured on poly-L-ornithine (PLO)-coated (TPS-PLO) plates and PLO and PN-coated (TPS-PLO-PN) plates showed excellent neuronal marker (βIII-tubulin and nestin) expression and the highest expansion rate among the culture plates investigated in this study. This result suggests that the TPS-PLO and TPS-PN-PLO plates maintained stable DPSCs proliferation and had good capabilities of differentiating into neuronal cells. TPS-PLO and TPS-PN-PLO plates may have high potentials as cell culture biomaterials for the differentiation of MSCs into several neural cells, such as cells in the central nervous system, retinal cells, retinal organoids and oligodendrocytes, which will expand the sources of cells for stem cell therapies in the future.

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

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

Effects of astrocytes and microglia on neuroinflammation after spinal cord injury and related immunomodulatory strategies

Spinal cord injury (SCI) is a catastrophic event which is still without adequate therapies. Neuroinflammation is the main pathogenesis of secondary damage post-SCI, leading to tissue loss and neurological dysfunction. Previous studies have shown that microglia and astrocytes are the major immune cells in the central nervous system (CNS) and play a crucial role in modulating neuroinflammatory responses. In this study, we mainly review the effects of neuroinflammation in SCI, focusing on the contributions of microglia and astrocytes and their cross-talk. Furthermore, we will also discuss therapeutic strategies on how to regulate their immunophenotype to suppress robust inflammation and facilitate injury prognosis.

ALG-bFGF Hydrogel Inhibiting Autophagy Contributes to Protection of Blood-Spinal Cord Barrier Integrity via PI3K/Akt/FOXO1/KLF4 Pathway After SCI

Promoting blood–spinal cord barrier (BSCB) repair at the early stage plays a crucial role in treatment of spinal cord injury (SCI). Excessive activation of autophagy can prevent recovery of BSCB after SCI. Basic fibroblast growth factor (bFGF) has been shown to promote BSCB repair and locomotor function recovery in SCI. However, the therapeutic effect of bFGF via direct administration on SCI is limited because of its rapid degradation and dilution at injury site. Based on these considerations, controlled release of bFGF in the lesion area is becoming an attractive strategy for SCI repair. At present, we have designed a sustained-release system of bFGF (called ALG-bFGF) using sodium alginate hydrogel, which is able to load large amounts of bFGF and suitable for in situ administration of bFGF in vivo. Here, traumatic SCI mice models and oxygen glucose deprivation (OGD)–stimulated human brain microvascular endothelial cells were performed to explore the effects and the underlying mechanisms of ALG-bFGF in promoting SCI repair. After a single in situ injection of ALG-bFGF hydrogel into the injured spinal cord, sustained release of bFGF from ALG hydrogel distinctly prevented BSCB destruction and improved motor functional recovery in mice after SCI, which showed better therapeutic effect than those in mice treated with bFGF solution or ALG. Evidences have demonstrated that autophagy is involved in maintaining BSCB integrity and functional restoration in animals after SCI. In this study, SCI/OGD exposure–induced significant upregulations of autophagy activation-related proteins (Beclin1, ATG5, LC3II/I) were distinctly decreased by ALG-bFGF hydrogel near the baseline and not less than it both in vivo and in vitro, and this inhibitory effect contributed to prevent BSCB destruction. Finally, PI3K inhibitor LY294002 and KLF4 inhibitor NSC-664704 were applied to further explore the underlying mechanism by which ALG-bFGF attenuated autophagy activation to alleviate BSCB destruction after SCI. The results further indicated that ALG-bFGF hydrogel maintaining BSCB integrity by inhibiting autophagy activation was regulated by PI3K/Akt/FOXO1/KLF4 pathway. In summary, our current study revealed a novel mechanism by which ALG-bFGF hydrogel improves BSCB and motor function recovery after SCI, providing an effective therapeutic strategy for SCI repair.

Dental-derived mesenchymal stem cell sheets: a prospective tissue engineering for regenerative medicine

Stem cells transplantation is the main method of tissue engineering regeneration treatment, the viability and therapeutic efficiency are limited. Scaffold materials also play an important role in tissue engineering, whereas there are still many limitations, such as rejection and toxic side effects caused by scaffold materials. Cell sheet engineering is a scaffold-free tissue technology, which avoids the side effects of traditional scaffolds and maximizes the function of stem cells. It is increasingly being used in the field of tissue regenerative medicine. Dental-derived mesenchymal stem cells (DMSCs) are multipotent cells that exist in various dental tissues and can be used in stem cell-based therapy, which is impactful in regenerative medicine. Emerging evidences show that cell sheets derived from DMSCs have better effects in the field of regenerative medicine applications. Extracellular matrix (ECM) is the main component of cell sheets, which is a dynamic repository of signalling biological molecules and has a variety of biological functions and may play an important role in the application of cell sheets. In this review, we summarized the application status, mechanisms that sheets and ECM may play and future prospect of DMSC sheets on regeneration medicine.

Functional hydrogels as therapeutic tools for spinal cord injury: New perspectives on immunopharmacological interventions

Spinal cord injury (SCI) is a complex medical and psychological challenge for which there is no curative therapy currently available. Despite major progress in pharmacological and surgical approaches, clinical trials for SCI patients have been uniformly disappointing thus far as there are many practical and biological issues yet to be resolved. Neuroinflammation is a critical event of the secondary injury phase after SCI, and recent research strategies have focused on modulating the immune response after injury to provide a more favorable recovery environment. Biomaterials can serve this purpose by providing physical and trophic support to the injured spinal cord after SCI. Of all potential biomaterials, functional hydrogels are emerging as a key component in novel treatment strategies for SCI, including controlled and localized delivery of immunomodulatory therapies to drive polarization of immune cells towards a pro-regenerative phenotype. Here, we extensively review recent developments in the use of functional hydrogels as immunomodulatory therapies for SCI. We briefly describe physicochemical properties of hydrogels and demonstrate how advanced fabrication methods lead to the required heterogeneity and hierarchical arrangements that increasingly mimic complex spinal cord tissue. We then summarize potential SCI therapeutic modalities including: (i) hydrogels alone; (ii) hydrogels as cellular or (iii) bioactive molecule delivery vehicles, and; (iv) combinatorial approaches. By linking the structural properties of hydrogels to their functions in treatment with particular focus on immunopharmacological stimuli, this may accelerate further development of functional hydrogels for SCI, and indeed next-generation central nervous system regenerative therapies.

Classification and Characteristics of Mesenchymal Stem Cells and Its Potential Therapeutic Mechanisms and Applications against Ischemic Stroke

Ischemic stroke is a serious cerebral disease that often induces death and long-term disability. As a currently available therapy for recanalization after ischemic stroke, thrombolysis, including intravenous thrombolysis and endovascular therapy, still cannot be applicable to all patients due to the narrow time window. Mesenchymal stem cell (MSC) transplantation therapy, which can trigger neuronal regeneration and repair, has been considered as a significant advance in treatment of ischemic stroke. MSC transplantation therapy has exhibited its potential to improve the neurological function in ischemic stroke. Our review describes the current progress and future perspective of MSC transplantation therapy in ischemic stroke treatment, including cell types, transplantation approaches, therapeutic mechanisms, and preliminary clinical trials of MSC transplantation, for providing us an update role of MSC transplantation in ischemic stroke treatment.

Improved functional recovery of rat transected spinal cord by peptide-grafted PNIPAM based hydrogel

Facilitating angiogenesis, reducing the formation of glial scar tissue, and the occurrence of a strong inflammatory response are of great importance for the repair of central nerve damage. In our previous study, a temperature-sensitive hydrogel grafted with bioactive isoleucine-lysine-valine-alanine-valine (IKVAV) peptide was prepared and it showed regular three-dimensional porous structure, rapid (de)swelling performance and good biological activity. Therefore, in this study, we used this hydrogel scaffold to treat for SCI to study the effect of it to facilitate angiogenesis, inhibit the differentiation and adhesion of keratinocytes, and further reduce the formation of glial scar tissue. The results reveal that the peptide hydrogel scaffold achieved excellent performance and can also promote the expression of angiogenic factors and reduce the secretion of pro-inflammatory factors to a certain extent. Particularly, it can also inhibit the formation of glial scar tissue and repair damaged tissue. The proposed strategy for developing this hydrogel scaffold provides a new insight into designing biomaterials for a broad range of applications in the tissue engineering of the central nervous system (CNS).

Dental Pulp Stem Cell-Derived Secretome and Its Regenerative Potential

The therapeutic potential of the dental pulp stem (DSC) cell-derived secretome, consisting of various biomolecules, is undergoing intense research. Despite promising in vitro and in vivo studies, most DSC secretome-based therapies have not been implemented in human medicine because the paracrine effect of the bioactive factors secreted by human dental pulp stem cells (hDPSCs) and human exfoliated deciduous teeth (SHEDs) is not completely understood. In this review, we outline the current data on the hDPSC- and SHED-derived secretome as a potential candidate in the regeneration of bone, cartilage, and nerve tissue. Published reports demonstrate that the dental MSC-derived secretome/conditional medium may be effective in treating neurodegenerative diseases, neural injuries, cartilage defects, and repairing bone by regulating neuroprotective, anti-inflammatory, antiapoptotic, and angiogenic processes through secretome paracrine mechanisms. Dental MSC-secretomes, similarly to the bone marrow MSC-secretome activate molecular and cellular mechanisms, which determine the effectiveness of cell-free therapy. Many reports emphasize that dental MSC-derived secretomes have potential application in tissue-regenerating therapy due to their multidirectional paracrine effect observed in the therapy of many different injured tissues.

Dental pulp stem cell-derived exosomes alleviate cerebral ischaemia-reperfusion injury through suppressing inflammatory response

Objectives

The study aimed to determine whether dental pulp stem cell‐derived exosomes (DPSC‐Exos) exert protective effects against cerebral ischaemia‐reperfusion (I/R) injury and explore its underlying mechanism.

Materials and Methods

Exosomes were isolated from the culture medium of human DPSC. Adult male C57BL/6 mice were subjected to 2 hours transient middle cerebral artery occlusion (tMCAO) injury followed by 2 hours reperfusion, after which singular injection of DPSC‐Exos via tail vein was administrated. Brain oedema, cerebral infarction and neurological impairment were measured on day 7 after exosomes injection. Then, oxygen‐glucose deprivation–reperfusion (OGD/R) induced BV2 cells were studied to analyse the therapeutic effects of DPSC‐Exos on I/R injury in vitro. Protein levels of TLR4, MyD88, NF‐κB p65, HMGB1, IL‐6, IL‐1β and TNF‐α were determined by western blot or enzyme‐linked immunosorbent assay. The cytoplasmic translocation of HMGB1 was detected by immunofluorescence staining.

Results

DPSC‐Exos alleviated brain oedema, cerebral infarction and neurological impairment in I/R mice. DPSC‐Exos inhibited the I/R‐mediated expression of TLR4, MyD88 and NF‐κB significantly. DPSC‐Exos also reduced the protein expression of IL‐6, IL‐1β and TNF‐α compared with those of the control both in vitro and in vivo. Meanwhile, DPSC‐Exos markedly decreased the HMGB1 cytoplasmic translocation induced by I/R damage.

Conclusions

DPSC‐Exos can ameliorate I/R‐induced cerebral injury in mice. Its anti‐inflammatory mechanism might be related with the inhibition of the HMGB1/TLR4/MyD88/NF‐κB pathway.

Titanium Nanotube Modified With Silver Cross-Linked Basic Fibroblast Growth Factor Improves Osteoblastic Activities of Dental Pulp Stem Cells and Antibacterial Effect

Titanium modifications with different silver loading methods demonstrate excellent antibacterial properties. Yet pure silver nanoparticles with limited bioactive properties may delay regeneration of bone surrounding the dental implant. Therefore, loading silver with bioactive drugs on titanium surfaces seems to be a very promising strategy. Herein, we designed a silver (Ag) step-by-step cross-linking with the basic fibroblast growth factor (bFGF) by polydopamine (PDA) and heparin on titanium nanotube (TNT) as its cargo (TNT/PDA/Ag/bFGF) to improve the implant surface. Our results showed that TNT/PDA/Ag/bFGF significantly enhanced the osteogenic differentiation of dental pulp stem cells (DPSCs). It also showed an excellent effect in bacterial inhibition and a reduction of pro-inflammatory factors through inhibition of M1 macrophage activity. These results showed that bFGF cross-linked silver coating on TNTs presented good osteogenic differentiation and early anti-infiammatory and antibacterial properties. Together, this novel design on titanium provides a promising therapeutic for dental implants.

Advances and Perspectives in Dental Pulp Stem Cell Based Neuroregeneration Therapies

Human dental pulp stem cells (hDPSCs) are some of the most promising stem cell types for regenerative therapies given their ability to grow in the absence of serum and their realistic possibility to be used in autologous grafts. In this review, we describe the particular advantages of hDPSCs for neuroregenerative cell therapies. We thoroughly discuss the knowledge about their embryonic origin and characteristics of their postnatal niche, as well as the current status of cell culture protocols to maximize their multilineage differentiation potential, highlighting some common issues when assessing neuronal differentiation fates of hDPSCs. We also review the recent progress on neuroprotective and immunomodulatory capacity of hDPSCs and their secreted extracellular vesicles, as well as their combination with scaffold materials to improve their functional integration on the injured central nervous system (CNS) and peripheral nervous system (PNS). Finally, we offer some perspectives on the current and possible future applications of hDPSCs in neuroregenerative cell therapies.

Investigation of PPARβ/δ within Human Dental Pulp Cells: A Preliminary In Vitro Study

Controlling the inflammatory response to restore tissue homeostasis is a crucial step to maintain tooth vitality after pathogen removal from caries-affected dental tissues. The nuclear peroxisome proliferator-activated receptor beta/delta (PPARβ/δ) is a ligand-activated transcription factor with emerging anti-inflammatory roles in many cells and tissues. However, its expression and functions are poorly understood in human dental pulp cells (hDPCs). Thus, this study evaluated PPARβ/δ expression and assessed the anti-inflammatory effects evoked by activation of PPARβ/δ in lipopolysaccharide- (LPS-) induced hDPCs. Our results showed that hDPCs constitutively expressed PPARβ/δ mRNA/protein, and treatment with LPS increased PPARβ/δ mRNA expression. The selective PPARβ/δ agonist GW0742 significantly decreased inflammation-related mRNA expression in hDPCs (IL6, IL1β, TNFα, MMP1, and MMP2) and RAW264.7 cells (Il6 and Tnfα). Further, PPARβ/δ agonist attenuated MMP2/9 gelatinolytic activity in hDPCs. Previously LPS-conditioned hDPCs increased the migration of RAW264.7 cells through the membrane of a Transwell coculture system. Conversely, pretreatment with GW0742 markedly decreased macrophage recruitment. These findings provide among the first evidence that hDPCs express PPARβ/δ. In addition, they suggest that activation of PPARβ/δ by GW0742 can attenuate some cellular and molecular in vitro aspects related to the inflammatory process, pointing out to investigate its potential target role in dental pulp inflammation.

Hypoxia response element-directed expression of bFGF in dental pulp stem cells improve the hypoxic environment by targeting pericytes in SCI rats

Cell-based transplantation strategies possess great potential for spinal cord injury (SCI) repair. Basic fibroblast growth factor (bFGF) has been reported to have multiple neuro-promoting effects on developing and adult nervous system of mammals and considered a promising therapy for nerve injury following SCI. Human dental pulp stem cells (DPSCs) are abundant stem cells with low immune rejection, which can be considered for cell replacement therapy. The purpose of this study was to investigate the roles of DPSCs which express bFGF under the regulation of five hypoxia-responsive elements (5HRE) using an adeno-associated virus (AAV-5HRE-bFGF-DPSCs) in SCI repairing model. In this study, DPSCs were revealed to differentiate into CD13⁺ pericytes and up-regulate N-cadherin expression to promote the re-attachment of CD13⁺ pericytes to vascular endothelial cells. The re-attachment of CD13⁺ pericytes to vascular endothelial cells subsequently increased the flow rate of blood in microvessels via the contraction of protuberance. As a result, increased numbers of red blood cells carried more oxygen to the damaged area and the local hypoxia microenvironment in SCI was improved. Thus, this study represents a step forward towards the potential use of AAV-5HRE-bFGF-DPSCs in SCI treatment in clinic.

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) 5HRE-bFGF-DPSCs secrete bFGF in a hypoxia dependent manner, making the administration more precise.

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CD13+ pericyte regulate vascular diameter and promote the recovery of hypoxia microenvironment via DDC-5HT-5HT-1B in SCI.

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5HRE-bFGF-DPSCs can differentiate into CD13+ pericyte to compensate for the mass death of CD13+ pericyte after SCI.

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5HRE-bFGF-DPSCs promote CD13+ pericyte adhesion to vascular endothelial cell by secreting bFGF through N-cadherin.

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5HRE-bFGF-DPSCs promote the recovery of SCI by restoring hypoxic microenvironment and inhibit autophagy pathway.

Sustained delivery of neurotrophic factors to treat spinal cord injury

Acute spinal cord injury (SCI) is a devastating condition that results in tremendous physical and psychological harm and a series of socioeconomic problems. Although neurons in the spinal cord need neurotrophic factors for their survival and development to reestablish their connections with their original targets, endogenous neurotrophic factors are scarce and the sustainable delivery of exogeneous neurotrophic factors is challenging. The widely studied neurotrophic factors such as brain-derived neurotrophic factor, neurotrophin-3, nerve growth factor, ciliary neurotrophic factor, basic fibroblast growth factor, and glial cell-derived neurotrophic factor have a relatively short cycle that is not sufficient enough for functionally significant neural regeneration after SCI. In the past decades, scholars have tried a variety of cellular and viral vehicles as well as tissue engineering scaffolds to safely and sustainably deliver those necessary neurotrophic factors to the injury site, and achieved satisfactory neural repair and functional recovery on many occasions. Here, we review the neurotrophic factors that have been used in trials to treat SCI, and vehicles that were commonly used for their sustained delivery.

A conductive dual-network hydrogel composed of oxidized dextran and hyaluronic-hydrazide as BDNF delivery systems for potential spinal cord injury repair

Spinal cord injury (SCI) often causes neuronal death and axonal degeneration. In this study, we report a new strategy for preparing injectable and conductive polysaccharides-based hydrogels that could sustainably deliver brain-derived neurotrophic factor (BDNF) for SCI repair. We used poly(lactic-co-glycolic acid) (PLGA) as a carrier to encapsulate BDNF. The resulting microspheres were then modified with tannic acid (TA). The polysaccharides-based hydrogel composed of oxidized dextran (Dex) and hyaluronic acid-hydrazide (HA) was mixed with TA-modified microspheres to form the ultimate BDNF@TA-PLGA/Dex-HA hydrogel. Our results showed that the hydrogel had properties similar to natural spinal cords. Specifically, the hydrogel had soft mechanical properties and high electrical conductivity. The cross-sectional morphology of the hydrogel exhibited a continuous and porous structure. The swelling and degradation behaviors of the Dex-HA hydrogel in vitro indicated the incorporation of TA into hydrogel matrix could improve the stability of the hydrogel matrix as well as extend the release time of BDNF from the matrix. Furthermore, results from immunostaining and real-time PCR demonstrated that BDNF@TA-PLGA/Dex-HA hydrogel could promote the differentiation of neural stem cells (NSCs) into neurons and inhibit astrocyte differentiation in vitro. These results show the great potential of this hydrogel as a biomimetic material in SCI regeneration.

Application of bioactive hydrogels combined with dental pulp stem cells for the repair of large gap peripheral nerve injuries

Due to the limitations in autogenous nerve grafting or Schwann cell transplantation, large gap peripheral nerve injuries require a bridging strategy supported by nerve conduit. Cell based therapies provide a novel treatment for peripheral nerve injuries. In this study, we first experimented an optimal scaffold material synthesis protocol, from where we selected the 10% GFD formula (10% GelMA hydrogel, recombinant human basic fibroblast growth factor and dental pulp stem cells (DPSCs)) to fill a cellulose/soy protein isolate composite membrane (CSM) tube to construct a third generation of nerve regeneration conduit, CSM-GFD. Then this CSM-GFD conduit was applied to repair a 15-mm long defect of sciatic nerve in a rat model. After 12 week post implant surgery, at histologic level, we found CSM-GFD conduit could regenerate nerve tissue like neuron and Schwann like nerve cells and myelinated nerve fibers. At physical level, CSM-GFD achieved functional recovery assessed by a sciatic functional index study. In both levels, CSM-GFD performed like what gold standard, the nerve autograft, could do. Further, we unveiled that almost all newly formed nerve tissue at defect site was originated from the direct differentiation of exogeneous DPSCs in CSM-GFD. In conclusion, we claimed that this third-generation nerve regeneration conduit, CSM-GFD, could be a promising tissue engineering approach to replace the conventional nerve autograft to treat the large gap defect in peripheral nerve injuries.

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A novel 3^rd generation nerve conduit was successfully constructed and applied for repairing peripheral nerve injuries (PNI).

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Dental pulp stem cells (DPSCs) was optimized as an ideal seeding cells for nerve regeneration.

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A bioactive system combining GelMA with human bFGF and DPSCs could reconstruct the long gap PNI within 12 weeks in vivo.

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Our system could achieve the same outcome in nerve repair as that of autografting, a routine treatment for PNI.

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The proposed bioactive system may trigger an evolutional change into the current clinical practice in managing PNI.

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The majority of the regenerated nerve tissue was originated from the donor’s dental pulp stem cells.