Tissue Regeneration Research Articles

Inflammation‐Responsive Functional Core–Shell Micro‐Hydrogels Promote Rotator Cuff Tendon‐To‐Bone Healing by Recruiting MSCs and Immuno‐Modulating Macrophages in Rats

AbstractRotator cuff injuries often necessitate surgical intervention, but the outcomes are often unsatisfactory. The underlying reasons can be attributed to multiple factors, with the intricate inflammatory activities and insufficient presence of stem cells being particularly significant. In this study, an innovative inflammation‐responsive core–shell micro‐hydrogel is designed for independent release of SDF‐1 and IL‐4 within a single delivery system to promote tendon‐to‐bone healing by recruiting MSCs and modulating M2 macrophages polarization. First, a MMP‐2 responsive hydrogel loaded with IL‐4 (GelMA‐MMP/IL‐4) is synthesized by cross‐linking gelatin methacrylate (GelMA) with MMP‐2 substrate peptide. Then, the resulting core particles are coated with a shell of chitosan /SDF‐1/hyaluronic acid (CS/HA/SDF‐1) using the layer‐by‐layer electrostatic deposition method to form a core–shell micro‐hydrogel composite. The core–shell micro‐hydrogel shows sustained release of SDF‐1 and MMP‐2‐responsive release of IL‐4 associated in situ MSCs homing and smart inflammation regulation by promoting M2 macrophages polarization. Additionally, by injecting these micro‐hydrogels into a rat rotator cuff tear and repair model, notable improvements of fibrocartilage layer are observed between tendon and bone. Notably, this study presents a new and potentially powerful environment‐responsive drug delivery strategy that offers valuable insights for regulating the intricate micro‐environment associated with tissue regeneration.

The Hippo Signaling Pathway, Reactive Oxygen Species Production, and Oxidative Stress: A Two-Way Traffic Regulation

The Hippo signaling pathway is recognized for its significant role in cell differentiation, proliferation, survival, and tissue regeneration. Recently, the Hippo signaling pathway was also found to be associated with oxidative stress and reactive oxygen species (ROS) regulation, which are important in the regulation of cell survival. Studies indicate a correlation between components of the Hippo signaling pathway, including MST1, YAP, and TAZ, and the generation of ROS. On the other hand, ROS and oxidative stress can activate key components of the Hippo signaling pathway. For example, ROS production activates MST1, which subsequently phosphorylates FOXO3, leading to apoptotic cell death. ROS was also found to regulate YAP, in addition to MST1/2. Oxidative stress and ROS formation can impair lipids, proteins, and DNA, leading to many disorders, including aging, neurodegeneration, atherosclerosis, and diabetes. Consequently, understanding the interplay between the Hippo signaling pathway, ROS, and oxidative stress is crucial for developing future disease management strategies. This paper aimed to review the association between the Hippo signaling pathway, regulation of ROS production, and oxidative stress to provide beneficial information in understanding cell function and pathological processes.

ETIOPATHOGENETIC MECHANISMS OF IMMUNE DYSFUNCTION IN COMBATANTS WITH LOWER LIMB SOFT TISSUE INJURIES UNDER CHRONIC STRESS

Introduction. Combat injuries, including gunshot, shrapnel, and mine-explosive wounds, affect a significant number of soldiers in modern warfare. Notably, most of these injuries involve damage to the soft tissues of the extremities. Surgeons have expressed concerns regarding the unsatisfactory treatment outcomes in this group of combatants, attributing one of the primary challenges to the limited understanding of immune dysfunction pathogenesis in military trauma cases. This study aims to address this gap by examining immune system dysfunctions in combat-related injuries. The objective of this study is to thoroughly analyze and synthesize the key stages of immune dysfunction occurring over extended periods post-combat trauma, including the subsequent development of traumatic disease and various wound complications. Materials and Methods. The rising prevalence of combat trauma among soldiers has intensified interest in studying this issue, prompting surgeons and traumatologists to address its various medical aspects comprehensively. The literature search focused on recent publications, allowing for a targeted analysis of the immunological aspects relevant to military medical traumatology. Results. In the initial stages of severe or combined injuries affecting various tissues—such as tubular bones, joints, blood vessels, and peripheral nerves—systemic inflammatory response syndrome (SIRS) commonly occurs. This stage is marked by an intense activation of innate antibacterial and immune-protective responses, leading to a significant increase in inflammation. This initial response is soon replaced by a prolonged phase known as compensatory anti-inflammatory response syndrome. During this period, immune-protective responses sharply decrease, certain immunocompetent cells become inhibited, and lymphopenia develops. This phase is often accompanied by infectious contamination of wounds with pathogenic and opportunistic microorganisms, resulting in both local purulent-necrotic processes and potentially severe systemic complications, such as septic shock, sepsis, multiple organ failure, and others. The final stage, known as persistent inflammatory, immunosuppressive, catabolic syndrome, is characterized by the chronic progression of traumatic disease, accompanied by ongoing immune system dysfunction in combatants. Conclusion. In the early period of traumatic injury, the wounded experience sharp inflammatory processes and activation of immune defense mechanisms. At subsequent stages, severe disruptions in the functioning of the immune system, damage to internal organs, and the development of catabolic syndrome are recorded. These changes, especially those resulted from exposure to chronic combat stress preceding the injury, aggravate the processes of infectious decontamination of wounds, regeneration of damaged tissues, and the general process of combatant rehabilitation.

Synthesis methods of Mg-based scaffolds and their applications in tissue engineering: A review

Repair and regeneration of damaged tissues due to disease and accidents have become a severe challenge to tissue engineers and researchers. In recent years, biocompatible metal materials such as stainless steels, cobalt alloys, titanium alloys, tantalum alloys, nitinol, and Mg alloys have been studied for tissue engineering applications; as suitable candidates in orthopedic and dentistry implants. These materials and their alloys are used for load-bearing and physiological roles in biological applications. Due to the suitable conditions provided by a porous material, many studies have been performed on the porous implants, including Mg-based scaffolds. Mg alloy scaffolds are attractive due to some outstanding features and susceptibilities, such as providing a cell matrix for cell proliferation, migration, and regeneration, providing metabolic substances for bone tissue growth, biocompatibility, good biodegradability, elastic modulus comparable to the natural bone, etc. Accordingly, in the present study, a general classification of all the production methods of Mg-based scaffolds is provided. Strengths and weaknesses, the effect of the production approach on the final properties of scaffolds, including mechanical and biological capabilities, and the impact of alloying elements and process parameters have been reviewed, and discussed. Finally, the manufacturing methods have been compared and the upcoming challenges have been stated.

Micro-thin hydrogel coating integrated in 3D printing for spatiotemporal delivery of bioactive small molecules

Three-dimensional (3D) printing incorporated with controlled delivery is an effective tool for complex tissue regeneration. Here, we explored a new strategy for spatiotemporal delivery of bioactive cues by establishing a precise-controlled micro-thin coating of hydrogel carriers on 3D-printed scaffolds. We optimized the printing parameters for three hydrogel carriers, fibrin cross-linked with genipin, methacrylate hyaluronic acid, and multidomain peptides, resulting in homogenous micro-coating on desired locations in 3D printed polycaprolactone microfibers at each layer. Using the optimized multi-head printing technique, we successfully established spatial-controlled micro-thin coating of hydrogel layers containing profibrogenic small molecules (SMs), Oxotremorine M and PPBP maleate, and a chondrogenic cue, Kartogenin. The delivered SMs showed sustained releases up to 28 d and guided regional differentiation of mesenchymal stem cells, thus leading to fibrous and cartilaginous tissue matrix formation at designated scaffold regionsin vitroandin vivo. Our micro-coating of hydrogel carriers may serve as an efficient approach to achieve spatiotemporal delivery of various bioactive cues through 3D printed scaffolds for engineering complex tissues.

Automatic And Portable Physiotherapy Hardware Device for Legs

This Project is to Design and fabricate a cheaper Continuous Passive Motion [CPM] Machine than what is available commercially and with more versatile features. In the tendency, continuous passive motion (CPM) was proposed as an orthopedic treatment and a physiotherapy method that promotes recovery from the injuries after surgery of joints. The CPM is intended to accelerate the regeneration of periarticular tissues, to prevent contracture, and to correct range of motion (ROM) and is more effective than conventional treatment method.

Amniotic Membrane Transplantation: Clinical Applications in Enhancing Wound Healing and Tissue Regeneration.

Chronic wounds and non-healing tissue defects pose significant clinical challenges, necessitating innovative therapeutic approaches. A comprehensive literature review of amniotic membrane transplantation for wound healing and tissue repair evaluates the efficacy and safety of amniotic membrane transplantation in enhancing wound healing and tissue repair. Amniotic membranes promote wound closure and reduce inflammation and scarring via abundant growth factors, cytokines, and extracellular matrix components, which foster conducive environments for tissue regeneration. Amniotic membrane transplantation is effective in various medical disciplines, including ophthalmology, dermatology, and orthopedics. Low immunogenicity and anti-microbial properties ensure their safe application. Amniotic membrane transplantation offers a promising therapeutic approach for wound healing and tissue repair, and further research is warranted to explore its regenerative potential fully.

Exposure to High Concentrations of Tetrabromobisphenol A Slows the Process of Tissue Regeneration and Induces an Imbalance of Metabolic Homeostasis in the Regenerated Intestines of Apostichopus japonicus

Background: Tissue regenerative capacity following evisceration, potentially influenced by environmental contaminants and intestinal microflora, is essential for the financial success of Apostichopus japonicus farming. However, the morphological structure, gut microbiome composition, and genes expression pattern of the regenerated gut after exposure to high levels of TBBPA remain poorly unclear. Methods: In this research, the effect of TBBPA exposure on tissue regeneration in A. japonicus was investigated through a comprehensive multi-omics approach. Results: Our results showed that the integrity, the intestinal wall thickness, and the villi length of the regenerated intestines in A. japonicus decreased after treatment with high levels of TBBPA. The findings from PCoA and NMDS analyses revealed that the microbial community composition was significantly altered following exposure to high concentrations of TBBPA in the regenerated intestines of A. japonicus. The KEGG pathway enrichment analysis indicated that the DEGs (differentially expressed genes) were predominantly enriched on metabolism and immunity-related signaling pathways after exposure to high levels of TBBPA. These included pathways involved in the PPAR signaling pathway, ECM receptor interaction, glycerolipid metabolism, and fatty acid degradation. Interestingly, the results have demonstrated that there are 77 transcript factors that were significantly different after exposure to TBBPA. Conclusions: These results suggested that high levels of exposure to TBBPA induces an imbalance of the metabolic homeostasis by regulating the expression levels of transcription factors in the regenerated intestines of A. japonicus.

Meniscus gene expression profiling of inner and outer zone meniscus tissue compared to cartilage and passaged monolayer meniscus cells

Meniscus injuries are common and while surgical strategies have improved, there is a need for alternative therapeutics to improve long-term outcomes and prevent post-traumatic osteoarthritis. Current research efforts in regenerative therapies and tissue engineering are hindered by a lack of understanding of meniscus cell biology and a poorly defined meniscus cell phenotype. This study utilized bulk RNA-sequencing to identify unique and overlapping transcriptomic profiles in cartilage, inner and outer zone meniscus tissue, and passaged inner and outer zone meniscus cells. The greatest transcriptomic differences were identified when comparing meniscus tissue to passaged monolayer cells (> 4,600 differentially expressed genes (DEGs)) and meniscus tissue to cartilage (> 3,100 DEGs). While zonal differences exist within the meniscus tissue (205 DEGs between inner and outer zone meniscus tissue), meniscus resident cells are more similar to each other than to either cartilage or passaged monolayer meniscus cells. Additionally, we identified and validated LUM, PRRX1, and SNTB1 as potential markers for meniscus tissue and ACTA2, TAGLN, SFRP2, and FSTL1 as novel markers for meniscus cell dedifferentiation. Our data contribute significantly to the current characterization of meniscus cells and provide an important foundation for future work in meniscus cell biology, regenerative medicine, and tissue engineering.

The Hippo pathway in oral diseases and treatments: A review

This review aims to provide a recent update on the Hippo pathway in oral diseases. The Hippo pathway plays a crucial role in organ development, tissue regeneration, wound healing, maintaining epithelial homeostasis, and modulating the immune system. Globally, billions of people suffer from various oral diseases, posing significant public health risks and resulting in substantial economic losses. This article reviews the recent advancements in the research on the Hippo signaling pathway and its effectors in various conditions related to oral health. The implications of Hippo signaling in various dental fields, including endodontics, orthodontics, periodontology, oral implantology, oral and maxillofacial surgery, and oncology are discussed. It provides readers with an overview of the regulatory role of the Hippo pathway in the development of various oral diseases and the potential for exploiting this pathway for developing targeted therapeutics.

Non-Thermal Atmospheric Pressure Plasma as an Adjunct to Intestinal Anastomosis: A Pilot Study on Preventing Anastomotic Leaks

Anastomotic leaks remain a significant challenge in intestinal surgery, often leading to severe complications. This study investigated a novel approach to enhance anastomotic healing and reduce the risk of leaks by combining traditional suturing and stapling techniques with non-thermal atmospheric pressure plasma (NTAPP) application. NTAPP, a cold atmospheric plasma generated through the ionization of ambient air, has been shown to possess antimicrobial, hemostatic, and wound-healing properties. NTAPP promotes sterilization, coagulation, and tissue regeneration by generating reactive oxygen and nitrogen species, potentially strengthening anastomotic union. This pilot study evaluated the efficacy of NTAPP in three patients undergoing intestinal anastomosis. Following the standard surgical procedure, NTAPP was applied directly to the anastomotic site. Postoperative outcomes were monitored for six months, including anastomotic leaks and healing rates. Preliminary results demonstrated promising outcomes. All three patients exhibited successful sealing of the anastomosis, with no evidence of leakage during the follow-up period, providing reassurance and confidence in the potential of sutures, staples, and NTAPP. These findings suggest that NTAPP can significantly improve the safety and efficacy of intestinal surgeries by reducing the incidence of anastomotic leaks. While further research with a larger sample is necessary to confirm these initial findings, the results of this study provide a strong foundation for exploring the potential of NTAPP as a valuable adjunct to conventional surgical techniques for preventing anastomotic leaks. This innovative approach could reduce postoperative complications, improve patient outcomes, and enhance the overall quality of care in intestinal surgery.

STEM CELL APPROACHES IN ORGAN REGENERATION AND REPAIR

Recent advances in stem cell research have provided new hope for treating a variety of diseases and conditions that currently have no effective cure. Stem cells have the unique ability to differentiate into various cell types, enabling them to support tissue growth and replace damaged or specialized cells throughout the lifespan. Among the most promising types of stem cells are mesenchymal stem cells (MSCs), which are easily harvested from adipose tissue and can be cultured and expanded in the lab. Due to their versatility, MSCs have become a focal point in tissue regeneration and have been widely used in animal studies and clinical trials involving humans. This review aims to summarize the current understanding of MSCs, focusing on the various types of stem cells isolated from different animal models such as horses, pigs, goats, dogs, rabbits, cats, rats, and mice. Given the growing interest in MSCs, we will also discuss their applications in veterinary and regenerative medicine. Current research highlights the potential of MSCs in treating conditions like heart failure, wound healing, and tooth regeneration, demonstrating their broad therapeutic potential. KEYWORDS: Mesenchymal stem cells (MSCs), animal models, cell-based therapy, regenerative medicine

Bioactive MgO/MgCO3/Polycaprolactone Multi-gradient Fibers Facilitate Peripheral Nerve Regeneration by Regulating Schwann Cell Function and Activating Wingless/Integrase-1 Signaling

AbstractPeripheral nerve defects present complex orthopedic challenges with limited efficacy of clinical interventions. The inadequate proliferation and dysfunction of Schwann cells within the nerve scaffold impede the effectiveness of nerve repair. Our previous studies suggested the effectiveness of a magnesium-encapsulated bioactive hydrogel in repairing nerve defects. However, its rapid release of magnesium ions limited its efficacy to long-term nerve regeneration, and its molecular mechanism remains unclear. This study utilized electrospinning technology to fabricate a MgO/MgCO3/polycaprolactone (PCL) multi-gradient nanofiber membrane for peripheral nerve regeneration. Our findings indicated that by carefully adjusting the concentration or proportion of rapidly degradable MgO and slowly degradable MgCO3, as well as the number of electrospun layers, the multi-gradient scaffold effectively sustained the release of Mg2+ over a period of 6 weeks. Additionally, this study provided insight into the mechanism of Mg2+-induced nerve regeneration and confirmed that Mg2+ effectively promoted Schwann cell proliferation, migration, and transition to a repair phenotype. By employing transcriptome sequencing technology, the study identified the Wingless/integrase-1 (Wnt) signaling pathway as a crucial mechanism influencing Schwann cell function during nerve regeneration. After implantation in 10 mm critically sized nerve defects in rats, the MgO/MgCO3/PCL multi-gradient nanofiber combined with a 3D-engineered PCL nerve conduit showed enhanced axonal regeneration, remyelination, and reinnervation of muscle tissue 12 weeks post-surgery. In conclusion, this study successfully developed an innovative multi-gradient long-acting MgO/MgCO3/PCL nanofiber with a tunable Mg2+ release property, which underscored the molecular mechanism of magnesium-encapsulated biomaterials in treating nervous system diseases and established a robust theoretical foundation for future clinical translation. Graphical abstract

Mesenchymal stem cell application in pulmonary disease treatment with emphasis on their interaction with lung-resident immune cells

Due to the vital importance of the lungs, lung-related diseases and their control are very important. Severe inflammatory responses mediated by immune cells were among the leading causes of lung tissue pathology and damage during the COVID-19 pandemic. In addition, uncontrolled immune cell responses can lead to lung tissue damage in other infectious and non-infectious diseases. It is essential to control immune responses in a way that leads to homeostasis. Immunosuppressive drugs only suppress inflammatory responses and do not affect the homeostasis of reactions. The therapeutic application of mesenchymal stem cells (MSCs), in addition to restoring immune homeostasis, can promote the regeneration of lung tissue through the production of growth factors and differentiation into lung-related cells. However, the communication between MSCs and immune cells after treatment of pulmonary diseases is essential, and investigating this can help develop a clinical perspective. Different studies in the clinical phase showed that MSCs can reverse fibrosis, increase regeneration, promote airway remodeling, and reduce damage to lung tissue. The proliferation and differentiation potential of MSCs is one of the mechanisms of their therapeutic effects. Furthermore, they can secrete exosomes that affect the function of lung cells and immune cells and change their function. Another important mechanism is that MSCs reduce harmful inflammatory responses through communication with innate and adaptive immune cells, which leads to a shift of the immune system toward regulatory and hemostatic responses.

Regulation of the Intestinal Stem Cell Pool and Proliferation in Drosophila

Understanding the regulation of somatic stem cells, both during homeostasis and in response to environmental challenges like injury, infection, chemical exposure, and nutritional changes, is critical because their dysregulation can result in tissue degeneration or tumorigenesis. The use of models such as the Drosophila and mammalian adult intestines offers valuable insights into tissue homeostasis and regeneration, advancing our knowledge of stem cell biology and cancer development. This review highlights significant findings from recent studies, unveiling the molecular mechanisms that govern self-renewal, proliferation, differentiation, and regeneration of intestinal stem cells (ISCs). These insights not only enhance our understanding of normal tissue maintenance but also provide critical perspectives on how ISC dysfunction can lead to pathological conditions such as colorectal cancer (CRC).

Design and self-assembly of new peptides and peptide bolaamphiphiles as antioxidant biocomposite scaffolds for potential tissue regeneration applications – a replica modeling and experimental study

ABSTRACT In this work, five new peptides derived from natural resources and two peptide bolaamphiphiles were designed. The self-assembling ability of the peptides and the bolaamphiphiles, as well as their predicted antioxidant activity was examined computationally. In particular, replica modeling molecular dynamics studies were carried out at three different temperatures. Results showed that the bolaamphiphiles as well as three of the peptides efficiently formed spherical or fibrous assemblies, particularly at physiological temperatures. In addition, stacking interactions and hydrogen bonds played a critical role in assembly formation. Furthermore, molecular docking studies with extracellular matrix proteins such as the triple helix motif of collagen and the fibronectin (III) motif of tenascin-X displayed binding interactions with the peptides and the bolaamphiphiles. The most optimal peptide bolaamphiphile WMYGGGWMY-CO-NH-(CH2)4-YMWGGGYMW was then synthesized in the laboratory and its ability to form functional scaffolds upon binding to collagen and tenascin-X was examined. The scaffolds were bioprinted with co-cultures of fibroblasts and keratinocytes. The cells not only proliferated over time but also showed strong adherence and spreading within the matrix. Thus, the peptides and the bolaamphiphiles studied in this work, may be potentially developed as scaffold components for tissue regeneration applications.

Conventional Versus Regenerative Methods for Wound Healing: A Comparative Experimental Study on a Sheep Model

Background and Objectives: Wound healing is a complex process involving cellular, anatomical, and functional repair, often hindered in chronic wounds associated with diseases like diabetes and vascular disorders. This study investigated the efficacy of conventional and regenerative wound healing approaches in a sheep surgical wound model. Materials and Methods: Six female Bergamasca sheep underwent five full-thickness skin lesions treated with various methods: sterile gauze (control), chlorhexidine, sodium hypochlorite, micronized dermis system application, and dermal matrix. Wound healing progression was monitored over 42 days through wound dimension measurements, exudate analysis, and histopathological evaluations. Results: The results indicated that all wounds healed completely by day 42, with significant reductions in wound size and exudate over time. Notably, Micronized dermis system application and dermal matrix treatments showed a faster evolution in exudate characteristics and improved collagen reorganization compared to other treatments. Histological analysis revealed earlier neovascularization and better reconstitution of hair follicles in these groups. Despite the lack of significant differences in healing time, both regenerative approaches enhanced wound healing phases, contributing to exudate control, angiogenesis promotion, and reduced scar formation. Conclusions: The findings suggest that while micronized dermis system application and dermal matrix do not accelerate acute wound healing compared to conventional methods, they offer potential benefits in managing exudate and improving tissue regeneration, warranting further investigation in chronic wound scenarios.

Intraosseous Delivery of Mesenchymal Stem Cells for the Treatment of Bone and Hematological Diseases

Mesenchymal stem cells are used most in regenerative medicine due to their capacities in differentiation and immune modulation. The intraosseous injection of MSC into the bone has been recommended because of expected outcomes for retention, bioavailability, and enhanced therapeutic efficacy, particularly in conditions involving the bone, such as osteoporosis and osteonecrosis. A review of the intraosseous delivery of mesenchymal stem cells in comparison with intravenous and intra-arterial delivery methods will be subjected to critical examination. This delivery mode fares better regarding paracrine signaling and immunomodulation attributes, which are the cornerstone of tissue regeneration and inflammation reduction. The local complications and technical challenges still apply with this method. This study was more focused on further research soon to be conducted to further elucidate long-term safety and efficacy of intraosseous mesenchymal stem cell therapy. Though much has been achieved with very impressive progress in this field, it is worth noting that more studies need to be put into place so that this technique can be established as a routine approach, especially with further research in biomaterials, gene therapy, and personalized medicine.

Design of cellulose nanocrystal‐integrated poly(vinyl alcohol)/polyethylene glycol electrospun nanofiber scaffolds for biomedical applications

AbstractThe present study aims to fabricate cellulose nanocrystals (CNCs) doped poly(vinyl alcohol) polyethylene glycol (PVA/PEG) nanocomposite films for biomedical applications. The nanocomposite films were prepared by using electrospinning techniques with varying percentages of CNCs (10% and 20%) mixed with PVA and PEG (50:50). The properties of the produced nanocomposites were evaluated using a battery of tests. The results of surface morphology and structural miscibility obtained from field emission‐scanning electron microscopy (FE‐SEM), atomic force microscopy, and Fourier transformer infra‐red studies revealed appreciable compatibility among the three components (CNCs, PVA, and PEG). FE‐SEM micrographs revealed that the nanomaterials underwent a dramatic transition from discontinuous to continuous fibers, with interconnected or network‐like fibers. The constructed scaffold material's stability went up from three to four phases, according to thermal and degradation experiments. In addition, research on biodegradation and water absorption found that CNCs outperformed pure PVA and PVA/PEG in terms of swelling percentage time and enzyme degradation rate. The hemolysis assay of the PVA/PEG/CNC scaffold showed good compatibility (below 5%) and according to the MTT assay, both NIH 3T3 and L929 cells survived well, indicating that the CNCs could serve as a useful scaffold for tissue engineering applications such skin tissue regeneration. In sum, the findings proved that biological domains including tissue engineering and wound healing can benefit from produced nanofiber scaffolds.

Adipose-derived stem cell exosomal miR-21-5p enhances angiogenesis in endothelial progenitor cells to promote bone repair via the NOTCH1/DLL4/VEGFA signaling pathway

BackgroundAngiogenesis is essential for repairing critical-sized bone defects. Although adipose-derived stem cell (ADSC)-derived exosomes have been shown to enhance the angiogenesis of endothelial progenitor cells (EPCs), the underlying mechanisms remain unclear. This study aims to explore the effects and mechanisms of ADSC-derived exosomes in enhancing bone repair by promoting EPC angiogenesis.MethodsTransmission electron microscopy, nanoparticle tracking analysis, and Dil reagent kit were employed to identify ADSC-derived exosomes and their internalization by EPCs. Micro-CT analysis, H&E staining, and Masson staining were used to assess bone mineral density (BMD), bone volume fraction (BV/TV), trabecular thickness (Tb.Th), and trabecular number (Tb.N), as well as the pathological changes and fibrosis at defect sites. Cell viability, migration, invasion, and tube formation of EPCs were evaluated using CCK-8, wound healing, Transwell, and tube formation assays. Immunohistochemical staining, RT-PCR, and Western blotting were utilized to measure the gene and protein expression of markers such as CD31, VEGFA, OCN, RUNX2, NOTCH1, and DLL4. Gene sequencing and bioinformatics analyses were conducted to identify the most highly expressed miRNA in exosomes, while miRDB and dual-luciferase reporter assays were used to explore the interaction between miR-21-5p and NOTCH1.ResultsThe ADSC-derived exosomes, averaging 126 nm in diameter, were internalized by EPCs. In vivo, these exosomes promoted new bone formation, increased BMD, BV/TV, Tb.Th, and Tb.N, reduced pathological damage to cranial defect tissues, enhanced vascular and bone tissue regeneration, and upregulated OCN and RUNX2 expression. In vitro, ADSC-derived exosomes enhanced EPC viability, migration, invasion, and tube formation. Both in vivo and in vitro experiments demonstrated that ADSC-derived exosomes upregulated CD31 and VEGFA expression. miR-21-5p, the most highly expressed miRNA in ADSC-derived exosomes, was found to target NOTCH1. Overexpression of miR-21-5p in these exosomes facilitated EPC migration, tube formation, and VEGFA expression while downregulating NOTCH1 and DLL4 expression. Inhibition of miR-21-5p produced opposite effects on EPCs.ConclusionsThese findings indicate that miR-21-5p in ADSC-derived exosomes promotes angiogenesis in EPCs to accelerate bone repair by targeting the NOTCH1/DLL4/VEGFA signaling pathway, offering a potential therapeutic strategy for bone defect treatment.Graphical