Hydrogel-Embedded Poly(Lactic-co-Glycolic Acid) Microspheres for the Delivery of hMSC-Derived Exosomes to Promote Bioactive Annulus Fibrosus Repair

Innovating intervertebral disc degeneration therapy: Harnessing the power of extracellular vesicles

Intervertebral disc degeneration is the leading cause of low back pain, imposing significant burdens on patients, societies, and economies. Advancements in regenerative medicine have spotlighted extracellular vesicles as promising nanoparticles for intervertebral disc degeneration treatment. Extracellular vesicles retain the potential of cell therapy and serve as carriers to deliver their cargo to target cells, thereby regulating cell activity. This review summarizes the biogenesis and molecular composition of extracellular vesicles and explores their therapeutic roles in intervertebral disc degeneration treatment through various mechanisms. These mechanisms include mitigating cell loss and senescence, delaying extracellular matrix degeneration, and modulating the inflammatory microenvironment. Additionally, it highlights recent efforts in engineering extracellular vesicles to enhance their targeting and therapeutic efficacy. The integration of extracellular vesicle-based acellular therapy is anticipated to drive significant advancements in disc regenerative medicine.

The translational potential of this article

Existing clinical treatment strategies often fail to effectively address the challenges associated with regenerating degenerated intervertebral discs. As a new regenerative medicine strategy, the extracellular vesicle strategy avoids the risks associated with cell transplantation and shows great promise in treating intervertebral disc degeneration by carrying therapeutic cargo. This review comprehensively examines the latest research, underlying mechanisms, and therapeutic potential of extracellular vesicles, offering a promising new strategy for intervertebral disc degeneration treatment.

Hydrogel microspheres for bone regeneration through regulation of the regenerative microenvironment

Bone defects are a prevalent category of skeletal tissue disorders in clinical practice, with a range of pathogenic factors and frequently suboptimal clinical treatment effects. In bone regeneration of bone defects, the bone regeneration microenvironment-composed of physiological, chemical, and physical components-is the core element that dynamically coordinates to promote bone regeneration. In recent years, medical biomaterials with bioactivity and functional tunability have been widely researched upon and applied in the fields of tissue replacement/regeneration, and remodelling of organ structure and function. The biomaterial treatment system based on the comprehensive regulation strategy of bone regeneration microenvironment is expected to solve the clinical problem of bone defect. Hydrogel microspheres (HMS) possess a highly specific surface area and porosity, an easily adjustable physical structure, and high encapsulation efficiency for drugs and stem cells. They can serve as highly efficient carriers for bioactive factors, gene agents, and stem cells, showing potential advantages in the comprehensive regulation of bone regeneration microenvironment to enhance bone regeneration. This review aims to clarify the components of the bone regeneration microenvironment, the application of HMS in bone regeneration, and the associated mechanisms. It also discusses various preparation materials and methods of HMS and their applications in bone tissue engineering. Furthermore, it elaborates on the relevant mechanisms by which HMS regulates the physiological, chemical, and physical microenvironment in bone regeneration to achieve bone regeneration. Finally, we discuss the future prospects of the HMS system application for comprehensive regulation of bone regeneration microenvironment, to provide novel perspectives for the research and application of HMS in the bone tissue engineering field.

Advances in application of hypoxia-preconditioned mesenchymal stem cell-derived exosomes

Mesenchymal stem cells (MSCs) primarily secrete physiologically functional exosomes via paracrine effects that act on various adjacent and distant cells, thus exerting their therapeutic effects. In recent years, hypoxic preconditioning, as a novel MSC culture mode, has emerged as a research hotspot. Many previous studies have shown the role and underlying regulatory mechanisms of hypoxic preconditioning in various diseases, which has provided sufficient reference materials for the MSC research field. Therefore, this review summarizes the progress in application of hypoxia-preconditioned MSC-derived exosomes that substantially increases and improves the biological activity of specific molecules, such as microRNA.

Exosome-loaded biomaterials for tendon/ligament repair

Exosomes, a specialised type of extracellular vesicle, have attracted significant attention in the realm of tendon/ligament repair as a potential biologic therapeutic tool. While the competence of key substances responsible for the delivery function was gradually elucidated, series of shortcomings exemplified by the limited stability still need to be improved. Therefore, how to take maximum advantage of the biological characteristics of exosomes is of great importance. Recently, the comprehensive exploration and application of biomedical engineering has improved the availability of exosomes and revealed the future direction of exosomes combined with biomaterials. This review delves into the present application of biomaterials such as nanomaterials, hydrogels, and electrospun scaffolds, serving as the carriers of exosomes in tendon/ligament repair. By pinpointing and exploring their strengths and limitations, it offers valuable insights, paving the way the future direction of biomaterials in the application of exosomes in tendon/ligament repair in this field.

Extracellular Vesicles in the Repair of Bone and Cartilage Injury: From Macro‐Delivery to Micro‐Modification

Extracellular vesicles (EVs) are intermediaries in intercellular signal transmission and material exchange and have attracted significant attention from researchers in bone and cartilage repair. These nanoscale vesicles hold immense potential in facilitating bone and cartilage repair and regeneration by regulating the microenvironment at an injury site. However, their in vivo utilization is limited by their self‐clearance and random distribution. Therefore, various delivery platforms have been developed to improve EV targeting and retention rates in target organs while achieving a controlled release of EVs. Additionally, engineering modification of EVs has been proposed to effectively enhance EVs' intrinsic targeting and drug‐loading abilities and further improve their therapeutic effects on bone and cartilage injuries. This review aims to introduce the biogenesis of EVs and their regulatory mechanisms in the microenvironment of bone and cartilage injuries and comprehensively discuss the application of EV‐delivery platforms of different materials and various EV engineering modification methods in treating bone and cartilage injuries. The review's findings can help advance EV research and develop new strategies for improving the therapy of bone and cartilage injuries.

Hydrogels in Gene Delivery Techniques for Regenerative Medicine and Tissue Engineering

Hydrogels are 3D networks swollen with water. They are biocompatible, strong, and moldable and are emerging as a promising biomedical material for regenerative medicine and tissue engineering to deliver therapeutic genes. The excellent natural extracellular matrix simulation properties of hydrogels enable them to be co-cultured with cells or enhance the expression of viral or non-viral vectors. Its biocompatibility, high strength, and degradation performance also make the action process of carriers in tissues more ideal, making it an ideal biomedical material. It has been shown that hydrogel-based gene delivery technologies have the potential to play therapy-relevant roles in organs such as bone, cartilage, nerve, skin, reproductive organs, and liver in animal experiments and preclinical trials. This paper reviews recent articles on hydrogels in gene delivery and explains the manufacture, applications, developmental timeline, limitations, and future directions of hydrogel-based gene delivery techniques.

Visualization Analysis of Small Extracellular Vesicles in the Application of Bone-Related Diseases

Small extracellular vesicles were shown to have similar functional roles to their parent cells without the defect of potential tumorigenicity, which made them a great candidate for regenerative medicine. The last twenty years have witnessed the rapid development of research on small extracellular vesicles. In this paper, we employed a scientometric synthesis method to conduct a retrospective analysis of small extracellular vesicles in the field of bone-related diseases. The overall background analysis consisted the visualization of the countries, institutions, journals, and authors involved in research. The current status of the research direction and future trends were presented through the analysis of references and keywords, which showed that engineering strategies, mesenchymal stem cell derived exosomes, and cartilage damage were the most concerning topics, and scaffold, osteoarthritis, platelet-rich plasma, and senescence were the future trends. We also discussed the current problems and challenges in practical applications, including the in-sight mechanisms, the building of relevant animal models, and the problems in clinical trials. By using CiteSpace, VOSviewer, and Bibliometrix, the presented data avoided subjective selectivity and tendency well, which made the conclusion more reliable and comprehensive. We hope that the findings can provide new perspectives for researchers to understand the evolution of this field over time and to search for novel research directions.

Developing hydrogels for gene therapy and tissue engineering

Hydrogels are a class of highly absorbent and easily modified polymer materials suitable for use as slow-release carriers for drugs. Gene therapy is highly specific and can overcome the limitations of traditional tissue engineering techniques and has significant advantages in tissue repair. However, therapeutic genes are often affected by cellular barriers and enzyme sensitivity, and carrier loading of therapeutic genes is essential. Therapeutic gene hydrogels can well overcome these difficulties. Moreover, gene-therapeutic hydrogels have made considerable progress. This review summarizes the recent research on carrier gene hydrogels for the treatment of tissue damage through a summary of the most current research frontiers. We initially introduce the classification of hydrogels and their cross-linking methods, followed by a detailed overview of the types and modifications of therapeutic genes, a detailed discussion on the loading of therapeutic genes in hydrogels and their characterization features, a summary of the design of hydrogels for therapeutic gene release, and an overview of their applications in tissue engineering. Finally, we provide comments and look forward to the shortcomings and future directions of hydrogels for gene therapy. We hope that this article will provide researchers in related fields with more comprehensive and systematic strategies for tissue engineering repair and further promote the development of the field of hydrogels for gene therapy.

The current status and development trend of hydrogel application in spinal surgery

Spinal diseases often result in compromised mobility and diminished quality of life due to the intricate anatomy surrounding the nervous system. Medication and surgical interventions remain the primary treatment methods for spinal conditions. However, currently available medications have limited efficacy in treating spinal surgical diseases and cannot achieve a complete cure. Furthermore, surgical intervention frequently results in inevitable alterations and impairments to the initial anatomical integrity of the spinal structure, accompanied by the consequential loss of certain physiological functionalities. Changes in spine surgery treatment concepts and modalities in the last decade have led to a deepening of minimally invasive treatment, with treatment strategies focusing more on repairing and reconstructing the patient's spine and preserving physiological functions. Therefore, developing novel and more efficient treatment strategies to reduce spinal lesions and iatrogenic injuries is essential. In recent years, significant advancements in biomedical research have led to the discovery that hydrogels possess excellent biocompatibility, biodegradability, and adjustable mechanical properties. The application of hydrogel-based biotechnology in spinal surgery has demonstrated remarkable therapeutic potential. This review presents the therapeutic strategies for spinal diseases based on hydrogel tissue engineering technology.

Extracellular Vesicles and Hydrogels: An Innovative Approach to Tissue Regeneration

Extracellular vesicles have emerged as promising tools in regenerative medicine due to their inherent ability to facilitate intercellular communication and modulate cellular functions. These nanosized vesicles transport bioactive molecules, such as proteins, lipids, and nucleic acids, which can affect the behavior of recipient cells and promote tissue regeneration. However, the therapeutic application of these vesicles is frequently constrained by their rapid clearance from the body and inability to maintain a sustained presence at the injury site. In order to overcome these obstacles, hydrogels have been used as extracellular vesicle delivery vehicles, providing a localized and controlled release system that improves their therapeutic efficacy. This Review will examine the role of extracellular vesicle-loaded hydrogels in tissue regeneration, discussing potential applications, current challenges, and future directions. We will investigate the origins, composition, and characterization techniques of extracellular vesicles, focusing on recent advances in exosome profiling and the role of machine learning in this field. In addition, we will investigate the properties of hydrogels that make them ideal extracellular vesicle carriers. Recent studies utilizing this combination for tissue regeneration will be highlighted, providing a comprehensive overview of the current research landscape and potential future directions.

Can extracellular vesicles be considered as a potential frontier in the treatment of intervertebral disc disease?

As a global public health problem, low back pain (LBP) caused by intervertebral disc degeneration (IDD) seriously affects patients' quality of life. In addition, the prevalence of IDD tends to be younger, which brings a huge burden to individuals and society economically. Current treatments do not delay or reverse the progression of IDD. The emergence of biologic therapies has brought new hope for the treatment of IDD. Among them, extracellular vesicles (EVs), as nanoscale bioactive substances that mediate cellular communication, have now produced many surprising results in the research of the treatment of IDD. This article reviews the mechanisms and roles of EVs in delaying IDD and describes the prospects and challenges of EVs.

Hydrogel-Loaded Exosomes: A Promising Therapeutic Strategy for Musculoskeletal Disorders

Clinical treatment strategies for musculoskeletal disorders have been a hot research topic. Accumulating evidence suggests that hydrogels loaded with MSC-derived EVs show great potential in improving musculoskeletal injuries. The ideal hydrogels should be capable of promoting the development of new tissues and simulating the characteristics of target tissues, with the properties matching the cell-matrix constituents of autologous tissues. Although there have been numerous reports of hydrogels loaded with MSC-derived EVs for the repair of musculoskeletal injuries, such as intervertebral disc injury, tendinopathy, bone fractures, and cartilage injuries, there are still many hurdles to overcome before the clinical application of modified hydrogels. In this review, we focus on the advantages of the isolation technique of EVs in combination with different types of hydrogels. In this context, the efficacy of hydrogels loaded with MSC-derived EVs in different musculoskeletal injuries is discussed in detail to provide a reference for the future application of hydrogels loaded with MSC-derived EVs in the clinical treatment of musculoskeletal injuries.

Application of stem cells in regeneration medicine

Regeneration is a complex process affected by many elements independent or combined, including inflammation, proliferation, and tissue remodeling. Stem cells is a class of primitive cells with the potentiality of differentiation, regenerate with self-replication, multidirectional differentiation, and immunomodulatory functions. Stem cells and their cytokines not only inextricably linked to the regeneration of ectodermal and skin tissues, but also can be used for the treatment of a variety of chronic wounds. Stem cells can produce exosomes in a paracrine manner. Stem cell exosomes play an important role in tissue regeneration, repair, and accelerated wound healing, the biological properties of which are similar with stem cells, while stem cell exosomes are safer and more effective. Skin and bone tissues are critical organs in the body, which are essential for sustaining life activities. The weak repairing ability leads a pronounced impact on the quality of life of patients, which could be alleviated by stem cell exosomes treatment. However, there are obstacles that stem cells and stem cells exosomes trough skin for improved bioavailability. This paper summarizes the applications and mechanisms of stem cells and stem cells exosomes for skin and bone healing. We also propose new ways of utilizing stem cells and their exosomes through different nanoformulations, liposomes and nanoliposomes, polymer micelles, microspheres, hydrogels, and scaffold microneedles, to improve their use in tissue healing and regeneration.

An Inquiry-Based Learning STEM Outreach Module to Teach Principles of Bioadhesives and Tissue Repair

Bioadhesives are an important subset of biomaterials, which aid wound healing, hemostasis, and tissue repair. In order to advance the field of bioadhesives to promote more regenerative healing, there is a societal need to teach diverse trainees about their design, engineering, and testing. To address this, we deployed a hands-on, inquiry-based learning (IBL) bioadhesives module to middle school students from underserved communities in the Young Eisner Scholars (YES) program. The module, which lasted approximately 3 hr, was designed to teach students about applications of bioadhesives, engineering bioadhesives for various biomedical applications, and mechanically testing their adhesive strength using standard practices. Students who participated in our IBL bioadhesives module displayed significant learning gains by pre/post-test assessment, demonstrating that the module was effective for middle school outreach. Pre/post-survey assessments showed no significant differences in attitudes towards STEM, which was likely due to the fact that students in YES had a strong predisposition for STEM. Overall, results motivate the use of this module, or similar hands-on IBL modules, for outreach with K-12 students who are underrepresented in STEM.

Emerging tissue engineering strategies for annulus fibrosus therapy

Low back pain is a major public health concern experienced by 80% of the world's population during their lifetime, which is closely associated with intervertebral disc (IVD) herniation. IVD herniation manifests as the nucleus pulposus (NP) protruding beyond the boundaries of the intervertebral disc due to disruption of the annulus fibrosus (AF). With a deepening understanding of the importance of the AF structure in the pathogenesis of intervertebral disc degeneration, numerous advanced therapeutic strategies for AF based on tissue engineering, cellular regeneration, and gene therapy have emerged. However, there is still no consensus concerning the optimal approach for AF regeneration. In this review, we summarized strategies in the field of AF repair and highlighted ideal cell types and pro-differentiation targeting approaches for AF repair, and discussed the prospects and difficulties of implant systems combining cells and biomaterials to guide future research directions. STATEMENT OF SIGNIFICANCE: Low back pain is a major public health concern experienced by 80% of the world's population during their lifetime, which is closely associated with intervertebral disc (IVD) herniation. However, there is still no consensus concerning the optimal approach for annulus fibrosus (AF) regeneration. In this review, we summarized strategies in the field of AF repair and highlighted ideal cell types and pro-differentiation targeting approaches for AF repair, and discussed the prospects and difficulties of implant systems combining cells and biomaterials to guide future research directions.

Teaching Tissue Repair Through an Inquiry-Based Learning Bioadhesives Module

Bioadhesives are an important class of biomaterials for wound healing, hemostasis, and tissue repair. To develop the next generation of bioadhesives, there is a societal need to teach trainees about their design, engineering, and testing. This study designed, implemented, and evaluated a hands-on, inquiry-based learning (IBL) module to teach bioadhesives to undergraduate, master's, and PhD/postdoctoral trainees. Approximately 30 trainees across three international institutions participated in this IBL bioadhesives module, which was designed to last approximately 3 h. This IBL module was designed to teach trainees about how bioadhesives are used for tissue repair, how to engineer bioadhesives for different biomedical applications, and how to assess the efficacy of bioadhesives. The IBL bioadhesives module resulted in significant learning gains for all cohorts; whereby, trainees scored an average of 45.5% on the pre-test assessment and 69.0% on the post-test assessment. The undergraduate cohort experienced the greatest learning gains of 34.2 points, which was expected since they had the least theoretical and applied knowledge about bioadhesives. Validated pre/post-survey assessments showed that trainees also experienced significant improvements in scientific literacy from completing this module. Similar to the pre/post-test, improvements in scientific literacy were most significant for the undergraduate cohort since they had the least amount of experience with scientific inquiry. Instructors can use this module, as described, to introduce undergraduate, master's, and PhD/postdoctoral trainees to principles of bioadhesives.

Application of stem cells combined with biomaterial in the treatment of intervertebral disc degeneration

As the world population is aging, intervertebral disc degeneration (IDD) is becoming a global health issue of increasing concern. A variety of disc degeneration diseases (DDDs) have been proven to be associated with IDD, and these illnesses have significant adverse effects on both individuals and society. The application of stem cells in regenerative medicine, such as blood and circulation, has been demonstrated by numerous studies. Similarly, stem cells have made exciting progress in the treatment of IDD. However, due to complex anatomical structures and functional requirements, traditional stem cell injection makes it difficult to meet people's expectations. With the continuous development of tissue engineering and biomaterials, stem cell combined with biomaterials has far more prospects than before. This review aims to objectively and comprehensively summarize the development of stem cells combined with contemporary biomaterials and the difficulties that need to be overcome.