Injectable hydrogels for sustained delivery of extracellular vesicles in cartilage regeneration

Innovative injectable, self-healing, exosome cross-linked biomimetic hydrogel for cartilage regeneration

The limited self-healing capacity of cartilage hinders its repair and regeneration at the defect sites. Recent research into small-molecular compounds has shown promise in achieving a better regeneration of cartilage. In this study, we encapsulate kartogenin (KGN) and transforming growth factor β1 (TGF-β1) within mesenchymal stem cells derived exosomes (EKT), and then coated them with succinylated chitosan (sCH) to create positively charged exosomes, termed CEKT. These CEKT exhibit exceptional chondrogenic promoting capabilities shown during in vitro studies with bone marrow derived mesenchymal stem cells (BMSCs). They also can penetrate deep into cartilage tissue derived from porcine knee joints guided by their positive charge. Subsequently, a dynamic exosomes-crosslinked hydrogel (Gel-CEKT) is fabricated by crosslinking CEKT with oxidized chondroitin sulfate (oCS) and Wharton's jelly (WJ) through imine bond formation. Physicochemical studies revealed the injectability, excellent adhesive, and self-healing abilities of this hydrogel, which enables minimally invasive and precise treatment of cartilage defects, assisted by the enriched and sustained administration of CEKT. In vitro cell experiments show that Gel-CEKT can efficiently recruit BMSCs and significantly promote the gene expression of Sox9 and protein expression of collagen II and aggrecan. Furthermore, we show in a rat model of cartilage defect that the Gel-CEKT demonstrates superior performance compared to Gel@EKT, which has freely encapsulated exosomes in the hydrogel. The freely encapsulated exosomes are rapidly released, whereas the exosome-crosslinked gel structure ensures sustained retention and functionality at the site of defect. This leads to impressive outcomings, including extensive new cartilage tissue formation, a smoother cartilage surface, significant chondrocyte production, and seamless integration with orderly and continuous structure formation between cartilage and subchondral bone. This study underscores the potential of exosomes-crosslinked hydrogels as a novel and promising therapeutic approach for clinical cartilage regeneration.

Cathepsin K Inhibitors as Potential Drugs for the Treatment of Osteoarthritis

Links between cathepsin K and the pathophysiology of osteoarthritis (OA) can be established, not least because of the overabundance of cathepsin K in the serum of OA patients and the upregulation of cathepsin K in degraded cartilage in animal models of OA. Chondrocytes, chondroclasts, or osteoclasts contribute to the accumulated cathepsin K at the diseased osteochondral junction. After a general presentation of OA and cartilage physiology, as well as its degradation processes, we describe the function of cathepsin K and its effect on cartilage degradation via type II collagen cleavage. An overview of the most promising cathepsin K inhibitors is then presented, together with their in vitro effects. Although intensive research on cathepsin K inhibitors initially focused on bone resorption, there is growing interest in the potential of these drugs to prevent cartilage degradation. In this review, we summarize the pre-clinical and clinical trials that support the use of cathepsin K inhibitors in the treatment of OA. To date, no molecules of this type are commercially available, although a few have undergone clinical trials, but we believe that the development of cathepsin K inhibitors could broaden the therapeutic arsenal for the treatment of OA.

Skin regenerative potential of hydrogel matrices incorporated with stem cell-derived extracellular vesicles enriched with MicroRNAs: a systematic review

Stem cell-derived extracellular vesicles (SC-EVs) are one huge promise in skin regenerative medicine, similar in advantages to stem cells with low immunerejection and tumor formations. These microvesicles are laden with microRNAs, which assist in wound healing via angiogenesis and immune modulation. However, quick degradation and poor cellular uptake limit their regenerative capacity. Thanks to their adjustable characteristics, hydrogels can act as vehicles for transporting and sustainably releasing miRNA-SC-EVs at injury sites. Therefore, a systematic literature review was conducted on miRNA-enriched SC-EVs incorporated into hydrogels in animal skin regeneration models published from 2010 to 2024 (PROSPERO ID: CRD42024588072). Out of the 89 records, 12 met the criteria. Diabetic wounds are characterized by chronic inflammation, oxidative stress, and defective macrophage polarization, resulting in less satisfactory regeneration. The hydrogels tackled these issues by shifting macrophages from a pro-inflammatory M1 phenotype to a healing M2 phenotype, promoting collagen production, enhancing fibroblast movement, and boosting angiogenesis. Burn injuries frequently lead to slow recovery due to hypertrophic scarring, extended inflammation, and infection. Hyaluronic acid (HA)-derived hydrogels, infused with miR-21-5p and surface-treated with polydopamine and cationic antimicrobial peptides, promoted wound healing by lowering scarring and demonstrating anti-inflammatory, anti-apoptotic, and pro-angiogenic characteristics. The cell adhesion of these hydrogels can be enhanced by adding MOFs, chitosan, and extracellular matrix elements. The application of stimulus-responsive or stage-specific hydrogels is another mode of targeted healing. Further research and clinical trials will enhance the wound-healing efficiency of hybrid hydrogels.

External stimuli-driven catalytic hydrogels for biomedical applications

Hydrogels, bearing three-dimensional networks formed through chemical or physical crosslinking of hydrophilic macromolecules, benefit from their biocompatibility, tunable properties, and high loading capacities, and thus hold great promise for biomedical applications. Recent advancements have increasingly focused on the integration of non-invasive external stimuli-such as light, heat, electricity, magnetism, and ultrasound-into hydrogel design. These external stimuli-driven catalytic hydrogels can dynamically respond to these stimuli, allowing for high spatial and temporal precision in their application. This capability enables in situ activation, controlled degradation, and catalytic reactions, making them ideal for next-generation clinical interventions. This review discusses the design strategies for external stimuli-driven catalytic hydrogels, concentrating on essential mechanisms of catalytic processes aimed at optimizing therapeutic efficacy. The discussion highlights the importance of precise control over the chemical and physical properties of hydrogels in response to specific stimuli, elucidating the regulatory mechanisms that dictate hydrogel behavior and deepening the understanding of their applications with enhanced spatial and temporal resolution.

Effects of Hydrogels on Mesenchymal Stem/Stromal Cells Paracrine Activity and Extracellular Vesicles Production

Mesenchymal stem/stromal cells (MSCs) are a valuable source of paracrine factors, as they have a remarkable secretory capacity, and there is a sizeable knowledge base to develop industrial and clinical production protocols. Promising cell-free approaches for tissue regeneration and immunomodulation are driving research towards secretome applications, among which extracellular vesicles (EVs) are steadily gaining attention. However, the manufacturing and application of EVs is limited by insufficient yields, knowledge gaps, and low standardization. Facing these limitations, hydrogels represent a versatile three-dimensional (3D) culture platform that can incorporate extracellular matrix (ECM) components to mimic the natural stem cell environment in vitro; via these niche-mimicking properties, hydrogels can regulate MSCs' morphology, adhesion, proliferation, differentiation and secretion capacities. However, the impact of the hydrogel's architectural, biochemical and biomechanical properties on the production of EVs remains poorly understood, as the field is still in its infancy and the interdependency of culture parameters compromises the comparability of the studies. Therefore, this review summarizes and discusses the reported effects of hydrogel encapsulation and culture on the secretion of MSC-EVs. Considering the effects of cell-material interactions on the overall paracrine activity of MSCs, we identify persistent challenges from low standardization and process control, and outline future paths of research, such as the synergic use of hydrogels and bioreactors to enhance MSC-EV generation.

Engineered Extracellular Vesicles as a New Class of Nanomedicine

Extracellular vesicles (EVs) are secreted from biological cells and contain many molecules with diagnostic values or therapeutic functions. There has been great interest in academic and industrial communities to utilize EVs as tools for diagnosis or therapeutics. In addition, EVs can also serve as delivery vehicles for therapeutic molecules. An indicator of the enormous interest in EVs is the large number of review articles published on EVs, with the focus ranging from their biology to their applications. An emerging trend in EV research is to produce and utilize "engineered EVs", which are essentially the enhanced version of EVs. EV engineering can be conducted by cell culture condition control, genetic engineering, or chemical engineering. Given their nanometer-scale sizes and therapeutic potentials, engineered EVs are an emerging class of nanomedicines. So far, an overwhelming majority of the research on engineered EVs is preclinical studies; there are only a very small number of reported clinical trials. This Review focuses on engineered EVs, with a more specific focus being their applications in therapeutics. The various approaches to producing engineered EVs and their applications in various diseases are reviewed. Furthermore, in vivo imaging of EVs, the mechanistic understandings, and the clinical translation aspects are discussed. The discussion is primarily on preclinical studies while briefly mentioning the clinical trials. With continued interdisciplinary research efforts from biologists, pharmacists, physicians, bioengineers, and chemical engineers, engineered EVs could become a powerful solution for many major diseases such as neurological, immunological, and cardiovascular diseases.

Silk fibroin and hydroxypropyl cellulose composite injectable hydrogel-containing extracellular vesicles for myocardial infarction repair

Extracellular vesicles (EVs) have been recognized as one of the promising specific drugs for myocardial infarction (MI) prognosis. Nevertheless, low intramyocardial retention of EVs remains a major impediment to their clinical application. In this study, we developed a silk fibroin/hydroxypropyl cellulose (SF/HPC) composite hydrogel combined with AC16 cell-derived EVs targeted modification by folic acid for the treatment of acute myocardial infarction repair. EVs were functionalized by distearoylphosphatidyl ethanolamine-polyethylene glycol (DSPE-PEG-FA) via noncovalent interaction for targeting and accelerating myocardial infarction repair.In vitro, cytocompatibility analyses revealed that the as-prepared hydrogels had excellent cell viability by MTT assay and the functionalized EVs had higher cell migration by scratch assay.In vivo, the composite hydrogels can promote myocardial tissue repair effects by delaying the process of myocardial fibrosis and promoting angiogenesis of infarct area in MI rat model.

Advances in Polysaccharides for Cartilage Tissue Engineering Repair: A Review

Cartilage repair has been a significant challenge in orthopedics that has not yet been fully resolved. Due to the absence of blood vessels and the almost cell-free nature of mature cartilage tissue, the limited ability to repair cartilage has resulted in significant socioeconomic pressures. Polysaccharide materials have recently been widely used for cartilage tissue repair due to their excellent cell loading, biocompatibility, and chemical modifiability. They also provide a suitable microenvironment for cartilage repair and regeneration. In this Review, we summarize the techniques used clinically for cartilage repair, focusing on polysaccharides, polysaccharides for cartilage repair, and the differences between these and other materials. In addition, we summarize the techniques of tissue engineering strategies for cartilage repair and provide an outlook on developing next-generation cartilage repair and regeneration materials from polysaccharides. This Review will provide theoretical guidance for developing polysaccharide-based cartilage repair and regeneration materials with clinical applications for cartilage tissue repair and regeneration.

Harnessing the multifunctionality of lipid-based drug delivery systems for the local treatment of osteoarthritis

Osteoarthritis (OA) is a widespread joint condition affecting millions globally, presenting a growing socioeconomic burden thus making the development of more effective therapeutic strategies crucial. This review emphasizes recent advancements in lipid-based drug delivery systems (DDSs) for intra-articular administration of OA therapeutics, encompassing non-steroidal anti-inflammatory drugs, corticosteroids, small molecule disease-modifying OA drugs, and RNA therapeutics. Liposomes, lipid nanoparticles, lipidic mesophases, extracellular vesicles and composite systems exhibit enhanced stability, targeted delivery, and extended joint retention, which contribute to improved therapeutic outcomes and minimized systemic drug exposure. Although active targeting strategies hold promise, further research is needed to assess their targeting efficiency in physiologically relevant conditions. Simultaneously, multifunctional DDSs capable of delivering combinations of distinct therapeutic classes offer synergistic effects and superior OA treatment outcomes. The development of such long-acting systems that resist rapid clearance from the joint space is crucial, where particle size and targeting capabilities emerge as vital factors. Additionally, combining cartilage lubrication properties with sustained drug delivery has demonstrated potential in animal models, meriting further investigation in human clinical trials. This review highlights the crucial need for direct, head-to-head comparisons of novel DDSs with standard treatments, particularly within the same drug class. These comparisons are essential in accurately evaluating their effectiveness, safety, and clinical applicability, and are set to significantly shape the future of OA therapy.

Targeted heart repair by Tβ4-loaded cardiac-resident macrophage-derived extracellular vesicles modified with monocyte membranes

Recent studies have demonstrated the critical role of cardiac-resident macrophages (cMacs) in the maintenance of physiological homeostasis. However, recruitment of circulating monocyte-derived macrophages decreases cMac levels post-myocardial infarction (MI). Transplanting cMacs is not an ideal option due to their low survival rates and the risk of immunological rejection. However, extracellular vesicle therapy has the potential to provide a feasible and safe alternative for cardiac repair. In this study, cell membrane-modified extracellular vesicles (MmEVs) were developed for heart repair by modifying cMac-derived extracellular vesicles (mEVs) with monocyte membranes, resulting in immune evasion and sequential targeted localization to damaged regions through expression of CD47 on MmEVs and strong affinity between monocyte membrane proteins and CCL2. Additionally, to fully exploit the potential clinical application of MmEVs and achieve a better curative effect, thymosin β4 (Tβ4) was loaded into the nanoparticles, resulting in Tβ4-MmEVs. In vitro experiments indicated that both the MmEVs and Tβ4-MmEVs promoted cardiomyocyte proliferation and endothelial cell migration. Animal experiments suggested that MI mice treated with MmEVs and Tβ4-MmEVs exhibited reduced myocardial fibrosis and increased vascular density compared to the control group. Thus, we posit that these targeted nanoparticles hold significant potential for MI adjuvant therapy and may open new avenues for cardiac repair and regeneration. STATEMENT OF SIGNIFICANCE: Extracellular vesicles (EVs) derived from bioactive parent cell sources involved in pathological and repair processes for cardiovascular disease have emerged as a compelling strategy for regenerative therapy. In this study, we constructed monocyte membrane-modified extracellular vesicles loaded with a drug (Tβ4-MmEVs) for heart repair that exhibit extraordinary abilities of immune evasion and sequential localization to damaged regions owing to the presence of CD47 and the strong affinity between monocytes and damaged cardiomyocytes and endothelial cells. The bioactivities of Tβ4-MmEVs on enhancing cardiomyocyte and endothelial cell proliferation were validated both in vitro and in vivo. Effective development and implementation of therapeutically membrane-modified nanoparticles from homologous origins can provide a reference for adjuvant therapy in clinical MI management.

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.

Engineered extracellular vesicles as therapeutics of degenerative orthopedic diseases

Degenerative orthopedic diseases, as a global public health problem, have made serious negative impact on patients' quality of life and socio-economic burden. Traditional treatments, including chemical drugs and surgical treatments, have obvious side effects and unsatisfactory efficacy. Therefore, biological therapy has become the focus of researches on degenerative orthopedic diseases. Extracellular vesicles (EVs), with superior properties of immunoregulatory, growth support, and drug delivery capabilities, have emerged as a new cell-free strategy for the treatment of many diseases, including degenerative orthopedic diseases. An increasing number of studies have shown that EVs can be engineered through cargo loading, surface modification, and chemical synthesis to improve efficiency, specificity, and safety. Herein, a comprehensive overview of recent advances in engineering strategies and applications of engineered EVs as well as related researches in degenerative orthopedic diseases, including osteoarthritis (OA), osteoporosis (OP), intervertebral disc degeneration (IDD) and osteonecrosis of the femoral head (ONFH), is provided. In addition, we analyze the potential and challenges of applying engineered EVs to clinical practice.