The biogenesis of EVs is complex, and the types of EVs formed by different cells are heterogeneous. In the following, the biogenesis of EVs is briefly summarized according to different types, as is briefly shown in Figure 1.

Exosomes are secreted into the extracellular space by donor cells and alter the microenvironment through cell-to-cell interactions through fusion with the plasma membrane and subsequent endocytosis and release of cargo (Alptekin et al., 2022). EV uptake by cells appears to occur through a variety of endocytic pathways, including clathrin-dependent endocytosis and clathrin-independent pathways, such as fossa protein-mediated uptake, macropinocytosis, phagocytosis, and lipid raft-mediated internalization, and heterogeneous EV populations may enter cells by different route, depending on the proteins and glycoproteins found on the surface of the vesicle and target cells (Mulcahy et al., 2014). Specific protein-protein interactions can mediate EV attachment and uptake into cells. These proteins include tetratransmembrane proteins, integrins and immunoglobulins, proteoglycans, and lectins (Raposo et al., 1996; Théry et al., 1999; Tumne et al., 2009; Barrès et al., 2010; Christianson et al., 2013; Svensson et al., 2013). Endocytosis, including caveolin-dependent endocytosis, macropinocytosis, and lipid-raft mediated internalization, is a rapid and common pathway for EV uptake, which requires energy and cytoskeleton (Hao et al., 2007; Barrès et al., 2010; Feng et al., 2010).

In addition, it has been reported that viruses may have adopted existing EV-mediated communication pathways as their infection strategies, and exposure of phosphatidylserine groups on exosome surfaces has been observed in some studies, which may be one of the common targeting mechanisms of both exosomes and viruses (Feng et al., 2010; Fitzner et al., 2011; van Dongen et al., 2016).

At present, extracellular vesicles have been widely used and reported in clinical trials (Shah et al., 2018; Maacha et al., 2019; Elsharkasy et al., 2020; Hu et al., 2021; Russell et al., 2022).

The important role of extracellular vesicles as diagnostic biomarkers in the diagnosis of cancer (Krug et al., 2018; McKiernan et al., 2018), infection (Kornek et al., 2012; Delabranche et al., 2013), autoimmune disease (Burbano et al., 2019; Cuomo-Haymour et al., 2022) has been reported. Some of the protein, DNA, mRNA, miRNA, lncRNA, circRNA, and other cargo carried by extracellular vesicles in blood or tissue fluid will show specific increase or decrease under specific disease conditions, and can reflect disease degree and prognosis to a certain extent (Becker et al., 2016; Merchant et al., 2017; Wang et al., 2019; Thietart and Rautou, 2020).

Extracellular vesicles with therapeutic effects are widely used in the treatment of cancer (Shuen et al., 2022), cardiovascular disease (Lin et al., 2021; Reddel et al., 2021), inflammatory disease (Robbins and Morelli, 2014; Arab et al., 2020), degenerative disease (Liu et al., 2022a; Yin et al., 2022a). In addition, extracellular vesicles have been reported for the treatment of maternal and neonatal diseases (Mohammad et al., 2022Mohammad et al., 2022). We believe that clinical application of extracellular vesicles in more disease models is promising.

OA is a degenerative disease that worsens as people age and can lead to chronic pain and stiffness (Glyn-Jones et al., 2015a). The pathological characteristics of OA are very complicated, mainly involving cartilage degeneration, chondrocyte necrosis, matrix destruction, synovial hyperplasia, bone spurs formation, and subchondral osteomalacia (Xia et al., 2014; Abramoff and Caldera, 2020). At present, the research on the treatment of OA with EVs mostly focuses on their functions of chondrogenesis, anti-inflammation, and regulation of ECM as is shown in Table 1.

One of the important pathogenesis of OA is the imbalance between anabolism and catabolism of chondrocytes. Aging, trauma, biomechanics, obesity, and changes in biological rhythms can lead to chondrocyte hypertrophy or apoptosis, metabolic disorders, and cellular senescence, which in turn cause the destruction of cartilage homeostasis and induce OA (Glyn-Jones et al., 2015b). WNT5A, as a Wnt protein, plays an important role in the pathogenesis of OA, and it can mediate the destruction and degradation of cartilage. WNT5A has been reported to promote chondrocyte catabolism through noncanonical Wnt signaling, while also mediating cartilage destruction through the NF-kB pathway (Ge et al., 2009; Ge et al., 2011; Huang et al., 2017). EVs can enhance cartilage development and inhibit OA by targeting WNT5A. For example, Mao et al. found that miR-92a-3p in MSC-derived Exos could inhibit OA cartilage degradation by directly targeting WNT5A (Mao et al., 2018).

As an important part of articular cartilage, ECM can not only maintain the living environment of chondrocytes; but also play a supporting and nutritional role for chondrocytes. Its homeostasis plays a crucial role in maintaining the normal function of chondrocytes and timely responding to changes in the external environment. In the pathological setting of OA, loss of ECM leads to articular cartilage degeneration and articular structural deformity (Shi et al., 2019). EVs can promote the synthesis of cartilage matrix by up-regulating the expression of genes related to cartilage repair and syntheses such as SOX9, col2, and downregulate the genes of catabolic factors like MMP13, ADAMTS5, and MMP3 to inhibit degradation (Stella et al., 2017; Yafei et al., 2017; Hao et al., 2019; Shipin et al., 2019). Wnt/β-catenin and TGF-β signal pathways are common pathways involved in the synthesis of extracellular matrix and have been extensively studied (Wang et al., 2020a; Ming-Li et al., 2021). For example, PRP-derived EVs can promote the secretion of ECM by inhibiting the Wnt pathway and promoting the TGF-β pathway. Notably, this study also reported that PRP-EVs could promote chondrocyte proliferation and reduce the production of proinflammatory mediators (Liu et al., 2019).

In OA pathology, inflammatory or stress-induced signaling pathways may be activated in synovium and cartilage due to changes in the joint environment, leading to the production of cytokines, chemokines, adipokines, Toll-like receptor ligands, and other inflammatory mediators such as bone morphogenetic proteins (Elsa et al., 2022). These inflammatory mediators in turn lead to cartilage destruction and even ECM degradation through various signaling pathways such as ERK1/2 signaling (Robinson et al., 2016). Inhibiting the production of inflammatory mediators is one of the important mechanisms of native EVs in the treatment of OA. Zhang et al. found that MSC-Exos could activate AKT, ERK, and AMPK through adenosine receptors thereby inhibiting the production of NO and MMP13 (Shipin et al., 2019).

OP is a systemic disease characterized by low bone mass and destruction of bone microstructure, resulting in increased bone fragility and susceptibility to fractures (Wang et al., 2009; Compston et al., 2022). It usually develops slowly over several years and will cause great physical and psychological pain to patients. OP is usually caused by the imbalance between bone resorption and bone remodeling. When bone resorption exceeds bone formation, it often leads to the loss of bone mass and eventually leads to OP (Sambrook, 1996; Kleerekoper and Sullivan, 2022). At present, studies have found that EVs could maintain the stability of bone resorption and bone formation, thus slowing down the development of OP.

MSCs-derived EVs have been discovered to inhibit OP by promoting osteoblast proliferation and differentiation (Yue et al., 2018; Do-Kyun et al., 2021). In a study, osteogenesis-induced Exos derived from HucmSCs can participate in bone development and differentiation by highly expressing 221 microRNAs compared with Exos derived from unstimulated HucmSCs, suggesting that the mechanism of EVs involved in osteogenic differentiation is dependent on microRNA delivery. Interestingly, this study also revealed that the expressions of hsa-mir-2110 and hsa-mir-328-3p were gradually increased during osteogenic differentiation and regulated the target genes related to osteogenic differentiation (Yahao and Xinjia, 2021). The specific mechanisms of these two miRNAs still need to be further elucidated. In addition to miRNAs, studies have reported that lncRNA MALAT1 in EVs can reduce osteoporosis by MicroRNA-34c/satb2 axis, suggesting that lncRNA can be used as a promising new regulator of osteogenesis in MSCs-EVs (Wang et al., 2020a). CTHRC1 and OPG proteins, as bone-promoting proteins, have also been found in USCs in recent years (Kimura et al., 2008; Chun-Yuan et al., 2019). Chen et al. found that USC-EVs can promote bone formation by transferring these two proteins and thus provide a novel approach to osteogenic therapy (Chun-Yuan et al., 2019). Osteoclasts are the only cells with the ability to dissolve bone tissue and play an important role in bone remodeling. Its abnormal formation and activity can lead to the development of osteoporosis. EVs can inhibit osteoclast activity by activating a variety of pathways such as OPG/RANKL/RANK and Wnt/β-Catenin signaling pathways. For example, miR-27a delivered by MSCs-EVs could activate the Wnt/β-Catenin signaling pathway by inhibiting DKK2 and further inhibiting osteoclast activity and OP progression (Yue et al., 2018). Exosomes secreted by vascular endothelial cells (EC-exos) exhibit more effective bone targeting than exosomes derived from osteoblasts or bone marrow mesenchymal stem cells (Song et al., 2019). Bone targeting EVs have been used to improve bone diseases including osteoarthritis, osteoporosis and bone tumors (Ren et al., 2022). It is worth noting that there are not many reports about other specific types of EVs other than Exos. MSCs can engulf ApoBDs through integrin αvβ3 and reactivate the ApoBDs-derived ubiquitin ligase RNF146 and Mir-3283p to inhibit Axin1, thereby activating Wnt/β-catenin pathway and playing an important role in the process of osteogenic differentiation (Dawei et al., 2018). The specific types of EVs such as apoBDs and MVs still need to be further studied.

IDD is a common bone degenerative disease, which is usually caused by the deterioration of one or more intervertebral discs in the spine with age, leading to back or neck pain. The intervertebral disc is a fibrocartilage structure, that is composed of three parts including the outer annulus fibrosus (AF), the inner nucleus pulposus (NP), as well as cartilaginous endplate (CEP) that connects the vertebral bodies (Zhichao et al., 2022). This complex structure plays an important role in reducing the stress caused by impact, absorbing shock for the spine, and protecting the nerves between the vertebrae. The pathogenetic changes of IDD are complex, including abnormal ECM synthesis and degradation, apoptosis, angiogenesis, inflammation, CEP calcification, and so on.

So far, a large number of literature have reported the therapeutic effects of native EVs in IDD (Krut et al., 2021). Senescence and apoptosis of NPCs, EPCs and DCs are considered to be one of the factors that promote the progression of IDD (DiStefano et al., 2022). Studies have shown that the cargo present in native-EV can target to reduce cell senescence and apoptosis, as well as promote the proliferation of NPCs, EPCs, and DCs (Jimenez et al., 1988; Yongjin et al., 2021). As is reported in the literature, native EVs may exert their therapeutic effect by acting on PI3K/AKT pathway, MAPK/ERK pathway, TGF-β pathway, and Wnt pathway (Jun et al., 2019; Tao et al., 2020; Shaoqian and Lei, 2021; Liwen et al., 2022a). For instance, cui et al. discovered that MiR-129-5p delivered by BMMSCs-derived EVs can decrease the apoptosis of NPCs and alleviate IDD by targeting the LRG1/p38 MAPK pathway (Shaoqian and Lei, 2021). Besides miRNA, proteins such as NAMPT and MATN3 encapsulated in native EVs can also alleviate IDD. MATN3 in USC-Exos is proved by Guo et al. that can activate TGF-β to promote the proliferation and suppress the senescence of NPCs (Guo et al., 2021). Adipo-sEVs can attenuate IVDD in rats by delivering NAMPT to restore senescent NPCs and EPCs (Yongjin et al., 2021).

Oxidative stress and inflammation are reported to play an important role in the development of IDD. The increased level of ROS and the production of inflammatory cytokines in IDD can activate multiple signaling pathways such as the NF-KB pathway, which can cause the damage of degenerative ID cells, and increased catabolism of extracellular matrix, leading to the deterioration of ID structure and function (Feng et al., 2017; Guang-Zhi et al., 2020; Hainian et al., 2020). The endoplasmic reticulum (ER) has been reported to be an organelle involved in oxidative stress and inflammation (Yan et al., 2021a; Dong et al., 2021). Inflammatory cytokines can activate ER stress by activating PERK and IRE1-α, thereby inducing apoptosis (Zhiwei et al., 2019; Wen et al., 2021). Exos can alleviate IDD by inhibiting ER stress. Liao et al. discovered that MSC-EVs could alleviate the advanced glycation end products (AGE)-induced ER stress of NPC cells and inhibit the excessive unfolded protein response (UPR) to alleviate apoptosis via the AKT/ERK pathway (Zhiwei et al., 2019). Another study found that USCs-exos could inhibit NPC cell apoptosis in a dose-dependent manner by inhibiting ER stress (HongFei et al., 2020). Mitochondria is another organelle closely related to oxidative stress and inflammation, and its damage will lead to the rise of intracellular ROS, promoting inflammation generation and cell death (Liang et al., 2022a). It has been reported that MSC-evs can attenuate mitochondrial dysfunction in NPC by supplementing mitochondria-associated proteins, thereby inhibiting ROS production and NLRP3 activation (Chen et al., 2019). These results suggest that both the ER and mitochondria are important targets for EV therapy.

The imbalance of homeostasis of ECM is reported to promote the progression of IDD. Hence, enhancing extracellular matrix synthesis and reducing its degeneration are essential for IDD. MMPs are a family of proteases involved in the degradation of ECM in various tissues throughout the body and play an important role in promoting IDD. Xing et al. found that ADSCs-EVs can reduce the activity of MMPs to maintain ECM homeostasis (Hongyuan et al., 2021). In addition, miR-17-5p delivered by MSCs-evs is reported to upregulate the synthesis of Col II and Aggrecan, as well as reduce the production of MMP13 and ADAMTS5 via TLR4/PI3K/AKT pathway (Zhi-Min et al., 2021). Cir0072464 in BMMSCs-evs can target miR-431 and promote the expression of NRF2 to facilitate ECM synthesis (Yu et al., 2022).

Osteonecrosis is the destruction of blood supply to the bone caused by different causes, which leads to the degeneration and necrosis of subchondral bone and finally results in the degenerative and destructive changes of the joint (Pavelka, 2000Pavelka, 2000). Since osteonecrosis mostly occurs in the femoral head, current research usually focuses on the treatment of osteonecrosis of the femoral head (ONFH) (Cohen-Rosenblum and Cui, 2019). It has been reported that the angiogenic and apoptotic activities of bone microvascular endothelial cells (BMESs) are altered in patients with osteonecrosis of the femoral head, which suggests that ONFH could be treated by promoting angiogenesis and increasing osteogenesis (Weinstein, 2011; Noam et al., 2019). BMMSCs have multi-directional bone tissue differentiation potential, so they are widely used in the field of ONFH treatment. However, researchers have found that although BMMSCs have good characteristics of easy to extract and obtain immunogenicity, their proliferation, and osteogenic potential gradually decline with age. Guo et al. (2016) discovered the integration of BMSCs and SMSC-EVs would play a better role in proliferation and anti-apoptosis, which suggested that MSCs combined with EVs therapy had better application potential. EVs therapy alone has similarly been reported to have the potential to treat ONFH. BMMSCs-Exos can promote osteogenesis by up-regulating the gene expressions of Bmp2, Bmp6, Bmpr1b, Mmp9, and Sox9 and activate osteoblast differentiation, and in the transforming growth factor-β/bone morphogenetic protein pathways to inhibit ONFH (Shanhong et al., 2022). The PI3K/AKT pathway is another pathway in which EVs have been reported to be potentially involved in the treatment of ONFH (Jinhui et al., 2022; Xiaolin et al., 2023). Liu et al. revealed that iPS-MSC-Exo could promote the proliferation, migration, and tube-forming of endothelial cells via PI3K/AKT pathway (Xiaolin et al., 2023).

Tendinopathy, characterized by degenerative changes in cellular structure along with tendon mechanical properties, is a painful and swelling disease that can finally lead to the rupture of the tendon (Woodley et al., 2006; Millar et al., 2021). ECM disruption is one of the important pathogenesis of tendinopathy. MMP, as one of the proteolytic enzymes that degrade ECM, can be activated by inflammatory factors or mechanical stress to hydrolyze ECM and promote tissue damage (Godoy-Santos et al., 2012; Baroneza et al., 2014). However, TIMP, a natural inhibitor of MMP, can inhibit tissue degradation and antagonize MMP (Thornton et al., 2008). Wang et al. found that TCS-EV could reduce the expression of MMP-3 and increase the expression of TIMP3 and Col1a1, thereby improving the biomechanical properties of the tendon (Yunjiao et al., 2022). In another study, BMMSC-EVs can promote tendon repair by upregulating tenogenic differentiation and tendon matrix formation-related genes such as Col-1a1, SCX, and so on (Zhengzhou et al., 2019). Inflammation also contributes to the progression of tendinopathy and EVs can exert anti-inflammatory effects through a variety of mechanisms (D’Addona et al., 2017; Dakin et al., 2017). For example, inflammation-stimulated ASCs can reduce the inflammation response of the tendon by inhibiting NF-KB activity and the expression of proinflammatory cytokine II 1b (Shen et al., 2020).

EV is a delivery tool with good biocompatibility, which can load bioactive molecules to achieve efficient intracellular delivery. Loading drugs, proteins, RNA and other molecules into EV can enable EV to obtain specific therapeutic functions. The engineered EVs usually have better performance and therapeutic potential than native EV. The loading methods of these EV cargoes can generally be divided into passive loading and active loading (Luan et al., 2017; Zhang et al., 2021b; Zhang et al., 2021b).

The modification of EV includes the modification of EV membrane, such as the receptor loading and targeted modification of EV membrane, and the artificial bionic nano vesicle system designed based on the material science method.

In OA patients, the abnormal expression of microRNA (miRNA) is associated with cartilage lesions (Glyn-Jones et al., 2015b). Engineered EVs designed for elevated or silenced miRNA expression have been shown to effectively inhibit inflammation, matrix degradation, apoptosis, chondrocyte proliferation and migration, and improve chondrocyte matrix secretion. In the treatment of degenerative osteoarthropathy, it shows better performance and broader prospects than native EV or drug direct treatment (Liang et al., 2020; Esmaeili et al., 2021; Sun et al., 2022b; Wan et al., 2022).

Engineered EVs can provide combinatorial effects between their natural cargo and externally added drugs or biomaterials, while also directing the treatment toward the desired goal. Loading bioactive molecules and drugs into electric vesicles for the treatment of OA is a common method for electric vesicle engineering in the field of OA (Zhang et al., 2022; Zhuang et al., 2022).

For promoting chondrogenesis and cartilage regeneration, Kartogenin (KGN), as yiz red, has been found to induce the differentiation of SF-MSCs into chondrocytes in vitro and in vivo. After being loaded with engineered EVs loading of MSC-binding peptide E7, it can target SF-MSCs and increase their effective concentration in cells. It can strongly promote chondrogenesis of SF-MSCs both in vitro and in vivo, showing a more significant effect than KGN direct treatment (Xiao et al., 2020).

To regulate the microenvironment of cartilage tissue, the engineered EVs obtained by gene transfection can effectively wrap miR-140, and the binding of chondrocyte affinity peptide (CAP) to EV membrane gives it the ability to specifically target chondrocytes. Then, by reversing IL-1β-induced activation of MMP-13, which resulted in the reduction of MMP-13 and Adamts-5 protein levels in cartilage tissue, OA progression was significantly inhibited, showing a more significantly enhanced effect than simple use of native EV (256). In order to overcome the side effect of MSC-EV reducing ECM secretion, miR-140-5p was highly expressed in EVs by gene transfection, thus enhancing the proliferation and migration of ACs without destroying ECM secretion (Shi-Cong et al., 2017).

To solve the problem of limited distribution and insufficient bioavailability of MSC-EV after an intraarticular injection, MSC-sEV was modified with a new cationic amphiphilic polymer ε-polylysine-polyethylene-stearyl phosphatidylethanolamine (PPD) to reverse the surface charge of MSC-sEV. Results showed that PPD-sEV regulated chondrocyte absorption and homeostasis more effectively than unmodified MSC-sEV, significantly enhancing chondrogenic absorption, cartilage penetration and joint retention (Feng et al., 2021). To address the issues of rapid joint clearance of drugs (i.e., short half-life) and therapeutic targets deep in the cartilage that drugs cannot reach, one study used micellar nanoparticles loaded with phospholipase a2 inhibitors to penetrate deep into the cartilage matrix, reduce inflammation, prolong joint space retention, In vitro model of cartilage explants and two animal models of OA showed a significant effect of slowing down the progression of OA (Wei et al., 2021b).

In addition to drug delivery vesicles, perhaps engineered electric vesicles could also be used as non-viral gene-editing tools for osteoarthritis treatment. However, special attention should be paid to its immunogenicity, biocompatibility and potential tumorigenicity (Shi-Cong et al., 2017).

The pathogenesis of osteoporosis includes excessive bone resorption, insufficient bone formation and insufficient vascularization (Liang et al., 2022b). Engineered EVs carrying therapeutic molecules are promising as alternative therapies for osteoporosis, requiring the design of specific functionalized vesicles and appropriate engineering strategies.

In order to enhance osteogenesis, studies have reported that EVs modified with bone-targeting peptide can specifically deliver siRNA to osteoblasts, silence Shn3 gene, and reduce the expression of RANKL in osteoblasts, thus showing more significant functions of enhancing osteogenic differentiation, inhibiting osteoclast differentiation, and promoting blood vessel formation than native EV (Yongzhi et al., 2022). In another study, BMSCS-Mir-29a-ExOS-treated mice showed significant increases in bone mineral density (BMD), trabecular volume (BV/TV), and trabecular number (Tb. N) compared with BMSCs-Exos and PBS-treated mice. These results indicate that engineered EVs have a strong ability to enhance bone mass in mice (Lu et al., 2020).

In vivo treatment of osteoporosis, intravenous injection is often used. Therefore, how to deliver EVs to bone tissues in a high concentration, tissue-specific and tissue-targeted manner, rather than aggregation with other organs or tissues, is a key issue for EV engineering in osteoporosis treatment. A study reported that although bone marrow stromal cell (ST) -derived EVs (STExos) significantly enhanced osteoblast differentiation of BMSCs in vitro, STExos accumulated in the liver and lung after intravenous administration, resulting in ineffective improvement of osteoporotic phenotype in a mouse model of postmenopausal osteoporosis induced by ovariectomy (OVX) (Zhong-Wei et al., 2019). The StexO-aptamer complex was combined with BMSC-specific aptamer on the surface of STExo to test its ability to enhance bone mass in OVX mice and accelerate bone healing in femur fracture mouse model (Zhong-Wei et al., 2019). Another study reported the use of Ale-N3 to modify EVs derived from murine mesenchymal stem cells to generate Ale-EVs system with high affinity for bone by utilizing the specific binding properties of alendronate and hydroxyapatite, achieving the purpose of improving tissue-specific targeting of EVS (Wang et al., 2020b).

Synthetic nanovesicles have also been used in the treatment of OP. To inhibit osteoclast function and promote osteoclast apoptosis, NaHCO3-coated tetracycline modified nanoliposomes (NaHCO3-tnl) can spontaneously generate “nano-sacrifice layer” on the bone surface. Once H+ is secreted by osteoclasts, NaHCO3-TNL releases the bicarbonate radical (HCO3-), which neutralizes the acidic environment (Lin et al., 2020a).

In recent years, some studies have shown that engineered electric vehicles play a more important and superior role than native electric vehicles in protecting NPC and delaying the progress of IDD. Engineered EVs for IDD therapy are mainly obtained through genetic engineering (Zhang et al., 2021c; Zhiwei et al., 2021; Luo et al., 2022). The second most common method is mechanical method (Sun et al., 2020; Tang et al., 2021).

Targeting EV endocytic pathways and NPC pyroptosis, a previous study has reported that, compared with the EVs of the negative control group, the modified engineered EVs obtained by Cavin-2 gene editing in MSCs significantly increased the uptake rate of EVs by TNF-α-treated NPCs, reduced the death of NPCs, and delayed the progress of IDD in vitro organ models (Zhiwei et al., 2021). For anti-oxidant and anti-inflammatory, transfection of NPC with FOXF1 by engineered EVs can significantly change gene expression by up-regulating FOXF1 and KRT19 and down-regulating IL-1β, IL-6, MMP13, and NGF, which offers a potential approach for the treatment of IVD degeneration and associated back pain (Tang et al., 2021). Aiming at regulating cartilage differentiation, engineered EVs overexpressing miR-15a by gene transfection can promote chondrogenic differentiation of nucleus pulposus mesenchymal stem cells by PI3K/Akt and Wnt3a/β-catenin axes to down-regulating MMP-3 (Zhang et al., 2021c). Targeting the autophagy and senescence pathways in nasopharyngeal carcinoma, overexpression of EVs Sphk2 secreted by transgenic chondroendplate stem cells (CESCs) can penetrate the ring of fibers (AF), transport Sphk2 to nucleus pulposus (NPC), activate PI3K/AKT signaling pathway, regulate autophagy/senescence in nasopharyngeal carcinoma in vivo and in vitro, and prevent intervertebral disc degeneration. The performance is better than that of native CESC-EVs (Luo et al., 2022). Moreover, EVs can also be designed for anti-angiogenesis. EVs produced by notochord cells under extrusion load overexpress microRNA (miR)-140-5p, which can transfer to endothelial cells and regulate downstream Wnt/β-catenin pathway to inhibit angiogenesis (Sun et al., 2020).

Engineered EVs approach can also be used to explore the mechanisms related to IDD and its treatment. For example, by silencing or overexpressing miR-129-5p and SOX4 in human mesenchymal stem cells EVs (hBMSC-EVs), it was demonstrated that hBMSC-EVs enhanced the proliferation of NPC and the synthesis of ECM by delivering miR-129-5p into NPCS, targeting SOX4 and inactivating the Wnt/β-catenin axis (Wang et al., 2021). Moreover, By changing the expression of miR-194-5p in MSC-EVs, the mechanism is elucidated by which MSC-EVs can effectively enhance proliferation and osteogenic differentiation, and reduce the apoptosis of TNF-α-treated NP cells (Zhongyi et al., 2021). When microRNA-31-5p levels in mesenchymal stem cell-derived EVs (MSC-EVs) were downregulated, the therapeutical effect of MSC-EVs in IVDD was inhibited (Lin et al., 2020b).

Although the above studies have explored the application of engineered EVs in the field of IDD, there is still space for further exploration in the innovation of engineering methods and EV action pathways and mechanisms. Of course, this also requires further exploration of IDD mechanisms and related research and application of biomaterials.

Because of the low incidence rate and the characteristics of the disease models, compared with OA, OP, and IDD, there are few studies on engineered EVs treatment of other degenerative bone diseases. At present, there is no research on engineered EVs for the treatment of osteonecrosis or degenerative tendinopathy. But a previous study has reported that the delivery of recombinant human bone morphogenetic protein 2 (rhBMP-2) using hydrogel can increase bone formation when used to treat drug-related jaw necrosis (MRONJ) (Brierly et al., 2019). Another study has shown that platelet-derived EV increases the expression of tendon markers, promotes remodeling of healthy extracellular matrix (ECM) and synthesis of anti-inflammatory mediators, and promotes the recovery of the human tendon-derived cell (hTDC) phenotype from a diseased state to a healthy state (Graça et al., 2022). The engineered EVs are likely to become a potential new treatment strategy for Osteonecrosis and degenerative tendinopathy in the future. Engineered EVs targeting diseased tissues can be used as a highly effective drug delivery tool with good biocompatibility and play an important role in tendinopathy and degenerative tendinopathy.