Long thought of to be vesicles that primarily recycled waste biomolecules from cells, extracellular vesicles (EVs) have now emerged as a new class of nanotherapeutics for regenerative medicine. Recent studies have proven their potential as mediators of cell proliferation, immunomodulation, extracellular matrix organization and angiogenesis, and are currently being used as treatments for a variety of diseases and injuries. They are now being used in combination with a variety of more traditional biomaterials and tissue engineering strategies to stimulate tissue repair and wound healing. However, the clinical translation of EVs has been greatly slowed due to difficulties in EV isolation and purification, as well as their limited yields and functional heterogeneity. Thus, a field of EV engineering has emerged in order to augment the natural properties of EVs and to recapitulate their function in semi-synthetic and synthetic EVs. Here, we have reviewed current technologies and techniques in this growing field of EV engineering while highlighting possible future applications for regenerative medicine.

The network structure and biological components of natural extracellular matrix (ECM) are indispensable for promoting tissue regeneration. Electrospun nanofibrous scaffolds have been widely used in regenerative medicine to provide structural support for cell growth and tissue regeneration due to their natural ECM mimicking architecture, however, they lack biological functions. Extracellular vesicles (EVs) are potent vehicles of intercellular communication due to their ability to transfer RNAs, proteins, and lipids, thereby mediating significant biological functions in different biological systems. Matrix-bound nanovesicles (MBVs) are identified as an integral and functional component of ECM bioscaffolds mediating significant regenerative functions. Therefore, to engineer EVs modified electrospun scaffolds, mimicking the structure of the natural EV-ECM complex and the physiological interactions between the ECM and EVs, will be attractive and promising in tissue regeneration. Previously, using one-bead one-compound (OBOC) combinatorial technology, we identified LLP2A, an integrin α4β1 ligand, which had a strong binding to human placenta-derived mesenchymal stem cells (PMSCs). In this study, we isolated PMSCs derived EVs (PMSC-EVs) and demonstrated they expressed integrin α4β1 and could improve endothelial cell (EC) migration and vascular sprouting in an ex vivo rat aortic ring assay. LLP2A treated culture surface significantly improved PMSC-EV attachment, and the PMSC-EV treated culture surface significantly enhanced the expression of angiogenic genes and suppressed apoptotic activity. We then developed an approach to enable "Click chemistry" to immobilize LLP2A onto the surface of electrospun scaffolds as a linker to immobilize PMSC-EVs onto the scaffold. The PMSC-EV modified electrospun scaffolds significantly promoted EC survival and angiogenic gene expression, such as KDR and TIE2, and suppressed the expression of Hao et al. Scaffolds Modified With Extracellular Vesicles apoptotic markers, such as caspase 9 and caspase 3. Thus, PMSC-EVs hold promising potential to functionalize biomaterial constructs and improve the vascularization and regenerative potential. The EVs modified biomaterial scaffolds can be widely used for different tissue engineering applications.

Mesenchymal stem/stromal cells (MSCs) are extensively studied as cell-therapy agents for neurological diseases. Recent studies consider exosomes secreted by MSCs as important mediators for MSCs’ neuroprotective functions. Exosomes transfer functional molecules including proteins, lipids, metabolites, DNAs, and coding and non-coding RNAs from MSCs to their target cells. Emerging evidence shows that exosomal microRNAs (miRNAs) play a key role in the neuroprotective properties of these exosomes by targeting several genes and regulating various biological processes. Multiple exosomal miRNAs have been identified to have neuroprotective effects by promoting neurogenesis, neurite remodeling and survival, and neuroplasticity. Thus, exosomal miRNAs have significant therapeutic potential for neurological disorders such as stroke, traumatic brain injury, and neuroinflammatory or neurodegenerative diseases and disorders. This review discusses the neuroprotective effects of selected miRNAs (miR-21, miR-17-92, miR-133, miR-138, miR-124, miR-30, miR146a, and miR-29b) and explores their mechanisms of action and applications for the treatment of various neurological disease and disorders. It also provides an overview of state-of-the-art bioengineering approaches for isolating exosomes, optimizing their yield and manipulating the miRNA content of their cargo to improve their therapeutic potential.

contributing factors of these diseases are numerous, including genetics, diet, smoking, and lack of exercise. [1][2][3] With development of angiography, drug-eluting stents, balloon catheters, bypass surgery, and new disease-modifying drug therapies, there has been significant improvement in the care and treatment of patients with CVD. [4] Despite these innovations and progress, CVD is still the leading cause of death in the US and worldwide. Furthermore, these treatment options bring their own set of complications, including intimal hyperplasia and thrombosis, as well as drug therapy side effects. Therefore, broader therapeutic interventions are still needed in order to ameliorate the devastating impacts of CVD. Recently, a new class of therapeutics has emerged that is known as extracellular vesicles (EVs). EVs are membranebound vesicles released by different types of prokaryotic and eukaryotic cells, and are ubiquitously found in most body fluids such as blood, urine, breast milk, saliva, and cerebrospinal fluid. [5] In general, EVs can be classified into three subclasses which are differentiated by their biogenesis mechanisms. [5,6] The first class of EVs is microvesicles, also known as ectosomes or microparticles. They are produced by the outward budding and fission of the plasma membrane and range from 50 nm to 1 micron in size. [7,8] The second EV subset are termed apoptotic bodies (50 nm to 5 microns) and are released when plasma membrane blebbing occurs during late apoptosis. The final EV subset is known as exosomes. Exosomes are the smallest type of EV (also often referred to as sEV), ranging between 50-150 nm, and originate from the inward budding of multivesicular bodies (MVB). Exosomes are released into the extracellular space upon fusion of MVBs with the plasma membrane, specifically at the lipid raft subdomains. [9,10] All subsets of vesicles contain bioactive cargo, including proteins, mRNAs, microRNAs (miRNAs, miRs), and lipids, that are efficiently delivered to recipient cells to regulate different biological processes. [6,8,[11][12][13] Within the cardiovascular system, EVs play important roles in maintaining normal physiological function by facilitating cellular crosstalk. [8,11,14] Under disease or injury conditions, EV phenotypes are seen to shift in order to indicate cardiovascular dysfunction and to restore physiological balance. However, administration of EVs as therapeutics has been limited due to difficulties in isolation and standardization, ineffective targeting, and poor retention. [15,16] Advances in research and technology have addressed these challenges by engineering EVs to augment Cardiovascular diseases (CVD) remain one of the leading causes of mortality worldwide. Despite recent advances in diagnosis and interventions, there is still a crucial need for new multifaceted therapeutics that can address the complicated pathophysiological mechanisms driving CVD. Extracellular vesicles (EVs) are nanovesicles that are secreted by all types of cells to transport molecular cargo and regu...