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Extracellular vesicles (EVs) are cell-secreted nanovesicles that play an important role in long-range cell-cell communication. Although EVs pose a promising alternative to cell-based therapy, targeted in vivo delivery still falls short. Many studies have explored the surface modification of EVs to enhance their targeting capabilities. However, to our knowledge, there are no standardized practices to confirm the successful surface modification of EVs or calculate the degree of conjugation on EV surfaces (conjugation efficiency). These pieces of information are essential in the reproducibility of targeted EV therapeutics and the determination of optimized conjugation conditions for EVs to see significant therapeutic effects in vitro and in vivo. This review will discuss the vast array of techniques adopted, technologies developed, and efficiency definitions made by studies that have calculated EV/nanoparticle surface conjugation efficiency and how differences between studies may contribute to differently reported conjugation efficiencies.

Lipid rafts are highly ordered regions of the plasma membrane enriched in signaling proteins and lipids. Their biological potential is realized in exosomes, a subclass of extracellular vesicles (EVs) that originate from the lipid raft domains. Previous studies have shown that EVs derived from human placental mesenchymal stromal cells (PMSCs) possess strong neuroprotective and angiogenic properties. However, clinical translation of EVs is challenged by very low, impure, and heterogeneous yields. Therefore, in this study, lipid rafts are validated as a functional biomaterial that can recapitulate the exosomal membrane and then be synthesized into biomimetic nanovesicles. Lipidomic and proteomic analyses show that lipid raft isolates retain functional lipids and proteins comparable to PMSC-EV membranes. PMSC-derived lipid raft nanovesicles (LRNVs) are then synthesized at high yields using a facile, extrusion-based methodology. Evaluation of biological properties reveals that LRNVs can promote neurogenesis and angiogenesis through modulation of lipid raft-dependent signaling pathways. A proof-of-concept methodology further shows that LRNVs could be loaded with proteins or other bioactive cargo for greater disease-specific functionalities, thus presenting a novel type of biomimetic nanovesicles that can be leveraged as targeted therapeutics for regenerative medicine.

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder affecting over five million people globally and has no established cure. Current AD-related treatments only alleviate cognitive and behavioral symptoms and do not address disease onset or progression, underlining the unmet need to create an effective, innovative AD therapeutic. Extracellular vesicles (EVs) have emerged as a new class of nanotherapeutics. These secreted, lipid-bound cellular signaling carriers show promise for potential clinical applications for neurodegenerative diseases like AD. Additionally, analyzing contents and characteristics of patient-derived EVs may address the unmet need for earlier AD diagnostic techniques, informing physicians of altered genetic expression or cellular communications specific to healthy and diseased physiological states. There are numerous recent advances in regenerative medicine using EVs and include bioengineering perspectives to modify EVs, target glial cells in neurodegenerative diseases like AD, and potentially use EVs to diagnose and treat AD earlier. This article is categorized under: Neurological Diseases > Biomedical Engineering Neurological Diseases > Molecular and Cellular Physiology Neurological Diseases > Stem Cells and Development.

Collagen is the most widespread extracellular matrix (ECM) protein in the body and is important in maintaining the functionality of organs and tissues. Studies have explored interventions using collagen-targeting tissue engineered techniques, using collagen hybridizing or collagen binding peptides, to target or treat dysregulated or injured collagen in developmental defects, injuries, and diseases. Researchers have used collagen-targeting peptides to deliver growth factors, drugs, and genetic materials, to develop bioactive surfaces, and to detect the distribution and status of collagen. All of these approaches have been used for various regenerative medicine applications, including neovascularization, wound healing, and tissue regeneration. In this review, we describe in depth the collagen-targeting approaches for regenerative therapeutics and compare the benefits of using the different molecules for various present and future applications.

Extracellular vesicles (EVs) are cell-secreted nanoscale vesicles with important roles in cell-cell communication and drug delivery. Although EVs pose a promising alternative to cell-based therapy, targeted delivery in vivo is lacking. Their surface is often modified to endow them with active targeting molecules to enable specific cell uptake and tailor EV biodistribution. A dominant paradigm has been to evaluate the EV surface functionalization using bulk analysis assays, such as western blotting and bead-based flow cytometry. Yet, the heterogeneity of EVs is now recognized as a major bottleneck for their clinical translation. Here, we engineer the EV surface at the single-vesicle level. We applied orthogonal platforms with single vesicle resolution to determine and optimize the efficiency of conjugating the myelin-targeting aptamer LJM-3064 to single EVs (Apt-EVs). The aptamers were conjugated using either lipid insertion or covalent protein modification, followed by an assessment of single-EV integrity and stability. We observed unique aptamer conjugation to single EVs that depends on EV size. Our study underscores the importance of single vesicle analysis for engineering EVs and provides a novel single-EV-based framework for modifying EV surfaces.