Surface functionalization strategies of extracellular vesicles

Extracellular vesicles (EVs) are lipid-protein bilayer vesicular constructs secreted to the extracellular spaces by cells. All cells secrete EVs as a regular biological process that appears to be conserved throughout the evolution. The specific molecular information of EVs (lipid and protein profile) can be used as a unique biomarker to understand respective cellular conditions, for example, EVs derived from cancer has been used to study its severity. Similarly, due to its role in intracellular communication, it has been exploited as a perfect candidate for drug delivery and therapy. With these significant promises, the functionalization of EVs to add diverse functionality for biomedical applications has garnered rapid attention. EVs can be functionalized with exogenous imaging and targeting moiety that allows the real-time tracking of EVs and provides a targeted therapeutic effect. EVs functionalization can add vital functionality that can lead to a better understanding of EVs mechanism and processes that accelerates its biomedical application. In this report, a multimodal approach of EVs functionalization including physical, biological, and chemical approach has been reviewed by focusing each approach separately. The physical approach of EVs functionalization includes methods like sonication, extrusion, and freeze-thaw that can change the surface properties of EVs via membrane rearrangements. The biological approach discusses genetically and metabolically engineering cells to express protein or cargo molecule of interest in secreted EVs. The chemical approach includes different facile click type chemistries that can be used to covalently conjugate EVs lipid or protein construct with different linker groups for diverse functionality. Different chemistry like thiol-maleimide, EDC/NHS, azide-alkyne cycloaddition, and amidation chemistry have been discussed to functionalize EVs. Finally, a comparative discussion of all approaches has been done focusing on the significances of each approach. The collective knowledge of the major approach of surface functionalization can be used to improve the limitation of one technique by combining with another. An optimized surface functionalization approach developed accordingly can efficiently add required functionality to EVs while maintaining its natural integrity.