Breaking barriers: Engineering extracellular vesicles for enhanced endosomal escape and therapeutic delivery

Extracellular vesicles (EVs) have emerged as promising natural nanocarriers with superior biocompatibility, immune tolerance, and tissue tropism compared to synthetic nanoparticles. However, despite their efficient cellular uptake, the clinical translation of EV-based therapeutics is fundamentally constrained by inefficient endosomal escape, which remains the principal bottleneck to achieving functional cytosolic delivery. To address this challenge, a variety of engineering strategies have been developed, including post-isolation surface decoration with peptides and polymers, genetic incorporation of fusogenic proteins and channel-forming modules, and biophysical remodeling of membrane lipid composition. These modifications aim to enhance intracellular delivery by improving membrane fusion and facilitating endosomal membrane destabilization. Concurrently, the development of advanced quantitative assays has enabled more accurate evaluation of endosomal escape efficiency. This review summarizes recent advances in engineering approaches and analytical methodologies and discusses future perspectives for overcoming biological and manufacturing hurdles to realize the clinical potential of EV-based therapeutics.