Surface adhesion and membrane fluctuations influence the elastic modulus of extracellular vesicles
Elastic properties of nanoscale extracellular vesicles (EVs) are believed to influence their cellular interactions, thus having a profound implication in intercellular communication. Yet, an accurate quantification of the elasticity of such small lipid vesicles is difficult even with AFM-based nanoindentation experiments as it crucially depends on the reliability of the theoretical interpretation of such measurements. Here we describe a complete method composed of theoretical framework, experimental procedure, and appropriate statistical approach for an accurate determination of bending modulus and effective elastic modulus of EVs. Further, we experimentally demonstrate that the quantification of EVs by the elastic modulus from AFM-based force spectroscopy measurement is marred by the interplay of their compositionally inhomogeneous fluid membrane with the adhesion forces from the substrate and thermal effects - two exquisite phenomena that could thus far only be theoretically predicted. The effects result in a large spreading of elastic modulus even for a single EV. Our unified model is then applied to genetically engineered classes of EVs to understand how the alterations in tetraspanin expression may influence their elastic modulus.