Vesicles were adhered to freshly cleaved mica by incubation at room temperature for 15 minutes followed by washing [44 ]. Atomic force microscopy was performed using an MFP-3D-Bio model (Asylum Research) with a pyramidal tip (Bruker; MLCT, triangular, resonant frequency: ~125 kHz) as described previously [30 (link)]. Briefly, vesicles with a size range between 50~300 nm were found by scanning in a tapping (AC) mode and indented until reaching 0.5 nN at 250 nm/s to generate a force-displacement curve. The data were analysed and converted to Young’s modulus (E) using MATLAB by modeling EVs as thin elastic shells [46 (link)]. The slope of the approach curve was calculated over a sliding interval and the surface of the vesicle was determined by a high and sustained change in slope. The linear region was used to calculate E via the equation
With F as measured cantilever force and δ as tip displacement. The constant is determined by vesicle geometry and assumed to be ~0.87nm.
With F as measured cantilever force and δ as tip displacement. The constant is determined by vesicle geometry and assumed to be ~0.87nm.
