Bursting of condensates

Numerous biomolecular shell-forming condensates are reported in cells and bioengineered in vitro. The relationship between the molecular structure of shell-forming condensates and their biophysical properties remains largely unexplored. To fill this gap, we characterize shell-forming condensates of bioengineered spider silk proteins based on Araneus diadematus major ampulla gland silk fibroin 3 (ADF3) using micropipette aspiration. We observe that condensates can burst during aspiration like soap bubbles or polymersomes, demonstrating the formation of a dense protein layer (shell) at the condensate interface. The tendency to burst is more pronounced for condensates formed from proteins with weakly dimerizing terminal blocks. We develop a model to analyse the aspiration and bursting of the condensates, to obtain the surface and bulk viscosity, and to estimate the shell thickness and viscosity. Understanding and controlling the bursting of condensates will open avenues for their use in materials, as compartments for reactions or drug delivery systems.