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Cells offer numerous inspiring examples where proteins and membranes combine\nto form complex structures that are key to intracellular compartmentalization,\ncargo transport, and specialization of cell morphology. Despite this wealth of\nexamples, we still lack the design principles to control membrane morphology in\nsynthetic systems. Here we show that even the relatively simple case of\nspherical nanoparticles binding to lipid-bilayer membrane vesicles results in a\nremarkably rich set of morphologies that can be controlled quantitatively via\nthe particle binding energy. We find that when the binding energy is weak\nrelative to a characteristic membrane-bending energy, the vesicles adhere to\none another and form a soft solid, which could be used as a useful platform for\ncontrolled release. When the binding energy is larger, the vesicles undergo a\nremarkable destruction process consisting first of invaginated tubules,\nfollowed by vesicles turning inside-out, yielding a network of\nnanoparticle-membrane tubules. We propose that the crossover from one behavior\nto the other is triggered by the transition from partial to complete wrapping\nof nanoparticles. This model is confirmed by computer simulations and by\nquantitative estimates of the binding energy. These findings open the door to a\nnew class of vesicle-based, closed-cell gels that are more than 99% water and\ncan encapsulate and release on demand. Our results also show how to\nintentionally drive dramatic shape changes in vesicles as a step toward\nshape-responsive particles. Finally, they help us to unify the wide range of\npreviously observed responses of vesicles and cells to added nanoparticles.\n