An example of such structural complexity is the formation of cytoskeleton-like structures. The cytoskeleton component actin is known to produce tight, stiff networks together with the crosslinker filamin, once it polymerizes from G-actin to F-actin at high Mg 2+ concentrations. Using bioPISA to encapsulate filamin and fluorescently-labelled actin, we observed magnesium-triggered changes in GUVs' internal architecture (Figure ). This led to subcompartmentalized vesicles with condensed actin, resembling a hybrid of PDMS-PMOXA GUVs encapsulating actin (which can form internal vesicles), and actinosomes (which create protein shells around coacervates) (Figure , Figure ). These structures did not form in absence of Mg 2+ (Figure ) or without actin (Figure ), confirming that actin polymerization in the confined space of the GUVs let to their formation. However, many cell types do not rely only on biomolecules to modify their architecture, but can also use minerals to produce matrices and scaffolds, 78 becoming of interest for materials science and architecture as well. A biomineralizing system was developed, where encapsulated alkaline phosphatase (ALP) (Figure ) converted the dissolved calcium glycerophosphate (CaGP) to insoluble calcium phosphate. This precipitation reaction imitated the biological mechanism in which osteoblasts produce the mineral matrix of bones (Figure ). The reaction produced the expected white precipitate of calcium phosphate only in presence of ALP in the GUV and CaGP (Figure ) added outside. By adsorbing fluorescein to the mineral, 81 the resulting particles could be imaged (Figure , Figure ). Due to the intravesicular localization of ALP, the calcium phosphate precipitated within the GUVs, causing the destabilization of the polymer membrane, which adsorbed on the phosphate particles. Thanks to an encapsulated enzyme, the GUVs could turn into a new organic-inorganic hybrid material, where the biomineral could be wholly contained within the polymer matrix.