Phase Separation of Oppositely Charged Polymers Regulates Bioinspired Silicification

In nature, simple organisms evolved mechanisms to form intricate biosilica nanostructures, far exceeding current synthetic manufacturing. Based on the properties of extracted biomacromolecules, polycation–polyanion pairs were suggested as moderators of biosilica formation. However, the chemical principles of this polymer‐induced silicification remain unclear. Here, we used a biomimetic polycation–polyanion system to study polymer‐induced silicification. We demonstrate that it is the polymer phase separation process, rather than silica–polymer interactions, which controls silica precipitation. Since ionic strength controls this electrostatic phase separation, it can be used to tune the morphology and structure of the precipitates. In situ cryo electron microscopy highlights the pivotal role of the hydrated polymer condensates in this process. These results pave the road for developing nanoscale morphologies of bioinspired silica based on the chemistry of liquid‐liquid phase separation.