Scheme 1. Biomimetic mineralization of OVA@ZIF and sustained release of antigens. (A) Synthetic scheme of μ-OVA@ZIF and n-OVA@ZIF. In a “one pot” reaction, Zn²⁺, mIM, and ovalbumin are suspended in water and react for 1 h at room temperature. By adjusting the ligand-to-metal ratio, we can tune the size of these ZIFs. We formulated a 1 : 16, micron-sized (∼1 μm) and 1 : 32 nano-sized (∼200 nm) μ-OVA@ZIF and n-OVA@ZIF, respectively. (B) Sustained release of antigens following vaccination, allowing for the formation of GCs. The ZIF-8 crystals slowly degrade in the body, exposing the antigen to the immune system and allowing for a constant supply of antigen to the GC.