4D Mapping of ZIF Biocomposites for High Protein Loading and Tunable Release Profiles

Metal–organic framework (MOF) biocomposites consist of MOF matrices into which biomacromolecules (e.g., proteins/enzymes) are immobilized for applications in drug delivery and biocatalysis. Zeolitic Imidazolate Frameworks (ZIFs) based on Zn²⁺ and 2-methylimidazole are the most studied MOFs for protein encapsulation. How varying the Zn²⁺:2-methylimidazole:protein ratio, total precursor concentration, and washing procedure yields distinct Zeolitic Imidazolate Framework (ZIF) phases (ZIF-C, sod, dia) and amorphous forms is systematically investigated. Each phase is found to strongly influence crucial properties, including encapsulation efficiency (EE%), loading capacity (LC%), and release kinetics. Notably, unprecedented LC values (e.g., ≈85%) are achieved with negligible presence of unreacted MOF precursors, ensuring a minimal carrier fraction while enabling high protein content. Using bovine serum albumin as a model protein, the relationships between precursors, crystallographic phase, EE%, LC%, and release profiles are established. α-1-antitrypsin, a protein-based biotherapeutic, is further encapsulated in ZIF-C, sod, and dia, and retained inhibitor activity upon release is examined. Moreover, it is shown that blending different phases enables multi-step release profiles, which are highly desirable for controlled drug delivery. These results highlight the importance of systematic phase control to tune protein loading and release, offering structure-property guidelines for the rational design of ZIF-based biocomposites as drug-delivery platforms.