Tuning Pore Microenvironments in Covalent Organic Frameworks for Controlled Enzyme Loading and Release

Covalent Organic Frameworks (COFs) with tunable pore environments provide a versatile platform for enzyme delivery; however, the relationship between pore microenvironment and enzyme loading and release behavior remains insufficiently explored. Herein, we report the synthesis of a series of TPE-based imine-linked COFs, constructed from tetrakis(4-aminophenyl)ethene (TPE-NH₂) and three dialdehyde linkers bearing different functional groups (─H, ─CH₃, and N, S-containing heterocycles). These COFs exhibit distinct hydrophobic-hydrophilic characteristics while maintaining comparable structural backbones that allowed the selected COFs to act as models for the systematic investigation of their effect on papain loading, release, and activity. Furthermore, in situ FTIR spectroscopy directly probed the dynamic enzyme-framework interactions during loading, providing molecular-level evidence that supports the proposed role of the pore microenvironment in governing enzyme behavior. These results indicate that hydrophobic frameworks exhibit lower relative loading capacities, facilitate release, and partially compromise enzymatic activity for the model protein, whereas hydrophilic frameworks promote efficient loading, slow release, and lead to relatively lower retained activity. Together, this work provides molecular-level insights into how pore microenvironments regulate enzyme loading, release, and retained activity, establishing rational design principles for COF-based protein delivery and biocatalytic platforms.