Metal-Organic Framework-Templated Biomaterials: Recent Progress in Synthesis, Functionalization, and Applications.

Abstract

The integration of a porous crystalline framework with soft polymers to create novel biomaterials has tremendous potential yet remains very challenging to date. Metal-organic framework (MOF)-templated polymers (MTPs) have emerged as persistent modular materials that can be tailored for desired biofunctions. These represent a novel class of hierarchically structured assemblies that combine the advantages of MOFs (precisely controlled structure, enormous diversity in framework topology, and high porosity) with the intrinsic behaviors of polymers (soft texture, flexibility, biocompatibility, and improved stability under physiological conditions). Transformation of surface-anchored MOFs (SURMOFs) via orthogonal covalent cross-linking yields surface-anchored polymeric gels (SURGELs) that open up exciting new opportunities to create soft nanoporous materials. SURGELs overcome the main drawbacks of SURMOFs, such as their limited stability under physiological conditions and their potential to release toxic metal ions, a substantial problem for applications in life sciences. MOF (SURMOF)-templated polymerization processes control the synthesis on a molecular level. Additionally, the morphology of the original MOF crystal template is replicated in the final network polymers. The MOF-templated polymerization can be induced by light, a catalyst, or temperature using several types of reactions, including thiol-ene, metal-free alkyne-azide click reactions, and Glaser-Hay coupling. In the case of photoinduced reactions, the cross-linking process can be locally confined, allowing control of the macroscopic patterning of the resulting network polymer. The use of layer-by-layer (lbl) techniques in the SURMOF synthesis serves the purpose of precise, layer-selective incorporation of functionalities via the combination of the postsynthetic modification and heteroepitaxy strategies. Transforming the functionalized SURMOF into a SURGEL allows the fabrication of polymers with desired bioactive functions at the internal or external surfaces. This Account highlights our ongoing research and inspiring progress in transforming SURMOFs into persistent, modular nanoporous materials tailored with biofunctions. Using cell culture studies, we present various aspects of SURGEL materials, such as the ability to deliver bioactive molecules to adhering cells on SURGEL surfaces, applications to advanced drug delivery systems, the ability to tune cell adhesion via surface modification, and the development of porphyrin-based SURGEL thin films with antimicrobial properties. Then we critically examine the challenges and limitations of current systems and discuss future research directions and new approaches for advancing MOF-templated biocompatible materials, emphasizing the need to include responsive and adaptive functionalities into the system. We emphasize that the hierarchical structure, ranging from the molecular to the macroscopic scale, allows for optimization of the material properties across all length scales relevant for cell-material interactions.