MRI‐Active Metal‐Organic Frameworks: Concepts for the Translation from Lab to Clinic

Reticular Chemistry of the Fcu-Type Gd(III)-Doped Metal-Organic Framework for T1 -Weighted Magnetic Resonance Imaging

Nanoscale metal-organic frameworks (nanoMOFs) are emerging as an important class of nanomaterials for the systematical investigation of biomedically relevant structure-property relationship (SPR) due to their highly tailorable features. In this work, the reticular chemistry approach is shown to explore the SPR of a fcu-type Zr(IV)-nanoMOF for T1 -weighted magnetic resonance imaging (MRI). Isoreticular replacement of the eight-coordinated square-antiprismatic Zr(IV) by nine-coordinated Gd(III) brings a stoichiometric water capped on the square-antiprismatic site, enabling the relaxation transfer in the inner-sphere, giving the r1 value of 4.55 mM-1 ·s-1 at the doping ratio of Gd : Zr = 1 : 1. Then, these isoreticular engineering studies provide feasible ways to facilitate the relaxation transfer in the second- and outer-sphere of the Gd(III)-doped Zr-oxo cluster for the relaxation respectively. Finally, these in vitro and in vivo MRI studies revealed that the Gd(III)-doped Zr-oxo cluster aggregated underlying the fcu-type framework surpasses its discrete molecular cluster for MRI. These results demonstrated that there is plenty of room inside MOFs for T1 -weighted MRI by reticular chemistry.

"Non-cytotoxic" doses of metal-organic framework nanoparticles increase endothelial permeability by inducing actin reorganization

Cytotoxicity of nanoparticles is routinely characterized by biochemical assays such as cell viability and membrane integrity assays. However, these approaches overlook cellular biophysical properties including changes in the actin cytoskeleton, cell stiffness, and cell morphology, particularly when cells are exposed to "non-cytotoxic" doses of nanoparticles. Zeolitic imidazolate framework-8 nanoparticles (ZIF-8 NPs), a member of metal-organic framework family, has received increasing interest in various fields such as environmental and biomedical sciences. ZIF-8 NPs may enter the blood circulation system after unintended oral and inhalational exposure or intended intravenous injection for diagnostic and therapeutic applications, yet the effect of ZIF-8 NPs on vascular endothelial cells is not well understood. Here, the biophysical impact of "non-cytotoxic" dose ZIF-8 NPs on human aortic endothelial cells (HAECs) is investigated. We demonstrate that "non-cytotoxic" doses of ZIF-8 NPs, pre-defined by a series of biochemical assays, can increase the endothelial permeability of HAEC monolayers by causing cell junction disruption and intercellular gap formation, which can be attributed to actin reorganization within adjacent HAECs. Nanomechanical atomic force microscopy and super resolution fluorescence microscopy further confirm that "non-cytotoxic" doses of ZIF-8 NPs change the actin structure and cell morphology of HAECs at the single cell level. Finally, the underlying mechanism of actin reorganization induced by the "non-cytotoxic" dose ZIF-8 NPs is elucidated. Together, this study indicates that the "non-cytotoxic" doses of ZIF-8 NPs, intentionally or unintentionally introduced into blood circulation, may still pose a threat to human health, considering increased endothelial permeability is essential to the progression of a variety of diseases. From a broad view of cytotoxicity evaluation, it is important to consider the biophysical properties of cells, since they can serve as novel and more sensitive markers to assess nanomaterial's cytotoxicity.

Recent Advances in Metal-Organic Frameworks for Applications in Magnetic Resonance Imaging

Diagnostics is an important part of medical practice. The information required for diagnosis is typically collected by performing diagnostic tests, some of which include imaging. Magnetic resonance imaging (MRI) is one of the most widely used and effective imaging techniques. To improve the sensitivity and specificity of MRI, contrast agents are used. In this review, the usage of metal-organic frameworks (MOFs) and composite materials based on them as contrast agents for MRI is discussed. MOFs are crystalline porous coordination polymers. Due to their huge design variety and high density of metal ions, they have been studied as a highly promising class of materials for developing MRI contrast agents. This review highlights the most important studies and focuses on the progress of the field over the last five years. The materials are classified based on their design and structural properties into three groups: MRI-active MOFs, composite materials based on MOFs, and MRI-active compounds loaded in MOFs. Moreover, an overview of MOF-based materials for heteronuclear MRI including 129Xe and 19F MRI is given.

Biomimetic Mineralization of Iron-Fumarate Nanoparticles for Protective Encapsulation and Intracellular Delivery of Proteins

Biomimetic mineralization of proteins and nucleic acids into hybrid metal-organic nanoparticles allows for protection and cellular delivery of these sensitive and generally membrane-impermeable biomolecules. Although the concept is not necessarily restricted to zeolitic imidazolate frameworks (ZIFs), so far reports about intracellular delivery of functional proteins have focused on ZIF structures. Here, we present a green room-temperature synthesis of amorphous iron-fumarate nanoparticles under mildly acidic conditions in water to encapsulate bovine serum albumin (BSA), horseradish peroxidase (HRP), green fluorescent protein (GFP), and Cas9/sgRNA ribonucleoproteins (RNPs). The synthesis conditions preserve the activity of enzymatic model proteins and the resulting nanoparticles deliver functional HRP and Cas9 RNPs into cells. Incorporation into the iron-fumarate nanoparticles preserves and protects the activity of RNPs composed of the acid-sensitive Cas9 protein and hydrolytically labile RNA even during exposure to pH 3.5 and storage for 2 months at 4 °C, which are conditions that strongly impair the functionality of unprotected RNPs. Thus, the biomimetic mineralization into iron-fumarate nanoparticles presents a versatile platform for the delivery of biomolecules and protects them from degradation during storage under challenging conditions.

Reticular Nanoscience: Bottom-Up Assembly Nanotechnology

The chemistry of metal-organic and covalent organic frameworks (MOFs and COFs) is perhaps the most diverse and inclusive among the chemical sciences, and yet it can be radically expanded by blending it with nanotechnology. The result is reticular nanoscience, an area of reticular chemistry that has an immense potential in virtually any technological field. In this perspective, we explore the extension of such an interdisciplinary reach by surveying the explored and unexplored possibilities that framework nanoparticles can offer. We localize these unique nanosized reticular materials at the juncture between the molecular and the macroscopic worlds, and describe the resulting synthetic and analytical chemistry, which is fundamentally different from conventional frameworks. Such differences are mirrored in the properties that reticular nanoparticles exhibit, which we described while referring to the present state-of-the-art and future promising applications in medicine, catalysis, energy-related applications, and sensors. Finally, the bottom-up approach of reticular nanoscience, inspired by nature, is brought to its full extension by introducing the concept of augmented reticular chemistry. Its approach departs from a single-particle scale to reach higher mesoscopic and even macroscopic dimensions, where framework nanoparticles become building units themselves and the resulting supermaterials approach new levels of sophistication of structures and properties.