Expanding the ZIFs Repertoire for Biological Applications with the Targeted Synthesis of ZIF-20 Nanoparticles

Owing to their facile synthesis, tailorable porosity, diverse compositions, and low toxicity, zeolitic imidazolate framework (ZIF) nanoparticles (NPs) have emerged as attractive platforms for a variety of biologically relevant applications. To date, a small subset of ZIFs representing only two topologies and very few linker chemistries have been studied in this realm. We seek to expand the bio-design space for ZIF NPs through the targeted synthesis of a hierarchically complex ZIF based on two types of cages, ZIF-20, with lta topology. This study demonstrates the rapid synthesis and size tunability of ZIF-20 particles across the micro and nanoregimes via microwave heating and the use of a modulating agent. To evaluate the utility of ZIF particles for biological applications, we examine their stability in biologically relevant media and demonstrate biocompatibility with A549 human epithelial cells. Further, the ability to encapsulate and release methylene blue, a therapeutic and bioimaging agent, is validated. Importantly, ZIF-20 NPs display a unique behavior relative to previously studied ZIFs based on their specific structural and chemical features. This finding highlights the need to expand the design space across the broader ZIFs family, to exploit a wider range of relevant properties for biological applications and beyond.

Prolonged release and shelf-life of anticoagulant sulfated polysaccharides encapsulated with ZIF-8

Natural active polysaccharides are attracting increased attention from pharmaceutical industries for their valuable biological activities. However, the application of polysaccharides has been restricted due to their relatively large molecular weight, complex structure, and instability. Metal-organic frameworks (MOFs) have emerged to help deliver cargo to specific locations, achieving the objectives of eliminating the potential damage to the body, protecting the drugs, and improving therapeutic effectiveness. Here, a pH-responsive zeolitic imidazolate framework (ZIF-8) was synthesized to encapsulated three sulfated polysaccharides (heparin, fucan sulfate, fucosylated chondroitin sulfate) and a non-sulfated polysaccharide, hyaluronic acid. The resulting polysaccharides@ZIF-8 biocomposites showed differences in terms of morphology, particle size, encapsulation, and release efficiency. These biocomposites retained antithrombotic activity and the framework ZIF-8 effectively protected these polysaccharides from degradation and prolonged shelf-life of the anticoagulants from the unfavorable environment.

A Versatile Competitive Coordination Strategy for Tailoring Bioactive Zeolitic Imidazolate Framework Composites

Zeolitic imidazolate frameworks (ZIFs) serving as platforms for bioactive guest encapsulation have attracted growing attention, yet the tailoring of its architectures and bioactivity remains a major challenge. Herein, a versatile competitive coordination strategy is proposed by using amorphous zinc nucleotide gel as template for step-by-step growth of ZIFs, which enables the tailoring of bioactive ZIF composites under facile conditions. Mechanism investigation reveals that introduced nucleotide determines the hierarchical pore structure and hydrophilicity, leading to customized activity retention and stability of the resultant bioactive ZIF composites. Furthermore, nucleoside monophosphate enhances the acidic tolerance of ZIFs. To the authors' knowledge, this is the first example showing the dynamic evolution of amorphous gels to crystalline ZIFs for in situ encapsulation of enzymes with tailored catalytic performance. This study provides insights for rational design of ZIF-based biocomposites and broadens the application of bioactive metal-organic frameworks.

Metal-organic frameworks for therapeutic gas delivery

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S) are gaseous signaling molecules (gasotransmitters) that regulate both physiological and pathological processes and offer therapeutic potential for the treatment of many diseases, such as cancer, cardiovascular disease, renal disease, bacterial and viral infections. However, the inherent labile nature of therapeutic gases results in difficulties in direct gases administration and their controlled delivery at clinically relevant ranges. Metal-organic frameworks (MOFs) with highly porous, stable, and easy-to-tailor properties have shown promising therapeutic gas delivery potential. Herein, we highlight the recent advances of MOF-based platforms for therapeutic gas delivery, either by endogenous (i.e., direct transfer of gases to targets) or exogenous (i.e., stimulating triggered release of gases) means. Reports that involve in vitro and/or in vivo studies are highlighted due to their high potential for clinical translation. Current challenges for clinical requirements and possible future innovative designs to meet variable healthcare needs are discussed.

Degradation Mechanism of Porous Metal-Organic Frameworks by In Situ Atomic Force Microscopy

In recent years, Metal-Organic Frameworks (MOFs) have attracted a growing interest for biomedical applications. The design of MOFs should take into consideration the subtle balance between stability and biodegradability. However, only few studies have focused on the MOFs' stability in physiological media and their degradation mechanism. Here, we investigate the degradation of mesoporous iron (III) carboxylate MOFs, which are among the most employed MOFs for drug delivery, by a set of complementary methods. In situ AFM allowed monitoring with nanoscale resolution the morphological, dimensional, and mechanical properties of a series of MOFs in phosphate buffer saline and in real time. Depending on the synthetic route, the external surface presented either well-defined crystalline planes or initial defects, which influenced the degradation mechanism of the particles. Moreover, MOF stability was investigated under different pH conditions, from acidic to neutral. Interestingly, despite pronounced erosion, especially at neutral pH, the dimensions of the crystals were unchanged. It was revealed that the external surfaces of MOF crystals rapidly respond to in situ changes of the composition of the media they are in contact with. These observations are of a crucial importance for the design of nanosized MOFs for drug delivery applications.

Stimuli-responsive metal-organic framework nanoparticles for controlled drug delivery and medical applications

Stimuli-responsive metal-organic framework nanoparticles, NMOFs, provide a versatile platform for the controlled release of drugs and biomedical applications. The porous structure of NMOFs, their biocompatibility, low toxicity, and efficient permeability turn the NMOFs into ideal carriers for therapeutic applications. Two general methods to gate the drug-loaded NMOFs and to release the loads were developed: by one method, the loaded NMOFs are coated or surface-modified with stimuli-responsive gates being unlocked in the presence of appropriate chemical (e.g., ions or reducing agents), physical (e.g., light or heat), or biomarker (e.g., miRNA or ATP) triggers. By a second approach, the drug-loaded NMOFs include encoded structural information or co-added agents to induce the structural distortion or stimulate the degradation of the NMOFs. Different chemical triggers such as pH changes, ions, ATP, or redox agents, and physical stimuli such as light or heat are applied to degrade the NMOFs, resulting in the release of the loads. In addition, enzymes, DNAzymes, and disease-specific biomarkers are used to unlock the gated NMOFs. The triggered release of drugs for cancer therapy, anti-blood clotting, and the design of autonomous insulin-delivery systems ("artificial pancreas") are discussed. Specifically, multi-drug carrier systems and functional NMOFs exhibiting dual and cooperative therapeutic functions are introduced. The future perspectives and applications of stimuli-responsive particles are addressed.

Integrated Microfluidic Synthesis of Aptamer Functionalized Biozeolitic Imidazolate Framework (BioZIF-8) Targeting Lymph Node and Tumor

Targeted delivery of therapeutic molecules using nanomaterials is desired to elicit specific responses toward diseases. Such an integrated synthesis of functional material using a microfluidic approach is a great challenge. Functional metal organic frameworks (MOFs) with unique structural diversity possess a complicated synthesis procedure thereby requiring a modest, straightforward approach to synthesize size-controllable MOFs. Here, we develop an integrated microfluidic chip to synthesize the aptamer-modified biozeolitic imidazolate framework (BioZIF-8) to target the lymph node and tumor. The first stage of the microfluidic chip forms the ZIF-8 encapsulating biomolecules (bovine serum albumin, small interfering ribonucleic acid, and doxorubicin). The second stage modifies the surface of BioZIF-8 with the aptamer. Our approach reduces the overall synthesis time (∼3 mg/10 min against 15 h for the conventional two-step method) and encapsulates a higher number of biomolecules. The microfluidic approach realizes the rapid and fine-tuned synthesis of functional MOFs integrated into one-step.

Versatile Nanoscale Metal-Organic Frameworks (nMOFs): An Emerging 3D Nanoplatform for Drug Delivery and Therapeutic Applications

For decades, nanoscale metal-organic frameworks (nMOFs) have attracted extensive interest in biomedicine due to their distinct characteristics, including facile synthesis, porous interior, and tunable biocompatibility. With high porosity, versatile nMOFs allow for the facile encapsulation of various therapeutic agents with exceptionally high payloads. Constructed from metal ions and organic linkers through coordination bonds, nMOFs with plentiful functional groups enable the surface modification for active targeting and enhanced biocompatibility. This review outlines the up-to-date progresses on the exploration of nMOFs in the field of biomedicine. First, the classification and synthesis of nMOFs are discussed, followed by the concrete introduction of drug loading strategies of nMOFs and mechanisms of stimulation-responsive drug release. Second, the smart designs of the nMOFs-based platforms for anticancer and antibacterial treatment are summarized. Finally, the basic challenges faced by nMOFs research and the great potential of biomimetic nMOFs are presented. This review article affords an inspiring insight into the interdisciplinary research of nMOFs and their biomedical applications, which holds great expectation for their further clinical translation.

Development of MOF Reinforcement for Structural Stability and Toughness Enhancement of Biodegradable Bioinks

Three-dimensional (3D) bioprinting is a technology that can precisely fabricate customized tissues and organs. Hydrogel materials that can embed living cells for use in 3D printing are called bioinks. However, there are only limited options of bioinks currently because they require the following features at once, such as printability, repetitive layer-by-layer stacking (stackability), structure stabilization, and biological properties. A polyurethane-gelatin double network hydrogel bioink was previously reported to own tunable modulus through changing the solid content, but cell viability at the high solid content is inevitably reduced. In the present study, the reinforcement effects of a metal-organic framework (MOF), zeolitic imidazolate framework-8 (ZIF-8), in the PUG bioink were evaluated. The printability, stackability, thermoresponsiveness, and shear-thinning behavior of the PUG-ZIF-8 composite hydrogels were examined. It was found that the PUG composite hydrogel containing 1250 μg/mL ZIF-8 crystals showed significant structural stability and modulus enhancement (∼2.5-fold). However, the PUG bioink containing 1250 μg/mL ZIF-8 crystals may lead to cell senescence or death. The cytocompatible concentration of ZIF-8 crystals in the bioink was about 875 μg/mL, and this concentration was much higher than the reported tolerable amount (∼50 μg/mL) of ZIF-8 for biomedical applications. The strong reinforcement effect of ZIF-8 and the drug-loading/sensing possibilities of MOFs may open new opportunities for using MOFs in 3D bioprinting applications.

Core–shell ZIF-8@polydopamine nanoparticles obtained by mitigating the polydopamine coating induced self-etching of MOFs: prototypical metal ion reservoirs for sticking to and killing bacteria

ZIF-8@PDA nanoparticles can work as metal ion reservoirs that locally release metal ions to kill bacteria after sticking to them.

Biocompatibility and biodegradability of metal organic frameworks for biomedical applications

Metal organic frameworks (MOFs) are a unique class of smart hybrid materials that have recently attracted significant interest for catalysis, separation and biomedical applications. Different strategies have been developed to overcome the limitations of MOFs for bio-applications in order to produce a system with high biocompatibility and biodegradability. In this review, we outline the chemical and physical factors that dictate the biocompatibility and biodegradability characteristics of MOFs including the nature of the metal ions and organic ligands, size, surface properties and colloidal stability. This review includes the in vitro biodegradation and in vivo biodistribution studies of MOFs to better understand their pharmacokinetics, organ toxicity and immune response. Such studies can guide the design of future bio-friendly systems that bring us closer to safely translating these platforms into the pharmaceutical consumer market.

Copper-doped metal–organic frameworks for the controlled generation of nitric oxide from endogenous S-nitrosothiols

We report the synthesis of a catalyst, copper-doped zeolitic imidazolate framework ZIF-8, that generates nitric oxide from naturally occurring endogenous nitric oxide donors, S-nitrosoglutathione and S-nitrosocysteine.

Capture and Decomposition of the Nerve Agent Simulant, DMCP, Using the Zeolitic Imidazolate Framework (ZIF-8)

Understanding mechanisms of decontamination of chemical warfare agents (CWA) is an area of intense research aimed at developing new filtration materials to protect soldiers and civilians in case of state-sponsored or terrorist attack. In this study, we employed complementary structural, chemical, and dynamic probes and in situ data collection, to elucidate the complex chemistry, capture, and decomposition of the CWA simulant, dimethyl chlorophosphonate (DMCP). Our work reveals key details of the reactive adsorption of DMCP and demonstrates the versatility of zeolitic imidazolate framework (ZIF-8) as a plausible material for CWA capture and decomposition. The in situ synchrotron-based powder X-ray diffraction (PXRD) and pair distribution function (PDF) studies, combined with Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), zinc K-edge X-ray absorption near edge structure (XANES), and Raman spectroscopies, showed that the unique structure, chemical state, and topology of ZIF-8 enable accessibility, adsorption, and hydrolysis of DMCP into the pores and revealed the importance of linker chemistry and Zn²⁺ sites for nerve agent decomposition. DMCP decontamination and decomposition product(s) formation were observed by thermogravimetric analysis, FT-IR spectroscopy, and phosphorus (P) K-edge XANES studies. Differential PDF analysis indicated that the average structure of ZIF-8 (at the 30 Å scale) remains unchanged after DMCP dosing and provided information on the dynamics of interactions of DMCP with the ZIF-8 framework. Using in situ PXRD and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), we showed that nearly 90% regeneration of the ZIF-8 structure and complete liberation of DMCP and decomposition products occur upon heating.

Zeolitic imidazolate frameworks in analytical sample preparation

Zeolitic imidazolate frameworks are a class of metal-organic frameworks that are topologically isomorphic with zeolites. Zeolitic imidazolate frameworks are composed of tetrahedrally coordinated metal ions connected by imidazolate linkers and have a high porosity and chemical stability. Here, we summarize the progress made in the application of zeolitic imidazolate frameworks in sample preparation for analytical purposes. This review is focused on analytical methods based on liquid chromatography, gas chromatography, or capillary electrophoresis, where the use of zeolitic imidazolate frameworks has contributed to increasing the sensitivity and selectivity of the method. While bulk zeolitic imidazolate frameworks have been directly used in analytical sample preparation protocols, a variety of strategies for their magnetization or their incorporation into sorbent particles, monoliths, fibers, stir bars, or thin films, have been developed. These modifications have facilitated the handling and application of zeolitic imidazolate frameworks for a number of analytical sample treatments including magnetic solid-phase extraction, solid-phase microextraction, stir bar sorptive extraction, or thin film microextraction, among other techniques.

BMP-6 carrying metal organic framework-embedded in bioresorbable electrospun fibers for enhanced bone regeneration

Biomolecule carrier structures have attracted substantial interest owing to their potential utilizations in the field of bone tissue engineering. In this study, MOF-embedded electrospun fiber scaffold for the controlled release of BMP-6 was developed for the first time, to enrich bone regeneration efficacy. The scaffolds were achieved by first, one-pot rapid crystallization of BMP-6 encapsulated ZIF-8 nanocrystals-as a novel carrier for growth factor molecules- and then electrospinning of the blending solution composed of poly (ε-caprolactone) and BMP-6 encapsulated ZIF-8 nanocrystals. BMP-6 molecule encapsulation efficiency for ZIF-8 nanocrystals was calculated as 98%. The in-vitro studies showed that, the bioactivity of BMP-6 was preserved and the release lasted up to 30 days. The release kinetics fitted the Korsmeyer-Peppas model exhibiting a pseudo-Fickian behavior. The in-vitro osteogenesis studies revealed the superior effect of sustained release of BMP-6 towards osteogenic differentiation of MC3T3-E1 pre-osteoblasts. In-vivo studies also revealed that the sustained slow release of BMP-6 was responsible for the generation of well-mineralized, new bone formation in a rat cranial defect. Our results proved that; MOF-carriers embedded in electrospun scaffolds can be used as an effective platform for bone regeneration in bone tissue engineering applications. The proposed approach can easily be adapted for various growth factor molecules for different tissue engineering applications.

Coenzyme-dependent nanozymes playing dual roles in oxidase and reductase mimics with enhanced electron transport

Although nanozymes overcome a series of shortcomings of natural enzymes, their wide applications are hampered due to their limited varieties. In this work, we propose a coenzyme-dependent nanozyme, a synergistic composite comprising zeolitic imidazolate frameworks encapsulated with polyethylenimine (PEI) and functionalized with a flavin mononucleotide (PEI/ZIF-FMN). The flavin mononucleotide (FMN) plays the role of a prosthetic group, and the positively charged NH2 groups in PEI readily provide the binding affinity to nicotinamide adenine dinucleotide (NADH), which facilitates the electron transfer from NADH to FMN and terminal electron acceptors (such as O2) with a greatly enhanced (80 times) catalytic performance. The integrated nanoparticle-coenzyme composite works as an NADH oxidase mimic and couples with dehydrogenases for the tandem enzymatic reaction. PEI/ZIF-FMN also mediated the electron transfer from NADH to cytochrome c (Cyt c), thereby exhibiting Cyt c reductase-like activity.

Metal-organic frameworks for virus detection

Virus severely endangers human life and health, and the detection of viruses is essential for the prevention and treatment of associated diseases. Metal-organic framework (MOF), a novel hybrid porous material which is bridged by the metal clusters and organic linkers, has become a promising biosensor platform for virus detection due to its outstanding properties including high surface area, adjustable pore size, easy modification, etc. However, the MOF-based sensing platforms for virus detection are rarely summarized. This review systematically divided the detection platforms into nucleic acid and immunological (antigen and antibody) detection, and the underlying sensing mechanisms were interpreted. The nucleic acid sensing was discussed based on the properties of MOF (such as metal ion, functional group, geometry structure, size, porosity, stability, etc.), revealing the relationship between the sensing performance and properties of MOF. Moreover, antibodies sensing based on the fluorescence detection and antigens sensing based on molecular imprinting or electrochemical immunoassay were highlighted. Furthermore, the remaining challenges and future development of MOF for virus detection were further discussed and proposed. This review will provide valuable references for the construction of sophisticated sensing platform for the detection of viruses, especially the 2019 coronavirus.

Identifying Differing Intracellular Cargo Release Mechanisms by Monitoring In Vitro Drug Delivery from MOFs in Real Time

Metal-organic frameworks (MOFs) have been proposed as biocompatible candidates for the targeted intracellular delivery of chemotherapeutic payloads, but the site of drug loading and subsequent effect on intracellular release is often overlooked. Here, we analyze doxorubicin delivery to cancer cells by MIL-101(Cr) and UiO-66 in real time. Having experimentally and computationally verified that doxorubicin is pore loaded in MIL-101(Cr) and surface loaded on UiO-66, different time-dependent cytotoxicity profiles are observed by real-time cell analysis and confocal microscopy. The attenuated release of aggregated doxorubicin from the surface of Dox@UiO-66 results in a 12 to 16 h induction of cytotoxicity, while rapid release of pore-dispersed doxorubicin from Dox@MIL-101(Cr) leads to significantly higher intranuclear localization and rapid cell death. In verifying real-time cell analysis as a versatile tool to assess biocompatibility and drug delivery, we show that the localization of drugs in (or on) MOF nanoparticles controls delivery profiles and is key to understanding in vitro modes of action.

Fluorescence-Scattering Dual-Signal Response of Carbon Dots@ZIF-90 for Phosphate Ratiometric Detection

Ratiometric fluorescence has drawn extensive attention owing to its self-calibration property. However, it is difficult to obtain appropriate fluorescent materials that can be excited under one excitation and possess well-resolved signals simultaneously. In this work, with the optical properties of the fluorescence of carbon dots (CDs) and the second-order scattering (SOS) of ZIF-90 (zeolitic imidazole frameworks-90) nanoparticles, the synthesized CDs@ZIF-90 can be applied to phosphate (PO₄^3-) ratiometric detection. The fluorescence of CDs is greatly suppressed through encapsulating CDs into ZIF-90. Nevertheless, the SOS is quite obvious due to the high scattering intensity of large size ZIF-90. The competitive coordination between PO₄^3- and the metal node of ZIF-90 decomposes CDs@ZIF-90, leading to the restoration of fluorescence and the diminution of SOS. On the basis of the PO₄^3--induced ZIF-90 decomposition and CD release, a novel method for PO₄^3- ratiometric detection is developed through the dual-signal response of the fluorescence scattering. Under the optimal condition, the method shows a linear range from 1.0 to 50.0 μmol L^-1 with a detection limit of 0.23 μmol L^-1. Furthermore, the probes are employed to assess PO₄^3- in practical aqueous samples successfully. Compared with the traditional approach, which only records fluorescence signals, the method reported here provides a new strategy to design ratiometric sensors by fluorescence and scattering.

Controlled Transdermal Release of Antioxidant Ferulate by a Porous Sc(III) MOF

The Sc(III) MOF-type MFM-300(Sc) is demonstrated in this study to be stable under physiological conditions (PBS), biocompatible (to human skin cells), and an efficient drug carrier for the long-term controlled release (through human skin) of antioxidant ferulate. MFM-300(Sc) also preserves the antioxidant pharmacological effects of ferulate while enhancing the bio-preservation of dermal skin fibroblasts, during the delivery process. These discoveries pave the way toward the extended use of Sc(III)-based MOFs as drug delivery systems (DDSs).

Continuous-Flow Synthesis of ZIF-8 Biocomposites with Tunable Particle Size

Zeolitic imidazolate framework (ZIF) biocomposites show the capacity to protect and deliver biotherapeutics. To date, the progress in this research area is based on laboratory batch methods. Now, the first continuous flow synthetic method is presented for the encapsulation of a model protein (bovine serum albumin, BSA) and a clinical therapeutic (α1-antitrypsin, AAT) in ZIF-8. The in situ kinetics of nucleation, growth, and crystallization of BSA@ZIF-8 were studied by small-angle X-ray scattering. By controlling the injection time of ethanol, the particle growth could be quenched by ethanol-induced crystallization from amorphous particles to ZIF-8 crystals. The particle size of the biocomposite was tuned in the 40-100 nm range by varying residence time prior to introduction of ethanol. As a proof-of-concept, this procedure was used for the encapsulation of AAT in ZIF-8. Upon release of the biotherapeutic from the composite, the trypsin inhibitor function of AAT was preserved.

Phase dependent encapsulation and release profile of ZIF-based biocomposites

Biocomposites composed of Zeolitic Imidazolate Frameworks (ZIFs) are generating significant interest due to their facile synthesis, and capacity to protect proteins from harsh environments. Here we systematically varied the composition (i.e. relative amounts of ligand (2-methylimidazole), metal precursor (Zn(OAc)2·2H2O), and protein) and post synthetic treatments (i.e. washes with water or water/ethanol) to prepare a series of protein@ZIF biocomposites. These data were used to construct two ternary phase diagrams that showed the synthesis conditions employed gave rise to five different phases including, for the first time, biocomposites based on ZIF-CO3-1. We examined the influence of the different phases on two properties relevant to drug delivery applications: encapsulation efficiency and release profile. The encapsulation efficiencies of bovine serum albumin and insulin were phase dependent and ranged from 75% to 100%. In addition, release profiles showed that 100% protein release varied between 40 and 300 minutes depending on the phase. This study provides a detailed compositional map for the targeted preparation of ZIF-based biocomposites of specific phases and a tool for the straightforward analysis of the crystalline phases of ZIF based materials (web application named "ZIF phase analysis"). These data will facilitate the progress of ZIF bio-composites in the fields of biomedicine and biotechnology.

Comparison of different zinc precursors for the construction of zeolitic imidazolate framework-8 artificial shells on living cells

The robust cell-in-shell structure is highly desirable for endowing living cells with an artificial exoskeleton to defend them from many environmental factors such as osmotic pressure, shear force, heat, UV radiation, and enzymes. Cell encapsulation has shown potential applications in many fields and attracted increasing interest. However, the influences of the precursors on the cell viability during the shell formation process are not clear and seldom investigated. Here, zinc nitrite, zinc acetate and zinc sulfate were applied individually to synthesize zeolitic imidazolate framework-8 (ZIF-8) shells on living cells. All the zinc salt precursors could convert to a ZIF-8 layer on the living cell surface. The zinc salts and organic ligand did not exhibit obvious toxicity to yeast cells when applied individually. However, dead cells were observed during the living cell encapsulation process using different zinc precursors. Compared with zinc nitrate and zinc acetate, ZIF-8 formed by zinc sulfate led to a higher percentage of cell death, especially under high concentrations of zinc sulfate. Cell division was suppressed by the ZIF-8 shell but restored fully upon shell removal by EDTA solution or pH 4.0 buffer. Escherichia coli (E. coli) cells showed a lower percentage of cell death, indicating excellent tolerance to the ZIF-8 encapsulation process. This work illustrates the cell toxicity during the formation of ZIF-8 cell shells by different zinc salts and engineering of the cell growth by MOF coating, which could provide a foundation for further quantitative analysis and potential applications in biomedicine and bioengineering.

Magnetically responsive horseradish peroxidase@ZIF-8 for biocatalysis

A porous model bioreactor is obtained combining zeolitic imidazolate framework ZIF-8 with horseradish peroxidase and iron oxide magnetic nanoparticles in a one-pot process, in water at room temperature.

Synthesis and modification of ZIF-8 and its application in drug delivery and tumor therapy

Metal–organic frameworks have the properties of high porosity, variable pore sizes, and easy modification as drug delivery systems. In particular, ZIF-8 based on Zn²⁺ has been extensively studied in the medical field due to its low toxicity and good biocompatibility. This review introduces the preparation and functional modification of ZIF-8, and its application in drug delivery, focusing on the single-stimulus and multi-stimulus response release of drugs in ZIF-8 materials, the integrated role of diagnosis and treatment with ZIF-8 in cancer treatment, and its application in the synergistic therapy of multiple cancer treatment methods. We summarize the latest developments of ZIF-8 in the field of drug delivery and tumor therapy, and present the main challenges that remain to be resolved in the ZIF-8 drug delivery system.

Synthesis and modification of ZIF-8 and its application in drug delivery, stimulus response-controlled drug release and tumor therapy.

Colloidal metal-organic framework particles: the pioneering case of ZIF-8

The production of metal-organic frameworks (MOFs) in the form of colloids has brought a paradigm shift in the design of new functional porous materials. Along with their intrinsic interest as porous solids, and contrary to their bulk powder counterparts, colloidal MOF particles can additionally be dispersed, shaped, functionalized, transformed and assembled in a controlled manner, conferring them further properties and applications. In this regard, zeolitic imidazolate framework-8 (ZIF-8) has become a pioneering MOF constituent of colloidal science. Today, the understanding of the role of synthetic parameters, learned after one decade of research, enables the production of monodisperse colloidal ZIF-8 particles with tunable dimensions and morphologies, offering the opportunity to develop new functional materials and composites with novel and promising functionalities. This tutorial review provides a useful guide to prepare ZIF-8 in its colloidal form, covering the published studies on the synthesis of homogeneous ZIF-8 particles with controlled size and shape. In addition, we present the most relevant advances in the development of colloidal ZIF-8 hybrid single-particles, reflecting the great potential and rapid development of this interdisciplinary research field. Finally, we highlight how formulation of ZIF-8 as colloids has led to the emergence of novel physicochemical phenomena that are useful for practical applications. This review aims at promoting the development of MOFs as colloids, taking ZIF-8 as a pioneering and successful case that clearly shows the benefits of bridging MOF chemistry and colloidal science.

Metal-Organic Framework Encapsulating Hemoglobin as a High-Stable and Long-Circulating Oxygen Carriers to Treat Hemorrhagic Shock

As an oxygen-transporting protein, free hemoglobin (Hb) often suffers from the disadvantage of undesirable stability and short blood circulation, which severely impairs the potential clinical applications as the blood substitute. In this work, Hb was facilely encapsulated into a kind of metal-organic frameworks (MOFs) (ZIF-8) inspired by the natural biomineralization process. The obtained ZIF-8 encapsulating Hb (ZIF-8@Hb) showed the small hydrodynamic size of 180.8 nm and neutral zeta potential of -2.1 mV by adjusting the ratio of Hb in ZIF-8 frameworks. Intriguingly, Hb encapsulated by ZIF-8 exhibited significantly enhanced stability in alkaline, oxidation, high temperature, or enzymatic environment compared with free Hb because of the excellent protective MOF coatings. More importantly, the negative charge of Hb neutralized the original positive charge of ZIF-8, which led to the better biocompatibility, lower protein adsorption, and macrophage uptake of ZIF-8@Hb than bare ZIF-8 nanoparticles. Furthermore, ZIF-8@Hb displayed extended blood circulation with the elimination half-life of 13.9 h as well as reduced nonspecific distribution in normal organs compared with free Hb or ZIF-8 nanoparticles. With the above advantages, ZIF-8@Hb showed significantly extended survival time of mice in a disease model of hemorrhagic shock compared with free Hb or bare ZIF-8 nanoparticles. Overall, this work offers a high-stable and long-circulating oxygen carrier platform, which may find wide applications as a blood substitute to treat various oxygen-relevant diseases.

Light-controllable systems based on TiO2-ZIF-8 composites for targeted drug release: communicating with tumour cells

A model nanocomposite releases drug within 40 minutes under UV irradiation.

ZIF-8 self-etching method for Au/polydopamine hybrid cubic microcapsules with modulated nanostructures

A one-step strategy combining in situ redox-oxidation polymerization and a ZIF-8 sacrifice template is reported for constructing Au/PDA cubic microcapsules.