Nanoscale MOFs in nanomedicine applications: from drug delivery to therapeutic agents

Recent advances in continuous flow synthesis of metal-organic frameworks and their composites

Metal-organic frameworks (MOFs) and their composites have garnered significant attention in recent years due to their exceptional properties and diverse applications across various fields. The conventional batch synthesis methods for MOFs and their composites often suffer from challenges such as long reaction times, poor reproducibility, and limited scalability. Continuous flow synthesis has emerged as a promising alternative for overcoming these limitations. In this short review, we discuss the recent advancements, challenges, and future perspectives of continuous flow synthesis in the context of MOFs and their composites. The review delves into a brief overview of the fundamental principles of flow synthesis, highlighting its advantages over batch methods. Key benefits, including precise control over reaction parameters, improved scalability and efficiency, rapid optimization capabilities, enhanced reaction kinetics and mass transfer, and increased safety and environmental sustainability, are addressed. Additionally, the versatility and flexibility of flow synthesis techniques are discussed. The article then explores various flow synthesis methods applicable to MOF and MOF composite production. The techniques covered include continuous flow solvothermal synthesis, mechanochemical synthesis, microwave and ultrasound-assisted flow synthesis, microfluidic droplet synthesis, and aerosol synthesis. Notably, the combination of flow chemistry and aerosol synthesis with real-time characterization is also addressed. Furthermore, the impact of flow synthesis on the properties and performance of MOFs is explored. Finally, the review discusses current challenges and future perspectives in the field of continuous flow MOF synthesis, paving the way for further development and broader application of this promising technique.

Investigation on the Drug Release Efficacy of the Ibuprofen-Loaded ZIF-8/Fe3O4 NPs Nanocarrier

In this work, a one-pot multicomponent synthesis of the ibuprofen-loaded Fe3O4 nanoparticles-supported zeolitic imidazolate framework-8 (Ibu-ZIF-8/Fe3O4 NPs) nanohybrid was carried out. The ZIF-8/Fe3O4 NPs nanohybrid was used as a drug carrier for the in vitro release of ibuprofen in a PBS solution. The structure and morphology of the synthesized materials were investigated by powder X-ray diffraction (PXRD) analysis, transmission electron microscopy (TEM) analysis, UV-visible absorption studies, FTIR spectroscopy, and thermogravimetric analysis (TGA). The ibuprofen release kinetics was studied by UV-visible spectroscopy. The mechanism of drug delivery was thoroughly investigated and the Higuchi model was found as the best-fitted model for the ibuprofen release study. The 20 wt % Fe3O4 NPs-supported ZIF-8 nanohybrid exhibited more than 95% ibuprofen release efficiency in phosphate buffer saline of pH 7.4 within 2 h. The separation ability of the nanohybrid was very good, and it was easily separated by a simple commercial magnet. In order to investigate the cell viability, the cytotoxicity of ZIF-8, Fe3O4 NPs, and ZIF-8/20 wt % Fe3O4 NPs was investigated using MTT assays against Leishmania donovani promastigotes. The ZIF-8/20 wt % Fe3O4 NPs nanohybrid carrier exhibited a cell growth inhibition effect with a high correlation coefficient and low probability (p) values. The high release of drug molecules may be due to the more open site of the ZIF-8/Fe3O4 NPs nanohybrid. The drug release profile suggests that the nanohybrid can be potentially used as a drug carrier for targeted drug delivery systems.

A gold nanocluster/MIL-100(Fe) bimodal nanovector for the therapy of inflammatory disease through attenuation of Toll-like receptor signaling

A better understanding of the molecular and cellular events involved in the inflammation process has opened novel perspectives in the treatment of inflammatory diseases, particularly through the development of well-designed nanomedicines. Here we describe the design of a novel class of anti-inflammatory nanomedicine (denoted as Au@MIL) synthesized through a one-pot, cost-effective and green approach by coupling a benchmark mesoporous iron(III) carboxylate metal organic framework (MOF) (i.e. MIL-100(Fe)) and glutathionate protected gold nanoclusters (i.e. Au25SG18 NCs). This nano-carrier exhibits low toxicity and excellent colloidal stability combined with the high loading capacity of the glucocorticoid dexamethasone phosphate (DexP) whose pH-dependent delivery was observed. The drug loaded Au@MIL nanocarrier shows high anti-inflammatory activity due to its capacity to specifically hinder inflammatory cell growth, scavenge intracellular reactive oxygen species (ROS) and downregulate pro-inflammatory cytokine secretion. In addition, this formulation has the capacity to inhibit the Toll-like receptor (TLR) signaling cascade namely the nuclear factor kappa B (NF-κB) and the interferon regulatory factor (IRF) pathways. This not only provides a new avenue for the nanotherapy of inflammatory diseases but also enhances our fundamental knowledge of the role of nanoMOF based nanomedicine in the regulation of innate immune signaling.

Dynamic hydrogel-metal-organic framework system promotes bone regeneration in periodontitis through controlled drug delivery

Periodontitis is a prevalent chronic inflammatory disease, which leads to gradual degradation of alveolar bone. The challenges persist in achieving effective alveolar bone repair due to the unique bacterial microenvironment's impact on immune responses. This study explores a novel approach utilizing Metal-Organic Frameworks (MOFs) (comprising magnesium and gallic acid) for promoting bone regeneration in periodontitis, which focuses on the physiological roles of magnesium ions in bone repair and gallic acid's antioxidant and immunomodulatory properties. However, the dynamic oral environment and irregular periodontal pockets pose challenges for sustained drug delivery. A smart responsive hydrogel system, integrating Carboxymethyl Chitosan (CMCS), Dextran (DEX) and 4-formylphenylboronic acid (4-FPBA) was designed to address this problem. The injectable self-healing hydrogel forms a dual-crosslinked network, incorporating the MOF and rendering its on-demand release sensitive to reactive oxygen species (ROS) levels and pH levels of periodontitis. We seek to analyze the hydrogel's synergistic effects with MOFs in antibacterial functions, immunomodulation and promotion of bone regeneration in periodontitis. In vivo and in vitro experiment validated the system's efficacy in inhibiting inflammation-related genes and proteins expression to foster periodontal bone regeneration. This dynamic hydrogel system with MOFs, shows promise as a potential therapeutic avenue for addressing the challenges in bone regeneration in periodontitis.

Hyaluronic acid functionalized citric acid dendrimer/UiO-66-COOH as a stable and biocompatible platform for daunorubicin delivery

This work aimed to prepare a new system for daunorubicin (DNR) delivery to improve therapeutic efficiency and decrease unwanted side effects. Typically, at first, a carboxylic acid functional group containing metal-organic framework (UiO-66-COOH) was synthesized in a simple way. Then, a third generation of citric acid dendrimer (CAD G3) was grown on it (UiO-66-COOH-CAD G3). Finally, the system was functionalized with pre-modified hyaluronic acid (UiO-66-COOH-CAD-HA). SEM analysis displayed that the synthesized particles have a spherical shape with an average particle size ranging from 260 to 280 nm. An increase in hydrodynamic diameter from 223 nm for UiO-66-COOH to 481 nm for UiO-66-COOH-CAD-HA is a sign of success in the performed reactions. Also, the average pore size was calculated at about 4.04 nm. The DNR loading efficiency of UiO-66-COOH-CAD-HA was evaluated at ∼74 % (DNR@UiO-66-COOH-CAD-HA). It was observed that the drug release rate at a lower pH is more than higher pH. The maximum hemolysis of <3 % means that the UiO-66-COOH-CAD-HA is hemocompatible. The use of DNR-loaded UiO-66-COOH-CAD-HA led to cell-killing of 77.9 % for MDA-MB 231. These results specified the great potential of UiO-66-COOH-CAD-HA for tumor drug delivery, so it could be proposed as a new carrier for anticancer agents to minimize adverse effects and improve therapeutic efficacy.

Quest for a Desolvated Structure Unveils Breathing Phenomena in a MOF Leading to Greener Catalysis in a Solventless Setup: Insights from Combined Experimental and Computational Studies

The crystal structure of the metal-organic framework (MOF), {Mn2(1,4-bdc)2(DMF)2}n (1) (1,4-bdcH2, 1,4-benzenedicarboxylic acid; DMF, N,N-dimethylformamide), is known for a long time; however, its desolvated structure, {Mn2(1,4-bdc)2}n (1'), is not yet known. The first-principles-based computational simulation was used to unveil the structure of 1' that shows the expansion in the framework, leading to pore opening after the removal of coordinated DMF molecules. We have used 1' that contains open metal sites (OMSs) in the structure in cyanosilylation and CO2 cycloaddition reactions and recorded complete conversions in a solventless setup. The pore opening in 1' allows the facile diffusion of small aldehyde molecules into the channels, leading to complete conversion. The reactions with larger aldehydes, 2-naphthaldehyde and 9-anthracenecarboxaldehyde, also show 99.9% conversions, which are the highest reported until date in solventless conditions. The in silico simulations illustrate that larger aldehydes interact with Mn(II) OMSs on the surfaces, enabling a closer interaction and facilitating complete conversions. The catalyst shows high recyclability, exhibiting 99.9% conversions in the successive reaction cycles with negligible change in the structure. Our investigations illustrate that the catalyst 1' is economical, efficient, and robust and allows reactions in a solventless greener setup, and therefore the catalysis with 1' can be regarded as "green catalysis".

MOF magic: zirconium-based frameworks in theranostic and bio-imaging applications

Over the past two decades, metal-organic frameworks (MOFs) have garnered substantial scientific interest across diverse fields, spanning gas storage, catalysis, biotechnology, and more. Zirconium, abundant in nature and biologically relevant, offers an appealing combination of high content and low toxicity. Consequently, Zr-based MOFs have emerged as promising materials with significant potential in biomedical applications. These MOFs serve as effective nanocarriers for controlled drug delivery, particularly for challenging antitumor and retroviral drugs in cancer and AIDS treatment. Additionally, they exhibit prowess in bio-imaging applications. Beyond drug delivery, Zr-MOFs are notable for their mechanical, thermal, and chemical stability, making them increasingly relevant in engineering. The rising demand for stable, non-toxic Zr-MOFs facilitating facile nanoparticle formation, especially in drug delivery and imaging, is noteworthy. This review focuses on biocompatible zirconium-based metal-organic frameworks (Zr-MOFs) for controlled delivery in treating diseases like cancer and AIDS. These MOFs play a key role in theranostic approaches, integrating diagnostics and therapy. Additionally, their utility in bio-imaging underscores their versatility in advancing medical applications.

A critical review on metal-organic frameworks (MOFs) based nanomaterials for biomedical applications: Designing, recent trends, challenges, and prospects

Nanomaterials (NMs) have garnered significant attention in recent decades due to their versatile applications in a wide range of fields. Thanks to their tiny size, enhanced surface modifications, impressive volume-to-surface area ratio, magnetic properties, and customized optical dispersion. NMs experienced an incredible upsurge in biomedical applications including diagnostics, therapeutics, and drug delivery. This minireview will focus on notable examples of NMs that tackle important issues, demonstrating various aspects such as their design, synthesis, morphology, classification, and use in cutting-edge applications. Furthermore, we have classified and outlined the distinctive characteristics of the advanced NMs as nanoscale particles and hybrid NMs. Meanwhile, we emphasize the incredible potential of metal-organic frameworks (MOFs), a highly versatile group of NMs. These MOFs have gained recognition as promising candidates for a wide range of bio-applications, including bioimaging, biosensing, antiviral therapy, anticancer therapy, nanomedicines, theranostics, immunotherapy, photodynamic therapy, photothermal therapy, gene therapy, and drug delivery. Although advanced NMs have shown great potential in the biomedical field, their use in clinical applications is still limited by issues such as stability, cytotoxicity, biocompatibility, and health concerns. This review article provides a thorough analysis offering valuable insights for researchers investigating to explore new design, development, and expansion opportunities. Remarkably, we ponder the prospects of NMs and nanocomposites in conjunction with current technology.

Engineered Metallic Ion-Based Hydrogel for Tendon-Bone Reconstruction

Rotator cuff regeneration is hindered by compromised vascular architecture, inflammation, and instability of the reconstructed tendon-bone interface. Herein, inspired by the phenomenon of magnetic clasps being connected together by a specific structure, an engineered metallic ion-based hydrogel scaffold was constructed through a bioorthogonal click reaction between (DOPA)4-PEG5-N3 and DBCO-BMP-2 peptides and a photopolymerization process in the hydrogel matrix, exhibiting the potential for angiogenesis, bone regeneration, and modulation of the inflammatory milieu, which aimed at facilitating rotator cuff regeneration. In vitro studies showed that the composite hydrogel scaffold stimulated the angiogenic activity of human umbilical vein endothelial cells and osteogenic differentiation of bone marrow mesenchymal stem cells, transforming macrophages from M1 to M2. Moreover, imaging and immunohistochemical analysis of a rat rotator cuff injury models demonstrated that the composite hydrogel could effectively promote regeneration and exhibit remarkable biocompatibility. In summary, this composite hydrogel material established an effective platform for the release of metal ions and clickable peptides, which accelerated the regeneration of rotator cuff injuries and had broad prospects for application in rotator cuff therapy.

Stability of Zr-Based UiO-66 Metal-Organic Frameworks in Basic Solutions

Although Zr-based metal-organic frameworks (MOFs) exhibit robust chemical and physical stability in the presence of moisture and acidic conditions, their susceptibility to nucleophilic attacks from bases poses a critical challenge to their overall stability. Herein, we systematically investigate the stability of Zr-based UiO-66 (UiO = University of Oslo) MOFs in basic solutions. The impact of 11 standard bases, including inorganic salts and organic bases, on the stability of these MOFs is examined. The destruction of the framework is confirmed through powder X-ray diffraction (PXRD) patterns, and the monitored dissolution of ligands from the framework is assessed using nuclear magnetic resonance (NMR) spectroscopy. Our key findings reveal a direct correlation between the strength and concentration of the base and the destruction of the MOFs. The summarized data provide valuable insights that can guide the practical application of Zr-based UiO-66 MOFs under basic conditions, offering essential information for their optimal utilization in various settings.

Empowering the Water Oxidation Activity of the Bimetallic Metal-Organic Framework by Annexing Gold Nanoparticles over the Catalytic Surface

Electrocatalytic water splitting to an anodic oxygen evolution reaction (OER) and a cathodic hydrogen evolution reaction (HER) is believed to be the most important application for sustainable hydrogen generation. Being a four-electron, four-proton transfer process, the OER plays the main obstacle for the same. Therefore, designing an effective electrocatalyst to minimize the activation energy barrier for the OER is a research topic of prime importance. The metal-organic framework (MOF) with a highly porous network is considered an appropriate candidate for the OER in alkaline conditions. Apart from several MOFs, the bimetallic one has an advantageous electrocatalytic performance due to the synergistic electronic interaction between two metal ions. However, most bimetallic MOFs have an obstacle to electrocatalytic application due to their low conductive nature, and therefore, they possess a barrier for charge transfer kinetics at the interface. Surface functionalization via various nanoparticles (NPs) is believed to be the most effective strategy for nullifying the conductive issue. In this work, we have designed a CoNi-based bimetallic MOF that was surface-functionalized by Au NPs (Au@CoNi-Bpy-BTC) for the OER under alkaline conditions. Au@CoNi-Bpy-BTC required an overpotential of just 330 mV, which is 56 mV lower as compared to the pristine MOF. Impedance analysis confirms an improved conductivity and charge transfer at the interface, where Au@CoNi-Bpy-BTC possesses a lower Rct value than CoNi-Bpy-BTC materials. Moreover, the Au-decorated MOF shows an 8.5 times increase in the TOF value compared to the pristine MOF. Therefore, this noble strategy toward the surface functionalization of MOFs via noble metal NPs is believed to be the most effective strategy for developing effective electrocatalysts for electrocatalytic application in energy-related fields. Overall, this report displays an exceptional correlation between the decorated NPs over the MOF surface, which can regulate the OER activity, as confirmed by experimental analysis.

Platinum nanoparticle-anchored metal-organic complex nanospheres by a coordination-crystallization approach for enhanced sonodynamic therapy of tumors

The combination of noble metal nanoparticles with metal-organic complexes has attracted great attention for exploring new properties in biomedical application areas. So far, the preparation of noble metal nanoparticle-loaded metal-organic complexes often requires complex processes. Here, a simple coordination-crystallization approach was developed to prepare platinum nanoparticle-anchored metal-organic complexes (Pt-MOCs) by directly mixing disulfiram (DSF), chloroplatinic acid, and a reducing agent. The DSF and Pt ions first coordinate forming metal-organic complex nanospheres and then the Pt nanoparticles crystallized on the surface taking advantage of the coordination rate of the metal ions and organic ligand being greater than the reduction rate of the metal ions. The Pt-MOCs possess uniform and adjustable diameter (240-536 nm), and their surface potentials can also be modulated easily from -22 to +14 mV by adjusting the ratio of DSF and chloroplatinic acid. Phantom experiments show that the Pt-MOC nanospheres significantly improve the efficiency of singlet oxygen production after exposure to ultrasound irradiation. In vitro experiments show that the Pt-MOCs effectively produce reactive oxygen species and exhibit superior cytotoxicity for tumor cells under ultrasound irradiation compared to metal-organic complexes (MOCs) or Pt nanoparticles. Taken together, this work reports a coordination-crystallization approach to synthesize Pt-MOCs, which show excellent sonodynamic therapy for tumors.

Exploring the antimicrobial potential of isoniazid loaded Cu-based metal-organic frameworks as a novel strategy for effective killing of Mycobacterium tuberculosis

Tuberculosis (TB) remains one of the most infectious pathogens with the highest human mortality and morbidity. Biofilm formation during Mycobacterium tuberculosis (Mtb) infection is responsible for bacterial growth, communication, and, most essentially, increased resistance/tolerance to antibiotics leading to higher bacterial persistence. Thus, biofilm growth is presently considered a key virulence factor in the case of chronic disease. Metal-Organic Frameworks (MOFs) have recently emerged as a highly efficient system to improve existing antibiotics' therapeutic efficacy and reduce adverse effects. In this regard, we have synthesized Cu-MOF (IITI-3) using a solvothermal approach. IITI-3 was well characterized by various spectroscopic techniques. Herein, IITI-3 was first encapsulated with isoniazid (INH) to form INH@IITI-3 with 10 wt% loading within 1 hour. INH@IITI-3 was well characterized by PXRD, TGA, FTIR, and BET surface area analysis. Furthermore, the drug release kinetics studies of INH@IITI-3 have been performed at pH 5.8 and 7.4 to mimic the small intestine and blood pH, respectively. The results show that drug release follows first-order kinetics. Furthermore, the antimycobacterial activity of INH@IITI-3 demonstrated significant bacterial killing and altered the structural morphology of the bacteria. Moreover, INH@IITI-3 was able to inhibit the mycobacterial biofilm formation upon treatment and showed less cytotoxicity toward the murine RAW264.7 macrophages. Thus, this work significantly opens up new possibilities for the applications of INH@IITI-3 in biofilm infections in Mtb and further contributes to TB therapeutics.

Copper(II)-MOFs for bio-applications

The recent development and implementation of copper-based metal-organic frameworks in biological applications are reviewed. The advantages of the presence of copper in MOFs for relevant applications such as drug delivery, cancer treatment, sensing, and antimicrobial are highlighted. Advanced composites such as MOF-polymers are playing critical roles in developing materials for specific applications.

Asymmetric Ligands of a Metal-Organic Framework on Enhanced Photocatalytic CO2 Reduction

Metal-organic frameworks (MOFs) have been studied extensively in the catalytic field. However, the role of ligands in catalysis has been less well investigated. Here, an asymmetric ligand photocatalytic strategy for CO2 reduction in MOFs is first proposed. MOF-303(Al) with asymmetric ligands (pyrazolyldicarboxylic acid) exhibits synergistic catalytic effects. Specifically, pyrazoles participate in CO2 activation; i.e., pyrazole and μ2-OH form hydrogen bonds with CO2 to polarize C═O bonds. Furthermore, the lowest unoccupied molecular orbital (LUMO; A pyrazole) and highest occupied molecular orbital (HOMO; B pyrazole) act as the electron donor and acceptor to spatially separate the excited electron-hole, with A and B pyrazoles for CO2 and H2O adsorption to avoid competition, respectively. Owing to its advantages, MOF-303-modified g-C3N4 achieves nonsacrificial and transition-metal-free photocatalytic CO2 reduction to CO of 16.19 μmol·g-1·h-1, significantly higher than that of g-C3N4. This work provides fresh insights into asymmetric ligands in photocatalytic CO2 reduction.

The rise of metal-organic framework based micromotors

Micromotors (MMs) are micro and nanoscale devices capable of converting energy into autonomous motion. Metal-organic frameworks (MOFs) are crystalline materials that display exceptional properties such as high porosity, internal surface areas, and high biocompatibility. As such, MOFs have been used as active materials or building blocks for MMs. In this highlight, we describe the evolution of MOF-based MMs, focusing on the last 3 years. First, we covered the main propulsion mechanisms and designs, from catalytic to fuel-free MOF-based MMs. Secondly, we discuss recent applications of new fuel-free MOFs MM to give a critical overview of the current challenges of this blooming research field. The advantages and challenges discussed provide a useful guide for the design of the next generation MOF MMs toward real-world applications.

Development of Novel Paclitaxel-Loaded ZIF-8 Metal-Organic Framework Nanoparticles Modified with Peptide Dimers and an Evaluation of Its Inhibitory Effect against Prostate Cancer Cells

Prostate cancer (PC) is one of the common malignant tumors of the male genitourinary system. Here, we constructed PTX@ZIF-8, which is a metal-organic-framework-encapsulated drug delivery nanoparticle with paclitaxel (PTX) as a model drug, and further modified the synthesized peptide dimer (Di-PEG₂₀₀₀-COOH) onto the surface of PTX@ZIF-8 to prepare a nanotargeted drug delivery system (Di-PEG@PTX@ZIF-8) for the treatment of prostate cancer. This study investigated the morphology, particle size distribution, zeta potential, drug loading, encapsulation rate, stability, in vitro release behavior, and cytotoxicity of this targeted drug delivery system, and explored the uptake of Di-PEG@PTX@ZIF-8 by human prostate cancer Lncap cells at the in vitro cellular level, as well as the proliferation inhibition and promotion of apoptosis of Lncap cells by the composite nanoparticles. The results suggest that Di-PEG@PTX@ZIF-8, as a zeolitic imidazolate frameworks-8-loaded paclitaxel nanoparticle, has promising potential for the treatment of prostate cancer, which may provide a novel strategy for the delivery system targeting prostate cancer.