Metal-organic frameworks for stimuli-responsive drug delivery

Fluorinated solvent-assisted photocatalytic aerobic oxidative amidation of alcohols via visible-light-mediated HKUST-1/Cs-POMoW catalysis

Successful synthesis and characterization of HKUST-1/Cs-POMoW binary composite, and application in the photocatalytic aerobic oxidative amidation reaction of alcohols under light illuminating in the visible region.

Stabilization of liquid active guests via nanoconfinement into a flexible microporous metal–organic framework

The nanoconfinement of the three liquid guests within a MOF has been fully investigated in terms of host–guest interactions and framework rearrangement.

Recent developments in organic-inorganic hybrid metal phosphates and phosphites

The design and synthesis of crystalline materials have been a subject of intensive research because of their interesting structures, physicochemical properties, and potential applications. However, the crystalline structure of organic-inorganic hybrid materials collapses to lose the structural features of the original networks and/or frameworks when exposed to different stimuli such as pH, vapor, water, high temperature, and organic solvents. This hampers further studies focusing on practical applications. Although several review articles provide reasonable pathways for the preparation of stable metal-organic frameworks (MOFs) and coordination polymers (CPs), the synthesis and design of stable materials containing organic species remain challenging. In this frontier article, we discuss the development of crystalline MOF, CP, metallophosphate, and metallophosphite materials, and provide a feasible approach for the formation of stable organic-inorganic hybrid compounds that combine MOFs (or CPs) and phosphate (or phosphite) building elements. In addition to their interesting structures, the synthetic strategies and structural stabilities of such hybrid composites are also presented.

Recent advances in cell membrane coated metal-organic frameworks (MOFs) for tumor therapy

In improving the tumor-targeting ability of metal-organic frameworks (MOFs) for tumor therapy and avoiding the clearance as well as capture by the immune system, there are still several challenges, which limit the development and bio-applications of MOFs. To overcome these challenges, various targeted modification strategies have been proposed. Amongst all the strategies, a promising cell membrane coating method has been explored and utilized for the syntheses of new cell membrane biomimetic MOFs (CMMs). Through such coating, various source cell membranes (e.g., red blood cell, immune cell, cancer cell, platelet, and fusion cell membranes) can be endowed with excellent properties such as long blood circulation, immune escape, and targeting ability. In the presented perspective, the synthetic method, characterization, and research progress in tumor therapy based on CMMs have been summarized. This is because, like many other technologies, the cell membrane coating technology also has several challenges to overcome. Hence, addressing and overcoming such challenges will promote and extend the bio-applications of MOFs which in the future may become a prospective carrier for cancer nano-medicine. Finally, the prospects and challenges of utilizing CMMs for tumor therapy have been discussed.

Multifunctional metal-organic framework heterostructures for enhanced cancer therapy

Metal-organic frameworks (MOFs) are an emerging class of molecular crystalline materials built from metal ions or clusters bridged by organic linkers. By taking advantage of their synthetic tunability and structural regularity, MOFs can hierarchically integrate nanoparticles and/or biomolecules into a single framework to enable multifunctions. The MOF-protected heterostructures not only enhance the catalytic capacity of nanoparticle components but also retain the biological activity of biomolecules in an intracellular microenvironment. Therefore, the multifunctional MOF heterostructures have great advantages over single components in cancer therapy. In this review, we comprehensively summarize the general principle of the design and functional modulation of nanoscaled MOF heterostructures, and biomedical applications in enhanced therapy within the last five years. The functions of MOF heterostructures with a controlled size can be regulated by designing various functional ligands and in situ growth/postmodification of nanoparticles and/or biomolecules. The advances in the application of multifunctional MOF heterostructures are also explored for enhanced cancer therapies involving photodynamic therapy, photothermal therapy, chemotherapy, radiotherapy, immunotherapy, and theranostics. The remaining challenges and future opportunities in this field, in terms of precisely localized assembly, maximizing composite properties, and processing new techniques, are also presented. The introduction of multiple components into one crystalline MOF provides a promising approach to design all-in-one theranostics in clinical treatments.

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.

Engineered bovine serum albumin-based nanoparticles with pH-sensitivity for doxorubicin delivery and controlled release

In this work, we prepared a stimuli-responsive system for drug delivery and controlled release by engineering the bovine serum albumin (BSA). The doxorubicin (DOX)-loaded BSA nanoparticles (NPs) were conveniently prepared using desolvation method, followed by crosslinking through Schiff base bonds, leading to pH-sensitive DOX-loaded system (DOXs@BSA NPs). The resulted DOXs@BSA NPs showed high drug loading capacity (21.4%), and the particle size was about 130 nm with narrow polydispersity and high negative surface charge (-20.5 mV). The pH-sensitivity of DOXs@BSA NPs was evidenced by the size changes and charge reversal after incubation at different pH values. The DOXs@BSA NPs showed high serum stability which indicated the prolonged circulation time. The in vitro drug release experiment showed that the release of DOX was obviously accelerated by acidity because of disassembly of NPs induced by cleavage of Schiff base bonds. The drug release mechanism was thoroughly studied using a semi-empirical model, further confirming the pH played an important role in drug controlled release process. The results of cytotoxicity assay revealed that DOXs@BSA NPs exhibited much higher toxic effects for tumor cells in comparison to the free DOX control. Collectively, these results demonstrated that DOXs@BSA NPs might be potential application for drug delivery and controlled release in cancer chemotherapy. Moreover, this work also showed that preparation of stimuli-responsive drug delivery system by engineering the commercial biomaterials could be a promising method to develop multi-functional nanomedicine.

Light: A Magical Tool for Controlled Drug Delivery

Light is a particularly appealing tool for on-demand drug delivery due to its noninvasive nature, ease of application and exquisite temporal and spatial control. Great progress has been achieved in the development of novel light-driven drug delivery strategies with both breadth and depth. Light-controlled drug delivery platforms can be generally categorized into three groups: photochemical, photothermal, and photoisomerization-mediated therapies. Various advanced materials, such as metal nanoparticles, metal sulfides and oxides, metal-organic frameworks, carbon nanomaterials, upconversion nanoparticles, semiconductor nanoparticles, stimuli-responsive micelles, polymer- and liposome-based nanoparticles have been applied for light-stimulated drug delivery. In view of the increasing interest in on-demand targeted drug delivery, we review the development of light-responsive systems with a focus on recent advances, key limitations, and future directions.

Improved mechanical, water vapor barrier and UV-shielding properties of cellulose acetate films with flower-like metal-organic framework nanoparticles

Flower-like metal-organic frameworks (Cu-MOF) nanoparticles are successfully synthesized and incorporated into cellulose acetate (CA) matrix to prepare CA-based functional nanocomposite films via a simple solution-casting method. The effect of the incorporation of flower-like Cu-MOF on the morphological, mechanical, thermal, surface wettability, water vapor barrier, cytotoxicity, photostability and UV-shielding properties of CA films is fully investigated. Results reveal that the flower-like Cu-MOF has good compatibility with CA, providing uniform and compact nanocomposite films. The as-prepared nanocomposite films show improved mechanical properties, surface hydrophobicity, water vapor barrier ability compared to neat CA film, and exhibit super UV-shielding capability through the entire UV regions meanwhile retaining a high visible transparency. Moreover, the high transparency and UV-shielding ability of the nanocomposite films can be still maintained even after continuous UV-light (365 nm) irradiation for 12 h. In addition, MTT cytotoxicity assays towards normal human liver cells (HL-7702) reveal high cell viability (over 80%) and good biocompatibility for the CA/Cu-MOF nanocomposite films. These results indicate that the CA/Cu-MOF nanocomposite films with obviously improved physical and functional performances hold significant potential for transparent packaging and UV-protection applications.

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.

Cellular evaluation of the metal-organic framework PCN-224 associated with inflammation and autophagy

Metal-organic frameworks (MOFs) are innovative porous structures consisting of metal ions and organic ligands, which have been verified for extraordinary applications in nanomedicine and pharmaceuticals. PCN-224 is a type of Zr-based MOFs, which has recently emerged as one of the most attractive nanomaterials for various applications, such as drug delivery, bioimaging and cancer therapy due to its favorable and fascinating physical-chemical properties. However, the safety evaluation and the potential toxicological properties remain unclear. In this study, the general cytotoxicity of PCN-224 were examined in both human hepatocytes L-02 cells and mouse macrophages RAW264.7. Furthermore, the effect of inflammation and autophagy were measured in L-02 cells. The results indicated that PCN-224 was engulfed in L-02 cells and subsequently resulted in morphological changes, cell membrane destruction, and oxidative stress in L-02 cells. PCN-224 might trigger inflammation by promoting the secretion of inflammatory factors such as Tumor necrosis factors (TNF-α) and Interleukin (IL-6). PCN-224 might induce autophagosome accumulation and subsequently autophagic dysfunction. Additionally, PCN-224 induced cytotoxicity in RAW264.7 cells and increased the protein levels of the inflammasome component NLR Family Pyrin Domain Containing 3 (NLRP3) molecular, which indicated its cellular effects in different cell types. All of these results will support the reasonable use of PCN-224.

An efficient electrochemical assay for miR-3675-3p in human serum based on the nanohybrid of functionalized fullerene and metal-organic framework

Idiopathic pulmonary fibrosis (IPF) is an interstitial lung disease with unclear pathogenesis, for which diagnosis has been a great challenge. Recent researches have revealed that miR-3675-3p is a promising biomarker for IPF diagnosis. Herein, the present work describes a novel electrochemical microRNA biosensor for rapid and sensitive detection of miR-3675-3p based on multiple signal amplification strategies. First of all, fullerene (C₆₀) is doped with poly(amidoamine) (PAMAM)-functionalized metal-organic framework (MOF) to form a new nanohybrid of C₆₀@PAMAM-MOF, which exhibits more remarkable redox activity compared with the other two synthesized C₆₀-based nanohybrids when triggered by tetraoctylammonium bromide (TOAB). C₆₀@PAMAM-MOF also possesses a large specific surface area and abundant amino groups to anchor Au nanoparticles (AuNPs) for the immobilization of signal probe (SP) to form tracer label and enhance the electrochemical response signal. In addition, core@shell Au-Pt nanoparticles (Au@PtNPs) are absorbed on chitosan-acetylene black (CS-AB) to act as sensing platform, which can promote electron transfer and increase the loading of capture probe (CP). Under optimum conditions, the proposed biosensor displays a wide linear range for miR-3675-3p from 10 fM to 10 nM, with a limit of detection (LOD) as low as 2.99 fM. More significantly, this biosensor shows a lower LOD and wider linear range than that of qRT-PCR, and its trial application in human serum shows favorable results, which exhibits a promising prospect for IPF diagnosis.

Polydopamine-Modified Metal-Organic Frameworks, NH2-Fe-MIL-101, as pH-Sensitive Nanocarriers for Controlled Pesticide Release

Recently, metal-organic frameworks (MOFs) have become a dazzling star among porous materials used in many fields. Considering their intriguing features, MOFs have great prospects for application in the field of sustainable agriculture, especially as versatile pesticide-delivery vehicles. However, the study of MOF-based platforms for controlled pesticide release has just begun. Controlled pesticide release responsive to environmental stimuli is highly desirable for decreased agrochemical input, improved control efficacy and diminished adverse effects. In this work, simple, octahedral, iron-based MOFs (NH2-Fe-MIL-101) were synthesized through a microwave-assisted solvothermal method using Fe3+ as the node and 2-aminoterephthalic acid as the organic ligand. Diniconazole (Dini), as a model fungicide, was loaded into NH2-Fe-MIL-101 to afford Dini@NH2-Fe-MIL-101 with a satisfactory loading content of 28.1%. The subsequent polydopamine (PDA) modification could endow Dini with pH-sensitive release patterns. The release of Dini from PDA@Dini@NH2-Fe-MIL-101 was much faster in an acidic medium compared to that in neutral and basic media. Moreover, Dini@NH2-Fe-MIL-101 and PDA@Dini@NH2-Fe-MIL-101 displayed good bioactivities against the pathogenic fungus causing wheat head scab (Fusarium graminearum). This research sought to reveal the feasibility of versatile MOFs as a pesticide-delivery platform in sustainable crop protection.

Aptamer-functionalized molybdenum disulfide nanosheets for tumor cell targeting and lysosomal acidic environment/NIR laser responsive drug delivery to realize synergetic chemo-photothermal therapeutic effects

Molybdenum disulfide (MoS₂), one representative 2D nanomaterial, has recently emerged as a unique platform in the biomedical field. However, its application in drug delivery systems should be further exploited. Here, we report a novel tumor cell targeting and lysosomal acidic environment/NIR laser dual responsive drug delivery system for synergetic chemo-photothermal treatment of cancer cells. The MoS₂ nanosheets were loaded with chemotherapy drug doxorubicin (DOX) and coated with polydopamine (PDA) layer. Then, thiolated aptamer AS1411 and polyethylene glycol (PEG) were modified onto MoS₂ nanosheets through Michael addition reaction to construct DOX@Apt-PEG-PDA-MoS₂ nanosheets. The aptamer modification endowed the nanoplatform with targeting ability to breast cancer MCF-7 cells. MoS₂ and PDA converted 808 nm NIR laser into heat and played the role of photothermal therapy (PTT). Tumor lysosomal acidic environment and NIR laser irradiation accelerated the release of DOX from the nanosheets. The nanocarrier Apt-PEG-PDA-MoS₂ showed good biocompatibility, and DOX@Apt-PEG-PDA-MoS₂ showed synergetic chemo-photothermal therapy effects with significantly enhanced anti-tumor efficacy, suggesting that this MoS₂-based drug delivery platform is promising for targeted and synergetic treatment of cancer.

A Green-Emission Metal-Organic Framework-Based Nanoprobe for Imaging Dual Tumor Biomarkers in Living Cells

The modular nature of metal-organic frameworks (MOFs) permits their tunable structure and function for target application, such as in biomedicine. Herein, a green-emission Zr(IV)-MOF (BUT-88) was constructed from a customized luminescent carbazolyl ligand. BUT-88 represents the first bcu-type MOF with both organic linker and metal node in eight connections and shows medium-sized pores, rich accessible linking sites, and good water stability and biocompatibility. In virtue of these merits, BUT-88 was then fabricated into a MOF-based fluorescent nanoprobe, drDNA-BUT-88. Using it, the live-cell imaging of dual tumor biomarkers was achieved for the first time upon a MOF-based probe, offering enhanced detection precision in early cancer diagnosis. Particularly, the probe showed efficient ratiometric fluorescent sensing toward the cytoplasmic biomarker microRNA-21, further improving the detection accuracy at the cellular level. In this work, the elaborate combination of MOF engineering and the fluorescent detection technique has contributed a facile biosensing platform, unlocking more possibilities of MOF chemistry.

Aptamer-Pyropheophorbide a Conjugates with Tumor Spheroid Targeting and Penetration Abilities for Photodynamic Therapy

Pyropheophorbide a (Pyro) is a widely used photosensitizer for photodynamic therapy (PDT). However, poor water solubility, aggregation-induced fluorescence quenching, and lack of selectivity to targeted cells seriously limit its application. In this work, we prepared aptamer-Pyro conjugates (APCs) by linking Pyro to hydrophilic nucleic acid aptamer to enhance its water solubility and endow it with protein tyrosine kinase 7 (PTK7) overexpressed tumor spheroid specific targeting and penetration abilities for photodynamic therapy. The molecular conjugate was successfully synthesized and dissolved well in an aqueous solution. The APCs showed strong near-infrared fluorescence in the aqueous solution and produced singlet oxygen both in the solution and cells under laser irradiation, indicating its generation of singlet oxygen during PDT was guaranteed. Owing to the cancer cell targeting ability of the aptamer, the APCs specifically bound with PTK7 overexpressed cancerous cells and showed fluorescence signal for tumor cell imaging and diagnosis. The APCs exhibited favorable enhanced phototoxicity to target tumor cells compared with control cells. More importantly, due to the small size of the molecular conjugate, the APCs efficiently penetrated into the interior of multicellular tumor spheroids (MCTS) and caused cell damage. All these results indicated that the robust aptamer-Pyro conjugate is a promising selective tumor-targeting and penetrable molecule for cancer photodynamic therapy.

The Progress and Prospect of Zeolitic Imidazolate Frameworks in Cancer Therapy, Antibacterial Activity, and Biomineralization

The progressive development of zeolitic imidazolate frameworks (ZIFs), as a subfamily of metal-organic frameworks (MOFs), and their unique features, including tunable pore size, large surface area, high thermal stability, and biodegradability/biocompatibility, have made them attractive in the field of biomedicine, especially for drug delivery and biomineralization applications. The high porosity of ZIFs gives them the opportunity for encapsulating a high amount of therapeutic drugs, proteins, imaging cargos, or a combination of them to construct advanced multifunctional drug delivery systems (DDSs) with combined therapeutic and imaging capabilities. This review summarizes recent strategies on the design and fabrication of ZIF-based nansystems and their exploration in the biomedical field. First, recent developments for the adjustment of particle size, functionality, and morphology of ZIFs are discussed, which are important for achieving optimized therapeutic/theranostic nanosystems. Second, recent trends on the application of ZIF nanocarriers for the loading of diverse cargos, including anticancer medicines, antibiotic drugs, enzymes, proteins, photosensitizers, as well as imaging and photothermal agents, are investigated in order to understand how multifunctional DDSs can be designed based on the ZIF nanoparticles to treat different diseases, such as cancer and infection. Finally, prospects on the future research direction and applications of ZIF-based nanomedicines are discussed.

Incorporation of metal-organic frameworks into electrospun chitosan/poly (vinyl alcohol) nanofibrous membrane with enhanced antibacterial activity for wound dressing application

Developing wound dressing that inhibits bacterial infection for treating complex wound healing processes has been a research hotspot. Here, we report the fabrication of Cu-MOFs (HKUST-1) incorporated electrospun chitosan/polyvinyl alcohol (HKUST-1/chitosan/PVA) fibers through the blending electrospinning for wound therapy. HKUST-1/chitosan/PVA fibers displayed satisfying physical properties, such as mechanical property, water uptake, water vapor transmission rate, etc. Cytotoxicity test indicated that HKUST-1/chitosan/PVA fibers were biocompatible and could support cell adhesion. Due to the HKUST-1 incorporation, HKUST-1/chitosan/PVA fibers exhibited the good antibacterial activity against Escherichia coli and Staphylococcus aureus with 99% antibacterial efficiency. Furthermore, in animal studies, compared with commercial chitosan dressings and chitosan/PVA fibers, HKUST-1/chitosan/PVA fibers were more efficient to heal the wound with less inflammation. In summary, the HKUST-1/chitosan/PVA fibers with good physicochemical property, biocompatibility and antibacterial property is an excellent wound dressing for full-thickness skin repair.

Metal-Organic Frameworks for Biomedical Applications

Metal-organic frameworks (MOFs) are an interesting and useful class of coordination polymers, constructed from metal ion/cluster nodes and functional organic ligands through coordination bonds, and have attracted extensive research interest during the past decades. Due to the unique features of diverse compositions, facile synthesis, easy surface functionalization, high surface areas, adjustable porosity, and tunable biocompatibility, MOFs have been widely used in hydrogen/methane storage, catalysis, biological imaging and sensing, drug delivery, desalination, gas separation, magnetic and electronic devices, nonlinear optics, water vapor capture, etc. Notably, with the rapid development of synthetic methods and surface functionalization strategies, smart MOF-based nanocomposites with advanced bio-related properties have been designed and fabricated to meet the growing demands of MOF materials for biomedical applications. This work outlines the synthesis and functionalization and the recent advances of MOFs in biomedical fields, including cargo (drugs, nucleic acids, proteins, and dyes) delivery for cancer therapy, bioimaging, antimicrobial, biosensing, and biocatalysis. The prospects and challenges in the field of MOF-based biomedical materials are also discussed.

Metal–organic framework based antibiotic release and antimicrobial response: an overview

MOF and MOF based heterostructures for antibacterial applications.

Ionic liquid induced highly dense assembly of porphyrin in MOF nanosheets for photodynamic therapy

A facile fabrication of porphyrin-integrated MOF nanosheets as efficient photosensitizers for photodynamic therapy (PDT) is presented.