The biocompatibility of metal-organic framework coatings: an investigation on the stability of SURMOFs with regard to water and selected cell culture media

Impact of Surface Functionalization and Deposition Method on Cu-BDC surMOF Formation, Morphology, Crystallinity, and Stability

For direct integration into device architectures, surface-anchored metal-organic framework (surMOF) thin films are attractive systems for a wide variety of electronic, photonic, sensing, and gas storage applications. This research systematically investigates the effect of deposition method and surface functionalization on the film formation of a copper paddle-wheel-based surMOF. Solution-phase layer-by-layer (LBL) immersion and LBL spray deposition methods are employed to deposit copper benzene-1,4-dicarboxylate (Cu-BDC) on gold substrates functionalized with carboxyl- and hydroxyl-terminated alkanethiol self-assembled monolayers (SAMs). A difference in crystal orientation is observed by atomic force microscopy and X-ray diffractometry based on surface functionalization for films deposited by the LBL immersion method but not for spray-deposited films. Cu-BDC crystallites with a strong preferred orientation perpendicular to the substrate were observed for the films deposited by the LBL immersion method on carboxyl-terminated SAMs. These crystals could be removed upon testing adhesive properties, whereas all other Cu-BDC surMOF film structures demonstrated excellent adhesive properties. Additionally, film stability upon exposure to water or heat was investigated. Ellipsometric data provide insight into film formation elucidating 7 and 14 Å average thicknesses per deposition cycle for films deposited by the immersion method on 11-mercapto-1-undecanol (MUD) and 16-mercaptohexadecanoic acid (MHDA), respectively. In contrast, the films deposited by the spray method are thicker with the same average thickness per deposition cycle (21 Å) for both SAMs. While the spray method takes less time to grow thicker films, it produces similar crystallite structures, regardless of the surface functionalization. This research is fundamental to understanding the impact of deposition method and surface functionalization on surMOF film growth and to provide strategies for the preparation of high-quality surMOFs.

Enhancing Hydrogen Adsorption Capacity of Metal Organic Frameworks M(BDC)TED0.5 through Constructing a Bimetallic Structure

Metal organic frameworks (MOFs) have promising application prospects in the field of hydrogen storage. However, the successful application of MOFs in the field is still limited by their hydrogen storage capacity. Herein, a series of M _x M_1-x (BDC)TED_0.5 (M = Zn, Cu, Co, or Ni) with a bimetallic structure was constructed by introducing two metal ions in the synthesis process. The results of X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma showed that the bimetallic structure with different content ratios can be stably constructed by a hydrothermal method. Among them, the Cu-based bimetal MOFs Cu_0.625Ni_0.375(BDC)TED_0.5 exhibited the best hydrogen storage capacity of 2.04 wt% at 77 K and 1 bar, which was 22% higher than that of monometallic Ni(BDC)TED_0.5. The enhanced hydrogen storage capacity can be attributed to the improved specific surface area and micropore volume of bimetal MOFs by introducing an appropriate amount of bimetallic atoms.

VOC Mixture Sensing with a MOF Film Sensor Array: Detection and Discrimination of Xylene Isomers and Their Ternary Blends

Detection and recognition of volatile organic compounds (VOCs) are crucial in many applications. While pure VOCs can be detected by various sensors, the discrimination of VOCs in mixtures, especially of similar molecules, is hindered by cross-sensitivities. Isomer identification in mixtures is even harder. Metal-organic frameworks (MOFs) with their well-defined, nanoporous, and versatile structures have the potential to improve the VOC sensing performance by tailoring the adsorption affinities. Here, we detect and identify ternary xylene isomer mixtures by using an array of six gravimetric, quartz crystal microbalance (QCM)-based sensors coated with selected MOF films with different isomer affinities. We use classical molecular simulations to provide insights into the sensing mechanism. In addition to the attractive interaction between the analytes and the MOF film, the isomer discrimination is caused by the rigid crystalline framework sterically controlling the access of the isomers to different adsorption sites in the MOFs. The sensor array has a very low limit of detection of 1 ppm for each pure isomer and allows the isomer discrimination in mixtures. At 100 ppm, 16 different ternary o-p-m-xylene mixtures were identified with high classification accuracy (96.5%). This work shows the unprecedented performance of MOF-sensor arrays, also referred to as MOF-electronic nose (MOF-e-nose), for sensing VOC mixtures. Based on the study, guidelines for detecting and discriminating complex mixtures of volatile molecules are also provided.

Enhancement of the anticoagulant capacity of polyvinyl chloride tubing for cardiopulmonary bypass circuit using aluminum oxide nanoscale coating applied through atomic layer deposition

For cardiopulmonary bypass, the polyvinyl chloride (PVC) circuit which can initiate the activation of platelets and the coagulation cascade after blood cell contacting is the possible detrimental effect. Surface coating of the PVC tubing system can be an effective approach to enhance circuit's hemocompatibility. In this study, aluminum oxide (Al₂ O₃ ) thin films were deposited through thermal atomic layer deposition (T-ALD) or plasma-enhanced ALD (PE-ALD) on PVC samples, and the anticoagulation of the Al₂ O₃ -coated PVC samples was demonstrated. The results revealed that Al₂ O₃ deposition through ALD increased surface roughness, whereas T-ALD had a relative hydrophilicity compared with blank PVC and PE-ALD. Whole blood immersion tests showed that blood clots formed on blank PVC and that a large amount of red blood cells was found on PE-ALD substrates, whereas less blood cells were noted in T-ALD samples. Both T-ALD and PE-ALD Al₂ O₃ films did not cause activation of blood cells, as evidenced in CD3⁺ /CD4⁺ /CD8⁺ , CD61⁺ /CD62P⁺ , and CD45⁺ /CD42b⁺ populations. Analysis of serum coagulation factors showed that a lower amount of prothrombin was absorbed on T-ALD Al₂ O₃ samples than that on blank PVC. For albumin and fibrinogen immersion tests, immunostaining and scanning electron microscopy further revealed that a thin albumin layer was absorbed on T-ALD Al₂ O₃ substrates but not on PVC samples. This study revealed that deposition of Al₂ O₃ films by T-ALD can improve anticoagulation of the PVC tubing system.

Stability of Monolithic MOF Thin Films in Acidic and Alkaline Aqueous Media

In the context of thin film nanotechnologies, metal-organic frameworks (MOFs) are currently intensively explored in the context of both, novel applications and as alternatives to existing materials. When it comes to applications under relatively harsh conditions, in several cases it has been noticed that the stability of MOF thin films deviates from the corresponding standard, powdery form of MOFs. Here, we subjected SURMOFs, surface-anchored MOF thin films, fabricated using layer-by layer methods, to a thorough characterization after exposure to different harsh aqueous environments. The stability of three prototypal SURMOFs, HKUST-1, ZIF-8, and UiO-66-NH₂ was systematically investigated in acidic, neutral, and basic environments using X-ray diffraction and electron microscopy. While HKUST-1 films were rather unstable in aqueous media, ZIF-8 SURMOFs were preserved in alkaline environments when exposed for short periods of time, but in apparent contrast to results reported in the literature for the corresponding bulk powders- not stable in neutral and acidic environments. UiO-66-NH₂ SURMOFs were found to be stable over a large window of pH values.

A versatile and multifunctional metal-organic framework nanocomposite toward chemo-photodynamic therapy

Previously most of the applications of targeting components have been based on the enhanced permeability and retention effect achieved using folic acid, which consider the side effects of the targeting components to some extent. Herein, we report a new strategy to decorate the surface of MOFs using a pemetrexed (MTA) targeting molecule, affording a new drug delivery system of ALA@UIO-66-NH-FAM/MTA (ALA = 5-amino-levulinic acid and FAM = 5-carboxyfluorescein). The confocal microscopy and flow cytometry results showed that ALA@UIO-66-NH-FAM/MTA presented a better targeting effect compared to ALA@UIO-66-NH-FAM/FA (FA = folic acid) and indicated a gradually increasing tendency of the targeting effect with the increasing expression of folate receptors on the tumor cell cytomembrane. Furthermore, the cytotoxicity experiment indicates that the combination of chemotherapy and photodynamic therapy is a more effective therapy model than single chemotherapy and photodynamic therapy. This work demonstrates the first attempt at folic acid antagonist (MTA) modification for NMOFs, providing a new concept for the design of MOFs with folate receptor targeting capacity for clinical applications.

Recent Advances in Polymeric Nanocomposites of Metal-Organic Frameworks (MOFs)

Recently, metal-organic frameworks (MOFs) have garnered enormous attention from researchers owing to their superior physicochemical properties, which are of particular interest in various fields such as catalysis and the diverse areas of biomedicine. Despite their position in the utilization for various applications compared to other innovative nanocarriers such as dendrimers and mesoporous silica nanoparticles (MSNs), in terms of advantageous physicochemical attributes, as well as attractive textural properties, ease of characterization, and abundant surface chemistry for functionalization and other benefits, MOFs yet suffer from several issues such as poor degradability, which might lead to accumulation-induced biocompatibility risk. In addition, some of the MOFs suffer from a shortcoming of poor colloidal stability in the aqueous solution, hindering their applicability in diverse biomedical fields. To address these limitations, several advancements have been made to fabricate polymeric nanocomposites of MOFs for their utility in various biomedical fields. In this review, we aim to provide a brief emphasis on various organic polymers used for coating over MOFs to improve their physicochemical attributes considering a series of recently reported intriguing studies. Finally, we summarize with perspectives.

Copper metal-organic frameworks loaded on chitosan film for the efficient inhibition of bacteria and local infection therapy

Although multiple advanced antibacterial and sterilization materials are available, bacterial infections still remain a big challenge in wound healing as they usually induce serious complications and cannot be thoroughly eliminated. Herein, we report an antibacterial film composed of the naturally derived polysaccharide chitosan (CS) and a copper metal-organic framework (HKUST-1) as a multifunctional platform for antibacterial and local infection therapy applications. As expected, the as-prepared HKUST-1/CS film possessed versatile abilities such as slow release of copper ions and reduced cytotoxicity; moreover, fluorescent staining and morphological changes of the bacteria treated with the HKUST-1/CS film confirmed the antibacterial activity of the fabricated film. Furthermore, in vivo results revealed that the HKUST-1/CS film could simultaneously kill bacteria and promote vessel regeneration; this resulted in an enhanced wound closure rate during the local infection therapy process. Overall, these results highlight that the HKUST-1/CS film exhibits significant potential as a suitable and promising wound dressing.

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

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

Metal-Organic Frameworks Based Nano/Micro/Millimeter-Sized Self-Propelled Autonomous Machines

Synthetic nano/micro/millimeter-sized machines that harvest energy from the surrounding environment and then convert it to motion have had a significant impact on many research areas such as biology (sensing, imaging, and therapy) and environmental applications. Autonomous motion is a key element of these devices. A high surface area is preferable as it leads to increased propellant or cargo-loading capability. Integrating highly ordered and porous metal-organic frameworks (MOFs) with self-propelled machines is demonstrated to have a significant impact on the field of nano/micro/millimeter-sized devices for a wide range of applications. MOFs have shown great potential in many research fields due to their tailorable pore size. These fields include energy storage and conversion; catalysis, biomedical application (e.g., drug delivery, imaging, and cancer therapy), and environmental remediation. The marriage of motors and MOFs may provide opportunities for many new applications for synthetic nano/micro/millimeter-sized machines. Herein, MOF-based micro- and nanomachines are reviewed with a focus on the specific properties of MOFs.

A novel approach for the synthesis of phospholipid bilayer-coated zeolitic imidazolate frameworks: preparation and characterization as a pH-responsive drug delivery system

The first example of enveloping of the ZIF family by PLB as an effective biodegradable/biocompatible/responsive drug delivery system.

Excellent Efficacy of MOF Films for Bronze Artwork Conservation: The Key Role of HKUST-1 Film Nanocontainers in Selectively Positioning and Protecting Inhibitors

Development of metal-organic framework (MOF) films for selectively positioning inhibitors in metallic anticorrosion applications remains a substantial challenge due to the difficulty of controlling the arrangement of inhibitor molecules in MOF pores. Cetyltrimethyl ammonium bromide (CTAB), which contains hydrophobic and hydrophilic tails, was chosen as a prototypical inhibitor and was selectively located in the pores of the classic HKUST-1 thin film on a metallic surface. Experimental results reveal that the prepared CTAB@HKUST-1 film displays good metallic anticorrosion performances, especially for bronze conservation. A possible anticorrosion mechanism of CTAB@HKUST-1 is proposed and fully discussed. The study provides an avenue for developing MOF-based thin films for metallic anticorrosion applications to address the environmental development issues related to corrosion.

Dissolving uptake-hindering surface defects in metal-organic frameworks

Metal-organic frameworks (MOFs) have unique properties which make them perfectly suited for various adsorption and separation applications; however, their uses and efficiencies are often hindered by their limited stability. When most MOFs are exposed to water or humid air, the MOF structure, in particular at the surface, is destroyed, creating surface defects. These surface defects are surface barriers which tremendously hinder the uptake and release of guest molecules and, thus, massively decrease the performance in any application of MOFs. Here, the destruction by exposure to water vapor is investigated by using well-defined MOF films of type HKUST-1 as a model system for uptake experiments with different-sized probe molecules as well as for spectroscopic investigations, complemented by density functional theory calculations of the defect structure. In addition to the characterization of the surface defects, it is found that the pristine MOF structure can be regenerated. We show that the surface defects can be dissolved by exposure to the synthesis solvent, here ethanol, enabling fast uptake and release of guest molecules. These findings show that the storage of MOF materials in a synthesis solvent results in healing of surface defects and enables ideal performance of MOF materials.

Rapid Synthesis of Oxygen-Rich Covalent C2N (CNO) Nanosheets by Sacrifice of HKUST-1: Advanced Metal-Free Nanofillers for Polymers

A covalent oxygen-rich C₂N (CNO) network derived from metal-organic framework (HKUST-1) was innovatively synthesized by a rapid and green microwave irradiation method. This method can produce CNO multilayers efficiently, which paves a way for practical application of the nanosheets. Structural characterization and synthesis processes of CNO nanosheets were investigated to further understand the key role of HKUST-1. The as-prepared CNO has a layered feature, which theoretically favors to improve flame retardancy and mechanical performance of polymers. Desirable results were obtained as expected: the fire safety, antitensile, and impact resistance of polylactic acid (PLA) were prominently enhanced after adding CNO nanosheets, which can be attributed to the excellent dispersion and compatibility. PLA/CNO nanocomposite was self-distinguished at 2 wt % content of CNO, whereas the tensile strength was increased more than 36% compared with that of pure PLA, as well as the impact strength. This work broadens the application fields of CNO and endows it a possibility of actual application.

One-Step Assembly of a Biomimetic Biopolymer Coating for Particle Surface Engineering

Advances in material design and applications are highly dependent on the development of particle surface engineering strategies. However, few universal methods can functionalize particles of different compositions, sizes, shapes, and structures. The amyloid-like lysozyme assembly-mediated surface functionalization of inorganic, polymeric or metal micro/nanoparticles in a unique amyloid-like phase-transition buffer containing lysozyme are described. The rapid formation of a robust nanoscale phase-transitioned lysozyme (PTL) coating on the particle surfaces presents strong interfacial binding to resist mechanical and chemical peeling under harsh conditions and versatile surface functional groups to support various sequential surface chemical derivatizations, such as radical living graft polymerization, the electroless deposition of metals, biomineralization, and the facile synthesis of Janus particles and metal/protein capsules. Being distinct from other methods, the preparation of this pure protein coating under biocompatible conditions (e.g., neutral pH and nontoxic reagents) provides a reliable opportunity to directly modify living cell surfaces without affecting their biological activity. The PTL coating arms yeasts with a functional shell to protect their adhered body against foreign enzymatic digestion. The PTL coating further supports the surface immobilization of living yeasts for heterogeneous microbial reactions and the sequential surface chemical derivatization of the cell surfaces, e.g., radical living graft polymerization.

Surface-Anchored Metal-Organic Framework-Cotton Material for Tunable Antibacterial Copper Delivery

In the present study, a new copper metal-organic framework (MOF)-cotton material was strategically fabricated to exploit its antibacterial properties for postsynthetic modification (PSM) to introduce a free amine to tune the physicochemical properties of the material. A modified methodology for carboxymethylation of natural cotton was utilized to enhance the number of nucleation sites for the MOF growth. Subsequently, MOF Cu3(NH2BTC)2 was synthesized into a homogenous surface-supported film via a layer-by-layer dip-coating process. The resultant materials contained uniformly distributed 1 μm × 1 μm octahedral MOF crystals around each carboxymethylated fiber. Importantly, the accessible free amine of the MOF ligand allowed for the PSM of the MOF-cotton surface with valeric anhydride, yielding 23.5 ± 2.2% modified. The Cu2+ ion-releasing performance of the materials was probed under biological conditions per submersion in complex media at 37 °C. Indeed, PSM induces a change in the copper flux of the material over the first 6 h. The materials continue to slowly release Cu2+ ions beyond 24 h tested at a flux of 0.22 ± 0.003 μmol·cm-2·h-1 with the unmodified MOF-cotton and at 0.25 ± 0.004 μmol·cm-2·h-1 with the modified MOF-cotton. The antibacterial activity of the material was explored using Escherichia coli by testing the planktonic and attached bacteria under a variety of conditions. MOF-cotton materials elicit antibacterial effects, yielding a 4-log reduction or greater, after 24 h of exposure. Additionally, the MOF-cotton materials inhibit the attachment of bacteria, under both dry and wet conditions. A material of this type would be ideal for clothing, bandages, and other textile applications. As such, this work serves as a precedence toward developing uniform, tunable MOF-composite textile materials that can kill bacteria and prevent the attachment of bacteria to the surface.

Nanoscaled Metal-Organic Frameworks for Biosensing, Imaging, and Cancer Therapy

Owing to the progressive development of metal-organic frameworks (MOFs) synthetic processes and their unique characters associated with the excellent performance-selectable composition, tunable pore scale, large surface area, and good thermal stability, MOFs have captured the interest and the imagination of an increasing number of scientists working in different fields. In the area of biomedical applications, MOFs are especially involved in sensing, molecular imaging, and drug delivery, with strong contributions to the whole nanomedicine area. Recently, these materials have been scaled down to nanometer sizes with the advancement of chemical synthesis gradually reaching an adjustable level. This review mainly discusses and summarizes the general synthesis, properties, and biomedical applications of nanoscaled MOFs and their composites in biosensing, imaging, and cancer therapy within the latest three years. The remaining challenges and future opportunities in this field, in terms of processing techniques, maximizing composite properties, and prospects for clinical applications, are also indicated.

Substrate-Independent Epitaxial Growth of the Metal-Organic Framework MOF-508a

Plasmachemical deposition is a substrate-independent method for the conformal surface functionalization of solid substrates. Structurally well-defined pulsed plasma deposited poly(1-allylimidazole) layers provide surface imidazole linker groups for the directed liquid-phase epitaxial (layer-by-layer) growth of metal-organic frameworks (MOFs) at room temperature. For the case of microporous [Zn (benzene-1,4-dicarboxylate)-(4,4'-bipyridine)_0.5] (MOF-508), the MOF-508a polymorph containing two interpenetrating crystal lattice frameworks undergoes orientated Volmer-Weber growth and displays CO₂ gas capture behavior at atmospheric concentrations in proportion to the number of epitaxially grown MOF-508 layers.

Cu2+1O/graphene nanosheets supported on three dimensional copper foam for sensitive and efficient non-enzymatic detection of glucose

Three dimensional copper foam/Cu₂₊₁O/graphene nanosheets for sensitive and efficient non-enzymatic detection of glucose.

Metal-Organic Framework Colloids: Disassembly and Deaggregation

We demonstrate a high-resolution method as an efficient tool to in situ characterize partially reversible assembly and aggregation of metal-organic framework (MOF) colloids. Based on the gas-phase electrophoresis, the primary size and the degree of aggregation of the MOF-525 crystals are tunable by pH adjustment and mobility selection. These findings allow for the further size control of MOF colloids and prove the capability of semiquantitative analysis for the MOF-based platforms in a variety of aqueous formulations (e.g., biomedical applications).

Carbon nanotubes implanted manganese-based MOFs for simultaneous detection of biomolecules in body fluids

Metal–organic frameworks (MOFs) have recently attracted much interest in electrochemical fields due to their controlled porosity, large internal surface area, and countless structural topologies.

Adsorption on Mesoporous Metal-Organic Frameworks in Solution: Aromatic and Heterocyclic Compounds

Adsorption and desorption play major roles in separations, purification of water, waste streams, liquid fuels, catalysis, biomedicine and chromatography. Mesoporous metal-organic frameworks (MOFs) with pore sizes 2-50 nm are particularly suitable for adsorption of organic compounds in solution. Tens of thousands of aromatic and heterocyclic compounds are major components of liquid fuels, feedstock for industrial synthesis, solvents, dyestuffs, agricultural chemicals, medicinal drugs, food additives, and so forth. This Review provides a systematization and analysis of studies on adsorption/desorption on mesoporous MOFs in solution and their underlying chemical mechanisms. The (in)stability of mesoporous MOFs in water is critically discussed. Adsorption capacity and selectivity are covered for organic dyes, medicinal drugs, major components of liquid fuels, and miscellaneous industrial chemicals. Ionic interactions, Brønsted acid-base interactions, hydrogen bonding, coordination bonding, π-π interactions, and non-specific interactions are covered amongst adsorption mechanisms. The effects of post-synthetic modifications of mesoporous MOFs on their stability, adsorption capacity, selectivity, and mechanisms of adsorption and desorption are analyzed. To encourage research in this quickly growing field, we identify "niches" for which no application-oriented and/or mechanistic studies were reported. Perspectives and limitations of a wide use of mesoporous MOFs as industrial sorbents are discussed.

Nanostructured platforms for the sustained and local delivery of antibiotics in the treatment of osteomyelitis

This article provides a critical view of the current state of the development of nanoparticulate and other solid-state carriers for the local delivery of antibiotics in the treatment of osteomyelitis. Mentioned are the downsides of traditional means for treating bone infection, which involve systemic administration of antibiotics and surgical debridement, along with the rather imperfect local delivery options currently available in the clinic. Envisaged are more sophisticated carriers for the local and sustained delivery of antimicrobials, including bioresorbable polymeric, collagenous, liquid crystalline, and bioglass- and nanotube-based carriers, as well as those composed of calcium phosphate, the mineral component of bone and teeth. A special emphasis is placed on composite multifunctional antibiotic carriers of a nanoparticulate nature and on their ability to induce osteogenesis of hard tissues demineralized due to disease. An ideal carrier of this type would prevent the long-term, repetitive, and systemic administration of antibiotics and either minimize or completely eliminate the need for surgical debridement of necrotic tissue. Potential problems faced by even hypothetically "perfect" antibiotic delivery vehicles are mentioned too, including (i) intracellular bacterial colonies involved in recurrent, chronic osteomyelitis; (ii) the need for mechanical and release properties to be adjusted to the area of surgical placement; (iii) different environments in which in vitro and in vivo testings are carried out; (iv) unpredictable synergies between drug delivery system components; and (v) experimental sensitivity issues entailing the increasing subtlety of the design of nanoplatforms for the controlled delivery of therapeutics.

Crystal engineering, structure–function relationships, and the future of metal–organic frameworks

After twenty years of vigorous R&D, where are MOFs headed?

MOF positioning technology and device fabrication

Methods for permanent localisation, dynamic localisation and spatial control of functional materials within MOF crystals are critical for the development of miniaturised MOF-based devices for a number of technological applications.

Post-synthetic modification of metal-organic framework thin films using click chemistry: the importance of strained C-C triple bonds

In this work, we demonstrate that strain-promoted azide-alkyne cycloaddition (SPAAC) yields virtually complete conversion in the context of the post-synthetic modification (PSM) of metal-organic frameworks (MOFs). We use surface-anchored MOF (SURMOF) thin films, [Zn2(N3-bdc)2(dabco)], grown on modified Au substrates using liquid-phase epitaxy (LPE) as a model system to first show that, with standard click chemistry, presently, the most popular method for rendering additional functionality to MOFs via PSM, quantitative conversion yields, cannot be reached. In addition, it is virtually impossible to avoid contaminations of the product by the cytotoxic Cu(I) ions used as a catalyst, a substantial problem for applications in life sciences. Both problems could be overcome by SPAAC, where a metal catalyst is not needed. After optimization of reaction conditions, conversion yields of nearly 100% could be achieved. The consequences of these results for various applications of PSM-modified SURMOFs in the fields of membranes, optical coatings, catalysis, selective gas separation, and chemical sensing are briefly discussed.

Combining UV lithography and an imprinting technique for patterning metal-organic frameworks

Thin metal-organic framework (MOF) films are patterned using UV lithography and an imprinting technique. A UV lithographed SU-8 film is imprinted onto a film of MOF powder forming a 2D MOF patterned film. This straightforward method can be applied to most MOF materials, is versatile, cheap, and potentially useful for commercial applications such as lab-on-a-chip type devices.

Site-selective growth of surface-anchored metal-organic frameworks on self-assembled monolayer patterns prepared by AFM nanografting

Surface anchored metal-organic frameworks, SURMOFs, are highly porous materials, which can be grown on modified substrates as highly oriented, crystalline coatings by a quasi-epitaxial layer-by-layer method (liquid-phase epitaxy, or LPE). The chemical termination of the supporting substrate is crucial, because the most convenient method for substrate modification is the formation of a suitable self-assembled monolayer. The choice of a particular SAM also allows for control over the orientation of the SURMOF. Here, we demonstrate for the first time the site-selective growth of the SURMOF HKUST-1 on thiol-based self-assembled monolayers patterned by the nanografting technique, with an atomic force microscope as a structuring tool. Two different approaches were applied: The first one is based on 3-mercaptopropionic acid molecules which are grafted in a 1-decanethiolate SAM, which serves as a matrix for this nanolithography. The second approach uses 16-mercaptohexadecanoic acid, which is grafted in a matrix of an 1-octadecanethiolate SAM. In both cases a site-selective growth of the SURMOF is observed. In the latter case the roughness of the HKUST-1 is found to be significantly higher than for the 1-mercaptopropionic acid. The successful grafting process was verified by time-of-flight secondary ion mass spectrometry and atomic force microscopy. The SURMOF structures grown via LPE were investigated and characterized by atomic force microscopy and Fourier-transform infrared microscopy.

Deposition of Metal-Organic Frameworks by Liquid-Phase Epitaxy: The Influence of Substrate Functional Group Density on Film Orientation

The liquid phase epitaxy (LPE) of the metal-organic framework (MOF) HKUST-1 has been studied for three different COOH-terminated templating organic surfaces prepared by the adsorption of self-assembled monolayers (SAMs) on gold substrates. Three different SAMs were used, mercaptohexadecanoic acid (MHDA), 4’-carboxyterphenyl-4-methanethiol (TPMTA) and 9-carboxy-10-(mercaptomethyl)triptycene (CMMT). The XRD data demonstrate that highly oriented HKUST-1 SURMOFs with an orientation along the (100) direction was obtained on MHDA-SAMs. In the case of the TPMTA-SAM, the quality of the deposited SURMOF films was found to be substantially inferior. Surprisingly, for the CMMT-SAMs, a different growth direction was obtained; XRD data reveal the deposition of highly oriented HKUST-1 SURMOFs grown along the (111) direction.