Toxicological Impact and in Vivo Tracing of Rhodamine Functionalised ZIF-8 Nanoparticles

Design and fabrication of pH-responsive skin scaffolds based on carrageenan and konjac glucomannan for accelerated wound healing

The aim of this study was to utilize pH-responsive hydrogel skin scaffolds to achieve the sustained release of bioactive compounds (BCs) to promote wound healing. ZIF-8@flavanone nanoparticles were successfully synthesized through microfluidic channels and integrated into a hydrogel scaffold consisting of carrageenan (KC) and konjac glucomannan (KGM) to create a pH-responsive composite hydrogel scaffold. The unique pore structure of ZIF-8 efficiently loaded the active material, and the coordination bonds were disrupted in a slightly acidic environment, allowing the release of flavonoids. The natural macromolecular polysaccharides KC and KGM have good biocompatibility, and as a moist but not wet hydrogel scaffold substrate, they more closely resemble the growth environment of cells and are more favorable for wound healing. The hydrogel scaffolds developed in this study had a tensile strength of 1.15 MPa, an elongation at break of 320 %, good biocompatibility, a relative cell viability of 99.6 %, relative antimicrobial rate of 96.3 % (E. coli) and 95.8 % (S. aureus), respectively, and a release rate of 43.3 % at a pH of 5.0, and a wound closure rate at 15 d of 90.5 %, contributing to the improvement of wound healing performance and providing new possibilities for customized antimicrobial wound dressings.

Photosensitizable ZIF-8 BioMOF for Stimuli-Responsive Antimicrobial Phototherapy

Resistant pathogens are increasingly posing a heightened risk to healthcare systems, leading to a growing concern due to the lack of effective antimicrobial treatments. This has prompted the adoption of antimicrobial photodynamic therapy (aPDT), which eradicates microorganisms by generating reactive oxygen species (ROS) through the utilization of a photosensitizer, photons, and molecular oxygen. However, a challenge arises from the inherent characteristics of photosensitizers, including photobleaching, aggregation, and self-quenching. Consequently, a strategy has been devised to adsorb or bind photosensitizers to diverse carriers to facilitate their delivery. Notably, metal-organic frameworks (MOFs) have emerged as a promising means of transporting photosensitizers, even though achieving uniform particle sizes through room-temperature synthesis remains a complex task. In this work, we have tackled the issue of heterogeneous particle size distribution in MOFs, achieving a particle size of 150 ± 50 nm. Subsequently, we harnessed Zeolite Imidazolate Framework 8 (ZIF-8), an excellent subclass of biocompatible MOF, to effectively load two distinct categories of photosensitizers, namely, Rose Bengal (RB) and porphyrin, using a simple, straightforward, and single-step process. Our findings indicate that the prepared RB@ZIF-8 complex generates a more substantial amount of reactive singlet oxygen species when subjected to photoirradiation (using green light-emitting diode (LED)) at low concentrations, in comparison with porphyrin@ZIF-8, as demonstrated in in vitro experiments. Additionally, we investigated the pH-responsive behavior of the complex to ascertain its implications under biological conditions. Correspondingly, the RB@ZIF-8 complex exhibited a more favorable IC50 value against Escherichia coli compared to bare photosensitizers, ZIF-8 alone, and other photosensitizer-loaded ZIF-8 complexes. This underscores the potential of BioMOF as a promising strategy for combatting multidrug-resistant bacteria across a spectrum of infection scenarios, complemented by its responsiveness to stimuli.

Electrochemical and Biocatalytic Signal-Controlled Payload Release from a Metal-Organic Framework

A metal-organic framework (MOF), ZIF-8, which is stable at neutral and slightly basic pH values in aqueous solutions and destabilized/dissolved under acidic conditions, is loaded with a pH-insensitive fluorescent dye, rhodamine-B isothiocyanate, as a model payload species. Then, the MOF species are immobilized at an electrode surface. The local (interfacial) pH value is rapidly decreased by means of an electrochemically stimulated ascorbate oxidation at +0.4 V (Ag/AgCl/KCl). Oxygen reduction upon switching the applied potential to -0.8 V allows to return the local pH to the neutral/basic pH, then stopping rapidly the release process. The developed method allows electrochemical control over stimulated or inhibited payload release processes from the MOF. The pH variation proceeds in a thin film of the solution near the electrode surface. The switchable release process is realized in a buffer solution and undiluted human serum. As the second option, the pH decrease stimulating the release process is achieved upon an enzymatic reaction using esterase and ester substrate. This approach potentially allows the release activation controlled by numerous enzymes assembled in complex biocatalytic cascades. It is expected that related electrochemical or biocatalytic systems can represent novel signal-responding materials with switchable features for delivering (bio)molecules within biomedical applications.

How safe are nanoscale metal-organic frameworks?

Owing to the size scales that can be accessed, the nanoscale has opened doors to new physical and chemical properties, not seen in the bulk. These properties are leveraged by nanomaterials (NMs) across a plethora of applications. More recently, nanoscale metal-organic frameworks (nMOFs) have witnessed explosive growth due to the modularity of their chemical constituents, the ability to modify their composition and structure, and exceptional properties such as permanent porosity and high surface areas. These properties have prompted the investigation of these materials for applications in biological and environmental contexts. However, one aspect that is often ignored in these discussions is their safety at a nanoscale. In this mini review, we aim to initiate a discussion on the safety and toxicity of nMOFs, drawing parallels with the existing guidelines and literature on the safety of inorganic NMs. We first describe why nMOFs are of considerable interest to the scientific community followed by a discussion on routes through which they can be exposed to the environment and living organisms, particularly shedding light on their transformation mechanisms. The review also discusses the factors affecting toxicity of nMOFs, such as their size, shape, morphology, and composition. We briefly highlight potential mechanisms of toxicity and conclude with describing the need to transition towards data-intensive computational approaches such as machine learning to establish nMOFs as credible materials for their envisioned applications.

In Situ Nanoarchitectonics of a MOF Hydrogel: A Self-Adhesive and pH-Responsive Smart Platform for Phototherapeutic Delivery

Metal-organic frameworks (MOFs) have dramatically changed the fundamentals of drug delivery, catalysis, and gas storage as a result of their porous geometry, controlled architecture, and ease of postsynthetic modification. However, the biomedical applications of MOFs still remain a less explored area due to the constraints associated with handling, utilizing, and site-specific delivery. The major drawbacks associated with the synthesis of nano-MOFs are related to the lack of control over particle size and inhomogeneous dispersion during doping. Therefore, a smart strategy for the in situ growth of a nano-metal-organic framework (nMOF) has been devised to incorporate it into a biocompatible polyacrylamide/starch hydrogel (PSH) composite for therapeutic applications. In this study, the post-treatment of zinc metal ion cross-linked PSH with the ligand solution generated the nZIF-8@PAM/starch composites (nZIF-8, nano-zeolitic imidazolate framework-8). The ZIF-8 nanocrystals thus formed have been found to be evenly dispersed throughout the composites. This newly designed nanoarchitectonics of an MOF hydrogel was found to be self-adhesive, which also exhibited improved mechanical strength, a viscoelastic nature, and a pH-responsive behavior. Taking advantage of these properties, it has been utilized as a sustained-release drug delivery platform for a potential photosensitizer drug (Rose Bengal). The drug was initially diffused into the in situ hydrogel, and then the entire scaffold was analyzed for its potential in photodynamic therapy against bacterial strains such as E. coli and B. megaterium. The Rose Bengal loaded nano-MOF hydrogel composite exhibited remarkable IC₅₀ values within the range of 7.37 ± 0.04 and 0.51 ± 0.05 μg/mL for E. coli and B. megaterium. Further, reactive oxygen species (ROS) directed antimicrobial potential was validated using a fluorescence-based assay. This smart in situ nanoarchitectonics hydrogel platform can also serve as a potential biomaterial for topical treatment including wound healing, lesions, and melanoma.