Insights on Luminescent Micro- and Nanospheres of Infinite Coordination Polymers.

Coordination polymers have been extensively studied in recent years. Some of these materials can exhibit several properties such as permanent porosity, high surface area, thermostability and light emission, as well as open sites for chemical functionalization. Concerning the fact that this kind of compounds are usually solids, the size and morphology of the particles are important parameters when an application is desired. Inside this context, there is a subclass of coordination polymers, named infinite coordination polymers (ICPs), which auto-organize as micro- or nanoparticles with low crystallinity. Specifically, the particles exhibiting spherical shapes and reduced sizes can be better dispersed, enter cells much easier than bulk crystals and be converted to inorganic materials by topotactic transformation. Luminescent ICPs, in particular, can find applications in several areas, such as sensing probes, light-emitting devices and bioimaging. In this review, we present the state-of-the-art of ICP-based spherical particles, including the growth mechanisms, some applications for luminescent ICPs and the challenges to overcome in future commercial usage of these materials.

Biomimetic Growth of Metal-Organic Frameworks for the Stabilization of the Dentin Matrix and Control of Collagenolysis.

The dentin matrix is a collagenous scaffold structurally involved in anchoring resin-based materials to the tooth. Time-dependent degradation of this scaffold at the resin-dentin interface remains a core problem in adhesive dentistry, limiting the service life of dental fillings. This study explored the use of emergent materials termed metal-organic frameworks (MOFs)─formed by the self-assembly of metal ions and organic building blocks─to safeguard the collagen integrity in the functional dentin matrix. We demonstrate that collagen fibrils (from demineralized human dentin) can induce the biomimetic growth of MOF crystals as protective coatings to strengthen and stabilize the fibrils. Zeolitic imidazolate framework-8 (ZIF-8), a zinc-based microporous MOF, was used to fabricate the MOF composites via a "one-pot" reaction in water. The ZIF-modified dentin matrix presented superior mechanical strength and resistance to proteolysis, which can positively affect the longevity of collagen as an anchoring substrate. This work identifies a potential biomedical application of biomimetically synthesized MOFs in repairing dental tissues critical to restorative therapies.

Detection of anthrax biomarker and metallic ions in aqueous media using spherical-shaped lanthanide infinite coordination polymers.

We report a lanthanide-based infinite coordination polymer (ICP) system synthesized using pyrazole-3,5-dicarboxylic acid as linker, malonic acid as coordination modulator and water as solvent. The precursors self-assembly into microspherical particles, which are water-stable and exhibit excellent dispersibility. Bimetallic samples based on Tb3+ doped with Eu3+ were investigated as ratiometric dipicolinic acid (DPA) sensors, which is a biomarker for Bacillus anthracis spores. Along with the calibration curves, a detection in a real sample extracted from Bacillus subtilis (model organism) was performed. The samples proved to be highly sensitive and selective for ratiometric DPA detection. In a secondary study, the monometallic sample containing only Tb3+ was also investigated as a sensor for ionic species in aqueous media. The Cr3+, Fe3+, Cu2+, and Cr2O72- ionic species could be detected in water by luminescence quenching mechanism. Therefore, we found that the reported ICP system can be judiciously constructed in order to act as a multimodal probe for several chemical species.

MOF-Based Erodible System for On-Demand Release of Bioactive Flavonoid at the Polymer-Tissue Interface.

Plant-derived compounds incite applications virtually on every biomedical field due to the expedient antioxidant, anti-inflammatory and antimicrobial properties in conjunction with a natural character. Here, quercetin (QCT), a flavonoid with therapeutic potentials relevant to the oral environment, was encapsulated within metal-organic frameworks (MOFs) to address the concept of on-demand release of phytochemicals at the biointerface. We verified the applicability of a microporous MOF (ZIF-8) as a controlled-release system for QCT, as well as investigated the incorporation of QCT@ZIF-8 microparticles into a dental adhesive resin for desirable therapeutic capabilities at the tooth-restoration interface. QCT was encapsulated within the frameworks through a water-based, one-step synthetic process. The resulting QCT@ZIF-8 microparticles were characterized with respect to chemical composition, crystal structure, thermal behavior, micromorphology, and release profile under acidic and physiological conditions. A model dental adhesive formulation was enriched with the bioactive microparticles; both the degree of conversion (DC) of methacrylic double bonds and the polymer thermal behavior were accounted for. The results confirm that crystalline QCT@ZIF-8 microparticles with attractive loading capacities, submicron sizes, high thermal stability and responsiveness to environmental pH change were successfully manufactured. The concentration of QCT@ZIF-8 in the resin system was a key factor to maintain an optimal DC plateau and rate of polymerization. Essentially, one-step encapsulation of QCT in biocompatible ZIF-8 matrices can be easily achieved, and QCT@ZIF-8 microparticles proved as smart platforms to carry bioactive compounds with potential use to prevent microbial and enzymatic degradation of hard tissues and extracellular matrix components.

Advances in the use of MOFs for Cancer Diagnosis and Treatment: An Overview.

Nanoparticles as drug delivery systems and diagnostic agents have gained much attention in recent years, especially for cancer treatment. Nanocarriers improve the therapeutic efficiency and bioavailability of antitumor drugs, besides providing preferential accumulation at the target site. Among different types of nanocarriers for drug delivery assays, metal-organic frameworks (MOFs) have attracted increasing interest in the academic community. MOFs are an emerging class of coordination polymers constructed of metal nodes or clusters and organic linkers that show the capacity to combine a porous structure with high drug loading through distinct kinds of interactions, overcoming the limitations of traditional drug carriers explored up to date. Despite the rational design and synthesis of MOFs, structural aspects and some applications of these materials like gas adsorption have already been comprehensively described in recent years; it is time to demonstrate their potential applications in biomedicine. In this context, MOFs can be used as drug delivery systems and theranostic platforms due to their ability to release drugs and accommodate imaging agents. This review describes the intrinsic characteristics of nanocarriers used in cancer therapy and highlights the latest advances in MOFs as anticancer drug delivery systems and diagnostic agents.