Synthesis and In Vitro Characterization of Fe3+-Doped Layered Double Hydroxide Nanorings as a Potential Imageable Drug Delivery System

Layered double hydroxide-based nanomaterials for biomedical applications

Against the backdrop of increased public health awareness, inorganic nanomaterials have been widely explored as promising nanoagents for various kinds of biomedical applications. Layered double hydroxides (LDHs), with versatile physicochemical advantages including excellent biocompatibility, pH-sensitive biodegradability, highly tunable chemical composition and structure, and ease of composite formation with other materials, have shown great promise in biomedical applications. In this review, we comprehensively summarize the recent advances in LDH-based nanomaterials for biomedical applications. Firstly, the material categories and advantages of LDH-based nanomaterials are discussed. The preparation and surface modification of LDH-based nanomaterials, including pristine LDHs, LDH-based nanocomposites and LDH-derived nanomaterials, are then described. Thereafter, we systematically describe the great potential of LDHs in biomedical applications including drug/gene delivery, bioimaging diagnosis, cancer therapy, biosensing, tissue engineering, and anti-bacteria. Finally, on the basis of the current state of the art, we conclude with insights on the remaining challenges and future prospects in this rapidly emerging field.

Ferrous ions doped layered double hydroxide: smart 2D nanotheranostic platform with imaging-guided synergistic chemo/photothermal therapy for breast cancer

Developing simple and efficient nanotheranostic platforms with behavior responsive to the acid microenvironment of a tumor is of great significance for accurate tumor diagnosis and therapy. In this study, a smart 2D nanotheranostic platform has been successfully fabricated by doping functional ferrous ions into as-synthesized MgAl-layered double hydroxide (LDH) with doxurubicin (DOX) loading to form Fe-LDH/DOX NPs, which achieved magnetic resonance imaging (MRI)-guided synergistic chemo/photothermal therapy for breast cancer. The doping of ferrous ions into Fe-LDH/DOX enabled a strong photo-induced heating ability with a high photothermal conversion efficiency of 45.67%, which could be combined with the antitumor drug DOX to achieve the synergistic effect of photothermal therapy (PTT) and chemotherapy for killing tumor cells. Additionally, its in vitro pH-dependent degradation behavior and T₂-weighted MRI effect revealed that the as-prepared Fe-LDH/DOX is sensitive to the tumor acid microenvironment. Most importantly, the growth rate of tumors in 4T1 bearing mice could be effectively inhibited after the synergistic treatment of PTT and chemotherapy by Fe-LDH/DOX. These results show that doping functional metal ions into LDH NPs may open a novel approach to fabricating an LDH NP-based nanotheranostics platform with advanced diagnostic and therapeutic performances.

Advanced drug delivery applications of layered double hydroxide

Layered double hydroxides (LDHs), also known as anionic clays or hydrotalcite-like compounds, are a class of nanomaterials that attained great attention as a carrier for drug delivery applications. The lamellar structure of this compound exhibits a high surface-to-volume ratio which enables the intercalation of therapeutic agents and releases them at the target site, thereby reducing the adverse effect. Moreover, the intercalated drug can be released in a sustained manner, and hence the frequency of drug administration can be decreased. The co-precipitation, ion exchange, manual grinding, and sol-gel methods are the most employed for their synthesis. The unique properties like the ease of synthesis, low cost, high biocompatibility, and low toxicity render them suitable for biomedical applications. This review presents the advances in the structure, properties, method of preparation, types, functionalization, and drug delivery applications of LDH. Also, this review provides various new conceptual insights that can form the basis for new research questions related to the drug delivery applications of LDH.

A step towards gadolinium-free bioresponsive MRI contrast agent

The last 30 years of gadolinium-based "static" MRI contrast agents motivated to investigate bioresponsive agents with endogenous paramagnets. Iron(III) chelated by N,O-aminophenol skeleton of high versatility, and tuning potential was studied. The two-step convenient route of the ligand is characterized by high selectivity and allows for building a tunable chelate system. Functionalization with galactose endows a bioresponsive character sensitive to the enzyme activity. Direct relaxometric measurements of the resulting complexes revealed extremely high relaxivity of 5.62 mmol/dm³·s^-1 comparable to classic gadolinium complexes. Enzymatic hydrolysis leads to relaxivity change by over 80%. Phantom MRI studies prove the bioresponsive character by contras percentage change within the range 40-275%. Cytotoxicity studies showed 70-90% viability of HeLa cells of the iron complexes. Proposed iron-based chelates with galactosidase-sensitive fragment express unequivocal relaxivity and MRI contras change and good biocompatibility. Therefore, these complexes are a promising step towards modern, bioresponsive MRI contrast agents with a "human-friendly" metal.

Arsenic removal from water/wastewater using layered double hydroxide derived adsorbents, a critical review

Arsenic pollution has become a worldwide environmental concern. Dangerous arsenic concentrations in natural waters threaten the health of millions of people, and this has received significant attention. Among the various technologies that have been developed for arsenic removal from water, the use of adsorption technology is considered to be a prevailing method, because the adsorption approach usually has high removal efficiency and the advantage of convenience of handling. In recent years, layered double hydroxides (LDHs) have become prime candidates for arsenic removal, due to their hydrophilic nature and cationic layered structures. Research on arsenic removal using LDHs is mainly focused on (1) the influence of the synthesis method and composition of the LDH, (2) the influence of the particle size of the LDH, (3) the influence of the Mg/Al ratio in LDHs, (4) LDH-based hybrids and (5) the competition with other anions. This paper provides a review of the currently available literature focusing on arsenic removal using LDHs for the five parts mentioned above. In addition, based on this overview, a closing section will suggest research efforts for future work. It is expected that this review will provide a summary of the main research in this area, and will also shed light on the direction of future development.