Development of alginate film filled with halloysite-carbon dots for active food packaging.

The development of functional bionanocomposites for active food packaging is of current interest to replace non-biodegradable plastic coatings. In the present work, we report the synthesis of an alginate-based nanocomposite filled with modified halloysite nanotubes (HNTs) to develop coatings with improved barrier properties for food packaging. Firstly, HNTs were chemically modified by the introduction of carbon dots units (CDs) onto their external surface (HNTs-CDs) obtaining a nanomaterial where CDs are uniformly present onto the tubes as verified by morphological investigations, with good UV absorption and antioxidant properties. Afterwards, these were dispersed in the alginate matrix to obtain the alginate/HNTs-CDs nanocomposite (Alg/HNTs-CDs) whose morphology was imaged by AFM measurements. The UV and water barrier properties (in terms of moisture content and water vapor permeability) were investigated, and the antioxidant properties were evaluated as well. To confer some antimicrobial properties to the final nanocomposite, the synthetized filler was loaded with a natural extract (E) from M. cisplatensis. Finally, the extract kinetic release both from the filler and from the nanocomposite was studied in a medium mimicking a food simulant and preliminary studies on the effect of Alg/HNTs-CDs/E on coated and uncoated fruits, specifically apples and bananas were also carried out.

Comparison of Synthetic Pathways for Obtaining Fluorescent Nanomaterials Based on Halloysite and Carbon Dots for Potential Biological Sensing.

Recently, fluorescent sensors have gained considerable attention due to their high sensitivity, low cost and noninvasiveness. Among the different materials that can be used for this purpose, carbon dots (CDs) represent valuable candidates for applications in sensing. These, indeed, are easily synthesized, show high quantum yield and are highly biocompatible. However, it was pointed out that the photoluminescence properties of these nanomaterials are strictly dependent on the synthetic and purification methods adopted. The presence of halloysite nanotubes (HNTs), a natural, low cost and biocompatible clay mineral, has been found to be efficient in obtaining small and highly monodispersed CDs without long and tedious purification techniques. Herein, we report the comparison of synthetic pathways for obtaining halloysite-N-doped CDs (HNTs-NCDs) that could be used in biological sensing. One was based on the synthesis of N-doped CDs by a bottom-up approach on HNTs' surface by a MW pyrolysis process; the other one was based on the post-modification of pristine N-doped CDs with halloysite derivatives. The evaluation of the best synthetic route was performed by different physico-chemical techniques. It was found that the bottom-up approach led to the formation of N-doped CDs with different functional groups onto the HNTs' surface. This evidence was also translated in the different fluorescence quantum yields and the existence of several functional groups in the obtained materials was investigated by potentiometric titrations. Furthermore, the ability of the synthesized nanomaterials as sensors for Fe3+ ions detection was assessed by spectroscopic measurements, and the cellular uptake was verified by confocal/fluorescence microscopies as well.

Hectorite/Phenanthroline-Based Nanomaterial as Fluorescent Sensor for Zn Ion Detection: A Theoretical and Experimental Study.

The development of fluorescent materials that can act as sensors for the determination of metal ions in biological fluids is important since they show, among others, high sensitivity and specificity. However, most of the molecules that are used for these purposes possess a very low solubility in aqueous media, and, thus, it is necessary to adopt some derivation strategies. Clay minerals, for example, hectorite, as natural materials, are biocompatible and available in large amounts at a very low cost that have been extensively used as carrier systems for the delivery of different hydrophobic species. In the present work, we report the synthesis and characterization of a hectorite/phenanthroline nanomaterial as a potential fluorescent sensor for Zn ion detection in water. The interaction of phenanthroline with the Ht interlaminar space was thoroughly investigated, via both theoretical and experimental studies (i.e., thermogravimetry, FT-IR, UV-vis and fluorescence spectroscopies and XRD measurements), while its morphology was imaged by scanning electron microscopy. Afterwards, the possibility to use it as sensor for the detection of Zn2+ ions, in comparison to other metal ions, was investigated through fluorescent measurements, and the stability of the solid Ht/Phe/Zn complex was assessed by different experimental and theoretical measurements.

Thixotropic Hydrogels Based on Laponite® and Cucurbituril for Delivery of Lipophilic Drug Molecules.

Nowadays the use of hydrogels for biomedical purposes is increasing because of their interesting features that allow the development of targeted drug delivery systems. Herein, hydrogel based on Laponite® (Lap) clay mineral as gelator and cucurbit[6]uril (CB[6]) molecules were synthetized for the delivery of flufenamic acid (FFA) for potential topical application. Firstly, the interaction between CB[6] and FFA was assessed by UV-vis spectroscopic measurements and molecular modeling calculations. Then, the obtained complex was used as filler for Lap hydrogel (Lap/CB[6]/FFA). The properties of the hydrogel in terms of viscosity and, self-repair abilities were investigated; its morphology was imaged by scanning electron and polarized optical microscopies. Furthermore, the changes in the hydrodynamic radii and in the colloidal stability of CB[6]/Lap mixture were investigated in terms of translational diffusion from dynamic light scattering and ζ-potential measurements. Finally, the kinetic in vitro release of FFA, from Lap/CB[6]/FFA hydrogel, was studied in a medium mimicking the pH of skin and the obtained results were discussed both by an experimental point of view and by molecular modeling calculations.

Thixotropic Hydrogels Based on Laponite® and Cucurbituril for Delivery of Lipophilic Drug Molecules.

Invited for this month's cover are the collaborating groups of Prof. Serena Riela at University of Catania, Prof. César Viseras at University of Granada and Dr. Ignacio Sainz-Diaz at Instituto Andaluz de Ciencias de la Tierra. The cover picture shows the possible application of the developed system. In particular, flufenamic acid, anti-inflammatory and anti-pyretic drug, was complexed into cucurbituril cavity and the supramolecular system obtained was used as filler for laponite® hydrogel for its topical delivery. More information can be found in the Research Article by Viseras-Iborra, Riela, and co-workers.

Antioxidant Efficacy and "In Vivo" Safety of a Bentonite/Vitamin C Hybrid.

L-ascorbic acid (LAA), commonly known as vitamin C, is an excellent and recognized antioxidant molecule used in pharmaceutical and cosmetic formulations. Several strategies have been developed in order to preserve its chemical stability, connected with its antioxidant power, but there is little research regarding the employment of natural clays as LAA host. A safe bentonite (Bent)-which was verified by in vivo ophthalmic irritability and acute dermal toxicity assays-was used as carrier of LAA. The supramolecular complex between LAA and clay may constitute an excellent alternative, since the molecule integrity does not seem to be affected, at least from the point of view of its antioxidant capacity. The Bent/LAA hybrid was prepared and characterized through ultraviolet (UV) spectroscopy, X-ray diffraction (XRD), infrared (IR) spectroscopy, thermogravimetric analysis (TG/DTG) and zeta potential measurements. Photostability and antioxidant capacity tests were also performed. The LAA incorporation into Bent clay was demonstrated, as well as the drug stability due to the Bent photoprotective effect onto the LAA molecule. Moreover, the antioxidant capacity of the drug in the Bent/LAA composite was confirmed.

Antimicrobial Nanomaterials Based on Halloysite Clay Mineral: Research Advances and Outlook.

Bacterial infections represent one of the major causes of mortality worldwide. Therefore, over the years, several nanomaterials with antibacterial properties have been developed. In this context, clay minerals, because of their intrinsic properties, have been efficiently used as antimicrobial agents since ancient times. Halloysite nanotubes are one of the emerging nanomaterials that have found application as antimicrobial agents in several fields. In this review, we summarize some examples of the use of pristine and modified halloysite nanotubes as antimicrobial agents, scaffolds for wound healing and orthopedic implants, fillers for active food packaging, and carriers for pesticides in food pest control.