Chitosan-Coated Halloysite Nanotubes As Vehicle for Controlled Drug Delivery to MCF-7 Cancer Cells In Vitro

The aim of the work is to improve the release properties of curcumin onto human breast cancer cell lines using coated halloysite nanotubes (HNTs) with chitosan as a polycation. A loading efficiency of 70.2% (w/w) was attained for loading 4.9 mg of the drug into 0.204 g bed volume of HNTs using the vacuum suction method. Results acquired from Brunauer-Emmett-Teller (BET), Fourier-transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), scanning electron spectroscopy (SEM), zeta potential, and thermogravimetric analysis (TGA) indicated the presence of the drug and the biopolymer in and around the nanotubes. The release properties of drug-loaded HNTs (DLHNTs) and chitosan-coated drug-loaded HNTs (DLHNTs-CH) were evaluated. The release percentages of DLHNTs and DLHNTs-CH after 6 h were 50.7 and 37%, respectively. Based on the correlation coefficients obtained by fitting the release nature of curcumin from the two samples, the Korsmeyer-Peppas model was found to be the best-fitted model. In vitro cell viability studies were carried out on the human breast cancer cell line MCF-7, using the MTT and trypan blue exclusion assays. Prior to the Trypan blue assay, the IC₅₀ of curcumin was determined to be ~30 µM. After 24 h of incubation, the recorded cell viability values were 94, 68, 57, and 51% for HNTs, DLHNTs-CH, DLHNTs, and curcumin, respectively. In comparison to the release studies, it could be deducted that sustained lethal doses of curcumin were released from the DLHNTs-CH within the same time. It is concluded from this work that the "burst release" of naked drugs could be slowly administered using chitosan-coated HNTs as potential drug carriers.

Discovery of New Protein Targets of BPA Analogs and Derivatives Associated with Noncommunicable Diseases: A Virtual High-Throughput Screening

BACKGROUND

Bisphenol A analogs and derivatives (BPs) have emerged as new contaminants with little or no information about their toxicity. These have been found in numerous everyday products, from thermal paper receipts to plastic containers, and measured in human samples.

OBJECTIVES

The objectives of this research were to identify in silico new protein targets of BPs associated with seven noncommunicable diseases (NCDs), and to study their protein-ligand interactions using computer-aided tools.

METHODS

Fifty BPs were identified by a literature search and submitted to a virtual high-throughput screening (vHTS) with 328 proteins associated with NCDs. Protein-protein interactions between predicted targets were examined using STRING, and the protocol was validated in terms of binding site recognition and correlation between in silico affinities and in vitro data.

RESULTS

According to the vHTS, several BPs may target proteins associated with NCDs, some of them with stronger affinities than bisphenol A (BPA). The best affinity score (the highest in silico affinity absolute value) was obtained after docking 4,4'-bis(N-carbamoyl-4-methylbenzensulfonamide)diphenylmethane (BTUM) on estradiol 17-beta-dehydrogenase 1 (-13.7 kcal/mol). However, other molecules, such as bisphenol A bis(diphenyl phosphate) (BDP), bisphenol PH (BPPH), and Pergafast 201 also exhibited great affinities (top 10 affinity scores for each disease) with proteins related to NCDs.

DISCUSSION

Molecules such as BTUM, BDP, BPPH, and Pergafast 201 could be targeting key signaling pathways related to NCDs. These BPs should be prioritized for in vitro and in vivo toxicity testing and to further assess their possible role in the development of these diseases. https://doi.org/10.1289/EHP7466.

Flame Retardancy of Biobased Composites-Research Development

Due to the thermal and fire sensitivity of polymer bio-composite materials, especially in the case of plant-based fillers applied for them, next to intensive research on the better mechanical performance of composites, it is extremely important to improve their reaction to fire. This is necessary due to the current widespread practical use of bio-based composites. The first part of this work relates to an overview of the most commonly used techniques and different approaches towards the increasing the fire resistance of petrochemical-based polymeric materials. The next few sections present commonly used methods of reducing the flammability of polymers and characterize the most frequently used compounds. It is highlighted that despite adverse health effects in animals and humans, some of mentioned fire retardants (such as halogenated organic derivatives e.g., hexabromocyclododecane, polybrominated diphenyl ether) are unfortunately also still in use, even for bio-composite materials. The most recent studies related to the development of the flame retardation of polymeric materials are then summarized. Particular attention is paid to the issue of flame retardation of bio-based polymer composites and the specifics of reducing the flammability of these materials. Strategies for retarding composites are discussed on examples of particular bio-polymers (such as: polylactide, polyhydroxyalkanoates or polyamide-11), as well as polymers obtained on the basis of natural raw materials (e.g., bio-based polyurethanes or bio-based epoxies). The advantages and disadvantages of these strategies, as well as the flame retardants used in them, are highlighted.

Past, Present and Future Perspectives on Halloysite Clay Minerals

Halloysite nanotubes (HNTs), clay minerals belonging to the kaolin groups, are emerging nanomaterials which have attracted the attention of the scientific community due to their interesting features, such as low-cost, availability and biocompatibility. In addition, their large surface area and tubular structure have led to HNTs' application in different industrial purposes. This review reports a comprehensive overview of the historical background of HNT utilization in the last 20 years. In particular it will focus on the functionalization of the surfaces, both supramolecular and covalent, following applications in several fields, including biomedicine, environmental science and catalysis.

Functionalization of Halloysite Nanotubes via Grafting of Dendrimer for Efficient Intracellular Delivery of siRNA

Here, polyamidoamine grafted halloysite nanotubes (PAMAM- g-HNTs) were synthesized for loading of siRNA in order to intracellular delivery of siRNA and treat of breast cancer via gene therapy. The successful grafting of PAMAM on HNTs was confirmed by various analytical methods. The size, zeta potential, and grafting ratio of PAMAM- g-HNTs is ∼206.2 nm, +19.8 mV, and 3.04%, respectively. PAMAM- g-HNTs showed good cytocompatibility toward HUVECs (84.7%) and MCF-7 cells (82.3%) even at high concentration of 100 μg/mL. PAMAM- g-HNTs/siRNA exhibited enhanced cellular uptake efficiency of 94.3% compared with Lipofectamine 2000 (Lipo2000)/siRNA (83.6%). PAMAM- g-HNTs/small interfering RNA-vascular endothelial growth factor (siVEGF) led to 78.0% knockdown of cellular VEGF mRNA and induced 33.6% apoptosis in the MCF-7 cells, which is also much higher than that of Lipo2000/siVEGF. In vivo anti-cancer results demonstrated that PAMAM- g-HNTs/siVEGF treated 4T1-bearing mice showed enhanced anti-cancer efficacy than Lipo2000/siVEGF group. Also, the nanocarrier system showed negligible toxic effects toward the major organs of mice. In vivo fluorescence imaging studies showed that there is a slight decrease in the fluorescence signal of PAMAM- g-HNTs/cy5-siVEGF after 72 h post-injection. Therefore, PAMAM- g-HNTs show promising application as novel nanovectors for siRNA delivery and gene therapy of cancer.

Modified halloysite nanoclay as a vehicle for sustained drug delivery

This paper presents the effect of modified halloysite nanotubes on the sustained drug release mechanisms of sodium salicylate. Acid treatment and composite polymer-halloysite modification techniques were adopted in this study. After each modification, sodium salicylate drug was loaded, and in vitro release properties were evaluated and compared with the raw unmodified halloysite nanotubes. The results obtained from SEM, TEM and FTIR analyses indicate that both acid treatment and composite formation have no effect on the tubular structure and morphology of halloysite. However, modification of the halloysite nanotubes did influence the drug release rate. In the acid treatment modification, there was an improved loading of sodium salicylate drug which resulted in the sustain release of large amount of the sodium salicylate. In the polymer/halloysite composite formation, a consistent layer of polymer was formed around the halloysite during the composite formation and thus delayed release providing sustained release of sodium salicylate drug over a longer period of time as compared to the acid treated and unmodified halloysite. The results from the invitro release were best fitted with the Higuchi and the Koresymer-Peppas models.

Chemical modification of halloysite nanotubes for controlled loading and release

Clay minerals have been used for medical purposes from ancient times. Among them, the halloysite nanotube, an aluminosilicate of the kaolin group, is an emerging nanomaterial which possesses peculiar chemical characteristics. By means of suitable modifications, such as supramolecular functionalization or covalent modifications, it is possible to obtain novel nanomaterials with tunable properties for several applications. In this context the covalent grafting of suitable organic moieties on the external surface or in the halloysite lumen has been exploited to improve the loading and release of several biologically active molecules. The resulting hybrid nanomaterials have been applied as drug carrier and delivery systems, as fillers for hydrogels, in tissue regeneration and in the gene delivery field. Furthermore the loading and release of specific molecules have been also investigated for environmental purposes. This review summarizes the main developments in the halloysite modifications in the last 20 years with a particular attention to the development in the past two years.

Design and Physicochemical Characterization of Novel Organic–Inorganic Hybrids from Natural Aluminosilicate Nanotubes

Surface functionalization of tubular nano-clays of imogolite and halloysite using the selective binding of organophosphonic acids and organosilane compounds, and the use of the surface modified nanotubes in polymer hybrids were studied. Surface modification of imogolite with alkyl phosphonic acid salt through the specific interaction of phosphonic acid and the exterior alumina sites of imogolite was presented. SI-ATRP was performed with the selectively adsorbed phosphonic acid functionalized ATRP-initiator to prepare polymer brushes on the imogolite surface. Selective modification of halloysite nanotube exterior and inner surfaces was demonstrated. Aqueous phosphonic acid binds to alumina sites at the tube lumen to make the lumen hydrophobic. Subsequent modification with organosilane affords bifunctionalized halloysites with both the lumen and exterior surface modified. Loading of hydrophobic organic compound to the modified lumen was confirmed. SI-ATRP was performed through the selectively adsorbed DOPA-functionalized ATRP-initiator to prepare polymer brushes on the nanotube lumen. Also, surface modified halloysite was applied for preparation of novel intelligent polyurethane nanocomposites with improved thermal stability and mechanical properties.

Enhanced Therapeutic Efficacy of Doxorubicin for Breast Cancer Using Chitosan Oligosaccharide-Modified Halloysite Nanotubes

Halloysite nanotubes (HNTs) are natural aluminosilicates with unique hollow lumen structure, also having high specific area, good biocompatibility, nontoxicity, and low price. Here, we designed a chitosan oligosaccharide-grafted HNTs (HNTs-g-COS) as a doxorubicin (DOX) carrier for treating breast cancer both in vitro and in vivo. The structure of HNTs-g-COS was first characterized by various methods. HNTs-g-COS showed positively charged surface and improved hemocompatibility. DOX-loaded HNTs-g-COS (DOX@HNTs-g-COS) released in cell lysate in a controlled manner. The IC₅₀ value of DOX@HNTs-g-COS toward MCF-7 cells was 1.17 μg mL^-1, while it was 2.43 μg mL^-1 for free DOX. DOX@HNTs-g-COS increased the apoptosis effects of MCF-7 cells as shown in flow cytometry results. Also, reactive oxygen species of cells induced by DOX@HNTs-g-COS were drug-dose-dependent. DOX@HNTs-g-COS could enter the MCF-7 cells and induce mitochondrial damage as well as attack the nuclei. The in vivo antitumor effect of DOX@HNTs-g-COS was investigated in 4T1-bearing mice. The tumor-inhibition ratio of DOX@HNTs-g-COS was 83.5%, while it was 46.1% for free DOX. All mice treated with DOX@HNTs-g-COS survived over 60 days. DOX@HNTs-g-COS showed fewer ruptured cardiomyocytes and no obvious systemic toxicity. Therefore, the rational designed HNTs nanocarrier for chemotherapy drug showed promising applications in tumor treatment.

Bare Cd1-xZnxS ZB/WZ Heterophase Nanojunctions for Visible Light Photocatalytic Hydrogen Production with High Efficiency

In this work, we report the synthesis of Cd1-xZnxS zinc blende/wurtzite (ZB/WZ) heterophase nanojunctions with highly efficient charge separation by a solvothermal method in a mixed solution of diethylenetriamine (DETA) and distilled water. l-Cysteine was selected as a sulfur source and a protecting ligand for stabilization of the ZB/WZ homojunction. The optimal ternary chalcogenide Cd0.7Zn0.3S elongated nanocrystals (NCs) without any cocatalyst loading show very high visible light photocatalytic activity with H2 production efficiency of 3.13 mmol h(-1) and an apparent quantum efficiency of 65.7% at 420 nm. This is one of the best visible light photocatalysts ever reported for photocatalytic hydrogen production without any cocatalysts. The charge separation efficiency, having a critical role in enhancing photocatalytic activity for hydrogen production, was significantly improved. Highly efficient charge separation with a prolonged carrier lifetime is driven by the internal electrostatic field originating from the type-II staggered band alignment at the ZB/WZ junctions, as confirmed by steady and time-resolved photoluminescence spectra. Further, the strong binding between the l-cysteine ligand and Cd1-xZnxS elongated nanocrystals protects and stabilizes NCs; the l-cysteine ligand at the interface could trap holes from Cd1-xZnxS NCs, while photogenerated electrons transfer to Cd1-xZnxS catalytic sites for proton reduction. Our results demonstrate that Cd1-xZnxS ZB/WZ heterophase junctions stabilized by l-cysteine molecules can effectively separate charge carriers and achieve highly visible light photocatalytic hydrogen production. The present study provides a new insight into the design and fabrication of advanced materials with homojunction structures for photocatalytic applications and optoelectronic devices.

Halloysite Clay Nanotubes for Loading and Sustained Release of Functional Compounds

Halloysite is an alumosilicate tubular clay with a diameter of 50 nm, an inner lumen of 15 nm and a length of 600-900 nm. It is a natural biocompatible nanomaterial available in thousands of tons at low price, which makes it a good candidate for nanoarchitectural composites. The inner lumen of halloysite may be adjusted by etching to 20-30% of the tube volume and loading with functional agents (antioxidants, anticorrosion agents, flame-retardant agents, drugs, or proteins) allowing for formulations with sustained release tuned by the tube end-stoppers for hours and days. Clogging the tube ends in polymeric composites allows further extension of the release time. Thus, antioxidant-loaded halloysite doped into rubber enhances anti-aging properties for at least 12 months. The addition of 3-5 wt% of halloysite increases the strength of polymeric materials, and the possibility of the tube's orientation promises a gradient of properties. Halloysite nanotubes are a promising mesoporous media for catalytic nanoparticles that may be seeded on the tube surface or synthesized exclusively in the lumens, providing enhanced catalytic properties, especially at high temperatures. In vitro and in vivo studies on biological cells and worms indicate the safety of halloysite, and tests for efficient adsorption of mycotoxins in animals' stomachs are also carried out.

Halloysite clay nanotubes based phase change material composites with excellent thermal stability for energy saving and storage

Superhydrophobic halloysite clay nanotubes based PCM composites with excellent thermal stability have been fabricated. Taking advantage of the simple process and low cost, the composites may have great potential as solar energy storage systems.

Carbon hybridized halloysite nanotubes for high-performance hydrogen storage capacities

Hybrid nanotubes of carbon and halloysite nanotubes (HNTs) with different carbon:HNTs ratio were hydrothermally synthesized from natural halloysite and sucrose. The samples display uniformly cylindrical hollow tubular structure with different morphologies. These hybrid nanotubes were concluded to be promising medium for physisorption-based hydrogen storage. The hydrogen adsorption capacity of pristine HNTs was 0.35% at 2.65 MPa and 298 K, while that of carbon coated HNTs with the pre-set carbon:HNTs ratio of 3:1 (3C-HNTs) was 0.48% under the same condition. This carbon coated method could offer a new pattern for increasing the hydrogen adsorption capacity. It was also possible to enhance the hydrogen adsorption capacity through the spillover mechanism by incorporating palladium (Pd) in the samples of HNTs (Pd-HNTs) and 3C-HNTs (Pd-3C-HNTs and 3C-Pd-HNTs are the samples with different location of Pd nanoparticles). The hydrogen adsorption capacity of the Pd-HNTs was 0.50% at 2.65 MPa and 298 K, while those of Pd-3C-HNTs and 3C-Pd-HNTs were 0.58% and 0.63%, respectively. In particular, for this spillover mechanism of Pd-carbon-HNTs ternary system, the bidirectional transmission of atomic and molecular hydrogen (3C-Pd-HNTs) was concluded to be more effective than the unidirectional transmission (Pd-3C-HNTs) in this work for the first time.

Highly aging-resistant elastomers doped with antioxidant-loaded clay nanotubes

A novel aging-resistant styrene-butadiene rubber (SBR) composite is prepared using the antioxidant N-isopropyl-N'-phenyl-p-phenylenediamine (4010NA) loaded inside of halloysite clay nanotubes and used as filler. Loading the antioxidant inside of halloysite allows for its sustained release for nine months in the rubber matrix. By utilizing modified halloysite, the antioxidant concentration in this rubber nanoformulation is tripled without causing "blooming" defects. Furthermore, the halloysite is silanized to enhance its miscibility with rubber. The aging resistance of SBR-halloysite composites is studied by comparing the mechanical properties before and after thermal-oxidative aging. A seven-day test at 90 °C shows preservation of mechanical properties, and no 4010NA blooming is observed, even after one month. Styrene-butadiene rubber with 27 wt % halloysite loaded with 4010NA shows marked increase in aging resistance and promising future of halloysite as a functional rubber filler.

Clay nanotube encapsulation for functional biocomposites

Natural halloysite clay nanotubes with 50 nm outer- and 15 nm inner- diameters are described as miniature vehicles for sustained release of drugs and proteins. The release time may be adjusted from 10 to 200 h with the tube surface polymeric coating. An explanation of sustained release through locking electrical potential at the nanotube ends is suggested. These biocompatible ceramic tubes may be also used for architectural construction of nanoshells on microbes through alternation with polycations to enhance the intrinsic properties of biological cells. Halloysite nanotubes (pristine or drug-loaded) are well mixable with polar and low-polar polymers allowing for functional biocomposites with enhanced mechanical strength, adhesivity and slow release of drugs or other chemical agents. Halloysite is nontoxic abundantly available from natural deposit material which does not require exfoliation or other complicated energy consuming processing.

Halloysite clay nanotubes as a ceramic "skeleton" for functional biopolymer composites with sustained drug release

Halloysite, naturally occurring clay nanotubes, is described as an additive for functional polymer composites. Due to the empty tubular lumen capable of being loaded with chemically active agents, halloysite provides additional functions (drug delivery, antibiotic, flame-retardant, anticorrosion, and crack self-healing) to polymeric composites synergistically combined with enhanced tensile, impact and adhesive strength. Doping loaded clay nanotubes into a polymeric matrix provides a kind of ceramic "skeleton", and these "skeleton bones" are loaded with functional chemicals like real bones loaded with marrow. Tunable controlled release of active agents through synthesis of artificial nano-caps at the tube endings and halloysite lumen enlargement by selective etching allowed for tubular nanocontainers with chemicals release time from 10 to 200 h and a loading capacity of ca. 30 wt%. Halloysite is well mixable with polymers of high and medium polarities without any surface modification.