Halloysite Nanotubes-Induced Al Accumulation and Fibrotic Response in Lung of Mice after 30-Day Repeated Oral Administration

Recent advances in natural nanoclay for diagnosis and therapy of cancer: A review

Cancer is still one of the deadliest diseases, and diagnosing and treating it effectively remains difficult. As a result, advancements in earlier detection and better therapies are urgently needed. Conventional chemotherapy induces chemoresistance, has non-specific toxicity, and has a meager efficacy. Natural materials like nanosized clay mineral formations of various shapes (platy, tubular, spherical, and fibrous) with tunable physicochemical, morphological, and structural features serve as potential templates for these. As multifunctional biocompatible nanocarriers with numerous applications in cancer research, diagnosis, and therapy, their submicron size, individual morphology, high specific surface area, enhanced adsorption ability, cation exchange capacity, and multilayered organization of 0.7-1 nm thick single sheets have attracted significant interest. Kaolinite, halloysite, montmorillonite, laponite, bentonite, sepiolite, palygorskite, and allophane are the most typical nanoclay minerals explored for cancer. These multilayered minerals can function as nanocarriers to effectively carry a variety of anticancer medications to the tumor site and improve their stability, dispersibility, sustained release, and transport. Proteins and DNA/RNA can be transported using nanoclays with positive and negative surfaces. The platform for phototherapeutic agents can be nanoclays. Clays with bio-functionality have been developed using various surface engineering techniques, which could help treat cancer. The promise of nanoclays as distinctive crystalline materials with applications in cancer research, diagnostics, and therapy are examined in this review.

Halloysite nanotubes-cellulose ether based biocomposite matrix, a potential sustained release system for BCS class I drug verapamil hydrochloride: Compression characterization, in-vitro release kinetics, and in-vivo mechanistic physiologically based pharmacokinetic modeling studies

This study investigated the ability of natural nanotubular clay mineral (Halloysite) and cellulose ether based biocomposite matrix as a controlled release agent for Verapamil HCl (BCS Class-I). Drug-loaded halloysite was prepared and tablet formulations were designed by varying amount of hydroxy propyl methyl cellulose (HPMC K4M). Physical characterization was carried out using SEM, FTIR, and DSC. Tabletability profiles were evaluated using USP1062 guidelines. Drug release kinetics were studied, and physiologically based pharmacokinetic (PBPK) modeling was performed. Compressed tablets possess satisfactory yield pressure of 625 MPa with adequate hardness and disintegration within 30 min. The initial release of the drug was due to surface drug on tablets, while the prolonged release at later time points (around 80 % drug release at 12 h) were due to halloysite loading. The FTIR spectra exhibited electrostatic attraction between the positively charged drug and the negatively charged Si-O-Si functional group of halloysite, while the thermogram showed Verapamil HCl melting point at ~146 °C with enthalpy change of -126.82 J/g. PBPK modeling exhibited PK parameters of optimized matrix formulation (VER-HNT3%) comparable to in vivo data. The study effectively demonstrated the potential of prepared biocomposite matrix as a commercially viable oral release modifying agent for highly soluble drugs.

Functionally modified halloysite nanotubes for personalized bioapplications

Halloysite nanotubes (HNTs) are naturally aluminosilicate clay minerals that have the benefits of large surface areas, high mechanical properties, easy functionalization, and high biocompatibility, HNTs have been developed as multifunctional nanoplatforms for various bioapplications. Although some reviews have summarized the properties and bioapplications of HNTs, it remains unclear how to functionalize the modifications of HNTs for their personalized bioapplications. In this review, based on the physicochemical properties of HNTs, we summarized the methods of functionalized modifications (surface modification and structure modification) on HNTs. Also, we highlighted their personalized bioapplications (anti-bacterial, anti-inflammatory, wound healing, cancer theranostics, bone regenerative, and biosensing) by stressing on the main roles of HNTs. Finally, we provide perspectives on the future of functionalized modifications of HNTs for docking specific biological applications.

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.

Toxicological Evaluations in Macrophages and Mice Acutely and Chronically Exposed to Halloysite Clay Nanotubes Functionalized with Polystyrene

Halloysite clay nanotubes (HNTs) have been proposed as highly biocompatible for several biomedical applications. Various polymers have been used to functionalize HNTs, but scarce information exists about polystyrene for this purpose. This work evaluated polystyrene-functionalized HNTs (FHNTs) by comparing its effects with non-FHNTs and innocuous talc powder on in vitro and in vivo models. Monocyte-derived human or murine macrophages and the RAW 264.7 cell line were treated with 0.01, 0.1, 1, and 100 μg mL^-1 FHNTs, HNTs, or talc to evaluate the cytotoxic and cytokine response. Our results show that nanoclays did not cause cytotoxic damage to macrophages. Only the 100 μg mL^-1 concentration induced slight proinflammatory cytokine production at short exposure, followed by an anti-inflammatory response that increases over time. CD1 mice treated with a single dose of 1, 2.5, or 5 mg Kg^-1 of FHNTs or HNTs by oral and inhalation routes caused aluminum accumulation in the kidneys and lungs, without bodily signs of distress or histopathological changes in any treated mice, evaluated at 48 h and 30 days post-treatment. Nanoclay administration simultaneously by four different parenteral routes (20 mg Kg^-1) or the combination of administration routes (parenteral + oral or parenteral + inhalation; 25 mg Kg^-1) showed accumulation on the injection site and slight surrounding inflammation 30 days post-treatment. CD1 mice chronically exposed to HNTs or FHNTs in the bedding material (ca 1 mg) throughout the parental generation and two successive inbred generations for 8 months did not cause any inflammatory process or damage to the abdominal organs and the reproductive system of the mice of any of the generations, did not affect the number of newborn mice and their survival, and did not induce congenital malformations in the offspring. FHNTs showed a slightly less effect than HNTs in all experiments, suggesting that functionalization makes them less cytotoxic. Doses of up to 25 mg Kg^-1 by different administration routes and permanent exposure to 1 mg of HNTs or FHNTs for 8 months seem safe for CD1 mice. Our in vivo and in vitro results indicate that nanoclays are highly biocompatible, supporting their possible safe use for future biomedical and general-purpose applications.

Application of Halloysite Nanotubes in Cancer Therapy-A Review

Halloysite, a nanoclay characterized by a unique, tubular structure, with oppositely charged interior and exterior, suitable, nanometric-range size, high biocompatibility, and low cost, is recently gaining more and more interest as an important and versatile component of various biomaterials and delivery systems of biomedical relevance. One of the most recent, significant, and intensely studied fields in which halloysite nanotubes (HNTs) found diverse applications is cancer therapy. Even though this particular direction is mentioned in several more general reviews, it has never so far been discussed in detail. In our review, we offer an extended survey of the literature on that particular aspect of the biomedical application of HNTs. While historical perspective is also given, our paper is focused on the most recent developments in this field, including controlled delivery and release of anticancer agents and nucleic acids by HNT-based systems, targeting cancer cells using HNT as a carrier, and the capture and analysis of circulating tumor cells (CTCs) with nanostructured or magnetic HNT surfaces. The overview of the most up-to-date knowledge on the HNT interactions with cancer cells is also given.

Preclinical developments of natural-occurring halloysite clay nanotubes in cancer therapeutics

The natural world holds useful resources that can be exploited to design effective therapeutic approaches. Ready-to-use tubular nanoclays, such as halloysite clay nanotubes (HNTs), are widely available, cost-effective, and sustainable submicron crystalline materials that have been showing great potential towards chronic multifactorial and malignant diseases, standing out as a promising anticancer nanotherapeutic strategy. Currently, several preclinical studies have reported the application of HNTs in cancer research, diagnosis, monitoring, and therapeutics. This groundbreaking review highlights the preclinical knowledge hitherto collected concerning the application of HNTs towards cancer therapy. Despite their reproducibility issues, HNTs were used as nanoarchitectonic platforms for the delivery of conventional chemotherapeutic, natural-occurring, biopharmaceutical, and phototherapeutic anticancer agents in a wide range of in vitro and in vivo solid cancer models. Overall, in different types of cancer mice models, the intratumoral and intravenous administration of HNTs-based nanoplatforms induced tumor growth inhibition without causing significant toxic effects. Such evidence raises a relevant question: does the therapeutic benefit of the parenteral administration of HNTs in cancer outweigh their potential toxicological risk? To answer this question further long-term absorption-distribution-metabolism-excretion studies in healthy and cancer animal models need to be performed. In cancer therapeutics, HNTs are envisaged as promising platforms for cancer multi-agent therapy, enabling the combination of different therapeutic modalities. Furthermore, HNTs might constitute suitable nanotheranostic platforms. Nevertheless, to confirm the potential and safety of the application of HNTs as nanodelivery systems for cancer therapy, it is necessary to perform in-depth in vivo pharmacokinetics and pharmacodynamic studies to further the translation to clinical trials.

Antibody-Functionalized Halloysite Nanotubes for Targeting Bacterial Cells

Halloysite nanotubes (HNTs) are naturally occurring tubular clay particles which have emerged in recent years as a promising nanomaterial for numerous applications. Specifically, HNTs’ large pore volume and high specific surface area in combination with their biocompatibility make them ideal nanocarriers for bioactive compounds. This research aims to design and synthesize functionalized HNTs, which could selectively bind to target bacterial cells in suspension. Such a system can allow us to treat target cells within a challenging heterogeneous population, such as contaminated ecosystems or gut flora. HNTs functionalization is achieved by immobilizing specific antibodies onto the nanotube surface. The synthetic route is realized by the following subsequent steps: acidic etching of the HNTs, silanization of reactive surface hydroxyls, conjugation of protein A, and oriented immobilization of the antibody. HNT functionalization is studied by a set of analytical techniques including attenuated total reflectance Fourier-transform infrared spectroscopy, zeta potential measurements, thermal gravimetric analysis, scanning and transmission electron microscopy, as well as fluorescence microscopy. The selective binding of the functionalized HNTs to their target bacteria is observed upon incubation with live homogenous and heterogeneous cultures using fluorescence microscopy and high-throughput flow cytometry. Plate count and live/dead staining experiments demonstrate the biocompatibility of the antibody-HNT hybrid with its target bacteria. The suggested HNT-based smart carrier constitutes a generic platform for targeted delivery that could be selectively tailored against any microorganism by facile antibody adjustment.

Halloysite nanotubes - the nano-bio interface

The numerous biological applications of nanoparticles in general and nano-clays in particular are rooted in understanding and harnessing their dynamic nano-bio interface. Among clays, the intrinsically-mesoporous halloysite nanotubes (HNTs) have emerged in recent years as promising nanomaterials. The diverse interactions of these nanotubes with living cells, encompassing electrostatic, van der Waals, and ion exchange, along with cellular response, are crucial in determining the behaviour of HNTs in biological systems. Thus, rational engineering of the nanotube properties allows for vast applications ranging from bacteria encapsulation for bioremediation, through algae flocculation for aquaculture, to intracellular drug delivery. This review summarizes the many aspects of the nano-bio interface of HNTs with different cell types (bacteria, algae and fungi, and mammalian cells), highlighting biocompatibility/bio-adverse properties, interaction mechanisms, and the latest cutting-edge technologies.

Bionanocomposite Films Containing Halloysite Nanotubes and Natural Antioxidants with Enhanced Performance and Durability as Promising Materials for Cultural Heritage Protection

In the last decade, the interest toward the formulation of polymer films for cultural heritage protection continuously grew, and these films must be imperatively transparent, removable, and should not react/interact with surface of the artworks. In this research, bionanocomposite films, based on chitosan (Ch) and pectin (P) and containing naturally occurring fillers and antioxidants, were formulated by solvent casting methods and were accurately characterized. The natural halloysite nanotubes (HNT) have a two-fold role, specifically, physical compatibilizer and antioxidant carrier. Therefore, the theoretical solubility between Ch and P was estimated considering Hoy’s method for solubility of polymers, while the optimum ratio between biopolymer constituents was assessed by ζ-potential measurements. The transparency, wettability, and mechanical behavior of Ch:P films, also in presence of HNT without and with antioxidants, were investigated. The beneficial effects of natural antioxidants, such as vanillic acid (VA) and quercetin (Q), on Ch:P/HNT durability were found.

Halloysite Nanotubes Coated by Chitosan for the Controlled Release of Khellin

In this work, we have developed a novel strategy to prepare hybrid nanostructures with controlled release properties towards khellin by exploiting the electrostatic interactions between chitosan and halloysite nanotubes (HNT). Firstly, khellin was loaded into the HNT lumen by the vacuum-assisted procedure. The drug confinement within the halloysite cavity has been proved by water contact angle experiments on the HNT/khellin tablets. Therefore, the loaded nanotubes were coated with chitosan as a consequence of the attractions between the cationic biopolymer and the halloysite outer surface, which is negatively charged in a wide pH range. The effect of the ionic strength of the aqueous medium on the coating efficiency of the clay nanotubes was investigated. The surface charge properties of HNT/khellin and chitosan/HNT/khellin nanomaterials were determined by ζ potential experiments, while their morphology was explored through Scanning Electron Microscopy (SEM). Water contact angle experiments were conducted to explore the influence of the chitosan coating on the hydrophilic/hydrophobic character of halloysite external surface. Thermogravimetry (TG) experiments were conducted to study the thermal behavior of the composite nanomaterials. The amounts of loaded khellin and coated chitosan in the hybrid nanostructures were estimated by a quantitative analysis of the TG curves. The release kinetics of khellin were studied in aqueous solvents at different pH conditions (acidic, neutral and basic) and the obtained data were analyzed by the Korsmeyer-Peppas model. The release properties were interpreted on the basis of the TG and ζ potential results. In conclusion, this study demonstrates that halloysite nanotubes wrapped by chitosan layers can be effective as drug delivery systems.

Multifunctional HNT@Fe3O4@PPy@DOX Nanoplatform for Effective Chemo-Photothermal Combination Therapy of Breast Cancer with MR Imaging

Multifunctional nanoparticles for imaging and treatment in cancer are getting more and more attention recently. Herein, halloysite nanotubes (HNTs), natural clay nanotubes, are designed as multifunctional nanoplatform for targeted delivering photothermal therapy agents and chemotherapeutic drugs. Fe₃O₄ was anchored on the outer surfaces of HNTs and then doxorubicin (DOX) was loaded on the nanotubes. Afterward, a layer of polypyrrole (PPy), as photothermal agent, was wrapped on the tubes. The nanoplatform of HNT@Fe₃O₄@PPy@DOX can be guided to tumor tissue by an external magnetic field, and then performs chemo-photothermal combined therapy by 808 nm laser irradiation. HNT@Fe₃O₄@PPy@DOX shows the ability of T₂-weighted magnetic resonance imaging, which could be considered as a promising application in magnetic targeting tumor therapy. In vitro and in vivo experiments demonstrate that HNTs nanoplatform has good biocompatibility and produces a strong antitumor effect trigged by near-infrared laser irradiation. The novel chemo-photothermal therapy nanoplatform based on HNTs may be developed as a multifunctional nanoparticle for imaging and therapy in breast cancer.

Halloysite/Keratin Nanocomposite for Human Hair Photoprotection Coating

We propose a novel keratin treatment of human hair by its aqueous mixtures with natural halloysite clay nanotubes. The loaded clay nanotubes together with free keratin produce micrometer-thick protective coating on hair. First, colloidal and structural properties of halloysite/keratin dispersions and the nanotube loaded with this protein were investigated. Above the keratin isoelectric point (pH = 4), the protein adsorption into the positive halloysite lumen is favored because of the electrostatic attractions. The ζ-potential magnitude of these core-shell particles increased from -35 (in pristine form) to -43 mV allowing for an enhanced colloidal stability (15 h at pH = 6). This keratin-clay tubule nanocomposite was used for the immersion treatment of hair. Three-dimensional-measuring laser scanning microscopy demonstrated that 50-60% of the hair surface coverage can be achieved with 1 wt % suspension application. Hair samples have been exposed to UV irradiation for times up to 72 h to explore the protection capacity of this coating by monitoring the cysteine oxidation products. The nanocomposites of halloysite and keratin prevent the deterioration of human hair as evident by significant inhibition of cysteic acid. The successful hair structure protection was also visually confirmed by atomic force microscopy and dark-field hyperspectral microscopy. The proposed formulation represents a promising strategy for a sustainable medical coating on the hair, which remediates UV irradiation stress.

Nitric oxide synthase-mediated sub-chronic injury and recovery in the small intestine of mice after oral administration with halloysite nanotubes

Natural halloysite nanotubes (HNTs) with a hollow lumen have been widely applied in many fields, such as water purification, drug carriers, cosmetics, antibacterial, and scaffolds for tissue engineering. However, their in vivo toxicity is still largely unclear. The aim of this study is to evaluate sub-chronic oral toxicity of HNTs in the small intestine of mice. The results demonstrated that oral HNTs at low dose (5 mg/kg) for 30 days promoted mouse growth with no obvious adverse effect on the small intestine. The promotive effect on mouse growth disappeared after cessation of oral administration of HNTs. Oral HNTs at high dose (50 mg/kg) for 30 days induced aluminum (Al) and silicon (Si) accumulation and oxidative stress in the small intestine, which caused significant increases in the levels of cyclooxygenase-2 (COX-2) and nitric oxide synthase (iNOS) and inflammatory response and iNOS-mediated damages in the organ. Oral HNTs-induced changes in the small intestine at high dose were not observed after a 30-day recovery period. These findings provided the first evidence that oral HNTs-induced sub-chronic toxicity in the small intestine was reversible. The results suggest that HNTs at low concentration in environments have no adverse effect on mice, while there are health risks to mice under severe contamination by HNTs.

Halloysite Nanotubes: Interfacial Properties and Applications in Cultural Heritage

The peculiar surfaces of halloysite nanotubes and their biocompatibility are attracting the interest of researchers based on the wide range of attainable applications. The large aspect ratio of this nanotubular material ensures promising properties as a reinforcing agent in polymeric matrixes, such as cellulose and its derivatives, that entail strengthening due to, for instance, aging-induced degradation. The halloysite cavity has a suitable size for hosting a large variety of active species such as deacidifying (calcium hydroxide) and flame retardant agents (fluorinated surfactants) for a controlled and sustained release relevant to the conservation of cultural heritage. Additionally, anionic surfactants can be selectively adsorbed at the inner surface generating inorganic micelles able to solubilize hydrophobic species in a controlled cleaning protocol. We briefly discuss how the natural halloysite nanotubes can be supportive in various conservation processes of cultural heritage and present an outlook for future perspectives.

INOS-mediated acute stomach injury and recovery in mice after oral exposure to halloysite nanotubes

Natural halloysite nanotubes (HNTs) with a hollow lumen are already applied in numerous fields and enter the environment in increasing quantities, which may have effects on animal and human health. However their in vivo toxicity in mammals is still largely unclear. The aim of this study is to assess acute oral toxicity of HNTs in the stomach of mice and recovery. Oral HNTs at low dose (5 mg HNTs/kg BW) for 30 days increased in daily food and water intake and promoted mouse growth with no obvious adverse effect on the stomach. The promotive effect on mouse growth disappeared after cessation of oral administration of the nanotubes. Oral HNTs for 30 days at high dose (50 mg HNTs/kg BW) induced Si and Al accumulation in the stomach, which caused oxidative stress, inflammation and iNOS-mediated damage in the organ. The damage in the stomach led to slight atrophic gastritis and reduced mouse growth. Oral HNTs-induced changes at high dose were not observed after a 30-days recovery period. The findings provided the evidence that oral HNTs-induced acute toxicity in the stomach was reversible. More importantly, this research showed that Al and Si were cleared out of the mice by hepatic excretion and renal excretion, respectively, during the recovery period. The results suggest that HNTs at low concentration in environments have no adverse effect on mice, while there are health risks to mice under severe contamination by HNTs.

Naturally derived nano- and micro-drug delivery vehicles: halloysite, vaterite and nanocellulose

We discuss prospects for halloysite nanotubes, vaterite crystals and nanocellulose to enter the market of biomaterials for drug delivery and tissue engineering, and their potential for economically viable production from abundant natural sources.

Increased surface area of halloysite nanotubes due to surface modification predicts lung inflammation and acute phase response after pulmonary exposure in mice

The toxicological potential of halloysite nanotubes (HNTs) and variants after functional alterations to surface area are not clear. We assessed the toxicological response to HNTs (NaturalNano (NN)) before and after surface etching (NN-etched). Potential cytotoxicity of the two HNTs was screened in vitro in MutaTMMouse lung epithelial cells. Lung inflammation, acute phase response and genotoxicity were assessed 1, 3, and 28 days after a single intratracheal instillation of adult female C57BL/6 J BomTac mice. The doses were 6, 18 or 54 μg of HNTs, compared to vehicle controls and the Carbon black NP (Printex 90) of 162 μg/mouse. The cellular composition of bronchoalveolar lavage (BAL) fluid was determined as a measure of lung inflammation. The pulmonary and hepatic acute phase responses were assessed by Serumamyloida mRNA levels in lung and liver tissue by real-time quantitative PCR. Pulmonary and systemic genotoxicity were analyzed by the alkaline comet assay as DNA strand breaks in BAL cells, lung and liver tissue. The etched HNT (NN-etched) had 4-5 times larger BET surface area than the unmodified HNT (NN). Instillation of NN-etched at the highest dose induced influx of neutrophils into the lungs at all time points and increased Saa3 mRNA levels in lung tissue on day 1 and 3 after exposure. No genotoxicity was observed at any time point. In conclusion, functionalization by etching increased BET surface area of the studied NN and enhanced pulmonary inflammatory toxicity in mice.

Biomedical potential of clay nanotube formulations and their toxicity assessment

Introduction: Halloysite clay nanotubes (HNTs) are a naturally abundant and biocompatible aluminosilicate material with a structure able to encapsulate 10-20% of drugs. These features are attractive toward the clinical application in controlled drug delivery, tissue engineering and regenerative medicine. Areas covered: We describe the application of HNTs as a viable method for clinical purposes, particularly developing formulations for prophylaxis, diagnosis and therapeutics, having a special attention to these nanotubes bio-safety. HNTs may be used for pharmaceuticals, biopharmaceuticals, wound healing, bone regeneration, dental repair, hair surface engineering and biomimetic applications. Expert opinion: HNTs are a versatile, safe and biocompatible nanomaterial used for drug encapsulation for numerous clinical applications. The studies here reviewed confirm the HNTs biocompatibility, describing their low toxicity. Further developments will be made regarding the long-term efficacy of halloysite-based treatments in humans, concentrating mostly on topical applications.

Why does vacuum drive to the loading of halloysite nanotubes? The key role of water confinement

The filling of halloysite nanotubes with active compounds solubilized in aqueous solvent was investigated theoretically and experimentally. Based on Knudsen thermogravimetric data, we demonstrated the water confinement within the cavity of halloysite. This process is crucial to properly describe the driving mechanism of halloysite loading. In addition, Knudsen thermogravimetric experiments were conducted on kaolinite nanoplates as well as on halloysite nanotubes modified with an anionic surfactant (sodium dodecanoate) in order to explore the influence of both the nanoparticle morphology and the hydrophobic/hydrophilic character of the lumen on the confinement phenomenon. The analysis of the desorption isotherms allowed us to determine the water adsorption properties of the investigated nanoclays. The pore sizes of the nanotubes' lumen was determined by combining the vapor pressure of the confined water with the nanoparticles wettability, which was studied through contact angle measurements. The thermodynamic description of the water confinement inside the lumen was correlated to the influence of the vacuum pumping in the experimental loading of halloysite. Metoprolol tartrate, salicylic acid and malonic acid were selected as anionic guest molecules for the experimental filling of the positively charged halloysite lumen. According to the filling mechanism induced by the water confinement, the vacuum operation and the reduced pressure enhanced the loading of halloysite nanotubes for all the investigated bioactive compounds. This work represents a further and crucial step for the development of halloysite based nanocarriers being that the filling mechanism of the nanotube's cavity from aqueous dispersions was described according to the water confinement process.

Filling of Mater-Bi with Nanoclays to Enhance the Biofilm Rigidity

We investigated the efficacy of several nanoclays (halloysite, sepiolite and laponite) as nanofillers for Mater-Bi, which is a commercial bioplastic extensively used within food packaging applications. The preparation of Mater-Bi/nanoclay nanocomposite films was easily achieved by means of the solvent casting method from dichloroethane. The prepared bio-nanocomposites were characterized by dynamic mechanical analysis (DMA) in order to explore the effect of the addition of the nanoclays on the mechanical behavior of the Mater-Bi-based films. Tensile tests found that filling Mater-Bi with halloysite induced the most significant improvement of the mechanical performances under traction force, while DMA measurements under the oscillatory regime showed that the polymer glass transition was not affected by the addition of the nanoclay. The tensile properties of the Mater-Bi/halloysite nanotube (HNT) films were competitive compared to those of traditional petroleum plastics in terms of the elastic modulus and stress at the breaking point. Both the mechanical response to the temperature and the tensile properties make the bio-nanocomposites appropriate for food packaging and smart coating purposes. Here, we report a preliminary study of the development of sustainable hybrid materials that could be employed in numerous industrial and technological applications within materials science and pharmaceutics.

Halloysite Nanotubes as an Effective and Recyclable Adsorbent for Removal of Low-Concentration Antibiotics Ciprofloxacin

In this work, halloysite nanotubes (HNTs) without modification were used as an efficient adsorbent to explore its natural adsorption capability, which showed excellent adsorption ability for low-concentration ciprofloxacin (CIP). The physicochemical properties of HNTs before and after adsorption were investigated by several characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption–desorption analysis, X-ray diffractometer (XRD), and zeta potential analysis. The influences of temperature, initial CIP concentration, adsorbent dosage, and pH value on CIP adsorption performance were also studied. The kinetics analysis revealed that CIP adsorption on HNTs was a kind of monolayer adsorption process and followed a pseudo-second-order rate equation. The zeta potential result indicated that electrostatic interaction between HNTs and CIP molecules was possibly responsible for the adsorption performance. Moreover, HNTs showed no apparent loss in CIP adsorption capability after five cycles, exhibiting potential applications in wastewater treatment.

Microemulsion Encapsulated into Halloysite Nanotubes and their Applications for Cleaning of a Marble Surface

Halloysite nanotubes were used to incorporate anionic surfactant micelles and an organic solvent to generate a cleaning system to be applied in Cultural Heritage restoration. The targeted adsorption is driven by electrostatic interactions based on the nanotubes peculiar charge separation. Namely anionic species are driven to the positively charged inner surface while being prevented from interacting with the halloysite outer surface that possesses a positive charge density. The hybrid organic/inorganic emulsion was characterized by dynamic light scattering. Analysis of the autocorrelation function allowed us to define the presence of surfactant aggregates inside/outside the nanotube lumen as a function of the nanotube/surfactant ratio in an aqueous mixture. The application of this prepared emulsion for the controlled cleaning of a marble artifact is demonstrated. To this purpose, a membrane of nanofibrous polyacrylonitrile was prepared by electrospinning and was applied between the work of art and the cleaning agent to avoid the release of residues on the marble surface. This work represents a further step toward the opportunity to extend the use of emulsions for cleaning protocols for stone-based artifacts or in technological applications where surfactant separation is required by a simple centrifugation/sedimentation method.

Halloysite Nanotubes Loaded with Calcium Hydroxide: Alkaline Fillers for the Deacidification of Waterlogged Archeological Woods

A novel green protocol for the deacidifying consolidation of waterlogged archaeological woods through aqueous dispersions of polyethylene glycol (PEG) 1500 and halloysite nanotubes containing calcium hydroxide has been designed. First, we prepared functionalized halloysite nanotubes filled with Ca(OH)₂ in their lumen. The controlled and sustained release of Ca(OH)₂ from the halloysite lumen extended its neutralization action over time, allowing the development of a long-term deacidification of the wood samples. A preliminary thermomechanical characterization of clay/polymer nanocomposites allows us to determine the experimental conditions to maximize the consolidation efficiency of the wood samples. The penetration of the halloysite-Ca(OH)₂/PEG composite within the wooden pores conferred the robustness of the archaeological woods based on the clay/polymer composition of the consolidant mixture. Compared to the archeological woods treated with pure PEG 1500, the addition of modified nanotubes in the consolidant induced a remarkable improvement in the mechanical performance in terms of flexural strength and rigidity. The pH measurements of the treated woods showed that the halloysite-Ca(OH)₂ are effective alkaline fillers. Accordingly, the modified nanotubes provided a long-term protection for lignin present in the woods that are exposed to artificial aging under acidic atmosphere. The attained knowledge shows that an easy and green protocol for the long-term preservation of wooden artworks can be achieved by the combination of PEG polymers and alkaline tubular nanostructures obtained through the confinement of Ca(OH)₂ within the halloysite cavity.

In vitro and in vivo toxicity evaluation of halloysite nanotubes

Because of their outstanding properties, increasing numbers of research studies and emerging applications for manufacturing products are currently in progress for halloysite nanotubes (HNTs). Therefore, the impact of HNTs on the environment and human health should be taken into consideration. In order to clearly show the cell uptake of HNTs and the biodistribution of HNTs in zebrafish, HNTs are labeled with fluorescein isothiocyanate (FITC-HNTs). The cytotoxicity assays showed that the cell viabilities of human umbilical vein endothelial cells (HUVECs) and human breast adenocarcinoma (MCF-7) cells were above 60% after being treated with different concentrations of HNTs (2.5-200 μg mL^-1) for 72 h. Confocal laser scanning microscopy (CLSM) results showed the uptake of HNTs by HUVECs and MCF-7 cells. The in vivo toxicity of HNTs was then investigated in the early development of zebrafish embryos. The percent survival of zebrafish embryos and larvae showed no significant changes at different developmental stages (24, 48, 72, 96, and 120 hpf) when treated with various concentrations of HNTs (0.25-10 mg mL^-1). Besides, HNTs could promote the hatchability of zebrafish embryos and did not affect the morphological development of zebrafish at a concentration of ≤25 mg mL^-1. HNTs could also be ingested by zebrafish larvae and accumulated predominantly in the gastrointestinal tract. The fluorescence intensity of FITC-HNTs decreased gradually with time, which suggested that HNTs could be excreted by zebrafish larvae through the gastrointestinal metabolism. Therefore, it can be concluded that HNTs are relatively biocompatible nanomaterials, which can be utilized in many fields.

Thermal Properties of Multilayer Nanocomposites Based on Halloysite Nanotubes and Biopolymers

This paper reports a novel procedure to fabricate multilayer composite biofilms based on halloysite nanotubes (HNTs) and sustainable polymers. Among the biopolymers, the non-ionic (hydroxypropyl cellulose) and cationic (chitosan) molecules were selected. The nanocomposites were prepared by the sequential casting of ethanol solutions of hydroxypropyl cellulose and aqueous dispersions of chitosan/HNTs. The composition of the bio-nanocomposites was systematically changed in order to investigate the effect of the hydroxypropyl cellulose/HNTs ratio on the thermal properties of the films, which were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). DSC studies were conducted in the static air (oxidative atmosphere), while TG measurements were carried out under nitrogen flow (inert atmosphere). The analysis of DSC data provided the enthalpy and the temperature for the oxidative degradation of the bio-nanocomposites. These results were helpful to estimate the efficacy of the well-compacted middle layer of HNTs as a flame retardant. TG experiments were performed at a variable heating rate and the collected data were analyzed by the Friedman’s method (non-isothermal thermogravimetric approach) with the aim of studying the kinetics of the hydroxypropyl cellulose degradation in the multilayer nanocomposites. This work represents an advanced contribution for designing novel sustainable nanocomposites with excellent thermal behavior as a consequence of their peculiar multilayer structure.

Halloysite clay nanotubes for life sciences applications: From drug encapsulation to bioscaffold

Natural forming clay halloysite is an emerging nanomaterial carrier for sustained drug delivery. These 50 nm diameter aluminosilicate tubes, with inner - alumina and outer - silica surface layers, can be loaded with 10-30 wt% of drug molecules, DNA and enzymes. The opposite charge of the inner and outer halloysite surface allow for selective drug adsorption inside or outside the clay nanotubes. The drug loaded halloysite enhanced the zeta potential of minus 50-60 mV allowing for stable aqueous nanocolloids. Halloysite nanoformulations provide an extended 10-20 h release profile, and may be functionalized (e.g., clogging tubes' end with polymers extending release time to 1-2 weeks or allowing for triggered release), which renders these clay nanostructures as promising controlled delivery systems. Recent studies demonstrate the potential of abundantly available halloysite clay nanotubes for life science applications, from drug delivery via oral or topical administration, to tissue scaffolds and regenerative medicine, while assessing their cellular internalization, stability, biosafety and biocompatibility are featured. The benefits and limitations of halloysite clay nanotubes are discussed, as well as the directions for future developments.