•Recently, polysaccharides/halloysite sustainable nanocomposites have been developed.•Supramolecular interactions affect their structure and their mesoscopic properties.•Their functionalities can be ...controlled by the preparation protocol.•Their applications have been extended by the halloysite loading with active molecules.•Novel strategies for their preparation as delivery systems have been presented.
Biopolymers as alternative to fossils-derived polymers are attracting the interest of researcher in material science. Besides the economic advantages, the sustainability makes polysaccharides ideal candidates to prepare films and formulations. The addition of Halloysite nanotubes as green inorganic fillers was exploited to improve the physico-chemical properties and to introduce smart response abilities to the material. Halloysite is a natural tubular nanomaterial with hollow cavity and large aspect ratio. The effect of polymer charge on the morphology and mesoscopic properties of polysaccharides/halloysite nanocomposites has been highlighted. Different strategies (solvent casting, lyophilization, cryoscopic technique) for the preparation of nanocomposites have been described. In addition, we present novel protocols for the fabrication of polysaccharides/halloysite nanocomposites suitable as drug delivery systems. The emerging halloysite-based bionanocomposites are addressed to applications such as biomedicine, packaging, corrosion protection and restoration of cultural heritages. This review provides an overview of the recent progress achieved on halloysite-polysaccharides nanocomposites.
The aim of this study is the design and preparation of Mater-Bi/halloysite nanocomposite materials that could be employed as bioplastics alternative to the petroleum derived products. The ...biocomposite materials at variable halloysite content (from 0 to 30 wt%) were prepared by using the solvent casting method. We investigated the mechanical behaviour and the thermal properties of the prepared nanocomposites in order to estimate their suitability as biocompatible packaging materials. The thermo-mechanical characteristics were correlated to the nanocomposites' morphologies, which were studied by Scanning Electron Microscopy (SEM). As a general result, the physico-chemical performances of Mater-Bi were improved by the presence of small amounts of nanotubes, which evidenced a homogenous distribution in the polymer matrix. The strongest enhancements of the thermal stability and tensile properties were achieved for Mater-Bi/halloysite 10 wt%. A further addition of nanotubes determined the worsening of both thermal stability and mechanical behaviour.
The attained knowledge represents the starting step for the development of packaging films composed by Mater-Bi and halloysite nanotubes.
•Mater-Bi/halloysite nanocomposite films with variable filler content were prepared by casting methods•The thermal and mechanical properties of the nanocomposites were affected by their specific composition•Mater-Bi/halloysite 10 wt% evidenced the most promising performances in agreement with its uniformity•Mater-Bi/halloysite 30 wt% exhibited lower mechanical and thermal performances respect to pure Mater-Bi
Halloysite is natural tubular clay suitable as a component of biocompatible nanosystems with specific functionalities. The selective modification of halloysite inner/outer surfaces can be achieved by ...exploiting supramolecular and covalent interactions resulting in controlled colloidal stability adjusted to the solvent polarity. The functionalized halloysite nanotubes can be employed as reinforcing filler for polymers as well as carriers for the sustained release of active molecules, such as antioxidants, flame-retardants, corrosion inhibitors, biocides and drugs. The tubular morphology makes halloysite a perspective template for core-shell metal supports for mesoporous catalysts. The catalysts can be incorporated with selective and unselective metal binding on the nanotubes' outer surface or in the inner lumens. Micropatterns of self-assembled nanotubes have been realized by the droplet casting method. The selective modification of halloysite has been exploited to increase the nanotubes' ordering in the produced patterns. Pickering emulsions, induced by the self-assembly of halloysite nanotubes on oil-water interface, can be used for petroleum spill bioremediation and catalysis.
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•Stable colloids of functionalized halloysite can be doped into polymeric composites.•Tubes' lumen can encapsulate & sustainably release chemical inhibitors and drugs.•Halloysite makes excellent support for core-shell metal nanocatalysts.•Organized patterns on solid supports produced by clay nanotube self-assembly.•Pickering microemulsions for oil spill bioremediation also use similar self-assembly.
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.
Halloysite clay nanotubes are functionalized by exploiting the different charges between the inner positive and the outer negative surfaces; accordingly, a selective adsorption is pursued by ...employing anionic and cationic surfactants. The obtained hybrid materials dispersed in aqueous phase are studied from the physicochemical viewpoint to investigate the colloidal stability that is a crucial parameter for applications. It is demonstrated that the adsorption of anionic surfactant into the HNTs lumen increases the net negative charge of the nanotubes enhancing the electrostatic repulsions and consequently the dispersion stability. The solubilization capability of these functionalized nanotubes toward hydrophobic compounds is demonstrated. This paper puts forward an easy strategy to prepare hybrid materials, like inorganic micelles, that can be used in water for solubilization and delivery of a hydrophobic compound by taking advantage of the sustainable and biocompatible properties.
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.
An easy strategy to obtain nanohydrogels within the halloysite nanotube (HNTs) lumen was investigated. Inorganic reverse micelles based on HNTs and hexadecyltrimethylammonium bromides were dispersed ...in chloroform, and the hydrophilic cavity was used as a nanoreactor to confine the gel formation based on alginate cross-linked by calcium ions. Spectroscopy and electron microscopy experiments proved the confinement of the polymer into the HNT lumen and the formation of calcium-mediated networks. Biological tests proved the biocompatibility of the hybrid hydrogel. The nanogel in HNTs was suitable for drug loading and sustained release with the opportunity of triggered burst release by chemical stimuli. Here, we propose a new strategy based on inorganic reverse micelles for nanohydrogel formation, which are suitable for industrial and biological applications as well as for selective and triggered adsorption and/or release.
Besides surfactants, which decrease the interfacial tension between two immiscible liquids, also interfacially active particles can successfully stabilize an emulsion system by attaching at the ...liquid–liquid interface. The preparation of the resulting Pickering emulsions has been so far investigated starting from the study of the interactions arising between the dispersed droplets and the stabilizers, till the application of these systems in a wide range of different fields. This work is intended to provide an overall overview about the development of Pickering emulsions by considering the most general aspects and scanning the diverse types of solid stabilizers. Among them, Halloysite nanotubes play a major role as naturally derived clay with emulsifying capability owing to their cheap, abundant, green and biocompatible properties. Therefore, the design of Halloysite stabilized Pickering emulsions is the main content of this review, which will survey the role of nanotubes in providing colloidal stability and will comprehensively sum up the use of these particles in technological and industrial purposes: from environmental to catalytic, from health to cultural heritage related applications.
This review provides meaningful insights about the design of Halloysite stabilized Pickering emulsions. The general aspects about their properties are enlightened by focusing many different factors. Most importantly, the applications of the clay nanotubes stabilized droplets in both technological and industrial fields are considered: from environmental remediation to catalysis, from health science to cultural heritage conservation.
This work represents a contribution to the design, preparation, and characterization of nanocomposite materials based on biocompatible components. The effects of composition, filler geometry, and ...polymer charge were highlighted, and their role on the final properties of the nanocomposites was revealed. We combined some biopolymers (methylcellulose, alginate, chitosan) with two nanoclays (kaolinite sheets and halloysite nanotubes) to prepare nanocomposites by means of the casting method from water. The thermal stability, the surface wettability, and the mechanical properties of the obtained films were studied. SEM micrographs highlighted the surface morphology of the biocomposite materials. X-ray data allowed us to correlate the mesoscopic structure to the properties of these nanocomposites.
Excipients in pharmaceutical formulations are inactive ingredient from the biological point of view, but they have a key role in the preparation, and they can alter the stability of the active ...principle. In this work, we prepared acetaminophen tablets with different amounts of talc as excipient and the thermal stability was deeply investigated by thermogravimetric studies. Isoconversional analysis by Kissinger–Akahira–Sunose method and “Master plot” analysis have been successfully employed to describe the kinetics of degradation under inert atmosphere, and the shelf lives have been calculated as a function of the talc content. The shelf-life values as well as the activation energy, which is the dominant factor, evidenced that the inorganic filler enhances the drug degradation to a certain extend and that the composition dependence has a peculiar trend reflecting the particle cluster formation at a critical concentration value. An effort of physico-chemical explanation for this behaviour is put forward by a simple geometrical model from the microparticle-size analysis to predict the critical talc concentration.
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