Highly ordered and concentric ring patterns consisting of halloysite nanotubes (HNTs) with hierarchical cholesteric architectures are prepared by evaporation-induced self-assembly in a sphere-on-flat geometry. The structure and properties of HNTs are investigated. HNTs show a perfect tubular morphology on the nanoscale with high dispersion stability in water. Upon drying the HNTs aqueous suspension in a sphere-on-flat confined space, regular concentric HNTs rings are formed on the substrate via a self-assembly process. The widths of the inner and outer rings and the spacing between the adjacent rings increase with an increase in the concentration of the HNTs suspension. The highly ordered and concentric HNTs rings show a pronounced Maltese cross-like pattern under crossed polarizers, which suggests the formation of hierarchical cholesteric architectures. Scanning electron microscopy and atomic force microscopy observations show a disclination alignment of HNTs in the ring strips, especially with a high concentration of the HNTs suspension. The patterned rough surfaces of the HNTs show low cytotoxicity and can be used as a cell-supporting scaffold. The HNTs rings can guide the growth and orientation of C2C12 myoblast cells perpendicular to the rings. This work provides a simple, repeatable, mild, and high-efficiency method for obtaining HNTs with hierarchical architectures, which show potential for a large variety of applications, for example, in vascular grafts and skin regeneration.

•Alginate/HNTs composite hydrogels were fabricated using Ca2+ cross-linking method.•The hydrogen bond interactions between HNTs and alginate are confirmed.•HNTs can significantly enhance the mechanical properties of alginate hydrogel.•HNTs can improve the cell attachment and proliferation of alginate.Sodium alginate (SA)/halloysite nanotubes (HNTs) composite hydrogels were successfully prepared by solution blending and cross-linking with calcium ions. HNTs can improve the physical properties and cytocompatibility of composite hydrogels. The static and shear viscosity of SA/HNTs solution increase by the addition of HNTs. FTIR suggests the presence of hydrogen bond interactions between HNTs and SA. The crystal structure of HNTs is retained in the composites as showed by the X-ray diffraction result. A porous structure with pore size of 100–250 μm is found in the hydrogels, which can provide a space for cell growth and migration. The compressive mechanical properties of composite hydrogels significantly increase compared to the pure SA hydrogel. The SA/HNTs composite hydrogels with 80% HNTs loading exhibit the compressive stress at 80% strain of 2.99 MPa, while the stress at 80% strain of pure SA hydrogel is only 0.8 MPa. The dynamic storage modulus of composite hydrogels also markedly increases with HNTs concentration. The differential scanning calorimetry endothermic peak area and swelling ratios in NaCl solution of the composite hydrogels decrease by the addition of HNTs. Preosteoblast (MC3T3-E1) culture results reveal that the SA/HNTs composites especially at relatively low HNTs loading show a significant increase in cells adhesion and proliferation compared to the pure SA hydrogel. All the results demonstrate that the SA/HNTs composite hydrogels show a promising application in bone tissue engineering.

•PEI grafted halloysite were developed as a novel non-viral gene vector.•PEI-g-HNTs show lower cytotoxicity than PEI and bind DNA tightly•PEI-g-HNTs/pDNA complexes show high transfection efficiency towards cells•GFP protein expression at the N/P ratio of 20 is higher than other ratioInorganic nanoparticles have attracted much attentions in gene delivery because of their desirable characteristics including low toxicity, well-controlled characteristics, high gene delivery efficiency, and multi-functionalities. Here, natural occurred halloysite nanotubes (HNTs) were developed as a novel non-viral gene vector. To increase the efficiency of endocytosis, HNTs were firstly shortened into an appropriate size (~ 200 nm). Then polyethyleneimine (PEI) was grafted onto HNTs to bind green fluorescence protein (GFP) labeled pDNA. The structure and physical-chemical properties of PEI grafted HNTs (PEI-g-HNTs) were characterized by various methods. PEI-g-HNTs show lower cytotoxicity than PEI. PEI-g-HNTs are positively charged and can bind DNA tightly at designed N/P ratio from 5:1 to 40:1. PEI-g-HNTs/pDNA complexes show much higher transfection efficiency towards both 293T and HeLa cells compared with PEI/pDNA complexes at the equivalent N/P ratio. The transfection efficiencies of PEI-g-HNTs/pDNA complex towards HeLa cell can reach to 44.4% at N/P ratio of 20. PEI-g-HNTs/pDNA complexes possess a higher GFP protein expression than PEI/pDNA from simple western immunoblots. So, PEI-g-HNTs are potential gene vectors with good biocompatibility and high transfection efficiency, which have promising applications in cancer gene therapy.Download high-res image (299KB)Download full-size image

•Chitosan composites hydrogels were prepared by addition of halloysite nanotubes.•Mechanical property of chitosan composite hydrogels was increased by HNTs.•The pore size of chitosan hydrogels becomes smaller as the HNTs content increases.•Chitosan/HNTs composite hydrogels show low cytotoxicity towards MC3T3-E1 cells.•Composite hydrogels show an increased drug entrapment efficiency of doxorubicin.Here, chitosan composites hydrogels were prepared by addition of halloysite nanotubes (HNTs) in the chitosan KOH/LiOH/urea solution. The raw chitosan and chitosan/HNTs composite hydrogels were obtained by heat treatment at 60 °C for 8 h and then regeneration in ethanol solution. The viscosity of the composite solution is increased with HNTs content. The Fourier transform infrared spectroscopy (FT-IR) shows that the hydrogen bonds interactions exist between the HNTs and the chitosan. X-ray diffraction (XRD) results show that the crystal structure of HNT is not changed in the composite hydrogels. The compressive property test and storage modulus determination show that the mechanical properties and anti-deformation ability of the composite hydrogel significantly increase owing to the reinforcing effect of HNTs. The composites hydrogel with 66.7% HNTs can undergo 7 times compression cycles without breaking with compressive strength of 0.71 MPa at 70% deformation, while pure chitosan hydrogel is broken after bearing 5 compression cycles with compressive strength of 0.14 MPa and a maximum deformation of 59%. A porous structure with pore size of 100–500 μm is found in the composite hydrogels by scanning electron microscopy (SEM), and the pore size and the swelling ratio in NaCl solution decrease by the addition of HNTs and the immersing of ethanol. Chitosan/HNTs composite hydrogels show low cytotoxicity towards MC3T3-E1 cells. Also, the composite hydrogels show a maximum drug entrapment efficiency of 45.7% for doxorubicin (DOX) which is much higher than that of pure chitosan hydrogel (27.5%). All the results illustrate that the chitosan/HNTs composite hydrogels show promising applications as biomaterials.Download high-res image (197KB)Download full-size image

Here, polystyrene sulfonate sodium (PSS) modified Halloysite nanotubes (HNTs) were self-assembled into a patterned coating on a glass substrate with ordered nanotube arrays in a slit-like confined space. The microstructure of the formed patterned HNTs coating was investigated. The formed strips are more regular and almost parallel to each other with an increase in HNTs concentration. The HNTs coating formed from the 2% PSS-HNTs dispersion has the maximum nanotube alignment degree. The patterned HNTs coating was employed to capture tumor cells. The tumor cells can be captured by the HNTs coating effectively compared with a smooth glass surface due to the enhanced topographic interactions between the HNTs coating and cancer cells. The HNTs coating prepared from the 2% PSS-HNTs dispersion has the highest capture yield which is due to the ordered nanotube arrangement and the appropriate surface roughness. The HNTs coating was further conjugated with anti-EpCAM, which leads to the capture yield of MCF-7 cells reaching 92% within 3 h. The HNTs coating can capture 8 MCF-7 cells from 1 mL artificial blood samples spiked with 10 MCF-7 cells, showing the promising applications of HNTs in clinical circulating tumor cell capture for early diagnosis and monitoring of cancer patients.

Halloysite nanotubes (HNTs) have a unique tubular structure in nanoscale, and have shown potential as novel carriers for various drugs. Coating the nanotubes with a hydrophilic polymer shell can significantly decrease the toxicity and provide colloidal stability during blood circulation. Here, we synthesized chitosan grafted HNTs (HNTs-g-CS) and investigated their potential as a nano-formulation for the anticancer drug curcumin. The structure and properties of HNTs-g-CS were characterized using water contact angle, zeta-potential, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) techniques. HNTs-g-CS exhibit a maximum 90.8% entrapment efficiency and 3.4% loading capacity of curcumin, which are higher than those of raw HNTs. HNTs-g-CS also show no obvious hemolytic phenomenon and good stability in serum. The cumulative release ratio of curcumin from HNTs-g-CS/curcumin at cell lysate after 48 hours is 84.2%. The curcumin loaded HNTs-g-CS show specific toxicity to various cancer cell lines, including HepG2, MCF-7, SV-HUC-1, EJ, Caski and HeLa, and demonstrate an inhibition concentration of IC50 at 5.3–192 μM as assessed by cytotoxicity studies. The anticancer activity of this nanoformulation is extremely high in EJ cells compared with the other cancer cell lines. The cell uptake of HNTs-g-CS is confirmed by fluorescence microscopy. Flow cytometric analysis of curcumin loaded HNTs-g-CS shows that curcumin loaded HNTs-g-CS increase apoptosis on EJ cells. The content of ROS created by HNTs-g-CS/curcumin is more than that of free curcumin. All these results suggest that HNTs-g-CS are potential nanovehicles for anticancer drug delivery in cancer therapy.

Here, we used capillary tubes to evaporate an aqueous dispersion of halloysite nanotubes (HNTs) in a controlled manner to prepare a patterned surface with ordered alignment of the nanotubes . Sodium polystyrenesulfonate (PSS) was added to improve the surface charges of the tubes. An increased negative charge of HNTs is realized by PSS coating (from −26.1 mV to −52.2 mV). When the HNTs aqueous dispersion concentration is higher than 10%, liquid crystal phenomenon of the dispersion is found. A typical shear flow behavior and decreased viscosity upon shear is found when HNTs dispersions with concentrations higher than 10%. Upon drying the HNTs aqueous dispersion in capillary tubes, a regular pattern is formed in the wall of the tube. The width and spacing of the bands increase with HNTs dispersion concentration and decrease with the drying temperature for a given initial concentration. Morphology results show that an ordered alignment of HNTs is found especially for the sample of 10%. The patterned surface can be used as a model for preparing PDMS molding with regular micro-/nanostructure. Also, the HNTs rough surfaces can provide much higher tumor cell capture efficiency compared to blank glass surfaces. The HNTs ordered surfaces provide promising application for biomedical areas such as biosensors.Keywords: alignment; assembly; halloysite nanotube; patterned surface; tumor cell

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.Keywords: cell viability; drug delivery; nanotube; surface grafting; tumor therapy

•Chitin nanocrystals (CNCs) are well dispersed in chitosan (CS) solution.•CS/CNCs composite scaffolds exhibit improved compressive strength and modulus.•The porosity of CS/CNCs composite scaffold is in the range of 60%–84.0%.•The composite scaffolds shows good biocompatibility to MC3T3-E1 osteoblast cells.Chitin nanocrystals (CNCs) with length and width of 300 and 20 nm were uniformly dispersed in chitosan (CS) solution. The CS/CNCs composite scaffolds prepared utilizing a dispersion-based freeze dry approach exhibit significant enhancement in compressive strength and modulus compared with pure CS scaffold both in dry and wet state. A well-interconnected porous structure with size in the range of 100–200 μm and over 80% porosity are found in the composite scaffolds. The crystal structure of CNCs is retained in the composite scaffolds. The incorporation of CNCs leads to increase in the scaffold density and decrease in the water swelling ratio. Moreover, the composite scaffolds are successfully applied as scaffolds for MC3T3-E1 osteoblast cells, showing their excellent biocompatibility and low cytotoxicity. The results of fluorescent micrographs images reveal that CNCs can markedly promote the cell adhesion and proliferation of the osteoblast on CS. The biocompatible composite scaffolds with enhanced mechanical properties have potential application in bone tissue engineering.

This study aims to develop and characterize the nanocomposites using sulfur cross-linked carboxylated styrene-butadiene rubbers (S-xSBR) as the matrix and chitin nanocrystals (CNCs) as nanofillers. The composites’ morphology and properties were examined by light transmittances, fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), dynamic mechanical analysis (DMA), thermo gravimetric analyzer (TGA), and tensile properties determination. The addition of CNCs has slight effect on transparency of the composite films. FTIR data confirm the interfacial interactions between CNCs and S-xSBR via hydrogen bonds. CNCs are uniformly dispersed in the matrix from SEM result. The addition of CNCs can significantly improve the tensile strength and modulus both in static and dynamic states. The tensile modulus and tensile strength of S-xSBR/CNCs composites with the 4 wt.% CNCs is 62.5 % and 97.6 % higher than that of pure S-xSBR. The storage modulus, glass transition temperature, and the thermal stability of the composites are higher than those of the neat S-xSBR. The mechanical properties of the composite films are water-responsive, as the swollen samples exhibit obviously decreased strength and modulus. The greatest mechanical contrast is shown in the S-xSBR/CNCs composites with 2 wt.% CNCs loading whose tensile modulus decrease from 60.4 to 6.1 MPa after swelling equilibrium. The significant reinforcement effect of CNCs on S-xSBR is attributed to the unique structure of CNCs and the interfacial interactions in the composite.

•Chitosan–HNTs composite hydrogel beads were prepared by pH-precipitation method.•Inside of composite gel beads contains a large number of HNTs compared with the peel.•HNTs can accelerate dye adsorption and improve adsorption ability of chitosan.Composite hydrogel beads containing chitosan and halloysite nanotubes (HNTs) with a well defined structure were prepared by the dropping and pH-precipitation method. The influence of HNTs on the appearance, diameter, microstructures, and thermal stability of the chitosan beads was characterized. The composite hydrogels exhibit slightly increased diameter and improved thermal stability. A rough surface and high concentration of the nanotubes in the bead core are found in the composite beads. The hydrogel beads were employed as absorbents for removal of methylene blue and malachite green from aqueous solutions and the fundamental adsorption behavior was studied. Both Langmuir isotherm and Freundlich isotherm models can fit the isotherm absorption data well. The addition of HNTs can significantly increase the adsorption rate of chitosan beads for the two dyes. Moreover, with the increase of the amount of hydrogel beads in the dye solution, the removal ratio of dyes increases but the absorption amount per unit absorbent weight gradually reduces. The adsorption kinetics closely follows pseudo-second order model. The regeneration experimental shows that the adsorption ability of all the beads can be recovered especially for methylene blue. So the chitosan–HNTs composite hydrogels can be potentially used for the removal of dyes from wastewater.

Halloysite nanotubes (HNTs) are novel 1D natural nanomaterials with predominantly hollow tubular nanostructures and high aspect ratios. Due to their high mechanical strength, thermal stability, biocompatibility, and abundance, HNTs have a number of exciting potential applications in polymer nanocomposites. In this article, we review the recent progress toward the development of HNTs-polymer nanocomposites, while paying particular attention to interfacial interactions of the nanocomposites. The characteristics of the HNTs relative to the formation of the polymer nanocomposites are summarized first. The covalent or non-covalent functionalization methods for HNTs and various fabrication approaches for HNTs-polymer nanocomposites are introduced afterward. Polymer nanocomposites reinforced with HNTs possess highly increased tensile and flexural strength, elastic moduli, and improved toughness. HNTs-polymer nanocomposites also exhibit elevated thermal resistance, flame retardance and unique crystallization behavior. Due to the tubular microstructure and the biocompatibility of HNTs, HNTs-polymer nanocomposites have demonstrated good drug encapsulation and sustained release abilities, gaining them extensive use as tissue engineering scaffolds and drug carriers. Finally, we summarize the characteristics of HNTs-polymer nanocomposites and predict for the development of the potential applications in high-performance composites for aircraft/automobile industries, environmental protection, and biomaterials.

Halloysite nanotubes (HNTs) are novel 1D natural nanomaterials with predominantly hollow tubular nanostructures and high aspect ratios. Due to their high mechanical strength, thermal stability, biocompatibility, and abundance, HNTs have a number of exciting potential applications in polymer nanocomposites. In this article, we review the recent progress toward the development of HNTs-polymer nanocomposites, while paying particular attention to interfacial interactions of the nanocomposites. The characteristics of the HNTs relative to the formation of the polymer nanocomposites are summarized first. The covalent or non-covalent functionalization methods for HNTs and various fabrication approaches for HNTs-polymer nanocomposites are introduced afterward. Polymer nanocomposites reinforced with HNTs possess highly increased tensile and flexural strength, elastic moduli, and improved toughness. HNTs-polymer nanocomposites also exhibit elevated thermal resistance, flame retardance and unique crystallization behavior. Due to the tubular microstructure and the biocompatibility of HNTs, HNTs-polymer nanocomposites have demonstrated good drug encapsulation and sustained release abilities, gaining them extensive use as tissue engineering scaffolds and drug carriers. Finally, we summarize the characteristics of HNTs-polymer nanocomposites and predict for the development of the potential applications in high-performance composites for aircraft/automobile industries, environmental protection, and biomaterials.

Polypyrrole-wrapped halloysite nanotubes (PPy@HNTs) are prepared by polymerization of pyrrole on the surfaces of HNTs. PPy@HNTs show improved dispersion ability and stability in water compared with pure PPy due to the increased zeta potential. The PPy@HNTs dispersions are compounded with carboxylated styrene-butadiene rubber (xSBR) latex to prepare conductive xSBR/PPy@HNTs composites. The morphology, conductive performance, mechanical properties, and swelling performance of the xSBR/PPy@HNTs composites are determined. PPy@HNTs can be uniformly dispersed in the rubber matrix and form a conductive network. The conductivity of the composites increases with the loading of PPy@HNTs. When the content of PPy@HNTs is 10%, the conductivity of the xSBR rubber increases to 1.82 × 10−4 s/m which is much higher than the corresponding xSBR/neat PPy composites (4.62 × 10−8 s/m). Also, the composites show significantly improved mechanical properties both in static and dynamic condition. The tensile strength, Young's modulus, and storage modulus of the composites are substantially higher than those of pure xSBR. The rigid filler networks effectively limit the mobility of rubber molecule chains, which leads to decreased water swelling capacity and crosslink density. The prepared high performance rubber composites with good conductivity show promising applications in many areas such as piezoresistive sensor.

Halloysite nanotubes (HNTs) have a unique tubular structure in nanoscale, and have shown potential as novel carriers for various drugs. Coating the nanotubes with a hydrophilic polymer shell can significantly decrease the toxicity and provide colloidal stability during blood circulation. Here, we synthesized chitosan grafted HNTs (HNTs-g-CS) and investigated their potential as a nano-formulation for the anticancer drug curcumin. The structure and properties of HNTs-g-CS were characterized using water contact angle, zeta-potential, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) techniques. HNTs-g-CS exhibit a maximum 90.8% entrapment efficiency and 3.4% loading capacity of curcumin, which are higher than those of raw HNTs. HNTs-g-CS also show no obvious hemolytic phenomenon and good stability in serum. The cumulative release ratio of curcumin from HNTs-g-CS/curcumin at cell lysate after 48 hours is 84.2%. The curcumin loaded HNTs-g-CS show specific toxicity to various cancer cell lines, including HepG2, MCF-7, SV-HUC-1, EJ, Caski and HeLa, and demonstrate an inhibition concentration of IC50 at 5.3–192 μM as assessed by cytotoxicity studies. The anticancer activity of this nanoformulation is extremely high in EJ cells compared with the other cancer cell lines. The cell uptake of HNTs-g-CS is confirmed by fluorescence microscopy. Flow cytometric analysis of curcumin loaded HNTs-g-CS shows that curcumin loaded HNTs-g-CS increase apoptosis on EJ cells. The content of ROS created by HNTs-g-CS/curcumin is more than that of free curcumin. All these results suggest that HNTs-g-CS are potential nanovehicles for anticancer drug delivery in cancer therapy.

Here, polystyrene sulfonate sodium (PSS) modified Halloysite nanotubes (HNTs) were self-assembled into a patterned coating on a glass substrate with ordered nanotube arrays in a slit-like confined space. The microstructure of the formed patterned HNTs coating was investigated. The formed strips are more regular and almost parallel to each other with an increase in HNTs concentration. The HNTs coating formed from the 2% PSS-HNTs dispersion has the maximum nanotube alignment degree. The patterned HNTs coating was employed to capture tumor cells. The tumor cells can be captured by the HNTs coating effectively compared with a smooth glass surface due to the enhanced topographic interactions between the HNTs coating and cancer cells. The HNTs coating prepared from the 2% PSS-HNTs dispersion has the highest capture yield which is due to the ordered nanotube arrangement and the appropriate surface roughness. The HNTs coating was further conjugated with anti-EpCAM, which leads to the capture yield of MCF-7 cells reaching 92% within 3 h. The HNTs coating can capture 8 MCF-7 cells from 1 mL artificial blood samples spiked with 10 MCF-7 cells, showing the promising applications of HNTs in clinical circulating tumor cell capture for early diagnosis and monitoring of cancer patients.