Halloysite-Chitosan based Nano-Composites and Applications

Recent advance in research on halloysite nanotubes-polymer nanocomposite

In this study the compressive strength and durability of soft clay soil stabilized with halloysite nanotubes are investigated. Halloysite nanotubes are novel 1D natural nanomaterials which are widely used in reinforcing polymer, pollution remediation, and as nanoreactors for biocatalyst. The wide use of halloysite nanotubes is due to their high aspect ratio, appropriate mechanical strength, high thermal stability, nature-friendly and cost-effectiveness. However, the use of halloysite nanotubes as a stabilizing agent for improving the durability of soil is not clear. In this research, halloysite nanotubes was used in the amounts of 2%, 5% and 10% by the weight of dried soil. Unconfined compressive strength, wet/dry cycles and freeze/thaw cycles tests were performed to evaluate the strength and durability of stabilized soft clay soil. Experimental results showed that halloysite nanotubes considerably improves the compressive strength and durability of soft clay soil. The optimum amount of halloysite nanotubes for soil stabilizing in terms of compressive strength and durability was 5%. The compressive strength of soft clay increased as much as 129% by applying 5% halloysite nanotubes. Also, the specimen containing 5% halloysite nanotubes showed the least strength loss after wet/dry and freeze/thaw cycles. The soil sample containing 5% halloysite nanotubes lost 20% of its initial compressive strength after 8 cycles of freezing and thawing, while the soil sample without any halloysite content lost 100% of its compressive strength after the same number of freezing and thawing. Based on the obtained results, the use of halloysite nanotubes in order to enhance the strength and durability of soft clay is strongly recommended.

Rubber composites based on halloysite nanotubes (HNT) have attracted tremendous attention during the last decades owing to the improved mechanical, dynamic mechanical, and thermal properties [1–3]. Before exploring the various aspects of HNT/rubber composite systems, we first briefly describe the HNT. It was first introduced by Berthier long back in the year of 1826 [4]. HNTs are a type of naturally occurring silicates with rolled nanotubular or spiral morphology, which have an analogous chemical structure of kaolinite [5]. They are naturally occurring and economically viable, and many countries such as China, France, Belgium, and New Zealand have deposits of these clay minerals. The major origin of HNT is a clay mineral obtained from a weathering product of granitic and rhyolitic volcanic rocks. The chemical composition of HNT is reported as Al2(OH)4Si2O5∙nH2O with n 1⁄4 0 or 2 for the anhydrous and the fully hydrated halloysite, respectively. The nanotubular structure was evolved from kaolinite by rolling up the layers under natural conditions. Most of the HNTs are multiwall or double-wall nanotubes [6]. Usually, the inner diameter of HNT is in the range of 50–80 nm and length of about 1,000 nm. Based on the state of hydration, HNTs are classified in two categories: hydrated HNTs with a crystalline structure of 10 A (d001) spacing and dehydrated ones with 7 A (d001) spacing [7]. HNTcontains two different types of hydroxyl groups, inner and outer hydroxyl groups, which are positioned in between the layers and on the surface, respectively. Attributed to the multilayer structure, most of the hydroxyl groups are inner groups, and only a few hydroxyl groups are located on the surface of HNT. The surface of HNT is mainly composed of outer O–Si–O (silanol) groups and O–Al–O (aluminol) groups situated inside the lumen. It is interesting to note that the density of surface hydroxyl groups in HNT is rather lower compared to other silicates clay minerals, for instance, kaolinite and montmorillonites (Fig. 1).

In this work, the biocompatible and biodegradable polycaprolactone (PCL) was synthesized by a ring‐opening synthesis mechanism. To improve the mechanical and biological properties of the polymer, electrospun nanocomposite scaffolds were prepared using halloysite nanotubes (HNTs) as the reinforcing agent with the concentrations of 5, 10, 15, 20, and 25% (w/w) of PCL. PCL‐HNTs composites were prepared as fibrous nanomats by electrospinning method. The morphology and wettability of the electrospun PCL‐HNTs nanomats were investigated by scanning electron microscope images and water contact angel measurement and based on the structure of the fibers, fibers diameter and higher wettability, the PCL‐HNT composite containing 5% (w/w) of halloysite nanotubes (PCL + 5%HNTs) was selected as the proper composite and its application as tissue engineering scaffold was studied. The mechanical properties of the PCL + 5%HNTs composite was 2.6 times higher than that of PCL, as well as, comparatively higher thermal stability. To improve the antibacterial properties, HNTs were loaded with gentamycin sulfate (GM) prior to electrospinning and the PCl + 5%HNTs+GM composite were prepared and studied. The drug release profile showed that by the incorporation of HNTs into the PCL based composites, slow drug release was continued for 164 h, while neat HNTs were completed the drug release after 8 h. The GM loaded composite scaffold showed a high antibacterial effect for Staphylococcus aureus and Listeria monocytogenes, Escherichia coli. Adequate cell growth environment was provided by PCL + 5%HNTs, as indicated by the biocompatibility and protein adsorption test results. The hemolytic assay results showed a higher hemolysis value for the HNTs‐containing sample, but still lower than 5%.

Chapter 20 - An Overview on the Safety of Tubular Clay Minerals

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 (5mg/kg) for 30days 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 (50mg/kg) for 30days 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.

Augmentin loaded functionalized halloysite nanotubes: A sustainable emerging nanocarriers for biomedical applications

Chitosan/halloysite nanotubes microcomposites: A double header approach for sustained release of ciprofloxacin and its hemostatic effects

Polylactic acid (PLA) is a widely used biodegradable polymer due to its non‐toxicity, good processability, and remarkable properties although its low thermal stability restricts high‐temperature applications. Halloysite nanotubes (HNTs) with a hollow tubular structure and high aspect ratio have been investigated as effective fillers to enhance polymer performance. In this study, surface‐modified HNTs were incorporated into PLA via in situ polymerization to prepare PLA/HNT nanocomposites with 0, 3, 5, 7, and 10 wt% loadings. FT‐IR spectra indicated the formation of hydrogen bonding between PLA and HNT, while SEM images confirmed homogeneous dispersion and strong interfacial adhesion. Thermal analyses revealed that the incorporation of even a small amount of HNT (3–5 wt%) effectively enhanced the thermal stability of PLA/HNT nanocomposites, increasing its degradation temperature by approximately 10°C. Among them, 5 wt% HNT provided the optimal combination of enhanced thermal stability and mechanical performance without significant loss in tensile strength. These results suggest that surface‐modified PLA/HNT nanocomposites offer improved heat resistance and processing stability, making them promising candidates for advanced packaging, electronic, and biomedical applications.

Metal oxide nanoparticles deposited onto carbon-coated halloysite nanotubes

Crosslinked modified tapioca starch films with CNC and HNT have the potential to be good renewable and biodegradable food packaging. Starch, CNC, and HNT were used because of their availability and cheap cost. This study aimed to investigate the effect of varying concentrations of CNC and HNT on the morphology, mechanical and optical properties of crosslinked modified tapioca starch films as an initial step in developing an active food package. Both CNC and HNT have high crystallinity and a large amount of OH groups. The OH groups as well as the ion-dipole interaction in HNT increase the tensile strength of the films. The highest tensile strength and the lowest elongation were recorded in films containing 5% CNC and 5% HNT. Beyond 5%, the addition of these nanomaterials diminished the tensile strength due to agglomeration which is the weak point of the films. Below the 5%, the nanomaterials serve as good reinforcing agents which improve the tensile strength. In addition, all films have good transmission capacity for visible light, while films with HNT outperform films with CNC in UV blocking ability.

Cryogel composites based on hyaluronic acid and halloysite nanotubes as scaffold for tissue engineering.

The objective of this study was to develop a stable drug delivery platform that is biocompatible, biodegradable and would provide sustained combinatorial drug release for the control of bone infection while simultaneously supporting bone tissue regeneration. Chitosan has been widely used in tissue engineering and in a variety of biomedical applications due to its eco‐friendly and biodegradable properties and it possesses a physiochemistry similar to the extracellular matrix of bone. However, the application of chitosan has been limited by its inherent mechanical weakness. Halloysite nanotubes (HNTs) are a naturally‐occurring aluminosilicate clay with a hollow tubular structure. HNTs are widely used as a bulk filler to materially reinforce a variety of polymer materials from bone cement to rubber. They have also been shown to be a potent nanocontainer for the sustained release of varied bioactive factors. In this study, chitosan and HNTs and chitosan and HNTs, doped with gentamicin and BMP‐2, were combined in different wt./wt. ratios and cross‐linked with tripolyphosphate. The biodegradability, mechanical properties, and surface structure of the hybrid nanocomposites were tested. The ability of the nanocomposites to control bacterial growth while supporting bone tissue formation was also evaluated. Gentamicin was selected as a model drug to evaluate the drug release capability of the chitosan‐HNTs nanocomposites and with release, its effectiveness against E. coli was analyzed through growth inhibition studies. Results indicate that the addition of HNTs to the chitosan hydrogel significantly improved the gels’ mechanical properties, permitting an extended period of drug release, and without a negative affect on drug efficacy. The coatings were capable of inhibiting bacterial growth and osteoblasts cultured on the hydrogel surfaces showed enhanced growth and functionality. Our doped clay/chitosan nanocomposite may overcome the limitations of traditional anti‐bacterial hydrogels and its ability to support bone tissue formation may enable its use in bone defect repair results from osteomyelitis.Support or Funding InformationFunding for this project was provided by the Louisiana Governor's Biotechnology Initiative and Louisiana Board of Regents OPT‐IN program.

A novel surface modification method upon halloysite nanotubes: A desirable cross-linking agent to construct hydrogels

Natural halloysite nanotubes (HNTs), with nanotubular structure, are attracting considerable attention in recent years. The hollow tubular structure allows HNTs to play an important role in drug delivery system as drug carriers. However, the wide applications of HNTs in biomedicine have been hampered by the lack of sufficient intracellular researches so far. In this study, we systemically investigated the transport mechanisms of HNTs in A549 living cells. The colocalization and inhibition experiments illustrated FITC-labeled HNTs were readily internalized into cells by both clathrin- and caveolae-dependent endocytosis, and the transport pathway of HNTs is an actin- and microtubule-associated process via Golgi apparatus and lysosome. Meanwhile, the cell cycle assay clarified that HNTs can prompt the intracellular transportation of gemcitabine and enhance the gemcitabine concentration in A549 tumor cells. Such elucidation of intracellular transport pathway of HNTs offers insights into the site-specific delivery and cellular internalization of HNTs, which provide a reasonable guidance for the design of novel drug delivery system.