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Halloysite nanotubes (HNT) are naturally occurring clay nanotubes that can be used in advanced materials due to their unique hollow tubular structure, biodegradability, and mechanical and surface properties. However, alignment of these clay nanotubes is difficult due to the lack of direct methods.
​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​. Image credit: captureandcompose/Shutterstock.com
In this regard, an article published in the journal ACS Applied Nanomaterials proposes an efficient strategy for fabricating ordered HNT structures. By drying their aqueous dispersions using a magnetic rotor, clay nanotubes were aligned on a glass substrate.
As the water evaporates, the stirring of the GNT aqueous dispersion creates shear forces on the clay nanotubes, causing them to align in the form of growth rings. Various factors affecting HNT patterning were investigated, including HNT concentration, nanotube charge, drying temperature, rotor size, and droplet volume.
In addition to physical factors, scanning electron microscopy (SEM) and polarizing light microscopy (POM) have been used to study the microscopic morphology and birefringence of HNT wood rings.
The results show that when the HNT concentration exceeds 5 wt%, the clay nanotubes achieve perfect alignment, and a higher HNT concentration increases the surface roughness and thickness of the HNT pattern.
In addition, the HNT pattern promoted attachment and proliferation of mouse fibroblast (L929) cells, which were observed to grow along the clay nanotube alignment according to a contact-driven mechanism. Thus, the current simple and rapid method for aligning HNT on solid substrates has the potential to develop a cell-responsive matrix.
One-dimensional (1D) nanoparticles such as nanowires, nanotubes, nanofibers, nanorods and nanoribbons due to their outstanding mechanical, electronic, optical, thermal, biological and magnetic properties.
Halloysite nanotubes (HNTs) are natural clay nanotubes with an outer diameter of 50-70 nanometers and an inner cavity of 10-15 nanometers with the formula Al2Si2O5(OH)4·nH2O. One of the unique features of these nanotubes is a different internal/external chemical composition (aluminum oxide, Al2O3/silicon dioxide, SiO2), which allows their selective modification.
Due to biocompatibility and very low toxicity, these clay nanotubes can be used in biomedical, cosmetics and animal care applications because clay nanotubes have excellent nanosafety in various cell cultures. These clay nanotubes have the advantages of low cost, wide availability, and easy silane-based chemical modification.
Contact direction refers to the phenomenon of influencing cell orientation based on geometric patterns such as nano/micro grooves on a substrate. With the development of tissue engineering, the phenomenon of contact control has become widely used to influence the morphology and organization of cells. However, the biological process of exposure control remains unclear.
The present work demonstrates a simple process of formation of the HNT growth ring structure. In this process, after applying a drop of HNT dispersion to a round glass slide, the HNT drop is compressed between two contacting surfaces (the slide and the magnetic rotor) to become a dispersion that passes through the capillary. The action is preserved and facilitated. evaporation of more solvent at the edge of the capillary.
Here, the shear force generated by the rotating magnetic rotor causes the HNT at the edge of the capillary to deposit on the sliding surface in the correct direction. As the water evaporates, the contact force exceeds the pinning force, pushing the contact line towards the center. Therefore, under the synergistic effect of shear force and capillary force, after the complete evaporation of water, a tree-ring pattern of HNT is formed.
In addition, the POM results show the apparent birefringence of the anisotropic HNT structure, which the SEM images attribute to the parallel alignment of the clay nanotubes.
In addition, L929 cells cultured on annual-ring clay nanotubes with different concentrations of HNT were evaluated based on a contact-driven mechanism. Whereas, L929 cells showed random distribution on clay nanotubes in the form of growth rings with 0.5 wt.% HNT. In the structures of clay nanotubes with an NTG concentration of 5 and 10 wt %, elongated cells are found along the direction of the clay nanotubes.
In conclusion, macroscale HNT growth ring designs were fabricated using a cost-effective and innovative technique to arrange the nanoparticles in an orderly manner. The formation of the structure of clay nanotubes is significantly affected by the HNT concentration, temperature, surface charge, rotor size, and droplet volume. HNT concentrations from 5 to 10 wt.% gave highly ordered arrays of clay nanotubes, while at 5 wt.% these arrays showed birefringence with bright colors.
The alignment of the clay nanotubes along the direction of the shear force was confirmed using SEM images. With an increase in the NTT concentration, the thickness and roughness of the NTG coating increase. Thus, the present work proposes a simple method for constructing structures from nanoparticles over large areas.
Chen Yu, Wu F, He Yu, Feng Yu, Liu M (2022). A pattern of “tree rings” of halloysite nanotubes assembled by agitation is used to control cell alignment. Applied nanomaterials ACS. https://pubs.acs.org/doi/full/10.1021/acsanm.2c03255
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Bhavna Kaveti is a science writer from Hyderabad, India. She holds MSc and MD from the Vellore Institute of Technology, India. in organic and medicinal chemistry from the University of Guanajuato, Mexico. Her research work is related to the development and synthesis of bioactive molecules based on heterocycles, and she has experience in multi-step and multi-component synthesis. During her doctoral research, she worked on the synthesis of various heterocycle-based bound and fused peptidomimetic molecules that are expected to have the potential to further functionalize biological activity. While writing dissertations and research papers, she explored her passion for scientific writing and communication.
Cavity, Buffner. (September 28, 2022). Halloysite nanotubes are grown in the form of “annual rings” by a simple method. AZonano. Retrieved October 19, 2022 from https://www.azonano.com/news.aspx?newsID=39733.
Cavity, Buffner. “Halloysite nanotubes grown as ‘annual rings’ by a simple method”. AZonano. October 19, 2022 . October 19, 2022 .
Cavity, Buffner. “Halloysite nanotubes grown as ‘annual rings’ by a simple method”. AZonano. https://www.azonano.com/news.aspx?newsID=39733. (As of October 19, 2022).
Cavity, Buffner. 2022. Halloysite nanotubes grown in “annual rings” by a simple method. AZoNano, accessed 19 October 2022, https://www.azonano.com/news.aspx?newsID=39733.
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