Probing Antimicrobial Halloysite/Biopolymer Composites with Electron Microscopy: Advantages and Limitations

Abstract

Halloysite is a tubular clay nanomaterial of the kaolin group with a characteristic feature of oppositely charged outer and inner surfaces, allowing its selective spatial modification. The natural origin and specific properties of halloysite make it a potent material for inclusion in biopolymer composites with polysaccharides, nucleic acids and proteins. The applications of halloysite/biopolymer composites range from drug delivery and tissue engineering to food packaging and the creation of stable enzyme-based catalysts. Another important application field for the halloysite complexes with biopolymers is surface coatings resistant to formation of microbial biofilms (elaborated communities of various microorganisms attached to biotic or abiotic surfaces and embedded in an extracellular polymeric matrix). Within biofilms, the microorganisms are protected from the action of antibiotics, engendering the problem of hard-to-treat recurrent infectious diseases. The clay/biopolymer composites can be characterized by a number of methods, including dynamic light scattering, thermo gravimetric analysis, Fourier-transform infrared spectroscopy as well as a range of microscopic techniques. However, most of the above methods provide general information about a bulk sample. In contrast, the combination of electron microscopy with energy-dispersive X-ray spectroscopy allows assessment of the appearance and composition of biopolymeric coatings on individual nanotubes or the distribution of the nanotubes in biopolymeric matrices. In this review, recent contributions of electron microscopy to the studies of halloysite/biopolymer composites are reviewed along with the challenges and perspectives in the field.

Fireproof Nanocomposite Polyurethane Foams: A Review

“…Halloysite (or halloysite nanotubes (HNTs)) is a tubular (1D) aluminosilicate with the chemical formula Al 2 (OH) 4 Si 2 O 5 ·4H 2 O. Aluminosilicate nanosheets are rolled in such a way that the HNT exterior surface has a conner-shared tetrahedral SiO 4 layer, and thus, has a negative charge, whereas the nanotube lumen surface consists of an edge-shared octahedral AlO 6 layer and is positively charged [ 158 ]. Sepiolite nanofibers have a layer of magnesium ions with octahedral coordination and two layers of silica in a tetrahedron; the chemical formula of sepiolite is Mg 4 Si 6 O 15 (OH,F) 2 ·6H 2 O.…”

1,2,3-Oligotriazoles modified halloysite nanotubes as potential active biological species: synthesis and characterization

“…In the last years the use of scanning electron microscopy (SEM) to investigate the morphology of HNTs based nanomaterials has attracted attention due to the information which can be obtained by this technique. 31 Therefore, we imaged the surface morphology of the nanomaterials 4 and 6 by SEM (Figure 4). As it is possible to note, the tubular shape of the halloysite is maintained after the cycloaddition reaction.…”