Antimicrobial Nanomaterials Based on Halloysite Clay Mineral: Research Advances and Outlook

Abstract

Bacterial infections represent one of the major causes of mortality worldwide. Therefore, over the years, several nanomaterials with antibacterial properties have been developed. In this context, clay minerals, because of their intrinsic properties, have been efficiently used as antimicrobial agents since ancient times. Halloysite nanotubes are one of the emerging nanomaterials that have found application as antimicrobial agents in several fields. In this review, we summarize some examples of the use of pristine and modified halloysite nanotubes as antimicrobial agents, scaffolds for wound healing and orthopedic implants, fillers for active food packaging, and carriers for pesticides in food pest control.

Keywords: antibacterial; clay minerals; food packaging; halloysite nanotubes; orthopedic implants; pest control; wound healing.

Figure 1

Representation of 1:1 (TO) and 2:1 (TOT) arrangements in clay mineral structure. Reproduced with permission from [8].

Figure 2

SEM images of clay minerals: (a) pseudohexagonal crystals of kaolinite; (b) tubular crystals of halloysite; (c) spheroidal crystals of halloysite; (d) wavy subhedral montmorillonite crystals [9]; (e) flaky illite crystals; and (f) fibrous illite. Reproduced with permission from [10].

Figure 3

Cartoon representation of mechanisms that occur in the antibacterial activity of Al³⁺ and Fe²⁺ species of some clay minerals and bacteria. Reproduced with permission from [13].

Figure 4

Number of publications (papers, reviews, conference papers, notes, conference reviews) obtained by searching Scopus (October 2022) for the terms antibacterial activity and clay minerals and halloysite, respectively.

Figure 5

Comparison of the number of (a) scientific publications and (b) patents on the different applications fields of halloysite; (c) distribution (%) of scientific publications in “patent” and “journal” for halloysite. Data analysis of publications in October 2022 was performed using the SciFinder Scholar search system using searches for “Document type” the “Journal” and “Patent”, respectively.

Figure 6

A scheme of the nano–bio interface of HNTs and cells along with the relevant mechanisms and interactions. Reproduced with permission from [36].

Figure 7

Results from the agar diffusion assays are represented as a mean inhibition zone (in mm) against the different pathogens tested. (a) A. naeslundii; (b) F. nucleatum; (c) C. albicans; and (d) E. faecalis over time. Distinct letters indicate statistically significant differences between the groups when compared with the control. Reproduced with permission from [69].

Figure 8

Schematic showing the preparation process and application of Au@HNTs-chitin hydrogel. Reproduced with permission from [72].

Figure 9

Antibacterial activity of pectin/HNT/PO films against E. coli and S. aureus at 4, 37, and 65 °C incubated for 30 min. (a) Photographs of petri dishes; (b) viability (expressed as% bacterial viability) of E. coli and S. aureus onto pectin/HNT/CB[6]/PO films after incubation at the three different temperatures. Reproduced with permission from [76].

Figure 10

Fresh strawberry: (a) uncoated; (b) coated with pectin nanocomposite after 10 days of storage at room temperature, RH = 60%. Reproduced with permission from [77].

Figure 11

(a) Fluorescence images and (b) corresponding bacterial mortality data statistics of S. aureus co-cultured with different materials (PBS, cassia oil, rHNTs, and mHNTs). Scale bar 10 μm. Reproduced with permission from [82].

Figure 12

Schematic representation of the HNT/CPF pesticide. Reproduced with permission from [86].