Nanocellulose Sponges Containing Antibacterial Basil Extract

Abstract

Nanocellulose (NC) is a valuable material in tissue engineering, wound dressing, and drug delivery, but its lack of antimicrobial activity is a major drawback for these applications. In this work, basil ethanolic extract (BE) and basil seed mucilage (BSM) were used to endow nanocellulose with antibacterial activity. NC/BE and NC/BE/BSM sponges were obtained from nanocellulose suspensions and different amounts of BE and BSM after freeze-drying. Regardless of the BE or BSM content, the sponges started to decompose at a lower temperature due to the presence of highly volatile active compounds in BE. A SEM investigation revealed an opened-cell structure and nanofibrillar morphology for all the sponges, while highly impregnated nanofibers were observed by SEM in NC/BE sponges with higher amounts of BE. A quantitative evaluation of the porous morphology by microcomputer tomography showed that the open porosity of the sponges varied between 70% and 82%, being lower in the sponges with higher BE/BSM content due to the impregnation of cellulose nanofibers with BE/BSM, which led to smaller pores. The addition of BE increased the specific compression strength of the NC/BE sponges, with a higher amount of BE having a stronger effect. A slight inhibition of S. aureus growth was observed in the NC/BE sponges with a higher amount of BE, and no effect was observed in the unmodified NC. In addition, the NC/BE sponge with the highest amount of BE and the best antibacterial effect in the series showed no cytotoxic effect and did not interfere with the normal development of the L929 cell line, similar to the unmodified NC. This work uses a simple, straightforward method to obtain highly porous nanocellulose structures containing antibacterial basil extract for use in biomedical applications.

Keywords: antibacterial; basil extract; cellulose; microstructure; nanofibers; porosity.

Figure 1

Schematic representation of the synthesis of NC/BE and NC/BE/BSM sponges.

Figure 2

FT-IR spectra of nanocellulose—NC (A), basil extract—BE (B), and nanocellulose sponges with different proportions of BE or BE/basil mucilage (BSM) (C); FT-IR spectra in the region of 1800–1450 cm⁻¹ (D).

Figure 3

TG (A) and DTG (B) curves of unmodified NC (NC/BE 4/0), NC/BE, and NC/BE/BSM sponges.

Figure 4

SEM images of NC/BE sponges, magnification ×500: NC/BE 4/0 (A); NC/BE 4/2 (B); NC/BE 4/3 (C); NC/BE 4/4 (D).

Figure 5

SEM images of NC/BE and NC/BE/BSM sponges, magnification ×2000: NC/BE 4/0 (A); NC/BE 4/3 (B); NC/BE/BSM 4/3/2 (C); NC/BE 4/4 (D).

Figure 6

Micro-CT images of nanocellulose sponges containing different amounts of BE: BE 4/0 (A); BE 4/3 (B); BE 4/3/2 (C); BE 4/4 (D).

Figure 7

Micro-CT analysis: pore-size (A) and wall-thickness (B) distributions.

Figure 8

Compression stress—strain curves of NC, NC/BE, and NC/BE/BSM sponges (A); specific compression strength at 50% strain (B).

Figure 9

XRD patterns of NC (NC/BE 4/0), NC/BE (NC/BE 4/2, NC/BE 4/3, and NC/BE 4/4), and NC/BE/BSM 4/3/2 sponges.

Figure 10

Antibacterial activity of NC/BE 4/3 (A) and NC/BE 4/4 (B) against Staphylococcus aureus.

Figure 11

Cytotoxic effect of unmodified nanocellulose (NC/BE 4/0) (A) and NC/BE 4/4 (B) on the L929 fibroblast cell line.