Bacterial Cellulose Nanocomposites: Morphology and Mechanical Properties

Abstract

Bacterial cellulose (BC) is a promising material for biomedical applications due to its unique properties such as high mechanical strength and biocompatibility. This article describes the microbiological synthesis, modification, and characterization of the obtained BC-nanocomposites originating from symbiotic consortium Medusomyces gisevii. Two BC-modifications have been obtained: BC-Ag and BC-calcium phosphate (BC-Ca3(PO4)2). Structure and physicochemical properties of the BC and its modifications were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and infrared Fourier spectroscopy as well as by measurements of mechanical and water holding/absorbing capacities. Topographic analysis of the surface revealed multicomponent thick fibrils (150–160 nm in diameter and about 15 µm in length) constituted by 50–60 nm nanofibrils weaved into a left-hand helix. Distinctive features of Ca-phosphate-modified BC samples were (a) the presence of 500–700 nm entanglements and (b) inclusions of Ca3(PO4)2 crystals. The samples impregnated with Ag nanoparticles exhibited numerous roundish inclusions, about 110 nm in diameter. The boundaries between the organic and inorganic phases were very distinct in both cases. The Ag-modified samples also showed a prominent waving pattern in the packing of nanofibrils. The obtained BC gel films possessed water-holding capacity of about 62.35 g/g. However, the dried (to a constant mass) BC-films later exhibited a low water absorption capacity (3.82 g/g). It was found that decellularized BC samples had 2.4 times larger Young’s modulus and 2.2 times greater tensile strength as compared to dehydrated native BC films. We presume that this was caused by molecular compaction of the BC structure.

Industrial-Scale Production and Applications of Bacterial Cellulose

“…The dry BC films show a higher Young's modulus of 428.0 ± 24.1 MPa but a decreased deformability (7.5 ± 0.4%; Pogorelova et al, 2020). After rehydration, the BC films represent a compromise Young's modulus of 250.4 ± 20.1 MPa and an elongation of 18.5 ± 0.8% (Pogorelova et al, 2020). The water holding capability of BC wet films ranges from 60 to 700 times of its dry weights (Portela et al, 2019).…”

“…It is demonstrated that BC has a very high wet tensile strength, although it varies depending on the genera and strains of bacteria as well as the fermentation conditions (Krystynowicz et al, 2002 ; Yuan et al, 2018 ). Recently, the mechanical properties of wet BC pellicles and dry films are well-determined by Natalia et al (Pogorelova et al, 2020 ). The wet BC pellicles have an average Young's modulus of 1.5 ± 0.3 MPa and an average elongation of 49.0 ± 3.6% (Pogorelova et al, 2020 ).…”

“…Recently, the mechanical properties of wet BC pellicles and dry films are well-determined by Natalia et al (Pogorelova et al, 2020 ). The wet BC pellicles have an average Young's modulus of 1.5 ± 0.3 MPa and an average elongation of 49.0 ± 3.6% (Pogorelova et al, 2020 ). The dry BC films show a higher Young's modulus of 428.0 ± 24.1 MPa but a decreased deformability (7.5 ± 0.4%; Pogorelova et al, 2020 ).…”

“…The wet BC pellicles have an average Young's modulus of 1.5 ± 0.3 MPa and an average elongation of 49.0 ± 3.6% (Pogorelova et al, 2020 ). The dry BC films show a higher Young's modulus of 428.0 ± 24.1 MPa but a decreased deformability (7.5 ± 0.4%; Pogorelova et al, 2020 ). After rehydration, the BC films represent a compromise Young's modulus of 250.4 ± 20.1 MPa and an elongation of 18.5 ± 0.8% (Pogorelova et al, 2020 ).…”

“…The key chemical profile of cellulose molecules is their plentiful hydroxyl groups existed along the polymer chain (one anhydroglucose has three hydroxyl groups; Ross et al, 1991 ). As a result, a large number of hydrogen bonds are formed between hydroxyl groups and oxygen atoms of anhydroglucose units (Pogorelova et al, 2020 ). The hydrogen bonding and van der Waals force promote a parallel stacking of cellulose molecules into crystalline nanofibers, which further assemble into cellulose microfibrils (Chen W. S. et al, 2018 ).…”