High Molecular Weight Mixed-Linkage Glucan as a Mechanical and Hydration Modulator of Bacterial Cellulose: Characterization by Advanced NMR Spectroscopy

Abstract

Bacterial cellulose (BC) consists of a complex threedimensional organization of ultrafine fibers which provide unique material properties such as softness, biocompatibility, and water-retention ability, of key importance for biomedical applications. However, there is a poor understanding of the molecular features modulating the macroscopic properties of BC gels. We have examined chemically pure BC hydrogels and composites with arabinoxylan (BC−AX), xyloglucan (BC−XG), and high molecular weight mixed-linkage glucan (BC−MLG). Atomic force microscopy showed that MLG greatly reduced the mechanical stiffness of BC gels, while XG and AX did not exert a significant effect. A combination of advanced solid-state NMR methods allowed us to characterize the structure of BC ribbons at ultra-high resolution and to monitor local mobility and water interactions. This has enabled us to unravel the effect of AX, XG, and MLG on the short-range order, mobility, and hydration of BC fibers. Results show that BC−XG hydrogels present BC fibrils of increased surface area, which allows BC−XG gels to hold higher amounts of bound water. We report for the first time that the presence of high molecular weight MLG reduces the density of clusters of BC fibrils and dramatically increases water interactions with BC. Our data supports two key molecular features determining the reduced stiffness of BC−MLG hydrogels, that is, (i) the adsorption of MLG on the surface of BC fibrils precluding the formation of a dense network and (ii) the preorganization of bound water by MLG. Hence, we have produced and fully characterized BC−MLG hydrogels with novel properties which could be potentially employed as renewable materials for applications requiring high water retention capacity (e.g. personal hygiene products).

Chemoenzymatic Synthesis of Fluorinated Cellodextrins Identifies a New Allomorph for Cellulose‐Like Materials**

“…RSA values of about 16–23 % were obtained for the three monofluorinated EpCs, with 3F‐EpC showing the highest value (23 %; Table S3). Although the 1 H‐ 13 C CP/MAS NMR experiments were not fully quantitative, similar RSA values have been determined before for BC [55] …”

“…The only noticeable difference was the presence of a broad peak at about 61 ppm, which is characteristic of a surface/disordered population of C6 ( s C6, Figure 5 D). [54, 55] Hence, the peak at 63 ppm represents the interior/ordered domains of C6 ( i C6, Figure 5 D). The s C6 broad peak is typically observed in bacterial cellulose (BC), which consists of cellulose particles containing both I α and I β crystalline domains and disordered regions [55] .…”

“… [54, 55] Hence, the peak at 63 ppm represents the interior/ordered domains of C6 ( i C6, Figure 5 D). The s C6 broad peak is typically observed in bacterial cellulose (BC), which consists of cellulose particles containing both I α and I β crystalline domains and disordered regions [55] . Indeed, surface/disordered and interior/ordered domains are typically found in nanocrystalline cellulose, [54] bacterial cellulose [55] and plant cell walls [56] .…”

Bottom-up Chemoenzymatic Synthesis Towards Novel Fluorinated Cellulose-like Materials

“…61 ppm, which is characteristic of a surface/disordered population of C6 (sC6, Figure 5d). 59,60 Hence, the peak at 63 ppm represents the interior/ordered domains of C6 (iC6, Figure 5d). The sC6 broad peak is typically observed in bacterial cellulose, which consists of cellulose particles containing both Ia and Ib crystalline domains and disordered regions.…”

“…The sC6 broad peak is typically observed in bacterial cellulose, which consists of cellulose particles containing both Ia and Ib crystalline domains and disordered regions. 60 Indeed, surface/disordered and interior/ordered domains are typically found in nanocrystalline cellulose (CNC) 59 , bacterial cellulose (BC) 60 and plant cell walls (PCWs) 61 . We note that the presence of a fluorine atom substituting the 3-hydroxyl group of glucose might affect the formation of the characteristic O3-O6 intra-chain hydrogen bond between adjacent glucose residues in cellulose II allomorph (Figure 5b).…”