Hemicellulose-bacterial cellulose ribbon interactions affect the anisotropic mechanical behaviour of bacterial cellulose hydrogels

The aim of this study is to investigate the effect of hemicellulose-cellulose interactions on the anisotropic structure of the bacterial cellulose (BC) ribbon network. BC-arabinoxylan (BC-AX) and BC-mixed linkage glucan (BC-MLG) composites were prepared. The mechanical/rheological behaviour was evaluated by compression combined with small amplitude oscillatory shear (SAOS) and stress-relaxation tests. Microscopy revealed that the BC ribbons tended to orient parallel to the liquid/air interface. AX and MLG gathered on the surface of cellulose ribbons but had limited influence on the crystallinity of BC. BC hydrogels showed direction-dependent mechanical properties in compression and stress-relaxation tests. The peak compressive modulus of the tangential BC sample (compressed towards the side of the sample) was over 1000 kPa, whereas for the normal sample (compressed towards the top of sample) the value was only 280 kPa. The relaxation ability of the tangential sample was 48% lower than the normal sample at 1% compression ratio. AX and MLG reduced the anisotropic behaviour of the native BC in normal/tangential compression and stress-relaxation tests, especially in the highly-compressed composites. However, the rheological behaviour of BC and the composites was comparatively isotropic in SAOS. This study is beneficial for further understanding of the contribution of hemicelluloses to the mechanical properties of BC hydrogels, and may promote the application of BC-based materials in food and medical industries.