Ultra-Strong and Tough Bacterial Nanocellulose Sheets and Fibers via Rotational Fluid Flow Assisted Shear Alignment

Bacterial nanocellulose (BC) has emerged as an excellent alternative candidate to non-biodegradable polymers due to the remarkable mechanical properties of its basic nano-fibrillar building blocks. However, full utilization of the mechanical properties in BC structures is yet to be achieved due to the challenge of alignment of the nanofibrils. Herein, we report a facile bottom-up fabrication technique for producing ultra-strong BC sheets by using shear alignment from fluid flow in a rotational culture device, which enables in-situ layer-by-layer deposition of anisotropic cellulose nanofibrils. Specifically, we introduce a custom-designed culture device where the cellulose-producing bacteria are cultured in a cylindrical oxygen-permeable incubator that is continuously spun using a central shaft to produce a directional fluid flow. This flow results in consistent directional motion of the bacteria that significantly improves nanofibril alignment in the bulk BC sheets. The BC sheets produced from the rotation culture device after stretching displayed specific tensile strength (up to ~ 1 GPa/g-cm^-3) and are comparable to the highest tensile strength of BC sheet ever reported yet showing excellent flexibility that allows forming into desired shapes. We show that the BC sheets can be twisted and stretched to make BC micro-fibers of ~200 <i>µ</i>m diameter with tensile strength of 1.3 GPa, the highest reported to date among strong natural fibers. We also compare the mechanical, environmental, and cost-effective aspects of the BC fiber with widely used structural fibers such as E-glass and lightweight steel, showing the superiority of BC fiber. This fabrication technique yielding highly aligned, ultra-strong BC sheets and fibers would pave the way toward extensive applications of BC in a range of bio-degradable structural and functional materials.