High-strength, anisotropic bamboo hydrogel via in situ lignin modification for ion-selective transport and sensor

Biomass-based anisotropic hydrogels are severely limited in the practical production and applications due to the weak mechanical properties, time-consuming preparation process and toxic chemical reagents. Herein, a high-strength anisotropic bamboo-based hydrogel is fabricated via in situ lignin modification of natural bamboo and flexibility process, with directionally porous structure and superior mechanical properties. The lignin modification with an UV photocatalytic oxidation process maintains the heterostructure of natural bamboo and exposes polar groups, which provide the bonding sites for subsequent flexibility process. Then, the flexible polyacrylamide (PAM) molecular chains are polymerized in the modified bamboo (photonic bamboo) to construct superior-strength anisotropic bamboo/PAM composite hydrogel (BPCH). The synthesized BPCH has an axial tensile strength (123.5 MPa) and a Young's modulus (3.46 GPa) that significantly outdistance all previous biomass-based hydrogels. Benefiting from the unique porous micro-nanostructure, the BPCH serves as an excellent and stable nanofluidic channel for ion-selective transport and presents the ion conductivity of 5.75 × 10-4 S cm−1 at a low content. Additionally, the BPCH presents stable bending sensitivity to monitor both macroscopic and tiny human actions, such as finger bending, etc. This design offers a high-strength biomass templates and green process for next-generation anisotropic hydrogels, realizing the high value utilization of the bamboo in the micro/nanofluidic and sensor fields.