Bamboo-inspired anisotropic hydrogels with enhanced mechanical properties <i>via</i> cellulose nanocrystal-reinforced heterostructures

Mimicking anisotropic materials is challenging due to their complex structural and mechanical properties. In this study, we developed biomimetic hydrogels that replicate the anisotropic characteristics of bamboo by incorporating cellulose nanocrystals (CNCs) into polyethylene glycol diacrylate (PEGDA) hydrogels. The inclusion of CNCs significantly enhanced the mechanical strength, with a 0.5% CNCs concentration increasing the modulus by 1.9 times, from 110 kPa to 208 kPa. By utilizing CNCs-doped regions to mimic the vascular bundles of bamboo and the undoped regions to represent the parenchyma tissue, we created biomimetic anisotropic hydrogels. These hydrogels displayed pronounced anisotropy, with the axial modulus exceeding the radial modulus, successfully demonstrating the creation of anisotropic materials. This method was also successfully applied to polyacrylic acid (PAA) hydrogels, further highlighting its versatility. These anisotropic biomimetic hydrogels exhibit distinct mechanical sensing properties in different directions, with the axial direction being 1.36 times more sensitive than the radial direction. This generalizable approach offers valuable insights for developing other anisotropic materials.