Mechanically-directed assembly of nanostructured biopolymer with tunable anisotropy, hierarchy, and functionality

Abstract

Natural materials exhibit nano- to macro-scale structural hierarchy, whose novel properties are partially driven by their underlying nanostructural anisotropy. Here we expand on our mechanically-directed assembly technique, studying its ability to synthesize porous biopolymers with engineered 3-dimensional hierarchy and material properties. 3D-printing is used to create complex silicone molds into which cellulose or alginate prepolymer solutions are infiltrated and allowed to gel. By exposing these molded polymers to controlled treatments of polar solvent, tunable contractions can be induced. This applies precision mechanical strain on polymers as they further cross-link, leading to tunable nanoscale anisotropy within materials. A final critical-point drying step produces anisotropic, nanofibrillar aerogels exhibiting vibrant patterns of birefringence. Such materials present enhanced mechanical modulus and toughness. This approach appears generalizable across physically crosslinked polymers and can additionally be used to permanently align functional nanowires within materials. Taken together, mechanically-directed assembly is a straightforward, low-cost process to synthesize hierarchical materials with engineered chemical, electromagnetic, and mechanical properties

Keywords

• Hydrogels
• Biopolymer
• Hierarchical materials
• Nanomaterials
• 3D-printing