UC Irvine

Natural materials display a structural hierarchy that spans from the nano-scale to the macro-scale, with some of their unique properties partially driven by nanostructural anisotropy. In this research, we build upon our recently established technique of mechanically-directed assembly, examining its capacity to fabricate multi-functional, porous biopolymers with engineered anisotropy at the nano-scale in three dimensions. To do this, we employ 3D-printing technology to create complex molds made of silicone. Into these molds, we infiltrate cellulose and alginate prepolymer solutions, which are then allowed to solidify into a gel form. By subjecting these polymers to controlled exposure to a polar solvent, we can apply both precision mechanical strain and physical crosslinking to the polymers. This precisely applied strain leads to the programmability of anisotropy within the resultant material. In the final step of the process, we implement a critical-point drying technique, resulting in the formation of anisotropic, nanofibrillar aerogels. These aerogels display vibrant patterns of birefringence that are a direct result of the alignment of nanofibers within the material. Our method appears to be universally applicable across physically-crosslinked polymers. Additionally, it can be utilized to permanently align co-infiltrated functional nanowires within the polymers. In summary, our technique of mechanically-directed assembly allows for the simple, cost-effective production of hierarchical materials with meticulously engineered properties. These properties are structure-dependent and span the chemical and polymeric realm to include electronic, magnetic, and mechanical characteristics.