Wood and other plants perform photosynthesis to produce sugars, which can be used as an energy source, but also as a structural building block in living cells [1,2]. Nano-sized cellulose fibrils (nanofibrils) are enzymatically built from photosynthesis-generated sugars and are the main reinforcing unit of plant cell walls, with high aspect ratios and individual tensile strength several times higher than iron (see Figure 1 ). Nanofibrils consist of repeating regions of cellulose crystallites that provide strength, connected by amorphous sections of cellulose that yield flexibility. They bond to form larger macro-sized fibrils (macrofibrils). Macrofibrils and nanofibrils are immersed in ...