Overview of the design of bionic fine hierarchical structures for fog collection.

Nature always uses its special wisdom to construct elegant and suitable schemes. Consequently, organisms in the flora and fauna are endowed with fine hierarchical structures (HS) to adapt to the harsh environment due to many years of evolution. Water is one of the most important resources; however, easy access to it is one the biggest challenges faced by human beings. In this case, fog collection (FC) is considered an efficient method to collect water, where bionic HS can be the bridge to efficiently facilitate the process of the FC. In this review, firstly, we discuss the basic principles of FC. Secondly, the role of HS in FC is analyzed in terms of the microstructure of typical examples of plants and animals. Simultaneously, the water-harvesting function of HS in a relatively new organism, fungal filament, is also presented. Thirdly, the HS design in each representative work is analyzed from a biomimetic perspective (single to multiple biomimetic approaches). The role of HS in FC, and then the FC performance of each work are analyzed in order of spatial dimension from a bionic perspective. Finally, the challenges at this stage and the outlook for the future are presented.