The micro-nano structures in nature contain endless functions, which bring new opportunities for the innovation and development of material science and engineering technology. Inspired by biological functional surfaces, many new applications have been developed for biomimetic surfaces, such as structural colors, superhydrophobicity, self-cleaning, and optical performance improvement. Femtosecond laser direct writing technology is a processing method that can accurately control the material structures in the micro-nano scale. By adjusting the femtosecond laser processing parameters, 3D processing beyond the diffraction limit can be realized in a variety of material systems. The unique feature of the femtosecond laser direct writing technology is that it can realize the cross-scale modification of materials, and prepare more complex micro-nano structures through simulation and optimization. In this review, the characteristics and processing advantages of femtosecond laser are first introduced, and then the applications of femtosecond laser in the fields of structural colors, superhydrophobicity, anti-reflection, and bionic compound eyes are described in detail. In addition, the applications of the femtosecond laser fabrication of bionic functional micro-nano structures in other fields are briefly illustrated. Finally, the development of the femtosecond laser fabrication of bionic functional micro-nano structures is prospected.

In the long and brutal process of natural selection and biological evolution, various organisms have evolved their own unique functions to adapt to the environment. With the help of microscopic imaging, it has been found that the surfaces of many organisms are covered with many micro-nano structures. It is the different characteristics of these micro-nano structures that enable the organisms to adapt to extreme living environments. In line with the principle of learning from nature, researchers have carried out a lot of research on the micro-nano structures of biological surfaces, using different processing methods to imitate the structures of organisms in a variety of material systems, realizing the structural colors of material surfaces, superhydrophobicity, anti-reflection, large field of view angles and other functions. At present, nano-imprint printing, 3D printing, plasma etching, photolithography, ultra-fast laser processing, and other technologies have been used to achieve the preparation of bionic functional micro-nano structures. Among them, the femtosecond laser processing technology has the characteristics of high precision, cold processing, and diffraction limit breaking, and has an obvious technical complementarity with the traditional processing methods. Nature may be said to be the guide to the extreme manufacturing of modern industry. Therefore, the bionic design born from learning from nature presents unique functional characteristics due to the micro-nano structures of their unique surfaces widely used in radar, submarine, aircraft, corrosion resistant coating, and self-cleaning occasions. The femtosecond laser direct writing technology is widely used in the controllable fabrication of bionic micro-nano structures. A femtosecond laser has two obvious characteristics. One is that the duration of a femtosecond laser pulse is very short, which inhibits the formation of thermal action zones around the laser focus area. The other is that a femtosecond laser has a very high peak power, which far exceeds that of the Coulomb field in atoms. This kind of technology is highly accurate, simple, and efficient. Compared with other micro-nano manufacturing technologies, it also has the advantage of good compatibility with materials. Bioinspired micro-nano surfaces have been widely concerned in the industrial field and the academic circles due to their wide application background, such as self-cleaning, oil-water separation, and fog collection. This paper reviews the new progress in the preparation of biomimetic functional micro-nano structures by a femtosecond laser, and shows their properties in structural colors, surface wettability, optical performance regulation, and so on. The potential application prospects of the femtosecond laser preparation of biomimetic functional surfaces in present and future are discussed.

Due to the limitation of the length of this article, other excellent femtosecond laser fabrication of bionic micro-nano functional structures and their applications cannot be introduced in detail. The femtosecond laser direct writing technology can be used to simulate and fabricate the surface micro-nano structures of lotus leaves, nepenthes plants, rice leaves, butterfly wings, and gecko fingerprints. These structures include micro-pores, micro-columns, periodic structures, and self-assembled structures. The microstructures can realize self-cleaning, anti-ice, oil-water separation, bubble manipulation, structure colors, fog collection, underwater bubble collection, droplet transport, shock resistance, adhesion, and other functions. In this paper, the applications of femtosecond laser direct writing to fabricate bionic functional micro-nano structures in structural colors, superhydrophobicity, and optical performance control are reviewed. The biological surface micro-nano structures have provided infinite inspiration for researchers and stimulated a large number of excellent works on the ultra-fast laser fabrication of bionic functional surfaces. However, there are still some problems, such as how to quickly and efficiently simulate complex natural surfaces and how to accurately reproduce cross-scale micro-nano structures. There is no doubt that the solution of these problems will further enhance the competitiveness of the femtosecond laser fabrication of bionic functional micro-nano structures. It is believed that with the improvement of femtosecond laser micro-nano manufacturing capability and the continuous new inspiration brought to us by nature, the bionic multi-functional surfaces should create more application value in biological, medical, environmental protection, and other fields in future. Finally, an example is given to illustrate the new application of the laser micro-nano fabrication of complex high-resolution structures.