Wettability is as a crucial physical and chemical property of solid surfaces. Surfaces with unique wettability, especially, attract considerable attention. Their significant impact spans various domains, including energy use, environmental protection, chemical engineering, healthcare, sustainable development, military defense, manufacturing, and agricultural breeding. Consequently, special wettability, particularly extreme wettability (i.e., superwettability), is emerging as a hot research topic in the field of micro- and nano-manufacturing. The study of superwettability originates from observing nature’s unique wetting phenomena and deeply investigating their formation mechanisms. Numerous plants and animals have evolved surfaces with special wetting properties to adapt to their environments. Inspired by natural superwettability, a range of micro/nano-manufacturing technologies have been employed to create various superwetting materials. These technologies include machining, photolithography, chemical etching, template replication, plasma etching, vapor deposition, electrochemical methods, the sol-gel process, electrospinning, electrochemical deposition, self-assembly, and spray/dip coating. Although existing microfabrication methods can produce superwetting structures with outstanding properties, traditional approaches face several technical challenges in achieving superwettability. These include complex preparation steps, constraints to specific substrate materials, and a lack of flexibility. Notably, most micromachining methods are limited to processing certain materials (for example, lithography is restricted to photosensitive polymers) or struggle with the precise design of micro/nanostructures (such as chemical etching, which can rapidly create large areas of uniform microstructures but faces difficulties in patterning these structures). These limitations significantly hinder the practical application of surfaces with engineered superwettability. Developing a versatile microfabrication technology capable of preparing various superwetting surfaces remains a significant challenge.

The characteristics of ultrashort pulse width and ultrahigh peak power establish femtosecond lasers as pivotal tools in modern extreme and ultra-precision manufacturing. Given that surface microstructure significantly influences the wettability of solid materials, femtosecond laser processing can create a variety of superwettability by constructing specialized microscale and nanoscale structures on material surfaces. Superhydrophilicity can be realized by forming sufficiently rough microstructures on inherently hydrophilic materials. In the case of superhydrophobicity, materials are generally categorized into two types. For intrinsically hydrophobic materials, superhydrophobicity can be directly achieved by preparing hierarchical micro/nanostructures on the substrate surfaces. For inherently hydrophilic materials, after forming surface microstructures with a femtosecond laser, it is often necessary to further reduce the surface energy via chemical modification. On a superhydrophilic surface, water droplets spread rapidly, while a superhydrophobic surface functions to repel water, offering waterproofing. Superoleophobic surfaces are categorized into two types, effective in air and underwater, respectively. To create superoleophobic surfaces in air, re-entrant bending microstructures are introduced, combined with stringent low-surface-energy chemical modifications. These microstructures are directly crafted onto the surface of hydrophilic substrates to realize underwater superoleophobicity. Superoleophobic surfaces repel oily liquids and some organic liquids with low surface energy. Generally, superhydrophilic surfaces exhibit superaerophobicity underwater, and superhydrophobic surfaces demonstrate superaerophilicity underwater. The superaerophobic surface effectively repels bubble adhesion, while the superaerophilic surface can adsorb tiny bubbles in water. Slippery surfaces created using femtosecond laser-induced porous network microstructures enable droplet contact with the material surface in a liquid/liquid mode, repelling various liquids. Underwater superpolymphobicity is achieved by constructing micro/nanostructures on the surface of hydrophilic materials. This property is useful for preventing the adhesion of liquid polymers to solid materials and assisting in the design of polymer shapes. Irrespective of superhydrophobicity or superhydrophilicity, femtosecond laser-induced microstructures exhibit supermetalphobicity. By designing patterned microstructures on the surface of flexible materials using a femtosecond laser, liquid metals can be transformed into circuits, enabling the creation of flexible electronic devices. Superwetting surfaces with controllable adhesion are achievable through the femtosecond laser-based design of surface micro/nanostructures. The adhesion level of these prepared surfaces to droplets can range from very low to very high. Anisotropic wettability is attainable on the anisotropically structured surfaces crafted by the femtosecond laser. Reversibly switchable wettability on these laser-structured surfaces can be achieved through three approaches: adjusting surface chemistry, modifying surface microtopography, and altering the ambient environment. The special wettability endows femtosecond laser-treated materials with a range of practical applications, such as waterproofing, self-cleaning, droplet manipulation, liquid patterning, buoyancy enhancement, tiny drop and bubble release, oil-water separation, water/gas separation, anti-icing, anti-corrosion, underwater drag reduction, water/fog collection, microfluidics, flexible circuits/electronics, cell engineering, biomedical engineering, seawater desalination, surface-enhanced Raman scattering, and more.

This review comprehensively outlines the advancements in femtosecond laser processing for manipulating the surface wettability of materials. By employing femtosecond lasers to design micro/nanostructures on various material surfaces, a range of unique wettabilities has been achieved. These include superhydrophilicity, superhydrophobicity, superoleophobicity, underwater superaerophobicity and superaerophilicity, slippery liquid-infused porous surfaces, underwater superpolymphobicity, supermetalphobicity, controllable adhesion, anisotropic wettability, and smart switchable wettability. The practical applications of these femtosecond laser-structured superwetting materials have been diverse and significant.

Currently, the technology of femtosecond laser-controlled surface wettability faces several challenges. A major bottleneck is processing efficiency, which still restricts the broader application of femtosecond laser micromachining technology. Despite new strategies such as laser parallel processing and light-field regulation, efficiency falls short of industrial application requirements. Additionally, if the laser focus deviates significantly from the material surface, then the desired microstructures cannot be effectively prepared. This defocusing issue also makes it difficult to create uniform superwetting micro/nanostructures on complex curved surfaces. Moreover, similar to surfaces prepared by other methods, femtosecond laser-induced superwettability surfaces encounter stability issues in practical applications. These surfaces often lose their initial extreme wettability when exposed to friction or specific operating environments. Thus, future research in this field should address these bottlenecks, enhancing the practicality and scalability of superwetting materials prepared by femtosecond lasers for real-world applications.