Liquid/air accurate regulation has attracted growing attention in recent years for its diverse potential applications in bio-medicines, heat management, green energy, etc. Natural surfaces evolved innumerable hierarchical structures with exceptional functions to govern or regulate the liquid dynamic behaviors for their vital living, which have gradually been discovered as inspirations for creative design, such as fog harvesting, water fast transporting, and strong wet attachment. This review summarizes the current progress of bioinspired liquid/air regulations and their underlying mechanisms, including fast liquid/air spreading, liquid/air directional transport, and the interfacial liquid/air bridge acting forces. A fundamental understanding of both liquid/air dynamic behaviors on liquid–air–solid interfaces and their effects on the surface function has been increased with awareness of the importance of coupling effects from surface structures and material properties. The design principles and fabrication methods for bioinspired surface structure with unique liquid/air regulation are concluded, and several significant applications for electronics heat dissipation and biomedical devices are also presented. Finally, we provide new insights and future perspectives for the liquid/air regulation-based bioinspired functional materials.

Liquid transport regulation has attracted wide attention recently due to its potential applications in micro-fluidic devices, heat management, and mechanical engineering. Various liquid regulation strategies for direction guiding and speed enhancing have been developed with inspirations from nature, such as desert beetles and Nepenthes alata peristome with either gradient wettability or anisotropic structures, whereas their combined strategies for enhanced liquid regulations have barely been discussed due to the unclear coupling mechanisms. Herein, inspired by liquid transporting structure on Ligia exotica's leg, a smart flexible surface with gradient distributed and magnetized micro-cilia array is proposed to realize liquid spreading regulations in speed and direction. Different gradients and magnetic fields have been compared for liquid regulating performances, where the anisotropy ratio of liquid spreading could be enhanced from 0 on uniform surface to ∼0.3 on gradients surface, to even ∼0.6 by coupling magnetic field. The underlying liquid regulating mechanism has been established based on the mutual effects of liquid pinning and capillarity at different cilium inclined angles, cilium gap distance, and surface wettability. Finally, several liquid regulation applications are explored and offer potentials for fields of medicine and heat management.

Soft tissue sticking on electrosurgical scalpels in minimally invasive surgery can increase the difficulty of operation and easily lead to medical malpractice. It is significant to develop new methods for anti-sticking of soft tissue on electrosurgical scalpels. Based on the characteristics of biomimetic ultra-slippery surface, a self-lubricating slippery surface with wettability gradients on electrosurgical scalpel was designed and fabricated. Non-uniformly distributed cylindrical micro pillars, which constitute the wettability gradients, were prepared by an electrolytic etching process and the theoretic of the spontaneous liquid spreading process was analyzed. The silicophilic property of wettability gradients surface was modified by octadecyltrichlorosilane (OTS) self-assembling coat with biocompatible liquid lubricant dimethyl silicone oil. The contact angle of gradient’s surface at different temperatures was measured. The transportation behaviors of both water and dimethyl silicone oil on the wettability gradient’s surface were investigated; the results illustrate that the wettability gradient’s slippery surface can successfully self-lubricate from regions with low pillar density to regions with high pillar density, ascribed to the unbalanced Young’s force. The anti-sticking capability of the electrosurgical scalpel with self-lubricating slippery surface was tested. Both the adhesion force and adhesion mass under different cycles were calculated. The results suggest that the as-prepared slippery surface has excellent anti-sticking ability associated with better durability.

Porous structures can reduce the elastic modulus of implants, decrease stress shielding, and avoid bone loss in the alveolar bone and aseptic loosening of implants; however, there is a mismatch between yield strength and elastic modulus as well as biocompatibility problems. This study aimed to investigate the parametric design method of porous root-shaped implants to reduce the stress-shielding effect and improve the biocompatibility and long-term stability and effectiveness of the implants. Firstly, the porous structure part was parametrically designed, and the control of porosity gradient distribution was achieved by using the fitting relationship between porosity and bias and the position function of bias. In addition, the optimal distribution law of the porous structure was explored through mechanical and hydrodynamic analyses of the porous structure. Finally, the biomechanical properties were verified using simulated implant–bone tissue interface micromotion values. The results showed that the effects of marginal and central porosity on yield strength were linear, with the elastic modulus decreasing from 18.9 to 10.1 GPa in the range of 20–35% for marginal porosity, with a maximum decrease of 46.6%; the changes in the central porosity had a more consistent effect on the elastic modulus, ranging from 18.9 to 15.3 GPa in the range of 50–90%, with a maximum downward shift of 19%. The central porosity had a more significant effect on permeability, ranging from 1.9 × 10⁻⁷ m² to 4.9 × 10⁻⁷ m² with a maximum enhancement of 61.2%. The analysis showed that the edge structure had a more substantial impact on the mechanical properties. The central structure could increase the permeability more effectively. Hence, the porous structure with reasonable gradient distribution had a better match between mechanical properties and flow properties. The simulated implantation results showed that the porous implant with proper porosity gradient distribution had better biomechanical properties.

Reducing resistance to surface friction is challenging in the field of engineering. Natural biological systems have evolved unique functional surfaces or special physiological functions to adapt to their complex environments over centuries. Among these biological wonders, fish, one of the oldest in the vertebrate group, have garnered attention due to their exceptional fluid dynamics capabilities. Fish skin has inspired innovation in reducing surface friction due to its unique structures and material properties. Herein, drawing inspiration from the unique properties of fish scales, a periodic array of fish scales was fabricated by laser ablation on a polished aluminum template. The morphology of the biomimetic fish scale surface was characterized using scanning electron microscopy and a white-light interfering profilometer. Drag reduction performance was measured in a closed circulating water tunnel. The maximum drag reduction was 10.26% at a Reynolds number of 39,532, and the drag reduction performance gradually decreased with an increase in the distance between fish scales. The mechanism of the biomimetic drag reduction surface was analyzed using computational fluid dynamics. Streamwise vortices were generated at the valley of the biomimetic fish scale, replacing sliding friction with rolling friction. These results are expected to provide a foundation for in-depth analysis of the hydrodynamic performance of fish and serve as new inspiration for drag reduction and antifouling.