A strategy to simultaneously realize topographic functionality and multipronged robustness of biomimetic surfaces

The research on biomimetic surfaces has been the source of various new principles in physics and materials sciences. It has been discovered that when a surface is featured with certain topographies, it can realize fascinating functions such as self-cleaning, anti-icing, anti-bacteria, drag-reduction, water harvesting, oil-water separation, power-free liquid transport, heat transfer improvement, and desalination. Whilst this field is continuously progressing, the lack of a strategy to produce a biomimetic surface that lasts a long time in real-world applications has been a longstanding challenge. In general, biomimetic surface functions require two essential components, the specific 3D surface topographies and the material chemistry at the liquid-solid interface. However, both components are highly susceptible to material failure caused by stress concentration, short penetration distance for invasive matters, and the easy change of surface nature. While biological surfaces can repair damages, normally manmade ones quickly lose their biomimetic functions in real applications. On the other hand, while progresses have been achieved in pursuing robustness of a water-repelling surface, related work appeared to suggest it is unavoidable to sacrifice the freedom in topography control and thus the biomimetic functions. To date, it remains an unresolved question whether it is possible simultaneously to enable versatile topographic functionality and long-term real-world robustness. The present study can present, we believe, a positive answer to this question.

Herein, we propose a new concept that there is at least one possible general approach to realize robust biomimetic surfaces; in other words, there need not to be a tradeoff between robustness and topographic functions. This concept will be applicable to most of biomimetic geometries reported. To realize multipronged robustness without sacrificing topography freedom, we suggest using a continuous piece of inert and anti-crack material to make the entire coating, with all topographic structures being part of this continuum. We developed an innovative 3D microfabrication method which enables a practical fabrication route for this principle. In this way, this surface is excellently resistant to heat/light/chemicals/aging/peeling owing to the intrinsic inertness of the material. On the other hand, based on the combination of theoretical modeling and experimental investigation we discovered a preliminary geometry guideline that endowed single-order pillar coatings to have outstanding mechanical robustness, which is different from the common assumption in previous reports. One key part of our new principle is that the inelastic deformation of surface structures could not only be accepted for biomimetic materials, but also be exploited to achieve excellent mechanical robustness. This is different from the common assumption that a material is considered to have failed once inelastic deformation occurs. Based on the capability of our method for precise 3D topography control on Teflon surface, in preliminary work we already managed to create three examples, with functionality and robustness performances comparable to or surpassing previous reports. To our best knowledge this is the first strategy to realize tailored topographic functionality and multi-level robustness at the same time. In this project we will conduct systematic investigation to understand this phenomenon, and fully develop this strategy into a general new approach in biomimetic surfaces. With robustness as an addition to functionality, we anticipate a large number of researchers to change their fundamental ideas on biomimetic surfaces and find new possibilities to create innovative functional materials and implement biomimetic technologies.