One-shot stereolithography for biomimetic micro hemisphere covered with relief structure

Abstract

Biomimetic micro-structured surfaces have been attracting attention in recent years owing to their features, including optical reactivity, wetting property, and sliding property. One of the typical features of these functional structures is that densely arrayed dual-scale structures are present, such as several tens of micrometers of a hemisphere-like form covered with many several micrometer protrusions on the surface. A dual-scale structure similar to this is difficult to quickly and cheaply fabricate using existing methods: semiconductor process, micro stereolithography, and focused ion beam. In this research, a novel technique to fabricate a biomimetic hemisphere-like form covered with a relief structure is proposed. It utilizes the difference between the refractive indexes of two materials and the focusing cone-shaped light with a solid angle, which includes the critical angle formed when light enters from a side where the refractive index is higher than that of the other. In this situation, the refracted light radially expands. Thus, when the low-refractive-index medium is a photocurable resin, it is cured into a hemisphere-like form. In addition, properly modulating the light-intensity distribution of the incident light allows us to create many protrusions, such as a relief structure on the hemisphere surface. In this research, a theoretical model was constructed, and the proposed method was verified by simulation using Snell's law and the Lambert–Beer law. Moreover, apparatus to realize the proposed method was developed, and we practically verified that this method can fabricate a dual-scale structure such as a hemisphere-like form covered with a relief structure.