Development of fabrication process for stepwise gradient wrinkle pattern

Abstract

Surface wrinkling has recently attracted much attention as a useful method for fabricating micro- and nano- groove structures due to its facile and cost effective fabrication process. Along with the straightforward fabrication process, the wrinkle patterns have been widely utilized in various applications, such as optical device, microfluidic device based on anisotropic wetting and cell culture platform. In these applications, the wrinkle patterns with different feature sizes exhibit different surface properties such as transmittance and anisotropic wetting characteristics. Therefore, many efforts have been made to find an optimal wrinkle wavelength which enables to obtain the desired surface property. However, many experimental tasks are needed to fabricate a number of wrinkle platforms with different wavelengths to determine an optimal wrinkle feature size. Thus, many studies tried to fabricate a gradient wrinkle pattern, which contain various wrinkle groove structures with different feature sizes in a single platform to reduce the experimental tasks. Though a gradient surface wrinkle pattern has drawn much interest recently, the previous efforts have been limited to the generation of continuous gradient patterns of surface wrinkle with gradually varying wavelengths. Here, we suggest a simple fabrication process for a stepwise gradient wrinkle pattern which has spatially-controlled discrete wavelengths in distinct regions with clear boundary on a polydimethylsiloxane (PDMS) substrate. The stepwise gradient wrinkle pattern is achieved based on the sequential oxygen plasma treatment for the PDMS surface using a glass plate as an effective blocking mask for the plasma, resulting in the modulation of plasma dose on the specific regions of the PDMS surface. The fabricated stepwise gradient wrinkle pattern was characterized by evaluating the difference of anisotropic wetting behavior and transmittance depending on wrinkle feature sizes. Furthermore, its possibility of application as the cell screening platform was verified by observing the endothelial differentiation of the human adipose-derived stem cells (hASCs) on the PS platform fabricated through the PUA replication and hot embossing process. This fabrication process can be easily implemented in various application such as microfluidics, optics and bioengineering investigating effects of the wrinkle patterns with a wide range of wavelengths.