Development of Self-Attachable Microstructured Devices Based on Bioinspired Wing Tip Architectures

Abstract

Microstructured surfaces with diverse patterns are actively utilized for a wide range of advanced devices, such as flexible electronics, sensors, and microfluidics. Microstructures with unique patterns give microstructured devices a variety of functionality such as high stability on flexible substrates, transparency, and high sensor efficiency. To ensure high functionality and structural stability, they should form clean and conformal contact with various substrates with robust mechanical adhesion. However, microstructured surfaces generally hinder stable and close contact because they have a low contact area compared to planar surfaces. To overcome weak mechanical adhesion, the use of additional contact forming methods is essential. However, conventional contact forming methods, such as mechanical clampers, soldering, and chemical adhesives, form complicated, contaminated, and bulky contact interfaces. Additionally, the plasma bonding method, which is actively utilized for sealing microfluidics, has limitations in terms of the applicable substrate, and it is an irreversible process. Accordingly, the development of a new contact forming method is necessary. Herein, we present self-attachable microstructured devices with diverse patterned microstructures based on bioinspired wing tip architectures. Wing tips are applied in an easy, precise, and reproducible way through photolithography and replica molding processes. Contact forming based on wing tip architectures exhibited significant enhancement in mechanical adhesion, clean adhesion without residues, and high repeatability regardless of the patterns. In this thesis, the effect of wing tips on mechanical adhesion was demonstrated by measuring the adhesion strengths of diverse patterned microstructures. Also, adhesion strengths of diverse patterned microstructures with wing tips were measured and analyzed as functions of tip size, preload, and substrate. Diverse patterned microstructures with wing tips exhibited significantly higher adhesion strengths when compared to microstructures without wing tips for all cases of patterns, preloads, and substrates. Based on bioinspired wing tip architectures, we developed self-attachable flexible strain sensor as the first application. A self-attachable flexible strain sensor was designed and fabricated with three main components: serpentine patterns, wing tips, and multi-walled CNTs. Serpentine patterns increased electrical and structural stability in bending motion and wing tips increased the mechanical adhesion of the strain sensor. Additionally, multi-walled CNTs were used as conductive materials due to their excellent mechanical strength and flexibility. As a result, the strain sensors with wing tips exhibited stable sensing performance for bending motion with full attachment on PET film, whereas the strain sensors without wing tips exhibited poor sensing performance because of detachment. Subsequently, self-attachable microfluidic channels with wing tips were developed as the second application. The developed microfluidic channel was composed of loop double spiral patterned microstructures and bioinspired wing tip architectures. Based on the wing tip architectures, they exhibited strong adhesion strength and much better performance during the leakage and burst pressure tests than the structures without wing tips. In conclusion, self-attachable microstructured devices (flexible strain sensors, microfluidic channels) with bioinspired wing tip architectures were developed and experimentally demonstrated in this thesis. Based on the results of the thesis, bioinspired wing tip architectures are likely to be applied to various advanced microstructured devices to add universal self-attachability due to their simple and easy application.