Abstract: Natural surfaces have often served as blueprints for the design of highly functional engineered materials. Many of these natural surfaces consist of intricate micro/nano-architectures to achieve macroscopic functions, such as liquid repellency. Understanding the fundamental principles behind these natural surfaces will aid the design of super liquid-repellent materials for applications ranging from self-cleaning surfaces to anti-icing to anti-fouling coatings. Cutting-edge liquid-repellent materials are inspired by the lotus effect, where micro/nanoscale surface textures retain a thin air layer that enables liquid droplets to roll off the surface easily. However, the physical reasons for why these surface textures are micro/nano-sized have remained an open scientific question since 1944. In this talk, I will first discuss the science behind why micro/nano-textures are essential for maintaining the liquid repellency of many surfaces found in plants, insects, and animals. Following an example of the lotus effect, I will discuss two emergent classes of nature-inspired liquid repellent materials: Slippery Liquid-Infused Porous Surfaces (SLIPS) and Slippery Rough Surfaces (SRS). SLIPS is modelled after the slippery rim of a Nepenthes pitcher plant; whereas SRS is a cross-species bio-inspired material that combines the surface architectures of a pitcher plant and a lotus leaf. Both of these surfaces have resolved the longstanding limitations of the conventional liquid repellent materials in repelling complex biological fluids, maintaining low contact angle hysteresis, and functioning at high pressures. Perspectives on how nature-inspired materials may impact future applications in energy, water, and health will also be discussed.

Biosketch: Tak-Sing Wong is currently an Assistant Professor of Mechanical Engineering and Biomedical Engineering, and the holder of Wormley Family Early Career Professorship at The Pennsylvania State University. Dr. Wong was a Croucher Foundation Postdoctoral Fellow at the Wyss Institute for Biologically Inspired Engineering at Harvard University. He received his Ph.D. degree as an Intel Ph.D. Fellow (2009) in the Mechanical and Aerospace Engineering Department at UCLA, and his B.Eng. Degree (2003) in Mechanical Engineering from The Chinese University of Hong Kong (CUHK). Dr. Wong’s research focuses on surface and interface, micro- and nano-manufacturing, as well as designing biologically inspired materials with applications in energy, water, and health. His research has been published in Nature, Nature Materials, Nature Communications, and Proceedings of National Academy of Sciences USA (PNAS). His work on bio-inspired materials has been recognized with a 2012 R&D 100 Award, a National Science Foundation CAREER Award (2014), a DARPA Young Faculty Award (2014), as well as an invitation to the National Academy of Engineering’s U.S. Frontiers of Engineering symposium (2014). Recently, Dr. Wong has received the IEEE Early Career Award in Nanotechnology (2016), and the CUHK Faculty of Engineering Distinguished Alumni Award (2017). Dr. Wong has been named one of the world’s top 35 Innovators Under 35 (TR35) by MIT Technology Review for his contributions in bioinspired engineering.