Wet but non slippery (3): Bioinspired adhesives that work in humid and flooded conditions

• Applicants: Dr. Jon P. Barnes; Professor Dr. Hans-Jürgen Butt; Professorin Dr. Aránzazu del Campo Bécares; Professor Dr. Andreas Fery
• Subject Area: Synthesis and Properties of Functional Materials ; Biomaterials
• Term: from 2009 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 128737578

Tree and torrent frogs are able to adhere and move about their wet or even flooded environments without falling. The secret of their outstanding adhesive performance is the complex hierarchical structure of their attachment pads, including channels and protrusions of different length scales, different constitutional materials and a fluid secretion. Understanding the adhesion principles behind this original surface design opens the door to novel adhesion strategies for reversible attachment in artificial systems. Our collaborative project “Wet but non slippery” spans different fields like zoology, experimental physics and polymer chemistry expertise to lay the foundation for a rational design of such systems.During the first funding period of this proposal we made significant advances in the understanding the biological model, in no small way due to our advances in materials science providing both the tools and the theoretical background that complement the biological studies. In the second funding period we have added new design factors to build up hierarchical systems with additional functional levels like adhesion on-demand or adaptation to rough surfaces, including the dynamic variation of them during the attachment/detachment process. During the third funding period of our project we will focus on three main questions:1. The anisotropic morphology of the biological adhesive features and its role in mechanical stabilisation, directional adhesion/friction properties and detachment. We will investigate the morphology and arrangement (density, orientation, tilting angle) of the internal nanofribrils of the adhesive microstructures in the biological models, both in static and dynamic (i.e. under shear) conditions. We will build up artificial mimics where the microfeatures contain aligned nanofibrils. Adhesion/friction and mechanical measurements in these structures will help to clarify the role that oriented keratin fibers might have for directional and reversible attachment.2. The possible role of the blood vessels beneath the surface in inducing surface changes for triggering attachment or detachment. Studies in living animals and artificial mimics including embedded microchannels will be performed.3. Combining imaging, adhesion/friction measurements and novel mechanosensitive interfaces with theoretical modelling, we will more obtain detailed information on the acting forces and stress distribution maps in a wet soft contact situation at the micro, meso and nanoscale and during detachment.This information, together with our results from previous funding periods, will contribute to a fundamental understanding of how the superposition of material’s design factors and external forces acting in wet adhesives lead to optimized performance.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1420: Biomimetic Materials Research: Functionality by Hierarchical Structuring of Materials
• International Connection: United Kingdom