Among lizards and insects, Nature has evolved surface structures for controlled adhesion, tribology, and other surface properties that have no counterparts among man-made materials. The ability of lizards, for example, to adhere to a variety of rough and smooth surfaces using relatively stiff materials is remarkable. A common feature for contact and universal adhesion against an indeterminate surface, with important variations based on species, is the use of a hierarchical fibrillar structure with a plate-like spatular terminal element. It appears from recent studies that its unique surface properties, such as adhesion, tribology, and re-usability, result from optimized architectural design. This project aims to develop materials with fibrillar interfaces that mimic surface structures in lizards and insects. This work is being conducted jointly by three academic researchers working in close collaboration with an industrial research group at the DuPont Company. Their work requires the influence of several disciplines. Biological studies are undertaken to examine the details of the designs Nature has evolved and the materials she uses. The investigators develop theoretical models to understand how materials properties and architecture relate to performance. Phenomena that need to be understood are the enhanced contact compliance offered by these materials, constraints due to phenomena such as lateral collapse under the influence of surface forces, and mechanisms by which energy dissipation is enhanced during interfacial separation. These are converted into design criteria for biomimetic structures. The investigators fabricate fibrillar structures based on these design criteria using micro-lithographic techniques and test their performance as surfaces with useful properties. If successful in its ultimate aim, this program will provide society with an entirely new class of fastener materials. Anticipated properties, such as one-sidedness, re-usability, low rate-dependence, and designed directionality, form a unique set not accessible by extant fasteners, for example, pressure sensitive adhesives and hook/loop fasteners (e.g. Velcro). We expect the new material will find use in applications as diverse as apparel, semiconductor handling, and robotics. The project will train graduate students to work in a highly interdisciplinary manner. It balances high scientific quality and training with industrial relevance and interest.
