| AVS 62nd International Symposium & Exhibition | |
| Biomaterial Interfaces | Tuesday Sessions |
| Session BI-TuP |
| Session: | Biomaterial Interfaces Poster Session |
| Presenter: | James Fowler, Oregon State University |
| Authors: | J.E. Fowler, Oregon State University J. Franz, Max Planck Institute for Polymer Research, Germany S. Gorb, University of Kiel, Germany T. Weidner, Max Planck Institute for Polymer Research, Germany J.E. Baio, Oregon State University |
| Correspondent: | Click to Email |
Humans have always marveled at the ability of insects to cling and climb along virtually any surface – whether it’s vertically up a wall or upside-down supporting masses orders of magnitude greater than their own. Many insects have adapted to a range of environmental surfaces by evolving a wet adhesion process that combines an expansive array of hairy contacts on their feet, known as setae, and an adhesive fluid that forms contact between the setae and a substrate. Previous studies of this adhesion mechanism have focused almost exclusively on the mechanical and kinematic aspects of adhesion, and not on the molecular interactions at the fluid – substrate interface. In the work presented here, we probe the molecular interactions between the adhesive fluid taken from lady beetles (Cocinella septempunctata) on two model substrates (deuterated-PMMA and deuterated-polystyrene) with vibrational sum frequency generation (SFG) spectroscopy and scanning electron microscopy (SEM). High-resolution SEM images of individual seta-fluid footprints on both sets of surfaces indicate localized water-oil emulsion de-wetting with no sign of distinct patterning within the footprint. SFG spectra collected at the C-H stretching region (2800-3100 cm-1) contain peaks at 2848 cm-1 and 2867cm-1, characteristic of symmetric CH2 and CH3 stretches, respectively. For the fluid on both the PMMA and polystyrene, we observe a large ratio of the 2867/2848 cm-1 peaks suggesting a well-ordered hydrocarbon monolayer with methyl groups oriented normal to the substrate. Spectra at the amide I stretching region (1500-1800 cm-1) collected from the PMMA-fluid sample contain a single peak at 1700 cm-1 indicating the presence of ordered free fatty acids; however, this signal is absent from the polystyrene-fluid spectra. Combined, this set of SFG spectra demonstrate that during adhesion to a polar surface, fatty acids within the fluid form a highly ordered layer at the substrate surface. While on a non-polar surface, the mechanism changes and some other hydrocarbon species present within the fluid orders at the interface.