R. Copier

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Master thesis (1)

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Adhesive mechanisms and the role of positional adjustment on tree frog toe pads

Master thesis (2021) - R. Copier , D. Dodou , A. Sakes , R.A.J. van Ostayen , Julian K.A. Langowski

Objective: this paper aims to evaluate the adhesive and frictional properties of the keratinised epithelium on the adhesive pads of tree frogs. Modeling methods: two modeling methods have been developed. One of these methods involves the implementation of discrete fibres in a relatively compliant material matrix while the other method involves an anisotropic hyperelastic material model developed by Holzapfel et al. (HGO model). The adhesional and frictional behaviour of an epithelial cell is evaluated for the contact forces at the interface between the adhesive pads and the interface. These forces are dependent on the tree frog behaviour, which consists of proximal pulling on the limbs and adjustments in the body posture and the position of the limbs. Modeling results: a higher fibre density and fibre-matrix bonding is found to increase adhesive performance. An increase in the fibre-matrix stiffness ratio is found to be beneficial for adhesional performance, while an optimum value for this ratio is found for the frictional performance. The modeling results show that the proximal pulling on the limbs by the tree frog without positional adjustment has no significant effect on the adhesive and frictional performance. An adjustment in the body posture and the position of the limbs, however, is found to significantly increase the adhesive and frictional performance. Experimental methods: samples that mimic the tree frog epithelial composite structure are fabricated. These samples consist of a polydimethylsiloxane (PDMS) material matrix in which acrylonitril-butadieen-styreen (ABS) fibres are embedded. Experiments are performed to measure the frictional and adhesive performance of these samples. The experimental results are used to confirm the modelled results on the influence of the fibre-matrix stiffness ratio and the fibre density. Experimental results: for adhesion, the model results are in agreement with the experimental results. For the frictional response, the agreement between the model results and experimental results is less strong.