Contact Shape Controls Adhesion of Bioinspired Fibrillar Surfaces

Self Cite

We tested the adhesive response of polymer surfaces structured with arrays of cylindrical fibrils having diameters of 10 -20 mm and aspect ratios 1-2.4. Fibrils had two different tip shapes of end-flaps and round edges. A preloadinduced mechanical buckling instability of the fibrils was used to switch between the states of adhesion and non-adhesion. Non-adhesion in fibrils with round edges was reached at preloads that caused fibril buckling, whereas fibrils with end-flaps showed adhesion loss only at very high preloads. The round edge acted as a circumferential flaw prohibiting smooth tip contact recovery leading to an adhesion loss. In situ observations showed that, after reversal of buckling, the end-flaps unfold and re-form contact under prevailing compressive stress, retaining adhesion in spite of buckling. At very high preloads, however, end-flaps are unable to re-form contact resulting in adhesion loss. Additionally, the end-flaps showed varying contact adaptability as a function of the fibril -probe alignment, which further affects the preload for adhesion loss. The combined influence of preload, tip shape and alignment on adhesion can be used to switch adhesion in bioinspired fibrillar arrays.

Section: Fabrication Of Micropillars With End-flaps: Type 1 Fibrilssupporting

confidence: 76%

“…Thermal-strain-mismatch-induced cracking of SU-8 films was used to generate end-flaps (similar to mushroom-heads) on fibrils following the previous work of del Campo et al [11]. The photothermal cross-linking process in SU-8 is completed only after a post-exposure bake (T ¼ 958C) [12].…”

Section: Fabrication Of Micropillars With End-flaps: Type 1 Fibrilsmentioning

confidence: 99%

Preload-responsive adhesion: effects of aspect ratio, tip shape and alignment

Paretkar

Kamperman

Martina

et al. 2013

Self Cite

“…Isotropic microstructures often use unique geometries at the tips of the fibres to increase the adhesion, for example mushroom-shaped caps [31][32][33]. The performance of various tip shapes was characterized in previous work [34], showing that the mushroom shape enhances adhesion by several fold over a flat tip shape. Finally, anisotropic microstructures use the directional preference of the adhesive's shape, similar to the structures on a gecko toe, to turn adhesion on and off easily [35][36][37].…”

Section: Directional Dry Adhesivesmentioning

confidence: 99%

Improving controllable adhesion on both rough and smooth surfaces with a hybrid electrostatic/gecko-like adhesive

Ruffatto

Parness

Spenko

2014

119

This paper describes a novel, controllable adhesive that combines the benefits of electrostatic adhesives with gecko-like directional dry adhesives. When working in combination, the two technologies create a positive feedback cycle whose adhesion, depending on the surface type, is often greater than the sum of its parts. The directional dry adhesive brings the electrostatic adhesive closer to the surface, increasing its effect. Similarly, the electrostatic adhesion helps engage more of the directional dry adhesive fibrillar structures, particularly on rough surfaces. This paper presents the new hybrid adhesive's manufacturing process and compares its performance to three other adhesive technologies manufactured using a similar process: reinforced PDMS, electrostatic and directional dry adhesion. Tests were performed on a set of ceramic tiles with varying roughness to quantify its effect on shear adhesive force. The relative effectiveness of the hybrid adhesive increases as the surface roughness is increased. Experimental data are also presented for different substrate materials to demonstrate the enhanced performance achieved with the hybrid adhesive. Results show that the hybrid adhesive provides up to 5.1Â greater adhesion than the electrostatic adhesive or directional dry adhesive technologies alone.

“…However, these artificial adhesives with inclined micropillars demonstrated a relatively lower magnitude of interfacial friction and adhesion. This was because the micropillars did not have a laterally bulged, flat top tip, which has been regarded as an effective mechanism for enhancing adhesion and friction [4,[21][22][23][24]. To overcome this, Murphy et al proposed a micrometre-scale structure using an array of mushroom-shaped fibres, with titled stalks and laterally extended tip ends.…”

Section: Introductionmentioning

confidence: 99%

Rectangle-capped and tilted micropillar array for enhanced anisotropic anti-shearing in biomimetic adhesion

Wang

Tian

et al. 2015

Dry adhesion observed in the feet of various small creatures has attracted considerable attention owing to the unique advantages such as self-cleaning, adaptability to rough surfaces along with repeatable and reversible adhesiveness. Among these advantages, for practical applications, proper detachability is critical for dry adhesives with artificial microstructures. In this study, we present a microstructured array consisting of both asymmetric rectangle-capped tip and tilted shafts, which produce an orthogonal anisotropy of the shearing strength along the long and short dimensions of the tip, with a maximum anti-shearing in the two directions along the longer dimension. Meanwhile, the tilt feature can enhance anisotropic shearing adhesion by increasing shearing strength in the forward shearing direction and decreasing strength in the reverse shearing direction along the short dimension of the tip, leading to a minimum antishearing in only one of the two directions along the shorter dimension of the rectangular tip. Such a microstructured adhesive with only one weak shearing direction, leading to well-controlled attachment and detachment of the adhesive, is created in our experiment by conventional double-sided exposure of a photoresist followed by a moulding process.