Roles of discontinuities in bio-inspired adhesive pads.
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ABSTRACT:
SUBMITTER: Chung JY
PROVIDER: S-EPMC1578261 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:BackgroundMany arachnids possess adhesive pads on their feet that help them climb smooth surfaces and capture prey. Spider and gecko adhesives have converged on a branched, hairy structure, which theoretically allows them to adhere solely by dry (solid-solid) intermolecular interactions. Indeed, the consensus in the literature is that spiders and their smooth-padded relatives, the solifugids, adhere without the aid of a secretion.Methodology and principal findingsWe investigated the adhesive contact zone of living spiders, solifugids and mites using interference reflection microscopy, which allows the detection of thin liquid films. Like insects, all the arachnids we studied left behind hydrophobic fluid footprints on glass (mean refractive index: 1.48-1.50; contact angle: 3.7-11.2°). Fluid was not always secreted continuously, suggesting that pads can function in both wet and dry modes. We measured the attachment forces of single adhesive setae from tarantulas (Grammostola rosea) by attaching them to a bending beam with a known spring constant and filming the resulting deflection. Individual spider setae showed a lower static friction at rest (26%±2.8 SE of the peak friction) than single gecko setae (Thecadactylus rapicauda; 96%±1.7 SE). This may be explained by the fact that spider setae continued to release fluid after isolation from the animal, lubricating the contact zone.SignificanceThis finding implies that tarsal secretions occur within all major groups of terrestrial arthropods with adhesive pads. The presence of liquid in an adhesive contact zone has important consequences for attachment performance, improving adhesion to rough surfaces and introducing rate-dependent effects. Our results leave geckos and anoles as the only known representatives of truly dry adhesive pads in nature. Engineers seeking biological inspiration for synthetic adhesives should consider whether model species with fluid secretions are appropriate to their design goals.
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Project description:The development of mussel-inspired materials with enhanced mechanical and physiological characteristics is fascinating due to the resulting structural properties. In this work, based on a chemical reaction, 3-(3,4-dihydroxyphenyl)propionic acid and dopamine hydrochloride (DA), with a catechol group, were covalently grafted onto a bio-compatible polymer backbone of chitosan hydrochloride (CHI) and hyaluronic acid sodium (HA). A mussel-inspired water-resistant adhesive film that could adhere in water was then fabricated by an environmentally friendly layer-by-layer (LbL) process. The water-resistant adhesive film demonstrated a strong underwater mechanical connection (0.82 ± 0.19 MPa) and a high transmittance (more than 83%) in the visible region; these characteristics are beneficial for clinical observation. A free-standing water-resistant adhesive film with a high transmittance of over 83% was also demonstrated and obtained from a facial and effective mechanical exfoliation method. The free-standing film exhibited favorable adhesion capacity with porcine skin, making it attractive for applications in the biomedical field.
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