Stark Alyssa Y, McClung Brandon, Niewiarowski Peter H, Dhinojwala Ali
*Integrated Bioscience Program, The University of Akron, Akron, OH 44325, USA; Department of Polymer Science, The University of Akron, Akron, OH 44325, USA
*Integrated Bioscience Program, The University of Akron, Akron, OH 44325, USA; Department of Polymer Science, The University of Akron, Akron, OH 44325, USA.
Integr Comp Biol. 2014 Dec;54(6):1026-33. doi: 10.1093/icb/icu066. Epub 2014 Jun 17.
The gecko adhesive system is dependent on weak van der Waals interactions that are multiplied across thousands of fine hair-like structures (setae) on geckos' toe pads. Due to the requirements of van der Waals forces, we expect that any interruption between the setae and substrate, such as a water layer, will compromise adhesion. Our recent results suggest, however, that the air layer (plastron) surrounding the superhydrophobic toe pads aid in expelling water at the contact interface and create strong shear adhesion in water when in contact with hydrophobic surfaces. To test the function of the air plastron, we reduced the surface tension of water using two surfactants, a charged anionic surfactant and a neutral nonionic surfactant. We tested geckos on three substrates: hydrophilic glass and two hydrophobic surfaces, glass with a octadecyl trichlorosilane self-assembled monolayer (OTS-SAM) and polytetrafluoroethylene (PTFE). We found that the anionic surfactant inhibited the formation of the air plastron layer and significantly reduced shear adhesion to all three substrates. Interestingly, the air plastron was more stable in the nonionic surfactant treatments than the anionic surfactant treatments and we found that geckos adhered better in the nonionic surfactant than in the anionic surfactant on OTS-SAM and PTFE but not on glass. Our results have implications for the evolution of a superhydrophobic toe pad and highlight some of the challenges faced in designing synthetic adhesives that mimic geckos' toes.
壁虎的粘附系统依赖于微弱的范德华相互作用，这种相互作用通过壁虎脚趾垫上数千个细小的毛发状结构（刚毛）得以增强。由于范德华力的要求，我们预计刚毛与基质之间的任何中断，例如水层，都会损害粘附力。然而，我们最近的研究结果表明，超疏水脚趾垫周围的空气层（气盾）有助于在接触界面排出水分，并在与疏水表面接触时在水中产生强大的剪切粘附力。为了测试气盾的功能，我们使用了两种表面活性剂来降低水的表面张力，一种是带电荷的阴离子表面活性剂，另一种是中性非离子表面活性剂。我们在三种基质上对壁虎进行了测试：亲水性玻璃和两种疏水性表面，即带有十八烷基三氯硅烷自组装单分子层（OTS-SAM）的玻璃和聚四氟乙烯（PTFE）。我们发现阴离子表面活性剂抑制了气盾层的形成，并显著降低了对所有三种基质的剪切粘附力。有趣的是，在非离子表面活性剂处理中，气盾比在阴离子表面活性剂处理中更稳定，并且我们发现，在OTS-SAM和PTFE上，壁虎在非离子表面活性剂中的粘附性比在阴离子表面活性剂中更好，但在玻璃上并非如此。我们的研究结果对超疏水脚趾垫的进化具有启示意义，并突出了设计模仿壁虎脚趾的合成粘合剂所面临的一些挑战。
