Naoe Hosoda

In this study, a new synthetic procxe was proposed to solve the problems in the conventional copper‐free glycidyl triazolyl polymer (GTP) synthesis: (1) the explosion risk of the solid glycidyl azide polymer (GAP) and (2) large material loss of the electron‐deficient alkyne derivative. In order to demonstrate the superiority of the new synthetic procedure, five kinds of GTPs were synthesized with different types of alkyne derivatives. GAP was synthesized through the reaction between polyepichlorohydrin and sodium azide in N,N‐dimethylformamide. For handling impact‐ and friction‐sensitive solid GAP safely, it was purified through liquid–liquid extraction and stored as a stock solution without isolating it in the solid state. Through the new procedure utilizing a stock solution, the reaction efficiency in GTP synthesis was greatly improved, which resulted in reducing material loss (Feed ratio alkyne/azide: from 4.0 to 1.3) and reaction time (from 72 to 24 h). Thanks to the facile, efficient, and safe synthetic method, enough amounts of GTP samples could be prepared for characterizing not only physicochemical properties (density, molecular weight, glass transition temperature, thermal decomposition temperature, surface free energy) but also mechanical properties (Young's modulus, fracture stress and strain). The synthetic procedure reported herein will accelerate the research and development of functional GTPs with tunable physical properties.

Surface-activated bonding (SAB) of a 3D-printed Ti-6Al-4V pillar structure (fabricated by selective laser melting) to pure bulk aluminum at room temperature has been investigated. Argon beam irradiation was used to remove surface contaminants and “activate” the surfaces prior to bonding. The surface chemistry of the Ti-6Al-4V surface was analyzed using Electron Spectroscopy for Chemical Analysis (ESCA) to make sure any oxides had been removed by the irradiation procedure. The two materials were successfully bonded via SAB using special bonding apparatus, and scanning transmission electron microscopy (STEM) observation revealed a flat well-bonded interface with no obvious porosity. Furthermore, no thick reaction layer that could compromise the strength of the bond was evident. An oxide layer approximately 2 nm in thickness was observed at the interface by high-resolution TEM, but this is not considered sufficient to have a detrimental effect on bond integrity. The results of the investigation show that 3D-printed materials and structures can be successfully joined to aluminum by SAB techniques.

Many insects are able to walk vertically or upside down on both hard and soft surfaces. In beetles such as the ladybird (Coccinella septempunctata), intermolecular forces between tarsal setae on the footpads of the insects make this movement possible. In prior work, adhesion structures made from polydimethylsiloxane (PDMS) that mimic the action of the tarsal setae have been developed. It is proposed that these adhesion structures could be attached to a simplified version of the leg of a ladybird and used in practical applications. For example, the leg structures could potentially be employed in small surveillance drones to enable attachment to surfaces during flights, in order to preserve battery power. Alternatively, the structures could be used in small robotic devices to enable walking on steeply inclined surfaces. In this program of work, the morphology and movement of the leg of a ladybird were closely studied using a 3D X-ray microscope and a high-speed microscope. The positions of the tendons that facilitated movement were identified. From this knowledge, a simplified leg structure using pin-joints was designed and then fabricated using 3-D printing. The PDMS adhesion structures were then attached to the leg structure. The tendons in the actual insect leg were replicated using thread. Typical detachment forces of about 4 N indicated that the simplified leg structure was, in principle, more than capable of supporting the weight of a small device and then detach successfully. Attachment/detachment movement operations were performed using a linear actuator and controlled remotely. Therefore, proof of concept has been demonstrated for the use of such a simplified ladybird leg structure for the attachment/detachment of small robotic devices to horizontal, inclined, or vertical surfaces.

Why can beetles such as the ladybird beetle Coccinella septempunctata walk vertically or upside-down on a smooth glass plane? Intermolecular and/or capillary forces mediated by a secretion fluid on the hairy footpads have commonly been considered the predominant adhesion mechanism. However, the main contribution of physical phenomena to the resulting overall adhesive force has yet to be experimentally proved, because it is difficult to quantitatively analyse the pad secretion which directly affects the adhesion mechanism. We observed beetle secretion fluid by using inverted optical microscopy and cryo-scanning electron microscopy, which showed the fluid secretion layer and revealed that the contact fluid layer between the footpad and substrate was less than 10–20 nm thick, thus indicating the possibility of contribution of intermolecular forces. If intermolecular force is the main physical phenomenon of adhesion, the force will be proportional to the work of adhesion, which can be described by the sum of the square roots of dispersive and polar parts of surface free energy. We measured adhesion forces of ladybird beetle footpads to flat, smooth substrates with known surface free energies. The adhesive force was proportional to the square-root of the dispersive component of the substrate surface free energy and was not affected by the polar component. Therefore, intermolecular forces are the main adhesive component of the overall adhesion force of the ladybird beetle. The footpads adhere more strongly to surfaces with higher dispersive components, such as wax-covered plant leaves found in the natural habitat of ladybird beetles. Based on the present findings, we assume ladybird beetles have developed this improved performance as an adaptation to the variety of plant species in its habitat.

Footpads allow insects to walk on smooth surfaces. Specifically, liquid secretions on the footpad mediate adhesiveness through Van der Waals, Coulomb, and attractive capillary forces. Although the morphology and function of the footpad are well defined, the mechanism underlying their formation remains elusive. Here, we demonstrate that footpad hair in Drosophila is formed by the elongation of the hair cells and assembly of actin filaments. Knockdown of Actin5C caused a malformation of the hair structure, resulting in reduced ability to adhere to smooth substrates. We determined that functional footpads are created when hair cells form effective frameworks with actin filament bundles, thereby shaping the hair tip and facilitating cuticular deposition. We adapted this mechanism of microstructure formation to design a new artificial adhesive device⁠—a spatula-like fiber-framed adhesive device supported by nylon fibers with a gel material at the tip. This simple self-assembly mechanism facilitates the energy-efficient production of low-cost adhesion devices.

In recent years, the biomimetic potential of lignified or partially lignified fruit pericarps has moved into focus. For the transfer of functional principles into biomimetic applications, a profound understanding of the structural composition of the role models is important. The aim of this study was to qualitatively analyze and visualize the functional morphology of the coconut endocarp on several hierarchical levels, and to use these findings for a more precise evaluation of the toughening mechanisms in the endocarp. Eight hierarchical levels of the ripe coconut fruit were identified using different imaging techniques, including light and scanning electron microscopy as well as micro-computer-tomography. These range from the organ level of the fruit (H0) to the molecular composition (H7) of the endocarp components. A special focus was laid on the hierarchical levels of the endocarp (H3–H6). This investigation confirmed that all hierarchical levels influence the crack development in different ways and thus contribute to the pronounced fracture toughness of the coconut endocarp. By providing relevant morphological parameters at each hierarchical level with the associated toughening mechanisms, this lays the basis for transferring those properties into biomimetic technical applications.

これまでの接着・接合技術開発は，強固に接合することが信頼性の観点から重視されてきた。持続可能社会ではリサイクルを基調とした資源分別のために解体しやすいモノづくりが要求されており，接合部を簡単に分離できる新しい接着・接合技術の開発が求められている。本稿では，接着・剥離を自在に行っている生物の接着のしくみ及びそれをモデルとしたバイオミメティックな接着技術開発の現状について紹介する。

For the first time, we report the remarkable ability of the terrestrial leaf beetle Gastrophysa viridula to walk on solid substrates under water. These beetles have adhesive setae on their feet that produce a secretory fluid having a crucial role in adhesion on land. In air, adhesion is produced by capillary forces between the fluid-covered setae and the substrate. In general, capillary forces do not contribute to adhesion under water. However, our observations showed that these beetles may use air bubbles trapped between their adhesive setae to walk on flooded, inclined substrata or even under water. Beetle adhesion to hydrophilic surfaces under water was lower than that in air, whereas adhesion to hydrophobic surfaces under water was comparable to that in air. Oil-covered hairy pads had a pinning effect, retaining the air bubbles on their feet. Bubbles in contact with the hydrophobic substrate de-wetted the substrate and produced capillary adhesion. Additional capillary forces are generated by the pad's liquid bridges between the foot and the substrate. Inspired by this idea, we designed an artificial silicone polymer structure with underwater adhesive properties.