Gecko-Inspired Biomimetic Surfaces with Annular Wedge Structures Fabricated by Ultraprecision Machining and Replica Molding

Anisotropic Stick-Slip Frictional Surfaces via Titania Nanorod Patterning

Nanoscale or microscale surface texturing is an effective technique to tailor the tribological properties between two surfaces that are rubbed against each other. In order to achieve the desired frictional properties by a patterned surface, one needs an in-depth understanding of the underlying mechanisms. Here, we demonstrate anisotropic stick-slip friction achieved via a nanotextured surface of tilted titania nanorods (TiNRs). The surface was developed by using the glancing angle deposition (GLAD) technique, and exhibited load-dependent variations in stick-slip friction as well as frictional anisotropy in different sliding directions. For studying the frictional properties of the newly developed surface, lateral force microscopy (LFM) was performed in three different reciprocal orientations (0° rotated, 45° rotated, 90° rotated) using a custom-made colloidal alumina atomic force microscopy (AFM) probe. The frictional behavior was found to vary significantly with the orientation. At 0° rotated position) a prominent "stick-slip" was observed when scanning opposite to the tilt direction, whereas the phenomenon reduced significantly when the nanotextured surface was scanned along the tilt direction or rotated to different angles (45 and 90°) with respect to the sliding direction of the AFM cantilever supporting the probe. The experimental findings were interpreted based on the classical solution for large deflections of tilted elastic rods. Overall, the textured surface, LFM-based frictional measurement, and the quantitative analysis presented here provide a fundamental understanding of how friction can be significantly varied on a surface patterned with tilted TiNRs at a length scale of about 1 μm, which can be comprehensively applied to nanorod patterns of other materials on different substrates.

Straightforward Fabrication of Double Roughness Structures on a Microcrystalline Film of a Diarylethene Derivative

Double roughness structure mimicking the surface of a lotus leaf was prepared using a newly synthesized diarylethene having a six-membered perfluorocyclohexene ring. The cubic-shaped crystals of the open-ring isomer, with sizes of approximately 7 μm, appeared immediately following solution casting. Upon UV irradiation, each cubic crystal was covered with needle-shaped crystals of the closed-ring isomer to form double roughness structures within 1 h. This structure could bear the continuous impact of water droplets.

Gecko-Inspired Controllable Adhesive: Structure, Fabrication, and Application

The gecko can achieve flexible climbing on various vertical walls and even ceilings, which is closely related to its unique foot adhesion system. In the past two decades, the mechanism of the gecko adhesion system has been studied in-depth, and a verity of gecko-inspired adhesives have been proposed. In addition to its strong adhesion, its easy detachment is also the key to achieving efficient climbing locomotion for geckos. A similar controllable adhesion characteristic is also key to the research into artificial gecko-inspired adhesives. In this paper, the structures, fabrication methods, and applications of gecko-inspired controllable adhesives are summarized for future reference in adhesive development. Firstly, the controllable adhesion mechanism of geckos is introduced. Then, the control mechanism, adhesion performance, and preparation methods of gecko-inspired controllable adhesives are described. Subsequently, various successful applications of gecko-inspired controllable adhesives are presented. Finally, future challenges and opportunities to develop gecko-inspired controllable adhesive are presented.

Bioinspired nanoplatforms for human-machine interfaces: Recent progress in materials and device applications

The panoramic characteristics of human-machine interfaces (HMIs) have prompted the needs to update the biotechnology community with the recent trends, developments, and future research direction toward next-generation bioelectronics. Bioinspired materials are promising for integrating various bioelectronic devices to realize HMIs. With the advancement of scientific biotechnology, state-of-the-art bioelectronic applications have been extensively investigated to improve the quality of life by developing and integrating bioinspired nanoplatforms in HMIs. This review highlights recent trends and developments in the field of biotechnology based on bioinspired nanoplatforms by demonstrating recently explored materials and cutting-edge device applications. Section 1 introduces the recent trends and developments of bioinspired nanomaterials for HMIs. Section 2 reviews various flexible, wearable, biocompatible, and biodegradable nanoplatforms for bioinspired applications. Section 3 furnishes recently explored substrates as carriers for advanced nanomaterials in developing HMIs. Section 4 addresses recently invented biomimetic neuroelectronic, nanointerfaces, biointerfaces, and nano/microfluidic wearable bioelectronic devices for various HMI applications, such as healthcare, biopotential monitoring, and body fluid monitoring. Section 5 outlines designing and engineering of bioinspired sensors for HMIs. Finally, the challenges and opportunities for next-generation bioinspired nanoplatforms in extending the potential on HMIs are discussed for a near-future scenario. We believe this review can stimulate the integration of bioinspired nanoplatforms into the HMIs in addition to wearable electronic skin and health-monitoring devices while addressing prevailing and future healthcare and material-related problems in biotechnologies.

Recent Progress on the Use of Stimulus-Responsive Materials for Dry Adhesive Applications

Stimulus-responsive dry adhesives, inspired by the adhesive mechanisms displayed by the fibrillar structures present on the feet of geckos, have emerged as a promising area of research for applications such as robotic grippers and climbing robots. These stimulus-responsive dry adhesives exhibit some unique capabilities, as their ability to adhere to and detach from surfaces can be controlled with the help of an external stimulus. For example, studies have developed magnetic field-responsive dry adhesives and show that the adhesion of these materials can be turned on and off by controlling the applied magnetic field. Light-responsive adhesives have also been developed and shown to reverse their adhesion using infrared light as the stimulus. Such materials show tremendous promise in pick-and-place systems for handling delicate objects and microelectronic products. The focus of this article is to review the stimulus-responsive materials that have been used to develop dry adhesives. The mechanisms adopted by these stimulus-responsive materials to switch their adhesion are discussed. Applications of stimulus-responsive dry adhesives are presented, and last, the future perspective of these materials is discussed.

Preparation and Hydrophobicity of Bionic Structures Based on Composite Infiltration Model

The wettability, surface energy, structure, and morphology of a material’s surface will affect the interaction process between the material and the organism. Moreover, these factors are not independent of each other, but will affect each other, which together determine the biological surface of the material. Although two classic theories of surface wettability control have been established, including the Wenzel model and the Cassie–Baxter model, the mechanism of the microstructure parameters on the surface wettability has not been considered. This paper established a two-dimensional mathematical model of the composite wetting pattern based on microstructure parameters, revealed the mechanism of the microstructure parameters on the surface wettability, and then used ultra-precision cutting and molding composite preparation methods to quickly and efficiently prepare bionic structures, and the hydrophobic character of the microstructure was characterized by the contact angle meter, which provides theoretical support and preparation technology for the modification of the hydrophobic character of the material.