Use of Thin Sectioning (Nanoskiving) to Fabricate Nanostructures for Electronic and Optical Applications

This Review discusses nanoskiving—a simple and inexpensive method of nanofabrication, which minimizes requirements for access to cleanrooms and associated facilities, and which makes it possible to fabricate nanostructures from materials, and of geometries, to which more familiar methods of nanofabrication are not applicable. Nanoskiving requires three steps: 1) deposition of a metallic, semiconducting, ceramic, or polymeric thin film onto an epoxy substrate; 2) embedding this film in epoxy, to form an epoxy block, with the film as an inclusion; and 3) sectioning the epoxy block into slabs with an ultramicrotome. These slabs, which can be 30 nm–10 μm thick, contain nanostructures whose lateral dimensions are equal to the thicknesses of the embedded thin films. Electronic applications of structures produced by this method include nanoelectrodes for electrochemistry, chemoresistive nanowires, and heterostructures of organic semiconductors. Optical applications include surface plasmon resonators, plasmonic waveguides, and frequency-selective surfaces.Chemistry and Chemical Biolog

Miniature grating for spectrally-encoded endoscopy

Spectrally-encoded endoscopy (SEE) is an ultraminiature endoscopy technology that acquires high-definition images of internal organs through a sub-mm endoscopic probe. In SEE, a grating at the tip of the imaging optics diffracts the broadband light into multiple beams, where each beam with a distinctive wavelength is illuminated on a unique transverse location of the tissue. By encoding one transverse coordinate with the wavelength, SEE can image a line of the tissue at a time without using any beam scanning devices. This feature of the SEE technology allows the SEE probe to be miniaturized to sub-mm dimensions. While previous studies have shown that SEE has the potential to be utilized for various clinical imaging applications, the translation of SEE for medicine has been hampered by challenges in fabricating the miniature grating inherent to SEE probes. This paper describes a new fabrication method for SEE probes. The new method uses a soft lithographic approach to pattern a high-aspect-ratio grating at the tip of the miniature imaging optics. Using this technique, we have constructed a 500 μm-diameter SEE probe. The miniature grating at the tip of the probe had a measured diffraction efficiency of 75%. The new SEE probe was used to image a human finger and formalin fixed mouse embryos, demonstrating the capability of this device to visualize key anatomic features of tissues with high image contrast. In addition to providing high quality imaging SEE optics, the soft lithography method allows cost-effective and reliable fabrication of these miniature endoscopes, which will facilitate the clinical translation of SEE technology.Chemistry and Chemical Biolog

Patterning the Tips of Optical Fibers with Metallic Nanostructures Using Nanoskiving

Convenient and inexpensive methods to pattern the facets of optical fibers with metallic nanostructures would enable many applications. This communication reports a method to generate and transfer arrays of metallic nanostructures to the cleaved facets of optical fibers. The process relies on nanoskiving, in which an ultramicrotome, equipped with a diamond knife, sections epoxy nanostructures coated with thin metallic films and embedded in a block of epoxy. Sectioning produces arrays of nanostructures embedded in thin epoxy slabs, which can be transferred manually to the tips of optical fibers at a rate of approximately 2 min−1, with 88% yield. Etching the epoxy matrices leaves arrays of nanostructures supported directly by the facets of the optical fibers. Examples of structures transferred include gold crescents, rings, high-aspect-ratio concentric cylinders, and gratings of parallel nanowires.Chemistry and Chemical Biolog

Rapid fabrication of pressure-driven open-channel microfluidic devices in omniphobic RF paper

This paper describes the fabrication of pressure-driven, open-channel microfluidic systems with lateral dimensions of 45-300 microns carved in omniphobic paper using a craft-cutting tool. Vapor phase silanization with a fluorinated alkyltrichlorosilane renders paper omniphobic, but preserves its high gas permeability and mechanical properties. When sealed with tape, the carved channels form conduits capable of guiding liquid transport in the low-Reynolds number regime (i.e. laminar flow). These devices are compatible with complex fluids such as droplets of water in oil. The combination of omniphobic paper and a craft cutter enables the development of new types of valves and switches, such as “fold” valves and “porous switches,” which provide new methods to control fluid flow.Chemistry and Chemical Biolog

Robotic Tentacles with Three-Dimensional Mobility Based on Flexible Elastomers

Soft robotic tentacles that move in three dimensions upon pressurization are fabricated by composing flexible elastomers with different tensile strengths using soft lithographic molding. These actuators are able to grip complex shapes and manipulate delicate objects. Embedding functional components into these actuators (for example, a needle for delivering fluid, a video camera, and a suction cup) extends their capabilities.Engineering and Applied Science

The Influence of Airway Closure Technique for Right Pneumonectomy on Wall Tension During Positive Pressure Ventilation: An Experimental Study

Bronchopleural fistula (BPF) remains a significant source of morbidity and mortality after right pneumonectomy (RPN). Postoperative mechanical ventilation represents a primary risk factor for BPF. We undertook an experiment to determine the influence of airway diameter on suture line tension during mechanical ventilation after RPN. RPN was performed in 6 fresh human adult cadavers. After initial standard bronchial stump closure (BSC), the airway suture lines were subjected to 5 cm H2O incremental increases in airway pressures beginning at 5–40 cm H2O. To minimize airway diameter, a carinal resection was then performed with trachea to left main bronchial anastomosis and the airway suture lines subjected to similar incremental airway pressures. Wall tension (N/m) at the suture lines was measured using piezoresistive sensors at each pressure point. As delivered airway pressure increased, there was a concomitant increase in wall tension after BSC and carinal resection. At every point of incremental positive pressure, wall tension was however significantly lower after carinal resection when compared to BSC (P < 0.05). Additionally the differences in airway tension became even more significant with higher delivered airway pressure (P < 0.001). Airway diverticulum after BSC leads to significantly increased tension on the bronchial closure with positive airway pressure as compared to a closure which minimize airway diameter after RPN. This supports the role of Laplacian Law where small increases in airway diameter result in significant increases on closure site tension. Techniques which reduce airway diameter at the airway closure will more reliably reduce the incidence of BPF following RPN

Editorial for Special Issue on Flexible Electronics: Fabrication and Ubiquitous Integration

Based on the premise &#8220;anything thin is flexible&#8222;, the field of flexible electronics has been fueled from the ever-evolving advances in thin-film materials and devices. [...

Cross-scale design of energy dissipative composites using self-repairing interfaces based on sacrificial bonds

New composites with high energy dissipation and self-healing properties are required for structural materials, textiles, and protective equipment. This paper proposes a cross-scale strategy to design sacrificial bond composites (SBCs) using non-linear adhesive materials, like self-assembled proteins or mechanical adhesives, placed between opposite-facing magnets. Upon external loads, SBCs effectively dissipate deformation energy across their sacrificial bond interfaces following a biomimetic toughening mechanism similar to nacre’s. When the external load breaks the sacrificial bonds of a SBC, the opposite-facing magnets brings together the separated interface, allowing the reforming of its sacrificial bonds and the self-repairing of the composite after sustaining large strains. After mechanical failure at 600% strain, the consensus tetratricopeptide repeat (CTPR) protein films allows protein-based SBCs to recover 70% of their original tensile strength after letting their sacrificial bonds to reassemble for 1 h, at room temperature, in the presence of moisture. Mechanical adhesive-based SBCs, after their mechanical failure at 325% strain, are able to self-repair faster, regaining 85% of their tensile strength in less than 1 s. As a proof of concept, we demonstrate the fabrication of a reusable and lightweight fall arrest system exploiting mechanical adhesive interfaces and a protein-polyester yarn for the creation of high-energy dissipating textiles