Polydimethylsiloxane based dry adhesives produced using a replica molding technique.

Dry adhesives have gained considerable interest due to their applications in a wide variety of areas. This study used a replica molding technique to produce micron-sized pillars on the surface of polydimethylsiloxane (PDMS) and investigated their dry adhesion behaviour. Shear adhesion for the produced samples is measured using a tensile testing machine.

Evaluation of Physicochemical Properties of a Hydroxyapatite Polymer Nanocomposite for Use in Fused Filament Fabrication.

Over the last decade, there has been an increasing interest in the use of bioceramics for biomedical purposes. Bioceramics, specifically those made of calcium phosphate, are commonly used in dental and orthopaedic applications. In this context, hydroxyapatite (HA) is considered a viable option for hard tissue engineering applications given its compositional similarity to bioapatite.

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.

Rose Petal Mimetic Surfaces with Antibacterial Properties Produced Using Nanoimprint Lithography.

In this study, we produced bioinspired micro/nanotopography on the surface of poly(vinylidene fluoride--hexafluoropropylene) (PVDF-HFP) films and demonstrated that these films display antibacterial properties. In the first step, structures that are found on the surface of a rose petal were copied on the surface of PVDF-HFP films. Following this, a hydrothermal method was used to grow ZnO nanostructures on top of this rose petal mimetic surface.

Biomimetic Rose Petal Structures Obtained Using UV-Nanoimprint Lithography.

This study aims to produce a hydrophobic polymer film by mimicking the hierarchical micro/nanostructures found on the surface of rose petals. A simple and two-step UV-based nanoimprint lithography was used to copy rose petal structures on the surface of a polyurethane acrylate (PUA) film. In the first step, the rose petal was used as a template, and its negative replica was fabricated on a commercial UV-curable polymer film.

Modeling Impact Mechanics of 3D Helicoidally Architected Polymer Composites Enabled by Additive Manufacturing for Lightweight Silicon Photovoltaics Technology.

When silicon solar cells are used in the novel lightweight photovoltaic (PV) modules using a sandwich design with polycarbonate sheets on both the front and back sides of the cells, they are much more prone to impact loading, which may be prevalent in four-season countries during wintertime. Yet, the lightweight PV modules have recently become an increasingly important development, especially for certain segments of the renewable energy markets all over the world-such as exhibition halls, factories, supermarkets, farms, etc.-including in countries with harsh hailstorms during winter.

Characterising Penetrometer Tip Contact during Concrete Condition Assessment.

Concrete condition-assessing penetrometers need to be able to distinguish between making contact with a hard (concrete) surface as opposed to a semi-solid (corroded concrete) surface. We investigated whether different shaped tips of a cylindrical penetrometer were better than others at maintaining contact with concrete and not slipping. We designed a range of simple symmetric tip shapes, controlled by a single superellipse parameter.

Impact-Resistant and Tough 3D Helicoidally Architected Polymer Composites Enabling Next-Generation Lightweight Silicon Photovoltaics Module Design and Technology.

Lightweight photovoltaics (PV) modules are important for certain segments of the renewable energy markets-such as exhibition halls, factories, supermarkets, farms, etc. However, lightweight silicon-based PV modules have their own set of technical challenges or concerns. One of them, which is the subject of this paper, is the lack of impact resistance, especially against hailstorms in deep winter in countries with four seasons.

Helicoidally Arranged Polyacrylonitrile Fiber-Reinforced Strong and Impact-Resistant Thin Polyvinyl Alcohol Film Enabled by Electrospinning-Based Additive Manufacturing.

In this study, we demonstrate the use of parallel plate far field electrospinning (pp-FFES) based manufacturing system for the fabrication of polyacrylonitrile (PAN) fiber reinforced polyvinyl alcohol (PVA) strong polymer thin films (PVA SPTF). Parallel plate far field electrospinning (also known as the gap electrospinning) is generally used to produce uniaxially aligned fibers between the two parallel collector plates. In the first step, a disc containing PVA/H2O solution/bath (matrix material) was placed in between the two parallel plate collectors.

Tensile Properties of Composite Reinforced with Three-Dimensional Printed Fibers.

This study used melt-electrospinning writing to fabricate three-dimensional fiber constructs by embedding them in a polyvinyl alcohol (PVA) matrix to obtain thin composite films. Fourier transform infrared spectroscopy (FTIR) and dynamic scanning calorimetry (DSC) were used to demonstrate an interaction between the polycaprolactone (PCL) fibrous phase and the PVA matrix phase. Following this, the mechanical deformation behavior of the composite was investigated, and the effect of reinforcement with three-dimensional fibrous constructs was illustrated.

Emerging Developments in the Use of Electrospun Fibers and Membranes for Protective Clothing Applications.

There has been increased interest to develop protective fabrics and clothing for protecting the wearer from hazards such as chemical, biological, heat, UV, pollutants etc. Protective fabrics have been conventionally developed using a wide variety of techniques. However, these conventional protective fabrics lack breathability.

Inner Profile Measurement for Pipes Using Penetration Testing.

Penetration testing has been used to measure material properties for over fifty years. Currently, it is under-utilised as a contemporary scientific and engineering tool for investigating the condition of pipes whose inner surface has been exposed to chemical attack. We describe the design, development and calibration of a portable probe which uses a penetrative strain gauge load cell to measure where the semi-solid surface starts and stops within a pipe.

Electrospun Silver Coated Polyacrylonitrile Membranes for Water Filtration Applications.

The scarcity of drinking water and the contamination of water sources in underdeveloped countries are serious problems that require immediate low-tech and low-cost solutions. In this study, we fabricated polyacrylonitrile (PAN) porous membranes coated with silver nanoparticles (AgNP) and demonstrated their use for water filtration and water treatment applications. The membranes were prepared by electrospinning a PAN solution and treating in a hydroxylamine (NH₂OH) aqueous solution to form ⁻C(NH₂)N⁻OH groups that were used for functionalization (Ag⁺ ions) of the membrane.

Gecko-Inspired Dry Adhesive Based on Micro-Nanoscale Hierarchical Arrays for Application in Climbing Devices.

The unusual ability of geckos to climb vertical walls underlies a unique combination of a hierarchical structural design and a stiffer material composition. While a dense array of microscopic hierarchical structures enables the gecko toe pads to adhere to various surfaces, a stiffer material (β-keratin) composition enables them to maintain reliable adhesion over innumerable cycles. This unique strategy has been seldom implemented in engineered dry adhesives because fabrication of high-aspect-ratio hierarchical structures using a stiffer polymer is challenging.

Measuring the Pull-Off Force of an Individual Fiber Using a Novel Picoindenter/Scanning Electron Microscope Technique.

We employed a novel picoindenter (PI)/scanning electron microscopy (SEM) technique to measure the pull-off force of an individual electrospun poly(vinylidene fluoride) (PVDF) fibers. Individual fibers were deposited over a channel in a custom-designed silicon substrate, which was then attached to a picoindenter. The picoindenter was then positioned firmly on the sample stage of the SEM.

Thermoresponsive Cellulose Acetate-Poly(N-isopropylacrylamide) Core-Shell Fibers for Controlled Capture and Release of Moisture.

In this study, we used core-shell electrospinning to fabricate cellulose acetate-poly(N-isopropylacrylamide) (CA-PNIPAM) fibrous membranes and demonstrated the ability of these fibers to capture water from a high humid atmosphere and release it when thermally stimulated. The wettability of the fibers was controlled by using thermoresponsive PNIPAM as the shell layer. Scanning electron and fluorescence microscopes are used to investigate the microstructure of the fibers and confirm the presence of the core and shell phases within the fibers.

Cellulose Acetate-Poly(N-isopropylacrylamide)-Based Functional Surfaces with Temperature-Triggered Switchable Wettability.

Temperature-triggered switchable nanofibrous membranes are successfully fabricated from a mixture of cellulose acetate (CA) and poly(N-isopropylacrylamide) (PNIPAM) by employing a single-step direct electrospinning process. These hybrid CA-PNIPAM membranes demonstrate the ability to switch between two wetting states viz. superhydrophilic to highly hydrophobic states upon increasing the temperature.

Bio-inspired electrospun micro/nanofibers with special wettability.

Inspired by the extreme wetting states displayed by the natural materials, various techniques have been widely investigated to fabricate superhydrophobic and superhydrophilic surfaces. Electrospinning has gained huge amount of interest as fibers with suitable combination of surface chemistry and surface roughness can be easily obtained. This study provides a comprehensive overview of the progress that has been made on electrospun fibers that display superhydrophobicity, superhydrophilicity or a combination of both.

Use of facile mechanochemical method to functionalize carbon nanofibers with nanostructured polyaniline and their electrochemical capacitance.

A facile approach to functionalize carbon nanofibers [CNFs] with nanostructured polyaniline was developed via in situ mechanochemical polymerization of polyaniline in the presence of chemically treated CNFs. The nanostructured polyaniline grafting on the CNF was mainly in a form of branched nanofibers as well as rough nanolayers. The good dispersibility and processability of the hybrid nanocomposite could be attributed to its overall nanostructure which enhanced its accessibility to the electrolyte.

Self-assembly of graphene onto electrospun polyamide 66 nanofibers as transparent conductive thin films.

A simple method was developed to assemble graphite oxide (GO) densely onto electrospun (ES) polyamide 66 (PA66) nanofibrous membranes, used as a guide for the deposition of graphene nanosheet (GNS) conductive networks for preparing transparent conductive thin film (TCF). The main advantage of this technique by comparison with previous methods is that graphene does not form a uniform coating, but a percolated conductive network, when guided by PA66 nanofiber templates. A low surface coverage of the transparent substrate by GNS resulted in high transmittance.

Electrospinning induced ferroelectricity in poly(vinylidene fluoride) fibers.

Poly(vinylidene fluoride) (PVDF) fibers with diameters ranging from 70 to 400 nm are produced by electrospinning and the effect of fiber size on the ferroelectric β-crystalline phase is determined. Domain switching and associated ferro-/piezo-electric properties of the electrospun PVDF fibers were also determined. The fibers showed well-defined ferroelectric and piezoelectric properties.

One-dimensional multiferroic bismuth ferrite fibers obtained by electrospinning techniques.

We report the fabrication of novel multiferroic nanostructured bismuth ferrite (BiFeO(3)) fibers using the sol-gel based electrospinning technique. Phase pure BiFeO(3) fibers were prepared by thermally annealing the electrospun BiFeO(3)/polyvinylpyrrolidone composite fibers in air for 1 h at 600 °C. The x-ray diffraction pattern of the fibers (BiFeO(3)) obtained showed that their crystalline structures were rhombohedral perovskite structures.

How super is supercontraction? Persistent versus cyclic responses to humidity in spider dragline silk.

Spider dragline silk has enormous potential for the development of biomimetic fibers that combine strength and elasticity in low density polymers. These applications necessitate understanding how silk reacts to different environmental conditions. For instance, spider dragline silk ;supercontracts' in high humidity.

Supercontraction forces in spider dragline silk depend on hydration rate.

Spider dragline silk is a model biological polymer for biomimetic research due to its many desirable and unusual properties. 'Supercontraction' describes the dramatic shrinking of dragline silk fibers when wetted. In restrained silk fibers, supercontraction generates substantial stresses of 40-50 MPa above a critical humidity of approximately 70% relative humidity (RH).

Distal femoral fixation: a biomechanical comparison of trigen retrograde intramedullary (i.m.) nail, dynamic condylar screw (DCS), and locking compression plate (LCP) condylar plate.

Background: The purpose of this study was to establish if there are biomechanical differences between implants in stiffness of construct, microdisplacement, and fatigue failure in a supracondylar femoral fracture model.

Methods: A retrograde intramedullary (i.m.