Fingertip‐skin‐inspired highly sensitive and multifunctional sensor with hierarchically structured conductive graphite/polydimethylsiloxane foams

Fingertip skin exhibits high sensitivity in a broad pressure range, and can detect diverse stimuli, including textures, temperature, humidity, etc. Despite adopting diverse microstructures and functional materials, achieving skin sensor devices possessing high pressure sensitivity over a wide linear range and with multifunctional sensing capabilities is still challenging. Herein, inspired by the microstructures of fingertip skin, a highly sensitive skin sensor is demonstrated with a linear response over a broad pressure range and multifunctional sensing capabilities. The porous sensing layer is designed with hierarchical microstructures on the surface. By optimizing the porosity and the graphite concentration, a fabricated skin sensor device exhibits a superior sensitivity of 245 kPa−1 over a broad linear pressure range from 5 Pa to 120 kPa. For practical application demonstrations, the sensor devices are utilized to monitor subtle wrist pulse and diverse human motions including finger bending, wrist bending, and feet movement. Furthermore, this novel sensor device demonstrates potential applications in recognizing textures and detecting environmental temperatures, thereby marking an important progress for constructing advanced electronic skin

Macroporous materials: microfluidic fabrication, functionalization and applications

This article provides an up-to-date highly comprehensive overview (594 references) on the state of the art of the synthesis and design of macroporous materials using microfluidics and their applications in different fields

An x-ray tomography facility for quantitative prediction of mechanical and transport properties in geological, biological and synthetic systems

A fully integrated X-ray tomography facility with the ability to generate tomograms with 20483 voxels at 2 micron spatial resolution was built to satisfy the requirements of a virtual materials testing laboratory. The instrument comprises of a continuously pumped micro-focus X-ray gun, a milli-degree rotation stage and a high resolution and large field X-ray camera, configured in a cone beam geometry with a circular trajectory. The purpose of this facility is to routinely analyse and investigate real world biological, geological and synthetic materials at a scale in which the traditional domains of physics, chemistry, biology and geology merge. During the first 2 years of operation, approximately 4 Terabytes of data have been collected, processed and analysed, both as static and in some cases as composite dynamic data sets. This incorporates over 300 tomograms with 10243 voxels and 50 tomograms with 20483 voxels for a wide range of research fields. Specimens analysed include sedimentary rocks, soils, bone, soft tissue, ceramics, fibre-reinforced composites, foams, wood, paper, fossils, sphere packs, bio-morphs and small animals. In this paper, the flexibility of the facility is highlighted with some prime examples

Resistance network-based thermal conductivity model for metal foams

A network model for the estimation of effective thermal conductivity of open-celled metal foams is pre-sented. A nodal network representation of three aluminum foam samples from DUOCEL – 10 ppi, 20 ppi and 40 ppi – is constructed out of X-ray microtomography data obtained by computed tomography (CT) scanning of the samples using a commercial CT scanner. Image processing and 3D skeletonization are performed with commercially available image processing software. The effective thermal conductivity is estimated through a 1D conduction model, representing individual ligaments as an effective thermal resistance using the topological information from the scan data. The effective thermal conductivity data thus obtained are compared with the Lemlich theory and other pore-based models. Further, microstruc-tural characterization of foam features – pore size, ligament thickness, ligament length and pore shapes – is performed. All the three foam samples are observed to have similar pore shapes and volumetric poros-ity, while the other features scale with the pore size. For a given porosity the computed permeability is found to scale as the square of the pore diameter, as also noted by previous researchers

Stimulus-responsive Injectable Polysaccharide Scaffolds for Soft Tissue Engineering Prepared by O/W High Internal Phase Emulsion

This thesis describes work on the development of several novel stimuli-responsive porous hydrogels prepared from oil-in-water (o/w) high internal phase emulsion (HIPE) as injectable scaffolds for soft tissue engineering. Firstly, by copolymerising glycidyl methacrylate (GMA) derivatised dextran and N-isopropylacrylamide (NIPAAm) in the aqueous phase of a toluene-in-water HIPE, thermo-responsive polyHIPE hydrogels were obtained. The temperature depended modulus of these porous hydrogels, as revealed by oscillatory mechanical measurements, indicated improvements of the mechanical properties of these hydrogels when heated from room temperature to human body temperature, as the polyNIPAAm copolymer segments starts to phase separate from the aqueous phase and causes the hydrogel to form a more compact structure within the aqueous phase of the polyHIPE. Secondly ion responsive methacrylate modified alginate polyHIPE hydrogels were prepared. The physical dimensions, pore and pore throat sizes as well as water uptakes of these ion responsive hydrogels can be controllably decreased in the presence of Ca2+ ions and are fully recovered after disruption of the ionic crosslinking using a chelating agent (sodium citrate). These ion-responsive polyHIPE hydrogels also possess good mechanical properties (modulus up to 20 kPa). Both of these polyHIPE hydrogels could be easily extruded through a hypodermic needle while breaking into small fragments (about 0.5 to 3.0 mm in diameter), but the interconnected porous morphology was maintained after injection as revealed by SEM characterisation. Furthermore, the hydrogel fragments produced during injection can be crosslinked into a coherent scaffold under very mild condition using Ca2+ salts and alginate aqueous solution as the ionically crosslinkable adhesive. In order to increase the pore size of these covalently crosslinked polyHIPE hydrogels and also find a biocompatible nontoxic emulsifier as substitution to traditional surfactants, methyl myristate-in-water and soybean oil-in-water HIPEs solely stabilised by hydroxyapatite (HAp) nanoparticle were prepared. These Pickering- HIPEs were used as template to prepare polyHIPE hydrogels. Dextran-GMA, a water soluble monomer, was polymerised in the continuous phase of the HAp Pickering HIPEs leading to porous hydrogels with a tunable pore size varying from 1.5 μm to 41.0 μm. HAp is a nontoxic biocompatible emulsifier, which potentially provides extra functions, such as promoting hard tissue cell proliferation. HIPE-templated materials whose porous structure is maintained solely by the reversible physical aggregation between thermo-responsive dextran-b-polyNIPAAm block polymer chains in an aqueous environment (for this type of HIPE templated material we coined the name thermo-HIPEs) were prepared. No chemical reaction is required for the solidification of this porous material. This particular feature should provide a safer route to injectable scaffolds as issues of polymerisation/crosslinking chemistry or residual initiator fragments or monomers potentially being cytotoxic do not arise in our case, as all components are purified polymers prior to HIPE formation. Thermo-HIPEs with soybean oil or squalene as dispersed oil phase were prepared. Also in this HIPE system it was possible to replace the original surfactant Triton X405 with colloidal HAp nanoparticles or pH/thermo-responsive polyNIPAAm-co- AA microgel particles. The pore sizes and the mechanical properties of colloidal particles stabilised thermo-HIPEs showed improvement compared with thermo-HIPEs stabilised by Triton X405. In summary new injectable polyHIPEs have been prepared which retain their pore morphology during injection and can be solidified by either a thermal or ion (Ca2+) or chelating ion (Ca2+) stimulus. The materials used are intrinsically biocompatible and thus makes these porous injectable scaffolds excellent candidates for soft tissue engineering

Detergency and its implications for oil emulsion sieving and separation

Separating petroleum hydrocarbons from water is an important problem to address in order to mitigate the disastrous effects of hydrocarbons on aquatic ecosystems. A rational approach to address the problem of marine oil water separation is to disperse the oil with the aid of surfactants in order to minimize the formation of large slicks at the water surface and to maximize the oil-water interfacial area. Here we investigate the fundamental wetting and transport behavior of such surfactant-stabilized droplets and the flow conditions necessary to perform sieving and separation of these stabilized emulsions. We show that, for water soluble surfactants, such droplets are completely repelled by a range of materials (intrinsically underwater superoleophobic) due to the detergency effect; therefore, there is no need for surface micro/nanotexturing or chemical treatment to repel the oil and prevent fouling of the filter. We then simulate and experimentally investigate the effect of emulsion flow rate on the transport and impact behavior of such droplets on rigid meshes to identify the minimum pore opening (w) necessary to filter a droplet with a given diameter (d) in order to minimize the pressure drop across the mesh and therefore maximize the filtering efficiency, which is strongly dependent on w. We define a range of flow conditions and droplet sizes where minimum droplet deformation is to be expected and therefore find that the condition of is sufficient for efficient separation. With this new understanding, we demonstrate the use of a commercially available filter--without any additional surface engineering or functionalization--to separate oil droplets from a surfactant stabilized emulsion with a flux of 11,000 L m$^{-2}$ hr$^{-1}$ bar$^{-1}$. We believe these findings can inform the design of future oil separation materials