Shape-memory nanoparticles from inherently non-spherical polymer colloids

Samples of polymeric materials generally have no intrinsic shape; rather their macroscopic form is determined by external forces such as surface tension and memory of shear (for example, during extrusion, moulding or embossing). Hence, in the molten state, the thermodynamically most stable form for polymer (nano)particles is spherical. Here, we present the first example of polymer nanoparticles that have an intrinsic non-spherical shape. We observe the formation of high-aspect-ratio ellipsoidal polymer nanoparticles, of controlled diameter, made from main-chain liquid crystalline polymers using a mini-emulsion technique. The ellipsoidal shape is shown to be an equilibrium (reversible) characteristic and a direct result of the material shape memory when a liquid crystal nanoparticle is in its monodomain form.     

Protective clothing systems: A technique for evaluating restriction of wearer mobility

To allow designers to evaluate presently available protective clothing systems (as well as aiding the development of less restrictive systems), it is necessary to develop evaluation techniques to quantify the loss of mobility associated with wearing protective clothing. Using fire fighter turnout gear, this study illustrated the application of the Leighton Flexometer for the measurement of restriction to body movement caused by wearing protective clothing and equipment. Statistical analyses indicated significant differences in restriction to body movement between the designs of protective clothing and equipment configurations tested. Additionally, correlation coefficients between trials established values for tes-retest reliability.     

Extracellular-matrix tethering regulates stem-cell fate

To investigate how substrate properties influence stem-cell fate, we cultured single human epidermal stem cells on polydimethylsiloxane (PDMS) and polyacrylamide (PAAm) hydrogel surfaces, 0.1?kPa-2.3?MPa in stiffness, with a covalently attached collagen coating. Cell spreading and differentiation were unaffected by polydimethylsiloxane stiffness. However, cells on polyacrylamide of low elastic modulus (0.5?kPa) could not form stable focal adhesions and differentiated as a result of decreased activation of the extracellular-signal-related kinase (ERK)/mitogen-activated protein kinase (MAPK) signalling pathway. The differentiation of human mesenchymal stem cells was also unaffected by PDMS stiffness but regulated by the elastic modulus of PAAm. Dextran penetration measurements indicated that polyacrylamide substrates of low elastic modulus were more porous than stiff substrates, suggesting that the collagen anchoring points would be further apart. We then changed collagen crosslink concentration and used hydrogel-nanoparticle substrates to vary anchoring distance at constant substrate stiffness. Lower collagen anchoring density resulted in increased differentiation. We conclude that stem cells exert a mechanical force on collagen fibres and gauge the feedback to make cell-fate decisions.     

Fabrication of microgel particles with complex shape via selective polymerization of aqueous two-phase systems

Microgel particles are formed from aqueous-two-phase-system (ATPS) droplets in poly(dimethylsiloxane) (PDMS) microfluidic devices. The droplets consist of a dextran core and a photopolymerizable poly(ethylene glycol) diacrylate (PEGDA) shell. Upon UV exposure, the ATPS droplets undergo a shape-transformation yielding PEGDA microgel particles containing a socket.     

Transfer Printing Water‐Soluble Inorganic Salts

This paper reports the first example of the fabrication of KNO₃, K₂CO₃, CuSO₄, NaOH, and mixed‐inorganic‐salt (KNO₃ and KOH) patterns using a transfer‐printing (TP) technique. The transfer quality is found to be related to the concentration of the salt solutions. By varying the immersion time, it is possible to control the heights of the raised features of the transfer‐printed salts from the nanoscale to the submicrometer scale. Utilizing these inorganic salts as water‐soluble masks for microfabrication is demonstrated using patterned NaOH films. The use of water as a developer solvent demonstrates the potential utility of the patterning of inorganic salts as a low‐cost, simple, and, more importantly, environmentally friendly route towards accurate patterning of different materials.     

Radiometric Active Indoor Imaging in the W-Band

Millimeter wave passive imaging systems constitute a good compromise between resolution and penetration depth for a variety of imaging applications. In an outdoor scenario, the cold sky radiation, interacting with the reflectivity characteristics of the targets, constitutes the main source of contrast in the acquired images. In indoor applications such a source is not available, and higher thermal sensitivity is required. Alternatively, one has to provide an artificial illumination to the scene in order to increase its dynamic range. The implementation of an active source for a passive radiometer can, under certain conditions, increase the contrast of the images acquired and add extra information to the measurement. With such a setup, outdoor systems can be used for indoor observations (the absence of cold sky radiation is compensated with active illumination). The subject of our study is to better understand which kind of source and which setup can provide a diffuse illumination over the targets. This topic was investigated by conducting observations of various indoor scenes with two radiometers in the W-Band, using noise and continuous wave (CW) sources as illumination. In this paper we present the results achieved and our conclusions in order to provide an efficient illumination for indoor environment.