Foil Strain Gauges Using Piezoresistive Carbon Nanotube Yarn: Fabrication and Calibration.

Carbon nanotube yarns are micron-scale fibers comprised by tens of thousands of carbon nanotubes in their cross section and exhibiting piezoresistive characteristics that can be tapped to sense strain. This paper presents the details of novel foil strain gauge sensor configurations comprising carbon nanotube yarn as the piezoresistive sensing element. The foil strain gauge sensors are designed using the results of parametric studies that maximize the sensitivity of the sensors to mechanical loading. The fabrication details of the strain gauge sensors that exhibit the highest sensitivity, based on the modeling results, are described including the materials and procedures used in the first prototypes. Details of the calibration of the foil strain gauge sensors are also provided and discussed in the context of their electromechanical characterization when bonded to metallic specimens. This characterization included studying their response under monotonic and cyclic mechanical loading. It was shown that these foil strain gauge sensors comprising carbon nanotube yarn are sensitive enough to capture strain and can replicate the loading and unloading cycles. It was also observed that the loading rate affects their piezoresistive response and that the gauge factors were all above one order of magnitude higher than those of typical metallic foil strain gauges. Based on these calibration results on the initial sensor configurations, new foil strain gauge configurations will be designed and fabricated, to increase the strain gauge factors even more.

Structure and properties of iron oxide clusters: From Fe6 to Fe6 O20 and from Fe7 to Fe7 O24.

Geometrical and electronic structures of the neutral and singly negatively charged Fe6 On and Fe7 Om clusters in the range of 1 ≤ n ≤ 20 and 1 ≤ m ≤ 24, respectively, are computed using density functional theory with the generalized gradient approximation. The largest clusters in the two series, Fe6 O20 and Fe7 O24 , can be described as Fe(FeO4 )5 and Fe(FeO4 )6 or alternatively as [FeO5 ](FeO3 )5 and [FeO6 ](FeO3 )6 , respectively. The Fe6 O20 and Fe7 O24 clusters possess adiabatic electron affinities (EAad ) of 5.64 eV and 5.80 eV and can be attributed to the class of hyperhalogens since FeO4 is an unique closed-shell superhalogen with the EAad of 3.9 eV. The spin character of the lowest total energy states in both series changes from ferromagnetic to ferrimagnetic or antiferromagnetic when the first FeOFe bridge is formed. Oxidation decreases substantially the polarizability per atom of the initial bare clusters; namely, from 5.98 Å(3) of Fe6 to 2.47 Å(3) of Fe6 O20 and from 5.67 Å(3) of Fe7 to 2.38 Å(3) of Fe7 O24 . The results of our computations pertaining to the binding energies of O, Fe, O2 , and FeO in the Fe7 Om series provide an explanation for the experimentally observed abundance of the iron oxide nanoparticles with stoichiometric compositions. © 2016 Wiley Periodicals, Inc.

Translocation of cell penetrating peptide engrafted nanoparticles across skin layers.

The objective of the current study was to evaluate the ability of cell penetrating peptides (CPP) to translocate the lipid payload into the skin layers. Fluorescent dye (DID-oil) encapsulated nano lipid crystal nanoparticles (FNLCN) were prepared using Compritol, Miglyol and DOGS-NTA-Ni lipids by hot melt homogenization technique. The FNLCN surface was coated with TAT peptide (FNLCNT) or control YKA peptide (FNLCNY) and in vitro rat skin permeation studies were performed using Franz diffusion cells. Observation of lateral skin sections obtained using cryotome with a confocal microscope demonstrated that skin permeation of FNLCNT was time dependent and after 24h, fluorescence was observed upto a depth of 120 microm which was localized in the hair follicles and epidermis. In case of FNLCN and FNLCNY formulations fluorescence was mainly observed in the hair follicles. This observation was further supported by confocal Raman spectroscopy where higher fluorescence signal intensity was observed at 80 and 120 microm depth with FNLCNT treated skin and intensity of fluorescence peaks was in the ratio of 2:1:1 and 5:3:1 for FNLCNT, FNLCN, and FNLCNY treated skin sections, respectively. Furthermore, replacement of DID-oil with celecoxib (Cxb), a model lipophilic drug showed similar results and after 24h, the CXBNT formulation increased the Cxb concentration in SC by 3 and 6 fold and in epidermis by 2 and 3 fold as compared to CXBN and CXBNY formulations respectively. Our results strongly suggest that CPP can translocate nanoparticles with their payloads into deeper skin layers.