Physico-Chemical model and computer simulations of silicon nanowire growth

A model of catalytically enhanced CVD growth of a silicon nanowire assembly on a substrate is developed, and growth process is simulated. Thermodynamic-kinetic theory is used for modeling of molecular transport in the gas phase, processes near catalyst surface and nanowire side of variable curvature, bulk diffusion of silicon adatoms through catalyst – body, and 2D nucleation. The simulation of atomic transport across surfaces is based on a long-wave approach of lattice gas approximation. To determine a character of atomic transport in TiSi₂-catalyst that is of great importance for application in Si-based technology, a density functional theory is used. The main result of modeling is that it is found a relationship between growth conditions (an initial radius of catalyst particles, their density, substrate temperature, content, pressure of gas, as well as properties of materials used) and, on the other hand, a growth rate, shape, composition, and type of atomic structure (amorphous or crystalline) of the nanowires grown. Besides, available experimental data published previously are discussed, and a qualitative agreement between theory and various experiments is obtained. This agreement gives rise to use the found relationship for controlling the nanowire growth

Myelinated fibers of the mouse spinal cord after a 30-day space flight

© 2016, Pleiades Publishing, Ltd.Myelinated fibers and myelin-forming cells in the spinal cord at the L3–L5 level were studied in C57BL/6N mice that had spent 30 days in space. Signs of destruction of myelin in different areas of white matter, reduction of the thickness of myelin sheath and axon diameter, decreased number of myelin-forming cells were detected in “flight” mice. The stay of mice in space during 30 days had a negative impact on the structure of myelinated fibers and caused reduced expression of the markers myelin-forming cells. These findings can complement the pathogenetic picture of the development of hypogravity motor syndrome

Myelinated fibers of the mouse spinal cord after a 30-day space flight

© 2016, Pleiades Publishing, Ltd.Myelinated fibers and myelin-forming cells in the spinal cord at the L3–L5 level were studied in C57BL/6N mice that had spent 30 days in space. Signs of destruction of myelin in different areas of white matter, reduction of the thickness of myelin sheath and axon diameter, decreased number of myelin-forming cells were detected in “flight” mice. The stay of mice in space during 30 days had a negative impact on the structure of myelinated fibers and caused reduced expression of the markers myelin-forming cells. These findings can complement the pathogenetic picture of the development of hypogravity motor syndrome

Genotoxicity of charged particles of importance in space flight using murine kidney epithelial cells

Ionizing radiation presents significant challenges for human space flight including an increased cancer risk. High-energy heavy ions in the galactic cosmic radiation can produce qualitative and quantitative differences in biological effects when compared with sparsely ionizing radiations. Mutations are induced by charged particle exposure and are integral to the formation and/or progression of human cancers. Most cancer-associated mutations occur on autosomal chromosomes, and most solid cancers occur in epithelial tissues. Here, a combined in vitro/in vivo approach was used to evaluate cell killing and the induction of mutations at a model autosomal locus, Aprt, in mouse kidney epithelium. For in vitro exposures, Aprt heterozygous kidney cells (clones 1a, 4a or 6a) were used from C57BL/6×DBA/2 mice. Additional experiments were performed using whole body irradiation of mice with the same genotype. Both males and females were irradiated in approximately equal numbers. Irradiations were performed at the NASA Space Radiation Laboratories at Brookhaven National Laboratory. For in vitro studies, cells from primary kidney clones were irradiated and seeded at limiting dilution immediately post-irradiation to determine the toxicity of the treatment. The irradiated kidney cells were also seeded in mutation assays within 1 week post-irradiation to determine the Aprt mutant fraction at the earliest time post-exposure. This work was complemented by studies wherein mice were exposed to the same ions with kidneys harvested several months post-irradiation to determine the residual toxicity and the Aprt mutant fraction. Our previous studies focused on sparsely ionizing 1 GeV protons (LET = 0.24 keV/??m) and densely ionizing 1 GeV/amu Fe ions (LET = 151 keV/??m). Our most recent studies have included work with Si ions (240 MeV/amu for in vitro studies, LET = 78 keV/??m; 263 MeV/amu initial energy for in vivo studies to achieve 78 keV/??m near the midline of the animal) and O ions (250 MeV/amu in vitro studies only, LET = 25 keV/??m). Toxicity for the cultured kidney cells in vitro follows this pattern: Fe > Si > O > protons when the results are expressed per unit dose. D0 values were 92 cGy for Fe ions, 103 cGy for Si ions, 192 cGy for O ions and 340 cGy for protons. With regard to the induction of Aprt mutations, Fe ions were more mutagenic than protons. Si ions were also quite mutagenic with evidence for a linear dose???response for Aprt mutations in kidney cells exposed in vitro or in kidneys harvested from mice irradiated several months earlier. These results are consistent with the linear dose???response data obtained previously for Aprt mutation induction following Fe ion exposure in vitro or in vivo, but the results for Si ions differ from the curvilinear dose???response data we recently published following similar exposures to energetic protons. Our most recent studies examined the molecular characteristics of Si ion-induced Aprt mutants following in vitro exposure. A dose of 160 cGy was used to collect 58 Aprt kidney cell mutants. Mutational events were classified as follows based on PCR-based analyses of polymorphic markers along mouse chromosome 8: intragenic events, apparent mitotic recombination, interstitial deletions of Aprt only, multilocus deletions, discontinuous loss of heterozygosity or whole chromosome loss. The results for this group of mutants will be compared against our previous studies on Aprt mutants arising after exposure to sparsely ionizing 1 GeV protons or densely ionizing 1 GeV/amu Fe ions. Additional studies are ongoing to define mutational spectra following Si ion exposure to kidney epithelium in vivo

Myelinated fibers of the mouse spinal cord after a 30-day space flight

© 2016, Pleiades Publishing, Ltd.Myelinated fibers and myelin-forming cells in the spinal cord at the L3–L5 level were studied in C57BL/6N mice that had spent 30 days in space. Signs of destruction of myelin in different areas of white matter, reduction of the thickness of myelin sheath and axon diameter, decreased number of myelin-forming cells were detected in “flight” mice. The stay of mice in space during 30 days had a negative impact on the structure of myelinated fibers and caused reduced expression of the markers myelin-forming cells. These findings can complement the pathogenetic picture of the development of hypogravity motor syndrome

Myelinated fibers of the mouse spinal cord after a 30-day space flight

© 2016, Pleiades Publishing, Ltd.Myelinated fibers and myelin-forming cells in the spinal cord at the L3–L5 level were studied in C57BL/6N mice that had spent 30 days in space. Signs of destruction of myelin in different areas of white matter, reduction of the thickness of myelin sheath and axon diameter, decreased number of myelin-forming cells were detected in “flight” mice. The stay of mice in space during 30 days had a negative impact on the structure of myelinated fibers and caused reduced expression of the markers myelin-forming cells. These findings can complement the pathogenetic picture of the development of hypogravity motor syndrome

Autosomal Mutants of Proton-Exposed Kidney Cells Display Frequent Loss of Heterozygosity on Nonselected Chromosomes

High-energy protons found in the space environment can induce mutations and cancer, which are inextricably linked. We hypothesized that some mutants isolated from proton exposed kidneys arose through a genome-wide incident that causes loss of heterozygosity (LOH)-generating mutations on multiple chromosomes (termed here genomic LOH). To test this hypothesis, we examined 11 pairs of nonselected chromosomes for LOH events in mutant cells isolated from the kidneys of mice exposed to 4 or 5 Gy of 1 GeV protons. The mutant kidney cells were selected for loss of expression of the chromosome 8-encoded Aprt gene. Genomic LOH events were also assessed in Aprt mutants isolated from isogenic cultured kidney epithelial cells exposed to 5 Gy of protons in vitro. Control groups were spontaneous Aprt mutants and clones isolated without selection from the proton-exposed kidneys or cultures. The in vivo results showed significant increases in genomic LOH events in the Aprt mutants from proton-exposed kidneys when compared with spontaneous Aprt mutants and when compared with nonmutant (i.e., nonselected) clones from the proton-exposed kidneys. A bias for LOH events affecting chromosome 14 was observed in the proton-induced Aprt mutants, though LOH for this chromosome did not confer increased radiation resistance. Genomic LOH events were observed in Aprt mutants isolated from proton-exposed cultured kidney cells; however the incidence was fivefold lower than in Aprt mutants isolated from exposed intact kidneys, suggesting a more permissive environment in the intact organ and/or the evolution of kidney clones prior to their isolation from the tissue. We conclude that proton exposure creates a subset of viable cells with LOH events on multiple chromosomes, that these cells form and persist in vivo, and that they can be isolated from an intact tissue by selection for a mutation on a single chromosome

Embedded sensors for Micro Transdermal Interface Platforms (MicroTIPs)

Wearable 'smart patches' of the future will incorporate microneedle technologies that painlessly interact with the body, using closed-loop theranostic systems to continuously monitor the physiological status of the body and deliver appropriate therapeutic agents when needed. Among other components, these Micro Transdermal Interface Platforms (MicroTIPs) will require embedded sensors to verify that the patch is operating as intende