12 research outputs found
Preparation and Structural Characterization of Free-Standing Octacalcium-Phosphate-Rich Thin Films
Free-standing films of calcium phosphates
exhibit many favorable
properties for tissue engineering. In this work, a thin film of calcium
phosphate is prepared in a liposome suspension using the method of
ammonia gas diffusion. The thickness of the film is about 10 ÎĽm,
and the lateral dimensions are on the length scale of millimeter.
The results of powder X-ray diffraction and transmission electron
microscopy show that the thin films contain the mineral phases of
hydroxyapatite and octacalcium phosphate (OCP). Using solid-state
NMR spectroscopy, in particular the technique of heteronuclear correlation
spectroscopy with variable contact time, the major crystalline phase
of the thin film has been confirmed to be OCP
Multiscale mechanisms of nutritionally induced property variation in spider silks
<div><p>Variability in spider major ampullate (MA) silk properties at different scales has proven difficult to determine and remains an obstacle to the development of synthetic fibers mimicking MA silk performance. A multitude of techniques may be used to measure multiscale aspects of silk properties. Here we fed five species of Araneoid spider solutions that either contained protein or were protein deprived and performed silk tensile tests, small and wide-angle X-ray scattering (SAXS/WAXS), amino acid composition analyses, and silk gene expression analyses, to resolve persistent questions about how nutrient deprivation induces variations in MA silk mechanical properties across scales. Our analyses found that the properties of each spider’s silk varied differently in response to variations in their protein intake. We found changes in the crystalline and non-crystalline nanostructures to play specific roles in inducing the property variations we found. Across treatment <i>MaSp</i> expression patterns differed in each of the five species. We found that in most species <i>MaSp</i> expression and amino acid composition variations did not conform with our predictions based on a traditional <i>MaSp</i> expression model. In general, changes to the silk’s alanine and proline compositions influenced the alignment of the proteins within the silk’s amorphous region, which influenced silk extensibility and toughness. Variations in structural alignment in the crystalline and non-crystalline regions influenced ultimate strength independent of genetic expression. Our study provides the deepest insights thus far into the mechanisms of how MA silk properties vary from gene expression to nanostructure formations to fiber mechanics. Such knowledge is imperative for promoting the production of synthetic silk fibers.</p></div
Comparisons of the expressions of the MaSp1 genes previously isolated from the <i>Argiope trifasciata</i> (MaSp1a) and <i>Latrodectus hesperus</i> (MaSp1b), and the MaSp2 genes from <i>Argiope trifasciata</i> (MaSp2a) and <i>Latrodectus hesperus</i> (MaSp2b), across treatments for each of the five spiders.
<p>Where P = protein fed and N = protein deprived treatments, <i>Ak</i> = Argiope <i>keyserlingi</i>, <i>Et</i> = <i>Eriophora transmarina</i>, <i>Lh</i> = <i>Latrodectus hasselti Np</i> = <i>Nephila plumipes</i>, <i>Pg</i> = <i>Phonognatha graeffei</i>.</p
WAXS derived intensity <i>vs</i> 2<i>θ</i> plots for MA silks of each species.
<p>Where P = protein fed and N = protein deprived treatments, <i>Ak</i> = Argiope <i>keyserlingi</i>, <i>Et</i> = <i>Eriophora transmarina</i>, <i>Lh</i> = <i>Latrodectus hasselti Np</i> = <i>Nephila plumipes</i>, <i>Pg</i> = <i>Phonognatha graeffei</i>.</p
Flow diagram of the methods implemented to examine the consequences of protein deprivation on MA silk gene expression, protein nanostructures, and mechanical properties for five species of spiders.
<p>Flow diagram of the methods implemented to examine the consequences of protein deprivation on MA silk gene expression, protein nanostructures, and mechanical properties for five species of spiders.</p
WAXS images derived for MA silks of each species of spider.
<p>Where P = protein fed and N = protein deprived treatments, <i>Ak</i> = Argiope <i>keyserlingi</i>, <i>Et</i> = <i>Eriophora transmarina</i>, <i>Lh</i> = <i>Latrodectus hasselti Np</i> = <i>Nephila plumipes</i>, <i>Pg</i> = <i>Phonognatha graeffei</i>.</p
Summary of the consequences of protein deprivation on silk properties for the five species examined.
<p>Summary of the consequences of protein deprivation on silk properties for the five species examined.</p
SAXS derived intensity <i>vs</i> waveband parameter (<i>q</i>) plots for the MA silks each of the 5 species’ MA silk.
<p>Where P = protein fed and N = protein deprived treatments, <i>Ak</i> = Argiope <i>keyserlingi</i>, <i>Et</i> = <i>Eriophora transmarina</i>, <i>Lh</i> = <i>Latrodectus hasselti Np</i> = <i>Nephila plumipes</i>, <i>Pg</i> = <i>Phonognatha graeffei</i>.</p
Mechanical Performance of Spider Silk Is Robust to Nutrient-Mediated Changes in Protein Composition
Spider major ampullate (MA) silk
is sought after as a biomimetic
because of its high strength and extensibility. While the secondary
structures of MA silk proteins (spidroins) influences silk mechanics,
structural variations induced by spinning processes have additional
effects. Silk properties may be induced by spiders feeding on diets
that vary in certain nutrients, thus providing researchers an opportunity
to assess the interplay between spidroin chemistry and spinning processes
on the performance of MA silk. Here, we determined the relative influence
of spidroin expression and spinning processes on MA silk mechanics
when <i>Nephila pilipes</i> were fed solutions with or without
protein. We found that spidroin expression differed across treatments
but that its influence on mechanics was minimal. Mechanical tests
of supercontracted fibers and X-ray diffraction analyses revealed
that increased alignment in the amorphous region and to a lesser extent
in the crystalline region led to increased fiber strength and extensibility
in spiders on protein rich diets
Reversible Li Intercalation in Layered Cathodes Enabled by Dopant-Induced Medium-Range Orders
Doping could effectively tune the electrochemical performance
of
layered oxide cathodes in Li-ion batteries, whereas the working mechanism
is usually oversimplified (i.e., a “pillar” effect).
Although the Jahn–Teller effect is generally regarded as the
fundamental origin of structural instability in some oxides, more
polyhedral distortions are associated with pseudo-JTE (PJTE), which
involves vibronic couplings. In this work, the atomic structures of
doped LiCoO2 by Mg cations, F anions, and both were investigated
thoroughly to reveal the atomic environments of these dopants and
their influence on electrochemical performance. The function of these
dopants as pillars is well discussed from the view of PJTE manipulation.
Briefly, the MgO4 tetrahedra in Mg-doped LiCoO2 could suppress the charge transfer from the ligand to Co in neighboring
octahedra, thus depressing PJTE. Although F doping does increase the
ligand-field strength, the induced octahedral distortion reduces the
structural stability dramatically. Comparatively, Mg/F co-doping generates
the CoO5F–MgO4F2–CoO5F medium-range orders (MROs), which could depress both structural
distortion and charge transfer in Co-centered octahedra for reduced
PJTE. The reduced PJTE accounts for the improved electrochemical performance,
making the co-doped LiCoO2 offer the best performance:
a 70% capacity retention after 200 cycles within the potential range
of 2.8–4.6 V, followed by Mg-doped LiCoO2. In contrast,
although F-doping could induce an extra rock salt-like surface layer
for higher capacity, its cycling improvement is rather limited. These
results highlight the importance of structural modulation in enhancing
the material performance and propose that the manipulation of PJTE
would be an effective strategy in developing novel high-performance
oxide cathodes