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Micro-Raman spectroscopy and X-ray diffraction were used to study time-dependent structural changes in sputtered Ce 1-x Gd x O 2-x/2 films. The F 2 g peak position was measured at five well-defined film locations; X-ray diffraction assessed in-plane compressive strain and unit cell volume. For x = 0.05, at all locations monitored post-annealing, the F 2 g frequency continued to increase during two weeks and for x = 0.10, at 4 of 5 locations during six weeks. This time-dependent behavior is attributed to relaxation of local elastic dipolar strain fields. Raman spectroscopy can properly evaluate strain in thin films of these materials only when mechanical properties, defect structure, temporal and thermal history are considered. [ABSTRACT FROM AUTHOR]

We describe a technique for measuring the activation energy of ion diffusion in ionic and mixed ionic/electronic conductors. The technique is based on monitoring small changes in refractive index near the interface of a semitransparent gold electrode with the sample surface. Constant bias voltage is applied to the sample to weakly perturb the distribution of charge carriers near this front electrode. The relaxation process induced by bias removal is probed by applying alternating voltage and monitoring by ellipsometry with lock-in detection the changes in the refractive index dominated by changes in material polarizability. Since the ionic contribution to the total material polarizability is much larger than that of electrons or protons, the diffusion of ions can be distinguished. Measurements were made as a function of temperature on single crystals of 8 mol% Y-stabilized zirconia (YSZ8), on ceramic pellets of 20 mol% Gd doped CeO 2 (GDC20) and on single crystals of 0.03 mol% Fe-doped SrTiO 3 (Fe-STO). In YSZ8, a single moving species (oxygen vacancies) with activation energy of 0.8 eV was detected. The “wet” and “dry” states of GDC20 can be clearly distinguished: in the “wet” state there are mobile species other than oxygen vacancies, most likely protons. In Fe-doped SrTiO 3 , the proposed technique can reliably measure the activation energy of oxygen ion diffusion on a background of the much larger electronic conductivity. [ABSTRACT FROM AUTHOR]

Background Aggrecan is the major non-collagenous component of the intervertebral disc. It is a large proteoglycan possessing numerous glycosaminoglycan chains and the ability to form aggregates in association with hyaluronan. Its abundance and unique molecular features provide the disc with its osmotic properties and ability to withstand compressive loads. Degradation and loss of aggrecan result in impairment of disc function and the onset of degeneration. Scope of review This review summarizes current knowledge concerning the structure and function of aggrecan in the normal intervertebral disc and how and why these change in aging and degenerative disc disease. It also outlines how supplementation with aggrecan or a biomimetic may be of therapeutic value in treating the degenerate disc. Major conclusions Aggrecan abundance reaches a plateau in the early twenties, declining thereafter due to proteolysis, mainly by matrix metalloproteinases and aggrecanases, though degradation of hyaluronan and non-enzymic glycation may also participate. Aggrecan loss is an early event in disc degeneration, although it is a lengthy process as degradation products may accumulate in the disc for decades. The low turnover rate of the remaining aggrecan is an additional contributing factor, preventing protein renewal. It may be possible to retard the degenerative process by restoring the aggrecan content of the disc, or by supplementing with a bioimimetic possessing similar osmotic properties. General significance This review provides a basis for scientists and clinicians to understand and appreciate the central role of aggrecan in the function, degeneration and repair of the intervertebral disc. [ABSTRACT FROM AUTHOR]

Abstract: Measurements of the elastic modulus of pure and doped ceria are summarized from the literature and analyzed with a view towards understanding the experimentally established dependence on temperature, doping level and oxygen vacancy concentration. At least two chemical properties affect the elastic modulus of pure and doped ceria: (i) the presence of vacancies decreases the strength of the chemical bonds; and (ii) low-temperature adaptation of the fluorite structure to the presence of oxygen vacancies is accompanied by an increase in unit cell volume. [Copyright &y& Elsevier]

Knowledge of rates of protein turnover is important for a quantitative understanding of tissue synthesis and catabolism. In this work, we have used the racemization of aspartic acid as a marker for the turnover of collagen obtained from healthy and pathological human intervertebral disc matrices. We measured the ratio of the D- and L-isomers in collagen extracted from these tissues as a function of age between 16 and 77 years. For collagen taken from healthy discs, the fractional increase of D-Asp was found to be 6.74 × 10-4/year; for degenerate discs, the corresponding rate was 5.18 × 10-4/year, Using the racemization rate found previously for the stable population of collagen molecules in dentin, we found that the rate of collagen turnover (kT) in discs is not constant but rather a decreasing function of age. The average turnover rate in normal disc between the ages of 20 and 40 is 0.00728 ± 0.00275/year, and that between the ages of 50 and 80 is 0.00323 ± 0.000947/year, which correspond to average half-lives of 95 and 215 years, respectively. Turnover of collagen from degenerate discs may be more rapid than that found for normal discs; however, statistical analysis leaves this point uncertain. The finding of a similar correlation between the accumulation of D-Asp and that of pentosidine for three normal collagenous tissues further supports the idea that the accumulation of pentosidine in a particular tissue can, along with the racemization of aspartic acid, be used as a reliable measure of protein turnover. [ABSTRACT FROM AUTHOR]

Abstract: Specific interfacial interactions in multi-component systems such as composites improve the chemical compatibility between the filler and the matrix, prevent the filler from aggregating and strengthen the interface. Carbon nanotube (CNT) based polyacrylonitrile (PAN) composites were prepared either by extrusion or electrospinning to yield fibers with diameters on two different scales – micro- and nanometric. Introduction of a third component, ethylene carbonate, a plasticizer which is capable of forming strong dipolar interactions with the nitrile group of the polymer, had a four-fold effect. It enabled melt-processing of the polymer, caused a structural transition in the crystalline matrix, improved the uniformity and decreased the diameter of the electrospun fibers. It also indirectly revealed a preferred interaction between the π-electrons of the CNT and the nitrile groups of PAN, as was identified based on synchrotron microbeam WAXD, DSC, 13C NMR and FTIR of CNT-filled and unfilled PAN fibers. The nature of CNT and PAN interaction was modeled by charge-transfer of CNT π-electrons from the highest occupied molecular orbital to the empty nitrile π∗ orbital of PAN. [Copyright &y& Elsevier]

Experimental data that define conditions under which cholesterol crystallites form in cholesterol/phospholipid model membranes are reviewed. Structural features of the phospholipids that determine cholesterol crystallization include the length and degree of unsaturation of the acyl chains, the presence of charge on the headgroups and interheadgroup hydrogen bonds. [Copyright &y& Elsevier]

Abstract Young's, shear and bulk moduli of Ce 1-x Sm x O 2-x/2 (x ≤ 0.55) were studied using ultrasonic time of flight and nanoindentation techniques. Sound velocity measurements, corrected for sample porosity, demonstrate decrease in the unrelaxed ceramic moduli with increasing Sm-content. Room temperature creep under indenter load-hold, as well as time-dependent material stiffness, reveal a transition from prominent anelasticity in the fluorite phase to prominent elasticity in the double fluorite phase. This supports rearrangement of elastic dipoles under anisotropic stress, which occurs more readily when oxygen vacancies are not ordered on the crystal lattice, as the source of ceria anelastic behavior. Graphical abstract Room temperature creep as well as time-dependent material stiffness reveal a transition from prominent anelasticity in the fluorite phase (F m 3 ¯ m) to prominent elasticity in the double fluorite phase(I a 3 ¯). Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Solid-state drawing to high extension ratios of melt-extruded VGCF-iPP nanocomposite filaments results in remarkable increases in modulus and strength, which mask any contribution of nano-reinforcement or inter-particle confinement observed previously. Based on X-ray diffraction and thermal analyses it is shown that the drawing process involves crumpling of the original 'shish-kebab' structure, accompanied by lateral shrinkage of the 'kebabs', disappearance and reorientation of daughter lamellae and significant increases in the degree of crystallinity by solid-state recrystallization. The effects of the initial diameter of the as-extruded filaments and those of the nanofibers and the 'shish-kebab' structure are dominated by the drawing process, which produces a highly aligned fibrillar structure with superior mechanical properties. A cartoon model of the effect of solid-state drawing of extruded iPP and nanocomposite filaments on the transition from 'shish-kebab' to fibril morphology is presented. Graphical abstract Image Highlights • Drawing of VGCF-iPP nanocomposite filaments generates high mechanical properties. • Drawing induces solid-state recrystallization by crumpling of 'shish-kebab' structure. • Shrinkage of 'kebabs' and reorientation of daughter lamellae increase crystallinity. • Effects of confinement and nanoreinforcement are dominated by a fibrillar structure. [ABSTRACT FROM AUTHOR]

10 mol% Gd-doped ceria (10GDC) ceramics, with grain size in the single micron range, display electrostrictive behavior under ambient conditions of temperature and pressure. In weak, quasi-static electric fields, i.e. <1 kV/cm, frequency <1 Hz, the longitudinal strain is measured to be proportional to the square of the applied electric field, albeit with the corresponding electrostrictive strain coefficient ( M 33 ) displaying large variability between samples: −(2-20)·10 −17 (m/V) 2 . Nevertheless, | M 33 | of all samples exceeds the values expected on the basis of the classical (Newnham) electrostriction scaling law by up to two orders of magnitude. A systematic study reveals the functional dependence of M 33 on frequency: above 10 Hz, |M 33 | decreases to ≈10 −18 (m/V) 2 , which may be characterized as non-Debye relaxation with non-ideality factor 0.35–1.13. For frequencies ≤1.5 Hz, increasing the field strength beyond 1 kV/cm results in an exponential decrease in | M 33 | : the longitudinal strain saturates at 1-4 ppm. Dielectric impedance spectra suggest that partitioning of the applied voltage between grain boundaries and grain cores may be a factor contributing both to the large variability in the electrostriction parameters, and to the strong dependence on electric field amplitude. The frequency dependence may have two sources: the slow electric field-driven reorganization of the Ce-containing active complexes in the electrostrictive medium as well as the influence of the grain boundaries. 10GDC ceramics may therefore be added to the list of non-classical electrostrictors which includes reduced and Gd-doped ceria thin films and (Nb,Y)-doped bismuth oxide ceramics. [ABSTRACT FROM AUTHOR]

The Young's, shear and bulk moduli of dense (> 95%) Gd-doped ceria (Ce 1 - x Gd x O 2 - x/2 ) ceramics were determined as a function of Gd content using the ultrasonic pulse-echo method and corrected for porosity according to both static and dynamic models. With increasing defect concentration (0–20 mol% Gd), the Young's and shear moduli decrease linearly by 10% while for 29 mol%, the values lie above the linear fit; the bulk modulus decreases linearly within the complete range. We conclude that structural changes, induced by oxygen vacancy ordering for x > 0.2, may influence the uniaxial and shear moduli, leaving the bulk modulus unaffected. [ABSTRACT FROM AUTHOR]

Cholesterol has limited solubility in phospholipid bilayers. The solubility limit is strongly dependent on the nature of the lipid with which the cholesterol is mixed while properties of the crystals formed can be modified by phospholipid-cholesterol interactions. In this review we summarize the various methods that have been developed to prepare hydrated mixtures of cholesterol and phospholipid. We point out some of the factors that determine the form adopted when cholesterol crystallizes in such mixtures, i.e. two- or three-dimensional, monohydrate or anhydrous. These differences can greatly affect the ability to experimentally detect the presence of these crystals in a membrane. Several methods for detecting cholesterol crystals are discussed and compared including DSC, X-ray and GIXRD diffraction methods, NMR and EPR spectroscopy. The importance of the history of the sample in determining the amount and nature of the cholesterol crystals formed is emphasized. [ABSTRACT FROM AUTHOR]

Abstract: Although Gd-doped ceria is one of the most important and well-studied of oxygen ion conductors, the relationship between its mechanical and electrical properties is not completely understood. In particular the low temperature electrical behavior of Gd-doped ceria, and its response to mechanical strain, have not been characterized. We have used impedance spectroscopy (1Hz–1MHz) to investigate the dielectric properties of both Si substrate-supported and self-supported Ce0.8Gd0.2O1.9 thin (450±50nm) films in the temperature range of 35–440K. We find that the grain boundary electronic conductivity for both types of Ce0.8Gd0.2O1.9 films freezes out between 120 and 150K. Upon cooling to 40K, the effective dielectric constant of the substrate-supported films decreases uniformly, remaining within the range of 20.5±2.5. In contrast, all (17) self-supported films investigated exhibit small (~2%) but readily detectable instability of the dielectric constant between 80 and 140K. Furthermore, below 90K, the dielectric constant of the self-supported films depends on the applied voltage and displays hysteretic behavior. This strongly suggests that even below 100K, the self-supported films can undergo structural changes. Comparison of the lattice parameter at 300K and at 100K shows that the self-supported films contract upon cooling with a thermal expansion coefficient close to that of the bulk material, whereas the substrate-supported films exhibit a thermal expansion coefficient which is approximately twice as large. On the basis of our earlier findings concerning the inelastic behavior of Gd-doped ceria films, we propose that a probable explanation for the observed differences between the self-supported and the substrate-supported films is that in the self-supported films, oxygen vacancy-cerium complexes are able to undergo partial ordering. In substrate-supported films these changes are suppressed by the tensile strain imposed by the substrate upon cooling. [Copyright &y& Elsevier]

Abstract: In this study a nanocomposite monofilament composed of a nematic thermotropic liquid crystalline polymer (TLCP) mixed with 1.5wt.% of carbon nanoparticles (CNP) was prepared by melt extrusion. The nanoparticles had either a fibrous (VGCF) or layered (GNP) geometry. The tensile strength and modulus of the fibers increased with the draw down ratio of the filament; a positive effect on the tensile modulus is displayed by fibrous CNP, achieving values higher than those of high property organic fibers utilized as reinforcement for composite materials. Thermotropic transitions were characterized by DSC and in situ synchrotron WAXD. In particular, it was shown that the breadth of the temperature span of the crystalline–nematic transition correlated inversely with the draw down ratio. At high draw down ratio, addition of CNP also increased the relative amount of oriented polymer chains and contributed to sharpening of the mesomorphic transition. [Copyright &y& Elsevier]

We have used the racemization of aspartic acid as a marker for the "molecular age" of aggrecan components of the human intervertebral disc matrix (aggregating and non-aggregating proteoglycans as well as the different buoyant density fractions of aggrecan). By measuring the D/LAsp ratio of the various aggrecan species as a function of age and using the values of the racemization constant, ki, found earlier for aggrecan in articular cartilage, we were able to establish directly the relative residence time of these molecules in human intervertebral disc matrix. For Al preparations taken from normal tissue, turnover rates of 0.059 ± 0.01 and 0.063 ± 0.01/year correspond to half-life values of 12 ± 2.0 and 11.23 ± 1.9 years for nucleus pulposus and annulus fibrosus, respectively; the turnover rates of 0.084 ± 0.022 and 0.092 ± 0.034/year for degenerate tissue correspond to half-life values of 8.77 ± 2.2 and 8.41 ± 2.8 years, suggesting increased rate of removal of small aggrecan fragments. For the large monomer, fraction A1D1, turnover is 0.13 ± 0.04/year, corresponding to a half-life of 5.56 ± 1.58 years, similar to 3.4 years in human articular cartilage. For the binding region (A1D6), turnover is 0.033 ± 0.0012/year, corresponding to a half-life of 21.53 ± 0.6 years, similar to 23.5 years in articular cartilage. Al preparations from nucleus pulposus contain a lower proportion of aggregating proteoglycans as compared with annulus fibrosus, suggesting increased proteolytic modification in the nucleus pulposus. D/LASP values in aggregating and non-aggregating proteoglycans of a 24-year-old individual show similar results, suggesting that the non-aggregating molecules are synthesized initially as aggregating proteoglycans, which thereafter undergo cleavage and detachment from hyaluronan. [ABSTRACT FROM AUTHOR]

This paper presents the structural details of nylon 66 transcrystallinity induced by aramid (kevlar 29, 49 and 149) and carbon (pitch based) fibers, as determined by high spatial resolution X-ray diffraction. Using stepwise scanning, the orientation of the lamellae in the transcrystalline layer was measured as a function of distance from the fiber. The main observation is that this orientation is distinct for each system and almost independent of distance from the fiber. Of particular interest is the bi-layered transcrystallinity formed on a surface treated kevlar 49 fiber, in which the lamellar a* axis is nearly perpendicular and at an angle of ∼12° to the fiber in the outer and inner layer, respectively. The crystallographic analysis generates grids of oriented lamellae with respect to the fiber axis. [Copyright &y& Elsevier]

Addition of the local anesthetic tetracaine (TTC) to multilamellar dispersions of natural phosphatidylserine (PS) causes changes in the thermotropic properties of the membrane, which can be detected by differential scanning calorimetry, and in the structure of the membrane as detected by X-ray diffraction. At molar ratio [PS]/[TTC]∼8.5, the melting temperature of the phospholipid shifts downwards by approximately 2.5 °C. The melting endotherm is broadened; however, there is little change in the enthalpy of melting. In ternary mixtures (PS–TTC–cholesterol), the thermotropic changes are enhanced. At [PS]/[TTC]∼13, the onset of phase separation of cholesterol crystals from PS in the liquid crystalline state occurs at molar fraction cholesterol (Xchol)∼0.28, marginally smaller than that found in the absence of the anesthetic. [Copyright &y& Elsevier]

Abstract: Background: Aging and degeneration of human intervertebral disc (IVD) are associated with biochemical changes, including racemization and glycation. These changes can only be counteracted by protein turnover. Little is known about the longevity of IVD elastin in health or disease. Yet, such knowledge is important for a quantitative understanding of tissue synthesis and degradation. Methods: We have measured the accumulation of d-Asp and pentosidine in IVD elastin. Samples representing a broad range of ages (28–82years) and degeneration grades (1–5) were analyzed. Results: d/l-Asp for elastin increased linearly with age from 3.2% (early 30s) to 14.8% (early 80s) for normal tissue (grades 1–2) and from 1.7% (late 20s) to 6.0% (until the mid 50s) for degenerate tissue (grades 3–5) with accumulation rates of 16.2±3.1×10−4 and 11.7±3.8×10−4 year−1, respectively; no significant difference was found between these values (p<0.05). Above the mid 50s, a decrease in d-Asp accumulation was recorded in the degenerate tissue. d-Asp accumulation correlated well with pentosidine content for elastin from healthy and degenerate tissues combined. We conclude that IVD elastin is metabolically‐stable and long‐lived in both healthy and degenerate human IVDs, with signs of new synthesis in the latter. The correlation of d‐Asp with pentosidine content suggests that both these agents may be used as markers in the overall aging process of IVD. General significance: Accumulation of modified IVD elastin argues for its longevity and may have a negative impact on its role in disc function. Weak signs of newly synthesized molecules may act to counteract this effect in degenerate tissue. [Copyright &y& Elsevier]

High-density ceramics of ceria doped with 0, 3, 5, 10, 15 and 20mol.% Gd and with grain sizes exceeding 1.5μm were investigated by nanoindentation. The deduced elastic moduli are independent of Gd content and remain close to the value reported for bulk ceramics (210±5% GPa). All ceramics exhibit transient creep with displacement proportional to the 1/3 power of the time. For 0.05

Abstract: In the present work, we demonstrate that phosphatidylcholine with (16:1)9 acyl chains undergoes polymorphic rearrangements in mixtures with 0.6–0.8mol fraction cholesterol. Studies were performed using differential scanning calorimetry, X-ray diffraction, cryo-electron microscopy, 31P NMR static powder patterns and 13C MAS/NMR. Mixtures of phosphatidylcholine with (16:1)9 acyl chains and 0.6mol fraction cholesterol, after being heated to 100°C, can form an ordered array with periodicity 14nm which may be indicative of a cubic phase. Our results indicate that the formation of highly curved bilayer structures, such as those required for membrane fusion, can occur in mixtures of cholesterol with certain phosphatidylcholines that do not form non-lamellar structures in the absence of cholesterol. We also determine the polymorphic behavior of mixtures of symmetric phosphatidylcholines with cholesterol. Species of phosphatidylcholine with (20:1)11, (22:1)13 or (24:1)15 acyl chains in mixtures with 0.6–0.8mol fraction cholesterol undergo a transition to the hexagonal phase at temperatures 70–80°C. This is not the case for phosphatidylcholine with (18:1)6 acyl chains which remains in the lamellar phase up to 100°C when mixed with as much as 0.8mol fraction cholesterol. Thus, the polymorphic behavior of mixtures of phosphatidylcholine and cholesterol is not uncommon and is dependent on the intrinsic curvature of the phospholipid. Crystals of cholesterol can be detected in mixtures of all of these phosphatidylcholines at sufficiently high cholesterol mole fraction. What is unusual about the formation of these crystals in several cases is that cholesterol crystals are present in the monohydrate form in preference to the anhydrous form. Furthermore, after heating to 100°C and recooling, the cholesterol crystals are again observed to be in the monohydrate form, although pure cholesterol crystals require many hours to rehydrate after being heated to 100°C. Both the nature of the acyl chain as well as the mole fraction cholesterol determine whether cholesterol crystals in mixtures with the phospholipids will be in the monohydrate or in the anhydrous form. [Copyright &y& Elsevier]

We have studied the properties of mixtures of cholesterol with dioleoylphosphatidylcholine (DOPC), and with several other phospholipids, including 1-stearoyl-2-oleoylphosphatidylcholine (SOPC) and dioleoleoylphosphatidylserine (DOPS), as a function of cholesterol molar fraction and of temperature. Mixtures of DOPC with a cholesterol molar fraction of 0.4 or greater display polymorphic behavior. This polymorphism includes the formation of structures that give rise to isotropic peaks in 31P NMR at cholesterol molar fractions between 0.4 and 0.6, dependent on the thermal history of the sample. Cryo-electron microscopy studies demonstrate the formation of small globular aggregates that would contribute to a narrowing of the 31P NMR powder pattern. At molar fraction cholesterol 0.6 and higher and at temperatures above 70°C, the mixtures with DOPC convert to the hexagonal phase. Lipid polymorphism is accompanied by the phase separation of cholesterol crystals in the anhydrous form and/or the monohydrate form. The crystals that are formed have substantially altered kinetics of hydration and dehydration, compared with both pure cholesterol monohydrate crystals and with crystals formed in the presence of the other phospholipids that do not form the hexagonal phase in the presence of cholesterol. This fact demonstrates that these cholesterol crystals are in intimate contact with the DOPC phospholipid and are not present as morphologically separate structures. [Copyright &y& Elsevier]

• Oligo-amines with +3 to +6 positive charges efficiently conjugate lipid bilayers. • Conjugation did not cause any significant denaturation of the two membrane proteins studied. • Membrane conjugation is fully reversible upon addition of NaCl. • Membrane conjugation can be achieved between pH 2.5 to pH 7. • Membrane conjugation is achieved in the absence of polymers (e.g. PEGs) or metals (e.g. Ca2+). We report the first observation of an efficient, native membrane conjugation mechanism via positively charged, linear oligo-amines. Clustering of membrane fragments relies on electrostatic interactions between the net negative charge of the membranes and the positively charged, water-soluble mediators. This conjugation principle is demonstrated with two different bacterial membranes in which are embedded either the intrinsic membrane protein (MP) bacteriorhodopsin (bR) or the more recently identified xanthorhodopsin (XR). As determined by their characteristic UV–vis absorption spectra and by circular dichroism, the MPs are not significantly perturbed by the oligo-amines carrying from +3 to +6 positive charges. Light microscopy and scanning electron microscope (SEM) imaging provide direct evidence for membrane conjugation. Process efficiency was found to be correlated with the net charge of the oligo-amine used. Membrane conjugation is accomplished within a wide range of pH values (7−2.5); is reversed by NaCl; and does not require the presence of a precipitant (e.g. PEG) nor Ca2+ ions. Some evidence for bilayer fusion is also observed, but only in the presence of the +6 oligo-amine analog. [ABSTRACT FROM AUTHOR]