Raman polarization analysis of highly crystalline polyethylene fiber

The complex orientation dependence in space of Raman active vibrations in the orthorhombic structure of polyethylene (PE) is discussed in terms of Raman tensor elements as intrinsic physical parameters of the lattice. Building upon the symmetry assignment of these vibrational modes, we systematically studied, from both theoretical and experimental viewpoints, the changes of polarized intensity for the A(g) and the B-2g + B-3g vibrational modes with respect to PE molecular orientation. After explicitly expanding the Raman selection rules associated with the Ag and the B-2g + B-3g modes, introducing them into general expressions of the orientation distribution function, and validating them by means of a least-square fitting procedure on experimental data, we compare here two mesostructural models for a highly crystallized and self-aligned PE fiber structure. Stereological arguments are shown concerning the arrangement of orthorhombic fibrils in such a sample that unfold the correct values of five independent Raman tensor elements for orthorhombic PE. Copyright (C) 2010 John Wiley & Sons, Ltd

Raman tensor analysis of hexagonal polyoxymethylene and its application to study the molecular arrangement in highly crystalline electrospun nanofibers

The orientation dependence in space of Raman-active vibrations in the hexagonal structure of polyoxymethylene (POM) is discussed in terms of Raman tensor elements as intrinsic physical parameters of the lattice. The variation of polarized intensity for the A1 and the E1 vibrational modes with respect to the POM molecular orientation is systematically studied, from both theoretical and experimental viewpoints, according to the symmetry assignments of each vibrational mode. A set of working equations including the Raman selection rules associated with the A1 and the E1 modes and the orientation distribution function are explicitly formulated and validated by means of a least-square fitting procedure on experimental data. In addition, an approach based on the introduction of orientation distribution functions is applied to quantitatively assess and compare on a statistical base the molecular orientation of two different types of electrospun POM nanofibers. Copyright (c) 2012 John Wiley & Sons, Ltd

New method to measure thermal shock resistance in ceramics using a piezo-spectroscopic technique

A new method for assessing the critical temperature in thermally shocked ceramics is proposed. It is based on the measurement of stress relaxation of residual stresses as a consequence of thermal shock. The change in the stress-field is determined by piezo-spectroscopic technique. The technique is described and the results analyzed. The values obtained are compared with those obtained by the conventional method based on strength degradation measured on test pieces quenched at different temperatures. The agreement among the data is very good

Data-Driven Innovations in Joint Replacement: Do Ceramic Femoral Heads Contribute to Polyethylene Oxidation?

Renewed attention is being paid to biomaterials used in total hip arthroplasty (THA) given the continued clinical problems of osteolysis and aseptic loosening which result from the long-term wear of acetabular polyethylene (PE) bearing surfaces. One advantage of using ceramic femoral heads is low PE wear, presumably because of the ceramics ' bioinert behavior. However, beyond simple mechanical abrasion, marked differences have been found in the degradation of PE when coupled with different ceramic materials. This study examined the surface characteristics and performance of oxide-based (zirconia-toughened alumina, ZTA) and non-oxide (silicon nitride, Si3N4) femoral heads. Under articulation, ZTA femoral heads were found to release detectable amounts of oxygen from their surfaces into the tribolayer, which resulted in enhanced PE oxidation. In contrast, femoral heads made from Si3N4 scavenged oxygen from the tribolayer, thereby limiting the degradation of PE. This work is the first to challenge the assumption that ceramic materials are inherently stable in vivo, and suggests that the longevity of THA prostheses may depend on the material properties of the ceramic used during surgery. Neglecting these important physical chemistry aspects impedes the scientific development of new materials and favors monopolistic economics in the market, leading to limited choices for surgeons

Epithelial anion secretion of human bronchial ciliary epithelium

Background: Airway epithelia play key roles in maintaining the volume and composition of airway surface liquid by regulating trans-epithelial ion transport. However, little information is available on ion transport in upper airway epithelia. Objectives: To clarify the anion transport such as Cl-and HCO3-in human bronchial ciliary epithelium cells. Methods: Airway cells were collected by brushing bronchus during bronchoscopy, after purification of progenitor cells, air liquid interface cultured and induced differentiation into ciliated cells. Trans-epithelial ion transport of airway epithelia was analyzed measuring the short circuit current (Isc) and surface pH using surface enhanced Raman spectroscopy Results: In human bronchial ciliary epithelia, the amount of anion secretion was equal to that of Na+absorption. To focus on the anion transport, experiments were carried out under a condition of blocking Na+absorption by benzamil. Under a Cl-/HCO3--containing condition, the basolateral addition of DIDS, a blocker of anion exchanger, Na+/bicarbonate cotransporters and Cl- channels, decreased Isc. Under a Cl--free HCO3--containing condition, Isc was smaller than that under a Cl-/HCO3--containing condition. Finally, under a HCO3--free Cl--containing condition, Isc was smaller than that under a Cl-/HCO3--containing condition and similar to that under a Cl--free HCO3--containing condition. Apical surface pH showed a decreasing trend after addition of DIDS, NPPB, and a Cl--free HCO3--containing solution. Conclusion: Human bronchial ciliary cells secrete not only Cl-but also HCO3-via cooperationbetween Cl- channel and anion exchanger, contributing to control of the volume and composition of airway surface liquid

Fast curing of restorative materials through the soft light energy release

Objective. The effect of a novel light curing process, namely soft light energy release (SLER (R)), on shrinkage, mechanical strength and residual stress of four dental restorative materials (DEI experience, Gradia Direct, Enamel Plus HFO and Venus) was investigated.Methods. Composite specimens were fast cured through high level of power density and soft light energy release. Temperature, linear shrinkage and light power measurements were acquired in parallel in order to assess the effect of light modulation on temperature and shrinkage profiles during the light curing process and the following dark reaction phase. The small punch test and Raman spectroscopy were adopted to investigate the effect of SLER (R) on mechanical strength and on internal stress, respectively.Results. The soft light energy release photo- polymerization allows to reduce of about 20% the shrinkage rate and to increase the strength of fast light cured specimens. In addition, a more relaxed and homogeneous internal stress distribution was observed.Significance. Properties of fast cured restorative materials can be improved by adopting the soft light energy release process. (C) 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved

Chemically driven tetragonal-to-monoclinic polymorphic transformation in retrieved ZTA femoral heads from dual mobility hip implants

Two short-term (two and nine months) retrieved zirconia-toughened alumina (ZTA) femoral heads and nine pristine femoral heads from the same manufacturer have been investigated with respect to their surface stability by means of confocal Raman spectroscopy. Quantitative estimations of monoclinic volume fraction have been carried out in both non-wear and main wear zones of the retrieved heads, which invariantly showed high volume fractions of monoclinic polymorph. In-depth (sub-surface) profiles, non-destructively collected in the main wear zones with the Raman probe in confocal configuration, indeed confirmed that polymorphic transformation was extended down to 100 mu m below the bearing surface of the femoral heads. Acceleration of tetragonal-to-monoclinic transformation rate leads to unexpectedly high fractions of monoclinic phase within very short-term in-vivo exposures. Phase transformation in-vivo is much more marked than what one could actually predict according to simply simulating a hydrothermal environment in-vitro and could not be simply ascribed to the mechanical stress fields generated during normal service at the bearing surface. Instead, the chemical consequences of metal contamination on the ZTA femoral head surface are shown to play the most detrimental role in phase destabilization. (C) 2015 Elsevier Ltd. All rights reserved

Effect of pH and monovalent cations on the Raman spectrum of water: Basics revisited and application to measure concentration gradients at water/solid interface in Si3N4 biomaterial

The effect of hydrogen carbonate (HCO3-) and cations (Na+, K+) solvated in water were revisited according to high spectrally resolved Raman measurements. Water solutions with different bicarbonate concentrations or added with increasing amounts of monovalent cations were examined with respect to their Raman spectra both in the bulk state and at the solid/liquid interface with a silicon nitride (Si3N4) bioceramic. Spectroscopic calibrations confirmed that the Raman emission from OH-stretching in water is sensitive to molarity variations (in the order of tens of mM). The concentration gradient developed at the solid/liquid interface in cation-added solutions interacting with a Si3N4 surface was measured and found to be peculiar to individual cations. Local variation in pH was detected in ionic solutions interacting with Si3N4 samples, which might represent a useful property for Si3N4 in a number of biomedical applications. (C) 2015 Elsevier B.V. All rights reserved