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Polarized Raman spectroscopy is applied to non-destructively unfold the variation of crystallographic orientation in wurtzitic GaN films that occurred during their growth on (0001)-oriented sapphire substrates as a function of growth conditions. Variations of polarized Raman spectra were clearly observed at different locations along the growth direction by systematically performing line scans on cross sections of different film/substrate systems. Such variations showed a strong dependence on the type of buffer layer, deposition temperature, and reactor pressure. The observed trends suggested the occurrence of inhomogeneous lateral growth of GaN films near the buffer layer and a continuous adjustment of the structure of the tilted-grown epilayer during the growth process until reaching the expected stable structure. The large elastic/thermal mismatch, which could not be fully relaxed by the effect of the buffer layer, resulted in a non-uniform distribution of residual strain. Such strain, mainly stored at the interface, gradually relaxed by the occurrence of tilting and twisting of the crystal cells along the film growth direction: a process that spontaneously occurred minimizing the strain energy stored in the film/substrate system. Varying reactor pressure caused a variation of residual strain in the epilayer and thus a different adjustment of the GaN microstructure during the growth process. Relatively homogenous GaN films with a low density of dislocations could be achieved on patterned sapphire substrates, despite the presence of crystallographic tilting of the film. [ABSTRACT FROM AUTHOR]

Raman spectroscopy was applied with a high spectral resolution to a structural study of Influenza (type A) virus before and after its inoculation into Madin–Darby canine kidney cells. This study exploits the fact that the major virus and cell constituents, namely DNA/RNA, lipid, and protein molecules, exhibit peculiar fingerprints in the Raman spectrum, which clearly differed between cells and viruses, as well as before and after virus inoculation into cells. These vibrational features, which allowed us to discuss viral assembly, membrane lipid evolution, and nucleoprotein interactions of the virus with the host cells, reflected the ability of the virus to alter host cells' pathways to enhance its replication efficiency. Upon comparing Raman signals from the host cells before and after virus inoculation, we were also able to discuss in detail cell metabolic reactions against the presence of the virus in terms of compositional variations of lipid species, the formation of fatty acids, dephosphorylation of high‐energy adenosine triphosphate molecules, and enzymatic hydrolysis of the hemagglutinin glycoprotein. [ABSTRACT FROM AUTHOR]

In this paper, Raman spectral mappings were carried out on Vickers indentation prints introduced on DLC films prepared with different substrate bias voltages (SBV). The mapping results showed clear differences in the intensity ratio, I D / I G , and band shifts for D and G peaks in samples fabricated with and without applying SBV. These spectral characteristics arose from the cumulative effect of a compressive (residual) stress field and structural alterations including sp2 and sp3 carbon disorder upon generation of the indentation print. Additional quantitative stress analyses, which employed spectral line scans on the film cross sections, revealed clear differences in magnitude for the compressive stresses stored in the films, as well as in-depth structural variations resulting from different SBV being applied during fabrication. An increasing level of residual compressive stress in the DLC films with increasing SBV may directly contribute to the observed decreased adhesion to the substrates and to the increased Vickers hardness. Unlabelled Image • Raman mappings were conducted around Vickers indentation prints on DLC films. • Applying SBV showed clear influences on I D / I G , and band shifts for D and G peaks. • Stress and structural alterations influence sp2 and sp3 carbon disorder. • Residual stresses and in-depth structural variations varied with SBV. • Residual compressive stress influenced film adhesion and Vickers hardness. [ABSTRACT FROM AUTHOR]

Over the next two decades, a strong demographic demand for arthroplastic devices coupled with a decreased efficacy of antibiotics has been predicted to result in an exponential increase in the number of periprosthetic joint infections (PJIs). Advanced strategies are therefore required to improve the local peri-implant immune response and curb the pathogenic events of bacterial adhesion and biofilm formation. The use of biomaterials that autonomously counter infections is one approach to improve orthopedic outcomes. Using conventional molecular biology characterization methods and advanced Raman spectroscopy, this study examined the bacteriostatic response of two bioceramic materials commonly employed as prosthetic implants: zirconia-toughened alumina (ZTA) and silicon nitride (Si3N4). Unlike the ZTA, it was found that non-oxide Si3N4 possesses an inherently anti-infective surface chemistry, which acts in a responsive way against bacterial loading. The mechanistic details of its behavior are elucidated. Non-oxide bioceramics appear to be promising, but their full development requires a transitional approach that integrates the fundamental biochemical concepts with clinical outcomes. [ABSTRACT FROM AUTHOR]

Purpose: The purposes of this study were to document novel Raman spectroscopic findings in femoral heads affected by osteonecrosis and to identify molecular structure differences based on aetiology.Methods: We obtained 13 femoral heads with osteonecrosis from 13 different patients who underwent total hip arthroplasty. Comparisons were made between the viable zones of each femoral head examined. The samples were scanned with X-ray micro-CT for structural mapping and a central coronal section slab was prepared for Raman spectroscopy and histological analyses. Raman spectra were collected at different locations, including the viable and necrotic zones of the femoral head, using a highly spectrally resolved Raman microprobe.Results: Significant alterations in the spectral morphology in the high wavenumber region were found, with a pronounced inhibition of peculiar lipid signals in the frequency interval 2851 ~ 2890 cm-1 and at ~ 1750 cm-1. The necrotic zone in steroid-associated osteonecrosis showed an increase in the ratio of lipid-related bands to protein-related bands, while alcohol-associated osteonecrosis exhibited a decrease in this ratio.Conclusions: We systematically found a decrease in Raman intensity for sphingomyelin and phenylalanine fingerprint bands in the necrotic zones, and these differences may be related to the etiology of osteonecrosis. [ABSTRACT FROM AUTHOR]

The Raman spectroscopic method has quantitatively been applied to the analysis of local crystallographic orientation in both single-crystal hydroxyapatite and human teeth. Raman selection rules for all the vibrational modes of the hexagonal structure were expanded into explicit functions of Euler angles in space and six Raman tensor elements (RTE). A theoretical treatment has also been put forward according to the orientation distribution function (ODF) formalism, which allows one to resolve the statistical orientation patterns of the nm-sized hydroxyapatite crystallite comprised in the Raman microprobe. Close-form solutions could be obtained for the Euler angles and their statistical distributions resolved with respect to the direction of the average texture axis. Polarized Raman spectra from single-crystalline hydroxyapatite and textured polycrystalline (teeth enamel) samples were compared, and a validation of the proposed Raman method could be obtained through confirming the agreement between RTE values obtained from different samples. [ABSTRACT FROM AUTHOR]

Three types of commercially available ultra-high molecular weight polyethylene (UHMWPE) acetabular cups currently used in total hip arthroplasty have been studied by means of Raman micro-spectroscopy to unfold the microstructural modification induced by the oxidative degradation after accelerated aging with and without lipid absorption. The three investigated materials were produced by three different manufacturing procedures, as follows: irradiation followed by remelting, one-step irradiation followed by annealing, 3-step irradiation and annealing. Clear microstructural differences were observed in terms of phase contents (i.e. amorphous, crystalline and intermediate phase fraction). The three-step annealed material showed the highest crystallinity fraction in the bulk, while the remelted polyethylene is clearly characterized by the lowest content of crystalline phase and the highest content of amorphous phase. After accelerated aging either with or without lipids, the amount of amorphous phase decreased in all the samples as a consequence of the oxidation-induced recrystallization. The most remarkable variations of phase contents were detected in the remelted and in the single-step annealed materials. The presence of lipids triggered oxidative degradation especially in the remelted polyethylene. Such experimental evidence might be explained by the highest amount of amorphous phase in which lipids can be absorbed prior to accelerated aging. The results of these spectroscopic characterizations help to rationalize the complex effect of different irradiation and post-irradiation treatments on the UHMWPE microstructure and gives useful information on how significantly any single step of the manufacturing procedures might affect the oxidative degradation of the polymer. [ABSTRACT FROM AUTHOR]

In this paper, polarized Raman spectroscopy is applied to quantitatively assess crystallographic alteration and interfacial residual stress with a micron-scale resolution in highly 〈0 0 0 1〉 oriented (textured) polycrystalline wurtzitic AlN films grown on (0 0 1)-oriented Si substrates. Raman selection rules for the wurtzite structure of AlN were explicitly put forward and a set of Raman tensor elements determined from experimentally retrieved angular dependences of Raman band intensities upon in-plane rotation measurements. An appreciably high degree of homogeneity in the AlN film (i.e., with respect to both in-plane and out-of-plane Euler angles, retrieved according to the proposed spectroscopic algorithm) could be observed in spectral line scans randomly selected on the cross-section of the film/substrate system. These characterizations indicated negligible structural alterations, such as grain tilting and twisting during film growth. However, a non-uniform stress distribution in the AlN film along the film thickness direction was found, which remained stored during manufacturing of the AlN film. A quite remarkable magnitude of compressive residual stress (∼−1.5 GPa) could be measured at the film/substrate interface. Finally, a Raman (non-destructive) statistical characterization of the film system in terms of micromechanical homogeneity by spectral surface mapping is presented, which provides a prompt overall view of the film quality. The proposed procedure should generally be applicable in crystallographic and micromechanical quality control of electronic film devices exhibiting a Raman spectrum. [ABSTRACT FROM AUTHOR]

Diamond-like carbon (DLC) films represent promising surface treatments for biomedical implants. In this paper, using Raman and X-ray photoelectron spectroscopies, we analyzed the effects of secondary phases present in ZrO 2 substrates on the structure of DLC films fabricated by plasma-based ion implantation and deposition method, and the structural stability of the films in response to applied indentation prints. The results revealed oxygen incorporation in DLC films from the oxide substrates during deposition, and a clear dependence of sp3 carbon content on the oxygen fraction of the substrate and on gas pressure. Moreover, a pronounced structural distortion of the DLC films at the film/substrate interface was observed, which resulted from polymorphic transformation on the zirconia surface during deposition, while a pronounced change in Raman spectral morphology of carbon induced by structural alterations could also be observed around the indentation prints. The findings clearly pointed at the need to take into considerations the structural alterations of the DLC film structure at the interface associated with interfacial defects and film adhesion, especially for biomedical applications that involve surface loading. [Display omitted] • Effects of secondary phases in ZrO 2 substrates on the DLC structure were clarified. • Structural stability of the films in response to applied loads was investigated. • Oxygen incorporation in DLC films depended on both substrate and gas pressure. • Phase transformation of zirconia contributed to structural distortion of DLC films. • Structural alterations were induced around the indentation prints on the DLC films. [ABSTRACT FROM AUTHOR]

Abstract: Raman spectroscopy and scanning electron microscopy, combined with the Vickers indentation method, were applied to analyze the fracture behavior of a thin (i.e., 1μm in thickness) aluminum nitride (AlN) film deposited on a (001)Si substrate. A series of indentations were introduced in the AlN/Si system with applying gradually increasing loads, and the stress intensity factor, K R, stored at the tip of cracks propagated from the indentation corners was determined according to the shift of selected Raman bands from wurtzitic AlN in response to the crack-tip residual stress field. A steeply rising crack resistance curve was found in the AlN film, starting from an intrinsic toughness, K I0 =0.6MPam1/2, for crack initiation up to K R ≅5MPam1/2 (at a crack length of ~120μm). Such rising R-curve behavior was attributed to the presence of a compressive residual stress field stored in the AlN film. The results obtained by Raman spectroscopy were consistently supported by direct crack opening displacement measurements in a scanning electron microscope. [Copyright &y& Elsevier]

A quantitative polarized Raman analysis of ferroelectric grain/domain orientation in LiSbO3 (LS-modified) (K0.5Na0.5)NbO3 (KNN) ceramics is presented, based on the analysis of the complex orientation dependence in space of their Raman-active modes. Complete sets of Raman tensor elements of Ag, and Eg phonon modes for orthorhombic/tetragonal structures of KNN have been determined. Through this spectroscopic algorithm, quantitative information could be extracted in terms of three Euler angles in space for KNN samples consisting of mixed phases, thus enabling quantitative visualization of the local distribution of grains/domains in the solid angle. As an application of the method, we quantitatively examined the unknown crystallographic grain orientation patterns on the surfaces of pure KNN and of KNN-0.05LS ceramics. These two samples were useful to clarify a polymorphic phase transition from the orthorhombic to the tetragonal phase taking place in the LS-modified KNN system. Thus, we demonstrated that polarized Raman spectroscopy is a valuable and efficient tool for nondestructive three-dimensional assessments of grain/domain orientation in ferroelectric materials with complex polymorphic structures. We believe that the data shown here represent a typical scenario encountered in grain/domain orientation assessments of piezoelectric perovskites. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In the current study, high-temperature stability was investigated in two types of zirconia ceramics stabilized with two different additives, namely, calcia and yttria. The evolutions of structure and oxygen-vacancy-related defects upon annealing in air were investigated as a function of temperature by combining X-ray diffractometry with Raman, X-ray photoelectron and cathodoluminescence spectroscopies. We systematically characterized variations in the concentration of oxygen vacancies and hydroxyl groups during thermal treatments and linked them to structural alterations and polymorphic transformation. With this approach, we clarified how the combined effects of different dopants and temperature impacted on structural development and on the thermal stability of the oxygen-vacancy-related defect complex. [ABSTRACT FROM AUTHOR]

[Display omitted] • Analytical algorithms were proposed for fast determining amylose content in rice. • Linear and branched polysaccharide structures were characterized and compared. • Vadiation of the new algorithm was made by comparing with colorimetry method. Analytical algorithms based on Raman spectroscopy are proposed for the determination of amylopectin and amylose concentrations in polished white rice, and applied to characterize and compare linear and branched polysaccharide structures in nine different types of Japanese rice. A selected algorithm used symmetric bending vibrations of the C O C glycosidic linkage from a relatively narrow spectral zone between 830 and 895 cm−1. It specifically compared the intensity of Raman signals from two types of bending common to both starch components (C1-O-C5 and C1-O-C4 at 868 and 855 cm−1, respectively) and that at the branch point peculiar to amylopectin (C1-O-C6 at 844 cm−1). Raman data were confronted with data collected by conventional amylose-iodine colorimetry method. Consistency was found between Raman and colorimetric methods over the entire series of tested rice cultivars, thus validating the newly proposed spectroscopic algorithm. The amylose content of the tested rice species broadly varied between 1.2 and 20.4%. The proposed Raman algorithm allows fast and nondestructive determination of amylose content in rice with minimal sample preparation. These characteristics might be key in the development of portable Raman devices capable to promptly screen polysaccharides in different rice cultivars with respect to their interannual and plantation-related fluctuations. [ABSTRACT FROM AUTHOR]

In this study, electrospun scaffolds were fabricated using polycaprolactone (PCL) loaded with varying concentrations of β-carotene (1.2%, 2.4%, and 3.6%) via the electrospinning technique. The electrospinning process involved the melting of PCL in acetic acid, followed by the incorporation of β-carotene powder under constant stirring. Raman spectroscopy revealed a homogeneous distribution of β-carotene within the PCL matrix. However, the β-carotene appeared in particulate form, rather than being dissolved and blended with the PCL matrix, a result also confirmed by thermogravimetric analysis. Additionally, X-ray diffraction analysis indicated a decrease in crystallinity with increasing β-carotene concentration. Mechanical testing of the scaffolds demonstrated an increase in ultimate strain, accompanied by a reduction in ultimate stress, indicating a potential plasticizing effect. Moreover, antimicrobial assays revealed a marginal antibacterial effect against Escherichia coli for scaffolds with higher β-carotene concentrations. Conversely, preliminary biological assessment using KUSA-A1 mesenchymal cells indicated enhanced cellular proliferation in response to the scaffolds, suggesting the potential biocompatibility and cell-stimulating properties of β-carotene-loaded PCL scaffolds. Overall, this study provides insights into the fabrication and characterization of electrospun PCL scaffolds containing β-carotene, laying the groundwork for further exploration in tissue engineering and regenerative medicine applications. [ABSTRACT FROM AUTHOR]

An improved method of confocal/polarized Raman spectroscopy is proposed, which enables the determination of the full set of tensor components in three dimensionally graded stress fields in sapphire single-crystal. From the experimental side, the proposed method employs a simple back-scattered configuration for the optical microprobe and relies on the experimental knowledge of the matrix of piezospectroscopic (PS) coefficients of sapphire (i.e., the proportionality constants relating the frequency shifts of individual Raman bands to the magnitude of an uniaxial stress applied along different crystallographic directions). From the theoretical side, the complete set of stress tensor components were generally expressed as a function of the PS coefficients for any unknown multiaxial stress state by means of the Euler transformation matrix, leading to a system of linear equations; such equations link each stress component to the experimentally observed spectral shifts of different Raman bands. The proposed PS method does not require a direct knowledge of the secular equation, but local crystallographic orientations should be retrieved from polarized Raman intensities. With probe averaging effects being systematically removed by probe deconvolutive routines, the PS method is shown to correctly resolve multiaxial stress tensor fields with steep gradients in space. [ABSTRACT FROM AUTHOR]

The recent increase of the number of unidentified cadavers has become a serious problem throughout the world. As a simple and objective method for age estimation, we attempted to utilize Raman spectrometry for forensic identification. Raman spectroscopy is an optical-based vibrational spectroscopic technique that provides detailed information regarding a sample's molecular composition and structures. Building upon our previous proof-of-concept study, we measured the Raman spectra of abdominal skin samples from 132 autopsy cases and the protein-folding intensity ratio, RPF, defined as the ratio between the Raman signals from a random coil an α-helix. There was a strong negative correlation between age and RPF with a Pearson correlation coefficient of r = 0.878. Four models, based on linear (RPF), squared (RPF2), sex, and RPF by sex interaction terms, were examined. The results of cross validation suggested that the second model including linear and squared terms was the best model with the lowest root mean squared error (11.3 years of age) and the highest coefficient of determination (0.743). Our results indicate that the there was a high correlation between the age and RPF and the Raman biological clock of protein folding can be used as a simple and objective forensic age estimation method for unidentified cadavers. [ABSTRACT FROM AUTHOR]

Raman spectroscopy was applied to study the structural differences between herpes simplex virus Type I (HSV-1) and Epstein–Barr virus (EBV). Raman spectra were first collected with statistical validity on clusters of the respective virions and analyzed according to principal component analysis (PCA). Then, average spectra were computed and a machine-learning approach applied to deconvolute them into sub-band components in order to perform comparative analyses. The Raman results revealed marked structural differences between the two viral strains, which could mainly be traced back to the massive presence of carbohydrates in the glycoproteins of EBV virions. Clear differences could also be recorded for selected tyrosine and tryptophan Raman bands sensitive to pH at the virion/environment interface. According to the observed spectral differences, Raman signatures of known biomolecules were interpreted to link structural differences with the viral functions of the two strains. The present study confirms the unique ability of Raman spectroscopy for answering structural questions at the molecular level in virology and, despite the structural complexity of viral structures, its capacity to readily and reliably differentiate between different virus types and strains. [ABSTRACT FROM AUTHOR]

The stress dependence of the Raman spectrum of a relaxor-based polycrystalline ferroelectric lead zirconate titanate–lead nickel niobate–lead zinc niobate (PZT–PNN–PZN) has been investigated using polarized Raman microprobe spectroscopy. Emphasis has been placed on explicitly working out the second harmonic equations that relate Raman intensities to the angle between the laser polarization direction and selected crystalline axes. Based on these assessments, the effect under polarized light of crystal orientation on the intensity of selected Raman modes has been rationalized and the obtained experimental data interpreted. Raman spectra were collected with both parallel and cross polarization filters and their dependence on stress calibrated with loading the PZT–PNN–PZN samples in a four-point flexural jig. The use of polarized light allowed us to clarify the effect of domain orientation on the Raman spectrum of PZT–PNN–PZN and to perform precise calibrations of the stress dependence of the A1(TO4) Raman mode, independent of domain orientation in both poled and unpoled PZT–PNN–PZN samples. This study demonstrates the feasibility of microscopic stress (in addition to local domain orientation) evaluations in PZT materials using a polarized Raman microprobe. [ABSTRACT FROM AUTHOR]

The aim of this study was to elucidate the chemistry of cellular degeneration in human neuroblastoma cells upon exposure to outer-membrane vesicles (OMVs) produced by Porphyromonas gingivalis (Pg) oral bacteria by monitoring their metabolomic evolution using in situ Raman spectroscopy. Pg-OMVs are a key factor in Alzheimer's disease (AD) pathogenesis, as they act as efficient vectors for the delivery of toxins promoting neuronal damage. However, the chemical mechanisms underlying the direct impact of Pg-OMVs on cell metabolites at the molecular scale still remain conspicuously unclear. A widely used in vitro model employing neuroblastoma SH-SY5Y cells (a sub-line of the SK-N-SH cell line) was spectroscopically analyzed in situ before and 6 h after Pg-OMV contamination. Concurrently, Raman characterizations were also performed on isolated Pg-OMVs, which included phosphorylated dihydroceramide (PDHC) lipids and lipopolysaccharide (LPS), the latter in turn being contaminated with a highly pathogenic class of cysteine proteases, a key factor in neuronal cell degradation. Raman characterizations located lipopolysaccharide fingerprints in the vesicle structure and unveiled so far unproved aspects of the chemistry behind protein degradation induced by Pg-OMV contamination of SH-SY5Y cells. The observed alterations of cells' Raman profiles were then discussed in view of key factors including the formation of amyloid β (Aβ) plaques and hyperphosphorylated Tau neurofibrillary tangles, and the formation of cholesterol agglomerates that exacerbate AD pathologies. [ABSTRACT FROM AUTHOR]

Hydrolytic reactions taking place at the surface of a silicon nitride (Si3N4) bioceramic were found to induce instantaneous inactivation of Human herpesvirus 1 (HHV-1, also known as Herpes simplex virus 1 or HSV-1). Si3N4 is a non-oxide ceramic compound with strong antibacterial and antiviral properties that has been proven safe for human cells. HSV-1 is a double-stranded DNA virus that infects a variety of host tissues through a lytic and latent cycle. Real-time reverse transcription (RT)-polymerase chain reaction (PCR) tests of HSV-1 DNA after instantaneous contact with Si3N4 showed that ammonia and its nitrogen radical byproducts, produced upon Si3N4 hydrolysis, directly reacted with viral proteins and fragmented the virus DNA, irreversibly damaging its structure. A comparison carried out upon testing HSV-1 against ZrO2 particles under identical experimental conditions showed a significantly weaker (but not null) antiviral effect, which was attributed to oxygen radical influence. The results of this study extend the effectiveness of Si3N4's antiviral properties beyond their previously proven efficacy against a large variety of single-stranded enveloped and non-enveloped RNA viruses. Possible applications include the development of antiviral creams or gels and oral rinses to exploit an extremely efficient, localized, and instantaneous viral reduction by means of a safe and more effective alternative to conventional antiviral creams. Upon incorporating a minor fraction of micrometric Si3N4 particles into polymeric matrices, antiherpetic devices could be fabricated, which would effectively impede viral reactivation and enable high local effectiveness for extended periods of time. [ABSTRACT FROM AUTHOR]

This study probed in vitro the mechanisms of competition/coexistence between Streptococcus sanguinis (known for being correlated with health in the oral cavity) and Streptococcus mutans (responsible for aciduric oral environment and formation of caries) by means of quantitative Raman spectroscopy and imaging. In situ Raman assessments of live bacterial culture/coculture focusing on biofilm exopolysaccharides supported the hypothesis that both species engaged in antagonistic interactions. Experiments of simultaneous colonization always resulted in coexistence, but they also revealed fundamental alterations of the biofilm with respect to their water-insoluble glucan structure. Raman spectra (collected at fixed time but different bacterial ratios) showed clear changes in chemical bonds in glucans, which pointed to an action by Streptococcus sanguinis to discontinue the impermeability of the biofilm constructed by Streptococcus mutans. The concurrent effects of glycosidic bond cleavage in water-insoluble α − 1,3–glucan and oxidation at various sites in glucans' molecular chains supported the hypothesis that secretion of oxygen radicals was the main "chemical weapon" used by Streptococcus sanguinis in coculture. [ABSTRACT FROM AUTHOR]

This study targets on-site/real-time taxonomic identification and metabolic profiling of seven different Candida auris clades/subclades by means of Raman spectroscopy and imaging. Representative Raman spectra from different Candida auris samples were systematically deconvoluted by means of a customized machine-learning algorithm linked to a Raman database in order to decode structural differences at the molecular scale. Raman analyses of metabolites revealed clear differences in cell walls and membrane structure among clades/subclades. Such differences are key in maintaining the integrity and physical strength of the cell walls in the dynamic response to external stress and drugs. It was found that Candida cells use the glucan structure of the extracellular matrix, the degree of α-chitin crystallinity, and the concentration of hydrogen bonds between its antiparallel chains to tailor cell walls' flexibility. Besides being an effective ploy in survivorship by providing stiff shields in the α–1,3–glucan polymorph, the α–1,3–glycosidic linkages are also water-insoluble, thus forming a rigid and hydrophobic scaffold surrounded by a matrix of pliable and hydrated β–glucans. Raman analysis revealed a variety of strategies by different clades to balance stiffness, hydrophobicity, and impermeability in their cell walls. The selected strategies lead to differences in resistance toward specific environmental stresses of cationic/osmotic, oxidative, and nitrosative origins. A statistical validation based on principal component analysis was found only partially capable of distinguishing among Raman spectra of clades and subclades. Raman barcoding based on an algorithm converting spectrally deconvoluted Raman sub-bands into barcodes allowed for circumventing any speciation deficiency. Empowered by barcoding bioinformatics, Raman analyses, which are fast and require no sample preparation, allow on-site speciation and real-time selection of appropriate treatments. [ABSTRACT FROM AUTHOR]

This study presents a set of vibrational characterizations on a nanogel-cross-linked porous freeze-dried gel (NanoCliP-FD gel) scaffold for tissue engineering and regenerative therapy. This scaffold is designed for the in vitro culture of high-quality cartilage tissue to be then transplanted in vivo to enable recovery from congenital malformations in the maxillofacial area or crippling jaw disease. The three-dimensional scaffold for in-plate culture is designed with interface chemistry capable of stimulating cartilage formation and maintaining its structure through counteracting the dedifferentiation of mesenchymal stem cells (MSCs) during the formation of cartilage tissue. The developed interface chemistry enabled high efficiency in both growth rate and tissue quality, thus satisfying the requirements of large volumes, high matrix quality, and superior mechanical properties needed in cartilage transplants. We characterized the cartilage tissue in vitro grown on a NanoCliP-FD gel scaffold by human periodontal ligament-derived stem cells (a type of MSC) with cartilage grown by the same cells and under the same conditions on a conventional (porous) atelocollagen scaffold. The cartilage tissues produced by the MSCs on different scaffolds were comparatively evaluated by immunohistochemical and spectroscopic analyses. Cartilage differentiation occurred at a higher rate when MSCs were cultured on the NanoCliP-FD gel scaffold compared to the atelocollagen scaffold, and produced a tissue richer in cartilage matrix. In situ spectroscopic analyses revealed the cell/scaffold interactive mechanisms by which the NanoCliP-FD gel scaffold stimulated such increased efficiency in cartilage matrix formation. In addition to demonstrating the high potential of human periodontal ligament-derived stem cell cultures on NanoCliP-FD gel scaffolds in regenerative cartilage therapy, the present study also highlights the novelty of Raman spectroscopy as a non-destructive method for the concurrent evaluation of matrix quality and cell metabolic response. In situ Raman analyses on living cells unveiled for the first time the underlying physiological mechanisms behind such improved chondrocyte performance. [ABSTRACT FROM AUTHOR]

Oral candidiasis, a common opportunistic infection of the oral cavity, is mainly caused by the following four Candida species (in decreasing incidence rate): Candida albicans, Candida glabrata, Candida tropicalis, and Candida krusei. This study offers in-depth Raman spectroscopy analyses of these species and proposes procedures for an accurate and rapid identification of oral yeast species. We first obtained average spectra for different Candida species and systematically analyzed them in order to decode structural differences among species at the molecular scale. Then, we searched for a statistical validation through a chemometric method based on principal component analysis (PCA). This method was found only partially capable to mechanistically distinguish among Candida species. We thus proposed a new Raman barcoding approach based on an algorithm that converts spectrally deconvoluted Raman sub-bands into barcodes. Barcode-assisted Raman analyses could enable on-site identification in nearly real-time, thus implementing preventive oral control, enabling prompt selection of the most effective drug, and increasing the probability to interrupt disease transmission. [ABSTRACT FROM AUTHOR]

The multiple mutations of the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) virus have created variants with structural differences in both their spike and nucleocapsid proteins. While the functional relevance of these mutations is under continuous scrutiny, current findings have documented their detrimental impact in terms of affinity with host receptors, antibody resistance, and diagnostic sensitivity. Raman spectra collected on two British variant sub‐types found in Japan (QK002 and QHN001) are compared with that of the original Japanese isolate (JPN/TY/WK‐521), and found bold vibrational differences. These included: i) fractions of sulfur‐containing amino acid rotamers, ii) hydrophobic interactions of tyrosine phenol ring, iii) apparent fractions of RNA purines and pyrimidines, and iv) protein secondary structures. Building upon molecular scale results and their statistical validations, the authors propose to represent virus variants with a barcode specially tailored on Raman spectrum. Raman spectroscopy enables fast identification of virus variants, while the Raman barcode facilitates electronic recordkeeping and translates molecular characteristics into information rapidly accessible by users. [ABSTRACT FROM AUTHOR]

Abstract: Cubic gallium oxynitride was synthesized using a solvothermal processing route. Crystal structure, chemical composition, optical properties and the influence of heat treatment in either reactive or inert atmospheres have been investigated. Despite a strongly distorted lattice revealed using X-ray diffraction, the Raman active modes of a cubic gallium oxynitride structure could be observed. With diffusive reflectance UV–Vis spectroscopy a band gap at around 4.8eV has been observed. Additionally, cathodoluminescence spectroscopy exhibited observable luminescence caused by defect-related transitions within the optical gap. Cathodoluminescence and photoluminescence spectra collected after heat treatments showed significant changes in the defect structure. In particular, for annealing in ammonia the main spectral modifications were related to the substitution of oxygen by nitrogen on anion sites. [Copyright &y& Elsevier]

Abstract: Residual (elastic) stress profiles developed in self-mating alumina heads upon long-term exposure in the human body have been quantitatively determined by means of three different piezo-spectroscopic (PS) approaches available to the alumina lattice. The PS measurements, collected at exactly the same area of the sample, included fluorescence spectroscopy (fs), Raman spectroscopy (rs) (in-depth resolutions both in the order of the tens of μm), and cathodoluminescence spectroscopy (cs) (in-depth resolution down to the tens of nm). The lateral spatial resolution was in the order of the tens of μm, of the single μm, and of the hundredths of nm for fs and rs and cs, respectively. Owing to the precise knowledge of the response functions in space of the three probes, deconvoluted stress profiles could be obtained in zone of different wear severity. The profiles revealed high stress gradients along the material subsurface, “cleaned” from averaging effects related to the finite probe volume. The subsurface stress field in heavily worn zones entailed a surface layer under strong compression, an abrupt compressive-to-tensile transition up to a similar stress magnitude, and a deeper-lying region of tension which ultimately relaxed in the unstressed bulk. The opposite trend was observed in mildly worn zones of the femoral head, with moderate tensile stresses in the immediate surface and weak counterbalancing stresses of compressive nature along the subsurface. A wear mechanism for self-mating alumina hip surfaces was then drawn consistently with the newly available residual stress profiles. [Copyright &y& Elsevier]

• For the first time, dentin demineralization has been studied with different spectroscopic techniques. • Results from different techniques were successfully correlated. • Raman spectroscopy proved to be a good diagnostic tool for evaluation of dentin demineralization. • The quantification algorithms can be easily calibrated for in vivo applications. Early detection of dental caries and variations in composition/structure of both enamel and dentin represents an important issue in modern dentistry. Demineralization has been associated to teeth discoloration, development of caries, and formation of cavities. In this study, we systematically monitored the processes of demineralization/remineralization in dentin samples by means of three different spectroscopic techniques, namely, Raman spectroscopy, X-Ray Photo-electron spectroscopy (XPS), and X-Ray Diffractometry (XRD). Bovine dentin samples were first exposed to acidic solutions and their structure systematically monitored as a function of time and pH. Then, the samples were rinsed in artificial saliva to simulate remineralization. The above three spectroscopic techniques provided quantitative structural information spanning from the nanometer to the millimeter scale of sample penetration depth. An irreversible level of demineralization was reached when dentin was exposed to pH 2 beyond a time threshold of 6 h, successive treatments with artificial saliva being unable to restore the mineral fraction. On the other hand, short-term treatments at pH 5 and long-term treatments at pH 6 could partially or completely recover the dentin structure within one week of remineralization treatment. Two specific Raman parameters, namely, the bandwidth of the symmetric phosphate-stretching signal and the mineral-to-matrix intensity ratio, showed strong correlations with XPS and XRD data, and matched laser microscopy observations. Such correlations open the path to apply Raman spectroscopy in monitoring dentin demineralization in vivo and provide quantitative working algorithms for the prevention of oral caries. [ABSTRACT FROM AUTHOR]

This study is aimed at establishing a method of polarized/confocal Raman spectroscopy capable of quantitatively assessing crystallographic orientation in wurtzitic GaN with a micron-scale resolution. First, Raman selection rules are explicitly put forward from a theoretical viewpoint in their complete form; then, experimentally retrieved intensities of the Raman signal as a function of Euler angles are fitted to the obtained theoretical dependencies in order to quantify a set of Raman tensor elements using experiments on known crystallographic planes of a wurtzitic GaN single-crystal. According to the above two procedures, a spectroscopic algorithm, incorporating the use of Raman tensor elements and Euler angles in tandem, becomes available for estimating unknown crystallographic orientations. As an application of the developed method, a confocal Raman probe was used to non-destructively unfold the relative orientation of a wurtzitic GaN epilayer with respect to (0001)-oriented sapphire substrate. The microscopic distribution of tilt/twist angles in space for the GaN lattice could be measured in a bulk region of the sample with no cut or other sample manipulations being necessary. Polarized/confocal Raman spectroscopy provides a practical and convenient tool for characterizing on the micron scale the interfacial disorder that affects energy transport phenomena at GaN/substrate interfaces. [ABSTRACT FROM AUTHOR]

• Printing temperature does not affect PLA characteristics in the investigated range. • UV and hydrothermal aging cause very specific morphological and chemical changes. • Aging also leads to change in thermal and mechanical behavior of PLA. • Non-destructive techniques correlated PLA properties with aging timing and mode. Polylactic acid (PLA) is a biodegradable and biocompatible thermoplastic that is commonly used in 3D printing. Despite being widely utilized, PLA is susceptible to degradation by both UV light and hydrothermal conditions. This study investigated the effects of 3D printing temperature, UV light exposure, and hydrothermal aging on the properties of PLA. Samples were 3D printed at temperatures of 190, 205, 220 and 235 °C. The specimens were then aged under UV light and thermal cycling or hydrothermally at 80 °C for up to 6 weeks. The aged materials were then characterized using X-ray diffraction (XRD), thermos-gravimetric analysis (TGA), microscopy, mechanical testing, and ultimately Raman spectroscopy. Results showed that the PLA cristallinity increases with aging time in both hydrothermal and under UV exposure conditions, while mechanical strength decreases. Additionally, the UV exposure caused the formation of monomers and oligomers on the outermost layers. Printing temperature was shown to play only a minor role in the determination of the chemophysical properties of the 3D printed components, with faster degradation occurring on samples printed at higher temperatures, which also resulted in higher amounts of monomer when exposed to UV light for 6 weeks. The relative intensities of specific regions of the Raman spectra obtained on the aged samples could be successfully correlated with both the mechanical strength and chemo-physical properties such as the decomposition temperature. The algorithms developed in this study enable non-destructive analysis of PLA components, allowing for the determination of the extent of structural degradation due to environmental aging and the expected residual mechanical resistance. [ABSTRACT FROM AUTHOR]

Protein and amino acid structures of Norovirus-like particles (NoVLP) have been investigated by Raman spectroscopy before and after encapsulation into Bombyx mori cypovirus (BmCPV) cubic microcrystals, which are usually referred to as cubes or polyhedra. Two different types of tag were used in co-expression, namely VP3 and H1 tags. VP3 tag is derived from a capsid protein VP4 from BmCPV and H1 tag is N-terminal α-helix of BmCPV polyhedrin, respectively. A major capsid protein VP1 of NoVLP G11.4 was fused with H1 or VP3 tags, and then encapsulated into BmCPV polyhedra. Analyses of the spectroscopic data permitted the assignment of conformation-sensitive Raman bands to viral amino acid constituents and the observation of structural similarities or differences between differently tagged samples. Three separate Raman zones were attentioned, namely, the ring-mode structure region (1000–1500 cm −1 ), the C O and C C double-bond region and its surroundings (1500–1750 cm −1 ), and the high-frequency C H stretching region (2800–3100 cm −1 ). Structural fingerprints could be found in specific spectral zones for differently co-expressed samples. One clear characteristic of the H1-tagged VP1 polyhedra was the increase in tyrosine fraction, which played a critical role in binding neighboring strands through its unpaired negatively charged COO – sites. This feature could consistently be detected in different regions, but it was best represented by Raman signals associated with negatively charged COO – sites and H1 helices in the double-bond region. Such peculiar chemical features were revealed by two relatively broad bands at 1570 and 1630 cm −1 , which were assigned to COO – anti-symmetric stretching and amide I in 3 10 -helix extensions to α-helices at N-termini, respectively. These specific features did not display in the spectrum of the VP3-tagged VP1 polyhedra. Concurrently, a strong reduction of C H bond Raman signal was noticed in the high frequency stretching region of the Raman spectrum upon H1-tagged VP1 polyhedra. The Raman activity most strikingly also represented fingerprints of tagged NoVLP VP1 after its encapsulation into BmCPV polyhedra, opening thus the possibility to in situ advanced experiments in the fields of drug delivery and regenerative medicine. [ABSTRACT FROM AUTHOR]

The Raman spectroscopic method has been applied to quantitatively assess the in vitro degree of demineralization in healthy human teeth. Based on previous evaluations of Raman selection rules (empowered by an orientation distribution function (ODF) statistical algorithm) and on a newly proposed analysis of phonon density of states (PDOS) for selected vibrational modes of the hexagonal structure of hydroxyapatite, a molecular-scale evaluation of the demineralization process upon in vitro exposure to a highly acidic beverage (i.e., CocaCola™ Classic, pH = 2.5) could be obtained. The Raman method proved quite sensitive and spectroscopic features could be directly related to an increase in off-stoichiometry of the enamel surface structure since the very early stage of the demineralization process (i.e., when yet invisible to other conventional analytical techniques). The proposed Raman spectroscopic algorithm might possess some generality for caries risk assessment, allowing a prompt non-contact diagnostic practice in dentistry. [ABSTRACT FROM AUTHOR]

The purpose of this work is to establish a protocol, which combines CAD modeling to non-destructive microscopic techniques of confocal Raman micro-spectroscopy and laser microscopy, to assess the in-vivo hydrothermal stability of ZTA femoral head retrievals. The combined effects of wear, biological environment, and in vivo occurring peculiar events as metal staining were evaluated on five retrieved ZTA femoral heads with implantation time ranging from 9 to 106 months. The protocol relies on the application of a polar grid on the entire surface of the head, which divides it into small sectors; each sector is then automatically screened with micrometer resolution. Maps are finally linked to each other and an in-toto view of the retrieved head becomes available in three dimensions. Upon combining analytical techniques with a solid modeling computer-aided design (CAD) software, it becomes possible to develop a 3D model of the femoral head, which comprehensively describes topographic, crystallographic, and micromechanical characteristics of the entire surface and immediate sub-surface. The combination of CAD, polarized Raman spectroscopy, and laser microscopy has led to in-toto screening of femoral head with micrometer-scale resolution, thus providing a new and comprehensive protocol for both quality assessments on new components and failure analysis on retrievals. [ABSTRACT FROM AUTHOR]

The effect of hydrogen carbonate (HCO 3 − ) 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 (Si 3 N 4 ) 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 Si 3 N 4 surface was measured and found to be peculiar to individual cations. Local variation in pH was detected in ionic solutions interacting with Si 3 N 4 samples, which might represent a useful property for Si 3 N 4 in a number of biomedical applications. [ABSTRACT FROM AUTHOR]

A systematic investigation, based on highly spectrally resolved Raman spectroscopy, was undertaken to research the efficacy of vibrational assessments in locating chemical and crystallographic fingerprints for the characterization of dental caries and the early detection of non-cavitated carious lesions. Raman results published by other authors have indicated possible approaches for this method. However, they conspicuously lacked physical insight at the molecular scale and, thus, the rigor necessary to prove the efficacy of this spectroscopy method. After solving basic physical challenges in a companion paper, we apply them here in the form of newly developed Raman algorithms for practical dental research. Relevant differences in mineral crystallite (average) orientation and texture distribution were revealed for diseased enamel at different stages compared with healthy mineralized enamel. Clear spectroscopy features could be directly translated in terms of a rigorous and quantitative classification of crystallography and chemical characteristics of diseased enamel structures. The Raman procedure enabled us to trace back otherwise invisible characteristics in early caries, in the translucent zone (i.e., the advancing front of the disease) and in the body of lesion of cavitated caries. [ABSTRACT FROM AUTHOR]

Treatment modification to improve the durability of bamboo against biotic and abiotic factors often results in adverse effects to its mechanical properties due to changes in hygroscopic characteristics. This study aims at exploring in more detail, the effect of treatment modification, in particular smoke treatment, on the hygroscopic nature of bamboo. In the first part of this study, changes to its chemical structure were investigated by Raman and Fourier-transform infrared (FTIR) spectroscopic techniques. From Raman analysis, specific bands attributed to lignin component in bamboo, namely at 1600 cm−1 and 1632 cm−1, which varied in intensities among treated and untreated specimens, could be considered to assess the extent of treatment modification. Besides, FTIR results showed that the chemical constituents of bamboo inner and outermost surfaces vary extensively with distinctive changes during treatment modification. The steam component in smoke treatment is assumed to cause a slight increase in the moisture content in the outermost surface of smoked bamboo as evidenced by FTIR results. In addition, the hydrophobic surface of smoked bamboo, which was affected during smoke treatment modification due to superior mean roughness parameter in its outermost surface, impacted its water-repelling ability. From FTIR results, an increase in lignin in bamboo was confirmed at peak 1114 cm−1, which occurred as a result of thermal effect above a temperature of 100 °C leading to poly-condensation reactions. The increase in lignin is assumed to cause an overall increase in hardness of smoked bamboo which was found to be two-fold higher when compared with the untreated ones. The approach of this research investigation, which has shown the benefit of using spectroscopic techniques to monitor and understand the changes in the hygroscopic nature of bamboo surfaces, can likewise be considered to predict the corresponding effects of treatment modification or degradation on the mechanical properties of natural materials. [ABSTRACT FROM AUTHOR]

Abstract: Ferroelectric domain orientation in barium titanate (BaTiO3; BT) single-crystal has been investigated with respect to its geometrical distribution in the solid angle by using polarised Raman spectroscopy. After retrieving the angular dependence of the intensity of selected Raman modes of BT and their defocusing properties at selected laser wavelength (in-depth probe response function), both in-plane and out-of-plane domain fractions could be visualised and mapped with microscopic resolution by Raman spectroscopic assessments. It is demonstrated that polarised Raman spectroscopy is a valuable and efficient tool for fully 3D, non-destructive assessments of domain orientation in ferroelectrics. [Copyright &y& Elsevier]

Tooth loss impairs mastication, deglutition and esthetics and affects systemic health through nutritional deficiency, weight loss, muscle weakness, delayed wound healing, and bone fragility. Approximately 90% of tooth loss is due to dental caries and periodontal disease. Accordingly, early treatment of dental caries is essential to maintaining quality of life. To date, the clinical diagnosis of dental caries has been based on each dentist's subjective assessment, but this visual method lacks objectivity. To improve diagnostic ability, highly sensitive quantitative methods have been developed for the diagnosis and prevention of dental caries and are gradually becoming a mandatory item in modern dentistry. High-resolution Raman spectroscopy is a suitable tool for recognizing the subtle structural changes that occur in dental enamel in already developed or, more importantly, incipient dental caries. Raman analysis could soon emerge as a breakthrough in dentistry because of its high diagnostic sensitivity. In this study, we build upon our previous findings in a new analysis of dental caries using Raman spectroscopy imaging and discuss the possibility of using Raman photonic imaging in support of objective diagnostics in dentistry. Our findings support the Raman method of caries detection in comparison with other conventional or new approaches. [ABSTRACT FROM AUTHOR]

The transplantation of engineered three-dimensional (3D) bone graft substitutes is a viable approach to the regeneration of severe bone defects. For large bone defects, an appropriate 3D scaffold may be necessary to support and stimulate bone regeneration, even when a sufficient number of cells and cell cytokines are available. In this study, we evaluated the in vivo performance of a nanogel tectonic 3D scaffold specifically developed for bone tissue engineering, referred to as nanogel cross-linked porous-freeze-dry (NanoCliP-FD) gel. Samples were characterized by a combination of micro-computed tomography scanning, Raman spectroscopy, histological analyses, and synchrotron radiation–based Fourier transform infrared spectroscopy. NanoCliP-FD gel is a modified version of a previously developed nanogel cross-linked porous (NanoCliP) gel and was designed to achieve highly improved functionality in bone mineralization. Spectroscopic imaging of the bone tissue grown in vivo upon application of NanoCliP-FD gel enables an evaluation of bone quality and can be employed to judge the feasibility of NanoCliP-FD gel scaffolding as a therapeutic modality for bone diseases associated with large bone defects. [ABSTRACT FROM AUTHOR]

Gram-negative bacteria represent a substantial fraction of pathogens responsible for periprosthetic infections. Given the increasing resistance of such bacteria to antibiotics, significant efforts are nowadays paid in developing new biomaterial surfaces, which offer resistance against bacterial adhesion and/or possess inherent antibacterial effects. Non-oxide silicon nitride (Si 3 N 4) bioceramic in its polycrystalline form is a biomaterial with inherent antibacterial properties. Building upon previous phenomenological findings, the present study focuses on vibrational analyses of the metabolic response of Escherichia coli at the molecular level. A time-lapse study is conducted upon exposing the bacteria in vitro to Si 3 N 4 bioceramic surfaces. A comparison is carried out with the as-cultured bacterial strain and with bacteria exposed to other commercially available biomaterials, namely, Ti-alloy (Ti6Al4V-ELI) and zirconia-toughened alumina (ZTA) oxide bioceramic tested under exactly the same experimental conditions. The metabolic pathways before and after exposure to different substrates were monitored by means of Raman and FTIR spectroscopies. Results indicated the development of significant osmotic stress in the bacterial strain and constant concentration decreases of its cellular compounds markers over time upon exposure to Si 3 N 4. This ultimately led to bacterial lysis (also confirmed by conventional fluorescence microscopy assays). The main antibacterial effect was of chemical origin and driven by the elution of nitrogen ions from the Si 3 N 4 surface, successively converted into ammonia (NH 3) or ammonium (NH 4)+ in aqueous solution, depending on environmental pH. The presence of these nitrogen species created osmotic stress in the cytoplasmic space. In answer to the osmotic stress, metabolic rates changed rapidly, the bacterial membrane was damaged, and lysis occurred almost completely within 48 h exposure. The antibacterial behavior exerted by the Si 3 N 4 substrate on E. coli was more effective than that observed on the biomedical Ti6Al4V alloy. Conversely, no lysis but bacterial proliferation was recorded for E. coli exposed to ZTA bioceramic oxide substrates. Unlabelled Image • Silicon nitride (Si 3 N 4) bioceramic induces lysis of Escherichia coli. • Inherent antibacterial properties of Si 3 N 4 are of chemical origin. • Raman spectroscopy reveals metabolic response of Escherichia coli to Si 3 N 4. • Antibacterial effect is driven by elution of nitrogen ions from the Si 3 N 4 surface. • Proliferation of Escherichia coli bacteria is found on zirconia-toughened alumina. [ABSTRACT FROM AUTHOR]