Keith Rogers

Lack of OH in nanocrystalline apatite as a function of degree of atomic order: implications for bone and biomaterials

Using laser Raman microprobe spectroscopy, we have characterized the degree of hydroxylation and the state of atomic order of several natural and synthetic calcium phosphate phases, including apatite of biological (human bone, heated human bone, mouse bone, human and boar dentin, and human and boar enamel), geological, and synthetic origin. Common belief holds that all the studied phases are hydroxylapatite, i.e., an OH-containing mineral with the composition Ca10(PO4)6(OH)2. We observe, however, that OH-incorporation into the apatite crystal lattice is reduced for nanocrystalline samples. Among the biological samples, no OH-band was detected in the Raman spectrum of bone (the most nanocrystalline biological apatite), whereas a weak OH-band occurs in dentin and a strong OH-band in tooth enamel. We agree with others, who used NMR, IR spectroscopy, and inelastic neutron scattering, that-contrary to the general medical nomenclature-bone apatite is not hydroxylated and therefore not hydroxylapatite. Crystallographically, this observation is unexpected; it therefore remains unclear what atom(s) occupy the OH-site and how charge balance is maintained within the crystal. For non-bone apatites that do show an OH-band in their Raman spectra, there is a strong correlation between the concentration of hydroxyl groups (based on the ratio of the areas of the 3572 deltacm(-1) OH-peak to the 960 deltacm(-1) P-O phosphate peak) and the crystallographic degree of atomic order (based on the relative width of the 960 deltacm(-1) P-O phosphate peak) of the samples. We hypothesize that the body biochemically imposes a specific state of atomic order and crystallinity (and, thus, concentration of hydroxyl) on its different apatite precipitates (bone, dentin, enamel) in order to enhance their ability to carry out tissue-specific functions.

AN X-RAY DIFFRACTION STUDY OF THE EFFECTS OF HEAT TREATMENT ON BONE MINERAL MICROSTRUCTURE

A series of human cortical bone specimens has been heated to temperatures up to 1200 degrees C and the mineral content examined in detail by X-ray diffraction. Line profile analysis of the diffraction data has been undertaken to characterise the microstructural (crystallite size and microstrain) features of the mineral at each temperature. Individual profile fitting of several maxima from each diffractogram has also provided precise lattice parameters of the apatite at each temperature. The apatite did not show any significant decomposition over the temperature range although CaO was increasingly formed at temperatures above 600 degrees C. Both finite crystallite size and microstrain contributed significantly to the diffraction peak broadening below 600 degrees C. When heated to > 800 degrees C, the small, rod-like mineral crystallites changed from a highly anisotropically strained state to one with significantly larger equidimensional crystals possessing little microstrain. The findings are discussed in the context of graft bone substitutes and surgical heating of bone.

Subsurface probing of calcifications with spatially offset Raman spectroscopy (SORS): future possibilities for the diagnosis of breast cancer

Breast calcifications are often the only mammographic features indicating the presence of a cancerous lesion. Calcium oxalate (type I) may be found in and around benign lesions, however calcium hydroxyapatite (type II) is usually found within proliferative lesions, which can include both benign and malignant pathologies. However, the composition of type II calcifications has been demonstrated to vary between benign and malignant proliferative lesions, and could be an indicator for the possible disease state. Raman spectroscopy has previously been demonstrated as a powerful tool for non-destructive analysis of tissues, utilising laser light to probe chemical composition. Raman spectroscopy is traditionally a surface technique. However, we have recently developed methods that permit its application for obtaining sample composition to clinically relevant depths of many mm. We report the first demonstration of spatially offset Raman spectroscopy (SORS) for potential in vivo breast analysis. This study evaluates the possibility of utilising SORS for measuring calcification composition through varying thicknesses of tissues (2 to 10 mm), which is about one to two orders of magnitude deeper than has been possible with conventional Raman approaches. SORS can be used to distinguish non-invasively between calcification types I and II (and carbonate substitution of phosphate in calcium hydroxyapatite) within tissue of up to 10 mm deep. This result secures the first step in taking this technique forward for clinical applications seeking to use Raman spectroscopy as an adjunct to mammography for early diagnosis of breast cancer, by utilising both soft tissue and calcification signals. Non-invasive elucidation of calcification composition, and hence type, associated with benign or malignant lesions, could eliminate the requirement for biopsy in many patients.

New relationships between breast microcalcifications and cancer

Background:Breast microcalcifications are key diagnostically significant radiological features for localisation of malignancy. This study explores the hypothesis that breast calcification composition is directly related to the local tissue pathological state.Methods:A total of 236 human breast calcifications from 110 patients were analysed by mid-Fouries transform infrared (FTIR) spectroscopy from three different pathology types (112 invasive carcinoma (IC), 64 in-situ carcinomas and 60 benign). The biochemical composition and the incorporation of carbonate into the hydroxyapatite lattice of the microcalcifications were studied by infrared microspectroscopy. This allowed the spectrally identified composition to be directly correlated with the histopathology grading of the surrounding tissue.Results:The carbonate content of breast microcalcifications was shown to significantly decrease when progressing from benign to malignant disease. In this study, we report significant correlations (P<0.001) between microcalcification chemical composition (carbonate content and protein matrix : mineral ratios) and distinct pathology grades (benign, in-situ carcinoma and ICs). Furthermore, a significant correlation (P<0.001) was observed between carbonate concentrations and carcinoma in-situ sub-grades. Using the two measures of pathology-specific calcification composition (carbonate content and protein matrix : mineral ratios) as the inputs to a two-metric discriminant model sensitivities of 79, 84 and 90% and specificities of 98, 82 and 96% were achieved for benign, ductal carcinoma in situ and invasive malignancies, respectively.Conclusions:We present the first demonstration of a direct link between the chemical nature of microcalcifications and the grade of the pathological breast disease. This suggests that microcalcifications have a significant association with cancer progression, and could be used for future objective analytical classification of breast pathology. A simple two-metric model has been demonstrated, more complex spectral analysis may yeild greater discrimination performance. Furthermore there appears to be a sequential progression of calcification composition.

An X-ray diffraction study of semiconductor and metallic vanadium dioxide

Powder diffraction data for semiconductor and metallic states of vanadium dioxide are presented. The structures are refined by Rietveld methods using a monoclinic cell ( a = 5.7529A, b = 4.5263A, c = 5.3825A, β = 122.61°) and space group P2 1 / c for the room temperature data, and a tetragonal cell ( a =4.5540A, c = 2.8557A) and space group P4 2 /mnm for data collected at 400 K. The similarity between the corresponding X-ray diffraction patterns is discussed. The transition process from the monoclinic to tetragonal phase is investigated and initial evidence for the coexistence of phases over a small temperature range is presented.

Depth profiling of calcifications in breast tissue using picosecond Kerr-gated Raman spectroscopy

Breast calcifications are found in both benign and malignant lesions and their composition can indicate the disease state. Calcium oxalate (dihydrate) (COD) is associated with benign lesions, however calcium hydroxyapatite (HAP) is found mainly in proliferative lesions including carcinoma. The diagnostic practices of mammography and histopathology examine the morphology of the specimen. They can not reliably distinguish between the two types of calcification, which may indicate the presence of a cancerous lesion during mammography. We demonstrate for the first time that Kerr-gated Raman spectroscopy is capable of non-destructive probing of sufficient biochemical information from calcifications buried within tissue, and this information can potentially be used as a first step in identifying the type of lesion. The method uses a picosecond pulsed laser combined with fast temporal gating of Raman scattered light to enable spectra to be collected from a specific depth within scattering media by collecting signals emerging from the sample at a given time delay following the laser pulse. Spectra characteristic of both HAP and COD were obtained at depths of up to 0.96 mm, in both chicken breast and fatty tissue; and normal and cancerous human breast by utilising different time delays. This presents great potential for the use of Raman spectroscopy as an adjunct to mammography in the early diagnosis of breast cancer.

Growth of Ti:sapphire single crystal thin films by pulsed laser deposition

This paper documents the growth of single crystal Ti:sapphire thin films, typically 10µm thick, on undoped sapphire substrates using Pulsed Laser Deposition from a Ti:sapphire single crystal target with a doping level of 0.1 % wt Ti2O3. These thin films are shown to have very high crystal quality using Ion Beam Channelling and X-Ray Diffraction Techniques. The degree of titanium incorporation into the films is investigated using Inductively Coupled Plasma Mass Spectrometry and Particle Induced X-ray Emission. These techniques show that levels of up to 0.08% wt Ti2O3 are present in the deposited layers.

Characterization of epitaxially grown films of vanadium oxides

The growth of VO2 and V2O3 thin films by reactive sputtering has been investigated. Previously reported studies of such thin films have often presented ambiguous results concerning the precise nature of the layers produced. A thorough and comprehensive characterization program including x‐ray diffraction, scanning electron microscopy, Rutherford‐backscattering spectroscopy, and electrical conductivity measurements has been undertaken to ensure that the films produced were of a true epitaxial nature.

Electrodeposition and characterisation of CdTe films for solar cell applications

Thin film CdS/CdTe solar cells have been prepared by electrodeposition of CdTe on CdS coated conducting glass from an acidic electrolyte containing a high concentration of Cd2+ and a low concentration of TeO2. Deposition of a 2 μm CdTe film from stirred solutions typically requires 3 h. High quality CdTe films have been grown much more rapidly using a channel flow cell: 2 μm films were deposited in around 24 min. The CdTe|CdS thin film structures obtained in this way were characterised by photocurrent spectroscopy, electrolyte electroreflectance/absorbance spectroscopy (EER/A), XRD and AFM. CdS|CdTe films prepared by both methods were annealed at 415°C to effect type conversion of the CdTe layer. As deposited CdTe is generally n-type and exhibits strong preferential 〈111〉 orientation. Type conversion is not necessarily accompanied by recrystallisation: most of the CdTe films deposited from stirred solution did not recrystallise. Recrystallisation did occur for films grown by pulsing the potential periodically from 50 mV to>350 mV versus Cd2+/Cd during deposition. Evidence for sulphur and tellurium diffusion leading to alloy formation during annealing was obtained from bandgap shifts detected by photocurrent spectroscopy and EER/A and from changes in lattice parameters measured by XRD. The composition of the annealed electrodeposited structures approached CdS0.95Te0.05|CdTe0.95S0.05 after 15 min. Test solar cells with AM 1.5 efficiencies approaching 6% were fabricated. Recrystallised samples gave higher solar cell efficiencies than non-recrystallised samples.

Intra-crystalline protein diagenesis (IcPD) in Patella vulgata. Part I: Isolation and testing of the closed system

This study successfully isolates a fraction of intra-crystalline proteins from shells of the marine gastropod Patella vulgata and assesses the suitability of these proteins for IcPD (Intra-crystalline Protein Diagenesis) geochronology. We discuss the mineralogical composition of this gastropod, investigated for the first time by X-ray diffraction mapping, and use the results to inform our sampling strategy. The potential of the calcitic rim and of a bulk sample (containing both apex and rim) of the shell to act as stable repositories for the intra-crystalline proteins during diagenesis is examined. The composition and the diagenetic behaviour of the intra-crystalline proteins isolated from different locations within the shell are compared, highlighting the necessity of targeting consistent sampling positions. We induced artificial diagenesis of both intra-crystalline and whole-shell proteins by conducting high-temperature experiments in hydrous environment; this allowed us to quantify the loss of amino acids by leaching and therefore evaluate the open- or closed-system behaviour of the different fractions of proteins. The results obtained provide further confirmation that patterns of diagenesis vary according to the protein sequence, structure, and location within or outside the intra-crystalline fraction. As Patella is frequently found in the fossil record, both in archaeological and geological contexts, the application of IcPD geochronology to this biomineral opens up the possibility to obtain reliable age information from a range of sites in different areas of the world.