Resolution-enhanced Fourier transform infrared spectroscopy study of the environment of phosphate ion in the early deposits of a solid phase of calcium phosphate in bone and enamel and their evolution with age: 2. Investigations in the nu3PO4 domain

Extracellular matrix mineralization in murine MC3T3-E1 osteoblast cultures: an ultrastructural, compositional and comparative analysis with mouse bone

Bone cell culture systems are essential tools for the study of the molecular mechanisms regulating extracellular matrix mineralization. MC3T3-E1 osteoblast cell cultures are the most commonly used in vitro model of bone matrix mineralization. Despite the widespread use of this cell line to study biomineralization, there is as yet no systematic characterization of the mineral phase produced in these cultures. Here we provide a comprehensive, multi-technique biophysical characterization of this cell culture mineral and extracellular matrix, and compare it to mouse bone and synthetic apatite mineral standards, to determine the suitability of MC3T3-E1 cultures for biomineralization studies. Elemental compositional analysis by energy-dispersive X-ray spectroscopy (EDS) showed calcium and phosphorus, and trace amounts of sodium and magnesium, in both biological samples. X-ray diffraction (XRD) on resin-embedded intact cultures demonstrated that similar to 1-month-old mouse bone, apatite crystals grew with preferential orientations along the (100), (101) and (111) mineral planes indicative of guided biogenic growth as opposed to dystrophic calcification. XRD of crystals isolated from the cultures revealed that the mineral phase was poorly crystalline hydroxyapatite with 10 to 20nm-sized nanocrystallites. Consistent with the XRD observations, electron diffraction patterns indicated that culture mineral had low crystallinity typical of biological apatites. Fourier-transform infrared spectroscopy (FTIR) confirmed apatitic carbonate and phosphate within the biological samples. With all techniques utilized, cell culture mineral and mouse bone mineral were remarkably similar. Scanning (SEM) and transmission (TEM) electron microscopy showed that the cultures had a dense fibrillar collagen matrix with small, 100nm-sized, collagen fibril-associated mineralization foci which coalesced to form larger mineral aggregates, and where mineralized sites showed the accumulation of the mineral-binding protein osteopontin. Light microscopy, confocal microscopy and three-dimensional reconstructions showed that some cells had dendritic processes and became embedded within the mineral in an osteocyte-like manner. In conclusion, we have documented characteristics of the mineral and matrix phases of MC3T3-E1 osteoblast cultures, and have determined that the structural and compositional properties of the mineral are highly similar to that of mouse bone.

Effects of long-term alendronate treatment on postmenopausal osteoporosis bone material properties

Raman microspectroscopic analysis of iliac crest from patients that were treated with alendronate (ALN) for 10 years revealed minimal, transient alterations in bone material properties confined to actively forming bone surfaces compared to patients that were on ALN for 5 years. These changes were not encountered in the bulk tissue.

INTRODUCTION

Alendronate (ALN) and other bisphosphonates (BPs) are the most widely prescribed therapy for postmenopausal osteoporosis. Despite their overall excellent safety record and efficacy in reducing fractures, questions have been raised regarding potential detrimental effects that may be related to prolonged bone turnover reduction, although no definite cause-effect relationship has been established to date. The purpose of the present study was to evaluate bone material properties in patients that were receiving ALN for 5 or 10 years.

METHODS

Raman microspectroscopic analysis was used to analyze iliac crest biopsies from postmenopausal women with osteoporosis who had been treated with ALN for 5 years and were then re-randomized to placebo (PBO, N = 14), 5 mg/day ALN (N = 10), or 10 mg/day ALN (N = 6) for another 5 years. The parameters monitored and expressed as a function of tissue age were (i) the mineral/matrix ratio (MM), (ii) the relative proteoglycan content (PG), (iii) the relative lipid content (LPD), (iv) the mineral maturity/crystallinity (MMC), and (v) the relative pyridinoline content (PYD).

RESULTS

The obtained data indicate that 10-year ALN use results in minimal, transient bone tissue composition changes compared to use for 5 years, confined to actively forming trabecular surfaces, implying potential differences in bone matrix maturation that nevertheless did not result in differences of these values in bulk tissue.

CONCLUSIONS

The data suggest that prolonged reduction in bone turnover during 10 years of therapy with ALN by itself is unlikely to be associated with adverse effects on bone material properties.

Vibrational spectroscopic imaging for the evaluation of matrix and mineral chemistry

Metabolic bone diseases manifesting fragility fractures (such as osteoporosis) are routinely diagnosed based on bone mineral density (BMD) measurements, and the effect of various therapies also evaluated based on the same outcome. Although useful, it is well recognized that this metric does not fully account for either fracture incidence or the effect of various therapies on fracture incidence, thus, the emergence of bone quality as a contributing factor in the determination of bone strength. Infrared and Raman vibrational spectroscopic techniques are particularly well-suited for the determination of bone quality as they provide quantitative and qualitative information of the mineral and organic matrix bone components, simultaneously. Through the use of microspectroscopic techniques, this information is available in a spatially resolved manner, thus, the outcomes may be easily correlated with outcomes from techniques such as histology, histomorphometry, and nanoindentation, linking metabolic status with material properties.

Polyelectrolyte multilayer-calcium phosphate composite coatings for metal implants

The preparation of organic-inorganic composite coatings with the purpose to increase the bioactivity of bioinert metal implants was investigated. As substrates, glass plates and rough titanium surfaces (Ti-SLA) were employed. The method comprises the deposition of polyelectrolyte multilayers (PEMLs) followed by immersion of the coated substrate into a calcifying solution of low supersaturation (MCS). Single or mixed PEMLs were constructed from poly-L-lysine (PLL) alternating with poly-L-glutamate, (PGA), poly-L-aspartate (PAA), and/or chondroitin sulfate (CS). ATR-FTIR spectra reveal that (PLL/PGA)10 multilayers and mixed multilayers with a (PLL/PGA)5 base contain intermolecular β-sheet structures, which are absent in pure (PLL/PAA)10 and (PLL/CS)10 assemblies. All PEML coatings had a grainy topography with aggregate sizes and size distributions increasing in the order: (PLL/PGA)n < (PLL/PAA)n < (PLL/CS)n. In mixed multilayers with a (PLL/PGA)n base and a (PLL/PAA)n or (PLL/CS)n top, the aggregate sizes were greatly reduced. The PEMLs promoted calcium phosphate nucleation and early crystal growth, the intensity of the effect depending on the composition of the terminal layer(s) of the polymer. In contrast, crystal morphology and structure depended on the supersaturation, pH, and ionic strength of the MCS, rather than on the composition of the organic matrix. Crystals grown on both uncoated and coated substrates were mostly platelets of calcium deficient carbonate apatite, with the Ca/P ratio depending on the precipitation conditions.

Strontium ranelate changes the composition and crystal structure of the biological bone-like apatite produced in osteoblast cell cultures

We evaluate the effects of strontium ranelate on the composition and crystal structure of the biological bone-like apatite produced in osteoblast cell cultures, a system that gave us the advantage of obtaining mineral samples produced exclusively during treatment. Cells were treated with strontium ranelate at concentrations of 0.05 and 0.5 mM Sr(2+). Mineral substances were isolated and analyzed by using a combination of methods: Fourier transform infrared spectroscopy, solid-state (1)H nuclear magnetic resonance, X-ray diffraction, micro-Raman spectroscopy and energy dispersive X-ray spectroscopy. The minerals produced in all cell cultures were typical bone-like apatites. No changes occurred in the local structural order or crystal size of the minerals. However, we noticed several relevant changes in the mineral produced under 0.5 mM Sr(2+): (1) increase in type-B CO3 (2-) substitutions, which often lead to the creation of vacancies in Ca(2+) and OH(-) sites; (2) incorporation of Sr(2+) by substituting slightly less than 10 % of Ca(2+) in the apatite crystal lattice, resulting in an increase in both lattice parameters a and c; (3) change in the PO4 (3-) environments, possibly because of the expansion of the lattice; (4) the Ca/P ratio of this mineral was reduced, but its (Ca+Sr)/P ratio was the same as that of the control, indicating that its overall cation/P ratio was preserved. Thus, strontium ranelate changes the composition and crystal structure of the biological bone-like apatite produced in osteoblast cell cultures.

Bifunctional designed peptides induce mineralization and binding to TiO2

A limitation of titanium implants is the rather poor bonding between the metal and the surrounding tissue. In this research, we aimed at developing functional peptides in the form of monomolecular coatings intended to improve adhesion between the native oxide of the metal (TiO2) and the calcium-phosphate mineralization layer with which it is in contact. Accordingly, a bifunctional peptide with a β-strand motif assumed to strongly bind to the oxide through two phosphorylated serine residues, both situated on the same face of the strand, was designed. The β-strand motif was extended by a mineralization "tail" composed of consecutive acidic amino acids capable of adsorbing calcium ions. This peptide was studied together with two additional control peptides, one serving to elucidate the role of the β-strand in stabilizing bonding with the oxide and the other demonstrating the ability of the tail to induce mineralization. The strong adsorption of the three peptides to the oxide surface was revealed by HPLC. That peptide presenting the mineralization tail showed the highest levels of adsorbed calcium and phosphate ions, as well as the largest area of cellular adherence, demonstrating its potential advantages for use with titanium implants in bone tissue.

The role of Carboxydothermus hydrogenoformans in the conversion of calcium phosphate from amorphous to crystalline state

Two previously unknown modes of biomineralization observed in the presence of Carboxydothermus hydrogenoformans are presented. Following the addition of NaHCO₃ and the formation of an amorphous calcium phosphate precipitate in a DSMZ medium inoculated with C. hydrogenoformans, two distinct crystalline solids were recovered after 15 and 30 days of incubation. The first of these solids occurred as micrometric clusters of blocky, angular crystals, which were associated with bacterial biofilm. The second solid occurred as 30–50 nm nanorods that were found scattered among the organic products of bacterial lysis. The biphasic mixture of solids was clearly dominated by the first phase. The X-ray diffractometry (XRD) peaks and Fourier transform infrared spectroscopy (FTIR) spectrum of this biphasic material consistently showed features characteristic of Mg-whitlockite. No organic content or protein could be identified by dissolving the solids. In both cases, the mode of biomineralization appears to be biologically induced rather than biologically controlled. Since Mg is known to be a strong inhibitor of the nucleation and growth of CaP, C. hydrogenoformans may act by providing sites that chelate Mg or form complexes with it, thus decreasing its activity as nucleation and crystal growth inhibitor. The synthesis of whitlockite and nano-HAP-like material by C. hydrogenoformans demonstrates the versatility of this organism also known for its ability to perform the water-gas shift reaction, and may have applications in bacterially mediated synthesis of CaP materials, as an environmentally friendly alternative process.

Chemically specific imaging and in-situ chemical analysis of articular cartilage with stimulated Raman scattering

Stimulated Raman scattering (SRS) has been applied to unstained samples of articular cartilage enabling the investigation of living cells within fresh tissue. Hyperspectral SRS measurements over the CH vibrational region showed variations in protein and lipid content within the cells, pericellular matrix and interterritorial matrix. Changes in the cells and pericellular matrix were investigated as a function of depth into the cartilage. Lipid was detected in the pericellular matrix of superficial zone chondrocytes. The spectral profile of lipid droplets within the chondrocytes indicated that they contained predominantly unsaturated lipids. The mineral content has been imaged by using the PO₄³⁻ vibration at 959 cm⁻¹ and the CO₃²⁻ vibration at 1070 cm⁻¹. Both changes in cells and mineralization are known to be important factors in the progression of osteoarthritis. SRS enables these to be visualized in fresh unstained tissue and consequently should benefit osteoarthiritis research.

Injectable biphasic calcium phosphate cements as a potential bone substitute

Apatitic calcium phosphate cements (CPCs) have been widely used as bone grafts due to their excellent osteoconductive properties, but the degradation properties are insufficient to stimulate bone healing in large bone defects. A novel approach to overcome the lack of degradability of apatitic CPC involves the development of biphasic CPCs (BCPC) based on tricalcium phosphate (TCP) in both α- and β-polymorphs. The aim of the current study was to prepare and analyze the physicochemical properties of BCPCs based on dual phase α/β-TCP as obtained by heat treatment of pure α-TCP. The handling and mechanical characteristics of the samples as well as the degradation behavior under in vitro condition were investigated and compared with a standard monophasic α-TCP-based CPC. The results showed that different heat treatments of commercially available α-TCP allowed the formation of biphasic calcium phosphate powder with a variety of α/β-TCP ratios. The use of biphasic powder particles as a reactant for CPCs resulted into increased setting and injectability times of the final BCPCs. During hardening of the cements, the amount of apatite formation decreased with increasing β-TCP content in the biphasic precursor powders. The morphology of the monophasic CPC consisted of plate-like crystals, whereas needle-like crystals were observed for BCPCs. In vitro degradation tests demonstrated that dissolution rate and corresponding calcium release from the set cements increased considerably with increasing β-TCP content, suggesting that apatitic CPCs can be rendered degradable by using biphasic α/β-TCP as powder precursor phase.

Accurate characterization of pure silicon-substituted hydroxyapatite powders synthesized by a new precipitation route

This paper presents a new aqueous precipitation method to prepare silicon-substituted hydroxyapatites Ca10(PO4)6-y(SiO4)y(OH)2-y(VOH)y (SiHAs) and details the characterization of powders with varying Si content up to y=1.25molmolSiHA(-1). X-ray diffraction, transmission electron microscopy, solid-state nuclear magnetic resonance and Fourier transform infrared spectroscopy were used to accurately characterize samples calcined at 400°C for 2h and 1000°C for 15h. This method allows the synthesis of monophasic SiHAs with controlled stoichiometry. The theoretical maximum limit of incorporation of Si into the hexagonal apatitic structure is y<1.5. This limit depends on the OH content in the channel, which is a function of the Si content, temperature and atmosphere of calcination. These results, particularly those from infrared spectroscopy, raise serious reservations about the phase purity of previously prepared and biologically evaluated SiHA powders, pellets and scaffolds in the literature.

XANES analysis of dried and calcined bones

The structure of dried and calcined bones from chicken, bovine, deer, pig, sheep and chamois was examined using X-ray Absorption Near Edge Structure (XANES) spectroscopy. The oxygen K-edge absorption edge indicates that the surface of dried bone has a larger proportion of carbonate than the interior that is made up of phosphates. The phosphorus L and K edge clearly indicate that pyrophosphates, α-tricalcium phosphate (α-TCP) and hydrogen phosphates of Ca do not exist in either the dried bone or calcined bone and phosphorus exists as either β-tricalcium phosphate (β-TCP) or hydroxyapatite, both in the dried and calcined conditions. The Ca K-edge analysis indicates that β-TCP is the likely form of phosphate in both the dried and calcined conditions.

Fourier transform infrared spectroscopic imaging parameters describing acid phosphate substitution in biologic hydroxyapatite

Acid phosphate substitution into mineralized tissues is an important determinant of their mechanical properties and their response to treatment. This study identifies and validates Fourier transform infrared spectroscopic imaging (FTIRI) spectral parameters that provide information on the acid phosphate (HPO4) substitution into hydroxyapatite in developing mineralized tissues. Curve fitting and Fourier self-deconvolution were used to identify subband positions in model compounds (with and without HPO4). The intensity of subbands at 1127 and 1110 cm(-1) correlated with the acid phosphate content in these models. Peak height ratios of these subbands to the ν3 vibration at 1096 cm(-1) found in stoichiometric apatite were evaluated in the model compounds and mixtures thereof. FTIRI spectra of bones and teeth at different developmental ages were analyzed using these spectral parameters. Factor analysis (a chemometric technique) was also conducted on the tissue samples and resulted in factor loadings with spectral features corresponding to the HPO4 vibrations described above. Images of both factor correlation coefficients and the peak height ratios 1127/1096 and 1112/1096 cm(-1) demonstrated higher acid phosphate content in younger vs. more mature regions in the same specimen. Maps of the distribution of acid phosphate content will be useful for characterizing the extent of new bone formation, the areas of potential decreased strength, and the effects of therapies such as those used in metabolic bone diseases (osteoporosis, chronic kidney disease) on mineral composition. Because of the wider range of values obtained with the 1127/1096 cm(-1) parameter compared to the 1110/1096 cm(-1) parameter and the smaller scatter in the slope, it is suggested that this ratio should be the parameter of choice.

Photoacoustic FTIR spectroscopic study of undisturbed human cortical bone

Chemical pretreatment has been the prevailing sample preparation procedure for infrared (IR) spectroscopic studies on bone. However, experiments have indicated that chemical pretreatment can potentially affect the interactions between the components. Typically the IR techniques have involved transmission experiments. Here we report experimental studies using photoacoustic Fourier transform infrared spectroscopy (PA-FTIR). As a nondestructive technique, PA-FTIR can detect absorbance spectrum from a sample at controllable sampling depth and with little or no sample preparation. Additionally, the coupling inert gas, helium, which is utilized in the PA-FTIR system, can inhibit bacteria growth of bone by displacing oxygen. Therefore, we used this technique to study the undisturbed human cortical bone. It is found that photoacoustic mode (linear-scan, LS-PA-FTIR) can obtain basically similar spectra of bone as compared to the traditional transmission mode, but it seems more sensitive to amide III and ν(2) carbonate bands. The ν(3) phosphate band is indicative of detailed mineral structure and symmetry of native bone. The PA-FTIR depth profiling experiments on human cortical bone also indicate the influence of water on OH band and the cutting effects on amide I and mineral bands. Our results indicate that phosphate ion geometry appears less symmetric in its undisturbed state as detected by the PA-FTIR as compared to higher symmetry observed using transmission techniques on disturbed samples. Moreover, the PA-FTIR spectra indicate a band at 1747 cm(-1) possibly resulting from CO stretching of lipids, cholesterol esters, and triglycerides from the arteries. Comparison of the spectra in transverse and longitudinal cross-sections demonstrates that, the surface area of the longitudinal section bone appears to have more organic matrix exposed and with higher mineral stoichiometry.

Effects of 3 years treatment with once-yearly zoledronic acid on the kinetics of bone matrix maturation in osteoporotic patients

Once-yearly administration of intravenous zoledronic acid for 3 years in humans affects the kinetics of matrix filling in by mineral, independent of bone turnover.

INTRODUCTION

Yearly 5-mg infusions of zoledronic acid (ZOL) for 3 years have shown pronounced antifracture efficacy. The purpose of the present study was to test whether ZOL affects the kinetics of forming bone material properties maturation.

METHODS

Iliac crest biopsies from the HORIZON-PFT clinical trial were analyzed by Raman microspectroscopy in actively bone-forming surfaces as a function of tissue age in trabecular and osteonal bone, to determine ZOL's effect on bone material quality indices maturation kinetics.

RESULTS

Mineral/matrix ratio increased in both groups as a function of tissue age, at both osteonal- and trabecular-forming surfaces; ZOL exhibiting the greatest increase in the trabecular surfaces only. The proteoglycan content showed a dependency on tissue age in both trabecular and osteonal surfaces, with ZOL exhibiting lower values in the tissue age 8-22 days in the trabecular surfaces. Mineral crystallinity (crystallite length and thickness) showed a dependence on tissue age, with ZOL exhibiting lower crystallite length compared with placebo only in the 8- to 22-day-old tissue at trabecular surfaces, while crystal thickness was lower in the 1- to 5-day-old tissue at both osteonal and trabecular surfaces.

CONCLUSIONS

The results of the present study suggest that once-yearly administration of intravenous ZOL for 3 years in humans does not exert any adverse effects on the evolution of bone material properties at actively forming osteonal and trabecular surfaces, while it may have a beneficial effect on the progression of the mineral-to-matrix ratio and mineral maturity bone quality indices.

Fourier transform infrared imaging as a tool to chemically and spatially characterize matrix-mineral deposition in osteoblasts

Mineralizing osteoblasts are regularly used to study osteogenesis and model in vivo bone formation. Thus, it is important to verify that the mineral and matrix being formed in situ are comparable to those found in vivo. However, it has been shown that histochemical techniques alone are not sufficient for identifying calcium phosphate-containing mineral. The goal of the present study was to demonstrate the use of Fourier transform infrared imaging (FTIRI) as a tool for characterizing the spatial distribution and colocalization of the collagen matrix and the mineral phase during the mineralization process of osteoblasts in situ. MC3T3-E1 mouse osteoblasts were mineralized in culture for 28 days and FTIRI was used to evaluate the collagen content, collagen cross-linking, mineralization level and speciation, and mineral crystallinity in a spatially resolved fashion as a function of time. To test whether FTIRI could detect subtle changes in the mineralization process, cells were treated with risedronate (RIS). Results showed that collagen deposition and mineralization progressed over time and that the apatite mineral was associated with a collagenous matrix rather than ectopic mineral. The process was temporarily slowed by RIS, where the inhibition of osteoblast function caused slowed collagen production and cross-linking, leading to decreased mineralization. This study demonstrates that FTIRI is a complementary tool to histochemistry for spatially correlating the collagen matrix distribution and the nature of the resultant mineral during the process of osteoblast mineralization. It can further be used to detect small perturbations in the osteoid and mineral deposition process.

Regulation of enamel hardness by its crystallographic dimensions

Enamel is a composite biomaterial comprising a minor organic matrix (~2%) and a hierarchically organized inorganic ultrastructure (~96-98%). Surprisingly, to date there is no available information in the literature regarding the possible role of the enamel ultrastructure on the nanoscale level in tooth macroscopic properties. Understanding this relationship is of special interest for restorative purposes in dentistry. Accordingly, this study was designed to investigate how enamel nanocrystals regulate its hardness. We performed microindentation analysis on 100 extracted human teeth. The tooth enamel hardness was quantified and correlated with changes in enamel chemical composition and crystallographic dimensions obtained from Fourier transform infrared spectroscopy and X-ray diffraction, respectively. Enamel hardness was not related to the variability in organic content, but was associated with the size of apatite crystals along the c-axis. This association followed the Hall-Petch model for polycrystalline materials, indicating that the optimal size of apatite nanocrystals (larger than the critical size) provides enamel with the greatest hardness, which enables teeth to survive the heavy wear over a human lifetime.

Effect of hydrazine based deproteination protocol on bone mineral crystal structure

In several bone deproteination protocols the chemical agent used for protein cleavage is hydrazine. The effect of hydrazine deproteination method on the crystal size and crystallinity of the bone mineral was studied. Bovine bones were subjected to this protocol and the crystal size and crystallinity of the remaining bone mineral were determined by X-ray Diffraction (XRD), by measuring the width at the half of the maximum intensity of the (002) reflection. It was found that hydrazine deproteination induces noteworthy increase of crystal size and crystallinity. The effect was enhanced by increasing hydrazine temperature from 25 to 55°C. Furthermore, infrared spectroscopy revealed that hydrazine facilitates the removal of carbonate and acid phosphate ions from bone mineral. It is proposed that the mechanism of modification of crystal size and crystallinity lies on the removal of these ions thus, resulting in crystal re-organization.

Control of surface topography in biomimetic calcium phosphate coatings

The behavior of cells responsible for bone formation, osseointegration, and bone bonding in vivo are governed by both the surface chemistry and topography of scaffold matrices. Bone-like apatite coatings represent a promising method to improve the osteoconductivity and bonding of synthetic scaffold materials to mineralized tissues for regenerative procedures in orthopedics and dentistry. Polycaprolactone (PCL) films were coated with calcium phosphates (CaP) by incubation in simulated body fluid (SBF). We investigated the effect of SBF ion concentration and soaking time on the surface properties of the resulting apatite coatings. CaP coatings were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), and energy dispersive X-ray spectrometry (EDX). Young's modulus (E(s)) was determined by nanoindentation, and surface roughness was assessed by atomic force microscopy (AFM) and mechanical stylus profilometry. CaP such as carbonate-substituted apatite were deposited onto PCL films. SEM and AFM images of the apatite coatings revealed an increase in topographical complexity and surface roughness with increasing ion concentration of SBF solutions. Young's moduli (E(s)) of various CaP coatings were not significantly different, regardless of the CaP phase or surface roughness. Thus, SBF with high ion concentrations may be used to coat synthetic polymers with CaP layers of different surface topography and roughness to improve the osteoconductivity and bone-bonding ability of the scaffold.

In vitro bioactivity of 70 wt.% SiO2 — 30 wt.% CaO sol-gel glass, doped with 1, 3 and 5 wt.% NbF5

The 70SiO2-30CaO (wt.%) sol-gel glasses doped with 1, 3 and 5 NbF5 (wt.%) were prepared via polystep sol-gel route. The synthesized glasses were characterized by XRD, FTIR and SEM. Changes in 1.5 SBF solutions were measured by ICP-AES. XRD of the glasses stabilized at 700°C for 6 hours proved the presence of niocalite. FTIR was consistent with XRD data. The in vitro bioactivity study of all glasses prepared were carried out by soaking in 1.5 simulated body fluid (1.5 SBF) at 37°C for 6 and 12 days in static conditions. The FTIR reveals the formation of A-type and B-type carbonate containing hydroxyapatite (CO3HA) layer. Changes in 1.5 SBF solutions, after 6 days of soaking, show that the Ca concentration increased significantly, compared to the initial Ca content in the 1.5 SBF solution before in vitro test. After 12 days of immersion, the Ca concentration decreased, i.e., the formation of HA phase consumed Ca from 1.5 SBF solution. For all soaking times, the concentration of P is much lower than that the used 1.5 SBF. Based on these results we suggest that Ca and P play an active role in the future of the glasses. SEM depicts that the different morphology of hydroxyapatite can be formed as a function of soaking time.

Nano-FTIR chemical mapping of minerals in biological materials

Methods for imaging of nanocomposites based on X-ray, electron, tunneling or force microscopy provide information about the shapes of nanoparticles; however, all of these methods fail on chemical recognition. Neither do they allow local identification of mineral type. We demonstrate that infrared near-field microscopy solves these requirements at 20 nm spatial resolution, highlighting, in its first application to natural nanostructures, the mineral particles in shell and bone. "Nano-FTIR" spectral images result from Fourier-transform infrared (FTIR) spectroscopy combined with scattering scanning near-field optical microscopy (s-SNOM). On polished sections of Mytilus edulis shells we observe a reproducible vibrational (phonon) resonance within all biocalcite microcrystals, and distinctly different spectra on bioaragonite. Surprisingly, we discover sparse, previously unknown, 20 nm thin nanoparticles with distinctly different spectra that are characteristic of crystalline phosphate. Multicomponent phosphate bands are observed on human tooth sections. These spectra vary characteristically near tubuli in dentin, proving a chemical or structural variation of the apatite nanocrystals. The infrared band strength correlates with the mineral density determined by electron microscopy. Since nano-FTIR sensitively responds to structural disorder it is well suited for the study of biomineral formation and aging. Generally, nano-FTIR is suitable for the analysis and identification of composite materials in any discipline, from testing during nanofabrication to even the clinical investigation of osteopathies.

Ultrastructural and mineral phase characterization of the bone-like matrix assembled in F-OST osteoblast cultures

Cell cultures are often used to study bone mineralization; however, not all systems achieve a bone-like matrix formation. In this study, the mineralized matrix assembled in F-OST osteoblast cultures was analyzed, with the aim of establishing a novel model for bone mineralization. The ultrastructure of the cultures was investigated using scanning electron microscopy, atomic force microscopy, and transmission electron microscopy (TEM). The mineral phase was characterized using conventional and high-resolution TEM, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and solid-state (31)P and (1)H nuclear magnetic resonance. F-OST osteoblast cultures presented a clear nodular mineralization pattern. The chief features of the mineralizing nodules were globular accretions ranging from about 100 nm to 1.5 μm in diameter, loaded with needle-shaped crystallites. Accretions seemed to bud from the cell membrane, increase in size, and coalesce into larger ones. Arrays of loosely packed, randomly oriented collagen fibrils were seen along with the accretions. Mineralized fibrils were often observed, sometimes in close association with accretions. The mineral phase was characterized as a poorly crystalline hydroxyapatite. The Ca/P atomic ratio was 1.49 ± 0.06. The presence of OH was evident. The lattice parameters were a = 9.435 Å and c = 6.860 Å. The average crystallite size was 20 nm long and 10 nm wide. Carbonate substitutions were seen in phosphate and OH sites. Water was also found within the apatitic core. In conclusion, F-OST osteoblast cultures produce a bone-like matrix and may provide a good model for bone mineralization studies.

Infrared assessment of bone quality: a review

BACKGROUND

Bone strength depends on both bone quantity and quality. The former is routinely estimated in clinical settings through bone mineral density measurements but not the latter. Bone quality encompasses the structural and material properties of bone. Although its importance is appreciated, its contribution in determining bone strength has been difficult to precisely quantify partly because it is multifactorial and requires investigation of all bone hierarchical levels. Fourier transform infrared spectroscopy provides one way to explore these levels.

QUESTIONS/PURPOSES

The purposes of our review were to (1) provide a brief overview of Fourier transform infrared spectroscopy as a way to establish bone quality, (2) review the major bone material parameters determined from Fourier transform infrared spectroscopy, and (3) review the role of Fourier transform infrared microspectroscopic analysis in establishing bone quality.

METHODS

We used the ISI Web of Knowledge database initially to identify articles containing the Boolean term "infrared" AND "bone." We then focused on articles on infrared spectroscopy in bone-related journals.

RESULTS

Infrared spectroscopy provides information on bone material properties. Their microspectroscopic versions allow one to establish these properties as a function of anatomic location, mineralization extent, and bone metabolic activity. It provides answers pertaining to the contribution of mineral to matrix ratio, mineral maturity, mineral carbonate substitution, and collagen crosslinks to bone strength. Alterations of bone material properties have been identified in disease (especially osteoporosis) not attainable by other techniques.

CONCLUSIONS

Infrared spectroscopic analysis is a powerful tool for establishing the important material properties contributing to bone strength and thus has helped better understand changes in fragile bone.

Comparison between infrared and Raman spectroscopic analysis of maturing rabbit cortical bone

The molecular composition of the organic and inorganic matrices of bone undergoes alterations during maturation. The aim of this study was to compare Fourier transform infrared (FT-IR) and near-infrared (NIR) Raman microspectroscopy techniques for characterization of the composition of growing and developing bone from young to skeletally mature rabbits. Moreover, the specificity and differences of the techniques for determining bone composition were clarified. The humeri of female New Zealand White rabbits, with age range from young to skeletally mature animals (four age groups, n = 7 per group), were studied. Spectral peak areas, intensities, and ratios related to organic and inorganic matrices of bone were analyzed and compared between the age groups and between FT-IR and Raman microspectroscopic techniques. Specifically, the degree of mineralization, type-B carbonate substitution, crystallinity of hydroxyapatite (HA), mineral content, and collagen maturity were examined. Significant changes during maturation were observed in various compositional parameters with one or both techniques. Overall, the compositional parameters calculated from the Raman spectra correlated with analogous parameters calculated from the IR spectra. Collagen cross-linking (XLR), as determined through peak fitting and directly from the IR spectra, were highly correlated. The mineral/matrix ratio in the Raman spectra was evaluated with multiple different peaks representing the organic matrix. The results showed high correlation with each other. After comparison with the bone mineral density (BMD) values from micro-computed tomography (micro-CT) imaging measurements and crystal size from XRD measurements, it is suggested that Raman microspectroscopy is more sensitive than FT-IR microspectroscopy for the inorganic matrix of the bone. In the literature, similar spectroscopic parameters obtained with FT-IR and NIR Raman microspectroscopic techniques are often compared. According to the present results, however, caution is required when performing this kind of comparison.

Na-doped β-tricalcium phosphate: physico-chemical and in vitro biological properties

Synthetic calcium phosphate ceramics as β-tricalcium phosphate (Ca(3)(PO(4))(2); β-TCP) are currently successfully used in human bone surgery. The aim of this work was to evaluate the influence of the presence of sodium ion in β-TCP on its mechanical and biological properties. Five Na-doped-β-TCP [Ca(10.5-x/2)Na(x)(PO(4))(7), 0 ≤ x ≤ 1] microporous pellets were prepared via solid phase synthesis, and their physico-chemical data (lattice compacity, density, porosity, compressive strength, infrared spectra) denote an increase of the mechanical properties and a decrease of the solubility when the sodium content is raised. On the other hand, the in vitro study of MC3T3-E1 cell activity (morphology, MTS assay and ALP activity) shows that the incorporation of sodium does not modify the bioactivity of the β-TCP. These results strongly suggest that Na-doped-β-TCP appear to be good candidates for their use as bone substitutes.

Room temperature synthesis of highly hemocompatible hydroxyapatite, study of their physical properties and spectroscopic correlation of particle size

Needle shaped nanoparticles of hydroxyapatite (HA) have been synthesized at room temperature using orthophosphoric acid as the source of (PO4)3- ions, while calcium chloride, the calcium source, is suitably complexed with citric acid/tartaric acid/acetic acid. The presence of ligands inhibits the growth along [001] and [100] directions of the crystal and thus, helps in formation of needle shaped nanoparticles. The chemical compositions of the samples have been established through AAS and FTIR spectroscopy, while the crystallinity has been assessed through XRD and by the spectral changes in the υ1 and υ3 frequencies of the phosphate group in the respective FTIR spectra. The particle sizes of the samples have been determined from line broadening studies and correlations have been established between the curve fitted percentage area of FTIR and full width half height (FWHH) of the XRD peaks. TEM studies revealed the particle to be needle-shaped with a length and diameter in the range of 20-65 nm and 4-11 nm respectively. Changes in the surface charge of the water dispersed HA samples have been determined at different pH and the isoelectric point for the samples have been found in the range of 3.1-3.4. Finally, the morphology, surface area and hemocompatibility characteristics of the HA samples, prepared by using different complexing agents, have been compared.

Effect of surface-exposed chemical groups on calcium-phosphate mineralization in water-treatment systems

Calcium-phosphate-scale formation on reverse osmosis (RO) membranes is a major limiting factor for cost-effective desalination of wastewater. We determined the effects of various organic chemical groups found on membrane surfaces on calcium-phosphate scaling. Langmuir films exposing different functional groups were equilibrated with a solution simulating the ionic profile of secondary effluent (SSE). Surface pressure-area (Langmuir) isotherms combined with ICP elemental analyses of the interfacial precipitate suggested acceleration of calcium-phosphate mineralization by the surface functional groups in the order: PO(4) > COOH ∼ NH(2) > COOH:NH(2) (1:1) > OH > ethylene glycol. Immersion of gold-coated silicon wafers self-assembled with different alkanethiols in SSE solution showed formation of a hydroxyapatite precipitate by X-ray diffraction and ATR-IR analysis. Data showed diverse influences of functional groups on mineralization, implying low calcium-phosphate scaling for uncharged surfaces or surfaces coated with both positively and negatively charged groups. This information is valuable for understanding scaling processes, and for designing of novel low-scaling membranes for water desalination.

Aging and bone

Bones provide mechanical and protective function, while also serving as housing for marrow and a site for regulation of calcium ion homeostasis. The properties of bones do not remain constant with age; rather, they change throughout life, in some cases improving in function, but in others, function deteriorates. Here we review the modifications in the mechanical function and shape of bones, the bone cells, the matrix they produce, and the mineral that is deposited on this matrix, while presenting recent theories about the factors leading to these changes.

Mineral maturity and crystallinity index are distinct characteristics of bone mineral

The purpose of this study was to test the hypothesis that mineral maturity and crystallinity index are two different characteristics of bone mineral. To this end, Fourier transform infrared microspectroscopy (FTIRM) was used. To test our hypothesis, synthetic apatites and human bone samples were used for the validation of the two parameters using FTIRM. Iliac crest samples from seven human controls and two with skeletal fluorosis were analyzed at the bone structural unit (BSU) level by FTIRM on sections 2-4 mum thick. Mineral maturity and crystallinity index were highly correlated in synthetic apatites but poorly correlated in normal human bone. In skeletal fluorosis, crystallinity index was increased and maturity decreased, supporting the fact of separate measurement of these two parameters. Moreover, results obtained in fluorosis suggested that mineral characteristics can be modified independently of bone remodeling. In conclusion, mineral maturity and crystallinity index are two different parameters measured separately by FTIRM and offering new perspectives to assess bone mineral traits in osteoporosis.

Glucuronic acid and phosphoserine act as mineralization mediators of collagen I based biomimetic substrates

Glucuronic acid (GlcA) and phosphoserine (pS) carrying acidic functional groups were used as model molecules for glycosaminoglycans and phosphoproteins, respectively to mimic effects of native biomolecules and influence the mineralization behaviour of collagen I. Collagen substrates modified with GlcA showed a stable interaction between GlcA and collagen fibrils. Substrates were mineralized using the electrochemically assisted deposition (ECAD) in a Ca(2+)/H( x )PO (4) ((3-x)) electrolyte at physiological pH and temperature. During mineralization of collagen-GlcA matrices, crystalline hydroxyapatite (HA) formed earlier with increasing GlcA content of the collagen matrix, while the addition of pS to the electrolyte succeeded in inhibiting the transformation of preformed amorphous calcium phosphate (ACP) to HA. The lower density of the resulting mineralization and the coalesced aggregates formed at a certain pS concentration suggest an interaction between calcium and the phosphate groups of pS involving the formation of complexes. Combining GlcA-modified collagen and pS-modified electrolyte showed dose-dependent cooperative effects.

Correlations among mineral components, progressive calcification process and clinical symptoms of calcific tendonitis

OBJECTIVE

To establish the correlations among the mineral components, progressive calcification process and clinical symptoms of calcific tendonitis.

METHODS

The morphology of the calcified deposits on the shoulders of 28 patients with calcific tendonitis was determined by high-resolution ultrasonography. The calcified deposit from each patient was aspirated and determined by the Fourier transform infrared and Raman microspectroscopies. The curve-fitting program was applied to estimate the chemical component in the calcified deposits of calcific tendonitis.

RESULTS

The morphology of calcified deposits for 28 patients was classified into four shapes: arc shape (7 patients), fragmented/punctuate shape (4 patients), nodular shape (13 patients) and cystic shape (4 patients). These classified shapes markedly correlated with the pain levels in patients. The infrared spectra of all the calcified deposits for 28 patients were easily classified into three types in the blind study and corresponded to the formative, resting and resorptive phases in the progressive calcification process of calcific tendonitis. With the progressive calcification, the IR wavenumber at 1018 cm(-1) assigned to poorly crystalline, non-stoichiometric apatite for the formative phase was shifted to 1028 cm(-1) for the resting phase and then to 1031 cm(-1) due to matured crystalline stoichiometric apatite for the resorptive phase. The curve-fitted results revealed that calcified deposits in calcific tendonitis were composed of different quantities of A-type and B-type carbonated apatites in the three phases. A significant difference was found in carbonated apatite content among the three phases (P < 0.001).

CONCLUSIONS

The different quantities of A-type and B-type carbonated apatites determined by vibrational microspectroscopy in calcified deposits were well correlated with those of the four shapes of morphologic classification, with the three phases in the progressive calcification process and with the clinical symptoms of calcific tendonitis.

Transient amorphous calcium phosphate in forming enamel

Enamel, the hardest tissue in the body, begins as a three-dimensional network of nanometer size mineral particles, suspended in a protein gel. This mineral network serves as a template for mature enamel formation. To further understand the mechanisms of enamel formation we characterized the forming enamel mineral at an early secretory stage using X-ray absorption near-edge structure (XANES) spectromicroscopy, transmission electron microscopy (TEM), FTIR microspectroscopy and polarized light microscopy. We show that the newly formed enamel mineral is amorphous calcium phosphate (ACP), which eventually transforms into apatitic crystals. Interestingly, the size, shape and spatial organization of these amorphous mineral particles and older crystals are essentially the same, indicating that the mineral morphology and organization in enamel is determined prior to its crystallization. Mineralization via transient amorphous phases has been previously reported in chiton teeth, mollusk shells, echinoderm spicules and spines, and recent reports strongly suggest the presence of transient amorphous mineral in forming vertebrate bones. The present finding of transient ACP in murine tooth enamel suggests that this strategy might be universal.

Solubility of Mg-containing beta-tricalcium phosphate at 25 degrees C

The equilibrium solubility of Mg-containing beta-tricalcium phosphate (betaMgTCP) with various magnesium contents was determined by immersing betaMgTCP powder for 27 months in a CH(3)COOH-CH(3)COONa buffer solution at 25 degrees C under a nitrogen gas atmosphere. The negative logarithm of the solubility product (pK(sp)) of betaMgTCP was expressed as pK(sp)=28.87432+1.40348C-0.3163C(2)+0.04218C(3)-0.00275C(4)+0.0000681659C(5), where C is the magnesium content in betaMgTCP (mol.%). The solubility of betaMgTCP decreased with increasing magnesium content owing to the increased structural stability and possible formation of a whitlockite-type phase on the surface. As a result, betaMgTCP with 10.1 mol.% magnesium had a lower solubility than that of hydroxyapatite below pH 6.0. betaMgTCP was found to be more soluble than zinc-containing beta-tricalcium phosphate given the same molar content of zinc or magnesium. The solubility of betaMgTCP and release rate of magnesium from betaMgTCP can be controlled by adjusting the Mg content by selecting the appropriate pK(sp).

Fourier transform infrared imaging microspectroscopy and tissue-level mechanical testing reveal intraspecies variation in mouse bone mineral and matrix composition

Fracture susceptibility is heritable and dependent upon bone morphology and quality. However, studies of bone quality are typically overshadowed by emphasis on bone geometry and bone mineral density. Given that differences in mineral and matrix composition exist in a variety of species, we hypothesized that genetic variation in bone quality and tissue-level mechanical properties would also exist within species. Sixteen-week-old female A/J, C57BL/6J (B6), and C3H/HeJ (C3H) inbred mouse femora were analyzed using Fourier transform infrared imaging and tissue-level mechanical testing for variation in mineral composition, mineral maturity, collagen cross-link ratio, and tissue-level mechanical properties. A/J femora had an increased mineral-to-matrix ratio compared to B6. The C3H mineral-to-matrix ratio was intermediate of A/J and B6. C3H femora had reduced acid phosphate and carbonate levels and an increased collagen cross-link ratio compared to A/J and B6. Modulus values paralleled mineral-to-matrix values, with A/J femora being the most stiff, B6 being the least stiff, and C3H having intermediate stiffness. In addition, work-to-failure varied among the strains, with the highly mineralized and brittle A/J femora performing the least amount of work-to-failure. Inbred mice are therefore able to differentially modulate the composition of their bone mineral and the maturity of their bone matrix in conjunction with tissue-level mechanical properties. These results suggest that specific combinations of bone quality and morphological traits are genetically regulated such that mechanically functional bones can be constructed in different ways.

A comparison of the physical and chemical differences between cancellous and cortical bovine bone mineral at two ages

To assess possible differences between the mineral phases of cortical and cancellous bone, the structure and composition of isolated bovine mineral crystals from young (1-3 months) and old (4-5 years) postnatal bovine animals were analyzed by a variety of complementary techniques: chemical analyses, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and (31)P solid-state magic angle spinning nuclear magnetic resonance spectroscopy (NMR). This combination of methods represents the most complete physicochemical characterization of cancellous and cortical bone mineral completed thus far. Spectra obtained from XRD, FTIR, and (31)P NMR all confirmed that the mineral was calcium phosphate in the form of carbonated apatite; however, a crystal maturation process was evident between the young and old and between cancellous and cortical mineral crystals. Two-way analyses of variance showed larger increases of crystal size and Ca/P ratio for the cortical vs. cancellous bone of 1-3 month than the 4-5 year animals. The Ca/(P + CO(3)) remained nearly constant within a given bone type and in both bone types at 4-5 years. The carbonate and phosphate FTIR band ratios revealed a decrease of labile ions with age and in cortical, relative to cancellous, bone. Overall, the same aging or maturation trends were observed for young vs. old and cancellous vs. cortical. Based on the larger proportion of newly formed bone in cancellous bone relative to cortical bone, the major differences between the cancellous and cortical mineral crystals must be ascribed to differences in average age of the crystals.

Effects of hydrogen peroxide on human dentin structure

It has been hypothesized that hydrogen peroxide (H(2)O(2)) bleaching may cause destruction of dentin by a mechanism of protein oxidation. However, to our knowledge, there has been no direct chemical evidence to validate this viewpoint. To investigate the effects of H(2)O(2) on the structure of human dentin, we used Fourier transform infrared spectroscopy (FTIR) and attenuated total reflection (ATR) spectroscopy. Human intact dentin specimens were treated either with 30% H(2)O(2) or Hanks' balanced salt solution (HBSS). Significant differences were observed in ATR spectra parameters. Additionally, demineralized dentin specimens were also tested. They were completely dissolved in the H(2)O(2), but remained intact in the 0.1 N HCl and HBSS. The results suggested that H(2)O(2) attacked both the organic and mineral components of dentin. Destruction of the organic components was mainly because of the oxidizing ability of H(2)O(2), while changes in the mineral components were probably due to its acidity.

Vibrational Properties of Sodium Substituted β-Tricalcium Phosphate

The infrared and Raman spectra of Na substituted β-TCP are presented for various levels of substitution. The influence of Na content on main vibrational modes appears significant and among them the ν1 symmetric stretching band is very sensitive to PO4 3- tetrahedrons environment. Thus, this mode was particularly investigated and has been decomposed using Lorentzian shapes components. We assigned the calculated components to the different types of PO4 3- tetrahedrons present in the crystalline structure.