Cortical bone composition and orientation as a function of animal and tissue age in mice by Raman spectroscopy

Quality assessment of regenerated bone in intraosseous and intramuscular scaffolds by spectroscopy and nanoindentation

The efficiency of synthetic bone grafts can be evaluated either in osseous sites, to analyze osteoconduction or ectopically, in intramuscular or subcutaneous sites, to assess osteoinduction. Bone regeneration is usually evaluated in terms of the presence and quantity of newly formed bone, but little information is normally provided on the quality of this bone. Here, we propose a novel approach to evaluate bone quality by the combined use of spectroscopy techniques and nanoindentation. Calcium phosphate scaffolds with different architectures, either foamed or 3D-printed, that were implanted in osseous or intramuscular defects in Beagle dogs for 6 or 12 weeks were analyzed. ATR-FTIR and Raman spectroscopy were performed, and mineral-to-matrix ratio, crystallinity, and mineral and collagen maturity were calculated and mapped for the newly regenerated bone and the mature cortical bone from the same specimen. For all the parameters studied, the newly-formed bone showed lower values than the mature host bone. Hardness and elastic modulus were determined by nanoindentation and, in line with what was observed by spectroscopy, lower values were observed in the regenerated bone than in the cortical bone. While, as expected, all techniques pointed to an increase in the maturity of the newly-formed bone between 6 and 12 weeks, the bone found in the intramuscular samples after 12 weeks presented lower mineralization than the intraosseous counterparts. Moreover, scaffold architecture also played a role in bone maturity, with the foamed scaffolds showing higher mineralization and crystallinity than the 3D-printed scaffolds after 12 weeks.

Ancient and modern bone diagnosis: Towards a better understanding of chemical and structural feature alterations

Chemical and structural alterations hold great importance in the field of diagenesis. Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy (ATR-FTIR) is a valuable method for examining bio-apatite composition changes. Infrared spectroscopy (IR) and X-ray diffraction (XRD) were employed to analyze both modern and archaeological bone specimens. Organic and mineral component changes in modern and ancient samples were investigated. Ancient bone samples were collected from two archaeological sites in Jordan, dating back to the Iron and Byzantine ages. IR results indicated that collagen cross-links and mineral maturity are higher in modern bones compared to ancient bones. Additionally, the crystallinity index is higher in modern bones than in archaeological bones, while the carbonate to phosphate ratio (C/P) is lower in modern bones than in ancient ones. Curve fitting was applied to reveal the carbonate substitution inside the hydroxyapatite lattice within the IR region from 850 to 890 cm-1. A2-type carbonates (identified as υ2 of CO32-) denote hydroxyl site substitution, and B-type carbonates represent a substitution to the phosphate site. The full width at half maximum (FWHM) of the peak at 604 cm-1 from IR spectra reveals that crystallinity is higher in modern bones, as confirmed by the FWHM of the (002)-apatite pattern in XRD. Statistical analysis was conducted to validate these findings, ensuring the robustness of the results. Finally, the results obtained in this investigation align with previous literature reports regarding ATR-FTIR ratios. This suggests that modern bones have better crystallinity compared to ancient bones. Furthermore, the ATR-FTIR ratios indicate that the hydroxyl and phosphate sites of modern bones undergo more substitution than older bones. The findings of this study not only enhance our understanding of the diagnostic processes in archaeological bone specimens but also have broader implications for fields such as archaeology, anthropology, and forensics, where the analysis of bone composition and structural changes can provide valuable insights into the history and characteristics of ancient remains.

Bone hierarchical organization through the lens of materials science: Present opportunities and future challenges

Multiscale characterization is essential to better understand the hierarchical architecture of bone and an array of analytical methods contributes to exploring the various structural and compositional aspects. Incorporating X-ray tomography, X-ray scattering, vibrational spectroscopy, and atom probe tomography alongside electron microscopy provides a comprehensive approach, offering insights into the diverse levels of organization within bone. X-ray scattering techniques reveal information about collagen-mineral spatial relationships, while X-ray tomography captures 3D structural details, especially at the microscale. Electron microscopy, such as scanning and transmission electron microscopy, extends resolution to the nanoscale, showcasing intricate features such as collagen fibril organization. Additionally, atom probe tomography achieves sub-nanoscale resolution and high chemical sensitivity, enabling detailed examination of bone composition. Despite various technical challenges, a correlative approach allows for a comprehensive understanding of bone material properties. Real-time investigations through in situ and in operando approaches shed light on the dynamic processes in bone. Recently developed techniques such as liquid, in situ transmission electron microscopy provide insights into calcium phosphate formation and collagen mineralization. Mechanical models developed in the effort to link structure, composition, and function currently remain oversimplified but can be improved. In conclusion, correlative analytical platforms provide a holistic perspective of bone extracellular matrix and are essential for unraveling the intricate interplay between structure and composition within bone.

Raman spectroscopy and U-Net deep neural network in antiresorptive drug-related osteonecrosis of the jaw

OBJECTIVE

Application of an optical method for the identification of antiresorptive drug-related osteonecrosis of the jaw (ARONJ).

METHODS

We introduce shifted-excitation Raman difference spectroscopy followed by U-Net deep neural network refinement to determine bone tissue viability. The obtained results are validated through established histological methods.

RESULTS

Discrimination of osteonecrosis from physiological tissues was evaluated at 119 distinct measurement loci in 40 surgical specimens from 28 patients. Mean Raman spectra were refined from 11,900 raw spectra, and characteristic peaks were assigned to their respective molecular origin. Then, following principal component and linear discriminant analyses, osteonecrotic lesions were distinguished from physiological tissue entities, such as viable bone, with a sensitivity, specificity, and overall accuracy of 100%. Moreover, bone mineral content, quality, maturity, and crystallinity were quantified, revealing an increased mineral-to-matrix ratio and decreased carbonate-to-phosphate ratio in ARONJ lesions compared to physiological bone.

CONCLUSION

The results demonstrate feasibility with high classification accuracy in this collective. The differentiation was determined by the spectral features of the organic and mineral composition of bone. This merely optical, noninvasive technique is a promising candidate to ameliorate both the diagnosis and treatment of ARONJ in the future.

Evaluation and 3D imaging of mineral structure changes of the rabbit (New Zealand) skull during developmental periods

This study aimed to determine the morphometric measurements anatomically and CT images of skulls of healthy male and female rabbits during postnatal development, to analyse the data statistically and to demonstrate the structural changes in bone. A total of 40 rabbits (20 females and 20 males) were divided into four groups including prepubertal period (group I (0-1 month)), period between adolescence and adulthood (group II (3-5 month)) and later (young adult period as group III (1-3 years) and old adult period as group IV (3-5 years)), with five animals in each group. After the morphometric measurements, the surface area and volume values of the skull were calculated. The skulls were reconstructed using a 3D Slicer (5.0.2), which is used for 3D modelling. The cranial bones in each group were then crushed using a grinder so that the powdered samples were obtained for XRF (X-ray fluorescence technique). The p-value was statistically highly significant between group and gender (p < 0.001). In morphometric measurements, males were generally higher than females. Only PL, GBOC and GNB measurements were higher in females. The p-value between groups (in all measurements), between genders (in TL, GLN, FL, VL, OZB and GBN parameters) and between groups and genders (in TL, DL and VL parameters) was statistically highly significant (p < 0.001). The p-value between the groups, p-value between sexes and p-value between group and sex in Si, P, K, Ca, Ni, Zn, Sr, Sr and Ca/P elements were statistically significant (p < 0.001). Consequently, metric, volume and surface area measurements were taken through 3D modelling of skull bone in prepubertal period (group I), period between adolescence and adulthood (group II) and later (young adult period as group III and old adult period as group IV) of rabbits and the change in the mineral structure during postnatal development and effect of sex on this change were investigated. This might be the first study to assess both metric and mineral changes at four age intervals taken during the life span of rabbits.

Discrimination of ivory from extant and extinct elephant species using Raman spectroscopy: A potential non-destructive technique for combating illegal wildlife trade

The use of elephant ivory as a commodity is a factor in declining elephant populations. Despite recent worldwide elephant ivory trade bans, mammoth ivory trade remains unregulated. This complicates law enforcement efforts, as distinguishing between ivory from extant and extinct species requires costly, destructive and time consuming methods. Elephant and mammoth ivory mainly consists of dentine, a mineralized connective tissue that contains an organic collagenous component and an inorganic component of calcium phosphate minerals, similar in structure to hydroxyapatite crystals. Raman spectroscopy is a non-invasive laser-based technique that has previously been used for the study of bone and mineral chemistry. Ivory and bone have similar biochemical properties, making Raman spectroscopy a promising method for species identification based on ivory. This study aimed to test the hypothesis that it is possible to identify differences in the chemistry of mammoth and elephant ivory using Raman spectroscopy. Mammoth and elephant tusks were obtained from the Natural History Museum in London, UK. Included in this study were eight samples of ivory from Mammuthus primigenius, two samples of carved ivory bangles from Africa (Loxodonta species), and one cross section of a tusk from Elephas maximus. The ivory was scanned using an inVia Raman micro spectrometer equipped with a x50 objective lens and a 785nm laser. Spectra were acquired using line maps and individual spectral points were acquired randomly or at points of interest on all samples. The data was then analysed using principal component analysis (PCA) with use of an in-house MATLAB script. Univariate analysis of peak intensity ratios of phosphate to amide I and III peaks, and carbonate to phosphate peaks showed statistical differences (p<0.0001) in the average peak intensity ratios between Mammuthus primigenius, Loxodonta spp. and Elephas maximus. Full width at half maximum hight (FWHM)analysis of the phosphate peak demonstrated higher crystal maturity of Mammuthus primigenius compared to living elephant species. The results of the study have established that spectra acquired by Raman spectroscopy can be separated into distinct classes through PCA. In conclusion, this study has shown that well-preserved mammoth and elephant ivory has the potential to be characterized using Raman spectroscopy, providing a promising method for species identification. The results of this study will be valuable in developing quick and non-destructive methods for the identification of ivory, which will have direct applications in archaeology and the regulation of international trade.

Periodontal Disease Monitoring by Raman Spectroscopy of Phosphates: New Insights into Pyrophosphate Activity

(1) Background: The intent of this survey was to investigate the quality of the alveolar bone by revealing the different phases for calcified tissues independent of the medical history of the patient in relation to periodontal disease by means of Raman spectroscopy and then to correlate the results by suggesting a possible mechanism for the medical impairment; (2) Methods: The investigation was mainly based on Raman spectroscopy that was performed in vivo during surgery for the selected group of patients. The targeted peaks for the Raman spectra were according to the reference compounds (e.g., calcium phosphates, other phosphates); (3) Results: The variation in the intensity of the spectrum correlated to the specific bone constituents' concentrations highlights the bone quality, while some compounds (such as pyrophosphate, PPi) are strongly related to the patient's medical status, and they provide information regarding a physiological process that occurred in the calcified tissues. Moreover, bone sample fluorescence is related to the collagen (Col) content, enabling a complete evaluation of bone quality, revealing the importance of collagen matrix acting as a load-bearing element for Calcium phosphate (CaP) deposition during the complex bone mineralization process; (4) Conclusions: We highlight that Raman spectroscopy can be considered a viable investigative method for in vivo and rapid bone quality valuation through oral health monitoring.

Characterization of rat vertebrae cortical bone microstructures using confocal Raman microscopy combined to tomography and electron microscopy

BACKGROUND

The rat vertebrae is a good model to study bone regeneration after implantation of biomaterials used to treat bone loss, a major problem in oral and dental surgery. However, the precise characterization of bone microstructures in the rat vertebrae has not been reported. Therefore, the aim of this study was to achieve the complete analysis of such bone, at different scales, in order to have a clear model of healthy bone for comparison with regenerated bone.

METHODS

In order to image the cortical bone of rat caudal vertebra, confocal Raman microscopy was combined with high resolution X-ray micro computed tomography (micro-CT), with scanning electron microscopy (SEM) using backscatter electron imaging and with more conventional histology coloration techniques. SEM and Raman microscopy were done in various regions of the cortical bone corresponding to external, middle and internal areas. The spongy bone was imaged in parallel. Micro-CT was performed on the whole vertebra to monitor the network of haversian canals in the cortical bone. Osteonic canals characteristics, and relative chemical composition were analysed in several regions of interest, in cortical and spongy bone. Five rats were included in this study.

RESULTS

On micro-CT images, differences in intensity were observed in the cortical bone, substantiated by SEM. Chemical analysis with Raman spectra confirmed the difference in composition between the different regions of the cortical and spongy bone. PCA and k-mean cluster analysis separated these groups, except for the external and middle cortical bone. Peak intensity ratio confirmed these results with a CO3 to ν2 PO4 ratio significantly different for the internal cortical bone. Grayscale images stack extracted from micro-CT showed that global architecture of cortical bone was characterized by a dense and complex network of haversian osteonic canals, starting from the surface towards the vertebrae center. The mean diameter of the canals was 18.4 µm (SD 8.6 µm) and the mean length was 450 µm (SD 152 µm). Finally, Raman reconstructed images of the lamellar bone showed an enlargement of the lamellar layer width, both in circumferential lamellar bone and around haversian canals.

CONCLUSIONS

Micro-CT and confocal Raman microscopy are good tools to complete classical analysis using optical and electron microscopy. The results and measurements presented in a rat model known for its small inter-individual differences provide the main characteristics of a mature bone. This study will allow the community working on this rat vertebrate model to have a set of characteristics, in particular on the structure of the haversian canals.

Bone intrinsic material and compositional properties in postmenopausal women diagnosed with long-term Type-1 diabetes

The incidence of diabetes mellitus and the associated complications are growing worldwide, affecting the patients' quality of life and exerting a considerable burden on health systems. Yet, the increase in fracture risk in type 1 diabetes (T1D) patients is not fully captured by bone mineral density (BMD), leading to the hypothesis that alterations in bone quality are responsible for the increased risk. Material/compositional properties are important aspects of bone quality, yet information on human bone material/compositional properties in T1D is rather sparse. The purpose of the present study is to measure both the intrinsic material behaviour by nanoindentation, and material compositional properties by Raman spectroscopy as a function of tissue age and microanatomical location (cement lines) in bone tissue from iliac crest biopsies from postmenopausal women diagnosed with long-term T1D (N = 8), and appropriate sex-, age-, BMD- and clinically-matched controls (postmenopausal women; N = 5). The results suggest elevation of advanced glycation endproducts (AGE) content in the T1D and show significant differences in mineral maturity / crystallinity (MMC) and glycosaminoglycan (GAG) content between the T1D and control groups. Furthermore, both hardness and modulus by nanoindentation are greater in T1D. These data suggest a significant deterioration of material strength properties (toughness) and compositional properties in T1D compared with controls.

The feasibility of discriminating BRONJ lesion bone with Raman spectroscopy

Background

With the frequent use of Bisphosphonates (BPs), the morbidity of BP-related osteonecrosis of the jaw (BRONJ) is also increasing. However, the prevention and treatment of BRONJ is faced with enormous challenges. This study aimed to illuminate the influence of BP administration in the rat mandible and explore the feasibility of discriminating BRONJ lesion bone with Raman spectroscopy.

Materials and methods

First, we explored the time- and mode-dependent effects of BP administration on the rat mandible with Raman spectroscopy. Second, the BRONJ rat model was constructed, and the lesion and healthy bone components were analyzed using Raman spectroscopy.

Results

When only BPs were administered, no rats showed BRONJ symptoms, and no difference could be found in the Raman spectra. However, when combined with local surgery, six (6/8) rats showed BRONJ symptoms. The Raman spectra also showed a significant difference between the lesion and healthy bone.

Conclusion

In the progression of BRONJ, BPs and local stimulation play an essential role. Both BPs administration and local stimulation need to be controlled to prevent BRONJ. Moreover, BRONJ lesion bone in rats could be discriminated with Raman spectroscopy. This novel method would become a complement in the treatment of BRONJ in the future.

Bone structure and composition in a hyperglycemic, obese, and leptin receptor-deficient rat: Microscale characterization of femur and calvarium

Metabolic abnormalities, such as diabetes mellitus and obesity, can impact bone quantity and/or bone quality. In this work, we characterize bone material properties, in terms of structure and composition, in a novel rat model with congenic leptin receptor (LepR) deficiency, severe obesity, and hyperglycemia (type 2 diabetes-like condition). Femurs and calvaria (parietal region) from 20-week-old male rats are examined to probe bones formed both by endochondral and intramembranous ossification. Compared to the healthy controls, the LepR-deficient animals display significant alterations in femur microarchitecture and in calvarium morphology when analyzed by micro-computed X-ray tomography (micro-CT). In particular, shorter femurs with reduced bone volume, combined with thinner parietal bones and shorter sagittal suture, point towards a delay in the skeletal development of the LepR-deficient rodents. On the other hand, LepR-deficient animals and healthy controls display analogous bone matrix composition, which is assessed in terms of tissue mineral density by micro-CT, degree of mineralization by quantitative backscattered electron imaging, and various metrics extrapolated from Raman hyperspectral images. Some specific microstructural features, i.e., mineralized cartilage islands in the femurs and hyper-mineralized areas in the parietal bones, also show comparable distribution and characteristics in both groups. Overall, the altered bone microarchitecture in the LepR-deficient animals indicates compromised bone quality, despite the normal bone matrix composition. The delayed development is also consistent with observations in humans with congenic Lep/LepR deficiency, making this animal model a suitable candidate for translational research.

Physical and chemical characterization of femur during and after body development period in male and female rats

The aim of this study was to determine the physical and chemical characteristics of the bone structures during four developmental periods. Forty Wistar Albino rats (20 male and 20 female) were divided into four groups including prepubertal period (group I), period between adolescence and adulthood (group II) and later (young adult period as group III and old adult period as group IV). The bones were analysed by morphometric measurements, XRF (X-ray fluorescence) analysis for mineral levels and BET analysis (Brunaurer-Emmett-Teller) for surface area and porosity. In morphometric measurements, the GL (greatest length) and the GLC (greatest length from caput femoris) values increased gradually from the first to the fourth group, and these values were higher in the males than the females. Phosphorus and calcium values were higher in the males in adult groups (third and fourth) compared to that for the females; however, they were higher in the females in groups up to adulthood (first and second). While the Ca/P ratio reached the highest value in the second group in the male, it decreased gradually afterwards. In females, the rate, which was close to each other in the first three groups, increased in the fourth group. Surface area size in the female and the male rats was the highest in the second group. In conclusion, changes in the rat bone structure during the development and adulthood periods of the body were revealed, and it was determined that the gender factor was effective in these changes.

Increased Advanced Glycation Endproducts, Stiffness, and Hardness in Iliac Crest Bone From Postmenopausal Women With Type 2 Diabetes Mellitus on Insulin

Individuals with type 2 diabetes mellitus (T2DM) have a greater risk of bone fracture compared with those with normal glucose tolerance (NGT). In contrast, individuals with impaired glucose tolerance (IGT) have a lower or similar risk of fracture. Our objective was to understand how progressive glycemic derangement affects advanced glycation endproduct (AGE) content, composition, and mechanical properties of iliac bone from postmenopausal women with NGT (n = 35, age = 65 ± 7 years, HbA1c = 5.8% ± 0.3%), IGT (n = 26, age = 64 ± 5 years, HbA1c = 6.0% ± 0.4%), and T2DM on insulin (n = 25, age = 64 ± 6 years, HbA1c = 9.1% ± 2.2%). AGEs were assessed in all samples using high-performance liquid chromatography to measure pentosidine and in NGT/T2DM samples using multiphoton microscopy to spatially resolve the density of fluorescent AGEs (fAGEs). A subset of samples (n = 14 NGT, n = 14 T2DM) was analyzed with nanoindentation and Raman microscopy. Bone tissue from the T2DM group had greater concentrations of (i) pentosidine versus IGT (cortical +24%, p = 0.087; trabecular +35%, p = 0.007) and versus NGT (cortical +40%, p = 0.003; trabecular +35%, p = 0.004) and (ii) fAGE cross-link density versus NGT (cortical +71%, p < 0.001; trabecular +44%, p < 0.001). Bone pentosidine content in the IGT group was lower than in the T2DM group and did not differ from the NGT group, indicating that the greater AGE content observed in T2DM occurs with progressive diabetes. Individuals with T2DM on metformin had lower cortical bone pentosidine compared with individuals not on metformin (-35%, p = 0.017). Cortical bone from the T2DM group was stiffer (+9%, p = 0.021) and harder (+8%, p = 0.039) versus the NGT group. Bone tissue AGEs, which embrittle bone, increased with worsening glycemic control assessed by HbA1c (Pen: R2  = 0.28, p < 0.001; fAGE density: R2  = 0.30, p < 0.001). These relationships suggest a potential mechanism by which bone fragility may increase despite greater tissue stiffness and hardness in individuals with T2DM; our results suggest that it occurs in the transition from IGT to overt T2DM. © 2022 American Society for Bone and Mineral Research (ASBMR).

Cortical bone material / compositional properties in growing children and young adults aged 1.5-23 years, as a function of gender, age, metabolic activity, and growth spurt

Bone material / compositional properties are significant determinants of bone quality, thus strength. Raman spectroscopic analysis provides information on the quantity and quality of all three bone tissue components (mineral, organic matrix, and tissue water). The overwhelming majority of the published reports on the subject concern adults. We have previously reported on these properties in growing children and young adults, in the cancellous compartment. The purpose of the present study was to create normative reference data of bone material / compositional properties for children and young adults, in the cortical compartment. We performed Raman (Senterra (Bruker Optik GmbH), 50× objective, with an excitation of 785 nm (100 mW) and a lateral resolution of ~0.6 μm) microspectroscopic analysis of transiliac bone samples from 54 individuals between 1.5 and 23 years of age, with no known metabolic bone disease, and which have been previously used to establish histomorphometric, bone mineralization density distribution, and cancellous bone quality reference values. The bone quality indices that were determined were: mineral/matrix ratio (MM) from the integrated areas of the v₂PO₄ (410-460 cm^-1) and the amide III (1215-1300 cm^-1) bands, tissue water in nanopores approximated by the ratio of the integrated spectral area ~ 494-509 cm^-1 to Amide III band, the glycosaminoglycan (GAG) content (ratio of integrated area 1365-1390 cm^-1 to the Amide III band, the sulfated proteoglycan (sPG) content as the ratio of the integrated peaks ~1062 cm^-1 and 1365-1390 cm^-1, the pyridinoline (Pyd) content estimated from the ratio of the absorbance height at 1660 cm^-1 / area of the amide I (1620-1700 cm^-1) band, and the mineral maturity / crystallinity (MMC) estimated from the inverse of the full width at half height of the v₁PO₄ (930-980 cm^-1) band. Analyses were performed at the three distinct cortical surfaces (endosteal, osteonal, periosteal) at specific anatomical microlocations, namely the osteoid, and the three precisely known tissue ages based on the presence of fluorescence double labels. Measurements were also taken in interstitial bone, a much older tissue that has undergone extensive secondary mineralization. Overall, significant dependencies of the measured parameters on tissue age were observed, while at any given tissue age, sex and subject age were minimal confounders. The established Raman database in the cortical compartments complements the previously published one in cancellous bone, and provides healthy baseline bone quality indices that may serve as a valuable tool to identify alterations due to pediatric disease.

Treatment of postmenopausal osteoporosis patients with teriparatide for 24 months reverts forming bone quality indices to premenopausal healthy control values

Postmenopausal osteoporosis (PMOP) therapies are frequently evaluated by bone mineral density (BMD) gains against patients receiving placebo (calcium and vitamin D supplementation, a mild bone turnover-suppressing intervention), which is not equivalent to either healthy or treatment-naive PMOP. The aim of the present observational study was to assess the effects of TPTD treatment in PMOP (20 μg, once daily) at 6 (TPTD 6m; n = 28, age 65 ± 7.3 years), and 24 (TPTD 24m; n = 32, age 67.4 ± 6.15 years) months on bone quality indices at actively forming trabecular surfaces (with fluorescent double labels). Data from the TPTD-treated PMOP patients were compared with those in healthy adult premenopausal women (HC; n = 62, age 40.5 ± 10.6 years), and PMOP receiving placebo (PMOP-PLC; n = 94, age 70.6 ± 4.5 years). Iliac crest biopsies were analyzed by Raman microspectroscopy at three distinct tissue ages: mid-distance between the second label and the bone surface, mid-distance between the two labels, and 1 μm behind the first label. Mineral to matrix ratio (MM), mineral maturity/crystallinity (MMC), tissue water (TW), glycosaminoglycan (GAGs), and pyridinoline (Pyd) content were determined. Outcomes were compared by ANCOVA with subject age and tissue age as covariates, and health status as a fixed factor, followed by Sidak's post-hoc testing (significance assigned to p < 0.05). Both TPTD groups increased MM compared to PMOP-PLC. While TPTD 6m had values similar to HC, TPTD 24m had higher values compared to either HC or TPTD 6m. Both TPTD groups had lower MMC values compared to PMOP-PLC and similar to HC. TPTD 6m patients had higher TW content compared to HC, while TPTD 24m had values similar to HC and lower than either PMOP-PLC or TPTD 6m. Both TPTD groups had lower GAG content compared to HC group, while TPTD 6m had higher values compared to PMOP-PLC. Finally, TPTD 6m patients had higher Pyd content compared to HC and lower compared to PMOP-PLC, while TPTD 24m had lower values compared to PMOP-PLC and TPTD 6m, and similar to HC group. The results of the present study indicate that effects of TPTD on forming trabecular bone quality indices depend on treatment duration. At the recommended length of 24 m, TPTD restores bone mineral and organic matrix quality indices (MMC, TW, Pyd content) to premenopausal healthy (HC) levels.

Matrix/mineral ratio and domain size variation with bone tissue age: A photothermal infrared study

Atomic force microscopy-infrared spectroscopy (AFM-IR) and optical photothermal infrared spectroscopy (O-PTIR), which feature spectroscopic imaging spatial resolution down to ∼ 50 nm and ∼ 500 nm, respectively, were employed to characterize the nano- to microscale chemical compositional changes in bone. Since these changes are known to be age dependent, fluorescently labelled bone samples were employed. The average matrix/mineral ratio values decrease as the bone tissue matures as measured by both AFM-IR and O-PTIR, which agrees with previously published FTIR and Raman spectroscopy results. IR ratio maps obtained by AFM-IR reveal variation in matrix/mineral ratio-generating micron-scale bands running parallel to the bone surface as well as smaller domains within these bands ranging from ∼ 50 to 700 nm in size, which is consistent with the previously published length scale of nanomechanical heterogeneity. The matrix/mineral changes do not exhibit a smooth gradient with tissue age. Rather, the matrix/mineral transition occurs sharply within the length scale of 100-200 nm. O-PTIR also reveals matrix/mineral band domains running parallel to the bone surface, resulting in waves of matrix/mineral ratios progressing from the youngest to most mature tissue. Both AFM-IR and O-PTIR show a greater variation in matrix/mineral ratio value for younger tissue as compared to older tissue. Together, this data confirms O-PTIR and AFM-IR as techniques that visualize bulk spectroscopic data consistent with higher-order imaging techniques such as Raman and FTIR, while revealing novel insight into how mineralization patterns vary as bone tissue ages.

Bone matrix quality in a developing high-fat diet mouse model is altered by RAGE deletion

Overweightness and obesity in adolescents are epidemics linked to chronic low-grade inflammation and elevated fracture risk. The increased fracture risk observed in overweight/obese adolescence contrasts the traditional concept that high body mass is protective against fracture, and thus highlights the need to determine why weight gain becomes detrimental to fracture during growth and maturity. The Receptor for Advanced Glycation End products (RAGE) is a central inflammatory regulator that can influence bone metabolism. It remains unknown how RAGE removal impacts skeletal fragility in overweightness/obesity, and whether increased fracture risk in adolescents could result from low-grade inflammation deteriorating bone quality. We characterized the multiscale structural, mechanical, and chemical properties of tibiae extracted from adolescent C57BL/6J (WT) and RAGE null (KO) mice fed either low-fat (LF) or high-fat (HF) diet for 12 weeks starting at 6 weeks of age using micro-computed tomography, strength, Raman spectroscopy, and nanoindentation. Overweight/obese WT HF mice possessed degraded mineral-crystal quality and increased matrix glycoxidation in the form of pentosidine and carboxymethyl-lysine, with HF diet in females only showing reduced cortical surface expansion and TMD independently of RAGE ablation. Furthermore, in contrast to males, HF diet in females led to more material damage and plastic deformation. RAGE KO mitigated glycoxidative matrix accumulation, preserved mineral quantity, and led to increased E/H ratio in females. Taken together, these results highlight the complex, multi-scale and sex-dependent relationships between bone quality and function under overweightness, and identifies RAGE-controlled glycoxidation as a target to potentially preserve matrix quality and mechanical integrity.

Bone quality in an ovariectomized monkey animal model treated with two doses of teriparatide for either 18 months, or 12 months followed by withdrawal for 6 months

Previous studies of ovariectomized (OVX) monkeys, treated with recombinant human parathyroid hormone (PTH) (1-34) at 1 or 5 μg/kg/day for 18 months or for 12 months followed by 6 months withdrawal from treatment, displayed significant changes in geometry, histomorphometry, and bone quality, but without strict tissue age criteria, of the midshaft humerus. Since bone quality significantly depends on tissue age among other factors, the aim of the present study was to establish the bone-turnover independent effects of two doses of PTH, as well as the effects of treatment withdrawal on bone quality by measuring bone material composition at precisely known tissue ages ranging from osteoid, to mineralized tissue older than 373 days. Raman microspectroscopic analysis of bone tissue from the mid-shaft humerus of OVX monkeys demonstrated that the clinically relevant dose of PTH administered for 18 months reverses the effects of ovariectomy on bone quality when compared against SHAM. Both doses investigated in this study restore the mineralization regulation mechanisms to SHAM levels. The study also showed that the beneficial effects induced by 12 months of clinically relevant PTH therapy were sustained after six months of therapy withdrawal.

Vertebrate Taphonomy and Diagenesis: Implications of Structural and Compositional Alterations of Phosphate Biominerals

Biominerals are recorders of evolution and palaeoenvironments. Predation is one of the most frequent modes leading to the concentration of small vertebrates in fossil assemblages. Consumption by predators produces damages on bones and teeth from prey species, and one of the greatest challenges to taphonomists is differentiating original biological and secondary, geologically altered attributes of fossils. Excellent morphological preservation is often used to assume that the structure and composition of fossils are not modified. Nevertheless, during predation and fossilization, both the physical structure and chemical composition of enamel, dentine and bone are altered, the degree and extent of which varies from site to site, depending on the nature of the burial environment. A relationship between the surficial alterations and the compositional changes which take place during fossilization has yet to be established. Herein, I present a review of old and recent taphonomic studies that collectively reveal the wide diversity of microstructural and chemical changes that typically take place during fossilization of vertebrate remains, including common taphonomic biases and the challenges inherent to reconstructing the history of vertebrate fossil assemblages.

Non‐Obese MKR Mouse Model of Type 2 Diabetes Reveals Skeletal Alterations in Mineralization and Material Properties

Obesity is a common comorbidity of type 2 diabetes (T2D). Therefore, increased risk of fragility fractures in T2D is often confounded by the effects of obesity. This study was conducted to elucidate the mechanistic basis by which T2D alone leads to skeletal fragility. We hypothesized that obesity independent T2D would deteriorate bone's material quality by accumulating defects in the mineral matrix and undesired modifications in its organic matrix associated with increased oxidative stress and hyperglycemia. To test this hypothesis, we used 15‐week‐old male non‐obese mice with engineered muscle creatine kinase promoter/human dominant negative insulin growth factor 1 (IGF‐I) receptor (MKR) and FVB/N wild‐type (WT) controls (n = 12/group). MKR mice exhibit reduced insulin production and loss of glycemic control leading to diabetic hyperglycemia, verified by fasting blood glucose measurements (>250 mg/dL), without an increase in body weight. MKR mice showed a significant decrease in femoral radial geometry (cortical area, moment of inertia, cortical thickness, endosteal diameter, and periosteal diameter). Bone mineral density (BMD), as assessed by micro–computed tomography (μCT), remained unchanged; however, the quality of bone mineral was altered. In contrast to controls, MKR mice had significantly increased hydroxyapatite crystal thickness, measured by small‐angle X‐ray scattering, and elongated c‐axis length of the crystals evaluated by confocal Raman spectroscopy. There was an increase in changes in the organic matrix of MKR mice, associated with enhanced glycoxidation (carboxymethyl‐lysine [CML] and pentosidine) and overall glycation (fluorescent advanced glycation end products), both of which were associated with various measures of bone fragility. Moreover, increased CML formation positively correlated with elongated mineral crystal length, supporting the role of this negatively charged side chain to attract calcium ions, promote growth of hydroxyapatite, and build a physical link between mineral and collagen. Collectively, our results show, for the first time, changes in bone matrix in a non‐obese T2D model in which skeletal fragility is attributable to alterations in the mineral quality and undesired organic matrix modifications. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Biochemical and Morphological Abnormalities of Subchondral Bone and Their Association with Cartilage Degeneration in Spontaneous Osteoarthritis

This study aims to investigate how biochemical composition in subchondral bone (SB) relates to the sulfated glycosaminoglycan (sGAG) content of articular cartilage (AC) in the knee joint of guinea pigs from the early to moderate osteoarthritis (OA). Male Dunkin Hartley strain guinea pigs were grouped according to age (1, 3, 6, and 9 months, with 10 guinea pigs in each group). The biochemical properties of the AC and SB in the tibial plateau of the guinea pigs were determined through histology and Raman spectroscopy, respectively. Furthermore, the microstructures of the SB were investigated using micro-computed tomography (micro-CT) and histology. Increased thickness and bone mineral density (BMD) and decreased porosity were observed in the subchondral plate (SP) with the progression of spontaneous OA, accompanied by a decreasing trend in sGAG integrated optical density (IOD) of AC. Compared with the changes in the microstructure of subchondral bone, the content of sGAG was more correlated to the changes in the mineral/matrix ratio of subchondral bone. The mineralization of the matrix was significantly correlated to the content of sGAG compared with crystallinity/maturity and Type B carbonate substitution. PO₄^3- ν1/Amide III was more correlated to the content of sGAG than PO₄^3- ν1/Amide I, PO₄^3- ν1/CH₂ wag during the progression of spontaneous osteoarthritis. This study demonstrated that the mineralization of subchondral bone plays a crucial role in the pathogenesis of OA. Future studies may access to the mineralization of subchondral bone in addition to its microstructure in the study for pathogenesis and early diagnosis of osteoarthritis.

Measures of Bone Mineral Carbonate Content and Mineral Maturity/Crystallinity for FT-IR and Raman Spectroscopic Imaging Differentially Relate to Physical-Chemical Properties of Carbonate-Substituted Hydroxyapatite

Bone mineral carbonate content assessed by vibrational spectroscopy relates to fracture incidence, and mineral maturity/ crystallinity (MMC) relates to tissue age. As FT-IR and Raman spectroscopy become more widely used to characterize the chemical composition of bone in pre-clinical and translational studies, their bone mineral outcomes require improved validation to inform interpretation of spectroscopic data. In this study, our objectives were (1) to relate Raman and FT-IR carbonate:phosphate ratios calculated through direct integration of peaks to gold-standard analytical measures of carbonate content and underlying subband ratios; (2) to relate Raman and FT-IR MMC measures to gold-standard analytical measures of crystal size in chemical standards and native bone powders. Raman and FT-IR direct integration carbonate:phosphate ratios increased with carbonate content (Raman: p < 0.01, R² = 0.87; FT-IR: p < 0.01, R² = 0.96) and Raman was more sensitive to carbonate content than the FT-IR (Raman slope + 95% vs FT-IR slope, p < 0.01). MMC increased with crystal size for both Raman and FT-IR (Raman: p < 0.01, R² = 0.76; FT-IR p < 0.01, R² = 0.73) and FT-IR was more sensitive to crystal size than Raman (c-axis length: slope FT-IR MMC + 111% vs Raman MMC, p < 0.01). Additionally, FT-IR but not Raman spectroscopy detected differences in the relationship between MMC and crystal size of carbonated hydroxyapatite (CHA) vs poorly crystalline hydroxyapatites (HA) (slope CHA + 87% vs HA, p < 0.01). Combined, these results contribute to the ability of future studies to elucidate the relationships between carbonate content and fracture and provide insight to the strengths and limitations of FT-IR and Raman spectroscopy of native bone mineral.

Compressive Strength of Iliac Bone ECM Is Not Reduced in Osteogenesis Imperfecta and Increases With Mineralization

Osteogenesis imperfecta (OI) is an inheritable, genetic, and collagen-related disorder leading to an increase in bone fragility, but the origin of its "brittle behavior" is unclear. Because of its complex hierarchical structure, bone behaves differently at various length scales. This study aims to compare mechanical properties of human OI bone with healthy control bone at the extracellular matrix (ECM) level and to quantify the influence of the degree of mineralization. Degree of mineralization and mechanical properties were analyzed under dry conditions in 12 fixed and embedded transiliac crest biopsies (control n = 6, OI type I n = 3, OI type IV n = 2, and OI type III n = 1). Mean degree of mineralization was measured by microcomputed tomography at the biopsy level and the mineral-to-matrix ratio was assessed by Raman spectroscopy at the ECM level. Both methods revealed that the degree of mineralization is higher for OI bone compared with healthy control. Micropillar compression is a novel technique for quantifying post-yield properties of bone at the ECM level. Micropillars (d = 5 μm, h = 10 μm) were fabricated using focused ion beam milling and quasi-statically compressed to capture key post-yield properties such as ultimate strength. The qualitative inspection of the stress-strain curves showed that both OI and healthy control bone have a ductile response at the ECM level. The quantitative results showed that compressive strength is not reduced in OI bone and is increasing with OI severity. Nanoindentation measurements revealed that OI bone tends to have a higher Young's modulus, hardness, and dissipated energy compared with healthy bone. Micropillar strength and indentation modulus increased linearly and significantly (p < .0001) with mineral-to-matrix ratio. In conclusion, this study indicates that compressive mechanical properties of dry OI bone at the iliac crest are not inferior to healthy control at the ECM level and increase with mineralization. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Time-Space-Resolved Chemical Deconvolution of Cementitious Colloidal Systems Using Raman Spectroscopy

Concrete is one of the most used materials in the world, second only to water. One of the key advantages of this versatile material is its workability in the early stages before setting. Here, we use in situ underwater Raman microspectroscopy to investigate and visualize the early hydration kinetics of ordinary Portland cement (OPC) with submicron spatial and high temporal resolution. First, the spectral features of the C-S-H gel were analyzed in the hydroxyl stretching region to confirm the coexistence of Ca-OH and Si-OH bonds in a highly disordered C-S-H gel. Second, the disordered calcium hydroxide (Ca(OH)₂) is experimentally identified for the first time in the mixture before setting, suggesting that Ca(OH)₂ crystallization and growth are essential in the setting of cement paste. Finally, the phase transformations of clinker, C-S-H, and Ca(OH)₂ are spatially and temporally resolved, and the hydration kinetics are studied by analyzing the spatial relationships of these phases using two-point correlation functions. The results quantitatively validate that the setting occurs as a percolation process, wherein the hydration products intersect and form an interconnected network. This time-space-resolved characterization method can map and quantitatively analyze the heterogeneous reaction of the cementitious colloidal system and thus provide potential application value in the field of cement chemistry and materials design more broadly.

Magnesium whitlockite - omnipresent in pathological mineralisation of soft tissues but not a significant inorganic constituent of bone

Whitlockite is a calcium phosphate that was first identified in minerals collected from the Palermo Quarry, New Hampshire. The terms magnesium whitlockite [Mg-whitlockite; Ca₁₈Mg₂(HPO₄)₂(PO₄)₁₂] and beta-tricalcium phosphate [β-TCP; β-Ca₃(PO₄)₂] are often used interchangeably since Mg-whitlockite is not easily distinguished from β-Ca₃(PO₄)₂ by powder X-ray diffraction although their crystalline structures differ significantly. Being both osteoconductive and bioresorbable, Mg-whitlockite is pursued as a synthetic bone graft substitute. In recent years, advances in development of synthetic Mg-whitlockite have been accompanied by claims that Mg-whitlockite is the second most abundant inorganic constituent of bone, occupying as much as 20-35 wt% of the inorganic fraction. To find evidence in support of this notion, this review presents an exhaustive summary of Mg-whitlockite identification in biological tissues. Mg-whitlockite is mainly found in association with pathological mineralisation of various soft tissues and dental calculus, and occasionally with enamel and dentine. With the exception of high-temperature treated tumoural calcified deposits around interphalangeal and metacarpal joints and rhomboidal Mg-whitlockite crystals in post-apoptotic osteocyte lacunae in human alveolar bone, this unusual mineral has never been detected in the extracellular matrix of mammalian bone. Characterisation techniques capable of unequivocally distinguishing between different calcium phosphate phases, such as high-resolution imaging, crystallography, and/or spectroscopy have exclusively identified bone mineral as poorly crystalline, ion-substituted, carbonated apatite. The idea that Mg-whitlockite is a significant constituent of bone mineral remains unsubstantiated. Contrary to claims that such biomaterials represent a bioinspired/biomimetic approach to bone repair, Mg-whitlockite remains, exclusively, a pathological biomineral. STATEMENT OF SIGNIFICANCE: Magnesium whitlockite (Mg-whitlockite) is a unique calcium phosphate that typically features in pathological calcification of soft tissues; however, an alarming trend emerging in the synthetic bioceramics community claims that Mg-whitlockite occupies 20-35 wt% of bone mineral and therefore synthetic Mg-whitlockite represents a biomimetic approach towards bone regeneration. By providing an overview of Mg-whitlockite detection in biological tissues and scrutinising a diverse cross-section of literature relevant to bone composition analysis, this review concludes that Mg-whitlockite is exclusively a pathological biomineral, and having never been reported in bone extracellular matrix, Mg-whitlockite does not constitute a biomimetic strategy for bone repair.

Interplay between mineral crystallinity and mineral accumulation in health and postmenopausal osteoporosis

Osteoporosis is characterized by an imbalance between bone formation and resorption rates, resulting in bone loss. For ethical reasons, effects of antiosteoporosis drugs are compared against patients receiving vitamin D and calcium supplementation which is a mild antiresorptive regimen. Bone formation may be resolved into two phases: the initial formation of mineral crystals (primary nucleation) and the subsequent mineral accumulation (secondary nucleation and mineral growth) on them. In this study, we used Raman microspectroscopic analysis of iliac crest biopsies from healthy females (N = 108), postmenopausal osteoporosis patients receiving vitamin D and calcium supplementation (PMOP-S; N = 66), and treatment-naïve postmenopausal osteoporosis patients (PMOP-TN; N = 12) to test the hypothesis that at forming trabecular surfaces, mineral maturity / crystallinity of the youngest crystallites associates with the amount of subsequent mineral accumulation. The surfaces of analysis were chosen based on the presence of fluorescent double labels, defining three distinct tissue ages. The results indicated that when adjusted for age and tissue age, there were no differences in amount of mineral formed between healthy females and either PMOP-S or PMOP-TN, while both PMOP-S and PMOP-TN had larger crystallites compared to healthy females. Moreover, significant differences existed between PMOP-S and PMOP-TN in size of initial crystals formed as well as rate of mineral accumulation and maturation. These findings suggest an additional mechanism that may contribute to the decreased mineral content evident in PMOP, and provide a potential target for the development of new interventions. STATEMENT OF SIGNIFICANCE: We used Raman microspectroscopic analysis of iliac crest biopsies from healthy females and postmenopausal osteoporosis patients (PMOP) receiving placebo to test the hypothesis that at forming trabecular surfaces, mineral maturity / crystallinity (MMC) of the youngest crystallites associates with the amount of subsequent mineral accumulation. This can affect bone mechanical properties as larger crystallites have been shown to result in compromised mechanical attributes; and larger crystallites grow slower compared to smaller ones. The results of the present analysis indicate that increased MMC of the youngest formed mineral may contribute to the bone mineral loss evident in PMOP and the accompanying increased fracture risk independently of bone turnover rate.

Effect of hormone replacement therapy on bone formation quality and mineralization regulation mechanisms in early postmenopausal women

Post-menopausal osteoporosis is characterized by a negative imbalance between bone formation and bone resorption resulting in a net bone loss, increasing the risk of fracture. One of the earliest interventions to protect against this was hormonal replacement therapy (HRT). Bone strength depends on both the amount and quality of bone, the latter including compositional / material and structural properties. Bone compositional / material properties are greatly dependent on both patient-, and tissue-age. Raman spectroscopy is an analytical tool ideally suited for the determination of bone compositional / material properties as a function of tissue age as it is capable of analyzing areas ~1 × 1 μm² in tetracycline labeled bone forming areas. Using such analysis of humeri from an ovariectomized primate animal model, we reported that loss of estrogen results in alteration in the mineralization regulation mechanisms by osteoid organic matrix attributes at actively forming bone surfaces. In the present work, we used Raman microspectroscopic techniques to compare osteoid and youngest mineralized tissue composition, as well as relationships between osteoid organic matrix quality and quality attributes of the earliest mineralized tissue in paired iliac crest biopsies obtained from early postmenopausal women before and after two years of HRT therapy. Significant correlations between osteoid proteoglycans, sulfated proteoglycans, pyridinoline, and earliest mineralized tissue mineral content were observed, suggesting that in addition to changes in bone turnover rates, HRT affects the osteoid composition, mineralization regulation mechanisms, and potentially fibrillogenesis.

Breast cancer-secreted factors perturb murine bone growth in regions prone to metastasis

Breast cancer frequently metastasizes to bone, causing osteolytic lesions. However, how factors secreted by primary tumors affect the bone microenvironment before the osteolytic phase of metastatic tumor growth remains unclear. Understanding these changes is critical as they may regulate metastatic dissemination and progression. To mimic premetastatic bone adaptation, immunocompromised mice were injected with MDA-MB-231-conditioned medium [tumor-conditioned media (TCM)]. Subsequently, the bones of these mice were subjected to multiscale, correlative analysis including RNA sequencing, histology, micro-computed tomography, x-ray scattering analysis, and Raman imaging. In contrast to overt metastasis causing osteolysis, TCM treatment induced new bone formation that was characterized by increased mineral apposition rate relative to control bones, altered bone quality with less matrix and more carbonate substitution, and the deposition of disoriented mineral near the growth plate. Our study suggests that breast cancer-secreted factors may promote perturbed bone growth before metastasis, which could affect initial seeding of tumor cells.

Lacunar-canalicular bone remodeling: Impacts on bone quality and tools for assessment

Osteocytes can resorb as well as replace bone adjacent to the expansive lacunar-canalicular system (LCS). Suppressed LCS remodeling decreases bone fracture toughness, but it is unclear how altered LCS remodeling impacts bone quality. The first goal of this review is to assess how LCS remodeling impacts LCS morphology as well as the composition and mechanical properties of surrounding bone tissue. The second goal is to compare tools available for the assessment of bone quality at length-scales that are physiologically-relevant to LCS remodeling. We find that changes to LCS morphology occur in response to a variety of physiological conditions and diseases and can be classified in two general phenotypes. In the 'aging phenotype', seen in aging and in some disuse models, the LCS is truncated and osteocytes apoptosis is increased. In the 'osteocytic osteolysis' phenotype, which is adaptive in some physiological settings and possibly maladaptive in others, the LCS enlarges and osteocytes generally maintain viability. Bone composition and mechanical properties vary near the osteocyte and change with at least some conditions that alter LCS morphology. However, few studies have evaluated bone composition and mechanical properties close to the LCS and so the impacts of LCS remodeling phenotypes on bone tissue quality are still undetermined. We summarize the current understanding of how LCS remodeling impacts LCS morphology, tissue-scale bone composition and mechanical properties, and whole-bone material properties. Tools are compared for assessing tissue-scale bone properties, as well as the resolution, advantages, and limitations of these techniques.

The Effect of Ethanol Consumption on Composition and Morphology of Femur Cortical Bone in Wild-Type and ALDH2*2-Homozygous Mice

ALDH2 inactivating mutation (ALDH2*2) is the most abundant mutation leading to bone morphological aberration. Osteoporosis has long been associated with changes in bone biomaterial in elderly populations. Such changes can be exacerbated with elevated ethanol consumption and in subjects with impaired ethanol metabolism, such as carriers of aldehyde dehydrogenase 2 (ALDH2)-deficient gene, ALDH2*2. So far, little is known about bone compositional changes besides a decrease in mineralization. Raman spectroscopic imaging has been utilized to study the changes in overall composition of C57BL/6 female femur bone sections, as well as in compound spatial distribution. Raman maps of bone sections were analyzed using multilinear regression with these four isolated components, resulting in maps of their relative distribution. A 15-week treatment of both wild-type (WT) and ALDH2*2/*2 mice with 20% ethanol in the drinking water resulted in a significantly lower mineral content (p < 0.05) in the bones. There was no significant change in mineral and collagen content due to the mutation alone (p > 0.4). Highly localized islets of elongated adipose tissue were observed on most maps. Elevated fat content was found in ALDH2*2 knock-in mice consuming ethanol (p < 0.0001) and this effect appeared cumulative. This work conclusively demonstrates that that osteocytes in femurs of older female mice accumulate fat, as has been previously theorized, and that fat accumulation is likely modulated by levels of acetaldehyde, the ethanol metabolite.

Combining polarized Raman spectroscopy and micropillar compression to study microscale structure-property relationships in mineralized tissues

Bone is a natural composite possessing outstanding mechanical properties combined with a lightweight design. The key feature contributing to this unusual combination of properties is the bone hierarchical organization ranging from the nano- to the macro-scale. Bone anisotropic mechanical properties from two orthogonal planes (along and perpendicular to the main bone axis) have already been widely studied. In this work, we demonstrate the dependence of the microscale compressive mechanical properties on the angle between loading direction and the mineralized collagen fibril orientation in the range between 0° and 82°. For this, we calibrated polarized Raman spectroscopy for quantitative collagen fibril orientation determination and validated the method using widely used techniques (small angle X-ray scattering, micro-computed tomography). We then performed compression tests on bovine cortical bone micropillars with known mineralized collagen fibril angles. A strong dependence of the compressive micromechanical properties of bone on the fibril orientation was found with a high degree of anisotropy for both the elastic modulus (E_a/E_t=3.80) and the yield stress (σ_a^y/σ_t^y=2.54). Moreover, the post-yield behavior was found to depend on the MCF orientation with a transition between softening to hardening behavior at approximately 50°. The combination of methods described in this work allows to reliably determine structure-property relationships of bone at the microscale, which may be used as a measure of bone quality.

Bone tissue material composition is compromised in premenopausal women with Type 2 diabetes

Type 2 diabetes mellitus (T2DM) patients are at an increased risk of fracture despite normal to high bone mineral density (BMD) values. In this cross-sectional study we establish bone compositional properties in tetracycline labeled iliac crest biopsies from premenopausal women diagnosed with T2DM (N = 26). Within group comparisons were made as a function of tissue age (TA), presence of chronic complications (CC), glycosylated haemoglobin (HbA1c) levels, and morphometric fracture (MFx). We also compared these data at actively trabecular bone forming surfaces against sex- and age-matched healthy controls (N = 32). The bone quality indices determined by Raman microspectroscopic analysis were: mineral/matrix (MM), tissue water content (nanoporosity; NanoP), mineral maturity/crystallinity (MMC), and glycosaminoglycan (GAG), pyridinoline (Pyd), N-(carboxymethyl)lysine (CML), and pentosidine (PEN) content. Within the T2DM group, at the oldest tissue, CML and PEN contents were significantly elevated in the cancellous compared to cortical compartment. The outcomes were not dependent on MFx. On the other hand, both were significantly elevated in patients with CC, as well as those with HbA1c levels > 7%. At actively forming surfaces, the cortical compartment had higher NanoP compared to cancellous. Still within the T2DM group, patients with MFx had significantly elevated MM and GAGs compared to the ones that did not. At actively forming trabecular surfaces, compared to healthy women, T2DM patients had elevated GAGs content and MMC. The results of this study indicate increased AGEs in those with poor glycation control and chronic complications. Additionally, T2DM patients had elevated MMC and decreased GAGs content compared to healthy controls. These alterations may be contributing to the T2DM inherent elevated fracture risk and suggest a role for hyperglycemia on bone quality.

Mechano-chemistry of human femoral diaphysis revealed by correlative Brillouin-Raman microspectroscopy

Brillouin–Raman microspectroscopy is presented as an innovative label-free all-optical investigation approachable to characterize the chemical composition and the mechanical properties of human tissues at micrometric resolution. Brillouin maps unveil mechanical heterogeneities in a human femoral diaphysis, showing a ubiquitous co-existence of hard and soft components, even in the most compact sections. The novel correlative analysis of Brillouin and Raman maps shows that the relative intensity of Brillouin peaks is a good proxy for the fraction of mineralized fibers and that the stiffness (longitudinal elastic modulus) of the hard component is linearly dependent on the hydroxyapatite concentration. For the soft component, a gradient of composition is found, ranging from an abundance of proteins in the more compact, external, bone to abundance of lipids, carotenoids, and heme groups approaching the trabecular, inner, part of the diaphysis. This work unveils the strong potential of correlative mechano-chemical characterization of human tissues at a micrometric resolution for both fundamental and translational research.

Towards refining Raman spectroscopy-based assessment of bone composition

Various compositional parameters are derived using intensity ratios and integral area ratios of different spectral peaks and bands in the Raman spectrum of bone. The [Formula: see text]1-, [Formula: see text]2-,[Formula: see text]3-, [Formula: see text]4 PO43-, and [Formula: see text] CO32- bands represent the inorganic phase while amide I, amide III, Proline, Hydroxyproline, Phenylalanine, δ(CH3), δ(CH2), and [Formula: see text](C-H) represent the organic phase. Here, using high-resolution Raman spectroscopy, it is demonstrated that all PO43- bands of bone either partially overlap with or are positioned close to spectral contributions from the organic component. Assigned to the organic component, a shoulder at 393 cm-1 compromises accurate estimation of [Formula: see text]2 PO43- integral area, i.e., phosphate/apatite content, with implications for apatite-to-collagen and carbonate-to-phosphate ratios. Another feature at 621 cm-1 may be inaccurately interpreted as [Formula: see text]4 PO43- band broadening. In the 1020-1080 cm-1 range, the ~ 1047 cm-1 [Formula: see text]3 PO43- sub-component is obscured by the 1033 cm-1 Phenylalanine peak, while the ~ 1076 cm-1 [Formula: see text]3 PO43- sub-component is masked by the [Formula: see text]1 CO32- band. With [Formula: see text]1 PO43- peak broadening, [Formula: see text]2 PO43- integral area increases exponentially and individual peaks comprising the [Formula: see text]4 PO43- band merge together. Therefore, [Formula: see text]2 PO43- and [Formula: see text]4 PO43- band profiles are sensitive to changes in mineral crystallinity.

Raman and Fourier transform infrared imaging for characterization of bone material properties

As the application of Raman spectroscopy to study bone has grown over the past decade, making it a peer technology to FTIR spectroscopy, it has become critical to understand their complimentary roles. Recent technological advancements have allowed these techniques to collect grids of spectra in a spatially resolved fashion to generate compositional images. The advantage of imaging with these techniques is that it allows the heterogenous bone tissue composition to be resolved and quantified. In this review we compare, for non-experts in the field of vibrational spectroscopy, the instrumentation and underlying physical principles of FTIR imaging (FTIRI) and Raman imaging. Additionally, we discuss the strengths and limitations of FTIR and Raman spectroscopy, address sample preparation, and discuss outcomes to provide researchers insight into which techniques are best suited for a given research question. We then briefly discuss previous applications of FTIRI and Raman imaging to characterize bone tissue composition and relationships of compositional outcomes with mechanical performance. Finally, we discuss emerging technical developments in FTIRI and Raman imaging which provide new opportunities to identify changes in bone tissue composition with disease, age, and drug treatment.

Raman spectroscopy investigation shows that mineral maturity is greater in CD-1 than in C57BL/6 mice distal femurs after sexual maturity

Purpose/Aim of the study mice are the most often used pre-clinical lab models for studying the pathologies of bone mineralization. However, recent evidence suggests that two of the most often used mice strains (C57BL/6J and CD-1) might show differences in the bone mineralization process. This study sought to investigate the main compositional properties of bone tissue between nonpathological C57BL/6J and CD-1 murine knee joints. Materials and Methods : to this end, medial and lateral condylar subchondral bones and the adjacent diaphyseal cortical bone of 13 murine femurs (n = 7 C57BL/6J and n = 6 CD-1 at eight weeks old, just after sexual maturation) were analyzed with ex vivo Raman spectroscopy. Results : regardless of the bone tissue analyzed, our results showed that CD-1 laboratory mice present a more mature mineral phase than C57BL/6J laboratory mice, but present no difference in maturity of the collagen phase. For both strains, the subchondral bone of the medial condylar and cortical bone from the diaphysis have similar compositional properties, and CD-1 presents less variation than C57BL/6J. Furthermore, we depict a novel parametric relationship between the crystallinity and carbonate-to-amide-I ratio that might help in deciphering the mineral maturation process that occurs during bone's mineralization. Conclusions : Our results suggest that the timing of bone maturation might be different between non-pathological C57BL/6J and CD-1 murine knee femurs.

Raman microspectroscopy demonstrates reduced mineralization of subchondral bone marrow lesions in knee osteoarthritis patients

INTRODUCTION

Bone marrow lesions (BMLs) are frequently identified by MRI in the subchondral bone in knee osteoarthritis (KOA). BMLs are known to be closely associated with joint pain, loss of the cartilage and structural changes in the subchondral trabecular bone (SCTB). Despite this, understanding of the nature of BMLs at the trabecular tissue level is incomplete. Thus, we used Raman microspectroscopy to examine the biochemical properties of SCTB from KOA patients with presence or absence of BMLs (OA-BML, OA No-BML; respectively), in comparison with age-matched cadaveric non-symptomatic controls (Non-OA CTL).

METHODS

Tibial plateau (TP) specimens were collected from 19 KOA arthroplasty patients (6-Male, 13-Female; aged 56-74 years). BMLs were identified ex-vivo by MRI, using PDFS- and T1-weighted sequences. The KOA specimens were then categorized into an OA-BML group (n = 12; containing a BML within the medial condyle only) and an OA No-BML group (n = 7; with no BMLs identified in the TP). The control (CTL) group consisted of Non-OA cadaveric TP samples with no BMLs and no macroscopic or microscopic evidence of OA-related changes (n = 8; 5-Male, 3-Female; aged 44-80 years). Confocal Raman microspectroscopy, with high spatial resolution, was used to quantify the biochemical properties of SCTB tissue of both the medial and the lateral condyle in each group.

RESULTS

The ratios of peak intensity and integrated area of bone matrix mineral (Phosphate (v1), Phosphate (v2) and Phosphate (v4)), to surrogates of the organic phase of bone matrix (Amide I, Proline and Amide III), were calculated. Within the medial compartment, the mineral:organic matrix ratios were significantly lower for OA-BML, compared to Non-OA CTL. These ratios were also significantly lower for the OA-BML medial compartment, compared to the OA-BML lateral compartment. There were no group or compartmental differences for Carbonate:Phosphate (v1, v2 and v4), Amide III (α-helix):Amide III (random-coil), Hydroxyproline:Proline, or Crystallinity.

CONCLUSION

As measured by Raman microspectroscopy, SCTB tissue in BML zones in KOA is significantly less mineralized than the corresponding zones in individuals without OA. These data are consistent with those obtained using other methods (e.g. Fourier transform infrared spectroscopy; FTIR) and with the increased rate of bone remodeling observed in BML zones. Reduced mineralization may change the biomechanical properties of the trabecular bone in BMLs and the mechanical interaction between subchondral bone and its overlying cartilage, with potential implications for the development and progression of OA.

Raman fingerprints as promising markers of cellular senescence and aging

Due to our aging population, understanding of the underlying molecular mechanisms constantly gains more and more importance. Senescent cells, defined by being irreversibly growth arrested and associated with a specific gene expression and secretory pattern, accumulate with age and thus contribute to several age-related diseases. However, their specific detection, especially in vivo, is still a major challenge. Raman microspectroscopy is able to record biochemical fingerprints of cells and tissues, allowing a distinction between different cellular states, or between healthy and cancer tissue. Similarly, Raman microspectroscopy was already successfully used to distinguish senescent from non-senescent cells, as well as to investigate other molecular changes that occur at cell and tissue level during aging. This review is intended to give an overview about various applications of Raman microspectroscopy to study aging, especially in the context of detecting senescent cells.

Sequential Treatment of Estrogen Deficient, Osteopenic Rats with Alendronate, Parathyroid Hormone (1-34), or Raloxifene Alters Cortical Bone Mineral and Matrix Composition

Anti-resorptive and anabolic treatments can be used sequentially to treat osteoporosis, but their effects on bone composition are incompletely understood. Osteocytes may influence bone tissue composition with sequential therapies because bisphosphonates diffuse into the canalicular network and anabolic treatments increase osteocyte lacunar size. Cortical bone composition of osteopenic, ovariectomized (OVX) rats was compared to that of Sham-operated rats and OVX rats given monotherapy or sequential regimens of single approved anti-osteoporosis medications. Adult female Sprague-Dawley rats were OVX (N = 37) or Sham-OVXd (N = 6). After 2 months, seven groups of OVX rats were given three consecutive 3-month periods of treatment with vehicle (V), h-PTH (1-34) (P), alendronate (A), or raloxifene (R), using the following orders: VVV, PVV, RRR, RPR, AAA, AVA, and APA. Compositional properties around osteocyte lacunae of the left tibial cortex were assessed from Raman spectra in perilacunar and non-perilacunar bone matrix regions. Sequential treatments involving parathyroid hormone (PTH) caused lower mean collagen maturity relative to monotherapies. Mean mineral:matrix ratio was 2.2% greater, mean collagen maturity was 1.4% greater, and mean carbonate:phosphate ratio was 2.2% lower in the perilacunar than in the non-perilacunar bone matrix region (all P < 0.05). These data demonstrate cortical bone tissue composition differences around osteocytes caused by sequential treatment with anti-osteoporosis medications. We speculate that the region-specific differences demonstrate the ability of osteocytes to alter bone tissue composition adjacent to lacunae.

Impact microindentation assesses subperiosteal bone material properties in humans

Impact microindentation (IMI) is a Reference Point Indentation technique measuring tissue-level properties of cortical bone in humans in vivo. The nature, however, of the properties that can affect bone strength is incompletely understood. In the present study we examined bone material properties in transiliac bone biopsies obtained concurrently with measurements of Bone Material Strength index (BMSi) by IMI in 12 patients with different skeletal disorders and a wide range of BMD, with or without fractures (8 males, 4 females, mean age 48±12.2 (SD) years, range 15-60 years). IMI was performed in the mid-shaft of the right tibia with a hand-held microindenter (OsteoProbe). Cancellous and cortical bone mineralization density distributions (BMDD) were measured in the entire biopsy bone area by quantitative backscattered electron imaging. Raman measurements were obtained right at the outer edge of the cortex, and 5, 50, 100, 500μm inwards. The calculated parameters were: i) Mineral and organic matrix content as well as the mineral / matrix ratio. ii) Nanoporosity. iii) Glycosaminoglycan content. iv) Pyridinoline content. v) Maturity/crystallinity of the apatite crystallites. There was no relationship between BMSi values with any measurement of mineral content of whole bone tissue (BMD, BMDD) or maturity/crystallinity of bone mineral. On the other hand, a positive correlation between BMSi and local mineral content, and an inverse correlation between BMSi and nanoporosity at the mineralized subperiosteal edge of the sample and at 5μm inwards was found. A positive correlation was also observed between BMSi and pyridinoline content at the same locations. These results indicate that local mineral content, nanoporosity and pyridinoline content at the subperiosteal site in the transiliac bone biopsy are linked to the BMSi values measured in the tibia. As both high porosity at the nano level and low pyridinoline content of the bone matrix can negatively impact bone strength, our findings suggest that BMSi most likely assesses subperiosteal bone material properties.

Organic matrix quality discriminates between age- and BMD-matched fracturing versus non-fracturing post-menopausal women: A pilot study

Women with similar areal Bone Mineral Densities (BMD) may show divergent fracture incidence due to differences in bone quality. The hypothesis tested in the present pilot study is that postmenopausal (PM) women who have sustained osteoporotic fractures have altered organic matrix quality compared to those who have not. We used Raman microspectroscopy to analyze transiliac biopsies collected from fracturing (n = 6, mean age 62.5 ± 7.4 yrs; Cases) and non-fracturing PM women (n = 6, age- and BMD-matched; mean age 62.2 ± 7.3 yrs; Controls). Previous results show differences in intrinsic material properties by nanoindentation that are more homogenously distributed and could facilitate microcrack propagation in Cases, along with lower mineral carbonate/phosphate ratio by Fourier transform infrared spectroscopic imaging, and no differences in bone tissue mineralization by digitized microradiography. No differences between groups were seen by conventional histomorphometry. Spectra were acquired 2 μm away from previously performed nanoindents, in cortical and cancellous compartments. The determined parameters were: mineral to matrix ratio (MM), and nanoporosity (a surrogate for tissue water (TW)), glycosaminoglycan (GAG), pyridinoline (Pyd; trivalent enzymatic collagen cross-link), N(6)-carboxymethyllysine (CML; advanced glycation endproduct), and pentosidine (PEN; advanced glycation endproduct) content. ANCOVA indicated no differences in any of the spectroscopic outcomes between cancellous and cortical compartments. On the other hand, Cases had lower nanoporosity (TW) and GAG, and elevated Pyd, and CML content compared to Controls. In conclusion, the results of the present study indicate significant differences in organic matrix quality in PM women that sustain fragility fractures versus age- and BMD-matched controls, highlighting its importance as a potential independent determinant of fracture incidence.

The microbial metagenome and bone tissue composition in mice with microbiome-induced reductions in bone strength

The genetic components of microbial species that inhabit the body are known collectively as the microbiome. Modifications to the microbiome have been implicated in disease processes throughout the body and have recently been shown to influence bone. Prior work has associated changes in the microbial taxonomy (phyla, class, species, etc.) in the gut with bone phenotypes but has provided limited information regarding mechanisms. With the goal of achieving a more mechanistic understanding of the effects of the microbiome on bone, we perform a metagenomic analysis of the gut microbiome that provides information on the functional capacity of the microbes (all microbial genes present) rather than only characterizing the microbial taxa. Male C57Bl/6 mice were subjected to disruption of the gut microbiota (ΔMicrobiome) using oral antibiotics (from 4 to 16 weeks of age) or remained untreated (n = 6-7/group). Disruption of the gut microbiome in this manner has been shown to lead to reductions in tissue mechanical properties and whole bone strength in adulthood with only minor changes in bone geometry and density. ΔMicrobiome led to modifications in the abundance of microbial genes responsible for the synthesis of the bacterial cell wall and capsule; bacterially synthesized carbohydrates; and bacterially synthesized vitamins (B and K) (p < 0.01). Follow up analysis focused on vitamin K, a factor that has previously been associated with bone health. The vitamin K content of the cecum, liver and kidneys was primarily microbe-derived forms of vitamin K (menaquinones) and was decreased by 32-66% in ∆Microbiome mice compared to untreated animals (p < 0.01). Bone mineral crystallinity determined using Raman spectroscopy was decreased in ∆Microbiome mice (p = 0.01). This study illustrates the use of metagenomic analysis to link the microbiome to bone phenotypes and provides preliminary findings implicating microbially synthesized vitamin-K as a regulator of bone matrix quality.

Stroke Prevents Exercise-induced Gains in Bone Microstructure But Not Composition in Mice

Ischemic stroke induces rapid loss in bone mineral density up to 13 times greater than during normal aging, leading to markedly increased risk of fracture. Little is known about skeletal changes following stroke beyond density loss. In this study we use a mild-moderate middle cerebral artery occlusion model to determine the effects of ischemic stroke without bedrest on bone microstructure, dynamic bone formation, and tissue composition. Twenty-seven 12-week-old male C57Bl/6J mice received either a stroke or sham surgery and then either received daily treadmill exercise or remained sedentary for four weeks. All mice were ambulatory immediately following stroke, and limb coordination during treadmill exercise was unaffected by stroke, indicating similar mechanical loading across limbs for surgery groups. Stroke did not directly detriment microstructure, but exercise only stimulated adaptation in sham group, not stroke group, with increased bone volume fraction and trabecular thickness in the sham distal femoral metaphysis. Stroke differentially decreased cortical area in the affected limb relative to the unaffected limb of the distal femoral metaphysis, and endosteal bone formation rate in the affected tibial diaphysis. Although exercise failed to improve bone microstructure following stroke, exercise increased mineral-to-matrix content in stroke but not sham. Together, these results show that stroke inhibits exercise-induced changes to femoral microstructure but not tibial composition, even without changes to gait. Similarly, affected-unaffected limb differences in cortical bone structure and bone formation rate in ambulatory mice show that stroke affects bone health even without bedrest.

The contribution of the pericanalicular matrix to mineral content in human osteonal bone

The osteocyte lacunar-canalicular network (LCN) penetrates bone and houses the osteocytes and their processes. Despite its rather low volume fraction, the LCN represents an outstanding large surface that is possibly used by the osteocytes to interact with the surrounding mineralized bone matrix thereby contributing to mineral homeostasis. The aim of this study was to quantitatively describe such contributions by spatially correlating the local density of the LCN with the mineral content at the same location in micrometer-sized volume elements in human osteons. For this purpose, 65 osteons from the femur midshaft from healthy adults (n = 4) and children (n = 2) were structurally characterized with two different techniques. The 3D structure of the LCN in the osteons was imaged with confocal laser scanning microscopy after staining the bone samples with rhodamine. Subsequent image analysis provided the canalicular length density, i.e. the total length of the canaliculi per unit volume (μm/μm³). Quantitative information on the mineral content (wt%Ca) from the identical regions was obtained using quantitative backscattered electron imaging. As the LCN-porosity lowers the mineral content, a negative correlation between Ca content and network density was expected. Calculations predict a reduction of around -0.97 fmol Ca per μm of network. However, the experiment revealed for 62 out of 65 osteons a positive correlation resulting in an average additional Ca loading of +1.15 fmol per μm of canalicular network, i.e. an accumulation of mineral has occurred at dense network regions. We hypothesize that this accumulation happens in the close vicinity of canaliculi forming mineral reservoirs that can be utilized by osteocytes. Significant differences found between individuals indicate that the extent of mineral loading of the reservoir zone reflects an important parameter for mineral homeostasis.

Hypermineralization in the femoral neck of the elderly

Hip fragility depends on the decline in bone mass as well as changes in bone microstructure and the properties of bone mineral and organic matrix. Although it is well-established that low bone mass or osteoporosis is a key factor in hip fracture risk, it is striking to observe that 92% of 24 patients who have sustained an intracapsular hip fracture showed hypermineralization at the superior-anterior quadrant, a critical region associated with increased hip fracture risk. In-depth material studies on a total of 12 human cadaver femurs revealed increased degree of mineralization in the hypermineralized tissue: calcium weight percentage as measured by quantitative backscattered electron imaging increased by approximately 15% compared with lamellar bone; mineral-to-matrix ratio obtained by Raman microspectroscopy imaging also increased. Immunohistochemistry revealed localized type II collagen in the hypermineralized region, implying its cartilaginous nature. At the ultrastructural level, X-ray scattering revealed significantly smaller (on average 2.3 nm thick and 15.6 nm long) and less ordered bone minerals in the hypermineralized tissue. Finally, the hypermineralized tissue was more brittle than lamellar bone under hydrated state - cracks propagated easily in the hypermineralized region but stopped at the lamellar boundary. This study demonstrates that hypermineralization of femoral neck cortical bone is a source of bone fragility which is worth considering in future fracture risk assessment when the origin of hip fracture is unclear based on current evaluation standards. STATEMENT OF SIGNIFICANCE: Hypermineralization of femoral cortical bone in older adults might occur in many more hip fracture cases than presently known. Yet, this tissue remains largely unknown to the orthopedic community possibly due to coarse resolution of clinical imaging. The current study showed the hypermineralized tissue had reduced fracture resistance which could be attributed to the material changes in mineral content, organic matrix, and mineral platelets properties. It thus could be a source for fracture initiation. Consequently, we believe hypermineralization of femoral neck cortical bone should be considered in hip fragility assessment, especially when low bone mass cannot be identified as a primary contributor to hip fracture.

Heterogeneous bioapatite carbonation in western painted turtles is unchanged after anoxia

Adsorbed and structurally incorporated carbonate in bioapatite, the primary mineral phase of bone, is observed across vertebrates, typically at 2-8 wt%, and supports critical physiological and biochemical functions. Several turtle species contain elevated bone-associated carbonate, a property linked to pH buffering and overwintering survival. Prior studies of turtle bone utilized bulk analyses, which do not provide spatial resolution of carbonate. Using Raman spectroscopy, the goals of this study were to: (1) quantify and spatially resolve carbonate heterogeneity within the turtle shell; (2) determine if cortical and trabecular bone contain distinct carbonate concentrations; and (3) assess if simulated overwintering conditions result in decreased bioapatite carbonation. Here, we demonstrate the potential for Raman spectroscopic analysis to spatially resolve bioapatite carbonation, using the western painted turtle as a model species. Carbonate concentration was highly variable within cortical and trabecular bone, based on calibrated Raman spot analyses and mapping, suggesting heterogeneous carbonate distribution among crystallites. Mean carbonate concentration did not significantly differ between cortical and trabecular bone, which indicates random distribution of crystallites with elevated and depleted carbonate. Carbonate concentrations (range: 5-22 wt%) were not significantly different in overwintering and control animals, deviating from previous bulk analyses. In reconciling bulk and Raman analyses, two hypotheses explain how overwintering turtles potentially access carbonate: (1) mobilization of mineral-associated, surface components of bone crystallites; and (2) selective, dispersed crystallite dissolution. Elevated bioapatite carbonate in the western painted turtle, averaging 11.8 wt%, represents the highest carbonation observed in vertebrates, and is one physiological trait that facilitates overwintering survival.

Multiscale characterization of cortical bone composition, microstructure, and nanomechanical properties in experimentally induced osteoporosis

Cortical bone plays a vital role in determining overall bone strength. We investigate the structural, compositional, and nanomechanical properties of cortical bone following ovariectomy (OVX) of 12-week-old Sprague Dawley rats, since this animal model is frequently employed to evaluate the performance of implantable biomaterials in compromised bone healing conditions. Morphological parameters and material properties of bone in the geometrical center of the femoral cortex were investigated four and eight weeks post-OVX and in unoperated controls (Ctrl), using X-ray micro-computed tomography, backscattered electron scanning electron microscopy, Raman spectroscopy, and nanoindentation. The OVX animals showed increase in body weight, diminished bone mineral density, increased intracortical porosity, but increased bone mass through periosteal apposition (e.g., increases in periosteal perimeter, cortical cross-sectional thickness, and cross-sectional area). However, osteocyte densities, osteocyte lacunar dimensions, and the nanomechanical behavior on the single mineralized collagen fibril level remained unaffected. Our correlative multiscale investigation provides structural, chemical, and nanomechanical evidence substantiating earlier reports suggesting that rats ovariectomized at 12 weeks undergo simultaneous bone loss and growth, resulting in the effects of OVX being less obvious. Periosteal apposition contradicts the conventional view of bone loss in osteoporosis but appears advantageous for the greater functional demand imposed on the skeleton by increased body weight and fragility induced by increased intracortical porosity. Through a variety of morphological changes, it is likely that 12-week-old rats are able to adapt to OVX-related microstructural and compositional alterations. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 997-1007, 2018.

Raman and Fourier Transform Infrared (FT-IR) Mineral to Matrix Ratios Correlate with Physical Chemical Properties of Model Compounds and Native Bone Tissue

Raman and Fourier transform infrared (FT-IR) spectroscopic imaging techniques can be used to characterize bone composition. In this study, our objective was to validate the Raman mineral:matrix ratios (ν₁ PO₄:amide III, ν₁ PO₄:amide I, ν₁ PO₄:Proline + hydroxyproline, ν₁ PO₄:Phenylalanine, ν₁ PO₄:δ CH₂ peak area ratios) by correlating them to ash fraction and the IR mineral:matrix ratio (ν₃ PO₄:amide I peak area ratio) in chemical standards and native bone tissue. Chemical standards consisting of varying ratios of synthetic hydroxyapatite (HA) and collagen, as well as bone tissue from humans, sheep, and mice, were characterized with confocal Raman spectroscopy and FT-IR spectroscopy and gravimetric analysis. Raman and IR mineral:matrix ratio values from chemical standards increased reciprocally with ash fraction (Raman ν₁ PO₄/Amide III: P < 0.01, R²= 0.966; Raman ν₁ PO₄/Amide I: P < 0.01, R²= 0.919; Raman ν₁ PO₄/Proline + Hydroxyproline: P < 0.01, R²= 0.976; Raman ν₁ PO₄/Phenylalanine: P < 0.01, R²= 0.911; Raman ν₁ PO₄/δ CH₂: P < 0.01, R²= 0.894; IR P < 0.01, R²= 0.91). Fourier transform infrared mineral:matrix ratio values from native bone tissue were also similar to theoretical mineral:matrix ratio values for a given ash fraction. Raman and IR mineral:matrix ratio values were strongly correlated ( P < 0.01, R²= 0.82). These results were confirmed by calculating the mineral:matrix ratio for theoretical IR spectra, developed by applying the Beer-Lambert law to calculate the relative extinction coefficients of HA and collagen over the same range of wavenumbers (800-1800 cm^-1). The results confirm that the Raman mineral:matrix bone composition parameter correlates strongly to ash fraction and to its IR counterpart. Finally, the mineral:matrix ratio values of the native bone tissue are similar to those of both chemical standards and theoretical values, confirming the biological relevance of the chemical standards and the characterization techniques.

Maxillary Sinus Lift with Beta-Tricalcium Phosphate (β-TCP) in Edentulous Patients: A Nanotomographic and Raman Study

Sinus lift elevation restores bone mass at the maxilla in edentulate patients before the placement of dental implants. It consists of opening the lateral side of the sinus and grafting beta-tricalcium phosphate granules (β-TCP) under the olfactory membrane. Bone biopsies were obtained in five patients after 60 weeks. They were embedded undecalcified in poly(methyl methacrylate) (pMMA); blocks were analyzed by nanocomputed tomography (nanoCT); specific areas were studied by Raman microspectroscopy. Remnants of β-TCP were osseointegrated and covered with mineralized bone; osteoid tissue was also filling the inner porosity. Macrophages having engulfed numerous β-TCP grains were observed in marrow spaces. β-TCP was identified by nanoCT as osseointegrated particles and as granules in the cytoplasm of macrophages. Raman microspectroscopy permitted to compare the spectra of β-TCP and bone in different areas. The ratio of the ~820 cm^-1 band of pMMA (-CH₂ groups) on the ν1 phosphate band at 960 cm^-1 reflected tissue hydration because water was substituted by MMA during histological processing. In bone, the ratio of the ~960 cm^-1 phosphate to the amide 1 band and the ratio ν2 phosphate band by the 1240-1250 amide III band reflect the mineralization degree. Specific bands of β-TCP were found in osseointegrated β-TCP granules and in the grains phagocytized by the macrophages. The hydration degree was maximal for β-TCP phagocytized by macrophages. Raman microspectroscopy associated with nanoCT is a powerful tool in the analysis of the biomaterial degradation and osseointegration.

Vibrational spectroscopic techniques to assess bone quality

Although musculoskeletal diseases such as osteoporosis are diagnosed and treatment outcome is evaluated based mainly on routine clinical outcomes of bone mineral density (BMD) by DXA and biochemical markers, it is recognized that these two indicators, as valuable as they have proven to be in the everyday clinical practice, do not fully account for manifested bone strength. Thus, the term bone quality was introduced, to complement considerations based on bone turnover rates and BMD. Bone quality is an "umbrella" term that incorporates the structural and material/compositional characteristics of bone tissue. Vibrational spectroscopic techniques such as Fourier transform infrared microspectroscopy (FTIRM) and imaging (FTIRI), and Raman spectroscopy, are suitable analytical tools for the determination of bone quality as they provide simultaneous, quantitative, and qualitative information on all main bone tissue components (mineral, organic matrix, tissue water), in a spatially resolved manner. Moreover, the results of such analyses may be readily combined with the outcomes of other techniques such as histology/histomorphometry, small angle X-ray scattering, quantitative backscattered electron imaging, and nanoindentation.