X-ray diffraction as a promising tool to characterize bone nanocomposites

The elasto-plastic nano- and microscale compressive behaviour of rehydrated mineralised collagen fibres

The hierarchical design of bio-based nanostructured materials such as bone enables them to combine unique structure-mechanical properties. As one of its main components, water plays an important role in bone's material multiscale mechanical interplay. However, its influence has not been quantified at the length-scale of a mineralised collagen fibre. Here, we couple in situ micropillar compression, and simultaneous synchrotron small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) with a statistical constitutive model. Since the synchrotron data contain statistical information on the nanostructure, we establish a direct connection between experiment and model to identify the rehydrated elasto-plastic micro- and nanomechanical fibre behaviour. Rehydration led to a decrease of 65%-75% in fibre yield stress and compressive strength, and 70% in stiffness with a 3x higher effect on stresses than strains. While in agreement with bone extracellular matrix, the decrease is 1.5-3x higher compared to micro-indentation and macro-compression. Hydration influences mineral more than fibril strain with the highest difference to the macroscale when comparing mineral and tissue levels. The effect of hydration seems to be strongly mediated by ultrastructural interfaces while results provide insights towards mechanical consequences of reported water-mediated structuring of bone apatite. The missing reinforcing capacity of surrounding tissue for an excised fibril array is more pronounced in wet than dry conditions, mainly related to fibril swelling. Differences leading to higher compressive strength between mineralised tissues seem not to depend on rehydration while the lack of kink bands supports the role of water as an elastic embedding influencing energy-absorption mechanisms. STATEMENT OF SIGNIFICANCE: Characterising structure-property-function relationships in hierarchical biological materials helps us to elucidate mechanisms that enable their unique properties. Experimental and computational methods can advance our understanding of their complex behaviour with the potential to inform bio-inspired material development. In this study, we close a gap for bone's fundamental mechanical building block at micro- and nanometre length scales. We establish a direct connection between experiments and simulations by coupling in situ synchrotron tests with a statistical model and quantify the behaviour of rehydrated single mineralised collagen fibres. Results suggest a high influence of hydration on structural interfaces, and the role of water as an elastic embedding by outlining important differences between wet and dry elasto-plastic properties of mineral nanocrystals, fibrils and fibres.

Influence of Scaffold Microarchitecture on Angiogenesis and Regulation of Cell Differentiation during the Early Phase of Bone Healing: A Transcriptomics and Histological Analysis

The early phase of bone healing is a complex and poorly understood process. With additive manufacturing, we can generate a specific and customizable library of bone substitutes to explore this phase. In this study, we produced tricalcium phosphate-based scaffolds with microarchitectures composed of filaments of 0.50 mm in diameter, named Fil050G, and 1.25 mm named Fil125G, respectively. The implants were removed after only 10 days in vivo followed by RNA sequencing (RNAseq) and histological analysis. RNAseq results revealed upregulation of adaptive immune response, regulation of cell adhesion, and cell migration-related genes in both of our two constructs. However, significant overexpression of genes linked to angiogenesis, regulation of cell differentiation, ossification, and bone development was observed solely in Fil050G scaffolds. Moreover, quantitative immunohistochemistry of structures positive for laminin revealed a significantly higher number of blood vessels in Fil050G samples. Furthermore, µCT detected a higher amount of mineralized tissue in Fil050G samples suggesting a superior osteoconductive potential. Hence, different filament diameters and distances in bone substitutes significantly influence angiogenesis and regulation of cell differentiation involved in the early phase of bone regeneration, which precedes osteoconductivity and bony bridging seen in later phases and as consequence, impacts the overall clinical outcome.

Effect of Mechanical Stimuli and Zoledronic Acid on the Femoral Bone Morphology in Rats with Obesity and Limited Mobility

Our study aimed to compare the impact of zoledronic acid and whole-body vibration (WBV) as a non-pharmacological method of treatment for early obesity/immobility-related osteoporosis in male rat models. In total, 36 male Wistar rats were assigned to the following groups: obese control with immobility (Control, n = 12) and two experimental groups (n = 12 each), including obese and immobile rats subjected to whole-body vibration with an acceleration level of 3 m/s² g (obesity and immobility + WBV) and obese and immobile rats that received an intramuscular injection of zoledronic acid at a dose of 0.025 mg/kg (obesity and immobility + ZOL). After the 8th and 16th week of treatment, n = 6 rats from each group were euthanized and isolated femora were subjected to a histological examination of bone, and analysis of the expression of osteoprotegerin (OPG) and the receptor activator of nuclear factor kappa-B ligand (RANKL) involved in bone turnover and the amount of thin collagen fibers (PSR stain). The obtained results showed that short-term vibrotherapy (up to 8 weeks) can lead to improvement in bone remodeling in rat models with obesity and limited mobility.

Fast X-ray diffraction (XRD) tomography for enhanced identification of materials

X-ray computed tomography (CT) is a commercially established modality for imaging large objects like passenger luggage. CT can provide the density and the effective atomic number, which is not always sufficient to identify threats like explosives and narcotics, since they can have a similar composition to benign plastics, glass, or light metals. In these cases, X-ray diffraction (XRD) may be better suited to distinguish the threats. Unfortunately, the diffracted photon flux is typically much weaker than the transmitted one. Measurement of quality XRD data is therefore slower compared to CT, which is an economic challenge for potential customers like airports. In this article we numerically analyze a novel low-cost scanner design which captures CT and XRD signals simultaneously, and uses the least possible collimation to maximize the flux. To simulate a realistic instrument, we propose a forward model that includes the resolution-limiting effects of the polychromatic spectrum, the detector, and all the finite-size geometric factors. We then show how to reconstruct XRD patterns from a large phantom with multiple diffracting objects. We include a reasonable amount of photon counting noise (Poisson statistics), as well as measurement bias (incoherent scattering). Our XRD reconstruction adds material-specific information, albeit at a low resolution, to the already existing CT image, thus improving threat detection. Our theoretical model is implemented in GPU (Graphics Processing Unit) accelerated software which can be used to further optimize scanner designs for applications in security, healthcare, and manufacturing quality control.

Techniques for Bone Assessment and Characterization: Porcine Hard Palate Case Study

The hard palate plate has an important structural function that separates the nasal cavity and the nasopharynx. Incomplete regeneration of palatal fistulae in children with a cleft palate deformity after primary palatoplasty is a relatively common complication. To date, the information about the physicochemical bone features of this region is deficient, due to the low availability of human samples. Swine and human bone share anatomical similarities. Specifically, pig bones are widely used as experimental animal models in dental, orthopedic, or surgical techniques. The aim of this study was to show different techniques to evaluate and characterize alternative properties of pig hard palate bone, compared to commercial hydroxyapatite, one of the most used biomaterials for bone tissue regeneration. Chemical analyses by Energy dispersive spectroscopy (EDS) and X-ray fluorescence (XRF) showed calcium and phosphate ions as the main constituents of bone, while magnesium, iron, sodium, potassium, and zinc ions were minor constituents. The calcium phosphate molar ratio (Ca/P) in the bone was low (1.1 ± 0.2) due to the very young specimen sample used. The FTIR spectrum shows the presence of phosphates ions (PO₄^3-) and the main characteristics of collagen type I. The XRD results showed that the hard palate bone has a mixture of calcium, octacalcium dihydrogen phosphate (OCP), and apatite, where OCP is the predominant phase. Besides, this research demonstrated that the young bone has low crystallinity and small crystal size compared with commercial hydroxyapatite (HA). The palatine process of maxilla density and porosity data reported, suggest that the palate bone is getting closer to the compact bone with a 52.78 ± 2.91% porosity and their mechanical properties depend on the preparation conditions and the area of the bone analyzed.

Impact of Whole Body Vibration and Zoledronic Acid on Femoral Structure after Ovariectomy: Morphological Evaluation

Our study aimed to evaluate the effect of whole body vibration (WBV) treatment as an non-pharmacological method of treatment for early osteopenia in ovariectomized female rats. In total, 48 female Wistar rats were assigned to two groups: sham-operated control (SHAM, n = 12) and ovariectomized (n = 36). Four weeks after ovariectomy, the animals were divided into three experimental groups (n = 12 each): ovariectomized (OVX), ovariectomized subjected to whole body vibration with acceleration level of 0.3 g (OVX + WBV), or ovariectomized subjected to i.m. injection of Zoledronic acid at a dose of 0.025 mg/kg (OVX + ZOL). After the 8th and 16th week of treatment n = 6 rats from each group were euthanized and isolated femora were subjected to histological examination of trabecular bone and analysis of the expression of collagen 1 (Col1), osteoprotegerin (OPG), and receptor activator of nuclear factor kappa-Β ligand (RANKL) involved in bone turnover. The obtained results indicated that widespread vibration therapy can provide negative outcomes such as deterioration of trabecular bone histomorphometry.

Abdalla M, Bechelany M. Review on Natural, Incidental, Bioinspired, and Engineered Nanomaterials: History, Definitions, Classifications, Synthesis, Properties, Market, Toxicities, Risks, and Regulations

Nanomaterials are becoming important materials in several fields and industries thanks to their very reduced size and shape-related features. Scientists think that nanoparticles and nanostructured materials originated during the Big Bang process from meteorites leading to the formation of the universe and Earth. Since 1990, the term nanotechnology became very popular due to advances in imaging technologies that paved the way to specific industrial applications. Currently, nanoparticles and nanostructured materials are synthesized on a large scale and are indispensable for many industries. This fact fosters and supports research in biochemistry, biophysics, and biochemical engineering applications. Recently, nanotechnology has been combined with other sciences to fabricate new forms of nanomaterials that could be used, for instance, for diagnostic tools, drug delivery systems, energy generation/storage, environmental remediation as well as agriculture and food processing. In contrast with traditional materials, specific features can be integrated into nanoparticles, nanostructures, and nanosystems by simply modifying their scale, shape, and composition. This article first summarizes the history of nanomaterials and nanotechnology. Followed by the progress that led to improved synthesis processes to produce different nanoparticles and nanostructures characterized by specific features. The content finally presents various origins and sources of nanomaterials, synthesis strategies, their toxicity, risks, regulations, and self-aggregation.

LDN Protects Bone Property Deterioration at Different Hierarchical Levels in T2DM Mice Bone

Type 2 diabetes mellitus (T2DM) commonly affects bone quality at different hierarchical levels and leads to an increase in the risk of bone fracture. Earlier, some anti-diabetic drugs showed positive effects on bone mechanical properties. Recently, we have investigated that low-dose naltrexone (LDN), a TLR4 antagonist treatment, improves glucose tolerance in high-fat diet (HFD)-induced T2DM mice and also gives protection against HFD-induced weight gain. However, effects on bone are still unknown. In this study, the effects of LDN on the bone properties at different hierarchical levels in T2DM mice bone were investigated. In order to investigate these, four different groups of bone (divided based on diet and treatment) were considered in this present study. These are (a) normal control diet treated with saline water, (b) normal control diet treated with LDN, (c) HFD treated with saline water, and (d) HFD treated with LDN. Bone properties were measured in terms of fracture toughness, nano-Young's modulus, hardness, mineral crystal size, bone composition, and bulk mineral to matrix ratio. Results indicated that fracture toughness, nano-Young's modulus, and hardness were decreased in T2DM bone as compared to normal bone, and interestingly, treatment with the LDN increases these material properties in T2DM mice bone. Similarly, as compared to the normal bone, decrease in the mineral crystal size and bulk mineral-to-matrix ratio was observed in the T2DM bone, whereas LDN treatment protects these alterations in the T2DM mice bone. The bone size (bone geometry) was increased in the case of HFD-induced T2DM bone; however, LDN cannot protect to increase the bone size in the T2DM mice bone. In conclusion, LDN can be used to control the T2DM-affected bone properties at different hierarchical levels.

Using X-ray diffraction in characterization of bone remodeling and nanocomposites in ovariectomized rats osteopenia model

Sedentary lifestyle and physiological menopause are among the risk factors of osteopenia, especially in elderly people. However, bone mineral density decrease can also be observed in young individuals, for instance, due to deficiency of female sex hormones after surgical interventions, particularly ovariectomy. Our research enabled us to assess the efficacy of whole-body vibration in preventing the loss of bone mineral density in the ovariectomy rat osteopenia model. Thus, whole-body vibration with acceleration level 0.3 g and frequency 50 Hz was used on young female rats, which had been subjected to ovariectomy (n = 18). It had been conducted for 24 weeks, exposure time – 30 minutes per day, 5 times a week. Assessment of mineral component loss of the tibia was performed by means of X-ray diffraction. Bone remodeling was assessed by determining hormones: parathyroid hormone and calcitonin, Ca and P in the blood. X-ray diffraction is an effective method, which enables the evaluation a nanocomposites structure of the bone tissue in the experiment. In the article, we applied this method to determine the loss of bone mineral mass after ovariectomy and the impact of whole-body vibration under such conditions. In the ovariectomy group, the volume of a mineral component significantly decreased starting already from the 16th week (р<0.05) versus control. However, in the group with ovariectomy + whole-body vibration, the loss of a mineral component was insignificant during 8-16 weeks of the investigation, compared with the control group. On the 24th day, the spectrums almost did not differ from ovariectomized rats group. Meanwhile, hormone levels changed in ovariectomized rats group. It should be emphasized that the aforementioned whole-body vibration parameters do not cause severe bone damage or further negative consequences.

Effect of zoledronic acid on bone nanocomposites organization and prevention of bone mineral density loss in ovariectomized rats

OBJECTIVES

Osteoporosis often occurs in individuals of different age groups, frequently during menopause and after ovariectomy. It increases the risk of pathological fractures almost twice. The aim of our research was to assess bone metabolism, nanocomposite structure of the tibia under conditions of ovariectomy and zoledronic acid treatment.

METHODS

X-ray diffraction has been performed for nanostructure analysis of mineral crystallites and crystal lattice of hydroxyapatite in the tibia samples of ovariectomized rats with additional application of bisphosphonate zoledronic acid (0.025 mg/kg). Markers of remodeling - osteocalcin, alkaline phosphatase, tartrate resistant acid phosphatase 5b - were determined. Quantitative amount of calcium in the bones was detected by atomic absorption method.

RESULTS

Zoledronic acid prevented loss of mineral mass after ovariectomy. Rats after ovariectomy, treated with zoledronic acid, showed statistically higher (р<0.05) values of crystalline phase and calcium content compared with the SHAM-surgery and ovariectomy groups (р<0.05). Zoledronic acid inhibited bone remodeling, which is proved by tartrate resistant acid phosphatase 5b reduction and inhibition of osteoclasts during the experiment.

CONCLUSIONS

These results enable to suggest that zoledronic acid can improve mineral mass of the bone during menopause in individuals of different age groups.

Effects of mechanical stimuli on structure and organization of bone nanocomposites in rats with glucocorticoid-induced osteoporosis

Objective. Clinical use of glucocorticoids is a frequent cause of secondary osteoporosis, which reduces the mineral density of bones and results in pathological fractures. Mechanical stimulation as non-physiological high-frequency vibration with low acceleration prevents the loss of a crystalline component and stimulates the anabolic remodeling of the bone. The aim of the present research was to assess the impact of mechanical vibration on the bone structure in rats, which received glucocorticoids.Methods. Wistar rats were randomized into three groups: Vehicle control (Veh), Methylprednisolone sodium succinate (Mps), and Mps combined with whole-body vibration (WBV). Rats of Mps+WBV and Mps groups received 3 mg/kg/day of methylprednisolone every other day for 24 weeks and rats of Veh group received 0.9% saline (sodium chloride). The group of rats Mps+WBV was subjected to WBV for 30 minutes per day for five days a week with parameters 0.3 g and frequency 50 Hz. Relative amount of crystalline component and collagen in the bones was determined by X-ray diffraction (XRD) and calcium level - by atomic absorption spectroscopy. Bone tissue metabolism was assessed by determining the concentration of markers, in particular osteocalcin and Tartrate-resistant acid phosphatase (TRAP5b).Results. Glucocorticoids induced a considerable increase in the rats body mass (+13%) and decreased the content of mineral component in the femoral neck (-17%) in Mps group compared with Veh. The process of the bone metabolism was significantly accelerated, which is proven by an increased level of remodeling markers. It should be mentioned that WBV did not allow significant decrease in mineral component of the bone to 16th week of the experiment compared with Mps group, although these parameters did not achieve the indices in the Vehicle control group (-10%). Our investigation allows to suggest that mechanical high-frequency vibration of low intensity can partially inhibit the harmful consequences of glucocorticoids on bone structure in rats. Despite the positive impact of vibration on the bone tissue after Mps introduction in the 8th-16th week, this influence was not statistically reliable in the 24th week of the experiment.Conclusions. The results of our investigation on animal model indicate that non-physiological vertical mechanical vibrations are an effective means to prevent loss of a mineral bone component during treatment with glucocorticoids.

Ovine Bone Morphology and Deformation Analysis Using Synchrotron X-ray Imaging and Scattering

Bone is a natural hierarchical composite tissue incorporating hard mineral nano-crystals of hydroxyapatite (HAp) and organic binding material containing elastic collagen fibers. In the study, we investigated the structure and deformation of ovine bone by the combination of high-energy synchrotron X-ray tomographic imaging and scattering. X-ray experiments were performed prior to and under three-point bending loading by using a specially developed in situ load cell constructed from aluminium alloy frame, fast-drying epoxy resin for sample fixation, and a titanium bolt for contact loading. Firstly, multiple radiographic projection images were acquired and tomographic reconstruction was performed using SAVU software, following segmentation using Avizo. Secondly, Wide Angle X-ray Scattering (WAXS) and Small Angle X-ray Scattering (SAXS) 2D scattering patterns were collected from HAp and collagen. Both sample shape and deformation affect the observed scattering. Novel combined tomographic and diffraction analysis presented below paves the way for advanced characterization of complex shape samples using the Dual Imaging and Diffraction (DIAD) paradigm.

Biomechanical properties enhancement of gamma radiation-sterilized cortical bone using antioxidants

Gamma radiation sterilization is the method used by the majority of tissue banks to reduce disease transmission from infected donors to recipients through bone allografts. However, many studies have reported that gamma radiation impairs the structural and mechanical properties of bone via formation of free radicals, the effect of which could be reduced using free radical scavengers. The aim of this study is to examine the radioprotective role of hydroxytyrosol (HT) and alpha lipoic acid (ALA) on the mechanical properties of gamma-sterilized cortical bone of bovine femur, using three-point bending and microhardness tests. Specimens of bovine femurs were soaked in ALA and HT for 3 and 7 days, respectively, before being exposed to 35-kGy gamma radiation. In unirradiated samples, both HT and ALA pre-treatment improved the cortical bone bending plastic properties (maximum bending stress, maximum bending strain, and toughness) without affecting microhardness. Irradiation resulted in a drastic reduction of the plastic properties and an increased microhardness. ALA treatment before irradiation alleviated the aforementioned reductions in maximum bending stress, maximum bending strain, and toughness. In addition, under ALA treatment, the microhardness was not increased after irradiation. For HT treatment, similar effects were found. In conclusion, the results indicate that HT and ALA can be used before irradiation to enhance the mechanical properties of gamma-sterilized bone allografts.

Ontogenetic variability in crystallography and mosaicity of conodont apatite: implications for microstructure, palaeothermometry and geochemistry

X-ray diffraction data from Silurian conodonts belonging to various developmental stages of the species Dapsilodus obliquicostatus demonstrate changes in crystallography and degree of nanocrystallite ordering (mosaicity) in both lamellar crown tissue and white matter. The exclusive use of a single species in this study, combined with systematic testing of each element type at multiple locations, provided insight into microstructural and crystallographic differentiation between element type (Sa , Sb -c , M) as well as between juveniles and adults. A relative increase in the unit cell dimensions a/c ratio of nanocrystallites during growth was apparent in areas demonstrating single-crystal behaviour, but no such relationship was seen in dominantly polycrystalline areas. Systematic variations in mosaicity were identified, with mosaicity (as a proxy for disorder) increasing during growth, as well as along elements from tip to base. These results provide potential insight into the integrity of conodont apatite as a recorder of palaeoseawater chemistry, as well as demonstrate the need to consider the influence of ontogeny and element type on the use of conodonts in palaeothermometry and geochemical investigations.

Compressive behaviour of uniaxially aligned individual mineralised collagen fibres at the micro- and nanoscale

The increasing incidence of osteoporotic bone fractures makes fracture risk prediction an important clinical challenge. Computational models can be utilised to facilitate such analyses. However, they critically depend on bone's underlying hierarchical material description. To understand bone's irreversible behaviour at the micro- and nanoscale, we developed an in situ testing protocol that allows us to directly relate the experimental data to the mechanical behaviour of individual mineralised collagen fibres and its main constitutive phases, the mineralised collagen fibrils and the mineral nanocrystals, by combining micropillar compression of single fibres with small angle X-ray scattering (SAXS) and X-ray diffraction (XRD). Failure modes were assessed by SEM. Strain ratios in the elastic region at fibre, fibril and mineral levels were found to be approximately 22:5:2 with strain ratios at the point of compressive strength of 0.23 ± 0.11 for fibril-to-fibre and 0.07 ± 0.01 for mineral-to-fibre levels. Mineral-to-fibre levels showed highest strain ratios around the apparent yield point, fibril-to-fibre around apparent strength. The mineralised collagen fibrils showed a delayed mechanical response, contrary to the mineral phase, which points towards preceding deformations of mineral nanocrystals in the extrafibrillar matrix. No damage was measured at the level of the mineralised collagen fibre which indicates an incomplete separation of the mineral and collagen, and an extrafibrillar interface failure. The formation of kink bands and the gradual recruitment of fibrils upon compressive loading presumably led to localised strains. Our results from a well-controlled fibrillar architecture provide valuable input for micromechanical models and computational non-linear bone strength analyses that may provide further insights for personalised diagnosis and treatment as well as bio-inspired implants for patients with bone diseases. STATEMENT OF SIGNIFICANCE: Musculoskeletal diseases such as osteoporosis, osteoarthritis or bone cancer significantly challenge health care systems and make fracture risk prediction and treatment optimisation important clinical goals. Computational methods such as finite element models have the potential to optimise analyses but highly depend on underlying material descriptions. We developed an in situ testing set-up to directly relate experimental data to the mechanical behaviour of bone's fundamental building block, the individual mineralised collagen fibre and its main constituents. Low multilevel strain ratios suggest high deformations in the extrafibrillar matrix and energy dissipation at the interfaces, the absence of damage indicates both an incomplete separation between mineral and collagen and an extrafibrillar interface failure. The formation of kink bands in the fibril-reinforced composite presumably led to localised strains. The deformation behaviour of a well-controlled fibrillar architecture provides valuable input for non-linear bone strength analyses.

Polarization induced contrast X-ray fluorescence at submicrometer resolution reveals nanometer apatite crystal orientations across entire tooth sections

For biomedical research, successful imaging of calcified microstructures often relies on absorption differences between features, or on employing dies with selective affinity to areas of interest. When texture is concerned, e.g. for crystal orientation studies, polarization induced contrast is of particular interest. This requires sufficient interaction of the incoming radiation with the volume of interest in the sample to produce orientation-based contrast. Here we demonstrate polarization induced contrast at the calcium K-edge using submicron sized monochromatic synchrotron X-ray beams. We exploit the orientation dependent subtle absorption differences of hydroxyl-apatite crystals in teeth, with respect to the polarization field of the beam. Interaction occurs with the fully mineralized samples, such that differences in density do not contribute to the contrast. Our results show how polarization induced contrast X-ray fluorescence mapping at specific energies of the calcium K-edge reveals the micrometer and submicrometer crystal arrangements in human tooth tissues. This facilitates combining both high spatial resolution and large fields of view, achieved in relatively short acquisition times in reflection geometry. In enamel we observe the varying crystal orientations of the micron sized prisms exposed on our prepared surface. We easily reproduce crystal orientation maps, typically observed in polished thin sections. We even reveal maps of submicrometer mineralization fronts in spherulites in intertubular dentine. This Ca K-edge polarization sensitive method (XRF-PIC) does not require thin samples for transmission nor extensive sample preparation. It can be used on both fresh, moist samples as well as fossilized samples where the information of interests lies in the crystal orientations and where the crystalline domains extend several micrometers beneath the exposed surface.

The bone degenerative processes in senile fishes from Holocene Brazilian shell mounds

Zooarchaeological collections from shell mounds in Rio de Janeiro (2,470-4,632 cal BP) contain a high prevalence of swollen fish bones belonging to the Atlantic spadefish (Chaetodipterus faber), crevalle jack (Caranx hippos) and fat snook (Centropomus parallelus). Given the lack of knowledge of the bone degenerative process in senile fishes, this study analysed hyperostotic bone in zooarchaeological and modern specimens to obtain high-resolution morphology and microstructure reconstruction. We used microCT as well as X-ray diffraction to characterize the crystallographic changes associated with fish senility. Our results showed that trabecular microstructures in hyperostotic bones were consistent with estimated values of the per cent bone volume-to-total volume ratio (BV/TV) and were greater than 60% in cortical bone. Hyperostotic bones indicated a high radiograph density, and X-ray diffractograms showed a decrease in hydroxyapatite [Ca₁₀ (PO₄ )₆ (OH)₂ ] and calcite (CaCO₃ ) neocrystallization. These crystalline and density changes revealed an advanced stage of fish senile and indicate the vulnerability of ageing fish populations.

Raman spectroscopic investigation on the molecular structure of apatite and collagen in osteoporotic cortical bone

This study employed highly spectrally resolved Raman spectroscopy to examine the molecular composition of cortical bone tissue obtained from murine females in their healthy and ovariectomy- (OVX-) induced osteoporotic states. The aim of the study was to identify structural differences at the molecular scale both in apatite mineral and collagen fibrils between the two groups of samples. Raman spectroscopy was used to determine the chemical composition of cortical bone in regions including characteristic bands of both bone mineral and bone matrix. The results demonstrated that the mineral apatite of bone did not undergo significant amorphization in its diseased state, with the Raman microprobe also failing in recognizing a direct role of carbonate content in the embrittlement of OVX-diseased bone. On the other hand, complex off-stoichiometry variations could be detected in the columnar Ca-structure of the bony hydroxyapatite according to morphological variations of the Raman band belonging to the symmetric phosphate stretching (A₁) band at ~959cm^-1. A fundamental role was also recognized for collagen quality on the process of bone embrittlement. The so-called matrix maturity ratio, as systematically measured on Raman spectra in the Amide I region, increased with statistical significance in OVX-treated samples as compared to control samples. An 8% increase could be associated to a 115% increase in elastic stress intensification in the mineral phase of OVX-diseased tissue as compared to the control one, thus proving a degradation in the (elastic) energy-dissipative capacity of a diseased bone matrix.

Bone quality assessment techniques: geometric, compositional, and mechanical characterization from macroscale to nanoscale

This review presents an overview of the characterization techniques available to experimentally evaluate bone quality, defined as the geometric and material factors that contribute to fracture resistance independently of areal bone mineral density (aBMD) assessed by dual energy x-ray absorptiometry. The methods available for characterization of the geometric, compositional, and mechanical properties of bone across multiple length scales are summarized, along with their outcomes and their advantages and disadvantages. Examples of how each technique is used are discussed, as well as practical concerns such as sample preparation and whether or not each testing method is destructive. Techniques that can be used in vivo and those that have been recently improved or developed are emphasized, including high resolution peripheral quantitative computed tomography to evaluate geometric properties and reference point indentation to evaluate material properties. Because no single method can completely characterize bone quality, we provide a framework for how multiple characterization methods can be used together to generate a more comprehensive analysis of bone quality to complement aBMD in fracture risk assessment.

Nanostructure and elastic modulus of single trabecula in bovine cancellous bone

We aimed to investigate the elastic modulus of trabeculae using tensile tests and assess the effects of nanostructure at the hydroxyapatite (HAp) crystal scale on the elastic modulus. In the experiments, 18 trabeculae that were at least 3mm in length in the proximal epiphysis of three adult bovine femurs were used. Tensile tests were conducted using a small tensile testing device coupled with microscopy under air-dried condition. The c-axis orientation of HAp crystals and the degree of orientation were measured by X-ray diffraction. To observe the deformation behavior of HAp crystals under tensile loading, the same tensile tests were conducted in X-ray diffraction measurements. The mineral content of specimens was evaluated using energy dispersive X-ray spectrometry. The elastic modulus of a single trabecula varied from 4.5 to 23.6 GPa, and the average was 11.5 ± 5.0 GPa. The c-axis of HAp crystals was aligned with the trabecular axis and the crystals were lineally deformed under tensile loading. The ratio of the HAp crystal strain to the tissue strain (strain ratio) had a significant correlation with the elastic modulus (r=0.79; P<0.001). However, the mineral content and the degree of orientation did not vary widely and did not correlate with the elastic modulus in this study. It suggests that the strain ratio may represent the nanostructure of a single trabecula and would determine the elastic modulus as well as mineral content and orientation.

Effects of growth on residual stress distribution along the radial depth of cortical cylinders from bovine femurs

Residual stress is defined as the stress that remains in bone tissue without any external forces. This study investigated the effects of growth on residual stress distributions from the surface to deeper regions of cortical cylinders obtained from less-than-one-month-old (Group Y) and two-year-old (Group M) bovine femurs. In these experiments, five diaphysis specimens from each group were used. Residual stress was measured using a high-energy synchrotron white X-ray beam to penetrate X-rays into the deeper region of the bone specimens. The measurements in the cortical cylinders from Groups Y and M were performed at 0.5- and 1-mm intervals, respectively, from the outer surface to the deeper region of the diaphysis specimens at four positions: anterior, posterior, lateral, and medial. The residual stress was calculated on the basis of variation in the interplanar spacing of hydroxyapatite crystals in the bone tissue. According to the results, the diaphysis specimens from Group Y were not subjected to large residual stresses (average -1.2 MPa and 2.4 MPa at the surface region and 1.5mm depth, respectively). In Group M, the surface region of the diaphysis specimens was subjected to tensile residual stresses (average 6.7 MPa) and the deeper region was subjected to compressive stresses (average -8.2 MPa at 3mm depth). There was a strong significant difference between both these regions. The value of residual stresses at the surface region of the diaphysis specimens in both the groups had a positive statistical correlation with the cortical thickness at the measured locations.

Influence of osteon area fraction and degree of orientation of HAp crystals on mechanical properties in bovine femur

Cortical bone has a hierarchical structure, spanning from the macrostructure at several millimeters or whole bone level, the microstructure at several hundred micrometers level, to the nanostructure at hydroxyapatite (HAp) crystals and collagen fibrils levels. The aim of the study is to understand the relationship between the HAp crystal orientation and the elastic modulus and the relationship between the osteon area fraction and the deformation behavior of HAp crystals in cortical bone. In the experiments, five strip specimens (40×2×1mm(3)) aligned with the bone axis were taken from the cortical bone of a bovine femur. The degree of c-axis orientation of HAp crystals in the specimens was measured with the X-ray diffraction technique with the imaging plate. To measure the deformation behavior of HAp crystals in the specimens, tensile tests under X-ray irradiation were conducted. The specimens were cut at the X-ray measurement positions and osteon area fraction and porosity at the transverse cross-sections were observed. Further, the volume fraction of HAp of the specimens was measured. Results showed the degree of c-axis orientation of HAp crystals was positively correlated with the elastic modulus of the specimens (r=0.94). The volume fraction of HAp and the porosity showed no statistical correlation with the elastic modulus and the tensile strength. The HAp crystal strain ε(H) increased linearly with the bone tissue strain ε. The average value of ε(H)/ε was 0.69±0.13 and there was no correlation between the osteon area fraction and ε(H)/ε (r=-0.27, p=0.33). The results suggest that the degree of c-axis orientation of HAp crystals affects the elastic modulus and the magnitude of HAp crystal strain does not depend on the osteon area fraction.