Hierarchical microimaging of bone structure and function

Ex vivo loading of trussed implants for spine fusion induces heterogeneous strains consistent with homeostatic bone mechanobiology

A truss structure was recently introduced as an interbody fusion cage. As a truss system, some of the connected elements may be in a state of compression and others in tension. This study aimed to quantify both the mean and variance of strut strains in such an implant when loaded in a simulated fusion condition with vertebral body or contoured plastic loading platens ex vivo. Cages were each instrumented with 78 fiducial spheres, loaded between platens (vertebral body or contoured plastic), imaged using high resolution micro-CT, and analyzed for deformation and strain of each of the 221 struts. With repeated loading of a cage by vertebral platens, the distribution (variance, indicated by SD) of strut strains widened from 50N control (4±114με, mean±SD) to 1000N (-23±273με) and 2000N (-48±414με), and between 1000N and 2000N. With similar loading of multiple cages, the strain distribution at 2000N (23±389με) increased from 50N control. With repeated loading by contoured plastic platens, induced strains at 2000N had a distribution similar to that induced by vertebral platens (84±426με). In all studies, cages exhibited increases in strut strain amplitude when loaded from 50N to 1000N or 2000N. Correspondingly, at 2000N, 59-64% of struts exhibited strain amplitudes consistent with mechanobiologically-regulated bone homeostasis. At 2000N, vertically-oriented struts exhibited deformation of -2.87±2.04μm and strain of -199±133με, indicating overall cage compression. Thus, using an ex vivo 3-D experimental biomechanical analysis method, a truss implant can have strains induced by physiological loading that are heterogeneous and of amplitudes consistent with mechanobiological bone homeostasis.

Cortical Bone Porosity: What Is It, Why Is It Important, and How Can We Detect It?

There is growing recognition of the role of micro-architecture in osteoporotic bone loss and fragility. This trend has been driven by advances in imaging technology, which have enabled a transition from measures of mass to micro-architecture. Imaging trabecular bone has been a key research focus, but advances in resolution have also enabled the detection of cortical bone micro-architecture, particularly the network of vascular canals, commonly referred to as 'cortical porosity.' This review aims to provide an overview of what this level of porosity is, why it is important, and how it can be characterized by imaging. Moving beyond a 'trabeculocentric' view of bone loss holds the potential to improve diagnosis and monitoring of interventions. Furthermore, cortical porosity is intimately linked to the remodeling process, which underpins bone loss, and thus a larger potential exists to improve our fundamental understanding of bone health through imaging of both humans and animal models.

High-fat diet induced changes in lumbar vertebra of the male rat offsprings

In obesity, bone marrow adiposity increases and proinflammatory cytokines excretion activates RANK/RANKL/OPG system, which leads to increased bone resorption. The aim of this study was to analyze trabecular and cortical bone parameters in animals exposed to the high-fat diet in utero and after lactation. Skeletal organ of interest was the fifth lumbar vertebra, which is not exposed to biomechanical loading in rats. Further aims were to determine TNF-α and IL-6 serum concentrations, and the intensity of the TNF-α immunohistochemical staining in the bone marrow. Ten female Sprague Dawley rats, nine weeks old, were randomly divided in two groups and fed either standard laboratory chow or food rich in saturated fatty acids during five weeks, and then mated with genetically similar male subjects. After birth and lactation male offsprings from both groups were divided in four subgroups depending on the diet they were fed until twenty-two weeks of age. The highest cholesterol and triglyceride concentration were found in both groups of offsprings fed with high-fat diet. The lowest trabecular bone volume, lowest trabecular number and highest trabecular separation were found in offsprings fed with high-fat diet of mothers on standard laboratory chow. The same group of offsprings was also characterized by the highest intensity of TNF-α immunostaining in the bone marrow and the highest TNF-α serum concentration, which suggest that this proinflammatory cytokine has interfered with bone metabolism, possibly by stimulation of bone resorption, which led to inadequate trabecular bone development and bone modeling of the fifth lumbar vertebra.

Long-term Observation of Regenerated Periodontium Induced by FGF-2 in the Beagle Dog 2-Wall Periodontal Defect Model

The long-term stability and qualitative characteristics of periodontium regenerated by FGF-2 treatment were compared with normal physiological healing tissue controls in a Beagle dog 2-wall periodontal defect model 13 months after treatment by assessing tissue histology and three-dimensional microstructure using micro-computed tomography (μCT). After FGF-2 (0.3%) or vehicle treatment at the defect sites, serial changes in the bone mineral content (BMC) were observed using periodic X-ray imaging. Tissues were harvested at 13 months, evaluated histomorphometrically, and the cortical bone volume and trabecular bone structure of the newly formed bone were analyzed using μCT. FGF-2 significantly increased the BMC of the defect area at 2 months compared with that of the control group, and this difference was unchanged through 13 months. The cortical bone volume was significantly increased by FGF-2, but there was no difference between the groups in trabecular bone structure. Bone maturation was occurring in both groups because of the lower cortical volume and denser trabecular bone than what is found in intact bone. FGF-2 also increased the area of newly formed bone as assessed histomorphometrically, but the ratios of trabecular bone in the defect area were similar between the control and FGF-2 groups. These results suggest that FGF-2 stimulates neogenesis of alveolar bone that is of similar quality to that of the control group. The lengths of the regenerated periodontal ligament and cementum, measured as the distance from the defect bottom to the apical end of the gingival epithelium, and height and area of the newly formed bone in the FGF-2 group were larger than those in the control group. The present study demonstrated that, within the limitation of artificial periodontal defect model, the periodontal tissue regenerated by FGF-2 was maintained for 13 months after treatment and was qualitatively equivalent to that generated through the physiological healing process.

Osteocyte-directed bone demineralization along canaliculi

The mammalian skeleton stores calcium and phosphate ions in bone matrix. Osteocytes in osteocyte lacunae extend numerous dendrites into canaliculi less than a micron in diameter and which are distributed throughout bone matrix. Although osteoclasts are the primary bone-resorbing cells, osteocytes also reportedly dissolve hydroxyapatite at peri-lacunar bone matrix. However, robust three-dimensional evidence for peri-canalicular bone mineral dissolution has been lacking. Here we applied a previously reported Talbot-defocus multiscan tomography method for synchrotron X-ray microscopy and analyzed the degree of bone mineralization in mouse cortical bone around the lacuno-canalicular network, which is connected both to blood vessels and the peri- and endosteum. We detected cylindrical low mineral density regions spreading around canaliculi derived from a subset of osteocytes. Transmission electron microscopy revealed both intact and demineralized bone matrix around the canaliculus. Peri-canalicular low mineral density regions were also observed in osteopetrotic mice lacking osteoclasts, indicating that osteoclasts are dispensable for peri-canalicular demineralization. These data suggest demineralization can occur from within bone through the canalicular system, and that peri-canalicular demineralization occurs not uniformly but directed by individual osteocytes. Blockade of peri-canalicular demineralization may be a therapeutic strategy to increase bone mass and quality.

MorphoTester: An Open Source Application for Morphological Topographic Analysis

The increased prevalence and affordability of 3D scanning technology is beginning to have significant effects on the research questions and approaches available for studies of morphology. As the current trend of larger and more precise 3D datasets is unlikely to slow in the future, there is a need for efficient and capable tools for high-throughput quantitative analysis of biological shape. The promise and the challenge of implementing relatively automated methods for characterizing surface shape can be seen in the example of dental topographic analysis. Dental topographic analysis comprises a suite of techniques for quantifying tooth surfaces and component features. Topographic techniques have provided insight on mammalian molar form-function relationships and these methods could be applied to address other topics and questions. At the same time implementing multiple complementary topographic methods can have high time and labor costs, and comparability of data formats and approaches is difficult to predict. To address these challenges I present MorphoTester, an open source application for visualizing and quantifying topography from 3D triangulated polygon meshes. This application is Python-based and is free to use. MorphoTester implements three commonly used dental topographic metrics–Dirichlet normal energy, relief index, and orientation patch count rotated (OPCR). Previous OPCR algorithms have used raster-based grid data, which is not directly interchangeable with vector-based triangulated polygon meshes. A 3D-OPCR algorithm is provided here for quantifying complexity from polygon meshes. The efficacy of this metric is tested in a sample of mandibular second molars belonging to four species of cercopithecoid primates. Results suggest that 3D-OPCR is at least as effective for quantifying complexity as previous approaches, and may be more effective due to finer resolution of surface data considered here. MorphoTester represents an advancement in the automated quantification of morphology, and can be modified to adapt to future needs and priorities.

Patterns of activity adaptation in humeral trabecular bone in Neolithic humans and present-day people

OBJECTIVE

The annual turnover rate of trabecular bone by far exceeds that of cortical bone and, therefore, is very sensitive to its daily loading regime. Here we test the hypothesis that the study of the trabecular bone architecture of the human humerus is able to differentiate between different habitual manual activities.

MATERIALS AND METHODS

For this purpose, we compared the trabecular architecture of the humeral head in a Neolithic population to that of a sample of contemporary Europeans using micro-computed tomography (microCT). We defined in each specimen a spherical volume of interest with a diameter of 57.5 ± 2.5% of the maximal diameter of the humeral head to metrically analyze the bulk of humeral head trabecular architecture. We subsequently quantified the trabecular architectures in the VOIs, measuring seven standard 3D-morphometric parameters, and used univariate and multivariate statistical analyses for comparisons within and between populations.

RESULTS

Univariate statistical analysis showed significant differences in a combination of 3D-morphometric parameters. A principal components analysis of the 3D-morphometrics of the trabecular architectures separated the Neolithic from the contemporary samples on the basis of differences in their gross trabecular architecture, including differences in the bone volume fraction (BV/TV), the number of trabeculae per unit length (Tb N), and the distance between trabeculae (Tb Sp).

DISCUSSION

We interpret the significant differences found in the humeral trabecular bone of the Neolithic and the contemporary group as likely reflecting the distinct manual working routines. The trabecular bone configuration in the Neolithic sample shows presumably functional signatures of prehistoric subsistence techniques and activity levels.

Prediction of local ultimate strain and toughness of trabecular bone tissue by Raman material composition analysis

Clinical studies indicate that bone mineral density correlates with fracture risk at the population level but does not correlate with individual fracture risk well. Current research aims to better understand the failure mechanism of bone and to identify key determinants of bone quality, thus improving fracture risk prediction. To get a better understanding of bone strength, it is important to analyze tissue-level properties not influenced by macro- or microarchitectural factors. The aim of this pilot study was to identify whether and to what extent material properties are correlated with mechanical properties at the tissue level. The influence of macro- or microarchitectural factors was excluded by testing individual trabeculae. Previously reported data of mechanical parameters measured in single trabeculae under tension and bending and its compositional properties measured by Raman spectroscopy was evaluated. Linear and multivariate regressions show that bone matrix quality but not quantity was significantly and independently correlated with the tissue-level ultimate strain and postyield work (r = 0.65–0.94). Principal component analysis extracted three independent components explaining 86% of the total variance, representing elastic, yield, and ultimate components according to the included mechanical parameters. Some matrix parameters were both included in the ultimate component, indicating that the variation in ultimate strain and postyield work could be largely explained by Raman-derived compositional parameters.

Micro-CT analysis of the rodent jaw bone micro-architecture: A systematic review

Introduction

Knowledge about macro- and micro-structural characteristics may improve in vivo estimation of the quality and quantity of regenerated bone tissue. For this reason, micro-CT imaging has been applied to evaluate alveolar bone remodelling, alterations of periodontal ligament thickness and cortical and trabecular bone changes in rodent jaw bones. In this paper, we provide a systematic review on the available micro-CT literature on jaw bone micro-architecture.

Methodology

A detailed search through the PubMed database was performed. Articles published up to December 2013 and related to maxilla, mandible and condyle with quantitatively analysed bone micro-architectural parameters were considered eligible for inclusion. Two reviewers assessed the search results according to inclusion criteria designed to identify animal studies quantifying the bone micro-architecture of the jaw rodent bones in physiological or drug-induced disease status, or in response to interventions such as mechanical loading, hormonal treatment and other metabolic alterations. Finally, the reporting quality of the included publications was evaluated using the tailored ARRIVE guidelines outlined by Vignoletti and Abrahamsson (2012).

Results

Database search, additional manual searching and assessment of the inclusion and exclusion criteria retrieved 127 potentially relevant articles. Eventually, 14 maxilla, 20 mandible and 12 condyle articles with focus on bone healing were retained, and were analysed together with 3 methodological papers. Each study was described systematically in terms of subject, experimental intervention, follow-up period, selected region of interest used in the micro-CT analysis, parameters quantified, micro-CT scanner device and software. The evidence level evaluated by the ARRIVE guidelines showed high mean scores (between 18 and 25; range: 0–25), indicating that most of the selected studies are well-reported. The major obstacles identified were related to sample size calculation, absence of adverse event descriptions, randomization or blinding procedures.

Conclusions

The evaluated studies are highly heterogeneous in terms of research topic and the different regions of interest. These results illustrate the need for a standardized methodology in micro-CT analysis. While the analysed studies do well according to the ARRIVE guidelines, the micro-CT procedure is often insufficiently described. Therefore we recommend to extend the ARRIVE guidelines for micro-CT studies.

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This review investigates discrepancies between reports using micro-CT imaging of rodent jaw bone, the applied methodology and reported results.

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Knowledge about the bone micro-architecture of the rodent jaw is scarce.

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Jaw bone micro-architecture varies according to ROI selections and the methodology applied to define a specific region are insufficient.

Non-linear pattern formation in bone growth and architecture

The three-dimensional morphology of bone arises through adaptation to its required engineering performance. Genetically and adaptively bone travels along a complex spatiotemporal trajectory to acquire optimal architecture. On a cellular, micro-anatomical scale, what mechanisms coordinate the activity of osteoblasts and osteoclasts to produce complex and efficient bone architectures? One mechanism is examined here - chaotic non-linear pattern formation (NPF) - which underlies in a unifying way natural structures as disparate as trabecular bone, swarms of birds flying, island formation, fluid turbulence, and others. At the heart of NPF is the fact that simple rules operating between interacting elements, and Turing-like interaction between global and local signals, lead to complex and structured patterns. The study of "group intelligence" exhibited by swarming birds or shoaling fish has led to an embodiment of NPF called "particle swarm optimization" (PSO). This theoretical model could be applicable to the behavior of osteoblasts, osteoclasts, and osteocytes, seeing them operating "socially" in response simultaneously to both global and local signals (endocrine, cytokine, mechanical), resulting in their clustered activity at formation and resorption sites. This represents problem-solving by social intelligence, and could potentially add further realism to in silico computer simulation of bone modeling. What insights has NPF provided to bone biology? One example concerns the genetic disorder juvenile Pagets disease or idiopathic hyperphosphatasia, where the anomalous parallel trabecular architecture characteristic of this pathology is consistent with an NPF paradigm by analogy with known experimental NPF systems. Here, coupling or "feedback" between osteoblasts and osteoclasts is the critical element. This NPF paradigm implies a profound link between bone regulation and its architecture: in bone the architecture is the regulation. The former is the emergent consequence of the latter.

Microcomputed tomography: approaches and applications in bioengineering

Microcomputed tomography (microCT) has become a standard and essential tool for quantifying structure-function relationships, disease progression, and regeneration in preclinical models and has facilitated numerous scientific and bioengineering advancements over the past 30 years. In this article, we recount the early events that led to the initial development of microCT and review microCT approaches for quantitative evaluation of bone, cartilage, and cardiovascular structures, with applications in fundamental structure-function analysis, disease, tissue engineering, and numerical modeling. Finally, we address several next-generation approaches under active investigation to improve spatial resolution, acquisition time, tissue contrast, radiation dose, and functional and molecular information.

Micro- and nano-CT for the study of bone ultrastructure

Micro-computed tomography (micro-CT)-a version of X-ray CT operating at high spatial resolution-has had a considerable success for the investigation of trabecular bone micro-architecture. Currently, there is a lot of interest in exploiting CT techniques at even higher spatial resolutions to assess bone tissue at the cellular scale. After recalling the basic principles of micro-CT, we review the different existing system, based on either standard X-ray tubes or synchrotron sources. Then, we present recent applications of micro- and nano-CT for the analysis of osteocyte lacunae and the lacunar-canalicular network. We also address the question of the quantification of bone ultrastructure to go beyond the sole visualization.

Raman spectroscopy of soft musculoskeletal tissues

Tendon, ligament, and joint tissues are important in maintaining daily function. They can be affected by disease, age, and injury. Slow tissue turnover, hierarchical structure and function, and nonlinear mechanical properties present challenges to diagnosing and treating soft musculoskeletal tissues. Understanding these tissues in health, disease, and injury is important to improving pharmacologic and surgical repair outcomes. Raman spectroscopy is an important tool in the examination of soft musculoskeletal tissues. This article highlights exciting basic science and clinical/translational Raman studies of cartilage, tendon, and ligament.

Modic (endplate) changes in the lumbar spine: bone micro-architecture and remodelling

PURPOSE

In the literature, inter-vertebral MRI signal intensity changes (Modic changes) were associated with corresponding histological observations on endplate biopsies. However, tissue-level studies were limited. No quantitative histomorphometric study on bone biopsies has yet been conducted for Modic changes. The aim of this study was to characterise the bone micro-architectural parameters and bone remodelling indices associated with Modic changes.

METHODS

Forty patients suffering from disabling low back pain, undergoing elective spinal surgery, and exhibiting Modic changes on MRI (Modic 1, n = 9; Modic 2, n = 25; Modic 3, n = 6), had a transpedicular vertebral body biopsy taken of subchondral bone. Biopsies were first examined by micro-CT, for 3D morphometric analysis of bone volume fraction (BV/TV), trabecular thickness (Tb.Th), trabecular separation, trabecular number, and structure model index. Then, samples underwent histological analysis, for determination of bone remodelling indices: osteoid surface to bone surface ratio (OS/BS), eroded surface to bone surface (ES/BS) and osteoid surface to eroded surface ratio (OS/ES).

RESULTS

Micro-CT analysis revealed significantly higher BV/TV (up to 70% increase, p < 0.01) and Tb.Th (up to +57%, p < 0.01) in Modic 3 biopsies, compared to Modic 1 and 2. Histological analysis showed significantly lower OS/BS in Modic 2 biopsies (more than 28% decrease, p < 0.05) compared to 1 and 3. ES/BS progressively decreased from Modic 1 to 2 to 3, whereas OS/ES progressively increased with significantly higher values in Modic 3 (up to 159% increase, p < 0.05) than in Modic 1 and 2.

CONCLUSIONS

Significant differences were found in bone micro-architectural parameters and remodelling indices among Modic types. Modic 1 biopsies had evidence of highest bone turnover, possibly due to an inflammatory process; Modic 2 biopsies were consistent with a reduced bone formation/remodelling stage; Modic 3 biopsies suggested a more stable sclerotic phase, with significantly increased BV/TV and Tb.Th compared to Modic 1 and 2, linked to increased bone formation and reduced resorption.

Normal variation in cortical osteocyte lacunar parameters in healthy young males

The most abundant cell in bone, osteocytes form an interconnected system upon which the regulation of healthy bone relies. Although the complete nature of the role of osteocytes has yet to be defined, they are generally accepted to play a part in the sensing of load and the initiation of damage repair. A previous study conducted by our group identified variation of up to 30% in osteocyte lacunar density and morphological parameters between regions of a single cross-section of human femoral shaft; that study, however, was limited to a single individual. The aim of the current study was to determine whether this pattern consistently occurs in healthy young male femora. Anterior, posterior, medial and lateral blocks were prepared from the proximal femoral shaft of seven males and synchrotron radiation micro-CT imaged. Average lacunar densities (± SD) from the anterior, posterior, medial and lateral regions were 23 394 ± 1705, 30 180 ± 4860, 35 946 ± 5990 and 29 678 ± 6081 lacunae per mm(3) of bone tissue, respectively. These values were significantly different between the anterior and both the medial and posterior regions (P < 0.05). The density of the combined anterior and posterior regions was also significantly lower (P = 0.006) than the density of the combined medial and lateral regions. Although no difference was found in predominant orientation, shape differences were found; with the combined anterior-posterior regions having lacunae that were significantly more elongated and less flat than the combined medial-lateral values (P < 0.001). As expected, in this larger study, there was a dramatic difference in lacunar density between the medial and anterior region (up to ~ 54%). The study clearly demonstrates that the high variation seen in osteocyte lacunar density as well as other lacunar parameters, noted in a number of biomechanical, age and pathology studies, are well within the range of normal variation; however, the reasons for and consequences of this variation remain unclear. Lacunar parameters including abundance and shape are being increasingly incorporated into computational modeling of bone biology and this paper represents a more comprehensive description of normal healthy lacunae.

3D osteocyte lacunar morphometric properties and distributions in human femoral cortical bone using synchrotron radiation micro-CT images

Osteocytes, the most numerous bone cells, are thought to be actively involved in the bone modeling and remodeling processes. The morphology of osteocyte is hypothesized to adapt according to the physiological mechanical loading. Three-dimensional micro-CT has recently been used to study osteocyte lacunae. In this work, we proposed a computationally efficient and validated automated image analysis method to quantify the 3D shape descriptors of osteocyte lacunae and their distribution in human femurs. Thirteen samples were imaged using Synchrotron Radiation (SR) micro-CT at ID19 of the ESRF with 1.4μm isotropic voxel resolution. With a field of view of about 2.9×2.9×1.4mm(3), the 3D images include several tens of thousands of osteocyte lacunae. We designed an automated quantification method to segment and extract 3D cell descriptors from osteocyte lacunae. An image moment-based approach was used to calculate the volume, length, width, height and anisotropy of each osteocyte lacuna. We employed a fast algorithm to further efficiently calculate the surface area, the Euler number and the structure model index (SMI) of each lacuna. We also introduced the 3D lacunar density map to directly visualize the lacunar density variation over a large field of view. We reported the lacunar morphometric properties and distributions as well as cortical bone histomorphometric indices on the 13 bone samples. The mean volume and surface were found to be 409.5±149.7μm(3) and 336.2±94.5μm(2). The average dimensions were of 18.9±4.9μm in length, 9.2±2.1μm in width and 4.8±1.1μm in depth. We found lacunar number density and six osteocyte lacunar descriptors, three axis lengths, two anisotropy ratios and SMI, that are significantly correlated to bone porosity at a same local region. The proposed method allowed an automatic and efficient direct 3D analysis of a large population of bone cells and is expected to provide reliable biological information for better understanding the bone quality and diseases at cellular level.

A novel in vivo vascular imaging approach for hierarchical quantification of vasculature using contrast enhanced micro-computed tomography

The vasculature of body tissues is continuously subject to remodeling processes originating at the micro-vascular level. The formation of new blood vessels (angiogenesis) is essential for a number of physiological and pathophysiological processes such as tissue regeneration, tumor development and the integration of artificial tissues. There are currently no time-lapsed in vivo imaging techniques providing information on the vascular network at the capillary level in a non-destructive, three-dimensional and high-resolution fashion. This paper presents a novel imaging framework based on contrast enhanced micro-computed tomography (micro-CT) for hierarchical in vivo quantification of blood vessels in mice, ranging from largest to smallest structures. The framework combines for the first time a standard morphometric approach with densitometric analysis. Validation tests showed that the method is precise and robust. Furthermore, the framework is sensitive in detecting different perfusion levels after the implementation of a murine ischemia-reperfusion model. Correlation with both histological data and micro-CT analysis of vascular corrosion casts confirmed accuracy of the method. The newly developed time-lapsed imaging approach shows high potential for in vivo monitoring of a number of different physiological and pathological conditions in angiogenesis and vascular development.

3D assessment of cortical bone porosity and tissue mineral density using high-resolution µCT: effects of resolution and threshold method

Current micro-computed tomography (µCT) systems allow scanning bone at resolutions capable of three-dimensional (3D) characterization of intracortical vascular porosity and osteocyte lacunae. However, the scanning and reconstruction parameters along with the image segmentation method affect the accuracy of the measurements. In this study, the effects of scanning resolution and image threshold method in quantifying small features of cortical bone (vascular porosity, vascular canal diameter and separation, lacunar porosity and density, and tissue mineral density) were analyzed. Cortical bone from the tibia of Sprague-Dawley rats was scanned at 1-µm and 4-µm resolution, reconstructions were density-calibrated, and volumes of interest were segmented using approaches based on edge-detection or histogram analysis. In 1-µm resolution scans, the osteocyte lacunar spaces could be visualized, and it was possible to separate the lacunar porosity from the vascular porosity. At 4-µm resolution, the vascular porosity and vascular canal diameter were underestimated, and osteocyte lacunae were not effectively detected, whereas the vascular canal separation and tissue mineral density were overestimated compared to 1-µm resolution. Resolution had a much greater effect on the measurements than did threshold method, showing partial volume effects at resolutions coarser than 2 µm in two separate analyses, one of which assessed the effect of resolution on an object of known size with similar architecture to a vascular pore. Although there was little difference when using the edge-detection versus histogram-based threshold approaches, edge-detection was somewhat more effective in delineating canal architecture at finer resolutions (1-2 µm). In addition, use of a high-resolution (1 µm) density-based threshold on lower resolution (4 µm) density-calibrated images was not effective in improving the lower-resolution measurements. In conclusion, if measuring cortical vascular microarchitecture, especially in small animals, a µCT resolution of 1 to 2 µm is appropriate, whereas a resolution of at least 1 µm is necessary when assessing osteocyte lacunar porosity.

A comparative analysis of water-soluble and blood-pool contrast agents for in vivo vascular imaging with micro-CT

RATIONALE AND OBJECTIVES

In recent years, micro-computed tomography (micro-CT) has emerged as a high-resolution modality for vascular exploration in vivo. Several x-ray contrast agents for in vivo imaging are on the market and are based on different formulations. The objective of this study was to compare contrast-related and pharmacokinetic properties of a water-soluble compound containing iomeprol (Iomeron 400) and blood-pool agents (eXIA160XL, AuroVist 15 nm, and ExiTron nano 12000) for the identification of suitable in vivo vascular imaging applications.

MATERIALS AND METHODS

Forty-four healthy C57BL/6J mice were used in this study. Iomeprol was administered with a continuous infusion protocol; the other agents as a bolus. Anatomical micro-CT was applied at the head, neck, and lower hind limb before (baseline) and immediately after contrast injection, and used to quantify contrast-related properties of the agents. Dynamic micro-CT was applied at the same regions to characterize the agents pharmacokinetics.

RESULTS

All contrast media revealed safe, except for eXIA160XL, which caused death in four of eight tested animals and was therefore excluded early from the study. AuroVist 15 nm provided the highest attenuation (2.33/mm) as compared to iomeprol (1.97/mm) and ExiTron nano 12000 (1.58/mm) and a maximum temporal variation of contrast of 20% after 30 minutes, but the appearance of a dark skin staining did not allow multiple injections of the agent. Iomeprol passively diffused across capillary membranes, and after 30 minutes doubled the tissue contrast with respect to its initial levels. ExiTron nano 12000 revealed temporal variations of contrast below 10% and significantly reduced clearance rates after the third consecutive injection.

CONCLUSION

AuroVist 15 nm is best suited for anatomical investigation of the vascular network, while the high extravasation levels of iomeprol can be exploited for perfusion analysis. ExiTron nano 12000 is indicated for use in longitudinal monitoring with repeated injections.

Biomechanism of impact resistance in the woodpecker's head and its application

The woodpecker does not suffer head/eye impact injuries while drumming on a tree trunk with high acceleration (more than 1000×g) and high frequency. The mechanism that protects the woodpecker's head has aroused the interest of ornithologists, biologists and scientists in the areas of mechanical engineering, material science and electronics engineering. This article reviews the literature on the biomechanisms and materials responsible for protecting the woodpecker from head impact injury and their applications in engineering and human protection.

Graphene--nanotube--iron hierarchical nanostructure as lithium ion battery anode

In this study, we report a novel route via microwave irradiation to synthesize a bio-inspired hierarchical graphene--nanotube--iron three-dimensional nanostructure as an anode material in lithium-ion batteries. The nanostructure comprises vertically aligned carbon nanotubes grown directly on graphene sheets along with shorter branches of carbon nanotubes stemming out from both the graphene sheets and the vertically aligned carbon nanotubes. This bio-inspired hierarchical structure provides a three-dimensional conductive network for efficient charge-transfer and prevents the agglomeration and restacking of the graphene sheets enabling Li-ions to have greater access to the electrode material. In addition, functional iron-oxide nanoparticles decorated within the three-dimensional hierarchical structure provides outstanding lithium storage characteristics, resulting in very high specific capacities. The anode material delivers a reversible capacity of ~1024 mA · h · g(-1) even after prolonged cycling along with a Coulombic efficiency in excess of 99%, which reflects the ability of the hierarchical network to prevent agglomeration of the iron-oxide nanoparticles.

3D characterization of pores in the cortical bone of human femur in the elderly at different locations as determined by synchrotron micro-computed tomography images

Diaphysis, inferior, and lateral superior regions of the femoral neck are subjected to diverse mechanical loads. Using micro-CT based on synchrotron radiation, three-dimensional morphology and connectivity of the pore network are location dependent, underlying different remodeling mechanisms.

INTRODUCTION

The three-dimensional (3D) morphology and connectivity of the pore network at various locations in human femurs subjected to diverse mechanical loads were assessed using micro-CT based on synchrotron radiation.

METHODS

The cortex from 20 human femurs (mean age, 78.3 ± 12.4 years) was taken from the diaphysis (D), the inferior (IN), and the lateral superior (LS) regions of the femoral neck. The voxel size of the 3D reconstructed image was 7.5 μm. Cortical thickness and pore volume/tissue volume (Po.V/TV), pore diameter (Po.Dm) and spacing (Po.Sp) were determined. The pore surface/pore volume ratio (Po.S/Po.V), the number of pores (Po.N), the degrees of anisotropy (DA), and the connectivity density (ConnD), the degree of mineralization (DMB) were also determined.

RESULTS

The characteristics of the pore network in femoral cortical bone were found to be location dependent. There was greater porosity, Po.Dm, and Po.N, and more large (180-270 μm), extra-large (270-360 μm) and giant pores (>360 μm) in the LS compared to the IN and D. The difference in porosity in between the periosteal and endosteal layers was mostly due to an increase of Po.Dm rather than Po.N. There was a lower DMB of bone in the LS, which is consistent with a higher remodeling rate.

CONCLUSION

The results provide evidence for large variations in the structure of the internal pore network in cortical bone. These variations could involve different underlying remodeling mechanisms.

Oral administration of hyaluronan reduces bone turnover in ovariectomized rats

The effect of oral hyaluronan (HA) on bone loss in ovariectomized (OVX) 3-month-old rats was measured using serum markers of bone turnover and bone mineral density. OVX rats were administered 1 mg/kg HA (OVX + HA) or phosphate-buffered saline (PBS) (OVX + PBS) by oral gavage (5 days/week for 54 days). Additional controls included sham ovariectomy with PBS gavage (Sham + PBS) and no treatment. Oral administration of HA resulted in approximately 50% (p < 0.05) increases in serum HA. Gel filtration analyses showed this was high molecular weight HA (300-500 kDa). Osteopenia was mild due to the young age of the animals. Thus, ovariectomy resulted in a 30% increase in serum collagen N-terminal telopeptides (p < 0.001), a 20% increase in serum nitrate/nitrite levels (p = 0.05), and a 5-6% decrease in femur bone mineral density/content (p < 0.05). HA gavage blunted the development of osteopenia in this model as determined by preventing the 30% increase in serum collagen N-terminal telopeptide levels (p < 0.001) and by reducing bone mineral content loss from 6 to 4%. These results show that oral supplements of HA (gavage solution, 0.12% solution) significantly reduce bone turnover associated with mild osteopenia in rats.

Variation in osteocyte lacunar morphology and density in the human femur--a synchrotron radiation micro-CT study

In recent years there has been growing interest in the spatial properties of osteocytes (including density and morphology) and how these potentially relate to adaptation, disease and aging. This interest has, in part, arisen from the availability of increasingly high-resolution 3D imaging modalities such as synchrotron radiation (SR) micro-CT. As resolution increases, field of view generally decreases. Thus, while increasingly detailed spatial information is obtained, it is unclear how representative this information is of the skeleton or even the isolated bone. The purpose of this research was to describe the variation in osteocyte lacunar density, morphology and orientation within the femur from a healthy young male human. Multiple anterior, posterior, medial and lateral blocks (2 mm × 2 mm) were prepared from the proximal femoral shaft and SR micro-CT imaged at the Advanced Photon Source. Average lacunar densities (± standard deviation) from the anterior, posterior, medial and lateral regions were 27,169 ± 1935, 26,3643 ± 1262, 37,521 ± 6416 and 33,972 ± 2513 lacunae per mm(3) of bone tissue, respectively. These values were significantly different between the medial and both the anterior and posterior regions (p<0.05). The density of the combined anterior and posterior regions was also significantly lower (p=0.001) than the density of the combined medial and lateral regions. Although no difference was found in predominant orientation, shape differences were found; with the combined anterior and posterior regions having more elongated (p=0.004) and flattened (p=0.045) lacunae, than those of the medial and lateral regions. This study reveals variation in osteocyte lacunar density and morphology within the cross-section of a single bone and that this variation can be considerable (up to 30% difference in density between regions). The underlying functional significance of the observed variation in lacunar density likely relates to localized variations in loading conditions as the pattern corresponds well with mechanical axes. Lower density and more elongate shapes being associated with the antero-posterior oriented neutral axis. Our findings demonstrate that the functional and pathological interpretations that are increasingly being drawn from high resolution imaging of osteocyte lacunae need to be better situated within the broader context of normal variation, including that which occurs even within a single skeletal element.

Three-dimensional microarchitecture of adolescent cancellous bone

This study investigated microarchitectural, mechanical, collagen and mineral properties of normal adolescent cancellous bone, and compared them with adult and aging cancellous bone, to obtain more insight into the subchondral bone adaptations during development and growth. Twenty-three human proximal tibiae were harvested and divided into 3 groups according to their ages: adolescence (9 to 17 years, n=6), young adult (18 to 24 years, n=9), and adult (25 to 30 years, n=8). Twelve cubic cancellous bone samples with dimensions of 8×8×8 mm(3) were produced from each tibia, 6 from each medial and lateral condyle. These samples were micro-CT scanned (vivaCT 40, Scanco Medical AG, Switzerland) resulting in cubic voxel sizes of 10.5*10.5*10.5 μm(3). Microarchitectural properties were calculated. The samples were then tested in compression followed by collagen and mineral determination. Interestingly, the adolescent cancellous bone had similar bone volume fraction (BV/TV), structure type (plate, rod or mixtures), and connectivity (3-D trabecular networks) as the adult cancellous bone. The adolescent cancellous bone had significantly lower bone surface density (bone surface per total volume of specimen) but higher collagen concentration (collagen weight per dry weight of specimen) than the adult cancellous bone; and significant greater trabecular separation (mean distance between trabeculae), significant lower trabecular number (number of trabeculae per volume), tissue density (dry weight per volume of bone matrix excluding marrow space) and mineral concentration (ash weight per dry weight of specimen) than the young adult and adult cancellous bones. Despite these differences, ultimate stress and failure energy were not significantly different among the three groups, only the Young's modulus in anterior-posterior direction was significantly lower in adolescence. Apparent density appears to be the single best predictor of mechanical properties. In conclusion, adolescent cancellous bone has similar bone volume fraction, structure type, and connectivity as the young adult and adult cancellous bones, and significant lower tissue density, bone surface density and mineral concentration but higher collagen concentration than in the young adult and adult bone. Despite these differences, the mechanical properties did not show significant difference among the three groups except less stiffness in anterior-posterior direction in the adolescents.

Finite element analysis of a micromechanical model of bone and a new 3D approach to validation

Finite Element Analysis (FEA) is now widely used to analyse the mechanical behaviour of bone structures. Ideally, simulations are validated against experimental data. To date, validation of Finite Element Models (FEMs) has been 2 Dimensional (2D) only, being based on comparison with surface-mounted strain gauge readings. In this study we present a novel 3-Dimensional (3D) approach to validation that allows comparison of modelled with experimental results between any two points in 3D space throughout the structure, providing magnitude and direction data for comparison, internally and externally. Specifically, we validate a FEM of a rat tibia, including trabecular network geometry, using a material testing stage housed within a microCT scanner. We further apply novel landmark based morphometric approaches to more effectively compare modelled and experimental results. 542 landmark points on the cortical and trabecular bone surfaces of the model were selected and validated in 3D against experimental data. This approach may hold considerable potential in fields wherein a better understanding of the mechanical behaviour of trabecular networks is important, e.g., the studies of osteoporosis and trabecular loss after orthopaedic implant insertion.

X-ray phase nanotomography resolves the 3D human bone ultrastructure

Bone strength and failure are increasingly thought to be due to ultrastructural properties, such as the morphology of the lacuno-canalicular network, the collagen fiber orientation and the mineralization on the nanoscale. However, these properties have not been studied in 3D so far. Here we report the investigation of the human bone ultrastructure with X-ray phase nanotomography, which now provides the required sensitivity, spatial resolution and field of view. The 3D organization of the lacuno-canalicular network is studied in detail over several cells in osteonal and interstitial tissue. Nanoscale density variations are revealed and show that the cement line separating these tissues is hypermineralized. Finally, we show that the collagen fibers are organized as a twisted plywood structure in 3D.

Fibre bundles in the human extensor carpi ulnaris tendon are arranged in a spiral

The extensor carpi ulnaris musculotendinous unit has important agonist and antagonist action in wrist motion, including the dart-throwing action, and is a dynamic stabilizer of the distal radioulnar joint during forearm rotation. Despite its functional and clinical importance, little is known about its internal structure. Investigation of the ultrastructure of the human extensor carpi ulnaris (ECU) tendon was undertaken using plane polarized light microscopy and microcomputer tomography with 3D reconstruction. The study demonstrates that the tendon comprises fibre bundles (fascicles) approximately 0.1 mm in diameter that are arranged in a gradual spiral. The spiralling fibres make an angle of 8º to the longitudinal axis of the tendon. The spiral structure of the human ECU tendon has important biomechanical implications, allowing fascicular sliding during forearm rotation. The observed features may prevent injury.

MRI texture analysis of femoral neck: Detection of exercise load-associated differences in trabecular bone

PURPOSE

To assess the ability of co-occurrence matrix-based texture parameters to detect exercise load-associated differences in MRI texture at the femoral neck cross-section.

MATERIALS AND METHODS

A total of 91 top-level female athletes representing five differently loading sports and 20 referents participated in this cross-sectional study. Axial T1-weighted FLASH and T2*-weighted MEDIC sequence images of the proximal femur were obtained with a 1.5T MRI. The femoral neck trabecular bone at the level of the insertion of articular capsule was divided manually into regions of interest representing four anatomical sectors (anterior, posterior, superior, and inferior). Selected co-occurrence matrix-based texture parameters were used to evaluate differences in apparent trabecular structure between the exercise loading groups and anatomical sectors of the femoral neck.

RESULTS

Significant differences in the trabecular bone texture, particularly at the superior femoral neck, were observed between athletes representing odd-impact (soccer and squash) and high-magnitude exercise loading (power-lifting) groups and the nonathletic reference group.

CONCLUSION

MRI texture analysis provides a quantitative method for detecting and classifying apparent structural differences in trabecular bone that are associated with specific exercise loading.

Surgical treatment options in patients with impaired bone quality

BACKGROUND

Bone quality should play an important role in decision-making for orthopaedic treatment options, implant selection, and affect ultimate surgical outcomes. The development of decision-making tools, currently typified by clinical guidelines, is highly dependent on the precise definition of the term(s) and the appropriate design of basic and clinical studies. This review was performed to determine the extent to which the issue of bone quality has been subjected to this type of process.

QUESTIONS/PURPOSES

We address the following issues: (1) current methods of clinically assessing bone quality; (2) emerging technologies; (3) how bone quality connects with surgical decision-making and the ultimate surgical outcome; and (4) gaps in knowledge that need to be closed to better characterize bone quality for more relevance to clinical decision-making.

METHODS

PubMed was used to identify selected papers relevant to our discussion. Additional sources were found using the references cited by identified papers.

RESULTS

Bone mineral density remains the most commonly validated clinical reference; however, it has had limited specificity for surgical decision-making. Other structural and geometric measures have not yet received enough study to provide definitive clinical applicability. A major gap remains between the basic research agenda for understanding bone quality and the transfer of these concepts to evidence-based practice.

CONCLUSIONS

Basic bone quality needs better definition through the systematic study of emerging technologies that offer a more precise clinical characterization of bone. Collaboration between basic scientists and clinicians needs to improve to facilitate the development of key questions for sound clinical studies.

Defects in hepatic Notch signaling result in disruption of the communicating intrahepatic bile duct network in mice

Abnormal Notch signaling in humans results in Alagille syndrome, a pleiotropic disease characterized by a paucity of intrahepatic bile ducts (IHBDs). It is not clear how IHBD paucity develops as a consequence of atypical Notch signaling, whether by a developmental lack of bile duct formation, a post-natal lack of branching and elongation or an inability to maintain formed ducts. Previous studies have focused on the role of Notch in IHBD development, and demonstrated a dosage requirement of Notch signaling for proper IHBD formation. In this study, we use resin casting and X-ray microtomography (microCT) analysis to address the role of Notch signaling in the maintenance of formed IHBDs upon chronic loss or gain of Notch function. Our data show that constitutive expression of the Notch1 intracellular domain in bi-potential hepatoblast progenitor cells (BHPCs) results in increased IHBD branches at post-natal day 60 (P60), which are maintained at P90 and P120. By contrast, loss of Notch signaling via BHPC-specific deletion of RBP-J (RBP KO), the DNA-binding partner for all Notch receptors, results in progressive loss of intact IHBD branches with age. Interestingly, in RBP KO mice, we observed a reduction in bile ducts per portal vein at P60; no further reduction had occurred at P120. Thus, bile duct structures are not lost with age; instead, we propose a model in which BHPC-specific loss of Notch signaling results in an initial developmental defect resulting in fewer bile ducts being formed, and in an acquired post-natal defect in the maintenance of intact IHBD architecture as a result of irresolvable cholestasis. Our studies reveal a previously unappreciated role for Notch signaling in the post-natal maintenance of an intact communicating IHBD structure, and suggest that liver defects observed in Alagille syndrome patients might be more complex than bile duct paucity.

Phenotypic characterization of skeletal abnormalities of Osteopotentia mutant mice by micro-CT: a descriptive approach with emphasis on reconstruction techniques

PURPOSE

The novel protein osteopotentia (Opt) has recently been described as an essential regulator of postnatal osteoblast maturation and might possibly be responsible for some of the rarer types of osteogenesis imperfecta. Our aim was the evaluation of micro CT for the qualitative morphological assessment of skeletal abnormalities of Osteopotentia-mutant mice in comparison to radiography and histology.

MATERIALS AND METHODS

Four homozygous mice with insertional mutations in the Opt gene and three wild-type controls were examined ex vivo using radiography and micro-CT. Two of the homozygous animals were evaluated histologically (trichrome reagent). For the micro-CT evaluation three-dimensional (3D) surface reconstructions and two-dimensional (2D) multiplanar reformations (MPRs) were applied.

RESULTS

The Opt-homozygous mice exhibited severe growth. The radiographic examinations showed osteopenia and fractures with hypertrophic callus formation and pseudarthroses of the forelimbs and ribs. Micro-CT confirmed these findings and was able to demonstrate additional fractures especially at smaller bones such as the metacarpals and phalanges. Additional characterization and superior delineation of cortices and fracture fragments was achieved by 2D MPRs. Histological correlation verified several of these imaging findings.

CONCLUSION

Micro-CT is able to screen Opt-mutant mice for osseous pathologies and furthermore characterize these anomalies. The modality seems superior to conventional radiography, but is not able to demonstrate cellular pathology. However, histology is destructive and more time- and material-consuming than micro-CT. Additional information may be gathered by 2D MPRs.

Towards quantitative 3D imaging of the osteocyte lacuno-canalicular network

Osteocytes are the most abundant cells in bone and the only cells embedded in the bone mineral matrix. They form an extended, three-dimensional (3D) network, whose processes interconnecting the cell bodies reside in thin canals, the canaliculi. Together with the osteocyte lacunae, the canaliculi form the lacuno-canalicular network (LCN). As the negative imprint of the cellular network within bone tissue, the LCN morphology is considered to play a central role for bone mechanosensation and mechanotransduction. However, the LCN has neither been visualized nor quantified in an adequate way up to now. On this account, this article summarizes the current state of knowledge of the LCN morphology and then reviews different imaging methods regarding the quantitative 3D assessment of bone tissue in general and of the LCN in particular. These imaging methods will provide new insights in the field of bone mechanosensation and mechanotransduction and thus, into processes of strain sensation and transduction, which are tightly associated with osteocyte viability and bone quality.

An experimentally validated micromechanical model of a rat vertebra under compressive loading

In recent years, finite element analysis (FEA) has been increasingly applied to examine and predict the mechanical behaviour of craniofacial and other bony structures. Traditional methods used to determine material properties and validate finite element models (FEMs) have met with variable success, and can be time-consuming. An implicit assumption underlying many FE studies is that relatively high localized stress/strain magnitudes identified in FEMs are likely to predict material failure. Here we present a new approach that may offer some advantages over previous approaches. Recently developed technology now allows us to both image and conduct mechanical tests on samples in situ using a materials testing stage (MTS) fitted inside the microCT scanner. Thus, micro-finite element models can be created and validated using both quantitative and qualitative means. In this study, a rat vertebra was tested under compressive loading until failure using an MTS. MicroCT imaging of the vertebra before mechanical testing was used to create a high resolution finite element model of the vertebra. Load-displacement data recorded during the test were used to calculate the effective Young's modulus of the bone (found to be 128 MPa). The microCT image of the compressed vertebra was used to assess the predictive qualities of the FE model. The model showed the highest stress concentrations in the areas that failed during the test. Clearly, our analyses do not directly address biomechanics of the craniofacial region; however, the methodology adopted here could easily be applied to examine the properties and behaviour of specific craniofacial structures, or whole craniofacial regions of small vertebrates. Experimentally validated micro-FE analyses are a powerful method in the study of materials with complex microstructures such as bone.

On the effect of X-ray irradiation on the deformation and fracture behavior of human cortical bone

In situ mechanical testing coupled with imaging using high-energy synchrotron X-ray diffraction or tomography is gaining in popularity as a technique to investigate micrometer and even sub-micrometer deformation and fracture mechanisms in mineralized tissues, such as bone and teeth. However, the role of the irradiation in affecting the nature and properties of the tissue is not always taken into account. Accordingly, we examine here the effect of X-ray synchrotron-source irradiation on the mechanistic aspects of deformation and fracture in human cortical bone. Specifically, the strength, ductility and fracture resistance (both work-of-fracture and resistance-curve fracture toughness) of human femoral bone in the transverse (breaking) orientation were evaluated following exposures to 0.05, 70, 210 and 630 kGrays (kGy) irradiation. Our results show that the radiation typically used in tomography imaging can have a major and deleterious impact on the strength, post-yield behavior and fracture toughness of cortical bone, with the severity of the effect progressively increasing with higher doses of radiation. Plasticity was essentially suppressed after as little as 70 kGy of radiation; the fracture toughness was decreased by a factor of five after 210 kGy of radiation. Mechanistically, the irradiation was found to alter the salient toughening mechanisms, manifest by the progressive elimination of the bone's capacity for plastic deformation which restricts the intrinsic toughening from the formation "plastic zones" around crack-like defects. Deep-ultraviolet Raman spectroscopy indicated that this behavior could be related to degradation in the collagen integrity.