Bone Toughness Research Articles

Spatiotemporal Characterization of Microstructure Morphology, Mechanical Properties and Bone Remodeling of Rat Tibia Under Uniaxial Compressive Overload Loading.

Bone tissue is subjected to increased mechanical stress during high-intensity work. Inadequate bone remodeling reparability can result in the continuous accumulation of microdamage, leading to stress fractures. The aim of this work was to investigate the characteristics and repair mechanisms of tibial microdamage under several degrees of overload. Also, we aimed at better understanding the effects of overload on the multi-scale structure and mechanical properties of bone. Sixty 5-month female rats were divided into three groups with different time points. Micro-CT was used to evaluate the three-dimensional microstructure, and three-point bending, quasi-static fracture toughness and creep mechanical test were carried out to evaluate the mechanical properties. SEM was used to observe the morphological characteristics of fracture surfaces. Section staining was used to count the microdamage parameters and numbers of osteoblasts and osteoclasts. The microarchitectures of cancellous and cortical bones in the three overload groups showed different degrees of damage. Overload led to a messy crystal structure of cortical bone, with slender microcracks mixed in, and a large number of broken fibers of cancellous bone. The properties associated with the elastic plasticity, fracture toughness, and viscoelasticity of cortical bone reduced in three groups, with that corresponding to day 30 presenting the highest damage. The accumulation of microdamage mainly occurred in the first 14days, that is, the crack density peaked on day 14. Peak-targeted bone remodeling of cortical and cancellous bones occurred mainly between days 14 and 30. The influence of overload mechanical environment on bone quality at different time points was deeply investigated, which is of great significance for the etiology and treatment of stress fractures.

Nano-scale modeling of energy dissipation in a single lamella reveals the significant contribution of collagen-mineral sliding to intrinsic bone toughness

Although collagen-mineral sliding is recognized as one of the intrinsic mechanisms that contribute to the bone toughness, its precise role in energy release at the nano-scale, as well as its relationship to other intrinsic toughness mechanisms, remains unclear. This lack of understanding stems from the challenges associated with quantifying the specific nature of contact at the mineral-collagen interface, and the energy dissipation capacity resulting from plastic deformation at this scale. To address this issue, we developed a three-dimensional model of mineralized collagen fibril using ABAQUS, incorporating hyperelastic isotropic collagen, elastic isotropic mineral, and a cohesive contact formulation to represent the collagen-mineral interface. Knowing the properties of collagen and mineral and using a parametric modeling approach, we estimated the properties of contact based on experimental measurements of the stress-strain behavior in a single bone lamella, considering the angle of the collagen fibril in relation to the loading axis. By comparing the experimental elastic modulus with the model predictions, we determined that the cohesive contact exhibited a maximum strength of 9 MPa and a fracture energy of 50 mJ/m2 within the bone. Further analysis indicated that fracture energy at the collagen-mineral interface is potentially closer to 5 mJ/m2. Using these findings, we concluded that the interfaces were responsible for 52% to 98% of the energy release in mineralized collagen fibrils, depending on collagen angle, both directly and indirectly by influencing stress and strain in adjacent collagen fibril. The results of this study demonstrated that plastic deformation at the collagen-mineral interface is the primary mechanism underlying bone toughness at the nano-scale. Importantly, we found that these conclusions held true regardless of the angle of the collagen fibril relative to the loading axis. The modeling framework presented in this study provides a valuable tool for investigating the elastic and post-yield behavior of bone across different mineral volume fractions at the nano-scale, and at the lamellar level.

Glycemic Marker Correlation with Collagen Denaturation and Non-Enzymatic Collagen Cross-Linking in Age-Associated Bone Resistance

The primary clinical indicator of fracture risk among the elderly is low bone mass, yet it accounts for less than half of fractures in individuals over 50 years. Age is recognized to influence bone quality, affecting bone structure and properties. Previous research indicates that age diminishes tissue plasticity and toughness conferred by collagen, suggesting that age-related changes in the collagen environment may contribute to bone fragility. This study explores the relationship between age-related collagen impairment, specifically the accumulation of non-enzymatic collagen cross-linking and molecular collagen denaturation, and bone toughness in middle-aged and older patients (postmenopausal 50–70 years old and senile osteoporosis age > 70 years old). Additionally, it examines the influence of blood glucose and HbA1c levels, as well as body mass index (BMI), on these factors. Despite not finding any differences in fracture toughness between groups, we found a significant correlation between hemoglobin A1c and collagen integrity (collagen denaturation and non-enzymatic cross-linking).

Predicting the Fracture Toughness of Human Cancellous Bone in Fractured Neck of Femur Patients Using Bone Volume and Micro-Architecture.

The current protocol used to determine if an individual is osteoporotic relies on assessment of the individual's bone mineral density (BMD), which allows clinicians to judge the condition of a patient with respect to their peers. This, in essence, evaluates a person's fracture risk, because BMD is a good surrogate measure for strength and stiffness. In recent studies, the authors were the first to produce fracture toughness (FT) data from osteoporotic (OP) and osteoarthritic (OA) patients, by using a testing technique which basically analyzes the prerequisite stress conditions for the onset of growth of a major crack through cancellous bone tissue. FT depends mainly on bone quantity (BV/TV, bone volume/tissue volume), but also on bone micro-architecture (mArch), the inner trabecular design of the bone. The working research hypothesis of the present study is that mArch offers added prediction power to BV/TV in determining FT parameters. Consequently, our aim was to investigate the use of predictive models for fracture toughness and also to investigate if there are any significant differences between the models produced from samples loaded across (AC, transverse to) the main trabecular orientation and along (AL, in parallel) the trabeculae. In multilinear regression analysis, we found that the strength of the relationships varied for a crack growing in these two orthogonal directions. Adding mArch variables in the Ac direction helped to increase the R2 to 0.798. However, in the AL direction, adding the mArch parameters did not add any predictive power to using BV/TV alone; BV/TV on its own could produce R2 = 0.730. The present results also imply that the anisotropic layout of the trabeculae makes it more difficult for a major crack to grow transversely across them. Cancellous bone models and remodels itself in a certain way to resist fracture in a specific direction, and thus, we should be mindful that architectural quality as well as bone quantity are needed to understand the resistance to fracture.

In Vivo Assessment of Bone Quality Without X-rays.

This review summarizes recent advances in the assessment of bone quality using non-X-ray techniques. Quantitative ultrasound (QUS) provides multiple measurements of bone characteristics based on the propagation of sound through bone, the attenuation of that sound, and different processing techniques. QUS parameters and model predictions based on backscattered signals can discriminate non-fracture from fracture cases with accuracy comparable to standard bone mineral density (BMD). With advances in magnetic resonance imaging (MRI), bound water and pore water, or a porosity index, can be quantified in several long bones in vivo. Since such imaging-derived measurements correlate with the fracture resistance of bone, they potentially provide new BMD-independent predictors of fracture risk. While numerous measurements of mineral, organic matrix, and bound water by Raman spectroscopy correlate with the strength and toughness of cortical bone, the clinical assessment of person's bone quality using spatially offset Raman spectroscopy (SORS) requires advanced spectral processing techniques that minimize contaminating signals from fat, skin, and blood. Limiting exposure of patients to ionizing radiation, QUS, MRI, and SORS has the potential to improve the assessment of fracture risk and track changes of new therapies that target bone matrix and micro-structure.

Effect of gamma irradiation and supercritical carbon dioxide sterilization with Novakill™ or ethanol on the fracture toughness of cortical bone.

Sterilization of structural bone allografts is a critical process prior to their clinical use in large cortical bone defects. Gamma irradiation protocols are known to affect tissue integrity in a dose dependent manner. Alternative sterilization treatments, such as supercritical carbon dioxide (SCCO2 ), are gaining popularity due to advantages such as minimal exposure to denaturants, the lack of toxic residues, superior tissue penetration, and minor impacts on mechanical properties including strength and stiffness. The impact of SCCO2 on the fracture toughness of bone tissue, however, remains unknown. Here, we evaluate crack initiation and growth toughness after 2, 6, and 24 h SCCO2 -treatment using Novakill™ and ethanol as additives on ~11 samples per group obtained from a pair of femur diaphyses of a canine. All mechanical testing was performed at ambient air after 24 h soaking in Hanks' balanced salt solution (HBSS). Results show no statistically significant difference in the failure characteristics of the Novakill™-treated groups whereas crack growth toughness after 6 and 24 h of treatment with ethanol significantly increases by 37% (p = .010) and 34% (p = .038), respectively, compared to an untreated control group. In contrast, standard 25 kGy gamma irradiation causes significantly reduced crack growth resistance by 40% (p = .007) compared to untreated bone. FTIR vibrational spectroscopy, conducted after testing, reveals a consistent trend of statistically significant differences (p < .001) with fracture toughness. These trends align with variations in the ratios of enzymatic mature to immature crosslinks in the collagen structure, suggesting a potential association with fracture toughness. Additional Raman spectroscopy after testing shows a similar trend with statistically significant differences (p < .005), which further supports that collagen structural changes occur in the SCF-treated groups with ethanol after 6 and 24 h. Our work reveals the benefits of SCCO2 sterilization compared to gamma irradiation.

When Cortical Bone Matrix Properties Are Indiscernible between Elderly Men with and without Type 2 Diabetes, Fracture Resistance Follows Suit.

Type 2 diabetes mellitus (T2DM) is a metabolic disease affecting bone tissue and leading to increased fracture risk in men and women, independent of bone mineral density (BMD). Thus, bone material quality (i.e., properties that contribute to bone toughness but are not attributed to bone mass or quantity) is suggested to contribute to higher fracture risk in diabetic patients and has been shown to be altered. Fracture toughness properties are assumed to decline with aging and age-related disease, while toughness of human T2DM bone is mostly determined from compression testing of trabecular bone. In this case-control study, we determined fracture resistance in T2DM cortical bone tissue from male individuals in combination with a multiscale approach to assess bone material quality indices. All cortical bone samples stem from male nonosteoporotic individuals and show no significant differences in microstructure in both groups, control and T2DM. Bone material quality analyses reveal that both control and T2DM groups exhibit no significant differences in bone matrix composition assessed with Raman spectroscopy, in BMD distribution determined with quantitative back-scattered electron imaging, and in nanoscale local biomechanical properties assessed via nanoindentation. Finally, notched three-point bending tests revealed that the fracture resistance (measured from the total, elastic, and plastic J-integral) does not significantly differ in T2DM and control group, when both groups exhibit no significant differences in bone microstructure and material quality. This supports recent studies suggesting that not all T2DM patients are affected by a higher fracture risk but that individual risk profiles contribute to fracture susceptibility, which should spur further research on improving bone material quality assessment in vivo and identifying risk factors that increase bone fragility in T2DM. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

In Vivo Assessment of Skin Surface Pattern: Exploring Its Potential as an Indicator of Bone Biomechanical Properties.

The mechanical properties of bone tissue are the result of a complex process involving collagen-crystal interactions. The mineral density of the bone tissue is correlated with bone strength, whereas the characteristics of collagen are often associated with the ductility and toughness of the bone. From a clinical perspective, bone mineral density alone does not satisfactorily explain skeletal fragility. However, reliable in vivo markers of collagen quality that can be easily used in clinical practice are not available. Hence, the objective of the present study is to examine the relationship between skin surface morphology and changes in the mechanical properties of the bone. An experimental study was conducted on healthy children (n = 11), children with osteogenesis imperfecta (n = 13), and women over 60 years of age (n = 22). For each patient, the skin characteristic length (SCL) of the forearm skin surface was measured. The SCL quantifies the geometric patterns formed by wrinkles on the skin's surface, both in terms of size and elongation. The greater the SCL, the more deficient was the organic collagen matrix. In addition, the bone volume fraction and mechanical properties of the explanted femoral head were determined for the elderly female group. The mean SCL values of the healthy children group were significantly lower than those of the elderly women and osteogenesis imperfecta groups. For the aged women group, no significant differences were indicated in the elastic mechanical parameters, whereas bone toughness and ductility decreased significantly as the SCL increased. In conclusion, in bone collagen pathology or bone aging, the SCL is significantly impaired. This in vivo skin surface parameter can be a non-invasive tool to improve the estimation of bone matrix quality and to identify subjects at high risk of bone fracture.

Microstructural fatigue fracture behavior of glycated cortical bone.

The current study aims to simulate fatigue microdamage accumulation in glycated cortical bone with increased advanced glycation end-products (AGEs) using a phase field fatigue framework. We link the material degradation in the fracture toughness of cortical bone to the high levels of AGEs in this tissue. We simulate fatigue fracture in 2D models of cortical bone microstructure extracted from human tibias. The results present that the mismatch between the critical energy release rate of microstructural features (e.g., osteons and interstitial tissue) can alter crack initiation and propagation patterns. Moreover, the high AGEs content through the increased mismatch ratio can cause the activation or deactivation of bone toughening mechanisms under cyclic loading. The fatigue fracture simulations also show that the lifetime of diabetic cortical bone samples can be dependent on the geometry of microstructural features and the mismatch ratio between the features. Additionally, the results indicate that the trapped cracks in cement lines in the diabetic cortical microstructure can prevent further crack growth under cyclic loading. The present findings show that alterations in the materials heterogeneity of microstructural features can change the fatigue fracture response, lifetime, and fragility of cortical bone with high AGEs contents. Cortical bone models are created from microscopy images taken from the cortical cross-section of human tibias. Increased glycation contents in the cortical bone sample can change the crack growth trajectories.

The influence of different shaped osteocyte lacunae on microcrack initiation and propagation

BackgroundThe morphology of osteocyte lacunae varies in bones of different ages and bone pathologies. Osteocyte lacunae can cause stress concentration and initiate microcracks. However, the influence of changes in osteocyte lacunar shape on microcrack is unknown. Therefore, the aim of this study was to determine the effects of osteocyte lacunae with different shapes on microcrack initiation and propagation. MethodsOsteon models containing osteocyte lacunae with different shapes were established. The progressive damage analysis method, based on computer simulations, was used to study the evolution of microdamage within the osteon, including the processes of intralaminar and interlaminar microdamage. FindingsModels with larger DoE values can effectively delay or prevent the formation of linear microcracks, which ensures high fracture toughness of cortical bone. It is subjected to stronger mechanical stimulation, making it more sensitive to loads. Models with smaller DoE values increase the load threshold for microdamage generation and reduces its impact on bone mechanical performance, making it less susceptible to microdamage than models with larger DoE values. InterpretationThese findings enhance the limited knowledge of the influence of the lacunar shape on microdamage and contribute to a better understanding of bone biomechanics.

Physiochemical Dissolution Governs Early Modifications in Acid-Exposed Murine Bone with Long-term Recovery

Metabolic acidosis (MA), a disease affecting millions annually, is clinically characterized by a decrease in systemic pH and bicarbonate. MA has been shown to have skeletal consequences, such as increased bone loss and fractures. However, the mechanisms impacting the mechanics of bone remain unknown. To determine this, we characterized the skeletal phenotypes resulting from two independent regimes of ammonium chloride (NH4Cl) acid-dosing in skeletally mature CD-1 mice for 1, 3, 7, and 14 days to establish the temporal progression of materials-level skeletal defects. The classical, flat-dose model resulted in a temporary decrease in blood pH but did not reduce blood bicarbonate levels. Minimal alterations were observed in bone composition, structure, mechanics, and cellular behavior. However, the graded administration of NH4Cl maintained MA for up to 14 days. This resulted in decreased bone mineral content, collagen organization, and bone volume while increasing mineral crystallinity at early time points followed by a return to baseline. Changes to the matrix lead to a potential decrease in bone toughness at early time points, which may explain the increased fracture risk seen clinically. However, there were no changes in bone formation rate nor osteoclast number or activity during any time point. After 14 days, the bones were fully recovered even though the mice were still under acidotic conditions. Ultimately, we conclude that physicochemical dissolution is the main mechanism for early changes in murine bone, which is influenced by the dosing of exogenous acid loading. This knowledge will aid the discovery of treatments that prevent acidosis-induced bone dissolution.

Germ-Free C57BL/6 Mice Have Increased Bone Mass and Altered Matrix Properties but Not Decreased Bone Fracture Resistance.

The gut microbiome impacts bone mass, which implies a disruption to bone homeostasis. However, it is not yet clear how the gut microbiome affects the regulation of bone mass and bone quality. We hypothesized that germ-free (GF) mice have increased bone mass and decreased bone toughness compared with conventionally housed mice. We tested this hypothesis using adult (20- to 21-week-old) C57BL/6J GF and conventionally raised female and male mice (n = 6-10/group). Trabecular microarchitecture and cortical geometry were measured from micro-CT of the femur distal metaphysis and cortical midshaft. Whole-femur strength and estimated material properties were measured using three-point bending and notched fracture toughness. Bone matrix properties were measured for the cortical femur by quantitative back-scattered electron imaging and nanoindentation, and, for the humerus, by Raman spectroscopy and fluorescent advanced glycation end product (fAGE) assay. Shifts in cortical tissue metabolism were measured from the contralateral humerus. GF mice had reduced bone resorption, increased trabecular bone microarchitecture, increased tissue strength and decreased whole-bone strengththat was not explained by differences in bone size, increased tissue mineralization and fAGEs, and altered collagen structure that did not decrease fracture toughness. We observed several sex differences in GF mice, most notably for bone tissue metabolism. Male GF mice had a greater signature of amino acid metabolism, and female GF mice had a greater signature of lipid metabolism, exceeding the metabolic sex differences of the conventional mice. Together, these data demonstrate that the GF state in C57BL/6J mice alters bone mass and matrix properties but does not decrease bone fracture resistance. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Modelling and finite element analysis of fractured femur bone with locking compression plate under fatigue load condition

Orthopaedic Surgeons are facing difficulties to cure the bone fracture which is developed in the bone of the human due to accidents. Fractured bones are externally joined with the support of screws and locking compression plates. In this present work, the femur bone, locking compression plate and screws were modelled with the help of CREO 2.0 and fatigue analysis was performed for existing joining plate materials using Stainless steel using ANSYS Workbench software. Then crack was generated in the modelled bone and assembled with screws and locking compression plates. Currently used plate materials are replaced with bio compatible materials like Cobalt-chromium (Co-Cr) material, Titanium aluminum Vanadium material (Ti-6Al-4V), 316 Stainless Steel (316 SS) and better and optimum material was identified with improved fatigue life. The finite element analysis was also performed for femur bone with or without Locking compression plates and screws for different implant materials like Cobalt-chromium (Co-Cr) material, Titanium aluminum Vanadium material and 316L stainless steel. Predicted facture toughness and critical strain energy release rate values of femur bone with locking compression plate were 88% and 93% lesser than the predicted facture toughness and critical strain energy release rate values of bone respectively without locking compression plate for 316 SS material. It was observed that the developed crack in the femur bone will not propagate further and it retains the strength of the bone. Predicted fatigue life of the bone for Co-Cr material was higher than 316 SS and Titanium aluminum Vanadium material. Cobalt-chromium alloy implant material was suggested for younger age patients during their bone fracture surgery.

CRACK RESISTANCE CHARACTERISTICS OF MICROSTRUCTURE OF HAVERSIAN CORTICAL BONE

Background: The current research on crack propagation resistance characteristics of osteons is based on the single osteon model, which cannot reflect the interaction among osteons and the influence of material-property changes on the crack propagation. Moreover, the Haversian canal and the cement line were not included in the model, which could not reflect the influence of the true structural characteristics of the cortical bone on the microcracks. Objective: To investigate the effects of osteons, cement line and its material parameters on the stress intensity factor at the crack-tip based on theoretical formula calculation and finite element calculation. Results: The single osteon model, multi-osteon model and Haversian cortical bone model were established according to the microstructural characteristics of Haversian cortical bone. The calculation results of the first two models show that the “soft” osteon accelerates the crack propagation and the “hard” osteon hinders crack propagation, and the effect of multi-osteon model on a microcrack is significantly larger than that of single bone model. The calculation results of Haversian cortical bone model show that the stress intensity factors at both ends of the microcrack decreased when the distance from the “soft” osteon was within a certain range ([Formula: see text]). The stress intensity factor of endpoint ‘a’ in the crack-tip increases sharply when the microcrack is close to the osteon. Conclusions: The analysis results of the three models present that the microcrack propagation is affected by the material properties as well as the quantity of osteon, and the cement line is conductive to enhance the fracture toughness of the cortical bone.

Structural role of osteocalcin and its modification in bone fracture.

Osteocalcin (OC), an abundant non-collagenous protein in bone extracellular matrix, plays a vital role in both its biological and mechanical function. OC undergoes post-translational modification, such as glycation; however, it remains unknown whether glycation of OC affects bone's resistance to fracture. Here, for the first time, we demonstrate the formation of pentosidine, an advanced glycation end-product (AGE) cross-link on mouse OC analyzed by ultra-performance liquid chromatography. Next, we establish that the presence of OC in mouse bone matrix is associated with lower interlamellar separation (distance) and thicker bridges spanning the lamellae, both of which are critical for maintaining bone's structural integrity. Furthermore, to determine the impact of modification of OC by glycation on bone toughness, we glycated bone samples in vitro from wild-type (WT) and osteocalcin deficient (Oc-/-) mice, and compared the differences in total fluorescent AGEs and fracture toughness between the Oc -/- glycated and control mouse bones and the WT glycated and control mouse bones. We determined that glycation resulted in significantly higher AGEs in WT compared to Oc-/- mouse bones (delta-WT > delta-OC, p = 0.025). This observed change corresponded to a significant decrease in fracture toughness between WT and Oc-/- mice (delta-WT vs delta-OC, p = 0.018). Thus, we propose a molecular deformation and fracture mechanics model that corroborates our experimental findings and provides evidence to support a 37%-90% loss in energy dissipation of OC due to formation of pentosidine cross-link by glycation. We anticipate that our study will aid in elucidating the effects of a major non-collagenous bone matrix protein, osteocalcin, and its modifications on bone fragility and help identify potential therapeutic targets for maintaining skeletal health.

Effect of ribose incubation on physical, chemical, and mechanical properties of human cortical bone

Raman spectroscopy (RS) is sensitive to the accumulation of advanced glycation end-products (AGEs), and it measures matrix-sensitive properties that correlate with the fracture toughness of human cortical bone. However, it is unclear whether sugar-mediated accumulation of AGEs affects the fracture toughness of human cortical bone in a manner that is consistent with the negative correlations between amide I sub-peak ratios and fracture toughness. Upon machining 64 single-edge notched beam (SENB) specimens from cadaveric femurs (8 male and 7 female donors between 46 years and 61 years of age), pairs of SENB specimens were incubated in 15 mL of phosphate buffered saline with or without 0.1 M ribose for 4 weeks at 37 °C. After acquiring 10 Raman spectra per bone specimen (n = 32 per incubation group), paired SENB specimens were loaded in three-point bending at a quasi-static or a high loading rate approximating 10−4 s−1 or 10−2 s−1, respectively (n = 16 per incubation group per loading rate). While 2 amide I sub-peak ratios, I1670/I1640 and I1670/I1610, decreased by 3–5% with a 100% increase in AGE content, as confirmed by fluorescence measurements, the ribose incubation to accumulate AGEs in bone did not affect linear elastic (KIc) nor non-linear elastic (KJc) measurements of bone's ability to resist crack growth. Moreover, AGE accumulation did not affect the change in these properties when the loading rate changed. Increasing the loading rate increased KIc but decreased KJc. Ribose incubation did not affect mineral-related RS properties such as mineral-to-matrix ratios, Type B carbonate substitutions, and crystallinity. It did however increase the thermal stability of demineralized bone (differential scanning calorimetry), without affecting the network connectivity of the organic matrix (i.e., maximum slope during a hydrothermal isometric tension test of demineralized bone). In conclusion, RS is sensitive to AGE accumulation via the amide I band (plus the hydroxyproline-to-proline ratio), but the increase in AGE content due to ribose incubation was not sufficient to affect the fracture toughness of human cortical bone.

A steered molecular dynamics investigation on the role of glycation on the energy dissipation capacity of osteopontin at mineral interfaces in bone.

Type-2 Diabetes (T2D) is associated with a 3-fold increase in bone fracture risk. T2D impairs bone quality, whereby the intrinsic material properties of the bone matrix are altered, through glycation of collagenous and non-collagenous proteins (NCPs). There is a distinct lack of understanding of how altered protein configurations impair whole-bone biomechanics, particularly in the case of NCPs since their structural roles in bone are only now emerging. In this study, the effect of glycation on the energy dissipation behaviour of OPN, the most abundant NCP, on HydroxyApatite (HAp) mineral surfaces was investigated. The adsorption modes of OPN on the surface was obtained by conventional MD by comparing the residues residence time for each protein orientation with their average values. Then, energy dissipation of OPN was obtained through Steered Molecular Dynamics (SMD) by pulling simulations perpendicular to the surface. Two different glycation possibilities were considered whereby (a) Glycation occurred prior to Adsorption (GA) or (b) Adsorption took place before Glycation (AG). The simulation results showed that AG has the same adsorption modes as the healthy OPN, while the GA experienced a different mode. It was found that energy dissipation in absence of glycation was EOPN = 2646 kcal/mol. For glycated groups energy dissipation values were EOPN-AG = 2324 kcal/mol and EOPN-GA = 773 kcal/mol. The simulation results showed that OPN had reduced capacity for energy dissipation for either glycation case. However, it was notable that if OPN glycation occurred before its adsorption on HAp, its energy dissipation capacity was greatly reduced, which was caused by changes to the adsorption mode itself. The current study for the first time showed that the glycation sequence could negatively affects energy dissipation behaviour of OPN, which could have consequence for bone toughness.

A review on prediction of bone fracture using LEFM

Bone fractures are significant health concerns, particularly for the elderly population with osteoporosis. Prediction of the risk of fracture and its prevention can help in reducing the socioeconomic burden of osteoporotic fractures. The risk of bone fractures has been investigated at various length scales using analytical methods, computational models and physical experiments. Over the last few decades, significant developments have been reported on linear elastic fracture mechanics (LEFM) applications in predicting crack initiation and propagation. The objective of this study was to review the state-of-the-art of LEFM in the prediction of bone fractures. A brief overview of the LEFM was presented. Bone structural aspects associated with bone fractures were summarized along with the bone toughening mechanisms. Critical reviews of the literature on the use of LEFM-based modeling techniques for predicting bone fractures at various length scales were presented. The critical modeling parameters, challenges and limitations of using LEFM in simulating bone fractures were identified, showing future research directions.

Accumulation of fluorescent advanced glycation end products and carboxymethyl-lysine in human cortical and trabecular bone

Chemical crosslinks known as advanced glycation end-products (AGEs) are associated with increased bone fracture risk and deteriorated bone mechanical properties. However, measurement of bone AGEs via ex vivo and in vitro methods has been limited to quantification of bulk fluorescent AGEs (fAGEs) and pentosidine only, which is a crosslinking fluorescent AGE. However, a non-crosslinking and non-fluorescent AGE such as carboxymethyl-lysine (CML) is found to be 40–100 times higher in quantity than pentosidine, but only one previous study has reported it in cortical bone, and one study reported it in trabecular bone. In our study, we wanted to investigate if accumulation of CML differs in cortical and trabecular compartments and if they are more strongly associated with bone mechanical properties than with fAGEs. We hypothesized that CML and fAGEs level would be higher in the trabecular compartment and show negative correlations to mechanical properties in cortical and trabecular bone. We obtained human cadaveric cortical and trabecular bone specimens, induced the formation of AGEs via the established in vitro ribosylation method, imaged specimens by microcomputed tomography to assess specimen geometry and microarchitecture, and mechanically tested cortical specimens by cyclic reference point indentation and fracture toughness tests and trabecular specimens by compression tests, followed by measurement of fAGEs and CML. fAGEs were 22 % higher in cortical bone (687 ± 44.8 ng Q/mg collagen) compared to trabecular bone (859 ± 317.1 ng Q/mg collagen), whereas CML levels were found to be 148 % higher in trabecular bone (6189.9 ± 866 ng/mg of protein) compared to cortical bone (924.6 ± 576.3 ng/mg of protein). Pooling the specimens from both the control and ribose groups, Spearman correlation analysis indicated that CML levels, but not fAGEs, are moderately associated with cortical porosity (r = +0.505, p ≤ 0.05) and mechanical properties such indentation depth (r = +0.460, p ≤ 0.05), total indentation depth (r = +0.440, p ≤ 0.05), and average energy dissipated (r = +0.465, p ≤ 0.05) in cortical bone. fAGEs showed a trend towards negative association with crack propagation toughness in cortical bone (r = −0.365, p = 0.055). No significant correlations were observed between CML and microarchitecture or mechanical properties in trabecular bone. CML levels were also associated with fAGEs in cortical bone (r = +0.596, p ≤ 0.05) but not in trabecular bone. Our preliminary findings indicate that CML, a non-crosslinking AGE, may affect bone material and mechanical properties differently than bulk fluorescent AGEs, given the higher accumulation of CML in each bone compartment. This study provides direction to future studies to quantify crosslinking and non-crosslinking AGEs separately as their effect on material and mechanical properties may be different and it would help identify better biomarkers for bone strength prediction.

Unraveling the effect of collagen damage on bone fracture using in situ synchrotron microtomography with deep learning

When studying bone fragility diseases, it is difficult to identify which factors reduce bone’s resistance to fracture because these diseases alter bone at many length scales. Here, we investigate the contribution of nanoscale collagen behavior on macroscale toughness and microscale toughening mechanisms using a bovine heat-treatment fragility model. This model is assessed by developing an in situ toughness testing technique for synchrotron radiation micro-computed tomography to study the evolution of microscale crack growth in 3D. Low-dose imaging is employed with deep learning to denoise images while maintaining bone’s innate mechanical properties. We show that collagen damage significantly reduces macroscale toughness and post-yield properties. We also find that bone samples with a compromised collagen network have reduced amounts of crack deflection, the main microscale mechanism of fracture resistance. This research demonstrates that collagen damage at the nanoscale adversely affects bone’s toughening mechanisms at the microscale and reduces the overall toughness of bone.