Crack propagation in cortical bone is affected by the characteristics of the cement line: a parameter study using an XFEM interface damage model

From bone to nacre - development of biomimetic materials for bone implants: a review

The field of bone repair and regeneration has undergone significant advancements, yet challenges persist in achieving optimal bone implants or scaffolds, particularly load-bearing bone implants. This review explores the current landscape of bone implants, emphasizing the complexity of bone anatomy and the emerging paradigm of biomimicry inspired by natural structures. Nature, as a master architect, offers insights into the design of biomaterials that can closely emulate the mechanical properties and hierarchical organization of bone. By drawing parallels with nacre, the mollusk shells renowned for their exceptional strength and toughness, researchers have endeavored to develop bone implants with enhanced biocompatibility and mechanical robustness. This paper surveys the literature on various nacre-inspired composites, particularly ceramic/polymer composites like calcium phosphate (CaP), which exhibit promising similarities to native bone tissue. By harnessing the principles of hierarchical organization and organic-inorganic interfaces observed in natural structures, researchers aim to overcome existing limitations in bone implant technology, paving the way for more durable, biocompatible, and functionally integrated solutions in orthopedic and dental applications.

A proposal for the combined analysis of bone quantity and quality of human cortical bone by quasi-brittle fracture mechanics

Quasi-brittle fracture mechanics is used to evaluate fracture of human cortical bone in aging. The approach is demonstrated using cortical bone bars extracted from one 92-year-old human male cadaver. In-situ fracture mechanics experiments in a 3D X-ray microscope are conducted. The evolution of the fracture process zone is documented. Fully developed fracture process zone lengths at peak load are found to span about three osteon diameters. Crack deflection and arrest at cement lines is a key process to build extrinsic toughness. Strength and toughness are found as size-dependent, not only for laboratory-scale experimental specimens but also for the whole femur. A scaling law for the length fracture process zone is used. Then, size-independent, tissue fracture properties are calculated. Linear elastic fracture mechanics applied to laboratory beam specimens underestimates the tissue toughness by 60%. Tissue fracture properties are used to predict the load capacity of the femur in bending within the range of documented data. The quasi-brittle fracture mechanics approach allows for the assessment of the combined effect of bone quantity and bone quality on fracture risk. However, further work is needed considering a larger range of subjects and in the model validation at the organ length scale.

Characterization of damage mechanisms in cortical bone: Quantification of fracture resistance, critical strains, and crack tortuosity

One step towards understanding bone fragility and degenerative diseases is to unravel the links between fracture resistance and the compositional and structural characteristics of cortical bone. In this study, we explore an optical method for automatic crack detection to generate full fracture resistance curves of cortical bone. We quantify fracture toughness, critical failure strains at the crack tip, and crack tortuosity in three directions and analyze how they relate to cortical bone microstructure. A three-point bending fracture test of single-edge notched beam specimens in three directions (cracks propagating transverse, radial and longitudinal to the microstructure) from bovine cortical bone was combined with 2D-digital image correlation. Crack growth was automatically monitored by analyzing discontinuities in the displacement field using phase congruency analysis. Fracture resistance was analyzed using J-R-curves and strains were quantified at the crack tip. Post-testing, a subset of specimens was scanned using micro-tomography to visualize cracks and to quantify their tortuosity. Both fracture toughness and crack tortuosity were significantly higher in the transverse direction compared to the other directions. Similar fracture toughness was found for radial and longitudinal directions, albeit 20% higher crack tortuosity in the radial specimens. This suggests that radial crack deflections are not as efficient toughening mechanisms. Strains at crack initiation were ∼0.4% for all tissue orientations, while at fully developed damage process zones failure strains were significantly higher in the transverse direction (∼1.5%). Altogether, we present unique quantitative data including different aspects of bone damage in three directions, illustrating the importance of cortical bone microstructure.

A numerical study of dehydration induced fracture toughness degradation in human cortical bone

A 2D plane strain extended finite element method (XFEM) model was developed to simulate three-point bending fracture toughness tests for human bone conducted in hydrated and dehydrated conditions. Bone microstructures and crack paths observed by micro-CT imaging were simulated using an XFEM damage model. Critical damage strains for the osteons, matrix, and cement lines were deduced for both hydrated and dehydrated conditions and it was found that dehydration decreases the critical damage strains by about 50%. Subsequent parametric studies using the various microstructural models were performed to understand the impact of individual critical damage strain variations on the fracture behavior. The study revealed the significant impact of the cement line critical damage strains on the crack paths and fracture toughness during the early stages of crack growth. Furthermore, a significant sensitivity of crack growth resistance and crack paths on critical strain values of the cement lines was found to exist for the hydrated environments where a small change in critical strain values of the cement lines can alter the crack path to give a significant reduction in fracture resistance. In contrast, in the dehydrated state where toughness is low, the sensitivity to changes in critical strain values of the cement lines is low. Overall, our XFEM model was able to provide new insights into how dehydration affects the micromechanisms of fracture in bone and this approach could be further extended to study the effects of aging, disease, and medical therapies on bone fracture.

XFEM for Composites, Biological, and Bioinspired Materials: A Review

The eXtended finite element method (XFEM) is a powerful tool for structural mechanics, assisting engineers and designers in understanding how a material architecture responds to stresses and consequently assisting the creation of mechanically improved structures. The XFEM method has unraveled the extraordinary relationships between material topology and fracture behavior in biological and engineered materials, enhancing peculiar fracture toughening mechanisms, such as crack deflection and arrest. Despite its extensive use, a detailed revision of case studies involving XFEM with a focus on the applications rather than the method of numerical modeling is in great need. In this review, XFEM is introduced and briefly compared to other computational fracture models such as the contour integral method, virtual crack closing technique, cohesive zone model, and phase-field model, highlighting the pros and cons of the methods (e.g., numerical convergence, commercial software implementation, pre-set of crack parameters, and calculation speed). The use of XFEM in material design is demonstrated and discussed, focusing on presenting the current research on composites and biological and bioinspired materials, but also briefly introducing its application to other fields. This review concludes with a discussion of the XFEM drawbacks and provides an overview of the future perspectives of this method in applied material science research, such as the merging of XFEM and artificial intelligence techniques.

An integrated experimental-computational framework to assess the influence of microstructure and material properties on fracture toughness in clinical specimens of human femoral cortical bone

Microstructural and compositional changes that occur due to aging, pathological conditions, or pharmacological treatments alter cortical bone fracture resistance. However, the relative importance of these changes to the fracture resistance of cortical bone has not been quantified in detail. In this technical note, we developed an integrated experimental-computational framework utilizing human femoral cortical bone biopsies to advance the understanding of how fracture resistance of cortical bone is modulated due to modifications in its microstructure and material properties. Four human biopsy samples from individuals with varying fragility fracture history and osteoporosis treatment status were converted to finite element models incorporating specimen-specific material properties and were analyzed using fracture mechanics-based modeling. The results showed that cement line density and osteonal volume had a significant effect on crack volume. The removal of cement lines substantially increased the crack volume in the osteons and interstitial bone, representing straight crack growth, compared to models with cement lines due to the lack of crack deflection in the models without cement lines. Crack volume in the osteons and interstitial bone increased when mean elastic modulus and ultimate strength increased and mean fracture toughness decreased. Crack volume in the osteons and interstitial bone was reduced when material property heterogeneity was incorporated in the models. Although both the microstructure and the heterogeneity of the material properties of the cortical bone independently increased the fracture toughness, the relative contribution of the microstructure was more significant. The integrated experimental-computational framework developed here can identify the most critical microscale features of cortical bone modulated by pathological processes or pharmacological treatments that drive changes in fracture resistance and improve our understanding of the relative influence of microstructure and material properties on fracture resistance of cortical bone.

Multiscale theoretical model shows that aging-related mechanical degradation of cortical bone is driven by microstructural changes in addition to porosity

This study aims to gain mechanistic understanding of how aging-related changes in the microstructure of cortical bone drive mechanical consequences at the macroscale. To that end, cortical bone was modeled as a bundle of elastic-plastic, parallel fibers, which represented osteons and interstitial tissue, loaded in uniaxial tension. Distinct material properties were assigned to each fiber in either the osteon or interstitial fiber "families." Models representative of mature (20-60 yrs.) bone, and elderly (60+) bone were created by modeling aging via the following changes to the input parameters: (i) increasing porosity from 5% to 15%, (ii) increasing the ratio of the number of osteon fibers relative to interstitial fibers from 40% to 50%, and (iii) changing the fiber material properties from representing mature bone samples to representing elderly bone samples (i.e., increased strength and decreased toughness of interstitial fibers together with decreased toughness of osteon fibers). To understand the respective contributions of these changes, additional models isolating one or two of each of these were also created. From the computed stress-strain curve for the fiber bundle, the yield point (ϵy, σy), ultimate point (ϵu, σu), and toughness (UT) for the bundle as a whole were measured. We found that changes to all three input parameters were required for the model to capture the aging-related decline in cortical bone mechanical properties consistent with those previously reported in the literature. In both mature and elderly bundles, rupture of the interstitial fibers drove the initial loss of strength following the ultimate point. Plasticity and more gradual rupture of the osteons drove the remainder of the response. Both the onset and completion of interstitial fiber rupture occurred at lower strains in the elderly vs. mature case. These findings point to the importance of studying microstructural changes beyond porosity, such as the area fraction of osteons and the material properties of osteon and interstitial tissue, in order to further understanding of aging-related changes in bone.

Mineralized Collagen Fibrils: An Essential Component in Determining the Mechanical Behavior of Cortical Bone

Bone comprises mechanically different materials in a specific hierarchical structure. Mineralized collagen fibrils (MCFs), represented by tropocollagen molecules and hydroxyapatite nanocrystals, are the fundamental unit of bone. The mechanical characterization of MCFs provides the unique adaptive mechanical competence to bone to withstand mechanical load. The structural and mechanical role of MCFs is critical in the deformation mechanisms of bone and the marvelous strength and toughness possessed by bone. However, the role of MCFs in the mechanical behavior of bone across multiple length scales is not fully understood. In the present study, we shed light upon the latest progress regarding bone deformation at multiple hierarchical levels and emphasize the role of MCFs during bone deformation. We propose the concept of hierarchical deformation of bone to describe the interconnected deformation process across multiple length scales of bone under mechanical loading. Furthermore, how the deterioration of bone caused by aging and diseases impairs the hierarchical deformation process of the cortical bone is discussed. The present work expects to provide insights on the characterization of MCFs in the mechanical properties of bone and lays the framework for the understanding of the multiscale deformation mechanics of bone.

On the fracture behavior of cortical bone microstructure: The effects of morphology and material characteristics of bone structural components

Bone encompasses a complex arrangement of materials at different length scales, which endows it with a range of mechanical, chemical, and biological capabilities. Changes in the microstructure and characteristics of the material, as well as the accumulation of microcracks, affect the bone fracture properties. In this study, two-dimensional finite element models of the microstructure of cortical bone were considered. The eXtended Finite Element Method (XFEM) developed by Abaqus software was used for the analysis of the microcrack propagation in the model as well as for local sensitivity analysis. The stress-strain behavior obtained for the different introduced models was substantially different, confirming the importance of bone tissue microstructure for its failure behavior. Considering the role of interfaces, the results highlighted the effect of cement lines on the crack deflection path and global fracture behavior of the bone microstructure. Furthermore, bone micromorphology and areal fraction of cortical bone tissue components such as osteons, cement lines, and pores affected the bone fracture behavior; specifically, pores altered the crack propagation path since increasing porosity reduced the maximum stress needed to start crack propagation. Therefore, cement line structure, mineralization, and areal fraction are important parameters in bone fracture. The parameter-wise sensitivity analysis demonstrated that areal fraction and strain energy release rate had the greatest and the lowest effect on ultimate strength, respectively. Furthermore, the component-wise sensitivity analysis revealed that for the areal fraction parameter, pores had the greatest effect on ultimate strength, whereas for the other parameters such as elastic modulus and strain energy release rate, cement lines had the most important effect on the ultimate strength. In conclusion, the finding of the current study can help to predict the fracture mechanisms in bone by taking the morphological and material properties of its microstructure into account.

Bionic design based on micro-nano structure of osteon and its low-velocity impact damage behavior

It is found that the osteon is composed of thin and thick lamellae which are periodic and approximately concentric, every 5 lamellae is a cycle, the periodic helix angle of mineralized collagen fibers in two adjacent sub-lamellae is 30°. Four bionic composite models with different fiber helix angles were established and fabricated according to the microstructure of mineralized collagen fibers in osteon. Based on the impact analysis of four kinds of bionic composite models, the effects of the fiber periodic spiral structure on the impact resistance and energy dissipation of multi-layer bionic composite were investigated. The analysis results show that the fiber helix angle affects the impact damage resistance and energy dissipation of multi-layer fiber reinforced composites. Among the 4 kinds of multi-layer composite models, the composite model with helix angle of 30° has better comprehensive ability to resist impact damage. The test results show that the impact damage area of the specimen with 30° helix angle is smallest among the 4 types of bionic specimens, which is consistent with the results of finite-element impact analysis. Furthermore, in the case of without impact damage, the smaller the fiber helix angle is, the more uniform the stress distribution is and more energy is dissipated in the impact process. The periodic spiral structure of mineralized collagen fibers in osteon are the result of natural selection of biological evolution. This structure can effectively improve the ability of cortical bone to resist external impact. The research results can provide useful guidance for the design and manufacture of high-performance and strong impact resistant bionic composites.

Bending Study of Six Biological Models for Design of High Strength and Tough Structures

High strength and tough structures are beneficial to increasing engineering components service span. Nonetheless, improving structure strength and, simultaneously, toughness is difficult, since these two properties are generally mutually exclusive. Biological organisms exhibit both excellent strength and toughness. Using bionic structures from these biological organisms can be solutions for improving these properties of engineering components. To effectively apply biological models to design biomimetic structures, this paper analyses strengthening and toughening mechanisms of six fundamentally biological models obtained from biological organisms. Numerical models of three-point bending test are established to predict crack propagation behaviors of the six biological models. Furthermore, the strength and toughness of six biomimetic composites are experimentally evaluated. It is identified that the helical model possesses the highest toughness and satisfying strength. This work provides more detailed evidence for engineers to designate bionic models to the design of biomimetic composites with high strength and toughness.

Bone Abrasive Machining: Influence of Tool Geometry and Cortical Bone Anisotropic Structure on Crack Propagation

The abrasive machining of cortical tissue is used in many arthroplasties and craniofacial surgery procedures. However, this method requires further research due to the processes’ complexity and the tissue’s composite structure. Therefore, studies were carried out to assess the impact of grid geometry and the anisotropic structure of bone tissue on the cutting process and crack propagation. The analysis was performed based on an orthogonal cutting in three directions. The grain shape has been simplified, and the cutting forces, crack path and surface quality were monitored. The results indicate that a depth of cut at 100−25 µm allows the most accurate cutting control. A transverse cutting direction results in the greatest surface irregularity: Iz = 17.7%, Vvc = 3.29 mL/m2 and df = 5.22 µm and generates the most uncontrolled cracks. Maximum fracture force values of FF > 80 N were generated for d = 175 µm. For d < 5 µm, no cracks or only slight penetration occurs. A positive γ provides greater repeatability and crack control. Negative γ generates penetrating cracks and uncontrolled material damage. The individual types of cracks have a characteristic course of changes in Fx. The clearance angle did not affect the crack propagation.

2D size of trabecular bone structure units (BSU) correlate more strongly with 3D architectural parameters than age in human vertebrae

Bone tissue is continuously remodeled. In trabecular bone, each remodeling transaction forms a microscopic bone structural unit (BSU), also known as a hemiosteon or a trabecular packet, which is bonded to existing tissue by osteopontin-rich cement lines. The size and shape of the BSUs are determined by the size and shape of the resorption cavity, and whether the cavity is potentially over- or under-filled by the subsequent bone formation. The present study focuses on the recently formed trabecular BSUs, and how their 2D size and shape changes with age and trabecular microstructure. The study was performed using osteopontin-immunostained frontal sections of L2 vertebrae from 8 young (aged 18.5-37.6 years) and 8 old (aged 69.1-96.4 years) control females, which underwent microcomputed tomography (μCT) imaging prior to sectioning. The contour of 4230 BSU profiles (181-385 per vertebra) within 1024 trabecular profiles were outlined, and their 2D width, length, area, and shape were assessed. Of these BSUs, 22 (0.5%) were generated by modeling-based bone formation (i.e. without prior resorption), while 99.5% were generated by remodeling-based bone formation (i.e. with prior resorption). The distributions of BSU profile width, length, and area were significantly smaller in the old versus young females (p < 0.005), and the median profile width, length, and area were negative correlated with age (p < 0.018). Importantly, these BSU profile size parameters were more strongly correlated with trabecular bone volume (BV/TV, p < 0.002) and structure model index (SMI, p < 0.008) assessed by μCT, than age. Moreover, the 2D BSU size parameters were positively correlated to the area of the individual trabecular profiles (p < 0.0001), which were significantly smaller in the old versus young females (p < 0.024). The BSU shape parameters (aspect ratio, circularity, and solidity) were not correlated with age, BV/TV, or SMI. Collectively, the study supports the notion that not only the BSU profile width, but also its length and area, are more influenced by the age-related bone loss and shift from plates to rods (SMI), than age itself. This implies that BSU profile size is mainly driven by changes in the trabecular microstructure, which affect the size of the resorption cavity that the BSU refills.

A review on experimental and numerical investigations of cortical bone fracture

This paper comprehensively reviews the various experimental and numerical techniques, which were considered to determine the fracture characteristics of the cortical bone. This study also provides some recommendations along with the critical review, which would be beneficial for future research of fracture analysis of cortical bone. Cortical bone fractures due to sports activities, climbing, running, and engagement in transport or industrial accidents. Individuals having different diseases are also at high risk of cortical bone fracture. It has been observed that osteon orientation influences cortical bone fracture toughness and fracture mechanisms. Apart from this, recent studies indicate that fracture parameters of cortical bone also depend on many factors such as age, sex, temperature, osteoporosis, orientation, location, loading condition, strain rate, and storage facility, etc. The cortical bone regains its fracture toughness due to various toughening mechanisms. Owing to these factors, several experimental, clinical, and numerical investigations have been carried out to determine the fracture parameters of the cortical bone. Cortical bone is the dense outer surface of the bone and contributes to 80%–82% of the skeleton mass. Cortical bone experiences load far exceeding body weight due to muscle contraction and the dynamics of motion. It is very important to know the fracture pattern, direction of fracture, location of the fracture, and toughening mechanism of cortical bone. A basic understanding of the different factors that affect the fracture parameters and fracture mechanisms of the cortical bone is necessary to prevent the failure and fracture of cortical bone. This review has summarized the advancement considered in the various experimental techniques and numerical methods to get complete information about the fracture mechanisms of cortical bone.

Damage analysis of human cortical bone under compressive and tensile loadings

Developing advanced fracture tools can increase the understanding of crack growth trajectories in human cortical bone. The present study investigates fracture micromechanics of human cortical bone under compressive and tensile loadings utilizing a phase field method. We construct two-dimensional finite element models from cortical microstructure of a human tibia cross section. We apply compression on the cortical bone models to create compressive microcracks. Then, we simulate the fracture of these models under tension to discover influential parameters on microcracks formation and post-yielding behavior. The results show that cement lines are susceptible sites to damage nucleation under compression rather than tension. The findings of this study also indicate a higher accumulation of initial damage (induced by compression) can lead to a lower microscopic stiffness as well as a less resistant material to damage initiation under tension. The simulations further indicate that the post-yielding properties (e.g., toughness) can be dependent on different variables such as morphological information of the osteons, the initial accumulation of microcracks, and the total length of cement lines.

Computational homogenisation based extraction of transverse tensile cohesive responses of cortical bone tissue

The numerical assessment of fracture properties of cortical bone is important in providing suggestions on patient-specific clinical treatments. We present a generic finite element modelling framework incorporating computational fracture approaches and computational homogenisation techniques. Finite element computations for statistical volume elements (SVEs) at the microscale are performed for different sizes with random osteon packing with a fixed volume fraction. These SVEs are loaded in the transverse direction under tension. The minimal SVE size in terms of ensuring a representative effective cohesive law is suggested to be 0.6 mm. Since cement lines as weak interfaces play a key role in bone fracture, the effects of their fracture properties on the effective fracture strength and toughness are investigated. The extracted effective fracture properties can be used as homogenised inputs to a discrete crack simulation at macroscopic or structural scale. The extrinsic toughening mechanisms observed in the SVE models are discussed with a comparison against experimental observations from the literature, giving beneficial insights to cortical bone failure.

Computational study of the mechanical influence of lacunae and perilacunar zones in cortical bone microcracking

The mechanical behavior of cortical bone is influenced by microstructural components such as osteons, Haversian canals, and osteocyte lacunae that arise from biological remodeling processes. This study takes a computational approach to investigate the role of the perilacunar zones formed by the local remodeling processes of lacunar-dwelling osteocytes by utilizing phase-field finite element models based on histological imaging of human bone. The models simulated the microdamage accumulation that occurs in cortical bone under transverse compression in bone without lacunae, with lacunae, and with a perilacunar zone surrounding lacunae in order to investigate the role of these features. The results of the simulations found that while lacunae create stress concentration which initiate further damage, perilacunar regions can delay or prevent the emergence and growth of microcracks.

Fracture behavior of human cortical bone: Role of advanced glycation end-products and microstructural features

Diabetes is associated with increased fracture risk in human bone, especially in the elderly population. In the present study, we investigate how simulated advanced glycation end-products (AGEs) and materials heterogeneity affect crack growth trajectory in human cortical bone. We used a phase field fracture framework on 2D models of cortical microstructure created from human tibias to analyze crack propagation. The increased AGEs level results in a higher rate of crack formation. The simulations also indicate that the mismatch between the fracture properties (e.g., critical energy release rate) of osteons and interstitial tissue can alter the post-yielding behavior. The results show that if the critical energy release rate of cement lines is lower than that of osteons and the surrounding interstitial matrix, cracks can be arrested by cement lines. Additionally, activation of toughening mechanisms such as crack merging and branching depends on bone microstructural morphology (i.e., osteons geometrical parameters, canals, and lacunae porosities). In conclusion, the present findings suggest that materials heterogeneity of microstructural features and the crack-microstructure interactions can play important roles in bone fragility.

Effect of ageing on microstructure and fracture behavior of cortical bone as determined by experiment and Extended Finite Element Method (XFEM)

Bone fracture is a severe health concern; therefore, understanding the causes of bone fracture are crucial. This paper investigates the microstructure and fracture behaviour of cadaveric cortical bone of two different groups (Young, n= 6; Aged, n=7). The microstructure is obtained from µ-CT images, and the material parameters are measured with nanoindentation. Fracture behaviour in transverse and longitudinal orientations is investigated experimentally and numerically. The results show that the Haversian canal (HC) size increases and the osteon wall thickness (OWT) decreases significantly in the aged group, whereas a nonsignificant difference is found in tissue properties. The crack initiation (J_ic) and crack growth (J_grow) toughness of the aged group are found to be significantly lower (p<0.01) than the young group in the transverse orientation; however, for the longitudinal orientation, only the value of J_ic in the aged group is found significantly lower. Further, a 4-phase XFEM (based on micro-CT image) model is developed to investigate the crack propagation behaviour in both orientations. For the transverse orientation, results show that in the aged group, the crack initially follows the cementline and then penetrates the osteon, whereas, in the young group, it propagates along the cementline. These results are in agreement with experimental results where the decrease in J_grow is more significant than the J_ic in the aged group. This study suggests that ageing leads to a larger HC and reduced OWT, which weakens the crack deflection ability and causes fragility fracture. Further, the XFEM results indicate that the presence of a small microcrack in the vicinity of a major crack tip causes an increase in the critical stress intensity factor.

The influence of microstructure on crack propagation in cortical bone at the mesoscale

The microstructure of cortical bone is key for the tissue's high toughness and strength and efficient toughening mechanisms have been identified at the microscale, for example when propagating cracks interact with the osteonal microstructure. Finite element models have been proposed as suitable tools for analyzing the complex link between the local tissue structure and the fracture resistance of cortical bone. However, previous models that could capture realistic crack paths in cortical bone were due to the required computational effort limited to idealized osteon geometries and small (<1 mm²) model domains. The objective of this study was therefore to bridge the gap between experimental and numerical analysis of crack propagation in cortical bone by introducing image-based models at the mesoscale. Tissue orientation maps from high-resolution micro-CT images were used to define the distribution and orientation of weak interfaces in the models. Crack propagation was simulated using the extended finite element method in combination with an interface damage model, previously developed to simulate crack propagation in microstructural osteon models. The results showed that image-based mesoscale models can be used to capture interactions between cracks and microstructure. The simulated crack paths predicted the general trends seen in experiments with more irregular patterns for cracks propagating perpendicular compared to parallel to the osteon orientation. In all, the proposed method enabled an efficient description of the tissue level microstructure, which is a necessity to predict realistic crack paths in cortical bone and is an important step towards simulating crack propagation in bone models in 3D.

Advanced Modeling Methods-Applications to Bone Fracture Mechanics

PURPOSE OF REVIEW

The goal of this review is to summarize recent advances in modeling of bone fracture using fracture mechanics-based approaches at multiple length scales spanning nano- to macroscale.

RECENT FINDINGS

Despite the additional information that fracture mechanics-based models provide over strength-based ones, the application of this approach to assessing bone fracture is still somewhat limited. Macroscale fracture models of bone have demonstrated the potential of this approach in uncovering the contributions of geometry, material property variation, as well as loading mode and rate on whole bone fracture response. Cortical and cancellous microscale models of bone have advanced the understanding of individual contributions of microstructure, microarchitecture, local material properties, and material distribution on microscale fracture resistance of bone. Nano/submicroscale models have provided additional insight into the effect of specific changes in mineral, collagen, and non-collagenous proteins as well as their interaction on energy dissipation and fracture resistance at small length scales. Advanced modeling approaches based on fracture mechanics provide unique information about the underlying multiscale fracture mechanisms in bone and how these mechanisms are influenced by the structural and material constituents of bone at different length scales. Fracture mechanics-based modeling provides a powerful approach that complements experimental evaluations and advances the understanding of critical determinants of fracture risk.