Mechanical Properties Of Cortical Bone Research Articles

Predicting altered bone biomechanics in juvenile mice: insights from microgravity simulation, loading interventions, and Raman Spectroscopy

BackgroundMicrogravity, a condition experienced in a spatial environment, poses unique challenges to the skeletal system, particularly in juvenile organisms. This study aimed to investigate alterations in bone biomechanics of juvenile mice due to unloading – that simulates microgravity in the laboratory—and the effects of a bone-loading intervention. We compared bone compositional and mechanical properties between 21-six-week-old C57Bl/6 from a control group (wild type) and a group that underwent a tail-suspension unloading protocol to mimic microgravity (MG). The second group (MG) experienced additional in vivo loading protocol (MG + LDG) on the right hind leg, where dynamic compressive loading was applied to the right knee using a custom-built loading device.ResultsOur results show that after two weeks, we successfully induced bone alterations by (i) decreasing the energy dissipated before fracture and (ii) decreasing the yield and maximum stress. In addition, we showed that Mineral to matrix component [ν1PO4/Amide I], Carbonate to Amide [CO3/Amide I], and Crystallinity [1/FWHM(ν1PO4)] are strongly linked in physiological bone but not in microgravity even after loading intervention. While Crystallinity is very sensitive to bone deformation (strain) alterations coming from simulated microgravity, we show that Carbonate to Amide [CO3/Amide I] – a common marker of turnover rate/remodeling activity—is a specific predictor of bone deformation for bone after simulated microgravity. Our results also invalidate the current parameters of the loading intervention to prevent bone alterations entirely in juvenile mice.ConclusionsOur study successfully induced bone alterations in juvenile mice by using an unloading protocol to simulate microgravity, and we provided a new Raman Spectroscopy (RS) dataset of juvenile mice that contributes to the prediction of cortical bone mechanical properties, where the degree of interrelationship for RS data for physiological bone is improved compared to the most recent evidence.

Mimicking the mechanical properties of cortical bone with an additively manufactured biodegradable Zn-3Mg alloy

Additively manufactured (AM) biodegradable zinc (Zn) alloys have recently emerged as promising porous bone-substituting materials, due to their moderate degradation rates, good biocompatibility, geometrically ordered microarchitectures, and bone-mimicking mechanical properties. While AM Zn alloy porous scaffolds mimicking the mechanical properties of trabecular bone have been previously reported, mimicking the mechanical properties of cortical bone remains a formidable challenge. To overcome this challenge, we developed the AM Zn-3Mg alloy. We used laser powder bed fusion to process Zn-3Mg and compared it with pure Zn. The AM Zn-3Mg alloy exhibited significantly refined grains and a unique microstructure with interlaced α-Zn/Mg2Zn11 phases. The compressive properties of the solid Zn-3Mg specimens greatly exceeded their tensile properties, with a compressive yield strength of up to 601 MPa and an ultimate strain of >60%. We then designed and fabricated functionally graded porous structures with a solid core and achieved cortical bone-mimicking mechanical properties, including a compressive yield strength of >120 MPa and an elastic modulus of ≈20 GPa. The biodegradation rates of the Zn-3Mg specimens were lower than those of pure Zn and could be adjusted by tuning the AM process parameters. The Zn-3Mg specimens also exhibited improved biocompatibility as compared to pure Zn, including higher metabolic activity and enhanced osteogenic behavior of MC3T3 cells cultured with the extracts from the Zn-3Mg alloy specimens. Altogether, these results marked major progress in developing AM porous biodegradable metallic bone substitutes, which paved the way toward clinical adoption of Zn-based scaffolds for the treatment of load-bearing bony defects. Statement of SignificanceOur study presents a significant advancement in the realm of biodegradable metallic bone substitutes through the development of an additively manufactured Zn-3Mg alloy. This novel alloy showcases refined grains and a distinctive microstructure, enabling the fabrication of functionally graded porous structures with mechanical properties resembling cortical bone. The achieved compressive yield strength and elastic modulus signify a critical leap toward mimicking the mechanical behavior of load-bearing bone. Moreover, our findings reveal tunable biodegradation rates and enhanced biocompatibility compared to pure Zn, emphasizing the potential clinical utility of Zn-based scaffolds for treating load-bearing bony defects. This breakthrough opens doors for the wider adoption of zinc-based materials in regenerative orthopedics.

Biomechanical and physical properties selection of Ti-Ha-CaCO<sub>3</sub> biocomposite prostheses for replacement of bone atrophy

Traditional prosthetic materials often lack the desired properties to mimic the mechanical behaviour of natural bone, leading to complications and reduced implant longevity. This study aims to conduct a biomechanical and physical properties selection analysis for biocomposite prostheses' suitable for replacing bone atrophy. This involves evaluating the mechanical properties of developed biocomposites with different structures (dense, porous and gradient) to ensure compatibility with the mechanical properties of bone. The radar chart was adopted to compare and evaluate the mechanical strength of various biocomposite implants and identify the most suitable prosthesis for load-bearing bone replacement. The study utilises powder metallurgy, scanning electron microscopy (SEM), and ImageJ software to produce and characterise the pore size distribution of the biocomposites, respectively. The findings of this study revealed the gradient and porous biocomposites exhibited desired mechanical properties with porosity of 20.67 and 27.72 % pore size up to 134 and 256 μm, compressive strength of 174 and 149.29 MPa and compressive modulus of 30.42 and 28.3 GPa respectively. The SEM analysis, coupled with pore size distribution and porosity percentage measurements, offers valuable information for designing and fabricating biomaterials with enhanced properties. The gradient biocomposite was identified to be the best sample for load-bearing bone replacements by the selection analysis because of its high compressive strength and low modulus, which is within the established cortical bone mechanical properties.

Immature porcine cortical bone mechanical properties and composition change with maturation and displacement rate

Computational models of mature bone have been used to predict fracture; however, analogous study of immature diaphyseal fracture has not been conducted due to sparse experimental mechanical data. A model of immature bone fracture may be used to aid in the differentiation of accidental and non-accidental trauma fractures in young, newly ambulatory children (0–3 years). The objective of this study was to characterize the evolution of tissue-level mechanical behavior, composition, and microstructure of maturing cortical porcine bone with uniaxial tension, Raman spectroscopy, and light microscopy as a function of maturation. We asked: 1) How do the monotonic uniaxial tensile properties change with maturation and displacement rate; 2) How does the composition and microstructure change with maturation; and 3) Is there a correlation between composition and tensile properties with maturation? Elastic modulus (p < 0.001), fracture stress (p < 0.001), and energy absorption (p < 0.014) increased as a function of maturation at the quasistatic rate by 110%, 86%, and 96%, respectively. Fracture stress also increased by 90% with maturation at the faster rate (p = 0.001). Fracture stress increased as a function of increasing displacement rate by 28% (newborn p = 0.048; 1-month p = 0.004; 3-month p= < 0.001), and fracture strain decreased by 68% with increasing displacement rate (newborn p = 0.002; 1-month p = 0.036; 3-month p < 0.001). Carbonate-to-phosphate ratio was positively linearly related to elastic modulus, and fracture stress was positively related to carbonate-to-phosphate ratio and matrix maturation ratio. The results of this study support that immature bone is strain-rate dependent and becomes more brittle at faster rates, contributing to the foundation upon which a computational model can be built to evaluate immature bone fracture.

Impact of heavy alcohol consumption on cortical bone mechanical properties in male rhesus macaques

Chronic heavy alcohol consumption may influence the skeleton by suppressing intracortical bone remodeling which may impact the quality of bone and its mechanical properties. However, this aspect has not been thoroughly assessed in either humans or animal models whose cortical bone microstructure resembles the microstructure of human cortical bone. The current study is the first to investigate the effects of chronic heavy alcohol consumption on various mechanical properties of bone in a non-human primate model with intracortical remodeling. Male rhesus macaques (5.3 years old at the initiation of treatment) were induced to drink alcohol and then given the choice to voluntarily self-administer water or ethanol (4 % w/v) for approximately 14 months, followed by three abstinence phases (lasting 34, 41, and 39–46 days) with approximately 3 months of ethanol access in between. During the initial 14 months of open-access, monkeys in the alcohol group consumed an average of 2.9 ± 0.8 g/kg/d ethanol (mean ± SD) resulting in a blood ethanol concentration of 89 ± 47 mg/dl in longitudinal samples taken at 7 h after the daily sessions began. To understand the impact of alcohol consumption on material properties, various mechanical tests were conducted on the distal tibia diaphysis of 2–5 monkeys per test group, including dynamic mechanical analysis (DMA) testing, nano-indentation, microhardness testing, compression testing, and fracture resistance curve (R-curve) testing. Additionally, compositional analyses were performed using Fourier-transform infrared (FTIR) spectroscopy. Significant differences in microhardness, compressive stress-strain response, and composition were not observed with alcohol consumption, and only minor differences were detected in hardness and elastic modulus of the matrix and osteons from nanoindentation. Furthermore, the R-curves of both groups overlapped, with similar crack initiation toughness, despite a significant decrease in crack growth toughness (p = 0.032) with alcohol consumption. However, storage modulus (p = 0.029) and loss factor (p = 0.015) from DMA testing were significantly increased in the alcohol group compared to the control group, while loss modulus remained unchanged. These results indicate that heavy alcohol consumption may have only a minor influence on the material properties and the composition of cortical bone in young adult male rhesus macaques.

Expanding the mechanical and mass-transport combination for bone scaffolds: Through stretched structure

Optimizing the mechanical and mass-transport properties of porous biomaterials simultaneously can be challenging, as they often correspond one-to-one through structure. For instance, increasing permeability by reducing relative density frequently leads to lower mechanical properties. In this study, we introduced a stretched structure to optimize the two properties simultaneously. Initially, the stretched scaffolds were evaluated at the same porosity, revealing that the elastic modulus and permeability of the stretched scaffold are approximately twice that of the original type. Subsequently, the orientation dependence of these properties was investigated. The results suggest that the stiffness of the stretched structure in the width direction is compromised, aligning with the mechanical properties of cortical bone in shaft bones. The permeability of the stretched structure exhibits significant anisotropy, with values much higher than those of original structure. Moreover, our biological experiments demonstrate that extremely stretched structures exhibit low and uneven curvature, potentially impeding cell growth. Hence, striking a balance between curvature and the stretching method employed is crucial. The stretching method can also be applied to other strut-based structures, enabling greater design flexibility in achieving a desirable mechanical and mass-transport combination, providing a foundation for high-performance artificial bone prostheses.

Dissolution-precipitation synthesis and cold sintering of mussel shells-derived hydroxyapatite and hydroxyapatite/chitosan composites for bone tissue engineering

In the present work, seafood by-products and derivates were exploited as raw materials to produce nanocrystalline calcium phosphates-based composites in light of the rising demand for waste recovery and valorisation. Mussel shells were transformed into hydroxyapatite by dissolution-precipitation synthesis at 45 °C, whereas chitosan from shrimp shells was introduced as a reinforcing biopolymer to produce hydroxyapatite/chitosan composites. The synthesised hydroxyapatite and hydroxyapatite/chitosan composite powders were cold sintered at room temperature under 1 GPa pressure for 10 min. The materials were consolidated up to ∼90% relative density and characterized mechanically. By increasing the polymer content up to 10 wt%, the flexural strength of the sintered pellets increases from ∼45 MPa to ∼57 MPa while the hardness decreases from ∼1.1 GPa to ∼0.8 GPa, thus better addressing the mechanical properties of cortical bone. Furthermore, hydroxyapatite/chitosan composites were proven to be bioactive, this demonstrating their potential use in bone tissue engineering applications.

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.

Effects of different preservation on the mechanical properties of cortical bone under quasi-static and dynamic compression.

Introduction: Mechanical properties of biological tissue are important for numerical simulations. Preservative treatments are necessary for disinfection and long-term storage when conducting biomechanical experimentation on materials. However, few studies have been focused on the effect of preservation on the mechanical properties of bone in a wide strain rate. The purpose of this study was to evaluate the influence of formalin and dehydration on the intrinsic mechanical properties of cortical bone from quasi-static to dynamic compression. Methods: Cube specimens were prepared from pig femur and divided into three groups (fresh, formalin, and dehydration). All samples underwent static and dynamic compression at a strain rate from 10-3s-1 to 103s-1. The ultimate stress, ultimate strain, elastic modulus, and strain-rate sensitivity exponent were calculated. A one-way ANOVA test was performed to determine if the preservation method showed significant differences in mechanical properties under at different strain rates. The morphology of the macroscopic and microscopic structure of bones was observed. Results: The results show that ultimate stress and ultimate strain increased as the strain rate increased, while the elastic modulus decreased. Formalin fixation and dehydration did not affect elastic modulus significantly whereas significantly increased the ultimate strain and ultimate stress. The strain-rate sensitivity exponent was the highest in the fresh group, followed by the formalin group and dehydration group. Different fracture mechanisms were observed on the fractured surface, with fresh and preserved bone tending to fracture along the oblique direction, and dried bone tending to fracture along the axial direction. Discussion: In conclusion, preservation with both formalin and dehydration showed an influence on mechanical properties. The influence of the preservation method on material properties should be fully considered in developing a numerical simulation model, especially for high strain rate simulation.

Spatial Variation in Young Ovine Cortical Bone Properties.

Significant effort continues to be made to understand whether differences exist in the structural, compositional, and mechanical properties of cortical bone subjected to different strain modes or magnitudes. We evaluated juvenile sheep femora (age = 4 months) from the anterior and posterior quadrants at three points along the diaphysis as a model system for variability in loading. Micro-CT scans (50 micron) were used to measure cortical thickness and mineral density. Three point bending tests were performed to measure the flexural modulus, strength, and post-yield displacement. There was no difference in cortical thickness or density between anterior or posterior quadrants; however, density was consistently higher in the middle diaphysis. Interestingly, bending modulus and strength were higher in anterior quadrants compared to posterior quadrants. Together, our results suggest that there is a differential spatial response of bone in terms of elastic bending modulus and mechanical strength. The origins of this difference may lie within the variation in ongoing mineralization, in combination with the collagen-rich plexiform structure, and whether this is related to strain mode remains to be explored. These data suggest that in young ovine cortical bone, modulation of strength occurs via potentially complex interactions of both mineral and collagen-components that may be different in regions of bone exposed to variable amounts of strain. Further work is needed to confirm the physiological load state of bone during growth to better elucidate the degree to which these variations are a function of the local mechanical environment.

Heterogeneity in mechanical properties of cortical bone for the selection and design of anatomic site-specific nanoparticle reinforced bone tissue engineering scaffold

Bone tissue has the potential to self-heal and renew, but large-scale bone abnormalities caused by infection, trauma, or any malignancy shall require intervention from external sources. To mimic the host tissue i.e., bone mechanical properties, the scaffolds for bone tissue engineering are designed. However, the host tissue mechanical properties are anatomic site-specific as per the location where a scaffold has to be implanted to facilitate tissue regeneration. This is because of the heterogeneous and hierarchical structure of bone that consists of mineral nano-particles, water, collagenous protein, etc. which makes bone a more complex material. Fabricating nano-scaffolds becomes a challenging task that can resemble the bone properties in form of biological, chemical, or mechanical. As a result, it is required to examine the change in mechanical properties of a bone throughout the site to build efficient nano-scaffolds for tissue engineering/bone regeneration. The mechanical characteristics of cortical bone were investigated at three diaphysis regions of the femoral cortical bone under tension and compression stress. The obtained mechanical properties have been compared statistically using a t-test at p < 0.05 and found a statistical difference in the mechanical properties for different diaphysis locations. The findings of this research may be helpful for the researchers working on the design of nanoparticle-based composite biomaterials to mimic the anatomic site-specific mechanical properties of bone for tissue engineering applications.

Can guided wave ultrasound predict bone mechanical properties at the femoral neck in patients undergoing hip arthroplasty?

The bone quality of patients undergoing hip replacement surgery is poorly predicted by radiographs alone. With better bone quality information available to a surgeon, the operation can be performed more safely. The aim of this study was to investigate whether ultrasound signals of cortical bone at peripheral sites such as the tibia and radius can be used to predict the compressive mechanical properties of cortical bone at the femoral neck.We recruited 19 patients undergoing elective hip arthroplasty and assessed the radius and tibia of these patients with the Azalée guided wave ultrasound to estimate the porosity and thickness of the cortex. Excess bone tissues were collected from the femoral neck and the compressive mechanical properties of the cortex were characterised under a mechanical loading rig to determine stiffness, ultimate strength, and density. The correlations between the ultrasound measurements and mechanical properties were analysed using linear regression, Pearson correlation statistics, and multiple regression analysis.Cortical mechanical properties were weakly to moderately correlated with the ultrasound measurements at various sites (R2 = 0.00–0.36). The significant correlations found were not consistent across all 4 peripheral measurement sites. Additionally, weak to moderate ability of the ultrasound to predict mechanical properties at the neck of femur with multiple regression analysis was found (R2 = 0.00–0.48). Again, this was inconsistent across the different anatomical sites. Overall, the results demonstrate the need for ultrasound scans to be collected directly from clinically relevant sites such as the femoral neck due to the inconsistency of mechanical properties across various sites.

Type I Diabetes Mellitus and Insulin Therapy on Bone Microarchitecture, Composition and Mechanical Properties

The aim of this study was to evaluate the microarchitecture, composition and mechanical properties of cortical bone of rats with type I diabetes mellitus (TIDM) and submitted to insulin therapy (IT). Thirty rats were divided into three groups (n=10): non-diabetic, diabetic and diabetic+insulin. TIDM was induced by intravenous injection of streptozotocin. In diabetic+insulin group, 4IU insulin was administered twice per day (1I U at 7 am and 3I U at 7 pm). The animals were euthanized five weeks after TIDM induction; the tibiae were removed and submitted to microcomputed tomography (micro-CT, 8 μm), fourier transform infrared spectroscopy (FTIR) and dynamic microhardness indentation. Micro-CT analysis showed that diabetic group had lower bone surface/tissue volume ratio (BS/BV) (p=0.018), cortical thickness (Ct.Th) (p<0.001) and degree of anisotropy (Ct.DA) (p=0.034) values compared to non-diabetic group. The diabetic group showed lower Ct.Th than diabetic + insulin group (p=0.018). The non-diabetic group had lower fractal dimension (Ct.FD) values compared to diabetic groups (p<0.001). The ATR-FTIR analyses showed lower values for all measured parameters in the diabetic group than the non-diabetic group (amide I ratio: p=0.046; crystallinity index: p=0.038; matrix:mineral ratios - M:MI: p=0.006; M:MIII: p=0.028). The diabetic+ insulin group showed a lower crystallinity index (p=0.022) and M:MI ratio (p=0.002) than nondiabetic and diabetic groups, respectively. The diabetic group showed lower Vickers hardness values than non-diabetic (p<0.001) and diabetic+insulin (p=0.003) groups. TIDM negatively affects bone microarchitecture, collagen maturation, mineralization and bone microhardness. Moreover, insulin minimized the effect of TIDM on cortical thickness and organic/mineral matrix.

Mechanical Characterisation and Numerical Modelling of TPMS-Based Gyroid and Diamond Ti6Al4V Scaffolds for Bone Implants: An Integrated Approach for Translational Consideration.

Additive manufacturing has been used to develop a variety of scaffold designs for clinical and industrial applications. Mechanical properties (i.e., compression, tension, bending, and torsion response) of these scaffolds are significantly important for load-bearing orthopaedic implants. In this study, we designed and additively manufactured porous metallic biomaterials based on two different types of triply periodic minimal surface structures (i.e., gyroid and diamond) that mimic the mechanical properties of bone, such as porosity, stiffness, and strength. Physical and mechanical properties, including compressive, tensile, bending, and torsional stiffness and strength of the developed scaffolds, were then characterised experimentally and numerically using finite element method. Sheet thickness was constant at 300 μm, and the unit cell size was varied to generate different pore sizes and porosities. Gyroid scaffolds had a pore size in the range of 600–1200 μm and a porosity in the range of 54–72%, respectively. Corresponding values for the diamond were 900–1500 μm and 56–70%. Both structure types were validated experimentally, and a wide range of mechanical properties (including stiffness and yield strength) were predicted using the finite element method. The stiffness and strength of both structures are comparable to that of cortical bone, hence reducing the risks of scaffold failure. The results demonstrate that the developed scaffolds mimic the physical and mechanical properties of cortical bone and can be suitable for bone replacement and orthopaedic implants. However, an optimal design should be chosen based on specific performance requirements.

The multiscale meso-mechanics model of viscoelastic cortical bone.

Cortical bone is a complex hierarchical structure consisting of biological fiber composites with transversely isotropic constituents, whose microstructures deserve extensive study to understand the mechanism of living organisms and explore development of biomimetic materials. Based on this, we establish a three-level hierarchical structure from microscale to macroscale and propose a multiscale micromechanics model of cortical bone, which considers Haversian canal, osteonal lamellae, cement line and interstitial lamellae. In order to study the microstructural effect on the elastic behavior of hierarchical structures, the Mori-Tanaka model and locally exact homogenization theory are introduced for the homogenization of heterogeneous materials of microstructure at each level. Within sub-microscale, Haversian canal and Osteonal lamella are treated as fiber and matrix, whose homogenization is surrounded with cement line matrix in microstructure (or what we called "osteon") for the second homogenization; finally, osteon and interstitial lamella establish the meso-structure for the third homogenization, predicting the effective moduli of cortical bone. The correctness of the model in this paper is verified against the data in literature with good agreement. Finally, the dynamic viscoelastic response of cortical bones is investigated from a multiscale perspective, where the measured data are substituted into the present models to study the hydration and aging effect on bones' stiffness and viscoelasticity. It is demonstrated that the hydration is much more influential in affecting the storage and loss moduli of cortical bone than the aging effect. We also present a few numerical investigations on microstructural material and geometric parameters on the overall mechanical properties of cortical bone.

Bioinspired laminated bioceramics with high toughness for bone tissue engineering.

For the research of biomaterials in bone tissue engineering, it is still a challenge to fabricate bioceramics that overcome brittleness while maintaining the great biological performance. Here, inspired by the toughness of natural materials with hierarchical laminated structure, we presented a directional assembly-sintering approach to fabricate laminated MXene/calcium silicate-based (L-M/CS) bioceramics. Benefiting from the orderly laminated structure, the L-M/CS bioceramics exhibited significantly enhanced toughness (2.23 MPa·m1/2) and high flexural strength (145 MPa), which were close to the mechanical properties of cortical bone. Furthermore, the L-M/CS bioceramics possessed more suitable degradability than traditional CaSiO3 bioceramics due to the newly formed CaTiSiO5 after sintering. Moreover, the L-M/CS bioceramics showed good biocompatibility and could stimulate the expression of osteogenesis-related genes. The mechanism of promoting osteogenic differentiation had been shown to be related to the Wnt signaling pathway. This work not only fabricated calcium silicate-based bioceramics with excellent mechanical and biological properties for bone tissue engineering but also provided a strategy for the combination of bionics and bioceramics.

Multiscale approach incorporating tropocollagen scale to assess the effect of molecular age-related modifications on elastic constants of cortical bone based on finite element and homogenization methods

With osteoporosis and aging, structural changes occur at all hierarchical levels of bone from the molecular scale to the whole tissue, which requires multiscale modeling to analyze the effect of these modifications on the mechanical behavior of bone and its remodeling process. In this paper, a novel hybrid multiscale model for cortical bone incorporating the tropocollagen molecule based on the combination of finite element method and different homogenization techniques was developed. The objective was to investigate the influence of age-related structural alterations that occur at the molecular level, namely the decrease in both molecular diameter (due to the loss of hydration) and number of hydrogen bonds, on mechanical properties of the bone tissue. The proposed multiscale hierarchical approach is divided in two phases: (i) in Step 0, a realistic 3D finite element model for tropocollagen was used to estimate the effective elastic properties at the molecular scale as a function of the collagen molecule’s degree of hydration (represented by its external diameter) and the number of its intramolecular hydrogen bonds, and (ii) in Steps 1–10, the effective elastic constants at the higher scales from mineralized fibril to continuum cortical bone tissue were predicted analytically using homogenization equations. The results obtained in healthy mature cortical bone at different scales are in good agreement with the experimental data and multiscale models reported in the literature. Moreover, our model made it possible to visualize the influence of the two parameters (molecular diameter and number of hydrogen bonds) that represent the main age-related alterations at the molecular scale on the mechanical properties of cortical bone, at its different hierarchical levels. Keywords: Bone aging, multiscale model, tropocollagen, cortical bone, finite element modeling, homogenization method.

Effect of osteoporosis-related reduction in the mechanical properties of bone on the acetabular fracture during a sideways fall: A parametric finite element approach.

The incidence of acetabular fractures due to low-energy falls is increasing among the geriatric population. Studies have shown that several biomechanical factors such as body configuration, impact velocity, and trochanteric soft-tissue thickness contribute to the severity and type of acetabular fracture. The effect of reduction in apparent density and elastic modulus of bone as well as other bone mechanical properties due to osteoporosis on low-energy acetabular fractures has not been investigated. The current comprehensive finite element study aimed to study the effect of reduction in bone mechanical properties (trabecular, cortical, and trabecular + cortical) on the risk and type of acetabular fracture. Also, the effect of reduction in the mechanical properties of bone on the load-transferring mechanism within the pelvic girdle was examined. We observed that while the reduction in the mechanical properties of trabecular bone considerably affects the severity and area of trabecular bone failure, reduction in mechanical properties of cortical bone moderately influences both cortical and trabecular bone failure. The results also indicated that by reducing bone mechanical properties, the type of acetabular fracture turns from elementary to associated, which requires a more extensive intervention and rehabilitation period. Finally, we observed that the cortical bone plays a substantial role in load transfer, and by increasing reduction in the mechanical properties of cortical bone, a greater share of load is transmitted toward the pubic symphysis. This study increases our understanding of the effect of osteoporosis progression on the incidence of low-energy acetabular fractures. The osteoporosis-related reduction in the mechanical properties of cortical bone appears to affect both the cortical and trabecular bones. Also, during the extreme reduction in the mechanical properties of bone, the acetabular fracture type will be more complicated. Finally, during the final stages of osteoporosis (high reduction in mechanical properties of bone) a smaller share of impact load is transferred by impact-side hemipelvis to the sacrum, therefore, an osteoporotic pelvis might mitigate the risk of sacral fracture.

Influence of bone quality and pedicle screw design on the fixation strength during Axial Pull-out test: A 2D Axisymmetric FE study.

Pedicle screw fixations are widely used to provide support and improve stability for the treatment of spinal pathologies. The effectiveness of treatment depends on the anchorage strength between the screw and bone. In this study, the influence of pedicle screw half-angle and bone quality on the displacement of fixation and stress transfer are analyzed using a 2D axisymmetric finite element model. The pedicle screw proximal half-angle is varied between 0° and 60° in steps of 10°, along with two different distal half-angles of 30° and 40°. Three bone models are considered for cancellous bone to simulate various degrees of bone quality, namely, poor, moderate and good. The mechanical properties of cortical bone are kept constant throughout the study. The material properties and boundary conditions are applied based on previous studies. Frictional contact is considered between the bone and screw. Results show that, the displacement of fixation is observed to be minimum at a proximal half angle of 0° and maximum at an angle of 60°, independent of bone quality. The highest implant displacement is observed in case of poor bone quality. All the bone model showed similar patterns of stress distribution, with high stress concentration around the first few threads. The highest peak von Mises stress is obtained at a proximal half-angle of 60°. Furthermore, the stress transfer increased with increase in proximal half-angle and bone quality, with maximum stress transfer at a proximal half-angle of 60°. It appears that, this study might aid to improve the design of pedicle screw for treatment of degenerative spinal diseases.Clinical Relevance- This study analyses the impact of bone quality on pedicle screw design.

Evaluation of mechanical properties of Ti-25Nb BCC porous cell structure and their association with structure porosity: A combined finite element analysis and analytical approach for orthopedic application.

Ti-based alloys have been commonly employed in manufacturing implants for orthopedic applications. Binary Titanium-Niobium (Ti-25Nb) alloy is a promising material for potential applications in orthopedics because of their lower elastic moduli and superior biocompatibility than the conventional Ti-based alloys. Implants with porous structures encourage bone ingrowth and reduce the effect of stress-shielding further. This study is aimed at establishing the relationship between the mechanical performance and structural parameters of porous body-centered-cubic (BCC) structures made up of Ti-25Nb (25% by wt.). Solid models of BCC porous structures were constructed (unit cell size: 2 mm; overall size: 8 × 8 × 8 mm3). Finite element analysis (FEA) of the BCC structures with porosity ranging from 29% to 79% (seven porosities) was conducted under tension, bending, and torsional loads. The Gibson-Ashby model and Exponential regression model were also employed to determine the stiffness of the above porous structures. The functional relationships between effective Young's modulus, effective yield strength, and porosity generated from both the models were found to match the FEA results well. Results indicated that porosity in the range of 50%-70% can be used to design graded porous stems to mimic the mechanical properties of cortical bone.