Mechanical Properties Of Human Bone Research Articles

Anatomic variability of the human femur and its implications for the use of artificial bones in biomechanical testing.

Aside from human bones, epoxy-based synthetic bones are regarded as the gold standard for biomechanical testing os osteosyntheses. There is a significant discrepancy in biomechanical testing between the determination of fracture stability due to implant treatment in experimental methods and their ability to predict the outcome of stability and fracture healing in a patient. One possible explanation for this disparity is the absence of population-specific variables such as age, gender, and ethnicity in artificial bone, which may influence the geometry and mechanical properties of bone. The goal of this review was to determine whether commercially available artificial bones adequately represent human anatomical variability for mechanical testing of femoral osteosyntheses. To summarize, the availability of suitable bone surrogates currently limits the validity of mechanical evaluations of implant-bone constructs. The currently available synthetic bones neither accurately reflect the local mechanical properties of human bone, nor adequately represent the necessary variability between various populations, limiting their generalized clinical relevance.

Biomechanical validation of novel polyurethane-resin synthetic osteoporotic femoral bones in axial compression, four-point bending and torsion

In addition to human donor bones, bone models made of synthetic materials are the gold standard substitutes for biomechanical testing of osteosyntheses. However, commercially available artificial bone models are not able to adequately reproduce the mechanical properties of human bone, especially not human osteoporotic bone.To overcome this issue, new types of polyurethane-based synthetic osteoporotic bone models have been developed. Its base materials for the cancellous bone portion and for the cortical portion have already been morphologically and mechanically validated against human bone. Thus, the aim of this study was to combine the two validated base materials for the two bone components to produce femur models with real human geometry, one with a hollow intramedullary canal and one with an intramedullary canal filled with synthetic cancellous bone, and mechanically validate them in comparison to fresh frozen human bone.These custom-made synthetic bone models were fabricated from a computer-tomography data set in a 2-step casting process to achieve not only the real geometry but also realistic cortical thicknesses of the femur. The synthetic bones were tested for axial compression, four-point bending in two planes, and torsion and validated against human osteoporotic bone.The results showed that the mechanical properties of the polyurethane-based synthetic bone models with hollow intramedullary canals are in the range of those of the human osteoporotic femur. Both, the femur models with the hollow and spongy-bone-filled intramedullary canal, showed no substantial differences in bending stiffness and axial compression stiffness compared to human osteoporotic bone. Torsional stiffnesses were slightly higher but within the range of human osteoporotic femurs.Concluding, this study shows that the innovative polyurethane-based femur models are comparable to human bones in terms of bending, axial compression, and torsional stiffness.

Manufacture and property characterization of interconnected pore-gradient TPMS materials

The fabrication of interconnected pore-gradient metallic artificial implants mirroring bone structures with excellent mechanical properties is a significant challenge in biomedical applications. Utilizing selective laser melting (SLM) on stainless-steel 316 alloy, we generated four triply periodic minimal surface (TPMS) structures, integrating TiB2 nanoparticles for cell size grading of diamond structure. The resulting nanocomposite improved the mechanical properties, including nano-hardness, ultimate compressive stress and Young's modulus, compared to plain stainless-steel. These enhancements were attributed to the uniform dispersion of TiB2 nanoparticles in both grain interior and boundaries, as well as the refinement of the matrix grain structure. The incorporation of TiB2 in the interconnected pore-gradient structure effectively matched the ultimate compressive stress (223 ± 17.3 MPa) to closely match that of human cortical bone (205 ± 17.3 MPa). This technique, therefore, appears capable of overcoming existing challenges in aligning the microstructures and mechanical properties of human bones.

In-Silico Prediction of Mechanical Behaviour of Uniform Gyroid Scaffolds Affected by Its Design Parameters for Bone Tissue Engineering Applications

Due to their excellent properties, triply periodic minimal surfaces (TPMS) have been applied to design scaffolds for bone tissue engineering applications. Predicting the mechanical response of bone scaffolds in different loading conditions is vital to designing scaffolds. The optimal mechanical properties can be achieved by tuning their geometrical parameters to mimic the mechanical properties of natural bone. In this study, we designed gyroid scaffolds of different user-specific pore and strut sizes using a combined TPMS and signed distance field (SDF) method to obtain varying architecture and porosities. The designed scaffolds were converted to various meshes such as surface, volume, and finite element (FE) volume meshes to create FE models with different boundary and loading conditions. The designed scaffolds under compressive loading were numerically evaluated using a finite element method (FEM) to predict and compare effective elastic moduli. The effective elastic moduli range from 0.05 GPa to 1.93 GPa was predicted for scaffolds of different architectures comparable to human trabecular bone. The results assert that the optimal mechanical properties of the scaffolds can be achieved by tuning their design and morphological parameters to match the mechanical properties of human bone.

Preparation and properties of artificial bone with lead-free piezoelectric materials

In order to fabricate the artificial bone with high bioactive property, lead-free barium titanate (BaTiO3, BT) piezoelectric material added hydroxyapatite (HA) composites were prepared in this study. Compared with the pure HA materials, the introduction of BT can increase the electrical properties of the samples while ensuring good biological properties. The electrical properties, such as piezoelectric constant d33, hysteresis loop and dielectric spectrum were measured, respectively. The bending strength, Vickers hardness, cytotoxicity and osteogenic property of the BT/HA composites were also discussed. It is revealed that the non-toxic sample with 95 wt% BT and 5 wt% HA (95BT+5HA) has the best osteoinductivity, the piezoelectric constant d33 of which is 79.2 pC N-1. The bending strength and Vickers hardness of the 95BT+5HA sample are 138.3 MPa and 472.4, respectively, realizing the desired mechanical properties of human bones. Comprehensive analyses of various properties show that the 95BT+5HA composite can meet the requirements of artificial bone, and is expected to be a promising generation of substitute bone materials.

Outlook of magnesium alloy for rhinoplasty material

Rhinoplasty is one of the famous cosmetic surgeries all over the world, as it not only benefits congenital nasal bone dysplasia patients, but also satisfy a part of people who want to look more beautiful and perfect. The materials commonly used in current rhinoplasty are prone to failure of rhinoplasty because of autologous absorption, loosening and slipping of nasal scaffold due to poor tissue compatibility, and difficulties in secondary repair[1-2]. Biodegradable magnesium alloy material is one of the most ideal biomedical materials with great application value. Mechanically, the biodegradable magnesium alloy material has good mechanical properties, similar to the mechanical properties of human bone; the density is similar to that of human bone. Biologically, degradable magnesium alloy material has the characteristics of excellent biocompatibility, biological activity, degradation products can be easily absorbed or excreted by human tissues; degradable magnesium alloy can induce cell differentiation growth and blood vessel growth[3]. This article analyzes the possibility of using degradable magnesium alloy material as a scaffold material for rhinoplasty and suggests that this porous nasal scaffold can be prepared by 3D printing method. By using this method, a restorative nasal plastic effect can be obtained by guiding the regrowth of autologous nasal bone tissue. From a long-term perspective, the surgical results achieved by using magnesium alloy as a scaffold material for rhinoplasty are what the medical aesthetic community has been seeking. The use of biodegradable magnesium alloy as a rhinoplasty material is a new approach that is feasible and has potential for future economic and social benefits, but this approach needs further research and experiments to be validated in the future.

Properties of Additive-Manufactured Open Porous Titanium Structures for Patient-Specific Load-Bearing Implants

Additive manufacturing has been well established in many sectors, including the medical industry. For load-bearing bone implants, titanium and its alloys, such as Ti6Al4V, are widely used due to their high strength to weight ratio and osseointegrative properties. However, bone resorption and loosening of implants is related to the significantly higher stiffness of dense Ti6Al4V, leading to stress shielding. With the aging of population, there is an increasing need for orthopedic implants with a high success rate and a long implant life span. Besides that the treatment of non-healing segmental bone defects, where the self-repairing properties of bone tissue are not sufficient, is still a challenge. In both fields of application, patient-specific titanium implants combined with functionally graded porosity designed according to locally expected loads unlock new possibilities. Many studies underline the huge potential of the new design freedom to generate open porous structures and more personalized implants with enhanced mechanical properties that also integrate well with surrounding tissues. Integration of functionally graded open porosity into implants allows for the implant to more closely mimic the mechanical properties of human bone and its internal architecture. The results of this work represent the basis for developing complex porous titanium structures with various pore sizes and shapes to tailor structural mechanical properties and biological responses. Therefore, 3D porous structures with various pore sizes and shapes were designed and manufactured in Ti6Al4V using laser powder bed fusion (PBF-LB/M). Based on these structures, the correlation of pore size and shape with cell ingrowth, morphology, metabolic activity, and early markers for bone formation (ALP activity) was investigated in static cell cultures using the osteosarcoma cell line Saos-2. Mechanical properties, such as stiffness and compression strength, were investigated with compression testing. The present study concludes that cell morphology, metabolic activity, and ALP activity are widely independent of pore shape and size within the tested range of 400–700 µm pore size. Furthermore, the mechanical properties of the evaluated structures were in the range of cortical and trabecular bone. This opens the possibility to design mechanical properties with gradient porosity without decisively affecting biological responses.

The effect of eggshell as a reinforcement on the mechanical and Corrosion properties of Mg-Zn-Mn matrix composite

Magnesium is a promising lightweight metal required in many industries such as automobile, aerospace, electronics, etc. It is also a biodegradable material, which eliminates the secondary removal procedure of the implant. Furthermore, its mechanical properties are similar to the mechanical properties of human bone. In this research, eggshells were used as an environmentally friendly composite reinforcement material in the Mg-2.5Zn-1Mn matrix. Composites were prepared using the powder metallurgy route. The effect of eggshells on the morphology, mechanical, and corrosion behaviour of Mg-2.5Zn-1Mn alloy was investigated. The results revealed an enhancement in grain refining ability and mechanical properties of Mg-2.5Zn-1Mn with eggshell additives. The corrosion behaviour improved at a higher percentage of eggshells (10%).

Effect of Dipping Number on Morphology of Ta2O5 Coatings Made by Sol-Gel Method on AZ91 Mg Alloy

Yapılan çalışma, sol-jel yöntemi kullanılarak üretilen Ta2O5 kaplı AZ91 Magnezyum (Mg) alaşımlarının karakterizasyonuna yöneliktir. Mg alaşımları hafiflikleri ve insan kemiğinin mekanik özelliklerine yakın mekanik özellikleri nedeni ile ortopedik uygulamalarda kullanım açısından ciddi bir potansiyele sahiptir. Fakat korozyon dayanımları vücut içinde uzun süreli kullanımlar için yetersiz kalmaktadır. Tantal (Ta) ise yüzeyinde oluşan oksit tabakası sayesinde korozyon dayanımı çok yüksek olan ve vücut için toksik etki yaratmayan bir elementtir. Yapılan çalışmada toz metalurji yöntemi ile üretilen AZ91 Mg alaşımları üzerine sol-jel yöntemi ile farklı daldırma sayılarında Ta2O5 kaplanması ve daldırma sayılarındaki bu değişimin kaplamaların morfolojisine etkisinin incelenmesi amaçlanmıştır. Numuneler farklı daldırma sayılarında kaplandıktan sonra morfolojilerindeki değişim elektron mikroskobu (SEM-EDS) ve X-ışını kırınımı (XRD) kullanılarak incelenmiştir. Çalışmanın sonucunda sol-jel yönteminde karşılaşılan çatlaklı yapılarda, adacıklar arası mesafelerin kısaldığı gözlemlenmiştir. Artan daldırma sayısı ile ortalama 1, 3 ve 7 µm kalınlıklarda kaplama tabakasına sahip numuneler üretilmiş ve yüzeyde daha homojen bir kaplama yapısı oluşumu sağlanmıştır.

Additively Manufactured Absorbable Porous Metal Implants – Processing, Alloying and Corrosion Behavior

Treating large bone defects is still a clinical challenge without perfect solution, mainly due to the unavailability of suitable bone implants. Additively manufactured (AM) absorbable porous metals provide unparalleled opportunities to realize the challenging requirements for bone-mimetic implants. Firstly, multi-scale geometries of such implants can be customized to mimic the micro-architecture and mechanical properties of human bone. The interconnected porous structure additionally increases the surface area to facilitate adhesion and proliferation of bone cells. Finally, their absorption properties are tunable to maintain the structural integrity of the implant throughout the bone healing process, ensuring sufficient loadbearing when needed and full disintegration after their job is done. Such a combination of properties paves the way for complete bone regeneration and remodeling. It is important to thoroughly characterize the biodegradation behavior, mechanical properties, and bone regeneration ability when developing ideal porous absorbable metal implants. We review the state-of-the-art of absorbable porous metals manufactured by selective laser melting (SLM), with a focus on geometrical design, material type, processing, and post-treatment. The impact of the latter aspects on absorption behavior, resulting mechanical properties, and cytocompatibility will also be briefly discussed. In comparison to their solid inert counterparts, AM absorbable porous metals (APMs) have shown many unique properties and hold tremendous potential to further optimize their application-specific performance due to their flexible geometrical design. We further highlight challenges in adopting AM APMs for future Orthopedic solutions.

On the Microstructural and Cyclic Mechanical Properties of Pure Iron Processed by Electron Beam Melting

Additive manufacturing (AM) processes such as electron beam melting (EBM) are characterized by unprecedented design freedom. Topology optimization and design of the microstructure of metallic materials are enabled by rapid progress in this field. The latter is of highest importance as many applications demand appropriate mechanical as well as functional material properties. For instance, biodegradable implants have to meet mechanical properties of human bone and at the same time guarantee adequate cytocompatibility and degradation rate. In this field, pure iron has come into focus in recent studies due to its low toxicity. Hierarchical microstructures resulting from the EBM solidification processes and intrinsic heat treatment, respectively, allow for an adjustment of the degradation behavior and may promote enhanced fatigue strength. Herein, commercially pure iron (cp‐Fe) is processed by EBM. Microstructural analysis as well as an evaluation of the cyclic mechanical material properties are conducted. The results are compared to a hot‐rolled (HR) reference material. A contradiction observed as the EBM‐processed cp‐Fe (EBM Fe) shows lower ultimate tensile strength under monotonic loading but improved fatigue properties compared to the HR Fe. It is revealed that such a unique behavior originates from prevailing microstructural features in the EBM as‐built condition.

Custom-made polyurethane-based synthetic bones mimic screw cut-through of intramedullary nails in human long bones

Intramedullary nails are considered the gold standard for the treatment of tibial shaft fractures. Thereby, the screw-bone interface is considered the weakest link. For biomechanical evaluation of osteosyntheses synthetic bones are often used to overcome the disadvantages of human specimens. However, commercially available synthetic bones cannot adequately mimic the local mechanical properties of human bone. Thus, the aim of this study was to develop and evaluate novel cortical bone surrogate materials that mimic human tibial shafts in the screw-loosening mechanisms of intramedullary nails.Bone surrogates, based on two different polyurethanes, were developed and shaped as simple tubes with varying cortical thicknesses to simulate the diaphyseal cortex of human tibiae. Fresh frozen human tibiae and commercially available synthetic bones with similar cortical thickness were used as references. All specimens were treated with a nail dummy and bicortical locking screws to simulate treatment of a distal tibia shaft fracture. The nail-bone construct was loaded in a combined axial-torsional-sinusoidal loading protocol to simulate the physiological load during human gait. The loads to failure as well as the number of load cycles were evaluated. Furthermore, the cut-through length of the screws was analysed by additional micro computed -tomography images of the tested specimens.The failure load of custom made synthetic bone tubes with 6 mm cortical thickness (3242 ± 136 N) was in accordance with the failure load of human samples (3300 ± 307 N, p = 0.418) with a similar cortical thickness of 4.9 ± 1.4 mm. Commercially available synthetic bones with similar cortical thickness of 4.5 ± 0.7 mm were significantly stronger (4575 ± 795 N, p = 0.008). Oval-shaped migration patterns were “cut” into the cortices by the screws due to the cyclical loading. The cut-through length of the self-developed synthetic bones with 6 mm cortices (0.8 ± 0.6 mm, p = 0.516) matched the cut-through of the human tibiae (0.7 ± 0.6 mm). The cut-through of commercially available epoxy-based synthetic bones deviated from the human reference (0.2 ± 0.1 mm, p < 0.001).The results of this study indicate that the novel bone surrogates realistically mimic the failure and screw migration behaviour in human tibiae. Thus, they offer a new possibility to serve as substrate for biomechanical testing. The use of commercially available surrogates is discouraged for biomechanical testing as there is a risk of drawing incorrect conclusions.

Automated Polyaxial Screw Placement Using a Commercial-Robot-Based, Image-Guided Spine Surgery System

Robotic spine surgery systems, used for placing pedicle screws, have been in clinical use since 2004; however, these systems act only as a positioner for guide tubes, which the surgeon uses to manually advance tools to prepare the site and place hardware (e.g., pedicle screws). This article presents the development, operation, and evaluation of a new, commercial-robot-based, image-guided surgery system that automates the process of bone preparation and polyaxial screw placement. The system is based on the KUKA LBR iiwa 7-axis collaborative robot. Fiducial marker and screw locations are defined on a pre-operative CT image using the 3D Slicer open source image visualization platform. The system uses the robot’s internal localization system for registration, by touching fiducial markers in a hand-guiding mode. A rotary-motor end effector with exchangeable tools is used for both hole-drilling and screw placement. A novel single-motor based mechanism was developed for placing polyaxial pedicle screws. An accuracy test was performed by placing polyaxial screws in synthetic vertebrae which mimic the mechanical properties of human bone. In placing 10 screws, the entry point accuracy was 0.49 ± 0.17 mm and the destination point accuracy was 1.49 ± 0.46 mm. The results compare favorably to evaluations of commercial robotic spine surgery systems.

Synthesis and characterization of an open-pore toxic-element-free Ti-based bulk metallic glass foam for bio-implant application

A series of porous toxic-element-free Ti42Zr40Si15Ta3 bulk metallic glass with 13–54 vol.% porosity are produced via powder metallurgy by the space holder method. The amorphous nature, foam morphology, mechanical properties, electrochemical response in simulation body fluid and in-vivo biocompatibility responses are systematically investigated. Results show that these open-cell Ti-based bulk metallic glass foams (BMGFs) exhibit yield strength from 140 to 730 MPa and Young’s moduli from 8 to 53 GPa, matching very well with the mechanical properties of human bone and the estimated data by theoretical models. Compared to the bulk metallic glass (BMG) of the same composition, the high exposed surface area of the produced Ti-based BMGFs exhibited higher current in the cyclic voltammetry (CV) and potential state tests. However, no specific peak corresponding to the oxidation or reduction response of the composition elements is found in the electrochemical test. Moreover, the six-month in-vivo tests in New Zealand white rabbits shows that the good osteo-integration between the newly growth bone and the implanted Ti-based BMGFs, making them promising new candidates for bio-implant applications in avoiding stress shielding or bio-unfriendly symptoms.

Diagonal-symmetrical and Midline-symmetrical Unit Cells with Same Porosity for Bone Implant: Mechanical Properties Evaluation

In this study, mechanical properties of bionic porous structures with diagonal-symmetrical and midline-symmetrical unit cells were studied when the porosities were same. Three typical unit cells (Diamond (DO), Rhombic Dodecahedron (RD), and Octet Truss (OT)) were selected, in which DO has diagonal-symmetrical shape, while RD and OT share midline-symmetrical structure. Based on the same porosity, corresponding models were designed, and Ti6Al4V samples were manufactured by electron beam melting. Then, using Mechanical Properties Testing (MPT) and Finite Element Analysis (FEA) methodologies, mechanical properties and transmissions of different porous structures were evaluated. Besides, composition and details before and after printing were analyzed with Energy Dispersive Spectrometer (EDS), X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). MPT results showed that midline-symmetrical shape would have superior compressive performance than diagonal-symmetrical shape, but opposite trend for the torsion performance, which were in line with FEA prediction. Furthermore, effective modulus of DO, RD and OT were 2.59 GPa, 4.89 GPa, and 1.77 GPa, approximating the mechanical properties of human bones. Additionally, manufacturing defects and discrepancies between FEA and MPT were found. This study would provide great helps for unit cell selection and initial mechanical properties matching for optimum bone implants.

A viscoelastic system for determining acoustical and mechanical parameters of the bone

Human bones are energy absorbing complex composite structures that have an irregular hollow structure filled with marrow and surrounded by soft tissue and muscles. To date, no satisfactory evidence exists either supporting or refuting the usefulness of vibro-acoustic technique to determine the acoustical and mechanical parameters of the bone. The aim of the paper is to use acoustic wave propagation techniques and viscoelastic bone system to analyse and assess the acoustical and mechanical properties of human bone which may be used to monitor the bone condition and diagnose the osteoporosis at an early stage, by demonstrating if variations in sound propagation through the bone can be detected.

Mechanical behaviours and mass transport properties of bone-mimicking scaffolds consisted of gyroid structures manufactured using selective laser melting

Bone scaffolds created in porous structures manufactured using selective laser melting (SLM) are widely used in tissue engineering, since the elastic moduli of the scaffolds are easily adjusted according to the moduli of the tissues, and the large surfaces the scaffolds provide are beneficial to cell growth. SLM-built gyroid structures composed of 316L stainless steel have demonstrated superior properties such as good corrosion resistance, strong biocompatibility, self-supported performance, and excellent mechanical properties. In this study, gyroid structures of different volume fraction were modelled and manufactured using SLM; the mechanical properties of the structures were then investigated under quasi-static compression loads. The elastic moduli and yield stresses of the structures were calculated from stress-strain diagrams, which were developed by conducting quasi-static compression tests. In order to estimate the discrepancies between the designed and as-produced gyroid structures, optical microscopy and micro-CT scanner were used to observe the structures’ micromorphology. Since good fluidness is conducive to the transport of nutrients, computational fluid dynamics (CFD) values were used to investigate the pressure and flow velocity of the channel of the three kinds of gyroid structures. The results show that the sizes of the as-produced structures were larger than their computer aided design (CAD) sizes, but the manufacturing errors are within a relatively stable range. The elastic moduli and yield stresses of the structures improved as their volume fractions increased. Gyroid structure can match the mechanical properties of human bone by changing the porosity of scaffold. The process of compression failure showed that 316L gyroid structures manufactured using SLM demonstrated high degrees of toughness. The results obtained from CFD simulation showed that gyroid structures have good fluidity, which has an accelerated effect on the fluid in the middle of the channel, and it is suitable for transport nutrients. Therefore, we could predict the scaffold's permeability by conducting CFD simulation to ensure an appropriate permeability before the scaffold being manufactured. SLM-built gyroid structures that composed of 316L stainless steel were suitable to be designed as bone scaffolds in terms of mechanical properties and mass-transport properties, and had significant promise.

Analysis of Compression and Permeability Behavior of Porous Ti6Al4V by Computed Microtomography

Porous materials were developed as a good alternative to replace different bones in the human body as they improve osseointegration, tissue ingrowth and simulate the mechanical properties of human bones. Such characteristics highly depend on the pore features and volume fraction. Samples with a pore volume fraction between 16 and 60% and a pore size distribution of 100–500 µm were analyzed by computed microtomography. 3D images acquisition was performed at 10 µm pixel resolution, which permitted to observe the complete sample. Features like size, shape, orientation, connectivity and pore coordination were determined from the 3D image analysis. Compression behavior was evaluated by interrupted compression testing and, after that, new 3D images were acquired. In order to evaluate permeability, numerical simulations of flow throughout the 3D images were carried out by using Avizo® software. It was found that shape and pore size distribution was similar in all samples, showing good distribution of the pore formers inside the matrix. Full connectivity of pores was obtained with 32% volume fraction and above, and the coordination number follows the Artz model. The pores showed a radial orientation, which induces anisotropy in the flow properties. The compression showed two different behaviors, pore closing and pore coalescence. Values of permeability match with those reported for bones as well as the anisotropy in the radial and vertical directions. It is concluded that the sample with 60 vol% of pores could be consider to be used for bone implants.

Axial and shear pullout forces of composite, porcine and human metatarsal and cuboid bones

ObjectivesThe varying mechanical properties of human bone have influence on the study results. Pullout and shear forces of human bone were compared to different substitutes to evaluate their suitability for biomechanical studies. MethodsAfter bone mineral density (BMD) determination, axial pullout tests were performed with cortical 3.5 mm nonlocking (NL) and 2.7 mm head locking (HL) screws on human, porcine and polyurethane composite bones. Porcine and human constructs were additionally loaded in shear direction. ResultsApparent BMD was significantly lower in osteoporotic (159 mgHA/ccm ± 56) and nonosteoporotic (229 mgHA/ccm ± 25) human bone than that in porcine bone (325 mgHA/ccm ± 42; p < 0.01). Axial construct stiffness and ultimate pullout force of porcine bone (NL: 666N/mm ± 226, 910N ± 140; HL: 309N/mm ± 88, 744N ± 185) was significantly different from composite bone (NL: 1284N/mm ± 161; 1175N ± 116; HL: 1241N/mm ± 172, 1185N ± 225) and osteoporotic human bone (NL: 204N/mm ± 121, 185N ± 113; HL: 201N/mm ± 65; 189N ± 58) but not from nonosteoporotic human bone (NL: 620N/mm ± 205, 852N ± 281; HL: 399N/mm ± 224; 567N ± 242). Porcine bone exhibited an ultimate shear force (NL: 278N ± 99; HL: 431N ± 155) comparable to nonosteoporotic human bone (NL: 207 ± 68: HL: 374N ± 137). ConclusionScrew pullout and shear forces of porcine bone are close to nonosteoporotic human bone. The translational potential of this articleHuman bone specimens used in biomechanical studies are predominantly of osteoporotic bone quality. Conclusions on nonosteoporotic human bone behaviour are difficult. Alternatives such as porcine bone and composite bone were investigated, and it could be shown that screw pullout and screw shear forces of porcine bone are close to nonosteoporotic human bone.

Multiscale modeling of human bone

A multiscale modeling technique was developed to predict mechanical properties of human bone, which utilizes the hierarchies of human bone in different length scales from nanoscale to macroscale. Bone has a unique structure displaying high stiffness with minimal weight. This is achieved through a hierarchy of complex geometries composed of three major materials: hydroxyapatite, collagen and water. The identifiable hierarchical structures of bone are hydroxyapatite, tropocollagen, fibril, fiber, lamellar layer, trabecular bone, cancellous bone and cortical bone. A helical spring model was used to represent the stiffness of collagen. A unit cell-based micromechanics model computed both the normal and shear stiffness of fibrils, fibers, and lamellar layers. A laminated composite model was applied to cortical and trabecular bone, while a simplified finite element model for the tetrakaidecahedral shape was used to evaluate cancellous bone. Modeling bone from nanoscale components to macroscale structures allows the influence of each structure to be assessed. It was found that the distribution of hydroxyapatite within the tropocollagen matrix at the fibril level influences the macroscale properties significantly. Additionally, the multiscale analysis model can vary any parameter of any hierarchical level to determine its effect on the bone property. With so little known about the detailed structure of nanoscale and microscale bone, a model encompassing the complete hierarchy of bone can be used to help validate assumptions or hypotheses about those structures.