Mechanical Properties Of Cancellous Bone Research Articles

Data-Driven Based Characterization of Anisotropic Mechanical Properties for Cancellous Bone From Low-Resolution CT Images.

Exploring the anisotropic mechanical behavior of cancellous bone is crucial for in-vivo bone biomechanical analysis. However, it is challenging to characterize anisotropic mechanical behaviors under low-resolution (LR) clinical CT images due to a lack of microstructural information. The data-driven method proposed in this article accurately characterizes the anisotropic mechanical properties of cancellous bone from LR clinical CT images. The trabecular bone cubes of sheep are used to obtain a high-resolution (HR) micro-CT and an LR clinical CT image dataset. First, an auto-encoder model is trained using HR image data. Microstructural features are extracted by the encoder. A fast super-resolution (FSR) model is trained to map LR bone cubes to the features extracted from corresponding HR samples. The pretrained FSR model is used to convert LR clinical CT images to encoded microstructural features. The features are later used to predict target histomorphological parameters, anisotropic elastic tensors, and fabric tensors based on a fully connected neural network. The data-driven model accurately predicts the elastic tensor and fabric tensor of trabecular bones with LR CT images with 0.6 mm/pixel spatial resolution. It was verified that LR clinical CT images could generate microstructural information using a generative deep-learning model and an up-sampling operation. This study proves that clinical medical images of cancellous bone can be used for analysis of complex mechanical properties using a data-driven method, which is useful for real-time bone defect diagnosis and personalized bone prosthesis design in clinical application.

Mechanical parameter assessment of fresh human cancellous bone of the femoral head in atraumatic femoral head necrosis and primary coxarthrosis

BackgroundAtraumatic femoral head necrosis is a rare pathological change of the femoral head. It is characterized by local necrosis of the cancellous bone as a result of reduced blood supply to the bone. Even today it remains unclear how to assess the hardness of the necrosis, whether it is soft tissue that is easily removed, or hard tissue that is difficult to resect. MethodsFemoral heads with primary coxarthrosis were selected as a comparison group. For this purpose, 49 femoral heads obtained during total hip arthroplasty surgery with either condition (23 femoral head necrosis, 26 coxarthrosis) were transferred to the testing laboratory in fresh condition. Cylindrical specimens were obtained using a tenon cutter along the main trabecular load direction in the subchondral region of the femoral head. Additionally, thin bone slices were extracted proximal and distal to the specimens for density measurements. Brass plates were glued to the circular surfaces of the specimens. After curing of the adhesive, the specimens were mounted in the testing machine and destructive uniaxial compression tests were conducted. FindingsThe recorded mean compressive strengths and elastic moduli were almost identical for both groups, but the necrosis group showed significantly higher data scattering and range regarding the elastic modulus. The mean density of the coxarthrosis specimens was significantly higher than that of the necrotic specimens. InterpretationThe mechanical properties of cancellous bone vary considerably in the presence of femoral head necrosis. The existence of hard necrosis implies a potential challenge regarding the clinical resection of these tissues.

Effects of Donepezil on the Musculoskeletal System in Female Rats.

The extension of human life makes it more and more important to prevent and treat diseases of the elderly, including Alzheimer's disease (AD) and osteoporosis. Little is known about the effects of drugs used in the treatment of AD on the musculoskeletal system. The aim of the present study was to investigate the effects of donepezil, an acetylcholinesterase inhibitor, on the musculoskeletal system in rats with normal and reduced estrogen levels. The study was carried out on four groups of mature female rats: non-ovariectomized (NOVX) control rats, NOVX rats treated with donepezil, ovariectomized (OVX) control rats and OVX rats treated with donepezil. Donepezil (1 mg/kg p.o.) was administered for four weeks, starting one week after the ovariectomy. The serum concentrations of CTX-I, osteocalcin and other biochemical parameters, bone mass, density, mineralization, histomorphometric parameters and mechanical properties, and skeletal muscle mass and strength were examined. Estrogen deficiency increased bone resorption and formation and worsened cancellous bone mechanical properties and histomorphometric parameters. In NOVX rats, donepezil decreased bone volume to tissue volume ratio in the distal femoral metaphysis, increased the serum phosphorus concentration and tended to decrease skeletal muscle strength. No significant bone effects of donepezil were observed in OVX rats. The results of the present study indicate slightly unfavorable effects of donepezil on the musculoskeletal system in rats with normal estrogen levels.

Relationship between mechanical and microstructural parameters of rat lumbar spine in different ages

Exploring the relationships between microstructure and mechanical properties of bones may provide effective suggestions for increasing bone strength and reducing osteoporotic fracture. In this research, the tissue-level mechanical parameters, microstructure parameters of cancellous bone, and apparent mechanical parameters of L6 vertebral body were calculated in female SD rats aged 1-, 3-, 5-, 7-, 9-, 11-, 13-, 15-, 16-, and 17-month-old. Data were processed with Kruskal–Wallis test, linear regression and Spearman’s rank correlation analysis. Appropriately increasing the plate Tb.N could enhance mechanical properties of bone. Tb.Th and Tb.N were two key factors in determining the tissue-level mechanical properties of cancellous bone. The microstructure could significantly predict mechanical parameters. Our findings may help to further understand the mechanism of osteoporotic fractures.

Selected mechanical properties of human cancellous bone subjected to different treatments: short-term immersion in physiological saline and acetone treatment with subsequent immersion in physiological saline

BackgroundPhysiological saline (0.9% NaCl) and acetone are extensively used for storage (as well as hydration) and removal of bone marrow, respectively, of cancellous bone during preparation and mechanical testing. Our study aimed to investigate the mechanical properties of cancellous bone subjected to short-term immersion in saline and acetone treatment with subsequent immersion in saline.MethodsCylindrical samples (Ø6 × 12 mm) were harvested from three positions (left, middle, and right) of 1 thoracic vertebral body, 19 lumbar vertebral bodies, and 5 sacral bones, as well as from 9 femoral heads. All samples were divided into two groups according to the different treatments, (i) samples from the left and middle sides were immersed in saline at 4℃ for 43 h (saline-immersed group, n = 48); (ii) samples from the respective right side were treated with a combination of acetone and ultrasonic bath (4 h), air-dried at room temperature (21℃, 15 h), and then immersed in saline at room temperature (21℃, 24 h) (acetone and saline-treated group, n = 38). All samples were subjected, both before and after treatment, to a non-destructive compression test with a strain of 0.45%, and finally destructive tests with a strain of 50%. Actual density (ρact), initial modulus (E0), maximum stress (σmax), energy absorption (W), and plateau stress (σp) were calculated as evaluation indicators.ResultsBased on visual observation, a combination of acetone and ultrasonic bath for 4 h failed to completely remove bone marrow from cancellous bone samples. The mean values of ρact, σmax, W, and σp were significantly higher in the femoral head than in the spine. There was no significant difference in E0 between non-treated and saline-immersed samples (non-treated 63.98 ± 20.23 vs. saline-immersed 66.29 ± 20.61, p = 0.132). The average E0 of acetone and saline-treated samples was significantly higher than that of non-treated ones (non-treated 62.17 ± 21.08 vs. acetone and saline-treated 74.97 ± 23.98, p = 0.043).ConclusionShort-term storage in physiological saline is an appropriate choice and has no effect on the E0 of cancellous bone. Treatment of cancellous bone with acetone resulted in changes in mechanical properties that could not be reversed by subsequent immersion in physiological saline.

Mechanical Behaviour of Cancellous bone: Compression and Three-Point Bending Test

The mechanical properties of cancellous bone are fundamental in providing structural support and flexibility during physical activities. Characterization of cancellous bone properties and its mechanical behaviour were found crucial as information of the elastic and failure properties of the tissue may potentially be used to study the effects of drug treatments, aging and disease at the tissue level. This study aims to present the difference of mechanical properties of cancellous bone between compressive and three-point bending loads. Cancellous bone specimens from the femoral and tibial condyles of bovines were mechanically tested using three-point bending test and compression test and correlated with morphological parameters such as bone volume fraction and porosity. From the results, significant difference of mechanical properties was found between cancellous bone specimens tested with compressive and three-point bending load. From compressive load, the maximum stress reached 4.2 MPa, whereas in three-point bending, maximum flexural stress reached 17.0 MPa. Cancellous bone strength was found to be much higher when tested with three-point bending load, although correlations with morphological parameters such as bone volume fraction (BV/TV) and porosity were found lower compared to that in compressive load. In conclusion, there are no correlation between compression and three-point bending with morphology indices (BV/TV and porosity).

Fabrication of porous TiO2 foams by powder metallurgy technique and study of bulk crushing strength for biomedical application.

Despite the importance of porous titanium oxide (PA-TiO2) in diverse functional applications, very little information is available on the compatible mechanical properties for potential biomedical applications. In this study, PA-TiO2 foam was synthesized using space-holding powder metallurgy and sintering methods to produce interconnected opened-cell structure with surface morphology of mountain-like features associated with the extensive rift valley system. Three different types of PA-TiO2 foams with porosities of 35-52% and mean pore diameter of 190-210μm were fabricated for evaluating the effect of porosity on mechanical properties of bulk PA-TiO2. The modulus of elasticity of PA-TiO2 foams exhibited in the range of 45-262MPa which was within the range of modulus of elasticity of human cancellous bone. Cytotoxicity test is performed in vitro analysis to observe the effect of cell toxicity to produce osteointegration when used as implantable materials. There was no cytotoxicity effect found and remarkable cell growth was observed for human cancerous (HeLa) cell line. However, there was no cytotoxicity effect found and cell growth was not observed for Vero cell line. This study suggested that PA-TiO2 facilitates cell growth without spreading toxicity and has mechanical properties of cancellous bone. Hence, it has potential application as implant and medical devices in biomedical applications.

Characteristics and structure of porous TNM alloy for biomedical applications

In this study, a biomedical porous Ti–5Nb–5Mo (TNM) alloy was fabricated by mechanical alloying (MA), with ball milling times of 3 h, 15 h and 30 h. The particle sizes of Ti–5Nb–5Mo increased as the milling times increased from 3 h (35 μm) to 15 h (72 μm). The ball milling process produced alloy particles that gathered together, resulting in a larger overall particle size. The ball milled Ti–5Nb–5Mo particles were significantly refined, and Nb and Mo were integrated into and uniformly distributed within the matrix. XRD analysis showed that the porous Ti–5Nb–5Mo sample was composed of α phase. The compressive strength and modulus of all the porous Ti–5Nb–5Mo sample matched the necessary mechanical properties of cancellous bones; in particular, the B3S15 specimen (balling 3 h and sintering 10 h) had the highest strength and was selected for bioactivity and cytocompatibility testing. After soaking in a simulated body fluid for 4 days, the alkali-heat treated porous B3S10 alloy formed a dense apatite layer on its surface. The specimen exhibited better apatite-forming ability, and its surface proved beneficial to the spread, proliferation, and differentiation of osteoblast-like cells. This result confirms that both a porous structure and alkali heat treatment are favorable for cell growth. Most importantly, this study reveals that porous TNM satisfies the requirements demanded by an implant material: an adequate mechanical strength and elastic modulus, and good biocompatibility.

Characterization of Ultralow Density Cellular Solids: Lessons from 30 years of Bone Biomechanics Research.

Advances in additive manufacturing techniques have enabled the development of micro-architectured materials displaying a combination of low-density and lightweight structures with high specific strength and toughness. The mechanical performance of micro-architectured materials can be assessed using standard techniques; however, when studying low- and ultralow density micro-architectured materials, standard characterization techniques can be subject to experimental artifacts. Additionally, quantitative assessment and comparisons of microarchitectures with distinct lattice patterns is not always straightforward. Cancellous bone is a natural, ultralow density (porosity often exceeding 90%), irregular, cellular solid that has been thoroughly characterized in terms of micro-architecture and mechanical performance over the past 30 years. However, most the literature on cancellous bone mechanical properties and micro-structure-function relationships is in the medical literature and is not immediately accessible to materials designers. Here we provide a brief review of state-of-the-art approaches for characterizing the micro-architecture and mechanical performance of ultralow density cancellous bone, including methods of addressing experimental artifacts during mechanical characterization of ultralow density cellular solids, methods of quantifying microarchitecture, and currently understood structure-function relationships.

Negligible Effect of Estrogen Deficiency on Development of Skeletal Changes Induced by Type 1 Diabetes in Experimental Rat Models.

Although postmenopausal osteoporosis often occurs concurrently with diabetes, little is known about interactions between estrogen deficiency and hyperglycemia in the skeletal system. In the present study, the effects of estrogen deficiency on the development of biochemical, microstructural, and mechanical changes induced by streptozotocin-induced diabetes mellitus (DM) in the rat skeletal system were investigated. The experiments were carried out on nonovariectomized (NOVX) and ovariectomized (OVX) control and diabetic mature female Wistar rats. Serum levels of bone turnover markers (CTX-I and osteocalcin) and 23 cytokines, bone mass and mineralization, histomorphometric parameters, and mechanical properties of cancellous and compact bone were determined. The results were subjected to two-way ANOVA and principal component analysis (PCA). Estrogen deficiency induced osteoporotic changes, with increased bone resorption and formation, and worsening of microstructure (femoral metaphyseal BV/TV decreased by 13.0%) and mechanical properties of cancellous bone (the maximum load in the proximal tibial metaphysis decreased by 34.2%). DM in both the NOVX and OVX rats decreased bone mass, increased bone resorption and decreased bone formation, and worsened cancellous bone microarchitecture (for example, the femoral metaphyseal BV/TV decreased by 17.3% and 18.1%, respectively, in relation to the NOVX controls) and strength (the maximum load in the proximal tibial metaphysis decreased by 35.4% and 48.1%, respectively, in relation to the NOVX controls). Only in the diabetic rats, profound increases in some cytokine levels were noted. In conclusion, the changes induced by DM in female rats were only slightly intensified by estrogen deficiency. Despite similar effects on bone microstructure and strength, the influence of DM on the skeletal system was based on more profound systemic homeostasis changes than those induced by estrogen deficiency.

Misalignment Error in Cancellous Bone Apparent Elastic Modulus Depends on Bone Volume Fraction and Degree of Anisotropy.

Cancellous bone is an anisotropic structure with architectural and mechanical properties that vary due to both skeletal site and disease state. This anisotropy means that, in order to accurately and consistently measure the mechanical properties of cancellous bone, experiments should be performed along the primary mechanical axis (PMA), that is, the orientation in which the mechanical properties are at their maximum value. Unfortunately, some degree of misalignment will always be present, and the magnitude of the resulting error is expected to be architecture dependent. The goal of this work is to quantify the dependence of the misalignment error, expressed in terms of change in apparent elastic modulus (ΔE), on both the bone volume fraction (BV/TV) and the degree of anisotropy (DA). Finite element method (FEM) models of bovine cancellous bone from five different skeletal sites were created at 5 deg and 20 deg from the PMA determined for each region. An additional set of models was created using image dilation/erosion steps in order to control for BV/TV and better isolate the effect of DA. Misalignment error was found to increase with increasing DA and decreasing BV/TV. At 5 deg misaligned from the PMA, error is relatively low (<5%) in all cases but increases to 8-24% error at 20 deg. These results suggest that great care is needed to avoid introducing misalignment error into experimental studies, particularly when studying regions with high anisotropy and/or low bone volume fraction, such as vertebral or osteoporotic bone.

Identification of effective elastic modulus using modal analysis; application to canine cancellous bone

Mechanical properties of cancellous bone is of increasing interest due to its involvement in aging pathologies and oncology. Characterization of fragile bone tissue is challenging and available methodologies include quasi-static compressive tests of small size specimens, ultrasound and indentation techniques. We hypothesized that modal analysis of flexure beams could be a complementary methodology to obtain Young modulus.The sampling methodology was adapted such that the uniqueness of the linear dynamic response was available to determine the elastic modulus from natural frequencies and mode shapes. In a first step, the methodology was validated using a synthetic bone model as control. Then, water-jet cutting allowed collecting fourteen small beam-like specimens in canine distal femurs. X-ray microtomography confirmed the microarchitecture preservation, the homogeneity and the isotropy at the specimen scale to derive effective properties. The first natural frequency in clamped-free boundary conditions was used to obtain mean values of Young modulus, which ranged from 210 MPa to 280 MPa depending on the specimen collection site. Experimental tests were rapid and reproducible and our preliminary results were in good agreement with literature data. In conclusion, beam modal analysis could be considered for exploring mechanical properties of fragile and scarce biological tissues.

Bone mineral density, mechanical properties, and trabecular orientation of cancellous bone within humeral heads affected by advanced shoulder arthropathy.

The mechanical properties of cancellous bone in the humeral head are increasingly interesting due to the increased popularity of stemless prosthetic fixation in the cancellous bone of the metaphysis. Age or pathology‐related systemic osteoporosis, inactivity, or pathology of the shoulder joint may influence the primary bonding of implants that rely on good cancellous bone quality. We assessed the bone mineral density (BMD) and anisotropy using micro‐computed tomography (micro‐CT) (0.04 mm voxel size) and correlated the results with indentation load/displacement response. Resected parts of humeral heads (from patients undergoing total shoulder replacement, n = 18) were used as probes. The region of interest was defined as 2 mm medial from the resection plane, presuming that it mirrored the bone quality lateral to the resection plane. The indentation tests were performed with a large probe (diameter 10 mm) in a single destructive loading procedure. The BMD and trabecular orientation were determined by micro‐CT. Our results showed a correlation between the BMD and the slope of the load/displacement curve. Furthermore, the trabeculae were predominantly oriented orthogonal to the joint surface. In conclusion, the predominant factor determining the bone quality and mechanical resistance to pressure appears to be the BMD, while trabecular orientation could not be related to load/displacement response. Statement of clinical significance: Bone quality predominately determines the mechanical properties of cancellous bone. This might be crucial when prosthetic implants need to be anchored in metaphyseal bone. Therefore, clinical decision‐making processes should also include local BMD measurements.

Anisotropic and strain rate-dependent mechanical properties and constitutive modeling of the cancellous bone from piglet cervical vertebrae

Background and objectiveCharacterizing the mechanical properties of the cancellous bone from the cervical vertebrae of child or child surrogate is important for the development of spine finite element models and the investigation of injury mechanism, however, there is currently no public data available as far as we know. MethodsCompression tests were conducted on the specimens from the cervical vertebrae of 8-week-old piglets (child surrogates) in axial and radial directions at the strain rates of 0.01, 0.1, 1 and 10/s. The influences of directionality and strain rate on the mechanical properties of the vertebral cancellous bone were statistically investigated. The typical transversely isotropic model, which was added a strain rate item and a plasticity item, was implemented into LS-DYNA finite element code. Based on the material subroutine code, simulation was conducted on the vertebral tissue under compression in axial and radial directions at different strain rates. ResultsThe mechanical properties of the cancellous bone of cervical vertebrae were obtained and most of the stress-strain curves showed major linear elastic stage and short plastic stage before fracture. Significant anisotropic behavior was observed for the vertebral tissue in axial and radial directions. The elastic modulus, ultimate stress,yield stress, and ultimate strain of the speimens in axial direction was obtained, with on average, 2.5 ± 0.6 times, 2.1 ± 0.15 times, and 2.1 ± 0.1 times higher and 0.86 ± 0.076 times lower respecitvely, than those in radial direction. In addition, with the strain rate varying from 0.01/s to 10/s, the mechanical parameters, like elastic modulus, yield and ultimte stresses exhibited significant strain rate effect, however, no significant difference was found for the ultimate strain. ConclusionsThe cervical vertebrae showed significant anisotropic and strain rate-dependent behaviors. The self-developed subroutine codes based on the strain rate-dependent transversely isotropic elastic and plastic constitutive model can simulate the behaviors well.

Nanocomposite-coated porous templates for engineered bone scaffolds: a parametric study of layer-by-layer assembly conditions

Using the layer-by-layer (LbL) assembly technique to deposit mechanically reinforcing coatings onto porous templates is a route for fabricating engineered bone scaffold materials with a combination of high porosity, strength, and stiffness. LbL assembly involves the sequential deposition of nano- to micro-scale multilayer coatings from aqueous solutions. Here, a design of experiments (DOE) approach was used to evaluate LbL assembly of polyethyleneimine (PEI), polyacrylic acid (PAA), and nanoclay coatings onto open-cell polyurethane foam templates. The thickness of the coatings, and the porosity, elastic modulus and collapse stress of coated foam templates were most strongly affected by the pH of PAA solutions, salt concentration, and interactions between these factors. The mechanical properties of coated foams correlated with the thickness of the coatings, but were also ascribed to changes in the coating properties due to the different assembly conditions. A DOE optimization aimed to balance the trade-off between higher mechanical properties but lower porosity of foam templates with increasing coating thickness. Micromechanical modeling predicted that deposition of 116 QLs would achieve mechanical properties of cancellous bone (>0.05 GPa stiffness and >2 MPa strength) at a suitable porosity of >70%. When capped with a final layer of PAA and cross-linked via thermal treatment, the PEI/PAA/PEI/nanoclay coatings exhibited good indirect cytotoxicity with mesenchymal stem cells. The ability of LbL assembly to deposit a wide range of functional constituents within multilayer-structured coatings makes the general strategy of templated LbL assembly a powerful route for fabricating engineered tissue scaffolds that can be applied onto various porous template materials to achieve a wide range of properties, pore structures, and multifunctionality.

Decoupled effects of bone mass, microarchitecture and tissue property on the mechanical deterioration of osteoporotic bones

Based on the theory of composite mechanics, a three-pillar framework “bone mass-microarchitecture-tissue property” instead of “bone mass-bone quality”, is proposed to quantitively characterize the mechanical deterioration of osteoporotic cancellous bones related to the three aspects, and accordingly the individual and integrative influences of bone mass, microarchitecture and tissue property on the mechanical properties of cancellous bones are investigated via the μCT-based finite element method (FEM) simulations of bone samples from healthy and ovariectomy-induced osteoporosis mice. Comparisons among the healthy, mild osteoporotic and severe osteoporotic bones clearly show that the healthy bones have a larger bone volume density and an optimized architecture exhibiting longitudinal superiority able to more efficiently resist the daily loadings which are commonly along their longitudinal direction, while osteoporosis does not only significantly reduce the bone volume density but also greatly deteriorate the microarchitectural topology, resulting in a distinct reduction in the magnitude of effective Young's moduli and a breakdown of the longitudinal superiority as well. Furthermore, through modeling in silico we decoupled the three major factors to probe into their individual effects on the mechanical deterioration of osteoporotic bones. It was found that sole bone loss would exponentially decrease the effective Young's moduli of cancellous bones, microarchitecture plays a dominant role in defining the anisotropic characteristics of bones such as the longitudinal superiority; and change of tissue property seems having a slight and linear influence on the effective Young's moduli of cancellous bones.

Combining ultrasonic and computed tomography scanning to characterize mechanical properties of cancellous bone in necrotic human femoral heads

Image-based finite element modelling has been commonly used to determine the biomechanical behaviours of human femora, particularly for the diagnosis of femoral head necrosis. One of the fundamental aspects of biomechanical modelling is the relationship between bone density, which is obtained from images, and elastic modulus. While there exist some empirical equations relating density with elastic modulus, the characterization of this relationship remains incomplete, especially for necrotic femoral heads. The objective of this study was to determine the relationship between density and elastic modulus by combining ultrasonic scanning and computed tomography (CT). Bone specimens were surgically removed from the femora of eight persons (seven females and one male in the age range of 55–68 years old) and underwent both ultrasonic and CT scanning. The images were processed with MATLAB scripts, and a bilinear interpolation algorithm was used to determine the relationship between the CT-measured densities and ultrasound-measured elastic moduli. The results showed different density–elastic modulus relations between the hardening strap of the necrotic region and non-hardening strap areas of the necrotic region. The uniqueness of this study is the characterization of mechanical properties (in the present study, the density–modulus relationship) from clinical images, which would be valuable in computational biomechanics used for the diagnosis and treatment evaluation of femoral head necrosis.

Effect of porosity variation strategy on the performance of functionally graded Ti-6Al-4V scaffolds for bone tissue engineering

Functionally graded scaffold (FGS) is designed to mimic the morphology, mechanical and biological properties of natural bone closely. Porosity variation strategy between different regions in FGS plays a crucial role in influencing its mechanical and biological performance. A combination of modeling tool and scripting language can effectively enhance the ability to optimize FGS design. This study was aimed at determining the effect of porosity variation strategy on the mechanical performance and permeability of the as-built and as-heat-treated FGSs. Ti-6Al-4V FGSs with sizes of 10 × 10 × 15 mm and diamond lattice structures were designed and fabricated by means of selective laser melting. A wide range of porosities in the FGSs (38–75%) were achieved by applying six different porosity variation strategies. The elastic modulus (3.7–5.7 GPa) and yield strength (27.1–84.7 MPa) of the as-built FGSs were found to vary between the corresponding mechanical properties of cancellous bone and cortical bone. Heat treatment reduced the strengths by 13–56%. Porosity variation strategy strongly affected the deformation behavior and failure mechanisms of the FGSs. The sigmoid function-controlled FGSs showed gradual failure behavior and sample Sigk0.5b8 showed superior overall performance. The results demonstrated that porosity variation strategy is a feasible means for tailor design of FGS.

Photopolymerization for filling porous ceramic matrix: Improvement of mechanical properties and drug delivering behavior

This work presents the photopolymerisation of composite scaffolds where a prefabricated ceramic scaffold was impregnated with poly(ethylene) glycol dimethacrylate (PEGDMA) macromonomer solution. The PEGDMA solution penetrates the porosity of ceramic scaffold where it cures in situ thereby enhancing their mechanical properties. The mechanical properties of the obtained composite approximate the mechanical properties of cancellous bone. The Young´s Modulus of the composite developed is 106 ± 5 MPa. PEGDMA is a polymer that shows excellent percentages of gel fraction (96%), which preserves when ceramic scaffold is introduced, and swelling (134%). Furthermore, thanks to their swelling properties, the composite is able to control the release vancomycin and dexamethasone. The efficacy of in situ delivery of vancomycin is demonstrated by the inhibition of bacteria colony proliferation. Dexamethasone released is recorded for up to 10 days using ultra violet‐visible spectroscopy. These excellent results make photopolymerization and PEGDMA strong candidates for the manufacture of different loaded bone void fillers. POLYM. COMPOS., 40:1654–1662, 2019. © 2018 Society of Plastics Engineers

Mechanical properties of cancellous bone from the acetabulum in relation to acetabular shell fixation and compared with the corresponding femoral head

To gain initial stability for cementless fixation the acetabular components of a total hip replacement are press-fit into the acetabulum. Uneven stiffness of the acetabular bone will result in irregular deformation of the shell which may hinder insertion of the liner or lead to premature loosening. To investigate this, we removed bone cores from the ilium, ischium and pubis within each acetabulum and from selected sites in corresponding femoral heads from four cadavers for mechanical testing in unconfined compression. From a stress-relaxation test over 300 s, the residual stress, its percentage of the initial stress and the stress half-life were calculated. Maximum modulus, yield stress and energy to yield (resilience) were calculated from a load-displacement test. Acetabular bone had a modulus about 10–20%, yield stress about 25% and resilience about 40% of the values for the femoral head. The stress half-life was typically between 2–4 s and the residual stress was about 60% of peak stress in both acetabulum and femur. Pubic bone was mechanically the poorest. These results may explain uneven deformation of press-fit acetabular shells as they are inserted. The measured half-life of stress-relaxation indicates that waiting a few minutes between insertion of the shell and the liner may allow seating of a poorly congruent liner.