Properties Of Human Cortical Bone Research Articles

Novel bioactive and biocompatible alumina-wollastonite porous constructs mimicking physical properties of human cortical bone

A new procedure for the bioactivation of alumina-based porous ceramic constructs was introduced. The constructs were built with the aim of mimicking the structural and mechanical properties of the human cortical bone. Bioactivation was achieved by adding wollastonite and acidic surface treatment (piranha solution). Structural studies (SEM, CAT) confirmed that adequate pore size and interconnectivity were obtained. Uniaxial compression tests showed that the values of Young’s moduli and compressive strength were reduced, from 5 to 1 GPa, and from 45 to 15 MPa, respectively, as the wollastonite content increased from 0 to 40 wt.%. Proliferative, histological and fluorescence results confirmed that cell proliferation rate of bone-marrow-derived mesenchymal stem cells were significantly enhanced by increasing wollastonite content. No cytotoxic effect was observed. In summary, the fabricated bioceramics exhibited suggestive structural and mechanical properties and they could be useful for the practical bone tissue engineering applications without any adverse biological effects.

Orientation of carbon fiber in magnesium-doped hydroxyapatite and its effect on mechanical and tribological properties of carbon fiber reinforced composites

Carbon fiber (CF) reinforced magnesium-doped hydroxyapatite (Mg-HA) composites have been shown possess excellent mechanical performance and tailored biological properties. In order to further explore the effect of the orientation for short CF reinforced Mg-HA composites for mechanical and tribological properties. Micro-sized CF was oriented in Mg-HA by a self-developed mold and highly oriented CF reinforced magnesium doped hydroxyapatite (OCF/Mg-HA) composites were prepared by spark plasma sintering (SPS). The morphology, structure, wettability, mechanical properties and tribological properties of the composites were investigated. The results show that the average contact angle of oriented CF/Mg-HA composites was 67.65° and had good hydrophilicity. Compressive strength of OCF/Mg-HA in the direction parallel to the fiber was 129.8 MPa, which met the requirements of mechanical properties of human cortical bone. In addition, the wear resistance of OCF/Mg-HA ceramics was significantly improved by the addition of CF. The average friction coefficient of OCF/Mg-HA ceramics in the direction parallel to the fiber was 0.157. OCF/Mg-HA ceramics exhibited excellent tribological properties and mechanical properties which were close to that of human load-bearing bone due to the oriented arrangement of CF. This laid a foundation for the clinical application of OCF/Mg-HA ceramics in the repair of bone defects at load-bearing sites.

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

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

Design of a Novel Trabecular Acetabular Cup and Selective Laser Melting Fabrication.

The acetabular cups used in total hip arthroplasty are mostly made of dense metal materials with an elastic moduli much higher than that of human bone. This leads to stress shielding after implantation, which may cause aseptic loosening of the implant. Selective laser melting (SLM) technology allows us to produce tiny and complex porous structures and to reduce the elastic moduli of dense metals, thereby avoiding stress shielding. In the present study, rhombic dodecahedron porous structures with cell sizes of 1 mm, 1.5 mm, and 2 mm were designed. The strut diameter was changed to ensure that the porosity and pore size would meet the bone ingrowth requirements. Then, porous Ti6Al4V alloy specimens were printed using SLM, and compressive tests were carried out. The results showed that the compressive strength and elastic modulus values of the specimens with a cell size of 1.5 mm were in the range of 78.16–242.94 MPa and 1.74–4.17 GPa, respectively, which are in line with the mechanical properties of human cortical bone. Finite element analysis of a total hip joint model was carried out to simulate gait, and the surface of the trabecular acetabular cup was divided into 10 regions according to the stress distribution, with the stress interval in the range of 37.44–219.24 MPa. According to the compression test results, the gradient structure of Ti6Al4V alloy with different porosity was designed for trabecular coating. The gradient porous structure meets the mechanical requirements and is closer to the natural structure of human bone than the uniformly distributed porous structure.

Water bound to hydroxyproline is correlated with post-yield mechanical properties of human cortical bone

Water bound to hydroxyproline is correlated with post-yield mechanical properties of human cortical bone

Raman spectroscopic determination of bone matrix quantity and quality augments prediction of human cortical bone mechanical properties

Being independent contributors to bone mechanical resistance at the apparent level, quality and quantity of bone primary constituents are essential factors in better fracture risk assessment. Raman spectroscopy (RS) holds great potential for being a clinical tool with providing quality and quantity measurements of the bone mineralized matrix. Beyond mineral quality and quantity, recent years have revealed newly developed RS-derived bone compositional measurements focusing on organic matrix and water though their associations with bone mechanics have not been fully established yet. Herein, the author reported first thorough characterization study investigating associations between twenty different RS-derived measurements and mechanical properties of human cortical bone (i.e., yield and ultimate strength, elastic modulus, toughness, post-yield toughness, and post-yield strain). Forty-five rectangular human cortical beams harvested from all four anatomical quadrants of two male donors were tested under three-point bending. Raman spectra of each specimen were collected at the spectral range of 800 to 4000 cm−1. While correlations were tested among RS-derived measurements via Spearman’s rank correlations, multivariate linear regression using mixed effects were used to determine the best RS-derived measurement or the combination of RS-derived measurements in predicting various mechanical properties of human cortical bone. Most of the RS-derived measurements were associated with the mechanical properties (Rm2 ranges from 8.9 to 68.3%, p < 0.05). The various linear combinations of six RS-derived measurements focusing on different aspects of bone matrix (i.e., ν1PO4/Amide I, ν1PO4/Amide III, Carbonate/ν1PO4, ~I1670/I1640, ~I3453/I2949, ~I3584/I2949) improved the prediction (Rm2 = 43.5 to 70.2%, p < 0.05). While a causal relationship still needs to be investigated, RS has a great potential to establish a robust patient-specific fracture risk prediction with the latest advances in technologies.

Optimization of Two-Dimensional Finite Element on Primary Bone Type-7 Fracture Model

Optimization works is an important method for Finite Element (FE) analysis to get better accuracy in simulation study before proceed for further analysis. In this present work, convergence study of local crack tip meshing involving radius of first row element, a/n (DELR) and number of crack tip element (NTHET) is employed on single edge crack in homogenous properties of human cortical bone. Mode I and Mode II Type -7 penetration were determined by using FE analysis and compared with the experimental results. Based on the results, a good agreement is found between numerical and experimental results. The first section in your paper

Correlations of cortical bone microstructural and mechanical properties with water proton fractions obtained from ultrashort echo time (UTE) MRI tricomponent T2* model.

Mechanical and microstructural evaluations of cortical bone using ultrashort echo time magnetic resonance imaging (UTE-MRI) have been performed increasingly in recent years. UTE-MRI acquires considerable signal from cortical bone and enables quantitative bone evaluations. Fitting bone apparent transverse magnetization (T2*) decay using a bicomponent model has been regularly performed to estimate bound water (BW) and pore water (PW) in the quantification of bone matrix and porosity, respectively. Human cortical bone possesses a considerable amount of fat, which appears as MRI T2* signal oscillation and can subsequently lead to BW overestimation when using a bicomponent model. Tricomponent T2* fitting model has been developed to improve BW and PW estimations by accounting for fat contribution in the MRI signal. This study aimed to investigate the correlations of microstructural and mechanical properties of human cortical bone with water pool fractions obtained from a tricomponent T2* model. 135 cortical bone strips (~4 × 2 × 40 mm3 ) from tibial and femoral midshafts of 37 donors (61 ± 24 years old) were scanned using ten sets of dual-echo 3D-UTE-Cones sequences (TE = 0.032-24.0 ms) on a 3 T MRI scanner for T2* fitting analyses. Average bone porosity and pore size were measured using microcomputed tomography (μCT) at 9 μm voxel size. Bone mechanical properties were measured using 4-point bending tests. Using a tricomponent model, bound water fraction (FracBW ) showed significant strong (R = 0.70, P < 0.01) and moderate (R = 0.58-0.62, P < 0.01) correlations with porosity and mechanical properties, respectively. Correlations of bone microstructural and mechanical properties with water pool fractions were higher for tricomponent model results compared with the bicomponent model. The tricomponent T2* fitting model is suggested as a useful technique for cortical bone evaluation where the MRI contribution of bone fat is accounted for.

In Vitro-Induced High Sugar Environments Deteriorate Human Cortical Bone Elastic Modulus and Fracture Toughness.

Advanced glycation end-products (AGEs) have been suggested to contribute to bone fragility in type 2 diabetes (T2D). AGEs can be induced through in vitro sugar incubations but there is limited data on the effect of total fluorescent AGEs on mechanical properties of human cortical bone, which may have altered characteristics in T2D. Thus, to examine the effect of AGEs on bone directly in T2D patients with uncontrolled sugar levels, it is essential to first understand the fundamental mechanisms by studying the effects of controlled in vitro-induced AGEs on cortical bone mechanical behavior. Here, human cortical bone specimens from female cadaveric tibias (ages 57-87) were incubated in an in vitro 0.6 M ribose or vehicle solution (n = 20/group) for 10 days at 37°C, their mechanical properties were assessed by microindentation and fracture toughness tests, and induced AGE levels were quantified through a fluorometric assay. Results indicated that ribose-incubated bone had significantly more AGEs (+81%, p ≤ 0.005), lower elastic modulus assessed by traditional microindentation, and lower fracture toughness compared with vehicle controls. Furthermore, based on pooled data, increased AGEs were significantly correlated with deteriorated mechanical properties. The findings presented here show that the accumulation of AGEs allows for lower stiffness and increased ability to initiate a crack in human cortical bone. Statement of clinical significance: High sugar levels as in T2D results in deteriorated bone quality via AGE accumulation with a consequent weakening in bone's mechanical integrity. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:972-983, 2020.

Ribose pre-treatment can protect the fatigue life of γ-irradiation sterilized bone.

Structural bone allografts are often sterilized with γ-irradiation to decrease infection risk, which unfortunately degrades the bone collagen connectivity, making the bone weak and brittle. In previous studies, we successfully protected the quasi-static mechanical properties of human cortical bone by pre-treating with ribose, prior to irradiation. This study focused on the quasi-static and fatigue tensile properties of ribose treated irradiated sterilized bone allografts. Seventy-five samples were cut from the mid-shaft diaphysis of human femurs into standardized dog-bone shape geometries for quasi-static and fatigue tensile testing. Specimens were prepared in sets of three adjacent specimens. Each set was made of a normal (N), irradiated (I) and ribose pre-treated+irradiation (R) group. The R group was incubated in a 1.2M ribose solution before γ-irradiation. The quasi-static tensile and decalcified tests were conducted to failure under displacement control. The fatigue samples were tested under cyclic loading (10Hz, peak stress of 45MP, minimum-to-maximum stress ratio of 0.1) until failure or reaching 10 million cycles. Ribose pre-treatment significantly improved significantly the mechanical properties of irradiation sterilized human bone in the quasi-static tensile and decalcified tests. The fatigue life of the irradiated group was impaired by 99% in comparison to the normal control. Surprisingly, the R-group has significantly superior properties over the I-group and N-group (p < 0.01, p < 0.05) (> 100%). This study shows that incubating human cortical bone in a ribose solution prior to irradiation can indeed improve the fatigue life of irradiation-sterilized cortical bone allografts.

Manipulating the Amount and Structure of the Organic Matrix Affects the Water Compartments of Human Cortical Bone.

Being predictors of the mechanical properties of human cortical bone, bound and pore water measurements by magnetic resonance (MR) imaging are being developed for the clinical assessment of fracture risk. While pore water is a surrogate of cortical bone porosity, the determinants of bound water are unknown. Manipulation of organic matrix properties by oxidative deproteinization, thermal denaturation, or nonenzymatic glycation lowers bone toughness. Because bound water contributes to bone toughness, we hypothesized that each of these matrix manipulations affect bound water fraction (Vbw/Vbone). Immersing cadaveric bone samples in sodium hypochlorite (NaClO) for 96 hours did not affect tissue mineral density or cortical porosity, but rather decreased Vbw/Vbone and increased short‐T2 pore water signals as determined by 1H nuclear MR relaxometry (1H NMR). Moreover, the post treatment Vbw/Vbone linearly correlated with the remaining weight fraction of the organic matrix. Heating bone samples at 110°C, 120°C, 130°C, and then 140°C (∼24 hours per temperature and rehydration for ∼24 hours before 1H NMR analysis) did not affect Vbw/Vbone. After subsequently heating them at 200°C, Vbw/Vbone increased. Boiling bone samples followed by heating at 110°C, 120°C, and then 130°C in water under pressure (8 hours per temperature) had a similar effect on Vbw/Vbone. Raman spectroscopy analysis confirmed that the increase in Vbw/Vbone coincided with an increase in an Amide I subpeak ratio that is sensitive to changes in the helical structure of collagen I. Glycation of bone by ribose for 4 weeks, but not in glucose for 16 weeks, decreased Vbw/Vbone, although the effect was less pronounced than that of oxidative deproteinization or thermal denaturation. We propose that MR measurements of bound water reflect the amount of bone organic matrix and can be modulated by collagen I helicity and by sugar‐derived post translational modifications of the matrix. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Development of a novel method for the strengthening and toughening of irradiation-sterilized bone allografts.

Reconstruction of large skeletal defects is a significant and challenging issue. Bone allografts are often used for such reconstructions. However, sterilizing bone allografts by using γ-irradiation, damages collagen and causes the bone to become weak, brittle and less fatigue resistant. In a previous study, we successfully protected the mechanical properties of human cortical bone by conducting a pre-treatment with ribose, a natural and biocompatible agent. This study focuses on examining possible mechanisms by which ribose might protect the bone. We examined the mechanical properties, crosslinking, connectivity and free radical scavenging potentials of the ribose treatment. Human cortical bone beams were treated with varying concentration of ribose (0.06-1.2M) and γ-irradiation before testing them in 3-point bending. The connectivity and amounts of crosslinking were determined with Hydrothermal-Isometric-Tension testing and High-Performance-Liquid-Chromatography, respectively. The free radical content was measured using Electron Paramagnetic Resonance. Ribose pre-treatment improved the mechanical properties of irradiation sterilized human bone in a pre-treatment concentration-dependent manner. The 1.2M pre-treatment provided >100% of ultimate strength of normal controls and protected 76% of the work-to-fracture (toughness) lost in the irradiated controls. Similarly, the ribose pre-treatment improved the thermo-mechanical properties of irradiation-sterilized human bone collagen in a concentration-dependent manner. Greater free radical content and pentosidine content were modified in the ribose treated bone. This study shows that the mechanical properties of irradiation-sterilized cortical bone allografts can be protected by incubating the bone in a ribose solution prior to irradiation.

Strain rate influence on human cortical bone toughness: A comparative study of four paired anatomical sites

Bone fracture is a major health issue worldwide and consequently there have been extensive investigations into the fracture behavior of human cortical bone. However, the fracture properties of human cortical bone under fall-like loading conditions remains poorly documented. Further, most published research has been performed on femoral diaphyseal bone, whereas it is known that the femoral neck and the radius are the most vulnerable sites to fracture. Hence, the aim of this study is to provide information on human cortical bone fracture behavior by comparing different anatomical sites including the radius and the femoral neck acquired from 32 elderly subjects (50 – 98 y.o.). In order to investigate the intrinsic fracture behavior of human cortical bone, toughness experiments were performed at two different strain rates: standard quasi-static conditions, and a higher strain rate representative of a fall from a standing position. The tests were performed on paired femoral neck, femoral, tibial and radius diaphyseal samples. Linear elastic fracture toughness and the non-linear J-integral method were used to take into account both the elastic and non-elastic behavior of cortical bone. Under quasi-static conditions, the radius presents a significantly higher toughness than the other sites. At the higher strain rate, all sites showed a significantly lower toughness. Also, at the high strain rate, there is no significant difference in fracture properties between the four anatomical sites. These results suggest that regardless of the anatomical site (femur, femoral neck, tibia and radius), the bone has the same fracture properties under fall loading conditions. This should be considered in biomechanical models under fall-like loading conditions.

The incorporation of fluoride and strontium in hydroxyapatite affects the composition, structure, and mechanical properties of human cortical bone.

Strontium ranelate and fluoride salts are therapeutic options to reduce fracture risk in osteoporosis. Incorporation of these elements in the physiological hydroxyapatite matrix of bone is accompanied by changes in bone remodeling, composition, and structure. However, a direct comparison of the effectiveness of strontium and fluoride treatment in human cortical bone with a focus on the resulting mechanical properties remains to be established. Study groups are composed of undecalcified specimens from healthy controls, treatment-naïve osteoporosis cases, and strontium ranelate or fluoride-treated osteoporosis cases. Concentrations of both elements were determined using instrumental neutron activation analysis (INAA). Backscattered electron imaging was carried out to investigate the calcium content and the cortical microstructure. In comparison to osteoporotic patients, fluoride and strontium-treated patients have a lower cortical porosity indicating an improvement in bone microstructure. Mechanical properties were assessed via reference point indentation as a measure of bone's resistance to deformation. The strontium-incorporation led to significantly lower total indentation distance values compared to osteoporotic cases; controls have the highest resistance to indentation. In conclusion, osteoporosis treatment with strontium and fluoride showed positive effects on the microstructure and the mechanical characteristics of bone in comparison to treatment-naïve osteoporotic bone. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 433-442, 2017.

Recent advances in resonant ultrasound spectroscopy to measure bone stiffness tensor

Resonant Ultrasound Spectroscopy (RUS) is a method to measure the elasticity tensor of a material. RUS is particularly advantageous to measure small samples of anisotropic materials. In RUS, resonant frequencies of a sample are measured and computed frequencies of a numerical model of the sample are fitted, yielding the stiffness tensor. RUS was developed in the 1990s, but until recently, it was in practice limited to measure materials with a high quality factor. We have adapted the method to measure bone whose quality factor is about 25. Our strategy combines Bayesian methods to retrieve overlapped resonant peaks in the RUS spectra and to solve the inverse problem using a limited number of resonant frequencies. The method allows a quasi-automated processing of RUS spectra where it is not necessary to know a priori the pairing between measured and computed frequencies. In the last years we have extensively used RUS to document the anisotropic elastic properties of human cortical bone and to investigate the determinants of elastic properties. We present in this talk 1) recent advances in signal processing for RUS; 2) a discussion on the precision of bone elasticity measurement; and 3) a new perspective regarding cortical bone elasticity determinants.

Combined effect of magnesia and zirconia on the bioactivity of calcium silicate ceramics at C\\S ratio less than unity

This paper describes the effect of magnesia in the presence of zirconia on the bioactivity, microstructure and physico-mechanical properties of calcium silicate composition adjusted at calcia/silica ratio(C/S) of 0.5. A mixture from calcium carbonate and silica was conducted at C/S of 0.5. 20wt.% of magnesia and 5-25wt.% of ZrO2 were added. Each mixture was mixed with ethanol in a planetary ball mill, dried, formed and fired at a temperature of 1325±5°C. Phase composition, FE-SEM, and physico-mechanical properties of the fired specimens were determined and explained. The in vitro bioactivities of these specimens were investigated by analysis of their abilities to form apatite in the simulated body fluid (SBF) for a short time (7days) using SEM-EDS. The findings indicated that the surface of the specimens containing 5 and 15wt.% ZrO2 were completely covered by single and multilayered hydroxyapatite (HA) precipitate typical to “cauliflower” morphology, respectively. The surface of the specimen containing 25wt.% ZrO2 did not cover, but there are some scattered HA precipitate. The differences among the results were rationalized based on the phase composition. Vickers hardness and fracture toughness of the specimens of highly promised bioactivity were 2.32–2.57GPa and 1.80–1.50MPa. m1/2, respectively. The properties of these specimens are similar to the properties of human cortical bone. Consequently, these composites might be used as bone implant materials.

Effects of high-dose gamma irradiation on tensile properties of human cortical bone: Comparison of different radioprotective treatment methods

There are growing interests in the radioprotective methods that can reduce the damaging effects of ionizing radiation on sterilized bone allografts. The aim of this study was to investigate the effects of 50kGy (single dose, and fractionated) gamma irradiation, in presence and absence of l-Cysteine (LC) free radical scavenger, on tensile properties of human femoral cortical bone. A total of 48 standard tensile test specimens was prepared from diaphysis of femurs of three male cadavers (age: 52, 52, and 54 years). The specimens were assigned to six groups (n=8) according to different irradiation schemes, i.e.; Control (Non-irradiated), LC-treated control, a single dose of 50kGy (sole irradiation), a single dose of 50kGy in presence of LC, 10 fractions of 5kGy (sole irradiation), and 10 fractions of 5kGy in presence of LC. Uniaxial tensile tests were carried out to evaluate the variations in tensile properties of the specimens. Fractographic analysis was performed to examine the microstructural features of the fracture surfaces. The results of multivariate analysis showed that fractionation of the radiation dose, as well as the LC treatment of the 50kGy irradiated specimens, significantly reduced the radiation-induced impairment of the tensile properties of the specimens (P<0.05). The fractographic observations were consistent with the mechanical test results. In summary, this study showed that the detrimental effects of gamma sterilization on tensile properties of human cortical bone can be substantially reduced by free radical scavenger treatment, dose fractionation, and the combined treatment of these two methods.

Zirconia Effect on the Bioactivity and the Mechanical Properties of Calcium Magnesium Silicate Ceramics at (CaO+MgO)/SiO2 Molar Ratio Close to Unity

New ceramic composites from calcia-magnesia-silica system at a molar ratio of (CaO-MgO)/SiO2 closes to the unity and the addition of different amounts of zirconia (5 wt %, 15 wt % and 25 wt %) have been investigated. These systems powders were formed and fired at 1310 ± 20°C for 2 hr. Phase composition, microstructure, physical and mechanical properties of these composites were determined. The in-vitro bioactivities of these sintered composites were investigated by analysis of their ability for the formation of hydroxyapatite (HA) using SEM-EDS after their soaking in the simulated body fluid (SBF) for 7 days. The findings indicated that beginning of HA formation on the surface of all investigated composites. However, the composite containing 5 wt % ZrO2 gave clear tendency toward the formation-ability of HA typical to cauliflower morphology. The mechanical properties of the promised bioactive composite in term of Vickers hardness and fracture toughness were ~3 Gpa and ~2 Mpa. m1/2, respectively. The ceramic composite containing 5 wt % ZrO2 might be nominated to be implanted material because their property is quite similar to the properties of human cortical bone.

Influence of short-term fixation with mixed formalin or ethanol solution on the mechanical properties of human cortical bone

Abstract Bone specimens obtained for biomechanical experiments are fresh-frozen for storage to slow down tissue degradation and autolysis in long-term storage. Alternatively, due to infectious risks related to the fresh tissues, fixative agents are commonly used. However, fixatives will likely change the mechanical properties of bone. Existing studies on this issue gave controversial results that are hardly comparable due to a variety of measurement approaches. For this reason, the influence of ethanol and a formalin-based fixative agent was evaluated on the mechanical properties of human cortical bone specimens by means of four-point-bending tests. 127 prismatic specimens with rectangular cross sections (2.5 x 2.5 x 20 mm3) were obtained from different regions of two fresh human femora (medial, lateral, dorsal, ventral). Specimens were either fixed in ethanol or in a mixed formalin solution or frozen following a given scheme. After two weeks of storage the samples were re-hydrated in isotonic saline and subsequently tested mechanically. The elastic bending modulus and ultimate bending strength were computed considering the actual dimensions of each specific specimen. For statistical analysis a one-way-ANOVA and an LSD post-hoc-test were performed. For ultimate bending strength no significant differences due to formalin or ethanol fixation, as compared to unfixed-fresh bone specimens could be found. And only for few cases significant differences in elastic bending modulus were observed when the two bones were evaluated separately. Since more differences of significant level due to the anatomical region of the samples were determined, the original location seems to have more influence on the evaluated mechanical properties than the method of (chemical) fixation. Consequently, ethanol and the mixed formalin solution can be recommended as a fixation agent for samples in biomechanical testing, if these samples are rinsed in isotonic saline prior to static mechanical testing.

Effects of bone density in the time-dependent mechanical properties of human cortical bone by nanoindentation

Effects of bone density in the time-dependent mechanical properties of human cortical bone by nanoindentation