Analysis of bone tissue mechanical properties

This paper deals with the torsional moment depending on the angle of torsion of the compact bone in laboratory animals and humans. Based on the data from laboratory animals, obtained by measurement, the data on dependence of the torsional moment and the angle of torsion were assumed for humans. Measurements were carried out on four groups of compact bone in laboratory animals. One was the control group, and three other groups were treated by various vitamin D3 metabolites. Equal measurements were performed in only one group of compact bone in humans, due to the impossibility to treat humans with vitamin D3 metabolites. Functional relations between the angle of torsion and the torsional moment for all groups of animal body tissue were determined by measurements, and the results were used to assume the reaction of human compact bone tissue if treated by vitamin D3 metabolites.     

Effects of tissue preservation temperature on high strain-rate material properties of brain

Postmortem preservation conditions may be one of factors contributing to wide material property variations in brain tissues in literature. The objective of present study was to determine the effects of preservation temperatures on high strain-rate material properties of brain tissues using the split Hopkinson pressure bar (SHPB). Porcine brains were harvested immediately after sacrifice, sliced into 2 mm thickness, preserved in ice cold (group A, 10 samples) and 37°C (group B, 9 samples) saline solution and warmed to 37°C just prior to the test. A SHPB with tube aluminum transmission bar and semi-conductor strain gauges were used to enhance transmitted wave signals. Data were gathered using a digital acquisition system and processed to obtain stress-strain curves. All tests were conducted within 4 h postmortem. The mean strain-rate was 2487±72 s(-1). A repeated measures model with specimen-level random effects was used to analyze log transformed stress-strain responses through the entire loading range. The mean stress-strain curves with ±95% confidence bands demonstrated typical power relationships with the power value of 2.4519 (standard error, 0.0436) for group A and 2.2657 (standard error, 0.0443) for group B, indicating that responses for the two groups are significantly different. Stresses and tangent moduli rose with increasing strain levels in both groups. These findings indicate that storage temperatures affected brain tissue material properties and preserving tissues at 37°C produced a stiffer response at high strain-rates. Therefore, it is necessary to incorporate material properties obtained from appropriately preserved tissues to accurately predict the responses of brain using stress analyses models, such as finite element simulations.     

Effects of hydration on mechanical properties of a highly sclerotized tissue

The jaws of the bloodworm Glycera dibranchiata consist principally of protein and melanin scaffolds with small amounts of unmineralized copper (Cu) and mineralized atacamite (Cu₂Cl(OH)₃) fibers in distinct regions. Remarkably, when tested in air, the regions containing unmineralized Cu are the hardest, stiffest, and most abrasion resistant. To establish the functions of jaw constituents in physiologically relevant environments, this study examines the effects of hydration on their response to indentation, scratching, and wear. Although all jaw regions are degraded by the presence of water, the ones containing unmineralized Cu are affected least. Notably, scratch depths in the bulk and the atacamite-containing regions double when wet, whereas the corresponding increase in the regions with unmineralized Cu is ∼20%. The results support the view that Cu ions are involved in the formation of intermolecular coordination complexes, creating a cross-linked molecular network that is both mechanically robust and resistant to water ingress. Hydration effects are greatest during wear testing, rates of material removal in water being about three times those in air. The mechanism underlying accelerated wear is suspected to involve coupled effects of near-surface damage and enhanced water ingress, resulting in increased plasticization and susceptibility to plastic plowing.     

Effects of differences in mineralization on the mechanical properties of bone

There is a considerable variation in the mineralization of bone; normal, non-pathological compact bone has ash masses ranging from 45 to 85% by mass. This range of mineralization results in an even greater range of mechanical properties. The Young modulus of elasticity can range from 4 to 32 GPa, bending strength from 50 to 300 MPa, and the work of fracture from 200 to 7000 Jm-2. It is not possible for any one type of bone to have high values for all three properties. Very high values of mineralization produce high values of Young modulus but low values of work of fracture (which is a measure of fracture toughness). Rather low values of mineralization are associated with high values of work of fracture but low values of Young modulus and intermediate values of bending strength. The reason for the high value for the Young modulus associated with high mineralization is intuitively obvious, but has not yet been rigorously modelled. The low fracture toughness associated with high mineralization may be caused by the failure of various crack-stopping mechanisms that can act when the mineral crystals in bone have not coalesced, but which become ineffective when the volume fraction of mineral becomes too high. The adoption of different degrees of mineralization by different bones, leading to different sets of mechanical properties, is shown to be adaptive in most cases studied, but some puzzles still remain.     

Effects of collagenase and elastase on the mechanical properties of lung tissue strips

The dynamic stiffness (H), dampingcoefficient (G), and harmonic distortion (k_d)characterizing tissue nonlinearity of lung parenchymal strips fromguinea pigs were assessed before and after treatment with elastase orcollagenase between 0.1 and 3.74 Hz. After digestion, data wereobtained both at the same mean length and at the same mean force of thestrip as before digestion. At the same mean length, G and H decreasedby ~33% after elastase and by ~47% after collagenase treatment.At the same mean force, G and H increased by ~7% after elastase andby ~25% after collagenase treatment. The k_dincreased more after collagenase (40%) than after elastase (20%)treatment. These findings suggest that, after digestion, the fractionof intact fibers decreases, which, at the same mean length, leads to adecrease in moduli. At the same mean force, collagen fibers operate ata higher portion of their stress-strain curve, which results in anincrease in moduli. Also, G and H were coupled so that hysteresivity(G/H) did not change after treatments. However,k_d was decoupled from elasticity and wassensitive to stretching of collagen, which may be of value in detectingstructural alterations in the connective tissue of the lung.

     

Effects of boron and calcium supplementation on mechanical properties of bone in rats

OBJECTIVE: The objective of this study was to consider the effects of boron (B) and calcium (Ca) supplementation on mechanical properties of bone tissues and mineral content of the selected bones in rats. METHODS: Adult male Sprague Dawley rats underwent three different treatments with boron and calcium in their drinking water, while taking diet ad libitum for 4 weeks. Rats in the three treatment groups received 2 mg B/d, 300 mg Ca/d, and a combination of 2 mg B+ 300 mg Ca/d, respectively. After the experimental period body weights were recorded and bone mechanical properties were determined on the tibiae, femurs, and fifth lumbar vertebral bones and the mineral contents of these bones was calculated as the ash percentage. RESULTS: Better measurement of bone mechanical properties were observed for boron supplementation. The stiffness of the lumbar vertebral bones tended to increase in all groups and was significant for Ca supplementation. The significant maximal load obtained for boron in all bones indicates higher strength and less strength for apparently a high level of calcium, while this negative defect in the case of lumbar vertebral bones was corrected in the presence of boron. Highest mean energy to maximal load was shown with boron supplementation, demonstrating significant values with Ca group, and lower energy for the lumbar vertebral bones in Ca group in comparison with the controls. Less deformation at the yield points was shown in Ca group. There were no significant differences in ash weights among the four groups. CONCLUSIONS: Additional and longer studies are warranted to further determine the effects of supplemental boron with different calcium levels and possibly other minerals involved in bone mechanical properties in rats.     

Effects of static magnetic fields on bone microstructure and mechanical properties in mice

All the living organisms originate, evolve and live under geomagnetic field (GMF, 20–70 µT). With rapid development in science and technology, exposure to various static magnetic fields (SMFs) from natural and man-made sources remains a public environmental topic in consideration of its probable health risk for humans. Many animal studies related to health effect have demonstrated that SMF could improve bone formation and enhance bone healing. Moreover, most of the studies focused on local SMF generated by rod-type magnet. It was difficult to come to a conclusion that how SMF affected bone metabolism in mice. The present study employed hypomagnetic field (HyMF, 500 nT), and moderate SMF (MMF, 0.2 T) to systematically investigate the effects of SMF with continuous exposure on microstructure and mechanical properties of bone. Our results clearly indicated that 4-week MMF exposure did not affect bone biomechanical properties or bone microarchitecture, while HyMF significantly inhibited the growth of mice and elasticity of bone. Furthermore, mineral elements might mediate the biological effect of SMF.     

Incompatible mechanical properties in compact bone

The covariation of a number of mechanical of properties, and some physical characteristics, of compact bones from a wide range of bones were examined. Young's modulus was well predicted by a combination of mineral content and porosity. Increasing Young's modulus was associated with: increasing stress at yield, increasing bending strength, and a somewhat higher resilience, tensile strength and fatigue strength. Contrarily, in the post-yield region a higher Young's modulus (and more clearly, a higher mineral content) was associated with: a reduced work to fracture in tension, a reduced impact strength and an increased notch sensitivity in impact. Increasing porosity is associated with deleterious effects in the pre-yield region, but has little effect in the post-yield region. Bone, like many other materials, is unable to have good qualities in both the pre- and post-yield regions. Since an increase in mineral or Young's modulus is more potent, that is deleterious, in the post-yield than it is advantageous in the pre-yield region, it is likely that mineral content will be selected to be slightly lower than would be the case if it were equally potent in both regions. As is usual in biology, different adaptive extremes are incompatible.     

Multi-axial mechanical properties of human trabecular bone

In the context of osteoporosis, evaluation of bone fracture risk and improved design of epiphyseal bone implants rely on accurate knowledge of the mechanical properties of trabecular bone. A multi-axial loading chamber was designed, built and applied to explore the compressive multi-axial yield and strength properties of human trabecular bone from different anatomical locations. A thorough experimental protocol was elaborated for extraction of cylindrical bone samples, assessment of their morphology by micro-computed tomography and application of different mechanical tests: torsion, uni-axial traction, uni-axial compression and multi-axial compression. A total of 128 bone samples were processed through the protocol and subjected to one of the mechanical tests up to yield and failure. The elastic data were analyzed using a tensorial fabric–elasticity relationship, while the yield and strength data were analyzed with fabric-based, conewise generalized Hill criteria. For each loading mode and more importantly for the combined results, strong relationships were demonstrated between volume fraction, fabric and the elastic, yield and strength properties of human trabecular bone. Despite the reviewed limitations, the obtained results will help improve the simulation of the damage behavior of human bones and bone-implant systems using the finite element method.     

Processing of ovine cardiac valve allografts: 1. Effects of preservation method on structure and mechanical properties.

It is essential to have some method of preservation of allograft valves during the time between procurement and implantation. Cryopreservation is the most commonly-used storage method today but it has the major disadvantage of high cost, and because its aim is to preserve living cells only relatively gentle antimicrobial treatments are used. This study addresses two interrelated questions: Is it necessary to maintain living donor cells in the tissue graft?Can more effective measures be used to reduce the risk of transmission of diseases, especially viral diseases, via human tissue grafts. In this paper, were port an investigation of four preservation methods that could be combined with more effective disinfection: cryopreservation with dimethyl sulphoxide, storage at ～4 °C in a high concentration of glycerol as used for the preservation of skin, snap-freezing by immersion in liquid nitrogen and vitrification. Snap freezing was mechanically damaging and vitrification proved to be impracticable but two methods, cryopreservation and storage in 85%glycerol, were judged worthy of further study. Cryopreservation was shown to maintain cellular viability and excellent microscopic structure with unchangedmechanical properties. The glycerol-preserved valves did not contain any living cells but the connective tissue matrix and mechanical properties were well preserved. The importance of living cells in allograft valves is uncertain. If living cells are unimportant then either method could be combined with more effective disinfection methods: in that case the simplicity and economy of the glycerol method would be advantageous. These questions are addressed in the two later papers in this series.     

Effects of gamma irradiation on mechanical properties of defatted trabecular bone allografts assessed by speed-of-sound measurement

New sterilization methods for human bone allografts may lead to alterations in bone mechanical properties, which strongly influence short- and medium-term outcomes. In many sterilization procedures, bone allografts are subjected to gamma irradiation, usually with 25 KGy, after treatment and packaging. We used speed-of-sound (SOS) measurements to evaluate the effects of gamma irradiation on bone. All bone specimens were subjected to the same microbial inactivation procedure. They were then separated into three groups, of which one was treated and not irradiated and two were exposed to 10 and 25 KGy of gamma radiation, respectively. SOS was measured using high- and low-frequency ultrasound beams in each orthogonal direction. SOS and Young modulus were altered significantly in the three groups, compared to native untreated bone. Exposure to 10 or 25 KGy had no noticeable effect on the study variables. The impact of irradiation was small compared to the effects of physical or chemical defatting. Reducing the radiation dose used in everyday practice failed to improve graft mechanical properties in this study.     

Characterization of the mechanical properties of bovine cortical bone treated with a novel tissue sterilization process

Over the past decade chemical processing and engineering of musculoskeletal tissue (tendon and bone) has improved dramatically. The use of bone allograft and xenograft in reconstructive orthopedic and maxillofacial surgeries is increasing, yet severe complications can occur if the material is contaminated in any way. A novel tissue sterilization process, BioCleanse^®, has been developed to clean and sterilize musculoskeletal tissue for implantation. The present study was designed to determine the effect of this novel cleaning process on the biomechanical properties of bovine cortical bone prior to implantation. The mechanical properties of treated bovine bone material were compared to human samples with respect to failure under compression, shear and three-point bending. The data demonstrate that bovine bone treated with the novel sterilization procedure has favorable biomechanical properties compared to that of human bone treated in a similar fashion.