Biomedical subjects

Xiaodu Wang

Publications and source records attributed to Xiaodu Wang.

10 recordsLinked to original sources

PubMed2007

A novel approach to assess post-yield energy dissipation of bone in tension.

In this study, we proposed a novel approach to assess the energy dissipation during the post-yield deformation of bone. Based on the stress-strain behavior in an incremental and cyclic loading-unloading-reloading scheme in uniaxial tension, we partitioned the post-yield energy dissipation of bone into three distinct pathways: released elastic strain energy (U(er)); irreversible energy (U(i)); and hysteresis energy (U(h)). Among them, U(er) depends on the stiffness loss, U(i) is the energy permanently consumed, and U(h) reflects changes in the viscoelastic behavior of bone in the process of post-yield deformation. As an example, bone specimens from human cadaveric femurs of middle-aged and elderly donors were tested using this approach. The results of this study indicate that there exist age-related differences in post-yield energy dissipation and modulus degradation. These results implicate that this novel approach could detect the age-related differences in energy dissipation of bone and may aid in understanding the underlying mechanisms of such changes.

Aged↗

PubMed2006

Age-related effect on the concentration of collagen crosslinks in human osteonal and interstitial bone tissue.

Collagen crosslinks are important to the quality of bone and may be contributors to the age-related increase in bone fracture. This study was performed to investigate whether age and gender effects on collagen crosslinks are similar in osteonal and interstitial bone tissues. Forty human cadaveric femurs were collected and divided into two age groups: middle-aged (42-63 years of age) and elderly (69-90 years of age) with ten males and ten females in each group (n = 10). Micro-cores of bone tissue from both secondary osteons and interstitial regions in the medial quadrant of the diaphysis were extracted using a custom-modified, computer-controlled milling machine. The bone specimens were then analyzed using high performance liquid chromatography to determine the effects of age and gender on the concentration of mature, enzymatic crosslinks (hydroxylysyl-pyridinoline-HP and lysyl-pyridinoline-LP) and a non-enzymatic crosslink (pentosidine-PE) at these two microstructural sites. The results indicate that age has a significant effect on the concentration of LP and PE, while gender has a significant effect on HP and LP. In addition, the concentration of the crosslinks in the secondary osteons is significantly different from that in the interstitial bone regions. These results suggest that the amount of non-enzymatic crosslinking may increase while that of mature enzymatic crosslinking may decrease with age. Such changes could potentially reduce the inherent quality of the bone tissue in the elderly skeleton.

Adult↗

PubMed2006

Prediction of microdamage formation using a mineral-collagen composite model of bone.

Age-related changes in bone quality are mainly manifested in the reduced toughness. Since the post-yield deformation of bone is realized through microdamage formation (e.g., microcracking and diffuse damage), it is necessary to understand the mechanism of microdamage formation in bone in order to elucidate underlying mechanisms of age-related bone fractures. In this study, a two-dimensional shear lag model was developed to predict stress concentration fields around an initial crack in a mineral-collagen composite. In this model, non-linear elasticity was assumed for the collagen phase, and linear elasticity for the mineral. Based on the pattern of the stress concentration fields, the condition for microdamage formation was discussed. The results of our analyses indicate that: (1) an initial crack formed in mineral phase may cause stress concentration in the adjacent mineral layers; (2) the pattern of stress concentration fields depends not only on the spatial but also mechanical properties of the collagen and mineral phases; (3) the pattern of the stress concentration fields could determine either coalescence or scattering of nano cracks around the initial crack.

Animals↗

PubMed2006

The influence of water removal on the strength and toughness of cortical bone.

Although the effects of dehydration on the mechanical behavior of cortical bone are known, the underlying mechanisms for such effects are not clear. We hypothesize that the interactions of water with the collagen and mineral phases each have a unique influence on mechanical behavior. To study this, strength, toughness, and stiffness were measured with three-point bend specimens made from the mid-diaphysis of human cadaveric femurs and divided into six test groups: control (hydrated), drying in a vacuum oven at room temperature (21 degrees C) for 30 min and at 21, 50, 70, or 110 degrees C for 4 h. The experimental data indicated that water loss significantly increased with each increase in drying condition. Bone strength increased with a 5% loss of water by weight, which was caused by drying at 21 degrees C for 4 h. With water loss exceeding 9%, caused by higher drying temperatures (> or =70 degrees C), strength actually decreased. Drying at 21 degrees C (irrespective of time in vacuum) significantly decreased bone toughness through a loss of plasticity. However, drying at 70 degrees C and above caused toughness to decrease through decreases in strength and fracture strain. Stiffness linearly increased with an increase in water loss. From an energy perspective, the water-mineral interaction is removed at higher temperatures than the water-collagen interaction. Therefore, we speculate that loss of water in the collagen phase decreases the toughness of bone, whereas loss of water associated with the mineral phase decreases both bone strength and toughness.

Adult↗

PubMed2005

Effect of ultrastructural changes on the toughness of bone.

The ultrastructure of bone can be considered as a conjunction between the biology and the biomechanics of the tissue. It is the result of cellular and molecular activities of bone formation, and its organization dominates the mechanical behavior of bone. Following this perspective, the objective of this review is to provide a current understanding of bone ultrastructure and its relationships with the toughness of the tissue. Therefore, we first provide a discussion on the organization of bone constituents, namely collagen, mineral, and water. Then, we present evidence on how the toughness of bone relates to its ultrastructure through the formation of micro damage. In addition, attention is given to how damage accumulation serves as a toughening mechanism. Finally, we describe how changes in the ultrastructure-caused by osteogenesis imperfecta, gamma irradiation, fluoride treatment, and aging affect the toughness and competence of bone.

Aging↗

PubMed2004

The toughness of cortical bone and its relationship with age.

Toughness is a quantitative measure of bone quality in terms of its susceptibility to fracture. Thus, to elucidate the underlying mechanisms of age-related bone fractures, it is necessary to understand age-related changes in the toughness of bone. The objective of this review is to provide current understanding on the structure-function relationships of cortical bone and its correlation with the toughness of the tissue from the perspective of basic engineering principles. The review is written for the readers in the musculoskeletal research field, who may not have a strong engineering background. For better understanding of toughening mechanisms, this review intends to focus on correlations of the toughness of cortical bone with its constituents and microstructural characteristics. In addition, a special emphasis is placed on age-related changes in the toughness of bone.

Aging↗

PubMed2003

Determination of cortical bone porosity and pore size distribution using a low field pulsed NMR approach.

The objective of this study was first to prove the concept of a low field pulsed nuclear magnetic resonance (NMR) process for assessing the cortical porosity and pore size distribution of human bone in vitro, and then to apply the technique to detect age-related changes of bone in these parameters. The Carr-Purcell-Meiboom-Gill NMR spin echo train method is used to determine the porosity, and an inversion NMR spin-spin relaxation (T(2)) spectrum is used to assess the pore size distribution in cortical bone. Using these techniques, cortical porosity and pore size distribution of 19 specimens of human cadaveric bone, ranging from 16 to 89 years of age, were assessed. The NMR results were compared with the histomorphometric data of the same bone samples to verify the efficacy of the NMR approach. Moreover, a coefficient (surface relaxivity) relating the pore size to the T(2) relaxation time was determined empirically for the Haversian canals and the osteocytic lacunae. The results of this study demonstrate that the in vitro NMR approach using T(2) relaxation techniques can directly assess the porosity and pore size distribution (Haversian canals and osteocytic lacunae) in human cortical bone. In addition, this study indicates that the age-related changes in cortical porosity relate predominantly to Haversian canals, whereas the porosity of osteocytic lacunae appears to be independent of age.

Adolescent↗

PubMed2003

Age-related changes of noncalcified collagen in human cortical bone.

It is well known that osteoid, which contains a noncalcified collagenous matrix, is formed during the initial stage of bone formation during the bone remodeling process. Thus, synthesis of defective collagen molecules in osteoid may cause abnormal bone formation, thereby leading to changes in bone quality. The objective of this study was to investigate age-related changes in noncalcified collagen molecules in osteoid and its likely effects on the mechanical integrity of human cortical bone. Thirty human cadaveric femurs were divided into three age groups: young adults, middle age, and the elderly, respectively. A novel high performance liquid chromatography approach was employed to quantify the denaturation of noncalcified collagenous matrix in addition to mechanical tests of bone. Bulk concentrations of both enzymatic and nonenzymatic collagen cross links in bone also were measured. Moreover, the number of newly formed osteons per unit area and the bony area fraction of these osteons were estimated. The results of this study indicate that denaturation of the noncalcified collagenous matrix in bone increases with increasing age. In addition, such collagen denaturation in osteoid exhibited a correlation with nonenzymatic collagen cross links as well as the strength and toughness of bone. These results suggest that age-related changes in the noncalcified collagenous matrix induced by bone remodeling may have likely effects on bone quality.

Adult↗

PubMed2002

Collagen and bone viscoelasticity: a dynamic mechanical analysis.

The purpose of this study was to explore the effects of changes in Type I collagen on the viscoelasticity of bone. Bone coupons were heated at either 100 or 200 degrees C to induce the thermal denaturation of Type I collagen. Half of these specimens were rehydrated after heat treatment; the other half were tested in a dry condition. The degree of denatured collagen (DC%) was analyzed by a selective digestion technique with the use of alpha-chymotrypsin. Isothermal (37 degrees C) and variable temperature tests (scans from 35 to 200 degrees C) were performed with the use of a dynamic mechanical analyzer to evaluate changes in bone viscoelastic properties as a function of collagen damage, specifically, changes in the loss factor (tan delta) and storage modulus (E') were assessed. Significant collagen denaturation occurred only when bone was heated at 200 degrees C irrespective of the hydration condition. Also, DC% did not show a significant effect on tan delta. However, higher values of tan delta were observed in wet samples compared to dry specimens. The temperature-scan tests revealed that the hydration condition, but not DC%, significantly affected the behavior of tan delta. However, E' was not strongly influenced either by DC% or by water content. These results suggest that at a constant frequency the denaturation of collagen triple-helical molecules may have few effects on the viscoelasticity of bone, but moisture may play a prominent role in determining this property.

Biomechanical Phenomena↗

PubMedDate not supplied

Effect of diabetes mellitus on the material properties of the distal tibia.

This investigation evaluates the effects of diabetes on the mechanical properties of human bone, specifically, the tibia. Seven diabetic and seven nondiabetic human (male) cadaveric distal tibiae were used in this study. The average age of the diabetic cadaveric samples was 51 years (range, 46-61 years), and the average age of the nondiabetic cadaveric samples was 75 years (range, 67-85 years). Three-point bending tests for strength and stiffness were performed on a small sample of each distal tibia. Each specimen was loaded at a constant rate until failure. From the recorded curve of load versus displacement, the ultimate and yield strength of bone and the bending modulus of bone were calculated. The diabetic samples were generally weaker than the older, nondiabetic samples, but no statistically significant differences were found in the elastic modulus (P = .29), yield strength (P = .90), ultimate strength (P = .46), and fracture toughness (P = .78), leading to speculation that diabetes has an effect similar to that of aging on the musculoskeletal system.

Aged↗