Huijie Leng

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Papers by Huijie Leng

A Semi-Empirical Elastic-Plastic-Visco-Damage Constitutive Model of Cortical Bone

by Huijie Leng and Xiaodu Wang

ASME 2010 Summer Bioengineering Conference, Parts A and B, 2010

ABSTRACT Bone quality can be characterized by toughness of bone which quantifies the energy requi... more ABSTRACT Bone quality can be characterized by toughness of bone which quantifies the energy required for failure. As much of the toughness of bone occurs after yielding, elucidating the underlying mechanism of post-yield behavior of bone is critical for further development of clinical strategies to predict and prevent age and disease related bone fractures. However, the underlying mechanism of the post-yield behavior of cortical bone is so far poorly understood, which makes it difficult to establish physically sound constitutive models for cortical bone that could accurately predict the mechanical behavior of the tissue. The absence of the constitutive equations has significantly hindered the application of bone mechanics in solving biomedical problems. Besides, an accurate constitutive model is always required in numerical modeling and simulating the mechanical behavior of bone under different loading conditions. Based on the experimental results obtained in our lab, the objective of this study was to develop and verify a constitutive model of cortical bone under compression, which accounted for damage accumulation, plastic deformation and viscoelastic properties.

A Semi-Empirical Constitutive Model for Post Yield Behavior of Bone in Tension

by Huijie Leng and Xiaodu Wang

ASME 2007 Summer Bioengineering Conference, 2007

ABSTRACT

Low Mineralization Tends to Facilitate the Formation of Diffuse Damage in Bone

by Huijie Leng and Xiaodu Wang

ASME 2009 Summer Bioengineering Conference, Parts A and B, 2009

ABSTRACT Microdamage formation in bone is dependent on its ultra-structural and material properti... more ABSTRACT Microdamage formation in bone is dependent on its ultra-structural and material properties. Previous studies of probabilistic failure analysis of mineral-collagen composites have indicated that mineral modulus affects the formation of microdamage in bone [1]. Therefore, the hypothesis of this study is that mineralization influences the morphology of microdamage in bone. To test this hypothesis, bone femurs from two types of mice (C57BL/6J and C3H/HeJ) with various bone mineral density [2] were fatigued to produce microdamage and the differences of microdamage morphology were then examined. In addition, nanoindentation techniques were employed to assess the difference of mineralization between these two mice strains.

Progressive Energy Dissipations of Human Cortical Bone in Compression

by Huijie Leng and Xiaodu Wang

ASME 2008 Summer Bioengineering Conference, Parts A and B, 2008

ABSTRACT Bone fracture has imposed a significant burden on the health of society. The “bone quali... more ABSTRACT Bone fracture has imposed a significant burden on the health of society. The “bone quality” is used to refer to factors affecting bone fracture risk [1]. Energy dissipation till fracture, known as toughness, is a major measure of bone quality [2]. However, underlying mechanisms of energy dissipation in bone is still not clear. It has been well documented that the post-yield behavior of bone determines the major part of the toughness of bone [3, 4]. Therefore, it is important to study post-yield behaviors of human bone, especially the different pathways for energy dissipation, in order to better understand how age-related change affects bone quality. Bone behaves differently under different loading modes [5]. Different from loading in tension, after reaching the maximum stress, cortical bone in compression can continue to bear load till large deformation without brittle failure and dramatic reduction in elastic modulus [5, 6]. However, few studies of progression of post-yield behaviors of cortical bone in compression were reported in the literature.

Synthesis of a Barium Sulfate Nanoparticle Contrast Agent for Micro-Computed Tomography of Bone Microstructure

Lu/Ceramic, 2006

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The Assessment of Loosely and Tightly Bound Water in Water Distribution Changes of Human Cortical Bone by NMR

ASME 2008 Summer Bioengineering Conference, Parts A and B, 2008

ABSTRACT Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Associat... more

Kinetic Effects on Hydroxyapatite Whiskers Synthesized by the Chelate Decomposition Method

Journal of the American Ceramic Society, 2006

Hydroxyapatite (HA) whiskers have been synthesized using a number of chemical solution methods, i... more Hydroxyapatite (HA) whiskers have been synthesized using a number of chemical solution methods, including the chelate decomposition method. Numerous previous studies have investigated the effects of the reagents, reagent concentrations, solution pH, and reaction temperature on HA whisker morphology and composition. However, purely kinetic effects, such as the reaction heating and stirring rates, have not been rigorously investigated and are rarely reported in the literature. Therefore, the objective of this study was to investigate kinetic effects on the morphology of HA whiskers synthesized using the chelate decomposition method. In order to study the kinetic effects on the morphology of HA whiskers, three experimental parameters were varied independently: the reaction heating rate (0.361-3.01C/min), stirring rate (0-250 rpm), and temperature (801-2001C). At all heating and stirring rates, precipitated whiskers were confirmed by XRD and FT-IR to comprise phase-pure, calcium-deficient HA (Ca/P 5 1.57-1.62). The length and aspect ratio of HA whiskers increased with decreased heating rate, decreased stirring rate, and increased reaction temperature. The mean length and aspect ratio of HA whiskers increased approximately twofold with decreased heating rate over the range studied, following a power-law relationship. Therefore, the reaction heating rate is a key variable that can be used to tailor the morphology of HA whiskers and ought to be reported in the literature. The reaction heating rate and temperature had relatively little effect on the width of HA whiskers. However, the precipitate morphology was altered significantly from microscale whiskers to nano-scale plates with increased stirring rate. These results offered new insights and provided clarification regarding the reaction mechanism, which is discussed in detail.

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Finding of Microdamage Morphology Differences in Mouse Femoral Bones with Distinct Mineralization Levels

by Huijie Leng and Xiaodu Wang

Journal of Mechanics in Medicine and Biology, 2011

Constitutive relationship of tissue behavior with damage accumulation of human cortical bone

by Huijie Leng and Xiaodu Wang

Journal of Biomechanics, 2010

Microdamage accumulation has been identified as a major conduit for bone tissues to absorb fractu... more Microdamage accumulation has been identified as a major conduit for bone tissues to absorb fracture energy. Due to the poor understanding of its underlying mechanism, however, an adequate constitutive relationship between damage accumulation and the mechanical behavior of bone has not yet been established. In this study, the constitutive relationship between the damage accumulation induced by overload and the evolution of mechanical properties of bone with incremental deformation was established based on the experimental results obtained from a novel progressive loading protocol developed in our laboratory. First, a decayed exponential model was proposed to capture the damage accumulation (modulus loss) with increase in applied strain. Next, a power law function was proposed to represent the progression of plastic deformation with damage accumulation. Finally, a linear combination of the Kohlrausch-Williams-Watts (KWW) and the Debye functions was used to depict the viscoelastic behavior of bone associated with damage accumulation. The results of this study may help in developing a constitutive model for predicting the mechanical behavior of cortical bone tissues.

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Progressive post-yield behavior of human cortical bone in compression for middle-aged and elderly groups

by Xiaodu Wang and Huijie Leng

Journal of Biomechanics, 2009

In this study, a progressive loading regimen (load-dwell-unloading-dwell-reloading) was applied o... more In this study, a progressive loading regimen (load-dwell-unloading-dwell-reloading) was applied on bone samples to examine the compressive post-yield response of bone at increasing strain levels. Cortical bone specimens from human tibiae of two age groups (middle-aged group: 53±2 years, 4 females and 4 males, elderly group: 83±6 years, 4 females and 4 males) were loaded in compression using the progressive loading scheme. Modulus degradation, plastic deformation, viscous response, and energy dissipation of bone during post-yield deformation were assessed. Although initial modulus was not significantly different between the two age groups, the degradation of modulus with the applied strain in the elderly group was faster than in the middleaged group. The modulus loss (or microdamage accumulation) of bone occurred prior to plastic deformation. Plastic strain had a similar linear relationship with the applied strain for both middleaged and the elderly group although middle-aged bone yielded at a greater strain. The viscoelastic time constant changed similarly with increasing strain for the two groups, whereas a higher magnitude of stress relaxation was observed in the middle-aged group. Energy dissipation was investigated through three pathways: elastic release strain energy, hysteresis energy, and plastic strain energy. The middle-aged group had significantly greater capacity of energy dissipation than the elderly group in all three pathways. The information obtained may provide important insights in age-related effects on bone fragility.

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Aging and orientation effects on ultimate strength and strain of human collagen network

by Huijie Leng and Xiaodu Wang

Bone, 2008

The collagen phase plays an important role in mechanical behaviors of cortical bone. However, agi... more The collagen phase plays an important role in mechanical behaviors of cortical bone. However, aging effects on the mechanical behavior of the collagen phase is still poorly understood. In this study, micro-tensile tests were performed on demineralized human cortical bone samples from young, middle-aged, and elderly donors and aging effects on the mechanical properties of the collagen phase in different orientations (i.e. longitudinal and transverse directions of bone) were examined. The results of this study indicated that the elastic modulus and ultimate strength of the demineralized bone specimens decreased with aging in both the longitudinal and transverse orientations. However, the failure strain exhibited no significant changes in both orientations regardless of aging. These results suggest that the stiffness and strength of the collagen phase in bone are deteriorated with aging in both longitudinal and transverse directions. However, the aging effect is not reflected in the failure strain of the collagen phase in both longitudinal and transverse orientations, implying that the maximum sustainable deformation of the collagen phase is independent of aging and orientation.

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Aging effects on compressive energy dissipation of cortical bone

by Xiaodu Wang and Huijie Leng

Bone, 2008

In this study, a progressive loading regimen (load-dwell-unloading-dwell-reloading) was applied o... more In this study, a progressive loading regimen (load-dwell-unloading-dwell-reloading) was applied on bone samples to examine the compressive post-yield response of bone at increasing strain levels. Cortical bone specimens from human tibiae of two age groups (middle-aged group: 5372 years, 4 females and 4 males, elderly group: 8376 years, 4 females and 4 males) were loaded in compression using the progressive loading scheme. Modulus degradation, plastic deformation, viscous response, and energy dissipation of bone during post-yield deformation were assessed. Although initial modulus was not significantly different between the two age groups, the degradation of modulus with the applied strain in the elderly group was faster than in the middle-aged group. The modulus loss (or microdamage accumulation) of bone occurred prior to plastic deformation. Plastic strain had a similar linear relationship with the applied strain for both middle-aged and the elderly group although middle-aged bone yielded at a greater strain. The viscoelastic time constant changed similarly with increasing strain for the two groups, whereas a higher magnitude of stress relaxation was observed in the middle-aged group. Energy dissipation was investigated through three pathways: elastic release strain energy, hysteresis energy, and plastic strain energy. The middle-aged group had significantly greater capacity of energy dissipation than the elderly group in all three pathways. The information obtained may provide important insights in age-related effects on bone fragility.

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Effect of age on mechanical properties of the collagen phase in different orientations of human cortical bone

by Huijie Leng and Xiaodu Wang

Bone, 2013

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Fundamental biomechanics in bone tissue engineering

Synthesis Lectures on …, 2010

The objective of this review is to provide basic information pertaining to biomechanical aspects ... more The objective of this review is to provide basic information pertaining to biomechanical aspects of bone as they relate to tissue engineering. The review is written for the general tissue engineering reader, who may not have a biomechanical engineering background. To this end, biomechanical characteristics and properties of normal and repair cortical and cancellous bone are presented. Also, this chapter intends to describe basic structure-function relationships of these two types of bone. Special emphasis is placed on salient classical and modern testing methods, with both material and structural properties described.

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Tailored surface treatment of 3D printed porous Ti6Al4V by micro-arc oxidation for enhanced osseointegration via optimized bone in-growth patterns and interlocked bone/implant interface

ACS applied materials & interfaces, Jan 24, 2016

3D printed porous titanium (Ti) hold enormous potential for load-bearing orthopedic applications.... more 3D printed porous titanium (Ti) hold enormous potential for load-bearing orthopedic applications. Altough 3D printing technique has good control over the macro-sturctures of porous Ti, the surface properties that affect tissue response are beyond its control, adding the need for tailored surface treatment to improve its osseointegration capacity. Here, one step micro-arc oxidation (MAO) process was applied to a 3D printed porous Ti6Al4V (Ti64) scaffold to endow the scaffold with a homogeneous layer of micro-porous TiO2 and significant amounts of amorphous calcium-phosphate. Following the treatment, the porous Ti64 scaffolds exhibited a drastically improved apatite forming ability, cyto-compatibility and alkaline phosphatase activity. In vivo test in a rabbit model showed that the bone in-growth at the untreated scaffold was in a pattern of distance osteogenesis by which bone formed only at the periphery of the scaffold. In contrast, the bone in-growth at the MAO-treated scaffold exh...

Vitamin D Prevents Articular Cartilage Erosion by Regulating Collagen II Turnover through TGF-β1 in Ovariectomized Rats

Osteoarthritis and cartilage / OARS, Osteoarthritis Research Society, Jan 3, 2015

To explore the effect of vitamin D on turnover of articular cartilage with ovariectomy (OVX) indu... more To explore the effect of vitamin D on turnover of articular cartilage with ovariectomy (OVX) induced OA, and to investigate TGF-β1 as a possible underlying mechanism mediated by 1α,25(OH)2D3. DESIGN: Sixty-six rats were randomly allocated into seven groups: sham plus control diet (SHAM+CTL), OVX+CTL diet, sham plus vitamin D-deficient (VDD) diet, OVX+VDD diet, and three groups of ovariectomized rats treated with different doses of 1α,25(OH)2D3. The cartilage erosion and the levels of serum 17β-estradiol, 1α,25(OH)2D3 and C-telopeptide of type II collagen (CTX-II) were measured. Transforming growth factor-β1 (TGF-β1), type II Collagen (CII), matrix metalloproteinases (MMP)-9,-13 in articular cartilage were assessed by immunohistochemistry. TGF-β1 and CTX-II expression were measured for articular cartilage chondrocytes treated with/without tumor necrosis factor (TNF-α), 1α,25(OH)2D3, and TGF-β receptor inhibitor (SB505124) in vitro. Cartilage erosion due to OVX was significantly reduc...

Single-dose local simvastatin injection improves implant fixation via increased angiogenesis and bone formation in an ovariectomized rat model

Medical science monitor : international medical journal of experimental and clinical research, 2015

Statins have been reported to promote bone formation. However, taken orally, their bioavailabilit... more Statins have been reported to promote bone formation. However, taken orally, their bioavailability is low to the bones. Implant therapies require a local repair response, topical application of osteoinductive agents, or biomaterials that promote implant fixation. The present study evaluated the effect of a single local injection of simvastatin on screw fixation in an ovariectomized rat model of osteoporosis. Dual-energy X-ray absorptiometry, micro-computed tomography, histology, and biomechanical tests revealed that 5 and 10 mg simvastatin significantly improved bone mineral density by 18.2% and 22.4%, respectively (P<0.05); increased bone volume fraction by 51.0% and 57.9%, trabecular thickness by 16.4% and 18.9%, trabeculae number by 112.0% and 107.1%, and percentage of osseointegration by 115.7% and 126.3%; and decreased trabeculae separation by 34.1% and 36.6%, respectively (all P<0.01). Bone mineral apposition rate was significantly increased (P<0.01). Furthermore, imp...

Biomechanical and Histological Evaluation of Roughened Surface Titanium Screws Fabricated by Electron Beam Melting

PLoS ONE, 2014

Various fabrication methods are used to improve the stability and osseointegration of screws with... more Various fabrication methods are used to improve the stability and osseointegration of screws within the host bone. The aim of this study was to investigate whether roughened surface titanium screws fabricated by electron beam melting can provide better stability and osseointegration as compared with smooth titanium screws in sheep cervical vertebrae. Roughened surface titanium screws, fabricated by electron beam melting, and conventional smooth surface titanium screws were implanted into sheep for 6 or 12 weeks (groups A and B, respectively). Bone ingrowth and implant stability were assessed with three-dimensional imaging and reconstruction, as well as histological and biomechanical tests. No screws in either group showed signs of loosening. Fibrous tissue formation could be seen around the screws at 6 weeks, which was replaced with bone at 12 weeks. Bone volume/total volume, bone surface area/bone volume, and the trabecular number were significantly higher for a define region of interest surrounding the roughened screws than that surrounding the smooth screws at 12 weeks. Indeed, for roughened screws, trabecular number was significantly higher at 12 weeks than at 6 weeks. On mechanical testing, the maximum pullout strength was significantly higher at 12 weeks than at 6 weeks, as expected; however, no significant differences were found between smooth and roughened screws at either time point. The maximum torque to extract the roughened screws was higher than that required for the smooth screws. Electron beam melting is a simple and effective method for producing a roughened surface on titanium screws. After 12 weeks, roughened titanium screws demonstrated a high degree of osseointegration and increased torsional resistance to extraction over smooth titanium screws.

Probabilistic Prediction of Microdamage Progression in Bone

ABSTRACT Age-related bone fractures are a major health concern to the elderly population. In addi... more ABSTRACT Age-related bone fractures are a major health concern to the elderly population. In addition to the loss of bone mass, the deterioration of bone quality is another major reason for such fractures. The decline of bone quality is manifested with the accumulation of microdamage in bone with age [1]. Two major types of microdamage have been observed in bone tissue: linear microcracks and diffuse damage [2]. Linear microcracks are individual cracks at a size of microns or larger and are usually visible under an optical microscope. On the other hand, diffuse damage is detectable only by staining and consists of an extensive network of fine, ultrastructural-level defects. The mechanisms for the formation of these two distinct types of microdamage in bone are still unclear. In this study, probabilistic finite element models of mineral-collagen composites were used to study the progression of microdamage in bone, thereby exploring the conditions under which linear microcracks and diffuse damage are produced in bone.

A Quantitative Study of the Relationship between the Distribution of Different Types of Collagen and the Mechanical Behavior of Rabbit Medial Collateral Ligaments

PLoS ONE, 2014

The mechanical properties of ligaments are key contributors to the stability and function of musc... more The mechanical properties of ligaments are key contributors to the stability and function of musculoskeletal joints. Ligaments are generally composed of ground substance, collagen (mainly type I and III collagen), and minimal elastin fibers. However, no consensus has been reached about whether the distribution of different types of collagen correlates with the mechanical behaviors of ligaments. The main objective of this study was to determine whether the collagen type distribution is correlated with the mechanical properties of ligaments. Using axial tensile tests and picrosirius red stainingpolarization observations, the mechanical behaviors and the ratios of the various types of collagen were investigated for twenty-four rabbit medial collateral ligaments from twenty-four rabbits of different ages, respectively. One-way analysis of variance was used in the comparison of the Young's modulus in the linear region of the stress-strain curves and the ratios of type I and III collagen for the specimens (the mid-substance specimens of the ligaments) with different ages. A multiple linear regression was performed using the collagen contents (the ratios of type I and III collagen) and the Young's modulus of the specimens. During the maturation of the ligaments, the type I collagen content increased, and the type III collagen content decreased. A significant and strong correlation (R 2~0 :839,Pv0:05) was identified by multiple linear regression between the collagen contents (i.e., the ratios of type I and type III collagen) and the mechanical properties of the specimens. The collagen content of ligaments might provide a new perspective for evaluating the linear modulus of global stress-strain curves for ligaments and open a new door for studying the mechanical behaviors and functions of connective tissues.

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