Biomedical subjects

Yi-Xian Qin

Publications and source records attributed to Yi-Xian Qin.

9 recordsLinked to original sources

PubMed2006

The effects of embedding material, loading rate and magnitude, and penetration depth in nanoindentation of trabecular bone.

Understanding the pathophysiology of metabolic bone disease requires the characterization of both the quantity as well as the quality (i.e., microarchitecture and material properties) of the bone tissue. Nanoindentation provides a powerful yet simple method to measure the nano/micro mechanical properties of bone, but no uniform testing methodology exists. This study examines the effects of embedding materials, rate and depth of indentation, and storage time on the measured modulus. Nineteen trabecular bone samples were evaluated for the study. Although there was an 8-fold increase in the stiffness of the soft to hard epoxy, bone tissue modulus was not affected by the stiffness of the embedding materials, but hardness was affected by both the embedding material modulus, for example from 0.70 +/- 0.20 GPa (ME(low)) to 0.45 +/- 0.21 GPa (ME(Med)) (p < 0.01), and viscosity (p < 0.01). No significant differences were found with regard to the tested rates and depths of indentation for either elastic modulus or hardness. The tissue modulus tested at the 6-month time point was significantly greater in comparison with that tested at 0 or 3 months (p < 0.01). The hardness, however, did not significantly change over the span of 6 months. The results show that while nanoindentation is powerful, it is particularly sensitive to certain testing variables.

Animals↗

PubMed2006

Low-level mechanical signals and their potential as a non-pharmacological intervention for osteoporosis.

BACKGROUND: exercise is recognised as a critical regulatory signal to the skeletal system, but which specific aspects of exercise are responsible for influencing bone mass and morphology and resisting fractures remains unknown. Recent data indicate that extremely low-level mechanical signals are anabolic to bone, and thus may be used, non-invasively, as a form of 'passive' exercise to positively influence skeletal status. OBJECTIVE: to summarise recent experimental studies on the effect of low-level mechanical signals (hypothesised to serve as a surrogate for the spectral content of muscle contractility) as a potential non-pharmacological intervention for osteoporosis. RESULTS: low magnitude mechanical signals are anabolic to bone if applied at a high frequency (15-90 Hz). Long-term animal studies (1 year) show that these low-magnitude mechanical signals can increase cancellous bone volume fraction, trabecular thickness, trabecular number and enhance bone stiffness and strength. Studies in the mouse have shown that these low-level signals will stimulate bone formation rate and labelled surface in cortical and cancellous bone, but the molecular and genetic regulation of this mechanosensitivity is extremely complex. Preliminary studies in children with disabling conditions and post-menopausal women indicate that such signals can be efficacious in reversing and/or preventing bone loss. CONCLUSIONS: considering that the strains (deformations) that result from these low-level vibrations are far below (<1/1000th) those which may cause damage to the bone, we believe they represent a unique, non-pharmacological prophylaxis for osteoporosis. Given that so many physiologic systems are tuned to specific frequencies, such as sight, hearing and touch, it should not be entirely surprising that the musculoskeletal system would be responsive to frequency as well.

Animals↗

PubMed2006

Determination of ultrasound phase velocity in trabecular bone using time dependent phase tracking technique.

Ultrasound velocity is one of the key acoustic parameters for noninvasive diagnosis of osteoporosis. Ultrasound phase velocity can be uniquely measured from the phase of the ultrasound signal at a specified frequency. Many previous studies used fast Fourier transform (FFT) to determine the phase velocity, which may cause errors due to the limitations of FFT. The new phase tracking technique applied an adaptive tracking algorithm to detect the time dependent phase and amplitude of the ultrasound signal at a specified frequency. This overcame the disadvantages of FFT to ensure the accuracy of the ultrasound phase velocity. As a result, the new method exhibited high accuracy in the measurement of ultrasound phase velocity of two phantom blocks with the error less than 0.4%. 41 cubic trabecular samples from sheep femoral condyles were used in the study. The phase velocity of the samples using the new method had significantly high correlation to the bulk stiffness of the samples (r = 0.84) compared to the phase velocity measured using fast Fourier transform FFT (r = 0.14). In conclusion, the new method provided an accurate measurement of the ultrasound phase velocity in bone.

Algorithms↗

PubMed2005

Interrelationship of trabecular mechanical and microstructural properties in sheep trabecular bone.

The ability to evaluate fracture risk at an early time point is essential for improved prognostics as well as enhanced treatment in cases of bone loss such as from osteoporosis. Improving the diagnostic ability is inherent upon both high-resolution non-invasive imaging, and a thorough understanding of how the derived indices of structure and density relate to its true mechanical behavior. Using sheep femoral trabecular bone with a range of strength, the interrelationship of mechanical and microstructural parameters was analyzed using multi-directional mechanical testing and micro-computed tomography. Forty-five cubic trabecular bone samples were harvested from 23 adult female sheep, some of whom had received hind-limb vibratory stimuli over the course of 2 years with consequently enhanced mechanical properties. These samples were pooled into a low, medium, or high strength group for further analysis. The findings show that microCT indices that are structural in nature, e.g., structural model index (SMI) (r2=0.85, p<0.0001) is as good as more density oriented indices like bone volume/total volume (BV/TV) (r2=0.81, p<0.0001) in predicting the ultimate strength of a region of trabecular bone. Additionally, those indices more related to global changes in trabecular structure such as connectivity density (ConnD) or degree of anisotropy (DA) are less able to predict the mechanical properties of bone. Interrelationships of trabecular indices such as trabecular number (TbN), thickness (TbTh), and spacing (TbSp) provide clues as to how the trabecular bone will remodel to ultimately achieve differences in the apparent mechanical properties. For instance, the analysis showed that a loss of bone primarily affects the connectedness and overall number of trabeculae, while increased strength results in an increase of the overall thickness of trabeculae while not improving the connectedness. Certainly, the microCT indices studied are able to predict the bulk mechanical properties of a trabecular ROI well, leaving unaccounted only about 15-20% of its inherent variability. Diagnostically, this implies that future work on the early prediction of fracture risk should continue to explore the role of bone quality as the key factors or as an adjuvant to bone quantity (e.g., apparent density).

Absorptiometry, Photon↗

PubMed2005

The influence of cortical end-plate on broadband ultrasound attenuation measurements at the human calcaneus using scanning confocal ultrasound.

Quantitative ultrasound (QUS) assessment, including broadband ultrasound attenuation (BUA), is an efficient technique for assessing bone quality in various statuses, e.g., osteoporosis. While assessing trabecular bone loss is essential to bone quality, the existence of cortical bone can substantially reduce the accuracy of BUA measurement. In this study, we developed an approach to quantify the influence of the cortical end-plate in the QUS on 18 cadaver calcanei using both analytical and experimental analyses. A simplified cortical-trabecular-cortical sandwich model has been developed for simulation of wave propagations. Results show that the cortical end-plate has a significant effect on BUA (yielding 8.5 +/- 3.6 dB/MHz in cortical bone alone), approximately 15% of the BUA value over the whole bone BUA measurement (54.1 +/- 20.1 dB/MHz). The phenomenon has been predicted by the developed analytical model with a high correlation (r2 = 0.63, p < 0.0001). The data have suggested that the mechanism of the BUA attributed to the cortical end-plate is primarily due to the ultrasonic wave transmission and reflection within the cortical layers. Therefore, the influence of the cortical end-plate in BUA can be quantified and incorporated into the QUS assessment for bone quality, which may provide insight into BUA measurement for accurate diagnosis of bone diseases.

Bone Density↗

PubMed2003

Combining high-resolution micro-computed tomography with material composition to define the quality of bone tissue.

Atraumatic fractures of the skeleton in osteoporotic patients are directly related to a deterioration of bone strength. However, the failure of the bone tissue to withstand functional load bearing cannot be explained as a simple decrease in bone mineral density (quantity); strength is also significantly dependent upon bone quality. While a formal definition of bone quality is somewhat elusive, at the very least, it incorporates architectural, physical, and biologic factors that are critical to bone strength. Such factors include bone morphology (ie, trabecular connectivity, cross-sectional geometry, longitudinal curvature); the tissue's material properties (eg, stiffness, strength); its chemical composition and architecture (eg, ratio of calcium to other components of the organic and/or inorganic phase, collagen orientation, porosity, permeability); and the viability of the tissue (eg, responsivity of the bone cell population). Combining high-resolution structural indices of bone, as determined by micro-computed tomography; material properties determined by nanoindentation; and the chemical make-up of bone, as determined by infrared spectroscopy, helps to provide critical information toward a more comprehensive assessment of the interdependence of bone quality, quantity, and fracture risk.

Animals↗

PubMed2003

Adaptations of trabecular bone to low magnitude vibrations result in more uniform stress and strain under load.

Extremely low magnitude mechanical stimuli (<10 microstrain) induced at high frequencies are anabolic to trabecular bone. Here, we used finite element (FE) modeling to investigate the mechanical implications of a one year mechanical intervention. Adult female sheep stood with their hindlimbs either on a vibrating plate (30 Hz, 0.3 g) for 20 min/d, 5 d/wk or on an inactive plate. Microcomputed tomography data of 1 cm bone cubes extracted from the medial femoral condyles were transformed into FE meshes. Simulated compressive loads applied to the trabecular meshes in the three orthogonal directions indicated that the low level mechanical intervention significantly increased the apparent trabecular tissue stiffness of the femoral condyle in the longitudinal (+17%, p<0.02), anterior-posterior (+29%, p<0.01), and medial-lateral (+37%, p<0.01) direction, thus reducing apparent strain magnitudes for a given applied load. For a given apparent input strain (or stress), the resultant stresses and strains within trabeculae were more uniformly distributed in the off-axis loading directions in cubes of mechanically loaded sheep. These data suggest that trabecular bone responds to low level mechanical loads with intricate adaptations beyond a simple reduction in apparent strain magnitude, producing a structure that is stiffer and less prone to fracture for a given load.

Adaptation, Physiological↗

PubMed2002

The pathway of bone fluid flow as defined by in vivo intramedullary pressure and streaming potential measurements.

The pathway for intracortical fluid flow response to a step-load was identified in vivo using intramedullary pressure (ImP) and streaming potential (SP) measurements, and allowed the development of a load-induced flow mechanism which considers mechanotransduction and mechanoelectrotransduction phenomena. An avian model was used for monitoring, simultaneously, ImP and SP under axial loading which generated peak strains of approximately 600 microstrain (microepsilon). ImP response to step-load decayed more quickly than SP relaxation, in which multiple time constants were observed during the relaxations. While the initial relaxation of SP showed a decay on the order of 200 ms, ImP decayed on the order of approximately 100 ms. After the initial decay (approximately 200 ms after loading), ImP quickly relaxed to base line, while SP continued to dominate relaxation. It appears that the decay of ImP is indicative of resistive fluid flow occurring primarily in the vasculature and other intraosseous channels such as lacunar-canalicular pores, and that SP represents the fluid flow in the smaller porosities, i.e., lacunar-canalicular system or even microspores. These results suggest that SP and ImP decays are determined by a hierarchical interdependent system of multiple porosities, and that the temporal dynamics of load-bearing define the manner in which the fluid patterns and pressures are distributed.

Animals↗

PubMed2002

Quantity and quality of trabecular bone in the femur are enhanced by a strongly anabolic, noninvasive mechanical intervention.

The skeleton's sensitivity to mechanical stimuli represents a critical determinant of bone mass and morphology. We have proposed that the extremely low level (< 10 microstrain), high frequency (20-50 Hz) mechanical strains, continually present during even subtle activities such as standing are as important to defining the skeleton as the larger strains typically associated with vigorous activity (>2000 microstrain). If these low-level strains are indeed anabolic, then this sensitivity could serve as the basis for a biomechanically based intervention for osteoporosis. To evaluate this hypothesis, the hindlimbs of adult female sheep were stimulated for 20 minutes/day using a noninvasive 0.3g vertical oscillation sufficient to induce approximately 5 microstrain on the cortex of the tibia. After 1 year of stimulation, the physical properties of 10-mm cubes of trabecular bone from the distal femoral condyle of experimental animals (n = 8) were compared with controls (n = 9), as evaluated using microcomputed tomography (microCT) scanning and materials testing. Bone mineral content (BMC) was 10.6% greater (p < 0.05), and the trabecular number (Tb.N) was 8.3% higher in the experimental animals (p < 0.01), and trabecular spacing decreased by 11.3% (p < 0.01), indicating that bone quantity was increased both by the creation of new trabeculae and the thickening of existing trabeculae. The trabecular bone pattern factor (TBPf) decreased 24.2% (p < 0.03), indicating trabecular morphology adapting from rod shape to plate shape. Significant increases in stiffness and strength were observed in the longitudinal direction (12.1% and 26.7%, respectively; both, p < 0.05), indicating that the adaptation occurred primarily in the plane of weightbearing. These results show that extremely low level mechanical stimuli improve both the quantity and the quality of trabecular bone. That these deformations are several orders of magnitude below those peak strains which arise during vigorous activity indicates that this biomechanically based signal may serve as an effective intervention for osteoporosis.

Animals↗