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Mechanical Stiffness (mechanical + stiffness)
Selected AbstractsHigh-sensitivity surface micromachinable accelerometer using a ferroelectric substrate and its characterizationIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 3 2007Seiji Aoyagi Member Abstract The present study reports the fabrication and characterization of a high-sensitivity surface micromachinable accelerometer using a ferroelectric material having a large dielectric constant, such as bulk PZT (,r = 2600). The measurement principle is the detection of capacitance change with respect to the dielectric mass movement in the fringe electrical field. Considering the practical fabrication, a ferroelectric material is used for the substrate instead of the suspended proof mass. Since capacitance is increased not mechanically but electrically, high sensitivity can be expected while maintaining mechanical stiffness, which has the advantage of preventing touch down of the proof mass and widening the allowable measuring range of acceleration. A fabricated sensor is characterized. A high sensitivity of several sub-pF/g is confirmed, which is hundreds of times higher compared to that of a sensor fabricated using the Parylene polymer (,r = 3.15). This sensitivity is an order higher compared to those of other reported capacitive microaccelerometers, which have comparable proof mass sizes and comparable detectable acceleration ranges to the newly fabricated sensor. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] A Three-Dimensional Simulation of Age-Related Remodeling in Trabecular Bone,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 4 2001J. C. Van Der Linden Abstract After peak bone mass has been reached, the bone remodeling process results in a decrease in bone mass and strength. The formation deficit, the deficit of bone formation compared with previous resorption, results in bone loss. Moreover, trabeculae disconnected by resorption cavities probably are not repaired. The contributions of these mechanisms to the total bone loss are unclear. To investigate these contributions and the concomitant changes in trabecular architecture and mechanical properties, we made a computer simulation model of bone remodeling using microcomputed tomography (micro-CT) scans of human vertebral trabecular bone specimens. Up to 50 years of physiological remodeling were simulated. Resorption cavities were created and refilled 3 months later. These cavities were not refilled completely, to simulate the formation deficit. Disconnected trabeculae were not repaired; loose fragments generated during the simulation were removed. Resorption depth, formation deficit, and remodeling space were based on biological data. The rate of bone loss varied between 0.3% and 1.1% per year. Stiffness anisotropy increased, and morphological anisotropy (mean intercept length [MIL]) was almost unaffected. Connectivity density increased or decreased, depending on the remodeling parameters. The formation deficit accounted for 69,95%, disconnected trabeculae for 1,21%, and loose fragments for 1,17% of the bone loss. Increasing formation deficit from 1.8% to 5.4% tripled bone loss but only doubled the decrease in stiffness. Increasing resorption depth from 28 to 56 ,m slightly increased bone loss but drastically decreased stiffness. Decreasing the formation deficit helps to prevent bone loss, but reducing resorption depth is more effective in preventing loss of mechanical stiffness. [source] Determination of ankle external fixation stiffness by expedited interactive finite element analysisJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2005Jonathan K. Nielsen Abstract Interactive finite element analysis holds the potential to quickly and accurately determine the mechanical stiffness of alternative external fixator frame configurations. Using as an example Ilizarov distraction of the ankle, a finite element model and graphical user interface were developed that provided rapid, construct-specific information on fixation rigidity. After input of specific construct variables, the finite element software determined the resulting tibial displacement for a given configuration in typically 15 s. The formulation was employed to investigate constructs used to treat end-stage arthritis, both in a parametric series and for five specific clinical distraction cases. Parametric testing of 15 individual variables revealed that tibial half-pins were much more effective than transfixion wires in limiting axial tibial displacement. Factors most strongly contributing to stiffening the construct included placing the tibia closer to the fixator rings, and mounting the pins to the rings at the nearest circumferential location to the bone. Benchtop mechanical validation results differed inappreciably from the finite element computations. © 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] Spatially-localized correlation of dGEMRIC-measured GAG distribution and mechanical stiffness in the human tibial plateauJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2005Joseph T. Samosky Abstract The concentration of glycosaminoglycan (GAG) in articular cartilage is known to be an important determinant of tissue mechanical properties based on numerous studies relating bulk GAG and mechanical properties. To date limited information exists regarding the relationship between GAG and mechanical properties on a spatially-localized basis in intact samples of native tissue. This relation can now be explored by using delayed gadolinium-enhanced MRI of cartilage (dGEMRIC,a recently available non-destructive magnetic resonance imaging method for measuring glycosaminoglycan concentration) combined with non-destructive mechanical indentation testing. In this study, three tibial plateaus from patients undergoing total knee arthroplasty were imaged by dGEMRIC. At 33,44 test locations for each tibial plateau, the load response to focal indentation was measured as an index of cartilage stiffness. Overall, a high correlation was found between the dGEMRIC index (T) and local stiffness (Pearson correlation coefficients r = 0.90, 0.64, 0.81; p < 0.0001) when the GAG at each test location was averaged over a depth of tissue comparable to that affected by the indentation. When GAG was averaged over larger depths, the correlations were generally lower. In addition, the correlations improved when the central and peripheral (submeniscal) areas of the tibial plateau were analyzed separately, suggesting that a factor other than GAG concentration is also contributing to indentation stiffness. The results demonstrate the importance of MRI in yielding spatial localization of GAG concentration in the evaluation of cartilage mechanical properties when heterogeneous samples are involved and suggest the possibility that the evaluation of mechanical properties may be improved further by adding other MRI parameters sensitive to the collagen component of cartilage. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] Noncontact photo-acoustic defect detection in drug tabletsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2007Ivin Varghese Abstract Quality assurance monitoring is of great importance in the pharmaceutical industry for the reason that if defects such as coating layer irregularities, internal cracks, and delamination are present in a drug tablet, the desired dose delivery and bioavailability can be compromised. The U.S. Food and Drug Administration (FDA) established the Process Analytical Technology (PAT) initiative, in order to ensure efficient quality monitoring at each stage of the manufacturing process by the integration of analysis systems into the evaluation procedure. Improving consistency and predictability of tablet action by improving quality and uniformity of tablet coatings as well as ensuring core integrity is required. An ideal technique for quality monitoring would be noninvasive, nondestructive, have a short measurement time, intrinsically safe, and relatively inexpensive. In the proposed acoustic system, a pulsed laser is utilized to generate noncontact mechanical excitations and interferometric detection of transient vibrations of the drug tablets is employed for sensing. Two novel methods to excite vibrational modes in drug tablets are developed and employed: (i) a vibration plate excited by a pulsed-laser and (ii) pulsed laser-induced plasma generated shockwave expansion. Damage in coat and/or core of a tablet weakens its mechanical stiffness and, consequently, affects its acoustic response to an external dynamic force field. From the analysis of frequency spectra and the time,frequency spectrograms obtained under both mechanisms, it can be concluded that defective tablets can be effectively differentiated from the defect-free ones and the proposed proof-of-concept techniques have potential to provide a technology platform to be used in the greater PAT effort. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96:2125,2133, 2007 [source] Neurite growth in 3D collagen gels with gradients of mechanical propertiesBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2009Harini G. Sundararaghavan Abstract We have designed and developed a microfluidic system to study the response of cells to controlled gradients of mechanical stiffness in 3D collagen gels. An ,H'-shaped, source,sink network was filled with a type I collagen solution, which self-assembled into a fibrillar gel. A 1D gradient of genipin,a natural crosslinker that also causes collagen to fluoresce upon crosslinking,was generated in the cross-channel through the 3D collagen gel to create a gradient of crosslinks and stiffness. The gradient of stiffness was observed via fluorescence. A separate, underlying channel in the microfluidic construct allowed the introduction of cells into the gradient. Neurites from chick dorsal root ganglia explants grew significantly longer down the gradient of stiffness than up the gradient and than in control gels not treated with genipin. No changes in cell adhesion, collagen fiber size, or density were observed following crosslinking with genipin, indicating that the primary effect of genipin was on the mechanical properties of the gel. These results demonstrate that (1) the microfluidic system can be used to study durotactic behavior of cells and (2) neurite growth can be directed and enhanced by a gradient of mechanical properties, with the goal of incorporating mechanical gradients into nerve and spinal cord regenerative therapies. Biotechnol. Bioeng. 2009;102: 632,643. © 2008 Wiley Periodicals, Inc. [source] 3231: The effect of riboflavin mediated corneal crosslinking on corneal hydrationACTA OPHTHALMOLOGICA, Issue 2010G KONTADAKIS Purpose To evaluate the primary effect of corneal collagen crosslinking on corneal hydration. Methods Twenty corneal buttons from freshly enucleated porcine eyes where immersed in riboflavin 0.1% in dextran 20% dilution for three hours in order for their hydration to reach an equilibrium. Corneal buttons where divided in two groups; the first group was stored in dark conditions while the other group was irradiated with UV radiation (390nm) for 30 minutes to stimulate collagen cross-linking according to the clinically applied protocol. After irradiation all corneas were immersed in dextran 20% solution for 30 additional minutes and subsequently weighted. Finally all corneal buttons were dehydrated for 48 hours in a desiccating oven set at 62Co and weighted again to obtain their dry mass. Hydration (%) of each button was calculated. Results were analyzed with non parametric tests. Results Irradiated group of corneas had statistically significant lower hydration than the non irradiated group. (p<0.05, Mann-Whitney Test). Mean hydration in the irradiated group was 71% and in the non-irradiated 75%. Conclusion Collagen crosslinking causes corneal dehydration that can be detected immediately after the procedure. This phenomenon may contribute to increased mechanical stiffness of the cornea. [source] | |||||||||||||