bluuebunny/crossref_metadata_2025 huggingface dataset:
The Load Sharing Contribution of Spinal Facet Joint During Impact Loading: A Porcine Biomechanical Model
Authors: Lai Cheng-Chuan , Wang Jaw-Lin , Chang Guan-Liang , Chung Cheng-Hsien
Published: May 2008

The components that share the loading of motion segment include the facet joint and disc. Nachemson [1] reported the facet joint share 18% of vertical loading in a motion segment; while many other researchers reported the load sharing percentage of facet joint ranges from 1% to 57% [2,3]. The current study developed a unique apparatus using an in vitro porcine spine model to quantify the alteration of loading in the facet joint under impact compressive loading at different loading conditions. A drop tower type impact apparatus was used to produce the impact energy for the motion segment. A 6-D load cell was placed under the specimen to detect the force and moment responses. The pressure sensor was inserted into the facet joint to find the contact force. The pointed axial compresive forces were applied at 8 locations from anterior to posterior of upper vertebrae to mimic different impact loading conditions. The impact energy was fixed at 1.2 J. We found that; when the loading was applied anteriorly, the facet joint sustained very small percentages of the loading; while the location of the loading moved posteriorly, the facet joint sharing percentages increased. The largest sharing percentages of facet joint reached 30% in the current study.
Effects of Blood Flow on Radiofrequency Ablation of Tumors: Finite Elements and In Vitro Models
Authors: Cebral Juan R. , Soto Orlando , Lutz Robert J. , Wood Bradford J.
Published: May 2008

The efficacy of radiofrequency ablation (RFA) treatments depends on the ability to ablate tumors completely while minimizing the damage to healthy tissue. Tissue cooling due to blood flow is an important factor affecting the size and shape of the ablation lesion. In this paper a new methodology for finite element modeling of the coupled electrical-thermal-flow process during RFA is presented. Our formulation treats heat losses due to blood flow explicitly rather than approximating the collective effects of blood vessles as a heat sink. Numerical models were compared to in vitro models using egg whites to simulate human tissue and a straight cylinder filled with a saline solution to simulate blood. Asymmetric burns were obtained close to the simulated blood vessels. Numerical results closely match the in vitro models.
Patient-Specific Modeling of Atherosclerotic Carotid Arteries From Multi-Modality Image Data
Authors: Cebral Juan R. , Putman Christopher , Pergolizzi Richard , Burgess James E.
Published: May 2008

Estimation of the wall shear stress distribution in stenotic carotid arteries is important for assessing risk of stroke. Since there are no reliable experimental methods to determine wall shear stress distributions, realistic patient-specific computational fluid dynamics models are constructed from medical images. Anatomical and physiologic data are obtained from multiple image modalities including 3D rotational angiography, contrast-enhanced magnetic resonance angiography, carotid duplex ultrasound and phase-contrast magnetic resonance. These images are used to construct patient-specific finite element grids and to solve the incompressible Navier-Stokes equations under physiological pulsatile flow conditions. The detailed knowledge of the carotid hemodynamics derived from these models can be used to enhance our understanding of the relationship between flow patterns and symptoms, and ultimately risk of stroke. This methodology can also be used to correllate flow patterns with the outcome of endovascular procedures such as angioplasty and stenting.
Quantifying Motion Across a Solid Lumbar Interbody Fusion Using a Finite Element Model
Authors: Khandha Ashutosh D. , Vadapalli Sasidhar S. , Holekamp Scott A. , Goel Vijay K. , Bono Christopher M. , Garfin Steve R.
Published: May 2008

Clinical assessment of pseudarthrosis or solid fusion is based on the residual motion across the “fused” segment (Kowalski et al, 2001). Dynamic flexion/extension (F/E) radiographs are commonly used to determine residual motion. Despite widespread use, it is unclear what the appropriate “cut-off” criteria to declare a fusion solid should be, with recommendations ranging from 0 to 5°. These values have not been derived by scientific methods. The present study was initiated to predict the angular sagittal motion across simulated lumbar interbody fusions (IF) using a Finite Element Model (FEM) of the ligamentous lumbar spinal segment. Anterior and posterior lumbar interbody fusions were simulated at the L3–L4 level as per the clinical procedure. Varying degrees of fusion were taken into account and the fusion mass was the simulated as a cancellous core with a cortical shell. The results indicated that 0.5° to 5.14° of angular motion can occur depending on fusion location and degree of completeness. While continuous bone might be noted at surgical exploration, this amount of motion may enable persistent loading of remaining structures, such as the annulus or spinal ligaments. In our view, this may prompt a redefinition of clinically “solid fusion”.
Knee Joint Loading Patterns During Activities of Daily Living in TKR Patients
Authors: Benson Lisa C. , LeBerge Martine , Pace Thomas B.
Published: May 2008

The kinetics and kinematics of the knee joint during a variety of activities of daily living were studied in a group of total knee replacement (TKR) patients. The parameters examined were those needed to program a force-controlled knee simulator (axial and anterior-posterior (AP) forces, internal-external (IE) moment, and flexion angle). These parameters were calculated for walking, fast walking, stand-to-sit, sit-to-stand, bending, stair ascent and stair descent using body-fixed inertial sensors, a force platform, and estimates of muscles forces. Peak values for loading patterns were not significantly different from those for an age-matched control group. Axial forces were lower in comparison to published results for normal and TKR populations, due to slower cadences and conservative estimates of muscle forces. Peak posterior forces and IE moments were higher than published results. These patterns were combined to form a spectrum loading pattern, with the activities occurring in approximately the same ratios of relative frequency as reported in the literature. The spectrum pattern can be used to program a force-controlled knee simulator in order to apply more relevant loading patterns to knee implants.
A Theoretical and Experimental Procedure for Designing of Oil Circulation Ratio Reduction
Authors: Toyama Toshiyuki , Uekawa Takashi , Hiodoshi Susumu , Hagiwara Shigeki
Published: May 2008

This report demonstrates the successful development of a design method reducing oil circulation ratio (hereafter OCR) in swing compressors, based on calculations from a simplified model and an actual experiment. The developed OCR analysis tool features the addition of oil circulation flow rate circuit to the oil supply circuit that diagnoses the pump, the oil feeding passage, and the bearings by electrical circuit. The oil circulation flow rate is affected by refrigerant flow. In consideration of the complementary effects of refrigerant gas and oil circulation flow rate, including wall impingement of oil droplets, the gravity of oil droplets, and buoyancy, calculations can be conducted as separation efficiency ratio. In the experiment, the behavior of oil droplets in refrigerant in a compressor outfitted with pressure-proof glass was observed with a high-speed camera. It was thereby ascertained that the predicted speed of oil droplets and the actual speed in the compressor were almost the same. The effects of a drop in oil level during operation due to the oil circulation flow rate can be taken into account, something previously impossible with conventional circuits. The conclusive analytical precision of OCR is a range of 30–115Hz with a margin of error of ±0.3wt%. Using this method, design points that have substantial impact on OCR reduction can be clarified. With structural changes to the motor-rotor as suggested from the analysis, OCR can be reduced. Consequently, a significant reduction in the period necessary for compressor development has been achieved.
Biomechanical Changes at Adjacent-Level Segments After Anterior Cervical Discectomy and Fusion
Authors: Natarajan R. N. , Andersson G. B. J. , An H. S.
Published: May 2008

It is well documented that there is significant motion in the unfused segments above and below a fused segment during anterior cervical discectomy and fusion but exact nature of this motion is not well known. The current finite element study showed that likelihood of adjacent segment degeneration is higher in a two level fusion than a one level fusion. Also, the analyses showed that two level fusion at upper cervical levels more likely to degenerate above and below than two level fusion at lower cervical levels.
Electric Field Effects on the Stability of Vapor Microlayers: Enhancement of Heat Transfer
Authors: Sankaran Subramanian , Allen Jeffrey S. , Gumennik Leonard
Published: May 2008

The effect of dc electric fields on destabilization of a vapor microlayer formed during film boiling at various subcooling levels is investigated. High voltage electric fields up to 2000 volts were applied between a 127 μm heater wire and a screen electrode that is concentrically placed at a radius of 25 mm. The qmax and qmin heat fluxes were also measured for the various subcooling and electric field strengths. Up to 50% increase in the qmax and the qmin heat fluxes were observed when using the electric fields in this range of experimental parameters. The relationship among subcooling level for a given fluid, the heat flux level, and the electric field strength required to reach the qmin condition is of interest. The preliminary experimental results and the bubble departure and transition boiling patterns resulting from destabilization of the vapor microlayer are discussed.
Stress Changes in Intervertebral Discs of the Cervical Spine After Partial Fusion
Authors: Tchako Abraham , Sadegh Ali M.
Published: May 2008

A detailed and validated 3D FE model of human cervical spine (Sadegh et al. 2000) was altered to simulate partial fusion. Five single level partially fused new models, one at each disc level, were used to study the change in stresses in adjacent levels. Two cases of partial fusion, 80% and 60% were considered. The fused models were loaded with a 50 N compressive pre-load and with a 1.5 Nm moment in flexion, extension, lateral bending and axial rotation. The previously obtained results of the unfused model (Tchako et al. 2002) and of the fused models were used to study the change in stresses in adjacent levels. The results indicate that, in general, there are stress changes as high as 94%, depending on the loading mode and location, in adjacent discs after discectomy and fusion. However, the difference between the stress change of 80% and 60% of partial fusion is insignificant.
Effect of Off-Axis Cell Orientation in Smooth Muscle Tissue
Authors: Sarma P. A. , Pidaparti Ramana M. , Meiss Richard A.
Published: May 2008

The cell alignment in a smooth muscle tissue plays a significant role in determining its mechanical properties. In addition to shortening strain, the off-axis cell orientation θ also modify the shear stress relationship significantly. A simulation model based on finite element analysis is developed to study the effect of stresses of tracheal smooth muscle tissue when its cells are orientated off-axially. Results obtained indicate that the maximum shear stress values of tracheal smooth muscle tissue at 45% strain are 2.5 times the values at 20% strain for all three off-axis orientation values θ = 15°, 30° and 45°.
Fracture of Thin Film Structures With Creeping Underlayer
Authors: Huang R. , Liang J. , Pre´vost J. H. , Suo Z.
Published: May 2008

Fracture in small structures has been studied intensely in recent years, motivated by diverse applications such as interconnects in mircoprocessors, resonant structures in microelectromehanical systems, thermal barrier coatings in gasturbine engines, and multilayers in medical implants. The applications typically require that materials with extremely different properties be integrated in small dimensions. The structural complexity, as well as the small feature sizes, can lead to unusual phenomena. For example, it is discovered that cracks can grow in brittle films under cyclic temperatures, driven by ratcheting plastic deformation in a metal underlayer. We will revisit this phenomenon toward the end of this paper.
Analysis of Finger Joint Kinematics Before and After MCP Joint Arthroplasty
Authors: McNeal David , elHassan Bassem , Amirouche Farid , Gonzalez Mark
Published: May 2008

The purpose of this study is to assess the kinematical changes in the flexion of the finger joints after MCP arthroplasty. Angular joint position in relation to its corresponding excursion was used to quantify the kinematics of the finger. The assessment used real time data acquisition and fresh-frozen cadaver hands. Several important benchmarks were considered in analyzing the data. First of all, the initiation of the digit was considered. When a tendon is pulled, motion is normally observed in the DIP first, followed by the PIP, and finally the MCP. This order should be maintained after the arthroplasty. For our kinematics study, it is also important to note any significant increase or decrease in the time of the initiation. Other benchmarks we considered include the starting and ending angle of the joints. The start and ending angle is important when studying the overall range of motion of the digit. The overall range of motion affects basic hand function and is one measure of successful arthroplasty. Excursion was also considered as an overall measure of how well the prosthesis mimics the original joint. Large changes in excursion could indicate that the original center of rotation has not been maintained.
Characterization of the Viscous Behavior of Compacted Ceramic Particles Under Shear and Pressure Loads
Authors: Zhou Fuping , Advani Suresh G. , Wetzel Eric D.
Published: May 2008

Ceramic armors are known to provide excellent ballistic resistance, but the precise mechanisms of projectile defeat in these systems are not fully understood. A critical stage in the penetration process is the flow of the pulverized ceramic past the projectile. To further understand this phenomenon, we are investigating the flow and energy dissipation of granular beds, specifically under conditions of high pressure. Two different viscometer systems are designed and fabricated to characterize the behavior of ceramic particles under shear stress and high pressures. The first system is a Couette flow device with ability to exert pressure on the particles during its rotation and measure the torque and angular velocity of the system. These data are used to extract viscosity and energy dissipation due to friction between particles as a function of the shear rate. The second system focuses on the movement of a cylinder through a bed of compacted ceramic particles. By measuring the force required to move the cylinder through the compacted bed, we can evaluate the effective resistance of the particle bed under various compaction pressures. By characterizing the friction coefficient, we obtain the apparent viscosity of the compacted granules under different pressure loads for low strain rates. This characterization should prove useful in understanding the shearing and dissipation mechanisms between granular particles under high pressures.
An Empirical Formula for the Estimation of the Residual Stress in Boron-Doped Silicon Films
Authors: Jeong Ok Chan , Yang Sang Sik
Published: May 2008

In this paper, a novel empirical formula is proposed to estimate the residual stress profile as a function of the boron-doped silicon film depth. The residual stress profile is derived from the proposed boron concentration profile, which is a second order function of the film depth, the boron diffusion length, and the correlation coefficient between the residual stress and the boron concentration. The proposed empirical formula is verified by the comparison of the previous results such as the residual stress profiles determined by the quantitative analysis method and the boron concentration profile measured by SIMS and spreading resistance. If the correlation coefficient increases, the residual average and maximum stresses are exponentially reduced. If the drive-in process time or the temperature increase, the compressive stress develops on the surface of the boron-doped silicon film due to the thermal oxidation process.
Vibration and Frequency Analysis of Non-Uniform Timoshenko Beams Subjected to Axial Forces
Authors: Ohadi A. R. , Mehdigholi H. , Esmailzadeh E.
Published: May 2008

Dynamic and stability analysis of non-uniform Timoshenko beam under axial loads is carried out. In the first case of study, the axial force is assumed to be perpendicular to the shear force, while for the second case the axial force is tangent to the axis of the beam column. For each case, a pair of differential equations coupled in terms of the flexural displacement and the angle of rotation due to bending was obtained. The parameters of the frequency equation were determined for various boundary conditions. Several illustrative examples of uniform and non-uniform beams with different boundary conditions such as clamped supported, elastically supported, and free end mass have been presented. The stability analysis, for the variation of the natural frequencies of the uniform and non-uniform beams with the axial force, has also been investigated.
Stiffness Comparison of Coracoclavicular Ligament and Anatomic Reconstruction Complexes: Overall and Individual Complex Components
Authors: Costic Ryan S. , Labriola Joanne E. , Rodosky Mark W. , Debski Richard E.
Published: May 2008

The stiffness of the coracoclavicular ligaments and their surgical replacments have previously been reported; however, the mechanism of failure and procedures for repair include both the clavicle and coracoid process which have not been investigated. Therfore, this study utilized a physiolgogic mechanism of injury to compare the stiffness of the coracoclavicluar ligament and anatomic reconstruction complexes, both overall and individual complex components. After dislocation of the coracoclavicular ligament complex, a 40% decrease of the clavicle stiffness was observed along with a more comparable stiffness of the reconstruction tendon graft to the intact coracoclavicular ligaments compared to current repair materials. These findings suggest all components of the coracoclavicluar complex following dislocation should be considered in selection of rehablilation protocols or surgical procedures.
Fiber Kinematics of Small Intestinal Submucosa Subjected to Biaxial Stretch
Authors: Gilbert Thomas W. , Grashow Jonathan , Woo Savio L.-Y. , Chancellor Michael B. , Sacks Michael S.
Published: May 2008

Small intestinal submucosa (SIS) of the porcine has been used extensively over the past decade for repair of a variety of connective tissues, and is now being considered for functional tissue engineering applications. Thus, it is important to consider the kinematics of its fibers. The current study investigated the fiber kinematics of SIS in response to multiple stretch patterns using a modified version of a biaxial stretching device integrated with a small angle light scattering (SALS) apparatus (Billiar and Sacks 1997). Each sample was loaded to equibiaxial strain of 10% by stretching in each of the following stretch patterns: 1) first in the preferred fiber direction, then in the cross-preferred direction, 2) first in the cross-preferred direction, then in the preferred direction, and 3) simultaneously in both directions equally. The collagen fiber distributions for the equibiaxial strain states were found to be relatively insensitive to the stretch pattern. Further, an affine transformation calculation based on Lanir (1979) and Billiar and Sacks (1997) was used to predict the strip biaxial and equibiaxial collagen fiber distributions and it was found that while the tissue generally followed the trends expected for an affine material, the intensity levels were not predictive.
Hypo-Osmolarity Decreases the Ability of Cells in Articular Cartilage to Survive a Load-Induced Injury
Authors: Levin Adam , Torzilli Peter A. , Chen C. T. Christopher
Published: May 2008

A recent study showed that exposure to hypotonic conditions increased chondrocyte surface area up to 234% by stretching the folded membrane, which may reduce the chondrocyte’s ability to deform under load. The goal of this study was to determine the effect of hypo-osmolarity on chondrocyte survival from load-induced injury. Bovine cartilage explants were incubated in either isotonic or hypotonic pH-buffered solution for 20 minutes, loaded with cyclic confined compression at 5MPa for 1 hour, and then assessed for cell viability using cell vital dyes and for pericellular matrix (PCM) using an type VI collagen antibody. Cell death in loaded explants was significantly greater than that of non-loaded controls (p<0.001). However, explants loaded in the hypotonic solution showed significantly greater cell death than those loaded in the isotonic solution. An increase of dead cells with flatten PCM were located in the superficial zone. Our findings suggest that hypo-osmolarity decreases the ability of chondrocytes in articular cartilage to survive from load-induced injury.
Dynamic Punch Shear Characterization of Woven Graphite/Epoxy Laminates
Authors: Hosur M. V. , Waliul Islam S. M. , Vaidya U. K. , Dutta P. K. , Jeelani S.
Published: May 2008

In many situations, composite structures are subjected to dynamic loading. To design such structures, there is a need of dynamic material properties. In the current investigations, a compression Split Hopkinson Pressure Bar was modified to load the samples in punch shear mode. Experimental studies were conducted to characterize 24 layer woven graphite/epoxy laminate samples. Laminates were manufactured using vacuum assisted resin infusion molding process with two types of fabric architecture: plain and 8-harness satin weave. Samples of nominal size 26 mm × 13 mm × 4 mm were subjected to dynamic punch shear tests at three different pressure settings that yielded strain rates in the range of 1200–3400/s. Results of the tests indicate that the dynamic shear strength increases with increase with the strain rate for both types of laminates. Plain weave graphite/epoxy laminates yielded higher shear strength as compared to satin weave graphite/epoxy laminates due to higher crimp angle.
Effect of Pharmaceutical Bone Growth Stimulation With Novel Anabolic Peptides: Biomechanical and Bone Density Measurements in a Rat Model
Authors: Askew Michael J. , Schneider Gary B. , Grecco Kristina J. , Hsu Jason , Mugler Emily , Noe Donald A.
Published: May 2008

Pharmaceutical bone growth stimulation holds promise for prevention and treatment bone disorders, and the enhancement of fracture healing. Bone growth hormones have begun to have limited clinical use, but can illicit adverse side effects. Recent studies have shown that short peptides (less than 15 amino acids) derived from the protein sequence of Vitamin D Binding Protein (DBP), can enhance bone formation (osteogenesis). These peptides may have potential as controllable bone growth stimulators without the adverse side effects and cost of bone growth hormones. Rats, injected every other day for two weeks with DBP-based peptide fragments ranging from 3 to 13 amino acids in length, were euthanized and the tibias and femurs were scanned by peripheral quantitative computerized tomography (pQCT) to determine bone density and cross-sectional geometric properties. The bones were then tested in three-point bending to determine strength and bending modulus. Injection of DBP-based peptides over only a 2-week period resulted in significant (p<0.05) increases in bone density and material properties in the experimental rat bones in comparison to controls injected with saline. The short length of these effective peptides suggests their use not only in systemic injections but also as clinically convenient pills taken orally for pharmaceutically induced bone growth stimulation.
Tuning the Static and Modal Response of Microcantilevers Through Lumped-Parameter Model-Based Design
Authors: Garcia Ephrahim , Lobontiu Nicolae , Nam Yoonsu
Published: May 2008

The paper introduces the circular-notch microcantilever design that can be utilized in mass detection and atomic force microscopy (AFM) microsystems. The microcantilever is modeled as a three degree-of-freedom member which is sensitive to bending and torsion. A lumped-parameter model is formulated that gives directly the stiffness closed-form equations and the inertia fractions about the degrees of freedom. It is thus possible to qualify and tune the static and modal responses of this specific microcantilever design in order to match or, on the contrary, to avoid, stiffness and frequency ranges that are of interest by means of only geometry alterations. The microcantilever’s sensitivity to bending and torsion can also be modified by simple manipulation of the defining geometric parameters. The analytical model predictions are confirmed through limit calculations and finite element simulation. The stiffness factors of the circular-notch microcantilever design are compared to the ones of a similar constant rectangular cross-section configuration by means of the analytical model developed herein.
Fiber-Matrix Interactions in Tendon Anisotropic Tensile Behavior
Authors: Lynch Heather Anne , Elliott Dawn M.
Published: May 2008

A three dimensional anisotropic model for tendon behavior was used to fit experimental stress-strain data. This model was motivated by tendon microstructure and included the contributions of fibers, matrix, and fiber-matrix interactions. Our results suggest that fiber-matrix interactions contribute to tendon mechanical behavior.
Elevated Joint Contact Forces in ACL-Reconstructed Knees: A Finite Element Analysis Driven by In Vivo Kinematic Data
Authors: Papaioannou George , Anderst William , Tashman Scott
Published: May 2008

Assessment of in vivo human cartilage loading generally requires computer modeling, since loads usually cannot be directly measured. The utility of these models for assessing knee behavior during complex activities has been limited by the relatively poor quality of experimental data on in vivo knee function. We have developed a method combining high-accuracy knee kinematics (from high-speed stereo-radiography) with subject-specific finite-element models to estimate in vivo cartilage contact pressures during stressful tasks. When applied to ACL reconstruction, significantly higher contact pressures were found in reconstructed knees as compared to the contralateral (uninjured) knees of the same individuals.
Preliminary Results of Cyclic Uniaxial Compression of Bovine Liver
Authors: Taylor Lawrence S. , Mejia Lito , Rubens Deborah J. , Parker Kevin J.
Published: May 2008

The frequency dependent viscoelastic properties of bovine liver are investigated in support of the development of an ultrasonic vibration imaging system for the detection of hard lesions in soft tissue. This system, which we call sonoelastography, is being applied to imaging coagulation necrosis lesions induced in liver tissue using radio frequency ablation. Detectability of lesions in sonoelastography depends on the relative contrast between the elastic modulus of the lesion and background tissue. Unconfined uniaxial cyclic compression is used to determine the complex Young’s modulus of bovine liver and is fit to a Kelvin-Voigt fractional derivative model (KVFD). Extracted model parameters and goodness of fit are presented.
A Finite Element Study of the Combined Effect of Fusion and Disc Degeneration on Adjacent Levels of the Lumbar Spine
Authors: Hariharan Lakshminarayan , Amirouche Farid , Varadarajan Ravikumar
Published: May 2008

Intervertebral disc degeneration is believed to be the main cause of low back pain and has mostly been treated with lumbar interbody fusion or arthrodesis. Although fusion is a very common solution to low back pain it has been associated with disc degeneration and degenerative spondylolisthesis in the adjacent segment. A number of studies have been performed to study the effect of fusion, however there has not been any significant study to observe a fused spine with a degenerated disc at an adjacent level. This study involved a finite element model of the Lumbar spine L1-L5 which was fused with a bone graft at the L4-L5 level and degenerated in two stages at the L3-L4 level and also analyzed with reduced disc heights all in different cases.
Decomposition-Based Assembly Synthesis of a 3D Body-in-White Model for Structural Stiffness
Authors: Lyu Naesung , Saitou Kazuhiro
Published: May 2008

This paper presents an extension of our previous work on decomposition-based assembly synthesis for structural stiffness [1], where the 3D finite element model of a vehicle body-in-white (BIW) is optimally decomposed into a set of components considering the stiffness of the assembled structure under given loading conditions, as well as the manufacturability and assembleability or components. Two case studies, each focusing on the decomposition of a different portion of a BIW, are discussed. In the first case study, the side frame is decomposed for the minimum distortion of front door frame geometry under global bending. In the second case study, the side/floor frame and floor panels are decomposed for the minimum floor deflections under global bending. In each case study, multi-objective genetic algorithm [2,3] with graph-based crossover [4,5], combined with FEM analyses, is used to obtain Pareto optimal solutions. Representative designs are selected from the Pareto front and trade-offs among stiffness, manufacturability, and assembleability are discussed.
Thermocapillary Instability With a Rotating Magnetic Field and System Rotation
Authors: Ma Nancy , Walker John S. , Witkowski Laurent Martin
Published: May 2008

This paper presents a linear stability analysis for the thermocapillary convection in a liquid bridge bounded by two planar liquid-solid interfaces at the same temperature and by a cylindrical free surface with an axisymmetric heat input. The two solid boundaries are rotated at the same angular velocity in one azimuthal direction, and a rotating magnetic field is applied in the opposite azimuthal direction. The critical values of the Reynolds number for the thermocapillary convection and the critical-mode frequencies are presented as functions of the magnetic Taylor number for the rotating magnetic field and of the Reynolds number for the angular velocity of the solid boundaries.
Flexural Rigidity of the Commissure Region of the Aortic Valve Leaflet
Authors: Mirnajafi Ali , McClure Leigh , Raymer Jeremy , Sacks Michael S.
Published: May 2008

Flexure is a major deformation mode of the aortic valve (AV) leaflet during valve function [1]. The structure of the AV must thus allow for low flexural rigidity yet also be of sufficient strength to support large tensile loads during valve closure. It well known that the AV is a heterogeneous structure uniquely adapted to provide efficient valve function. Yet, unlike the trilayered central leaflet region, the commissural region commissural region of the AV leaflet (Fig. 1) is composed of only a single layer of collagen fibers. The effect of this structural difference in the AV leaflets flexural rigidity and hence its function is unknown. Also, knowledge of the flexural rigidity of the AV leaflets can be used as design criteria in fabricating bioprosthetic and tissue engineered heart valve considering the fact that the commissural region is known to be a major site for porcine bioprosthetic failure [2]. Yet, to our knowledge the mechanical properties of the AV leaflet in the commissural area have never been measured, due to its small size (3–5 mm).
Simulation of a Fifteen Passenger Van Rollover and Occupant Kinematics
Authors: Poland Kristin M. , Bishop Jennifer , Beckjord Michele McDonald , Lack Shane
Published: May 2008

This study examined the occupant kinematics during the rollover of a 15-passenger van. The main focus of the investigation was to determine possible kinematics that led to ejection, the time period of the potential ejections, and to determine injury causing kinematics or impacts. The time during which the ejections occurred was used to determine whether all the ejections could have occurred during the first overturn or if at least two overturns were necessary. The occupants were simulated in the estraint condition similar to the accident, all restrained in lap belts, and all restrained in lap/shoulder belts. The results of the simulation indicated that predicted injury levels were reduced and full ejection was eliminated when occupants were properly restrained with lap/shoulder belts. The simulation did not account for intrusion when determining injury.
Effects of Partial and Total Meniscectomy on Kinematics of the Knee: A Magnetic Resonance Imaging Study
Authors: Yao Jiang , Snibbe Jason C. , Maloney Michael D. , Lerner Amy L.
Published: May 2008

Meniscal injuries frequently occur in combination with anterior cruciate ligament (ACL) tears. Tears in the menisci that occur acutely with ACL injury are located either medially or laterally, but in ACL deficient knees chronic instability most commonly leads to meniscal tears in the posterior horn of medial meniscus (Smith & Barrett, 2001). Levy et al. (1982) suggested that medial meniscus might act as a mechanical wedge preventing tibial anterior translation due to its firm attachment to the tibia at the posterior horn. Previous biomechanical studies infer the role of the meniscus through measurements of alternations in forces or knee motions (Shoemaker & Markolf, 1986; Allen, 2000), however no study has provided clear images of the motion or deformation of the meniscus itself. The objective of this study was to investigate the effects of anterior cruciate ligament resection, as well as partial and complete meniscectomies on knee kinematics in response to anterior loading. Application of loads during magnetic resonance (MR) imaging allows us to visualize the motion and deformation of the menisci, and therefore obtain a more clear understanding of its role in knee stability.
Optimization of Cryogen Spray Cooling for Port Wine Stain Laser Therapy Using Photoacoustic Measurement of Epidermal Melanin
Authors: Viator John A. , Aguilar Guillermo , Jacques Steven L. , Nelson J. Stuart
Published: May 2008

Treatment of vascular skin lesions, such as port wine stain (PWS) birthmarks, uses laser energy to thermally damage the hypervascular regions in the dermis. Delivery of sufficient laser energy to the dermis can be confounded by the more superficial epidermal melanin layer, a broadband optical absorber. Laser pulses directed at skin lesions may result in excessive heating and scarring of the epidermis, resulting also in limiting the energy available to treat the dermal lesion. Cryogen spray cooling is used to selectively cool the epidermis, allowing the use of higher laser fluences which cause thermal damage in the deeper lesion, while preventing hypertrophic scarring of the epidermis. In order to optimize cryogen cooling and laser pulse parameter for treatment, the depth profile of the epidermal melanin layer and vascular lesion must be known. We use a photoacoustic probe to determine this depth profile. A Q-switched Nd:YAG laser emitting 532 nm light pulses of 4 ns duration is used to excite acoustic waves in epidermal melanin and hemoglobin in the vascular lesions via a miniature probe incorporating a piezoelectric detector. We used acoustic propagation time to determine the spatial relationship of the absorbing structures, thereby giving the necessary means to determine cryogen spurt and laser pulse timing. We present a finite difference thermal model along with data from tissue phantoms showing the effectiveness of the photoacoustic method.
Modeling of Trabecular Bone as a Couple Stress Continuum
Authors: Yoo Andrew , Jasiuk Iwona
Published: May 2008

We model trabecular bone as an idealized periodic structure made of open cubic cells and represent it as a linear elastic couple stress continuum. We find couple stress moduli for such material using displacement and traction boundary conditions. Several different loadings are applied to obtain these couple stress constants: uniaxial extension (or tension), hydrostatic deformation (or pressure), applied curvature (or bending moment), and twist (or torsion).
Damage Identification Using Impedance Methods Coupled With Statistical Classifiers
Authors: Park Gyuhae , Rutherford Amanda C. , Sohn Hoon , Farrar Charles R.
Published: May 2008

This paper presents the use of statistically rigorous algorithms combined with active-sensing impedance methods for damage identification in engineering systems. In particular, we propose to use statistical pattern recognition methods to address damage classification and data mining issues associated with the examination of large numbers of impedance signals for health monitoring applications. The impedance-based structural health monitoring technique, which utilizes electromechanical coupling properties of piezoelectric materials, has shown feasibility for use in a variety of damage identification applications. Relying on high frequency local excitations (typically > 30 kHz), this technique is very sensitive to minor changes in structural integrity in the near field of piezoelectric sensors. In this study, in order to diagnosis damage with levels of statistical confidence, the impedance-based monitoring is cast in the context of an outlier detection framework. A modified autoregressive model with exogenous inputs (ARX) in the frequency domain is developed. The damage sensitive feature is then computed by differentiating the measured impedance and the output of the ARX model. Furthermore, because of the non-Gaussian nature of the feature distribution tails, extreme value statistics (EVS) are employed to develop a robust damage classifier. By incorporating EVS, we establish a rigorous impedance-based health monitoring algorithm, which is able to provide structural systems with self-contained and self-diagnostic components. This paper concludes with a numerical example on a 5 degree-of-freedom system and an experimental investigation on a multi-story building model to demonstrate the performance of the proposed concept.
An Implantable Microfabricated Drug Delivery System
Authors: Maloney John M.
Published: May 2008

We report on the development of a fully implantable drug delivery system capable of delivering hundreds of individual doses. This product is intended for the controlled release of potent therapeutic compounds that might otherwise require frequent injections. Our system has the following capabilities: • Stable, hermetic storage of therapeutic drugs in solid, liquid, or gel form; • Individual storage of discrete doses for multiple-drug regimens; • Wireless communication with an external controller for device monitoring and therapy modification; • Choice of preprogrammed release or release on command; • Controlled pulsatile or continuous release. MicroCHIPS’ drug release technology has been successfully demonstrated in vitro and in vivo. We are proceeding with long-term in vivo studies of a fully implantable device containing one hundred individual doses. A future device intended for human clinical trials will contain four hundred doses, enough for a daily release of drug for more than one year.
Microsystems for Manipulation and Characterization of Biological Systems
Authors: Okandan Murat
Published: May 2008

Microsystems provide some of the most intriguing options for studying and modifying cells and larger biological systems. During the last two decades, a large suite of micro- (electro-opto-chemo-mechanical) components have been fabricated and characterized in numerous labs around the world. Our group has been building on this technology base to develop devices for biological and medical applications. Using our surface micromachining technology (Sandia’s Ultra-planar, Multi-level MEMS Technology - SUMMiT™) as a starting point, we have developed a modified process flow (Surface micromachining with Integrated microFluidics Technology - SwIFT™) which incorporates silicon nitride layers that allow the creation of insulator lined, optically transparent microfluidic structures. Incorporation of mechanical, electrical and optical structures with microfluidic components enable the design and manufacture of highly functional devices in a batch-fabrication methodology. Some of the devices currently being tested include a microtransfection device, patch clamp array with integrated electronics, microfluidics and mechanical coupling to the cells, valves, pumps and channels with electrodes for manipulating (separating, concentrating) cells and particles.
Angiographic Quantification of Angiogenesis
Authors: Gounis Matthew J. , Lieber Baruch B. , Webster Keith A. , Wasserlauf Bernard J. , Prentice Howard M. , Wakhloo Ajay K.
Published: May 2008

Therapeutic angiogenesis is the attempt to increase vascular density by means of an exogenously administered proangiogenic agent and offers a potential treatment for diseases associated with tissue ischemia. Vascular endothelial growth factor (VEGF) expressed by gene therapy has been shown to be a potent stimulator of angiogenesis and to improve the function of ischemic tissues in patients [Isner, 1998]. Unregulated gene therapy is disconcerting since there is no assurance that the treatment will target the ischemic territory. A new regulated adeno-associated viral vector expressing VEGF165 that is conditionally silenced has been developed by one of the authors (KAW). The transgene expression is regulated by silencing the genes in the absence of the disease and at the same time having strong and local activation in the presence of the disease. The purpose of this work is to establish protocols and techniques to quantify the efficacy of therapeutic angiogenesis. The initial phase of this research involves assessment of angiogenesis using an unregulated, adenoviral vector that is encoded to express VEGF165. Using the rabbit hind limb ischemia model, angiography was performed on animals that were given the proangiogenic treatment and on a sham group, in which phosphate buffered saline (PBS) was injected. Angiographic contrast intensity curves were obtained, modeled, and the optimized model parameters provided insight into flow characteristics within the targeted vascular bed. In the second phase of the project the conditionally silent vector will be employed using the developed protocols and methods of the first phase to afford comparisons with the previous groups.
Dynamic Response in the Low-kHz Range and Delta-E Effect in Ferromagnetic Shape Memory Ni-Mn-Ga
Authors: Faidley LeAnn E. , Dapino Marcelo J. , Washington Gregory N. , Lograsso Thomas A.
Published: May 2008

Recent work on ferromagnetic shape memory nickel-manganese-gallium (Ni-Mn-Ga) has demonstrated several characteristics which make this material attractive as an active element for the next generation of intelligent transducers. Alloys of martensitic Ni-Mn-Ga can strain up to 6% as a result of the rotation of twin variants and associated twin boundary motion which occur in these materials in response to magnetic fields. The magnetic actuation holds promise in transducer design because it can lead to enhanced frequency response compared with shape memory alloys with comparable strains. In this paper, we report on experimental measurements collected from a Ni50Mn28.7Ga21.3 sample which has been tested in a solenoid transducer by means of a novel drive configuration consisting of a collinear uniaxial field-uniaxial stress pair. We have observed that the elastic modulus of a Ni-Mn-Ga sample driven in these conditions changes substantially in response to varying bias field. In this paper, we further investigate the dependence of the elastic modulus on ac field intensity and mechanical load as well as bias field. Quasistatic, white noise, and swept-sine excitations were employed to examine the behavior of Ni50Mn28.7Ga21.3 driven under various combinations of magnetic fields and mechanical loads. Mechanically free quasi-static tests demonstrate reversible strains of 6300 με which are consistent with prior measurements on samples with similar composition near the Heusler stoichiometry. Dynamic measurements reveal a significant stiffness increase, of up to 209%, with dc bias field. This frequency shift or ΔE effect is shown to originate in the Ni-Mn-Ga sample and is believed to stem from the reorientation of twin variants in response to varying dc field. These results might facilitate a new class of solenoid-based Ni-Mn-Ga transducers for tunable vibration absorber applications, and lay the ground work for developing methods and criteria for the implementation of broadband Ni-Mn-Ga transducer technologies.
Microscale Resolution of Moisture Content in Dried Sugar Matrices
Authors: Elliott Gloria D. , Azadivar Justin , Toner Mehmet
Published: May 2008

Currently many methods of drying are under investigation for the anhydrous preservation of mammalian cells, including convective drying (Bhowmick et al., 2003), vacuum drying (Elliott et al., 2002), room temperature desiccation cabinet drying (Acker et al., 2002), and freeze-drying (Wolkers et al., 2001). Independent of the drying method, cells are typically in an aqueous suspension at the onset. Generally the change in ‘system’ weight (cells and extracellular solution) is measured gravimetrically and this moisture loss in the system is assumed to equate to the loss of moisture within the suspended cells. This approach assumes that the intra- and extra cellular water contents are equivalent and that the dried sample is homogenous. These assumptions are not always valid. Oftentimes cells are seen to pool towards the middle of a droplet and macroscopic heterogeneities of moisture content within the droplet are sometimes visible by eye. Although important advances in mammalian cell preservation have been made using this approach, a convenient method of determining localized water content within such samples would advance the state-of-the-art in drying technologies. Because sugars are a common excipient used in drying, the current study investigates the spatial distribution of moisture content in dried sugar matrices using pyranine as a fluorescent probe of the local water environment. The pyranine molecule has two fluorescent states, emitting at 511 nm (green) and 440 nm (blue). Using calibration curves based on ratiometric measurements of blue to green pyranine fluorescence emissions the effect of drying substrate on moisture content uniformity is explored in pyranine-doped sucrose solutions.
Magnetoelectric Effect in Magnetostrictive/Polymer and Piezoelectric Composites
Authors: Nersessian Nersesse , Or Siu Wing , Carman Gregory P.
Published: May 2008

A 1200m V/cmOe magnetoelectric voltage coefficient was measured in a Terfenol-D/epoxy and PZT-5H[2-2] composite. The magnetoelectric effect is a result of a coupling between the magnetostrictive (Terfenol-D/epoxy) and piezoelectric (PZT-5H) layers. The coupling was achieved mechanically by bonding the piezoelectric layer in between two magnetostrictive layers. The maximum in magnetoelectric voltage coefficient was measured at a frequency of 8Hz and a bias magnetic field of 103kA/m. The magnetoelectric voltage coefficient was observed to be highly dependent upon the bias magnetic field.