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Today, a microprinted electronics circuits are gaining more and more importance, but still printed electronic devices such as transistors or OLEDs are unstable in air and shows a poor performance. Moreover, printed microelectronic elements do not meet quality and high-reliability requirements, essential in electronics applications. To fulfill these needs, hybrid electronic circuits, combining printed technology, and surface-mount technology, are recommended. This approach gets advantages from both methods:Surface-mount devices (SMD) elements provide a high device functionality whereas a printed pattern ensures the device flexibility and efficiency. In this work, silver nanoparticle-based aerosol jet ink (AgNP ink) is used to realize the approach of a hybrid circuit with aerosol jet printed pads and surface-mount devices. The ultrasonic atomization process ensures the high printing resolution and appropriate line formation. Electrical and mechanical characterization was performed to present the connection performance and quality. Cross section view and morphological inspection explain the joint high quality and good performance. Resistance characterization presents the high current conductance comparable with connections made by silver epoxy or ink-jet printing. Shear test results show an excellent connection strength complying with USA Military Standard. Finally, a flexible hybrid conductance touch sensor is manufactured, demonstrating the feasibility of the presented assembling solution.

The hypercomplex finite element method, ZFEM, allows the analyst to compute highly-accurate arbitrary-order shape, material property, and loading derivatives by augmenting the traditional finite element method with multiple imaginary degrees of freedom. In ZFEM, the real variables are converted to hypercomplex variables such as multicomplex, multidual, or quaternions. By uplifting the real variables to hypercomplex, derivatives are computed in an automated fashion using a standard finite element formulation. The use of multicomplex or multidual numbers provides higher-order derivatives. The drawback of ZFEM is that it increases the number of degrees of freedom of the real variable system by a factor 2 n , where n is the order of the required derivative. In consequence, ZFEM increases the memory consumption and the solution time of the system of equations compared to the real variable system. The block forward substitution method (BFS), proposed in this work, addresses the memory and runtime issues. This new method solves the original real-valued FEM system once. Then, the derivatives are computed using pseudo-loads with the original system of equations. In contrast with the conventional solution method of ZFEM, BFS computes the hypercomplex contributions to the stiffness matrix element-wise, and it never assembles nor solves the full hypercomplex system of equations. In effect, the BFS method generalizes the first-order semi-analytical complex variable method to any order derivative. The BFS method provides the capability to allow a combination of real-variable and hypercomplex-variable elements within the same model. The numerical results indicate that a first-order derivative can be obtained with 1% to 8% additional computational time of the real-variable analysis. This allows the computation of multiple first-order derivatives by post-processing of a single FEM analysis. Additionally, it was shown that fourth-order shape sensitivities can be computed in less than 5% additional runtime of the real-variable FEM analysis.

Background Microcalcifications within the fibrous cap of the arteriosclerotic plaques lead to the accrual of plaque-destabilizing mechanical stress. New techniques for plaque screening with small detectors and the ability to differentiate between the smooth and hard elements of plaque formation are necessary. Method Vascular plaque formations are characterized as calcium phosphate containing structures organized as hydroxylapatite resembling the mineral whitlockite. In transmission and reflexion studies with a simple millimeter wave (mm-wave)–demonstrator, we found that there is a narrow window for plaque detection in arterial vessels because of the tissue water content, the differentiation to fatty tissue, and the dielectric property of air or water, respectively. Result The new sensor is based on a sensing oscillator working around 27 GHz. The open-stub capacitance determines the operating frequency of the sensor oscillator. The capacitance depends on the dielectric properties of the surrounding material. The sensor components were completely built up in surface mount technique. Conclusion Completed with a catheter, the sensor based on microwave technology appears as a robust tool ready for further clinical use.

While bone mineral density has been traditionally used to quantify fracture risk for individuals with spinal cord injuries, recent studies are including engineering measurements such as section modulus and cross sectional moment of inertia. These are almost exclusively calculated by peripheral QCT scanners which, unlike DXA scanners, are rarely found in clinical settings. Using fifty-four fresh frozen femora, we developed and validated a pixel-by-pixel method to calculate engineering properties at the distal femur using a Hologic QDR-1000 W DXA scanner and compared them against similar parameters measured using a Stratec XCT-3000 peripheral QCT scanner. We found excellent agreement between standard DXA and pixel-by-pixel measured BMD (r 2 = 0.996). Cross-sectional moment of inertia about the anteroposterior axis measured using DXA and pQCT correlated very strongly (r 2 = 0.99). Cross-sectional moment of inertia about the anteroposterior axis measured using DXA also correlated strongly with pQCT measured bone strength index (r 2 = 0.99). These correlations indicate that DXA scans can measure equivalent pQCT parameters, and some existing DXA scans can be reprocessed with pixel-by-pixel techniques. Ultimately, these engineering parameters may help better quantify fracture-risk in fracture-prone populations such as those with spinal cord injuries.

Arteriosclerosis and associated cardiovascular disease remains the leading cause of mortality. Improved methods for vascular plaque detection allow early diagnose and better therapeutic options. Present diagnostic tools require intense technical expenditure and diminish value of modern screening methods. Our group developed an microwave sensor for on-site detection of plaque formation in arterial vessels. The sensor is an oscillator working around 27 GHz which is coupled to a microstrip stub line. The final flexible polyimid interposer has a length of 38 cm, a width of 1.2 mm and a thickness of 200 μm. Because of its minimal size the interposer completed a catheter with a diameter of 8F ready for further clinical use in cardiology and heart surgery.

Adequate diagnosis of upper urinary tract (UUT) tumors is essential for successful local treatment. Organsparing approaches are technically difficult and require consistent further development. Appropriate models for investigating new diagnostic and therapeutic methods are not yet available. This study demonstrates the incorporation of a fresh sample model into five different test levels (I-V) for improving the diagnosis and therapy of ureteral tumors. In these test levels, new diagnostic and ablation techniques are evaluated for feasibility, application safety, efficacy and accuracy. An assessment of their suitability for broad preclinical and clinical application also took economic aspects into account.

The goal is to use the hot bar method to join the conductive lines of a flexible interposer with copper wires, which are located inside of the catheter wall. These copper wires with a diameter of 150 μm were integrated during the extrusion process of a polyethylene catheter with a diameter of 3 mm and a wall thickness of 1 mm. The wires will be used as signal and power lines. Because the copper wires located inside the catheter wall, the polyethylene material above the copper wires must be removed for joining the interposer copper lines. The material ablation was done by a femtosecond laser. Detailed knowledge about the heat sensitive handling with the polyethylene catheter must obtained before start the joining procedures. For the setup of the final joining procedure, there were used different types of test vehicles. With the help of the test vehicles the joining method is evaluated. Therefore, a hot bar stamp is placed at the back of the polyimide layer. The investigated parameters of the hot bar are stamp temperature, stamp force and time. After the setup analysis of the sensor test vehicle, the optimal joining parameters will be discovered and the flexible interposer and the copper wires inside of the catheter wall could be joined in future steps. Finally, non-destructive (ultrasound, x-ray) and destructive methods (tweezer pull test, microsection) will be investigated to evaluate the joining quality and quantity of the test vehicle and the final sensor catheter.

The paper deals with the technique of a hot bar technology for joining conductor lines of flexible interposers directly with copper wires inside of a catheter wall. The copper wires were integrated during the extrusion process inside of the catheter wall. The main part of this paper is concentrating on the evaluation process of such a joining technique. There were used different solder materials. With the help of a design of experiments the process was planned. The final goal is a repeatable process for such a joining method and the integration of a flexible interposer directly inside of a connectable catheter wall.

Predictive biomechanical analysis of manual material handling (MMH) transfers is dependent on accurate prediction of foot locations relative to the task. Previous studies have classified common acyclic stepping patterns used during those transfer tasks, but the influence of walking distance prior to the transfer is not well understood. Twenty men and women performed transfers for a minimum of six different delivery distance conditions. The number of steps used by the participants ranged from two to seven. A theoretical framework for idealised step-scaling strategies is proposed and compared with the experimental data. The maximum observed increase in step length prior to delivery was 1.43 times the nominal step length calculated for each participant. The data suggest that although participants can scale their steps to facilitate the use of a single terminal stance at the transfer, the majority of participants chose to utilise a combination of stepping strategies if the preferred contralateral lead foot strategy could not be easily implemented.Accurate foot placements are needed for predictive biomechanical analysis of MMH. A laboratory study investigated the influence of previous step positions on MMH. A flexible step-scaling strategy, in which step lengths and strategy were varied, suggests that analysis based on simulated movements should consider multiple lifting postures.

The paper deals with a new technique for deviation of atherosclerotic plaque. There are two plaque types: The yellow and white plaque. The white plaque is hard, fibrous and dimensionally stable. The yellow plaque is soft with high-cholesterol ratio and dimensionally instable. Every hit with a medical tool can generate a critical medical case, because the plaque can be rapture and the plaque particles could cause in a stroke. A catheter with a BiCMOS microwave sensor was developed in the latest research. For a stable function and a high reliability a suitable electronic packaging has to be fulfill. The development starting with the sensor design up to a complete electronic packaging which allows a measurement in different liquids and tissues is discussed in this paper.

The focus of this work was the development of additive metal deposition techniques on Polydimethylsiloxane based foils. The metallic films provide electrical interconnection to commercial available surface-mount devices. Therefor two maskless techniques were investigated. First was Aerosol Jet® deposition using an Optomec 3D printer and second was a laser structured thin film, which was deposited with physical vapor deposition (PVD). In addition the contacting between the SMD's and the interposer with an adhesive and a reactive multi-layer foil were investigated. Finally demonstrators which showed the principal functionality were built. For this purpose a simple circuit, composed of battery powered LED's and a PIC® microcontroller, was developed. The circuit also includes a simple sensor logic which activates the LED's by touching a comb structure.

Tissue level density and elastic modulus are intrinsic properties that can be used to quantify bone material and analyses incorporating those quantities have been used to evaluate bone on a macroscopic scale. Micro-computed tomography (microCT) technology has been used to construct tissue level finite element models to simulate macroscopic fracture strength, however, a single method for assigning voxel-specific tissue density and elastic modulus based on those data has not been universally accepted. One method prevalent in the literature utilizes an empirical relationship that derives tissue stiffness as a function of bone calcium content weight fraction. To derive calcium content weight fraction from microCT scans, a measure of tissue density is required and a constant value is traditionally used. However, experimental data suggest a non-trivial amount of tissue heterogeneity suggesting a constant tissue density may not be appropriate. A theoretical derivation for determining the relationship between voxel-specific tissue density and microCT scan data (i.e., microCT derived tissue mineral density (TMD), mgHA/cm(3)) and bone constituent properties is proposed. Constant model parameters used in the derivation include the density of water, ash, and organics (i.e., bone constituents) and the volume fraction of the organics constituent. The effect of incorporating the theoretically derived tissue density (instead of a constant value) in determining voxel-specific elastic modulus resulted in a maximum observed increase of 12GPa (5.9GPa versus 17.9GPa, for the constant value and derived tissue density formulations, respectively) for a measured TMD of 1.02gHA/cm(3). Average and bounding quantities for the four constant model parameters were defined from the literature and the influence of those values on the derived tissue density and elastic modulus relationships were also evaluated. The theoretical relationships of tissue density and elastic modulus, with the average constant model parameters applied, were consistent with previously published empirical relationships derived from experimental data. Tissue density as a function of microCT TMD was formulated as a linear relationship and the density of water and ash was shown to solely influence the proportionality (i.e., slope) between those values. The density of water and organics (i.e., collagen) and the volume fraction of the organics constituent were shown to influence the constant offset (intercept) between tissue density and TMD with no influence from ash density. Incorporating tissue density heterogeneity into the derivation of elastic modulus resulted in a significant increase in predicted modulus (for microCT TMD ranges observed for healthy tissue) as compared to when a constant tissue density was used. The presented approach provides a novel method for deriving tissue-level bone material properties and quantifies the effect of assuming tissue homogeneity when calculating elastic modulus (when using a prevalent method in the literature) from microCT scan data.

PurposeThe aim of this paper is to present and evaluate a methodology for automatically constructing and applying the physiologically‐realistic boundary/loading conditions for use in the structural finite element analysis of the femur during various exertion tasks (e.g. gait/walking).Design/methodology/approachTo obtain physiologically‐realistic boundary/loading conditions needed in the femur structural finite element analysis, a whole‐body musculoskeletal inverse dynamics analysis is carried out and the resulting muscle forces and joint reaction forces/moments extracted.FindingsThe finite element results obtained are compared with their counterparts available in literature and it is found that the overall agreement is acceptable while the highly automated procedure for the finite element model generation developed in the present work made the analysis fairly easy and computationally highly efficient. Potential sources of errors in the current procedure have been identified and the measures for their mitigation recommended.Originality/valueThe present approach enables a more accurate determination of the physiological loads experienced by the orthopedic implants which can be of great value to implant designers and orthopedic surgeons.

The problem of size/thickness optimization of a distal femoral-fracture fixation-plate is addressed computationally using a combined finite-element/design-optimization procedure. To obtain realistic physiological loading conditions associated with normal living activities (cycling, in the present case), a musculoskeletal multi-body inverse-dynamics analysis is carried out of a human riding the bicycle. While optimizing the design of the femoral-fracture locking-plate, realistic functional requirements pertaining to attain the required level of fracture-femur fixation and longevity/lifecycle were used. It is argued that these types of analysis should be used to complement pre-clinical implant-evaluation tests, the tests which normally include a limited number of physiological loading conditions and single pass/fail outcomes/decisions with respect to a set of lower-bound implant–performance criteria.

The main causes for long-distance driving fatigue experienced by vehicle drivers are investigated computationally using musculoskeletal modeling and simulation methods. A rigid-body model of a prototypical adjustable car seat is constructed as a part of the present work and combined with a public-domain musculoskeletal model of a seated human. Seated-human/car-seat interactions associated with typical seating postures of the vehicle driver are analyzed using the inverse-dynamics approach while the ‘‘minimum-fatigue’’ criterion is utilized to deal with the muscle redundancy problem (i.e., with the problem that human-body contains more muscles than what would be typically needed to drive various body joints). The results obtained show that various seat adjustments (e.g., back-rest inclination, seat-pan horizontal track position, etc.), driver’s back supports (e.g., presence/absence of lumbar support) and the nature of seat upholstery (e.g., fabric vs. vinyl) can have complex influence on the muscle activation, joint forces, soft-tissue contact normal and shear stresses, all of which not only affect the comfort perception of the driver but also their feel of fatigue. Subsequently, the results of the present work along with relevant public-domain literature findings (e.g., subjective driving-fatigue assessments provided by human test subjects and human-body/seat contact-force measurements) are used to construct a preliminary long-distance driving-fatigue function. Relevance to industry: it is argued that the computer-aided engineering analysis introduced in the present work should help speed-up the design of new high-comfort car seats. These seats are currently being mainly designed using empiricism, legacy knowledge and extensive, time-consuming and costly prototyping and experimental/field testing.

The electronics packaging in microsystems technology for medical applications includes various tasks. The interdisciplinary approach is the most important basis for the success of a product. For the reliable operation of medical microsystems different factors must be considered. The functionalization of a catheter depends on different influence factors. The form factor takes the most important role. For a miniaturized and functional catheter tip, the diameter depends on the medical application. Other factors like the shape, reliability and also the cost must be considered. The paper shows the whole technology carrier of a medical product in relation to the field of electronics packaging.

The electronics packaging in microsystems technology for medical applications includes various tasks. The interdisciplinary approach is the most important basis for the success of a product. For the reliable operation of medical microsystems different factors must be considered. For example the functionalization of a catheter depends on different influence factors. The form factor takes the most important role. For a miniaturized and functional catheter tip, the diameter depends on the medical application. Other factors like the shape, reliability and also the cost must be considered. The paper shows the whole technology carrier of a medical product in relation to the field of electronics packaging. With the help of two examples the requirements for future products will be shown.

Background: Patient-specific femoral and tibial cutting blocks produced with use of data from preoperative computed tomography (CT) or magnetic resonance imaging (MRI) scans have been employed recently to optimize component alignment in total knee arthroplasty. We report the results of a randomized controlled trial in which CT scans were used to compare postoperative component alignment between patients treated with custom instruments and those managed with traditional instruments. Methods: The in-hospital data and early clinical outcomes, including Knee Society scores, were determined in a randomized clinical trial of forty-seven patients who had undergone a total of forty-eight primary total knee arthroplasties with patient-specific instruments (twenty-two knees) or standard instruments (twenty-six knees). Orientation of the implants was compared by using three-dimensional CT data. Results: No significant differences were found between the study and control groups with respect to any clinical outcome aftera minimum of six monthsof follow-up. The patient-specifictibialcutting blockwasabandoned in favorof a standard external alignment jig in seven of the twenty-two study knees because of possible malalignment. A detailed analysis of intent-to-treat and per-protocol groups of study and control knees did not show any significant improvement in component alignment, including femoral component rotation in the axial plane, in the patients treated with the custom instruments. The percentage of outliers—defined as less than 23 or more than 3 from the correct orientation of the tibial slope—was significantly higher in the group treated with use of patient-specific blocks than it was in the control group, in both the intent-to-treat (32% versus 8%, p = 0.032) and the per-protocol (47% versus 6%, p = 0.0008) analysis. Conclusions: There were no significant improvements in clinical outcomes or knee component alignment in patients treated with patient-specific cutting blocks as compared with those treated with standard instruments. The group treated with patient-specific cutting blocks had a significantly higher prevalence of malalignment in terms of tibial component slope than the knees treated with standard instruments. Level of Evidence: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Spiral humerus fractures associated with extreme muscular torsion loading have been well documented in literature. Throwing motions and arm wrestling are the two causes most often researched, while spiral fractures associated with gymnastics have received less attention. The purpose of this study is to explore the factors that may contribute to torsional failure of the humerus while performing a gymnastics move known as a muscle-up. Primary motivation for this study was the result of the author sustaining a spiral fracture to the distal aspect of her left humerus while attempting a muscle-up. To the author’s knowledge, no previous studies analyzing the forces imposed on the upper extremities during a muscle-up have been conducted. Utilizing the author’s estimated anthropometric measurements and the kinematic and kinetic constraints of the muscle-up activity, the torque acting about the long axis of the humerus was determined in two ways. First, an analytical approach was used to calculate the forces and moments within a simplified linkage representation of the upper extremity for several representative muscle-up postures. The second method was a computer simulation that modeled the entire body with muscles in several different kinematic positions and outputted internal body elbow joint net moments. The analytical approach resulted in torques between 12.0 N·m and 29.3 N·m. The kinetics derived with the computer simulation revealed joint reaction torques between 13 N·m and 38 N·m and net axial torques between 29.1 N·m and 69.1 N·m acting on the left humerus. The internal moments predicted using the computer simulation were above the author’s minimum predicted torque, 53 N·m, associated with humerus fracture initiation. Although there may be many factors that contribute to spiral humerus fracture, in this study, it was determined that the kinematic positions of the muscle-up movement are sufficiently extreme so as to produce torques capable of resulting in spiral humerus fracture.

Large variations in axial ulnar load strain calibration results suggest that animal-specific calibrations may be necessary. However, the optimal set of geometric measures for performing an animal-specific calibration are not known, potentially as a result of confounding effects associated with experimentally introduced variation. The purpose of this study was to characterize the inherent variability of ulnar geometric measures known to influence periosteal midshaft strain during axial ulnar exogenous loading, and to further quantify the relationship between the variance of those geometric measures and periosteal strain during axial loading. Thirty-nine right mouse forelimbs were scanned with microCT. Seven geometric measures that influence periosteal strain resulting from a combined axial and bending loading were computed and used to estimate animal-specific strains on the periosteal midshaft. Animal specific strains were estimated using a theoretical model based on the generalized flexure formula. The predicted mean and standard deviation of the simulated midshaft strain gauge measurement resulting from the inter-animal geometric differences was � 9857148 μe/N. The complete beam bending term associated with bending about the I min axis accounted for 89% of the variance and reduced the residual RMSE to 50.4 μe. Eccentricity associated with the axial loading contributed a substantial portion of variation to the computed strain suggesting that calibration procedures to account for animal differences should incorporate that variable. The method developed in this study provides a relatively simple procedure for computing animal-specific strains using microCT scan data, without the need of a load/ strain calibration study or computationally intensive finite element models. Published by Elsevier Ltd.

Musculoskeletal simulation software and model repositories have broadened the user base able to perform musculoskeletal analysis and have facilitated in the sharing of models. As the recognition of musculoskeletal modeling continues to grow as an engineering discipline, the consistency in results derived from different models and software is becoming more critical. The purpose of this study was to compare eight models from three software packages and evaluate differences in quadriceps moment arms, predicted muscle forces, and predicted tibiofemoral contact forces for an idealized knee-extension task spanning −125 to +10° of knee extension. Substantial variation among models was observed for the majority of aspects evaluated. Differences among models were influenced by knee angle, with better agreement of moment arms and tibiofemoral joint contact force occurring at low to moderate knee flexion angles. The results suggest a lack of consistency among models and that output differences are not simply an artifact of naturally occurring inter-individual differences. Although generic musculoskeletal models can easily be scaled to consistent limb lengths and use the same muscle recruitment algorithm, the results suggest those are not sufficient conditions to produce consistent muscle or joint contact forces, even for simplified models with no potential of co-contraction.

Jumping is a coordinated extension of the human body through combined strength and agility to perform a leap motion far enough for the feet to land on the ground. However, the repeated reaction forces and the resulting stresses on the ankle, knee and hip joints may cause injuries to a person. A primary mechanism of such injuries is suggested to be the acute high impact loads experienced during the landing in a horizontal jump. The goal of this study is to determine the reaction force distribution at the joints in the lower extremities during the horizontal jump. A detailed biomechanical system was constructed to calculate the reaction forces generated during the horizontal jump. The horizontal jump kinematics of a participant was measured using a three-dimensional motion capture system and the landing forces were measured using two force plates. Biomechanical simulation software was used to calculate the internal joint reaction forces at the ankle, knee, and hip. It was determined that the maximum reaction forces primarily occurred in the proximo/distal direction of the hip, 2,300 N; and ankle, 2,700 N. However, at the knee joint, the maximum reaction force was determined to be in antero/posterior direction, at 2,000 N; and proximo/distal direction, at 2,100 N, respectively.Copyright © 2012 by ASME

A distal radius fracture in middle-age and older adults is often considered a sentinel indicator of osteoporosis. Mechanical testing of cadaveric specimens is often used to quantify bone strength and develop insight for relating in-vivo measures to fracture force. Mechanical testing protocols using an intact forearm have been successful at replicating a Colles fracture, however, excised isolated radius protocols based on the intact forearm testing protocol have not been as successful. One protocol originally designed to replicate the physiological condition of a fall on an outstretched hand was reproduced in our laboratory, yet surprisingly the produced distal radius fracture patterns were not consistent among specimens nor was dorsal angulation of the distal fragment that is characteristic of a Colles fracture observed. The purpose of this study was to perform a mechanics-based analysis of the excised radius loading protocol in order to quantify the imposed and internal forces on the radius. An idealized beam model of the excised radius revealed that in the area of the distal radius where Colles fractures occur, 99.99% of the maximum strain on the bone outer surface was the result of pure compressive loading. This loading condition is in direct contrast to the accepted mechanics of a Colles fracture, which is characterized as a metaphyseal bending fracture with the volar cortex failing due to tensile stresses and the dorsal cortex exhibiting compression and comminution. The results suggest that additional research, particularly related to overcoming the difficulties of reliably supporting and applying a force to the distal end of the radius, is necessary for clinical fracture patterns to be reliably reproduced with an excised radius mechanical testing protocol.

Probabilistic engine health management (PHM) is expected to be a go-forward approach for the USAF and other DoD agencies to enable dramatic improvements in the assessment and management of military assets. As a result, accurate and information-rich probabilistic lifing methods are essential to assess the benefits of technology insertion programs for PHM. As such, under this program three technology thrusts were investigated: a) sensitivity methods probability-of-failure estimates with respect to POD curve parameters, b) complex variable methods for sensitivity analysis, and c) probabilistic sensitivity analysis with respect to bounds of truncated distributions.

The return of a patient to activities of daily living following a surgical intervention (i.e. joint replacement, rigid fixation, etc.) involving an implantable device is often used as one component to measure the success of the surgery [1]. The longevity of the implant subject to the forces imposed when performing those normal daily activities is another. As people are living longer and continuing to maintain active lifestyles, the paradigm of everyday activities that are used to evaluate implant longevity must also evolve. Although physiological boundary conditions during pre-clinical implant evaluations have been used for simulating the life span of a new device, only a small number of everyday activities used for deriving those forces have been widely characterized. The purpose of this paper is to demonstrate how musculoskeletal simulation can be used for providing the boundary conditions of a finite element model used to evaluate the design space of an implant subject to specific activities of daily living (Figure 1).Copyright © 2009 by ASME

The process of using activities of daily living to evaluate the performance of implantable devices under physiological loading conditions has been researched [1,2,3,4]. In particular, long-term stability of hip-implants, as related to fatigue, have been evaluated using normal walking [1,2,4], sit to stand [1], stair climbing [2,4], and combinations of everyday activities [3]. Current methods that utilize estimated physiological loading conditions are traditionally used as pass/fail tests to identify whether a particular design performs to a set of minimum specifications for long-term use. Such tests are also traditionally limited to a small number of physiologically representative loading conditions (i.e. walking, stair climbing, sit-to-stand).Copyright © 2009 by ASME

Industrial tasks performed by standing workers are among those most commonly simulated using digital human models. Workers often walk, turn, and take acyclic steps as they perform these tasks. Current human modeling tools lack the capability to simulate these whole body motions accurately. Most models simulate walking by replaying joint angle trajectories corresponding to a general gait pattern. Turning is simulated poorly if at all, and violations of kinematic constraints between the feet and ground are common. Moreover, current models do not accurately predict foot placement with respect to loads and other hand targets, diminishing the utility of the associated ergonomic analyses. A new approach to simulating stepping and walking in task-oriented activities is proposed. Foot placements and motions are predicted from operator and task characteristics using empirical models derived from laboratory data and validated using field data from an auto assembly plant. The motions of the pelvis and torso are predicted from the foot placements, operator characteristics, and task requirements. The lowerextremity motions are then generated using behaviorbased inverse kinematics that relies on laboratory observations to address kinematic redundancy while respecting boundary constraints. This modular approach is highly general and can simulate gait, transition stepping, and stepping for balance maintenance in a single integrated system that can be implemented in any digital human model.

Cyclical stepping (gait) has been studied extensively. Some of these results are reflected in the straight and curved path step-following algorithms in commercial digital human modeling (DHM) implementations. With the aid of these algorithms, DHM users define start, intermediate, and end path points and the software generates a walking-like motion along the path. Most of these algorithms have substantial limitations, among them that the figures exhibit "foot skate," meaning that the kinematic constraint of foot contact with the ground is not respected. Turning is accomplished by pivoting the entire figure, rather than through realistic lower-extremity motions. The simulation of the non-cyclical stepping motions accompanying manual material handling pickup and delivery tasks requires manual manikin manipulation. This paper proposes a paradigm for the simulation of stepping behavior in digital human models based on a model of foot placements and motions. Cyclical and non-cyclical transition stepping behaviors are handled with the same structure, allowing for smooth transitions between gait and non-cyclical behaviors. The model is based on a laboratory experiment in which participants used one or both hands to move heavy and light loads between shelves located in various positions one to five steps apart. The data were used to develop a model of the transition stepping that occurs at load pickup and delivery.

For many industrial tasks (push, pull, lift, carry, etc.), restrictions on grip locations and visibility constrain the hand and head positions and help to define feasible postures. In contrast, often the foot locations are minimally constrained and an ergonomics analyst can choose several different stances in selecting a posture to analyze. Also, because stance can be a critical determinant of a biomechanical assessment of the work posture, the lack of a valid method for placing the feet of a manikin with respect to the task compromises the accuracy of the analysis. To address this issue, foot locations and orientations were captured in a laboratory study of sagittal plane and asymmetric manual load transfers. A pilot study with four volunteers of varying anthropometry approached a load located on one of three shelves and transferred the load to one of six shelves. The data illustrate foot placements and behaviors that depend on pickup heights, the use of one or two hands to grasp the object, and the participantsʼ body dimensions. Two distinct pickup and delivery strategies were observed. Split stance, with one foot in front of the other, was markedly more frequent than parallel stance with the feet side by side. A statistical model was developed to predict foot placements at load pickup. This study confirms the importance of this topic and provides the basis for the much more comprehensive study that is now underway.

Simulations of humans performing seated reaches require accurate descriptions of the movements of the body segments that make up the torso. Data to generate such simulations were obtained in a laboratory study using industrial, auto, and truck seats. Twelve men and women reached to push-button targets located throughout their right-hand reach envelopes as their movements were recorded using an electromagnetic tracking system. The data illustrate complex patterns of motion that depend on target location and shoulder range of motion. Pelvis motion contributes substantially to seated reach capability. On padded seats, the effective center of rotation of the pelvis is often within the seat cushion below the pelvis rather than at the hips. Lumbar spine motions differ markedly depending on the location of the target. A categorization of reach targets into four zones differentiated by torso kinematics is proposed.

The problem of optimal size, shape, and placement of a proximal radius-fracture fixation-plate is addressed computationally using a combined finite-element/design-optimization procedure. To expand the set of physiological loading conditions experienced by the implant during normal everyday activities of the patient, beyond those typically covered by the pre-clinical implant-evaluation testing procedures, the case of a wheel-chair push exertion is considered. Toward that end, a musculoskeletal multi-body inverse-dynamics analysis is carried out of a human propelling a wheelchair. The results obtained are used as input to a finite-element structural analysis for evaluation of the maximum stress and fatigue life of the parametrically defined implant design. While optimizing the design of the radius-fracture fixation-plate, realistic functional requirements pertaining to the attainment of the required level of the devise safety factor and longevity/lifecycle were considered. It is argued that the type of analyses employed in the present work should be: (a) used to complement the standard experimental pre-clinical implant-evaluation tests (the tests which normally include a limited number of daily-living physiological loading conditions and which rely on single pass/fail outcomes/decisions with respect to a set of lower-bound implant-performance criteria) and (b) integrated early in the implant design and material/manufacturing-route selection process.

Most current applications of digital human figure modelsfor ergonomic assessments of manual tasks focus onthe analysis of a static posture. Tools available for staticanalysis include joint-specific strength, calculation ofjoint moments, balance maintenance capability, and low-back compression or shear force estimates. Yet, formany tasks, the inertial loads due to acceleration of bodysegments or external objects may contribute significantlyto internal body forces and tissue stresses. Due to thecomplexity of incorporating the dynamics of motion intoanalysis, most commercial software packages used forergonomic assessment do not have the capacity toinclude dynamic effects. Thus, commercial humanmodeling packages rarely provide an opportunity for theuser to determine if a static analysis is sufficient. Thegoal of this paper is to quantify the differences betweena static and dynamic analysis of a materials handlingtask using the AnyBody modeling system to include theeffects of motion. The feasibility and tractability ofperforming dynamical ergonomic analysis with theAnyBody model is assessed for the analysis of anasymmetric lifting task. Comparisons between low backmoments, compression and shear forces for dynamicand static analyses are presented.