The purpose of this work is to investigate the efficiency of wearable assistive devices under different load-carried walking. We designed an experimental platform, with a lightweight ankle-assisted robot. Eight subjects were tested in three experimental conditions: free walk with load (FWL), power-off with load (POFL), and power-on with load (PONF) for different levels of force at a walking speed of 3.6 km/h. We recorded the metabolic expenditure and kinematics of the subjects under three levels of load-carried (10%, 20%, and 30% of body mass). We define the critical force, where at a certain load, the robot inputs a certain force to the human body, and with the assistance of this force, the positive effect of the robot on the human body exactly compensates for the negative effect. The critical forces from the fit of the assistive force and metabolic cost curves were 130 N, 160 N and 215 N at three different load levels. The intrinsic weight of our device increases mechanical work at the ankle as the load weight rises, with 2.08 J, 2.43 J and 2.73 J for one leg during a gait cycle. With weight bearing increasing, the ratio of the mechanical work input by the robot to the mechanical work output by the weight of the device decreases (from 0.904, to 0.717 and 0.513), verifying that the walking assistance efficiency of such devices decreases as the weight rises.

Biomechanical testing of long bones can be subject to undesirable errors and uncertainty due to malalignment of specimens with respect to the mechanical axis of the test frame. To solve this problem, we designed a novel, customizable alignment and potting fixture for long bone testing. The fixture consisted of 3D-printed components modeled from specimen-specific CT scans to achieve a predetermined specimen alignment. We demonstrated the functionality of this fixture by comparing benchtop torsional test results to specimen-matched finite element models and found a strong and statistically significant correlation (R2 = 0.9536, p < 0.001). Additional computational models estimated the impact of malalignment on mechanical behavior in both torsion and axial compression. Results confirmed that torsion testing is relatively robust to alignment artifacts, with absolute percent errors less than 8% in all malalignment scenarios. In contrast, axial testing was highly sensitive to setup errors, experiencing absolute percent errors up to 40% with off-center malalignment and up to 130% with angular malalignment. This suggests that whenever appropriate, torsion tests should be used preferentially as a summary mechanical measure. When more challenging modes of loading are required, pre-test clinical-resolution CT scanning can be effectively used to create potting fixtures that allow for precise pre-planned specimen alignment. This may be particularly important for more sensitive biomechanical tests (e.g. axial compressive tests) that may be needed for industrial applications, such as orthopaedic implant design.

INTRODUCTION: The purpose of this study was a comprehensive assessment of the dynamic parameters of gait in patients who underwent Ilizarov treatment for nonunion of the tibia. MATERIALS AND METHODS: The experimental group consisted of24 individuals treated with the Ilizarov method for nonunion of the tibia.The control group comprised31healthy individuals,matched for BMI,sex,and age.The dynamic gait parameters in patients and in the control group were measured with a Zebris pedobarographic platform. RESULTS: The treatment group and the control group showed statistically significant differences in terms of the following gait parameters:Maximum force 1NOL(non-operated-limb),Time maximum force1OL(operated-limb),Time maximum force 1 NOL,Maximum force 2NOL,Time maximum force 2OL,and Maximum force forefoot OL.Most of the evaluated gait parameters were bilaterally similar in patients group.The only significant differences between the operated and non-operated limb were seen in terms of Time maximum force 2and Maximum force forefoot. CONCLUSIONS: The most pronounced abnormalities in dynamic gait parameters were observed in the forefoot.The patients treated with the Ilizarov method did not achieve a complete normalization of dynamic gait parameters,as their gait parameters did not equal those measured in the control group.The Ilizarov method for the treatment of tibial nonunion helps restore a symmetrical distribution of gait parameter values between the affected limb and the healthy limb.Patients with tibial nonunion treated with the Ilizarov method continue to show some abnormalities in their dynamic gait parameters after treatment.

Research examining gait biomechanics of persons with autism spectrum disorder (ASD) has grown significantly in recent years and has demonstrated that persons with ASD walk at slower self-selected speeds and with shorter strides, wider step widths, and reduced lower extremity range of motion and moments compared to neurotypical controls. In contrast to walking, running has yet to be examined in persons with ASD. The purpose of this study was to examine lower extremity running biomechanics in adolescents (13-18-year-olds) with ASD and matched (age, sex, and body mass index) neurotypical controls. Three-dimensional kinematics and ground reaction forces (GRF) were recorded while participants ran at two matched speeds: self-selected speed of adolescents with ASD and at 3.0m/s. Sagittal and frontal plane lower extremity biomechanics and vertical GRFs were compared using two-way ANOVAs via statistical parametric mapping. Adolescents with ASD ran with reduced stride length at self-selected speed and reduced vertical displacement, loading-propulsion GRFs, propulsion plantarflexion moments, loading-propulsion hip abduction moments, and loading knee abduction moments at both speeds. Running at 3.0m/s increased sagittal plane hip and knee moments surrounding initial contact and frontal plane knee angles during mid stance and propulsion compared to self-selected speeds. Reduced contributions from primarily the ankle plantarflexion but also knee abduction and hip abduction moments likely reduced the vertical GRF and displacement. As differences favored reduced loading, youth with ASD can safely be encouraged to engage in running as a physical activity.

Pulmonary hypertension (PH) is one of the least understood and highly elusive cardiovascular conditions associated with elevated pulmonary arterial pressure. Although the disease mechanisms are not completely understood, evidence has accumulated from human and animal studies that irreversible processes of pulmonary arterial wall damage, compensated by stress-mediated growth, play critical roles in eliciting the mechanisms of disease progression. This study aims to develop a thermodynamic modeling structure of the pulmonary artery for considering the coupled plastic-degradation-growth irreversible processes in order to investigate mechanical roles of the dissipative phenomena in the disease progression. The proposed model performs a model parameter study of plastic deformation and degradation processes coupled with dissipative growth subjected to elevated pulmonary arterial pressure, and computationally generate in silico simulations of PH progression using the clinical features of PH, found in human morphological and mechanical data. The results show that considering plastic deformation can provide much better fitting of the ex vivo inflation tests than a widely used pure hyperelastic model in higher pressure conditions. In addition, the parameter sensitivity study illustrates that arterial damage and growth causes the increased stiffness, and the full simulation (combining elastic-plastic-degradation-growth models) reveals a key recovery pathological process of compensating vessel damage by vascular adaptation by reducing the rate of vessel dilation and mediating vascular wall stress. Finally, the simulation results of luminal enlargement, arterial thickening, and arterial stiffness for an anisotropic growth are found to be close to values from literatures.

The creation of a communication between an artery and a vein (arteriovenous fistula or AVF), to speed up the blood purification during hemodialysis of patients with renal insufficiency, induces significant rheological and mechanical modifications of the vascular network. In this study, we investigated the impact of the creation of an AVF with a zero-dimensional network model of the vascular system of an upper limb and a one-dimensional model around the anastomosis. We compared the simulated distribution of flow rate in this vascular system with Doppler ultrasound measurements. We studied three configurations: before the creation of the AVF, after the creation of the AVF, and after a focal reduction due to a hyper flow rate. The 0D model predicted the bounds of the diameter of the superficial vein that respects the flow constraints, assuming a high capillary resistance. We indeed highlighted the importance of knowing the capillary resistance as it is a decisive parameter in the models. We also found that the model reproduced the Doppler measurements of flow rate in every configuration and predicted the distribution of flow in cases where the Doppler was not available. The 1D model allowed studying the impact of a venous constriction on the flow distribution, and the capillary resistance was still a crucial parameter.

Accurately capturing the bone and cartilage morphology and generating a mesh remains a critical step in the workflow of computational knee joint modeling. Currently there is no standardized method to compare meshes of different element types and nodal densities, making comparisons across research teams a significant challenge. The aim of this paper is to describe a method to quantify differences in knee joint bone and cartilages meshes, independent of bone and cartilage mesh topology. Bone mesh-to-mesh distances, subchondral bone boundaries and cartilage thicknesses from meshes of any type of mesh are obtained using a series of steps involving registration, resampling, and radial basis function fitting after which the comparisons are performed. Subchondral bone boundaries and cartilage thicknesses are calculated and visualized in a common frame of reference for comparison. The established method is applied to models developed by five modeling teams. Our approach to obtain bone mesh-to-mesh distances decreased the divergence seen in selecting a reference mesh (i.e. comparing mesh A-to-B vs. mesh B-to-A). In general the bone morphology was similar across teams. The cartilage thicknesses for all models were calculated and the mean absolute cartilage thickness difference was presented, the articulating areas had the best agreement across teams. The teams showed disagreement on the subchondral bone boundaries. The method presented in this paper allows for objective comparisons of bone and cartilage geometry that is agnostic to mesh type and nodal density.

Vertebral fractures are the most common osteoporotic fractures, but clinical means for assessment of vertebral bone integrity are limited in accuracy, as they typically use surrogate measures that are indirectly related to mechanics. The objective of this study was to examine the extent to which intravertebral strain distributions and changes in cancellous bone texture generated by a load of physiological magnitude can be characterized using a clinically available imaging modality. We hypothesized that digital tomosynthesis based digital volume correlation (DTS-DVC) and image texture based metrics of cancellous bone microstructure can detect development of mechanical strains under load. Isolated cadaveric T11 vertebrae and L2-L4 vertebral segments were DTS imaged in a nonloaded state and under physiological load levels. Axial strain, maximum principal strain, maximum compressive and tensile principal strains, and von Mises equivalent strain were calculated using the DVC technique. The change in textural parameters (line fraction deviation, anisotropy, and fractal parameters) under load was calculated within the cancellous centrum. The effect of load on measured strains and texture variables was tested using mixed model ANOVA, and relationships of strain and texture variables with donor age, bone density parameters, and bone size were examined using regression models. Magnitudes and heterogeneity of intravertebral strain measures correlated with applied loading and were significantly different from background noise. Image texture parameters were found to change with applied loading but these changes were not confirmed in a larger sample. DTS-DVC derived strains correlated with age more strongly than did BMD for T11.

The passive behavior of a compliant biped walking model, subject to variations in its design is investigated. A biped gait model is developed that allows for studying the effects of leg impedance, geometry, foot curvature and inertial properties on the stable gait performed passively. A set of non-dimensional parameters has been produced that fully defines the compass gait behavior, eliminating the dependence of our results on scale. Models emerging from parameter combinations were tested on their ability to perform stable passive walking on slope, and the characteristics of the gait performed in each case were recorded. Investigation of parameter ranges allowed us to draw relationships between various gait characteristics and specific, non-dimensional parameter selections. By mapping the changes in system behavior under simple design variations, this work facilitates the selection of design parameters at an early stage of designing bionic walking equipment, including prostheses and exoskeletons.

Cartilage defects are common in the knee joint of active athletes and remain a problem as a strong risk factor for osteoarthritis. We hypothesized that landing during sport activities, implication for sub-failure ACL loading, would generate greater contact pressures (CP) at the lateral knee compartment. The purpose of this study is to investigate tibiofemoral cartilage CP of athletes during landing. Tibiofemoral cartilage contact pressures (TCCP) under clinically relevant anterior cruciate ligament sub-failure external loadings were predicted using four dynamic explicit finite element (FE) models (2 males and 2 females) of the knee. Bipedal landing from a jump for five cases of varying magnitudes of external loadings (knee abduction moment, internal tibial torque, and anterior tibial shear) followed by an impact load were simulated. Lateral TCCP increased by up to 94% (under meniscus area) and %30 (under femoral condyle area) when external loads were incorporated with impact load in all the models compared to impact-only case. In addition, FE model predicted higher CP in lateral compartment by up to 37% (11.87MPa vs. 8.67MPa) and 52% (20.19MPa vs. 13.29MPa) for 90% and 50% percentile models, respectively. For the same percentile populations, CPs were higher by up to 25% and 82% in smaller size models than larger size models. We showed that sub-failure ACL loadings obtained from previously conducted in vivo study led to high pressures on the tibiofemoral cartilage. This knowledge is helpful in enhancing neuromuscular training for athletes to prevent cartilage damage.

The relationship between three-dimensional shape and patellofemoral mechanics is complicated. The Wiberg patella classification is a method of distinguishing shape differences in the axial plane of the patella that can be used to connect shape differences to observed mechanics. This study uses a statistical shape model to relate the Wiberg patella classification to patella height and investigates its role in force distribution within the patellofemoral joint. The Wiberg Type I patella is shortest and has a more symmetrical medial and lateral facet while the Type III patella is longest with a larger lateral facet compared to medial. We generated patellofemoral morphologies from the statistical shape model and integrated them into a musculoskeletal model with a twelve degrees-of-freedom knee. We simulated an overground walking trial with these morphologies and recorded patellofemoral mechanics and ligament forces. An increase in patellar ligament force corresponded with an increase in patella height. Wiberg Type III patellas had a sharper patella apex which related to lower ratios of quadriceps tendon forces to patellar ligament forces. The change in pivot point of the patella affects the ratio of forces as well as the patellofemoral reaction force. This study provides a better understating of how patella morphology affects fundamental patella mechanics which may help identify at-risk populations for pathology development.

The purpose of this study was to determine how tibiofemoral joint compressive forces and knee joint-spanning muscle forces during uphill walking change compared to level walking in patients with total knee arthroplasty (TKA). A musculoskeletal model capable of resolving total (TCF), medial (MCF), and lateral (LCF) tibiofemoral compressive forces was used to determine compressive forces and muscle forces during level and uphill walking on a 10° incline for twenty-five post TKA patients. A 2?2 (slope: level and 10° ? limb: replaced and non-replaced) repeated measures ANOVA was used to detect differences in knee contact forces between slope and limb conditions and their interaction. Peak loading-response TCF, MCF, and LCF were greater during uphill walking than level walking for non-replaced limbs. During uphill walking, peak loading-response TCF was smaller in the replaced limb compared to non-replaced limbs with no change in MCF or LCF. Peak knee extension moment and knee extensor muscle force were smaller in replaced limbs compared to non-replaced limbs during uphill walking. During level walking, replaced and non-replaced limbs experienced rather equal joint loading, however replaced limb experienced reduced joint loading during uphill walking. Differences in joint loading between replaced and non-replaced limbs were not present during level walking, suggesting compensation from the replaced limb during the more difficult task. Uphill walking following TKA promotes more balanced loading of replaced limbs during stance, however these benefits may come at the expense of increased loading on non-replaced limbs.

The increasing prevalence of pulmonary ailments including asthma, chronic obstructive pulmonary disorder (COPD), lung tuberculosis and lung cancer, coupled with the success of pulmonary therapy has led to a plethora of scientific research focusing on improving the efficacy of pulmonary drug delivery systems. Recent advances in nanoscience and nanoengineering help achieve this by developing stable, potent, inhalable nano-size drug formulations that potentially increase dosages at target sites with significant therapeutic effects. In this study, we numerically analyze a novel methodology of incorporating helical air-nanoparticle streams for pulmonary nano-therapeutics, using a customized version of the open-source computational fluid dynamics (CFD) toolbox OpenFOAM. As nanoparticles predominantly follow streamlines, helical airflow transports them in a centralized core along the human upper respiratory tract, thereby minimizing deposition and hence waste on the oropharyngeal walls, potentially also reducing the risk of drug-induced toxicity in healthy tissues. Advancing our previous study on micron-particle dynamics, helical streams are shown to improve the delivery of nanodrugs, to deeper lung regions when compared to a purely axial fluid-particle jet. For example, an optimal helical stream featuring a volumetric flow rate of 30 l/min, increased the delivery of 300 nm-particles to regions beyond generation 3 by 5%, in comparison to a conventional axial jet. Results from regional deposition studies are presented, to demonstrate the robustness of helical flows in pulmonary drug delivery; thus, paving the way towards successful implementation of the novel methodology in nanotherapeutics.

The objectives of this study are to experimentally investigate the effects of the dielectric material and the package stiffness on the durability and the efficiency of a previously developed triboelectric-based instrumented knee implant prototype. The proposed smart knee implant may provide useful information about prosthesis health and its functionality after a total knee replacement (TKR) by routine monitoring of tibiofemoral load transfer without the need for any external power source. The triboelectric powered load sensing by the proposed TKR system needs to be functional throughout the entire life of a knee replacement. The power output of the triboelectric system depends on the surface charge generations and accumulations on its dielectric material, and the force that transmits through its housing into the tribo-materials. The properties of the dielectric material and the package stiffness can significantly influence the reliability of the proposed device. For such a TKR system, a compliant mechanism with the ideal material selection can improve its state of the art. We investigated the performance of three vertical contact mode triboelectric generators made with three different dielectric materials: PDMS, FEP, and PTFE. To investigate the effect of package stiffness, we tested two Ti-PDMS-Ti harvesters inside a polyethylene and a Ti6Al4V package. At 1500N of sinusoidal loads, the harvesters could generate 67.73 µW and 19.81 µW of mean apparent power in parallel and single connections in the polyethylene package, which was 32 and 17 times greater than the power recorded in the Ti assembly, respectively.

Pedestrians are one of the most vulnerable road users. In 2019, the USA reported the highest number of pedestrian fatalities in nearly three decades. The pre-impact conditions of Car-to-Pedestrian Collisions (CPC) vary significantly in terms of vehicles characteristics (e.g. front-end geometry, stiffness, etc.) and pedestrian characteristics (e.g. anthropometry, posture, etc.). The influence of pedestrian gait posture on CPC injury outcomes has not been well analyzed. The purpose of this study was to numerically investigate the changes in pedestrian kinematics and injuries across various gait postures in two different vehicle impacts. Five finite element (FE) human body models, that represent the 50th percentile male through the gait cycle, were developed and used to perform CPC simulations with two generic vehicle models representing a low-profile and high-profile vehicle. In the impacts with the high-profile vehicle, the pedestrian models usually slid above the bonnet leading edge and reported shorter wrap around distances than the low-profile vehicle impacts. The pedestrian postures influenced the post-impact rotation of the pedestrian and consequently, the impacted head region. Pedestrian posture also influenced the risk of injuries in the lower and upper extremities. Higher bone bending moments were observed in the stance phase posture compared to the swing phase. The findings of this study should be taken into consideration when examining pedestrian protection protocols. In addition, the results of this study can be used to improve the design of active safety systems used to protect pedestrians in collisions.

Background: AISI 316 L stainless steel wire cerclage routinely used in sternotomy closure causes lateral cut-through damage and fracture, especially in cases of high-risk patients, which leads to postoperative complications. A biocompatible elastomer (Pellethane ® ) coating on the standard wire is proposed to mitigate the cut-through effect. Methods: Simplified peri-sternal and transsternal, sternum-cerclage contact models are created and statically analyzed in a finite element (FE) software to characterize the stress-reduction effect of the polymer coating for thicknesses between 0.5 and 1.125 mm. The performance of the polymer-coated cerclage in alleviating the detrimental cortical stresses is also compared to the standard steel cerclage in a full sternal closure FE model for the extreme cough loading scenario. Results: It was observed via the simplified contact simulations that the cortical stresses can be substantially decreased by increasing the coating thickness. The full closure coughing simulation on the human sternum further corroborated the simplified contact results. The stress reduction effect was found to be more prominent in the transsternal contacts in comparison to peri-sternal contacts. Conclusions: Bearing in mind the promising numerical simulation results, it is put forth that a standard steel wire coated with Pellethane will majorly address the cut-through complication.

Head surrogates are widely used in biomechanical research and headgear assessment. They are designed to approximate the inertial and mechanical properties of the head and are instrumented to measure global head kinematics. Due to the recent interest in studying disruption to the brain, some head models include internal fluid layers and brain tissue, and instrumentation to measure head intracranial biomechanics. However, it is unknown whether such models exhibit realistic human responses. Therefore, this study aims to assess the biofidelity and repeatability of a head model, the Blast Injury Protection Evaluation Device (BIPED), that can measure both global head kinematics and intraparenchymal pressure (IPP) for application in blunt impact, a common loading scenario in civilian life. Drop tests were conducted with the BIPED and the widely used Hybrid III headform. BIPED measures were compared to the Hybrid III data and published cadaveric data, and the biofidelity level of the global linear acceleration was quantified using CORrelation and Analysis (CORA) ratings. The repeatability of the acceleration and IPP measurements in multiple impact scenarios was evaluated via the coefficient of variation (COV) of the magnitudes and pulse durations. BIPED acceleration peaks were generally not significantly different from cadaver and Hybrid III data. The CORA ratings for the BIPED and Hybrid III accelerations ranged from 0.50 to 0.61 and 0.51 to 0.77, respectively. The COVs of acceleration and IPP were generally below 10%. This study is an important step toward a biofidelic head surrogate measuring both global kinematics and IPP in blunt impact.

This study aims to examine the relation between pullout strength and preload values of the cortical screw used in bone fracture fixation. The research question is that "Does the pullout strength of the cortical screw used in the bone fracture fixation change with the preload values of the screw change?". To perform this purpose, the finite element method was selected due to its ease to evaluate and calculate the stresses on the whole model. Models of a cortical screw, partial plate and bone were created using the SolidWorks program. The material properties of the bone were selected orthotropic material type. The bone fixed on the distal and proximal ends. The pullout forces were applied at the bottom of the plate. The screw has been loaded ranges from 100 N - 700 N as preload. The pullout forces were determined 200-400-600 N as in the literature. The results show that the pullout strength of the screw was changed when the preloaded values higher than 400 N. However, it was seen that the pullout strength does not substantially change when the preload values were lower than 400 N. In conclusion, the pullout strength of the screw altered when the preload values of the screw was changed.

In biomechanics, solid–fluid mixtures have commonly been used to model the response of hydrated biological tissues. In cartilage mechanics, this type of mixture, where the fluid and solid constituents are both assumed to be intrinsically incompressible, is often called a biphasic material. Various physiological processes involve the interaction of a viscous fluid with a porous-hydrated tissue, as encountered in synovial joint lubrication, cardiovascular mechanics, and respiratory mechanics. The objective of this study was to implement a finite element solver in the open-source software febio that models dynamic interactions between a viscous fluid and a biphasic domain, accommodating finite deformations of both domains as well as fluid exchanges between them. For compatibility with our recent implementation of solvers for computational fluid dynamics (CFD) and fluid–structure interactions (FSI), where the fluid is slightly compressible, this study employs a novel hybrid biphasic formulation where the porous skeleton is intrinsically incompressible but the fluid is also slightly compressible. The resulting biphasic-FSI (BFSI) implementation is verified against published analytical and numerical benchmark problems, as well as novel analytical solutions derived for the purposes of this study. An illustration of this BFSI solver is presented for two-dimensional (2D) airflow through a simulated face mask under five cycles of breathing, showing that masks significantly reduce air dispersion compared to the no-mask control analysis. In addition, we model three-dimensional (3D) blood flow in a bifurcated carotid artery assuming porous arterial walls and verify that mass is conserved across all fluid–permeable boundaries. The successful formulation and implementation of this BFSI solver offers enhanced multiphysics modeling capabilities that are accessible via an open-source software platform.

The field of tissue engineering has been continuously evolving since its inception over three decades ago with numerous new advancements in biomaterials and cell sources and widening applications to most tissues in the body. Despite the substantial promise and great opportunities for the advancement of current medical therapies and procedures, the field has yet to capture wide clinical translation due to some remaining challenges, including oxygen availability within constructs, both in vitro and in vivo. While this insufficiency of nutrients, specifically oxygen, is a limitation within the current frameworks of this field, the literature shows promise in new technological advances to efficiently provide adequate delivery of nutrients to cells. This review attempts to capture the most recent advances in the field of oxygen transport in hydrogel-based tissue engineering, including a comparison of current research as it pertains to the modeling, sensing, and optimization of oxygen within hydrogel constructs as well as new technological innovations to overcome traditional diffusion-based limitations. The application of these findings can further the advancement and development of better hydrogel-based tissue engineered constructs for future clinical translation and adoption.