Computational Human Torso Model Validation for Frontal Blunt Trauma

Recent research on behind-armor blunt trauma (BABT) has focused on the personal protection offered by lightweight armor. A finite element analysis was performed to improve the biofidelity of the US Army Research Laboratory (ARL) human torso model to prepare for simulating blunt chest impacts and BABT. The overly stiff linear elastic material models for the torso were replaced with material characterizations drawn from current literature. FE torso biofidelity was determined by comparing peak force, force-compression, peak compression, and energy absorption data with cadaver responses to a 23.5 kg pendulum impacting at the sternum at 6.7 m/s. Nonlinear foam, viscous foam, soft rubbers, fibrous hyperelastic rubbers, and low moduli elastic material were considered as material models for the flesh, organs, and bones. Simulations modifying one tissue type revealed that the flesh characterization was most crucial for predicting compression and force, followed closely by the organs characterizations. Combining multiple tissue modifications allowed the FE torso to mimic the cadaveric torsos by reducing peak force and increasing chest compression and energy absorption. Limitations imposed by the Lagrangian finite element approach are discussed with potential workarounds described. Proposed future work is split between considering additional impact scenarios accounting for position and biomaterial variability.

Determination of Mechanical Properties of Human Skull With Modal Analysis

Traumatic brain injury (TBI) may happen due to loads at high rates. Due to the limitations in experimental approaches, computational methods can simulate and quantify mechanical properties. The experiments show that the human skull has nonlinear mechanical behavior and is significantly strain rate dependent. In this study, we implement Mooney-Rivlin nonlinear hyper and linear-elastic constitutive models to the experimental tensile data at different strain rates; 0.005, 0.1, 10, and 150 1/sec. A dried human skull including frontal, parietal, and occipital bones, was modeled by the 3D laser scanner and discretized by HyperMesh software to perform modal analysis using LS-Dyna finite element software. Using a roving hammer experimental modal analysis scheme, the frequency response function (FRF) and the first three natural frequencies of the skull will be measured. We found these natural frequencies are 496.9 Hz, 560.9 HZ, and 1246 Hz. Performing numerical modal analysis on the skull with pre-assumed linear elastic properties at high strain rate showed close natural frequencies as obtained by experiments. This study provides a new insight into a better understanding of the nonlinearity dynamical behavior of the human skull.

The Strain Rates of the Brain and Skull Under Dynamic Loading

Accurate material properties of the brain and skull are needed to examine the biomechanics of head injury during highly dynamic loads such as blunt impact or blast. In this paper, a validated Finite Element Model (FEM) of a human head is used to study the biomechanics of the head in impact and blast leading to traumatic brain injuries (TBI). We simulate the head under various direction and velocity of impacts, as well as helmeted and un-helmeted head under blast waves. It is shown that the strain rates for the brain at impacts and blast scenarios are usually in the range of 36 to 241 s−1. The skull was found to experience a rate in the range of 14 to 182 s−1 under typical impact and blast cases. Results show for impact incidents the strain rates of brain and skull are approximately 1.9 and 0.7 times of the head acceleration. Also, this ratio of strain rate to head acceleration for the brain and skull was found to be 0.86 and 0.43 under blast loadings. These findings provide a good insight into measuring the brain tissue and cranial bone, and selecting material properties in advance for FEM of TBI.

Coupling Immunofluorescence and Optoelectrokinetic Technique for Escherichia Coli Detection and Quantification in Water

At least 2 billion people worldwide drink water from sources contaminated with feces, in other words, sources contaminated with E. coli. The traditional method for detecting E. coli, among other limitations, detects only culturable bacteria and takes about 24–48 hours to yield a result. Consequently, the aim of this work is to develop a rapid diagnostic procedure for E. coli by combining immunofluorescence and optoelectrokinetic patterning to specifically target and sensitively trap the whole organism. This is to ensure the populace have timely access to sustained “E. coli-free” water for both domestic and recreational activities. The procedure involves conjugation of streptavidin functionalized superparamagnetic fluorescent micro-beads with biotin-labelled anti-E. coli polyclonal antibody. The conjugate is introduced into a water sample containing E. coli among other contaminants, where it specifically and sensitively targets the bacteria in the sample solution which is quantified using an optoelectrokinetic patterning technique by introducing the targeted organism in a fabricated microfluidic chip and trapping it with an application of both laser beam and AC electric field simultaneously. Preliminary experiments have shown that increasing concentrations of E. coli in the microfluidic chamber varies directly with the electrical resistance of the entire system. This on-going research has the potential of sensitively isolating E. coli from a large pool of organic and inorganic contaminants in water in less than 4 hours.

Development of Stretch Stimulation Device for Three-Dimensional Culture of PC12 Cells

Enhancement of nerve axonal extension by using the extracellular environmental stimulation were reported. In this study, we focused on the stretch stimulation, and developed a 3D cell culture system to mimic the in vivo extracellular matrices and investigated the fundamental mechanism of axonal extension enhancement. Firstly, we fabricated the stretch stimulation device. The rat phenocromocytoma cells (PC12), the nerve-like cells, embedded in the collagen gel were poured into the stretch chamber. It was set in the stretch stimulation device, which could load the strain to the collagen gel. Secondly, we determined the structure of the stretch chamber to implement the uniform strain distribution in the culture region. Using the finite element (FE) analyses, we confirmed that the uniform strain is assigned in a region of 2.7 × 3.0 × 0.5 mm in the culture region, which is the candidate for the observation region. Thirdly, PC12 cells axonal extension under uniaxial cyclic stretch stimulation (4% strain, 1 Hz) of 24 hours was carried out. After 96 hours’ culture, we observed the 3D morphology of PC12 cells by the multiphoton excitation fluorescence microscope (MPM). Finally, we confirmed the availability of our stretch stimulation device and the enhancement effect of axonal extension.

Development of Three-Dimensional DC Electric Field Stimulation Bio-Reactor for Axonal Outgrowth Enhancement

Numerous studies of electrical stimulation effects on the nerve regeneration have been carried out. However, there were very few investigations which adopt the 3D culture that mimics the in vivo environment. In this study, we designed and fabricated a new 3D direct current electric field (DCEF) stimulation bio-reactor and investigated the effectiveness on the axonal outgrowth enhancement. We searched an optimum structure using the finite element (FE) analyses to obtain a uniform DCEF in the culture region. A measurement result of DCEF strength showed an agreement with FE results. The rat phenocromocytoma cells (PC12) were disseminated in the collagen gel and 3D culture was performed. We observed the morphologies of cell bodies and neurites using the multiphoton excitation fluorescence microscope (MPM). Both increases in 11.3% of mean axonal length and in 4.2% of axogenesis rate, under the condition of 5.0 mV/mm on 6 hours a day for 4 days, were obtained. Further, there was a tendency of longer connecting distance between cell bodies in the DCEF group than one in the Control group. As a result, we validated the efficacies of our stimulation, both for the axonal extension and the neural network generation, using our newly developed bio-reactor.

Development of Chemotherapy System Using Plasma Activated Medium to Enhance PC12 Axonal Extension

In recent years, plasma activated medicine using non-thermal atmospheric-pressure plasma (NTAPP) has attracted great interest for chemotherapy. In this study, we aim to develop a chemotherapy system with reactive species generated in a plasma activated medium (PAM) for PC12 treatment. We observe the morphology change of PC12 cells and evaluate the effectiveness of PAM and the reactive species on axonal-extension enhancement. First, we measured the amount of reactive species, such as H2O2, NO2, and NO3 in PAM. Second, we confirmed the stimulation effect of PAM on PC12 by measuring the axonal extension length of a 72-h culture after PAM stimulation. Experiments were conducted under 20 conditions to find an optimal condition. Using the grid method, significant axonal extension was confirmed. Next, the optimal conditions to promote PC12 axonal-extension was determined using the response surface method. Promotion of axonal extension was not confirmed in the cell culture using only H2O2. As a result, we presumed that the enhancement of axonal-extension was induced by the coupling effects of NO2, NO3 and H2O2, which are active species produced in PAM. Finally, we were able to declare that PAM exhibits a selective cell activation property for the chemotherapy of the central nervous system.

Non-Linear Analysis of Bio-Structures Through Refined Beam Models

A novel approach for the analysis of the non-linear behavior of bio-structures is presented here. This method is developed in the framework of the Carrera Unified Formulation (CUF), a higher-order 1D theory according to which the kinematics of the problem depends on the arbitrary expansion of the generalized unknowns. Taylor-like (TE) and Lagrange-like expansion functions (LE) are employed to describe the kinematic field along the cross-section and, the finite element method (FEM) is used to formulate the governing equations. In this work, the effects of material nonlinearities are investigated and, the problem is solved by using the Newton-Raphson method. An atherosclerotic plaque of an artery is introduced as a typical bio-structure with complex geometry and studied for both linear and non-linear material cases. The results from the proposed technique highlight the accuracy of the in-plane and out-of-plane stress/strain distributions for different 1D models. The 3D-like accuracy of local effect predictions, the possibility of dealing with complex geometries, and low computational costs of nonlinear analyses make the present formulation appealing for biomechanical applications.

Influence of Non-Newtonian Rheology on Mass Transfer From a Biofluid in Separated and Reattached Flows

Influence of the rheological model selection on the flow and mass transfer behavior of human blood in a separated and reattached flow region is investigated. Newtonian and non-Newtonian hemorheological models that account for the yield stress and shear-thinning characteristics of blood are used. The conservation of mass, momentum, and species equations as well as the Herschel-Bulkley constitutive equation are solved numerically using a finite-difference scheme. A parametric study is performed to reveal the impact of flow restriction and rheological modelling on blood-borne oxygen exchange with the confining walls. The wall mass transfer rates within the separated and reattached regions display a strong dependency on the used hemorheological model. Newtonian and non-Newtonian models result in a peak wall mass transfer rate within the recirculation region. However, non-Newtonian models that account for the yield stress and shear-thinning effects predict a substantial, highly localized, drop in the wall mass transfer rates of oxygen, at the reattachment point.

A Modular Test Platform for Micromechanical Tensile Testing of Soft Biomaterials

Mechanical properties of biomaterials are difficult to characterize experimentally because many relevant biomaterials such as hydrogels are very pliable and viscoelastic. Furthermore, test specimens such as blood clots retrieved from patients tend to be small in size, requiring fine positioning and sensitive force measurement. Mechanobiological studies require fast data recording, preferably under simultaneous microscope imaging, in order to monitor events such as structural remodeling or localized rupture while strain is being applied. A low-profile tensile tester that applies prescribed displacement up to several millimeters and measures forces with resolution on the order of micronewtons has been designed and tested, using alginate as a representative soft biomaterial. 1.5% alginate (cross-linked with 0.1 M and 0.2 M calcium chloride) has been chosen as a reference material because of its extensive use in tissue engineering and other biomedical applications. Prescribed displacement control with rates between 20 μm/s and 60 μm/s were applied using a commercial low-noise nanopositioner. Force data were recorded using data acquisition and signal conditioning hardware with sampling rates as high as 1 kHz. Elongation up to approximately 10 mm and force in the range of 250 mN were measured. The data were used to extract elastic and viscoelastic parameters for alginate specimens. Another biomaterial, 2% agarose, was also tested to show versatility of the apparatus for slightly stiffer materials. The apparatus is modular such that different load cells ranging in capacity from hundreds of millinewtons to tens of newtons can be used. The apparatus furthermore is compatible with real-time microscope imaging, particle tracing, and programmable positioning sequences.