Evaluation of biological cell properties using dynamic indentation measurement

Viscoelastic mechanical properties of biological cells are commonly measured using atomic force microscope (AFM) dynamic indentation with spherical tips. A semiempirical analysis based on numerical simulation is built to determine the cell mechanical properties. It is shown that the existing analysis cannot reflect the accurate values of cell elastic/dynamic modulus due to the effects of substrate, indenter tip size, and cell size. Among these factors, substrate not only increases the true contact radius but also interferes the indentation stress field, which can cause the overestimation of cell moduli. Typically, the substrate effect is much stronger than the other two influences in cell indentation; and, thus, the cell modulii are usually overestimated. It is estimated that the moduli can be overestimated by as high as over 200% using the existing analysis. In order to obtain the accurate properties of cells, correction factors that account for these effects are required in the existing analysis

Evaluation of biological cell properties using dynamic indentation measurement

Viscoelastic mechanical properties of biological cells are commonly measured using atomic force microscope (AFM) dynamic indentation with spherical tips. A semiempirical analysis based on numerical simulation is built to determine the cell mechanical properties. It is shown that the existing analysis cannot reflect the accurate values of cell elastic/dynamic modulus due to the effects of substrate, indenter tip size, and cell size. Among these factors, substrate not only increases the true contact radius but also interferes the indentation stress field, which can cause the overestimation of cell moduli. Typically, the substrate effect is much stronger than the other two influences in cell indentation; and, thus, the cell modulii are usually overestimated. It is estimated that the moduli can be overestimated by as high as over 200% using the existing analysis. In order to obtain the accurate properties of cells, correction factors that account for these effects are required in the existing analysis

Load Transfer Issues in the Tensile and Compressive Behavior of Multiwall Carbon Nanotubes

Carbon nanotubes (CNT) are considered to be ultra strong and stiff reinforcements for structural composite applications. The load transfer between the inner and outer nanotubes in multiwall carbon nanotubes (MWCNT) has to be clearly understood to realize their potential in not only composites, but also other applications such as nano-springs and nano-bearings. In this paper, we study the load transfer between the walls of multiwall nanotubes both in tension and compression using molecular dynamics simulations. It is found that very minimal load is transferred to the inner nanotube during tension. The load transfer in compression of capped nanotubes is much greater than that in tension. In the case of uncapped nanotubes, the inner nanotube is deformed in bending, only after the outer nanotube is extensively deformed by buckling. It is found that the presence of a few interstitial atoms between the walls of multiwall nanotube can improve the stiffness and enhance the load transfer to the inner nanotubes both in tension and compression

The Effect of Geometrical Factors on the Surface Pressure Distribution on a Human Phantom Model Following Shock Exposure: A Computational and Experimental Study

Experimental data and finite element simulations of an anthropometric surrogate headform was used to evaluate the effect of specimen location and orientation on surface pressures following shock exposures of varying intensity. It was found that surface pressure distributions changed with local flow field disturbances, making it necessary to use data reduction strategies to facilitate comparisons between test locations, shock wave intensities and headform orientations. Non-dimensional parameters, termed amplification factors, were developed to permit direct comparisons of pressure waveform characteristics between incident shock waves differing in intensity, irrespective of headform location and orientation. This approach proved to be a sensitive metric, highlighting the flow field disturbances which exist in different locations and indicating how geometric factors strongly influence the flow field and surface pressure distribution

Dynamic Response of Brain Subjected to Blast Loadings: Influence of Frequency Ranges

Blast wave induced a frequency spectrum and large deformation of the brain tissue. In this study, new material parameters for the brain material are determined from the experimental data pertaining to these large strain amplitudes and wide frequencies ranging (from 0.01 Hz to 10 MHz) using genetic algorithms. Both hyperelastic and viscoelastic behavior of the brain are implemented into 2D finite element models and the dynamic responses of brain are evaluated. The head, composed of triple layers of the skull, including two cortical layers and a middle dipole sponge-like layer, the dura, cerebrospinal fluid (CSF), the pia mater and the brain, is utilized to assess the effects of material model. The results elucidated that frequency ranges of the material play an important role in the dynamic response of the brain under blast loading conditions. An appropriate material model of the brain is essential to predict the blast-induced brain injury

Dynamic Response of Brain Subjected to Blast Loadings: Influence of Frequency Ranges

Blast wave induced a frequency spectrum and large deformation of the brain tissue. In this study, new material parameters for the brain material are determined from the experimental data pertaining to these large strain amplitudes and wide frequencies ranging (from 0.01 Hz to 10 MHz) using genetic algorithms. Both hyperelastic and viscoelastic behavior of the brain are implemented into 2D finite element models and the dynamic responses of brain are evaluated. The head, composed of triple layers of the skull, including two cortical layers and a middle dipole sponge-like layer, the dura, cerebrospinal fluid (CSF), the pia mater and the brain, is utilized to assess the effects of material model. The results elucidated that frequency ranges of the material play an important role in the dynamic response of the brain under blast loading conditions. An appropriate material model of the brain is essential to predict the blast-induced brain injury

第753回 千葉医学会例会・第一外科教室談話会 26.

<p>The representative incident shock wave profiles generated using helium as a driver gas and Mylar membrane (thickness of 1.016 mm), with accompanying secondary reflected shock and underpressure waves are presented (A). The profile of the secondary wave depends on the gap between the end plate reflector and the exit of the shock tube (B): 1. 0.625-inch, 2. 2-inch, 3. 4-inch, and 4. open end. C. Schematics of the 9-inch square cross section shock tube indicating the breech (I), transition (II), test section (III) and end plate (IV). Distribution of pressure sensor locations is also illustrated. Typically sensors B1, C1, T4, C2, D2 and D4 were used in our experiments to track the shock wave profile evolution along the entire length of the shock tube. The scale bar indicates the distance of specific sensor from the breech, i.e. Mylar membranes installation port.</p

Antioxidant gene therapy against neuronal cell death

Oxidative stress is a common hallmark of neuronal cell death associated with neurodegenerative disorders such as Alzheimer\u27s disease, Parkinson\u27s disease, as well as brain stroke/ischemia and traumatic brain injury. Increased accumulation of reactive species of both oxygen (ROS) and nitrogen (RNS) has been implicated inmitochondrial dysfunction, energy impairment, alterations in metal homeostasis and accumulation of aggregated proteins observed in neurodegenerative disorders, which lead to the activation/modulation of cell death mechanisms that include apoptotic, necrotic and autophagic pathways. Thus, the design of novel antioxidant strategies to selectively target oxidative stress and redox imbalance might represent important therapeutic approaches against neurological disorders. This work reviews the evidence demonstrating the ability of genetically encoded antioxidant systems to selectively counteract neuronal cell loss in neurodegenerative diseases and ischemic brain damage. Because gene therapy approaches to treat inherited and acquired disorders offer many unique advantages over conventional therapeutic approaches, we discussed basic research/clinical evidence and the potential of virus-mediated gene delivery techniques for antioxidant gene therapy

Role of Atomic Scale Interfaces in the Compressive Behavior of Carbon Nanotubes in Composites

Carbon nanotubes (CNT) are potentially promising fibers for ultra high strength composites. In order to fully har-ness the outstanding mechanical properties of carbon nanotubes as fiber reinforcements, it is essential to understand the nature of load transfer between fiber and matrix under various types of loading conditions that include tension, compression, torsion and a combination thereof. In this paper, we study the compressive behavior (buckling and post-buckling) of carbon nanotubes in the neat form, when they are embedded in polyethylene matrix and with in¬terface chemical modifications using molecular dynamics simulations based on Tersoff–Brenner potential. It is ob¬served that the critical load for buckling increases only very marginally for nanotubes embedded in polythene matrix (with non-bonded interface) compared to neat CNTs. When CNTs are chemically bonded to the matrix, the compres¬sive behavior occurs in two phases; pre- and post-buckling phases. First, the critical stress for buckling is found to re¬duce because the change in chemical bonding induces deviation from perfect cylindrical structure. In the post-buck¬ling phase, however, the nanotubes behave similar to short fibers and deform by crushing. The results are compared with continuum solutions, wherever applicable. It is shown that the continuum solutions should be applied carefully whenever the effect of nanoscale interfaces becomes a factor

The effect of heterogeneity on plane wave propagation through layered composites

When laminated composites are subjected to impact loading, the material response is critically determined by the interactions of multiple waves generated at the laminate interfaces. Due to the high complexity arising from the architectural details of composites, layered heterogeneous materials have been studied as the model system to understand the impact behavior of engineering composites. Previously, the present authors have developed an analytical solution to the problem of plate impact of layered systems; plate impact test is a standard boundary value problem used to study high velocity impact behavior both in the elastic and shock wave regimes. In this paper, we examine the various heterogeneity factors that affect the impact response of the laminated composite systems. We have identified three different heterogeneity factors (impedance mismatch, interface density and thickness ratio) and examine their effects on wave scattering. These effects are then used to explain some outstanding experimental observations in terms of shock wave structure (arrival time, sloping rise, peak stress and oscillatory pulse duration). It is shown that though the results pertain to layered systems, the observations can be qualitatively extended to real composites