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This paper presents a new analysis of the physics of closed head injury following brief, intense acceleration of the head. It focuses upon the buoyancy of the brain in cerebrospinal fluid, which protects against damage; the propagation of strain waves through the brain substance, which causes damage; and the concentration of strain in critical anatomic regions, which magnifies damage. Numerical methods are used to create animations or "movies" of brain motion and deformation. Initially, a 1 cm gap filled with cerebrospinal fluid (CSF) separates the brain from the skull. Whole head acceleration induces artificial gravity within the skull. The brain accelerates, because its density differs slightly from that of CSF, strikes the inner aspect of the skull, and then undergoes viscoelastic deformation. The computed pattern of brain motion correlates well with published high-speed photographic studies. The sites of greatest deformation correlate with sites of greatest pathological damage. This fresh biomechanical analysis allows one to visualize events within the skull during closed head injury and may inspire new approaches to prevention and treatment.

This paper presents a new analysis of the physics of closed head injury caused by intense acceleration of the head. At rest a 1 cm gap filled with cerebrospinal fluid (CSF) separates the adult human brain from the skull. During impact, whole head acceleration induces artificial gravity within the skull. Because its density differs slightly from that of CSF, the brain accelerates, strikes the inner aspect of the rigid skull, and undergoes viscoelastic deformation. Analytical methods for a lumped parameter model of the brain predict internal brain motions that correlate well with published high-speed photographic studies. The same methods predict a truncated hyperbolic strength-duration curve for impacts that produce a given critical compressive strain. A family of such curves exists for different critical strains. Each truncated hyperbolic curve defines a head injury criterion (HIC) or threshold for injury, which is little changed by small offsetting corrections for curvature of the brain and for viscous damping. Such curves predict results of experimental studies of closed head injury, known limits for safe versus dangerous falls, and the relative resistance of smaller versus larger animals to acceleration of the head. The underlying theory provides improved understanding of closed head injury and better guidance to designers of protective equipment and to those extrapolating research results from animals to man.

The proximal femoral nail antirotation device (PFNA) is a typical implant to the treatment of intertrochanteric fractures. However, re-fracture of the femur shaft after nailing are usually been reported. The purpose of this study was to investigate the biomechanical features in the healed proximal femur at different stages in the healing process. Stress and strain distributions, total strain energy density (SED) along the femur and PFNA were analyzed in walking and stair climbing. Results showed remarkable stress concentration occurred near the locking bolt hole with retained PFNA, decreased after PFNA removal. Stair climbing resulted in higher strain at the locking bolt hole than normal walking. The conclusion can be drawn that non-removal of PFNA after healing may result in high fractural risk near locking bolt on femoral shaft. Meanwhile, stair climbing should be avoided during healing.

The aim of this study was to enhance head-injury prediction, this paper investigated the behavior of cerebrospinal fluid (CSF) in finite element (FE) modeling. Nine different material properties selected according to material definitions and property values were used to represent CSF in FE head models. To evaluate the influence of CSF material parameters on brain mechanical responses, the models were validated against available cadaver experiment data. Results showed that coup pressure increased whereas contrecoup pressure decreased when the head sustained purely translational impact with increased bulk modulus when CSF was modeled as fluid. However, with increased bulk modulus, coup pressure, contrecoup pressure and relative skull-brain motions decreased under rotational impact. When CSF was assumed to be an elastic material, coup pressure increased whereas contrecoup pressure decreased with increased elastic modulus when the head was subjected to purely translational impact. However, the variation trend was not obvious during head rotation. Results also indicated that when subjected to brain strain and von Mises stress, the model was prone to underestimate brain injury when CSF was modeled as an elastic material, especially during purely translational impact to the head. The model with CSF as fluid reduced the strain rate of brain, which was more likely to be realistic than the model with CSF as a viscoelastic material. These findings suggested that significantly higher values of the bulk modulus of CSF modeled as fluid were needed to predict intracranial dynamic responses and brain injury during head impact.

The objective of this work is to determine the injury criterion for primary rat cortical astrocytes through an in vitro traumatic injury model. The compressed air pressure was used to reproduce typical blast pressure profile, which could induce biaxial strain up to 100% in millisecond for cells cultured on flexible membrane utilizing a controlled cellular injury (CCI) device. The nominal pressure and time settings could be adjusted to accommodate a wide range of membrane strain and strain rate, which was estimated from finite element models. The relationship between the peak membrane displacement/strain and the nominal settings of the CCI device was then established. The model was calibrated using both high-speed imaging system and a theoretical model. The viability and morphology of the astrocytes were characterized and correlated with the strain level. Three different regimes were identified in the stretch-induced dose-response curves of the primary cortical astrocytes, with a sharp decline from live to dead in a narrow range of membrane strain (18%–35%). The level of actin organization of the astrocytes decreased as the membrane strain increased. This work could facilitate the understanding of cellar behaviors subjected to mild blast loadings and the potential tissue engineering therapeutics.

Understanding the relationship between the changes in the axonal transport of the optic nerve (ON) and lamina cribrosa (LC) deformation will be helpful to estimate the degree of axonal transport block by measuring the LC deformation in vivo. First, the changes in the axonal transport of the ON were studied using an acute high intraocular pressure (IOP) model, which was established by perfusing saline water into the anterior chamber of cats. The IOP of cat was unilaterally elevated to and maintained at 30, 40, and 50mmHg. The axonal transport of the ON was examined by confocal laser scanning microscope. Then the deformations and stress distributions of the LC and ON were calculated using a three-dimensional finite element model of the LC microstructure including ON. The results showed axonal transport changes of ON increased with elevation of the IOPs. While Young’s modulus of the LC and ON were assumed as 0.1MPa and 0.03MPa, the numerical simulation results showed that LC had displacements of 0.02, 0.03, and 0.04mm backward at the IOPs of 30, 40, and 50mmHg, respectively. The calculated compressive strain applied to the ON were 0.0425, 0.0567, and 0.0709 under 30, 40, and 50mmHg IOP, respectively. The results of strain and stress analysis of LC and ON showed that the deformation of LC would compress the ON. The axonal transport abnormalities could be inferred by measuring the LC deformation in vivo.

In order to analyze the mechanical properties of a new type of retrievable vena cava filter, the Denali and Aeginsy retrievable filters are selected, and the in vivo and in vitro mechanical properties of the three types of retrievable vena cava filters are compared. The nonlinear deformation process of the filter which is pressed into the transport sheath, flicked and released into the vascular vessel is simulated by using the finite element method, and the mechanical behaviors of the filter and the blood vessel wall are analyzed. During the crimping process, the elastic strain peak value of the filter wall increases with increasing amount of grip. The maximum elastic strain peak value of the three filters is less than 8%, and the safety factor is greater than 2, which meets the strength requirement. Equivalent stress and strain on the vascular wall decreases along the direction of blood flow after the filter is opened. The peak value of equivalent stress and strain on the vascular wall corresponding to Aegisy filter is the largest, and the impact on the vascular wall is the largest. The total displacement of the three filters under the action of thrombus and blood fluids is not more than 80$\mu$m. The impact of the new filter on the vascular wall is smaller than that of Aegisy filter, and the total displacement after implantation is smaller than that of Denali filter. The results are valuable for the evaluation and clinical application of the new vena cava filter.

This paper presents a detailed investigation of the effects of piezoelectricity, spontaneous polarization and charge density on the electronic states and the quasi-Fermi level energy in wurtzite-type semiconductor heterojunctions. This has required a full solution to the coupled Schrödinger–Poisson–Navier model, as a generalization of earlier work on the Schrödinger–Poisson problem. Finite-element-based simulations have been performed on a AlN/GaN quantum well by using both one-step calculation as well as the self-consistent iterative scheme. Results have been provided for field distributions corresponding to cases with zero-displacement boundary conditions and also stress-free boundary conditions. It has been further demonstrated by using four case study examples that a complete self-consistent coupling of electromechanical fields is essential to accurately capture the electromechanical fields and electronic wavefunctions. We have demonstrated that electronic energies can change up to approximately 0.5 eV when comparing partial and complete coupling of electromechanical fields. Similarly, wavefunctions are significantly altered when following a self-consistent procedure as opposed to the partial-coupling case usually considered in literature. Hence, a complete self-consistent procedure is necessary when addressing problems requiring more accurate results on optoelectronic properties of low-dimensional nanostructures compared to those obtainable with conventional methodologies.

While microalgae oil was perceived as the preferred feedstock to supply the inelastic global demand for biofuel, industry and academia attempts to create viable microalgae-oil production processes has not reach the desired goal yet. UniVerve Ltd. has developed an innovative technological process that provides a scalable, cost effective and sustainable solution for the production of microalgae-biomass. The oil, which can be extracted with off-the-shelf wet-extraction technologies and used as an excellent feedstock for all kinds of biofuel, is expected to be produced at up to US$50 per barrel. As the biomass also contains omega-3, proteins and other valuable biomaterials that can be commercialized in the food and feed markets, a microalgae farm can serve the biofuel, food and feed industries, which currently face an increasing lack of quality feedstock at an affordable price.