Intracranial pressure (ICP) is derived from cerebral blood pressure and cerebrospinal fluid (CSF) circulatory dynamics and can be affected in the course of many diseases. Computer analysis of the ICP time pattern plays a crucial role in the diagnosis and treatment of those diseases. This study proposes the application of Linninger et al.'s [IEEE Trans. Biomed. Eng., vol. 52, no. 4, pp. 557-565, Apr. 2005] fluid-solid interaction model of CSF hydrodynamic in ventricular system based on our clinical data from a group of patients with brain parenchyma tumor. The clinical experiments include the arterial blood pressure (ABP), venous blood pressure, and ICP in the subarachnoid space (SAS). These data were used as inputs to the model that predicts the intracranial dynamic phenomena. In addition, the model has been modified by considering CSF pulsatile production rate as the major factor of CSF motion. The approximations of ventricle enlargement, CSF pressure distribution in the ventricular system and CSF velocity magnitude in the aqueduct and foramina were obtained in this study. The observation of reversal flow in the CSF flow pattern due to brain tissue compression is another finding in our investigation. Based on the experimental results, no existence of large transmural pressure differences were found in the brain system. The measured pressure drop in the ventricular system was less than 5 Pa. Moreover, the CSF flow pattern, ICP distribution, and velocity magnitude were in good agreement with the published models and CINE (phase-contrast magnetic resonance imaging) experiments, respectively.

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Brain tissue is a heterogeneous material with complicated microstructural features. Models based on microstructure can lead to more accurate and physically realistic predictions of mechanical characteristics of brain tissue. A two-step Mori-Tanaka/Voigt homogenization procedure is implemented into a 3D microstructurally-based multi-phase composite model, composed of randomly-oriented elastic axons, dendrites and neuronal cell bodies surrounded by an elastic matrix. The effects of microstructure-related scale on the effective elastic moduli of the cerebral cortex are analyzed by comparing the predictions from classical and micropolar continuum theories. For the first time, composite material rules and micropolar continuum theory have been utilized to investigate brain biomechanics. These findings can assist future efforts to be directed towards relating the microstructural aspects of the brain tissue to its macroscopic behavior

Characterizing the differences between the mechanical properties of brain tissue gray and white matters is of importance in biomechanics of brain tissue and may find a variety of different applications in medicine. In this study, a comparison has been made between mechanical behavior of bovine brain tissue white and gray matters. Through a linear elastic theory and using Bridgman method, necking phenomenon is considered for brain tissue in tension test. Results show that gray and white matters have different mechanical properties and differences between true and nominal values (the effect of cross section changes of the samples during the test) are not negligible. Besides, it is shown that for certain strains, linear elastic theory is acceptable for brain tissue modeling. These results are in agreement with the literature.

A detailed theoretical model that combines the conventional viscoelastic continuum description of cell motion with a dynamic active stress is presented. The model describes the ameboid cells movement comprising of protrusion and adhesion of the front edge followed by detachment and movement of the tail. Unlike the previous viscoelastic descriptions in which the cell movement is steady, the presented model describes the “walking” of the cell in response to specific active stress components acting separately on the front and rear of the cell. In this locomotive model first the tail of the cell is attached to the substrate and active stress is applied to the front of the cell. Consequently, the stress in the tail increases. When the stress in the tail exceeds a critical value, namely critical stress, the conditions are updated so that the front is fixed and the tail of the cell is detached from the substrate and moves towards the front. Consequently, the stress in the tail decreases. When the stress goes to zero, the starting conditions become active and the process continues. At start the cell is stretched and its length is increased as the front of cell migrates more than the rear. However, after several steps the front and rear move equally and the cell length stays constant during the movement. In this manuscript we analyzed such cell dynamics including the length variation and moving velocity. Finally, by considering this fact that at the single-cell level, interactions with the extracellular environment occur on a nanometer length scale, the value of critical stress was estimated.

In the plain strain biomechanical modeling of the brain in unilateral strain loading (conditions similar to those used in image guided systems), the intra-ventricular pressure gradients should be considered in order to achieve accurate results. In addition, the so-called "strain shadow effect" is emphasized.

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