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Abstract Frequency-domain analysis of brain tissue motion has received increased focus in recent years as an approach to describing the response of the brain to impact or vibration sources in the built environment. While researchers in many experimental and numerical studies have sought to identify natural resonant frequencies of the brain, sparse description of the associated vibration modes limits comparison of results between studies. We performed a modal analysis to extract the natural frequencies and associated mode shapes of a finite element (FE) model of the head. The vibration modes were characterized using two-dimensional (2D) plate deformation notation in the basic medical planes. Many of the vibration modes characterized are similar to those found in previous numerical and experimental studies. We propose this characterization method as an approach to increase compatibility of results between studies of brain vibration behavior. 

Abstract PurposeTo evaluate the population variation in head-to-helmet contact forces in helmet users. MethodsFour different size Kevlar composite helmets were instrumented with contact pressure sensors and chinstrap tension meters. A total number of 89 volunteers (25 female and 64 male volunteers) participated in the study. The length, width, and circumference of their heads were measured and each volunteer was assigned a helmet size. Volunteers were asked to wear the helmet in three different configurations and the chinstrap tension and contact force between the head and each of the seven interior pads were recorded. ResultsThe majority of forces measured on any individual pad were between 0 and 5 N. However, some users exhibited pressure points with forces as high as 30 N. The contact force distribution is non-uniform across the interior of the helmet, with the largest force concentrated at the front. Head shape is a major driver of the observed contact force. There was a statistically significant difference between female and male volunteers, and between groups with different experience levels. ConclusionsThe fit of helmet systems is highly subject specific. The current metrics used to assign helmet sizes may not accurately predict correct helmet fit. 

Abstract Maternal mortality due to cardiovascular disease is a rising concern in the U.S. Pregnancy triggers changes in the circulatory system, potentially influencing the structure of the central vasculature. Evidence suggests a link between a woman's pregnancy history and future cardiovascular health, but our understanding remains limited. To fill this gap, we examined the passive mechanics of the murine ascending thoracic aorta during late gestation. By performing biaxial mechanical testing on the ascending aorta, we were able to characterize the mechanical properties of both control and late-gestation tissues. By examining mechanical, structural, and geometric properties, we confirmed that remodeling of the aortic wall occurred. Morphological and mechanical properties of the tissue indicated an outward expansion of the tissue, as reflected in changes in wall thickness (∼12% increase) and luminal diameter (∼6% increase) at its physiologically loaded state in the pregnant group. With these geometric adaptations and despite increased hemodynamic loads, pregnancy did not induce significant changes in the tensile wall stress at the similar physiological pressure levels of the pregnant and control tissues. The alterations also included reduced intrinsic stiffness in the circumferential direction (∼18%) and reduced structural stiffness (∼26%) in the pregnant group. The observed vascular remodeling maintained the elastic stored energy of the aortic wall under systolic loads, indicating preservation of vascular function. Data from our study of pregnancy-related vascular remodeling will provide valuable insights for future investigations of maternal cardiovascular health. 

Abstract We examined the mechanical deformation of valve interstitial cells (VICs) in the anterior leaflet of the tricuspid valve and explored the relationship between the extracellular matrix (ECM) structure and cellular mechanics. Fresh porcine hearts were used to prepare specimens, subjected to biaxial tensile testing, and imaged using confocal microscopy with VIC nuclei staining. A multi-scale computational framework was developed to analyze cellular deformation and orientation within the ECM, using nuclear aspect ratio (NAR) as a metric. Experimental results showed that NAR values increased with mechanical loading, from 2.57±0.72 in a traction-free state to 3.4±1.29 at 130 kPa. Model predictions aligned with experimental findings. They also highlighted the significant impact of ECM fiber orientation on VIC nuclei deformation. These results indicate that mechanical forces profoundly influence cellular morphology and, potentially, their function. Further development of models is necessary to understand the complex interplay between the mechanical environment and cellular responses, crucial for identifying how mechanical forces affect tricuspid valve function and malfunction.