Biomechanical remodeling of the murine descending thoracic aorta during late-gestation pregnancy

Measurement and Assessment of Head-to-Helmet Contact Forces

PURPOSE

To evaluate the population variation in head-to-helmet contact forces in helmet users.

METHODS

Four 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.

RESULTS

The 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.

CONCLUSIONS

The fit of helmet systems is highly subject specific. The current metrics used to assign helmet sizes may not accurately predict correct helmet fit.

Toward a Consistent Framework for Describing the Free Vibration Modes of the Brain

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.

Vascular Remodeling During Late-Gestation Pregnancy: An In-Vitro Assessment of the Murine Ascending Thoracic Aorta

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.

Meta Data Analysis of Sex Distribution of Study Samples Reported in Summer Biomechanics, Bioengineering, and Biotransport Annual Conference Abstracts

The biased use of male subjects in biomedical research has created limitations, underscoring the importance of including women to enhance the outcomes of evidence-based medicine and to promote human health. While federal policies (e.g., the 1993 Revitalization Act and the 2016 Sex as a Biological Variable Act) have aimed to improve sex balance in studies funded by the National Institutes of Health (NIH), data on sex inclusivity in non-NIH funded research remain limited. The objective of this study was to analyze the trend of sex inclusion in abstracts submitted to the Summer Biomechanics, Bioengineering, & Biotransport Conference (SB3C) over 7 years. We scored every abstract accepted to SB3C, and the findings revealed that approximately 20% of total abstracts included sex-related information, and this trend remained stable. Surprisingly, there was no significant increase in abstracts, including both sexes and those with balanced female and male samples. The proportion of abstracts with balanced sexes was notably lower than those including both sexes. Additionally, we examined whether the exclusion of one sex from the corresponding studies was justified by the research questions. Female-only studies had a 50% justification rate, while male-only studies had only 2% justification. Disparity in sex inclusion in SB3C abstracts was apparent, prompting us to encourage scientists to be more mindful of the sex of the research samples. Addressing sex inclusivity in biomechanics and mechanobiology research is essential for advancing medical knowledge and for promoting better healthcare outcomes for everyone.

The Fbn1 gene variant governs passive ascending aortic mechanics in the mgΔlpn mouse model of Marfan syndrome when superimposed to perlecan haploinsufficiency

Introduction

Ascending thoracic aortic aneurysms arise from pathological tissue remodeling that leads to abnormal wall dilation and increases the risk of fatal dissection/rupture. Large variability in disease manifestations across family members who carry a causative genetic variant for thoracic aortic aneurysms suggests that genetic modifiers may exacerbate clinical outcomes. Decreased perlecan expression in the aorta of mgΔlpn mice with severe Marfan syndrome phenotype advocates for exploring perlecan-encoding Hspg2 as a candidate modifier gene.

Methods

To determine the effect of concurrent Hspg2 and Fbn1 mutations on the progression of thoracic aortopathy, we characterized the microstructure and passive mechanical response of the ascending thoracic aorta in female mice of four genetic backgrounds: wild-type, heterozygous with a mutation in the Fbn1 gene (mgΔlpn), heterozygous with a mutation in the Hspg2 gene (Hspg2+/-), and double mutants carrying both the Fbn1 and Hspg2 variants (dMut).

Results

Elastic fiber fragmentation and medial disarray progress from the internal elastic lamina outward as the ascending thoracic aorta dilates in mgΔlpn and dMut mice. Concurrent increase in total collagen content relative to elastin reduces energy storage capacity and cyclic distensibility of aortic tissues from mice that carry the Fbn1 variant. Inherent circumferential tissue stiffening strongly correlates with the severity of aortic dilatation in mgΔlpn and dMut mice. Perlecan haploinsufficiency superimposed to the mgΔlpn mutation curbs the viability of dMut mice, increases the occurrence of aortic enlargement, and reduces the axial stretch in aortic tissues.

Discussion

Overall, our findings show that dMut mice are more vulnerable than mgΔlpn mice without an Hspg2 mutation, yet later endpoints and additional structural and functional readouts are needed to identify causative mechanisms.