Sebastien Roth

Finite element modeling in biomechanics has been widely used for several decades to investigate the injury mechanisms and tolerance limits of various biological structures. The development of biomechanical models includes choosing an anthropometry, which generally leads to a 50th percentile male model. In that context, derived numerical injury metrics are dedicated to males, although conclusions of these studies are generalized to the whole population including female subjects. This study proposes to address the existing paucity concerning female blunt thoracic injuries and add to the understanding of thoracic injuries at a numerical level. Thus, a female finite element model of the thorax has been developed, named HUBxx, in the same way as the existing male geometry model is named HUByx. A 3-D reconstruction of the geometry of the various components of the model was based on literature data. Constitutive laws were implemented in the model for soft tissues and skeletal structures, and a numerical replication of existing experimental tests was carried out in the context of blunt ballistic impacts. The results show that the numerical responses of the HUBxx model are in good agreement with the female experimental corridors for both sternal and breast impacts, demonstrating its biofidelity and its ability to reproduce the mechanical response of the female thorax. In contrast, a male finite element model (SurHUByx FEM) scaled-down to female external anthropometric dimensions fails to reproduce the characteristics of the female experimental corridors. This study provides tools and data for specific investigations of female thoracic injuries, given the differences observed between males and females.

The digital twin: this term present in many scientific fields corresponds to a virtual model of a physical object. Used in several framework on the physics, the digital twin must be fidelic to reality, by closely reproducing the behavior and interaction with its environment. However, it is necessary, before using such a tool, to ensure that it is indeed realistic. In the context of impact biomechanics, one of the objectives of which is to understand the mechanisms of injury occurrence and the tolerance threshold, and ultimately to allow optimization of protective systems that would reduce the risk of injury occurrence, the concept of the digital twin relates to the development of a numerical model that must be biofidelic before it can be used for the development of protection systems. This paper raises the question of the biofidelity and the protecting ability of a digital twin and how one can trust the digital procedure to develop protecting devices, without data coming from physical procedures.

Pelvic organ prolapse (POP) is a prevalent condition affecting women, particularly those over the age of 50. The etiology and pathophysiology of this condition remain poorly understood within the medical community. In recent years, researchers, particularly medical engineers and biomechanical scientists, have initiated studies on this female pathology. Numerous finite element analyses have been conducted to determine the material properties of tissues involved in POP. Building on the material properties established in prior research, this study presents a patient-specific model derived from patient-specific MRI data. Intra-abdominal pressure (IAP) and boundary conditions were determined from MRI analysis, and the models were validated against MRI simulations encompassing 11 seconds with a 1-second step interval. This study compares the outcomes of our models with MRI results, providing insights into POP biomechanics. A good correlation was observed between MRI data and the finite element method (FEM) models in healthy patients, particularly for the bladder when fluid properties, such as urine, were included. A relative error between 18% and 26% was observed for bladder displacement. Moreover, the models provided acceptable results for the uterus, vagina, and rectum. Visual results supporting these findings are presented in this study.

Human surrogates have long been employed to simulate human behaviour, beginning in the automotive industry and now widely used throughout the safety framework to estimate human injury during and after accidents and impacts. In the specific context of blunt ballistics, various methods have been developed to investigate wound injuries, including tissue simulants such as clays or gelatine ballistic, physical dummies and numerical models. However, all of these surrogate entities must be biofidelic, meaning they must accurately represent the biological properties of the human body. This paper provides an overview of physical and numerical surrogates developed specifically for blunt ballistic impacts, including their properties, use and applications. The focus is on their ability to accurately represent the human body in the context of blunt ballistic impact.

The present paper explores a series of articles in the literature which deal with impact biomechanics of the head and thorax/abdomen segments, investigating the “sex specific properties/data” used in the studies. Statements in these studies are analyzed and point out, the use of male or female subjects for the developments of finite element models and their validation against experimental data. The present analysis raises the question about “androcentrism,” and how biomechanical engineering findings and the design of the derived protecting devices are focused on male subjects.

Hearing protection devices facing high-level impulse noises provide an attenuation, generally, between 20 and 40 dB. One reason for this limitation is the direct interactions between the protection device and the impulse waves. In the case of earplugs, direct transmissions through the earplug occur. These direct transmissions combine with the already well-studied indirect transmissions arising from wave propagation in the external ear's tissues (skin, cartilage, and bone). To evaluate the transmission induced directly by the earplug, an experimental protocol using a laser Doppler vibrometer was developed. Thus, the earplug's outer lateral face (OLF) displacements and acoustic pressure at the eardrum were measured simultaneously. Two earplugs (polyurethane foam and acrylonitrile butadiene styrene) inserted in an acoustic test fixture were stimulated with impulses ranging from 137 to 180 dB-peak. A slight earplug OLF movement in the ear canal varying from 1 μm to 0.1 mm could be observed, which is likely related to ear canal longitudinal compression. The earplug's OLF displacement and acoustic pressure variation at the eardrum strongly depended on the earplug type. These direct transmissions and underlying consequences considerably alter the protection efficiency.