In vitro biomechanical properties of porcine perineal tissues to better understand human perineal tears during delivery.

INTRODUCTION: Data concerning the mechanical properties of the perineum during delivery are very limited. In vivo experiments raise ethical issues. The aim of the study was to describe some of the biomechanical properties of each perineal tissue layer collected from sows in order to better understand perineal tears during childbirth. MATERIAL AND METHODS: Samples of each perineal tissue layer were obtained from the skin, the vagina, the external anal sphincter (EAS), the internal anal sphincter (IAS), and the anal mucosa of fresh dead sows. They were tested in quasi-static uniaxial tension using the testing machine Mach-1®. Tests were performed at a displacement velocity of 0.1 mm·s-1. Stress-strain curves of each perineal tissue layer before the first damage for each sow were obtained and modeled using a hyperelastic Yeoh model described by three coefficients: C1, C2, and C3. Pearson correlation coefficients were calculated to measure the correlation between the C1 hyperelastic coefficient and the duration between the first microfailure and the complete rupture for each perineal tissue layer. Pearson correlation was computed between C1 and the number of microfailures before complete rupture for each tissue. RESULTS: Ten samples of each perineal tissue layer were analyzed. Mean values of C1 and corresponding standard deviations were 46 ± 15, 165 ± 60, 27 ± 10, 19 ± 13, 145 ± 28 kPa for the perineal skin, the vagina, the EAS, the IAS, and the anal mucosa, respectively. According to this same sample order, the first microfailure in the population of 10 sows appeared at an average of 54%, 27%, 70%, 131%, and 22% of strain. A correlation was found between C1 hyperelastic coefficient and the duration between the first microfailure and the complete rupture (r = 0.7, p = 0.02) or the number of microfailures before complete rupture only for the vagina (r = 0.7, p = 0.02). CONCLUSIONS: In this population of fresh dead sow's perineum, the vagina and the anal mucosa were the stiffest tissues. The IAS and EAS were more extensible and less stiff. A significantly positive correlation was found between C1 and the duration between the first microfailure and the complete rupture of the vagina, and the duration between the first microfailure and the complete rupture of the vagina.

Towards the biomechanical modelling of the behaviour of ex-vivo porcine perineal tissues.

The perineum is a layered soft tissue structure with mechanical properties that maintain the integrity of the pelvic floor. During childbirth, the perineum undergoes significant deformation that often results in tears of various degrees of severity. To better understand the mechanisms underlying perineal tears, it is crucial to consider the mechanical properties of the different tissues that make up the perineum. Unfortunately, there is a lack of data on the mechanical properties of the perineum in the literature. The objective of this study is to partly fill these gaps. Hence sow perineums were dissected and the five perineal tissues involved in tears were characterized by uniaxial tension tests: Skin, Vagina, External Anal Sphincter, Internal Anal Sphincter and Anal Mucosa. From our knowledge, this study is the first to investigate all these tissues and to design a testing protocol to characterize their material properties. Six material models were used to fit the experimental data and the correlation between experimental and predicted data was evaluated for comparison. As a result, even if the tissues are of different nature, the best correlation was obtained with the Yeoh and Martins material models for all tissues. Moreover, these preliminary results show the difference in stiffness between the tissues which indicates that they might have different roles in the structure. These obtained results will serve as a basis to design an improved experimental protocol for a more robust structural model of the porcine perineum that can be used for the human perineum to predict perineal tears.

An agent-based model of vibration-induced intimal hyperplasia.

Acute exposure to hand-arm transmitted vibrations (HAVs) may decrease the wall shear stress (WSS) exerted by the blood flow on the arterial endothelium. In the case of chronic exposure to HAVs, these WSS changes can lead to arterial growth and remodeling potentially induced by an intimal hyperplasia phenomenon. Accordingly, we implemented an agent-based model (ABM) that captures the hemodynamics-driven and mechanoregulated cellular mechanisms involved in vibration-induced intimal hyperplasia. Our ABM was combined with flow loop experiments that investigated the WSS-modulated secretion of the platelet-derived growth factor BB (PDGF-BB) by the endothelial cells. The ABM rules parameters were then identified and calibrated using our experimental findings and literature data. The model was able to replicate the basal state (no vibration) as well as predict a 30% stenosis resulting from a chronic drop of WSS values mimicking exposure to vibration during a timeframe of 10 years. The study of the influence of different WSS-modulated phenomena on the model showed that the magnitude of stenosis largely depends on the migratory effects of PDGF-BB and the mitogenic effects of Transforming Growth Factor [Formula: see text] on the Smooth Muscle Cells. The results also proved that the fall in circumferential stress due to arterial layer thickening to a great extent accounts for the degradation of the Extracellular Matrix in the media.

In vivo skin anisotropy dataset from annular suction test.

To characterize the anisotropic and viscoelastic behaviors of the skin, we conducted an experimental campaign of in-vivo suction tests using the CutiScan®CS100 device from Courage and Khazaka electronics. In this data paper, we present the raw acquired data of the tests and their respective treated data. The tests were performed 30 times on the anterior forearm of a 28-year-old Caucasian male at different pressure set-points, ranging from 100 to 500 mbar with an increment of 20 mbar, at ambient temperature in a windowless room. The primary dataset consists of videos recorded by a probe camera associated with the CutiScan® device during the tests. After data treatment with DIC (Digital Image Correlation) technique and based on a homemade Python program, we have obtained secondary data tables and 2D displacement for all mapped grid nodes.

Multimodal investigation of a keloid scar by combining mechanical tests in vivo with diverse imaging techniques.

Keloids are pathologic scars, defined as fibroproliferative diseases resulting from abnormal wound responses, which grow beyond the original wound margins. They develop on specific pro-keloid anatomic sites frequently characterized by high stress states. The initiation and growth mechanisms of keloid are not well-understood. This study relates multimodal investigation of a keloid by using mechanical tests in vivo and imaging techniques. A single case composed of a keloid, the healthy skin surrounding the keloid, and the contralateral healthy skin on the upper arms of a woman has been investigated in extension and suction by using non-invasive devices dedicated to in vivo skin measurement. The thickness and microstructure of these soft tissues have been observed by echography, tomography and confocal microscopy. Displacement fields have been obtained by using digital image correlation. Unlike healthy skin, keloid is not a well-defined multilayer structure: the frontier between epidermis and dermis disappears. The mechanical behavior of keloid is highly different from healthy skin one. The R-parameters have been deduced from suction curves. Physical parameters as tissue extensibility, initial and final tangent moduli have been identified from the stress-strain curves. The extensibility (respectively, initial rigidity) of keloid is highly lower (respectively, higher) than that of healthy skin. To compare the final rigidity of keloid versus healthy skin, further tests have to be performed with higher strain values.