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International audience; The aim of this work is to characterize the mechanical parameters governing the in-plane behavior of human skin and, in particular, of a keloid-scar. We consider 2D hyperelastic bi-material model of a keloid and the surrounding healthy skin. The problem of finding the optimal model parameters that minimize the misfit between the model observations and the in vivo experimental measurements is solved using our in-house developed inverse solver that is based on the FEniCS finite element computational platform. The paper focuses on the model parameter sensitivity quantification with respect to the experimental measurements, such as the displacement field and reaction force measurements. The developed tools quantify the significance of different measurements on different model parameters and, in turn, give insight into a given model's ability to capture experimental measurements. Finally, an apriori estimate for the model parameter sensitivity is proposed that is independent of the actual measurements and that is defined in the whole computational domain. This estimate is primarily useful for the design of experiments, specifically, in localizing the optimal displacement field measurement sites for the maximum impact on model parameter inference.

International audience; A sustained exposure to Hand-Arm transmitted-Vibration may cause various vascular pathologies such as the vibration-induced Raynaud’s Syndrome. This disorder is characterized at the tissue level by an arterial growth and remodelling potentially induced by an intimal hyperplasia phenomenon. The proliferation and migration of the Vascular Smooth Muscle Cells (VSMCs) are the keystone of this intimal hyperplasia phenomenon. Wall Shear Stress (WSS) alterations play a key role in inducing such mechanisms. Moreover, finger-transmitted-vibration is likely to be responsible for a WSS decrease (Noel and Settembre 2017). So, the aim of our work is to develop an Agent-Based Model (ABM) of the WSS-modulated arterial growth induced by finger-transmitted vibration. This study is intended for the agent-based migration model.

International audience; In this pre-study, we present the validation of CutiscanVR device on healthy flat skin and its relevant sensitivity to environmental conditions. A primary application on the earlobe is presented as well.

International audience; 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 mechanicaltests 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.

International audience; Background/Purpose : This paper aims to present an ultra-light extensometer device dedicated to the mechanical characterization of the human skin in vivo.Methods : The device developed was conceived to be non invasive, to work with-out any stand and to perform various uniaxial tensile tests with either effort or displacement control. We also use specific guarding tabs to make in vivo extension tests analogous to traction tests.Results : Force displacement curves are derived from the data provided by the device's sensors. The latter are converted into stress strain curves thanks to complementary measurements of the skin thickness. We present typical experimental data and results that demonstrate the device ability to built stress strain curves characteristic of the human skin behavior. An additional imaging unit records a sequence of images of the solicited skin area for further calculations of the displacement fields by digital image correlation.Conclusion : The analysis of the displacement and deformation fields validates the guarding tab efficiency and the capacity of the device to characterize the mechanical behavior of the human skin in vivo.

International audience; Background/Purpose : The mechanical properties and behavior of the human skin in vivo are of medical importance, particularly to surgeons who have to consider the skin extension capabilities in the preparation of surgical acts. Variable data can be found in literature that result from diverse kinds of tests (in vivo, ex vivo, post-mortem) performed with different instruments.Methods : This paper presents the results of in vivo measurements performed on a cohort of 20 healthy volunteers with an ultralight homemade uniaxial extensometer. Different anatomical zones were explored under different directions of solicitation in order to document inter- and intra-individual variability as well as skin anisotropy.Results : The experimental data obtained are fitted with a phenomenological exponential model allowing the identification of three parameters characteristic of the tested skin behavior. These parameters can be related to the concept of skin extensibility used by surgeons.Conclusion : The inter- and intra-variability observed on that cohort confirms the need for a patient-specific approach based on the in vivo measurement of the mechanical behavior of the human skin of interest. Even the direction of higher skin stiffness is found to be individual dependent. The capability of the extensometer used in this study to fulfill such measurement needs is also demonstrated.

International audience; The V-Y advancement flap is a usual technique for the closure of skin defects. A triangular flap is incised adjacent to a skin defect of rectangular shape. As the flap is advanced to close the initial defect, two smaller defects in the shape of a parallelogram are formed with respect to a reflection symmetry. The height of the defects depends on the apex angle of the flap and the closure efforts are related to the defects height. Andrades et al. 2005 have performed a geometrical analysis of the V-Y flap technique in order to reach a compromise between the flap size and the defects width. However, the geometrical approach does not consider the mechanical properties of the skin. The present analysis based on the finite element method is proposed as a complement to the geometrical one. This analysis aims to highlight the major role of the skin elasticity for a full analysis of the V-Y advancement flap. Furthermore, the study of this technique shows that closing at the flap apex seems mechanically the most interesting step. Thus different strategies of defect closure at the flap apex stemming from surgeon’s know-how have been tested by numerical simulations.

International audience; Keloid scars are benign skin tumours that affect only humanity, especially among the Asian and African populations. Keloids consist in the excessive accumulation of dermal collagen that extends beyond the boundaries of the original wound (Kelly 2009). They are located on specific sites, tend to enlarge over time and pose aesthetic and psychological problems for patients. The physiopathology of keloids is unclear, and there is still no therapeutic consensus. Nevertheless, it appears that keloids result from a combination of genetic, cellular and mechanical factors (Salles et al. 2009).

The aim of this study consists in carrying out the V-Y advancement flap, which is a surgery technique for covering wounds with substance loss. In the V-Y advancement flap, a triangular flap is inci...