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Skin integrity assessment is a very important matter in the nursing care, especially for patients with low mobility. However, the methodology of skin analysis is limited by a lack of reliable yet portable tools. In this paper, a new sensor is proposed for skin mechanical impedance characterisation, aiming to provide an objective assessment of skin health. The device consists in a microcontroller connected to a Langevin transducer. Using the vector control method, the reference vibration of the transducer is assured, and the mechanical impedance is observed. To ensure the repeatability of the measurements, tests in the morning and in the afternoon were taken. To verify if the device can distinguish sites with different mechanical properties on the same body, tests were made on 2 different body sites: the palm of the hand and the volar forearm. Measurements of skin hydration were also taken, to find a potential correlation of these parameters and skin acoustical mechanical impedance. Results have shown that the measurements provided by the device are mostly reliable, and reveal a fair correlation between mechanical impedance and hydration, in the level of stratum corneum, the outermost layer of skin. Also, the device is able to show the difference on the mechanics of the skin in the different body sites tested, independently of the hydration.

Mechanical properties of skin are a clue for the diagnostic of pressure ulcers (PU) [1]. This project proposes a low- frequency ultrasound (LFU) device to identify the mechanical impedance (MI) of skin in different sites. The device’s goal is to identify the evolution of MI of skin over time and link it with the development of PU. In literature, studies involving LFU and PU focus on debridement through LFU cavitation [2]–[3]. Use of LFU on PU often present reduced pain and faster recovery. Although LFU for PU treatment is widely documented, the use of LFU for diagnosis is unexplored. Thus, a Langevin transducer (LT), with 60kHz of resonance frequency is proposed for PU detection. It is a high efficiency LFU device, based on the piezoelectric effect.

The study of skin mechanical impedance is a clue to analyse its health. We use a Langevin Transducer at 60kHz to excite the skin. In return we observe the acoustic forces generated by the interaction. To achieve that, the system is identified and presented in the rotating reference frame, and we describe the design of two PI controllers that accurately control the vibration velocity. However, in vivo analysis can be tricky when it comes to safety and duration of tests. Thus, phantom tissues are used as substitute to simulate skin behaviour. Due to its mechanical properties similar to skin, and its simple manipulation, Dragon Skin ®, a silicone rubber type of phantom, was chosen. The paper presents the characterisation of the mechanical impedance of three silicon phantoms with different properties based on force observation. The results show that the phantoms can be indeed identified based on this method.

Pressure ulcers are a concern not only for the patients who suffer from them, but also for public health. Its costs to the quality of life of patients and to the public finances can be reduced with an early diagnostic. Several efforts have been made to find a solution for this diagnostic, for example by analysing the hydration or the electrical impedance of the skin. So far, no method is sufficiently reliable. In this context, a low-frequency ultrasound device is proposed, with the aim of offering an alternative that can be reliable and non-invasive. The Langevin transducer is a highly efficient device that can provide a measurement of the mechanical characteristics of the skin. Initial results show that mechanical impedance can discriminate the skin according to the location of the measurement.

Dans le cadre de STINTS, le projet de thèse intitulé 'Dispositif d'ultrasons à basse fréquence pour l'évaluation de l'impédance mécanique de la peau'c - effectuer une nouvelle recherche sous la supervision de membres du personnel académique et de conseillers industriels dans le diagnostic et le traitement des ulcères de pression en collaboration avec d'autres ESR du consortium, identifier la réponse mécanique de la peau en fonction de facteurs liés à l'âge et au sexe. - distinguer les peaux saines des peaux saines par la modélisation proposée. - fournir les paramètres à un outil de diagnostic. - contribuer au développement de produits et de procédures de soins afin de minimiser l'apparition d'ulcères de pression - participer aux activités du programme STINTS: assister à des ateliers de formation, collaborer avec des partenaires du réseau et effectuer des détachements périodiques dans des organisations partenaires de STINTS - produire des résultats écrits au besoin pendant les études de doctorat et contribuer aux activités d'engagement et de diffusion de STINTS et présenter des rapports d'avancement réguliers comme l'exige le programme de recherche STINTS