Self-recording the skin hydration and Trans-Epidermal Water Loss parameters: A pilot study.

OBJECTIVE: To evaluate the reliability of data self-recorded by subjects enrolled in a study for skin surface hydration and Trans-Epidermal Water Loss (TEWL). METHODS: A connected device, previously described, simultaneously records both the hydration status and the TEWL on the same skin site. The effects of a Xanthane-based gel containing low concentrations of glycerol (3% or 7%) applied on both face and forearms of Caucasian women, were self-recorded at various times for 24 hours, outside of Research facility. RESULTS: In the first-hour post application, the skin hydration and TEWL values show a sharp increase and decrease, respectively. They progressively recover their initial values 24 hours post washing, on both skin sites. A significant dose effect of glycerol (ie, 3% vs 7%) was obtained on both skin sites. The repeatability of data was found acceptable in both parameters, although more precise on arms than face, probably linked to an easier handling of the device. CONCLUSION: The use of this skin measuring connected device outside of Research facility, following a training of subjects, leads to reliable data. Such approach could be extended to other connected devices.

Controlled mechanical vibration and impacts on skin biology.

BACKGROUND AND OBJECTIVE: Different biological models have shown how mechanical stimulation may induce physiological responses from solicited cells, tissues, or organs. In models of cultured skin cells, the frequency of the mechanical stress appears to be a paramount parameter, generating a biological response in some cells, particularly from dermal fibroblasts. Our objective was to explore in ex vivo human skin explants the effects of mechanical stimulation. MATERIALS AND METHODS: Mechanical stimulations were provided by a torque test device, with different end effectors, able to generate cyclic strains at different frequencies (from 40 to 120 Hz). Skin explant samples were stimulated twice daily by the device for one minute, over 10 days. RESULTS: At days 0, 5, and 10, samples were processed by immunohistological procedures, allowing some structural dermal proteins to be quantified (fluorescence). As compared to untreated skin explant samples, the stimulation procedure clearly led some proteins of the dermal-epidermal and some dermal proteins to be overexpressed. This stimulation was found to be frequency-dependent, with the greatest overall increases occurring at 60 and 90 Hz. CONCLUSION: For the first time, ultrafast ultrasound imaging in vitro (phantom mimicking skin mechanical properties) was used to analyze mechanical waves transmitted to the skin layers as a function of end effector shape.

Developing a new device for continuously recording, in vivo, the excretion rate of sweat (perspiration) in humans.

BACKGROUND: Some methodologies used for evaluating sweat production and antiperspirants are of a stationary aspect, that is, most often performed under warm (38°C) but resting conditions in a rather short period of time. The aim is to develop an electronic sensor apt at continuously recording sweat excretion, in vivo, during physical exercises, exposure to differently heated environments, or any other stimuli that may provoke sweat excretion. MATERIAL AND METHODS: A sensor (20 cm2 ) is wrapped under a double-layered textile pad. Fixed onto the armpits, these two arrays of electrodes are connected to electronic system through an analog multiplexer. A microcontroller is used to permanently record changes in the conductance between two electrodes during exposure of subjects to different sweat-inducing conditions or to assess the efficacy of applied aluminum hydrochloride (ACH)-based roll-ons at two concentrations (5% and 15%). RESULTS: In vitro calibration, using a NaCl 0.5% solution, allows changes in mV to be related with progressively increased volumes. In vivo, results show that casual physical exercise leads to sweat excretions much higher than in warm environment (37 or 45°C). Only, an exposure to a 50°C environment induced comparable sweat excretion. In this condition, sweat excretions were found similar in both armpits and both genders. Decreased sweat excretions were recorded following applications of ACH, with a dose effect. CONCLUSION: Developing phases of this new approach indicate that usual method or guidelines used to determine sweat excretions in vivo do not reflect true energy expenditure processes. As a consequence, they probably over-estimate the efficacy of antiperspirant agents or formulae.

Effects of a skin-massaging device on the ex-vivo expression of human dermis proteins and in-vivo facial wrinkles.

Mechanical and geometrical cues influence cell behaviour. At the tissue level, almost all organs exhibit immediate mechanical responsiveness, in particular by increasing their stiffness in direct proportion to an applied mechanical stress. It was recently shown in cultured-cell models, in particular with fibroblasts, that the frequency of the applied stress is a fundamental stimulating parameter. However, the influence of the stimulus frequency at the tissue level has remained elusive. Using a device to deliver an oscillating torque that generates cyclic strain at different frequencies, we studied the effect(s) of mild skin massage in an ex vivo model and in vivo. Skin explants were maintained ex vivo for 10 days and massaged twice daily for one minute at various frequencies within the range of 65-85 Hz. Biopsies were analysed at D0, D5 and D10 and processed for immuno-histological staining specific to various dermal proteins. As compared to untreated skin explants, the massaging procedure clearly led to higher rates of expression, in particular for decorin, fibrillin, tropoelastin, and procollagen-1. The mechanical stimulus thus evoked an anti-aging response. Strikingly, the expression was found to depend on the stimulus frequency with maximum expression at 75Hz. We then tested whether this mechanical stimulus had an anti-aging effect in vivo. Twenty Caucasian women (aged 65-75y) applied a commercial anti-aging cream to the face and neck, followed by daily treatments using the anti-aging massage device for 8 weeks. A control group of twenty-two women, with similar ages to the first group, applied the cream alone. At W0, W4 and W8, a blinded evaluator assessed the global facial wrinkles, skin texture, lip area, cheek wrinkles, neck sagging and neck texture using a clinical grading scale. We found that combining the massaging device with a skin anti-aging formulation amplified the beneficial effects of the cream.

Coupling of the mechanotransduction machinery and F-actin polymerization in the cochlear hair bundles.

Mechanoelectrical transduction (MET), the conversion of mechanical stimuli into electrical signals operated by the sensory cells of the inner ear, enables hearing and balance perception. Crucial to this process are the tip-links, oblique fibrous filaments that interconnect the actin-filled stereocilia of different rows within the hair bundle, and mechanically gate MET channels. In a recent study, we observed a complete regression of stereocilia from the short and medium but not the tall row upon the disappearance of the tip-links caused by the loss of one of their components, cadherin-23, or of one of their anchoring proteins, sans, in the auditory organs of engineered mutant mice. This indicates the existence of a coupling between the MET and F-actin polymerization machineries at the tips of the short and medium stereocilia rows in cochlear hair bundles. Here, we first present our findings in the mutant mice, and then discuss the possible effects of the tip-link tension on stereocilia F-actin polymerization, acting either directly or through Ca(2+)-dependent mechanisms that involve the gating of MET channels.

Usher type 1G protein sans is a critical component of the tip-link complex, a structure controlling actin polymerization in stereocilia.

The mechanotransducer channels of auditory hair cells are gated by tip-links, oblique filaments that interconnect the stereocilia of the hair bundle. Tip-links stretch from the tips of stereocilia in the short and middle rows to the sides of neighboring, taller stereocilia. They are made of cadherin-23 and protocadherin-15, products of the Usher syndrome type 1 genes USH1D and USH1F, respectively. In this study we address the role of sans, a putative scaffold protein and product of the USH1G gene. In Ush1g(-/-) mice, the cohesion of stereocilia is disrupted, and both the amplitude and the sensitivity of the transduction currents are reduced. In Ush1g(fl/fl)Myo15-cre(+/-) mice, the loss of sans occurs postnatally and the stereocilia remain cohesive. In these mice, there is a decrease in the amplitude of the total transducer current with no loss in sensitivity, and the tips of the stereocilia in the short and middle rows lose their prolate shape, features that can be attributed to the loss of tip-links. Furthermore, stereocilia from these rows undergo a dramatic reduction in length, suggesting that the mechanotransduction machinery has a positive effect on F-actin polymerization. Sans interacts with the cytoplasmic domains of cadherin-23 and protocadherin-15 in vitro and is absent from the hair bundle in mice defective for either of the two cadherins. Because sans localizes mainly to the tips of short- and middle-row stereocilia in vivo, we conclude that it belongs to a molecular complex at the lower end of the tip-link and plays a critical role in the maintenance of this link.

Harmonin-b, an actin-binding scaffold protein, is involved in the adaptation of mechanoelectrical transduction by sensory hair cells.

We assessed the involvement of harmonin-b, a submembranous protein containing PDZ domains, in the mechanoelectrical transduction machinery of inner ear hair cells. Harmonin-b is located in the region of the upper insertion point of the tip link that joins adjacent stereocilia from different rows and that is believed to gate transducer channel(s) located in the region of the tip link's lower insertion point. In Ush1c (dfcr-2J/dfcr-2J) mutant mice defective for harmonin-b, step deflections of the hair bundle evoked transduction currents with altered speed and extent of adaptation. In utricular hair cells, hair bundle morphology and maximal transduction currents were similar to those observed in wild-type mice, but adaptation was faster and more complete. Cochlear outer hair cells displayed reduced maximal transduction currents, which may be the consequence of moderate structural anomalies of their hair bundles. Their adaptation was slower and displayed a variable extent. The latter was positively correlated with the magnitude of the maximal transduction current, but the cells that showed the largest currents could be either hyperadaptive or hypoadaptive. To interpret our observations, we used a theoretical description of mechanoelectrical transduction based on the gating spring theory and a motor model of adaptation. Simulations could account for the characteristics of transduction currents in wild-type and mutant hair cells, both vestibular and cochlear. They led us to conclude that harmonin-b operates as an intracellular link that limits adaptation and engages adaptation motors, a dual role consistent with the scaffolding property of the protein and its binding to both actin filaments and the tip link component cadherin-23.