Variability in coefficient of restitution in human facial skin

Pencil-on-Paper Humidity Sensor Treated with NaCl Solution for Health Monitoring and Skin Characterization

Although flexible humidity sensors are essential for human health monitoring, it is still challenging to achieve high sensitivity and easy disposal with simple, low-cost fabrication processes. This study presents the design and fabrication of highly reliable hand-drawn interdigital electrodes from pencil-on-paper treated with NaCl solution for highly sensitive hydration sensors working over a wide range of relative humidity (RH) levels from 5.6% to 90%. The applications of the resulting flexible humidity sensor go beyond the monitoring of respiratory rate and proximity to characterizations of human skin types and evaluations of skin barrier functions through insensible sweat measurements. The sensor array can also be integrated with a diaper to result in smart diapers to alert for an early diaper change. The design and fabrication strategies presented in this work could also be leveraged for the development of wearable, self-powered, and recyclable sensors and actuators in the future.

Collision Pressure and Dissipated Power Dose in a Self-Oscillating Silicone Vocal Fold Model With a Posterior Glottal Opening

PURPOSE

The goal of this study was to experimentally evaluate how compensating for the adverse acoustic effects of a posterior glottal opening (PGO) by increasing subglottal pressure and changing supraglottal compression, as have been associated with vocal hyperfunction, influences the risk of vocal fold (VF) trauma.

METHOD

A self-oscillating synthetic silicone model of the VFs with an airflow bypass that modeled a PGO was investigated in a hemilaryngeal flow facility. The influence of compensatory mechanisms on collision pressure and dissipated collision power was investigated for different PGO areas and supraglottal compression. Compensatory behaviors were mimicked by increasing the subglottal pressure to achieve a target sound pressure level (SPL).

RESULTS

Increasing the subglottal pressure to compensate for decreased SPL due to a PGO produced higher values for both collision pressure and dissipated collision power. Whereas a 10-mm² PGO area produced a 12% increase in the peak collision pressure, the dissipated collision power increased by 122%, mainly due to an increase in the magnitude of the collision velocity. This suggests that the value of peak collision pressure may not fully capture the mechanisms by which phonotrauma occurs. It was also found that an optimal value of supraglottal compression exists that maximizes the radiated SPL, indicating the potential utility of supraglottal compression as a compensatory mechanism.

CONCLUSIONS

Larger PGO areas are expected to increase the risk of phonotrauma due to the concomitant increase in dissipated collision power associated with maintaining SPL. Furthermore, the risk of VF damage may not be fully characterized by only the peak collision pressure.

Skin biomechanical and viscoelastic properties measured with MyotonPRO in different areas of human body

BACKGROUND

There is still a lack of clinically practical device, which allows to perform rapid and accurate examination of the skin condition. For this reason, suitability of the MyotonPRO for the assessment of skin biomechanical and viscoelastic parameters was evaluated in this study. The aim of the study was to establish the reference values of five parameters measured by MyotonPRO various locations of human skin.

MATERIALS AND METHODS

Oscillation frequency, dynamic stiffness, logarithmic decrement, mechanical stress relaxation and creep were measured at three different skin locations (clavicula, volar forearm and shin), using L-shape short and medium arm probes in 32 young female volunteers. Mean values of obtained parameters recorded by both probes were compared among three skin locations while reliabilities of measurements were assessed. Additionally, relationships between all recorded parameters were examined RESULTS: There were no statistically significant differences between the mean values of five measured parameters obtained with both probes in all investigated areas. However, statistically significant differences of mean values of almost all parameters measured among three places examined were found. Despite considerable differences in mean values of obtained parameters, there were visible strong correlations between some studied parameters in all three investigated areas of skin.

CONCLUSION

It was demonstrated in all locations studied that the higher value of oscillation frequency corresponds to the higher value of dynamic stiffness, moreover such tissue recovers faster to its initial shape, and it was characterized by lower creep values. Such results indicate the existence of identical relationships between the same studied parameters in different areas of skin.

Vocal fold dynamics in a synthetic self-oscillating model: Contact pressure and dissipated-energy dose

The energy dissipated during vocal fold (VF) contact is a predictor of phonotrauma. Difficulty measuring contact pressure has forced prior energy dissipation estimates to rely upon generalized approximations of the contact dynamics. To address this shortcoming, contact pressure was measured in a self-oscillating synthetic VF model with high spatiotemporal resolution using a hemilaryngeal configuration. The approach yields a temporal resolution of less than 0.26 ms and a spatial resolution of 0.254 mm in the inferior-superior direction. The average contact pressure was found to be 32% of the peak contact pressure, 60% higher than the ratio estimated in prior studies. It was found that 52% of the total power was dissipated due to collision. The power dissipated during contact was an order of magnitude higher than the power dissipated due to internal friction during the non-contact phase of oscillation. Both the contact pressure magnitude and dissipated power were found to be maximums at the mid anterior-posterior position, supporting the idea that collision is responsible for the formation of benign lesions, which normally appear at the middle third of the VF.

Comparison of different MyotonPRO probes for skin stiffness evaluation in young women

BACKGROUND

Stiffness of skin is widely used parameter in many research areas, for example cosmetic industry, dermatology or rheumatology for assessing of skin condition as well as changes occurring in skin. In this pioneering study, we conducted measurements of skin stiffness using MyotonPRO -novel tool, which was mainly used to evaluate biomechanical properties of muscles, ligaments and tendons. We expected that MyotonPRO , which shows great reproducibility in previous studies, will also be able to measure skin stiffness.

MATERIALS AND METHODS

Four replaceable probes designed by MyotonPRO (L-shape short and medium arm, standard cylindrical flat-end probe and the same standard probe with disc attachment ) were tested for measurement of skin stiffness in young women (30 healthy females) at three different locations (clavicula, volar forearm and shin).

RESULTS

There was no significant difference between stiffness values obtained with L-shape short and L-shape medium arm probes in all investigated areas. Stiffness values recorded by regular probe and regular probe with disc attachment differ significantly from those collected with L-shape probes. There was also significant difference between values of stiffness obtained by standard with disc attachment and standard probes.

CONCLUSION

Both L-shape probes show a great reliability for skin stiffness assessment. Therefore, MyotonPRO can be considered a reliable device for assessing skin stiffness.

Influence of secondary aspiration on human aspiration efficiency

Computational fluid dynamics (CFD) was used to evaluate the contribution of secondary aspiration to human aspiration efficiency estimates using a humanoid model with realistic facial features. This study applied coefficient of restitution (CoR) values for working-aged human facial skin to the facial regions on the humanoid CFD model. Aspiration efficiencies for particles ranging from 7 to 116 μm were estimated for bounce (allowing for secondary aspiration) and no-bounce (CoR=0) simulations. Fluid simulations used the standard k-epsilon turbulence model over a range of test conditions: three freestream velocities, two breathing modes (mouth and nose breathing, using constant inhalation), three breathing velocities, and five orientations relative to the oncoming wind. Laminar particle trajectory simulations were used to examine inhaled particle transport and estimate aspiration efficiencies. Aspiration efficiency for the realistic CoR simulations, for both mouth- and nose-breathing, decreased with increasing particle size, with aspiration around 50% for 116 μm particles. For the CoR=0 simulations, aspiration decreased more rapidly with increasing particle size and approached zero for 116 μm compared to realistic CoR models (differences ranged from 0% to 80% over the particle sizes and velocity conditions). Differences in aspiration efficiency were larger with increasing particle size (>52 μm) and increased with decreasing freestream velocity and decreasing breathing rate. Secondary aspiration was more important when the humanoid faced the wind, but these contributions to overall aspiration estimates decreased as the humanoid rotated through 90°. There were minimal differences in aspiration between uniform CoR values of 0.5, 0.8, 1.0 and realistic regionally-applied CoR values, indicating differences between mannequin surfaces and between mannequin and human skin will have negligible effect on aspiration for facing-the-wind orientation.