Layer-by-Layer Assembly of Lipid Nanobubbles on Microneedles for Ultrasound-Assisted Transdermal Drug Delivery

Microneedles as a typical device for transdermal drug delivery provide an alternative route for drug administration with minimal digestion by organs and better patient compliance. However, diffusion of passively released drug molecules within the skin tissue mainly depends on the interstitial fluid, which may be affected by different physiological conditions of individuals. Herein, we propose a nanobubble-modified microneedle patch for ultrasound-assisted drug delivery, which provides additional driving force for penetration and diffusion of the drug molecules. Layer-by-layer self-assembled drug-containing nanobubbles on the surfaces of microneedles trigger active drug release upon application of ultrasound. The concomitant microstreaming caused by cavitation effects facilitates the penetration and diffusion of drug molecules in the gelatin gel model and the ex vivo porcine skin model. The proposed drug delivery strategy holds great promise for rapid transdermal drug delivery with enhanced penetration and diffusion of the released drugs.

Fetal Movement Counting Using Optical Fibre Sensors

Daily fetal movement counting based on maternal perception is widely deployed to monitor fetal wellbeing. However, the counting performed by the mother is prone to errors for various reasons. There are limited devices on the market that can provide reliable and automatic counting. This paper presents a prototype of a novel fetal movement monitoring device based on fibre Bragg grating sensors. Deformation of the skin caused by a fetal movement can lead to a change of the strain and stress on the optical fibre sensors, therefore can induce distortions to the breathing pattern of the mother. In the study data was gathered by the sensors through strain measurement and was post-processed using independent component analysis (ICA) and high-pass filtering to show the instances of the fetal movements. Information gathered during user trials with the prototype suggests that the system detects significantly higher numbers of fetus movements than that observed based on the mother's perception. Among the various techniques available for fetal movement monitoring, fibre optic sensing provides many advantages including multiplex capability, flexibility and minimal size, making the concept an attractive solution for reliable monitoring of antenatal fetal movements.

Evaluating age-related changes of some facial signs among men of four different ethnic groups

BACKGROUND

The alterations of some facial characteristics, with age, in men of different ethnic groups are a scarcely studied topic.

OBJECTIVE

To illustrate and grade, among men of four different ethnic descents (Asians, African-Americans, Caucasians, Indians), aged 18-80 year, the changes in the severity of some facial signs occurring with age.

METHODS

Digital Photographs (full face, profile, 45°) of 1058 subjects were taken under standard conditions of lightning. These allowed us to zoom in on 15-20 different facial signs on all subjects. Their observations by 15 trained experts, under calibrated screens, allowed these signs to be graded, with the help of four referential skin Atlases, specific to the gender and ethnic groups studied.

RESULTS

Most facial signs show a rather regular increase with age, with different kinetics according to the ethnic group. The major changes, in all four ethnic groups, mostly concern skin structural alterations (wrinkles, neck sagging or texture). The changes in the severity of some wrinkles (forehead, inter-ocular…) may be viewed as ethnic signatures. The modifications in pigmentation disorders seem more closely linked to the constitutive skin pigmentation (photo-types), among which pigmentary spots are confirmed as a more specific Asian trait.

CONCLUSION

Men of four different ethnic origins present different and ethnic-related facial alterations with increasing age, of different amplitudes.

Lab-on-Skin: A Review of Flexible and Stretchable Electronics for Wearable Health Monitoring

Skin is the largest organ of the human body, and it offers a diagnostic interface rich with vital biological signals from the inner organs, blood vessels, muscles, and dermis/epidermis. Soft, flexible, and stretchable electronic devices provide a novel platform to interface with soft tissues for robotic feedback and control, regenerative medicine, and continuous health monitoring. Here, we introduce the term "lab-on-skin" to describe a set of electronic devices that have physical properties, such as thickness, thermal mass, elastic modulus, and water-vapor permeability, which resemble those of the skin. These devices can conformally laminate on the epidermis to mitigate motion artifacts and mismatches in mechanical properties created by conventional, rigid electronics while simultaneously providing accurate, non-invasive, long-term, and continuous health monitoring. Recent progress in the design and fabrication of soft sensors with more advanced capabilities and enhanced reliability suggest an impending translation of these devices from the research lab to clinical environments. Regarding these advances, the first part of this manuscript reviews materials, design strategies, and powering systems used in soft electronics. Next, the paper provides an overview of applications of these devices in cardiology, dermatology, electrophysiology, and sweat diagnostics, with an emphasis on how these systems may replace conventional clinical tools. The review concludes with an outlook on current challenges and opportunities for future research directions in wearable health monitoring.

Scalp simulation - A novel approach to site-specific biomechanical modeling of the skin

OBJECTIVES

This study aimed to determine the hardness of the human scalp in vivo in order to identify an appropriate scalp simulant, from a range of commercially available silicone materials, for force impact assessment. Site-dependent variation in scalp hardness, and the applicability of contemporary skin simulants to the scalp were also considered.

MATERIALS AND METHODS

A Shore A-type durometer was used to collected hardness data from the scalps of 30 human participants (five males and five females in each of the three age categories: 18-30, 31-40, 41-50) and four commercially available silicones (light, medium, and heavy-bodied PVS, and duplication silicone). One-sample t-tests were used to compare the mean hardness of simulants to that of the scalp. Site-dependent variation in the hardness of the scalp was assessed using a mixed-model repeated measures ANOVA.

RESULTS

Mean human scalp hardness derived from participants was 20.6 Durometer Units (DU; SD = 3.4). Analysis revealed only the medium-bodied PVS to be an acceptable scalp simulant when compared to the mean hardness of the human scalp (p = 0.869). Scalp hardness varied significantly anteroposteriorly (with an observable linear trend, p < 0.001), but not mediolaterally (p = 0.271). Comparisons of simulants to site-specific variation in scalp hardness anteroposteriorly found the medium-bodied PVS to be only suitable in the central region of the scalp (p = 0.391). In contrast, the duplication silicone (p = 0.074) and light-bodied PVS (p = 0.147) were only comparable to the posterior region.

CONCLUSIONS

Contemporary skin simulants fail to accurately represent the scalp in terms of hardness. There is strong support for the use of medium-bodied PVS as a scalp simulant. Human scalp hardness varies significantly anteroposteriorly, but not mediolaterally, corresponding to regional anatomical variation within the scalp. A number of materials were identified as potential simulants for different regions of the scalp when more site-specific simulant research is required.

The effects of cyclic tensile and stress-relaxation tests on porcine skin

When a living tissue is subjected to cyclic stretching, the stress-strain curves show a shift down with the increase in the number of cycles until stabilization. This phenomenon is referred to in the literature as a preconditioning and is performed to obtain repeatable and predictable measurements. Preconditioning has been routinely performed in skin tissue tests; however, its effects on the mechanical properties of the material such as viscoelastic response, tangent modulus, sensitivity to strain rate, the stress relaxation rate, etc….remain unclear. In addition, various physical interpretations of this phenomenon have been proposed and there is no general agreement on its origin at the microscopic or mesoscopic scales. The purpose of this study was to investigate the effect of the cyclical stretching and the stress-relaxation tests on the mechanical properties of the porcine skin. Cyclic uniaxial tensile tests at large and constant strain were performed on different skin samples. The change in the reaction force, and skin's tangent modulus as a function of the number of cycles, as well as the strain rate effect on the mechanical behavior of skin samples after cycling were investigated. Stress-relaxation tests were also performed on skin samples. The change in the reaction force as a function of relaxation time and the strain rate effect on the mechanical behavior of skin samples after the stress-relaxation were investigated. The mechanical behavior of a skin sample under stress-relaxation test was modeled using a combination of hyperelasticity and viscoelasticity. Overall, the results showed that the mechanical behavior of the skin was strongly influenced by cycling and stress relaxation tests. Indeed, it was observed that the skin's resistance decreased by about half for two hours of cycling; the tangent modulus degraded by nearly 30% and skin samples became insensitive to the strain rates and accumulated progressively an inelastic deformation over time during cycling. Finally, the hysteresis loops became very narrow at the end of cycling and after relaxation process.

Estimating material parameters of human skin in vivo

An accurate mathematical representation of the mechanical behaviour of human skin is essential when simulating deformations occurring in the skin during body movements or clinical procedures. In this study constitutive stress-strain relationships based on experimental data from human skin in vivo were obtained. A series of multiaxial loading experiments were performed on the forearms of four age- and gender matched subjects. The tissue geometry, together with recorded displacements and boundary forces, were combined in an analysis using finite element modelling. A non-linear optimization technique was developed to estimate values for the material parameters of a previously published constitutive law, describing the stress-strain relationship as a non-linear anisotropic membrane. Ten sets of material parameters where estimated from the experiments, showing considerable differences in mechanical behaviour both between individual subjects as well as mirrored body locations on a single subject. The accuracy of applications that simulate large deformations of human skin could be improved by using the parameters found from the in vivo experiments as described in this study.

Treatment of Neck Lines and Forehead Rhytids with a Nonablative 1540-nm Er:Glass Laser: A Controlled Clinical Study Combined with the Measurement of the Thickness and the Mechanical Properties of the Skin

BACKGROUND

Nonablative remodeling has been recently proposed as a new, no-down-time, anti-aging treatment. Objective. The objective was to evaluate the efficacy and safety of nonablative skin remodeling with a 1540-nm Er:Glass laser on neck lines and forehead rhytids.

METHODS

Twenty female patients (mean age 45 years) were enrolled. Skin thickness and mechanical properties were measured before the first treatment, 1 month after the third treatment, 1 month after the fifth treatment, and 3 months after the fifth treatment.

RESULTS

All patients reported an improvement in both skin tone and texture. Using ultrasound imaging, dermal thickness of neck and forehead increased, respectively, by 70+/-13 microm (p<0.001) and 110+/-19 microm (p<0.003). A dramatic increase of initial stress of the forehead skin (firmness) was obtained, from 7.62+/-3.68 before treatment to 16.68+/-7.44 3 months after the fifth treatment (p<0.0002). No immediate or late adverse effects were noted throughout the treatment regimen.

CONCLUSION

This study demonstrates that irradiation with a 1540-nm Er:Glass laser emitting in a pulsed mode and coupled with an efficient contact cooling system increases dermal thickness and firmness, leading to a clinical improvement of neck lines and forehead rhydits.