Development of Capacitive Imaging Technology for Measuring Skin Hydration and Other Skin Properties

In this thesis, capacitive imaging systems are assessed for their suitability in skin research studies, as multi-purpose and portable laboratory equipment. The water content of the human skin, the status of the skin barrier, its permeability by solvents, and the skin texture are crucial pieces of information in pharmaceutical and cosmetic industries for the development of skin treatment products. Normally, multiple high-end scientific instruments with expensive dedicated analysis software are employed to measure the above skin properties. The aim of this work is to demonstrate how fingerprint sensors, originally designed for biometric security, can be exploited to achieve reliable skin hydration readings and analyse multiple other skin properties while maintaining low cost and portability. To begin with, the anatomy of human skin is summarised alongside the functional properties of each skin layer. The skin hydration instruments study the outermost layer of skin and its appendages, so their thickness, biology, functions, hydration levels and water holding capabilities are presented in the literature review in order to understand the target measurands. Since capacitive imaging, rather than single sensor, probes are employed in this work, the skin texture and its importance in cosmetic science are also studied as a part of the target measurand. In order to understand how this technology fits in the current skin research instrument market, well established measurement apparatuses are presented. These include opto-thermal transient emission radiometry and confocal Raman microspectroscopy for skin hydration and solvent permeation measurements as well as depth profiling. Then, electrical hygrometry and the dynamic vapour sortpion measurement principles are outlined, which focus on water diffusion and sorption measurements correspondingly. Since the skin texture will also be studied in this work, dermatoscopy is also summarised. A literature review on the non-invasive electrical-based measurement method is achieved, alongside the stratum corneum and viable skin capacitance and conductance as functions of sampling frequency. The latter allows to establish the criteria for the suitability of electrical based apparatuses in skin hydration measurements. More specifically, it is concluded that the measurement depth of the instrument should not be reaching viable skin and that the sampling frequency should be constant and below 100kHz for capacitive measurements. The presentation of existing electrical based skin hydration probes in the market demonstrates the current development stage of this technology, and it enables the expression of the research aim and its objectives for this work. In order to improve trust in the use of capacitive imaging technology for measuring skin hydration, apart from visualisation, established electrical based skin hydration probes are examined and compared with a capacitive imaging sensor. The criteria for this comparison derive from the literature review, i.e. the sampling frequency and the penetration depth of the electric field. The sampling frequency is measured directly on the hardware using an oscilloscope, while the measurement depth is estimated using an electrostatic model. The development of this model for different sensor geometries is presented and it is evaluated against different models as well as experimental results in the literature. It is concluded that low cost instruments tend to have high measurement depth that makes them unsuitable for stratum corneum hydration measurements. Higher end instruments, although they are using high sampling frequency, have safe penetration depth but low measurement sensitivity. The capacitive imaging sensor shown acceptable penetration depth, on the high end of the expected range, and good measurement sensitivity due to the miniaturisation of the technology. A common disadvantage of most of these instruments is that the readouts are provided in arbitrary units, so experimental results cannot be compared directly with the literature when different scientific equipment has been used. To overcome this disadvantage, and based on the previous analysis of capacitive measurement principle, a system calibration is proposed to convert system capacitance or arbitrary units to dielectric permittivity units, a property of the sample measurand. This allows the calculation of hydration and solvent percentage concentration within the sample and so direct comparison with a wider range of reported results in the literature. Furthermore, image analysis techniques are applied on the dielectric permittivity images to allow targeting and relocating skin regions of interest, as well as excluding pixels with bad sample contact that distort the results. Next, the measurement reliability of the capacitive imaging arrays is examined through in-vivo and in-vitro experiments as well as side-by-side comparative measurements with single sensor skin hydration probes. The advantages of the developed calibration method and image analysis tools are demonstrated via the introduction of new system applications in the skin research, including skin damage characterisation via occlusion, skin solvent penetration and water desorption in hair samples experiments. It has to be mentioned that a small number of subjects is used in these experiments and the results are compared with the literature, so the statistical significance is not clearly examined. Next, advanced image processing techniques are adapted and applied on the capacitive skin images to expand further the application of this technology. More specifically, the skin micro-relief aspects of interest in cosmetic industry are summarised, and algorithmic approaches for measuring the micro-relief orientation and intensity as well as the automatic skin grids account are reviewed and experimentally evaluated. The main research aim and its objective have been achieved, with their methodologies clearly presented the their implementations evaluated with experimental results. However, vulnerabilities of this technology have also been exposed and suggestions for further improvement are provided in the conclusions

Applications of Capacitive Imaging in Human Skin Texture and Hair Analysis

This article focuses on the extraction of information from human skin and scalp hair for evaluation of a subject’s condition in the cosmetic and pharmaceutical industries. It uses capacitive images from existing hand-held research equipment and it applies image processing algorithms to expand their possible applications. The literature review introduces the readers into the field of skin research, and it highlights pieces of information that can be extracted by in vivo skin and ex vivo hair measurements. Then, the selected scientific equipment is presented, and Maxwell-based electrostatic simulations are employed to evaluate the measurement apparatus. Image analysis algorithms are suggested for (a) the detection of polygons on the human skin texture, (b) the estimation of wrinkles length and (c) the observation of hair water sorption capabilities by capacitive imaging systems. Finally, experiments are conducted to evaluate the performance of the presented algorithms and the results are compared with the literature. The results indicate that capacitive imaging systems can be used for skin age classification, detection and tracking of skin artifacts (e.g., wrinkles, moles or scars) and calculation of water content in hair samples

Mobility-aware QoS assurance in software-defined radio access networks: an analytical study

Software-defined networking (SDN) has gained a tremendous attention in the recent years, both in academia and industry. This revolutionary networking paradigm is an attempt to bring the advances in computer science and software engineering into the information and communications technology (ICT) domain. The aim of these efforts is to pave the way for completely programmable networks and control-data plane separation. Recent studies on feasibility and applicability of SDN concepts in cellular networks show very promising results and this trend will most likely continue in near future. In this work, we study the benefits of SDN on the radio resource management (RRM) of future-generation cellular networks. Our considered cellular network architecture is in line with the recently proposed Long-Term Evolution (LTE) Release 12 concepts, such as user/control plane split, heterogeneous networks (HetNets) environment, and network densification through deployment of small cells. In particular, the aim of our RRM scheme is to enable the macro base station (BS) to efficiently allocate radio resources for small cell BSs in order to assure quality-of-service (QoS) of moving users/vehicles during handovers. We develop an approximate, but very time- and space-efficient algorithm for radio resource allocation within a HetNet. Experiments on commodity hardware show algorithm running times in the order of a few seconds, thus making it suitable even in cases of fast moving users/vehicles. We also confirm a good accuracy of our proposed algorithm by means of computer simulations

Final report for research project with title: Dynamics of Electrically-Induced Flow of Viscoelastic Fluids (grant number: PE8/906)

The interaction of an externally applied electric _eld with a liquid can give rise to interesting ow instabilities and pattern formation. For example, it has been demonstrated that the application of an electric _eld to an initially at polymer-air or polymer-polymer interface may result in an electrohydrodynamic instability which leads to the formation of columnar structures. This phenomenon could be exploited in order to form well-controlled patterns at the microscale and nanoscale with many practical engineering applications. The scope of the present research project is to achieve fundamental understanding of the electrically-induced ow of viscoelastic liquid _lms and to investigate the e_ect of various factors (e.g. the complex uid rheology, the presence of surface active materials or free charge along the liquid-air or liquid-liquid interfaces, geometric con_guration, etc) that may play an important role in such a process. It is well known that the dynamics and stability of liquid _lms can be very rich and it is characteristic that despite the fact that the _rst attempts to address the stability of a simple system such as a clean (without surfactants) Newtonian liquid _lm under the e_ect of gravity appear in the literature in the late 50's full understanding of the underlying mechanisms was not achieved until recently. One of the goals of the present study was to expand our understanding on the stability of the liquid _lms in the presence of surface active materials (surfactants). The reason for this is threefold. On one hand, the interaction of a surfactant-ladden _lm with an electric _eld is of interest for controlled pattern formation at the micro- and nano-scale. For example, ionic surfactants may interact with the electric _eld thereby a_ecting interfacial concentration and imposing speci_c patterns in the liquid. On the other hand, surfactants attribute non-Newtonian properties to the liquid, because the free surface attains surface elasticity and surface viscosity. Also, at high surfactant concentrations, micelles may form in the bulk and complicate its rheological behavior, rendering the solution viscoelastic. Finally, the governing equation that describes the conservation of surfactant concentration along the interface is identical to the equation that describes the conservation of free charge in the case of dielectric materials. These systems share many similar characteristics and it is possible to draw conclusions from the analogy between them. To this end, we formulated the Orr-Sommerfeld equation for a surfactant-laden _lm with appropriate boundary conditions, and solved it numerically for arbitrary disturbances and analytically for long-wave disturbances. The results from our analysis demonstrate the signi_cant e_ect of surfactant solubility and sorption kinetics on the stability characteristics and provided useful insight in the non-linear dynamics of the ow. The results from this this work have been published to the Journal of Fluid Mechanics. In a subsequent paper that has also been submitted for publication to the Journal of Fluid Mechanics we have investigated the role of surfactants on the mechanism of the long-wave instability in liquid _lm ows. We have also made announcements to several local and international conferences. A second goal of this research project was to develop a robust numerical algorithm capable of handling the ow of viscoelastic material with large interfacial deformations….

Micro-relief analysis with skin capacitive imaging

© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Background: In this study, the performance of capacitive imagining in skin micro-relief analysis was investigated. This measurement principle has been used for skin hydration measurements over the last decade and it is commercially available by various manufacturers. Strengthening its potential for new applications could offer an affordable and portable multi-purpose device for in vivo skin research. Previous studies in the literature have used a wide range of optical devices to determine how the skin surface topographic features are affected by chronological age, environmental influences and living habits. Material and methods: A capacitive system was used in order to capture hydration images from the middle volar forearm of twelve volunteers. The visual output of the system was studied and image processing algorithms were adapted to automatically extract skin micro-relief features. The change in the skin network of lines during arm extension, the lines’ anisotropy index and the number of closed polygons per skin surface area were plotted against the subjects’ chronological age. The results were compared with optical measurements from the literature to validate our algorithms and evaluate the capacitive imaging in skin micro-relief analysis. Results: The change in the intensity of primary and secondary lines during arm extension and the number of closed polygons per surface area were in agreement with the literature. The anisotropy index output gave inconclusive results. Conclusions: The experimental results show that the capacitive systems could only extract two-dimensional skin topographic features. This is the peer reviewed version of the following article:Bontozoglou, C., Zhang, X., and Xiao, P. (2019). Micro-relief analysis with skin capacitive imaging. Skin Research and Technology, 25(2), 165-170. which has been published in final form at https://www.doi.org/10.1111/srt.12628 This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions