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

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

Capacitive Contact Imaging For Skin Characterization

Capacitive contact imaging has shown potential in measuring skin properties including skin hydration and skin texture. Our previous studies showed it also can be used for solvent penetration measurements, skin damage assessments, as well as hair and nail water content measurements, despite the low water content. Through calibration we also measure the absolute permittivity of the skin, and from absolute permittivity we then work out the absolute water content (or solvent content) in skin. In this paper, we present our latest study of skin characterization, i.e. dry skin, hydrated skin, sweating, and damaged skin etc., using a commercial contact imaging system, the Epsilon (Biox Systems Ltd, England). We will first present the theoretical background and measurement principles, then illustrate the Epsilon calibrations. We will use experimental results to illustrate how the contact images can be used for skin characterization. Through image processing we can focus on the area that we are interested and eliminate the areas that we are not. We will also show latest results on skin solvent penetrations, and how to calculate the absolute solvent content in skin and diffusion coefficient of the solvent

Capacitive Imaging for Skin Characterizations and Solvent Penetration Measurements

Capacitive contact imaging has shown potential in measuring skin properties including hydration, micro relief analysis, as well as solvent penetration measurements. Through calibration, we can also measure the absolute permittivity of the skin, and from absolute permittivity we then work out the absolute water content and absolute solvent content in skin. This paper presents our latest study of capacitive contact imaging for skin characterizations and vivo skin solvent penetration. The results show that with capacitive contact imaging, it is possible not only to assess the skin damaging, but also potentially possible to differentiate different types of skin damages. The results also show that with capacitive contact imaging, it is also possible to measure the solvent penetration through skin and to quantify the solvent concentration within skin

Hair Water Content and Water Holding Capacity Measurements

We present our latest study on human hair water content and water holding capacity measurements by using capacitive contact imaging and condense-TEWL method. Previous studies showed that capacitive contact imaging based fingerprint sensors, originally designed for biometric applications, can be used for skin hydration imaging, skin surface analysis, 3D skin surface profiles, skin micro-relief as well as solvent penetration measurements. Through calibration, we can also measure the absolute dielectric constant, and from which we can calculate the absolute water content of the samples. In this study, we used capacitive contact imaging for hair water content measurements, and compared it with other measurement techniques. The results show that capacitive contact imaging can effectively differentiate different hairs from different people, normal hair from wet hair, and water content changes in hair. Healthy hair always contains certain amount of water, and they will contain different amount of water when exposed to different relatively humidity (RH) environments. We studied this water holding capacity by using the condenser-TEWL method through desorption process, in which small hair samples were placed inside the measurement chamber (22ºC and 11.3% RH). These hair samples, pre-conditioned at different higher RH, will therefore lose water until they reach equilibrium with the chamber RH. The dynamics of the equilibration process can be studied by measuring time-series curves of associated water vapour flux. The total quantity of water lost can then be calculated from such time-integrated flux curves. We have also developed mathematical models for modelling this hair desorption process. By fitting the normalized hair desorption data with the mathematical models, we can get the water diffusion coefficient information, which can then be related to the water holding capability of the hair samples

The Development of a Skin Image Analysis Tool by Using Machine Learning Algorithms

We present our latest research work on the development of a skin image analysis tool by using machine-learning algorithms. Skin imaging is very import in skin research. Over the years, we have used and developed different types of skin imaging techniques. As the number of skin images and the type of skin images increase, there is a need of a dedicated skin image analysis tool. In this paper, we report the development of such software tool by using the latest MATLAB App Designer. It is simple, user friendly and yet powerful. We intend to make it available on GitHub, so that others can benefit from the software. This is an ongoing project; we are reporting here what we have achieved so far, and more functions will be added to the software in the future

Extracranial Vertebral Artery Aneurysm Presenting as a Chronic Cervical Mass Lesion

Background. Aneurysms of the extracranial vertebral artery are rare and can provide a diagnostic and therapeutic challenge. Methods. We reviewed the clinical history of a patient presenting with cervical radiculopathy, who harboured an extracranial vertebral artery aneurysm eroding the cervical spine. Results. CT Angiography and MR Angiography set the diagnosis, by revealing a left C5-C6 vertebral artery aneurysm with cervical root impingement. Bony reconstruction depicted enlargement of the C6 transverse foramen and a marked enlargement of the C6-C7 intravertebral foramen. The lesion was treated by intravascular proximal vertebral artery occlusion. Conclusions. Extracranial vertebral artery aneurysms require a high index of clinical suspicion. This is the first report of a vertebral artery pseudoaneurysm presenting with bony erosion, which supports a less minacious portrayal of vertebral artery aneurysms

In Vivo Human Hair Hydration Measurements by Using Opto-Thermal Radiometry

© 2019, The Author(s). The water content in human hair is very important for its cosmetic properties and general health. However, to measure water content in hair, especially in vivo hair, is very difficult. Opto-thermal transient emission radiometry (OTTER) is a promising, infrared remote sensing technology that can be used for this kind of measurements. It can not only measure the water content but also the water depth profile in hair. By measuring the water content and its depth profile in hair, we can understand the status of hair, i.e., healthy or damaged, etc. In this paper, we will present our latest study on in vivo human hair hydration measurements by using OTTER. We will first present the theoretical background and then show the experimental results. We will also compare the OTTER hair results with other established measurement technique results, such as condenser trans-epidermal water loss method

In Vivo Human Hair Hydration Measurements by Using Opto-Thermal Radiometry

The water content in human hair is very important for its cosmetic properties and general health. However, to measure water content in hair, especially in vivo hair, is very difficult. Opto-thermal transient emission radiometry (OTTER) is a promising, infrared remote sensing technology that can be used for this kind of measurements. It can not only measure the water content but also the water depth profile in hair. By measuring the water content and its depth profile in hair, we can understand the status of hair, i.e., healthy or damaged, etc. In this paper, we will present our latest study on in vivo human hair hydration measurements by using OTTER. We will first present the theoretical background and then show the experimental results. We will also compare the OTTER hair results with other established measurement technique results, such as condenser trans-epidermal water loss metho