E-textile sensor for monitoring and evaluation of atopic dermatitis in skin

Abstract

Atopic dermatitis is one of the most common skin disorders, affecting nearly one fifth of the children and adolescents worldwide. It is characterised by relapsing skin lesions, which result in redness, itchiness, and dryness of the skin. Although research has discovered some of the reasons for the condition’s emergence, a dysfunction of the epidermal barrier in the skin and its ability to retain water and repel outside influences, there has not been much progress in providing effective treatment and diagnosis. This is due mainly because such treatments are monitored qualitatively, by observation, rather than quantitatively, by empirical data.
This thesis presents the development of a novel e-textile interdigitated capacitor (IDC) system to quantitatively assess the severity and treatment of AD in vivo. The IDC is made bespoke to be highly sensitive towards detecting the dysfunction of the skin barrier by measuring the hydration in the superficial layers of the skin – the stratum corneum (SC) and epidermis (EP). This device provides an empirical and universal scale that can be used to tailor treatments based on the specific severity state of the patient’s condition. It is housed in a compact, non-invasive and wearable package, to allow dermatologists to assess the patients’ condition remotely and continuously, introducing a new dimension of data on AD. The thesis details the development of the sensor from concept to operating prototype, spanning simulation modelling and analytical solutions, fabrication of the device, tests on skin replicas, and trials on patients.
A novel multilayer skin model was created in COMSOL®, incorporating frequency-dependent dielectric spectra for skin with AD. The model was used to determine the best geometry of the IDC for the application by controlling the parameters of the design. This study revealed novel insights into the depth-resolution of IDC sensors when subjected to multilayer media, presenting evidence that shallower penetration of electric field lines results from smaller electrode gaps. Simulations demonstrated that optimised IDC geometries with 50 – 100 µm electrode gaps are most sensitive to hydration changes in the SC, with maximum sensitivity in the 10 kHz – 1 MHz frequency range.
Prototypes were fabricated using two methods: etched copper on copper-polyimide substrates and printing silver on textile. Products from both methods were assessed using a novel hydration-gradient skin replica (also known as skin phantom) which simulated skin with different severity levels of AD. The results validated the findings of the FEA study, and the IDC with an electrode separation gap of 100 µm was confirmed as the chosen design for the study, balancing sensitivity and fabrication complexity. The early prototypes were robust under temperature and mechanical deformation but were heavily affected by humidity and lacked repeatability in readings. An encapsulation layer of 50 µm was introduced to solve this, which decreased the sensitivity, but achieved stability and prevented artefacts attributed to poor contact or moisture build-up.
The finished printed silver sensor was integrated in a complete wearable system housed in an e-textile armband with a capacitance-to-digital converter, BLE-enabled transmitting microcontroller, and a custom graphical user interface. The system is designed to be portable and easy to operate, allowing for both clinicians and patients to use the device and collect readings both in clinic and at home.
Clinical trials on thirteen patients with the condition confirmed that the e-textile IDC sensor distinguished between different severity states of the skin (lesional and non-lesional) with 100% sensitivity and specificity for individual patients. It reaffirmed the findings of the simulation and empirical studies that the chosen design is the most sensitive towards biomarkers of AD, revealing the highest change in capacitance arising from changes in the severity state of the skin. Differences in measured capacitance between the skin states were in the order of 3 to 5 pF. The sensor correlated significantly with Corneometer® measurements, a gold-standard for skin hydration testing (r = 0.595, p < 0.05). Furthermore, the e-textile IDC sensor demonstrated tighter clustering of the readings compared to other methods of assessment, indicating better variability and repeatability.
These findings demonstrate, for the first time, that a textile-integrated IDC can provide stable, quantitative, and clinically relevant measurements of AD severity in vivo. The work establishes a foundation for objective, continuous, and remote monitoring of AD, paving the way towards digital dermatology tools that can transform both clinical practice and at-home patient management.

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Identifiers

ORCID for Alexandar Todorov: orcid.org/0000-0002-6126-753X

ORCID for Stephen Beeby: orcid.org/0000-0002-0800-1759

ORCID for Russel Torah: orcid.org/0000-0002-5598-2860

ORCID for Michael R Ardern-Jones: orcid.org/0000-0003-1466-2016

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