Νικόλαος Κουρκουμέλης , Αναπληρωτής Καθηγητής, Ιατρική Σχολή, Πανεπιστήμιο Ιωαννίνων
Δημήτριος Εμφιετζόγλου , Καθηγητής, Ιατρική Σχολή, Πανεπιστήμιο Ιωαννίνων
Λουκάς Αστρακάς , Αναπληρωτής Καθηγητής, Ιατρική Σχολή, Πανεπιστήμιο Ιωαννίνων
Skin is a complex biological system with a set of conjugated natural processes. From a biomechanical point of view, skin is primarily a multi-phase and multi-scale structure that includes a rich set of mechanical properties and interactions. The biological nature of this structure makes it dynamic, and like most biological tissues, with intense variability. Skin is generally considered to be a multi-layered complex system consisting of three main distinct structures: the epidermis, the dermis and the subcutaneous tissue, each with different diffusion coefficients. The epidermis, which has no vessels, is divided into the stratum corneum and the living skin.
Biological tissues are generally characterized by strong light scattering, which is a significant obstacle to the application of optical methods in clinical practice, due to the internal heterogeneous composition. In any optical and microscopic technique, the image of a biological sample depends on the limited depth of light penetration within the biological tissues, which characterized by high opacity. Even though this phenomenon has been known for a long time, the study of Optical Clearing Agents (OCAs), which are able to reduce scattering in biological tissues, enhance image contrast, and increase the penetration depth, is relatively recent. In recent years, OCAs have been used extensively to reduce scattering, demonstrating their results in providing deeper imaging capabilities for a wide variety of optical techniques, including Optical Coherence Tomography (OCT).
In this thesis, the modeling of the diffusion of optical clearing agents on the skin and more specifically on the stratum corneum and viable epidermis, is studied, using the finite element method (Finite Element Method-FEM). The method divides a large entity into smaller, simpler parts called finite elements, and then assembles an extensive array of equations that models the whole system. For the implementation of the thesis was carried out using the software FEBioStudio® (Finite Elements for Biomechanics), which is specifically designed for biomechanics and biophysical applications.
The aim of this study was to examine the effect of two optical clearing agents, oleic acid (OA) and propylene glycol (PG), as enhancers of skin optical permeability, during an OCT examination. The use of the appropriate optical clearing agent, ensures the balance of the refractive index between the air and the extracellular matrix, facilitating the reduced scattering of optical rays into the tissue.
Based on the results of the study, it turns out that the most suitable index matching gel is propylene glycol, as it penetrates the skin and is evenly distributed, reducing scattering. In other words, the OCA that diffuses into the extracellular space is selected, adjusting the refractive index. Also, propylene glycol has the advantage of being free of toxic or other side effects.
Skin, Stratum corneum, SC, Viable Epidermis, VE, Index matching gel, Optical clearing agents, OCAs, Finite element method, FEBioStudio