Raman Maiti

In vivo measurement of skin surface strain and sub-surface layer deformation induced by natural tissue stretching.

Stratum corneum and epidermal layers change in terms of thickness and roughness with gender, age and anatomical site. Knowledge of the mechanical and tribological properties of skin associated with these structural changes are needed to aid in the design of exoskeletons, prostheses, orthotics, body mounted sensors used for kinematics measurements and in optimum use of wearable on-body devices. In this case study, optical coherence tomography (OCT) and digital image correlation (DIC) were combined to determine skin surface strain and sub-surface deformation behaviour of the volar forearm due to natural tissue stretching. The thickness of the epidermis together with geometry changes of the dermal-epidermal junction boundary were calculated during change in the arm angle, from flexion (90°) to full extension (180°). This posture change caused an increase in skin surface Lagrange strain, typically by 25% which induced considerable morphological changes in the upper skin layers evidenced by reduction of epidermal layer thickness (20%), flattening of the dermal-epidermal junction undulation (45-50% reduction of flatness being expressed as Ra and Rz roughness profile height change) and reduction of skin surface roughness Ra and Rz (40-50%). The newly developed method, DIC combined with OCT imaging, is a powerful, fast and non-invasive methodology to study structural skin changes in real time and the tissue response provoked by mechanical loading or stretching.

Optical coherence elastography for human finger-pad skin deformation studies

An optical coherence tomography (OCT) system with an A-scan rate of 20 kHz was developed for measuring the biomechanical properties of human finger-pad skin. Such an OCT system operates at a center wavelength of 890 nm with a spectral bandwidth of 150 nm resulting in a very good axial resolution of 2.6 μm. The measured sensitivity and sensitivity roll-off of the system were ~93 dB and ~6 dB mm-1, respectively. Elastographic B-scan images of the human finger-pad skin were constructed by using 1000 A-scans. Deformations of the human finger-pad before and after sliding, while pressed against a transparent optical glass plate under the action of 0.5-2 N force, were examined both at the surface and sub-surface. Biomechanical properties, i.e., deformation of the skin, finger-pad/glass interface contact area were studied.

Investigating a methodology to measure moisture in skin–textile friction experiments

During running, foot skin is subjected to continuous pressure and repeated shearing, along with high levels of humidity due to perspiration and heat (Baussan et al., 2012). Moisture content in the ...

Wear properties of diamond-like carbon coatings with silicon and chromium as adhesion layer using a high frequency reciprocating rig:

The application of diamond-like carbon coatings to bearing surfaces is widespread from machining to bio-implants and has resulted in significant study of coating properties. The aim of this investigation was to determine the performance of two diamond-like carbon coatings, using chromium and silicon as adhesion layers. Linear reciprocating wear tests were carried out at room temperature using an AISI 440C steel ball reciprocating against the diamond-like carbon-coated metal substrate. The performance of the coatings under different contact pressures (500–3000 MPa); peak sliding velocities (28–378 mm/s); and stroke length, (1.5–4 mm). An electric resistance measurement was used to monitor coating failure owing to the dielectric nature of the tested coatings. An increase in contact pressure resulted in a decrease in number of cycles to failure for both the coatings. However, the number of cycles to failure increased proportionally with sliding speed. In addition, artifacts on the coating and blister formation generated coating debris which acted as a third body during the wear process. The debris caused complete delamination of the coatings initially at the ends of the wear scar. The silicon adhesion layer-coating samples were found to provide a greater resistance to failure due to it being thicker, harder, and more elastic as compared to samples having a chromium adhesion layer.

Skin surface and sub-surface strain and deformation imaging using optical coherence tomography and digital image correlation

Bio-mechanical properties of the human skin deformed by external forces at difference skin/material interfaces attract much attention in medical research. For instance, such properties are important design factors when one designs a healthcare device, i.e., the device might be applied directly at skin/device interfaces. In this paper, we investigated the bio-mechanical properties, i.e., surface strain, morphological changes of the skin layers, etc., of the human finger-pad and forearm skin as a function of applied pressure by utilizing two non-invasive techniques, i.e., optical coherence tomography (OCT) and digital image correlation (DIC). Skin deformation results of the human finger-pad and forearm skin were obtained while pressed against a transparent optical glass plate under the action of 0.5-24 N force and stretching naturally from 90° flexion to 180° full extension respectively. The obtained OCT images showed the deformation results beneath the skin surface, however, DIC images gave overall information of strain at the surface.

Characterizing the microcirculation of atopic dermatitis using angiographic optical coherence tomography

Background and Aim: With inflammatory skin conditions such as atopic dermatitis (AD), epidermal thickness is mediated by both pathological hyperplasia and atrophy such as that resulting from corticosteroid treatment. Such changes are likely to influence the depth and shape of the underlying microcirculation. Optical coherence tomography (OCT) provides a non-invasive view into the tissue, however structural measures of epidermal thickness are made challenging due to the lack of a delineated dermal-epidermal junction in AD patients. Instead, angiographic extensions to OCT may allow for direct measurement of vascular depth, potentially presenting a more robust method of estimating the degree of epidermal thickening. Methods and results: To investigate microcirculatory changes within AD patients, volumes of angiographic OCT data were collected from 5 healthy volunteers and compared to that of 5 AD patients. Test sites included the cubital and popliteal fossa, which are commonly affected by AD. Measurements of the capillary loop and superficial arteriolar plexus (SAP) depth were acquired and used to estimate the lower and upper bounds of the undulating basement membrane of the dermal-epidermal junction. Furthermore, quantitative parameters such as vessel density and diameter were derived from each dataset and compared between groups. Capillary loop depth increased slightly for AD patients at the poplitial fossa and SAP was found to be measurably deeper in AD patients at both sites, likely due to localized epidermal hyperplasia.

Investigation into surface interaction between the contact lens, the upper eyelid and cornea using optical coherence tomography

Background and Aim: Over 50% of the total 125 million contact lens users complain of discomforts due to contact lenses. The aim of the project is to understand the effect of contact lenses on the morphological parameters of cornea and eyelid surfaces. Methods and results: Five volunteers were recruited for this study (3 soft contact lens users and 2 non-users). The volunteers were imaged using a slit lamp and Optical Coherence Tomography (OCT) before and after a period of 6-7 hours. There was a significant increase in epidermal thickness of the eyelid for contact lens users compared to non-users. In addition, the upper eyelid roughness for contact lens users and non-users increased significantly. This might be due to deposition of particles from the eyelid during the wiping process. Conclusions: Contact lens usage does affect the morphological parameters of eyelid. OCT is a powerful tool to measure these morphological changes in the eye. However, more volunteers must be recruited to get a better understanding of these changes.