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In this study, the effect of one cycle of winter to summer seasonal transition on the mechanical and physical properties of skin was investigated in vivo. Fourteen healthy skin volunteers aged between 22 and 42 years were studied at the volar lower and upper arms. The findings indicate a 22.15% and 34.29% decrease in trans-epidermal water loss (TEWL) and the average epidermal roughness (AER), respectively. Also, improved skin properties were observed such as a 25.48% rise in average epidermal hydration (AEH), 22.59% in skin thickness, 38.64% and 21.92% in melanin and redness, respectively, as well as an 8.25% rise in its firmness and 23.14% in elasticity when strained with uniaxial deformations. An inverse correlation was established between TEWL and AEH with a linear relationship between stratum corneum roughness versus TEWL as well as thickness and hydration. Also, the skin firmness exhibited a direct proportionality with TEWL and an inverse correlation with skin hydration where these relationships were stronger in summer than in winter. Furthermore, time-dependent results demonstrated three-staged elastic, viscoelastic and creep deformations with high, moderate and low strain rates respectively at both anatomical locations. The winter season displayed lower skin firmness and elasticity of 0.37 mm and 0.04 mm compared to 0.40 mm and 0.06 mm in summer accordingly. Anatomically, the two arm regions displayed different results with the upper arm having more consistent results than the lower arm. These results will find relevance in sensor skins and exoskeletons in Medicare, robotic and military technologies as well as innovations in cosmetics and dermatology.

In this chapter, we discuss the working principle of Optical Coherence Tomography (OCT), its capabilities for imaging skin, and how the technique is applied in clinical settings as well as in lab-based environments. Two case studies are then presented; the first to describe how OCT can be used for skin biomechanics measurements and the second to demonstrate its potential for diagnostic applications. Finally, we discuss the future potential of OCT for the diagnosis and management of diabetes-related complications.

This pilot study shows that Optical Coherence Tomography can be used to capture the morphology of the finger pad during sliding interaction with a grooved plate. The videos show how the finger pad ridges deform to slide or compress closer to the edge of the grooves. This study has demonstrated the future possibilities of investigating and visualising the interaction of a finger pad with a plate specimen of controlled roughness to improve and optimise surface characteristics of consumer products.

Studies on the variation of skin properties with gender, age and anatomical region, with regards to interaction with different materials have resulted in significant research output. Investigations on skin surface strain and sub-surface layer deformation during sliding, however, have not received as much attention. This novel study uses two non-invasive techniques, optical coherence tomography (OCT) and digital image correlation (DIC), to measure properties of the index finger of a 25 year old female when under normal and shear loading. Measurements were taken during static, and for the first time, dynamic phases. It was observed that the number of ridges in contact with a Quartz glass surface, observed under OCT, reduced when the finger started sliding. The sliding also resulted in deformation at the stratum corneum junction. The surface strain, analysed using DIC was higher nearer to the distal interphalangeal joint compared to the fingertip. This newly developed approach provides a powerful and non-invasive method to study the structural changes of finger-pad skin during loading and sliding. This approach can now be repeated at different anatomical locations for medical, bioengineering and consumer applications.

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.

Tribology is an important factor (among other factors) during biological interactions of devices and tissues. The paper discusses how new computational and experimental methods can be used to understand and improve the design and development of medical devices at macro and micro scales to sustain life beyond 50 years. We have used pre-clinical experiments and computational methods to understand interactions between orthopaedic implants at the macro scale. The computational model has been validated with experiments. Now this computational model can predict damage in implants for different patients. One such application was successfully tried and tested in collaboration with University National Autonomous Mexico. This methodology can be used in future to design patient specific, affordable (using 3D printing) and robust implants which will be useful for developing countries like Vietnam, India and Mexico. Improvement of catheter designs is important to reduce damage to the internal tissues while being used for cardiovascular problems. We are developing new experimental techniques (in micro scale) that can be used to understand the interaction of cells with the catheter material. These will help reduce the hospital costs incurred during longer stay of the patients admitted for cardiovascular related problems.

In recent years several high profile projects have questioned the repeatability and validity of scientific research in the fields of psychology and medicine. In general, these studies have shown or estimated that less than 50% of published research findings are true or replicable even when no breaches of ethics are made. This high percentage stems from widespread poor study design; either through the use of underpowered studies or designs that allow the introduction of bias into the results.\ud \ud In this work, we have aimed to assess, for the first time, the prevalence of good study design in the field of tribology. A set of simple criteria for factors such as randomisation, blinding, use of control and repeated tests has been made. These criteria have been used in a mass review of the output of five highly regarded tribology journals for the year 2017. In total 379 papers were reviewed by 26 reviewers, 28% of the total output of the journals selected for 2017.\ud \ud Our results show that the prevalence of these simple aspects of study design is poor. Out of 290 experimental studies, 2.2% used any form of blinding, 3.2% used randomisation of either the tests or the test samples, while none randomised both. 30% repeated experiments 3 or more times and 86% of those who repeated tests used single batches of test materials. 4.4% completed statistical tests on their data.\ud \ud Due to the low prevalence of repeated tests and statistical analysis it is impossible to give a realistic indication of the percentage of the published works that are likely to be false positives, however these results compare poorly to other more well studied fields. Finally, recommendations for improved study design for researchers and group design for research group leaders are given.

Background Changes in body posture cause changes in morphological properties at different skin sites. Although previous studies have reported the thickness of the skin, the details of the postures are not generally given. This paper presents the effect of a change in posture on parameters such as thickness and surface roughness in 21 load-bearing and non-load-bearing sites. Materials and methods A total of 12 volunteers (8 males and 4 females) were selected in an age group of 18–35 years and of Fitzpatrick skin type I-III. Images were captured using a clinically-approved VivoSight® optical coherence tomography system and analysed using an algorithm provided by Michelson Diagnostics. Results Overextension (extending joints to full capacity) resulted in changes to thickness, roughness and undulation of the skin around the body. Discussion and conclusion The load-bearing regions have thicker skin compared to non-load-bearing sites. This is the first time that undulation topography of the stratum corneum–stratum lucidum and the dermal–epidermal junction layers have been measured and reported using statistical values such as Ra. The data presented could help to define new skin layer models and to determine the variability of the skin around the body and between participants.

Vascular medical devices, such as stents, catheters and more advanced devices inevitably interact with surfaces within the human body. These interactions and the underlying biological and tribological (friction) mechanisms and resulting implications are not well understood, currently. For the further optimisation of these devices and the development of new and safer devices, a deeper understanding of vascular biotribology is required. Studies about this topic are scarce and no review is available. This review paper introduces vascular physiology relevant to interaction with medical devices and highlights where tribological effects may come into play. Furthermore, implications with existing medical devices are investigated in the context of biotribology and relevant studies are discussed. The different approaches to study the interactions are compared, and the current state of the field is reviewed. The aim of this paper is to provide an introduction to this interdisciplinary field, for both researchers with an engineering background and those with a biological background, and to present the current state of the field of research.

The effect of loading and boundary conditions on patellar mechanics is significant due to the complications arising in patella femoral joints during total knee replacements. To understand the patellar mechanics with respect to loading and motion, a computational model representing the patella femoral joint was developed and validated against experimental results. The computational model was created in IDEAS NX and simulated in MSC ADAMS/VIEW software. The results obtained in the form of internal external rotations and anterior posterior displacements for a new and experimentally simulated specimen for patella femoral joint under standard gait condition were compared with experimental measurements performed on the Leeds ProSim knee simulator. A good overall agreement between the computational prediction and the experimental data was obtained for patella femoral kinematics. Good agreement between the model and the past studies was observed when the ligament load was removed and the medial lateral displacement was constrained. The model is sensitive to ±5 % change in kinematics, frictional, force and stiffness coefficients and insensitive to time step.

In a pursuit to further improve the understanding of the factors influencing friction blister formation, friction between running sock textiles and the skin at the first metatarsal head (1MTH) region was investigated in three different moisture conditions (dry, low moisture and wet).Twenty-six participants were recruited and two running sock types were selected based on the variations of their fibre composition and knit structure: 1) a predominantly nylon anti-blister sock and 2) a cotton-rich sock. All friction tests were conducted in controlled room conditions with a temperature of between 20 to 22°C and a relative humidity of 40 to 60% using a bespoke rig developed at the University of Sheffield for foot friction studies. Water was applied to the inside of the plantar region of the sock textiles to different levels using a moisture control protocol. The moisture level of both the 1MTH region and the sock fabrics were monitored throughout testing using a Corneometer® device.Increasing sock moisture above the dry condition was found to increase foot-sock sliding friction for both sock materials tested. No significant correlation was found at the level p < 0.05 between foot hydration level and sliding friction over the hydration range tested. In dry conditions, the cotton-rich sock exhibited lower levels of friction compared with the anti-blister sock. However, in both low moisture and wet conditions, the anti-blister sock showed comparatively lower levels of friction than the cotton-rich sock. This suggests that for intensive athletic events where significant perspiration is likely to occur, the anti-blister sock would provide lower friction. This study offers a new approach to friction testing of sock materials and it is hoped that its outcomes will provide new insights on the preventative measures for friction blisters.

Measurement of sub-clinical atopic dermatitis (AD) is important for determining how long therapies should be continued after clinical clearance of visible AD lesions. An important biomarker of sub-clinical AD is epidermal hypertrophy, the structural measures of which often make optical coherence tomography (OCT) challenging due to the lack of a clearly delineated dermal-epidermal junction in AD patients. Alternatively, angiographic OCT measurements of vascular depth and morphology may represent a robust biomarker for quantifying the severity of clinical and sub-clinical AD. To investigate this, angiographic data sets were acquired from 32 patients with a range of AD severities. Deeper vascular layers within skin were found to correlate with increasing clinical severity. Furthermore, for AD patients exhibiting no clinical symptoms, the superficial plexus depth was found to be significantly deeper than healthy patients at both the elbow (p = 0.04) and knee (p

Complications of patellofemoral arthroplasty often occur soon after implantation and, as well as other factors, can be due to the design of the implant or its surgical positioning. A number of studies have previously considered the wear of ultra-high-molecular-weight polyethylene patellae following suboptimal implantation; however, studies have primarily been carried out under a limited number of degrees of freedom. The aim of this study was to develop a protocol to assess the wear of patellae under a malaligned condition in a six-axis patellofemoral joint simulator. The malalignment protocol hindered the tracking of the patella centrally in the trochlear groove and imparted a constant 5° external rotation (tilt) on the patella button. Following 3 million cycles of wear simulation, this condition had no influence on the wear of ultra-high-molecular-weight polyethylene patellae aged for 4 years compared to well-positioned non-aged implants (p > 0.05). However, under the malaligned condition, ultra-high-molecular-weight polyethylene patellae aged 8–10 years after unpacking (following sterilisation by gamma irradiation in an inert atmosphere) and worn ultra-high-molecular-weight polyethylene components also aged 4 years after unpacking (following the same sterilisation process) exhibited a high rate of wear. Fatigue failure due to elevated contact stress led to delamination of the ultra-high-molecular-weight polyethylene and in some cases complete failure of the patellae. The results suggest that suboptimal tracking of the patella in the trochlear groove and tilt of the patella button could have a significant effect on the wear of ultra-high-molecular-weight polyethylene and could lead to implant failure.

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.

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.

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.

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.

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.

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 ...

Total knee replacements (TKR) have been used for the past four decades [1]. Conventional knee (tibiofemoral) wear simulators have been used to facilitate improvements in the design of TKRs [2]. This, along with surgical improvements has caused the success rate of implants to increase to 97% over a period of ten years [3, 4, and 5]. However the decision to resurface the patella still remains an issue [6, 7]. Research has been performed into the in vitro wear simulation of the patella femoral joint (PFJ) [8, 9, and 10] but to date none of these simulations have employed all six degrees of freedom (DOF).Copyright © 2011 by ASME