In this review, we discuss the current knowledge on the tribology of human skin and present an analysis of the available experimental results for skin friction coefficients. Starting with an overview ...on the factors influencing the friction behaviour of skin, we discuss the up-to-date existing experimental data and compare the results for different anatomical skin areas and friction measurement techniques. For this purpose, we also estimated and analysed skin contact pressures applied during the various friction measurements. The detailed analyses show that substantial variations are a characteristic feature of friction coefficients measured for skin and that differences in skin hydration are the main cause thereof, followed by the influences of surface and material properties of the contacting materials. When the friction coefficients of skin are plotted as a function of the contact pressure, the majority of the literature data scatter over a wide range that can be explained by the adhesion friction model. The case of dry skin is reflected by relatively low and pressure-independent friction coefficients (greater than 0.2 and typically around 0.5), comparable to the dry friction of solids with rough surfaces. In contrast, the case of moist or wet skin is characterised by significantly higher (typically >1) friction coefficients that increase strongly with decreasing contact pressure and are essentially determined by the mechanical shear properties of wet skin. In several studies, effects of skin deformation mechanisms contributing to the total friction are evident from friction coefficients increasing with contact pressure. However, the corresponding friction coefficients still lie within the range delimited by the adhesion friction model. Further research effort towards the analysis of the microscopic contact area and mechanical properties of the upper skin layers is needed to improve our so far limited understanding of the complex tribological behaviour of human skin.
The friction of untreated human skin (finger) against a reference textile was investigated with 12 subjects using a force plate. In touch experiments, in which the subjects assessed the surface ...roughness of the textile at normal loads of 1.5
±
0.7
N, the average friction coefficients ranged from 0.27 to 0.71 and varied among individuals due to different states of skin hydration. In experiments, in which the subjects varied the normal load, the friction coefficients were in the same range and showed practically no load dependence, indicating that both adhesion and hysteresis are contributing to the friction behaviour. The results for human skin were compared with apparative friction measurements using different silicone and polyurethane materials as mechanical skin equivalents. A polyurethane coated polyamide fleece with a surface structure similar to that of skin showed the best correspondence with human skin under dry conditions. The friction coefficients of this material increased with the moisture content of the reference textile. A realistic skin model in combination with an objective friction test method would be very useful for the textile industry and allow the efficient development of new textiles with improved and skin-adapted surface and frictional properties for sport and medical applications.
In each individual, a highly positive linear correlation was found between skin moisture and friction coefficient (COF). No
correlation was observed between moisture and elasticity, as well as ...between elasticity and friction. Skin viscoelasticity
was comparable for women and men. The friction of female skin showed significantly higher moisture sensitivity. COFs increased
typically by 43% (women) and 26% (men) when skin hydration varied between very dry and normally moist skin. The COFs between
skin and completely wet fabric were more than twofold higher than the values for natural skin rubbed on a dry textile surface., The friction between the inner forearm and a hospital fabric was measured in the natural skin condition and in different hydration
states using a force plate. Eleven males and eleven females rubbed their forearm against the textile on the force plate using
defined normal loads and friction movements. Skin hydration and viscoelasticity were assessed by corneometry and the suction
chamber method, respectively., Friction and shear forces, as well as moisture between the human skin and textiles are critical factors in the formation of
skin injuries such as blisters, abrasions and decubitus. This study investigated how epidermal hydration affects the friction
between skin and textiles., Increasing skin hydration seems to cause gender-specific changes in the mechanical properties and/or surface topography of
human skin, leading to skin softening and increased real contact area and adhesion.
The friction behaviour of human skin was studied by combining friction measurements using a tri-axial force plate with skin contact area measurements using a pressure sensitive film. Four subjects ...carried out friction measurement series, in which they rubbed the index finger pad and the edge of the hand against a smooth and a rough glass surface under dry and wet conditions. The normal loads were varied up to values of 50
N, leading to skin contact pressures of up to 120
kPa. The analysis of the pressure dependence of friction coefficients of skin for contrasting sliding conditions allowed to determine the involved friction mechanisms on the basis of theoretical concepts for the friction of elastomers.
Adhesion was found to be involved in all investigated cases of friction between skin and glass. If adhesion mechanisms predominated (skin against smooth glass in the dry condition and skin against rough glass in the wet condition), the friction coefficients were generally high (typically >1) and decreased with increasing contact pressure according to power laws with typical exponents between −0.5 and −0.2. Contributions to the friction coefficient due to viscoelastic skin deformations were estimated to be relatively small (<0.2). In those cases where the deformation component of friction played an important role in connection with adhesion (skin against rough glass in the dry condition), the friction coefficients of skin were typically around 0.5 and their pressure dependence showed weak trends characterised by exponents ranging from −0.1 to +0.2. If hydrodynamic lubrication came into play (skin sliding on smooth glass in the wet condition), the friction coefficients were strongly reduced compared to dry friction (<1), and their decrease with increasing contact pressures was characterised by exponents of <−0.7.
Sleep spindles, as detected on scalp electroencephalography (EEG), are considered to be markers of thalamo-cortical network integrity. Since obstructive sleep apnea (OSA) is a known cause of brain ...dysfunction, the aim of this study was to investigate sleep spindle frequency distribution in OSA. Seven non-OSA subjects and 21 patients with OSA (11 mild and 10 moderate) were studied. A matching pursuit procedure was used for automatic detection of fast (≥13 Hz) and slow (<13 Hz) spindles obtained from 30 min samples of NREM sleep stage 2 taken from initial, middle and final night thirds (sections I, II and III) of frontal, central and parietal scalp regions.
Compared to non-OSA subjects, Moderate OSA patients had higher central and parietal slow spindle percentage (SSP) in all night sections studied, and higher frontal SSP in sections II and III. As the night progressed, there was a reduction in central and parietal SSP, while frontal SSP remained high. Frontal slow spindle percentage in night section III predicted OSA with good accuracy, with OSA likelihood increased by 12.1%for every SSP unit increase (OR 1.121, 95% CI 1.013-1.239, p=0.027).
These results are consistent with diffuse, predominantly frontal thalamo-cortical dysfunction during sleep in OSA, as more posterior brain regions appear to maintain some physiological spindle frequency modulation across the night. Displaying changes in an opposite direction to what is expected from the aging process itself, spindle frequency appears to be informative in OSA even with small sample sizes, and to represent a sensitive electrophysiological marker of brain dysfunction in OSA.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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► The tribological behaviour and mechanical resistance of a novel medical textile with drug delivery function is presented. ► Friction experiments that simulated cyclic dynamic ...contacts with skin under dry and wet conditions provided insights in the friction and lubrication behaviour of drug delivery fabrics. ► Loaded with phytotherapeutic substances, the drug delivery fabrics considerably reduced friction under wet conditions. ► The lubrication effects depended on the degree of dilution of the phytotherapeutic substances.
Textile-based drug delivery systems have a high potential for innovative medical and gerontechnological applications. In this study, the tribological behaviour and lubrication properties of a novel textile with drug delivery function/finishing was investigated by means of friction experiments that simulated cyclic dynamic contacts with skin under dry and wet conditions. The textile drug delivery system is based on a loadable biopolymer dressing on a polyester (PES) woven fabric. The fabrics were finished with low (LC) and highly cross-linked (HC) polysaccharide dressings and investigated in the unloaded condition as well as loaded with phytotherapeutic substances. The mechanical resistance and possible abrasion of the functional coatings on the textile substrate were assessed by friction measurements and scanning electron microscopical analyses.
Under dry contact conditions, all investigated fabrics (PES substrate alone and textiles with loaded and unloaded dressings) showed generally low friction coefficients (0.20–0.26). Under wet conditions, the measured friction coefficients were typically higher (0.34–0.51) by a factor of 1.5–2. In the wet condition, both loaded drug delivery textiles exhibited 7–29% lower friction (0.34–0.41) than the PES fabric with unloaded dressings (0.42–0.51), indicating pronounced lubrication effects. The lubrication effects as well as the abrasion resistance of the studied textiles with drug delivery function depended on the degree of dilution of the phytotherapeutic substances.
Lubricating formulations of textile-based drug delivery systems which reduce friction against the skin might be promising candidates for advanced medical textile finishes in connection with skin care and wound (decubitus ulcer) prevention.
Since the first electroencephalogram (EEG) was obtained, there have been many possibilities to use it as a tool to access brain cognitive dynamics. Mathematical (Math) problem solving is one of the ...most important cortical processes, but it is still far from being well understood. EEG is an inexpensive and simple indirect measure of brain operation, but only recently has low-cost equipment (mobile EEG) allowed sophisticated analyses in non-clinical settings. The main purpose of this work is to study EEG activation during a Math task in a realistic environment, using mobile EEG. A matching pursuit (MP)-based signal analysis technique was employed, since MP properties render it a priori suitable to study induced EEG activity over long time sequences, when it is not tightly locked to a given stimulus. The study sample comprised sixty healthy volunteers. Unlike the majority of previous studies, subjects were studied in a sitting position with their eyes open. They completed a written Math task outside the EEG lab, wearing a mobile EEG device (EPOC+). Theta 4 Hz–7.5 Hz, alpha (7.5 Hz–13 Hz and 0.5 Hz micro-bands in the 0.5 Hz–20 Hz range were studied with a low-density stochastic MP dictionary. Over 1-min windows, ongoing EEG alpha and theta activity was decomposed into numerous MP atoms with median duration around 3 s, similar to the duration of induced, time-locked activity obtained with event-related (des)synchronization (ERS/ERD) studies. Relative to Rest, there was lower right-side and posterior MP alpha atom/min during Math, whereas MP theta atom/min was significantly higher on anteriorly located electrodes, especially on the left side. MP alpha findings were particularly significant on a narrow range around 10 Hz–10.5 Hz, consistent with FFT alpha peak findings from ERS/ERD studies. With a streamlined protocol, these results replicate previous findings of EEG alpha and theta activation obtained during Math tasks with different signal analysis techniques and in different time frames. The efficient application to real-world, noisy EEG data with a low-resolution stochastic MP dictionary shows that this technique is very encouraging. These results provide support for studies of mathematical cognition with mobile EEG and matching pursuit.
Graphical abstract
Background/purpose: The mechanical properties of human skin are known to change with ageing, rendering skin less resistant to friction and shear forces, as well as more vulnerable to wounds. Until ...now, only few and contradictory results on the age‐dependent friction properties of skin have been reported. This study has investigated in detail the influence of age on the friction of human skin against textiles.
Methods: In vivo skin‐friction measurements on a force plate were combined with skin analyses concerning elasticity, hydration, pH value and sebum content. Thirty‐two young and 28 aged persons rubbed their volar forearm in a reciprocating motion against various textiles on the force plate, using defined normal loads and sliding velocities, representing clinically relevant contact conditions.
Results: Mean friction coefficients ranged from 0.30 ± 0.04 (polytetrafluoroethylene) to 0.43 ± 0.04 (cotton/polyester). No significant differences in the friction properties of skin were found between the age groups despite skin elasticity being significantly lower in the aged persons. Skin hydration was significantly higher in the elderly, whereas no significant differences were observed in either skin pH value or sebum content.
Conclusion: Adhesion is usually assumed to be the dominant factor in skin friction, but our observations imply that deformation is also an important factor in the friction of aged skin. In the elderly, lower skin elasticity and skin turgor are associated with more pronounced skin tissue displacements and greater shear forces during frictional contact, emphasizing the importance of friction reduction in wound‐prevention programmes.
Background:
The short-term outcomes of anterior cruciate ligament (ACL) reconstruction with bone–patellar tendon–bone or hamstring tendon (HT) graft are excellent with good clinical stability and ...patient-reported outcomes. Although some studies have reported the long-term outcomes of bone–patellar tendon–bone graft ACL reconstruction, few have reported the outcomes of HT graft ACL reconstruction.
Purpose:
To assess clinical and radiographic outcomes of HT graft ACL reconstruction with femoral cortical button fixation at a minimum 20-year follow-up.
Study Design:
Case series; Level of evidence, 4.
Methods:
A prospective study was performed in which all patients undergoing isolated transtibial primary ACL reconstruction between 1994 and 1996 with HT graft and femoral cortical button fixation were assessed clinically and radiographically. Follow-up was obtained in 48 of 94 patients (51%). Median (interquartile range) age at operation was 31 years (26-39 years); median follow-up was 21 years (20-22 years); 65% were male; and 48% had meniscal injury at surgery and underwent partial meniscectomy. Graft rupture, reoperation, and contralateral injury rates were assessed; clinical stability was measured using the KT-1000 arthrometer; patient-reported outcomes were assessed (International Knee Documentation Committee IKDC, Lysholm, Forgotten Joint Score, Tegner activity, Knee injury and Osteoarthritis Outcome Score KOOS, Anterior Cruciate Ligament Quality of Life ACL-QOL, EuroQol 5-Dimension 5-Level EQ-5D-5L); and radiographic osteoarthritis (defined as Kellgren-Lawrence grade ≥2) was assessed for the ipsilateral and the contralateral knee.
Results:
Graft rupture occurred in 4 patients (8%), contralateral injury in 4 patients (8%), and reoperation in 15 patients (31%), which consisted mainly of meniscal tears or hardware removal. In patients with an intact graft, excellent patient-reported outcome measures (PROMs) were noted, with a median Lysholm of 90 (78-100), subjective IKDC of 86 (72-95), and KOOS–Sports of 86 (58-100). There was low awareness of the operated knee (Forgotten Joint Score, 81 60-96) and good quality of life (ACL-QOL, 85 75-94; EQ-5D-5L, 0.87 0.83-1.00). Median side-to-side difference, as measured with the KT-1000 arthrometer, was 1 mm (-1 to 3 mm). Radiographic osteoarthritis was evident in 49% of ipsilateral and 10% of contralateral knees and was associated with meniscectomy at index surgery and decreased PROMs at follow-up.
Conclusion:
Long-term outcomes of transtibial HT graft ACL reconstruction with femoral cortical button fixation are generally good with a low failure rate, low awareness of the operated knee, and good clinical stability. Radiographic osteoarthritis was evident in approximately half of the patients at 20-year follow-up and was associated with meniscectomy at index surgery and decreased PROMs at follow-up.
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