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ABSTRACT: 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.
Colloids and surfaces. B, Biointerfaces 02/2013; 108C:103-109. · 2.60 Impact Factor
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ABSTRACT: This article deals with the tribology of lipid coatings that resemble those found on human skin. In order to simulate the
lipidic surface chemistry of human skin, an artificial sebum formulation that closely resembles human sebum was spray-coated
onto mechanical skin models in physiologically relevant concentrations (5–100μg/cm2). Water contact angles and surface free energies (SFEs) showed that model surfaces with ≤25μg/cm2 lipids appropriately mimic the physico-chemical properties of dry, sebum-poor skin regions. In friction experiments with
a steel ball, lipid-coated model surfaces demonstrated lubrication effects over a wide range of sliding velocities and normal
loads. In friction measurements on model surfaces as a function of lipid-film thickness, a clear minimum in the friction coefficient
(COF) was observed in the case of hydrophilic, high-SFE materials (steel, glass), with the lowest COF (≈0.5) against skin
model surfaces being found at 25μg/cm2 lipids. For hydrophobic, low-SFE polymers, the COF was considerably lower (0.4 for PP, 0.16 for PTFE) and relatively independent
of the lipid amount, indicating that both the mechanical and surface-chemical properties of the sliders strongly influence
the friction behaviour of the skin-model surfaces. Lipid-coated skin models might be a valuable tool not only for tribologists
but also for cosmetic chemists, in that they allow the objective study of friction, adhesion and wetting behaviour of liquids
and emulsions on simulated skin-surface conditions.
Tribology Letters 04/2012; 34(2):81-93. · 1.58 Impact Factor
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ABSTRACT: Background: Skin aging is a risk factor for a decubitus and biophysical skin properties could help to identify persons at risk. Whether such biophysical properties of aged human skin differ between areas is undetermined. Objective: To investigate whether viscoelasticity, hydration or friction differ between important areas for decubitus risk. Methods: Pilot study in 32 (18 female, 14 male) acute and subacute old patients aged 81.9 ± 5.9 years (±SD), without active skin disease after an average of 10 days of stay. Assessment of skin resilience/viscoelasticity (E) and hydration (H) at the volar forearm (VF), trochanter (TR) and the sacrum (SA), nutrition by a Mini Nutritional Assessment (MNA), total body water (TBW), lean body mass (LBM), % body fat (%F) by bioimpedance and routine laboratory parameters (hemoglobin, hematocrit, leukocytes, C-reactive protein, serum proteins and creatinine). Results: Mean body mass index (27 ± 4.2), MNA (22.5 ± 2.9), Braden score (20 ± 2.5), E (68.5 ± 6.0%) and H (38.3 ± 6.7) at any site and laboratory parameters did not differ by sex. Men had more TBW (+12 ± 1.5 liters), LBM (+9 ± 2 kg), less %F (-8.8 ± 2.1%), increased H-TR (+7.11 ± 2.8) and H-SA (+5.68 ± 2.5). Overall E-VF correlated significantly with E-TR (r(2) = 0.40, p < 0.0001) and E-SA (r(2) = 0.40, p < 0.0001). In contrast, skin hydration was not correlated. Conclusion: Results of forearm elasticity experiments can be used as a model for other body sites at risk for the development of pressure ulcers.
Gerontology 04/2012; · 2.78 Impact Factor
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S N Robinovitch,
S L Evans,
J Minns,
A C Laing,
P Kannus,
P A Cripton, S Derler,
S J Birge,
D Plant,
I D Cameron,
D P Kiel,
J Howland,
K Khan,
J B Lauritzen
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ABSTRACT: Hip protectors represent a promising strategy for preventing fall-related hip fractures. However, clinical trials have yielded conflicting results due, in part, to lack of agreement on techniques for measuring and optimizing the biomechanical performance of hip protectors as a prerequisite to clinical trials.
In November 2007, the International Hip Protector Research Group met in Copenhagen to address barriers to the clinical effectiveness of hip protectors. This paper represents an evidence-based consensus statement from the group on recommended methods for evaluating the biomechanical performance of hip protectors.
The primary outcome of testing should be the percent reduction (compared with the unpadded condition) in peak value of the axial compressive force applied to the femoral neck during a simulated fall on the greater trochanter. To provide reasonable results, the test system should accurately simulate the pelvic anatomy, and the impact velocity (3.4 m/s), pelvic stiffness (acceptable range: 39-55 kN/m), and effective mass of the body (acceptable range: 22-33 kg) during impact. Given the current lack of clear evidence regarding the clinical efficacy of specific hip protectors, the primary value of biomechanical testing at present is to compare the protective value of different products, as opposed to rejecting or accepting specific devices for market use.
Osteoporosis International 10/2009; 20(12):1977-88. · 4.58 Impact Factor
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I D Cameron,
S Robinovitch,
S Birge,
P Kannus,
K Khan,
J Lauritzen,
J Howland,
S Evans,
J Minns,
A Laing,
P Cripton, S Derler,
D Plant,
D P Kiel
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ABSTRACT: While hip protectors are effective in some clinical trials, many, including all in community settings, have been unable to demonstrate effectiveness. This is due partly to differences in the design and analysis. The aim of this report is to develop recommendations for subsequent clinical research.
In November of 2007, the International Hip Protector Research Group met to address barriers to the clinical effectiveness of hip protectors. This paper represents a consensus statement from the group on recommended methods for conducting future clinical trials of hip protectors.
Consensus recommendations include the following: the use of a hip protector that has undergone adequate biomechanical testing, the use of sham hip protectors, the conduct of clinical trials in populations with annual hip fracture incidence of at least 3%, a run-in period with demonstration of adequate adherence, surveillance of falls and adherence, and the inclusion of economic analyses. Larger and more costly clinical trials are required to definitively investigate effectiveness of hip protectors.
Osteoporosis International 10/2009; 21(1):1-10. · 4.58 Impact Factor
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ABSTRACT: 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.
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.
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.
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.
Skin Research and Technology 09/2009; 15(3):288-98. · 1.71 Impact Factor
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ABSTRACT: 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.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.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.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.
Journal of The Royal Society Interface 04/2008; 5(28):1317-28. · 4.40 Impact Factor
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ABSTRACT: Prolonged pressure as well as friction and shear forces at the skin-textile interface are decisive physical parameters in the development of decubitus. The present article describes the contact phenomena at the skin-textile interface and the development of a purpose-built textile friction analyser (TFA) for the tribological assessment of skin-fabric interactions, in connection with decubitus prevention.
Interface pressure distributions were recorded in the pelvic and femoral regions between supine persons and a foam mattress. Fabrics made of various natural and synthetic yarns were investigated using the TFA. A vertical load of 7.7 kPa was applied to the swatches, simulating high interface pressures at the skin-fabric interface and clinical conditions of bedridden persons. Fabrics were rubbed in reciprocating motions against a validated skin-simulating material to determine static as well as dynamic friction coefficients (COFs).
Maximum contact pressures ranged from 5.2 to 7.7 kPa (39-58 mmHg) and exceeded the capillary closure pressure (32 mmHg) in all investigated bedding positions. For both COFs, a factor of 2.5 was found between the samples with the lowest and highest values. Our results were in a similar range to COFs found in measurements on human skin in vivo. The results showed that our test method can detect differences of 0.01 in friction coefficients.
TFA measurements allow the objective and reliable study of the tribology of the skin-textile biointerface and will be used to develop medical textiles with improved performance and greater efficacy for decubitus prevention.
Skin Research and Technology 03/2008; 14(1):77-88. · 1.71 Impact Factor
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ABSTRACT: As in many countries, a significant increase in the number of hip fractures is predicted due to the demographic changes in the population. To reduce the consequences for the patients and the social costs, hip protectors are considered to be effective in reducing the impact force on the hip and so to reduce the risk of hip fractures. The effectiveness of hip protectors has been investigated as well in experimental impact tests as in clinical studies, but there is still an uncertainty about their mechanical protection effect. Therefore, laboratory tests are an effective way to investigate the mechanical behaviour of hip protectors. A fracture is initiated by exceeding an ultimate compressive or tensile stress. In our model, stresses in the femoral neck are estimated by using the Euler beam formula. A standard femur was defined consisting of all mechanical parameters that have been identified to influence the mechanical resistance to external loads, such as the effective cross-sectional area (CSA), cross-sectional moment of inertia (CSMI), femoral neck width (FNW), centre of mass and other geometric parameters of the femur. In this study the necessary formulae as well as first results of assessing hip protectors on the basis of stresses in the femoral neck are presented. The results show that the methodology facilitates assessment and improvement of hip protectors, as the biomechanical parameters of real femora are the basis of the model.
Medical Engineering & Physics 08/2006; 28(6):550-9. · 1.62 Impact Factor
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ABSTRACT: The potential of hip protectors to prevent femur fracture is addressed in this study. A mechanical model of the human hip was developed and used to perform impact tests with different types of hip protectors. In addition a finite element model of the test device was established which allows simulations of the impact tests. The different principles of energy-shunting systems and energy-absorbing systems were demonstrated. Furthermore misplacement of a hip protector can be simulated. Hence the FE model was shown to be a suitable tool for future hip protector design.
Technology and health care: official journal of the European Society for Engineering and Medicine 02/2004; 12(1):43-9.
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ABSTRACT: We discuss two methods (Zeeman modulation and Doppler modulation) for locking the frequency of a singlemode cw laser to an atomic absorption line. These methods do not require the laser frequency to be modulated directly. In the first scheme the absorption frequency of the atom is modulated via the Zeeman effect; in the second scheme the laser frequency is modulated indirectly via the Doppler effect in an atomic beam. We used the two methods successfully to lock two dye lasers to the transitions 6S((1/2)) ? 7S((1/2)) and 7S((1/2)) ? 15P(?) in atomic cesium.
Applied Optics 07/1988; 27(13):2662-5. · 1.41 Impact Factor
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ABSTRACT: 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.
Tribology International.
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ABSTRACT: 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.
Wear.
