René M. Rossi

Moisture Transport and Absorption in Multilayer Protective Clothing Fabrics

The distribution of moisture in state-of-the-art firefighter protective clothing was analyzed on a sweating torso. After one hour of sweating, only 35 % of moisture evaporated from the layers, but after another hour of drying out, only about 10 % of the supplied moisture remained in the clothing. Over 75 % of this moisture accumulated in the innermost three layers of the clothing system consisting of five and six layers, respectively. The interaction of the moisture transport properties of the different layers proved to be very important for the distribution of moisture. In particular, the neighboring layer of the underwear turned out to be dominant for the moisture distribution. Depending on its hygroscopic properties, it could even act as a water barrier.

Water vapor transfer and condensation effects in multilayer textile combinations

In cold environments, the moisture produced by the human body will partly condense within the layers of an ensemble. Water vapor transfer and moisture accumulation in the layers of different four-layer combinations are analyzed at several moderately cold temperatures with a sweating arm, which simulates the thermophysiological behavior of a mans arm. The permeability of the samples and their condensation rates strongly depend on the outside climate and the hydrophilicity of the outer layers. The differences in effective water vapor resistances between the ensembles are small in a climate of 20°C and 65% RH, but become larger with decreasing outside temperature. The formation of condensation is the smallest for samples with a hydrophilic membrane laminated on the hydrophilic inner side. Hydrophilic layers placed underneath the outer shell generally absorb more moisture than similar hydrophobic layers, revealing probable liquid moisture transfer from the outer shell to the inner layers of the combinations.

Quantitative Evaluation of air gap Thickness and Contact Area Between Body and Garment

The thermal, evaporative and wicking properties of clothing depend not only on the properties of the fabric but also on the thickness of air layers and the magnitude of the contact area and their variation. The aim of this study was to accurately determine the contact area and the air gap thickness between clothing and the human body in detail. These parameters were measured for a range of typical patterns of garments (tight- and loose fitting) covering either the upper or lower body and made of various types of fabrics (knitted and woven). The method consisted of imposing three-dimensional scans of the nude and dressed manikin and determining the distance between their surfaces by advanced three-dimensional scan post-processing. Due to this method the distribution of the air gap thickness and the contact area over body parts was obtained and this knowledge can be applied in models of heat and mass transfer in the clothing.

Evaporative cooling: effective latent heat of evaporation in relation to evaporation distance from the skin

Calculation of evaporative heat loss is essential to heat balance calculations. Despite recognition that the value for latent heat of evaporation, used in these calculations, may not always reflect the real cooling benefit to the body, only limited quantitative data on this is available, which has found little use in recent literature. In this experiment a thermal manikin, (MTNW, Seattle, WA) was used to determine the effective cooling power of moisture evaporation. The manikin measures both heat loss and mass loss independently, allowing a direct calculation of an effective latent heat of evaporation (λeff). The location of the evaporation was varied: from the skin or from the underwear or from the outerwear. Outerwear of different permeabilities was used, and different numbers of layers were used. Tests took place in 20°C, 0.5 m/s at different humidities and were performed both dry and with a wet layer, allowing the breakdown of heat loss in dry and evaporative components. For evaporation from the skin, λeff is close to the theoretical value (2,430 J/g) but starts to drop when more clothing is worn, e.g., by 11% for underwear and permeable coverall. When evaporation is from the underwear, λeff reduction is 28% wearing a permeable outer. When evaporation is from the outermost layer only, the reduction exceeds 62% (no base layer), increasing toward 80% with more layers between skin and wet outerwear. In semi- and impermeable outerwear, the added effect of condensation in the clothing opposes this effect. A general formula for the calculation of λeff was developed.

Temperature Analysis for the Prediction of Steam Formation and Transfer in Multilayer Thermal Protective Clothing at Low Level Thermal Radiation

It is important to understand the process of evaporation and steam transfer through firefighter protective clothing in order to be able to prevent steam burns. As humidity sensors are too slow to measure fast changes of humidity inside the clothing layers, temperature changes were used to analyze the evaporation of moisture. Temperature measurements turned out to be useful to predict the evaporation speed within the clothing layers, as temperatures remain constant during the evaporation. The measurements showed that the temperatures within the clothing layers containing a wet layer never rose higher than the temperatures within dry clothing. As soon as all moisture had evaporated, temperature increase followed exactly the curves of the measurements of dry samples.

Objective and subjective evaluation of the human thermal sensation of wet fabrics

The aim of the current study was to investigate if human subjects can distinguish five different drying states of three different fabrics. We defined five time-points (drying states) for each fabric with an in-house developed infrared test, as well as gravimetrically. This test records the surface temperature of wetted fabrics with an infrared camera during the drying process. In addition, the weight course during drying was recorded. The subjects evaluated fabrics with different wetting and wicking behaviours in a perception questionnaire. They answered questions about thermal sensation, thermal comfort, pain sensation and wetness perception. In conclusion, the human subjects could not differentiate the drying states of the fabrics as long as they contained water. Only the last drying state (100% dry, as measured with the infrared test) was distinguishable from the other four. However, the dry time-point of a fabric measured with the gravimetric method did not coincide with the drying time measured with the infrared test or perceived by human subjects.

Covalent immobilisation of VEGF on plasma-coated electrospun scaffolds for tissue engineering applications.

Recent findings in the field of biomaterials and tissue engineering provide evidence that surface immobilised growth factors display enhanced stability and induce prolonged function. Cell response can be regulated by material properties and at the site of interest. To this end, we developed scaffolds with covalently bound vascular endothelial growth factor (VEGF) and evaluated their mitogenic effect on endothelial cells in vitro. Nano- (254±133 nm) or micro-fibrous (4.0±0.4 μm) poly(ɛ-caprolactone) (PCL) non-wovens were produced by electrospinning and coated in a radio frequency (RF) plasma process to induce an oxygen functional hydrocarbon layer. Implemented carboxylic acid groups were converted into amine-reactive esters and covalently coupled to VEGF by forming stable amide bonds (standard EDC/NHS chemistry). Substrates were analysed by X-ray photoelectron spectroscopy (XPS), enzyme-linked immuno-assays (ELISA) and immunohistochemistry (anti-VEGF antibody and VEGF-R2 binding). Depending on the reaction conditions, immobilised VEGF was present at 127±47 ng to 941±199 ng per substrate (6mm diameter; concentrations of 4.5 ng mm(-2) or 33.3 ng mm(-2), respectively). Immunohistochemistry provided evidence for biological integrity of immobilised VEGF. Endothelial cell number of primary endothelial cells or immortalised endothelial cells were significantly enhanced on VEGF-functionalised scaffolds compared to native PCL scaffolds. This indicates a sustained activity of immobilised VEGF over a culture period of nine days. We present a versatile method for the fabrication of growth factor-loaded scaffolds at specific concentrations.

How to measure thermal effects of personal cooling systems: human, thermal manikin and human simulator study

Thermal effects, such as cooling power and thermophysiological responses initiated upon application of a personal cooling system, can be assessed with (i) humans, (ii) a thermal manikin and (iii) a thermophysiological human simulator. In order to compare these methods, a cooling shirt (mild cooling) and an ice vest (strong cooling) were measured using human participants and a thermal manikin. Under all conditions, cooling was provided for 45 min, while resting at a room temperature of 24.6-25.0 degrees C and a relative humidity of 22-24%. Subsequently, the thermophysiological human simulator was used under the same conditions to provide data on thermophysiological responses such as skin and rectal temperatures. The cooling power determined using the thermal manikin was 2 times higher for the cooling shirt and 1.5 times higher for the ice vest compared to the cooling power determined using human participants. For the thermophysiological human simulator, the cooling power of the cooling shirt was similar to that obtained using human participants. However, it was 2 times lower for the ice vest when using the thermophysiological human simulator. The thermophysiological human simulator is shown to be a useful tool to predict thermophysiological responses, especially upon application of mild cooling intensity. However, the thermophysiological human simulator needs to be further improved for strong cooling intensities under heterogeneous conditions.

An Optical Fibre-Based Sensor for Respiratory Monitoring

In this paper, a textile-based respiratory sensing system is presented. Highly flexible polymeric optical fibres (POFs) that react to applied pressure were integrated into a carrier fabric to form a wearable sensing system. After the evaluation of different optical fibres, different setups were compared. To demonstrate the feasibility of such a wearable sensor, the setup featuring the best performance was placed on the human torso, and thus it was possible to measure the respiratory rate. Furthermore, we show that such a wearable system enables to keep track of the way of breathing (diaphragmatic, upper costal and mixed) when the sensor is placed at different positions of the torso. A comparison of the results with the output of some commercial respiratory measurements devices confirmed the utility of such a monitoring device.

Body‐Monitoring and Health Supervision by Means of Optical Fiber‐Based Sensing Systems in Medical Textiles

Long-term monitoring with optical fibers has moved into the focus of attention due to the applicability for medical measurements. Within this Review, setups of flexible, unobtrusive body-monitoring systems based on optical fibers and the respective measured vital parameters are in focus. Optical principles are discussed as well as the interaction of light with tissue. Optical fiber-based sensors that are already used in first trials are primarily selected for the section on possible applications. These medical textiles include the supervision of respiration, cardiac output, blood pressure, blood flow and its saturation with hemoglobin as well as oxygen, pressure, shear stress, mobility, gait, temperature, and electrolyte balance. The implementation of these sensor concepts prompts the development of wearable smart textiles. Thus, current sensing techniques and possibilities within photonic textiles are reviewed leading to multiparameter designs. Evaluation of these designs should show the great potential of optical fibers for the introduction into textiles especially due to the benefit of immunity to electromagnetic radiation. Still, further improvement of the signal-to-noise ratio is often necessary to develop a commercial monitoring system.