Sorption-desorption Test Research Articles

Electrospun of functionalized mesoporous UiO-66 as the selective coating of solid phase microextraction Arrow for the determination of nine alkylphenols.

A solid-phase microextraction (SPME) Arrow and high-performance liquid chromatography-UV detector (HPLC-UV, detection at 225nm) based method was developed for the selective determination of nine alkylphenols (APs) in milk. The functionalized mesoporous UiO-66 (4-meso-UiO-66) was utilized as the new coating material, which was synthesized by post-modification of pore-expanded UiO-66-NH2 by an esterification reaction with 4-pentylbenzoic acid. It was fully characterized by X-ray photoelectron spectroscopy (XPS), fourier transformation infrared spectrometry, nitrogen sorption-desorption test, scanning electron microscopy, transmission electron microscopy, and X-ray diffractometer. The characterization results showed the ester groups and benzene rings were introduced into the 4-meso-UiO-66, and the mesoporous structure was predominant in the 4-meso-UiO-66. The extraction mechanism of 4-meso-UiO-66 to APs is the synergistic effect of Zr-O electrostatic interaction and the size exclusion effect resulting from XPS, selectivity test, and nitrogen sorption-desorption test. The electrospinning technique was utilized to fabricate the 4-meso-UiO-66 coated SPME Arrow and polyacrylonitrile (PAN) was used as the adhesive. The mass rate of 4-meso-UiO-66 to PAN and the electrospinning time were evaluated. The extraction and desorption parameters were also studied. The linear range of this method was 0.2-1000μg L-1 with a coefficient of determination greater than 0.9989 under the optimal conditions. The detection limits were 0.05-1μg L-1, the inter-day and intra-day precision (RSD) were 2.8-11.5%, and the recovery was 83.6%-112%. The reusability study showed that the extraction performance of this new SPME Arrow could be maintained after 80 adsorption-desorption cycles. This method showed excellent applicability for the selective determination of APs in milk.

How do the skin barrier and microbiome adapt to the extra-uterine environment after birth? Implications for the clinical practice.

The multiple protective functions of the skin derive from the interactions between epithelial skin and immune cells as well as the commensal microbiota. Developed in the last trimester of intra-uterine life, the skin barrier adapts dynamically after birth. Specific differences in the structure and physiology have been disclosed between infant and adult skin. The stratum corneum of infants is thinner and structured by thicker corneocytes with a more anisotropic surface in comparison to adult skin. Lower levels of the natural moisturizing factor and its constituents, together with the increased protease activity in the epidermis result in dry baby skin and ongoing adaptation of the desquamation to the extra-uterine environment. Infant epidermis is characterized by an accelerated proliferation rate and clinically competent permeability barrier in term neonates, despite the higher baseline values of transepidermal water loss in infants. The skin surface of newborns is less acidic, which could increase susceptibility to diaper and atopic dermatitis. Immediately after birth, skin is colonized by commensal bacteria-a process dependent on the mode of delivery and of major importance for the maturation of the immune system. Skin bacterial diversity and dysbiosis have been related to different pathology such as atopic and seborrheic dermatitis. This paper focuses on the ongoing structural, functional and biochemical adaptation of the human skin barrier after birth. We discuss the interactions on the 'skin barrier/ microbiota/ immune system' axis and their role in the development of competent functional integrity of the epidermal barrier.

Measurement of human skin moisture via high-frequency spectroscopy.

High-frequency spectroscopy (HFS) is an analytical method that is sensitive to slight changes in the dielectric properties of materials. Since water has high permittivity, HFS can be used to detect changes in water content in materials. In this study, we employed HFS to measure human skin moisture during a water sorption-desorption test. Skin without any treatment showed a resonance peak at approximately 1150MHz. Furthermore, the peak shifted to lower frequency immediately after the application of water to the skin and gradually returned to its original frequency as time progressed. The resonance frequency obtained via least-squares fitting showed that the applied water remained in the skin after 240s from the beginning of the measurement. These results illustrated that HFS measurements can monitor the progression of decreasing moisture content in human skin during a water sorption-desorption test.

Novel low cost Li4SiO4-based sorbent with naturally occurring wollastonite as Si-source for cyclic CO2 capture

Li4SiO4-based ceramic has been considered as one of the most promising candidates for high-temperature CO2 capture owing to its relatively high sorption capacity and desirable cyclic stability. Si-source is one of the most important factors affecting the cost as well as the CO2 capture performance of Li4SiO4 sorbent. In this work, naturally occurring wollastonite was firstly employed as the Si-source to produce Li4SiO4-based sorbent. The as-prepared sorbent was primarily composed of Li4SiO4 and CaO. It is believed that the enhanced CO2 capture performance was attributed to the effect of CaO as well as the occurrence of Li-Ca interactions (Li4SiO4+CaO+CO2↔Li2CaSiO4+Li2CO3), which were experimentally verified via in situ XRD test. As a result, the sorbent possesses a relative high capacity of ∼0.18 g/g at the initial cycles during the cyclic sorption-desorption test. However, its capacity gradually declined owing to the separation and formation of sintered CaO external shell. From the cost analysis, the as-prepared CaO-Li4SiO4 sorbent can effectively decrease the total raw material cost by reducing Li-demand. To sum up, the good comprehensive performance and relative low cost of as-prepared CaO-Li4SiO4 sorbent make it promising for its practical applications in the future.

Formulasi Sediaan Krim Pelembab Ekstrak Air Buah Pepaya (Carica Papaya L.)

Sucrose in papaya fruit was used as a moisturizer because it has worked as humectants, which reduce water evaporation on the surface of the skin. The purpose of this research was to determine the effect of the increasing concentrations of water extract of papaya fruit to evaluate its physical quality, effectiveness, safety, acceptability, and stability of the moisturizing cream water extract of papaya (Carica papaya L.). In this study, it used 3 formulas containing the extract of papaya fruit at concentration of 10% (formula 1), 20% (formula 2), 30% (formula 3), also blank containing base only, and base without extract and without moisturizing agent. The physical quality tests include organoleptic, pH, viscosity test, emulsion type test, dispersive power test, homogeneity, water washed power and adhesion test. The effectiveness of mouisturizer effect on the skin was tested with in vitro method: Sorption Desorption Test. Savety testing include irritation test and acceptability test. The data was analyzed using oneway ANOVA then continued with post hoc Tukey. The results showed that the increasing concentrations of the extract provides significant effect on efectivity, wherein the greater the concentration of water extract of papaya fruit (Carica papaya L.) were added, then the higher the ability to moisturize the skin and produce of moisturizer cream with pH test 6.04, viscosity 159710 cps, dispersive power 3.63 cm, water washed power 13.48 ml, adhesion 6005 second, and moisturizer cream stable during storage. The best formula is the formula 3 with a concentration extract of 30%.

Parametric study and effect of calcination and carbonation conditions on the CO2 capture performance of lithium orthosilicate sorbent

The world is currently facing the challenges of global warming and climate change. Numerous efforts have been taken to mitigate CO2 emission, among which is the use of solid sorbents for CO2 capture. In this work, Li4SiO4 was synthesised via a sol–gel method using lithium nitrate (LiNO3) and tetraethylorthosilicate (SiC8H20O4) as precursors. A parametric study of Li:Si molar ratio (1-5), calcination temperature (600–800 °C) and calcination time (1–8 h) were conducted during sorbent synthesis. Calcination temperature (700–800 °C) and carbonation temperature (500–700 °C) during CO2 sorption activity were also varied to confirm the optimum operating temperature. Sorbent with the highest CO2 sorption capacity was finally introduced to several cyclic tests to study the durability of the sorbent through 10 cycles of CO2 sorption–desorption test. The results showed that the calcination temperature of 800 °C and carbonation temperature of 700 °C were the best operating temperatures, with CO2 sorption capacity of 7.95 mmol CO2∙(g sorbent)− 1 (93% of the theoretical yield). Throughout the ten cyclic processes, CO2 sorption capacity of the sorbent had dropped approximately 16.2% from the first to the tenth cycle, which was a reasonable decline. Thus, it was concluded that Li4SiO4 is a potential CO2 solid sorbent for high temperature CO2 capture activity.

Sorption-desorption test for functional assessment of skin treated with a lipid system that mimics epidermal lamellar bodies.

Many skin diseases are associated with either increases or decreases in lamellar body secretion, or dysfunctional lamellar bodies. Consequently, diseased skin is characterized by reduced barrier function and altered lipid composition and organization. Human skin is commonly evaluated in vivo with non-invasive biophysical techniques. The dynamic functions of the skin are evaluated with repeat measurements such as the sorption-desorption test (SDT). The aim of this study was to evaluate in vivo skin hydration-dehydration kinetics after treatment with a lipid system that mimics the morphology, structure and composition of lamellar bodies in both healthy and irritated human skin. A patch with an aqueous solution of 2% sodium lauryl sulfate (SLS) was used to irritate the skin of the volunteers. The SDT was performed with the CM 820 corneometer. After treatment with this system, both healthy and SLS-irritated skin increased their ability to retain water and to release water slowly during the desorption phase. Treatment with this system seems to reinforce the barrier function in both healthy and SLS-irritated human skin. Therefore, the present study provides evidence that this system could be of interest for developing future treatments for protecting and repairing the skin.

Sunscreen formulations may serve as additional water barrier on skin surface: a clinical assessment.

Extended water exposure can cause stratum corneum swelling and a more porous skin barrier. People often wear water-resistant sunscreen formulations during extended period of water activities in the summer to protect skin from harmful UV rays. We wanted to evaluate whether sunscreen formulations can also serve as additional water barriers to help mitigate the disruption in stratum corneum caused by constant exposure to water. We conducted trans-epidermal water loss (TEWL) measurement in a controlled water patch (including salt and chlorine water) model and then applied this relevant model to study the effects of pre-treatments of sunscreen sprays and stick. We also conducted water sorption-desorption test invivo with and without sunscreens. Finally, we studied the effect of constant water exposure combined with a known irritant, sodium lauryl sulphate (SLS), in a randomized clinical trial. We found that application of sunscreen formulations help mitigate water-induced barrier disruption by repelling water at skin surface. Pre-treatment of sunscreen also statistically decreased the irritation in an acute patch test model. Hydrophobic sunscreen formulations can help protect skin from extended water exposure by serving as additional water barriers.

DIS에 의한 Polyethylene Glycol 함침 알로에 베라 겔의 보습 및 경피흡수 특성

This study was carried out to investigate the in vitro and in vivo moisturizing properties and percutaneous absorption of PEG-impregnated Aloe vera gel. The PEG-i-Aloe gel was obtained from dewatering and impregnation by soaking (DIS) of Aloe vera leaf slice. The moisturizing property of the obtained sample was evaluated by moisture determination using gravimetric method in desiccator under different RH% and by water sorption-desorption test on human skin. The transdermal penetration characteristics of PEG-i-Aloe gel was investigated by Franz diffusion cell in vitro transdermal absorption method. PEG-i-Aloe gel had high moisture retention ability and could significantly lead the enhancing skin hydration status as well as reducing the skin water loss due to the film formation as a skin barrier. The skin penetration rate of PEGi- Aloe gel at steady state was 9.76 <TEX>${\mu}g/(h{\cdot}cm^2)$</TEX> and the quantity of the transdermal absorption was 144 <TEX>${\mu}g/cm^2$</TEX> in 9 hr. The penetration mechanism was well fitted with Higuchi model (<TEX>$R^2$</TEX> = 0.974-0.994). The results show that PEG-i-Aloe gel has the significant moisturizing effect and strong penetration of the animal skin. It could be used as the moisturizing additive in cosmetic skin products.

Cosmetic effectiveness of topically applied hydrolysed keratin peptides and lipids derived from wool

Skin moisturisation, elasticity, feel and appearance can all be improved through the topical application of protein hydrolysates. Recent studies suggest that supplementing intercellular lipids of the stratum corneum can enhance the functioning of the skin. In this study, a hydrolysed keratin peptide (molecular weight <1000 Da) was prepared from wool and tested on skin in two different formulations: an aqueous solution and an internal wool lipids (IWL) liposome suspension. In vivo long-term studies were performed to evaluate the water barrier function of the skin after topical application of different formulations. During the treatment period, hydration and elasticity were determined. A sorption-desorption test was also performed to assess the hygroscopic properties and water-holding capacity of the different treated skin sites. Significant differences were found between the control and treated sites, with the treated areas showing an increase in hydration and elasticity as a result of keratin peptide application. Measurements also indicated that the keratin formulations reinforce the skin barrier integrity, improving its water-holding capacity. A combination of the keratin peptide with the IWL showed beneficial effects, indicating that this combination is suitable for designing new cosmetics products.

Skin conductance; validation of Skicon‐200EX® compared to the original model, Skicon‐100®

Measurement of skin surface and stratum corneum (SC) hydration during experimental trials needs devices with acceptable precision under conditions ranging from decreased, and normal to high hydration. The aim of this study was to validate the recent model of a commonly used device for measurement of skin conductance (Skicon-200EX) vs. the original model (Skicon-100) introduced 20 years ago. Twenty-six healthy Danish volunteers (16 women and 10 men, aged between 22 and 67, with a median age of 42 years) were studied using the Skicon-100 and the Skicon-200EX mounted with three different probes. Normal skin of the cheek, forearm, antecubital fossa, palm, lower leg, and popliteal fossa was studied. The sorption-desorption test was performed on the forearm. The two instruments displayed closely correlated conductance levels. However, the Skicon-200EX displayed systematically 1.6-fold higher values than the Skicon-100. Different body sites showed different levels depending on anatomical regions. The three probes measured systematically different levels with the original probe measuring lower values. The sorption-desorption test showed high skin conductance values which peaked a few minutes after hydration, in accordance with the original experiments of Tagami. The two Skicon instruments evaluated in this study correlated well, however, they displayed different levels depending on instrument main body and probes. Overall, the Skicon-200EX gave 1.6-fold higher value, and this instrument might be more sensitive than the original device, Skicon-100. In scientific reports, the type of instrument main body as well as probe shall be clearly specified.

Assessment of effects of an additional dietary natural mineral water uptake on skin hydration in healthy subjects by dynamic barrier function measurements and clinic scoring

The skin protects the body's organs and tissues from damage and physical, chemical and bacteriological injuries. It also prevents the transcutaneous loss of water. The present study was conducted to assess the effects of additional dietary natural mineral water uptake on skin hydration and cutaneous well-being in subjects with dry skin. Eighty subjects (44 women and 36 males, mean age 56+/-5.6 years) were included in the study, randomised per forearm and stratified by gender. Skin surface hydration, transepidermal water loss (TEWL), sorption-desorption test, skin colour, thickness and micro-relief were evaluated on the forearms. Clinical scoring of dryness, roughness and elasticity was performed by a dermatologist. An improvement of skin hydration was observed after additional water uptake, statistically modifying the hydration level as well as TEWL, the water-binding capacity of the uppermost layers of the stratum corneum. Improvements of softness, smoothness and skin-moisturising effect were perceived by healthy subjects, and skin micro-relief was improved. We suggest that natural mineral water supplementation may be used in order to improve the hydration of skin dryness as a complementary cosmetic approach.

Comparison of the Effects of Daily Applications between Topical Corticosteroid and Tacrolimus Ointments on Normal Skin: Evaluation with Noninvasive Methods

Objective: To evaluate the skin changes of the neck of normal individuals after repeated applications of moderate-strength corticosteroid or tracrolimus ointment for 3 weeks by use of noninvasive biophysical measurements. Methods: A 0.12% betamethasone-17-valerate ointment or a 0.1% tacrolimus ointment was applied to the right side of the neck of 8 adult volunteers twice daily for 3 weeks together with control petrolatum applied to the left side of the neck for comparison. Biophysical skin measurements were performed on the neck skin before, 1 and 3 weeks after the start of the treatment and 1 week after the cessation of the treatment. Results: A decrease in hygroscopicity and water-holding capacity of the stratum corneum (SC) when evaluated with the in vivo water sorption-desorption test was found on the corticosteroid-ointment-treated side after 3 weeks of the treatment as compared with the petrolatum-treated side. The erythematous reaction to a topically applied 0.1% aqueous solution of methyl nicotinate, a vasodilator, appeared more slowly on the corticosteroid-ointment-treated skin than on the control skin. No such changes were observed on the skin treated with 0.1% tacrolimus ointment. Conclusion: Tacrolimus appears to cause few if any functional changes in the SC of healthy human skin because of its poor permeability into skin with an intact barrier function.

Water sorption-desorption test and moisture accumulation test for functional assessment of atopic skin in children.

Sorption-desorption and moisture accumulation tests are simple and quick methods for the in vivo functional analysis of stratum corneum hydration kinetics. The aim of this study was to evaluate the hydration dynamics of the uninvolved and affected skin of children with atopic dermatitis and to compare them with the skin of healthy children. The study investigated 45 children. The dynamic tests were performed using the corneometer CM820. Numerical parameters were calculated. With the sorption-desorption test, eczematous skin showed lower water accumulation during the sorption phase, whereas water was released more slowly during the desorption phase. With the moisture accumulation test, increases in water accumulation velocity and in water accumulation were observed in atopic children. Dynamic tests showed that the stratum corneum of unaffected atopic skin was less hydrated but more easily hydratable than normal skin. Conversely, despite a lower absorption capability, eczematous skin showed a greater avidity to retain water. New functional parameters (water-sorption capacity and accumulated water decay) are proposed to describe more precisely the hydration kinetics of eczematous skin.

Assessment of the Water Content of the Stratum corneum Using a Sorption-Desorption Test

Background/Aim: Various instruments based on electrical properties of the skin are currently used to assess the stratum corneum (SC) hydration state or water holding capacity. However, no direct relation with the quantity of water measured is provided. The objective of the present study was to calibrate the Corneometer, a device displaying electrical-capacitance-related values (which reflect the skin hydration state), and the amount and behaviour of the water taken up by the outer part of the SC during a sorption-desorption test. Methods: The experiment was performed on the ventral forearms of 20 healthy volunteers after a rest in an environmentally controlled room. Corneometer and transepidermal water loss (TEWL) values were measured at intervals over the desorption process. The areas under the TEWL-versus-time curve provided the absolute amounts of residual sorbed water. Results: The decrease kinetics of both signals after subtraction of prehydration values were very similar and bi-exponential, both showing a rapid, then a slower phase. The absolute amount of water taken up by the SC (hygroscopicity) and the two desorption rates were obtained. The Corneometer values were mono-exponentially related to the amount of water remaining within the SC. This allowed the in vivo calibration of the Corneometer in terms of absolute amount of water over the desorption range. Conclusion: The method may be used to calibrate in vivo other electrical devices aimed at assessing SC hydration during a sorption-desorption test. It may also provide new ways to measure SC water uptake and water holding capacity following application of products.

Comparative study of five instruments measuring stratum corneum hydration (Corneometer CM 820 and CM 825, Skicon 200, Nova DPM 9003, DermaLab). Part II. In vivo

Background/aims: The hydration state of stratum corneum can be measured with different instruments. In the present study, five instruments were compared under different experimental in vivo conditions: Corneometer CM 820 and CM 825 (both capacitance based), Skicon 200 (conductance), Nova DPM (impedance based capacitance) and DermaLab (capacitance).Methods: Seven anatomical sites were tested, a sorption‐de‐sorption test (SDT) and a moisture accumulation test (MAT) were performed. Different hydration states were created on the volar forearms by occluded application of an oil‐in‐water (o/w) emulsion, glycerol and urea containing oil‐in‐water (o/w) emulsion, an untreated control site and a site after lipid extraction with acetone. Measurements were performed 15 min after removal of occlusion.Results: The coefficient of variation for CM 820 ranged between 9.3% and 23.7%; for CM 825 between 14.9% and 36.8%; for Skicon 200 between 53.0% and 167.3%; for Nova DPM between 36.4% and 95.8%; for DermaLab between 23.6% and 45.6%. All devices showed a highly significant correlation (P&lt;0.0001) with a high Spearman coefficient r ranging between 0.7928 and 0.9358.Conclusions: CM 820 and CM 825 seem to differentiate more precisely than Nova DPM, Skicon 200 and DermaLab in dry conditions according to previous findings, i.e., that conductance measurements might be more sensitive for hydrated skin and capacitance measurements might be more sensitive for dry skin conditions. The CM 825, the Skicon 200 and the Nova DPM are suitable for dynamic measurements of hydration parameters of the stratum corneum.

Effects of Prolonged Occlusion on Stratum corneum Barrier Function and Water Holding Capacity1

Purpose of the Study: We aimed to evaluate whether prolonged occlusion can induce stratum corneum barrier damage, alterations in stratum corneum hydration or water-holding capacity (WHC) lasting longer than the occlusion time. Materials and Methods: 12 subjects were occluded on the forearm for 24, 48, 72 and 96 h. Two hours after occlusion removal, transepidermal water loss (TEWL) and skin hydration were measured and a sorption-desorption test performed. Results: TEWL showed an increase reaching a plateau on day 2. Hydration and WHC did not show significant changes. Hygroscopicity showed the highest level on day 1, decreasing during the following days. A highly significant correlation between capacitance values and the WHC could be detected (p < 0.0001, r = 0.8206). No correlation could be detected between hygroscopicity and TEWL. Conclusions: Prolonged occlusion induces barrier damage without skin dryness. Occlusion also induces an increased hygroscopicity. A correlation between these two findings could not be proven.

Effects of systemic treatment with statins on skin barrier function and stratum corneum water-holding capacity.

Topical application of inhibitors of HMGCoA reductase, the rate-limiting enzyme of cholesterol synthesis, has been shown to induce impairment of barrier function. Assessing whether oral administration of statins used for reducing blood levels of cholesterol induces functional changes in stratum corneum barrier. 69 subjects of both sexes under-going treatment for hypercholesterolemia (mean age 48 +/- 11 years) entered the study; 43 had been treated with simvastatin and 11 with pravastatin for 6 months; 15 only on dietary regimen served as controls. Efficiency of stratum corneum water barrier was evaluated by transepidermal water loss (TEWL) measurement using an evaporimeter; water-holding capacity of the stratum corneum was assessed by the sorption-desorption test measured by capacitance. Statistical analysis was performed using ANOVA. No differences were found between the groups (simvastatin, pravastatin, diet) concerning both basal TEWL and the dynamic of water binding in the stratum corneum. Prolonged treatment with cholesterol-lowering drugs based on inhibition of HMGCoA reductase does not alter the permeability barrier of the skin.

Dry skin (xerosis) in patients undergoing maintenance haemodialysis: the role of decreased sweating of the eccrine sweat gland

The aetiology and the pathophysiological mechanisms underlying the development of dry skin in uraemia are still unclear, but the hydration status of stratum corneum clearly influences the appearance of skin. The xerotic skin texture is often referred to as 'dry skin' and has been suggested as a cause of uraemic pruritus. To understand the aetiology of dry skin in uraemia we measured the status of skin surface hydration of uraemic patients with the corneometer and skin surface hydrometer, the functional capacity and the urea concentration of stratum corneum and the response of eccrine sweat gland to sudorific agent (0.05% pilocarpine HCL) in 18 age-matched haemodialysis patients and 10 healthy volunteers. We also performed the water sorption-desorption test to uraemic and control subjects after application of urea in various concentrations. Uraemic patient's skin showed decreased water content compared to control subjects. However, we found no correlation between dry skin and pruritus. Although the urea concentration of the horny layer in uraemic patients was elevated compared to control subjects (28.2 microgram/cm2 vs 5.04 micrograms/cm2, P < 0.05), its moisturizing effect to relieve pruritus is questionable because its artificial application revealed no improvement of the functional capacity of horny layer in concentration 5 times higher than the physiological concentration. Uraemic patients showed decreased sweating response to sudorific agent. In conclusion, the functional abnormalities of eccrine sweat glands may be account for dry skin in uraemic patients at least in part, but there is no correlation between xerosis and pruritus.

Stratum corneum dynamic function measurements after moisturizer or irritant application.

Two simple tests were conducted which allowed the quantification of parameters that characterize the stratum corneum (SC) dynamic functions in vivo under physiological conditions after moisturizer applications for 1 h and after irritation with different concentrations of sodium lauryl sulphate (SLS; 0.5-4%) applied under occlusion for 15 min or 24 h. Both tests, the sorption-desorption test (SDT) and the moisture accumulation test (MAT), were performed with a Nova Dermal Phase Meter 9003. The following parameters were quantified: prehydration state (SDT, MAT), hygroscopicity, water-holding capacity (SDT), water accumulation velocity and water accumulation (MAT). These procedures allowed the demonstration of the water-holding effect of urea contained in moisturizers. Differences between the long and the short application time of SLS were characterized by differences in SC dynamic functions while the hydration state was not changed. An effect on transepidermal water loss (TEWL) was noted only after the long application time, although the MAT clearly showed dynamic parameters to be changed after 15 min of treatment. These tests were simple in practice and allowed the demonstration of functional modifications of the SC while other parameters remained unchanged. They gave insight into possible action mechanisms of urea and SLS in the SC.