Luís Monteiro Rodrigues

EEMCO Guidance to the in vivo Assessment of Tensile Functional Properties of the Skin

Tensile functions of the skin and subcutaneous tissues contribute to the appearance of the aged and photodamaged skin and to the effects of various other pathophysiological processes. The assessment of tensile functions of skin can be performed by distinct approaches mainly characterized by the orientation and magnitude of the imposed stress and strain over time. Testing methods are basically grouped into five major classes which include tensile, torsional, indentation, impact and elevation modes. Computed tensile variables are reproducible when the experimental procedure occurs under fully controlled conditions. Consistent and relevant information is yielded when the limitations and pitfalls typical for each test method are taken into consideration.

Is there any barrier impairment in sensitive skin?: a quantitative analysis of sensitive skin by mathematical modeling of transepidermal water loss desorption curves

Background/purpose: Sensitive skin is a vague, subjective and difficult to characterize affliction. It affects a large part of the population and is accompanied with great interest by the cosmetic industry. Some studies have suggested that sensitive skin is the result of impaired barrier function, which leads to the exposure of immune system cells and sensitive nerves, resulting in marked cutaneous responses to otherwise harmless stimuli. This study aimed to investigate the cutaneous barrier integrity of individuals with sensitive skin by a novel approach: a plastic occlusion stress test followed by measurement of transepidermal water loss (TEWL) desorption curves.

Cutaneous biocompatible rutin-loaded gelatin-based nanoparticles increase the SPF of the association of UVA and UVB filters

The encapsulation of natural ingredients, such as rutin, can offer improvements in sun protection effectiveness. This strategy can provide enhanced flavonoid content and produces an improved bioactive compound with new physical and functional characteristics. As an alternative to common synthetic-based sunscreens, rutin-entrapped gelatin nanoparticles (GNPs) were designed and associated with ethylhexyl dimethyl PABA (EHDP), ethylhexyl methoxycinnamate (EHMC) and methoxydibenzoylmethane (BMDBM) in sunscreen formulations. The purpose of this study was to develop rutin-loaded gelatin nanoparticles and characterize their physicochemical, thermal, functional and safety properties. Rutin-loaded gelatin nanoparticles increased antioxidant activity by 74% relative to free-rutin (FR) solution. Also, this new ingredient upgraded the Sun Protection Factor (SPF) by 48%, indicating its potential as a raw material for bioactive sunscreens. The safety profile indicated that GNPs and glutaraldehyde (GTA) decreased HaCaT cell viability in a concentration/time-dependent manner. However, both blank nanoparticles (B-NC) and rutin-loaded nanoparticles (R-NC) had good performance on skin compatibility tests. These results functionally characterized rutin-loaded nanoparticles as a safe SPF enhancer in sunscreens, especially in association with UV filters.

Modeling TEWL-desorption curves: a new practical approach for the quantitative in vivo assessment of skin barrier

Abstract:  The objective of the present study was to test the discriminative capacity of the mathematical modeling of the transepidermal water loss (TEWL) curves that result from a plastic occlusion stress test (POST) to variations in the skin barrier – insults inflicted to the skin or differences in two distinct anatomical regions. This study was exclusively performed in the arm. On the first part of the work, three different insults to the skin barrier were assessed: tape stripping, lipid extraction with ether : acetone, and skin‐surface biopsy. Anatomical differences were studied in the mid‐forearm and in the wrist. All sites were submitted to a POST, after which the desorption curves were recorded. The mathematical model was adjusted to the TEWL data points. Results indicate differences in the parameters obtained in the control and treated sites, which suggests differences in the water dynamics after the damage was inflicted and shows that the method is valid for the objectives proposed. There were also significant differences in the parameters obtained in the wrist and in the volar forearm, which indicates that the method is also sensitive to variations in skin histology and anatomy.

Exploring the influence of skin perfusion on transepidermal water loss

Background: Eventual relationships between the vascular function and transepidermal water loss (TEWL), in vivo, have not been entirely explored. By promoting local perfusion alterations through a well‐known challenge test, the ‘tourniquet‐cuff occlusion’ manoeuvre, the present study searches for other dynamical factors influencing the cutaneous barrier, further exploring the applicability of these flow‐related variables in dermatological research.

Basal transepidermal water loss: right/left forearm difference and motoric dominance

Background/alms: Evaporimetry and transepidermal water loss (TEWL) evaluations are among the most important means of approaching basic cutaneous physiology in terms of its epidermal barrier function. However, physiological skin complexity, together with the loose specifications currently available for analytical purposes, justify the need for further investigating and identifying eventual covariates and limiting factors with respect to both the epidermal barrier function issue and evaporimetry itself.

Transcutaneous flow related variables measured in vivo: the effects of gender

BackgoundThe identification of potential sources of error is a crucial step for any new assessment technique. This is the case for transcutaneous variables, such as flow and arterial gases, which have been applied as functional indicators of various aspects of human health. Regarding gender, a particular subject-related determinant, it is often claimed that women present higher transcutaneous oxygen pressure (tcpO2) values than men. However, the statistical significance of this finding is still uncertain.MethodsThe haemodynamical-vascular response to a local reactive hyperaemia procedure (the tourniquet cuff manoeuvre) was studied in two previously selected group of volunteers (n = 16; 8 women and 8 men). The effect of gender was assessed under standardised experimental conditions, using the transcutaneous flow-related variables tcpO2-tcpCO2 and Laser-doppler Flowmetry (LDF).ResultsRegarding tcpO2, statistically significant differences between genders were not found, although higher values were consistently found for the gases in the female group. Regarding LDF, high statistically significant differences (p < 0.005) were found, with the mens group presenting the highest values and variability. Other derived parameters used to characterise the vascular response following the cuff-deflation (t-peak) were similar in both groups.ConclusionsThe relative influence of gender was not clearly demonstrated using these experimental conditions. However the gender-related LDF differences suggest that further investigation should be done on this issue. Perhaps in the presence of certain pathological disparities involving peripheral vascular regulation, other relationships may be found between these variables.

Transepidermal water loss kinetic modeling approach for the parameterization of skin water dynamics

Background/aims: The evaluation of transepidermal water loss (TEWL) is one of the methods most frequently used in studies involving skin water dynamics. However, TEWL does not provide a direct measurement of epidermal barrier function, being rather a surrogate effect of it. In particular, when external stimuli change cutaneous water balance, these stimuli must be taken into account in order to achieve a rigorous interpretation of the results. Since TEWL is primarily attributed to the water flux from the deepest layers of the skin, through the epidermis, and towards the external environment, this whole process is reasonably compliant with Ficks first law of diffusion. Within this perspective, the aim of this work was to develop a two compartment mathematical model capable of quantitatively describing cutaneous water mass balance over time and thus to provide practical and objective comparable parameters that are particularly useful for studies critically depending on a precise evaluation of TEWL.

Comparative assessment of the performance of two generations of Tewameter: TM210 and TM300.

The measurement of transepidermal water loss (TEWL) has been established as one of the main parameters in the assessment of skin barrier function. One of the most widely employed devices to measure TEWL is the Tewameter®. Courage and Khazaka launched the TM300 in 2003 and successfully eliminated some of the limitations of the previous model. In the more recent device, the sensors inside the probe head can be pre‐heated to a temperature close to that of the skin, which considerably decreases sampling time. Additionally, the new technology of the probe does not require frequent and time‐consuming recalibration with different solutions. The main objective of this work was to perform a comparative assessment of the performance of the two different Tewameter® models. Fifteen volunteers were used in this study, which was conducted in the mid‐portion of the volar forearm. The standard measurements assessed differences in the basal values, time necessary for a stable value and coefficient of variability under normal and extreme conditions. The dynamic measurements performed were based on a plastic occlusion stress test (POST), involving the application of an occlusive patch for 24 h, after which the TEWL desorption curves were recorded. A mathematical model was adjusted to the data points using a specially modified simplex routine. Calculated parameters considered relevant to the study were t1/2evap (evaporation half‐life) and dynamic water mass (DWM). Results show slight differences in the performance the two models, which are nevertheless statistically significant. The TM300 seems to be more sensitive to differences in TEWL and presents a much quicker measurement capacity. These results confirm a marked improvement in the more recent Tewameter® model, when compared with its predecessor. The main conclusion of this work is that caution is advised when comparing results obtained with the two different models and that studies should be carried out entirely with the same device.

Assessment of moisturizers and barrier function restoration using dynamic methods

Background/purpose: Dynamic methods, such as the mathematical modelling of the transepidermal water loss curves that result from a plastic occlusion stress test (POST), enable the complete characterization of the dynamic water balance established between the deep and the superficial skin structures. Previous studies have indicated that this methodology was able to detect impaired barrier function and differentiate normal and dry skin. The objective of the present study is to apply the discriminative capacity of the model to the efficacy testing of moisturizing products.