Objective It is conventionally understood that occlusive effects are the retention of excessive water in the stratum corneum (SC), the increase of SC thickness (swelling) and a decrease of the transepidermal water loss. However, the influence of occlusion on water binding properties in the SC is unknown. Methods The action of plant‐derived jojoba and almond oils, as well as mineral‐derived paraffin oil and petrolatum topically applied on human skin, is investigated in vivo using confocal Raman microspectroscopy. To understand the oils’ influence on the SC on the molecular level, the depth‐dependent hydrogen bonding states of water in the SC and their relationship to the conformation of keratin, concentration of natural moisturizing factor (NMF) molecules and lipid organization were investigated. Results A significant SC swelling was observed only in petrolatum‐treated skin. The water concentration was increased in oil‐treated skin in the intermediate SC region (40–70% SC depth). Meanwhile, the amount of free, weakly and tightly bound water increased, and strongly bound water decreased in the uppermost SC region (0–30% SC depth). The NMF concentration of oil‐treated skin was significantly lower at 50–70% SC depth. The lateral organization of lipids in oil‐treated skin was lower at 0–30% SC depth. The secondary structure of keratin was changed towards an increase of β‐sheet content in mineral‐derived oil‐treated skin and changed towards an increase of α‐helix content in plant‐derived oil‐treated skin. Conclusion The occlusive properties can be summarized as the increase of free water and the transformation of water from a more strongly to a more weakly hydrogen bonding state in the uppermost SC, although some oils cause insignificant changes of the SC thickness. The accompanied changes in the keratin conformation at the intermediate swelling region of the SC also emphasize the role of keratin in the SC’s water‐transporting system, that is the water in the SC transports intercellularly and intracellularly in the intermediate swelling region and only intercellularly in the uppermost non‐swelling region. Bearing this in mind, almond, jojoba and paraffin oils, which are not occlusive from the conventional viewpoint, have an occlusion effect similar to petrolatum on the SC.

The main components of the stratum corneum (SC), water, lipids, and proteins, are non-homogeneously distributed throughout the depth. The quantitative determination of their concentration profiles and penetration depth of topically applied substances are urgent topics of dermatological and cosmetic research. Confocal Raman micro-spectroscopy has distinct advantages when determining semi-quantitative concentrations of SC components and topically applied substances non-invasively and in vivo. In this work, we applied a tailored multivariate curve resolution-alternating least squares (tMCR-ALS) method to analyze Raman spectra of the SC in the 2000-4000 cm À1 region for quantitatively determining the concentrations of water, lipids, proteins, and topically applied oils using substance-related spectral loadings which were allowed to change depth-dependently from the SC's surface toward its bottom. tMCR-ALS makes matching of depth-dependent signal attenuation, that is, the normalization on keratin, unnecessary and requires only a few additional experiments for calibration -Raman spectra of the pure materials and their densities.

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In this paper, we propose an approach to tune optimal parameters of a robust PID controller by means of computed torque control (CTC) strategy for trajectory tracking of a Delta parallel robot, using a hybrid optimization algorithm of Particle Swarm Optimization (PSO) and differential evolution (DE). It differs from previous works that they propose robust PID controller parameters tuning based on conventional gradient-based optimization algorithms and apply them to process control. First, we reduce the tuning problem of a robust PID controller with CTC strategy satisfying requirements including robustness and disturbance attenuation to an optimization problem with nonlinear constraints by considering the nonlinear dynamic model of a Delta parallel robot. Second, we set up the design characteristics for the trajectory tracking of a Delta parallel robot. Then, we propose a robust PID controller in a way of obtaining the global optimization solution of the nonlinear optimization problem by running a PSO-DE hybrid optimization algorithm of finding the global optimal solution by maintaining the diversity of swarm during evolution based on the evolution of cognitive experience. Simulation and experimental results demonstrate that the proposed controller outperforms previous works with respect to robust performance and active disturbance attenuation when it is applied to tracking control of a Delta parallel robot.

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