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Title: A study of evaporation and friction on hydrated forearm skin
Author: Wong, W. K. R.
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2008
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When skin is occluded by continuous wearing of incontinence pads, it becomes over-hydrated, making the skin more susceptible to mechanical damage and bacterial attack than normal skin. This project focused on understanding the impact of skin occlusion on (i) the hydration of the stratum comeum (SC) - the outermost layer of the skin, and (ii) friction between the skin and nonwoven materials. A methodology for measuring the excess water in over-hydrated skin using evaporimetry was developed, validated and used to compare the performances of five commonly used evaporimetry devices, and to investigate their strengths and limitations. All measurements were made on the volar forearm skin of one young female subject. Good reproducibility was found for each of the five devices, but some significant differences were found between measurements made with different devices. Some possible causes for these discrepancies were investigated with partial success: correction factors obtained from various calibration procedures were applied and reduced differences to some extent, but significant difference still remained. It was concluded that the methodology developed could be used with confidence to compare readings made with the same device, but it would be unwise to trust the absolute values obtained until the reasons for differences between devices have been more fully explained. A new approach for measuring the water distribution within the SC - Opto-Thermal Transient Emission Radiometry (OTTER) - was adopted in this work and a methodology was developed for measuring the saturation profile within over-hydrated SC. The relationship between the SC saturation at the surface (measured using OTTER) and the water vapour flux from over-hydrated SC (measured using evaporimetry) was investigated using the volar forearms of three young female subjects. As expected, strong correlation was found during desorption, with a dog-leg in the plot at about 36% saturation from two subjects, which was consistent with the transition between loosely and tightly bound water reported by Berardesca (1997). Two methods for measuring friction between nonwoven materials and the over-hydrated or normal skin were developed and validated, on the volar forearms of five young female subjects. Coefficients of friction were measured with the two methods and compared. Good reproducibility and remarkably good agreement was found between the two methods, even though one of the methods (curved friction) assumed the arm to be a rigid cylinder and the nonwoven material to be inextensible. Additional theoretical work (by Cottenden (2007)) and experimental work (by Karavokiros (2007)) was conducted to explain and extend the findings. The theoretical analysis showed that the equation describing friction around a cylinder is valid for any convex prism, and the experimental work supported the solution very well. It was concluded that the curved method developed was simple to run and produced results with good reproducibility.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available