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Re-pigmentation of skin following wounding

Yip, Christina

[Thesis]. Manchester, UK: The University of Manchester; 2013.

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Abstract

Human skin colour has significant aesthetic and cultural implications. Cutaneous injuries can result in dys-pigmented scars which are more noticeable, aesthetically unpleasant, and can lead to patient distress and social isolation. Management of dys-pigmented scars has been challenging with variable success. There is a limited understanding of the timing, progression and mechanisms of skin re-pigmentation following wounding. This thesis is a detailed sequential study, which describes and quantifies scar colour changes in pigs of different pigmented strains.The first result chapter describes the observational pigmentary changes in scars of four different pigmented pig strains (Hampshire, Yucatan, Tamworth and Duroc) over time. Two scar re-pigmentation progression patterns, specific to the darkly and the lightly pigmented pigs, are identified and all scar photographs of all pigs at all time-points are scored during non-invasive wound/ scar monitoring using a semi-quantitative scale. In the second result chapter, histo-chemical (DOPA-oxidase) staining was combined with immuno-histochemistry (HMB45) to establish the spatial and temporal distribution and activities of melanocytes in the regenerated epithelium of darkly pigmented pig strains. Results suggest a rise in both inactive and active melanocyte numbers in re-pigmenting scars at early time-points and by late time-points, scars achieved ‘complete re-pigmentation’ and melanocyte numbers were lowest. Late melanocyte proliferation was observed in two scars from two different pigs; one of which manifested this as hyper-pigmentation, macroscopically. In addition, histological analysis of the epidermal melanin staining (Warkel-Luna-Helwig) pattern showed good correlation with the macroscopic appearance of the scars. The effect of changes in scar basement membrane undulation on melanocyte packing density was investigated: changes were small and unlikely to impact melanocyte packing density; hence macroscopic scar colour. Macroscopic and microscopic observations of the pattern of re-pigmentation following creation of partial thickness wounds across the white and black belts of three Hampshire pigs were investigated.The final result chapter describes how colour changes were quantified for scars and normal skin of each pig, at all time-points during non-invasive scar monitoring; using a reflectance spectrophotometer. In addition, the sensitivity of objective colour measurements was investigated. Results using two statistical clustering techniques suggest that colour measurements differentiate scars from the surrounding normal skin and the tristimulus L*a*b* values of scars correlate well with their macroscopic colour appearances. Time-dependent colour changes in scars and normal skin were quantified independently, using polynomial analysis. The results suggest systematic colour changes in most scars of all pig groups, except Yucatans’, which on the other hand, showed systematic colour changes to their normal skin. These findings highlight the importance of independent analysis of scar and normal skin colour measurements with time post wounding. In conclusion, this thesis has investigated timing and progression patterns of scar re-pigmentation in pigs of different pigmented strains.