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Given an abstract of a paper, generate a title for this paper such that conveys the key focus of the paper.

Abstract: Cow snout epidermal cells digested by 0.25% trypsin were separated into three regions of keratinocytes by Percoll density gradient centrifugation. The membrane fluidity of keratinocytes in each region was measured by electron spin resonance using 5-doxyl stearic acid (5-DSA) as a labeling agent. The order parameter(s) showed higher values as the depth of the epidermis decreased: lower region of epidermis, 0.632; upper region, 0.645; and horny cells, 0.680. These data indicated that membrane fluidity of epidermal cells decreased as cells approached the surface.
Output:
Spin labeling study on membrane fluidity of epidermal cell (cow snout epidermis).