A method for improving the ex vivo viability of a skin tissue type by mounting samples (27) of the skin tissue type in a skin sample holder (23), applying separate tensions to at least some of the samples and measuring the ability of at least some of the skin tissue samples to maintain live skin characteristics, such as to determine one or more value of skin tension which improve the ex vivo viability of the skin sample type. Tension may be measured using a force meter. The viability may be determined by wounding the skin, e.g. using a laser source, and measuring keratin 17 expression. Cellular viability and/or metabolic activity may also be determined.