  Suction cups are widely used in applications such as in measurement of
mechanical properties of skin in vivo, in drug delivery devices or in
acupuncture treatment. Understanding the mechanical response of skin under
hypobaric pressure are of great importance for users of suction cups. The aims
of this work are to assess the capability of linear elasticity (Young's
modulus) or hyperelasticity in predicting hypobaric pressure induced 3D
stretching of the skin. Using experiments and computational Finite Element
Method modelling, this work demonstrated that although it was possible to
predict the suction dome apex height using both linear elasticity and
hyperelasticity for the typical range of hypobaric pressure in medical
applications (up to -10 psi), linear elasticity theory showed limitations when
predicting the strain distribution across the suction dome. The reason is that
the stretch ratio reaches values exceeding the initial linear elastic stage of
the stress-strain characteristic curve for skin. As a result, the linear
elasticity theory overpredicts the stretch along the rim of domes where there
is stress concentration. In addition, the modelling showed that the skin was
compressed consistently along the thickness direction, leading to reduced
thickness. Using hyperelasticity modelling to predict the 3D strain
distribution paves the way to accurately design safe commercial products that
interface with skin.
