Abstract: This invention concerns a contractile device. The device includes a body, which has a wall including a tessellation of elements. The body is deformable through pressurisation of fluid within the body between a first, extended state and a second, contracted state in which the axial length of the body is reduced and the internal volume increased compared to the first, normal state. The tessellation of elements includes a series of protruding and intruding formations which are arranged such that the body remains substantially cylindrical through its deformation between its normal and deformed states. The protruding and intruding formations of the tessellation of elements may be in the form of protruding and intruding pyramids.