An elongated fluid actuator arrangement includes a cylinder body comprising a first and second end portion. A piston body comprising a piston force area forming portion and a sleeve portion, which extends through said first and second end portions and exposes first and second outer section outside the cylinder body. A piston rod extends coaxially through said sleeve portion. The arrangement comprises a first and second extendable and contractible cover member each joined to the cylinder body and to the respective sleeve portion outer section.

An artificial muscle includes a housing including an electrode region, an expandable fluid region, a first film layer, and a second film layer. The first film layer and the second film layer each include an inner protective layer having a first elasticity, an outer protective layer having a second elasticity, and a reinforcing layer provided between the inner protective layer and the outer protective layer, the reinforcing layer having a third elasticity greater than the first elasticity of the inner protective layer and the second elasticity of the outer protective layer. The artificial muscle further includes an electrode pair positioned in the electrode region of the housing and between the first film layer and the second film layer, and a dielectric fluid housed within the housing.

A pneumatic stepper motor includes a housing, said housing accommodating at least part of: a rack or geared axle comprising a plurality of gear elements; and two pistons, each comprising at least two teeth, said pistons being arranged to cooperate with said rack or geared axle. The racks may either be straight or curved. The pistons are preferably double-acting pistons. A device includes at least one, and preferably a plurality of, such pneumatic stepper motor(s). The device may in particular be an MRI-compatible robotic system, more in particular for example an MRI-guided breast biopsy device.