Abstract: An apparatus is provided for mechanically loading a biological sample. The apparatus comprises: a container for housing the biological sample; a ferromagnetic element, for attachment to the biological sample within the container; and a solenoid for generating a magnetic field within the container, so as to apply a force to the ferromagnetic element. The solenoid is configured, when energised by a constant current, to produce a force on the ferromagnetic element that varies by less than a predetermined amount over a predetermined range of movement of the magnet within the container. A method of mechanically loading a biological sample is also disclosed.