Abstract: An actuator assembly (140) comprises first and second parts. A first axis (Z) is defined with reference to the second part. The actuator assembly (140) comprises shape-memory alloy wire (80) connected between the first and second parts for moving the first part relative to the second part in any of a set of directions that are at least partly perpendicular to the first axis (Z). The set of directions includes first and second directions. The actuator assembly (140) comprises a set of arms (170), each of which is connected between the first and second parts and extends partly around the first axis (Z). The set of arms (170) is configured to provide a biasing force that biases the first part towards a first position relative to the second part. The set of arms (170) has a first stiffness when the first part is moved away from the first position in the first direction and a second, lower stiffness when the first part is moved away from the first position in the second direction.