A bionic digit (1) that comprises an intermediate portion (15), a tip portion (23) and a hinge (27.29) connecting the tip portion (23) to the intermediate portion (15). The bionic digit (1) further comprises a linear actuator assembly (45) located within the intermediate portion (15) that is connected to the intermediate portion (15) and to the tip portion (23). The linear actuator assembly (45) is provided with a force generator (47), to which is connected a rotary drive shaft (49), and a ball screw (51) connected to the rotary drive shaft (49) for rotation therewith, wherein the ball screw (51) has a helical drive ball raceway (65) extending around its external surface, along at least part of its length, a plurality of drive balls (57), each drive ball (57) located within the helical drive ball raceway (65) and within a drive ball aperture (63) of a ball retention element (55) that is located around the ball screw (51), that is shorter than the ball screw (51) and that is moveable relative to the ball screw (51). Each drive ball (57) is also located within an annular groove (77) of a drive collar (53) that is positioned around the ball retention element (55), the drive collar (53) being rotatable relative to the ball retention element (55) and the ball screw (51) around the longitudinal axis L-L of the ball screw (51). The drive collar (53) has multiple annular grooves (77) that are parallel to each other and perpendicular to the longitudinal axis of the ball screw (51) and is provided with a first engagement element (79). The tip portion (23) is provided with a second engagement element (83) and the first engagement portion (79) and the second engagement portion (83) are engaged with each other.