A method of actuating a downhole device, comprising: disposing a packing member or centralizer intermediate a first collar, coupled to a first end of one or more first elongate shape memory elements, and a second collar, coupled to a second end of the one or more first elongate shape memory elements; disposing the packing member or centralizer within a bore; and raising the temperature of the one or more first elongate shape-memory elements to a transition temperature to shrink the one or more first elongate shape-memory elements in length to adduct the first and second collars to radially expand the packing member or centralizer to engage a wall of the bore, characterised in that the first collar is a first anchor collar and the second collar is a first moving collar, the method further comprising: slidably disposing the first moving collar and a second moving collar on a tubular intermediate the first anchor collar and a second anchor collar, with the first moving collar being disposed intermediate the second moving collar and the second anchor collar; disposing the packing member or centralizer on the tubular intermediate the first moving collar and the second moving collar; coupling a first end of one or more second elongate shape-memory elements to the second anchor collar and a second end of the one or more second elongate shape-memory elements to the second moving collar; and raising the temperature of the one or more second elongate shape-memory elements to the transition temperature to shrink the one or more second elongate shape-memory elements to move the second moving collar towards the second anchor collar to radially expand the packing member or centralizer to engage the wall of the bore. disposing a packing member or centralizer intermediate a first collar, coupled to a first end of one or more first elongate shape memory elements, and a second collar, coupled to a second end of the one or more first elongate shape memory elements; disposing the packing member or centralizer within a bore; and raising the temperature of the one or more first elongate shape-memory elements to a transition temperature to shrink the one or more first elongate shape-memory elements in length to adduct the first and second collars to radially expand the packing member or centralizer to engage a wall of the bore, characterised in that the first collar is a first anchor collar and the second collar is a first moving collar, the method further comprising: slidably disposing the first moving collar and a second moving collar on a tubular intermediate the first anchor collar and a second anchor collar, with the first moving collar being disposed intermediate the second moving collar and the second anchor collar; disposing the packing member or centralizer on the tubular intermediate the first moving collar and the second moving collar; coupling a first end of one or more second elongate shape-memory elements to the second anchor collar and a second end of the one or more second elongate shape-memory elements to the second moving collar; and raising the temperature of the one or more second elongate shape-memory elements to the transition temperature to shrink the one or more second elongate shape-memory elements to move the second moving collar towards the second anchor collar to radially expand the packing member or centralizer to engage the wall of the bore. slidably disposing the first moving collar and a second moving collar on a tubular intermediate the first anchor collar and a second anchor collar, with the first moving collar being disposed intermediate the second moving collar and the second anchor collar; disposing the packing member or centralizer on the tubular intermediate the first moving collar and the second moving collar; coupling a first end of one or more second elongate shape-memory elements to the second anchor collar and a second end of the one or more second elongate shape-memory elements to the second moving collar; and raising the temperature of the one or more second elongate shape-memory elements to the transition temperature to shrink the one or more second elongate shape-memory elements to move the second moving collar towards the second anchor collar to radially expand the packing member or centralizer to engage the wall of the bore.