Impeller for blood pump

A method comprising:

• inserting a blood pump into a body of subject, the blood pump including:
• an impeller that includes:
• proximal and distal bushings,
• at least one helical elongate element that extends from the proximal bushing to the distal bushing,
• a spring that is disposed inside of the helical elongate element, and along an axis around which the helical elongate element winds, and
• a film of material supported between the helical elongate element and the spring,
• a frame disposed around the impeller, the frame including proximal and distal bearings, and
• an axial shaft that passes through the proximal and distal bearings of the frame and the proximal and distal bushings of the impeller, the proximal bushing of the impeller being coupled to the axial shaft, such that the proximal bushing is held in an axially-fixed position with respect to the axial shaft, and the distal bushing of the impeller not being coupled to the axial shaft, such that the distal bushing is not held in an axially-fixed position with respect to the axial shaft,
• the impeller being maintained in a radially-constrained configuration by a delivery catheter while the impeller is inserted into the subject's body;
• when the impeller is disposed within the subject's body, causing the impeller to change from its radially-constrained configuration to a non-radially-constrained configuration by allowing the distal bushing to slide over the axial shaft, by releasing the impeller from the delivery catheter;
• and
• pumping blood through the subject's body using the impeller, while the impeller is disposed in its non-radially-constrained configuration.