Methods for crimping a polymeric scaffold to a delivery balloon and achieving stable mechanical properties in the scaffold after crimping

A method for crimping, comprising:

• providing a scaffold comprising a polymer characterized by a glass transition temperature (Tg) having a lower limit (Tg-low);
• using a crimping device, crimping the scaffold to a balloon while the scaffold has a temperature of between Tg-low and 5 degrees above Tg-low, including:
• crimping the scaffold from a first diameter to a second diameter, after crimping to the second diameter, removing the scaffold from the crimping device,
• returning the scaffold to the crimping device, wherein the scaffold is aligned on the balloon when the scaffold is returned to the crimping device, and
• crimping the scaffold to a third diameter that is less than the second diameter.

A method for making a medical device, comprising:

• forming a scaffold from a tube comprising a polymer, the scaffold having struts and an outer diameter, and the polymer is characterized by a glass transition temperature (Tg) having a lower limit (Tg-low);
• using a crimping device having a crimp head, crimping the scaffold to a balloon of a balloon catheter to cause the scaffold's polymer struts to become pressed into a surface of the balloon by the crimp head and causing balloon material to extend into spaces between the struts as an outer diameter of the scaffold is being reduced in size by the crimp head, the crimping including:
• increasing a retention between the scaffold and the balloon by raising the temperature of the scaffold to an elevated temperature of between about Tg-low and about 5 degrees above Tg-low, and
• holding the crimp head at the crimped diameter for a dwell period while the scaffold has the elevated temperature;
• wherein the scaffold is placed on the balloon such that when inflated a scaffold deployed diameter is at least 2.5 times higher than a crimped scaffold diameter.

A method of making a balloon-expanded scaffold, comprising:

• forming the scaffold from a polymer characterized by a glass transition temperature (Tg) having a lower limit (Tg-low);
• and
• crimping the scaffold to the balloon, including:
• a first diameter reduction, followed by a first dwell period, and
• a second diameter reduction, followed by a second dwell,
• wherein the period for the second dwell is at least 10 times longer than the period for the first dwell, and
• wherein the scaffold temperature during crimping is between about Tg-low and about 5 degrees centigrade above Tg-low.

A method of making a balloon-expandable scaffold, comprising:

• forming the scaffold from a polymer characterized by a glass transition temperature (Tg) having a lower limit (Tg-low), the scaffold including struts forming strut angles;
• and
• crimping the scaffold to the balloon, including:
• reducing a scaffold diameter to a first diameter, and
• reducing the scaffold diameter to a second diameter that is smaller than the first diameter, wherein the reducing to the first diameter occurs at a slower rate than the reducing to the second diameter, and
• wherein the scaffold temperature during crimping is between about Tg-low and about 5 degrees centigrade above Tg-low.