Sheaths used with polymer scaffolds
A medical device includes a polymer scaffold crimped to a catheter having an expansion balloon. A sheath pair is placed over the crimped scaffold after crimping to reduce recoil of the crimped polymer scaffold and maintain scaffold-balloon engagement relied on to hold the scaffold to the balloon when the scaffold is being delivered to a target in a body. The sheath pair is removed by a health professional before placing the scaffold within the body.
1. An apparatus, comprising:
a balloon catheter assembly having a distal end and a proximal end, the catheter including a scaffold comprising a polymer crimped to a balloon of the catheter at the catheter distal end;
a sheath disposed over the scaffold, the sheath applying a radially inward force on the crimped scaffold to limit recoil of the scaffold, the sheath comprising:
a protecting portion having a distal end, and
a constraining portion having a distal end, wherein the constraining portion distal end is distal of the catheter distal end, and
wherein the constraining and protecting portions are configured so that the sheath is capable of being removed from the scaffold by the following steps:
pulling an extension of the constraining portion distally to withdraw the constraining portion from the scaffold, and
after the constraining portion has been displaced distally, continuing to pull the constraining portion distally to remove both the constraining portion and the protecting portion from the scaffold;
wherein the scaffold is crimped by way of plastic deformation of the scaffold to the balloon such that when the sheath is removed the scaffold retains substantially the same diameter it had when disposed within the sheath; and
wherein a balloon material is disposed between struts of the scaffold to contribute to a retention force between the plastically deformed scaffold and a surface of the balloon to resist dislodgment of the scaffold from the balloon after the sheath is removed.
2. The apparatus of claim 1 , wherein the protecting portion and constraining portion comprise a unitary piece of flexible polymer material, and wherein a connector portion is deformed into, or shaped as a loop having one end at the constraining portion and the other end at the protecting portion such that the distal end of the protecting portion may be received within a proximal end of the constraining portion.
3. The apparatus of claim 1 , further including a connector portion connecting the protecting portion and constraining portion.
4. The apparatus of claim 1 , wherein the protecting portion includes a first and second portion disposed over at least a substantial portion of the scaffold, the first and second portions configured for deflecting radially away from the scaffold when the constraining portion is removed from the scaffold.
5. The apparatus of claim 4 , wherein the first portion is connected to a proximal end of the constraining portion.
6. The apparatus of claim 1 , wherein an inner surface of the constraining portion and/or an outer surface of the protecting portion in contact with the inner surface includes ridges, rings, or nubs, or is roughened to reduce frictional resistance to sliding motion.
7. The apparatus of Claim 6 , wherein the constraining portion includes embedded wires for forming the ridges or rings over the inner surface.
8. The apparatus of claim 1 , wherein the constraining portion includes a stepped down section.
9. An apparatus, comprising:
a balloon catheter assembly having a distal end and a proximal end, the catheter including a scaffold comprising a polymer crimped to a balloon of the catheter at the catheter distal end;
a unitary sheath disposed over the scaffold, the sheath applying a radially inward force on the crimped scaffold to limit recoil of the scaffold, the sheath comprising:
a distal end, and
a first and second half configured for being separated from each other when the sheath is being removed from the scaffold by pulling the sheath towards the catheter distal end, and
wherein the distal end is distal of the catheter distal end;
wherein the scaffold is crimped by way of plastic deformation of the scaffold to the balloon such that when the sheath is removed the scaffold retains substantially the same diameter it had when disposed within the sheath;
wherein a balloon material is disposed between struts of the scaffold to contribute to a retention force between the plastically deformed scaffold and a surface of the balloon to resist dislodgment of the scaffold from the balloon after the sheath is removed; and
wherein the apparatus is configured into an implantable medical device only after the sheath is removed.
10. The apparatus of claim 9 , the apparatus further including a stiffening mandrel disposed within a guidewire lumen of the catheter, wherein the apparatus is configured into the implantable medical device only after both the mandrel and sheath are removed from the catheter.
11. The apparatus of claim 9 , wherein the sheath comprises a cut made longitudinally over a portion of the sheath, wherein the first and second halves are formed from the cut.
12. The apparatus of claim 11 , wherein a distal mandrel portion extends distally of the catheter distal end and the sheath extends over the mandrel distal portion.