Patent Publication Number: US-11648140-B2

Title: Medical device delivery

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. patent application Ser. No. 15/951,890, filed Apr. 12, 2018, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Walls of the vasculature, particularly arterial walls, may develop areas of pathological dilatation called aneurysms that often have thin, weak walls that are prone to rupturing. Aneurysms are generally caused by weakening of the vessel wall due to disease, injury, or a congenital abnormality. Aneurysms occur in different parts of the body, and the most common are abdominal aortic aneurysms and cerebral (e.g., brain) aneurysms in the neurovasculature. When the weakened wall of an aneurysm ruptures, it can result in death, especially if it is a cerebral aneurysm that ruptures. 
     Aneurysms are generally treated by excluding or at least partially isolating the weakened part of the vessel from the arterial circulation. For example, conventional aneurysm treatments include: (i) surgical clipping, where a metal clip is secured around the base of the aneurysm; (ii) packing the aneurysm with small, flexible wire coils (micro-coils); (iii) using embolic materials to “fill” an aneurysm; (iv) using detachable balloons or coils to occlude the parent vessel that supplies the aneurysm; and (v) intravascular stenting. 
     Intravascular stents are well known in the medical arts for the treatment of vascular stenoses or aneurysms. Stents are prostheses that expand radially or otherwise within a vessel or lumen to support the vessel from collapsing. Methods for delivering these intravascular stents are also well known. 
     Conventional methods of introducing a compressed stent into a vessel and positioning it within an area of stenosis or an aneurysm include percutaneously advancing a distal portion of a guiding catheter through the vascular system of a patient until the distal portion is proximate the stenosis or aneurysm. A second, inner catheter and a guidewire within the inner catheter are advanced through the distal region of the guiding catheter. The guidewire is then advanced out of the distal region of the guiding catheter into the vessel until the distal portion of the guidewire carrying the compressed stent is positioned at the point of the lesion within the vessel. The compressed stent is then released and expanded so that it supports the vessel at the point of the lesion. 
     SUMMARY 
     The present technology is illustrated, for example, according to various aspects described below. Various examples of aspects of the present technology are described as numbered clauses (1, 2, 3, etc.) for convenience. These are provided as examples and do not limit the present technology. It is noted that any of the dependent clauses may be combined in any combination, and placed into a respective independent clause, e.g., Clause 1 or Clause 23. The other clauses can be presented in a similar manner. 
     Clause 1. A stent delivery system, comprising: 
     a core member configured for advancement within a corporeal lumen; 
     a stent extending along the core member, the stent characterized by a pore length; and 
     a coupling assembly positioned about the core member, the coupling assembly comprising: 
     a first plate rotatably coupled to the core member, the first plate including an outer surface having three or more projections engaging the stent; and 
     a second plate rotatably coupled to the core member, the second plate including an outer surface having three or more projections engaging the stent; 
     wherein the projections of the first plate are spaced longitudinally from the projections of the second plate by a first longitudinal distance that is slightly less than a whole number multiple of the pore length. 
     Clause 2. The system of any Clause 1, wherein, in a delivery configuration, the projections of the first plate are engaged with pores of the stent at a first longitudinal position, and wherein the projections of the second plate are engaged with pores of the stent at a second longitudinal position, and wherein the first longitudinal position and the second longitudinal position spaced apart by the first longitudinal distance. 
     Clause 3. The system of any one of Clauses 1-2, wherein the first longitudinal distance is less than two pore lengths. 
     Clause 4. The system of any one of Clauses 1-3, wherein a projection of the first plate engages a first pore of the stent, a projection of the second plate engages a second pore of the stent, and wherein the first pore and the second pore are longitudinally adjacent. 
     Clause 5. The system of any one of Clauses 1-4, wherein the projections of the first plate engage the stent at a position less than five pore lengths away from a proximal end of the stent. 
     Clause 6. The system of any one of Clauses 1-5, wherein the projections of the first plate engage the stent at a position less than three pore lengths away from a proximal end of the stent. 
     Clause 7. The system of any one of Clauses 1-7, wherein the first plate is configured to tilt with respect to a longitudinal axis of the core member. 
     Clause 8. The system of Clause 7, wherein the first plate is configured to tilt up to 30 degrees with respect to the longitudinal axis of the core member. 
     Clause 9. The system of any one of Clauses 7-8, wherein the first plate is configured to tilt up to 20 degrees with respect to the longitudinal axis of the core member. 
     Clause 10. The system of any one of Clauses 7-9, wherein the first plate is configured to tilt up to 10 degrees with respect to the longitudinal axis of the core member. 
     Clause 11. The system of any one of Clauses 1-11, wherein the second plate is configured to tilt with respect to a longitudinal axis of the core member. 
     Clause 12. The system of any Clause 11, wherein the second plate is configured to tilt up to 30 degrees with respect to the longitudinal axis of the core member. 
     Clause 13. The system of any one of Clauses 11-12, wherein the second plate is configured to tilt up to 20 degrees with respect to the longitudinal axis of the core member. 
     Clause 14. The system of any one of Clauses 11-13, wherein the second plate is configured to tilt up to 10 degrees with respect to the longitudinal axis of the core member. 
     Clause 15. The system of any one of Clauses 1-14, wherein the first longitudinal distance is less than a whole number multiple of the pore length by a decrement that is equal to 1% to 50% of the pore length. 
     Clause 16. The system of any one of Clauses 1-15, wherein the first longitudinal distance is less than a whole number multiple of the pore length by a decrement that is equal to 1% to 40% of the pore length. 
     Clause 17. The system of any one of Clauses 1-16, wherein the first longitudinal distance is less than a whole number multiple of the pore length by a decrement that is equal to 1% to 30% of the pore length. 
     Clause 18. The system of any one of Clauses 1-17, wherein the first longitudinal distance is less than a whole number multiple of the pore length by a decrement that is equal to 1% to 20% of the pore length. 
     Clause 19. The system of any one of Clauses 1-18, wherein the first longitudinal distance is less than a whole number multiple of the pore length by a decrement that is equal to 1% to 10% of the pore length. 
     Clause 20. The system of any one of Clauses 1-19, wherein the first longitudinal distance is less than a whole number multiple of the pore length by a decrement that is equal to 1% to 5% of the pore length. 
     Clause 21. The system of any one of Clauses 1-20, wherein the coupling assembly further comprises a spacer between the first plate and the second plate, and the spacer maintains the projections of the first plate and the second plate at the first longitudinal distance when the core member is in a straight orientation and the first plate and the second plate abut the spacer. 
     Clause 22. The system of any one of Clauses 1-21, wherein the projections of the first plate and the second plate engage the stent by projecting into pores of the stent. 
     Clause 23. The system of any one of Clauses 1-22, wherein the pore length of the stent is that attained when the outer diameter of the stent is equal to the inner diameter of a catheter that contains the stent and the coupling assembly and maintains engagement of the first and second plates and the stent. 
     Clause 24. The system of any one of Clauses 1-23, wherein: 
     the stent is a braided stent comprising braided filaments; 
     a projection of the first plate projects into a first pore of the stent; 
     a projection of the second plate projects into a second pore of the stent; 
     the first and second pores are longitudinally adjacent and separated by a filament crossing located longitudinally between the first pore and the second pore; 
     the projection of the first plate is longitudinally offset from a center of the first pore, in a direction toward the filament crossing; and 
     the projection of the second plate is longitudinally offset from a center of the second pore, in a direction toward the filament crossing and the projection of the first plate. 
     Clause 25. The system of any one of Clauses 1-24, further comprising a proximal restraint carried by the core member, wherein the coupling assembly is positioned distal of the proximal restraint. 
     Clause 26. A stent delivery system, comprising: 
     a core member; 
     a stent extending along the core member, the stent comprising a plurality of pores and being characterized by a pore length; and 
     a coupling assembly carried by the core member; the coupling assembly comprising: 
     a first stent engagement member rotatably coupled to the core member, the first stent engagement member including projections engaging a first plurality of pores of the stent; 
     a second stent engagement member rotatably coupled to the core member, the second stent engagement member including projections engaging a second plurality of pores of the stent, 
     wherein the projections of the first stent engagement member are spaced longitudinally from the projections of the second stent engagement member by a first longitudinal distance that is slightly less than a whole number multiple of the pore length. 
     Clause 27. The system of Clause 26, wherein the first plurality of pores and the second plurality of pores are longitudinally adjacent along a length of the stent. 
     Clause 28. The system of any one of Clauses 26-27, wherein the first plurality of pores are less than five pore lengths away from a proximal end of the stent. 
     Clause 29. The system of any one of Clauses 26-28, wherein the first plurality of pores are less than three pore lengths away from a proximal end of the stent. 
     Clause 30. The system of any one of Clauses 26-29, wherein the first engagement member is configured to tilt with respect to a longitudinal axis of the core member. 
     Clause 31. The system of Clause 30, wherein the first engagement member is configured to tilt up to 30 degrees with respect to the longitudinal axis of the core member. 
     Clause 32. The system of any one of Clauses 30-31, wherein the first engagement member is configured to tilt up to 20 degrees with respect to the longitudinal axis of the core member. 
     Clause 33. The system of any one of Clauses 30-32, wherein the first engagement member is configured to tilt up to 10 degrees with respect to the longitudinal axis of the core member. 
     Clause 34. The system of any one of Clauses 26-33, wherein the second engagement member is configured to tilt with respect to a longitudinal axis of the core member. 
     Clause 35. The system of Clause 34, wherein the second engagement member is configured to up to 30 degrees with respect to the longitudinal axis of the core member. 
     Clause 36. The system of any one of Clauses 34-35, wherein the second engagement member is configured to tilt up to 20 degrees with respect to the longitudinal axis of the core member. 
     Clause 37. The system of any one of Clauses 34-36, wherein the second engagement member is configured to tilt up to 10 degrees with respect to the longitudinal axis of the core member. 
     Clause 38. The system of any one of Clauses 26-37, wherein the first stent engagement member and the second stent engagement member are spaced apart by less than two pore lengths. 
     Clause 39. The system of any one of Clauses 26-38, wherein the first longitudinal distance is less than a whole number multiple of the pore length by a decrement that is equal to 1% to 50% of the pore length. 
     Clause 40. The system of any one of Clauses 26-39, wherein the first longitudinal distance is less than a whole number multiple of the pore length by a decrement that is equal to 1% to 40% of the pore length. 
     Clause 41. The system of any one of Clauses 26-40, wherein the first longitudinal distance is less than a whole number multiple of the pore length by a decrement that is equal to 1% to 30% of the pore length. 
     Clause 42. The system of any one of Clauses 26-41, wherein the first longitudinal distance is less than a whole number multiple of the pore length by a decrement that is equal to 1% to 20% of the pore length. 
     Clause 43. The system of any one of Clauses 26-42, wherein the first longitudinal distance is less than a whole number multiple of the pore length by a decrement that is equal to 1% to 10% of the pore length. 
     Clause 44. The system of any one of Clauses 26-43, wherein the first longitudinal distance is less than a whole number multiple of the pore length by a decrement that is equal to 1% to 5% of the pore length. 
     Clause 45. The system of any one of Clauses 26-44, wherein the coupling assembly further comprises a spacer between the first engagement member and the second engagement member, and the spacer maintains the projections of the first engagement member and the second engagement member at the first longitudinal distance when the core member is in a straight orientation and the first engagement member and the second engagement member abut the spacer. 
     Clause 46. The system of any one of Clauses 26-45, wherein the projections of the first engagement member and the second engagement member engage the stent by projecting into pores of the stent. 
     Clause 47. The system of any one of Clauses 26-46, wherein the pore length of the stent is that attained when the outer diameter of the stent is equal to the inner diameter of a catheter that contains the stent and the coupling assembly and maintains engagement of the first and second engagement members and the stent. 
     Clause 48. The system of any one of Clauses 26-47, wherein: 
     the stent is a braided stent comprising braided filaments; 
     a projection of the first engagement member projects into a first pore of the stent; 
     a projection of the second engagement member projects into a second pore of the stent; 
     the first and second pores are longitudinally adjacent and separated by a filament crossing located longitudinally between the first pore and the second pore; 
     the projection of the first engagement member is longitudinally offset from a center of the first pore, in a direction toward the filament crossing; and 
     the projection of the second engagement member is longitudinally offset from a center of the second pore, in a direction toward the filament crossing and the projection of the first engagement member. 
     Clause 49. The system of any one of Clauses 26-48, further comprising a proximal restraint carried by the core member, wherein the coupling assembly is positioned distal of the proximal restraint. 
     Clause 50. A method of advancing a stent within a catheter, the method comprising: 
     moving a core member distally within a lumen of the catheter, the core member carrying a coupling assembly engaged with at least a portion of the stent, the coupling assembly including: 
     a first stent engagement member rotatably carried by the core member and comprising projections engaged with the stent; and 
     a second stent engagement member rotatably carried by the core member and comprising projections engaged with the stent; 
     wherein the stent is characterized by a pore length; and 
     wherein the projections of the first stent engagement member are spaced longitudinally from the projections of the second stent engagement member; 
     by moving the core member distally, causing the stent to move distally within the catheter lumen with the first engagement member moving no more than a first lag distance relative to the stent before initiating distal movement of the stent; 
     wherein the first lag distance is no more than 40% of the pore length. 
     Clause 51. The method of Clause 50, wherein, after distally advancing the core member such that a portion of the stent is permitted to extend out of the catheter and expand, a proximal portion of the stent remains engaged with the first stent engagement member. 
     Clause 52. The method of Clause 51, further comprising proximally retracting the core member prior to releasing the stent such that the stent is recaptured to within the catheter lumen. 
     Clause 53. The method of Clause 52, wherein by proximally retracting the core member, the first stent engagement member pulls the stent proximally within the catheter lumen. 
     Clause 54. The method of any one of Clauses 52-53, wherein the portion of the stent expanded prior to recapture is at least 50% of the length of the stent. 
     Clause 55. The method of any one of Clauses 52-54, wherein the portion of the stent expanded prior to recapture is at least 75% of the length of the stent. 
     Clause 56. The method of any one of Clauses 52-55, wherein the portion of the stent expanded prior to recapture is at least 90% of the length of the stent. 
     Clause 57. The method of any one of Clauses 52-56, wherein the moving comprises causing the stent to rotate with respect to the core member. 
     Clause 58. The method of any one of Clauses 52-57, further comprising by proximally retracting the core member, causing the stent to move proximally within the catheter lumen with the first engagement member moving no more than a second lag distance relative to the stent before initiating proximal movement of the stent, wherein the second lag distance is no more than 40% of the pore length. 
     Clause 59. The method of any one of Clauses 50-58, wherein the projections of the first stent engagement member are spaced longitudinally from the projections of the second stent engagement member by a first longitudinal distance that is slightly less than a whole number multiple of the pore length. 
     Clause 60. The method of any one of Clauses 50-59, wherein the first lag distance is no more than 33% of the pore length. 
     Clause 61. The method of any one of Clauses 50-60, wherein the first lag distance is no more than 25% of the pore length. 
     Clause 62. The method of any one of Clauses 50-61, wherein the first lag distance is no more than 20% of the pore length. 
     Clause 63. The method of any one of Clauses 50-62, wherein the first lag distance is no more than 15% of the pore length. 
     Clause 64. The method of any one of Clauses 50-63, wherein the first lag distance is no more than 10% of the pore length. 
     Clause 65. The method of any one of Clauses 50-64, wherein the first lag distance is no more than 5% of the pore length. 
     Clause 66. A stent delivery system, comprising: 
     a core member configured for advancement within a corporeal lumen; 
     a stent engagement member coupled to the core member, the engagement member including: 
     a proximal end face; 
     a distal end face; 
     a side surface extending between the proximal end face and the distal end face, the side surface comprising three or more projections separated by recesses, wherein the projections are unevenly spaced apart from one another along the side surface; and 
     an aperture extending through the proximal end face and second end faces, the core member extending through the aperture such that the engagement member can rotate about the core member; and 
     a stent extending along the core member and over the engagement member. 
     Clause 67. The stent delivery system of Clause 66, wherein the projections are spaced apart such that each projection is substantially aligned with a pore of the stent when the stent is engaged with the engagement member. 
     Clause 68. The stent delivery system of any one of Clauses 66-17, wherein the stent comprises a braided stent having 48, 54, or 64 wires. 
     Clause 69. The stent delivery system of any one of Clauses 66-68, wherein the stent comprises a number of pores around its circumference at a given longitudinal position along the stent, and wherein the number of pores is not evenly divisible by the number of projections of the engagement member. 
     Clause 70. The stent delivery system of Clause 69, wherein the stent comprises 32 pores at a first longitudinal position along the stent, and wherein the stent engagement member has 3, 5, 6, or 7 projections. 
     Clause 71. The stent delivery system of any one of Clauses 69-70, wherein the stent comprises 24 pores at a first longitudinal position along the stent, and wherein the stent engagement member has 5, 7, or 9 projections. 
     Clause 72. The stent delivery system of any one of Clauses 69-71, wherein the stent comprises 27 pores at a first longitudinal position along the stent, and wherein the stent engagement member has 4,5,6,7, or 8 projections. 
     Clause 73. The stent delivery system of any one of Clauses 66-72, wherein the recesses each comprise a concave portion having a radius of curvature, and wherein the radius of curvature of the concave portions varies among the plurality of recesses. 
     Clause 74. The stent delivery system of any one of Clauses 66-73, wherein the recesses each comprise a concave portion having a surface area, and wherein the surface area of the concave portions varies among the plurality of recesses. 
     Clause 75. The stent delivery system of any one of Clauses 66-74, wherein the recesses each have an angular size, and the recesses vary in angular size. 
     Clause 76. The stent delivery system of any one of Clauses 66-75, wherein the engagement member comprises a first edge formed at the intersection of the proximal end face and the side surface, and a second edge formed at the intersection of the distal end face and the side surface, and wherein the first edge and the second edge are rounded. 
     Clause 77. The stent delivery system of any one of Clauses 66-76, wherein the projections each comprise a radially outermost contact region configured to engage the stent. 
     Clause 78. The stent delivery system of Clause 77, wherein each contact region includes: 
     a central portion; 
     a first shoulder portion extending from the central portion towards a first adjacent recess; and 
     a second shoulder portion extending from the central portion towards a second adjacent recess. 
     Clause 79. The stent delivery system of Clause 78, wherein the central portion comprises a substantially planar outer surface. 
     Clause 80. The stent delivery system of any one of Clauses 66-79, wherein the projections each comprise a radially outermost contact region configured to interlock with the stent. 
     Clause 81. The stent delivery system of any one of Clauses 66-80, wherein the projections each comprise a radially outermost contact region configured to project into one or more pores of the stent. 
     Clause 82. The stent delivery system of any one of Clauses 66-81, further comprising a catheter having an inner surface and a lumen through which the core member extends, wherein at least a portion of the stent is radially positioned between the engagement member side surface and the catheter inner surface. 
     Clause 83. The stent delivery system of any one of Clauses 66-82, wherein the engagement member has a thickness of between about 50-100 microns. 
     Clause 84. The stent delivery system of any one of Clauses 66-83, wherein the number of protrusions of is between three and six. 
     Clause 85. The stent delivery system of any one of Clauses 66-84, wherein the stent engagement member comprises a rigid plate. 
     Clause 86. The stent delivery system of any one of Clauses 66-85, wherein the stent engagement member comprises a sprocket. 
     Clause 87. The stent delivery system of any one of Clauses 66-86, wherein a radially largest dimension of the stent engagement member is at least five times greater than a thickness of the stent engagement member. 
     Clause 88. The stent delivery system of any one of Clauses 66-87, wherein the aperture is configured such that the engagement member can tilt with respect to a longitudinal axis of the core member. 
     Clause 89. The stent delivery system of any Clause 88, wherein the engagement member can tilt up to 30 degrees with respect to the longitudinal axis of the core member. 
     Clause 90. The stent delivery system of any one of Clauses 88-89, wherein the engagement member can tilt up to 20 degrees with respect to the longitudinal axis of the core member. 
     Clause 91. The stent delivery system of any one of Clauses 88-90, wherein the engagement member can tilt up to 10 degrees with respect to the longitudinal axis of the core member. 
     Clause 92. A stent engagement member for a stent delivery system, the engagement member comprising: 
     a first end face; 
     a second end face opposite the first end face; 
     a side surface extending between the proximal end face and the distal end face, the side surface comprising three or more projections separated by recesses, wherein the projections are unevenly spaced apart from one another along the side surface; and 
     a central opening extending through the proximal end face and second end faces, the opening configured to receive a core member therethrough. 
     Clause 93. The stent engagement member of Clause 92, wherein the recesses each comprise a concave portion having a radius of curvature, and wherein the radius of curvature of the concave portions varies among the plurality of recesses. 
     Clause 94. The stent delivery system of any one of Clauses 92-93, wherein the recesses each have an angular size, and the recesses vary in angular size. 
     Clause 95. The stent engagement member of any one of Clauses 92-94, wherein the recesses each comprise a concave portion having a surface area, and wherein the surface area of the concave portions varies among the plurality of recesses. 
     Clause 96. The engagement member system of any one of Clauses 92-95, wherein the engagement member comprises a first edge between the proximal end face and the side surface, and a second edge between the distal end face and the side surface, and wherein the first edge and the second edge are rounded. 
     Clause 97. The stent engagement member of any one of Clauses 92-96, wherein the projections each comprise a radially outermost contact region, wherein each contact region includes: 
     a central portion; 
     a first shoulder portion extending from the central portion towards a first adjacent recess; and 
     a second shoulder portion extending from the central portion towards a second adjacent recess. 
     Clause 98. The stent engagement member of Clause 97, wherein the central portion comprises a generally flat outer surface. 
     Clause 99. The stent engagement member of any one of Clauses 92-98, wherein the engagement member has a thickness of between about 50-100 microns. 
     Clause 100. The stent engagement member of any one of Clauses 92-99, wherein the number of protrusions of is between three and six. 
     Clause 101. The stent engagement member of any one of Clauses 92-100, wherein the stent engagement member comprises a rigid plate. 
     Clause 102. The stent engagement member of any one of Clauses 92-101, wherein the stent engagement member comprises a sprocket. 
     Clause 103. The stent engagement member of any one of Clauses 92-102, wherein a radially largest dimension of the stent engagement member is at least five times greater than a thickness of the stent engagement member. 
     Clause 104. The stent engagement member of any one of Clauses 92-103, wherein the aperture is configured such that the engagement member can tilt with respect to a longitudinal axis of the core member. 
     Clause 105. A method of advancing a stent delivery assembly through a catheter, the method comprising: 
     moving a core member distally within a lumen of the catheter, the core member carrying an engagement member engaged with at least a portion of a stent, the engagement member including: 
     a proximal end face, a distal end face, and a side surface extending between the proximal end face and the distal end face, the side surface comprising three or more projections separated by recesses, wherein the projections are unevenly spaced apart from one another along the side surface, and wherein the projections are in contact with an inner surface of the stent; and 
     an aperture extending through the proximal end face and second end faces, the core member extending through the aperture; 
     by moving the core member, pulling the stent distally within the catheter lumen; and 
     distally advancing the core member such that a portion of the stent carried by the core member is permitted to extend out of the catheter and expand. 
     Clause 106. The method of any Clause 105, wherein, after distally advancing the core member such that a portion of the stent is permitted to extend out of the catheter and expand, a proximal portion of the stent remains engaged with the stent engagement member. 
     Clause 107. The method of any one of Clauses 105-106, further comprising proximally retracting the core member prior to releasing the stent such that the stent is recaptured to within the catheter lumen. 
     Clause 108. The method of Clause 107, wherein by proximally retracting the core member, the stet engagement member pulls the stent proximally within the catheter lumen. 
     Clause 109. The method of Clause 108, wherein the portion of the stent expanded prior to recapture is at least 50% of the length of the stent. 
     Clause 110. The method of any one of Clauses 108-19, wherein the portion of the stent expanded prior to recapture is at least 75% of the length of the stent. 
     Clause 111. The method of any one of Clauses 108-110, wherein the portion of the stent expanded prior to recapture is at least 90% of the length of the stent. 
     Clause 112. The method of any one of Clauses 108-111, wherein the moving comprises causing the stent to rotate with respect to the core member. 
     Clause 113. A stent delivery system comprising: 
     a core member configured for advancement within a corporeal lumen; 
     a coupling assembly positioned about the core member, the coupling assembly comprising: 
     a first plate rotatably positioned about the core member, the first plate including an outer surface having three or more projections separated by recesses; 
     a pushing element positioned on the core member proximal of the first plate, the pushing element having a distal-facing engagement surface; and 
     a stent extending along the core member such that the stent is engaged by one or more projections of the first plate, the stent having a proximal edge; 
     wherein the distal-facing engagement surface of the pushing element abuts the proximal edge of the stent. 
     Clause 114. The system of any Clause 113, wherein the pushing element is configured to transmit distally directed force to the stent but not proximally directed force. 
     Clause 115. The system of any one of Clauses 113-114, wherein the coupling assembly is configured so that the first plate transmits proximally directed force to the stent but little or no distally directed force. 
     Clause 116. The system of any one of Clauses 113-115, wherein the coupling assembly further comprises a rigid first spacer situated between the first plate and the pushing element. 
     Clause 117. The system of Clause 116, wherein the first spacer comprises a solid tube of metal or rigid polymer. 
     Clause 118. The system of Clause 117, wherein the first spacer lacks flexibility-enhancing cuts. 
     Clause 119. The system of any one of Clauses 113-118, wherein the first spacer comprises a proximal end face, a distal end face, and an outer surface extending between the proximal end face and the distal end face along a longitudinal axis, and wherein the proximal end face and the distal end face are each substantially orthogonal to the longitudinal axis of the first spacer. 
     Clause 120. The system of any one of Clauses 113-119, wherein the first spacer comprises a flattened proximal end face configured to abut against the pushing element. 
     Clause 121. The system of any one of Clauses 113-120, wherein the stent forms a plurality of openings and the projections of the first plate engage the stent by extending into the openings. 
     Clause 122. The system of any one of Clauses 113-121, wherein the coupling assembly further comprises a second plate rotatably positioned about the core member, the second plate including an outer surface having three or more projections separated by recesses, and wherein one or more of the projections of the second plate engages the stent via openings formed in the stent. 
     Clause 123. The system of any one of Clauses 113-122, further comprising a sheath or catheter, wherein the core member, coupling assembly and stent are located within the sheath or catheter. 
     Clause 124. The system of any one of Clauses 113-123, wherein the pushing element comprises a proximal restraining member. 
     Clause 125. A medical device delivery system, comprising: 
     a core member; 
     a coupling assembly carried by the core member, the coupling assembly comprising: 
     a first device engagement member rotatably coupled to the core member, the first device engagement member including an outer surface having projections separated by recesses; and 
     a pushing element positioned on the core member proximal of the first device engagement member, the pushing element having a distal-facing engagement surface. 
     Clause 126. The system of Clause 125, further comprising: 
     a medical device extending along the core member such that the medical device is engaged by one or more projections of the first plate; 
     wherein the medical device has a proximal edge; 
     wherein the distal-facing engagement surface of the pushing element abuts the proximal edge of the medical device. 
     Clause 127. The system of Clause 126, wherein the pushing element is configured to transmit distally directed force to the medical device but not proximally directed force. 
     Clause 128. The system of any one of Clauses 126-127, wherein the coupling assembly is configured so that the first device engagement member transmits proximally directed force to the medical device but little or no distally directed force. 
     Clause 129. The system of any one of Clauses 125-128, wherein the coupling assembly further comprises a rigid first spacer situated between the first device engagement member and the pushing element. 
     Clause 130. The system of Clause 129, wherein the first spacer comprises a solid tube of metal or rigid polymer. 
     Clause 131. The system of Clause 130, wherein the first spacer lacks flexibility-enhancing cuts. 
     Clause 132. The system of any one of Clauses 126-131, wherein the medical device forms a plurality of openings and the projections of the first device engagement member engage the medical device by extending into the openings. 
     Clause 133. The system of Clause 132, wherein the coupling assembly further comprises a second device engagement member rotatably positioned about the core member, the second device engagement member including an outer surface having three or more projections separated by recesses, and wherein one or more of the projections of the second device engagement member engages the medical device via openings formed in the medical device. 
     Clause 134. The system of any one of Clauses 126-133, further comprising a sheath or catheter, wherein the core member, coupling assembly and medical device are located within the sheath or catheter. 
     Clause 135. The system of any one of Clauses 125-134, wherein the first device engagement member takes the form of a plate or sprocket. 
     Clause 136. A method of delivering a tubular medical device through a catheter, the method comprising: 
     manipulating a delivery system comprising a core member and a coupling assembly, the coupling assembly comprising: 
     a first device engagement member including an outer surface having projections separated by recesses, the projections engaging the medical device via openings in the medical device; and 
     a pushing element located on the core member, proximal of the first device engagement member; and 
     moving the medical device distally by transmitting distally-directed force to the medical device via the pushing element, and no distally-directed force to the medical device via the first device engagement member. 
     Clause 137. The method of Clause 136, further comprising moving the medical device proximally by transmitting proximally-directed force to the stent via the first device engagement member, and no proximally-directed force to the stent via the pushing element. 
     Clause 138. The method of Clause 137, wherein moving the medical device proximally comprises resheathing the medical device. 
     Clause 139. The method of any one of Clauses 137-138, wherein moving the medical device distally comprises partially expanding the medical device from the end of a catheter or sheath, and moving the medical device proximally comprises resheathing the medical device into the catheter or sheath. 
     Clause 140. The method of any one of Clauses 136-39, wherein the coupling assembly further comprises a first spacer located on the core member between the first device engagement member and the pushing element. 
     Clause 141. The method of Clause 140, further comprising maintaining engagement between the medical device and the pushing element via the first spacer. 
     Clause 142. The method of any one of Clauses 136-141, wherein the medical device comprises a stent. 
     Clause 143. The method of any one of Clauses 136-142, wherein the first device engagement member takes the form of a plate or sprocket. 
     Clause 144. A stent delivery system comprising: 
     a core member configured for advancement within a corporeal lumen; 
     a coupling assembly positioned about the core member, the coupling assembly comprising: 
     a first plate rotatably positioned about the core member, the first plate including an outer surface having three or more projections separated by recesses; 
     a coil spacer positioned about the core member proximal of and adjacent to the first plate; and 
     a stent extending along the core member such that the stent is engaged by one or more projections of the first plate and is thereby distally advanceable via the core member. 
     Clause 145. The system of Clause 144, wherein the coil spacer comprises a zero-pitch coil. 
     Clause 146. The system of any one of Clauses 144-145, wherein the coil spacer is axially substantially incompressible. 
     Clause 147. The system of any one of Clauses 144-146, wherein the coil spacer is rotatably positioned about the core member. 
     Clause 148. The system of any one of Clauses 144-147, wherein the coil spacer comprises a proximal end face, a distal end face, and an outer surface extending between the proximal end face and the distal end face along a longitudinal axis, and wherein the proximal end face and the distal end face are each substantially orthogonal to the longitudinal axis of the coil spacer. 
     Clause 149. The system of any one of Clauses 144-148, further comprising a proximal restraint coupled to the core member, and wherein the coil spacer comprises a flattened proximal end face configured to abut against the proximal restraint. 
     Clause 150. The system of any one of Clauses 144-149, wherein the coil spacer comprises a flattened distal end face configured to abut against the first plate. 
     Clause 151. The system of any one of Clauses 144-150, wherein the coil spacer has a length of between about 1-2 mm. 
     Clause 152. The system of any one of Clauses 144-151, wherein the coil spacer is coated with a lubricious material. 
     Clause 153. The system of Clause 152, wherein the lubricious material comprises PTFE. 
     Clause 154. The system of any one of Clauses 144-153, wherein an outer diameter of the coil spacer is less than or equal to a recess diameter of the first plate. 
     Clause 155. The system of any one of Clauses 144-154, wherein a largest radial dimension of the first plate a is configured to fit within a 0.017″, 0.021″ or 0.027″ inner diameter catheter. 
     Clause 156. The system of any one of Clauses 144-155, wherein the coil spacer comprises a wire having a square or rectangular cross section that is wound into a coil configuration. 
     Clause 157. The system of any one of Clauses 144-156, wherein the coil spacer comprises a wire that is wound into a coil configuration and the wound wire forms a number of winds, each with flat distal and proximal faces, wherein the faces of adjacent winds contact each other to enable the coil spacer to bear longitudinally compressive loads without shortening. 
     Clause 158. The system of any one of Clauses 144-157, further comprising a proximal restraint coupled to the core member proximal of and adjacent to the coil spacer so as to prevent longitudinal movement of the coil spacer proximal of the proximal restraint. 
     Clause 159. The system of any one of Clauses 144-158, wherein the coupling assembly further comprises a second plate rotatably positioned about the core member, the second plate including an outer surface having three or more projections separated by recesses, and wherein one or more of the projections of the second plate engages the stent such that the stent is distally advanceable via the core member. 
     Clause 160. The system of Clause 159, further comprising a distal restraint disposed distal to the second plate, the distal restraint being longitudinally fixed with respect to the core member. 
     Clause 161. The system of any one of Clauses 159-160, wherein a largest radial dimension of the first plate is at least 5 times greater than a largest width dimension of the first plate, and wherein a largest radial dimension of the second plate is at least 5 times greater than a largest width dimension of the second plate. 
     Clause 162. The system of any one of Clauses 159-161, wherein the coupling assembly further comprises a second spacer positioned about the core member and disposed between the first plate and the second plate. 
     Clause 163. The system of Clause 162, wherein the second spacer comprises a second coil spacer. 
     Clause 164. The system of any one of Clauses 162-163, wherein the second spacer comprises a solid tubular member. 
     Clause 165. The system of any one of Clauses 144-164, wherein the coupling assembly is rotatably positioned about the core member. 
     Clause 166. A medical device delivery system, comprising: 
     a core member; 
     a coupling assembly carried by the core member, the coupling assembly comprising: 
     a first device engagement member rotatably coupled to the core member, the first device engagement member including an outer surface having projections separated by recesses; and 
     a coil spacer coupled to the core member and disposed proximal of and adjacent to the first device engagement member. 
     Clause 167. The system of Clause 166, wherein the coil spacer comprises a zero-pitch coil. 
     Clause 168. The system of any one of Clauses 166-167, wherein the coil spacer is axially substantially incompressible. 
     Clause 169. The system of any one of Clauses 166-168, wherein the coil spacer is rotatably coupled to the core member. 
     Clause 170. The system of any one of Clauses 166-169, wherein the coil spacer comprises a proximal end face, a distal end face, and an outer surface extending between the proximal end face and the distal end face along a longitudinal axis, and wherein the proximal end face and the distal end face are each substantially planar and orthogonal to the longitudinal axis of the coil spacer. 
     Clause 171. The system of any one of Clauses 166-170, wherein the coil spacer comprises a flattened proximal end face configured to abut against a proximal restraint coupled to the core member. 
     Clause 172. The system of any one of Clauses 166-171, wherein the coil spacer comprises a flattened distal end face configured to abut against the first device engagement member. 
     Clause 173. The system of any one of Clauses 166-172, wherein the coil spacer has a length of between about 1-2 mm. 
     Clause 174. The system of any one of Clauses 166-173, wherein the coil spacer is coated with a lubricious material. 
     Clause 175. The system of Clause 174, wherein the lubricious material comprises PTFE. 
     Clause 176. The system of any one of Clauses 166-175, wherein an outer diameter of the coil spacer is less than or equal to a recess diameter of the first device engagement member. 
     Clause 177. The system of any one of Clauses 166-176, wherein the first device engagement member comprises a rigid plate or sprocket. 
     Clause 178. The system of Clause 177, wherein the coupling assembly further comprises a second device engagement member which comprises a rigid plate or sprocket. 
     Clause 179. The system of any one of Clauses 166-178, wherein the coil spacer comprises a wire having a square or rectangular cross section that is wound into a coil configuration. 
     Clause 180. The system of any one of Clauses 166-179, wherein the coil spacer comprises a wire that is wound into a coil configuration and the wound wire forms a number of winds, each with flat distal and proximal faces, wherein the faces of adjacent winds contact each other to enable the coil spacer to bear longitudinally compressive loads without shortening. 
     Clause 181. The system of any one of Clauses 166-180, further comprising a proximal restraint coupled to the core member proximal of and adjacent to the coil spacer so as to prevent longitudinal movement of the coil spacer proximal of the proximal restraint. 
     Clause 182. The system of any one of Clauses 166-181, wherein the coupling assembly further comprises a second device engagement member rotatably positioned about the core member, the second device engagement member including an outer surface having three or more projections separated by recesses. 
     Clause 183. The system of Clause 182, further comprising a distal restraint disposed distal to the second device engagement member, the distal restraint being longitudinally fixed with respect to the core member. 
     Clause 184. The system of any one of Clauses 182-183, wherein a largest radial dimension of the first device engagement member is at least 5 times greater than a largest width dimension of the first device engagement member, and wherein a largest radial dimension of the second device engagement member is at least 5 times greater than a largest width dimension of the second device engagement member. 
     Clause 185. The system of any one of Clauses 182-184, further comprising an expandable medical device extending along the core member such that the medical device is engaged by one or more projections of the first device engagement member and of the second device engagement member, and is thereby distally advanceable via the core member. 
     Clause 186. The system of Clause 185, wherein the medical device comprises a stent. 
     Clause 187. The system of any one of Clauses 182-186, wherein the coupling assembly further comprises a second spacer positioned about the core member and disposed between the first device engagement member and the second device engagement member. 
     Clause 188. The system of Clause 187, wherein the second spacer comprises a second coil spacer. 
     Clause 189. The system of Clause 187, wherein the second spacer comprises a solid tubular member. 
     Clause 190. The system of any one of Clauses 166-,189 wherein the coupling assembly is rotatably positioned about the core member. 
     Clause 191. The system of any one of Clauses 166-190, wherein the core member is configured for advancement within a corporeal lumen. 
     Clause 192. A method of advancing a medical device within a catheter, the method comprising: 
     moving a core member distally within a lumen of the catheter, the core member carrying a coupling assembly engaged with at least a portion of the medical device within the catheter, the coupling assembly including: 
     a first device engagement member rotatably carried by the core member and comprising projections engaged with the medical device; and 
     a coil spacer carried by the core member and positioned proximal of the first device engagement member; 
     by moving the core member distally, causing the medical device to move distally within the catheter; and 
     while moving the core member distally, transmitting distally-directed force from the core member to the first device engagement member and the medical device via the coil spacer, without longitudinal shortening of the coil spacer. 
     Clause 193. The method Clause 192, wherein the medical device comprises a stent. 
     Clause 194. The method of any one of Clauses 192-193, wherein moving the medical device distally further comprises causing the medical device to extend out of the catheter and expand. 
     Clause 195. The method of Clause 194, further comprising proximally retracting the core member prior to releasing the medical device such that the device is recaptured to within the catheter lumen. 
     Clause 196. The method of any one of Clauses 193-195, wherein, as a result of proximally retracting the core member, the first device engagement member pulls the stent proximally within the catheter lumen. 
     Clause 197. The method of any one of Clauses 195-196, wherein the portion of the medical device expanded prior to recapture is at least 50% of the length of the device. 
     Clause 198. The method of any one of Clauses 195-197, wherein the portion of the medical device expanded prior to recapture is at least 75% of the length of the device. 
     Clause 199. The method of any one of Clauses 195-198, wherein the portion of the medical device expanded prior to recapture is at least 90% of the length of the device. 
     Clause 200. The method of any one of Clauses 192-199, wherein the moving comprises causing the medical device to rotate with respect to the core member. 
     Clause 201. The method of any one of Clauses 192-200, further comprising advancing the core member and coil spacer through a bend in the catheter, and thereby bending the coil spacer. 
     Clause 202. The method of Clause 201, wherein bending the coil spacer comprises bending the coil spacer while transmitting distally-directed force from the core member to the first device engagement member and the medical device via the coil spacer. 
     Clause 203. The method of any one of Clauses 192-202, wherein the coupling assembly further comprises a second device engagement member rotatably carried by the core member and comprising projections engaged with the medical device. 
     Clause 204. The method of Clause 203, further comprising while moving the core member distally, transmitting distally-directed force from the core member to the second device engagement member and the medical device via the coil spacer. 
     Clause 205. The method of any one of Clauses 203-204, wherein the coupling assembly further comprises a second spacer carried by the core member and located between the first device engagement member and the second device engagement member. 
     Clause 206. The method of any one of Clauses 192-205, wherein the medical device comprises a flow-diverting stent, and further comprising deploying the stent from the catheter across an aneurysm to treat the aneurysm via flow diversion therapy. 
     Additional features and advantages of the present technology will be set forth in the description below, and in part will be apparent from the description, or may be learned by practice of the subject technology. The advantages of the present technology will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the present technology as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Instead, emphasis is placed on illustrating clearly the principles of the present technology. For ease of reference, throughout this disclosure identical reference numbers may be used to identify identical or at least generally similar or analogous components or features. 
         FIG.  1    is a schematic illustration of a medical device delivery system configured in accordance with some embodiments. 
         FIG.  2    is a side, cross-sectional view of a medical device delivery system, according to some embodiments. 
         FIG.  3 A  is an enlarged perspective view of a coupling assembly having stent engagement members in accordance with some embodiments. 
         FIG.  3 B  is an enlarged perspective view of the coupling assembly of  FIG.  3 A  with an overlying stent. 
         FIGS.  4 A and  4 B  are side and side cross-sectional views, respectively, of a spacer of the coupling assembly shown in  FIGS.  2 - 3 B . 
         FIGS.  5 A- 5 C  are side, top, and perspective views, respectively, of an individual engagement member of the coupling assembly shown in  FIGS.  2 - 3 B . 
         FIG.  6 A  is a schematic cross-sectional view of an engagement member and the stent of  FIG.  3 B . 
         FIG.  6 B  is an enlarged detail view of a portion of the stent shown in  FIG.  3 B . 
         FIG.  7 A  is a perspective view of another embodiment of an engagement member. 
         FIG.  7 B  is a schematic cross-sectional view of the engagement member of  FIG.  7 A  engaged with an overlying stent. 
         FIG.  8 A  is a perspective view of another embodiment of an engagement member. 
         FIG.  8 B  is a schematic cross-sectional view of the engagement member of  FIG.  8 A  engaged with an overlying stent. 
         FIGS.  9 A and  9 B  are side and bottom views, respectively, of another embodiment of a stent engagement member. 
         FIGS.  10 A and  10 B  are side and bottom views, respectively, of another embodiment of a stent engagement member. 
         FIGS.  11 A- 11 C  illustrate enlarged detail views of portions of stent engagement members in accordance with different embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Conventional stent engagement members include soft “pads” that rely on friction fit to secure a stent (such as a braided, knit or woven stent, or a laser-cut stent, or other tubular implant or medical device) against an inner wall of a catheter. Such friction-fit pads may require several different pad diameters to accommodate different stent sidewall thicknesses, which can vary based on the wire size (or combinations of wire sizes), or the sidewall thickness of the tube stock, used to form a given stent. That is, within a given catheter size, the internal diameter of the compressed (braided, knit or woven, or laser-cut) stent contained in the catheter will vary based on the sizes (diameters) of the wires, or the wall thickness of the tube stock, and possibly other parameters of the stent corresponding to different deployed sizes or target vessel sizes. This can require using different pad diameters to accommodate different stent sizes within a desired range (e.g. about 3.5 to 5 millimeters in pad diameter), which necessitates manufacturing the pads of various diameters to very small size tolerances. Embodiments of the present technology can allow a single size stent engagement member to be used with a relatively broad range of stent inner diameters within a given catheter size (e.g. a 0.027″, 0.021″, or 0.017″ inner diameter catheter). For example, a stent engagement member comprising a rigid plate, sprocket or member that has a plurality of projections separated by recesses can be used to secure a range of different stent sizes within a given catheter. 
     Specific details of several embodiments of the present technology are described herein with reference to  FIGS.  1 - 11 C . Although many of the embodiments are described with respect to devices, systems, and methods for delivery of stents, tubular implants such as filters, shunts or stent-grafts and other medical devices, other applications and other embodiments in addition to those described herein are within the scope of the present technology, and can be employed in any of the embodiments of systems disclosed herein, in place of a stent as is typically disclosed. It should be noted that other embodiments in addition to those disclosed herein are within the scope of the present technology. Further, embodiments of the present technology can have different configurations, components, and/or procedures than those shown or described herein. Moreover, embodiments of the present technology can have configurations, components, and/or procedures in addition to those shown or described herein and that these and other embodiments may not have several of the configurations, components, and/or procedures shown or described herein without deviating from the present technology. 
     As used herein, the terms “distal” and “proximal” define a position or direction with respect to a clinician or a clinician&#39;s control device (e.g., a handle of a delivery catheter). For example, the terms, “distal” and “distally” refer to a position distant from or in a direction away from a clinician or a clinician&#39;s control device along the length of device. In a related example, the terms “proximal” and “proximally” refer to a position near or in a direction toward a clinician or a clinician&#39;s control device along the length of device. The headings provided herein are for convenience only and should not be construed as limiting the subject matter disclosed. 
     Selected Examples of Coupling Assemblies for Medical Device Delivery Systems 
       FIGS.  1 - 11 C  depict embodiments of medical device delivery systems that may be used to deliver and/or deploy a medical device, such as but not limited to a stent, into a hollow anatomical structure such as a blood vessel. The stent can comprise a braided stent or other form of stent such as a woven stent, knit stent, laser-cut stent, roll-up stent, etc. The stent can optionally be configured to act as a “flow diverter” device for treatment of aneurysms, such as those found in blood vessels including arteries in the brain or within the cranium, or in other locations in the body such as peripheral arteries. The stent can optionally be similar to any of the versions or sizes of the PIPELINE™ Embolization Device marketed by Medtronic Neurovascular of Irvine, Calif. USA. The stent can alternatively comprise any suitable tubular medical device and/or other features, as described herein. In some embodiments, the stent can be any one of the stents described in U.S. application Ser. No. 15/892,268, filed Feb. 8, 2018, titled VASCULAR EXPANDABLE DEVICES, the entirety of which is hereby incorporated by reference herein and made a part of this specification. 
       FIG.  1    is a schematic illustration of a medical device delivery system  100  configured in accordance with an embodiment of the present technology. The system  100  can comprise an elongate tube or catheter  101  which slidably receives a core member or core assembly  103  configured to carry a stent  105  through the catheter  101 . The depicted catheter  101  has a proximal region  107  and an opposing distal region  109  which can be positioned at a treatment site within a patient, an internal lumen  111  extending from the proximal region  107  to the distal region  109 , and an inner surface  113  defining the lumen  111 . At the distal region  109 , the catheter  101  has a distal opening  115  through which the core member  103  may be advanced beyond the distal region  109  to expand or deploy the stent  105  within the blood vessel  116 . The proximal region  107  may include a catheter hub (not shown). The catheter  101  can define a generally longitudinal dimension extending between the proximal region  107  and the distal region  109 . When the delivery system  100  is in use, the longitudinal dimension need not be straight along some or any of its length. 
     The core member  103  is configured to extend generally longitudinally through the lumen  111  of the catheter  101 . The core member  103  can generally comprise any member(s) with sufficient flexibility and column strength to move the stent  105  or other medical device through the catheter  101 . The core member  103  can therefore comprise a wire, tube (e.g., hypotube), braid, coil, or other suitable member(s), or a combination of wire(s), tube(s), braid(s), coil(s), etc. 
     The system  100  can also include a coupling assembly  120  or resheathing assembly  120  configured to releasably retain the medical device or stent  105  with respect to the core member  103 . The coupling assembly  120  can be configured to engage the stent  105 , via mechanical interlock with the pores and filaments of the stent  105 , abutment of the proximal end or edge of the stent  105 , frictional engagement with the inner wall of the stent  105 , or any combination of these modes of action. The coupling assembly  120  can therefore cooperate with the overlying inner surface  113  of the catheter  101  to grip and/or abut the stent  105  such that the coupling assembly  120  can move the stent  105  along and within the catheter  101 , e.g., distal and/or proximal movement of the core member  103  relative to the catheter  101  results in a corresponding distal and/or proximal movement of the stent  105  within the catheter lumen  111 . 
     The coupling assembly  120  (or portion(s) thereof) can, in some embodiments, be configured to rotate about the core member  103 . In some such embodiments, the coupling assembly  120  can comprise a proximal restraint  119  and a distal restraint  121 . The proximal and distal restraints  119 ,  121  can be fixed to the core member  103  to prevent or limit proximal or distal movement of the coupling assembly  120  along the longitudinal dimension of the core member  103 . For example, the proximal and distal restraints  119 ,  121  can be soldered or fixed with adhesive to the core wire  103 . One or both of the proximal and distal restraints  119 ,  121  can have an outside diameter or other radially outermost dimension that is smaller than the outside diameter or other radially outermost dimension of the overall coupling assembly  120  such that one or both of the restraints  119 ,  121  do not contact the inner surface of the stent  105  during operation of the system  100 . (In some embodiments, as described in further detail below, the proximal restraint  119  can be sized to abut the proximal end of the stent  105 , and be employed to push the stent distally during delivery.) The distal restraint  121  can taper in the distal direction down towards the core member  103 . This tapering can reduce the risk of the distal restraint  121  contacting an inner surface of the stent  105 , particularly during navigation of tortuous vasculature, in which the system  100  can assume a highly curved configuration. 
     The coupling assembly  120  can also include first and second stent engagement members (or device engagement members, or resheathing members)  123   a - b  (together “engagement members  123 ”) and first and second spacers  125   a - b (together “spacers  125 ”) disposed about the core member  103  between the proximal and distal restraints  119 ,  121 . In the illustrated embodiment, from proximal to distal, the elements of the coupling assembly  120  include the proximal restraint  119 , followed by the first spacer  125   a , the first stent engagement member  123   a , the second spacer  125   b , the second stent engagement member  123   b , and finally the distal restraint  121 . In this configuration, the first spacer  125   a  defines the relative positioning of the first engagement member  123   a  and the proximal restraint  119 . The second spacer  125   b  defines the relative longitudinal spacing between the first engagement member  123   a  and the second engagement member  123   b.    
     As described in more detail below, one or both of the spacers  125  can take the form of a wire coil, a solid tube, or other structural element that can be mounted over the core member  103  to longitudinally separate adjacent components of the coupling assembly  120 . In some embodiments, one or both of the spacers  125  can be a zero-pitch coil with flattened ends as described in more detail below with respect to  FIGS.  4 A and  4 B . In some embodiments, one or both of the spacers  125  can be a solid tube (e.g., a laser-cut tube) that can be rotatably mounted or non-rotatably fixed (e.g., soldered) to the core member  103 . The spacers  125  can have a radially outermost dimension that is smaller than a radially outermost dimension of the engagement members  123  such that the spacers  125  do not contact the stent  105  during normal operation of the system  100 . As described in more detail below, the dimensions, construction, and configuration of the spacers  125  can be selected to achieve improved grip between the coupling assembly  120  and the overlying stent  105 . 
     As described in more detail below with respect to  FIGS.  3 A,  3 B, and  5 A- 11 C , one or both of the stent engagement members  123  can be a rigid plate, sprocket or member with a central aperture configured to receive the core member  103  therethrough. The stent engagement members  123  are configured to mechanically interlock with or engage the stent  105  such that the stent engagement members  123  restrain the stent  105  from moving longitudinally with respect to the core member  103 . 
     Although the embodiment illustrated in  FIG.  1    includes two stent engagement members  123  and two spacers  125 , the number of stent engagement members and spacers can vary. In at least one embodiment, the coupling assembly  120  includes only a single stent engagement member without any spacers. In other embodiments, the number of stent engagement members can vary, for example two, three, four, five, six, or more stent engagement members separated by spacers. 
     In the embodiment of the coupling assembly  120  depicted in  FIG.  1   , the proximal restraint  119  is configured to abut the proximal end or proximal edge of the stent  105 . In this arrangement the proximal restraint  119  can be used to move (e.g., push) the stent  105  distally through the catheter  101  in response to a distal push force applied to the core member  103 . Such a proximal restraint  119  can have a diameter that is slightly smaller than the inner diameter of the catheter  101 , leaving a small circumferential or radial gap between the outer edge of the proximal restraint  119  and the inner wall of the catheter  101 . In addition, the length of the proximal spacer  125   a  can be sized so that the proximal edge of the stent  105  abuts the distal face of the proximal spacer  119 . 
     When the proximal restraint  119  is configured to push the stent  105  distally, the proximal restraint accordingly transmits some, most or all of the distal longitudinal (push) force to the stent  105 , wholly or partially in place of the stent engagement member(s)  123 . In such a configuration, the stent engagement members  123  can transmit little or no push force to the stent  105  while the stent  105  is delivered distally along the length of the catheter. Advantageously, this reduces or eliminates the tendency of the stent engagement member(s)  123  to distort the pores of the stent  105  with which the engagement members are engaged, when the engagement members are employed to transmit force to and move the stent  105  within the catheter  101 . Use of the proximal restraint  119  to move the stent  105  in this manner can also reduce or eliminate longitudinal movement of the stent  105  relative to the core member  103  that sometimes accompanies the pore distortion described above. In most cases, the vast majority of the travel of the stent  105  within the catheter  101  is in the distal or “push” direction during delivery to the treatment location, in contrast to the relatively short travel involved in resheathing the stent  105 , in the proximal or “pull” direction. Therefore, configuring the proximal restraint  119  to transmit most or all of the push force to the stent  105  can significantly reduce or substantially eliminate such distortion and/or relative longitudinal movement of the stent. 
     The coupling assembly  120  of  FIG.  1    can therefore employ the proximal restraint  119  as a pushing element to transmit at least some, or most or all, distally-directed push force to the stent  105  during delivery. In such a coupling assembly  120 , the stent engagement member(s)  123  do not transmit any distally-directed push force to the stent  105  during delivery (or transmit only a small portion of such force, or do so only intermittently). The stent engagement member(s)  123  can transmit proximally-directed pull force to the stent  105  during retraction or resheathing, and the proximal restraint  119  can transmit no proximally-directed pull force to the stent (or it may do so occasionally or intermittently, for example when a portion of the stent  105  becomes trapped between the outer edge of the proximal restraint  119  and the inner wall of the catheter  101 ). 
     In some embodiments of the coupling assembly  120  of  FIG.  1   , the first spacer  125   a  can be a rigid tube. Such a rigid tube can comprise a solid (e.g., lacking flexibility-enhancing cuts such as spiral cuts or periodic arcuate cuts) tube of rigid material, e.g. a metal or rigid polymer. The use of a rigid tube as the first spacer  125   a  tends to reduce or eliminate lateral bending of the delivery system  100  around the junction of the proximal restraint  119  and the first spacer  125   a  as the delivery system is advanced through a tortuous path. A lack of bending in this area can be advantageous when the proximal restraint  119  is employed as a pushing element, to transmit distally-directed push forces to the stent  105  during delivery. When bending occurs, the distal face of the proximal restraint  119  may become poorly engaged with the proximal end of the stent  105 , for example engaged only along part of the circumference of the stent. This can lead to concentration of push force on only a small part of the stent, and/or slippage of the stent into the radial gap between the outer edge of the proximal restraint and the inner wall of the catheter  101 . Any of these failure modes can adversely affect the function of the delivery system, damage the stent, or both. 
     In some embodiments, the stent engagement member(s)  123  are employed for both distal and proximal movement of the stent  105  with respect to the catheter  101 . The engagement member(s)  123  transmit distally-directed force to the stent  105  to move it distally within the catheter  101  during delivery, and proximally-directed force to the stent  105  to move it proximally into the catheter  101  during resheathing. In such embodiments, the proximal restraint  119  can be made with a relatively small outer diameter, and/or be positioned sufficiently proximal of the proximal end of the stent  105 , to prevent the proximal restraint  119  from transmitting distally-directed push forces to the stent  105  during delivery. 
     In operation, the stent  105  can be moved distally or proximally within the catheter  101  via the core member  103  and the coupling assembly  120 . To move the stent  105  out of the catheter  101 , either the core member  103  is moved distally while the catheter  101  is held stationary or the core member  103  is held stationary while the catheter  101  is withdrawn proximally. When the core member  103  is moved distally, the distal face of the proximal restraint  119  bears against the proximal end or edge of the stent  105  and causes the stent to be advanced distally, and ultimately out of the distal region  109  of the catheter  101 . (In embodiments wherein the stent engagement member(s)  123  are employed to transmit pushing force to the stent  105 , the mechanical engagement or interlock between the stent engagement members  123  and the stent  105 , in response to the application of a distally-directed force to the core member  103 , causes the stent  105  to move distally through and out of the catheter  101 .) Conversely, to resheath or otherwise move the stent  105  into the catheter  101 , the relative movement between the core member  103  and the catheter  101  is reversed compared to moving the stent  105  out of the catheter such that the proximal region of the distal restraint  121  bears against the distal region of the second spacer  125   b  and thereby causes the spacers  125  and the stent engagement members  123  to be retracted relative to the catheter  101 . The mechanical engagement between the stent engagement members  123  and the stent  105  accordingly holds the stent  105  with respect to the core member  103  such that proximal movement of the stent  105  relative to the catheter  101  enables re-sheathing of the stent  105  back into the distal region  109  of the catheter  101 . This is useful when the stent  105  has been partially deployed and a portion of the stent  105  remains disposed between at least one of the stent engagement members  123  (e.g. the first stent engagement member  123   a ) and the inner surface  113  of the catheter  101  because the stent  105  can be withdrawn back into the distal opening  115  of the catheter  101  by moving the core member  103  proximally relative to the catheter  101  (and/or moving the catheter  101  distally relative to the core member  103 ). Resheathing in this manner remains possible until the stent engagement members  123  and/or catheter  101  have been moved to a point where the first stent engagement member  123   a  is beyond the distal opening  115  of the catheter  101  and the stent  105  is released from between the first stent engagement member  123   a  and the catheter  101 . 
     The stent engagement members  123  and the spacers  125  (or any of the engagement members or spacers disclosed herein) can be fixed to the core member  103  so as to be immovable relative to the core member  103 , in a longitudinal/sliding manner and/or in a radial/rotational manner. Alternatively, the spacers  125  and/or the stent engagement members  123  can be coupled to (e.g., mounted on) the core member  103  so that the spacers  125  and/or the stent engagement members  123  can rotate about the longitudinal axis of the core member  103 , and/or move or slide longitudinally along the core member  103 . In such embodiments, the spacers  125  and/or the stent engagement members  123  can each have an inner lumen or aperture that receives the core member  103  therein such that the spacers  125  and/or the stent engagement members  123  can slide and/or rotate relative to the core member  103 . Additionally, in such embodiments, the proximal and distal restraints  119 ,  121  can be spaced apart along the core member  103  by a longitudinal distance that is slightly greater than the combined length of the spacers  125  and the stent engagement members  123 , so as to leave one or more longitudinal gaps between the first and second spacers  125   a - b , respectively, and the proximal and distal restraints  119 ,  121 . When present, the longitudinal gap(s) allow the spacers  125  and the stent engagement members  123  to slide longitudinally along the core member  103  between the restraints  119 ,  121 . The longitudinal range of motion of the spacers  125  and the stent engagement members  123  between the restraints  119 ,  121  is approximately equal to the total combined length of the longitudinal gap(s), if any. 
     Instead of or in addition to the longitudinal gap(s), the coupling assembly  120  can include radial gaps between the outer surface of the core member  103  and the inner surface of the spacers  125  and the stent engagement members  123 . Such radial gaps can be formed when the spacers  125  and/or the stent engagement members  123  are constructed with holes that are somewhat larger than the outer diameter of the corresponding portion of the core member  103 . When present, the radial gaps allow the spacers  125  and/or the stent engagement members  123  to rotate about the longitudinal axis of the core member  103  between the restraints  119 ,  121 . The presence of longitudinal gaps of at least a minimal size on either side of the spacers  125  and the stent engagement members  123  can also facilitate the rotatability of the spacers  125  and the stent engagement members  123 . 
     In some embodiments, the stent engagement members  123  can be mounted onto the core member  103  to permit not only rotational movement but also a degree of tilting of the engagement members  123  with respect to a longitudinal axis of the core member  103 . For example, the holes in the stent engagement members  123  can be larger than the outer diameter of the corresponding portion of the core member  103 , thereby permitting both rotational movement and tilting with respect to the core member  103 . “Tilting” as used herein means that the long axis of the stent engagement member  123  (i.e., an axis extending along the longest dimension of the stent engagement member  123 , substantially parallel to the proximal-facing and distal-facing end faces of the stent engagement member  123 ) is non-orthogonal to a longitudinal axis of the core member  103 . For example, in one tilted configuration, the long axis of the first stent engagement member  123   a  can intersect the core member  103  at approximately 85 degrees, indicating 5 degrees of tilt. Depending on the dimensions of the stent engagement members  123  and the core member  103 , the degree of tilting permitted can vary. In some embodiments, one or both of the stent engagement members  123  can tilt with respect to the core member  103  by 30 degrees or less, 20 degrees or less, 10 degrees or less, or 5 degrees or less. In some embodiments, one or both of the stent engagement members  123  can tilt with respect to the core member by at least 5 degrees, by at least 10 degrees, by at least 20 degrees, or more. 
     By permitting one or both of the stent engagement members  123  to tilt with respect to the core member  103 , the coupling assembly  120  can better navigate tortuous anatomy in which the delivery system  100  assumes highly curved states. Additionally, tilting of the stent engagement members  123  can facilitate resheathability of the overlying stent  105  from a partially deployed state. For example, a stent  105  can be in a partially deployed state when a portion of the stent  105  has been moved distally beyond a distal end  113  of the catheter  101  such that the stent  105  has been released from the second stent engagement member  123   b  yet the stent  105  remains engaged with the first stent engagement member  123   a . From this partially deployed state, the stent  105  can be resheathed or recaptured by distally advancing the catheter  101  with respect to the coupling assembly  120  (or, alternatively, by proximally retracting the core member  103  and coupling assembly  120  with respect to the catheter  101 ). During this movement, as the stent  105  moves proximally with respect to the catheter  101 , the stent  105  begins to collapse along its length until it assumes an outer diameter corresponding to the inner diameter of the catheter  101  and engages the second stent engagement member  123   b . With continued distal movement of the catheter with respect to the coupling assembly  120 , the second stent engagement member  123   b  is eventually received within the lumen  111  of the catheter  101 , with the stent  105  interlocked with the stent engagement member  123   b  and held in that relationship by the catheter. When the second stent engagement member  123   b  initially contacts the distal end  113  of the catheter  101 , there is some risk that the proximal-facing end face of the second stent engagement member  123   b  will abut the distal end  113  of the catheter  101 , thereby inhibiting the second stent engagement member  123   b  from being retracted into the lumen  111  of the catheter  101 . By allowing the second stent engagement member  123   b  to tilt with respect to the core member  103 , when the proximal-facing end face of the second stent engagement member  123   b  abuts a distal end of the catheter  101 , the second stent engagement member  123   b  can tilt to permit at least a portion of the second stent engagement member  223   b  to easily enter the lumen  111  of the catheter  101 . Once at least a portion of the second stent engagement member  123   b  is positioned within the lumen  111 , the coupling assembly  120  can continue to be retracted until the second stent engagement member  123   b  is fully received within the lumen  111 , and the stent  105  can be fully resheathed or recaptured. 
       FIG.  2    illustrates a side cross-sectional view of another embodiment of a medical device delivery system  200  configured in accordance with an embodiment of the present technology. The delivery system  200  can be configured to carry a stent (or other vascular implant or device)  205  thereon to be advanced through a surrounding catheter to a target site in a patient, similar to the operation described above with respect to  FIG.  1   . (The surrounding catheter is omitted in  FIG.  2    for clarity). The delivery system  200  can be advanced distally with respect to a distal end of the catheter to expand or deploy the stent  205  at the target site. 
     The delivery system  200  can be used with any number of catheters. For example, the catheter can optionally comprise any of the various lengths of the MARKSMAN™ catheter available from Medtronic Neurovascular of Irvine, Calif. USA. The catheter can optionally comprise a microcatheter having an inner diameter of about 0.030 inches or less, and/or an outer diameter of 3 French or less near the distal region. Instead of or in addition to these specifications, the catheter can comprise a microcatheter which is configured to percutaneously access the internal carotid artery, or another location within the neurovasculature distal of the internal carotid artery. 
     The delivery system  200  can comprise a core member or core assembly  202  configured to extend generally longitudinally through the lumen of a catheter. The core member  202  can have a proximal region  204  and a distal region  206 , which can optionally include a tip coil  208 . The core member  202  can also comprise an intermediate portion  210  located between the proximal region  204  and the distal region  206 . The intermediate portion  210  is the portion of the core member  202  onto or over which the stent  205  extends when the core member  202  is in the pre-deployment configuration as shown in  FIG.  2   . 
     The core member  202  can generally comprise any member(s) with sufficient flexibility and column strength to move a stent or other medical device through a surrounding catheter. The core member  202  can therefore comprise a wire, tube (e.g., hypotube), braid, coil, or other suitable member(s), or a combination of wire(s), tube(s), braid(s), coil(s), etc. The embodiment of the core member  202  depicted in  FIG.  2    is of multi-member construction, comprising a wire  212  with a tube  214  surrounding the wire  212  along at least a portion of its length. An outer layer  218 , which can comprise a layer of lubricious material such as PTFE (polytetrafluoroethylene or TEFLON™) or other lubricious polymers, can cover some or all of the tube  214  and/or wire  212 . The wire  212  may taper or vary in diameter along some or all of its length. The wire  212  may include one or more fluorosafe markers (not shown), and such marker(s) can be located on a portion of the wire  212  that is not covered by the outer layer  218  (e.g., proximal of the outer layer  218 ). This portion of the wire  212  marked by the marker(s), and/or proximal of any outer layer  218 , can comprise a bare metal outer surface. 
     The core member  202  can further comprise a proximal coupling assembly  220  and/or a distal interface assembly  222  that can interconnect the stent  205  with the core member  202 . The proximal coupling assembly  220  can comprise one or more stent engagement members  223   a - b  (together “engagement members  223 ”) that are configured to mechanically engage or interlock with the stent  205 . In this manner, the proximal coupling assembly  220  cooperates with an overlying inner surface of a surrounding catheter (not shown) to grip the stent  205  such that the proximal coupling assembly  220  can move the stent  205  along and within the catheter, e.g., as the user pushes the core member  202  distally and/or pulls the core member proximally relative to the catheter, resulting in a corresponding distal and/or proximal movement of the stent  205  within the catheter lumen. 
     The proximal coupling assembly  220  can, in some embodiments, be similar to any of the versions or embodiments of the coupling assembly  120  described above with respect to  FIG.  1   . For example, the proximal coupling assembly  220  can include proximal and distal restraints  219 ,  221  that are fixed to the core member  202  (e.g., to the wire  212  thereof in the depicted embodiment) so as to be immovable relative to the core member  202 , either in a longitudinal/sliding manner or a radial/rotational manner. The proximal coupling assembly  220  can also include a plurality of stent engagement members  223  separated by spacers  225   a - b  (together “spacers  225 ”). The stent engagement members  223  and spacers  225  can be coupled to (e.g., mounted on) the core member  202  so that the proximal coupling assembly  220  can rotate about the longitudinal axis of the core member  202  (e.g., of the intermediate portion  210 ), and/or move or slide longitudinally along the core member  202 . In some embodiments, the proximal restraint  219  comprises a substantially cylindrical body with an outer diameter that is greater than or equal to an outer diameter of the first spacer  225   a . The distal restraint  221  can taper in the distal direction down towards the core member  202 . This tapering can reduce the risk of the distal restraint  221  contacting an inner surface of the overlying stent  205 , particularly during navigation of tortuous vasculature, in which the system  200  can assume a highly curved configuration. In some embodiments, the distal restraint  221  can have an outside diameter or other radially outermost dimension that is smaller than the outside diameter or other radially outermost dimension of the overall proximal coupling assembly  220 , so that distal restraint  221  will tend not to contact the inner surface of the overlying stent  205 . 
     In the proximal coupling assembly  220  shown in  FIG.  2   , the stent  205  can be moved distally or proximally within an overlying catheter (not shown) via the proximal coupling assembly  220 . In some embodiments, the stent  205  can be resheathed via the proximal coupling assembly  220  after partial deployment of the stent  205  from a distal opening of the catheter, in a manner similar to that described above with respect to the coupling assembly  120  in  FIG.  1   . 
     The proximal coupling assembly  220  can be configured and function in a manner similar to the embodiment of the coupling assembly  120  depicted in  FIG.  1   . Specifically, the proximal restraint  219  can be made to function as a pushing element by appropriately sizing the outer diameter of the proximal restraint  219  and the length of the first spacer  225   a , such that the distal face of the proximal restraint  219  abuts the proximal end or edge of the stent  105 . When the proximal coupling element  220  is so arranged, the proximal restraint  219  can transmit at least some, or most or all, distally-directed push force to the stent  205  during delivery, and the stent engagement member(s)  223  do not transmit any distally-directed push force to the stent  205  during delivery (or transmit only a small portion of such force, or do so only intermittently). The stent engagement member(s)  223  can transmit proximally-directed pull force to the stent  205  during retraction or resheathing, and the proximal restraint  219  can transmit no proximally-directed pull force to the stent (or it may do so occasionally or intermittently, for example when a portion of the stent  205  becomes trapped between the outer edge of the proximal restraint  219  and the inner wall of the catheter). Again similarly to the coupling assembly  120  shown in  FIG.  1   , the first spacer  225   a  can optionally take the form of a solid tube when the proximal coupling assembly  220  includes a proximal restraint  219  configured as a pushing element. 
     Although the proximal coupling assembly  220  can be configured in such a manner, with the proximal restraint  219  abutting the stent  205  so that the proximal restraint  219  can be used as a pushing element, the coupling assembly  220  is depicted with a different configuration in  FIGS.  2  and  3 A- 3 B . The depicted configuration entails use of the stent engagement members  223  for both distal (delivery) and proximal (resheathing) movement of the stent  205 , as described elsewhere herein. 
     Optionally, the proximal edge of the proximal coupling assembly  220  can be positioned just distal of the proximal edge of the stent  205  when in the delivery configuration. In some such embodiments, this enables the stent  205  to be re-sheathed when as little as a few millimeters of the stent remains in the catheter. Therefore, with stents of typical length, resheathability of 75% or more can be provided (i.e. the stent can be re-sheathed when 75% or more of it has been deployed). 
     With continued reference to  FIG.  2   , the distal interface assembly  222  can comprise a distal engagement member  224  that can take the form of, for example, a distal device cover or distal stent cover (generically, a “distal cover”). The distal cover  224  can be configured to reduce friction between the stent  205  (e.g., a distal portion thereof) and the inner surface of a surrounding catheter. For example, the distal cover  224  can be configured as a lubricious, flexible structure having a free first end or section  224   a  that can extend over at least a portion of the stent  205  and/or intermediate portion  266  of the core member  202 , and a fixed second end or section  224   b  that can be coupled (directly or indirectly) to the core member  202 . 
     The distal cover  224  can have a first or delivery position, configuration, or orientation in which the distal cover can extend proximally relative to the distal tip  264 , or proximally from the second section  224   b  or its (direct or indirect) attachment to the core member  202 , and at least partially surround or cover a distal portion of the stent  205 . The distal cover  224  can be movable from the first or delivery orientation to a second or resheathing position, configuration, or orientation (not shown) in which the distal cover can be everted such that the first end  224   a  of the distal cover is positioned distally relative to the second end  224   b  of the distal cover  224  to enable the resheathing of the core member  202 , either with the stent  205  carried thereby, or without the stent  205 . As shown in  FIG.  2   , the first section  224   a  of the distal cover  224  can originate from the proximal end of the second section  224   b . In another embodiment, the first section  224   a  can originate from the distal end of the second section  224   b.    
     The distal cover  224  can be manufactured using a lubricious and/or hydrophilic material such as PTFE or Teflon®, but may be made from other suitable lubricious materials or lubricious polymers. The distal cover can also comprise a radiopaque material which can be blended into the main material (e.g., PTFE) to impart radiopacity. The distal cover  224  can have a thickness of between about 0.0005″ and about 0.003″. In some embodiments, the distal cover can be one or more strips of PTFE having a thickness of about 0.001″. 
     The distal cover  224  (e.g., the second end  224   b  thereof) can be fixed to the core member  202  (e.g., to the wire  212  or distal tip thereof) so as to be immovable relative to the core member  202 , either in a longitudinal/sliding manner or a radial/rotational manner. Alternatively, as depicted in  FIG.  2   , the distal cover  224  (e.g., the second end  224   b  thereof) can be coupled to (e.g., mounted on) the core member  202  so that the distal cover  224  can rotate about a longitudinal axis of the core member  202  (e.g., of the wire  212 ), and/or move or slide longitudinally along the core member. In such embodiments, the second end  224   b  can have an inner lumen that receives the core member  202  therein such that the distal cover  224  can slide and/or rotate relative to the core member  202 . Additionally, in such embodiments, the distal interface assembly  222  can further comprise a proximal restraint  226  that is fixed to the core member  202  and located proximal of the (second end  224   b  of the) distal cover  224 , and/or a distal restraint  228  that is fixed to the core member  202  and located distal of the (second end  224   b  of the) distal cover  224 . The distal interface assembly  222  can comprise a radial gap between the outer surface of the core member  202  (e.g., of the wire  212 ) and the inner surface of the second end  224   b . Such a radial gap can be formed when the second end  224   b  is constructed with an inner luminal diameter that is somewhat larger than the outer diameter of the corresponding portion of the core member  202 . When present, the radial gap allows the distal cover  224  and/or second end  224   b  to rotate about the longitudinal axis of the core member  202  between the restraints  226 ,  228 . 
     In some embodiments, one or both of the proximal and distal restraints  226 ,  228  can have an outside diameter or other radially outermost dimension that is smaller than the (e.g., pre-deployment) outside diameter or other radially outermost dimension of the distal cover  224 , so that one or both of the restraints  226 ,  228  will tend not to bear against or contact the inner surface of the catheter during operation of the core member  202 . Alternatively, it can be preferable to make the outer diameters of the restraints  226  and  228  larger than the largest radial dimension of the pre-deployment distal cover  224 , and/or make the outer diameter of the proximal restraint  226  larger than the outer diameter of the distal restraint  228 . This configuration allows easy and smooth retrieval of the distal cover  224  and the restraints  226 ,  228  back into the catheter post stent deployment. 
     In operation, the distal cover  224 , and in particular the first section  224   a , can generally cover and protect a distal region of the stent  205  as the stent  205  is moved distally through a surrounding catheter. The distal cover  224  may serve as a bearing or buffer layer that, for example, inhibits filament ends of the distal region of the stent  205  (where the stent comprises a braided stent) from contacting an inner surface of the catheter, which could damage the stent  205  and/or catheter, or otherwise compromise the structural integrity of the stent  205 . Since the distal cover  224  may be made of a lubricious material, the distal cover  224  may exhibit a low coefficient of friction that allows the distal region of the stent to slide axially within the catheter with relative ease. The coefficient of friction between the distal cover and the inner surface of the catheter can be between about 0.02 and about 0.4. For example, in embodiments in which the distal cover and the catheter are formed from PTFE, the coefficient of friction can be about 0.04. Such embodiments can advantageously improve the ability of the core member  202  to pass through the catheter, especially in tortuous vasculature. 
     Structures other than the herein-described embodiments of the distal cover  224  may be used in the core member  202  and/or distal interface assembly  222  to cover or otherwise interface with the distal region of the stent  205 . For example, a protective coil or other sleeve having a longitudinally oriented, proximally open lumen may be employed. In other embodiments, the distal interface assembly  222  can omit the distal cover  224 , or the distal cover can be replaced with a component similar to the proximal coupling assembly  220 . Where the distal cover  224  is employed, it can be connected to the distal tip coil  208  (e.g., by being wrapped around and enclosing some or all of the winds of the coil  208 ) or being adhered to or coupled to the outer surface of the coil by an adhesive or a surrounding shrink tube. The distal cover  224  can be coupled (directly or indirectly) to other portions of the core member  202 , such as the wire  212 . 
     In embodiments of the core member  202  that employ both a rotatable proximal coupling assembly  220  and a rotatable distal cover  224 , the stent  205  can be rotatable with respect to the core member  202  about the longitudinal axis thereof, by virtue of the rotatable connections of the proximal coupling assembly  220  and distal cover  224 . In such embodiments, the stent  205 , proximal coupling assembly  220  and distal cover  224  can rotate together in this manner about the core member  202 . When the stent  205  can rotate about the core member  202 , the core member  202  can be advanced more easily through tortuous vessels as the tendency of the vessels to twist the stent  205  and/or core member  202  is negated by the rotation of the stent  205 , proximal coupling assembly  220 , and distal cover  224  about the core member  202 . In addition, the required push force or delivery force is reduced, as the user&#39;s input push force is not diverted into torsion of the stent  205  and/or core member  202 . The tendency of a twisted stent  205  and/or core member  202  to untwist suddenly or “whip” upon exiting tortuosity or deployment of the stent  205 , and the tendency of a twisted stent to resist expansion upon deployment, are also reduced or eliminated. Further, in some such embodiments of the core member  202 , the user can “steer” the core member  202  via the tip coil  208 , particularly if the coil  208  is bent at an angle in its unstressed configuration. Such a coil tip can be rotated about a longitudinal axis of the system  200  relative to the stent, coupling assembly  220  and/or distal cover  224  by rotating the distal region  206  of the core member  202 . Thus the user can point the coil tip  208  in the desired direction of travel of the core member  202 , and upon advancement of the core member the tip will guide the core member in the chosen direction. 
       FIG.  3 A  is an enlarged perspective view of the coupling assembly  220  of the medical device delivery system  200 , and  FIG.  3 B  illustrates the coupling assembly  220  with an overlying stent  205 . The coupling assembly  220  includes first and second engagement members  223   a - b  mounted over the core member  202  adjacent to first and second spacers  225   a - b . The proximal restraint  219  is disposed proximally to the proximal-most spacer  225   a , and the distal restraint  221  is disposed distally to the distal-most engagement member  223   b . As shown in  FIG.  3 B , the first and second stent engagement members  223   a  and  223   b  can interlock with the stent  205 , e.g. by projecting into the pores thereof. The engagement members  223  can thereby secure the stent  205 , in cooperation with an overlying catheter (not shown). 
       FIGS.  4 A and  4 B  are side and cross-sectional views, respectively of a spacer configuration which can serve as the first spacer  225   a  of the coupling assembly  220 , or as any spacer of any embodiment of the coupling assemblies or delivery systems disclosed herein. In at least some embodiments, the first spacer  225   a  includes a wire coil  230  defining a central lumen  232  through which the core member  202  extends. The coil  230  can have a proximal end face  234  and an opposing distal end face  236 . The end faces  234 ,  236  can be substantially planar and substantially orthogonal to a longitudinal axis of the coil  230 . For example, in some embodiments the end faces  234 ,  236  can be ground, polished, or otherwise flattened to provide planar surfaces that are substantially orthogonal to a long axis of the spacer  225   a . This can improve the pushability or column strength of the overall system  200  as the planar surface increases the contact area between the proximal restraint  219  and the proximal end face  234 , and also increase the contact area between the distal end face  236  of the spacer  225   a  and the first stent engagement member  223   a.    
     In some embodiments, the coil wire  230  is a zero-pitch coil configured such that, in an unconstrained condition, each winding of the coil  230  is in direct contact with an adjacent winding of the coil  230 . In such embodiments, the coil  230  can be substantially incompressible along an axial direction under the forces typically encountered during use of the delivery system  200 . This incompressibility can provide the pushability of a solid tube spacer while also permitting the bending flexibility of a coil. During bending of the coil  230 , one or more of the windings of the coil  230  may become partially separated from one another to accommodate the bending movement. In the absence of external forces, the coil  230  can return to its unconstrained state (i.e., having zero pitch). 
     With continued reference to  FIGS.  4 A and  4 B , the lumen  232  of the coil  230  can define an inner diameter ID that is slightly larger than a corresponding outer diameter of the core member  202 . For example, in some embodiments the lumen  232  can have a diameter of approximately between about 0.008″-0.02″, or between about 0.0160″-0.018″, or between about 0.0165″-0.017″. In at least some embodiments, the coil  230  can be free to rotate with respect to the core member  202 . In other embodiments, the coil wire  230  can be rotationally fixed with respect to the core member  202 , for example by attaching all or a portion of the coil  230  to the core member  202  using solder, adhesive, or other attachment technique. In some embodiments, the coil  230  can have a radially outermost diameter (OD) that is smaller than a radially outermost diameter of the stent engagement members  223  ( FIGS.  3 A and  3 B ) such that the coil  230  does not contact the overlying stent  205  during normal operation of the delivery system  200 . In some embodiments, the radially outermost diameter OD of the coil  230  can be between about 0.008″-0.02″, or between about 0.016″-0.018″, or between about 0.0165″-0.017″. 
     In some embodiments, the wire that forms the coil  230  can have an individual thickness or strand diameter SD ( FIG.  4 B ) of between about 0.0015-0.006″, or approximately 0.005″. The wire forming the coil  230  can have a square or rectangular cross-section along its length. With such a square or rectangular cross-section, the wire can form winds having flat surfaces that face in the distal and proximal directions. Longitudinally adjacent flat surfaces contact each other and the flat nature of the surfaces provides for a stable, non-bending structure under longitudinally compressive loads. At the same time, the overall coil configuration of the spacer is flexible and bendable under bending loads. The longitudinal length L of the spacer  225  can vary according to the desired positioning between a proximal restraint  219  and the first stent engagement member  223   a  ( FIGS.  3 A and  3 B ). For example, in some embodiments the longitudinal length L can be between about 0.03″-0.05″, or between about 0.036″-0.042″, or approximately 0.039″. In other embodiments, as mentioned above, the first spacer  225   a  can be a rigid and/or solid tube. 
     In some embodiments, the second spacer  225   b  can be configured similarly to the first spacer  225   a , i.e., the second spacer  225   b  can also be a coil such as a zero-pitch coil rotatably mounted over the core member  202 . In other embodiments, the second spacer  225   b  can be a solid tubular member. The second spacer  225   b  can have a substantially cylindrical outer surface, substantially planar proximal and distal end faces, and an inner lumen configured to slidably receive the core member  202  therethrough. As described in more detail below, the second spacer  225   b  can also be configured to have a longitudinal length to separate the first engagement member  223   a  and the second engagement member  223   b  by a desired amount. For example, in at least some embodiments, the second spacer  225   b  can have a length such that the first engagement member  223   a  is separated from the second engagement member  223   b  by approximately 1-3 times the pore pitch of the overlying stent  205 , for example in some embodiments approximately equal to the pore length of the overlying stent  205 . 
     In some embodiments, the first spacer  225   a  and/or the second spacer  225   b  can be coated with a lubricious material, for example PTFE, parylene, or other coating. The coating can be provided along an outer surface of the spacer  225 , within an interior lumen (e.g., lumen  232  of the coil  230 ), or both. In some embodiments, the lubricious coating improves the rotatability of the spacer  225  with respect to the core member  202  and can also reduce friction between the spacer  225  and the overlying stent  205  or catheter in the event that the spacer  225  contacts these components during use of the delivery system  200 . 
       FIGS.  5 A- 5 C  are side, end, and perspective views, respectively, of a stent engagement member  223  of the coupling assembly  220  shown in  FIGS.  3 A and  3 B .  FIG.  6 A  is a schematic cross-sectional view of the stent engagement member  223  engaging the stent  205  within an overlying catheter  267 , and  FIG.  6 B  is an enlarged detail view of a portion of the stent  205 . The depicted stent  205  is braided (although other types of stent, as disclosed elsewhere herein may be used) and includes a mesh  263  forming a plurality of pores  265  which are bounded by filaments, wires or struts and separated by points where the filaments, wires or struts cross (e.g., in the case of a braided or woven device) or intersect (e.g., in the case of a laser-cut device). 
     Referring to  FIGS.  3 A,  3 B, and  5 A- 6 B  together, each of the stent engagement members  223  can have a plate-like or sprocket-like configuration with first and second end faces  251 ,  253  and a side surface  255  extending between the first and second end faces  251 ,  253 . In the assembled delivery system  200 , the first and second end faces  251 ,  253  can be oriented and maintained substantially orthogonal to a long axis of the core member  202  (or the engagement members can be configured to tilt to a desired degree, as discussed elsewhere herein). This can be achieved by configuring the spacers  225  with distal and proximal end faces that are orthogonal to the longitudinal axis of each spacer  225  (and/or to the core member  202 ), and/or minimizing the amount of longitudinal movement space (or “play”) among the stent engagement members and spacers of the coupling assembly  220 . Each stent engagement member forms a plurality of radially extending projections  257  separated by recesses  259 . In the illustrated embodiment, there are four projections  257  separated by four recesses  259 . However, in other embodiments the number of projections can vary, for example two, three, four, five, six, seven, or more projections separated by a corresponding number of recesses. 
     In some embodiments, the projections  257  include rounded edges or convex portions and the recesses  259  include rounded depressions or convex portions. During use of the delivery system  200 , the rounded edges can reduce scraping of the projections  257  against the inner wall of an overlying catheter  267 , which reduces generation of particulates and damage to the catheter  267 . When the delivery system  200  is used with a braided stent such as the depicted stent  205 , the recesses  259  can be sized to accommodate the thickness of braid wire crossings such that each projection  257  can extend at least partially into a pore  265  of the stent  205  between the adjacent wire crossings and the wire crossings surrounding the pore  265  can be at least partially received within the recesses  259  of the stent engagement member. In other embodiments, the projections and/or the recesses can assume other forms, for example with sharper or flatter peaks formed by the projections  257 . 
     Each stent engagement member  223  can include an opening or central aperture  261  configured to receive the core member  202  therethrough. The opening of the aperture  261  can be larger than the diameter of the core member  202  such that the stent engagement members  223  can rotate about the long axis of the core member  202 . As noted above, in some embodiments, the aperture  261  can be sufficiently larger than the diameter of the core member  202  to permit a degree of tilting of the engagement members  223  with respect to a longitudinal axis of the core member  202 . 
     The stent engagement members  223  can be made to have a relatively thin and/or plate-like or sprocket-like configuration. Such a configuration can facilitate the formation of projections  257  that are small enough to fit inside the pores  265  of the stent  205 . Accordingly, the stent engagement members  223  may be characterized by a largest radial dimension or diameter D along the first and second end faces  251 ,  253 , and a thickness T measured along the side surface  255 . In some embodiments, the diameter D is at least five times greater than the thickness T. In at least one embodiment, the thickness T is between approximately 25-200 microns, or 50-100 microns, for example, approximately 80 microns. 
     To effectively push or pull the stent  205  along a surrounding catheter, the stent engagement members  223  can be made to be rigid (e.g., incompressible by the forces encountered in typical use of the delivery system). The rigidity of the stent engagement members  223  can be due to their material composition, their shape/construction, or both. In some embodiments, the stent engagement members  223  are made of metal (e.g., stainless steel, Nitinol, etc.) or rigid polymers (e.g., polyimide, PEEK), or both. In some embodiments, even if the stent engagement member is made of a rigid material, based on structural characteristics the stent engagement member itself may be non-rigid and at least partially compressible. 
     As noted above, the spacers  225  can be substantially cylindrical bodies having a smaller outer diameter than a largest outer diameter of the stent engagement members  223 . In some embodiments, the spacers  225  include a central aperture sized and configured to allow the spacers  225  to be rotatably mounted over the core member  202 . As mentioned previously, the spacers  225  can have end walls that are orthogonal to a long axis of the core member  202 . These orthogonal end walls can help preserve the orthogonal orientation of the stent engagement members  223  relative to the core member  202  to prevent loss of engagement with stent  205 . (Alternatively, the engagement members can be configured to tilt to a desired degree, as discussed elsewhere herein.) As described above, in some embodiments one or both of the first and second spacers  225   a  and  225   b  can be a wire coil defining a cylindrical body mounted over the core member  225   a , for example a zero-pitch coil. In other embodiments, one or both of the first and second spacers  225   a  and  225   b  can take other forms, for example a solid cylindrical tube or other element coupled to the core member  202 . 
     In some embodiments, the coupling assembly  220  can be configured to engage only a proximal portion (e.g., the proximalmost 5%, the proximalmost 10%, the proximalmost 20%, only a proximal half, etc.) of the stent  205 . In other embodiments, coupling assembly  220  can engage the stent  205  along substantially its entire length. 
     The stent engagement members  223  can mechanically interlock with or engage the stent  205  such that each projection  257  is at least partially received within one of the pores  265 . In some embodiments, the first engagement member  223   a  can engage with a proximal portion of the stent  205 , for example at a position less than 5 pores or pore lengths away from a proximal end of the stent, or less than 3 pores or pore lengths away from the proximal end of the stent  205 , etc. The spacers  225  can be configured with a length such that the projections  257  of adjacent stent engagement members  223  (e.g., the first stent engagement member  223   a  and adjacent second stent engagement member  223   b ) are spaced apart longitudinally by a distance that is substantially equal to the “pore length” (or “pore pitch”) of the stent  205  (defined herein as the longitudinal distance between the centers of longitudinally adjacent and non-overlapping pores  265  when the stent is in the compressed configuration wherein the outer diameter of the stent is equal to the inner diameter of the catheter) or, in some embodiments, a whole-number multiple of the pore length of the stent  205 . For example, in some embodiments, the first and second stent engagement members  223   a  and  223   b  are spaced apart by between about 1-3 times the pore length of the stent  205  when the stent is at the inner diameter of the catheter  267 . Accordingly, each projection can extend into and engage one of the pores  265  of the stent  205 . 
       FIG.  6 B  is a schematic illustration of a portion of the stent  205 , which includes a plurality of pores  265   a - 265   d . As noted above, projections  257  of the stent engagement member  223  can engage individual pores  265  of the stent  205 . In some embodiments, adjacent stent engagement members  223  engage longitudinally adjacent pores  265  of the stent  205 . As used herein, “longitudinally adjacent” means that there is not an intervening pore in the longitudinal direction between the two pores. Longitudinally adjacent pores, however, can be non-adjacent radially, e.g., a first pore located at the “twelve o&#39;clock” position on the circumference of the stent can be longitudinally adjacent to a second pore located at the “six o&#39;clock” position on the circumference of the stent (or at any point on the circumference in between) if, in the longitudinal direction, there is no intervening pore between the two. For example, referring to  FIG.  6 B , the first pore  265   a  is longitudinally adjacent to each of the second pore  265   b , the third pore  265   c , and the fourth pore  265   d . However, the first pore  265   a  is not longitudinally adjacent to the fifth pore  265   e , because there are intervening pores between the two. In other embodiments, adjacent stent engagement members  223  engage pores which are not longitudinally adjacent but are spaced apart longitudinally by one or more intervening pores, for example the first pore  265   a  and the fifth pore  265   e . Therefore, the first and second stent engagement members  223   a  and  223   b  can be spaced apart from one another by a longitudinal distance corresponding to the pore pitch of the stent  205 , or by a longitudinal distance corresponding to a whole number multiple of the pore pitch. 
     In some embodiments, the longitudinal spacing between the first and second stent engagement members  223   a  and  223   b  can be slightly less than the pore length (e.g., 50% less, 40% less, 30% less, 20% less, 10% less, or 5% less than the pore length, etc.), or slightly less than a whole number multiple of the pore length (e.g., less by a decrement equal to 50%, 40%, 30%, 20%, 10%, or 5% of a single pore length, etc.). This slightly smaller spacing between the first and second stent engagement members  223   a  and  223   b  can provide improved grip on the stent  205  by minimizing the longitudinal “play” between the projections  257  of the first and second engagement members  223   a  and  223   b  and the wire crossing(s) or intersection point(s) positioned between the engagement members. As a result, a longitudinal movement of the core member causes a corresponding longitudinal movement of the stent with minimal delay and high precision. For example, a proximal movement of the core member (and/or the engagement member(s) carried thereby) causes a proximal movement of the stent, with the engagement member(s) moving no more than a first lag distance relative to the stent before initiating proximal movement of the stent. The first lag distance can be more than 40% of the pore length of the stent, or no more than 33%, or no more than 25%, or no more than 20%, or no more than 15%, or no more than 10%, or no more than 5% of the pore length. Instead of or in addition to such a first pore length, a distal movement of the core member (and/or the engagement member(s) carried thereby) causes a distal movement of the stent, with the engagement member(s) moving no more than a second lag distance relative to the stent before initiating distal movement of the stent. The second lag distance can be more than 40% of the pore length of the stent, or no more than 33%, or no more than 25%, or no more than 20%, or no more than 15%, or no more than 10%, or no more than 5% of the pore length. 
     The interaction between the projections  257  and the pores  265  can produce a mechanical interlock between stent engagement member  223  and the pores  265 . This is in contrast to a conventional compressible pad that resiliently pushes against the stent as a whole, including the wire crossings. In at least some embodiments, the mechanical interlock provided by the stent engagement members  223  secures the stent  205  without pressing against the wire crossings of the stent  205 . In some embodiments, the stent engagement members  223  are configured to secure a range of different stent sizes within a given catheter size (e.g., within a 0.017″, 0.021″ or 0.027″ catheter (inside diameter)). 
     The stent engagement members  223  can be made of substantially rigid materials, for example metal, biocompatible polymers (e.g., PEEK), or other suitable materials. In some embodiments, the stent engagement members  223  can be made of stainless steel and manufactured using laser cutting followed by electropolishing. For example, a plurality of engagement members can be laser-cut from a sheet of stainless steel having the desired thickness (e.g., approximately 100 microns thick). Electropolishing can further reduce the thickness of the resulting stent engagement members, for example from 100 microns to approximately 80 microns. In other embodiments, the stent engagement members can be manufactured using other techniques, for example injection molding, chemical etching, or machining. 
     Note that various components of the delivery system  200  of  FIGS.  2 - 6    can be incorporated into the delivery system  100  of  FIG.  1   , and vice versa. For example, any of the disclosed embodiments of the coupling assembly  220  can be employed as the coupling assembly  120  of the delivery system  100 . Similarly, any of the embodiments of the stent engagement members  223  can be employed as the stent engagement member(s)  123  of the delivery system  100 , and/or any of the embodiments of the spacers  225  can be employed as the spacer(s)  125  of the delivery system  100 . Although many embodiments discussed herein include two engagement members  223 , in other embodiments the delivery system  200  can include three, four, or more engagement members separated from one another by additional spacers. The spacing of such additional engagement members can be regular or irregular. For example, in one embodiment a third engagement member can be provided at a position configured to engage a distal region of the overlying stent, while the first and second engagement members engage only a proximal region of the overlying stent. 
     Additional Examples of Stent Engagement Members for Coupling Assemblies 
     In various embodiments, the stent engagement members of the coupling assembly can take additional forms. For example, the number of projections, the contours of the projections and recesses, the material selected, and dimensions can all vary to achieve desired operation of the coupling assembly.  FIGS.  7 A- 11 C  illustrate various alternative embodiments of stent engagement members. These stent engagement members can be incorporated into and combined with the coupling assemblies  120  and  220  described above with respect to  FIGS.  1 - 6   . Additionally, aspects of these stent engagement members can be combined and intermixed such that features of any one of these stent engagement members (e.g., the number of protrusions or recesses, etc.) can be combined with the features of any of the other stent engagement members disclosed herein (e.g., the width of the contact region, spacing of the protrusions, etc.). In some embodiments, the individual stent engagement members of a given coupling assembly can be substantially identical in shape, size, and construction. In other embodiments, however, the properties of the individual stent engagement members can vary within a single coupling assembly, such as having different sizes, shapes, or material construction. For example, a single coupling assembly can have a first stent engagement member having a given number of protrusions, and a second stent engagement member having a different number of protrusions. 
       FIG.  7 A  illustrates a perspective view of another embodiment of a stent engagement member  723 , and  FIG.  7 B  illustrates a cross-sectional view of the stent engagement member  723  of  FIG.  7 A  engaged with an overlying stent  705  disposed within a catheter  767 . Embodiments of the engagement member  723  can be similar to those described above with respect to the engagement member  223 , except that the engagement member  723  includes three projections  757  separated by three recesses  759 . The engagement member  723  engages and mechanically interlocks with an overlying stent  705 , and the surrounding catheter  767  helps maintain such engagement until the interlocked portion of the stent exits the catheter. The stent  705  includes a mesh  763  defining a plurality of pores  765  which are separated by points where the wires, filaments, struts etc. of the mesh  763  cross (e.g., in the case of a braided stent) or intersect (e.g., in the case of a laser-cut stent). The radially extending projections  757  can each extend at least partially into a pore  765  of the stent  705  between adjacent crossing or intersection points and the crossing or intersection points surrounding the pore  765  can be at least partially received within the recesses  759  of the stent engagement member  723 . In other embodiments, the projections and/or the recesses can assume other forms, for example with sharper or flatter peaks formed by the projections  759 . The stent engagement member  723  includes an opening or central aperture  761  configured to receive a core member or core assembly therethrough. The opening of the aperture  761  can be larger than the diameter of the core member such that the stent engagement member  763  can rotate about the long axis of the core member. As noted above, in some embodiments, the aperture  761  can be sufficiently larger than the diameter of the core member to permit a degree of tilting of the engagement member  723  with respect to a longitudinal axis of the core member. 
       FIG.  8 A  illustrates a perspective view of another embodiment of a stent engagement member  823 , and  FIG.  8 B  illustrates a cross-sectional view of the stent engagement member  823  of  FIG.  8 A  engaged with an overlying stent  805  disposed within a catheter  867 . Embodiments of the engagement member  823  can be similar to those described above with respect to the engagement members  223  and  723 , except that the engagement member  823  includes six projections  857  separated by six recesses  859 . The stent  805  includes a mesh  863  defining a plurality of pores  865  which are separated by points where the wires, filaments, struts, etc. of the mesh cross or intersect. The radially extending projections  857  can each extend at least partially into a pore  865  of the stent  805  between adjacent crossing or intersection points, and the crossing or intersection points surrounding the pore  865  can be at least partially received within the recesses  859  of the stent engagement member  823 . In other embodiments, the projections and/or the recesses can assume other forms, for example with sharper or flatter peaks formed by the projections  859 . A central aperture  861  can be configured to receive a core member or core assembly therethrough and can be sized to permit the stent engagement member  823  to rotate and/or tilt with respect to the core member. 
     Depending on the particular construction of the overlying stent  705 ,  805 , in some embodiments the protrusions  757 ,  857  of the stent engagement members  723 ,  823  can be radially evenly spaced around the engagement members. For example, with respect to  FIG.  7 B , the center point of each protrusion  759  can be separated from the next protrusion  759  by 120 degrees. Similarly, as shown in  FIG.  8 B , the six protrusions  857  of the stent engagement member  823  can be radially evenly spaced around the engagement member  823 , such that each protrusion  857  is separated from an adjacent protrusion  857  by 60 degrees. In braided stents, the number of strands defines the number of available pores radially aligned along any particular longitudinal location of the stent. For example,  FIGS.  7 B and  8 B  illustrate a cross-sectional views of 48-wire braided stents  705 ,  805  engaged with the stent engagement members  723  and  823 , respectively. The 48-wire stents  705 ,  805  each defines 24 pores  765 ,  865  around the circumferences of the stents  705 ,  805 . In some embodiments, aligning each protrusion  757 ,  857  with a pore  765 ,  865  improves the strength with which the stent engagement member  723 ,  823  interlocks with the overlying stent  705 ,  805 , as well as overall mechanical fit and compatibility. Accordingly, it can be advantageous to align the protrusions  757 ,  857  with pores  765 ,  865  of the overlying stents  705 ,  805 . Since the stent  705  of  FIG.  7 B  includes 24 pores  765 , and since the 24 pores can be evenly divided into thirds, the three protrusions  757  of the stent engagement member  723  can be radially evenly spaced while each being aligned with one of the pores  765 . Similarly, since the stent  805  of  FIG.  8 B  includes 24 pores  865 , and since the 24 pores can be evenly divided into sixths, the six protrusions  857  of the stent engagement member  823  can be radially evenly spaced while each being aligned with one of the pores  865 . In other embodiments, the number of protrusions can be two, four, or eight, and the protrusions can be evenly spaced around the stent engagement member. 
     In other embodiments, the number of protrusions of the stent engagement member and the number and/or location of pores defined by the overlying stent can be such that even radial spacing of the protrusions would be disadvantageous. For example, a braided stent with 48 wires (and 24 pores) can be used with a stent engagement member that has 5 protrusions, in which case these protrusions cannot be evenly spaced around the engagement member and still each be aligned with pores of the stent. As another example, a braided stent with 54 wires will define 27 pores at a particular longitudinal position of the stent. Since the 27 pores cannot be evenly divided among four, five, or six protrusions, the protrusions may instead be unevenly radially spaced. In yet another example, a 64-wire stent will have 32 pores, which cannot be evenly divided among three, five, or six protrusions. In each of these cases, it can be advantageous to provide a stent engagement member with protrusions that are unevenly spaced apart from one another around a circumference of the engagement member. Similarly, in the case of a laser-cut stent, the pores may not be evenly radially spaced around the circumference of the device, and a stent engagement member with unevenly radially spaced can be useful with such a stent. 
       FIGS.  9 A- 10 B  illustrate two embodiments of such stent engagement members with unevenly spaced protrusions. Embodiments of the stent engagement members  923 ,  1023  described herein can be similar to the stent engagement members  123 ,  223 ,  723 , and  823  described above, except that at least some embodiments can include unevenly spaced protrusions.  FIGS.  9 A and  9 B  illustrate side and bottom views, respectively, of the stent engagement member  923 , which includes a six protrusions  957   a - f  separated by six recesses  959   a - f . As shown in  FIG.  9 A , the recesses  959   a - f  can be shaped and sized differently from one another such that the protrusions  959   a - f  are not evenly spaced around the periphery of the engagement member  923 . For example, the space or angular separation between the first protrusion  957   a  and second protrusion  957   b  is less than the space or angular separation between the second protrusion  957   b  and the third protrusion  957   c . In one example, the angle between the first protrusion  957   a  and the second protrusion  957   b  can be 55.8 degrees, while the angle between the second protrusion  957   b  and the third protrusion  957   c  can be 68.5 degrees. This varied spacing can be achieved, e.g., by varying the structure of the individual recesses  959   a - f . For example, each recess  959   a - f  can include a concave surface which curves inwardly between adjacent protrusions  959   a - f . Certain recesses can have a larger surface area and/or a larger radius of curvature than other protrusions, thereby extending the radial spacing between adjacent protrusions. For example, the second recess  959   b  has both a greater surface area and a greater radius of curvature than the first recess  959   a . This structure results in the spacing between the first and second protrusions  957   a  and  957   b  being smaller than the spacing between the second and third protrusions  957   b  and  957   c . In the illustrated embodiment, the first recess  959   a , third recess  959   c , fourth recess  9859   d , and sixth recess  959   d  are similarly configured to provide corresponding radial spacing between adjacent protrusions of approximately 55.8 degrees, while the second recess  959   b  and the fifth recess  959   e  are similarly configured to provide corresponding radial spacing between adjacent protrusions of approximately 68.5 degrees. This provides radial symmetry about certain axes, while also providing uneven spacing for improved engagement with an overlying stent. Other variations are possible, in which the particular angles between adjacent protrusions can be varied within ranges such that each protrusion  957   a - f  is configured to project into or mechanically interlock with a pore of an overlying stent. 
     As seen best in  FIG.  9 B , the engagement member  923  includes opposing first and second end faces  951 ,  953 , with a side surface  955  extending between the two. The protrusions  957   a - f  and the recesses  959   a - f  can all be disposed along the side surface  955 . In some embodiments, the edge formed at the intersection of the first end face  951  and the side surface  955  and the edge formed at the intersection of the second end face  953  and the side surface  955  can both be rounded. In particular, the edges at the projections  957   a - f  can be rounded, since in at least some embodiments only these outermost portions of the engagement member  923  contact (or otherwise engage with) an overlying stent or catheter. In contrast to embodiments in which there is a sharp edge between these surfaces (e.g., approximately a right-angle between two planar and orthogonal surfaces), the rounded edges can reduce scraping against a catheter inner wall, reducing damage and generation of particulate matter when an overlying catheter is moved with respect to the engagement member  923 . 
       FIGS.  10 A and  10 B  illustrate side and bottom views, respectively, of another embodiment of a stent engagement member  1023  with five protrusions  1057   a - e  that are unevenly spaced apart from one another by five recesses  1059   a - e . The recesses  1059   a - e  can be shaped and sized differently from one another such that the protrusions  1059   a - e  are not evenly spaced around the periphery of the engagement member  1023 . Rather, angle between the first protrusion  1057   a  and second protrusion  1057   b , and the angle between the first protrusion and the fifth protrusion  1057   e , can each be approximately 78.8 degrees. In contrast, the angle between the second protrusion  1057   b  and the fourth protrusion  1059   b , and the angle between the fourth protrusion  1057   d  and the fifth protrusion  1057   e , can each be approximately 67.7 degrees. Finally, the angle between the third protrusion  1057   c  and the fourth protrusion  1057   d  can be approximately 66.9 degrees. This varied spacing can be achieved by varying the structure of the individual recesses  1059   a - e . For example, the first recess  1059   a  has both a greater surface area and a greater radius of curvature than the second recess  1059   b , resulting in the spacing between the first and second protrusions  1057   a  and  1057   b  being greater than the spacing between the second and third protrusions  1057   b  and  1057   c . Other variations are possible, in which the particular angles between adjacent protrusions can be varied within ranges such that each protrusion  1057   a - e  is configured to project into or mechanically interlock with a pore of an overlying stent. 
     As seen best in  FIG.  10 B , the engagement member  1023  includes opposing first and second end faces  1051 ,  1053 , with a side surface  1055  extending between the two. The protrusions  1057   a - e  and the recesses  1059   a - e  can all be disposed along the side surface  1055 . As discussed above with reference to  FIG.  9 B , in some embodiments, the edges formed at the intersection of the first end face  1051  and the side surface  1055  and formed at the intersection of the second end face  1053  and the side surface  1055  can be rounded to reduce friction and damage to an overlying catheter or the stent. 
       FIGS.  11 A- 11 C  illustrate enlarged detail views of projections  1157   a - c  of stent engagement members in accordance with different embodiments. As described above with respect to engagement members  123 ,  223 ,  723 ,  823 ,  923 , and  1023 , engagement members can include a plurality of projections separated by recesses. The projections can form the radially outer-most components of the stent engagement members, which in use can contact an overlying stent or otherwise interlock with it, in cooperation with an overlying catheter inner wall. The projections  1157   a - c  each include an outermost contact region  1169 , characterized by a length D, which is configured to contact (or otherwise engage with) an overlying stent. The contact region  1169  can include a central portion  1171  flanked by opposing shoulder portions  1173   a  and  1173   b . The shoulder portions  1173   a  and  1173   b  can extend between the central portion  1171  and opposing extensions  1175   a  and  1175   b . The extensions  1175   a  and  1175   b  extend away from the contact region  1169  and towards corresponding recesses (not shown) of the stent engagement member. The central portion  1171  can have a substantially planar outermost surface, which can be coplanar with the adjacent shoulder portions  1173   a  and  1173   b . However, the shoulder portions  1173   a  and  1173   b  can have curved outer surfaces which joint the central portion  1171  and the adjacent extensions  1175   a  and  1175   b.    
     Together, the central portion  1171  and shoulder portions  1173   a ,  1173   b  define the length D of the contact region  1169 . In certain embodiments, it can be advantageous to increase the overall surface area of the contact region  1169  by increasing the length D as compared to embodiments in which there is little or no central portion  1171 . Among the embodiments shown in  FIGS.  11 A-C , the length D of the contact region  1169  is varied such that the length D is greatest in the protrusion  1157   a  of  FIG.  11 A , then smaller in the protrusion  1157   b  of  FIG.  11 B , and smallest in the protrusion  1157   c  of  FIG.  11 C . As a result, the protrusion  1157   a  has the greatest surface area configured to contact an overlying stent or catheter, followed by protrusion  1157   b  which has a smaller surface area configured to contact an overlying stent or catheter, and finally protrusion  1157   c  having a still smaller surface area configured to contact an overlying stent or catheter. In various embodiments, the length D of the contact region  1169  can be between about 0.001″-0.004″, or between about 0.002″-0-0.003″. For example, in some embodiments the contact region  1169  can have a length D of about 0.002″, about 0.0025″, or about 0.003″. As will be appreciated, the various embodiments of the contact region  1169  can generally comprise a flat or planar central region, and first and second shoulders on either side of the central region. The shoulders can be rounded in up to two directions (radially as seen in  FIGS.  11 A- 11 C , and/or axially as seen in  FIGS.  9 B and  10 B ). 
     Conclusion 
     This disclosure is not intended to be exhaustive or to limit the present technology to the precise forms disclosed herein. Although specific embodiments are disclosed herein for illustrative purposes, various equivalent modifications are possible without deviating from the present technology, as those of ordinary skill in the relevant art will recognize. In some cases, well-known structures and functions have not been shown and/or described in detail to avoid unnecessarily obscuring the description of the embodiments of the present technology. Although steps of methods may be presented herein in a particular order, in alternative embodiments the steps may have another suitable order. Similarly, certain aspects of the present technology disclosed in the context of particular embodiments can be combined or eliminated in other embodiments. Furthermore, while advantages associated with certain embodiments may have been disclosed in the context of those embodiments, other embodiments can also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages or other advantages disclosed herein to fall within the scope of the present technology. Accordingly, this disclosure and associated technology can encompass other embodiments not expressly shown and/or described herein. 
     Throughout this disclosure, the singular terms “a,” “an,” and “the” include plural referents unless the context clearly indicates otherwise. Similarly, unless the word “or” is expressly limited to mean only a single item exclusive from the other items in reference to a list of two or more items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. Additionally, the terms “comprising” and the like are used throughout this disclosure to mean including at least the recited feature(s) such that any greater number of the same feature(s) and/or one or more additional types of features are not precluded. Directional terms, such as “upper,” “lower,” “front,” “back,” “vertical,” and “horizontal,” may be used herein to express and clarify the relationship between various elements. It should be understood that such terms do not denote absolute orientation. Reference herein to “one embodiment,” “an embodiment,” or similar formulations means that a particular feature, structure, operation, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present technology. Thus, the appearances of such phrases or formulations herein are not necessarily all referring to the same embodiment. Furthermore, various particular features, structures, operations, or characteristics may be combined in any suitable manner in one or more embodiments.