Covering and method using electrospinning of very small fibers

• US 20030195611A1
• Filed: 12/06/2002
• Published: 10/16/2003
• Est. Priority Date: 04/11/2002
• Status: Abandoned Application

• Current Assignee: Stout Medical Group, L.P. (Alphatec Holdings Incorporated)
• Original Assignee: Stout Medical Group, L.P. (Alphatec Holdings Incorporated)
• Inventors: Schwartz, Robert S., Greenhalgh, Skott E., Kiefer, Rob
• Application Number:
  US10/314,086
• Publication Number:
  US 20030195611A1
• Time in Patent Office: Days
• US Class Current: 623/1.15
• CPC Class Codes: A61F 2/07 Stent-grafts
• CPC Class Codes: A61F 2/89 the wire-like elements comprising two or more adjacent rings flexibly connected by separate members
• CPC Class Codes: A61F 2002/072 Encapsulated stents, e.g. wire or whole stent embedded in lining
• CPC Class Codes: A61F 2002/075 the stent being loosely attached to the graft material, e.g. by stitching
• CPC Class Codes: A61L 31/16 Biologically active materials, e.g. therapeutic substances A61L31/047 takes precedence
• CPC Class Codes: D01D 5/0084 Coating by electro-spinning, i.e. the electro-spun fibres are not removed from the collecting device but remain integral with it, e.g. coating of prostheses

Abstract

A versatile covering process enabled through the identification and manipulation of a plurality of variables present in the electrospinning method of the present invention. By manipulating and controlling various identified variables, it is possible to use electrospinning to predictably produce thin materials having desirable characteristics. The fibers created by the electrospinning process have diameters averaging less than 100 micrometers. Proper manipulation of the identified variables ensures that these fibers are still wet upon contacting a target surface, thereby adhering with each other to form a cloth-like material and, if desired, adhering to the target surface to form a covering thereon. The extremely small size of these fibers, and the resulting interstices therebetween, provides an effective vehicle for drug and radiation delivery, and forms an effective membrane for use in fuel cells.

Claims

1. A method of producing a fibrous covering comprising:

charging a spinneret with an electric potential relative to a predetermined location on a target plate;

placing an object between said spinneret and said predetermined location on said target plate;

forcing a liquid through said spinneret, thereby transferring at least some of said electric potential to said liquid, such that said liquid forms a stream directed toward said predetermined location on said target plate due to the electric potential between said liquid and said predetermined location, and whereby said stream splays into a plurality of nanofibers due to the electric potential between said liquid and said predetermined location, and whereby at least some of said nanofibers collide with said object instead of reaching said target plate;

moving said predetermined location on said target plate relative to said object thereby causing said nanofibers to cover said object.

2. The method of claim 1 further comprising ensuring that said nanofibers are wet when said nanofibers collide with said object.

3. The method of claim 2 wherein ensuring that said nanofibers are wet when said nanofibers collide with said object comprises positioning said spinneret a predetermined distance from said object.

4. The method of claim 2 wherein ensuring that said nanofibers are wet when said nanofibers collide with said object comprises adjusting the air pressure between spinneret and the object to a predetermined pressure.

5. The method of claim 2 wherein ensuring that said nanofibers are wet when said nanofibers collide with said object comprises adjusting the air temperature between the spinneret and the object to a predetermined temperature.

6. The method of claim 1 further comprising rotating said object relative to said stream.

7. The method of claim 1 wherein moving said predetermined location on said target plate relative to said object comprises moving said object over said predetermined location on said target plate.

8. The method of claim 1 wherein moving said predetermined location on said target plate relative to said object comprises moving said predetermined location on said target plate under said object.

9. The method of claim 8 further comprising moving said spinneret in concert with said relative movement of said predetermined location on said target plate such that said spinneret remains substantially directly above said predetermined location.

10. The method of claim 1 wherein placing an object between said spinneret and said predetermined location on said target plate comprises placing a stent between said spinneret and said predetermined location on said target plate.

11. The method of claim 10 wherein moving said predetermined location on said target plate relative to said object comprises rotating said stent over said predetermined location on said target plate thereby covering the entire stent with nanofibers.

12. The method of claim 1 wherein forcing a liquid through said spinneret comprises forcing a mixture of a polymer and a solvent through said spinneret.

13. The method of claim 1 wherein placing an object between said spinneret and said predetermined location on said target plate comprises placing a substrate on said target plate.

14. The method of claim 13 further comprising removing said covering from said substrate, thus forming a free-standing material of nanofibers.

15. The method of claim 1 wherein placing an object between said spinneret and said predetermined location on said target plate comprises placing a scrim between said spinneret and said predetermined location on said target plate.

16. The method of claim 1 further comprising:

charging a second spinneret with an electric potential relative to said predetermined location on said target plate;

forcing a second liquid through said second spinneret, thereby transferring at least some of said electric potential to said liquid, such that said liquid forms a stream directed toward said predetermined -location on said target plate due to the electric potential between said liquid and said predetermined location, and whereby said stream splays into a plurality of nanofibers due to the electric potential between said liquid and said predetermined location, and whereby at least some of said nanofibers collide with said object instead of reaching said target plate.

17. The method of claim 1 further comprising stretching said material, thereby causing said nanofibers to align with each other.

18. The method of claim 12 wherein forcing a mixture of a polymer and a solvent through said spinneret comprises forcing a mixture of a polymer, belonging to the group PLA, PET, PGA, PCL, PDO, collagen, polytetrafluoroethylene, polyactive, polyurethane, polyester, polypropylene, polyethylene, silicone and PU and a solvent belonging to the group HFIP, dichloromethane, dimethylacetamide, chloroform, dimethylformamide, methylene chloride, and xylene.

19. The method of claim 1 further comprising texturing said nanofibers.

20. The method of claim 19 wherein texturing said nanofibers comprises heating said nanofibers and pressing said nanofibers onto a textured surface, thereby transferring the texture of the surface to the nanofibers.

21. The method of claim 19 wherein texturing said nanofibers comprises using a textured substrate as the object placed between said spinneret and said predetermined location on said target plate, the texture of the substrate thereby transferred to said nanofibers as the nanofibers dry on the textured substrate.

22. A method of covering an object with a material, comprising:

charging a spinneret with an electric potential relative to a predetermined location on a target plate;

placing an object to be covered between the-spinneret and the target plate;

forcing a liquid through said spinneret, thereby transferring at least some of said electric potential to said liquid, such that said liquid forms a stream directed toward said predetermined location on said target plate due to the electric potential between said liquid and said predetermined location, and whereby said stream splays into a plurality of nanofibers due to the electric potential between said liquid and said predetermined location; and

whereby said plurality of nanofibers collide with said object;

ensuring said nanofibers are wet enough to adhere to said object when said nanofibers collide with said object;

placing a material over said object while said nanofibers are still wet, such that said nanofibers bind said material to said object.

23. The method of claim 22 whereby forcing a liquid through said spinneret comprises forcing a first polymer dissolved in a solvent through said spinneret.

24. The method of claim 23 wherein placing a material over said object while said nanofibers are still wet comprises placing a material of said first polymer over said object while said nanofibers are still wet.

25. A method of bonding a substance to a structure comprising:

providing an electrospinning apparatus;

providing a bonding substance in liquid form;

introducing said bonding substance in liquid form to said electrospinning apparatus;

operating said electrospinning apparatus such that said bonding substance is splayed into nanofibers having an average diameter of less than 100 micrometers;

directing said nanofibers to a target structure;

ensuring said nanofibers remain sufficiently moist as said nanofibers contact said target structure such that said nanofibers form a thin covering on said target structure wherein said covering includes a plurality of randomly located interstitial spaces.

26. The method of claim 25 wherein providing an electrospinning apparatus comprises:

providing a needle operably connected to a fluid conduit;

providing a pump constructed and arranged to force fluid through said fluid conduit;

providing a target plate operably displaced from said needle; and

,

providing a power supply constructed and arranged to establish a variable, controllable electric potential between said target plate and said needle.

27. The method of claim 25 wherein providing a bonding substance in liquid form comprises providing a mixture of a polymer belonging to the group PLA, PET, PGA, PCL, PDO, collagen, polyactive, polytetrafluoroethylene, polyurethane, polyester, polypropylene, polyethylene, silicone and PU and a solvent belonging to the group HFIP, dichloromethane, dimethylacetamide, chloroform, dimethylformamide, methylene chloride, and xylene.

28. The method of claim 26 wherein introducing said bonding substance in liquid form to said electrospinning apparatus comprises forcing said bonding substance in liquid form through said fluid conduit.

29. The method of claim 28 wherein forcing said bonding substance in liquid form through said fluid conduit is accomplished using said pump to force said bonding substance in liquid form through said fluid conduit.

30. The method of claim 26 wherein operating said electrospinning apparatus such that said bonding substance is splayed into nanofibers having an average diameter of less than 100 micrometers comprises:

positioning said needle 12 inches above said target plate;

controlling said power supply to establish a 19 kV potential between said needle and said plate; and

,

energizing and setting said pump to force 0.60 mL/minute of said bonding agent through said fluid conduit.

31. A method of delivering a drug to a target site comprising:

charging a spinneret with an electric potential relative to a predetermined location on a target plate;

forcing a liquid containing a drug through said spinneret, thereby transferring at least some of said electric potential to said liquid, such that said liquid forms a stream directed toward said predetermined location on said target plate due to the electric potential between said liquid and said predetermined location, and whereby said stream splays into a plurality of nanofibers due to the electric potential between said liquid and said predetermined location;

ensuring said nanofibers are wet enough to adhere together when said nanofibers collide with said target plate, to form a cloth-like material;

placing said cloth-like material at a target site in vivo, thereby allowing tissue at the target site to elute said drug from said cloth-like material.

32. The method of claim 31 wherein ensuring said nanofibers are wet enough to adhere together when said nanofibers collide with said target plate, to form a cloth-like material comprises positioning said spinneret a predetermined distance from said target plate.

33. The method of claim 31 wherein ensuring said nanofibers are wet enough to adhere together when said nanofibers collide with said target plate, to form a cloth-like material comprises adjusting the air pressure between said spinneret and said target plate to a predetermined pressure.

34. The method of claim 31 wherein ensuring said nanofibers are wet enough to adhere together when said nanofibers collide with said target plate, to form a cloth-like material comprises adjusting the air temperature between said spinneret and said target plate to a predetermined temperature.

35. The method of claim 31 further comprising:

placing an object between said spinneret and said predetermined location on said target plate, such that at least some of said nanofibers collide with said object instead of reaching said target plate;

moving said predetermined location on said target plate relative to said object thereby causing said nanofibers to cover said object with said cloth-like material.

36. The method of claim 35 wherein placing an object between said spinneret and said predetermined location on said target plate comprises placing a stent between said spinneret and said predetermined location on said target plate.

37. The method of claim 35 wherein placing an object between said spinneret and said predetermined location on said target plate comprises placing a scrim between said spinneret and said predetermined location on said target plate.

38. The method of claim 35 further comprising priming said object with a priming solution prior to placing said object between said spinneret and said predetermined location on said target plate.

39. The method of claim 38 wherein priming said object comprises dip-coating said object in said liquid.

40. The method of claim 31 wherein forcing a liquid containing a drug through said spinneret comprises forcing a liquid containing a polymer, a drug and a solvent through said spinneret.

41. The method of claim 40 wherein forcing a liquid containing a polymer, a drug and a solvent through said spinneret comprises forcing a liquid containing a polymer selected from the group PLA, PET, PGA, PCL, PDO, collagen, polyactive, polytetrafluoroethylene, polyurethane, polyester, polypropylene, polyethylene, silicone and PU, a drug selected from the group rapamycin, taxol and warfin, and a solvent belonging to the group HFIP, dichloromethane, dimethylacetamide, chloroform, dimethylformamide, methylene chloride, and xylene.

42. The method of claim 41 wherein forcing a liquid containing a polymer, a drug and a solvent through said spinneret comprises forcing a liquid containing PLA at 15-20% by mass, HFIP at 80-85% by mass and a drug selected from the group rapamycin, taxol and warfin at 0.05-1% of the polymer mass.

43. The method of claim 42 wherein forcing a liquid containing a polymer, a drug and a solvent through said spinneret comprises forcing a liquid containing PLA at 17.9% by mass, HFIP at 82.1% by mass and a drug selected from the group rapamycin, taxol and warfarin at 0.05% of the polymer mass.

44. The method of claim 41 wherein forcing a liquid containing a polymer, a drug and a solvent through said spinneret comprises forcing a liquid containing a polymer selected from the group PET, PGA, PCL, PDO, collagen, polyactive, polytetrafluoroethylene, polyurethane, polyester, polypropylene, polyethylene, silicone and PU at 10-20% by mass, HFIP at 80-90% by mass and a drug selected from the group rapamycin, taxol and warfin at 0.05-1% of the polymer mass.

45. The method of claim 31 further comprising rinsing said cloth-like material in a cleaning solution to remove surface drugs prior to placing said cloth-like material at a target site in vivo.

46. The method of claim 45 wherein rinsing said cloth-like material comprises rinsing said cloth-like material in a cleaning solution selected from the group de-ionized water, CO₂, methanol, alcohol, xylene, and sterile water.

47. The method of claim 31 further comprising:

charging a second spinneret with an electric potential relative to said predetermined location on said target plate;

forcing a second liquid, containing a polymer and a solvent, through said second spinneret, thereby transferring at least some of said electric potential to said liquid, such that said liquid forms a stream directed toward said predetermined location on said target plate due to the electric potential between said liquid and said predetermined location, and whereby said stream splays into a plurality of nanofibers due to the electric potential between said liquid and said predetermined location.

48. The method of claim 31 wherein placing said cloth-like material at a target site in vivo comprises wrapping said material around an external wall of a blood vessel over an area of the blood vessel where intimal hyperplasia is to be prevented.

49. The method of claim 31 wherein forcing a liquid containing a drug through said spinneret, thereby transferring at least some of said electric potential to said liquid, such that said liquid forms a stream directed toward said predetermined location on said target plate due to the electric potential between said liquid and said predetermined location, and whereby said stream splays into a plurality of nanofibers due to the electric potential between said liquid and said predetermined location comprises forcing a liquid containing an immunosuppressant through said spinneret, thereby transferring at least some of said electric potential to said liquid, such that said liquid forms a stream directed toward said predetermined location on said target plate due to the electric potential between said liquid and said predetermined location, and whereby said stream splays into a plurality of nanofibers due to the electric potential between said liquid and said predetermined location

50. A material comprising a plurality of randomly-oriented inter-tangled, non-woven fibrils of a first polymer having an average diameter of less than 100 micrometers.

51. The material of claim 50 wherein said fibrils comprise a drug.

52. The material of claim 51 wherein said drug is an immunosuppressant.

53. The material of claim 52 wherein said drug belongs to the group rapamycin, taxol and warfin.

54. The material of claim 50 further comprising a drug trapped within interstices between and defined by said fibrils.

55. The material of claim 50 further comprising a plurality of drug-containing microspheres, each microsphere trapped within an interstice between and defined by said fibrils.

56. The material of claim 50 wherein said material further comprises a plurality of randomly-oriented inter-tangled, non-woven fibrils of a second polymer having an average diameter of less than 100 micrometers.

57. The material of claim 50 wherein said fibrils comprise perfluorosulfonate ionomer.

58. The material of claim 50 further comprising a scrim operably attached to said randomly-oriented inter-tangled, non-woven fibrils of a first polymer, such that said scrim is covered by said fibrils on at least one side of said scrim.

59. The material of claim 50 wherein said fibrils further comprise an isotope.

60. The material of claim 59 wherein said isotope comprises ¹⁶⁹thulium oxide.

61. The material of claim 59 wherein said isotope comprises ⁴⁵calcium chloride.

62. The material of claim 50 wherein said polymer has a viscosity of between 1 and 50 centipoise when in liquid form.

63. A method of delivering radiation to a target site comprising:

charging a spinneret with an electric potential relative to a predetermined location on a target plate;

forcing a liquid containing an isotope through said spinneret, thereby transferring at least some of said electric potential to said liquid, such that said liquid forms a stream directed toward said predetermined location on said target plate due to the electric potential between said liquid and said predetermined location, and whereby said stream splays into a plurality of nanofibers due to the electric potential between said liquid and said predetermined location;

positioning said spinneret a predetermined distance from said target plate such that said nanofibers are wet enough to adhere together when said nanofibers collide with said target plate, to form a cloth-like material;

placing said cloth-like material at a target site in vivo;

directing electromagnetic energy toward said cloth-like material.

64. The method of claim 63 wherein directing electromagnetic energy toward said cloth-like material occurs before placing said cloth-like material at a target site in vivo.

65. The method of claim 63 wherein directing electromagnetic energy toward said cloth-like material occurs after placing said cloth-like material at a target site in vivo.

66. The method of claim 64 wherein directing electromagnetic energy toward said cloth-like material comprises placing said cloth-like material in a nuclear reactor for a predetermined period at a predetermined power level.

67. The method of claim 66 wherein placing said cloth-like material in a nuclear reactor for a predetermined period at a predetermined power level comprises placing said cloth-like material in a nuclear reactor for between 30 and 60 minutes at a power level of between 1 and 10 megawatts.

68. The method of claim 67 wherein placing said cloth-like material in a nuclear reactor for a predetermined period at a predetermined power level comprises placing said cloth-like material in a nuclear reactor for between 40 and 50 minutes at a power level of between 3 and 7 megawatts.

69. The method of claim 67 wherein placing said cloth-like material in a nuclear reactor for a predetermined period at a predetermined power level comprises placing said cloth-like material in a nuclear reactor for approximately 42 minutes at a power level of approximately 5 megawatts.

70. A covering for a stent comprising:

a plurality of fibrils, of a first polymer, the fibrils having diameters that average less than 100 micrometers, the fibrils adhered to an outside surface of said stent, the fibrils intertangled with each other but not woven;

a drug, operably contained within the covering.

71. The stent covering of claim 70 wherein said drug is dissolved within said fibrils.

72. The stent covering of claim 70 wherein said drug is contained in liquid form within interstices defined by and located between said fibrils;

73. The stent covering of claim 70 wherein said drug is contained in microsphere form within interstices defined by and located between said fibrils.

74. A stent comprising:

a body lumen support structure;

a covering disposed on said support structure;

said covering comprised of a plurality of fibrils having an average diameter less than 100 micrometers;

said fibrils arranged in a substantially random pattern on said support structure so as to create a plurality of substantially random interstitial spaces within said covering; and

,

a therapeutic agent disposed within said covering.

75. A stent according to claim 74, wherein said therapeutic agent is a drug.

76. A stent according to claim 74, wherein said therapeutic agent belongs to the group, growth factor and cytokine.

77. A stent according to claim 74, wherein said therapeutic agent is living cells.

78. A stent according to claim 74, wherein said therapeutic agent is an anti-restenosis agent.

79. A stent according to claim 74, wherein said therapeutic agent is disposed within said interstitial spaces.

80. A stent according to claim 74, wherein at least a portion of said fibrils contain said therapeutic agent.

81. A stent according to claim 74, wherein said fibrils are comprised of a polymer.

82. A stent according to claim 74, wherein said fibrils are comprised of a polymer and a therapeutic agent.

83. A structure for maintaining the patency of a body lumen comprising:

a supporting scaffold;

a covering applied to said scaffold;

said covering comprising a plurality of nanofibers applied to said scaffold in a substantially wet state so as to maximize adherence of said nanofibers to one another and to said scaffold;

said nanofibers having an average diameter less than about 100 micrometers;

a plurality of interstitial spaces in said covering formed by said nanofibers.

84. A structure according to claim 83, further comprising a tissue treatment substance disposed in at least a portion of said interstitial spaces.

85. A structure according to claim 84, wherein said tissue treatment substance is an anti-restenosis drug.

86. A structure according to claim 83, wherein said nanofibers are comprised of a polymer.

87. A structure according to claim 83, wherein said nanofibers are comprised of a polymer and a tissue treatment substance.

88. A method of maintaining the patency of a body lumen comprising:

providing a stent frame;

covering said stent frame with wet fibrils, said fibrils having a diameter less than 100 micrometers in diameter;

allowing said wet fibrils to adhere to one another and to said stent frame so as to create a covering having a plurality of substantially randomly placed interstitial spaces;

loading said covering with a therapeutic agent;

introducing said sent frame into a body lumen;

allowing said therapeutic agent to affect tissue in said body lumen.

89. A method according to claim 88, wherein the loading of said covering with a therapeutic agent includes covering said stent frame with fibrils comprised of a polymer and said therapeutic agent.

90. A method according to claim 88, wherein the loading of said covering with a therapeutic agent includes filling at least a portion of said interstitial spaces with said therapeutic agent.

91. A method according to claim 88, wherein the allowing of said therapeutic agent to affect tissue includes allowing the elution of a drug into said tissue.

92. A method according to claim 91, wherein the elution includes elution of an anti-restenosis drug.

93. A method according to claim 88, wherein the covering of said stent frame is performed using electrospinning.

94. A method according to claim 88, wherein allowing said therapeutic agent to affect tissue in said body lumen comprises expanding said stent until said stent contacts said tissue in said body lumen.

95. A method according to claim 94, wherein expanding said stent causes said fibrils to align circumferentially, thereby increasing the radial strength of said covering.

96. A method of controlling the drug release rate of an implantable drug-containing object comprising covering the object with a fibrous fabric having interstices defined between the fibers that are small enough to control the rate at which a drug contained by the object may elute into tissue surrounding the object when the object is implanted.

97. The method of claim 96 wherein covering the object with a fibrous fabric having interstices defined between the fibers that are small enough to control the rate at which a drug contained by the object may elute into tissue surrounding the object when the object is implanted comprises covering the object with a polymer fabric having a plurality of fibrils having diameters that average less than 100 micrometers.

98. The method of claim 96 wherein covering the object with a fibrous fabric having interstices defined between the fibers that are small enough to control the rate at which a drug contained by the object may elute into tissue surrounding the object when the object is implanted comprises covering the object with a polymer fabric having a plurality of fibrils that are intertangled with each other but not woven.

99. A drug-eluting cloth comprising:

an inner layer of fibers of a first average diameter and defining interstices between the fibers;

a therapeutic releasably contained by the inner layer;

an outer layer of fibers of a second average diameter and defining interstices between said fibers that are smaller than the interstices of the inner layer such that the release rate of the therapeutic is controlled by the interstices of the outer layer;

wherein the outer layer is operably attached to and substantially encasing the inner layer.

100. The drug-eluting cloth of claim 99 wherein the fibers of the outer layer comprise electrospun fibrils having an average diameter of less than 100 micrometers.

101. The drug-eluting cloth of claim 99 wherein the fibers of the inner and outer layers comprise electrospun fibrils.

102. The drug-eluting cloth of claim 101 wherein the first average diameter is greater than the second average diameter.

103. A drug eluding cloth of claim 99 wherein the outer layer comprises a first polymer and the inner layer comprises a second polymer different than the first polymer.

104. The drug-eluting cloth of claim 99 wherein the therapeutic releasably contained by the inner layer is disposed in at least a portion of the interstices of the inner layer.

105. The drug-eluting cloth of claim 99 wherein the therapeutic releasably contained by the inner layer is encased in a plurality of microspheres, which are disposed in at least a portion of the interstices of the inner layer.

106. A method of coating an object comprising:

covering the object with a layer of fibers defining interstices between the fibers;

treating the covered object until at least a portion of the interstices are reduced.

107. The method of claim 106 wherein covering the object with a layer of fibers defining interstices between the fibers comprises electrospinning a polymer onto the object.

108. The method of claim 106 wherein covering the object with a layer of fibers defining interstices between the fibers comprises covering a stent with a layer of fibers defining interstices between the fibers, the stent defining spaces, the layer of fibers including bridge portions that span over the spaces.

109. The method of claim 106 wherein treating the covered object until at least a portion of the interstices are reduced comprises heating the covered object to a predetermined temperature until at least a portion of the interstices are reduced.

110. The method of claim 109 wherein heating the covered object to a predetermined temperature until at least a portion of the interstices are reduced comprises heating the covered stent to a predetermined temperature for a predetermined time until the bridge portions of the layers of fibers collapse and bond to the stent.

111. The method of claim 109 wherein heating the covered object to a predetermined temperature until at least a portion of the interstices are reduced comprises heating the covered object to a predetermined temperature until substantially all of the interstices are reduced.

112. The method of claim 109 wherein heating the covered object to a predetermined temperature until at least a portion of the interstices are reduced comprises heating the covered object to a predetermined temperature until the fibers melt, thereby substantially eliminating all of the interstices.

113. The method of claim 106 wherein treating the covered object until at least a portion of the interstices are reduced comprises exposing the covered object to a solvent gas atmosphere until at least a portion of the interstices are reduced.

114. A structure for maintaining the patency of a body lumen comprising:

a scaffolding structure having a side wall defining at least one space;

a fibrous coating attached to at least a portion of the scaffolding structure but not spanning the at least one space of the side wall.

115. The structure of claim 114 wherein said scaffolding structure comprises a braided wire stent.

116. The structure of claim 114 wherein said scaffolding structure comprises a non-braided stent.