Polymer fiber tubular structure having kinking resistance

1. An apparatus for forming a tubular structure having improved kinking resistance from a liquefied polymer, the apparatus comprising:

(a) a dispenser for dispensing the liquefied polymer;

(b) a precipitation electrode being at a first potential relative to said dispenser, said precipitation electrode being designed and constructed for generating a fibrous polymeric shell thereupon; and

(c) a pressing mechanism for increasing a local density of said polymeric shell in a plurality of predetermined sub-regions of said polymeric shell, thereby to provide a tubular structure having an alternating density in a longitudinal direction, wherein the alternating density regions formed comprises compressed sub-regions and non-compressed sub-regions in a longitudinal direction of the tubular structure, wherein a basis weight of said compressed sub-regions is larger than a basis weight of said non-compressed sub-regions.

2. The apparatus of claim 1 , wherein said pressing mechanism for increasing said local density comprises a plurality of rollers spaced apart from one another.

3. The apparatus of claim 1 , wherein said pressing mechanism for increasing said local density comprises a spiral pattern.

4. The apparatus of claim 1 , wherein said pressing mechanism for increasing said local density comprises a rigid irregular pattern.

5. The apparatus of claim 1 , wherein said precipitation electrode comprises at least one rotating mandrel.

6. The apparatus of claim 1 , wherein said dispenser is operable to move along said precipitation electrode.

7. The apparatus of claim 3 , wherein said dispenser comprises a mechanism for forming ajet of the liquefied polymer.

8. The apparatus of claim 7 , wherein said mechanism for forming ajet of the liquefied polymer includes a dispensing electrode.

9. The apparatus of claim 1 , further comprising a reservoir for holding the liquefied polymer.

10. The apparatus of claim 1 , further comprising a subsidiary electrode being at a second potential relative to said dispenser, and being for modifying an electric field generated between said precipitation electrode and said dispenser.

11. The apparatus of claim 10 , wherein said subsidiary electrode serves for reducing non-uniformities in said electric field.

12. The apparatus of claim 10 , wherein said subsidiary electrode serves for controlling fiber orientation of the tubular structure formed upon said precipitation electrode.

13. The apparatus of claim 10 , wherein said subsidiary electrode is of a shape selected from the group consisting of a plane, a cylinder, a torus and a wire.

14. The apparatus of claim 10 , wherein said subsidiary electrode is operative to move along said precipitation electrode.

15. The apparatus of claim 10 , wherein said subsidiary electrode is tilted at angle with respect to said precipitation electrode.

16. An apparatus for forming a tubular structure having improved kinking resistance from a liquefied polymer, the apparatus comprising:

(a) a dispenser for dispensing the liquefied polymer;

(b) a precipitation electrode being at a first potential relative to said dispenser, said precipitation electrode being designed and constructed for generating a fibrous polymeric shell thereupon;

(c) a pressing mechanism for increasing a local density of said polymeric shell in a plurality of predetermined sub-regions of said polymeric shell, thereby to provide a tubular structure having an alternating density in a longitudinal direction; wherein the alternating density regions formed comprises compressed sub-regions and non-compressed sub-regions in a longitudinal direction of the tubular structure, wherein a basis weight of said compressed sub-regions is larger than a basis weight of said non-compressed sub-regions and

(d) a system of electrodes, being laterally displaced from said dispenser, being at a third potential relative to said dispenser and capable of providing an electric field having at least one rotating component around a first axis defined between said dispenser and said precipitation electrode, for intertwining at least a portion of a plurality of polymer fibers dispensed by said dispenser, so as to provide at least one polymer fiber bundle moving in a direction of said precipitation electrode.

17. A method of forming a tubular structure having improved kinking resistance from a liquefied polymer, the method comprising:

(a) via electrospinning, dispensing the liquefied polymer from a dispenser in a direction of a precipitation electrode, hence forming fibrous polymeric shell; and

(b) applying pressure onto predetermined sub-regions of said polymeric shell such as to increase a local density of said polymeric shell in said plurality of predetermined sub-regions,

thereby providing a tubular structure having an alternating density in a longitudinal direction (b), wherein the alternating density regions formed comprises compressed sub-regions and non-compressed sub-regions in a longitudinal direction of the tubular structure, wherein a basis weight of said compressed sub-regions is larger than a basis weight of said non-compressed sub-regions.

18. A tubular structure having improved kinking resistance, comprising at least one layer of electrospun polymer fibers, each layer having a predetermined porosity and an alternating density characterized by compressed sub-regions and non-compressed sub-regions in a longitudinal direction of the tubular structure, wherein a basis weight of said compressed sub-regions is larger than a basis weight of said non-compressed sub-regions.

19. The apparatus of claim 16 , wherein said mechanism for increasing said local density comprises a plurality of rollers spaced apart from one another.

20. The apparatus of claim 16 , wherein said mechanism for increasing said local density comprises a spiral pattern.

21. The apparatus of claim 16 , wherein said mechanism for increasing said local density comprises a rigid irregular pattern.

22. The apparatus of claim 16 , further comprising a subsidiary electrode being at a second potential relative to said dispenser, and being for modifying an electric field generated between said precipitation electrode and said dispenser.

23. The apparatus of claim 22 , wherein said subsidiary electrode serves for reducing non-uniformities in said electric field.

24. The apparatus of claim 22 , wherein said subsidiary electrode serves for controlling fiber orientation of the tubular structure formed upon said precipitation electrode.

25. The apparatus of claim 22 , wherein said subsidiary electrode is of a shape selected from the group consisting of a plane, a cylinder, a torus and a wire.

26. The apparatus of claim 22 , wherein said subsidiary electrode is operative to move along said precipitation electrode.

27. The apparatus of claim 22 , wherein said subsidiary electrode is tilted at angle with respect to said precipitation electrode.

28. The method of claim 17 , further comprising independently repeating said steps (a) and (b) at least once.

29. The method of claim 17 , wherein said increasing said local density is done by pressing a plurality of rollers, spaced apart from one another, onto said polymeric shell.

30. The method of claim 17 , wherein said increasing said local density is done by pressing a spiral pattern onto said polymeric shell.

31. The method of claim 17 , wherein said increasing said local density is done by pressing a rigid irregular pattern onto said polymeric shell.

32. The method of claim 17 , further comprising reducing non-uniformities in an electric field generated between said precipitation electrode and said dispenser.

33. The method of claim 32 , wherein said reducing non-uniformities in said electric field is done by positioning a subsidiary electrode close to said precipitation electrode.

34. The method of claim 17 , further comprising controlling fiber orientation of the tubular structure formed upon said precipitation electrode.

35. The method of claim 34 , wherein said controlling fiber orientation is done by positioning a subsidiary electrode close to said precipitation electrode.

36. The tubular structure of claim 18 , capable of withstanding kinking collapse when bent at a bending radius which is lower than 25 mm.

37. The tubular structure of claim 18 , wherein said basis weight of said compressed sub-regions is at least 250 g/m 2 and said basis weight of said non-compressed sub-regions is not higher than 220 g/m 2 .