Biodegradable intravascular shape memory stent
Biodegradable self-expanding polymer stent has an outer diameter of 0.25-40 mm, length of 5-250 mm, and closed-cell wall structure formed by struts, where ratio of inner diameter values before crimping and after crimping is in a range of 3 to 5, and made of a copolymer obtained from L-lactide, D-lactide, D,L-lactide, meso-lactide, glycolide, ε-caprolactone, trimethylene carbonate, p-dioxanone and compounds comprising functional groups capable of photopolymerization; supramolecular structure of the copolymer is oriented substantially circularly in a transversal cross section of the stent. Method of manufacturing includes extruding a tube of a polymer material; annealing the extruded polymer tube; laser cutting the extruded polymer tube to form a stent workpiece; heating the stent to above glass transition temperature of the polymer, crimping the stent workpiece uniformly over the entire outer surface thereof, and quenching at about minus 20 degrees Celsius; placing the quenched stent on a delivery means.
1. A biodegradable self-expanding stent, the stent comprising:
a plurality of struts made of a polymer and arranged into a closed-cell structure, the closed-cell structure arranged into a tubular shape;
wherein a ratio of an inner diameter of the stent before crimping and to the inner diameter of the stent after crimping is between 3:1 and 5:1, and
wherein the struts have a decreased width or thickness in places of minimum mechanical stress compared to curved portions of the struts.
2. The stent of claim 1 , which an outer diameter of the stent before crimping is between about 0.25 mm and about 40 mm.
3. The stent of claim 1 , wherein a length of the stent is between 5 mm and 250 mm.
4. The stent of claim 1 , wherein an average molecular weight of the polymer is 20-600 kDa.
5. The stent of claim 1 , wherein the average molecular weight of the polymer is 100-400 kDa.
6. The stent of claim 1 , wherein a polydispersity index of the polymer is 1.3-2.5.
7. The stent of claim 6 , wherein the polydispersity index of the polymer is 1.5-2.0.
8. The stent of claim 1 , wherein a glass transition temperature of the polymer is over 37 degrees Celsius.
9. The stent of claim 8 , wherein the glass transition temperature of the polymer is over 42 degrees Celsius.
10. The stent of claim 1 , wherein the polymer is obtained by copolymerization of monomers selected from L-lactide, D-lactide, D,L-lactide, meso-lactide, glycolide, c-caprolactone, trimethylene carbonate, p-dioxanone and compounds comprising functional groups capable of photopolymerization.
11. The stent of claim 10 , wherein the polymer is a copolymer of L,L-lactide and c-caprolactone.
12. The stent of claim 1 , wherein a width of struts is 0.01-1 mm.
13. The stent of claim 1 , wherein a thickness of struts is 0.02-0.5 mm.
14. The stent of claim 1 , wherein the struts have an increased width or thickness in places of maximum mechanical stress, compared to linear portions of the struts.
15. The stent of claim 1 , wherein struts have elongated perforations in places of minimum mechanical stress.
16. The stent of claim 1 , wherein supramolecular structures of the polymer are oriented substantially circularly, when seen in a transversal cross section of the stent.
17. A method of manufacturing a biodegradable self-expanding stent, the method comprising:
extruding a tube of a polymer material using a rotational extrusion head to provide a substantially circular supramolecular structure of the polymer, when seen in a transversal cross section of the tube;
annealing the extruded tube;
laser carving the extruded tube to form a stent comprising a plurality of struts, wherein the struts form a closed-cell structure, and the closed-cell structure is arranged into a tubular form;
heating the stent to a temperature above a glass transition temperature of the polymer material, sharply crimping the stent uniformly over entire outer surface thereof, and subsequently quenching the stent to provide a ratio of the stent inner diameter values before and after crimping in a range of 3:1 to 5:1; and
placing the quenched stent on a delivery means or in a delivery means.
18. The method of claim 17 , wherein the quenching is performed at a temperature of minus 20 degrees Celsius or lower after the crimping.