Method of making porous self-cohered web materials
View Patent ↗The present invention is directed to a method of making implantable bioabsorbable non-woven self-cohered web materials having a high degree of porosity. The web materials are very supple and soft, while exhibiting proportionally increased mechanical strength in one or more directions. The web materials often possess a high degree of loft. The web materials can be formed into a variety of shapes and forms suitable for use as implantable medical devices or components thereof.
1. A method of making a highly porous self-cohered non-woven web comprising:
providing a non-woven, precursor web material comprising self-cohering filaments having an order-disorder transition temperature and a crystallization exotherm enthalpy wherein said self-cohering filaments are composed of a partially phase immiscible block copolymer or a blend of polymers or copolymers having sufficient melt miscibility to allow for extrusion into filaments;
softening said precursor web material at a temperature above its order-disorder transition temperature and below combinations of heat and time that would lead to a substantial reduction in crystallization exotherm enthalpy of said softened precursor web material;
stretching said softened precursor web material in at least one direction at a ratio of at least 2:1 to form an unannealed highly porous self-cohered stretched web with a total volume and void spaces of at least ninety percent of said total volume;
partially annealing said highly porous self-cohered stretched web material while restrained at maximum stretch;
releasing said highly porous self-cohered stretched web material from restraint at maximum stretch; and
increasing loft of said partially annealed highly porous self-cohered stretched web material by fully annealing said stretched web material after restraint on said stretched web material has been reduced.
2. The method of claim 1 wherein said highly porous self-cohered stretched web material is stretched at a ratio of three to one (3:1).
3. The method of claim 1 wherein said stretched self-cohered porous web material is stretched at a ratio of four to one (4:1).
4. The method of claim 1 wherein said stretched self-cohered porous web material is stretched at a ratio of five to one (5:1).
5. The method of claim 1 wherein said stretched self-cohered porous web material is stretched at a ratio of six to one (6:1).
6. The method of claim 1 wherein said stretched self-cohered porous web material is stretched at a ratio of seven to one (7:1).
7. The method of claim 1 wherein said stretched self-cohered porous web material is stretched at a ratio of eight to one (8:1).
8. The method of claim 1 wherein said stretched self-cohered porous web material is stretched at a ratio of nine to one (9:1).
9. The method of claim 1 wherein said stretched self-cohered porous web material is stretched at a ratio of ten to one (10:1).
10. The method of claim 1 further comprising forming said stretched self-cohered porous web material into a tubular construction.
11. The method of claim 1 wherein said precursor web material is stretched uni-axially.
12. The method of claim 1 wherein said precursor web material is stretched bi-axially.
13. The method of claim 1 wherein said precursor web material is stretched radially.
14. The method of claim 1 wherein said stretched web material is allowed to retract between ten percent and sixty percent from maximum stretching of said precursor polymeric web material.
15. A method of making a highly porous self-cohered non-woven web comprising:
providing a polymeric material capable of forming self-cohering spun filaments;
extruding said polymeric material through at least one heated spinneret forming at least one continuous filament;
collecting said continuous filament on a moving collector;
allowing said collected continuous filament to self-cohere to form a substantially amorphous, non-woven, self-cohered polymeric precursor web material having an order-disorder transition temperature and a crystallization exotherm enthalpy;
softening said polymeric precursor web material at a temperature above its order-disorder transition temperature and below combinations of heat and time that would lead to a substantial reduction in crystallization exotherm enthalpy of said softened precursor web material;
stretching said softened precursor polymeric web material in at least one direction at a ratio of at least 2:1 to form an unannealed highly porous self-cohered stretched web with a total volume and void spaces of at least ninety percent of said total volume;
partially annealing said highly porous self-cohered stretched web material while restrained at maximum stretch;
releasing said highly porous self-cohered stretched web material from restraint at maximum stretch; and
increasing loft of said partially annealed highly porous self-cohered stretched web material by fully annealing said stretched web material after restraint on said stretched web material has been reduced.