Modified porous polyolefin film and method of making
Disclosed herein is a porous hybrid elastomer/polyolefin film, which is a porous polyolefin film wherein at one or more isolated areas of the film pores are at least partly filled with an elastomer. This hybrid film shows improved resistance to tearing, whereas other properties like porosity, polarity, thickness, flexibility, and non-stickiness of the film are substantially retained. Other advantages include improved suture retention. The invention also provides a method to increase tear resistance of a porous polyolefin film comprising steps of providing a porous polyolefin film; identifying one or more locations on the film, at which locations tearing is likely to occur during intended use of the film; applying at the identified locations of the film an amount of a solution of an elastomer in solvent; and substantially removing the solvent; to result in a hybrid elastomer/polyolefin film having one or more isolated areas where pores in the film are at least partly filled with the elastomer. Further aspects concern uses of these hybrid films as a component of a medical implant or device, especially for use in contact with body tissue or fluids, such as in vascular applications like a vascular graft, a stent cover or a catheter balloon; and medical devices or implants comprising said porous hybrid films.
1. A porous hybrid film, comprising a porous polyolefin film wherein at one or more isolated areas forming 0.02-40 area % of the surface of the film, pores in a volume segment of the film across its thickness are at least partly filled with an elastomer at an amount of at least 20 vol % of the volume of the pores, and wherein outside said isolated areas the polyolefin film is substantially devoid of the elastomer, wherein the polyolefin is ultra-high molar mass polyethylene (UHMWPE) and wherein the elastomer is a thermoplastic polyurethane (TPU).
2. The porous hybrid film according to claim 1 , wherein the polyolefin film is a microporous ultra-high molar mass polyethylene (UHMWPE) film having a thickness of 0.5-50 μm.
3. The porous hybrid film according claim 1 , wherein an isolated area is a substantially circular spot on the film with a diameter of at most 5 mm or an elongated stripe with a width of at most 5 mm.
4. The porous hybrid film according to claim 1 , wherein the pores at an isolated area are at least 50 vol % filled with elastomer.
5. The porous hybrid film according to claim 1 , wherein the isolated areas constitute 0.2-25 area % of the surface of the film.
6. The porous hybrid film according to claim 1 , wherein the elastomer is a thermoplastic polyurethane comprising an aliphatic polyether and/or an aliphatic polycarbonate as soft block.
7. The porous hybrid film according to claim 6 , wherein the thermoplastic polyurethane comprises an apolar endgroup.
8. The porous hybrid film according to claim 7 , wherein the apolar endgroup comprises a C2-C20 alkyl, a C2-C16 fluoroalkyl, a C2-C16 fluoroalkyl ether, a poly(alkylene oxide) or a polysiloxane.
9. The porous hybrid film according to claim 1 , wherein the hybrid film has a porosity of 30-95 vol %.
10. The porous hybrid film according to claim 1 , wherein the pores at an isolated area are at least 80 vol % filled with elastomer.
11. A medical device or implant comprising a porous hybrid film according to claim 1 .
12. The medical device or implant according to claim 11 , wherein the device or implant is a vascular graft, a vascular occlusion device, a stent cover, or a catheter balloon.
13. The medical device or implant according to claim 11 , wherein the polyolefin film has a multitude of pores with maximum pore size of 50 μm as determined with a capillary flow porometer.
14. The medical device or implant according to claim 11 , wherein the TPU contains a combination of an aliphatic polycarbonate and a polysiloxane as soft blocks.
15. A method to increase tear resistance of a porous polyolefin film comprising steps of:
a. providing a porous polyolefin film;
b. identifying one or more locations on the film, at which locations tearing is likely to occur during intended use of the film;
c. applying at the identified locations of the film an amount of a solution of an elastomer in solvent; and
d. substantially removing the solvent;
to result in a porous hybrid film having one or more isolated areas forming 0.02-40 area % of the surface of the film, in which areas pores in a volume segment across the thickness of the film are at least partly filled with the elastomer, wherein outside said areas the original porosity of the polyolefin film is substantially unchanged and wherein the polyolefin is ultra-high molar mass polyethylene (UHMWPE) and the elastomer is a thermoplastic polyurethane (TPU).
16. The method according to claim 15 , wherein the TPU comprises one or more apolar endgroups.
17. The method according to claim 16 , wherein the apolar endgroup comprises a C2-C20 alkyl, a C2-C16 fluoroalkyl, a C2-C16 fluoroalkyl ether, a poly(alkylene oxide) or a polysiloxane.
18. The method according to claim 15 , wherein the solution of elastomer has a Brookfield viscosity of 1-500 mPa·s.
19. The method according to claim 15 , further comprising the step of compressing the film as obtained at a temperature below the melting temperature of the polyolefin.
20. The method according to claim 15 , wherein the TPU comprises an aliphatic polyether and/or an aliphatic polycarbonate as soft block.
21. The method according to claim 15 , wherein the isolated area is a substantially circular spot with a diameter of at most 5 mm or an elongated stripe with a width of at most 5 mm.
22. A medical device or implant comprising a porous hybrid film obtained by the method according to claim 15 .
23. The medical device or implant according to claim 22 , wherein the device or implant is a vascular graft, a vascular occlusion device, a stent cover, or a catheter balloon.