Polyurethane composite sheet, a method of making such composite sheet, and use thereof in making a medical implant
Disclosed herein is a polyurethane composite sheet comprising o a biocompatible and biostable polyurethane elastomer comprising polysiloxane segments, the polyurethane forming a continuous matrix of the sheet; and o a woven or braided fabric having a thickness of 15-150 μm and comprising biocompatible, high-strength polymer fibers; wherein the composite sheet comprises 10-90 mass % of polyurethane, has a thickness of 25-250 μm and an areal density of 5-300 g/m 2 ; and wherein the composite sheet has, in at least one direction, non-linear uniaxial tensile behavior characterized by a 1%-secant modulus of 20-200 MPa, a hardening transition point at 10-45%, and a tensile strength of at least 25 MPa (measured in water at 37° C.).
1. A polyurethane composite sheet comprising:
a fabric comprised of braided or woven strands of biocompatible, high-strength polymer fibers, the fabric having a thickness of 15-150 μm, a low areal density and an open structure; and
a biocompatible and biostable polyurethane elastomer comprising polysiloxane segments, the polyurethane elastomer forming a continuous matrix of the composite sheet which fully covers and embeds the strands of the fabric sufficient to render the composite sheet non-porous; wherein
the composite sheet comprises 10-90 mass % of the polyurethane elastomer, has a thickness of 25-250 μm and an areal density of 5-300 g/m 2 ; and wherein
the composite sheet has, in at least one direction, a non-linear uniaxial tensile behavior characterized by a 1%-secant modulus of 20-200 MPa, a hardening transition point at 10-45%, and a tensile strength of at least 25 MPa as measured in water at 37° C.
2. The polyurethane composite sheet according to claim 1 , wherein the polyurethane elastomer is a thermoplastic polyurethane elastomer (TPU) which comprises soft blocks that are based on a polysiloxane diol and one or more of an aliphatic polycarbonate diol and a poly (tetramethylene oxide) diol.
3. The polyurethane composite sheet according to claim 1 , wherein the polyurethane elastomer comprises one or more hydrophobic endgroups comprising a polysiloxane.
4. The polyurethane composite sheet according to claim 1 , wherein a highest flexural rigidity of the composite sheet is at most 45 Nm.
5. The polyurethane composite sheet according to claim 1 , wherein a largest difference in flexural rigidity/unit width of the polyurethane composite sheet as measured in any two orthogonal directions is at most 20 Nm.
6. The polyurethane composite sheet according to claim 1 , wherein the composite sheet has a largest difference in flexural rigidity/unit width of the polyurethane composite sheet of at most 20 Nm for each of i) a warp direction) (0°) relative to an angle of 45° with respect to warp and weft, and ii) a weft direction) (90°) relative to an angle of 45° with respect to warp and weft.
7. The polyurethane composite sheet according to claim 1 , wherein the composite sheet has a largest difference in flexural rigidity/unit width of the polyurethane composite sheet as measured in any two orthogonal directions of less than 60% of a higher measurement.
8. The polyurethane composite sheet according to claim 1 , wherein the composite sheet has a largest difference in flexural rigidity/unit width of the polyurethane composite sheet as measured in any two directions 45° apart of less than 60% of a highest measurement.
9. The polyurethane composite sheet according to claim 1 , wherein the composite sheet has a largest difference in flexural rigidity/unit width of the polyurethane composite sheet of less than 60% of a highest measurement for each of i) a warp direction) (0°) relative to an angle of 45° with respect to warp and weft, and ii) a weft direction (90°) relative to an angle of 45° with respect to warp and weft.
10. The polyurethane composite sheet according to claim 1 , wherein the fabric is a woven fabric having a warp strands per inch (EPI) and a weft strands per inch (PPI), wherein each of the EPI and the PPI is from 30 to 350 strands per inch.
11. The polyurethane composite sheet according to claim 1 , wherein the fabric is a woven fabric having a difference between warp strands per inch (EPI) and weft strands per inch (PPI) of at most 200.
12. The polyurethane composite sheet according to claim 1 , wherein the composite sheet has at least one textured surface having a surface roughness Sa of 3-12 μm and Sz of 20-100 μm as measured according to ISO25178.
13. The polyurethane composite sheet according to claim 1 , wherein the fabric is leno weave fabric or a mock leno weave fabric.
14. The polyurethane composite sheet according to claim 1 , wherein the fabric in the composite sheet is a woven fabric which includes warp and weft strands having a titer of 6-60 dtex.
15. The polyurethane composite sheet according to claim 1 , wherein the fibers are present as multifilament yarns that form strands of the fabric.
16. The polyurethane composite sheet according to claim 1 , wherein the high-strength polymer fibers are ultrahigh molecular weight polyethylene (UHMWPE) fibers or polyethylene terephthalate (PET) fibers each having a tenacity of 0.6-4.0 N/tex.
17. The polyurethane composite sheet according to claim 1 , wherein the fabric has a thickness of 20-100 μm and the composite sheet has a thickness of 25-125 μm.
18. A method of making the polyurethane composite sheet according to claim 1 , wherein the method comprises the steps of:
(a) providing the fabric comprising braided or woven strands of biocompatible, high-strength polymer fibers;
(b) optionally activating the surface of the fabric by pre-treating the surface of the fabric with a high-energy source; and
(c) embedding the fabric within the biocompatible and biostable polyurethane elastomer comprising polysiloxane segments thereby forming the non-porous polyurethane composite sheet.
19. An implantable medical device comprising the polyurethane composite sheet of claim 1 .