Knitted tissue scaffolds

1. A staple cartridge assembly for use with a surgical stapling instrument, comprising:

a staple cartridge having a plurality of staples and a cartridge deck, the cartridge deck having a plurality of staple cavities defined therein, wherein each staple of the plurality of staples is at least partially disposed within a corresponding staple cavity of the plurality of staple cavities; and

a knitted bioabsorbable scaffold that is configured to releasably mate to the cartridge deck, wherein the staples are deployable from the staple cartridge and through the scaffold into tissue captured against the scaffold to thereby staple the tissue to the scaffold and release the stapled scaffold from the cartridge deck, the scaffold comprising:

a first knitted fiber layer configured to be positioned against and in contact with tissue, the first knitted fiber layer having a first surface and a second surface that opposes the first surface, and a plurality of openings extending between the first and second surfaces, the first knitted fiber layer being formed of fibers that are knitted together and formed of a first bioabsorbable polymer;

a second knitted fiber layer configured to be positioned against the cartridge deck, the second knitted fiber layer having a third surface and a fourth surface that opposes the third surface, and a plurality of openings extending between the third and fourth surfaces, the second knitted fiber layer being formed of fibers that are knitted together and formed of the first bioabsorbable polymer, wherein the openings have a size that is less than ¼ of a width of a crown of the staples; and

a support layer disposed between the first and second knitted fiber layers, the support layer being formed of fibers of a second bioabsorbable polymer, wherein the fibers of the support layer consist of standing fibers having a plurality of voids therebetween, wherein the standing fibers are not fixedly attached to each other and are interconnected to the first and second knitted fiber layers, and wherein a ratio of the number of voids to the number of standing fibers within the support layer is at least 3:1.

2. The staple cartridge assembly of claim 1 , wherein at least one of the first knitted fiber layer and the second knitted fiber layer further includes fibers formed of a third bioabsorbable polymer.

3. The staple cartridge assembly of claim 1 , wherein the fibers of the support layer are connected to the first and second knitted fiber layers, such that the fibers of the support layer are slidably interconnected with the fibers of the first and second knitted fiber layers.

4. The staple cartridge assembly of claim 1 , wherein each opening of the plurality of openings in the first and second knitted fiber layers has a perimeter formed of the first and second bioabsorbable polymers.

5. The staple cartridge assembly of claim 1 , wherein each opening of the plurality of openings formed in the second knitted fiber layer has a diameter from 0.002 inches to 0.1 inches.

6. The staple cartridge assembly of claim 1 , wherein at least a portion of the plurality of the voids in the support layer each have a different size.

7. The staple cartridge assembly of claim 1 , wherein the standing fibers are oriented substantially perpendicular to the fibers of the first bioabsorbable polymer in the first and second knitted fiber layers.

8. The staple cartridge assembly of claim 1 , wherein the scaffold is configured to apply a stress of at least 3 gf/mm 2 to the captured tissue for at least 3 days when the scaffold is in a tissue deployed state.

9. A staple cartridge assembly for use with a surgical stapling instrument, comprising:

a staple cartridge having a plurality of staples and a cartridge deck, the cartridge deck having a plurality of staple cavities defined therein, wherein each staple of the plurality of staples is at least partially disposed within a corresponding staple cavity of the plurality of staple cavities; and

a knitted bioabsorbable scaffold that is configured to releasably mate to the cartridge deck, wherein the staples are deployable from the cartridge deck and through the scaffold into tissue captured against the scaffold to thereby staple the tissue to the scaffold and release the scaffold from the cartridge deck, the scaffold comprising:

a first knitted fiber layer configured to be positioned against and in contact with tissue, the first knitted fiber layer having a plurality of openings formed therein and extending completely therethrough, wherein the first knitted fiber layer is formed of multifilament fibers formed of a first bioabsorbable polymer and monofilament fibers formed of a second bioabsorbable polymer;

a second knitted fiber layer configured to be positioned against the cartridge deck, the second knitted fiber layer having a first surface and a second surface that opposes the first surface, and a plurality of openings extending completely therethrough, the second knitted fiber layer being formed of the multifilament and monofilament fibers, wherein the openings have a size that is less than ¼ of a width of a crown of the staples; and

a support layer consisting of spacer fibers extending from the first knitted fiber layer to the second knitted fiber layer, the spacer fibers having a plurality of voids therebetween, each spacer fiber being formed of the monofilament fibers, wherein portions of the spacer fibers are slidably intertwined with the first and second knitted fiber layers, and wherein a ratio of the number of voids to the number of spacer fibers within the support layer is at least 3:1.

10. The staple cartridge assembly of claim 9 , wherein each opening of the plurality of openings in the first and second knitted fiber layers has a perimeter formed of the multifilament and monofilament fibers.

11. The staple cartridge assembly of claim 9 , wherein each opening of the plurality of openings formed in the second knitted fiber layer has a diameter from 0.002 inches to 0.1 inches.

12. The staple cartridge assembly of claim 9 , wherein at least a portion of the plurality of voids in the support layer each have a different size.

13. The staple cartridge assembly of claim 9 , wherein the spacer fibers are oriented substantially perpendicular to the multifilament fibers of the first and second knitted fiber layers.

14. The staple cartridge assembly of claim 9 , wherein the scaffold is configured to apply a stress of at least 3 gf/mm 2 to the captured tissue for at least 3 days when the scaffold is in a tissue deployed state.

15. A scaffold for use with a surgical staple cartridge, comprising:

a first knitted fiber layer configured to be positioned against and in contact with tissue, the first knitted fiber layer having a first surface and a second surface that opposes the first surface, and a plurality of openings extending between the first and second surfaces, the first knitted fiber layer being formed of fibers that are knitted together and formed of a first bioabsorbable polymer;

a second knitted fiber layer configured to be positioned against a cartridge deck, the second knitted fiber layer having a third surface and a fourth surface that opposes the third surface, and a plurality of openings extending between the third and fourth surfaces, the second knitted fiber layer being formed of the fibers that are knitted together and formed of the first bioabsorbable polymer, wherein the openings have a size that is less than ¼ of a width of a crown of a staple within the cartridge deck; and

a support layer disposed between the first and second knitted fiber layers, the support layer being formed of fibers of a second bioabsorbable polymer, wherein the fibers of the support layer consist of standing fibers having a plurality of voids therebetween, wherein the standing fibers are not fixedly attached to each other and are interconnected to the first and second knitted fiber layers, and wherein a ratio of the number of voids to the number of standing fibers within the support layer is at least 3:1.

16. The staple cartridge assembly of claim 2 , wherein the third bioabsorbable polymer degrades at a rate greater than that of the first bioabsorbable polymer.

17. The staple cartridge assembly of claim 9 , wherein at least one of the first knitted fiber layer and the second knitted fiber layer further includes fibers formed of a third bioabsorbable polymer, and wherein the third bioabsorbable polymer degrades at a rate greater than that of at least the first bioabsorbable polymer.

18. The scaffold of claim 15 , wherein at least one of the first knitted fiber layer and the second knitted fiber layer further includes fibers formed of a third bioabsorbable polymer, and wherein the third bioabsorbable polymer degrades at a rate greater than that of the first bioabsorbable polymer.