Textiles: knitting – Fabrics or articles – Warp
Patent
1995-09-29
1998-03-31
Calvert, John J.
Textiles: knitting
Fabrics or articles
Warp
66170, 623 1, A61F 206, D04B 122
Patent
active
057325723
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to surgical prostheses and, in particular, to improved tubular grafts for use in cardiovascular surgery, to the fabric from which the grafts are constructed and to methods of manufacturing the fabric and the grafts.
For many years, tubular grafts have been used in cardiovascular surgery for the replacement and bypass of blood vessels. The tubular grafts used in such surgery are, in general, manufactured from woven or knitted textiles or from extruded polymers.
Vascular grafts are discussed in detail by King et al (Med. Prog. Technol., 9, 217-226 (1983)) and this article contains a description of the ideal vascular graft which would, among other characteristics, be easily handled and sutured, would have similar elasticity, flexibility and compliance to the host vessel and would be sufficiently strong and durable to last for the life expectancy of the patient. The graft must have both longitudinal and radial strength and, in fact, a high hoop modulus (radial strength and resistance to dilatation) is particularly important since this ensures that the graft maintains its diameter and, hence, maintains the flow characteristics considered necessary by the surgeon. In addition, graft dilatation has been associated with false aneurysm at the suture site and widely dilated grafts have also the potential for thromboembolism.
Woven grafts may be either shuttle or rapier loom woven and are, in general, structurally stable, although some weaves do have a tendency to fray at the cut ends.
However, a serious disadvantage of most woven grafts is that they have poor compliance, limited elongation and limited water permeability. These properties, in combination, mean that many woven grafts are difficult to handle during implantation and suturing.
Alternatively, textile grafts may be knitted and the currently available knitted grafts fall into two main categories. Weft knitted structures have yarns which lie predominantly in the transverse direction and are relatively easy to construct. However, they do have the disadvantages that they are generally unstable and, although they have a good hoop strength, they have a low hoop modulus.
Warp knits such as the reverse locknit have yarns lying predominantly in the lengthwise direction and are more stable than weft knits, being less likely to unravel, and have good fray resistance characteristics. However, although stronger than weft knitted structures, they still have a tendency to dilate.
A third type of construction for vascular grafts is to form them from an extruded polymer such as expanded polytetrafluoroethylene (ePTFE).
ePTFE grafts differ from textile ones in that they are microporous rather than macroporous. This gives a device which is blood tight at implant but limits healing by tissue ingrowth. Bleeding from suture holes is a greater problem with ePTFE devices.
Because they are made by extrusion, it is difficult to make bifurcated devices from ePTFE. In contrast, textile bifurcates can be manufactured continuously without the eed for joins.
For several reasons, therefore, textile grafts are to be preferred to ePTFE ones although, as discussed above, they do have their own associated problems. It would be extremely advantageous to develop a new fabric for the constructions of grafts which has neither the stiffness of traditional woven materials, nor the low radial modulus of conventional knitted textiles.
In a first aspect of the present invention, there is provided a tubular knitted fabric for a surgical graft, characterised in that the fabric contains a Korper chain and is knitted using a stitch which has an underlap of greater than two needle spaces in the bar nearer to the technical face.
In the context of the present invention, the term "underlap" refers to the yarn between loops. Each underlap extends across the fabric and up one stitch. The loops themselves are referred to as the "overlaps".
In the context of the present invention, the term "bar" or "guide bar" refers to the device which determines the route of yarn sheets in the fab
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patent: 5456711 (1995-10-01), Hudson
M.W. King et al., "Designing Polyester Vascular Prostheses for the Future", Medical Progress Through Technology, vol. 9, 1983, pp. 217-226.
Calvert John J.
Vascutek Limited
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