GB2567963A

GB2567963A - Medical implant and method of manufacturing a medical implant

Info

Publication number: GB2567963A
Application number: GB1816674.4A
Authority: GB
Inventors: Hull Andrew
Original assignee: LOCKDOWN MEDICAL Ltd
Current assignee: LOCKDOWN MEDICAL Ltd
Priority date: 2015-04-01
Filing date: 2016-04-01
Publication date: 2019-05-01
Also published as: GB2537052B; GB201816674D0; WO2016156874A1; GB2536941A; GB2537052A; GB201505660D0

Abstract

A medical implant comprising a first plurality (m) of core tows 31, 32, 33, each core tow comprising first strands of filament (80a, fig 2b) braided around the core of parallel second strands of filament (80b, fig 2b) in a first braid (3D), and a second plurality (n) of third strands of filament 80c braided around the core tows in a second, flat braid 90. The medical implant may be an artificial ligament, ligament augmentation device or delivery device for autologous grafts. A method of manufacturing a medical implant comprises an eleven-strand and three-core flat braid, wherein each core tow is a six-strand round braid made by braiding four strands of filament around a core of two parallel strands of filament. The method can adjust a braiding density of the flat braid to provide the medical implant with a plurality of sections of different lengths and braiding densities.

Description

The present invention concerns a medical implant and a method of manufacturing a medical implant. More specifically, the invention concerns a medical implant suitable for use as an artificial ligament, ligament augmentation device or delivery device for autologous grafts and a method of manufacturing such a medical implant.

It is desirable for a medical implant for use as an artificial ligament, ligament augmentation device or delivery device for autologous grafts to comprise an array of tows which can be manufactured quickly and easily using a braiding machine. On the other hand, it is also desirable for a medical implant for use in such a context to have good strength and resistance to wear and tear, which can only be provided by giving the array of tows a relatively complex structure, such that the substructure of filaments within each tow is different from the structure of the tows within the array. Moreover, it is also desirable for the array of tows to be substantially flat, in order to mimic the properties of a natural ligament. These constraints make it difficult to manufacture a medical implant for use as an artificial ligament, ligament augmentation device or delivery device for autologous grafts which comprises an array of tows made using a braiding machine.

Accordingly, in a first aspect, the present invention provides a medical implant comprising: a first plurality of core tows, each core tow comprising first strands of filament and a core of parallel second strands of filament, wherein the first strands of filament are braided around the core of parallel second strands of filament in a first braid; and a second plurality of third strands of filament, wherein the third strands of filament are braided around the core tows in a second, flat braid.

By the term “braided” is meant that any given strand of filament or tow passes successively over and under, over and under successive ones of the other strands of filament or tows with which it interacts.

By the term “around” is meant that the first strands of filament embrace all of the parallel second strands of filament and are braided with them as well as being braided with each other, and that the second plurality of third strands of filament embrace all of the first plurality of core tows and are braided with them as well as being braided with each other.

This structure is advantageous for reasons which include the following. The first plurality of core tows give the medical implant good longitudinal strength under tension and transmit loads in a direction along the core tows, thereby mimicking the properties of a natural ligament. In addition, the flat braid made by the second plurality of third strands of filament are braided around the core tows provides the medical implant with a large number of interstices between the third strands of filament, into which tissue from a patient in whom the medical implant is implanted can grow. This helps to aid binding of the implant with the patient’s natural tissue. On the other hand, since it is the core tows which take up and transmit loads when the medical implant is initially placed under tension, the third strands of filament are not initially placed under tension as well, but only start to come under tension as the load is increased, thereby relieving stresses on the patient’s natural tissue which has grown into the interstices between the third strands of filament. This helps to promote tissue regrowth and successful integration of the implant into the patient.

Preferably, there are four first strands of filament and two parallel second strands of filament.

Preferably, the first plurality is 3.

Preferably, the second plurality is 11.

The braiding density of the second plurality of third strands of filament may vary along a length of the flat braid.

In such a case, the flat braid preferably has sequentially a first section having a first length and a first braiding density, a second section having a second length longer than the first length and a second braiding density less than the first braiding density, and a third section having a third length shorter than the second length and a third braiding density similar to the first braiding density.

If so, it is preferable that the flat braid is arranged in a ring, the first section is aligned longitudinally and overlapping with the third section and the first and third sections are joined together to close the ring, the ring has opposite sides which are arranged alongside each other and joined together edgewise in a strip twice as wide as the flat braid, the strip has a first end and a second end, and the ring has a first opening located at the first end of the strip and a second opening located at the second end of the strip.

If so, the medical implant may further comprise whipping applied around the flat braid surrounding the first opening, and lashing applied around a neck of the first opening to form an eye.

Preferably, the first, second and third strands of filament are polyester filament of 1100 dtex, where dtex is an abbreviation for decitex, denoting the mass of the filament in grammes per 10 000 metres of length of the filament.

Preferably the medical implant of the invention is one of an artificial ligament, a ligament augmentation device and a delivery device for an autologous graft.

In a second aspect, the present invention also provides a method of manufacturing a medical implant comprising braiding first strands of filament around a core of parallel second strands of filament to make a first braid, using the first braid to provide each one of a first plurality (m) of core tows, drawing the core tows together under tension, as the core tows are drawn together, braiding a second plurality (n) of third strands of filament around the core tows to bind the core tows together in an n-strand and m-core flat braid, and severing the flat braid to provide an array of tows of the medical implant.

Preferably, braiding the first strands of filament around the core of parallel second strands of filament to make the first braid comprises braiding four first strands of filament around a core of two parallel second strands of filament to make a six-strand round braid.

Preferably, the method comprises: supplying the first plurality of core tows to a braiding machine for use by the machine in a process to braid the flat braid, the process comprising: providing the braiding machine with an arcuate track around a haul-off position for hauling off the flat braid under tension from the braiding machine, the arcuate track having one less consecutive loops than the second plurality; dispensing a first one of the core tows through a first one of the loops at a first end of the track towards the haul-off position; dispensing a second one of the core tows through a second one of the loops at a second end of the track towards the haul-off position; dispensing remaining ones of the core tows through respective ones of the loops located along the track between the first and second loops towards the haul-off position; mounting n bobbins movably on the track, each bobbin dispensing a respective one of the second plurality of third strands of filament towards the haul-off position; positioning the bobbins evenly along the consecutive loops of the arcuate track, such that each pair of adjacent bobbins is separated by 2 times the second plurality timesTT divided by the second plurality radians around the consecutive loops; braiding the n third strands of filament around the first plurality of core tows by simultaneously moving all of the bobbins along the track at the same speed, such that each bobbin successively moves along the track from the first end thereof and meanders along the consecutive loops along a first side of each consecutive loop which is alternately either nearer to or further from the haul-off position, until each bobbin reaches the second end of the track, passes around the second loop and meanders from the second end of the track along the ten consecutive loops along a second side of each consecutive loop which is alternately either further from or nearer to the haul-off position, until each bobbin returns to the first end of the track again; whereby on each complete circuit round the track, the respective strand of filament dispensed by each bobbin passes once around the first core tow, once around the second core tow and once around the remaining ones of the core tows, and when two bobbins pass each other moving in opposite directions along the track, the respective strands of filament respectively dispensed by the two bobbins passing each other in opposite directions are braided together; and hauling off the flat braid made by this process under tension from the braiding machine.

Moving the bobbins along the track may induce a variation in tension of the respective strands of filament dispensed by the bobbins, as a result of a variation in the overall length of each respective strand from a take-off point of the strand of filament from the respective bobbin to the haul-off position. In such a case, it is preferable to compensate for this variation in tension by mounting each of the bobbins on a respective carrier, each carrier having a movable tensioning mechanism able to impart a counteracting variation in tension to the respective strand of filament by movement of the tensioning mechanism in response to the variation in tension induced by movement of the respective bobbin.

A speed of the hauling off may be adjusted whilst maintaining a speed of movement of the bobbins along the track unaltered, to adjust a braiding density of the flat braid. If so, the speed of the hauling off may particularly be adjusted to provide the flat braid with sequentially a first, tighter section having a first length and a first braiding density, a second, looser section having a second length longer than the first length and a second braiding density less than the first braiding density, and a third, tighter section having the first length and the first braiding density again. The flat braid may then be folded in half to align the first and third sections with each other and to secure the first and third sections together.

Further features and advantages of the present invention will become apparent from the following detailed description, which is given by way of example and in association with the accompanying drawings, in which:

Fig. 1 is a perspective view showing a braiding machine suitable for use in a method of manufacturing a medical implant;

Fig. 2A shows a six-strand round braid for use as a core tow by the braiding machine of Fig. 1;

Fig. 2B is a close-up view of a part of Fig. 2A;

Fig. 3 is a perspective close-up view of a haul-off guide of the braiding machine of Fig. 1;

Fig. 4 is a perspective view showing a bobbin carrying a strand of filament, the bobbin being mounted on a carrier positionable on a track of the braiding machine of Fig. 1;

Figs. 5 and 6 are top plan views of the track of the braiding machine of Fig. 1, which together schematically show the path of a bobbin along the track;

Figs. 7 to 11 are top plan views schematically showing a series of steps in a braiding process for making an eleven-strand and three-core flat braid;

Fig. 12 shows an eleven-strand and three-core flat braid made by the braiding process of Figs. 7 to 11;

Fig. 13 schematically shows a step in making a medical implant from the flat braid made by the braiding process of Figs. 7 to 11; and

Fig. 14 schematically shows an example of a medical implant which is an artificial ligament comprising a flat braid made by the braiding process of Figs. 7 to 11.

Referring firstly to Fig. 1, there is shown a braiding machine 10 having an underframe 12 supporting a base 14, on an upper surface of which is mounted a cam plate 16. In the cam plate 16 is an arcuate track 50 having a plurality of consecutive loops 60, on which can be positioned one or more carriers 20, each for carrying a bobbin 70 wound with a strand of filament 80a. The underframe 12 of the braiding machine 10 also comprises a plurality of mounting positions 18 for further respective bobbins 70, each respectively wound with a core tow 31, 32, 33. The core tows 31, 32, 33 are each made by braiding four strands of filament 80b around a core of two parallel strands of filament 80c in order to make a six-strand round braid 30, as shown in Fig. 2A.

Fig. 2B shows a close-up view of a part of Fig. 2A. As can be seen in Fig. 2B, each individual strand of filament 80a, 80b successively passes over and under, over and under successive ones of the other strands of filament with which they interact, whereby the six strands of filament 80a, 80b are braided together to make the braid 30.

Referring back to Fig. 1, mounted in a respective one of a plurality of holes in the cam plate 16, each hole being located within a respective one of the loops 60 of the track 50, are respective core posts 131, 132, 133. Each of the core posts 131, 132, 133 has a respective through-hole from a bottom to a top end thereof. Thus, respective ones of the core tows 31, 32, 33 can pass from the bobbins 70 mounted in positions 18 on the underframe 12, through the respective holes in the cam plate 16 and through a respective through-hole from a bottom to a top end of each of the core posts 131, 132, 133, whereby respective ones of the core tows 31, 32, 33 can be dispensed through a respective one of the loops 60 of the track 50. A guide plate 130 also mounted on the underframe 12 is provided to guide each of the core tows 31, 32, 33 through the respective through-holes of the respective core posts 131, 132, 133, as well as to maintain tension in the core tows 31, 32, 33.

The braiding machine 10 further comprises a haul-off mechanism 100 having a haul-off arm 110, at an end of which is mounted a haul-off guide 120. Component elements 112, 114, 116, 118 of the haul-off arm 110 are adjustable to position the haul-off guide 120 in a hauloff position 40 located centrally above the arcuate track 50. A haul-off wheel 102 driven by a haul-off motor 104 in a direction indicated in Fig. 1 by arrow A hauls off material 90 braided by the braiding machine 10 from the haul-off position 40. The braided material 90 is guided by a pinion wheel 106 towards two idler wheels 108 which hold the braided material 90 against the haul-off wheel 102, such that when the haul-off wheel 102 turns in the direction indicated by arrow A, the braided material 90 is drawn through pinch points between haul-off wheel 102 and idler wheels 108 by friction. The speed of the motor 104, and therefore the speed of rotation of the haul-off wheel 102, may be adjusted by means of a control box 140, in order to adjust the speed of the hauling off.

Not visible in Fig. 1 is a motor and gear mechanism mounted on the underside of base 16 of the braiding machine 10, for driving the carriers 20 along the arcuate track 50. During operation of the braiding machine 10, this motor and gear mechanism drive the carriers 20 along the arcuate track 50 in a manner which will be described in greater detail below, in order to braid the strands of filament 80a wound on bobbins 70 carried by the carriers 20, together with the core tows 31, 32, 33. At the same time, the haul-off motor 104 pulls the braided material 90 formed from braiding the strands of filament 80a with the core tows 31,

32, 33 from the haul-off position 40. For correct operation of the braiding process, all of the bobbins 70 moving along the arcuate track 50 should be wound with a respective strand of filament 80a in the same sense.

Fig. 3 shows the haul-off guide 120 of the haul-off mechanism 100 of the braiding machine 10 of Fig. 1 in greater detail. The haul-off guide 120 has two guide plates 122, 124 mounted on a base plate 126. Each guide plate 122, 124 has a respective pair of guide fingers 128a, 128b, 129a, 129b, which guide the strands of filament 80a and core tows 31, 32, 33 towards the haul-off position 40.

Fig. 4 shows in more detail one of the bobbins 70 wound with a strand of filament 80a, mounted on a carrier 20 positionable on the track 50 of the braiding machine 10. The carrier 20 has a foot 22, on which the bobbin 70 rests and on which are also mounted a tensioning mechanism 24 and a branch 26. The tensioning mechanism 24 comprises a coiled spring 242 connected to a yoke 244 and thence to an arm 246, which terminates in a first eyelet 248. Yoke 244 and arm 246 are able to pivot up and down about a longitudinal axis of coiled spring 242 in directions indicated in Fig. 4 by arrow B, but coiled spring 242 biases arm 246 in a downward direction. The branch 26 carries a vertical rod 28 having a second eyelet 282 mounted along its length and a third eyelet 284 mounted on a distal end portion 286 thereof remote from the branch 26. The strand of filament 80a wound on the bobbin 70 is threaded through the second eyelet 282 on the rod 28, down to the first eyelet 248, up to the third eyelet 284 on the distal end portion 286 and thence to the haul-off position 40.

During operation of the braiding machine 10, as the carrier 20 moves along the track 50, the strand of filament 80a unwinds from the bobbin 70 and both the orientation of the carrier 20 relative to the haul-off position 40 and the distance of the carrier 20 from the haul-off position 40 change. This change in position and orientation of the carrier, as well as the unwinding of the strand of filament 80a from the bobbin 70, cause changes in the overall length of the strand of filament 80a from a take-off point 82 of the strand of filament 80a from the bobbin 70 to the haul-off position 40, which, if not compensated for, would cause a corresponding undesirable variation in the tension of the strand of filament 80a, affecting the density of the braided material 90 in an uncontrolled fashion. To compensate for this variation in the tension of the strand of filament 80a, therefore, the arm 246 of tensioning mechanism 24 moves up and down in the directions indicated by arrow B, as follows. When the strand of filament 80a becomes more tense as a result of movement of the carrier 20 along the track 50, this increased tension overcomes the tension in coiled spring 242 and pulls the arm 246 upwards, reducing the overall length of the strand of filament 80a from the take-off point 82 to the haul-off position 40, thereby tending to reduce the tension, whereas when the strand of filament 80a becomes less tense as a result of movement of the carrier 20 along the track 50, this reduced tension is instead overcome by the tension in coiled spring 242, which pulls the arm 246 downwards, increasing the overall length of the strand of filament 80a from the take-off point 82 to the haul-off position 40, thereby tending to increase the tension. Thus any variations in the tension of the strand of filament 80a induced by movement of the carrier 20 are counteracted by variations in the tension of the strand of filament 80a induced by movement of the arm 246 up or down in a negative feedback control of the tension.

Figs. 4 and 5 are top plan views of the track 50 of the braiding machine 10, which together schematically show how a bobbin 70 mounted on a carrier 20 moves along track 50 during operation of the machine 10. The track 50 comprises ten loops 60 linked consecutively together from a first loop 61 at a first end 51 of the track 50 to a second loop 62 at a second end 52 of the track. The ten loops 60 are arranged in a circular arc around the haul-off position 40, which arc occupies ten-twelfths of a circle, the remaining two-twelfths of the circle not forming part of the track. As previously mentioned above, the carriers 20 are driven along the arcuate track 50 by a motor and gear mechanism mounted on the underside of base 16 of the braiding machine 10. In order to braid eleven strands of filament 80a together with three core tows 31, 32, 33, eleven bobbins 70 each wound with a strand of filament 80a are driven along the ten consecutive loops 60 of the track 50 by the motor and gear mechanism.

Referring firstly to Fig. 5, in order to make a complete circuit of the track 50, each such bobbin 70 starts at the first end 51 of the track 50 and meanders along the ten consecutive loops 60 as indicated by the arrows 60a in Fig. 5 along a first side of each consecutive loop 60 which is alternately either nearer to or further from the haul-off position 40, until the bobbin 70 reaches the second end 52 of the track 50. Then, as shown in Fig. 6, the bobbin 70 passes around the loop 62 at the second end 52 of the track 50 and meanders back along the ten consecutive loops 60 as indicated by the arrows 60b in Fig. 6 along a second side of each consecutive loop 60 which is alternately either further from or nearer to the haul-off position 40, until the bobbin 70 returns to the first end 51 of the track 50 again. Throughout the movement of the bobbin 70 along the track 50, the branch 26 and vertical rod 28 lead the bobbin 70 in the direction of movement of the bobbin 70 so that the third eyelet 284 on the distal end portion 286 of the rod 28 from which the strand of filament 80a is dispensed towards the haul-off position 40 is always in front of the bobbin 70. This prevents the strand of filament 80a from becoming entangled around the bobbin 70 or components of the carrier 20 during the movement of the carrier 20 along the track 50.

The movement of one bobbin 70 mounted on a carrier 20 along track 50 during operation of the braiding machine 10 has just been described, wherein the bobbin 70 initially moves in an anticlockwise direction around the first loop 61 of the track 50. However, since the sequence of steps required for the bobbin 70 to make a complete circuit of the track 50 is entirely symmetrical with respect to the haul-off position 40, the bobbin 70 could equally well move in a direction opposite to that shown in Figs. 4 and 5 during operation of the braiding machine 10 and instead move initially in a clockwise direction around the first loop 61 of the track 50 and continue to move thereafter in a direction opposite to that shown in Figs. 4 and 5, until it returns to the first end 51 of the track 50 again. Reversing the direction of movement of the bobbin 70 in this way would only result in material 90 being braided in an opposite sense from that made by the sequence of steps shown in Figs. 4 and 5.

Having now described the movement of a single bobbin 70 wound with a strand of filament 80a along the track 50, the movement of all eleven bobbins 70 along the track 50 in order to braid eleven strands of filament 80a together with the three core tows 31, 32, 33 to make an eleven-strand and three-core flat braid will now be described with reference to Figs. 6 to 10. As may be seen in all of these figures, the three core tows 31, 32, 33, each of which is made as a six-strand round braid as described above, are positioned so that a first one 31 of them is located in front and to the left of the haul-off position 40, a second one 32 is located in front and to the right of the haul-off position and a third one 33 is located behind and adjacent to the haul-off position. The three core tows 31, 32, 33 therefore arrive at the hauloff position 40 parallel to each other, which allows them to be braided together in a flat braid, but also from well separated starting points, which minimises the risk of them becoming entangled. So that the strands of filament 80a respectively wound on to each of the eleven bobbins 70 moving along the track 50 can be braided around the three core tows 31, 32, 33, the first one 31 of the core tows passes through the first loop 61, the second one 32 of the core tows passes through the second loop 62 and the third one 33 of the core tows passes through a third one 63 of the loops 60, which loop 63 is located along the track 50 between the first loop 61 and the second loop 62.

As is also shown in Figs. 6 to 10, the eleven bobbins 70 are positioned evenly along the ten consecutive loops 60 of the arcuate track 50. Since each loop 60 is 2π radians in circumference and there are ten such loops, this means that each pair of adjacent bobbins is separated by 20π/11 radians around the ten consecutive loops 60. In Figs. 6 to 10, the eleven bobbins have been consecutively numbered 1 to 11, so that a pair of adjacent bobbins is represented by bobbins numbered 1 and 2, or 2 and 3, for example, up to 10 and

11, and then back to 11 and 1. During operation of the braiding machine 10, the motor and gear mechanism mounted on the underside of base 16 of the machine 10 drives the eleven bobbins 70 along the track 50 at the same speed as each other, so that the separation between each pair of adjacent bobbins remains constant at 20π/11 radians.

The directions of movement of each of the eleven bobbins in Figs. 6 to 10 can be determined by observing the position of the third eyelet 284 associated with each bobbin, which, as already noted above, always precedes the bobbin in its movement along the track 50. Comparing Fig. 8 with Fig. 7, therefore, it may be seen that bobbin number 1 has moved anticlockwise around loop 61 at the same time as the next adjacent bobbin number 2 has moved anticlockwise around the loop 60 in track 50 which is next-but-one adjacent from loop 61, bobbin number 3 has moved forwards by the same amount, and so on, until bobbin number 6 has moved clockwise round loop 62 and is approaching the second end 52 of the track 50. On the other hand, it may also be seen by comparing Fig. 8 with Fig. 7 that bobbin number 7 is moving from loop 62 on to the adjacent loop in a direction back towards the first end 51 of the track 50, as are bobbins numbers 8, 9 and 10, until bobbin number 11 has nearly reached loop 61 at the first end 51 of the track 50.

The progress of the eleven bobbins 70 along the track 50 continues as shown successively in Figs. 8 and 9 until, as shown in Fig. 11, bobbin number 11 reaches the position previously occupied by bobbin number 1 in Fig. 7, which in turn reaches the position previously occupied by bobbin number 2 in Fig. 7, which itself reaches the position previously occupied by bobbin number 3, and so on. Thus it can be seen that on each complete circuit round the track 50, each one of the eleven bobbins 70 passes once around the first core tow 31 by moving around the first loop 61, once around the second core tow 32 by moving around the second loop 62, and once around the third core tow 33 by passing round the third loop 63 firstly in one direction on a first side of the third loop 63 which is nearer to the haul-off position 40 and then in the opposite direction on a second side of the third loop 63 which is further from the haul-off position 40.

Moreover, when two bobbins pass each other moving in opposite directions along track 50, they cross over, so that the respective strands of filament 80a respectively carried by the two bobbins passing each other in opposite directions are braided together. For example, by comparing Fig. 8 with Fig. 9, it may be seen that bobbins numbers 1 and 11 are approaching each other in opposite directions in Fig. 8, but that in Fig. 9, bobbin number 11 has passed under the strand of filament 80a dispensed by bobbin number 1. A further example is provided by again comparing Fig. 8 with Fig. 9, where it may be seen that bobbins numbers and 10 are also approaching each other in opposite directions in Fig. 8, but that in Fig. 9, bobbin number 10 has passed under the strand of filament 80a dispensed from bobbin number 2. Fig. 9 also shows that bobbin number 2 is next approaching bobbin number 9 in an opposite direction thereto, whereas in Fig. 10, bobbin number 2 is moving to a side of one of the loops 60 which is nearer to the haul-off position 40, whereas bobbin number 9 is moving to a side of the same loop 60 which is further from the haul-off position 40, so that by Fig. 11, bobbin number 2 is just passing under the strand of filament 80a dispensed by bobbin number 9. Thus, from Fig. 8 to Fig. 11 bobbin number 2 passes successively over and under bobbins numbers 10 and 9. It can be seen that bobbin number 2 will continue to pass in a similar manner successively over and under bobbins numbers 8, 7, 6 and so on, whereby the strand of filament 80a dispensed by bobbin number 2 will be braided together with the respective strands of filament 80a dispensed by all other of the eleven bobbins 70 moving along the track 50. However, the motion of bobbin number 2 has only been taken as an example and the respective strands of filament 80a dispensed by all other ten of the eleven bobbins 70 will be similarly braided together by a similar process. Finally, it should also be noted that the diameter of the bobbins 70 and of each respective carrier 20 having a bobbin mounted thereon is small enough that when two bobbins pass each other in opposite directions in their respective movements along the track 50, they do not collide with each other. So, for example, as represented in Fig. 7 by bobbins numbers 6 and 7 or in Fig. 11 by bobbins numbers 5 and 6, these respective pairs of bobbins almost touch, but do not collide as the bobbins pass each other.

In general, the speed at which the haul-off motor 104 drives the haul-off wheel 102 to haul off the braided material 90 from the haul-off position 40 is chosen to be about the same as the speed at which the respective strands of filament 80a are dispensed by the eleven bobbins 70 as a result of a speed at which the motor and gear mechanism on the underside of base 16 of the braiding machine 10 drives the eleven bobbins 70 along the track 50. However, the speed of the hauling off can be adjusted by means of the control box 140 of the haul-off mechanism 100 whilst maintaining a speed of movement of the eleven bobbins 70 along the track 50 unaltered, in order to adjust a braiding density of the braided material 90. Thus if the speed of the hauling off is increased slightly relative to the speed at which the respective strands of filament 80a are dispensed by the eleven bobbins 70, this increases the tension at the haul-off position 40, resulting in a more tightly braided section of the braided material 90, whereas if the speed of the hauling off is decreased slightly relative to the speed at which the respective strands of filament 80a are dispensed by the eleven bobbins 70, this reduces the tension at the haul-off position 40, resulting in a more loosely braided section of the braided material 90. The braided material 90 output from the haul-off wheel 102 is then severed to provide an eleven-strand and three-core flat braid, possibly having a plurality of sections of different desired braiding densities. The braided material 90 may be severed using a hot knife, for example.

Fig. 12 shows an example of an eleven-strand and three-core flat braid 90 made by the braiding process shown in Figs. 6 to 10. The flat braid 90 comprises the three core tows 31, 32, 33 arranged in parallel and braided together by the strands of filament 80a. The flat braid 90 has a first, tighter section 91 and a second, looser section 92 made by adjusting the speed of the hauling off, as just described. If the flat braid 90 is provided with a third, tighter section of a similar length and density to the first, tighter section 91, the braid 90 may be folded in half and the first and third sections aligned with each other and secured together as part of a method of manufacturing an artificial ligament, a ligament augmentation device or a delivery device for autologous grafts.

For any such purpose, providing the strands of filament 80a, 80b, 80c as polyester filament of 1100 dtex is found to be suitable, where dtex is an abbreviation for decitex, denoting the mass of the filament in grammes per 10 000 metres of length of the filament.

Fig. 14 schematically shows an example of a medical implant 3, which is an artificial ligament 13 comprising a flat braid 90 having a first, tighter section 91, a second, looser section 92 and a third, tighter section 93. The first 91 and third 93 tighter sections of the flat braid 90 are aligned longitudinally and overlapping with each other, and are joined together by stitching 913 with one or more similar strands of filament to form the flat braid 90 into a closed ring 900, as shown in the step depicted in Fig. 13 of making the artificial ligament 13. Since the first 91 and third 93 sections of the flat braid 90 are more tightly braided together than the second section 92, each has a reduced thickness relative to the second section 92, so that they have a similar overall thickness to the second section 92 once they are overlapped with each other and joined together. The second, looser section 92 of the flat braid 90 is significantly longer than the first 91 and third 93 tighter sections of the flat braid 90 and therefore constitutes a majority of the artificial ligament 3.

The second, looser section 92 has two parts 92a, 92b on opposite sides 901, 902 of the ring 900. These opposite sides are arranged side by side with each other by being brought together in the directions indicated in Fig. 13 by the arrows C, C’ and are joined together edgewise by stitching 922 with one or more similar strands of filament to form a strip 905 twice as wide as the flat braid 90, but leaving an opening 5a, 5b in the ring at each respective end 3a, 3b of the artificial ligament 13. The opening 5a at one end 3a of the artificial ligament 13 is formed into an eye 7 by applying whipping 95 around the flat braid surrounding this opening 5a and by applying lashing 97 around a neck 99 of the opening 5a. This allows the eye 7 to be passed over the head of an anchor, such as may be implanted into a bone, without a risk of the stitching 922 being forced apart by radial stretching of the eye 7. On the other hand, the end 3b of the artificial ligament 13 may be sutured together with a natural ligament which can be passed through the opening 5b. Once sutured, the natural ligament can hold the artificial ligament 13 in tension longitudinally, thereby nullifying any risk that the stitching 922 will be forced apart by stretching of the opening 5b transversely to the length of the artificial ligament 13.

In other embodiments, the skilled person will understand that for different purposes, an artificial ligament comprising a flat braid manufactured according to this method could be provided with a respective eye similar to the eye 7 shown in Fig. 13 at each end of the artificial ligament or with a respective opening similar to the opening 5b shown in Fig. 13 at each end thereof instead.

In any case, the core tows 31, 32, 33 give the medical implant 3 good longitudinal strength under tension and transmit loads in a direction along the core tows 31, 32, 33, thereby mimicking the properties of a natural ligament. In addition, the flat braid 90 made by the third strands of filament 80c which are braided around the core tows 31, 32, 33 provides the medical implant 3 with a large number of interstices 81 between the third strands of filament 80c, into which tissue from a patient in whom the medical implant is implanted can grow. This helps to aid binding of the implant 3 with the patient’s natural tissue. On the other hand, since it is the core tows 31, 32, 33 which take up and transmit loads when the medical implant 3 is initially placed under tension, the third strands of filament 80c are not initially placed under tension as well, but only start to come under tension as the load is increased, thereby relieving stresses on the patient’s natural tissue which has grown into the interstices 81 between the third strands of filament 80c. This helps to promote tissue regrowth and successful integration of the implant 3 into the patient.

Claims

1.

2.

3.

4.

20

5.

6.

7.

A medical implant (3) comprising:

a first plurality (m) of core tows (31, 32, 33), each core tow (31, 32, 33) comprising first strands of filament (80a) and a core of parallel second strands of filament (80b), wherein the first strands of filament (80a) are braided around the core of parallel second strands of filament (80b) in a first braid (30); and a second plurality (n) of third strands of filament (80c), wherein the third strands of filament (80c) are braided around the core tows (31, 32, 33) in a second, flat braid (90).

A medical implant according to claim 1, wherein there are four first strands of filament (80a) and two parallel second strands of filament (80b).

A medical implant according to any one of the preceding claims, wherein m = 3.

A medical implant according to any one of the preceding claims, wherein n = 11.

A medical implant according to any one of the preceding claims, wherein the n third strands of filament (80c) have a braiding density and the braiding density varies along a length of the flat braid (90).

A medical implant according to claim 5, wherein the flat braid (90) has sequentially a first section (91) having a first length and a first braiding density, a second section (92) having a second length longer than the first length and a second braiding density less than the first braiding density, and a third section (93) having a third length shorter than the second length and a third braiding density similar to the first braiding density.

A medical implant according to claim 6, wherein:

the flat braid (90) is arranged in a ring (900);

the first section (91) is aligned longitudinally and overlapping with the third section (93) and the first (91) and third (93) sections are joined together to close the ring (900);

the ring (900) has opposite sides (901,902) arranged alongside each other and joined together edgewise in a strip (905) twice as wide as the flat braid (90);

the strip (905) has a first end (3a) and a second end (3b); and the ring (900) has a first opening (5a) located at the first end (3a) of the strip (905) and a second opening (5b) located at the second end (3b) of the strip (905).

8. A medical implant according to claim 7, wherein the first opening (5a) has a neck (99) and the medical implant further comprises:

whipping (95) applied around the flat braid (90) surrounding the first opening (5a); and lashing (97) applied around the neck (99) of the first opening (5a) to form an eye (7).

9. A medical implant according to any one of the preceding claims, wherein the first, second and third strands of filament (80a, 80b, 80c) are polyester filament of 1100 dtex.

10. A medical implant (3) according to any one of the preceding claims, wherein the medical implant is one of an artificial ligament (13), a ligament augmentation device and a delivery device for an autologous graft.

11. A method of manufacturing a medical implant (3) comprising:

braiding first strands of filament (80a) around a core of parallel second strands of filament (80b) to make a first braid (30);

using the first braid (30) to provide each one of a first plurality (m) of core tows (31, 32, 33);

drawing the core tows (31, 32, 33) together under tension;

as the core tows (31, 32, 33) are drawn together, braiding a second plurality (n) of third strands of filament (80c) around the core tows (31, 32, 33) to bind the core tows together in an n-strand and m-core flat braid (90); and severing the flat braid (90) to provide an array (1) of tows of the medical implant.

12. A method according to claim 11, wherein braiding the first strands of filament (80a) around the core of parallel second strands of filament (80b) to make the first braid (30) comprises braiding four first strands of filament (80a) around a core of two parallel second strands of filament (80b) to make a six-strand round braid (30).

13. A method according to claim 11 or claim 12, further comprising: supplying the core tows (31, 32, 33) to a braiding machine (10) for use by the machine in a process to braid the n-strand and m-core flat braid (90), the process comprising:

providing the braiding machine with an arcuate track (50) around a haul-off position (40) for hauling off the flat braid from the braiding machine under tension, the arcuate track having n-1 consecutive loops (60);

dispensing a first one of the core tows (31) through a first one (61) of the loops at a first end (51) of the track towards the haul-off position (40);

dispensing a second one of the core tows (32) through a second one (62) of the loops at a second end (52) of the track towards the haul-off position (40);

dispensing m-2 of the core tows (33) through a respective ones (63) of the loops located along the track between the first (61) and second (62) loops towards the haul-off position (40);

mounting n bobbins (70) movably on the track (50), each bobbin dispensing a respective one of the second plurality (n) of third strands of filament (80c) towards the haul-off position (40);

positioning the n bobbins (70) evenly along the n-1 consecutive loops (60) of the arcuate track (50), such that each pair of adjacent bobbins is separated by 2(η-1)π/η radians around the n-1 consecutive loops (60);

braiding the n third strands of filament (80c) around the m core tows (31, 32, 33) by simultaneously moving all of the n bobbins (70) along the track (50) at the same speed, such that each bobbin successively moves along the track from the first end (51) thereof and meanders along the n-1 consecutive loops (60) along a first side (60a) of each consecutive loop which is alternately either nearer to or further from the haul-off position (40), until each bobbin reaches the second end (52) of the track, passes around the second loop (62) and meanders from the second end of the track along the ten consecutive loops (60) along a second side (60b) of each consecutive loop which is alternately either further from or nearer to the haul-off position (40), until each bobbin returns to the first end (51) of the track again;

whereby on each complete circuit round the track (50), the respective strand of filament (80a) dispensed by each bobbin (70) passes once around the first core tow (31), once around the second core tow (32) and once around each of the m-2 core tows (33), and when two bobbins pass each other moving in opposite directions along the track (50), the respective third strands of filament (80c) respectively dispensed by the two bobbins passing each other in opposite directions are braided together; and hauling off the n-strand and m-core flat braid (90) made by this process under tension from the braiding machine (10).

14. A method according to claim 13, wherein moving the n bobbins (70) along the track (50) induces a variation in tension of the respective third strands of filament (80c) dispensed by the n bobbins (70), the method further comprising compensating for the variation in tension by mounting each of the n bobbins on a respective carrier (20) each having a moveable tensioning mechanism (24) able to impart a counteracting variation in tension to the respective strand of filament by movement of the tensioning mechanism in response to the variation in tension induced by movement of the respective bobbin.

15. A method according to claim 13 or claim 14, further comprising adjusting a speed of the hauling off whilst maintaining a speed of movement of the n bobbins along the track (50) unaltered, to adjust a braiding density of the n-strand and m-core flat braid (90).

16. A method according to claim 15, comprising:

adjusting a speed of the hauling off to provide the array (1) of tows with sequentially a first section (91) of the n-strand and m-core flat braid having a first length and a first braiding density, a second section (92) of the n-strand and m-core flat braid having a second length longer than the first length and a second braiding density less than the first braiding density, and a third section (93) of the n-strand and m-core flat braid having a third length shorter than the second length and a third braiding density similar to the first braiding density.

17. A method according to claim 16, further comprising: arranging the flat braid (90) into a ring (900);

aligning the first section (91) longitudinally and overlapping with the third section (93); joining the first (91) and third (93) sections together to close the ring (900); arranging opposite sides (901, 902) of the ring (900) alongside each other;

joining the opposite sides (901, 902) of the ring (900) together edgewise to form a strip (905) twice as wide as the flat braid (90); and leaving a first opening (5a) in the ring at a first end (3a) of the strip (905) and a second opening (5b) in the ring at a second end (3b) of the strip (905).

18. A method according to claim 17, further comprising:

applying whipping (95) around the flat braid (90) surrounding the first opening (5a) and applying lashing (97) around a neck (99) of the first opening (5a) to form an eye (7).

5

19. A method according to any one of claims 9 to 14, wherein m = 3.

20. A method according to any one of claims 9 to 15, wherein n = 11.

21. A method according to any one of claims 11 to 20, comprising providing the first,

10 second and third strands of filament (80a, 80b, 80c) as polyester filament of 1100 dtex.

12 12 18

Amendments to the claims have been made as follows: