Technical Field

The present invention relates to a hinge, in particular but not exclusively to a hinge for a medical device. More specifically, the present invention relates to a mechanical hinge for an orthotic device and an orthotic device including a hinge.

Background

An orthosis is a medical device which is applied externally to the body to protect or alter biomechanical function. Types of orthosis are usually referred to by the body parts they are in contact with, for example a Knee Ankle Foot Orthosis (KAFO) for a brace extending from a user’s foot to above the knee. Orthoses are traditionally made from metal, leather, plastics or more recently composite fibre materials. Some orthoses also comprise a metal component such as a hinge. For instance, a (KAFO) maybe provided to support the lower leg and knee of a patient who suffers from muscle weakness or paralysis. A KAFO may consist of a lower portion and an upper portion connected by a hinge. The hinge is provided adjacent to the patient’s knee, allowing the patient to bend their leg while wearing the KAFO.

Metal components, such as a hinge, are normally integrated into the composite material. A metal component subjected to the heat and pressure of a composite curing cycle can be prone to move during the curing process affecting the alignment of the orthotic composite and to expand, weakening the bond between the metal and the composite structure. Accordingly, the bond between the metal component and the composite structure tends to form a weak point in the final product which can fail over time and the metal at the exit point of the laminate can also fail due to stresses at the exit point. Summary

In accordance with some embodiments, there is provided a hinge for use in a knee joint of a leg orthosis to pivotally connect first and second parts of the orthosis, the hinge comprising:

a first plate for attachment to the first part of a leg orthosis; a second plate for attachment to the second part of a leg orthosis, the second plate disposed in a parallel plane to the first plate and pivotably connected to the first plate;

wherein the first and second plates respectively include first and second pivot points on the corresponding side of each plate;

a first link connecting the first pivot point on the first plate to the first pivot point of the second plate; and

a second link connecting the second pivot point on the first plate to the second pivot point on the second plate;

such that the first and second plates and first and second bars together form a four-bar linkage,

wherein the first and second plates respectively have smooth planar surfaces on corresponding sides, opposite to the sides on which the respective first and second pivot points are disposed.

The hinge can be used as part of a leg orthosis for example a Knee Ankle Foot Orthosis (KAFO) or a knee brace and in such a device the hinge can be used as a knee joint. However it can be appreciated that the orthosis may be considered to be any type of brace, splint, or other artificial external device serving to support the limbs or spine or to prevent or assist relative movement. The hinge may also be used as an alternative joint, for example an elbow or ankle joint.

The hinge is preferably in single shear, preferably the links and pivots being on only one side of the hinge. When in use the links and pivots can be disposed on an external side of the hinge. It can be appreciated that the hinge may also be in in double shear, it can be appreciated that the links and pivots are on both sides of the hinge, when in use on an internal and external side of the hinge.

It maybe appreciated that the word“internal” when talking about a side or face of a hinge or an orthosis can be considered to mean the side closest to or in contact with the patient’s body part and the word“external” to mean the side facing out away from the patient’s body part.

The orthosis can comprise at least a first portion and a second portion connected by the hinge, the first plate of the hinge being connected to the first portion and the second plate of the hinge being connected to the second portion. The second portion being an lower portion when considering a KAFO, the first portion being the upper portion.

The hinge may be at least partially glued to both the first portion of the orthosis and the second portion of the orthosis with a glue or adhesive, preferably a resin and more preferably an epoxy resin. However it can be envisaged that the first plate is fixedly coupled to the first portion by a mechanical fastening and the second plate is fixedly coupled to the second portion by a mechanical fastening. It can also be appreciated that the hinge may be removable to enable replacement of part of the orthosis as opposed to replacement of the complete device.

The first link may be substantially arc shaped having two arc ends, preferably the first pivot of the first plate and the first pivot of the second plate are located at each arc end. However it can be appreciated that the arc shaped link may include further protrusions or formations, or that the pivots are not located at each arc end. Preferably the second link maybe substantially linear, however alternative shapes can be envisaged. The relative length of the first link may be greater than the second link, the length being measured from the two furthest points of each link. At least one of the first and second links, or of the first and second plates of the hinge may include at least one stop portion to prevent the hinge moving past a pre- determined position. The second link may comprise the at least one stop portion to engage with either or both of the first pivot of the first plate and the second pivot of the first plate. It can be envisaged that the second link may comprise two stop portions, one to engage with the first pivot of the first plate and the second to engage with the second pivot of the first plate, or the first pivot of the first plate. Preferably the stop portions are substantially curved, however alternative shapes can be envisaged, preferably the stop portion extends the full thickness of the link, however it can be appreciated that the stop may be a protrusion extending less than the full thickness of the link. The stop portion may further comprise a bumper or shield of a different material to the hinge to dampen the sound of the hinge and reduce the forces in the hinge at the stop position and improve the lifetime of the stop portions of the hinge, and thus the hinge. The bumper can be made from any suitable material to reduce the forces in the stop portions or to dampen the sound of the hinge, an example of which is polyurethane, however an alternative polymer or rubber could be used for example. The bumper may be removable or fixed to the hinge. It can be appreciated that the bumper may be of the same material as the hinge, but may be removable so that just these parts can be replaced. It can be appreciated that the hinge may not comprise a bumper, or that the bumper may be located on the pivots. It can be appreciated that the bumper may be located elsewhere on the hinge where parts of the hinge are in contact.

The first pivot and second pivot of the first plate may have a corresponding first boss and second boss respectively, which can extend perpendicularly from a first face of the first plate. The first pivot and second pivot of the second plate may have a

corresponding first boss and second boss respectively, which can extend

perpendicularly from a first face of the second plate. It can be appreciated that at least one of the pivots may have a corresponding boss, or any combination of the pivots can have a corresponding boss. The corresponding boss may also extend from a face of the first or second link. The movement of the first and second plates and the first and second links of the hinge maybe in parallel planes. The first link and second link may lie in the same plane. Furthermore the first plate and second plate may lie in the same plane.

The hinge can be made from titanium, however it can be appreciated that the hinge may be made from any other metallic material such as aluminium or steel, furthermore it may be made of a plastic or composite material or any alternative which comprises the strength and weight properties required for an orthosis joint or hinge. The hinge may be dampened, for example by springs or hydraulics, and/ or powered by a motor or controller. It can also be appreciated that the hinge can be used as a joint or hinge in a robotic limb, preferably as a knee joint. The orthosis may further comprise a prosthetic member. It may be that there are a pair of hinges positioned on an external face of an orthosis, one disposed on each side of the joint, for example either side of a knee joint. The hinges maybe disposed on an external face of an orthosis.

The first plate of a hinge may be fixedly coupled to a first portion of an orthosis by a resin or glue, and the second plate of a hinge may be fixedly coupled to a second portion of an orthosis by a resin or glue, preferably the glue is an epoxy resin. The first plate of a hinge may be fixedly coupled to a first portion of an orthosis by a mechanical fastening and the second plate of a hinge may be fixedly coupled to a second portion of an orthosis by a mechanical fastening. It can be appreciated that a combination of mechanical fastening and glue may be used to fixedly couple the first and second plates to the orthosis.

The hinge may be connected to the orthosis after the curing process has taken place to avoid any of the disadvantages in some prior art devices. Furthermore, the hinge may be more strongly coupled to the first and second portions than would have been possible in some prior art devices. Far less metal may be used in the preparation of an orthosis, this can often mean a large weight saving. Connecting the hinge after the cure process may also enable adjustment after the orthosis has been prepared if there is any misalignment when fitted to a user. In another embodiment, there is provided a hinge for use in a knee joint of a leg orthosis to pivotally connect first and second parts of the orthosis, the hinge comprising:

a first plate for attachment to the first part of a leg orthosis; a second plate for attachment to the second part of a leg orthosis, the second plate disposed in a parallel plane to the first plate and pivotably connected to the first plate;

wherein the first and second plates respectively include first and second pivot points on the corresponding side of each plate;

a first link connecting the first pivot point on the first plate to the first pivot point of the second plate; and

a second link connecting the second pivot point on the first plate to the second pivot point on the second plate;

such that the first and second plates and first and second bars together form a four-bar linkage.

Optionally, the hinge could include any of the features already described above in reference to the previously described embodiment.

Furthermore, the first plate may have a respective first pivot side and a second opposite side, the second opposite side preferably being a substantially smooth planar surface. The second plate may have a respective first pivot side and a second opposite side, the second opposite side being a substantially smooth planar surface.

The second link may comprise at least one stop portion to prevent the hinge from moving past a pre-determined position. The second link may comprise two stop portions, a first stop portion to restrict movement beyond a first position and a second stop to restrict movement past a second position. The first position and second position maybe pre-determined positions to prevent over flexion or extension of a user’s joint when wearing the orthosis.

Optionally when the hinge is in a first position, the first stop portion may be configured to engage with the first pivot of the first plate.

Optionally when the hinge is in a second position, the second stop portion may be configured to engage with the first pivot of the first plate.

The hinge may be configured such that in a first position the first plate is in contact with the second plate. It can be appreciated that at least one of the first plate or the second plate is shaped to include a formation to abut the other of the first plate or the second plate.

In some embodiments the first plate has a thickness which is relatively less than the thickness of the first link. In some embodiments the second plate has a thickness which is relatively less than the thickness of the second link. The first and/ or second plates are configured such that the first and/ or second plates are suitable for location between an orthosis and a user’s knee when in use.

The links and pivots may be located only on one side of the hinge, preferably when in use, on an external side of the hinge, configured such that the links and pivots face out away from a user’s body part when in use. Optionally the links of the hinge are disposed on one side of the orthosis, configured to face away from the user’s body part when in use, and the first and second plates are disposed on the other side of the orthosis configured to face towards the user’s body part when in use. In some embodiments the plates and the links are disposed on the same side of the orthosis. All of the features described herein (including any accompanying claims, abstract and drawings), and/ or all of the steps of any method or apparatus so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and/ or steps are mutually exclusive.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying Figures, in which: - Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a plan view of the top of a hinge according to an embodiment of the invention in a second position;

Figure 2 is a plan view of the top of a hinge according to an embodiment of the invention in a first position;

Figure 3 is a plan view of the underside of the hinge of Figure 1;

Figure 4 is a side elevation of the hinge of Figure 1 looking in direction A;

Figure 5 is a side elevation of the hinge of Figure 1 looking in direction B;

Figure 6 is a side view of an orthotic composite including the hinge of Figure 1;

Figure 7 is a perspective view of the orthotic composite of Figure 6;

Detailed Description

Referring to the Figures, the hinge 1 comprises a first plate 2 and a second plate 3 and a first link 4 and a second link 5. The first plate 2 has a first pivot point 6 and second pivot point 7 and the second plate 3 has a first pivot point 8 and a second pivot point 9. The first pivot 6 on the first plate 2 is on the corresponding side to the first pivot 8 on the second plate 3 and the second pivot 7 on the first plate 2 is on the corresponding side to the second pivot 9 of the second plate 3. The first link 4 connects the first pivot point 6 of the first plate 2 and the first pivot point 8 of the second plate 3. The second link 5 connects the second pivot point 7 of the first plate 2 and the second pivot point 9 of the second plate 3. The first plate 2 is substantially oval shaped having a first end 13 of radius R and a second end 14 of less than radius R. The first plate further comprises a protrusion 15 in the edge of the plate as shown in Figure 3. The first plate is preferably fixed with respect to the first and second pivots 6,7. The first plate 2 has a first boss 18 and a second boss 19, the first boss 18 corresponding to the first pivot 6 and the second boss 19

corresponding to the second pivot 7. The face opposite to the bosses 18 and 19 is a smooth surface 26 free from any formations such as protrusions, lumps or recesses; however it can be envisaged that this surface may include formations. The second plate 3 is substantially kidney shaped having a bulge 16 at one end and a slight protrusion 17 seen in Figure 3. The second plate 3 is preferably fixed with respect to the first and second pivots 8,9. The second plate 3 has a first boss 24 and a second boss 25, the first boss 24 corresponding to the first pivot 8 and the second boss 25 corresponding to the second pivot 9. The face opposite to the bosses 24 and 25 is a smooth surface 27 free from any formations such as protrusions, lumps or recesses; however it can be envisaged that this surface may include formations.

The first link 4 is substantially arc shaped, the first pivots 6 and 8 are located at either arc end 10 of the substantially arc shaped first link 4 and the first link 4 is able to rotate with respect to first pivots 6, 8.

The second link 5 is substantially linear in shape and comprises a first stop 11 and a second stop 12. The first stop 11 is a profiled portion, shaped to engage with the first pivot 6 of the first plate 2 to prevent the hinge from moving past a first position. The second stop 12 is a profiled portion, shaped to engage with the second pivot 7 or first pivot 6 of the first plate 2, to prevent the hinge from moving past a second position. Preferably the profiled portion of the first stop 11 and second stop 12 is a curved face adapted to fit around the shape of the first and second pivots 6, 7 respectively of the first plate 2, however it can be appreciated that an alternative shape would still prevent the hinge from moving past a first or second position. The second link 5 is able to rotate with respect to second pivots 7, 9. The first and second positions are pre-determined positions.

The stop portions 11, 12 may further comprise a bumper 28 or shield of a different material to the hinge 1. This bumper provides a number of advantages for example to dampen the sound of the metal on metal engagement in the first and second positions, to reduce the forces in the stop portions 11, 12 when they are in contact with the respective pivots or parts of the hinge 1 and to improve the lifetime of the stop portions 11, 12 of the hinge, and therefore the hinge 1. The bumper 28 can be made from any suitable material known to someone skilled in the art to achieve the advantages described above, an example of which is polyurethane, however an alternative polymer or rubber could also be used, a simple spring or shock absorbent material could also be used. The bumper 28 maybe removable or fixed to the hinge, it can be deformable or substantially rigid. It can be appreciated that the bumper may be of the same material as the hinge, but that it is removable so that just these parts can be replaced. It can be appreciated that the hinge 1 may not comprise a bumper 28, or that the bumper may be located on the pivots. It can be appreciated that the bumper 28 may be located elsewhere on the hinge 1 where parts of the hinge 1 are in contact.

The combination of the first plate 2, the second plate 3, the first link 4 and the second link 5 when connected together by the pivot points form a four-bar linkage. The hinge 1 is a closed kinematic chain engineered for a particular movement. In this case the movement more closely follows the movement of a human knee and is therefore desirable for use in a Knee Ankle Foot Orthosis (KAFO) or Knee Brace, however it can be envisaged that the hinge 1 maybe used in an arm orthosis as an elbow joint, or as part of a robotic device or an alternative device where a joint with a similar range of motion to the hinge 1 is required. The hinge 1 with a bend and slide movement such as the one described below usually holds on to the leg of the patient better when in use as a knee joint, improving the function of the orthosis. The hinge is able to move from a first position as shown in Figure 2 to a second position as shown in Figure 1 and vice versa. As the hinge moves from the first position the first pivot 8 of the second plate 3 moves relatively towards the second joint 7 of the first plate 2 along a first curved path of motion, as the hinge approaches the second position the second joint 7 of the first plate 2 begins a second curved path of motion and diverges from joint 7 of the first plate 2 until the hinge is in the second position. The first curved path of motion has a different radius to the second curved path of motion.

At the same time, when the hinge is in the first position the protrusion 15 of the first plate 2 is substantially in contact with the bulge 16 of the second plate 3. In the second position the plates are not in contact. The first plate 2 further comprises an internal face 20 and an external face 21, the second plate 3 comprising an internal face 22 and an external face 23. It maybe appreciated that, in use, the internal faces 20 and 22 are considered the side closest to or in contact with the patient’s body part and the external faces 21 and 23 are the side facing out away from the patient’s body part.

Preferably the first boss 18 and second boss 19 of the first plate 2 are located on the external face 21 however it can be envisaged that the smooth surface 26 could be on the external face 21, preferably it is on the internal face 20. Preferably the first boss 24 and second boss 25 of the second plate 3 are located on the external face 23 however it can be envisaged that the smooth surface 27 could be on the external face 23, preferably it is on the internal face 22.

The first plate 2 and second plate 3 preferably have a thickness of between 0.1mm and 10mm, more preferably a thickness of between 0.25mm and 7mm and even more preferably a thickness of between imm and 4mm.

The first link 4 and second link 5 preferably have a thickness of between 0.1mm and 20mm, more preferably a thickness of between imm and 13mm and even more preferably a thickness of between 2mm and 10mm.

Preferably the first and second plates 2,3 have a thickness less than that of the first and second links 4,5. Thickness as described herein can be determined as the distance from the external face to the internal face of each component. For example with regard to the first plate, the thickness can be determined as the shortest distance from the internal face 20 to the external face 21.

Figures 6 and 7 show one embodiment of a KAFO 30 including the hinge 1 of Figures 1 to 5. The KAFO supports the lower leg and knee of a patient who suffers from ailments such as muscle weakness or paralysis. The KAFO 30 comprises an upper portion 31 connected to a lower portion 32 by the hinge 1. Preferably the orthosis comprises a pair of hinges 1, wherein in use the pair of hinges are disposed either side of the knee or joint. When the orthosis is a KAFO the first position can be considered an extended position corresponding to extension of a knee joint and the second position can be considered a flexed position corresponding to flexion of a knee joint. The lower portion 32 comprises a footplate 34, which supports the patient’s foot, a lower elongate strut 35 extending up the patient’s ankle and calf, and a lower cuff 36 by which the KAFO 30 is secured to the patient’s calf. The upper portion 31 comprises an upper elongate strut 37 extending up and around the patient’s thigh, and an upper cuff 38 by which the KAFO is secured to the patient’s thigh. The hinge 1 is provided adjacent to the patient’s knee, allowing the patient to bend their leg while wearing the KAFO 30. Many alternative arrangements in which the lower leg and knee of a patient are supported by an orthosis that includes an upper portion 31 and a lower portion 32 connected by the hinge 1 can be envisaged.

The upper portion 31 has an internal face 39 and an external face 40 and the lower portion 32 has an internal face 41 and an external face 42. It maybe appreciated that, in use, the internal faces 39 and 41 are considered the side closest to or in contact with the patient’s body part and the external faces 40 and 42 are the side facing out away from the patient’s body part.

Orthoses are traditionally made from metal, leather, plastics or more recently composite fibre materials. It has been found that composite fibre materials can be effectively employed to offer an orthotic force pattern, i.e. the application of a force on pressure tolerant areas of a person’s anatomy using an orthosis to force a

biomechanical change, whilst simultaneously being lightweight and strong. As explained in WO 2017/103621 Ai, an orthosis composite maybe produced by laying sheets of pre-impregnated carbon fibres on a tool, and then curing the sheets while they remain in place on the tool. Metal components such as a hinge 1 are traditionally integrated into the composite by providing a hinge comprising a first flange and a second flange, whereby the first flange is rotatably connected to the second flange. The first flange can be sandwiched between two or more layers of the sheets of pre- impregnated carbon fibres on the tool defining the lower portion of the KAFO and the second flange can be sandwiched between two or more layers of the sheets of pre- impregnated carbon fibres on the tool defining the upper portion of the KAFO. The sheets can then be cured and the cured product may then be removed from the tool to provide an orthotic composite.

However, any metal component which is used will be required to withstand the heat and pressure of the curing cycle. Furthermore, it is essential that the metal component does not move during the curing process, as this could affect the alignment of the orthotic composite. Similarly, the unavoidable expansion of the metal during the curing cycle can also weaken the bond between the metal and the composite structure. Accordingly, the bond between the metal component and the composite structure tends to form a weak point in the final product which can fail over time. Furthermore, the metal stem can also fail due to stresses at the exit point of the laminate. All these issues can require a remake of the device which can be costly and time consuming.

According to the present invention the hinge l is connected to the orthosis 30 after the curing process has taken place to avoid any of the disadvantages described above or in prior art devices. Furthermore, the hinge can be more strongly coupled to the first and second portions than would have been possible in prior art devices. Far less metal is used in the preparation of an orthosis, this can often mean a large weight saving.

Connecting the hinge after the cure process also enables adjustment after the orthosis is prepared if there is any misalignment when fitted to a user.

In the example of a KAFO, the first portion is the upper portion 31 and the second portion is the lower portion 32. Holes are drilled in the upper portion 31 or first portion which correspond to the locations of the first boss 18 and the second boss 19 of the first plate 2. Holes are also drilled in the lower portion 32 or second portion which correspond to the locations of the first boss 24 and the second boss 25 of the second plate 3. The bosses 18,19, are pushed through the drilled holes or coupled to the orthosis in the upper portion 31 disposing the smooth rear face 26 of the first plate 2 at an internal side of the orthosis, i.e. when in use the smooth rear face 26 facing the subject’s body part. The bosses 24,25, are pushed through the drilled holes or coupled to the orthosis in the lower portion 32 disposing the smooth rear face 27 of the second plate 3 at an internal side of the orthosis.

The first link 4 is then rotatably coupled to the first boss of the first plate and the first boss of the second plate to create the first pivot of the first plate and the first pivot of the second plate 3. The first link 4 is located on the opposite side of the orthosis to the first plate 2, the first plate 2 being on the internal side of the orthosis and the first link being on the external side of the orthosis. However it can be appreciated that the first link 4 is on an internal side and the first plate 2 is on an external side, or the links and plates are on the same side. The second link 5 is then rotatably coupled to the second boss of the first plate and the second boss of the second plate to create the second pivot of the first plate and the second pivot of the second plate 5. The second link 5 is located on the opposite side of the orthosis to the second plate 3, the second plate 5 being on the internal side of the orthosis and the second link being on the external side of the orthosis. However it can be appreciated that the second link 5 is on an internal side and the second plate 3 is on an external side, or the links and plates are on the same side.

Fixing the first plate 2 to the first portion or upper portion 31 and fixing the second plate to the second portion or lower portion 32 may comprise gluing the first plate 2 to the first portion or upper portion 31 and gluing the second plate 3 to second portion or lower portion 32. Preferably, the glue is an epoxy glue.

Alternatively, or additionally, the first plate 2 may be fixedly coupled to the first portion or upper portion 31 by a mechanical fastening. Furthermore, the second plate 3 may be fixedly coupled to the second portion or lower portion 32, by a mechanical fastening. Many means of mechanical fastening are known to those skilled in the art and can be used, and example of such fastening is a rivet or bolt however alternatives can be envisaged.

Accordingly, preferably both the first and second portions of the orthosis, in the case of a KAFO the upper and lower portions 31, 32 comprise a coupling portion which can be in the form of a proud portion 43 configured, in use, to be spaced apart from the subject’s body part, in the case of a KAFO the subject’s knee joint. The hinge 1 may have a corresponding profile to this proud portion 43 and be connected to the orthosis at this proud portion 43. It can be appreciated that the coupling portion may be an alternative to a proud portion, for example the coupling portion may be a recessed portion or any other shaped portion that the hinge is able to be fixedly connected to.

The joint or hinge may be adapted to move freely through a large range of motion, it may also be adapted to be locked or unlocked in specific positions during specific tasks, such as walking, sitting, standing or climbing stairs.

The joint or hinge may include electronics and be automatically actuated, it may also be dampened, for example by further comprising springs or hydraulic means or may further include a motor to drive the hinge. The joint or hinge may further comprise sensors to feedback information about the movement of a patient. An orthosis may be considered to be a brace, splint, or other artificial external device serving to support the limbs or spine or to prevent or assist relative movement.

The orthosis may comprise an upper-limb orthosis, a lower-limb orthosis or a spinal orthosis.

The upper limb orthosis may be selected from the group consisting of a clavicular and shoulder orthosis, an arm orthosis, an elbow orthosis, a forearm-wrist orthosis, a forearm-wrist-thumb orthosis, a forearm-wrist-hand orthosis, a hand orthosis, and an upper-extremity orthosis. Accordingly, the joint or hinge may be a wrist joint or and elbow joint.

The lower limb orthosis may be selected from the group consisting of an ankle-foot orthosis (AFO), a knee-ankle-foot orthosis (KAFO), a knee orthosis and a hip-knee- ankle-foot orthosis (HKAFO). Accordingly, the joint or hinge may be an ankle joint, a knee joint or a hip joint.

The orthosis may comprise a prosthetic component. The prosthetic component maybe an artificial limb.

Preferably, the composite material that the orthosis is made from comprises at least one composite sheet including an inner core of the plurality of fibres impregnated with a polymer resin. The or each composite sheet maybe of the type often referred to as a “pre-preg”, in that it comprises a fibre composite sheet p re-impregnated with resin.

The plurality of fibres may comprise carbon fibres, polymer fibres and/or glass fibres. The polymer fibres may comprise polyamide fibres and/or polyethylene fibres. The polyamide fibres may comprise aramid fibres, such as those sold under the brand name Kevlar®. The polyethylene fibres may comprise high molecular weight polyethylene fibres, such as those sold under the brand name Dyneema®.