WO2012069787A1

WO2012069787A1 - Auxetic material articles

Info

Publication number: WO2012069787A1
Application number: PCT/GB2011/001641
Authority: WO
Inventors: Stephen George Edward Barker; Julian Roger Wright
Original assignee: The University Of Exeter
Priority date: 2010-11-23
Filing date: 2011-11-23
Publication date: 2012-05-31
Also published as: GB201019796D0

Abstract

An auxetic material article comprising a fabric, for example a woven fabric including a warp and a weft, at least one of which is, at least in part, of an auxetic form, such that variation in the stiffness of the fabric in at least one direction is non-uniform under given applied loads.

Description

A u xe tic Material Articles

This invention relates to auxetic material articles, that is to say articles manufactured using auxetic materials, and in particular to articles in which the auxetic material is arranged or is of a type such as to provide the article with one or more regions that are of a different stiffness or resistance to stretching than other reagions thereof when a given stretching load is applied thereto. By way of example, the articles may take the form of compression, or graduated compression, hosiery, or other similar garments, or orthopaedic splints.

Compression and graduated compression hosiery is commonly used to assist in the return of venous blood back from a users lower limbs towards the heart (ie against the action of gravity). It has been known for some considerable time, that wearing graduated compression hosiery can help in preventing, or reducing the risk of deep vein thrombosis (DVT), for example in the hospital population, although it may also used in other situations. It can also help prevent swelling around the lower part of the limbs and can have benefits in terms of reducing the effects of tired, aching limbs towards the end of the routine working day. Three different levels of compression are in common usage. The lower level of compression, Class I compression, is typically used in the routine prevention of DVT, often in the hospital setting as mentioned above but also as, for example, 'flight socks'. Class II compression is typically used in the non-surgical treatment of varicose veins, or aiding in the prevention of recurrent venous ulceration. Class III compression is typically used in the treatment of lower limb lymphoedema, manifest with substantial lower limb swelling.

A typical article of lower limb compression hosiery is graduated in such a manner as to provide a relatively high level or degree of compression at the ankle, with less compression exerted towards the knee (and even less towards the upper thigh). Ideally, the compression is smoothly graduated between these points, but current materials and manufacturing techniques do not permit this in a convenient manner and so the compression profile is typically stepped and not fine tuned to suit the application in which the article is used. Current graduated compression hosiery products work passively. It is thought that a more active or dynamic product could result in enhanced performance by using the material stretch or relaxation that is induced with a change in limb volume through muscle expansion and contraction, to further improve venous return.

Splints are used routinely to provide support for virtually all joints in the body for example, at the wrist for aiding the symptoms of repetitive strain injury in typists, or for providing support for the knee in those with cruciate ligament damage.

Splints are often bulky and uncomfortable to wear for the often prolonged periods necessary. Like compression and graduated hosiery, they commonly cause sweating or sweat accumulation, leading to itching and chafing (which might affect compliance in their use). Furthermore, they provide support in a non-dynamic way. They are often stiffened with heavy support 'rods' of metal or dense polymer and often, because of their overall stiffness, do not conform especially well to the underlying body parts. It is an object of the invention to provide an auxetic material garment suitable for use in such applications, for example as an article of compression or graduated compression hosiery, or as an orthopaedic splint, in which at least some of the disadvantages associated with known such articles are overcome or are of reduced effect. According to the present invention there is provided an auxetic material article comprising a fabric, the fabric including at least one yarn which is, at least in part, of an auxetic form, the yarn being arranged in the fabric such that variations in the stiffness of the fabric in at least one direction under given applied loads are non-uniform. The fabric may be of woven form, including a warp and a weft, at least one of which is, at least in part, of auxetic material. Alternatively, the fabric may be of knitted form. It will be appreciated, however, that the invention is not restricted in this regard.

By using a fabric of non-uniform stiffness in at least one direction in the manufacture of such an article, the article can be of a form such that, for example, the degree of compression provided by the article can be selected such that it is suitable for use in the formation of compression or graduated compression hosiery, or in the formation of a splint. In particular, the compression profile achieved by the use of the article may be dynamic in that it may vary as the article is stretched and allowed to relax. Different regions of the fabric may be formed using different auxetic materials so as to provide the fabric with regions of different stiffness and thereby result in the stiffness of the fabric in at least one direction being non-uniform. Alternatively, rather than use different auxetic materials, an auxetic material of graded or graduated form, ie having regions that are relatively compliant and regions that are relatively stiff under a given applied load, may be used to result in the fabric having a stiffness that is non-uniform in at least one direction. The auxetic material conveniently takes the form of a pair of elastic threads of different degrees of elasticity intertwined with one another. For example, the auxetic material yarn may take the form described in WO2004/0088015. Alternatively, an auxetic material yarn of the. form described in PCT/GB2010/001166 may be used. The yarn described in PCT/GB2010/001 166 has the advantage that it is of relatively smooth outer surface, and so is relatively easy to weave, the yarn described in WO2004/0088015 perhaps being more difficult to handle as there is a risk of the outer thread becoming entangled with machinery, altering the pitch at which the outer thread is wrapped around the inner thread, or becoming tangled, trapped or snapping within the machinery leading to manufacturing delays.

The auxetic material threads are conveniently arranged such that when the fabric is stretched, some adjacent regions of the auxetic material threads are urged apart with the result that pores tend to open up in the fabric, enhancing the breathability of the fabric and an article manufactured therefrom, and thereby reducing the discomfort associated with sweating and the like.

Where the article comprises compression or graduated compression hosiery, then an end part of the hosiery located, in use, above a wearers knee, is conveniently provided with an auxetic material such that, in use, stretching resulting from muscle expansion will tend to result in the end part of the hosiery better gripping the adjacent skin and so reduce the risk of the hosiery moving or sliding down, in use, without requiring the hosiery to be excessively tight when the users muscles are relaxed. Such an arrangement will clearly have benefits in that it will be of enhanced comfort and improved wearability. Where the article takes the form of an orthopaedic splint, then the auxetic materials may be arranged such that, in addition to resulting in the enhanced support, the splint will provide dynamic resistance to movement so that, as a patient starts to recover strength and movement in a joint, the splint forces him to work harder against increasing resistance. The term 'incentive fatiguing' is used herein to describe such functionality. By using auxetic yarns in the manufacture of splints, as the splint is expanded so the energy required to expand the material further increases, but at the same time, the energy stored in the material will help in the return of the joint to the 'neutral' position, so enhancing the process of incentive fatiguing.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is an illustration of an article of graduated compression hosiery;

Figure 2 is a diagrammatic view illustrating part of a woven fabric of the article of Figure 1 ;

Figures 3a and 3b illustrate, diagrammatically, a pair of auxetic material threads;

Figures 4a and 4b illustrate, diagrammatically, another pair of auxetic material threads; and

Figure 5 is a representation of an orthopaedic splint.

Referring firstly to Figure 1 there is illustrated an article 10 of graduated compression hosiery comprising a piece of fabric 12 formed into an elongate tube of slightly tapering form. In the arrangement illustrated, the fabric 12 is a woven fabric and includes warp and weft threads 14, 16 (see Figure 2), and in this arrangement the threads 14 are of a substantially non-elastic material in the sense that, in normal use, little or no stretching thereof takes place. By way of example, these threads may be of cotton or nylon form. However, this need not always be the case. Furthermore, elastic materials could be used if desired. The threads 16 are of an auxetic material. Although as illustrated the threads 16, only, are of an auxetic material, the threads 14 could alternatively, or additionally, comprise auxetic materials. It will be appreciated, however, that the fabric could take other forms without departing from the scope of the invention. For example, it could be knitted or otherwise constructed.

Figures 3a and 3b illustrate a pair of the threads 16 in greater detail, Figure 3a illustrating the threads 16 in a relaxed state whilst Figure 3b illustrates the threads in a stretched condition. As shown, each thread 16 comprises an inner core 18 around which is wound an outer thread or wrap 20. The core 18 and the wrap 20 are both of an elastic material, but the elasticities of the core 18 and wrap 20 are not equal with the result that when the thread 16 is stretched by a limited amount, the wrap 20, which is of coiled or wound form when relaxed, and which is stiffer than the core 18, will tend to straighten and in so doing will force the core 18 to adopt a slightly coiled form. The application of a stretching load to the thread 16 thus results in an effective diameter thereof increasing. As the applied load increases, a point will be reached at which the wrap 20 can no longer simply straighten and in addition, must itself undergo elastic stretching. In such an arrangement, it will be appreciated that, during stretching, initially the thread 16 is relatively compliant but that once a predetermined point has been reached, the material becomes considerably more stiff. The point at which the stiffness changes depends primarily upon the pitch at which the wrap 20 is wound about the core 18 and so, by appropriate selection of the winding pitch, threads of different stiffness, and in which the stiffness changes after a preselected extension and applied loading, can be manufactured. Such a thread 16 is of substantially the form described and illustrated in WO2004/0088015. Although the description herein is of a thread of the form described in WO2004/0088015, it will be appreciated that the invention is not restricted to arrangements of this type and that threads of the type described in PCT/GB2010/001 166 could equally be used.

The fabric 12 is designed in such a fashion as to result in the degree of compression provided by the article to the limb of the user upon which it is worn to be of nonuniform. Ideally, the article provides a greater level of compression to the lower part of the limb than to an upper part thereof. As outlined hereinbefore, such an arrangement has blood circulatory benefits in that it aids in the return of blood from the lower part of the leg. It also results in the other advantages outlined hereinbefore. In known articles of compression and graduated compression hosiery, the applied compression is passive and results primarily from the elasticity of the materials used in the fabric. The normal design process results in a desired degree of compression being achieved at, say, the user's ankle and knee, but in between the mix of materials used most likely fails to provide a desired graduated compression profile. In accordance with the invention, at least some of the threads 16 of the fabric are of an auxetic material and the result of this is that as the user moves, and his muscles expand and contract, the threads 16 will repeatedly stretch and relax. Simply by varying the pitch at which the wrap 20 is wound about the core 18, the elasticity or stiffness of the thread 16 can be varied, and the point at which the stiffness changes can be preselected. The use of auxetic materials in the fabric with the wrap 20 applied at different pitches allows a substantially continuous desired graduated compression profile to be achieved. Furthermore, the compression provided by the article can become dynamic, or have an enhanced dynamic characteristic to accompany the inherent passive characteristic, in the sense that as a user moves and his muscles expand and contract the accompanying stretching and relaxation of the fabric 12 can result in the degree of compression provided to different parts of the users leg varying to achieve a desired effect and enhance blood return.

Consequently, as illustrated in Figure 1 , the threads 16 in a region 24a of the article 10 may be such that the wrap 20 thereof is wound at a relatively great pitch so as to result in the thread 16, and so the region 24a, being of relatively stiff form when subject to significant stretching in the direction A. A region 24b may have a winding pitch that is relatively low, resulting in that part of the article being less stiff for a given applied degree of stretching in the direction A. In between the regions 24a, 24b, the winding pitch may be varied substantially continuously so as to achieve a desired compression profile in the article. Clearly, therefore, the stiffness of the article in a direction B under a given applied load will not be uniform. Furthermore, the stiffness or resistance to stretching of each region is not uniform but rahter depends upon the applied loading and whether that loading exceeds the point at which stretching, rather than straightening, or the wrap 20 is required, the compression provided by the article is thus dynamic rather than passive.

It will be appreciated that depending upon the application in which the article is to be used, different compression profiles may be desired, and by appropriate modification of the winding pitch of the wrap 20, such a profile can be achieved in a relatively simple and convenient manner. Furthermore as, upon stretching of the thread 16, it takes on a slightly coiled form, it will be appreciated that upon stretching of the fabric 12, pores 22 will tend to open up between adjacent threads 16. Consequently, as the user moves the fabric 12 will become of improved 'breathability'. As the article will typically be worn for an extended period of time, it will be appreciated that enhancing the breathability of the fabric aids air flow and so reduces sweat accumulation, and consequently that comfort is improved.

In compression and graduated compression hosiery, one known problem is that the upper end of the article tends to roll or slip down, in use. The problem is particularly common where the user is active, or where the hosiery has been used for some time and some of the elasticity of the materials used has been lost. To counter such slipping, it is known to provide the upper end of the article with a band of a material that aids in gripping of the underlying skin. However, this approach is of limited benefit, and can result in discomfort to the user. By incorporating auxetic materials into the fabric 12, the article 10 may be designed in such a manner that, at rest, relatively little compression is provided by the end part of the fabric 12, but that when the user is active and the material becomes stretched, a greater degree of compression is provided, thereby enhancing grip and reducing the risk of slipping.

In the arrangement described hereinbefore, the pitch of the wrap 20 of each individual thread 16, or groups of threads 16, is selected to achieve a desired degree of stiffness to the associated part of the fabric 12, the pitch being substantially uniform along the entire length of each thread 16, but different threads or groups of threads having different pitches to achieve the desired compression profile. This need not be the case, and arrangements may be possible in which the pitch at which the wrap 20 is wound is not uniform along the length of each thread 16 but rather varies, possibly continuously, along the thread. Figures 4a and 4b are views similar to Figures 3a and 3b illustrating such a thread. Such an arrangement may permit further fine tuning of the compression profile that can be achieved. For example, it may allow a front part of the article 10 to have a different stiffness to a rear part.

As the material used in the fabric is uniform, and just the pitch of the wrap 20 is varied, it will be appreciated that the accuracy and smoothness of transition between parts of the article of different compression profiles can be enhanced. Another embodiment of the invention takes the form of an orthopaedic splint 30, for example in the form of a wrist support as shown in Figure 4. A splint 30 of this type is commonly used in the treatment of the symptoms of repetitive strain injury for example as experienced by typists. By appropriate modification, the invention could alternatively be applied to, for example, knee supports, or supports or splints for use with other joints.

By incorporating auxetic materials into the fabric of the splint 30, in much the same manner as described hereinbefore, the splint 30 can be designed in such a manner as to provide different regions thereof with different levels of stiffness, and thereby to provide different levels of support. The selection of which parts of the splint to form with a relatively high stiffness and which parts to be of lower stiffness will depend to a large extent upon the joint being supported and the nature of the injury or symptoms being treated. Furthermore, incentive fatiguing may be achieved by appropriate selection of which parts of the splint are of high stiffness. As a result, as a wearer regains use of a joint, the splint will encourage the wearer to work against the splint, and so strengthen the associated muscle groups. As with the compression and graduated compression hosiery described hereinbefore, the splint may be designed in such a manner that pores in the fabric material can open up, as the user moves, thereby enhancing breathability of the material, and hence comfort to the user, whilst still achieving a desired level of support. Also, as described hereinbefore, it may be desired to utilise individual auxetic threads of non-uniform or graded form so as to result in, for example, the formation of regions to the front of the splint of different stiffness to regions of the rear thereof.

A splint of the form described hereinbefore may be lighter and more flexible than a traditional splint incorporating a support rod, and so may be more comfortable to use. It may also conform more closely to the shape of the users joint and so provide a better support for the joint.

It will be appreciated that a wide range of modifications and alterations may be made to the arrangements described hereinbefore without departing from the scope of the invention.

Claims

CLAIMS:

1. An auxetic material article comprising a fabric, the fabric including at least one yarn which is, at least in part, of an auxetic form, the yarn being arranged in the fabric such that the stiffness of the fabric in at least one direction under given applied loads varies in a non-uniform manner, and hence in the fabric providing dynamic compression.

2. An article according to Claim 1 , wherein different regions of the fabric are formed using different auxetic materials so as to provide the fabric with a non-uniform compression profile.

3. An article according to Claim 1 or Claim 2, wherein an auxetic material of graded or graduated form, ie having regions that are relatively compliant and regions that are relatively stiff under a given applied load, is used to result in the fabric having a non-uniform compression profile.

4. An article according to any of the preceding claims, wherein the auxetic material takes the form of a pair of elastic threads of different degrees of elasticity intertwined with one another.

5. An article according to any of Claims 1 to 3, wherein the auxetic material comprises a coiled component located within a channel formed within an outer component.

6. An article according to any of the preceding claims, wherein the auxetic material threads are arranged such that when the fabric is stretched, some adjacent regions of the auxetic material threads are urged apart with the result that pores tend to open up in the fabric.

7. An article according to any of the preceding claims, and adapted for use as compression or graduated compression hosiery.

8. An article according to Claim 7, wherein an end part of the hosiery located, in use, above a wearers knee, is provided with an auxetic material such that, in use, stretching resulting from muscle expansion will tend to result in the end part of the hosiery better gripping the adjacent skin and so reduce the risk of the hosiery moving or sliding down, in use, without requiring the hosiery to be excessively tight when the users muscles are relaxed.

9. An article according to any of Claims 1 to 6, and adapted for use as an orthopaedic splint.

10. An article according to Claim 9, wherein the article provides dynamic resistance to movement so that, as a patient starts to recover strength and movement in a joint, the splint forces him to work harder against increasing resistance.

11. An article according to Claim 9 or Claim 10, wherein the article is adapted to provide differential support around a wearer's joint.