Abstract:
A thermoplastic material and more particularly a substrate coated or impregnated with a thermoplastic composition. The material ( 1 ) comprises a fibre-containing substrate having two surface layers ( 2 A,  2 B) and an intermediate spacing layer ( 3 ) with fibre strands ( 4 ) connected between the surface layers; wherein the substrate is impregnated with a thermoplastic composition. The material is suitable for producing for example orthopaedic devices. Also a method for preparing such devices and devices produced with the method.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a thermoplastic material and more particularly a fibre-containing substrate coated or impregnated with a thermoplastic composition. The material is suitable for producing for example orthopaedic devices. The invention also relates to a method for preparing such devices and devices produced with the method. 
       STATE OF THE ART 
       [0002]    Fabrics of various types, such as woven, knitted and non-woven materials, and having a certain thickness are known per se within various fields. It is also known to produce orthopaedic devices using substrates impregnated with thermoplastic compositions. 
         [0003]    U.S. Pat. No. 4,238,522 discloses orthopaedic devices, materials and methods, and more particularly a bandage material manufactured from a substrate consisting of netting which is impregnated with a thermoplastic composition. The document fails to disclose how a substantial thickness of the material may be obtained, except by wrapping the material in several layers. 
         [0004]    EP 0 934 749 discloses a supporting member manufactured by a plastics reinforced triaxially woven fabric. This material does not have a substantial thickness. 
         [0005]    U.S. Pat. No. 6,159,877 discloses a knit fabric material for orthopaedic support materials. The material is impregnated with a curable resin such that the prepared cast obtains a permanent shape that cannot later be altered. 
         [0006]    US 2002/0,143,282 discloses an orthopaedic casting material comprising a double-knit material impregnated with hardening material. Once the cast has been hardened the shape cannot be altered. 
         [0007]    US 2003/0,093,025 discloses an orthopaedic casting material comprising a double-knit material impregnated with hardening material. Once the cast has been hardened the shape cannot be altered. 
         [0008]    U.S. Pat. No. 5,284,031 discloses several knit ply fabrics with connecting layers. The document is only related to the fabric as such and is not concerned with producing composite materials wherein the fabric is impregnated with plastics. 
         [0009]    In the art of for example orthopaedic devices, it is desired to obtain a material which is at the same time strong, lightweight and thermoplastic, and that is shapable when heated to a temperature which is tolerable for a human body. Preferably, the material should permit air circulation to improve the comfort further. None of the materials enumerated above achieves all the objectives at the same time. 
       SUMMARY OF THE INVENTION 
       [0010]    A material with the above characteristics is provided by the invention. The material comprises a substrate having two surface layers and a spacing layer placed therebetween. The substrate is coated or impregnated with a thermoplastic composition. Because of the spacing layer and the thermoplastic composition the material obtained is strong, has low weight and is shapable at suitable temperatures. 
         [0011]    In a first aspect the invention provides a material comprising a fibre-containing substrate having two surface layers and an intermediate spacing layer with fibre strands connected between the surface layers; wherein the substrate is coated or impregnated with a thermoplastic composition. 
         [0012]    Preferably, the spacing layer comprises strands running directly between the surface layers. 
         [0013]    In a preferred embodiment, the substrate is a three-dimensional woven or knitted fabric. 
         [0014]    In a second aspect the invention provides a method of producing an orthopaedic device, comprising the steps of: heating a piece of such a material until shapable; shaping the material into a desired shape in conformance with a body part, suitably directly on the body part; and allowing the piece of material to cool while maintaining the desired shape. 
         [0015]    In a third aspect the invention provides an orthopaedic device thus produced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0016]    The invention will be described in detail below with reference to the accompanying drawings of which: 
           [0017]      FIG. 1  is a top view of a surface layer of a material of the invention; 
           [0018]      FIG. 2A  is a cross-sectional view of material seen as indicated by the arrows IIa in  FIG. 1 ; and 
           [0019]      FIG. 2B  is a cross-sectional view of material seen as indicated by the arrows IIb in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0020]    The material according to the invention is suitable for orthopaedic devices, such as orthoses, braces, splints etc. The material has the strength necessary to achieve support and/or immobilisation. It is lightweight and permits circulation of air to be comfortable. The material comprises two main components, a substrate which is generally a fabric with a certain thickness and a thermoplastic composition making the substrate rigid when its temperature is below the softening point. The fibres of the substrate are arranged such that the material is reinforced to obtain the necessary strength. 
         [0021]      FIGS. 1 ,  2 A and  2 B illustrate an example of a substrate coated or impregnated with a thermoplastic composition. Even if the fibres of the substrate are coated with the composition the structure of the substrate is visible. The figures show the finished material ready for use. 
         [0022]    The substrate of the material  1  in accordance with the invention is in the preferred embodiment a woven structure having surface layers  2 A and  2 B with openings  6  forming a netlike surface. The openings are holes through the whole material. Between the surface layers  2 A and  2 B there is a spacing layer  3 . In the surface layers the fibres are woven together to form strand bundles  5  which are visible as ridges in the material between the wholes. In the spacing layer  3  the fibres are not woven together but are rather running directly between the surface layers  2 A and  2 B. At some locations some single connecting fibre strands  4  are visible. The substrate is preferably made from one long monofilament, both in the surface layers  2 A and  2 B and the spacing layer  3 . 
         [0023]    The connecting fibre strands  4  have shapes that depend on the weave structure. As seen in the plane of  FIG. 2A , the strands  4  are running more or less straight between the surface layers, but with an angle to accommodate the openings  6 . As shown in the plane of  FIG. 2B , the strands  4  are more curved in this plane. When the material is softened the shape of the spacing layer strands  4  is also changed when shaping the whole material. 
         [0024]    A suitable fabric is commercially available from the Danish company Tytex A/S under the trade name Spacer Fabric. 
         [0025]    Other examples of fabrics are shown in U.S. Pat. No. 5,284,031 showing knitted fabrics. The invention is also applicable with non-woven materials such as felt. The main feature of the invention is that there should be connecting fibre strands between the surface layers. 
         [0026]    The substrate may be made from natural fibres such as cotton or wool, or synthetic fibres, such as nylon, polyester etc. Substrates made from polyester have proven to give excellent results. In the spacing layer  3  a certain rigidity of the fibres is advantageous. As a practical example only, the individual fibres may have a thickness of approximately 0.1 mm and the whole material may have thickness of about 5-10 mm (depending on the actual shape of the material). 
         [0027]    The thermoplastic composition may be selected from a range of compositions. It should have the ability to be shaped at a temperature which is tolerable to the human body. For example a softening point at maximum 65-75° C. is suitable. It should be capable of impregnating the substrate, in other words coating the strands of the substrate, the surface layers as well as the spacing layer. Suitable examples of compositions include polyols and the like. The preferred composition is polycaprolactone. 
         [0028]    In use, the material may be shaped directly on the body part of a patient, usually with a stocking or the like closest to the skin. The material is heated above the softening point usually above 70° C., for example in a hot water bath or with a hot-air gun. 
         [0029]    When the material is softened it is almost completely shapable to conform to the body part in question. By stretching the material the openings  6  will be contracted until eventually they are totally closed. The material may be stretched again in the perpendicular direction to open the openings  6  again. It is preferred that there remain some openings to permit air circulation through the material. 
         [0030]    To complete the orthopaedic device the material may be provided with padding, straps and fasteners etc. as known in the art. Fasteners may be applied permanently to the material. The material may be shaped with fasteners already applied. 
         [0031]    When the material is shaped to the desired form it is allowed to cool to regain its rigidity. Full strength is obtained gradually and well above normal body temperature. Then the device is fitted to the body part. If the fit is not perfect the first time the material may be heated again to adapt the shape. This shaping of the material may be repeated any number of times. 
         [0032]    Thus, the present invention provides a material having several advantages over the prior art. The material has the strength necessary to achieve support and/or immobilisation when used in an orthopaedic device. At the same time, it is lightweight and permits circulation of air. The scope of the invention is only limited by the claims below.