fig1 shows an embodiment of the present invention in which a base for a prosthesis for replacing an intervertebral disc is shown . said base comprises a flexible portion ( 1 ) in the centre thereof , which is enclosed by less flexible portions ( 2 ) on the upper side and on the bottom side . fig2 shows an embodiment for a prosthesis according to the present invention in which , as shown in fig1 , the whole is reinforced with fibres ( 3 ), which are provided around the whole of ( 1 ) and ( 2 ). a fibre of the type of lycra ( dupont de nemours ) or spandex ( brand ) is taken as an example . lycra fibres consist of a polyurethane and can be stretched up to eight times their original length . the monomers from which the hydrogel according to the present invention can be obtained by polymerisation may comprise hema and sodium methacrylate , among other substances . other monomers , whether or not in combination with each other and with the aforesaid substances , are also possible . the hydrophilic nature of said monomers may be based on adsorption as well as on electrostatic attraction of hydrophilic cations by a permanent charge . the polymerisation process may be initiated by chemical , thermal or optical ( uv radiation ) means . it has become apparent that a material obtained in such a manner attains a compression strength in the order of several mpa , whilst the weight percentage of water is higher than 50 %. an example of a method of manufacturing a flexible portion ( 1 ) of hydrogel according to the present invention comprises the cutting of slices ( 5 ) of 5 - 15 mm , preferably 8 - 10 mm , from a polymerised bar ( 6 ) of hydrogel , as shown in fig3 , which is made by polymerising a solution of at least one hydrogel monomer in a bar - shaped mould , using at least one polymerisation process . one method according to the present invention for manufacturing the prosthesis concerns the provision of fibres around the whole of the flexible portion ( 1 ) and at least one less flexible portion ( 2 ). fig4 shows a preferred method , in which the whole of the flexible portion ( 1 ) of hydrogel and the less flexible portions ( 2 ) is set up on a rotating shaft ( 4 ), after which the fibres ( 3 ) are provided around the whole of ( 1 ) and ( 2 ) by winding , as is shown in fig5 . in one method according to the present invention , which is carried out by using a device as shown in fig5 , anisotropy is introduced into the design through fibre reinforcement comparable with the way in which fibres are arranged in the natural annulus . part of the fibres , or all fibres , may be provided in the hydrogel as “ chopped fibres ”. using the construction according to the present invention , variations in the mechanical properties of the prosthesis can be effected in a simple manner . in the first place , variations in the composition of the hydrogel can influence the swelling behaviour . in the second place , it is possible to impart different mechanical properties for different directions of movements to the prosthesis by varying the fibre reinforcement on the geometry of the prosthesis . according to a preferred method , the fibre is stretched to 1 - 6 times , preferably 3 times its original length during provision of the fibre , so as to ensure homogeneous properties for the entire fibre reinforcement . this makes it possible to provide several layers of fibre material , preferably dozens or even hundreds of layers , in which the angle of the fibres at the side with respect to the axis of rotation is varied from 5 ° to 90 °, preferably from 45 ° to 60 °, during provision of the fibres . it is also possible to use other methods of providing fibres around the whole of the flexible portion and at least one less flexible portion , in particular other winding or knitting techniques . according to a preferred embodiment , the whole of the flexible portion and possibly a less flexible portion consisting of a fibre - reinforced hydrogel is immersed in a hydrogel monomer bath so as to produce the composite material as described above by having adsorption of the monomer to the fibres take place and subsequently initiating the polymerisation of the hydrogel so as to obtain the prosthesis according to the present invention . according to a special embodiment of the invention , the less flexible portions ( 2 ) of the prosthesis consists of a hardened portion of polymerised hydrogel material at the upper side and the bottom side of the flexible portion ( 1 ). according to a preferred embodiment of the present invention , the less flexible portions ( 2 ) consist of separate end plates , which cover the upper side and the bottom side of the flexible portion ( 1 ) of hydrogel . said less flexible portions ( 2 ) ensure that the fibres ( 3 ) are distributed homogeneously upon provision thereof , they prevent fibres from carving into the hydrogel and provide a location where the prosthesis can adhere to the adjacent vertebrae . the geometry of the less flexible portions ( 2 ) is preferably adapted to the geometry of the joint or the vertebra into which the prosthesis is to be implanted so as to ensure an optimum adhesion and pressure distribution . the geometry and the material of the prosthesis may be varied and selected by those skilled in this field of the art . the swelling characteristics of the prosthesis according to the present invention may be used for simplifying surgery . a frequent complication during surgery is the necessity to stretch and / or cut the ligaments of the vertebrae through upon implantation of the prosthesis . since the prosthesis is implanted in its final state , the adjacent vertebrae must be kept apart during surgery so as to make it possible to insert the prosthesis . in the long run , said overstretching of the ligaments may lead to calcification of the ligaments . the prosthesis according to the present invention may be placed in a salt bath prior to surgery so as to reduce its volume . this reduces the extent to which the ligaments of the vertebrae are overstretched during surgery and thus the risk of short - term as well as long - term complications , and in addition it accelerates the healing process after surgery . once the prosthesis according to the present invention is implanted in the body , osmotic action of the negatively charged groups in the hydrogel will cause it to absorb water in such a manner that it will assume the desired shape and the desired volume , filling the cavity between the adjacent vertebrae . subsequently , the prosthesis — like the natural disc — will exude bodily fluid during the day and absorb it during the night . the invention will now be explained in more detail by means of the following example . a monomer mixture of a hydrogel having a composition of hema is polymerised for 16 hours in a glass tube ( 22 mm diameter ) in a water bath having a temperature of 45 ° c . following that , the bar - shaped hydrogel material is removed from the glass tube and the two ends are cut off . the middle part is clamped in a metal tube , which is set up on the rotating part of a lathe as shown in fig3 . a knife is moved slowly ( 10 mm / min ) through the hydrogel bar ( 6 ) whilst being lubricated with a teflon spray , during which operation the bar ( 6 ) rotates at a speed of 100 revolutions per minute . two end plates having a diameter of 22 mm and a thickness of 0 . 5 mm are provided at the upper side and the bottom side of the slice of hydrogel ( 5 ), and the whole is placed on a rotating shaft ( 4 ) as shown in fig4 . subsequently , lycra fibres are provided by winding whilst being stretched to three times their original length . three layers are provided , with the fibres being provided in such a manner that the angle they include with the rotating shaft is 45 - 60 °. this angle is varied during the winding operation . the fibre is provided in 7500 revolutions . after winding , the whole of the flexible portion ( 1 ) of hydrogel enclosed between end plates ( 2 ) and wrapped in fibres ( 3 ) is immersed in a bath of hydrogel monomer ( hema ) so as to impregnate the fibres with the monomer . the prosthesis according to the present invention is obtained after polymerisation of the hydrogel under the influence of ultraviolet light . although the invention has been described above by means of special embodiments and an example , obvious variants will suggest themselves to those skilled in this field of the art after reading the foregoing , which variants fall within the scope of the appended claims .
the present application relates to a prosthesis comprising a flexible portion and at least one less flexible portion , which flexible portion comprises a fiber - reinforced hydrogel . in addition to that , the application relates to a prosthesis consisting of a fiber - reinforced hydrogel , which prosthesis is intended to replace cartilaginous materials . the application further relates to the use of the prosthesis and to a method for manufacturing the prosthesis . the application furthermore relates to a method of preparing the flexible portion for a prosthesis . finally , the application relates to a fiber material apparently intended for use in the prosthesis .