HYDROGEL-BASED PROSTHETIC DEVICE FOR REPLACING AT LEAST A PART OF THE NUCLEUS OF A SPINAL DISC

The present invention is a prosthetic for replacement of at least a part of the nucleus of a intravertebral disc. The prosthetic device is composed of at least two substantially parallel soft layers (13, 15, 17, 19) of an elastically deformable hydrogel and at least one more rigid layer (21, 23, 25), the more rigid layer having less compressibility than the soft layers, being adjacent to the soft layers, and firmly attached to them. In some embodiments, the soft layers have the same thickness and composition. Typically, the prosthesis has more than one more rigid layer and these more rigid layers have the same thickness and composition. The number of soft layers is usually one more than the number of more rigid layers, with, e.g., at least three soft layers. The invention also includes a method of prosthesis production, which involves prefabricating soft and more rigid layers; stacking at least two prefabricated soft and at least one prefabricated more rigid layer in a substantially parallel fashion into their final form, and, permitting the layers to firmly connect to one another by mutual interaction. In this method, at least one type of the layers is prefabricated in the dehydrated state, which is done by dehydrating stretched foil in an apparatus preventing its contraction and thereby decreasing its area. There is at least partial dehydration of the prosthesis under pressure applied in a direction tangent to the planes of the layers. In preferred embodiments, while in the state of almost full dehydration, the implant is sterilized using ionizing radiation or a gaseous chemical agent, after which it is partially rehydrated within a sterile wrapper using water vapor. L'invention concerne un dispositif prothétique destinée au remplacement d'une partie au moins du noyau d'un disque intervertébral. Ce dispositif prothétique est composé d'au moins deux couches (13, 15, 17, 19) molles sensiblement parallèles composées d'un hydrogel à déformation élastique, et d'au moins une couche (21, 23, 25) plus rigide présentant une compressibilité moins grande que les couches molles, adjacente aux couches molles et solidement fixée à ces dernières. Dans certaines formes de réalisation, les couches molles présentent une épaisseur et une composition identiques. En général cette prothèse comprend plusieurs couches à rigidité plus élevée, et ces couches plus rigides présentent une épaisseur et une composition identiques. Le nombre de couches molles compte en général une couc