Spinal intervertebral disk replacement material for nucleus pulposus and production method thereof

Abstract

To provide a spinal intervertebral disk replacement material for nucleus pulposus which is relatively superior in load resistance that causes smaller damage of the anulus fibrosus by insertion during operation, remains in the anulus fibrosus stably after operation, and also allows prevention of the damage of the vertebral body cartilage endplate and the anulus fibrosus surrounding the prosthetic portion by sliding, and a production method thereof. The present invention relates to a spinal intervertebral disk replacement material for nucleus pulposus, comprising a dry polyvinylalcohol gel having a percentage of saturated water content of 18 to 50 wt % that changes its shape at a shape deformation rate of 150 vol % or more by water absorption. The present invention also relates to a method of producing the spinal intervertebral disk replacement material for nucleus pulposus above, comprising a step of preparing a polyvinylalcohol gel having a percentage of saturated water content of 20 to 53 wt %, a step of converting the polyvinylalcohol gel into a polyvinylalcohol hydrogel in the hydrated state and forming it into a shape having a hollow region, a step of irradiating the polyvinylalcohol hydrogel with γ ray at an intensity of 20 to 100 kGy, and a step of drying the PVA hydrogel in such a manner that the resulting hydrogel is so deformed that the hollow region disappears.

1 . A spinal intervertebral disk replacement molded-dry-product for nucleus pulposus, comprising a polyvinylalcohol gel having a percentage of saturated water content of 18 to 50 wt % before irradiation and being irradiated with γ ray at an intensity of 20 to 100 kGy,
 wherein the molded-dry-product changes its shape into an almost cylindrical or almost elliptically cylindrical shape so that a hollow region comes into existence at a shape deformation rate of 150 vol % or more and at a volume swelling ratio of 135 vol % or less by water absorption.   
     
     
         2 . The spinal intervertebral disk replacement material for nucleus pulposus according to  claim 1 , wherein the percentage of saturated water content of said dry polyvinylalcohol gel is 23 to 35 wt %. 
     
     
         3 . The spinal intervertebral disk replacement molded-dry-product for nucleus pulposus according to  claim 1 , wherein molded-dry-product has a columnar shape in which a sectional view is almost elliptical and the internal face is in contact with itself. 
     
     
         4 . A method of producing the spinal intervertebral disk replacement molded-dry-product for nucleus pulposus according to any one of  claims 1  and  3 , comprising:
 preparing a polyvinylalcohol gel having a percentage of saturated water content of 20 to 53 wt %,   converting the polyvinylalcohol gel into a polyvinylalcohol hydrogel in the hydrated state and forming it into a shape having a hollow region,   irradiating the polyvinylalcohol hydrogel with γ ray at an intensity of 20 to 100 kGy in water at a low-oxygen concentration, and   drying the PVA hydrogel in such a manner that the resulting hydrogel is so deformed that the hollow region disappears.   
     
     
         5 . The spinal intervertebral disk replacement molded-dry-product for nucleus pulposus according to  claim 1 , wherein the γ-ray irradiation dose is 50 to 100 kGy. 
     
     
         6 . The method according to  claim 4 , wherein the γ-ray irradiation dose is 50 to 100 kGy.