Injectable Prosthetic Nucleus Pulposus Biocompatibility Evaluation

ObjectiveA neotype prosthetic nucleus pulposus was prepared in our previous work. As a new material, its cytotoxicity and biocompatibility must be evaluated before it is used in vivo.MethodsRefferring to the standard for the biological evaluation of medical devices,the cytotoxicity was detected by culturing the L929 cell in the leaching liquor of the material groups. Adopting MTT colorimetric method, the OD(optical density) and RGR(relative growth rate) of cell among the material groups and control group were compared. The samples are shaped into short columns long 1cm diameter 0.3 cm. Forty eight New Zealand white rabbits, weight range 2.5～3.0 kg, were divided into 3 groups according to different implantation. Group A: polyurethane, group B: silicone rubber, group C: macromolecular polyethylene as negative control. Make two partial-central incision 2 cm away from the spinal mid-line, separate the muscle to form an 1 cm cavity, implant the materials as grouped. Observe vital sign of the rabbit post-op, take muscle samples around the area at 1,4,12,26 weeks after the operation, take blood sample for routine, biochemistry and electrolyte, also observe main organs for biology changes. Examine the mechanical properties of the samples, use same origin non-implanted samples as control.ResultsThe OD and RGR of L929 cell in the material groups and the control group show no significant difference. The cytotoxicity of the material is located at level 0-1 according to the standard rank of cytotoxicity, which is an acceptable level. All rabbits survived in good condition after the surgery, all the incisions reach primary healing. Swelling and red could be seen in regional muscles at 1 week post-op, about symptom disappeared at 4 weeks post-op, connective tissue could be found arroud the implanted samples at 12 weeds and 26 weeks post-op. At 26 weeks post-op, no significant difference was found in the blood routine,biochemistry and electrolyte results(P>0.05). No ulceration, ecchymosis, swelling, hyperemia or bleeding had been observed in smooth surface organs. There was no significant difference in the percentage of each organ weight(P>0.05). Granulation tissue proliferation and inflammatory cell infiltration could be seen in histological observation of muscles at 1 week post-op. The inflammation disappeared and thin fibre vesica was formed at 4 weeks post-op. The fibre vesica was thicken gradually and achieved stability after 12 weeks. According to the GB/T 16175, the inflammatory reaction rank and the fibre vesica are the same as to the control group, and both reach required standard. No specific pathological changes were discovered in the organs at 26 weeks post-op. There was no significant difference in molecular weight between the implanted and non-implanted materials(P>0.05), also no significant difference in breaking tensile strength and elongation of group A(P>0.05), shore hardness of group B(P>0.05).ConclusionThe neotype artificial material does not show cytotoxicity or damage to regional tissue and main organs of the body, and have a good biocompatibility and a great biological safety.