[Experimental study of novel injectable nucleus pulposus prostheses implant]

To explore the histological and the hematological change of rabbits after implanting novel injectable artificial nucleus prostheses, and to evaluate the biological safety.

In accordance with Biological Evaluation of Medical Devices, materials of polyurethane, silicone rubber and macromolecular polyethylene for medical use were made into short column 1 cm in length and 0.3 cm in diameter. Forty-eight SPF New Zealand white rabbits weighing 2.5-3.0 kg were used, and cavity 1 cm in depth was made in the area 2 cm away from the spinal midline by separating muscle. Then according to different material being implanted, the rabbits were divided into 3 groups (n = 16): Group A, polyurethane; group B, silicone rubber; group C, macromolecular polyethylene for medical use as negative control. General condition of the rabbits was observed after operation. Gross and histology observation were conducted 1, 4, 12 and 26 weeks after operation. Blood routine, biochemical function and electrolyte assays were performed 26 weeks after operation to observe pathological changes of organs. Meanwhile, physicochemical properties of the materials were detected, and the material in the same batch was used as negative control.

All rabbits survived until the end of experiment, and all wounds healed by first intention. In each group, red swollen muscles were observed 1 week after operation and disappeared 4 weeks after operation, connective tissue around the implanted materials occurred 12 and 26 weeks after operation. At 26 weeks after operation, there were no significant differences among three groups in blood routine, biochemical function and electrolyte assays (P > 0.05). Organs had smooth surface without ulceration, ecchymosis, obvious swelling, hyperemia or bleeding, and nodules. There were no significant differences among three groups in percentage weight of each organ (P > 0.05). Histology observation: granulation tissue proliferation and inflammatory cell infiltration were observed in each group 1 week after operation, fibrous capsule formation around the materials and the disappearance of inflammatory cell infiltration were evident 4 weeks after operation, cyst wall grew over time and achieved stability 12 weeks after operation. The inflammatory response and the fiber cyst cavity of groups A and B met the standard of GB/T 16175 and were in line with group C. No specific pathological changes were discovered in the organs 26 weeks after operation. For group A, no significant difference was evident between before and after material implantation in terms of weight average molecular weight, number average molecular weight, tensile strength at break and elongation at break (P > 0.05). For group B, no significant difference was evident between before and after material implantation in shore hardness (P > 0.05).

Novel injectable nucleus pulposus prostheses do not damage local tissue and function of organs, but provide good biocompatibility and biological safety.