[In vivo biological safety study of porous zinc oxide/hydroxyapatite composite materials]

Abstract

Objective: To evaluate the in vivo biological safety of porous zinc oxide (ZnO)/hydroxyapatite (HA) composite materials.

Methods: The porous ZnO/HA composite materials and porous HA materials were prepared by the spark plasma sintering technology. First, the materials were characterized, including scanning electron microscopy to observe the material structure, in vitro degradation experiments to detect the degradation rate of the materials, and inductively coupled plasma emission spectrometer to detect the concentration of Zn ²⁺ dissolved out of the composite material degradation. Then the two kinds of material extracts were prepared for acute systemic toxicity test. Fifteen male Kunming mice were randomly divided into groups A, B, and C ( n=5) and injected intraperitoneally with normal saline, HA extracts, and ZnO/HA extracts, respectively. The body mass of the mice was recorded before injection and at 24, 48, and 72 hours after injection. The liver and kidney tissues were taken at 72 hours for HE staining to evaluate the safety of the composite material. Finally, the biological safety of the material in vivo was evaluated by implantation experiment. The eighteen male New Zealand white rabbits were randomly divided into HA group and ZnO/HA group ( n=9); a bilateral radius defect model (1 cm) was established, and the right forelimbs of the two groups were implanted with porous HA materials and porous ZnO/HA composite materials, respectively; the left untreated as a blank control. The general condition of the animals were observed after operation. The rabbit blood was collected at 1 day before operation and at 1 day, 1 week, 4 weeks, and 8 weeks after operation for routine blood test (inflammation-related indicators) and blood biochemistry (liver and kidney function-related indicators). X-ray films were taken at 4, 8, and 12 weeks after operation to observe the repair of bone defects.

Results: Material characterization showed that porous ZnO/HA composite materials had interconnected large and small pore structures with a pore size between 50 and 500 μm, which degraded faster than porous HA materials, and continuously and slowly dissolved Zn ²⁺. The acute systemic toxicity test showed that the mice in each group had no abnormal performance after injection, and the body mass increased ( P<0.05). HE staining showed that the cells shape and structure of liver and kidney tissue were normal. Animal implantation experiments showed that all rabbits survived until the experiment was completed; routine blood tests showed inflammation in each group (neutrophils, monocytes, and lymphocytes increased) at 1 day after operation, and all returned to normal at 8 weeks ( P>0.05); compared with 1 day before operation, the content of inflammatory cells in the HA group increased at 1 day, 1 week, and 4 weeks after operation ( P<0.05), and the ZnO/HA group increased at 1 day after operation ( P<0.05); blood biochemistry showed that the liver and kidney function indexes were in the normal range; X-ray films showed that the ZnO/HA group had better osseointegration than the HA group at 4 weeks after operation.

Conclusion: The porous ZnO/HA composite material has good in vivo biological safety and good bone repair ability, which is a potential bone repair material.

Keywords: Hydroxyapatite; bone repair; composite material; in vivo biological safety; rabbit; zinc oxide.