[Biocompatibility of graded zirconia-hydroxyapatite composite]

To evaluate the biocompatibility and safety of a novel orthopedics materials-graded zirconia (ZrO2)-hydroxyapatite (HA) composite biomaterials.

First, ultrafine powers of ZrO2 and HA powder were prepared by chemical precipitation method, then graded ZrO2-HA composite was synthesized by dry-laying and sintering method. After the physiological saline and culture medium extracts of the composite were prepared, four experiments were conducted as follows: (1) The mouse acute toxic test consists of 2 groups (n=10). The extracts were intravenously injected to mice in the first group, and physiological saline to mice in the second group. The dose was 50 g/kg. Their toxicity manifestation, morality and the change of weight were recorded. (2) The standard curve of proliferation and metabolism of L929 cells was established. (3) The cytotoxic test consists of 3 groups: materials group (extracts of the materials), positive control group (culture fluid with 0. 64% phenol), and negative control group (RPMI-1640 culture fluid). Each of three was cultured with cell suspension, and then the morphology of the cells was observed, the relative proliferation rate (RGR) was calculated, and the toxicity was classified. (4) In vitro hemolytic test was divided into 3 groups: extracts, sterile distilled water (positive control) and 0.9% physiological saline. In each of three, 0.2 ml anticoagulant diluted fresh rabbit blood was added. The percentage of hemolysis was tested. (5) The muscle and implantation test were divided into 4 groups (n=3). The composite biomaterials were implanted into pygal muscles on either side and lateral condyles of femurs. After surgery, the rats of four groups were sacrificed at 3, 6, 12 and 24 weeks respectively. Tissue slice and scanning electronic microscopy were performed.

(1) General acute toxic test: no mouse died within 3 weeks; no toxicity symptom or adverse effects were shown within 3 days. The weight of materials group increased by 3.57 +/- 0.49 g, and the control group by 3.62 +/- 0.61 g, showing no statistically significant difference (P>0.05). The standard curve of L929 cell proliferation and metabolism showed that their existed a positive correlation between the number of L929 cells and the proliferation. (3) Cytotoxic test: cytosomes in the positive control group diminished and appeared round, there were pyknotic nucleus, the attached cells agglomerated; the toxicity was level IV. The morphology of cells in materials group and negative control group was normal, and the number of them increased; the toxicity was level I and level 0, respectively. The MTT color experiments showed that positive control group was significantly lower than materials group and negative control group, showing statistically significant difference (P<0.01); there was no statistically significant difference between materials group and negative group. (4) Hemolytic test: in vitro hemolytic rate of negative control group was 0, of positive control group was 100%, and of materials group was 1.66%, which accords with the standard that hemolytic rate should be lower than 5% specified in ISO. (5) Implant test: No apparent rejection reaction took place after the composite was implanted; the composite bonded with the bones of the receptors firmly, which had good boned-induced effect.

Graded ZrO2-HA composite bioceramic has good biocompatibility and is suitable for orthopedic biomaterials.