[In vivo experiment of porous bioactive bone cement modified by bioglass and chitosan]

To investigate the biomechanical properties of porous bioactive bone cement (PBC) in vivo and to observe the degradation of PBC and new bone formation histologically.

According to the weight percentage (W/W, %) of polymethylmethacrylate (PMMA) to bioglass to chitosan, 3 kinds of PBS powders were obtained: PBC I (50: 40:10), PBC II (40:50:10), and PBC III (30:60:10). The bilateral femoral condylar defect model (4 mm in diameter and 10 mm in depth) was established in 32 10-month-old New Zealand white rabbits (male or female, weighing 4.0-4.5 kg), which were randomly divided into 4 groups (n = 8); pure PMMA (group A), PBC I (group B), PBC II (group C), and PBC III (group D) were implanted in the bilateral femoral condylar defects, respectively. Gross observation were done after operation. X-ray films were taken after 1 week. At 3 and 6 months after operation, the bone cement specimens were harvested for mechanical test and histological examination. Four kinds of unplanted cement were also used for biomechanical test as control.

All rabbits survived to the end of experiment. The X-ray films revealed the location of bone cement was at the right position after 1 week. Before implantation, at 3 months and 6 months after operation, the compressive strength and elastic modulus of groups C and D decreased significantly when compared with those of group A (P < 0.05), but no significant difference was found between groups C and D (P > 0.05); the compressive strength at each time point and elastic modulus at 3 and 6 months of group B decreased significantly when compared with those of group A (P < 0.05). Before implantation and at 3 months after operation, the compressive strength and elastic modulus of groups C and D decreased significantly when compared with those of group B (P < 0.05); at 6 months after operation, the compressive strength of group C and the elastic modulus of group D were significantly lower than those of group B (P < 0.05). The compressive strength and elastic modulus at 3 and 6 months after operation significantly decreased when compared with those before implantation in groups B, C, and D (P < 0.05), but no significant difference was found in group A (P < 0.05). At 3 months after operation, histological observation showed that a fibrous tissue layer formed between the PMMA cement and bone in group A, while chitosan particles degraded with different levels in groups B, C, and D, especially in group D. At 6 months after operation, chitosan particles partly degraded in groups B, C, and D with an amount of new bone ingrowth, and groups C and D was better than group B in bone growth; group A had no obvious change. Quantitative analysis results showed that the bone tissue percentage was gradually increased in the group A to group D, and the bone tissue percentage at 6 months after operation was significantly higher than that at 3 months within the group.

According to the weight percentage (W/W, %) of PMMA to bioglass to chitosan, PBCs made by the composition of 40:50:10 and 30:60:10 have better biocompatibility and biomechanical properties than PMMA cement, it may reduce the fracture risk of the adjacent vertebrae after vertebroplasty.