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Purpose/Aim of the study: To evaluate the biomechanical characteristics and biocompatibility of an injectable, biodegradable calcium phosphate cement (CPC) containing poly lactic-co-glycolic acid (PLGA). MATERIALS AND METHODS: A vertebral compression fracture model was established using 20 human cadaveric vertebrae (T11-L3) divided into CPC/PLGA composite versus PMMA groups for biomechanical testing. In addition, 35 New Zealand rabbits were used to evaluate biodegradability and osteoconductive properties of CPC/PLGA using a bone defect model. In vitro cytotoxicity was evaluated by culturing with L929 cells. RESULTS: The CPC/PLGA composite effectively restored vertebral biomechanical properties. Compared with controls, the maximum load and compression strength of the CPC/PLGA group were lower, and stiffness was lower after kyphoplasty (all p <.05). Degradation was much slower in the control CPC compared with CPC/PLGA group. The bone tissue percentage in the CPC/PLGA group (44.9 ± 23.7%) was significantly higher compared with control CPC group (25.7 ± 10.9%) (p <.05). The viability of cells cultured on CPC/PLGA was greater than 70% compared with the blanks. CONCLUSIONS: Our biodegradable CPC/PLGA composite showed good biomechanical properties, cytocompatibility, and osteoconductivity and may represent an ideal bone substitute for future applications.

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OBJECTIVE: To investigate the antitumor effect of calcium phosphate cement incorporated with doxorubicin microspheres. METHODS: The absorbance at 490 nm of SaoS-2 cells cultured for 5 days in the media containing the extract of the cement incorporating doxorubicin microspheres was measured using Cell Counting Kit-8. SaoS-2 cells were adjusted to the density of 2x10(7) ml(-1) and injected into the left buttock of nude mouse in the volume of 0.2 ml. The cell suspension (0.1 ml) mixed with an equal volume of the cement extract were injected into the right buttock and on the back of the bilateral ears of nude mice. At 12 days after the cell injection, the tumor tissues were obtained and weighed to calculate the tumor inhibition rate, and the pathological samples were observed with HE staining. RESULTS: The extract of the bone cement containing doxorubicin microspheres showed inhibitory effects on the tumor growth in a dose-dependent manner. The tumor inhibition rate reached 61.0% in high-dose group. Tumor necrosis was found in high dose group, but virtually absent in low-dose group. CONCLUSIONS: CPC containing doxorubicin PLGA microspheres can inhibit tumor cell growth both in vitro and in vivo.

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OBJECTIVE: The histological changes of rhBMP-2/calcium phosphate cement (CPC) were evaluated in vertebroplasty on nonhuman primate models in order to determine the feasibility of this carrier formulation instead of PMMA. METHODS: Percutaneous vertebroplasty (PVP) was performed in 4 adult rhesus monkeys which were evenly distributed in two groups. Ten vertebral bodies(VBs) from T10 to L7, of each rhesus were selected, and the 20 VBs in each group were randomly divided into 3 sub-groups. Group A:8 VBs, filled with rhBMP-2/CPC; Group B:6 VBs, filled with injectable PMMA; Group C:6 VBs, as control, filled with normal saline. The 2 rhesus monkeys in each group were killed at 2 and 6 months after operation, respectively, and the specimens of all the 40 VBs were collected for histological examination. RESULTS: In group A,radiographic and histologic studies confirmed that part of the rhBMP-2/CPC cement degraded with new bone and new vessels ingrowth into the material after 2 months. No gap, fibrous hyperplasia or sclerotic callus was found in the interface. After six months, the cement was almost completely replaced by mature bone tissue. In group B, no new bone formation and material degradation but inflammatory cell infiltration and fibrous membrane gap were found 2 months after operation. After 6 months, the inflammatory cell infiltration subsided, the fibrous membrane gap became narrower, but there were still no new bone formation and material degradation. In group C, the tunnels were filled with irregular new trabeculae after 2 months and unrecognizable from the surrounding mature bone after 6 months, indicating the completion of bone healing. CONCLUSIONS: With the characteristic of osteo-induction, the rhBMP-2/CPC can accelerate the healing of vertebral bone in nonhuman primates. Bone substitution is synchronous with material degradation, and the complete degradation of this material in late stage can avoid the potential adverse effects of PMMA on contiguous vertebral fracture and annulus degeneration. It might be a perfect bone substitute material for vertebroplasty instead of PMMA in the future.

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