Development Of A Novel Expandable Bone Cement And Related Physicochemical, Biocompatible Study

The incidence of osteoporosis characterized by bone mass reduction and micro-architectural of trabecular bone deterioration is raising, accompanied with the aging tendency of the population. Osteoporotic vertebral compression fractures(OVCFs) is a common complication of osteoporosis. It can not only raise intensive back pain in the osteoporotic patients, resulting in poor life quality, but also reduce the height of the vertebrate body and form the kyphosis deformity of the spine column. The spine column deformity can serious affect the cardiorespiratory function, lead to the increase of morbidity and mortality.Vertebroplasty is a typical and wide-used procedure in the treatment of OVCFs, which can restore the height of vertebral body effectively and relief the back pain significantly, hence improves the life quality enormously of the patients who has disturbed by OVCFs. Recently, poly methyl methacrylate(PMMA) has been commonly used in the vertebroplasty. However, studies have found that in the reaction of MMA monomers polymerized to PMMA, the volume of PMMA shrank around 3.82%~7.08%. The shrinkage effect could generate residual stress and provoke the minor crack in thebone-cement interface. The minor crack exists might affect the long-term stability and mechanical property of the vertebral bodies which underwent vertebroplasty. Meanwhile, defects like the relative high elastic modulus, intensive exothermic reaction during polymerization and nonabsordable have been acclaimed as the main reasons of the re-fracture in the adjacent levels, damage of neural tissue, and even bone necrosis. To develop a novel self-expandable and low modulus bone cement has been the research focus in the area of biomaterial innovation.In this study, PMMA bone cement(PBC) was modified by PAA using the solid-solid blending method to obtain an expandable, low elastic modulus and non-intensive exothermic reaction novel bone cement. The physicochemical, biomechanical and biocompatible properties has been assessed.Objective: To develop a new kind of expandable bone cement which could self-expand through water absorption, and to analysis its physicochemical, biomechanical and biocompatible properties to evaluate its prospect in clinical application.Methods: A new kind of PMMA based expandable bone cement(EBC) was developed by PAA modification through the solid-solid blending method. Expandable rate was tested to evaluate the expandable ability of EBC; Polymerization temperature, dough time, as well as setting time were tested according to the international standard--- Acrylic resin cement(ISO5833-2002). Scanning electron microscope(SEM) and micro computed tomography(micro-CT) were undertook to view the PAA-PMMA interface and the three dimensional structure of EBC. Intrusion test was carried out to evaluate the syringeability of EBC. Biomechanical properties including compressive strength and elastic modulus were tested by compressive experiment. Osteoblast was cultured with the medium containing the EBC or PBC extraction, and the biocompatibility was evaluated by cytotoxic test using CCK-8 method.Results:(1) The volume of EBC expanded about 8.80% after soaked in stimulate body fluid(SBF) for 24 hours. The polymerization temperature of EBC was 51.7℃which was significant lower than PBC(P<0.05). The dough time of EBC was 5.06 ± 0.46 min, it was significant longer than PBC, of which was 4.50 ± 0.27min(P<0.05). But there was nosignificant difference in setting time between EBC and PBC(P>0.05).(2) SEM and micro-CT results revealed that PAA could homogeneous distributed with PMMA. This characteristic made EBC expanded uniformly when uptook water.(3) The extent of intrusion of EBC and PBC were 4.27±0.12 mm and 5.04±1.44 mm respectively, and no significant difference(P>0.05) was detected.(4) Modified by PAA, the compressive strength and elastic modulus were 36.15 ± 11.19 MPa and 849.26 ± 324.47 MPa respectively, both of them were lower than PBC(P<0.05). Although lower than PBC, the compressive strength of EBC was still higher than the normal vertebral cancellous bone.(5) The result of CCK-8 cytotoxicity test indicated that there was no significant difference between two groups.Conclusion: The new kind of EBC could avoid the volumetric shrinkage through water absorption effectively. EBC was characteristic with lower polymerization temperature, longer dough time, and good syringeability after PAA modification. Meanwhile, the elastic modulus was more similar with vertebral cancellous bone which could reduce the risk of adjacent vertebral body re-fracture after vertebroplasty. In addition, similar to PBC, EBC have good biocompatibility.