Micro and nano MgO particles for the improvement of fracture toughness of bone-cement interfaces

Abstract

The objective of this study was to determine whether inclusion of magnesium oxide (MgO) in micro and nanoparticulate forms in poly methyl methacrylate (PMMA) cement has any influence on the fracture toughness of bone-cement interfaces. An interfacial fracture mechanics technique was used to compare the values of fracture toughness (KIC) among bone-PMMA, bone-PMMA with micro MgO particles and bone-PMMA with nano MgO particles interfaces. This study found that the values of KIC of bone-PMMA with micro MgO particles and bone-PMMA with nano MgO particles interfaces were significantly higher when compared to the values of KIC of the bone-PMMA interface (p<0.0001). Results indicated that the addition of the micro and nano MgO particles to PMMA improved the quality of bone-cement union.

Figure 1

Fabricated mold used for the preparation of cement and bone-cement specimens. The base plate contains (22×12×25) mm curing chamber, which has front, back and top openings. Two ABS plastic blocks were used to cover the front and back sides of the chamber. A custom made clamp was used to restrict the side blocks movement. The top plate can slide freely to the curing chambers using 4 round rods. The top plate has (22×12×23) mm extruded block at the center that can close the top side of the curing chamber and apply pressure during curing. A set of weights were placed at the top plate to provide 60 KPa pressure (Ries et al., 1998). Variable thickness of cement blocks (22×12×2~10 mm) were successfully cured using the mold.

Figure 2

(a) Tension test on a flat dumbbell-shaped cement specimen to measure the Young’s modulus and Poisson’s ratio of the cement specimen. Evex tensile stage, microstrain Inc. displacement variable reluctant transducer, and Nikon stereo microscope was used to record load, longitudinal displacement and transverse displacement during the experiment, (b) the schematic diagram and dimension of the flat dumbbell-shape specimen. The depth of the specimen is 4 mm, (c) the schematic diagram and dimension of the single edge sandwiched bone-cement specimen. The depth of the holder and specimen is 12 mm, and (d) tension test setup for the measurement of the interface fracture toughness of bone-cement specimen.

Figure 3

Particle-size distribution of the two MgO powders: (a) (micro size) and (b) (nano size).

Figure 4

(a) Longitudinal stress vs. longitudinal strain plots of a CBC, mCBC and nCBC specimen. (b) Transverse strain vs. longitudinal strain plots of a CBC, mCBC and nCBC specimen calculated at 30 sec and 60 sec test time. (c) Dot plots of the Poisson’s ratios of three CBC, mCBC and nCBC samples. Plots show the two Poisson’s ratio measurements for each sample at 30 sec and 60 sec test times.

Figure 5

Load versus displacement graphs of (a) bone-CBC, (b) bone-mCBC and (c) bone-nCBC specimens. The maximum loads for the fracture of the bone-cement specimen were recorded for the calculation of the fracture toughness of bone-cement specimen.