Abstract: Acrylic bone cement is widely used to anchor orthopedic implants to bone and mechanical failure of the cement mantle surrounding an implant can contribute to aseptic loosening. In an effort to enhance the mechanical properties of bone cement, a variety of nanoparticles and fibers can be incorporated into the cement matrix. Mesoporous silica nanoparticles (MSNs) are a class of particles that display high potential for use as reinforcement within bone cement. Therefore, the purpose of this study was to quantify the impact of modifying an acrylic cement with various low-loadings of mesoporous silica. Three types of MSNs (one plain variety and two modified with functional groups) at two loading ratios (0.1 and 0.2 wt/wt) were incorporated into a commercially available bone cement. The mechanical properties were characterized using four-point bending, microindentation and nanoindentation (static, stress relaxation, and creep) while material properties were assessed through dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, FTIR spectroscopy, and scanning electron microscopy. Four-point flexural testing and nanoindentation revealed minimal impact on the properties of the cements, except for several changes in the nano-level static mechanical properties. Conversely, microindentation testing demonstrated that the addition of MSNs significantly increased the microhardness. The stress relaxation and creep properties of the cements measured with nanoindentation displayed no effect resulting from the addition of MSNs. The measured material properties were consistent among all cements. Analysis of scanning electron micrographs images revealed that surface functionalization enhanced particle dispersion within the cement matrix and resulted in fewer particle agglomerates. These results suggest that the loading ratios of mesoporous silica used in this study were not an effective reinforcement material. Future work should be conducted to determine the impact of higher MSN loading ratios and alternative functional groups. (C) 2014 Elsevier Ltd. All rights reserved.

Abstract: Structural properties have been shown to be critical in the osteoconductive capacity and strength of bioactive ceramic bone scaffolds. Given the cellular foam-like structure of bone scaffolds, nanoindentation has been used as a technique to assess the mechanical properties of individual components of the scaffolds. Nevertheless, nanoindents placed on scaffolds may violate the rigid support assumption of the standard Oliver-Pharr method currently used in evaluating the Meyer hardness, H, and elastic modulus, E-s, of such structures. Thus, the objective of this research was to use the structural compliance method to assess whether or not specimen-scale flexing may occur during nanoindentation of bioceramic bone scaffolds and to remove the associated artifact on the H and E-s if it did occur. Scaffolds were fabricated using tricalcium phosphate and sintered at 950 degrees C and 1150 degrees C, and nanoindents were placed in three different (center, edge, and corner) scaffold locations. Using only the standard Oliver-Pharr analysis it was found that H and E-s were significantly affected by both sintering temperature and nanoindents location (p < 0.05). However, specimen-scale flexing occurred during nanoindentation in the 1150 degrees C corner location. After removing the effects of the flexing from the measurement using the structural compliance method, it was concluded that H and E-s were affected only by the sintering temperature (p < 0.05) irrespective of the nanoindent locations. These results show that specimen-scale flexing may occur during nanoindentation of components in porous bioceramic scaffolds or in similar structure biomaterials, and that the structural compliance method must be utilized to accurately assess H and E-s of these components. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.