Chem. Listy 105, s668s671 (2011) LMV 2010 Regular Papers s668 NANOINDENTATION OF TRABECULAR BONE – COMPARISON WITH UNIAXIAL TESTING OF SINGLE TRABECULA ONDěEJ JIROUŠEK a *, JIěÍ NċMEČEK b , DANIEL KYTÝě a , JIěÍ KUNECKÝ a , PETR ZLÁMAL a , and TOMÁŠ DOKTOR a a Institute of Theoretical and Applied Mechanics, Academy of Sciences of the Czech Republic, v.v.i., Prosecká 76, 190 00 Prague 9, b Czech Technical University in Prague, Faculty of Civil Engineering, Thákurova 7/2077, 166 29 Prague 6, Czech Republic jirousek@itam.cas.cz Keywords: trabecular bone, nanoindentation, micromechan- ics, constitutive modelling 1. Introduction Knowledge of deformation behaviour of trabecular bone in response to mechanical loading is important for better un- derstanding of the relationship between the microstructure and overall mechanical properties. Due to the increased com- putational power and powerful imaging techniques it is possi- ble to perform numerical simulations with microstructural finite element (FE) models reflecting the true microstructure of the complex material 1 . Information about the microstruc- ture can be obtained using the microfocus computed tomogra- phy (micro-CT). The deformation behaviour can be captured applying the micro-CT technique to a sample under gradual loading 2 . For the microstructural FE models it is necessary to measure the material properties at the level of single trabecu- la. One of the established methods for evaluation of the material properties at this level is nanoindentation 3 . It has been con- firmed by several authors that valid microstructural models of trabecular bone can be built using high-resolution micro-CT models and material properties from nanoindentation under wet conditions 4 . The agreement between experiments and micro-FE models has already been published, however, re- sults of experimental investigation using standard mechanical testing of single trabeculae remains scattered. One of the rea- sons for the high discrepancy in experimental results can be attributed to improper boundary conditions; second reason is difficult precise measurement of the strains. In this study a comparison between the mechanical properties assessed by nanoindentation and properties obtained from tension tests of extracted trabeculae is performed. 2. Materials and Methods Single trabecula tensile tests Small blocks of trabecular bone were extracted from proximal human femur (male, 72 years). The blocks were cleaned of marrow and grease in a nonionic detergent in an ultrasonic cleaner at a temperature not exceeding 37 °C. The cleaning was repetitive not to exceed the temperature limit. The sample was then dried at room temperature. Long straight trabeculae were identified in these blocks under a magnifying glass (4× magnification). The trabeculae were carefully ex- tracted using a sharp-tip scalpel. The ends of the trabeculae were dipped in a two-component glue (UHUplus schnellfest 2-K-Epoxidharzkleber, UHU GmbH & Co. KG, Baden, Ger- many) and stored for 48h at room temperature. The drops of glue at the trabecula ends were used for manipulation with the sample using a pair of tweezers. The manipulation droplets of glue were used to attach the sample to the end-plates of a laboratory uniaxial tension- compression device specially designed for these experiments. Fast-setting glue (Loctite Super Attak Ultra Plastik, Henkel Ireland Ltd., Ireland) was used for this purpose and the glue was allowed to set for 2 hours prior the experiment at room temperature. Tension-compression of the sample was provided by means of a precision linear stage M-UMR3.5 with differential micrometer DM11-5 (Newport Corp., USA, sensitivity 0.1 m, travel range 5 mm) while manipulation (centering) of the fixed end was provided by Y-Z translational stage (Standa Ltd., Lithuania, sensitivity 1 m, travel range 25 mm). The load was measured using a small-scale load cell FBB350 (FUTEK Advanced Sensor Technology, Inc., USA, load ca- pacity 4.5 N) attached to the Y-Z translational stage. The samples were tested in displacement-controlled uniaxial tension tests. The load was applied by moving the precision linear stage away from the fixed end of the sample. The whole experiment was captured using a high-resolution CCD camera (VDS Vosskuhler GmbH, Germany) attached to optical microscope (Navitar Imaging Inc., USA). The camera is attached to a PC by firewire cable enabling to capture 15 images per second with 24× magnification. 5mm Fig. 1. A block of trabecular bone after cleaning. Extracted tra- becula with droplets of glue covering the ends 250mm