Experimental and numerical characterizations of nano-indentation responses of low viscosity and high viscosity bone cements

The present work involves experimentally determining the nano-mechanical properties (elastic modulus, hardness, plasticity index, and recovery resistance) of low viscosity (LV) and high viscosity (HV) Poly (methyl methacrylate) (PMMA) bone cement from load-displacement data obtained using Berkovich indenter, and then the effect of indentation parameters on these properties are explored through a validated three-dimensional (3D) finite element (FE) simulation. The 3D FE model includes a specimen with bilinear isotropic elastic-plastic material model. The good agreement between experimental and simulated load-displacement data for both variants of the bone cement emphasizes the applicability of the 3D FE model to predict mechanical behavior at nano scale indentation for both PMMA bone cements. The experimental and numerical analysis yield significantly higher values of elastic modulus, hardness, plasticity index, and recovery resistance for LV compared to that of HV bone cement. The experimentally determined values of elastic modulus, hardness, plasticity index, and recovery resistance for LV bone cement are 5.04±0.21 GPa, 312.33±2.84 MPa, 0.51±0.04, and 258.90±3.34 GPa, respectively, whereas the corresponding values for HV bone cement are found to be 4.45±0.29 GPa, 301.41±3.67 MPa, 0.42±0.01, and 191.63±1.66 GPa. The simulated load-displacement data concludes a remarkable results (elastic modulus, hardness, plasticity index, and recovery resistance), which suggest that the both variants of PMMA bone cement attain higher peak load along with larger hysteresis curve for increased indenter tip radius for a given indentation depth. The friction coefficient along the contact surfaces of specimen with indenter has no pronounced effect on the measurement of mechanical properties of bone cements.