چكيده به لاتين
Poly (methyl methacrylate) (PMMA-based) bone cements are extensively used in the medicine, especially in orthopedics, in order to secure implants/prostheses and to stabilize vertebral fractures. Since the most reason of bone cements’ failure originates from mechanical deficiencies, numerous studies have been carried out to improve the mechanical properties of the bone cement. One of the recommended ways to address this problem is incorporation of biocompatible and reinforcing additives to the cement’s matrix. In other words, taking relatively mechanical and biological weaknesses of the cement into consideration, a reduction in interaction/adhesion of either cement-implant or cement-bone in common interfaces would appear over time so that this causes a destabilization and fracture of the configuration, and consequently the prosthesis system would fail. Incorporating biocompatible and reinforcing fillers into the cement matrix lead onto not only strength enhancement but also the bone growth motivation and as a result, more bone formation in the surrounding area, resulting in more stability and faster treatment. Despite the importance and wide usage of the bone cement, limited constitutive material models have been investigated to present the cement and its composites behaviors. In this respect, here, the aim of the thesis is twofold. Firstly, it presents an optimized viscoplastic model, being able to cover perfectly the behavior of the cement. Secondly, it assesses the effects of biocompatible (e.g. hydroxyapatite (HA)) and reinforcing (e.g. Alumina (Al2O3) as well as single-walled carbon nanotube (SWCNT)) additives on both mechanical properties and constitutive material model. Considering these goals and two-layer viscoplasticity model alongside its constitution, the optimal values of the model parameters (i.e. A, n & f) were obtained for each case study using a combination of experimental and finite element analyses by making an analogy between the numerical and experimental outcomes. The results indicated that the used viscoplastic constitutive material model could suitably present both elastoplastic and viscoelastic terms of the cement. Any increase in model parameters i.e. A, n, and f -when the other two parameters were kept fixed- resulted in greater depth in the load-displacement curve. Although A and f values readjusted to PMMA nano-composites with different nano-additives, parameter n had almost no obvious change in all case studies and it was approximately equal to 2. The experimental results also revealed that the mechanical properties of the cement were improved by adding Al2O3 (3 wt. %) and SWCNT nano-additives, meanwhile the incorporation of nano-HA decreased (for the sample of 15 wt. %) or made no significant change (for the rest of PMMA/HA nano-composites) in the mechanical properties of the cement.
