Stamatia Rokidi

Influence of artificially-induced porosity on the compressive strength of calcium phosphate bone cements.

The biological and mechanical nature of calcium phosphate cements (CPCs) matches well with that of bone tissues, thus they can be considered as an appropriate environment for bone repair as bone defect fillers. The current study focuses on the experimental characterization of the mechanical properties of CPCs that are favorably used in clinical applications. Aiming on evaluation of their mechanical performance, tests in compression loading were conducted in order to determine the mechanical properties of the material under study. In this context, experimental results occurring from the above mechanical tests on porous specimens that were fabricated from three different porous additives, namely albumin, gelatin and sodium alginate, are provided, while assessment of their mechanical properties in respect to the used porous media is performed. Additionally, samples reinforced with hydroxyapatite crystals were also tested in compression and the results are compared with those of the above tested porous CPCs. The knowledge obtained allows the improvement of their biomechanical properties by controlling their structure in a micro level, and finds a way to compromise between mechanical and biological response.

Calcification of Biomaterials

Biological fluids are supersaturated with respect to various sparingly soluble salts including phosphates, oxalates, and in some cases carbonates. The presence of surfaces provided by tissues (valves, aortas, or other membranes) provides substrates favoring heterogeneous nucleation of insoluble salts that adhere tenaciously. The investigation of the kinetics of crystal growth at sustained conditions is of paramount importance for understanding the role of the various substrates and of the mechanism underlying the formation of the various salts. Artificial tissues for heart or implant cements for bone restoration are substrates that favor the formation of metastable calcium phosphates like octacalcium phosphate. Crystal lattice compatibility results in higher rates of crystallization. Calcium oxalate may also form in supersaturated solutions, resulting in encrustations buildup in metallic stents by heterogeneous nucleation and growth.