Development of ceramic structures with complex shapes based on hydroxyapatite using the technique of casting in plaster molds with possible medical applications

The main objectives of this work are represented by both the development of hydroxyapatite (HAP) and the technique of casting it into plaster forms order to develop of ceramic structures with complex shapes for applications in neurosurgery. The tested models were made from ceramic powders based on HAP and, shaped by the casting technique in plaster molds. In order for the process of casting ceramic suspensions to be more efficient, specific techniques were performed such as: rheological curves of shear stress variation depending on the speed gradient and the dependence of the viscosity of the HAP suspensions on the speed gradient. Experimental models of cranial prostheses were developed in the form of a skull cap with an average thickness of similar to 3.5 mm, rods with a diameter of 5 mm, length of 50 mm. The samples were sintered at temperatures of 1275 degrees C and 1350 degrees C, for 2 hours. The variation of density and porosity with sintering temperature were determined by Archimedes' method and the mechanical properties were investigated by bending and compression tests. The average values for the bending strength, for the two obtained models, are in the range of 32.64-36.68 MPa and for the compression strength they range from 44.54 to 50.10 MPa. Furthermore, the obtained samples were characterized by scanning electron microscopy (SEM) and the X-ray diffraction data for the HAP powder were confirmed by FT-IR spectra and thermogravimetric measurements. In order to establish the biocompatibile character, a first set of bacteriological and sterility determinations was performed. The novelty of this work consists in the fact that both the rheological characteristics have been optimized (ceramic suspensions with a solid phase content of min. 60%) as well as the technique of casting ceramic suspensions in plaster molds through ultrasonic and with a raw density of min. 50% of rho th.