Al2O3-Phosphate Bioceramic Fabrication via Spark Plasma Sintering-Reactive Synthesis: In Vivo and Microbiological Investigation

Abstract

This research introduces a method to enhance the biocompatibility of bioinert Al2O3-based ceramics by incorporating calcium phosphates (hydroxyapatite (HAp) and tricalcium phosphate (TCP)) into alumina via spark plasma sintering-reactive sintering (SPS-RS). TGA/DTG/DTA and XRD revealed phase formation of HAp and TCP and determined the main temperature points of solid-phase reactions occurring in situ during the sintering of the CaO-CaHPO4 mixture within the volume of Al2O3 under SPS-RS conditions in the range of 900–1200 °C. SEM, EDX, low temperature, and nitrogen physisorption were used to monitor changes in the morphology, structure, and elemental composition of bioceramics. Structural meso- and macroporosity, with a mean mesopore size of 10 nm, were revealed in the ceramic volume, while sintering temperature was shown to play a destructive role towards the porous inorganic framework. The physico-chemical characterization demonstrated increased relative density (up to 95.1%), compressive strength (640 MPa and above), and Vickers microhardness (up to 700 HV) depending on the HAp and TCP content and sintering temperature. Four bioceramic samples with different contents of HAP (20 and 50 wt.%) were bio-tested in in vivo models. The samples were implanted into the soft tissues under the superficial fascia of the thorax of a laboratory animal (a New Zealand White rabbit, female) in the area of the trapezius muscle and the broadest muscle of the back. Based on the results of the assessment of the surrounding tissue reaction, the absence of specific inflammation, necrosis, and tumor formation in the tissues during the implantation period of 90 days was proven. Microbial tests and dynamics of Pseudomonas aeruginosa bacterial film formation on bioceramic surfaces were studied with respect to HAp content (20 and 50 wt.%) and holding time (18, 24, and 48 h) in the feed medium.