Proliferation and osteogenic response of MC3T3-E1 pre-osteoblastic cells on porous zirconia ceramics stabilized with magnesia or yttria

Dense zirconia ceramics are used in bone applications due to their mechanical strength and biocompatibility, but lack osseointegration. A porous interface in contact with bone tissue may lead to better bone bonding but the biological properties of porous zirconia are not widely explored. The present study focuses on the manufacturing of an yttria- (YSZ) and a magnesia-stabilized (MgSZ) porous zirconia, and on their in vitro biological investigation. The sintered ceramics had similar characteristics of porosity, pore size and interconnectivity. Their elastic moduli and compressive strength values were within the range of the values of human cortical bone. MC3T3-E1 pre-osteoblasts were used to investigate the proliferation, alkaline phosphatase (ALP) activity, collagen deposition and expression profile of four genes involved in bone metabolism of cells on porous ceramics. Scanning electron and fluorescence microscopy were employed to visualize cell morphology and growth. Pre-osteoblasts adhered well on both ceramics but cell numbers on YSZ were higher. Cells exhibited an increase in ALP activity and collagen deposition after 14 days on both MgSZ and YSZ, with higher levels on YSZ. Real-time quantitative polymerase chain reaction (qPCR) showed that the expression of bone sialoprotein (Bsp) and collagen type I (col1aI) were significantly higher on YSZ. No significant differences were found in their ability to regulate the early gene expression of Runx2 and Alp. Nevertheless, the biomineralized calcium content was similar on both ceramics after 21 days, indicating that despite chemical differences, both scaffolds direct the pre-osteoblasts toward a mature state capable of mineralizing the extracellular matrix.