Zirconia (ZrO2) and alumina (Al2O3) based ceramics are widely used for load-bearing applications in bone repair due to their excellent mechanical properties and biocompatibility. They are often regarded as bioinert since no direct bone-material interface is created unless a porous structure intercedes, leading to better bone bonding. In this regard, investigating interactions between cells and porous ceramics is of great interest. In the present study, we report on the successful fabrication of sintered alumina A-61, zirconia Z-50 and zirconia/alumina composite ZA-60 ceramics with medium porosities of 61, 50 and 60%, respectively, indicating a bimodal pore size distribution and good interconnectivity. They exhibit elastic moduli of 3-10 GPa and compressive strength values of 60-240 MPa, similar to those of human cortical bone.We performed in vitro cell-material investigations comparing the adhesion, proliferation and differentiation of mouse pre-osteoblasts MC3T3-E1 on the three porous materials. While all three ceramics demonstrate a strong cell attachment, better cell spreading is observed on zirconia-containing substrates. Significantly higher cell growth was quantified on the latter ceramics, revealing an increased alkaline phosphatase activity, higher collagen production and increased calcium biomineralization compared to A-61. Hence, these porous zirconia-containing ceramics elicit superior biological responses over porous alumina of similar porosity, promoting enhanced biological interaction, with potential use as non-degradable bone grafts or as implant coatings.

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.

It is acknowledged that cellular responses are highly affected by biomaterial porosity. The investigation of this effect is important for the development of implanted biomaterials that integrate with bone tissue. Zirconia and alumina ceramics exhibit outstanding mechanical properties and are among the most popular implant materials used in orthopedics, but few data exist regarding the effect of porosity on cellular responses to these materials. The present study investigates the effect of porosity on the attachment and proliferation of pre-osteoblastic cells on zirconia and alumina. For each composition, ceramics of three different porosities are fabricated by sintering, and characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray powder diffraction. Cell proliferation is quantified, and microscopy is employed to qualitatively support the proliferation results and evaluate cell morphology. Cell adhesion and metabolic activity are found comparable among low porosity zirconia and alumina. In contrast, higher porosity favors better cell spreading on zirconia and improves growth, but does not significantly affect cell response on alumina. Between the highest porosity materials, cell response on zirconia is found superior to alumina. Results show that an average pore size of ~150 μm and ~50% porosity can be considered beneficial to cellular growth on zirconia ceramics.

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We investigated the mechanochemical synthesis of complex slow release fertilizers (SRF) derived from glauconite. We studied the effectiveness of the mechanical intercalation of urea into glauconite using planetary and ring mills. The potassium-nitric complex SRFs were synthesized via a mechanochemical method mixing glauconite with urea in a 3:1 ratio. The obtained composites were analyzed using X-ray diffraction analysis, scanning electron microscopy, X-ray fluorescence analysis, and infrared spectroscopy. The results show that as duration of mechanochemical activation increases, the mineralogical, chemical, and structural characteristics of composites change. Essential modifications associated with a decrease in absorbed urea and the formation of microcrystallites were observed when the planetary milling time increased from 5 to 10 min and the ring milling from 15 to 30 min. Complete intercalation of urea into glauconite was achieved by 20 min grinding in a planetary mill or 60 min in a ring mill. Urea intercalation in glauconite occurs much faster when using a planetary mill compared to a ring mill.

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Porous zirconia (ZrO2), magnesia (MgO) and zirconia/magnesia (ZrO2/MgO) ceramics were synthesised by sintering and designated as ZrO2(100), ZrO2(75)MgO(25), ZrO2(50)MgO(50), ZrO2(25)MgO(75), MgO(100) based on their composition. The ceramic samples were characterised by means of scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and atomic absorption spectrometry to explore the incorporation of Mg atoms into the zirconia lattice. The resulting porosity of the samples was calculated based on the composition and density. The final porosity of the cylinder-shaped ceramic samples ranged between 30 and 37%. The mechanical analysis exhibited that the Young modulus increased and the microstress decreased with increasing magnesia amount, with values ranging from 175 GPa for zirconia to 301 GPa for magnesia. The adhesion, viability, proliferation and osteogenic activity of MC3T3-E1 pre-osteoblastic cells cultured on the zirconia/magnesia ceramics was found to increase, with the magnesia-containing ceramics exhibiting higher values of calcium mineralisation. The results from the mechanical analysis, the ALP activity, the calcium and collagen production demonstrate that the zirconia/magnesia ceramics possess robust osteoinductive capacity, therefore holding great potential for bone tissue engineering.

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