Transparent magnesium aluminate spinel: a prospective biomaterial for esthetic orthodontic brackets

Microarray illustrates enhanced mechanistic action towards osteogenesis for magnesium aluminate spinel ceramic-based polyphasic composite scaffold with mesenchymal stem cells and bone morphogenetic protein 2

Spinel (magnesium aluminate MgAl2 O4 ) ceramic-based polyphasic composite scaffold has been recently reported for craniofacial bone tissue engineering. Improving the osteogenic effects of such composite scaffolds with bone morphogenetic proteins (BMP2) is an intensely researched area. This study investigated the gene interactions of this scaffold with BMP2 and mesenchymal stem cells (MSCs). Human bone marrow MSCs were cultured in 3 groups: Group 1-Control (BMSCs), Group 2-BMSC with BMP2, and Group 3-BMSC with scaffold and BMP2. After RNA isolation, gene expression analysis was done by microarray. Differentially expressed genes (DEGs) (-1.0 > fold changes>1 and p value <.05) were studied for their function and gene ontologies using Database for Annotation, Visualization and Integrated Discovery (DAVID). They were further studied by protein-protein interaction network analysis using STRING and MCODE Cytoscape plugin database. Group 3 showed up regulation of 3222 genes against 2158 of Group 2. Group 3 had five annotation clusters with enrichment scores from 2.08 to 3.93. Group 2 had only one cluster. Group 3 showed activation of all major osteogenic pathways: TGF, BMP2, WNT, SMAD, and Notch gene signaling with effects of calcium and magnesium released from the scaffold. Downstream effect of all these caused significant activation of RUNX2, the key transcriptional regulator of osteogenesis in Group 3. STRING and MCODE Cytoscape plugin demonstrated the interactions. The enhanced MSC differentiation for osteogenesis with the addition of BMP2 to the polyphasic composite scaffold proposed promising clinical applications for bone tissue engineering.

Injection Molding of Magnesium Aluminate Spinel Nanocomposites for High-Throughput Manufacturing of Transparent Ceramics

Transparent ceramics like magnesium aluminate spinel (MAS) are considered the next step in material evolution showing unmatched mechanical, chemical and physical resistance combined with high optical transparency. Unfortunately, transparent ceramics are notoriously difficult to shape, especially on the microscale. Therefore, a thermoplastic MAS nanocomposite is developed that can be shaped by polymer injection molding at high speed and precision. The nanocomposite is converted to dense MAS by debinding, pre-sintering, and hot isostatic pressing yielding transparent ceramics with high optical transmission up to 84 % and high mechanical strength. A transparent macroscopic MAS components with wall thicknesses up to 4 mm as well as microstructured components with single micrometer resolution are shown. This work makes transparent MAS ceramics accessible to modern high-throughput polymer processing techniques for fast and cost-efficient manufacturing of macroscopic and microstructured components enabling a plethora of potential applications from optics and photonics, medicine to scratch and break-resistant transparent windows for consumer electronics.

3D Printing of MgAl2O4 Spinel Mesh and Densification Through Pressure-Less Sintering and Hot Isostatic Pressing

MgAl2O4 spinel mesh with micro-features of 410 and 250 μm unit cell length and rib thickness, respectively, was three-dimensional (3D) printed and sintered followed by Hot Isostatic Pressing (HIPing). A stable colloidal dispersion of spinel in polymer-water solution was prepared and 3D-printed using a 30-gauge needle (∼100 μm inner diameter) on a regenHU 3D-Discovery bioprinter. Samples were characterized for their density and microstructure. Samples with near theoretical density after HIPing was subjected to mechanical property evaluation such as hardness by Vickers indentation and elastic modulus using nanoindentation technique. Microstructure of sintered samples across the ribs have shown graded grain structure with finer grains near the edges (0.7 μm average) with occasional porosity and coarser grains toward the center of the rib (5.2 μm average). HIPing resulted in substantial grain growth and the average grain size was found to be 10.9 μm (with a variation in the grain size of 2.2 μm along the edges and 13.1 μm at the center of the rib) exhibiting close packed and dense microstructure. Finer grains toward the edges may probably be due to the flow behavior during printing process and lower distribution of the powder loading along the edges resulting in low green density. This relatively higher porosity pining the grain growth under the extremely low heating rate employed for the controlled shrinkage to maintain the integrity of the sample. 3D printed samples after HIPing exhibited a density of 3.57 g/cc and hardness of 12.95 GPa, which are at par with the samples processed through conventional ceramic processing techniques. Nanoindentation studies employing maximum load of 45 mN with depth have shown an elastic modulus of 238 ± 15 GPa. MgAl2O4 spinel mesh 3D printed in this study is a potential prospective candidate that can be explored for cranioplasty procedures and other biomedical applications.