Multiphase Mixed Material Derived From Calcite and Diammonium Hydrogen Phosphate Coated With Tetraethyl Orthosilicate: A Potential Implant Coating Material

A multiphase mixed material (M-PMM) made from calcite and diammonium hydrogen phosphate was prepared using the wet chemical method. To improve its bioactivity, the M-PMM was coated with tetraethyl orthosilicate (TEOS) at varying mass percentages of 5% and 10% producing 5%_TEOS-M-PMM and 10%_TEOS-M-PMM, respectively. In vitro mineralization studies were conducted by immersing the uncoated M-PMM, 5%_TEOS-M-PMM, and 10%_TEOS-M-PMM in simulated body fluid (SBF) for days 7, 14, and 21. Characterization of the uncoated and coated M-PMM was performed using X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersion X-ray spectroscopy (EDS), X-ray fluorescence (XRF), and scanning electron microscopy (SEM). The uncoated M-PMM was confirmed to consist of multiple phases, including calcite, mixed type-AB carbonate hydroxyapatite, and hydroxyapatite monoclinic2 by XRD and FTIR. EDS also confirmed the presence of silicon at the surface of the coated M-PMM, whereas XRD showed a decrease in crystallinity and crystallite size. The crystallinity and crystallite size were 81% and 20.88 ± 5.12 nm for uncoated M-PMM, respectively. The coated M-PMM had values of 79% and 17.27 ± 9.06 nm and 78% and 19.83 ± 9.91 nm for 5%_TEOS-M-PMM and 10%_TEOS-M-PMM, respectively. The larger surface area of the coated M-PMM in the SBF gave a better resorption of calcium and phosphate minerals, which was confirmed by XRF. Apatite-like bundles in the uncoated M-PMM and coated M-PMM after immersion in SBF from day 7 to day 21 were revealed by SEM. However, additional cuboid structures were seen in the coated M-PMM, which enhanced its cell viability and will aid in better osteointegration with biological tissues.