Synthetic mineral containing Sr, Ca, and Fe and its hybridization with soybean extract for synergetic bone regeneration

We synthesized layered metal hydroxide containing bone-regenerating elements such as Sr, Ca and Fe, inspired by the structure of natural mineral, hydrocalumite (HC). The obtained artificial mineral was found to have layered structure of HC with Sr, Ca and Fe in the framework (SCFL) structure according to X-ray diffraction patterns and X-ray photoelectron spectroscopy. Through field emission-scanning electron microscopic images, we verified that obtained SCFL has plate-like morphology with particle size range from 100 nm to 200 nm. Transmission electron microscopic and energy dispersive spectrometry mapping images showed homogeneous distribution of Sr²⁺ in SCFL lattice without forming significant Sr-impurities. Introduction of Sr into lattice was also demonstrated with the X-ray photoelectron spectroscopy. To utilize SCFL as synergetic osteoblast promoter, the soybean extract (Glycine max Merrill: GM) which has osteogenic isoflavonoids, was hybridized with SCFL (G-SCFL). After incorporation of GM into SCFL, the crystal structure, particle morphology and size were preserved. The quantification exhibited that GM was well incorporated in SCFL with encapsulation efficiency of 26.1%. Interestingly, the hybridization reaction showed different isoflavonoids encapsulation efficiency: 47.2% for genistein, 92.5% for daidzein, respectively. The osteogenic ability of G-SCFL hybrid was evaluated by measuring alkaline phosphatase (ALP) activity and visualizing collagen fiber formation on the osteoblast MG-63 cells. The G-SCFL exhibited enhanced maximum 3 times higher ALP activity than the simple mixture of equivalent amount of bone-regenerating moiety. In parallel, the formation of collagen between cells was more activated in the G-SCFL treated cells than mixture treated ones. It was also noteworthy that the G-SCFL did not show cytotoxicity towards MG-63 at the concentration where mixture showed 37.3% of lowered cell viability.