Nacre Compared to Aragonite as a Bone Substitute: Evaluation of Bioactivity and Biocompatibility

Abstract

Aragonite is a metastable polymorph of calcium carbonate found in mollusk's shells, appearing in tiles and prismatic columns, cemented in a protein matrix -mainly proteins -that acts as a framework on which the aragonite is nucleated forming nacre, besides selecting the morphology of the nucleated cristaline phase. The presence of the mineralyzing organic matrix may affect osteoinductive properties of biogenic aragonite, hypothesis tested by combinated tests, comparing viability and bioactivity of biomineralizated aragonite and nacre. Bioactivity was observed by deposition of Ca-P (presumably calcium phosphate) on the surface of samples immersed in Simulated Body Fluid; biocompatibility was verified by adhesion with VERO cells; cytotoxicity and alkaline phosphatase activity assays were performed with human adipose stem cells (hASC). Samples were characterized by scanning electron microscopy and X-ray diffraction. Both materials showed similar behaviour on bioactivity assay; in contrast, exhibited different behaviours in the presence of hASC.

Effects of the Sintering Process on Nacre-Derived Hydroxyapatite Scaffolds for Bone Engineering

“…Alkaline phosphatase is an early marker of osteoblast differentiation [ 17 ]. In the control group, this marker was continuously elevated in a time-dependent manner.…”

“…Inorganic aragonite tablets are predominantly calcium carbonate, homologous to calcium phosphate (hydroxyapatite) in human bone [ 16 ]. There are several methods for transforming the nacreous layer into hydroxyapatite which include sintering, wet chemical precipitation, hydrothermal, sol-gel, and ball-milling [ 8 , 11 , 17 , 18 ]. Wet chemical precipitation, hydrothermal, and sol-gel methods have mostly been used for the application of hydroxyapatite as a coating material on the surface of a metallic implant or scaffold [ 17 , 19 ].…”

“…There are several methods for transforming the nacreous layer into hydroxyapatite which include sintering, wet chemical precipitation, hydrothermal, sol-gel, and ball-milling [ 8 , 11 , 17 , 18 ]. Wet chemical precipitation, hydrothermal, and sol-gel methods have mostly been used for the application of hydroxyapatite as a coating material on the surface of a metallic implant or scaffold [ 17 , 19 ]. This type of combination overcomes the weakness of hydroxyapatite, as well as metal scaffolds, by enhancing the mechanical properties and corrosion resistance and, at the same time, promotes bone-bonding ability [ 19 ].…”

“…These microstructural properties can be controlled by modifying the sintering temperature. Better bioactivity for hydroxyapatite scaffold can be achieved using a lower sintering temperature, whereas better mechanical properties can be achieved using a higher sintering temperature [ 17 ]. In this study, a higher sintering temperature was used during the fabrication of the sinter hydroxyapatite scaffold.…”

“…The reusing of shell waste as biomaterial for bone tissue regeneration could potentially be used as an alternative to bone graft and would indirectly contribute to a green environment. Previous studies have assessed the effect of nacre hydroxyapatite scaffold and have basically emphasized the biological, chemical, physical, and regeneration properties of the scaffold, or the combined effect of these properties [ 17 , 20 , 21 , 22 ]. The effect of the sintering process on nacre hydroxyapatite scaffold for in vitro physical and osteogenic potentials has not been well documented.…”