In vitro bioactivity of silicon‐substituted hydroxyapatites

Abstract

Silicon-containing hydroxyapatites were synthesized by the controlled crystallization method. Chemical analysis, N(2) adsorption, Hg porosimetry, X-ray diffraction, scanning electron microscopy-energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used to characterize the hydroxyapatite and to monitor the development of a calcium phosphate layer onto the surface of the substrate immersed in a simulated body fluid, that is, in vitro bioactivity tests. The influence of the silicon content and the nature of the starting calcium and phosphorus sources on the in vitro bioactivity of the resulting materials were studied. A sample of silicocarnotite, whose structure is related to that of hydroxyapatite and contains isolated SiO(4) (4-) anions that isomorphically substitute some PO(4) (3-) anions, was prepared and used as reference material for XPS studies. An increase of the unit cell parameters with the Si content was observed, which indicated that SiO(4) (4-) units are present in lattice positions, replacing some PO(4) (3-) groups. By using XPS it was possible to assess the presence of monomeric SiO(4) (4-) units in the surface of apatite samples containing 0.8 wt % of silicon, regardless the nature of the starting raw materials, either Ca(NO(3))(2)/(NH(4))(2)HPO(4)/Si(OCOCH(3))(4) or Ca(OH)(2)/H(3)PO(4)/Si(OCOCH(3))(4). However, an increase of the silicon content up to 1.6 wt % leads to the polymerization of the silicate species at the surface. This technique shows silicon enrichment at the surface of the three samples. The in vitro bioactivity assays showed that the formation of an apatite-like layer onto the surface of silicon-containing substrates is strongly enhanced as compared with pure silicon-free hydroxyapatite. The samples containing monomeric silicate species showed higher in vitro bioactivity than that of silicon-rich sample containing polymeric silicate species. The use of calcium and phosphate salts as precursors lead to materials with higher bioactivity.

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“…The ability of biomaterials to form apatite in PBS depends on the heating challenge that fully induces the grain transformation. These results www.scienceasia.org contradict those reported previously, indicating that the formation of bone apatite on fully sintered HA and TCP ceramics has been hardly detectable 31,32 . Indeed, the nature and crystallinity of apatite forming phases depend on various parameters, including concentrations of phosphate/carbonate sources, ionic strength and pH of the soaked solution, and the kinetics of the nucleation and growth processes 33 .…”

Organic/Inorganic bioactive materials Part III: in vitro bioactivity of gelatin/silicocarnotite hybrids

“…It is known that silicocarnotite is a calcium silicophosphate with carnotite structure. Some authors determined that the silicocarnotite structure is very similar to hydroxyapatite and examined its in vitro bioactivity [34]. They concluded that the introduction of silicon in HA lattice improved in vitro bioactive response as compared to the apatite without silicon content [34].…”

“…Some authors determined that the silicocarnotite structure is very similar to hydroxyapatite and examined its in vitro bioactivity [34]. They concluded that the introduction of silicon in HA lattice improved in vitro bioactive response as compared to the apatite without silicon content [34]. Others suggested that the loss of all -OH from HA due to SiO 4 substitution results in silicocarnotite structure.…”

Sol-gel bioactive glass-ceramics Part I: Calcium phosphate silicate/wollastonite glass-ceramics

“…The amount of silicon incorporated has an important influence on its thermal stability and phase composition [2,[19][20][21][22][23][24] Magnetron co-sputtering method is used in [25,26] to prepare of SiHA materials with 0.8, 2.2 and 4.9 wt.% silicon content. The in vitro cellular response indicated an increase in the growth of human osteoblast (HOB) cell on the synthesized coatings, along with formation of extracellular matrix.…”