Phase transformations, microstructure formation and in vitro osteoblast response in calcium silicate/brushite cement composites.

Self-setting simple calcium silicate/brushite (B) biocements with various Ca/P ratios were prepared by mutual mixing of both monocalcium silicate hydrate (CSH) or ß-wollastonite (woll) powders with B and the addition of 2 wt% NaH2PO4 solution as a hardening liquid. The phase composition of the final composites and the texture of the surface calcium phosphate/silica layer were controlled by the starting Ca/P ratio in composites and the pH during setting. It was verified that the presence of continuous bone-like calcium phosphate coating on the surface of the samples was not essential for in vitro osteoblast proliferation. The nanocrystalline calcium deficient hydroxyapatite and amorphous silica were found as the main setting products in composite mixtures with a Ca/P ratio close to the region of the formation of deficient hydroxyapatite-like calcium phosphates. No CSH phase with a lower Ca/Si ratio was identified after transformation. The results confirmed a small effect of the monocalcium silicate addition on the compressive strength (CS) of cements up to 30 wt% (around 20-25 MPa) and a significant rise of the value in 50 woll/B cement (65 MPa). The final setting times of the cement composites varied between 5 and 43 min depending on the P/L ratio and the type of monocalcium silicate phase in the cement mixture. 10CSH/B and 50 woll/B cements with different textures but free of both the needle-like and perpendicularly-oriented hydroxyapatite particles on the surface of the samples had low cytotoxicity.

Carbonate release from carbonated hydroxyapatite in the wide temperature rage.

Synthetic carbonated apatite ceramics are considered as promising alternative to auto- and allograft materials for bone substitute. The aim of this study was to investigate the thermal stability of an AB-type carbonated apatite in the wide temperature range. The data on the thermal stability have to allow the conditions of the sintering of the ceramics to be controlled. Initial carbonated apatite powders were prepared by interaction between calcium oxide and ammonium hydrogen phosphate with addition of ammonium carbonate. Decomposition process was monitored by infra red spectroscopy, weight loss and X-ray diffraction of solid, and by infra red analysis of condensed gas phase resulted from the thermal decomposition of the sample in equilibrium conditions. Features of carbon monoxide and carbon dioxide release were revealed. The synthesized AB-type carbonated apatite is started to decompose at about 400 degrees Celsius releasing mainly carbon dioxide, but retained some carbonate groups and apatite structure at the temperature 1100 degrees Celsius useful to prepare porous carbonate-apatite ceramics intended for bone tissue engineering scaffolds.