A Comparative Study of the Sintering Behavior of Pure and Manganese-Substituted Hydroxyapatite

Abstract

Hydroxyapatite (HA) is a widely studied biomaterial for its similar chemical composition to bone and its osteoconductive properties. The crystal structure of HA is flexible, allowing for a wide range of substitutions which can alter bioactivity, biodegradation, and mechanical properties of the substituted apatite. The thermal stability of a substituted apatite is an indication of its biodegradation in vivo. In this study, we investigated the thermal stability and mechanical properties of manganese-substituted hydroxyapatite (MnHA) as it is reported that manganese can enhance cell attachment compared to pure HA. Pure HA and MnHA pellets were sintered over the following temperature ranges: 900 to 1300 °C and 700 to 1300 °C respectively. The sintered pellets were characterized via density measurements, mechanical testing, X-ray diffraction, and field emission electron microscopy. It was found that MnHA was less stable than HA decomposing around 800 °C compared to 1200 °C for HA. The flexural strength of MnHA was weaker than HA due to the decomposition of MnHA at a significantly lower temperature of 800 °C compared to 1100 °C for HA. The low thermal stability of MnHA suggests that a faster in vivo dissolution rate compared to pure HA is expected.

Intrafibrillar Mineralized Collagen–Hydroxyapatite-Based Scaffolds for Bone Regeneration

“…As shown in Figure A, in addition to the broad diffraction peak at about 20° from all samples attributed to collagen, a lower angle shift was observed on the apatite characteristic peaks from the Fe-bearing groups, suggesting that iron existed in the Fe 3+ state in the apatite lattices, which is probably due to the occurrence of oxidation during collagen polymerization process resulting in partial transition of Fe 2+ to Fe 3+ . However, the incorporation of Mn did not result in the peak shift of apatite, which is in agreement with previous reports. , Figure B shows the FTIR spectra obtained from various scaffolds. No obvious difference was detected among samples.…”

RETRACTED: A Si-αTCP Scaffold for Biomedical Applications: An Experimental Study Using the Rabbit Tibia Model

“…Ionic substitution plays a key role in the biological chemistry of bone apatite, whose crystallographic structure is similar to that of hydroxyapatite (Ca 5 (PO 4 ) 3 OH). Several anionic (CO 3 = ) and cationic (K, Na, Sr, Mg) substitutions were induced in crystals of bone apatite [40][41][42][43][44][45][46][47]. These ionic substitutions resulted in microscopic crystals, which were not only appropriately insoluble for stability but also adequately reactive to allow the remodeling process of resorption and re-precipitation in vivo.…”

Porous hydroxyapatite scaffolds fabricated from nano-sized powder via honeycomb extrusion

“…Upon removal from the furnace, a noticeable change in colour occurred in the HA extrudates between de-binding and sintering, whereby the extrudate displayed a blue appearance, having previously been white. This behaviour is common when upon sintering of HA [350,[359][360][361], and is attributed to manganese contamination during synthesis, and the oxidation thereof [360].…”