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Chemistry, ultrastructure and porosity of monophasic and biphasic bone forming materials derived from marine algae

The research on bioceramics during the last decades has proved that the bioactivity of inorganic bone grafts depends fundamentally on an optimal combination of chemistry and structural porosity. This study presents a comparison of a resorbable monophasic hydroxyapatite (HA) and several newly developed resorbable biphasic hydroxyapatite – ß‐tricalcium phosphate (HA/TCP) composites both derived from naturally grown red marine algae with respect to the phase composition, microstructure and porosity. The highly porous three dimensional mineral scaffold of the native alga is maintained in the final products all investigated materials and possesses a pronounced interconnecting microporous structure. There are generally high values of specific porosity calculated for all tested materials: 1.07 cm3/g for pure phycogenic HA and between 0.65 cm3/g and 1.04 cm3/g for phycogenic biphasic HA/TCP composites with various HA/TCP ratios. The ultrastructure of the phycogenic HA/TCP composites changes significantly with the building and the increase of the ß‐TCP phase due to the bigger polyedric ß‐TCP crystals compared to the finer polycrystalline HA. Despite these structural changes the interconnected porous scaffold is kept throughout the production process. In all investigated materials the porosity is mainly based on pores with pore sizes between 1 and 10 μm in diameter, which is given by the structure of the natural alga. The specific chemistry combined with the structural porosity is decisive for the high in‐vivo bioactivity of the studied materials.