Effect of phosphoric acid on the properties of magnesium oxychloride cement as a biomaterial

Magnesium oxychloride cement (MOC) has been used in civil engineering for more than 100 years, but its application has been limited by its poor water resistance. This property, however, could be exploited in the formulation of a resorbable orthopaedic biomaterial. In this study, H3PO4 was added to control the degradation process of MOC to provide a predictable and clinically appropriate resorption time. The effects of H3PO4 on the phases, microstructures, mechanical properties, hydration and degradation of MOC have been evaluated. The results revealed that the crystalline phases in MOC before and after adding H3PO4 were the same, but that the needle-like phase 5 (5 Mg(OH)2·MgCl2·8H2O) crystals were formed more extensively in MOC with H3PO4 than that in MOC without H3PO4. Furthermore, the addition of H3PO4 was shown to retard the hydration process. H3PO4 did significantly improve the water resistance of MOC though its addition resulting in a reduction in compressive strength.