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 H ₃PO₄. 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.