Regulation of the protein-loading capacity of hydroxyapatite by mercaptosuccinic acid modification

Loading and releasing protein in a controllable way is extremely important for the protein vehicles used in bone tissue engineering. To obtain a suitable carrier material for basic proteins, such as BMP or bFGF, hydroxyapatite particles containing mercaptosuccinic acid (mercaptosuccinic acid (Mer), (Mer-HAp)) were synthesized. Physicochemical evaluation of Mer-HAp suggested that Mer was contained in HAp particles: it either simply adsorbed onto HAp crystals or was trapped among the HAp crystals. A protein adsorption study using basic and acidic model proteins indicated that the synthesized Mer-HAp had selective loading properties of the basic protein. The loaded protein was gradually released from Mer-HAp in phosphate buffered saline. The protein release rate was different in each Mer-HAp synthesized with a different concentration of Mer. In addition, the protein release from Mer-HAp showed a similar profile with the Ca dissolution in different pH solutions, indicating that the Mer-HAp dissolution was concerned with the protein release from Mer-HAp. Thus, Mer-HAp is a useful candidate for the basic protein carrier because it has properties which enable the loading and releasing of protein in a controllable way.