The bone graft system comprises a solid inorganic component, which is bone graft material, and a hydrogel. The hydrogel contains >；2 ppm of silicon ions, calculated as parts by weight of Si per million of the aqueous component of the hydrogel. Preferably, the solid inorganic component comprises hydroxyapatite or a silicon-containing hydroxyapatite, and may be a silicon-containing hydroxyapatite having a Ca/P ratio in the range 2.05 to 2.55 and a Ca/(P+Si) molar ratio less than 1.66. Bone healing is promoted by delivery of silicon ion release from the hydrogel and by the solid inorganic component stimulating cell behavior.
