The invention relates to an open implant constituted of an osteogenic composition comprising at least: one osteogenic growth factor/amphiphilic anionic polysaccharide complex, one soluble salt of a cation at least divalent, and one organic support, said organic support comprising no demineralized bone matrix. In one embodiment, said implant is in the form of a lyophilizate. It also relates to the method for the preparation thereof.