Osseous substitute presenting an activity ON osseous regeneration and comprises fucan presenting a weight average molar mass of 5000-100000 g/mol and preferably 10000-40000 g/mol. INDEPENDENT CLAIM are included for: (1) the preparation of osseous substitute comprising covering the biomaterial surface by a coating of fucans (2) a culture medium for a osteocompetent type cell of bone marrow, bone or periosteum and comprising fucans presenting a weight average molar mass of 5000-100000 g/mol and preferably 10000-40000 g/mol (3) cell culture of osteocompetent cells of bone marrow, bone or periosteum and comprising cultivating the cells in the culture medium or in the osseous substitute and (4) a medical device presenting an activity ON osseous regeneration and comprising fucans presenting a weight average molar mass of 5000-100000 g/mol and preferably 10000-40000 g/mol.
