The present invention discloses a low viscosity composition comprising enamel matrix derivative (EMD) proteins in a suitable pharmaceutical carrier, said composition having a pH between pH 3.8-4.2, and a viscosity of less than 50 mPa s at 22° C., which, when applied to a porous bone graft material, improves and/or enhances bioactivity and osteoconduction of said bone graft material. The present invention consequently discloses a bone graft material which has been bioactivated using a low viscosity composition comprising enamel matrix derivative (EMD) proteins and which displays enhanced biocompatibility and improved bone regeneration after implantation.