In the field of biomaterials applied in bony restoration, systems based on amorphous silicate network present the ability to link to bone matrix. Amorphous geopolymers of the potassium-poly(sialate)-nanopolymer type with a mole ratio Si:Al = 31 were studied for their use as potential biomaterials. This implied a heat treatment at 500 degrees C in order to reduce the alkalinity of the geopolymer matrix from pH 11.5 to pH 7.1 and to provide high porosity for biological compatibility. Al-27 and Si-29 MAS NMR spectroscopy has been used to characterise the foamed geopolymers obtained after different thermal treatments at 250 and 500 degrees C, and with three different mole ratios K2O/SiO2 for the potassium silicate: 0.54; 0.67 and 0.84. Best results in terms of biological compatibility were obtained with a geopolymer matrix resulting from a mole ratio K2O/SiO2. of 0.54, heat-treated at 500 degrees C.