[0021] Preferably, in the method according to any of the invention, the concentration of the silica precursor is comprised between (about) 0.1 M and (about) 2 M, the concentration of the alginate is preferably comprised between (about) 0.5% wt and (about) 5% wt and the concentration of the silica concentrator, preferably the silica concentration, preferably the polycation PDADMAC is comprised between (about) 0.4% wt and (about) 10% wt.