the preferred long chain polyamine is PDADMAC;
the alginate used in the beads' formation may be an alginate of an alkaline metal, preferably sodium alginate;
the (external) porous shell comprises pores having a size ranging from (about) 1 to (about) 500 nm;
the thickness of the (external) porous shell is comprised between (about) 1 and (about) 10 μηι;
the content in silica of the (external) porous shell is comprised between (about) 0.1 and (about) 1 M, preferably between (about) 0.5 and (about) 0.8 M;
an intermediate layer of hybrid calcium alginate-silica is formed between the porous core and the (external) porous shell;