The present invention relates to a cell-occlusive membrane, obtainable by reaction of at least two precursors in the presence of water. The first precursor A comprises a core and n chains each having a conjugated unsaturated group or a conjugated unsaturated bond, and the second precursor B comprises a core and m chains each having a thiol group, wherein m is greater than or equal to 2, n is greater than or equal to 2, and m+n is greater than or equal 5. The reaction forms a three dimensional network with crosslinking-points. The adjacent crosslinking-points are connected by a chain having less than 600 atoms.