When crosslinked GO networks are employed to reinforce calcium alginate composites, the morphology of these samples are very different from that of calcium alginate composites prepared with uncrosslinked GO nanosheets (Fig 5). Thus, Fig 5A shows that most GO nanosheets are separated or form small aggregates around the alginate polymer matrix in comparison with the continuous crosslinked GO networks present in cGO/Alg, which can be clearly appreciated (Fig 5B, dark phase) by confocal microscopy in contrast to calcium alginate (light phase).Additionally, continuous irregular tubes of crosslinked GO with divalent calcium atoms can also be visualised in this confocal image forming sometimes right angles between them (see Fig 5D). However, there are three huge irregular micrometer-size continuous GO forms in GO/Alg, which indicate that GO crosslinking also occurs in GO/Alg during the gelation process.