A series of calcium alginate composite hydrogels with several calcium chloride contents ranging from 3 to 18 wt.% with and without 0.1 wt.% of graphene oxide (GO) was prepared in order to study the effect of crosslinking and nanofilling on water diffusion and compression performance. Thus, for high crosslinker contents, these composite hydrogels exhibited ultrafast diffusion of liquid water and excellent compression properties as compared with control (0 wt.% GO and the same crosslinking). These remarkable results are produced due to calcium cations are able to crosslink alginate and also graphene oxide nanosheets to form large crosslinked GO networks inside the calcium alginate hydrogels. Besides, these crosslinked GO/calcium alginate networks present nanochannels, as confirmed by electron microscopy, able to improve significantly water diffusion. Thus, these composite materials are very promising for many industrial applications demanding low-cost hydrogels with improved mechanical and water diffusion properties.

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Alginate-based materials hold great promise in bioengineering applications such as skin wound healing and scaffolds for tissue engineering. Nevertheless, cell adhesion of mammalian cells on these hydrophilic materials is very poor. In cases such as polycaprolactone, poly(hydroxy-3-butyrate-co-3-valerate) and gelatin, the incorporation of hydrophobic carbon nanofibers (CNFs) and hydrophilic graphene oxide (GO) has shown significant improvement of cell adhesion and proliferation. The incorporation of these carbon nanomaterials (CNMs) into alginate films can enhance their mechanical performance, wettability, water diffusion and antibacterial properties. Herein, we report the effect of adding these CNMs into alginate films on cell adhesion for the first time. Thus, the results of this study showed that these nanocomposites are non-cytotoxic in human keratinocyte HaCaT cells. Nevertheless, contrary to what has been reported for other polymers, cell adhesion on these advanced alginate-based composites was not improved. Therefore, both types of composite films possess similar biological behavior, in terms of cell adhesion and non-cytotoxicity, and enhanced physical and antibacterial properties in comparison to neat alginate for potential biomedical and bioengineering applications.

A series of alginate films was synthesised with several calcium chloride cross-linker contents (from 3 to 18% w/w) with and without a very low amount (0.1% w/w) of carbon nanofibers (CNFs) in order to reduce the production costs as much as possible. The results of this study showed a very significant enhancement of liquid water diffusion and mechanical compressive modulus for high calcium chloride contents when this minuscule amount of CNFs is incorporated into calcium alginate hydrogels. These excellent results are attributed to a double cross-linking process, in which calcium cations are capable of cross-linking both alginate chains and CNFs creating a reinforced structure exhibiting ultrafast water diffusion through carbon nanochannels. Thus, these excellent results render these new alginate composites very promising for many bioengineering fields in need of low-cost advanced hydrogels with superior water diffusion and compression properties.

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