The Emerging Applications of Graphene Oxide and Graphene in Tissue Engineering - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 288

electrode for neural stem cells [84]. They showed that the cells were more
electrophysiologically active upon electrical stimulation through the gra-
phene electrodes compared to non-stimulated samples. Another interesting
study was performed by Heo et al. , who examined the cell-cell interactions
by applying a contact-free electrical fi eld stimulation through graphene/
polyethylene terephthalate electrodes [90]. The authors used human neu-
ral cells as a model and found that the application of an electric fi eld with
this novel stimulator led to an effective cell-cell interaction. As indicated
by the authors, the high electrical conductivity of graphene made the
electrodes highly sensitive to small changes during the application of the
biphasic electrical signals. Therefore, a weak electric fi eld (4.5 mV/mm
voltage and 10 s duration over a 32 min period) was suffi cient to obtain
effective cell-cell communication without damaging the cell membrane.
This fi nding is of great importance for the fabrication of high performance
stimulator devices using graphene, which would not be harmful for the
human nervous system, consisting of fi ne and sensitive neural networks.
Various cell behaviors, such as cell migration, proliferation, differentia-
tion, and apoptosis can also be regulated by applying electrical fi elds [91].
Therefore, many research opportunities exist to evaluate cell and tissue
responses to direct and alternative electric fi elds applied through graphene
electrodes. Other advantages of these electrodes include their exceptional
optical transparency and biocompatibility. In addition, the electronic prop-
erties of graphene nanosheets can be precisely controlled [92]. Therefore,
they can be adjusted for various cellular interfacing, stimulation regimes,
and monitoring applications in both in vitro and in vivo conditions.
Graphene has also been used as a supplementary material for com-
monly used biomaterials to enhance their properties. For example, cova-
lently bonded PCL and graphene composites were synthesized and
proposed as biocompatible materials for TE applications [93]. The PCL/
graphene composites exhibited better homogeneity compared to the pris-
tine PCL materials. As a result, the tensile strength, Young's modulus, and,
more importantly, electrical conductivity of the composites were substan-
tially improved compared to the neat PCLs.

12.5 Conclusions and Future Directions

This chapter has discussed the impact of GO and graphene as a new class
of biomimetic materials and their recent cell and TE applications. In addi-
tion, it discussed the use of graphene-based materials as biocompatible
materials for the adhesion, proliferation, and differentiation of various cell
types, such as neurons, osteoblasts, and stem cells. In general, as shown
in Table 12.1, these functional materials have been employed in three
main categories, namely, as biocompatible cell culture substrates, in stem
cell biology and engineering, and in the fabrication of high-performance