Layer-by-layer assembled graphene oxide composite films for enhanced mechanical properties and fibroblast cell affinity.

The mechanical properties of films are of great importance for their use as biocompatible surface coatings or for drug encapsulation and release. In this study, layer-by-layer (LbL) assembled graphene oxide (GO) nanocomposite films were constructed, aimed at improving the mechanical properties of polyelectrolyte multilayer (PEM) films containing poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). The mechanical properties of the films were evaluated via a nanoindentation technique. It was demonstrated that the elastic modulus (Er) could be improved by up to 181% by one layer of GO deposition in ten bilayers of polyelectrolyte, while the Er value of [(PAH/GO)10/PAH/PSS]30 film showed more than 5-fold enhancement over the native PEM film (PAH/PSS)330. The hardness (H) also increased significantly, from 0.295 GPa to 2.79 GPa for the (PAH/PSS)330 film and the [(PAH/GO)10/PAH/PSS]30 film, respectively. These results support the idea that the mechanical properties of the film could be tuned by varying the number of layers of GO in the multilayer architecture. Furthermore, the effect of the LbL-assembled GO composite films on fibroblast cell behavior was investigated. Cell proliferation and cell adhesion were qualified by MTT assay and fluorescent labeling using an image analysis system. Obviously, when compared with the native PEM films, the cells showed faster proliferation and larger spreading area, and formed more numerous and better organized adhesion points on the GO composite films. This indicated a higher affinity of fibroblasts for the LbL-assembled GO nanocomposites. The strategy promises a new way to construct nanofilms that are simultaneously mechanically rigid and bioactive, which is crucial for cell-contacting biomedical and biotechnological applications.