OPF/GO hydrogel supports cell growth without toxicity. (A) Representative morphological images of cardiac fibroblast cells cultured for 48 h on OPF- or OPF/GO-coated substrates. (B) Rat cardiac fibroblast cells were plated on the surfaces of wells coated with OPF or OPF/GO, grown for 48 h, and then stained with live & dead kit. (C) Immunofluorescence images of cardiac fibroblasts seeded on OPF- or OPF/GO-coated substrates (vimentin, red). (D) An MTT assay of cardiac fibroblasts cultured on the surface of pure OPF and different composite OPF/GO (0.3 mg/mL, 0.6 mg/mL, 1.0 mg/mL) (n=3, *P<0.05). MTT indicates 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazoliumbromide.