Tadepalli Sirimuvva, Hamper Henry, Park Sang Hyun, Cao Sisi, Naik Rajesh R, Singamaneni Srikanth
Department of Mechanical Engineering and Materials Science and Institute of Materials Science and Engineering, Washington University in St. Louis, St. Louis, Missouri 63130, United States.
711 Human Performance Wing, Wright-Patterson Air Force Base, Dayton, Ohio 45433, United States.
ACS Biomater Sci Eng. 2016 Jul 11;2(7):1084-1092. doi: 10.1021/acsbiomaterials.6b00232. Epub 2016 Jun 14.
Graphene oxide-silk composites have gained a significant interest in the recent times because of the unique mechanical properties of both GO and silk and their ability to form layered structures that exhibit a striking resemblance to the layered (brick-mortar) composites found in nature. However, various aspects of the interaction between silk and graphene oxide (e.g., conformation and distribution of the silk chains on chemically heterogeneous GO surface) are not completely understood. In this study, we demonstrate that the interaction between the silk fibroin chains and GO can be modulated by altering the pH of the silk fibroin solution. We employed atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy to probe the distribution and the secondary structure of silk fibroin adsorbed on GO. In acidic pH conditions (i.e., pH < pI), a high density of silk chains were found to adsorb on the GO surface, whereas an increase in pH resulted in a progressive decrease in the density of the adsorbed silk chains. This pH-dependent adsorption is ascribed to the electrostatic interactions between the negatively charged GO surface and the tunable ionization of the silk molecules. The secondary structure of silk fibroin chains adsorbed on GO was also found to be highly dependent on the pH. This study provides a deeper understanding of the interaction between GO and silk fibroin that is critical for the design and fabrication of bioinspired nanocomposites with tailored mechanical properties.
近年来，氧化石墨烯-丝复合材料因其独特的机械性能以及形成与自然界中分层（砖-砂浆）复合材料极为相似的分层结构的能力而备受关注。然而，丝与氧化石墨烯之间相互作用的各个方面（例如，丝链在化学性质不均一的氧化石墨烯表面的构象和分布）尚未完全明确。在本研究中，我们证明了通过改变丝素蛋白溶液的pH值，可以调节丝素蛋白链与氧化石墨烯之间的相互作用。我们采用原子力显微镜（AFM）和傅里叶变换红外（FTIR）光谱来探测吸附在氧化石墨烯上的丝素蛋白的分布和二级结构。在酸性pH条件下（即pH < pI），发现高密度的丝链吸附在氧化石墨烯表面，而pH值升高导致吸附的丝链密度逐渐降低。这种pH依赖的吸附归因于带负电荷的氧化石墨烯表面与丝分子可调节的电离之间的静电相互作用。还发现吸附在氧化石墨烯上的丝素蛋白链的二级结构高度依赖于pH值。这项研究为深入理解氧化石墨烯与丝素蛋白之间的相互作用提供了帮助，这对于设计和制造具有定制机械性能的仿生纳米复合材料至关重要。
