Use of graphene as protection film in biological environments

Corrosion of metal in biomedical devices could cause serious health problems to patients. Currently ceramics coating materials used in metal implants can reduce corrosion to some extent with limitations. Here we proposed graphene as a biocompatible protective film for metal potentially for biomedical application. We confirmed graphene effectively inhibits Cu surface from corrosion in different biological aqueous environments. Results from cell viability tests suggested that graphene greatly eliminates the toxicity of Cu by inhibiting corrosion and reducing the concentration of Cu(2+) ions produced. We demonstrated that additional thiol derivatives assembled on graphene coated Cu surface can prominently enhance durability of sole graphene protection limited by the defects in graphene film. We also demonstrated that graphene coating reduced the immune response to metal in a clinical setting for the first time through the lymphocyte transformation test. Finally, an animal experiment showed the effective protection of graphene to Cu under in vivo condition. Our results open up the potential for using graphene coating to protect metal surface in biomedical application

Use of graphene as protection film in biological environments

Corrosion of metal in biomedical devices could cause serious health problems to patients. Currently ceramics coating materials used in metal implants can reduce corrosion to some extent with limitations. Here we proposed graphene as a biocompatible protective film for metal potentially for biomedical application. We confirmed graphene effectively inhibits Cu surface from corrosion in different biological aqueous environments. Results from cell viability tests suggested that graphene greatly eliminates the toxicity of Cu by inhibiting corrosion and reducing the concentration of Cu2+ ions produced. We demonstrated that additional thiol derivatives assembled on graphene coated Cu surface can prominently enhance durability of sole graphene protection limited by the defects in graphene film. We also demonstrated that graphene coating reduced the immune response to metal in a clinical setting for the first time through the lymphocyte transformation test. Finally, an animal experiment showed the effective protection of graphene to Cu under in vivo condition. Our results open up the potential for using graphene coating to protect metal surface in biomedical application

Understanding Interactions of Nanomaterials with Biological Environments

Nanomaterials with sizes comparable to that of features of mammalian cells have a variety of applications in the clinical setting. In this thesis, I focused on functionalized silicon nanowires (SiNWs) as well as graphene for both biological and biomedical applications. First, I demonstrated the potential of using graphene as a protective coating in biological environments. As a preliminary test, I carried out a chemical experiment was conducted in a 37 °C oven for several days in order to mimic in vitro and in vivo conditions. This test was used to confirm that the presence of a graphene layer on copper substrates effectively inhibited the corrosion of the underlying metal substrate by ensuring that the Cu2+ ion concentration was low in aqueous biological media. For the in vitro studies, osteosarcoma cells were incubated in the presences of the samples and the viability of the cells was measured daily using the metabolic activity assay, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT). The MTT dye undergoes a color change when exposed to metabolic activity, so the solution was purple when exposed to living cells and yellow when the cells had died. Absorbance measurements were obtained for the samples as well as the control (cells without the presence of samples) and the measurements were converted to viability. The results of this cell viability test suggested that the graphene coating effectively protected the metal substrate from corrosion and thus, protected the cells from exposure to Cu2+ ions. Additionally, to boost the protective properties of graphene, a thiol coating was assembled on the copper surface to fill in any defects in the graphene coating. This was also tested with transferred graphene, which showed acceptable protection when the thiol coating was utilized. Importantly, since metal ions are known to cause inflammatory reactions in many patients, a lymphocyte transformation test was carried out to confirm that the graphene layer present on the copper substrate inhibited an immune response. Finally, an in vivo experiment was carried out by surgically inserting either bare copper foil or copper foil with a coating of single layer graphene next to the spine of a live rat. This was used to confirm that graphene exhibits protective properties under typical physiological conditions. Lastly, I utilized functionalized silicon nanowires to show, for the first time, that the uptake mechanism of these high aspect ratio one-dimensional (1D) nanomaterials occurs via a physically-driven membrane wrapping mechanism. Experiments were carried out at two different incubation temperatures, 37 °C and 4 °C, in order to confirm that the process is physically driven rather than receptor-mediated. We chose 4 °C because it is well understood that many endocytic pathways are temperature dependent and that these pathways are limited to high temperatures, so uptake at a lower temperature suggest that the uptake is physically driven. For all experiments, the SiNWs with length of 5 µm were co-cultured with CHO-β cells and imaged at various time points. First, optical microscopy was used to confirm that the wires were binding and interacting at both incubation temperatures. These results showed that the interaction of the wires was insensitive to temperature. Next, to capture snapshots of the key features of the uptake process, I fixed the cells after culture with the wires and utilized cross-sectional TEM to visualize the cell membrane. From the samples incubated at both 37 °C and 4 °C, I was able to visualize the wires binding tangent to the membrane, the membrane changing shape to accommodate the wires, and a pocket of membrane surrounding the internalized wires. This confirmed that the membrane wrapped around the wire in order to internalize it. Finally, a fluorescent confocal experiment was carried out to further understand the membrane interactions as well as gather three-dimensional (3D) information through a z-axis scan. To visualize the cell membrane, the cells were stained with DiI (red) after the removal of the wires and images were taken at steps along the z-axis. Notably, when the SiNWs were incubated with DiI without the presence of cells, they did not fluoresce. However, after co-culture with the cells, the wires that were internalized fluoresced. These results further confirmed that the internalization pathway occurred through membrane wrapping

Parallel Nanoshaping of Brittle Semiconductor Nanowires for Strained Electronics

Semiconductor nanowires (SCNWs) provide a unique tunability of electro-optical property than their bulk counterparts (e.g., polycrystalline thin films) due to size effects. Nanoscale straining of SCNWs is desirable to enable new ways to tune the properties of SCNWs, such as electronic transport, band structure, and quantum properties. However, there are two bottlenecks to prevent the real applications of straining engineering of SCNWs: strainability and scalability. Unlike metallic nanowires which are highly flexible and mechanically robust for parallel shaping, SCNWs are brittle in nature and could easily break at strains slightly higher than their elastic limits. In addition, the ability to generate nanoshaping in large scale is limited with the current technologies, such as the straining of nanowires with sophisticated manipulators, nanocombing NWs with U-shaped trenches, or buckling NWs with prestretched elastic substrates, which are incompatible with semiconductor technology. Here we present a top-down fabrication methodology to achieve large scale nanoshaping of SCNWs in parallel with tunable elastic strains. This method utilizes nanosecond pulsed laser to generate shock pressure and conformably deform the SCNWs onto 3D-nanostructured silicon substrates in a scalable and ultrafast manner. A polymer dielectric nanolayer is integrated in the process for cushioning the high strain-rate deformation, suppressing the generation of dislocations or cracks, and providing self-preserving mechanism for elastic strain storage in SCNWs. The elastic strain limits have been studied as functions of laser intensity, dimensions of nanowires, and the geometry of nanomolds. As a result of 3D straining, the inhomogeneous elastic strains in GeNWs result in notable Raman peak shifts and broadening, which bring more tunability of the electrical–optical property in SCNWs than traditional strain engineering. We have achieved the first 3D nanostraining enhanced germanium field-effect transistors from GeNWs. Due to laser shock induced straining effect, a more than 2-fold hole mobility enhancement and a 120% transconductance enhancement are obtained from the fabricated back-gated field effect transistors. The presented nanoshaping of SCNWs provide new ways to manipulate nanomaterials with tunable electrical–optical properties and open up many opportunities for nanoelectronics, the nanoelectrical–mechanical system, and quantum devices