Biofunctional Carbon Nanotubes and Dynamically Growing Membranes: Electrical Signals in Living and Self-Assembled Systems

The profound influence of electric fields on living cells and self-assembling materials offers unique opportunities to generate therapies and materials in medicine, energy, and other disciplines. In this work a new class of molecules have been investigated that self-assemble around electronically conductive carbon nanotubes and present bioactive epitopes on their surfaces, generating materials capable of interfacing with cells and applying electrical signals to them. The self-assembly of these molecules generated dispersions of monolayer-thick coated carbon nanotubes which were deposited as thin films to create conductive, bioactive surfaces. Cardiomyocytes attached to these surfaces, proliferated, and had contractile and electrical activity across entire macroscopic cultures. In another part of this study the discovery of a highly aligned peptide amphiphile gel with an ability to both encapsulate carbon nanotubes and yield a continuous, macroscopic, three-dimensional cardiac syncytium capable of propagating electrical signals across the entire construct, led to a study of the ability of various peptide amphiphiles to disperse carbon nanotubes. Spectroscopic and microscopic observations of these dispersions revealed a strong interdependence between the molecular structure of the peptide amphiphile and its ability to individually isolate carbon nanotubes. Molecules with two different beta-sheet forming regions and varying formal charge all produced stable dispersions of nanotubes, but only the most highly charged molecule yielded photoluminescent nanotubes. Peptide amphiphile nanostructures encapsulating carbon nanotubes were directly observed by microscopy with different molecular structures producing twisted ribbons or cylinders (and corresponding quenched or photoluminescent nanotubes) with only a change in the molecular terminus from -NH2 to -COOH. These studies highlight the profound changes in self-assembly and nanotube isolation ability that occur with very minor changes in molecular structure. Lastly, the effects of electric fields on structures comprised of charged peptide amphiphiles and biopolymers such as hyaluronic acid were studied. Experiments revealed that electric fields caused changes in their structure and properties including differences in growth rate of self-assembling membranes, rotation of growth direction, the formation of structural gradients and undulations, and an increase in mechanical stiffness. In summary, these studies inform possible future designs of self-assembling and carbon nanotube-containing biomaterials for applications in medicine and other areas.