Hierarchically structured polydimethylsiloxane films for ultra-soft neural interfaces

Long-term interfacing with neural tissue is key for the diagnosis and therapy of neurological disorder. Coatings with dedicated micro- and nanostructures have been proposed, such as gold nanowires, platinum nanostructured by electrochemical roughening, columnar and porous titanium nitride, carbon nanotubes, and conductive polymers. The performance of these coatings, however, is limited because of the mechanical mismatch between implant and neural tissue. Herein, we show that micro- and nanostructured, soft and conductive elastomer films can be obtained by depositing gold on nanometer-thin thiol-functionalized polydimethylsiloxane (PDMS) films. Additionally, microstructured polyether ether ketone (PEEK) films enable directional ordering in topology. The formation of soft and conductive PDMS films with oriented wrinkles on the macroscopic scale was controlled by the ratio between the metal/elastomter thicknesses and the depth of thermally imprinted trenches. Four-point probe measurements revealed that the electrical conductivity is one order of magnitude higher than that of recently presented hydrogel formulations. Nano-indentations proved that the submicrometer-thin conductive elastomer exhibit an average elastic modulus well below 10 MPa. This material system can be made tens of micrometers thin, and, therefore, has the potential to address several challenges of current implantable neural interfaces for the central nervous system, e.g. fabrication of softer and more flexible micrometer-thin spinal cord arrays.