Development of flexible arrays for in vivo neuronal recording and stimulation

Abstract

Recent developments in low-power electronics and semiconductor fabrication techniques have found many applications in the life sciences. High-density electrode arrays are becoming well established as tools for the measurement of neuronal signals. The fabrication of arrays on flexible materials allows for 2D position sensitive recording of cellular activity in vivo and for the possibility of direct in vivo stimulus. Using flexible polymer materials, compliant with semiconductor fabrication techniques, we demonstrate a process allowing the fabrication of flexible multi-site microelectrode neuronal recording and stimulating arrays. We describe the development of both 8 and 61 electrode arrays on polyimide substrates with 50 and 5 μ m minimum linewidths respectively. Further studies have realised 8-electrode arrays using gold on Polydimethylsiloxane (PDMS), an alternative biocompatible material, with linewidths of 14 μ m . Implementing low noise amplification, 2.6 μ V rms (bandpass typically 80–2000 Hz), the polyimide 8-electrode arrays have been used to record electroretinogram and ganglion cell action potentials in situ from the frog retina ( Rana temporaria). Such arrays coupled to pixellated CMOS sensors, incorporating on-board neural networking should allow for the recovery of basic functionality in the human retina. More specifically, where retinal degeneration has affected only the photosensitive elements of the eye we can utilise the remaining neuronal pathways. Initial stimulation studies for electro-deposited platinum electrodes of 4 nA/ μ m 2 indicate upper breakdown limits for charge density approaching 40 μ C m - 2 . Investigations of lifetime stimulation of a 50 μ m diameter electrode, of typical impedance less than 20 k Ω at 1 kHz, suggest operational limits over lifetime in the order of 10 μ C m - 2 . These charge densities are adequate for neuronal cell stimulation.