Collagenase-aided intracortical microelectrode array insertion: Effects on insertion force and recording performance

Intracortical microelectrodes puncture the intact pia mater membrane during insertion, a process that can cause brain dimpling and trauma. To ensure that the device is able to withstand forces during implantation without buckling, the selection of acceptable implant materials and geometries is limited to rigid designs with large cross-sectional areas. Such designs likely increase insertion trauma and potentially exacerbate the chronic tissue response. In this paper, a technique that may relax the mechanical requirements of implanted microelectrodes through enzymatic (collagenase mediated) manipulation of the pia mater is quantified experimentally. Measurements of the insertion force profiles were obtained with a load cell during computer controlled (10 mu m/s) insertion of microwire arrays into the cortex of rats. It was observed that collagenase application reduced the peak insertion force experienced by the microwire arrays by almost 40% on average (4.04 +/- 2.03 mN versus 2.36 +/- 1.17 mN; control versus treated sites). Peak insertion force magnitudes were highly dependent on implant location with anterior sites registering lower peaks than more posterior sites. Chronic neural recording performance (up to one month) did not appear to be adversely affected by the collagenase treatment, suggesting the overall safety of the technique. Our data suggest that controlled application of collagenase is a useful method in enabling implantation of thinner microelectrodes, potentially facilitating reduced insertion trauma and lower immune response. Furthermore, due to dependence of insertion force on anatomical location, the intended target region should be considered in implant design.