Assessment of subdural insertion force of single-tine microelectrodes in rat cerebral cortex

We investigated the implant mechanics of single tine silicon microelectrodes and conventional tungsten needle electrodes in rat cerebral cortex. Seven acute rat experiments were performed in which the force during a series of insertion/retraction into brain tissue (depth = 2 mm, velocity = 2 mm/s, 2 repetitions) were measured. We compared the single tine VSAMUEL microelectrode (opening angle = V, cross sectional area = 950 mum(2)) with a group of five commonly used single tine microelectrodes (opening angle = 3degrees-10degrees, cross sectional area = 750-1962 mum(2)). Initially, we observed dimpling of the brain surface before the first penetration (0.62 +/- 0.23 mN). The force maintained to increase after penetration until advancement had stopped (first penetration: 0.87 +/- 0.13 mN). A tension force was measured during the needle retraction phase (first retraction: 0.54 +/- 0.13 mN). The force was statistically significantly lower during the second insertion phase (Turkey-Kramer multiple comparison, alpha = 0.05). The insertion properties of the VSAMUEL probes were not significantly different from other commonly used microelectrodes. We showed that the microelectrodes had to survive a compression force of approximately 1 mN when inserted into rat cerebral cortex tissue and a tension force of 0.5 mN when retracted.