FlexDrive

From OpenOptogenetics.org

The Open Ephys innitiative has introduced a chronic drive implant for extracellular electrophysiology that can be used to individually position up to 16 microwire electrodes or electrode bundles in mice, with up to 64 channels. The implant weighs approximately 2 grams, is easy to build, and accommodates arbitrary spatial arrangements of electrodes and optical fibers.

Information on the flexDrive is available on the Open Ephys website.
Frontiers in Systems Neuroscience paper describing the flexDrive, by Voigts et al (2013).

(A) Isometric view of the flexDrive showing the one-piece spring (blue) that acts as the drive mechanism. (B) Illustration of the flexDrive implanted in a 6 month old C57/bl6 mouse. Due to the low implant weight (~2 g), the impact of the drive on natural behavior is minimal. (C) Cross section of the drive and its placement on the mouse skull. In this example, electrodes target the thalamus. (D) Cortical action potentials recorded from a stereotrode (12 μm nichrome wire, gold plated to ~300 KΩ) on a flexDrive showing eight clusters (color coded clusters, non-clustered spikes in gray) and average and 95% percentiles of the waveforms on the two electrode contacts. From Voigts et al., 2013.