A 3D-printed modular implant for extracellular recordings.

Background: Chronic implants for neural data acquisition must meet several criteria that can be difficult to integrate. Surgical procedures should be as short as possible to reduce unnecessary stress and risks, yet implants must precisely fit to the location of interest and last long periods of time. Implants also must be lightweight but stable enough to withstand the subject's daily life and experimental needs.

New Method: Here we introduce a novel, 3D-printed and open-source modular implant. Our modular design philosophy allows altering parts of the implant either before implantation or later, during the course of experiments. The implant consists of a base individually designed, for instance using an MRI of the subject for an exact skull fit. This base remains permanently on the subject and can contain multiple sites for craniotomies, microdrives and head stage connectors. All movable components (drives with probes, connectors, reference/ground points) are securely screwed onto this base, allowing for replacement and recovery.

Results: After implantation of the bases, self-made microdrives carrying commercial silicon probes were implanted. Once the experimental goals were achieved, they were recovered for further use. Should the quality of the data decrease during the experimental period, the components were replaced, allowing for the experimentation to continue. On an exemplary free-moving subject, under wireless electrophysiological data collection, we reliably obtained single and multi unit data up to 86 days after a silicon probe implantation. In this specific case, after this time we successfully substituted the components and collected similar quality data for additional 11 days.

Comparison With Existing Methods: Our approach allows to remove, reposition and exchange components during minimally invasive procedures, not requiring new incisions, bone drilling (unless new craniotomies are planned sequentially) or removal of dental cement or glue structures. Splitting complex implantations into multiple shorter procedures reduce the risks inherent to long surgical procedures. A careful plan of action allows to re-use and reduce subject's usage.

Conclusion: This novel approach reduces the duration of surgical procedures. It allows for minimally invasive follow-up procedures, including component replacements between experiments. The design is stable, proven to yield good results, in a very long-term period. This approach increases the chance of successful long experimental paradigms, and help reducing the use of subjects.