Custom-fit radiolucent cranial implants for neurophysiological recording and stimulation

•We designed radiolucent cranial implants that were customized to match the contour of the skull of non-human primates.•Screws were encased within the walls of the implant itself to prevent skin recession that is commonly observed in legged designs as well as to avoid the use of dental acrylic.•Implants were stable and neural activity was successfully recorded/stimulated for multiple years, with no signs of infection.•These methods may have broader applicability to other animal models as well as to human implant design, including brain–machine interfaces.

BackgroundRecording and manipulating neural activity in awake behaving animal models requires long-term implantation of cranial implants that must address a variety of design considerations, which include preventing infection, minimizing tissue damage, mechanical strength of the implant, and MRI compatibility.New methodHere we address these issues by designing legless, custom-fit cranial implants using structural MRI-based reconstruction of the skull and that are made from carbon-reinforced PEEK.ResultsWe report several novel custom-fit radiolucent implant designs, which include a legless recording chamber, a legless stimulation chamber, a multi-channel microdrive and a head post. The fit to the skull was excellent in all cases, with no visible gaps between the base of the implants and the skull. The wound margin was minimal in size and showed no sign of infection or skin recession.Comparison with existing methodsCranial implants used for neurophysiological investigation in awake behaving animals often employ methyl methacrylate (MMA) to serve as a bonding agent to secure the implant to the skull. Other designs rely on radially extending legs to secure the implant. Both of these methods have significant drawbacks. MMA is toxic to bone and frequently leads to infection while radially extending legs cause the skin to recede away from the implant, ultimately exposing bone and proliferating granulation tissue.ConclusionsThese radiolucent implants constitute a set of technologies suitable for reliable long-term recording, which minimize infection and tissue damage.