Modular, cement-free, customized headpost and connector-chamber implants for macaques

Background: Neurophysiological studies with awake macaques typically require chronic cranial implants. Headpost and connector-chamber implants are used to allow head stabilization and to house connectors of chronically implanted electrodes, respectively. New method: We present long-lasting, modular, cement-free headpost implants made of titanium that consist of two pieces: a baseplate and a top part. The baseplate is implanted first, covered by muscle and skin and allowed to heal and osseointegrate for several weeks to months. The percutaneous part is added in a second, brief surgery. Using a punch tool, a perfectly round skin cut is achieved providing a tight fit around the implant without any sutures. We describe the design, planning and production of manually bent and CNC-milled baseplates. We also developed a remote headposting technique that increases handling safety. Finally, we present a modular, footless connector chamber that is implanted in a similar two-step approach and achieves a minimized footprint on the skull. Results: Twelve adult male macaques were successfully implanted with a headpost and one with the connector chamber. To date, we report no implant failure, great headpost stability and implant condition, in four cases even more than 9 years post-implantation. Comparison with existing methods: The methods presented here build on several related previous methods and provide additional refinements to further increase implant longevity and handling safety. Conclusions: Optimized implants can remain stable and healthy for at least 9 years and thereby exceed the typical experiment durations. This minimizes implant-related complications and corrective surgeries and thereby significantly improves animal welfare.

Automated summary

In this study, a long-lasting, modular, cement-free headpost implant made of titanium was developed. It consists of a baseplate and a top part, with the baseplate being implanted first and the percutaneous part added in a second surgery. A remote headposting technique was also developed to increase handling safety. The implant remained stable and healthy for at least 9 years, minimizing complications and improving animal welfare.