A Neural Implant Design Toolbox for Nonhuman Primates

Our research offers an efficient and automated method for brain and skull modeling, which is beneficial for neurosurgical planning and designing custom implants. It facilitates a simultaneous extraction of brain and skull models using a single software platform, which eliminates a requirement for extra imaging processes like commuted tomography scans. Virtual brain and skull modeling for medical imaging such as MRI or CT scans has been increasingly adopted for NHP neurosurgical planning in recent years.

These models used alongside 3D design software and 3D printing enable the creation of customized implants tailored to specific experiments in animals. Many non-human primate neuroscience experiments require the use of chronic cranial chambers and head posts. The use of generic implants introduces gaps between the implant and the skull, which can result in higher rates of infection, osteonecrosis and implant instability, therefore, compromising experiments and the wellbeing of the animal.

Our custom implants reduce gaps and subsequent issues. Our protocol provides researchers with a more accurate and time effective neurosurgical planning procedure. It increases surgical planning efficacy, and reduces complications associated with NHP neuroscience experiments that's improving scientific results overall.

To begin, acquire a T1 quick magnetization prepared gradient echo or MP-RAGE file of the skull and brain using a 3T MRI machine. Enter the name of the MP-RAGE file in the command window and verify that the MRI image is displayed correctly. Follow the command line instructions to isolate the skull.

Select a threshold value that effectively separates the skull from other tissues without losing skull matter, and press Y to confirm this value. Use a similar method for brain isolation. Input a threshold value for the brain when prompted and adjust as needed to ensure the brain is distinctly separated from the skull and other tissues.

Press Y to confirm the selected value. To determine craniotomy coordinates, choose a Z frame and select a point on the chosen Z frame for the craniotomy center. On the figure showing the brain and skull, place points to cover the region of interest for precise skull representation.

To import the file into CAD software for custom chamber design, open the software, then go to File, click Open and select the STL reduction file from the directory. After that, click Options and in the Import As menu, select Surface Body and click OK.Now view the skull surface for the chamber in CAD software, ensuring the edges of the selected area are clearly visible in the skull representation. To sketch the chamber skirt shape onto the created plane, make the inner circle of the chamber and center it around the point on the upper plane.

Using a mix of arcs and lines, construct the outer boundary of the chamber skirt to maximize the area, then extrude to the lower of the two surfaces. Next, perform an extrude cut from the upper plane to the higher of the two copied surfaces following the shape of the chamber outline. Delete both remaining copies of the imported surface to expose the chamber skirt and inner ring.

Use the move or copy function to shift the skirt directly below the chamber top, ensuring precise downward translation. Then extrude the objects from the chamber tops bottom towards the skirt to connect them. Using the extrude boss or base, select the bottom surface of the chamber top and create a sketch with the same inner and outer radii as the ring, centered around the central axis.

Set the extrusion direction to up to body, targeting the chamber skirt. To design the head post, save brain and skull STL files for potential 3D printing. Use STL size reduction to extract the region of the skull surrounding the chamber for the creation of a head post footprint for import into design software.

Then select Y to activate STL size reduction. Choose points on the image showing the brain and skull together, ensuring close and even distribution across the gray skull area. Import the size reduced file as a surface body into CAD software for designing the custom head post footprint.

Afterward, use extrude boss or base to select the new plane and sketch the head post footprint using arcs and lines. Use arcs for smooth edges around the footprint and extrude the sketch to the imported surface. Perform an extruded cut from the flat surface of the head post footprint to the copied surface.

Subsequently delete the original surface and its copy. Now create a new plane parallel to the reference plane translated upwards or downwards to hover at least one millimeter above the head post bottom. Use the measure tool and the evaluate tab for precise translation length.

Then make a circular extrusion from this new plane to the head post bottom to create a centered platform for the head post top. Align the head post top and bottom using move or copy. Specify the head post top as the body to move and set three mates in the constraints menu.

Ensure the outlined edges of the last mate pair surfaces are mated concentrically. Then mate a vertical line on the back leg of the head post with a horizontal line on the back of the head post top perpendicularly. Verify each connection's direction and adjust mating directions in the menu as necessary.