In this segment, Fran Romano, a mechanical engineer on Neuralink's surgery engineering team, explains how the company creates patient‑specific physical 3D models—called proxies—to rehearse neurosurgical procedures. Because the Neuralink brain‑computer‑interface surgery is novel, no existing training tools exist, so the team converts each patient’s CT and MRI scans into a series of realistic components: a silicone scalp mold dyed to match skin tone, a machined plastic skull cap derived from the CT data, a hydrogel brain replica formed from an MRI‑based mold, 3D‑printed veins, and inkjet‑printed arteries using collagen‑infused “sausage skin.” To mimic brain motion, a pneumatic system inflates a balloon inside the hydrogel at a heart‑rate‑like 60 beats per minute, reproducing the unexpectedly large 3 mm peak‑to‑peak movement observed in real surgeries. The assembled head—including neck and body mount—is 3‑D printed from the participant’s scans, allowing the neurosurgeon to perform multiple mock surgeries on the exact anatomy before the actual operation, aiming for a “no surprises” and “boring” surgery. The process highlights the integration of medical imaging, additive manufacturing, material science, and mechanical simulation to create high‑fidelity surgical training tools.
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The surgeon comes up to me and goes, "I thought that was an actual person for a second." I've had surgeons tell us that it's the best proxy in the world. Nobody makes anything like it. Please, can you sell this to us? I'm Fran Romano. I'm a mechanical engineer on the surgery engineering team here at Neuralink. It's also fun to tell people that don't work here that I make fake people. We build physical 3D models that we call proxies that mimic a person's anatomy and gets mechanical properties pretty close to what we want them to be. The Neuralink surgery doesn't exist. We couldn't copy something else, so we were developing the procedure itself. We figured out how to take CT and MRI data and convert that into physical things that our neurosurgical staff could practice the procedure on. The best thing to do is just buy the thing that already works. Unfortunately, I couldn't just go buy the proxy that his hit all of the things we wanted to hit. Nothing on the shelf existed, so we had to build our own. Today we're gonna build a full proxy. The items we're gonna make are the scalp, the head, the skull cap, the veins, the brain itself, and then we're gonna put it all together and run a fake surgery on it. So step 1, we'd start with the scalp. We have these custom scalp molds that are patient-specific. We're gonna mix some silicone together, add some dye to mimic the skin tone. And then pour it into the mold. 4 hours later, we'll demold the silicone, and we'll have a patient-specific scalp. Step 2 would be the skull cap. They actually machine skulls out of a block of plastic. You'll see the machinist go in and an anatomically accurate skull come out of a chunk of plastic. Third step will be assembling the brain. That starts actually the night before, where we will pour a custom hydroshell into a proxy mold. The mold is built from the MRI of the patient that we're building the brain from. We'll freeze that overnight. So your brain has two types of blood vessels in it. It has veins and arteries. Arteries bring the blood in and veins bring the blood out. You can see where the blood flow is. And so from the scan, we can extract that region right where we're gonna drill the hole and then 3D print those veins. Spray paint them to look real. The harder one are the arteries. We actually just take a regular inkjet printer, feed sausage skin collagen into it, print some artery-looking pattern onto it. Use your brain. Switch to Brex to upgrade your finances. When we first started, we had to rely on literature and surgeon experience of how much the brain moves. Our original estimate was half a millimeter peak to peak. When we did our first surgery, it was 3 millimeters peak to peak. It's about 6 times what we were expecting. The way we did that is we took a party balloon and we put it into the hydrogel, and then we connected that party balloon to a little pneumatic pump. Typically, we keep it at 60 revolutions per minute or 60 beats per minute, which is kind of like your resting heart rate under anesthesia. To make the head, we'll use the CT scan from our participants. We'll convert that into a 3D model and then 3D print it here at Ehrlich. So we basically have someone's full head from the neck up with a hole in it that will fit the skull cap and the brain. That whole assembly will go inside of the head. Once all of that is screwed in together, we'll cover it with the scalp. We also want to add the head onto a body, and so we kind of core out the neck and add like a little hole that we can attach to a body. Then it's ready to ship off for surgery. So this is the exact, uh, the exact mask shape and So for our third participant, we got the scans and 2 weeks later we did the actual surgery. Can I show Brad? Yes, definitely. It's probably warmer than that though. So in between that time, we built his head, did 2 full mocks on his head before the actual surgery. Basically, his actual surgery was the third time our neurosurgeon saw that anatomy. The motto is, is no surprises. We want surgery to be boring. And if you're practicing on the person's anatomy the day before the surgery, there's very few surprises.
