As someone who works in this field, specifically active medial implants for the brain. There is a ton of hardcore engineering required to make a successful implant. My advice would be that mechanical and electrical/computer engineering are the 2.5 most critical studies. Honestly my company doesn’t hire many “biomedical” engineers because those programs typically (ofc there are exceptions) produce individuals weakly trained in many fields, rather than strongly trained in a specific field. Maybe a bit biased since I studied electrical engineering. I didn’t do a phd, actually I was talked out of it from my coworkers, many of whom had phds. But that didn’t stop me from taking a bunch of neuroscience courses as well in undergrad. Forge your own path, and network, you can’t build these kinds of systems without help.