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Rotational atherectomy is an early version of this

One significant obstacle is that blood vessels do not grow to a standard gauge.

Variable diameter pigs exist. For blood vessels you would want a nano-pig with an “iris” kind of mechanism which moves to match the vessel diameter.

the problem is managing what you "scrape" off. such particles are ideal for causing strokes.

Just have more nanobots guarding the brain blood vessels and breaking up any big bits?