Run both sides of the brush through the bench grinder's spinning brush and the wheel will "Comb" the wire brushes bristles, straightening them out. This works just as well for stainless and brass brushes.
Not only will the combing straighten out the bristles, but it will shine them up as well. Now your brushes can live to be as old as mine.
I hope this helps and saves a few old wire brushes from the trash heap... And a few fingers from multiple tiny puncture wounds:)