Leo I can go a step further. We (the better half and myself) made something very similar to what you suggested. We bought a sports bra and some nylon scouring pads (we had reservations about metal) and then poked holes through the pad with a skewer. Then we pulled out a whole heap of bristles from a scrubbing brush and fed them through the pad. Glued the pad into the bra over the nipple. Its now one of her favourite toys. Using a sports bra was fairly ingenious as the compression adds further to the sensations caused by the scouring pads and bristles (so I'm told )

I'm currently working on an improved version that fills the entire cup, but it takes forever to fed all those seperate bristles through the pad. Oh well - its a long term project.