FTM masculinization surgery usually is done with bilateral mastectomies with free nipple grafts. A free nipple graft involves removing the nipple and areola from its original position on the breast and moving it to a new area on the chest wall. When this is done, the nipple/areola graft has to obtain a blood supply so that it can retain its color and the nipple can have some projection. If the nipple has lost that because of the transfer, then a few things can be done to try to help give it back its volume. Fillers (like a hyaluronic acid) may give some bulk to the area, but they are not permanent. If, however, the fillers give the projection you desire, you can try a more permanent filler like your own fat. Other materials, like cartilage, may be too stiff and may resorb with time. There is, unfortunately, no great fix to this problem. Talk to your plastic surgeon about your options. Good luck!