Nevertheless, after a thorough examination your plastic surgeon can offer you diameter improvement by adipose tissue transfer or fat grafting. There are no study that showed any need for stem cells in that area neither its safety. Fat grafting has been studied thoroughly and is validated in that case.
It has to be done with a very specific technique using small aliquots of fat harvested with special cannulas, treated and centrifuged at particular speed, and then reinjected with other cannulas in fine quantities.
The result expected, if done in the right indication is satisfactory. This is not a treatment for sexual dysfunction it as only a treatment for diameter enhancement.