They then used a combination of nutrients to coax them to developing into round cells which were just a few steps away from mature sperm and appeared genetically normal.
The University of Pittsburgh School of Medicine team, led by Dr James Easley, believe they have cracked the most difficult part of sperm development. This means that by tweaking the procedure it should be relatively easy to get to the next stage - elongated cells that, while yet to grow tails, should be able to fertilise eggs.
The technique is still many years away from use in clinics and, as the law stands, lab-grown sperm are banned from use. But in the shorter-term, the breakthrough, detailed in the journal Cell Reports, could lead to new infertility drugs and contraceptives.
All of the early-stage sperm were made from male skin samples. Attempts at using female skin failed, suggesting men will always have an important role in the creation of life.
Other research teams are trying to make eggs from women's skin, raising the possibility of eggs and sperm being used to create children through entirely artificial means.
- DAILY MAIL