Since scientists first began working with stem cells, they have done everything from growing sheets of new skin to creating the different blood cell types.

Now researchers at Newcastle University have created IVD human sperm. IVD stands for in-vitro-designed. That's sperm cells created in the lab using embryonic stem cells.

The potential is of course to help infertile couples. But it is not without unresolved moral and ethical questions.

In this new approach, scientists take stem cells from a male and treat them with retinoic acid. This chemical sets them on the developmental path to becoming sperm cells. Not all cells become sperm but there are enough mature-looking sperm that are fully mobile.

While IVD could mean a promising new approach to infertility, huge issues remain. First, they don't know if these IVD sperm will successfully fertilize an egg. Some scientists question just how close these IVD sperm are to naturally occurring sperm.

Previous experiments using IVD mouse sperm cells produced offspring that died five months after birth. This shows fertilization is achievable but problems still exist with viability of the offspring. This would have to be completely resolved and understood before the procedure is ever tried with humans.

Perhaps the biggest barriers are legal. The scientist behind this research moved to England in order to work on human stem cells since restrictive German laws kept him from doing so.

However, while English law has allowed the experiments to date, existing laws ban IVD sperm or eggs as fertility treatments. Researchers will have to navigate through these issues as they further their work.

Yet, this is an important new development that someday may give hope to infertile couples wishing to have children of their own.