This chapter describes the existing knowledge regarding the ideal molecular profile of sperm cells, in order to define the model to be mimicked when stem cells are employed in order to create male gametes. Sperm production is defective in a significant proportion of males aiming at fatherhood. Interestingly, there are a significant proportion of infertile males presenting normal sperm counts, thus diagnosed as having idiopathic infertility. To date, there are a lot of studies concerning DNA analysis of human spermatozoa suggesting that the determination of DNA fragmentation levels can be a parameter of semen quality, directly implicated in male fertility. Sperm membrane lipid composition is of special interest, given their involvement in fertilization, capacitation, spermatozoa, and oocyte interaction. The future vision shows the possibility to create sperm cells from adult stem cells, with all the requirements to succeed fulfilled, thus guaranteeing a safe and successful use.

Sperm cryopreservation is a widely used and established method in humans, animals, fish, and insects. In humans, sperm cryopreservation is a widely used technique in assisted reproductive technologies (ART) and fertility preservation in patients with cancer. Sperm cryopreservation describes a complex multistep process for preserving male gametes. The process involves collecting a sperm sample, then gradually cooling the sample in the presence of a cryoprotective agent, followed by storage of the sample for future use. Cryoprotectants such as glycerol revolutionized cryopreservation techniques and paved the way for storing sperm samples for up to several years. As new cryoprotectants were discovered, the main issue was the degree of protection that they could provide for a sperm from damage caused by rapid freezing. Future studies are expected to concentrate on advancing technology to achieve the goal of damage-free sperm after cryopreservation.

In the UK, strict adherence to guidelines laid down by the Human Fertilisation and Embryology Authority (HFEA) has made the recruitment of sperm donors an arduous task. In donor insemination, the protection of the recipient and potential offspring from sexually transmitted and other inheritable disorders is paramount. When compared with embryos, the cryopreservation of sperm is usually relatively crude. Density gradient centrifugation (DGC) is almost universally accepted as the superior sperm preparation method for assisted reproductive techniques, donor insemination being no exception. Donor insemination provides an excellent research model. Several authors have used the system to examine the influence of semen parameters and sperm function testing on success rates. Donor insemination also provides an excellent tool to examine other factors governing success, for example, timing of inseminations and subtle female factors as the male gametes are of reasonably standardized quality.