In every ejaculate there are sperm cells with abnormal membranes that are programmed to “die”, this process is called apoptosis or programmed cell death. These sperm cells, from very early stages, present certain markers in their membrane which were identified. Some of these markers are: activation of caspase, decrease of mitochondrial membrane potential (MMP) and translocation of phosphatidylserine (PS).

Based on this last marker, a semen enhancement technique called *MACS (Magnetic-activated cell sorting)* has been designed. This technique consists of using magnetic microparticles combined with Annexin V, which has great affinity with the phospholipid phosphatidylserine found in the external membrane of these apoptotic sperm cells and which, after applying a magnetic field, are then withheld allowing those optimal sperm cells to pass through.