Our efforts started with a licensing agreement in 2004. Our magnetic beads with a proprietary ligand attached to the beads were used in over 1000 bull semen samples from several hundred bulls that were subsequently artificially inseminated in the United States. The aim is to remove unwanted sperm cells from mammalian semen. Our method is less expensive than those using Flow Cytometry.

We removed acrosomal-damaged sperm cells from bull semen and evaluated the morphology and motility of the purified semen. Using CASA instrumentation it was found that the purified semen performed better than unpurified in the 24 hour stress test. 

Using the same procedure, we purified also horse semen and we had a favourable result using traditional test methods. The ligand on the magnetic beads used in these separations recognized selected surface markers know to be indicative of damaged cells. 

Another university evaluated our magnetic beads targeted to the ubiquitin surface marker on bull sperm cells.  The resulting ubiquitin-free sperm cells are essentially free of apoptotic sperm cells. Effective separations were also achieved with ubiquitin-targeted magnetic beads which had a Fluorescent dye attached to enhance visibility. 

In addition, we incorporated magnetic beads containing the appropriate ligand with semen in French straws that were subsequently frozen. Upon thawing of the straws the beads interacted with the unwanted sperm cells which was collected magnetically at the tip of the straw and cut off prior to the evaluation. This experiment was a simulation of the AI procedure and was designed to show that damaged sperm cells could be removed from semen immediately prior to use.

Safety issues   

The magnetic beads we use are comparable in composition to MRI contrast agents used to enhance images and improve discrimination of target cells; e.g., resolution of 1 micron cancer cells. The separation procedure is a negative depletion in which the magnetic beads attach to the targeted surface marker and are colleted against the wall of a tube by application of an external laboratory magnet. The remaining semen is decanted while the tube is still in the magnetic field.  The unwanted semen remains attached to the wall of the tube as long as the external magnet is in place.  No electromagnets are needed.  We use hand held high strength rare earth magnets in the procedure.

These magnet are inexpensive and can be reused for as long as they are intact.

Procedure for the capture of purified semen

During the regular processing of semen and before the addition of extenders the magnetic beads are added and occasionally gently agitated for 10-15 minutes to allow contact between the magnetic beads and the targeted sperm.

It is suggested the semen is diluted in a normal semen buffer to decrease the viscosity and increase contact time of bead to target. Normal temperatures apply that are used in the processing of the semen. After the collection phase of the target, the sample is placed in a magnetic field for 10 minutes. [Speed of collection is a function of the diameter of the collecting tube with collection = 1/ distance2]. In other words a narrower tube will collect faster than a wider tube.

Procedure for beads with straws

It is our belief that one should first separate defective cells using the above procedure prior to loading the semen into straws.  Then, a second quantity of beads should be mixed with the semen which is then loaded into straws and frozen. This allows the beads in the straws to target cells damaged by the freezing process. However, we are not opposed to separating only once by adding the beads just prior to freezing.