Objective: To develop a method of freezing small amounts of spermatozoa in polymerized alginic acid <font>drop</font>s, which can be liquified after thawing for recovery of the spermatozoa. Design: Prospective clinical study. Setting: Medical School, RWTH Aachen, Aachen Germany. Patient(s): None. Intervention(s): Validation of the encapsulation method with bovine sperm; cryopreservation of human spermatozoa in alginic capsules. Main Outcome Measure(s): We optimized the cryopreservation method by testing different parameters influencing the freezing procedure, such as concentration of alginic acid, size of <font>drop</font>s, time of polymerization, and culture media. Result(s): The final protocol was as follows: encapsulation by 7.3 mg/mL alginic acid forming 10-_L <font>drop</font>s polymerized for 30 seconds and liquefied for 2.5 minutes in sodium citrate. Cryopreservation of human spermatozoa by this protocol resulted in a decreased motility of 18.3% compared with standard protocols but a 19.9% higher vitality of the immotile spermatozoa. Conclusion(s): No difference in viability of spermatozoa after both sperm-freezing procedures could be observed. Further investigation will be undertaken to reduce the amount of immotile but viable sperm after microencapsulation in alginic acid.
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