Impedance based MEMS sensor for monitoring time sensitive oocyte cryopreservation
[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] In recent centuries, women in their 30s and 40s have represented an increasing portion of fertility patients who have had difficulties in fertilization. Those patients' problems are poor oocyte quality and other reproductive sequelae like chromosomally abnormal pregnancies, such as Down's syndrome and miscarriage. Hence, these troubles along with other reasons such as diseases, including cancer, inspire researchers to study, develop and improve oocyte cryopreservation. Oocyte cryopreservation is considered a critical technique in assisted reproductive treatments (ARTs). However, the technical difficulties connected with the unique properties of the mammalian oocyte and a lack of deep understanding of oocyte cryobiology are what is behind the need for pushing for the clinical application of oocyte cryopreservation. The definition of optimal cryopreservation protocols enormously rely on the knowledge of cell membrane permeability to water and cryoprotective agents. This paper presents an innovative technique for oocyte cryopreservation by minimizing the damage to the oocyte via feedback control of the CPA concentration during equilibration. Hence, this technique differs from the current cryopreservation protocol for human female fertility that is unreliable and subject to significant user variation. The oocyte cryopreservation is achieved by equilibrating individual oocytes with high concentrations of permeating chemicals known as cryoprotectants or CPAs. This equilibration causes two modes of damage to oocytes: mechanical damage due to osmotically driven water influx and efflux, and toxic damage due to prolonged exposure to too-high CPA concentrations. Our device allows feedback control with minimal intervention; all measurements are translated directly into voltages that can be used to inform the control system to enable processing oocytes with nearly zero user intervention. Also, a goal state is given and concentrations are changed so that the desired state is achieved and maintained.
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