Experimental determination of surface heat transfer coefficient in a dry ice-ethanol cooling bath using a numerical approach

Background: Dry ice-ethanol bath (-78ºC) have been widely used in low temperature biological research to attain rapid cooling of samples below freezing temperature. The prediction of cooling rates of biological samples immersed in dry ice-ethanol bath is of practical interest in cryopreservation. The cooling rate can be obtained using mathematical models representing the heat conduction equation in transient state. Additionally, at the solid cryogenic-fluid interface, the knowledge of the surface heat transfer coefficient (h) is necessary for the convective boundary condition in order to correctly establish the mathematical problem. Objective: The study was to apply numerical modeling to obtain the surface heat transfer coefficient of a dry ice-ethanol bath. Materials and methods: A numerical finite element solution of heat conduction equation was used to obtain surface heat transfer coefficients from measured temperatures at the center of polytetrafluoroethylene and polymethylmetacrylate cylinders immersed in a dry ice-ethanol cooling bath. The numerical model considered the temperature dependence of thermophysical properties of plastic materials used. Results: A negative linear relationship is observed between cylinder diameter and heat transfer coefficient in the liquid bath, the calculated h values were 308, 135 and 62.5 W/(m2K) for PMMA 1.3, PTFE 2.59 and 3.14 cm in diameter, respectively. Conclusion: The calculated heat transfer coefficients were consistent among several replicates; h in dry ice-ethanol showed an inverse relationship with cylinder diameter.Centro de Investigación y Desarrollo en Criotecnología de Alimento

Producción de embriones de búfalo por fertilización in vitro luego de la maduración de los ovocitos durante el transporte prolongado

El búfalo (Bubalus bubalis) es una especie con excelente adaptación a sectores inundables. El mejoramiento genético a través de superovulación y transferencia embrionaria ha tenido escasos resultados debido a dificultades en la detección de celo, pobre respuesta ovárica y limitada recuperación de embriones post-lavaje. La técnica de fertilización in vitro de embriones (FIV) es una biotecnología de gran impacto en el progreso genético. El objetivo del presente trabajo fue estudiar los eventos tempranos de la FIV, analizando la tasa de maduración y desarrollo embrionario post-fertilización de ovocitos madurados in vitro (IVM) durante el transporte. Ovocitos bovinos y bubalinos fueron obtenidos por punción folicular de ovarios post-mortem e IVM durante el transporte por un período de 18 h. Se realizó la FIV con toros de fertilidad comprobada, con una concentración en microgotas de inseminación de 3-4 x 106 espermatozoides motiles/ml por un período de 6 horas. Los embriones fueron cultivados en medio oviductal sintético SOFaa en incubadora gaseada y ambiente humidificado a 38,5ºC durante 9 días. Se evaluaron las tasas de IVM, clivaje (día 2 post-fertilización) y blastocisto (días 7 a 9). Los resultados fueron analizados estadísticamente utilizando Fischer’s Exact Test (

Resurrection of a Bull by Cloning from Organs Frozen without Cryoprotectant in a −80°C Freezer for a Decade

Frozen animal tissues without cryoprotectant have been thought to be inappropriate for use as a nuclear donor for somatic cell nuclear transfer (SCNT). We report the cloning of a bull using cells retrieved from testicles that had been taken from a dead animal and frozen without cryoprotectant in a −80°C freezer for 10 years. We obtained live cells from defrosted pieces of the spermatic cords of frozen testicles. The cells proliferated actively in culture and were apparently normal. We transferred 16 SCNT embryos from these cells into 16 synchronized recipient animals. We obtained five pregnancies and four cloned calves developed to term. Our results indicate that complete genome sets are maintained in mammalian organs even after long-term frozen-storage without cryoprotectant, and that live clones can be produced from the recovered cells