Experimental Study On Gradient Freezing To The Effect Of Cryopeservation Of Porcine Aortic Valves

Object To investigate effects of the optimization cooling pacing in cryopeservation of porcine aortic valves.To promote the biovaive'preserve and prolong the lifespan of biovalve.Methods Got the porcine heart in 20 minutes in clearing condition,then quickly put in iced sodium chloride,prepared biovalve and a part of tissue had a detection of bacteriology;Measured the phase change of the porcine aortic valves(0℃—4℃)by the programmed freezing instrument.Cooled down the temperature on different velocity -1℃/min,-2℃/min,-3℃/min.-4℃/min,-5℃/min in phase change and classed into five groups by these velocity.Under the phase change temperature,went on coiling in the rate of -1℃/min till -80℃.Keep up -80℃for 24 hours and stored in liguid nitrogen. Analyzed in the aspect of histology,biochemistry,ultrastructure,biomechanics, ascertainment the optimization cooling pacing in cryopeservation of porcine aortic valvesfor prolonging the lifespan of biovalve.Results The result of histology indicate that compared with other groups,the porcine aortic valves of the fouth group(cooling pacing is -4℃/min in phase change)is the best.The endotheliocyte and fibroreticulate texture is integrated,and the histologic layer is clear.In other groups,many endotheliocytes are ablate.Collagen fibers is loose. The comparative study between the fouth group and others:the thickness has no signment different(F=0.807;P=0.54);the water content in the valve,denaturation temperature,stress-strain,destroying stress is significantly increased(P＜0.05),the index in other four groups has no signment different.Conclusion It is the phase change of porcine aortic valves that 0℃—-4℃.The cooling pacing is optimization that used -4℃/min in phase change and -1℃/min in other stages.