Effect of altered hydration on the internal shear properties of porcine aortic valve cusps

Background. Dehydration of tissue due to glutaraldehyde fixation has been reported and was examined in this study of porcine aortic valve cusps. The effect of altered hydration on cusp internal shear properties was also examined. Methods. Hydration level was assessed by wet mass measurement of cusps stored in solutions for times up to 1000 minutes. Solutions used in this study included Hanks solution, porcine blood, 0.5% glutaraldehyde, and several dextran solutions. Shear testing was performed on physiologically hydrated, superhydrated, and dehydrated cusps. Results. There was very little difference between the physiologic and superhydrated leaflets; however, dehydration caused significant stiffening with increased hysteresis and stress relaxation. Conclusions. Glutaraldehyde has been shown to increase shear stiffness of valve cusps. Tissue dehydration also increased shear stiffness but increased stress relaxation and hysteresis, which was contrary to observations reported after glutaraldehyde fixation. The significant effect of dehydration on cusp mechanical properties does not account for the effects observed after glutaraldehyde fixation, but it demonstrates that hydration level is an important factor that affects internal shear properties of valve cusps.