An efficient technique for adjusting and maintaining specific hydration levels in soft biological tissues in vitro

Elucidating how mechanics is affected by hydration in soft biological tissues is critical for understanding the potential effects of diseases where tissue extracellular matrix (ECM) is altered. The ability to control ECM water content is necessary for studying hydration-dependent tissue mechanics and for minimizing confounding effects caused by differences in tissue water content among specimens. In this paper, we describe an approach to adjust and maintain water content using a two-stage hydration technique, in order to overcome unique challenges faced in mechanical testing of biological tissues. Bovine aortic tissue was selected to demonstrate the approach. A liquid phase approach using PEG solutions allowed for efficient initial adjustment of tissue hydration. This was followed by a vapor phase approach using a humidity chamber for maintaining stable water content for a defined test duration of 45 min. Incubation in PEG solution brought bovine aortic tissue samples to equilibrium water content in approximately 6 h, much more efficiently than using a humidity chamber alone. Characteristic relationships between tissue water content and PEG concentration as well as relative humidity were obtained. It was found that PEG concentrations ranging from 0 to 40% had an inverse relationship with tissue water content ranging from 80 to 380%, which corresponded to relative humidities between 53 and 99%.