Long-term cyclic distention enhances the mechanical properties of collagen-based media-equivalents

In this study, we sought to identify the key parameters involved in long-term cyclic distension (CD) as they pertain to the development of collagen-based media-equivalents (MEs). By using only highly compacted, cross-linked constructs, we avoided the complicating issues of irrecoverable creep and transient alignment, and isolated the effects of cyclic mechanical loading on ME development. Our system allowed us to study this development over a wide range of parameters including strain amplitude, pulse frequency, pulse shape, and culture time. We found that in most cases involving cyclic distension, MEs were both stronger and stiffer than constructs that were grown under static conditions. The mechanical properties were not significantly different from static controls after two weeks of CD, however, five weeks of CD was sufficient to note significant increases in both stiffness and strength. The strain, stretch time, and relaxation time were all important variables in determining ME mechanical properties. While we were unable to detect a significant net change in the amount of total collagen, we observed significant deposition of insoluble elastin in our CDMEs, something that has never been previously reported using adult smooth muscle cells. Finally, these changes in ME development did not depend on the age of the MEs prior to the initiation of CD.