Online monitoring of collagen fibre alignment in tissue-engineered tendon by PSOCT

One of the major challenges in engineering a functional tendon is to be able to monitor the evolving arrangement of collagen fibres, which leads to the formation of a complex extracellular matrix. Polarization-sensitive optical coherence tomography (PSOCT) is a non-destructive imaging technique capable of examining the organization of tissues online. In this study, PSOCT was used for the first time to visualize the evolution of the collagen fibre alignment in tissue-engineered tendons in response to varying growth environments. The tendon constructs consisted of rat tenocytes embedded in collagen hydrogels and cultured in Flexcell Tissue Train Culture plates. They were subjected to cyclical loading for 1 h at 1 Hz every day, using the Flexcell system. Different strain level and cell seeding densities were examined at different time points over a 14 day period. The birefringence, a characteristic of the growing tendon, was found to increase over culture time and with the increase of cell-seeding densities. In addition, it was revealed that the effect of contraction of tenocytes on the fibre alignment was greater than the application of external forces during stretching. These results demonstrate that PSOCT can be a powerful tool for monitoring the change in collagen organization online and non-destructively at different time points in growing engineered tendons.