Characterization of Engineered Tissue by Multimodal Optical Imaging and Biaxial Mechanical Testing
To better understand the relationships between mechanical stimuli and cellular responses, we developed a 3D tissue bioreactor coupling to both a biaxial mechanical testing platform and a stage for multimodal microscopy. Fibroblast seeded cruciform fibrin gels were investigated. A multimodal nonlinear optical microscopy-optical coherence microscopy (NLOM-OCM) system was developed to delineate relative spatial distributions of original fibrin, deposited collagen and fibroblasts non-invasively. Serial in-culture mechanical testing platform was also applied to track the evolution of bulk mechanical properties under sterile conditions. Wall stress depends on sample thickness and our multimodal imaging system measured evolving construct thickness as a function of mechanical stretch during biaxial tests. Through one month culture, cell and deposited collagen randomly distributed in non-stretched constructs. While under stretched condition, cell and deposited collagen fibers, which aligned with cell bodies, appeared preferentially parallel with principal stretch. Surprisingly both non-stretched and stretched constructs showed isotropic mechanical properties with increasing stiffness with culture time. In summary, our biaxial bioreactor system integrating both NLOM-OCM and mechanical testing provided complementary microstructural information and mechanical properties and thus may broaden fundamental understanding of soft tissue mechanics and mechanobiology.