Extracellular Matrix Architecture and Biomechanics of 3D Engineered Microtissues

Mechanical forces are responsible for facilitating various biological functions. Single cells are the fundamental units of force generation in all organisms, but the properties of physiological organ systems are governed by tissue level interactions between the cells and the surrounding extracellular matrix (ECM). The structure and stiffness of the ECM in living tissues plays a significant role in facilitating cellular functions and maintaining tissue homeostasis. However, the wide variation and complexity in tissue composition across different tissue types make comparative study of the impact of matrix architecture and alignment on tissue mechanics difficult. To elucidate the impact of ECM alignment on tissue mechanics, I present a microtissue-based platform capable of controlling the degree of ECM alignment in 3D self-assembled fibroblast populated collagen matrix, anchored around multiple elastic micropillars. The platform allows culture of microtissues with varying geometries but same initial cell and matrix composition. The pillars provide structural constraints, control matrix alignment, enable measurement of the microtissues’ contractile forces, and the ability to apply tensile strain using magnetic particles. Along with experimental measurements, I have utilized finite element models (FEM) to simulate the microtissues’ mechanics. The FEMs when coupled with mechanical measurements obtained using the micro-cantilever tissue gauges (μTUG) platform, enabled analysis of spatial variation in the microtissues’ Young’s moduli across different regions. It was observed that microtissue regions with higher degree of ECM alignment were significantly stiffer than the unaligned regions and the stiffness was not affected by suppression of cellular contractile forces in matured microtissues. The results showed the effect of ECM alignment on the stiffness and mechanics in microtissues having same composition and maturation conditions but different geometries, along with demonstrating the versatility of a platform capable of studying the impact of cell-ECM interactions on various biological functions. Periodic contractile forces play critical roles in organ maturation during embryonic stages and homeostatic performance of the cardio-vascular system. To exert periodic forces on tissues in a controlled environment while simultaneously measuring the tissue’s mechanical properties, I contributed to the design of a lid-based magnetic μTUG platform capable of applying periodic loads to multiple microtissues simultaneously. I further designed and developed newer generations of magnetic μTUG devices capable of long term periodic actuations of microtissues, which will be used for future studies involving tissue maturation under cyclic strains. One of the experimental platforms described here was used to elucidate the effect of ECM alignment on tissue stiffness in a controlled setting, while the other demonstrated the capability of mimicking in-vivo level periodic strains in model microtissue constructs. However, both of these systems are quite versatile and will potentially be used in tissue engineering and drug testing applications or fundamental investigations elucidating the intricate interplays between cells and the ECM