title: Force-driven evolution of mesoscale structure in engineered 3D microtissues and the modulation of tissue stiffening.
abstract: The complex structures of tissues determine their mechanical strength. In engineered tissues formed through self-assembly in a mold, artificially imposed boundary constraints have been found to induce anisotropic clustering of the cells and the extracellular matrix in local regions. To understand how such tissue remodeling at the intermediate length-scale (mesoscale) affects tissue stiffening, we used a novel microtissue mechanical testing system to manipulate the remodeling of the tissue structures and to measure the subsequent changes in tissue stiffness. Microtissues were formed through cell driven self-assembly of collagen matrix in arrays of micro-patterned wells, each containing two flexible micropillars that measured the microtissues' contractile forces and elastic moduli via magnetic actuation. We manipulated tissue remodeling by inducing myofibroblast differentiation with TGF-β1, by varying the micropillar spring constants or by blocking cell contractility with blebbistatin and collagen cross-linking with BAPN. We showed that increased anisotropic compaction of the collagen matrix, caused by increased micropillar spring constant or elevated cell contraction force, contributed to tissue stiffening. Conversely, collagen matrix and tissue stiffness were not affected by inhibition of cell-generated contraction forces. Together, these measurements showed that mesoscale tissue remodeling is an important middle step linking tissue compaction forces and tissue stiffening.
authors.affiliation: Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA. Electronic address: rgzhao@buffalo.edu.
authors.forename: Ruogang
authors.initials: R
authors.lastname: Zhao
authors.affiliation: Department of Bioengineering, University of Pennsylvania, 510 Skirkanich Hall, 210 South 33rd Street, Philadelphia, PA 19104, USA.
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Chen
authors.affiliation: Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA.
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Reich
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D055595:Mechanical Phenomena; D051379:Mice; D041681:NIH 3T3 Cells; D023822:Tissue Engineering / Q000379:methods*; D053773:Transforming Growth Factor beta1 / Q000378:metabolism
chemical_list: D053773:Transforming Growth Factor beta1
keywords: Engineered microtissue; Magnetic actuation; Soft tissue biomechanics; Tissue structure