464918 Tissue Origami: Directed Folding of Tissues By Programmed Cell Contractility Networks

Friday, November 18, 2016: 3:51 PM
Continental 6 (Hilton San Francisco Union Square)
Alex J. Hughes, Max Coyle, Jesse Zhang and Zev Gartner, UCSF Mission Bay, San Francisco, CA

A major barrier to the engineering of complex tissues is the difficulty in controlling tissue structure across a wide range of length scales. Further, proper function of synthetic biological tissues is hampered by mass transport limitations, and the lack of extracellular matrix (ECM) physicochemical anisotropies that guide appropriate cell behaviors in space and time. In biology, tissues are typically built over a range of length scales via self-organized morphogenesis processes in which extracellular matrix remodeling occurs at the same time as cell division, migration, and fate specification. We take a biomimetic approach to building tissues by engineering the spatial organization of sheets of ECM gels via contractile networks of cells. Such contractile networks are co-patterned with ÒpassengerÓ cell types that can be guided into prescribed 3D topologies that instruct cell self-organization processes. Thus, the folding trajectory and form is combined with control over the type and placement of different cell types on the sheet, enabling control over 3D tissue architecture in concert with cellular interfaces.

Introduction: Living tissues are characterized by the specific arrangement of biological cells in layers of ECM. Interfaces between cells and their matrix microenvironment are often folded into arrays of functional units such as the epithelial acini of the breast and the crypts and villi of the intestine. In many cases, the curvature and spatial organization of the ECM is relevant to tissue development and function. For example, the specification of endoderm cell fate at crypts in the gut is governed by cell-cell signaling networks that are influenced by the folding state of tissue layers. We seek to build folds of specific geometry in ECM-mimetic gels in order to understand the systems-level interactions between cells in folded tissues. Moreover, we rely on the intrinsic contractility of cells to sculpt the physicochemical anisotropy of the ECM to mimic in vivo tissues.

Materials and Methods: We build arrays of contractile tissues at the upper and lower surface of 250 micron-thick matrigel-collagen ECM-mimetic gels using DNA-patterned assembly of cells (Figure 1a). The type and location of cells on each surface of the gel prescribe the final folded geometry of the ECM. Collagen fibers are pre-labeled with fluorescent dye in order to track curvature of the sheet over time via confocal microscopy.

Results and Discussion: Regular arrays of contractile mammary epithelial cells placed on one side of circular ECM gels yield cap-shaped objects with maximum curvatures that increase over time. The curvature at a given timepoint increases monotonically as the spacing between tissues on the sheet is decreased (and more tissues are added, Figure 1b), scales linearly with cell contractility, and is partially blocked by blebbistatin. We found that anisotropic grids of fibroblast tissues produce consistent anisotropic folds along controlled axes, allowing us to fabricate a range of 3D topographies and predict them with a biophysical FEA model (Figure 1c). For example, we constructed the Miura-ori fold (Figure 1d), which resembles folds of the gut epithelium in development.

Figure 1. Engineering tissue curvature via cellular contractility. (a) microfluidic apparatus for building thin ECM sheets with contractile tissue actuators at prescribed positions in xy. (b) ECM curvature increases with tissue density. (c) Various folds can be prescribed in ECM sheets and predicted via FEA modeling. (d) The Miura-ori fold.

Conclusions: We report engineering control over the 3D shape of biomimetic ECM scaffolds by leveraging tissues as mechanical actuators. Our ability to design specific fold geometries in concert with cell compositions and spatial arrangement in ECM sheets could improve drug toxicity screens and enable studies of the necessary conditions for topological transitions in tissue development.

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