(786c) Tissue Origami: Directed Folding of Tissues By Programmed Cell Contractility Networks

Authors: 
Hughes, A. J., UC Berkeley - UCSF
Gartner, Z., UCSF

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.