Engler, Adam J.

Kiang, Jennifer

Sniadecki, Nathan

Elsevier - Publisher Connector 

Dynamic Surface Topography Influences Cell Function 

Wednesday, February 29, 2012 705a3573-Pos Board B434
Tissue Geometry Regulates Collective Cell Motility
Sriram Manivannan, Jason P. Gleghorn, Jacquelyn Nestor,
Celeste M. Nelson.
Princeton University, Princeton, NJ, USA.
Collective cell migration plays an important role in embryonic development,
wound repair and cancer invasion. Certain cell types have an intrinsic ability
to organize themselves and move collectively when they are confined within
monolayers. Here, we explored the role of tissue geometry on the collective
motility of epithelial cells. In particular, we used microlithography and time-
lapse imaging to ask whether tissue geometry affects multicellular polarity
and supracellular organization that are necessary for collective cell motion.
We found that epithelial cells within monolayers tended to rotate as a group,
and that increasing the size of the tissue increased the collectiveness of
group rotation. The shape and boundary conditions of the tissue organized
the motion of the cells by altering group rotation and coherence. The motil-
ity parameters of individual cells, including speed and persistence, were also
affected by tissue geometry. Our results suggest that the overall architecture
of the tissue in which cells reside instructs their movements with respect to
each other within a collective. Accurate recapitulation of in vivo tissue struc-
ture will benefit future studies of processes which involve collective cell
migration.
3574-Pos Board B435
Fibronectin Matrix Assembly Regulates Shear Stress-Induced Structural
Remodeling and Motility
Rachel E. Evans, Brian P. Helmke.
University of Virginia, Charlottesville, VA, USA.
Complex spatial profiles of shear stress have been implicated in focal develop-
ment of atherosclerotic lesions by mechanisms involving force transmission
through endothelial cell (EC) focal adhesions to cytoskeleton. Fibronectin is
a primary component of the provisional extracellular matrix (ECM) deposited
in atherosclerotic lesions. Integrin-mediated mechanosignaling pathways in
ECs are required for both adaptation to shear stress and fibronectin fibrillogen-
esis, but how fibronectin assembly state modulates EC responses to shear stress
remains unknown. To investigate this question, focal adhesion displacement,
cytoskeletal reorganization, and migration were measured before and after
a step increase from 0 to 12 dyn/cm2 steady unidirectional shear stress acting
on ECs interacting with either assembled, fibrillar fibronectin matrix or unas-
sembled, fragmented fibronectin on glass. Shear stress onset induced the arrest
of focal adhesion displacement in ECs on unassembled fibronectin but not in
cells on assembled fibronectin. In subconfluent layers, ECs on unassembled fi-
bronectin migrated downstream after shear stress onset, but cells on assembled
fibronectin migrated in random directions associated with local fibril orienta-
tions. In confluent monolayers, ECs interacting with unassembled fibronectin
aligned in the flow direction faster than in monolayers on fibrillar fibronectin
matrix, suggesting that fibronectin assembly regulated shear stress-induced cy-
toskeletal remodeling. Since cytoskeletal remodeling and focal adhesion dis-
placement reflect early mechanosensing events after the onset of shear stress,
these data suggest that fibronectin assembly regulates mechanosensitivity at
the cell-matrix interface, which leads to shear stress-induced adaptation of
cell motility and alignment.
3575-Pos Board B436
Human Mesenchymal Stem Cells Migration on Matrices with Distinct
Elasticity Gradient Magnitudes
Ludovic G. Vincent, Yu Suk Choi, Adam J. Engler.
University of California San Diego, La Jolla, CA, USA.
Adult mesenchymal stem cells (MSCs) respond to extracellular niche elastic-
ity, which varies dramatically between tissues that MSCs inhabit. Similarly, as
MSCs egress from bone marrow and hone to tissues, they may encounter stiff-
ness gradients brought on either by pathological conditions, e.g. myocardial
infarction ~8.751.5kPa/mm, or through normal tissue variation, e.g. muscle
~0.650.9kPa/mm. We have recently shown that MSCs can undergo directed
migration in response to shallow, physiological (~1kPa/mm) stiffness gradi-
ents before differentiating, suggesting the importance of spatial changes in
stiffness. Such gradients, however, contain aphysical ranges, e.g. 1-15kPa,
and more refined gradients of both range and gradient strength that mimic tis-
sue interfaces are needed to better understand how mechanical cues dictate
MSC migration versus differentiation. Using a polydimethylsiloxane micro-
channel mixer, we generated a polymer solution with a one-dimensional
crosslinker concentration of constant monomer and photoinitiator but varyingcrosslinker. Photopolymerizing the solution inside the device yields a 3mm
wide hydrogel with varying mechanical properties. Stiffness gradients of vary-
ing strength (1-30kPa/mm) and range (0.1-100 kPa) are achieved by varying
the relative concentration of crosslinker from the input solutions. MSCs re-
sponded to stiffness gradients with a physiological range, e.g. mimicking
the myotendenous junction, but of varying strength, i.e. 1-30kPa/mm. How-
ever, migration velocities of MSCs on gels of varying gradient strength
were similar. Cell morphology was stiffness dependent with cells exhibiting
increased spread areas on the stiffer regions, suggesting that the previously
observed correlation between substrate mechanics, cell motility, and morphol-
ogy exists over a physiological stiffness range but is independent of gradient
strength. Efforts to define optimal myogenic stiffness and studies with C2C12
muscle cells are ongoing. These findings imply that MSCs in vivo may con-
tribute better to repairs in stiffer regions of tissues where they may preferen-
tially accumulate.
3576-Pos Board B437
Dynamic Surface Topography Influences Cell Function
Jennifer Kiang1, Nathan Sniadecki2, Adam J. Engler1.
1University of California, San Diego, La Jolla, CA, USA, 2University of
Washington, Seattle, WA, USA.
Micro- and nano-scale changes in surface topography can modulate mesenchy-
mal stem cell (MSC) differentiation; rough surfaces have been shown to induce
osteogenesis to varying degrees depending on the scale and nature of the topo-
graphical features. While responses to static surfaces are novel, topography in
vivo is constantly being remodeled by cells within the niche. To better under-
stand how mesenchymal stem cells respond to changes in topography over
time, we developed a soft polyacrylamide hydrogel with magnetic nickel mi-
crowires randomly oriented in the surface of the material. Varying the magnetic
field around the microwires can reversibly induce their alignment with the di-
rection of the field, causing the smooth hydrogel surface to develop small wrin-
kles. By varying the density of wires in the hydrogel, surface roughness
changes, DRRMS, can range from 0.05 to 0.62 mm as measured by traction force
microscopy; this range encompasses roughness values for static surfaces. Time-
dependent topographical changes are achieved by oscillating the field around
the microwires, and ongoing efforts using step function and cyclic changes
in topography indicate that both smooth muscle cells and MSCs change their
behavior in response to dynamic surface topography, e.g. distinct changes in
cytoskeletal structure as well as lineage marker expression is expected. Being
able to dynamically study how cells respond to changes in topography will im-
prove our current understanding of topography-driven effects on stem cell
differentiation.
3577-Pos Board B438
Nanotopography Driven Mesenchymal Stem Cell Differentiation and
Proliferation
Dustin R. Berger, Ketul Popat, Ashok Prasad.
Colorado State University, Fort Collins, CO, USA.
Plastic-adherent, fibroblast-like populations of bone marrow cells, termed
multipotent mesenchymal stromal/stem cells (MSCs), constitute a tissue spe-
cific stem cell population that is responsible for tissue homeostasis and repair
of bone, cartilage and adipose tissue. Previous work with MSCs had shown
that they are capable of differentiation into specific lineages in response to
the physical properties of the extracellular matrix such as matrix elasticity
and cell geometry. Remarkably MSCs have been demonstrated to differenti-
ate into bone-forming osteoblast cells by modifying the substrate nanotopog-
raphy. In this work, the role of nanotopography on the long-term response of
MSCs is explored using biodegradeable polycaprolactone (PCL) nanopillar
and nanofiber surfaces seeded with rat MSCs and cultured in normal growth
media for four weeks. We found that after four weeks in culture under normal
expansion media conditions, MSCs cultured on nanofibers exhibit better ad-
herence, significantly increased proliferation, and maintain increasingly dense
fibroblast-like morphologies. In contrast, MSCs seeded on nanopillar surfaces
display lowered adherence, reduced proliferation, and adopt highly elongated
cellular morphologies. Cell shape and area quantification reveals that MSCs
cultured on smooth substrates adopt uniformly spread morphologies covering
large surface areas, while MSCs cultured on nanopillars have significantly
larger length-to-width ratios and significantly reduced coverage areas. Immu-
nofluorescent staining of MSCs on PCL nanopillars reveals the presence of
two bone marker proteins, osteopontin and osteocalcin, providing evidence
for differentiation into osteoblast-like cells. Unlike the nanopillar topography,
MSCs cultured on nanofiber and smooth PCL surfaces did not appear to


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