Effects of hydrogel compliance
on EC spreading. (a) Average circularity
values for cells encapsulated in 5% PEG hydrogels with ratios of 100/0,
75/25, 50/50, 25/75, or 0/100 PEG–PQ/PEGPQ(alloc). Cell spreading,
as assessed by lower circularity, increased as the hydrogels became
more compliant. 25/75 and 0/100 PEG–PQ/PEG–PQ(alloc)
exhibited significantly lower circularities than the other formulations
and ECs in the 100% PEG–PQ(alloc) hydrogel were the most spread
(p < 0.005). (b-f) Histograms that summarize the
measured circularity for all the cells assessed in each hydrogel formulation.
While a population of highly rounded cells (circularity ∼0.8)
can be found in all hydrogels, populations of spread cells begin to
emerge as the compliance decreases. Nuclear (DAPI, blue) and actin
(green) staining of characteristic cells show more developed actin
networks with identifiable stress fibers in highly spread cells as
compared to diffuse bands surrounding the nucleus in rounded cells
(inset). Scale bar represents 30 μm.